Apuntes de gestión de activos (Course notes on physical asset management)


El Arte de mantener


Artículos en revistas Web of Science (WOS papers)


38

An asset-management oriented methodology for
mine haul-fleet usage scheduling

Reliability Engineering and System Safety, 180 (2018) 336-344.

C. Nakousi (b), R. Pascual(a), A. Anani (b), F. Kristjanpoller (c), P. Lillo (b)
a Mechanical Engineering Department, Universidad de Concepción, Edmundo Larenas 219, Concepción, Chile.
b Mining Engineering Department, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, Chile
c Industrial Engineering Department, Universidad Técnica Federico Santa María, Valparaiso, Chile

Abstract

Different complexities force mining companies to find efficient ways to respond to demand challenges and ensure long-term sustainability. It explains, in part, the increase in the use of prescriptive analytics to optimize physical-asset life-cycle costs and decrease greenhouse gas (GHG) emissions. Mining, being an asset-intensive industry, provides huge improvement opportunities. This is especially true for scheduling practices of mine haulage fleet usage in long term planning. Fleet aging implies important cost increases in maintenance and repair (M&R), and overhauls. Fleets are often heterogeneous in term of truck performance, fuel consumption and GHG emissions. Sub-optimal scheduling decisions may induce severe cost over-runs and increased emissions. This paper proposes an original mixed integer programming formulation to optimize mine haulage equipment scheduling in the long term. The model considers the effects of equipment aging, fuel consumption, payload capacity and cycle times. Our formulation handles different aspects that according to author's knowledge have not been considered in the literature as a whole: (i) joint minimization of fuel, M&R, and overhaul costs, (ii) reduction of GHG emissions, (iii) heterogeneous equipment performance metrics, (iv)increase in cycle times due to mine aging. The case study shows a cost reduction of 13% in the discounted .ows associated with fuel, M&R, and overhauls in a time horizon of 10 years. This .gure translates into an NPV gain of 13.1 million USD. Additionally, GHG emissions are reduced by an average of 3,470 tons/year or 11% overall.

Keywords: physical asset management, greenhouse gas emissions, mixed integer programming model, haulage fleet scheduling.





37


A Real Options Approach for Joint Overhaul and Replacement Strategies with Mean Reverting Prices
Annals of Operations Research
https://doi.org/10.1007/s10479-018-2906-z

A.F. Mac Cawley, R. Cubillos,  R. Pascual

Abstract


Due to its significant impact on economic performance, an effective equipment overhaul and replacement strategy is a key aspect of physical asset management in capital-intensive industries, such as the mining industry. Classical approaches suggest periodic interventions based on the physical condition of the equipment, considering factors such as availability and operational costs. These fixed models generally ignore two important aspects: first, the flexibility of the decision to overhaul or replace, which may be re-evaluated within a given period, and second, the uncertainty around economic factors that may affect future maintenance decisions, such as the product price. This work improves on classical models by considering the effect of integrated price uncertainty in the definition of joint overhaul and replacement strategy, using a real options approach and a mean reversion binomial model to represent the uncertainty in price. More specifically, we develop a real options model and use a backwards recursion algorithm to determine an optimal intervention policy that maximizes expected profits. We then present a numerical study of the mining industry to validate the effectiveness of the proposed methodology. Results show that the option-based decision model economically outperforms the classical periodic strategy approach from with net present value increments ranging from 36.8% to 8.6%, according to the number of periods in the maintenance cycle, offering evidence that a new approach to equipment overhaul and replacement strategy is needed. 
Keywords Periodic maintenance, Joint Replacement and Overhaul policy · Real options · Mean Reversion


full paper


36

Graphical Analysis for Overall Effectiveness Management: A Graphical Method to Support Operation and Maintenance Performance Assessment


P. Viveros, F. Kristjanpoller, M. López, A. Crespo, R. Pascual

aceptado en Quality and Reliability Engineering International


Abstract

This article presents a graphical tool for the monitoring of performance indicators called GAOEM (Graphical Analysis for Overall Effectiveness Management). GAOEM is used in a real industrial process, integrating the main indicators of maintenance and operations management and performing an adaptation on the indicator of the overall effectiveness, the OEE/OAE. GAOEM facilitates control and analysis by using specific indicators (graphic panel). It also facilitates an efficient reading and interpreting of the data, enriching the analysis, the search for phenomena of interest and improvement opportunities and supporting the decision making. GAOEM requires three categories of inputs data, which are: interventions data, time data and production/process data. With this information the basic performance indicators are calculated, being these indicators fundamental for the control and monitoring of the performance level. Later these indicators will be the base for calculation of both partial and total effectiveness. GAOEM can be used as a diagnosis, analysis, control and monitoring tool for the indicators of interest, as well as a tool for searching of phenomena typical of the life cycle of assets and also those that result from improper operation and/or maintenance, identifying its root causes.


35

Value-based optimization of replacement intervals for critical spare components

David R. Godoy (a), Peter Knights (b), Rodrigo Pascual (a)
(a) Physical Asset Management Lab, Department of Mining Engineering, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
(b) School of Mechanical and Mining Engineering, The University of Queensland, QLD 4072, St. Lucia, Brisbane, Australia


International Journal of Mining, Reclamation & Environment
32(4), 264-272, 2017 
DOI: 10.1080/17480930.2017.1278660

Abstract

Highly competitive industries, such as mining, face constant pressure for continuous improvement. This increasing need for efficiency demands the use of models of reliability and benefit, especially for significant investment equipment and components. Critical major components -e.g. mill liners, shovel swing transmissions or haul truck engines- are related to lengthy shutdowns with a considerable impact on the financial structure. In this context, cost optimization is a widely-used principle to schedule component replacements. However, this practice traditionally does not consider external factors of interest, such as business-market conditions, which can radically change decisions. To overcome this limitation, we have proposed a criterion based on the estimation of revenues -under several commodity price scenarios- at both the component intervention epoch and time-window during major shut-downs. The aim of this work is to guide the decision about the best epoch to replace, considering the maximization of value-adding rather than simply minimization of costs. The paper presents a model to evaluate such optimal value by estimating the net benefit subject to certain interest rate for discounting, considering the copper price, component survival probabilities using condition-based maintenance, cost, and expected downtime. Results show the influence of business objectives to identify the real value of waiting the right epoch to perform a replacement, in order to optimize the decision benefit, satisfying both reliability constraints and time-windows. In conclusion, business profitability opportunities increase when maximization of value-adding is included as part of a complete view of asset management system.

Keywords: Value-based optimization, Critical spare components, Optimal replacement.

paper


34

A special issue on Statistical methods in mining industry
Orietta Nicolis (1) Rodrigo Pascual (2,3)

1 Institute of Statistics, Universidad de Valparaíso, 2340000 Valparaiso, Chile
2 Department of Mining Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile
3 Mechanical Engineering Department, Universidad de Concepción, Concepcion, Chile


publicado on line en Applied Stochastic Modelling in Business and Industry

DOI: 10.1002/asmb.2339


Abstract

In this special issue, we selected four papers where some statistical methods are used for taking decisions, assessing the security of mining equipments, and predicting the proportion of a certain mineral in rock samples. While the papers of Neira et al and Stehlík et al use the concepts of the reliability theory based on typical failure distributions (such as the Weibull, Gamma, and Beta distributions), the work of Jiang et al uses nonparametric statistical methods for analyzing the failures. A different issue has been proposed by Huerta et al for predicting the proportion of a mineral in rocks. In particular, in the work of Neira et al, a statistical method inspired from reliability engineering has been proposed for monitoring the “health” of microseismic sensing networks, that is, its capability to properly register all the microseismic activity above a certain energy level. The monitoring of the health of a microseismic network has been addressed in this work by describing and characterizing the faulty behavior of each sensor in analogy with standard ideas and methods of reliability theory. In particular, the proposed method analyzes two relevant features of each of the sensors' behavior, namely, what type of noise is or might be affecting the registering process and how effective at registering microseisms the sensor is. Once the noisy activations and the types of noise have been identified, a Weibull distribution has been fitted to the time differences of consecutive noisy activations (failures). The estimated parameters are then used to compute the reliability of each sensor with respect to the different types of noise. In order to estimate the noise that is present in the seismograms, three indicators have been proposed: two of these are based on the power spectral density (PSD) and the third is given by the signal-to-noise ratio (SNR). In all cases, the computed value of the indicator is compared with a threshold to assess if an activation is noisy or not. Then, the ratio of activations is extracted by evaluating the quotient between the number of satisfactory activations registered by a sensor and the number of satisfactory activations that the sensor was supposed to register in a given period of time. Also, the authors propose a new indicator, computed for each individual sensor, that conveys both the information of the reliability of the sensors and their ratio of activations. The proposed methodology is then applied to the microseismic data registered at the Chilean underground mine El Teniente. The study illustrates the capability of the proposed methodology to discriminate and rank sensors with satisfactory, poor, or defective sensing performances, as well as to characterize their failure profile or type of information that can be used to plan or optimize the network maintenance procedures.



33

Technology Investment Effects in Performance Based Maintenance Contracts

 International Journal of Production Research, 56(7), 2628-2645, 2018.

DOI: 10.1080/00207543.2017.1374573

R. Ulloa, A. F. Mac Cawley,  G. Santelices, and R. Pascual

a Department of Industrial and Systems Engineering. Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile;

b Department of Mining Engineering. Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile.

This work analyzes the effects of a fixed initial investment in technology or infrastructure on performance based maintenance contracts. We present a mathematical expression which reflects the trade-off between an upfront technology investment by the vendor and the cost of required future interventions. Developing a mathematical model of a performance-based maintenance contract that uses this technology trade-off expression and determines the value of the contract for each party. Contractually, the client indicates the duration of the contract and the optimal number of maintenance interventions to maximize asset availability; the vendor quotes the cost for the requested interventions. We investigate how the initial investment and the contract parameters affect the net present value for each party and supply chain. Demonstrating the existence of an optimal relation between the number of preventive maintenance interventions and level of investment. Deriving the optimal contract parameters for the client, vendor and chain and show that lack of coordination. To achieve coordination, we present a revenue sharing mechanism which maximizes the value of the chain. Finally, we present an industry study case with data from the mining sector. Results indicate that by investing and coordinating, the entire supply chain can improve the contract NPV by 149.7%.

Link al paper


32

Reliability Assessment Methodology for Massive Manufacturing Using Multi-Function Equipment

Pulicado on line en: Complexity


M. López-Campos ,1 F. Kristjanpoller,1 P. Viveros,1 and R. Pascual 2
1 Department of Industrial Engineering, Universidad Técnica Federico Santa María, Av. España 1680, 2340000 Valparaiso, Chile

2 Department of Mining Engineering, Pontificia Universidad Católica de Chile, Av. Vicu˜na Mackenna 4860, Santiago, Chile

Experience reveals that reliability varies depending on the characteristics of operation. The manufacturing process based on multifunction equipment gives a usual case of variation in operating conditions. Thiswork presents a methodology for the reliability analysis of multifunction processes, using the RCM approach, and a modification of the Universal Generating Function (UGF) under a massive manufacturing context. The result is a characterization of reliability, for each piece of equipment and for the production system. The methodology is applied in a workshop of a textile industry, where there is prior evidence that the failure behavior varies according to the type of function executed by multifunction machines.

Link al paper



31

Optimal Channel Coordination in Use-based Product-Service System Contracts

 International Journal of Production Research,

Vol. 55, No. 23, 6946–6956, 2017.

 https://doi.org/10.1080/00207543.2017.1332793

DOI: 10.1080/00207543.2017.1332793

Rodrigo Pascual^a, Matías Siña^a, Gabriel Santelices^a, Milton Román^b, Enrique López Droguett^c
a Mining Engineering Department, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, Chile
b DICTUC Tire, Vicuña Mackenna 4860, Santiago, Chile
c Mechanical Engineering Department, Universidad de Chile, Beaucheff 850, Santiago, Chile

Abstract

Nowadays, service economy efficiencies are key to keep competitiveness and increase market advantages. The development of Product-Service Systems (PSS) can be an interesting strategy as they seek to improve the business performance of all the participants in the value chain. This paper proposes a novel reliability-based reward scheme for use-oriented PSS contracts. In a PSS instead of paying for the product, the client pays a fee for its performance. The contribution of this work to the existing literature is to provide a quantitative tool for the development of a use-oriented PSS contract based on non-repairable component reliability and risk sharing. It can be extended to other performance metrics such as availability and reliability. A well designed PSS achieves a mutual growth agreement for the client and the supplier if it aligns their interests through channel coordination. This is achieved by balancing the improvement in the expected cost and profit for the client and the supplier respectively. The improvement is measured with respect to a baseline scenario where no PSS contract exists. The methodology is tested using a case study that analyses mining haul-truck tires. The results show a significant overall improvement in the main key performance indicators and environmental impact of the value chain.

Keywords: Product-Service Systems, Physical Asset Management, Service Contracts, Channel Coordination.



30

Modeling age replacement policy under multiple time scales and stochastic usage profiles

Nicole Belen Diaz, Rodrigo Pascual,  Fabrizio Ruggeri,  Enrique López Droguett

International Journal of Production Economics

188 (2017) 22–28

http://dx.doi.org/10.1016/j.ijpe.2017.03.009



Abstract


This paper offers an original methodology to set multi-dimensional maintenance policies for machines whose aging processes require using multiple time scales. It can be considered a generalization of the traditional approach, that usually employs a unique time scale and sets a single age limit to carry out preventive maintenance actions. The methodology also considers situations in which a set of machines are operated usingmultiple usage profiles. We define usage profile as the relationship between the use of a machine in terms of one main time scale and another scale. In our case study the age of a mining haul-truck component can be best modeled as a combination of operating hours and load cycles since
the last overhaul. We compare the results obtained with respect to using a single time scale policy. The comparison shows the importance of the bias in decision making that may arise due to incomplete modelling of the components' aging process.

Keywords: physical asset management; maintenance policy; multiple time scales; multiple usage profiles; maintenance decision support system.





29

Integrating Mining Loading and Hauling Equipment Selection and Replacement Decisions 

Using Stochastic Linear Programming

Gabriel Santelices (a), Rodrigo Pascual (a), Armin Lüer-Villagra (c), Alejandro Mac Cawley (b), Diego Galar (d)

International Journal of Mining, Reclamation and Environment, 

Volume 31, 2017 - Issue 1, pp 52-65.

DOI: 10.1080/17480930.2015.1115589

(a) Department of Mining Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile 
(b) Department of Industrial Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile 
(c) Department of Engineering Sciences, Universidad Andres Bello, Santiago, Chile
(d) Division of Operation and Maintenance Engineering, Luleå University of Technology, Luleå, Sweden.


Abstract


Equipment selection is a key strategic decision in the design of a material handling system, because an improper one will lead to operational problems and unnecessary investment costs. It involves determining the number and combination of loaders and trucks which will move the material, fulfilling a specified production schedule. Previous works have addressed this problem with deterministic approaches, without considering the interdependent availability of trucks and loaders. In order to fill this gap, we developed a stochastic model that combines the selection and equipment replacement problems, subject to a stochastic production rate constraint. This is a new idea that will help decision makers to decide faster and more reliable. The proposed model optimizes the fleet by minimizing the total life-cycle costs. To solve it we used a linearization approach that reduces the computational effort. We tested our approach with a benchmark model, using a mining case study. Results indicate that the solutions ensure with a high probability a determined production target, producing good robust solutions compared to the deterministic counterpart.


Keywords: Equipment Selection, Equipment Replacement, Production Assurance, Linear Stochastic Programming, Mining Industry.

Optimal Repairable Spare-Parts Procurement Policy under Total Business Volume Discount Environment

Reliability Engineering & System Safety, Volume 159, March 2017, Pages 276–282, 2017.



Rodrigo Pascual (a), Gabriel Santelices (a), Armin Luer-Villagra (b), Jorge Vera (c),
Alejandro Mac Cawley(c,d)

a Department of Mining Engineering, Pontificia Universidad Católica de Chile, Av. Vicuña
Mackenna 4860, Santiago, Chile.

b Department of Engineering Sciences, Universidad Andrés Bello, Santiago, Chile.

c Department of Industrial Engineering, Pontificia Universidad Católica de Chile, Av.
Vicuña Mackenna 4860, Santiago, Chile.

d Department of Agricultural Economics, Pontificia Universidad Católica de Chile, Av.
Vicuña Mackenna 4860, Santiago, Chile.

Abstract
In asset intensive fields, were components are expensive and high system availability is required, spare parts procurement is a critical issue. While vendors offer total business volume discounts (TBVD), companies must define the procurement
and stocking policy of their spare parts in order to obtain a competitive advantage and gain market share. To determine an optimal procurement policy of spare parts, this work presents an optimization model that maximizes the availability of the equipment subject to a budget constraint, under a TBVD environment, using a single-echelon structure where parts can be repaired. The model determines the optimal number of repairable spare parts to be stocked, giving emphasis on asset availability, procurement costs and service levels as the main decision criteria. To improve the time required to obtain the model solution, a heuristic procedure that achieves high quality solutions in a fast and time-consistent way was implemented. Results show that accounting for TBVD, in an optimal procurement policy of spare parts, produces better overall results and yields a better availability performance.

Keywords: Reliability, Repairable Spare Parts, Line Replaceable Units,
Business Volume Discount, Inventory Policy


27

Channel Coordination on Fixed Term Maintenance Outsourcing Contracts

IIE Transactions, 48:7, 651-660, 2016.

DOI: 10.1080/0740817X.2015.1122255

G. Santelices*, R. Pascual*, H. Liao**, S. Maturana***

*Mining Engineering Department, Pontificia Universidad Católica de Chile, Santiago, Chile.
** Systems Engineering Department, University of Arizona, Arizona, USA.
*** Systems Engineering Department, Pontificia Universidad Católica de Chile, Santiago, Chile.


Abstract


This article studies the positive and negative effects that fixed term maintenance contracts may have on related decision making. We present an original model to estimate such effects and select the optimal preventive maintenance intervals and contract terms for pieces of equipment which are serviced by an external party. In the context of the contract, the intention of each party is in general to maximize its own profit, which usually leads to unaligned interests and decisions. To resolve this issue, we propose incentive schemes to assure the contract sustainability by achieving channel coordination between the client and its service vendor. Special focus is put on how the project net present value analysis of both parties affects decision-making regarding equipment maintenance. Our model considers a new alternative of negotiating contracts with non-constant maintenance intervals. The proposed model helps to identify conditions that justify maintenance deferrals with its associated negligence, in terms of lifecycle reduction and performance deterioration, when no channel coordination is promoted. Additionally, we present a simple procedure to settle an optimal contract duration, benefiting both parties. The proposed methodology is tested using a baseline case study from the literature. It illustrates how return on investment analysis may significantly impact optimal maintenance intervals during the contract for both parties. Accordingly, incentives need to be reevaluated to achieve channel coordination. The suggested approach can be easily implemented in commercial spreadsheets, facilitating sensitivity analyses. 

Keywords: Fixed Term Contracts, Preventive Maintenance, Channel Coordination, Non-constant intervals, Net Present Value Analysis.




26

  A structured methodology to optimize throughput of production lines

R. Pascual*, R. Madariaga*, G. Santelices*, D. Godoy*, E. Lopez Droguett**

International Journal of Mining, Reclamation and Environment
30:1, 25-36, 2016.
DOI: 10.1080/17480930.2014.962235


*Physical Asset Management Lab, Department of Mining Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile
**Center for Risk Analysis, Reliability and Environmental Modeling, Federal University of Pernambuco, Recife-PE, Brazil

Abstract

The increasing social and environmental demands, financial and operational restraints, and high qualifications requirements constantly affect the competitiveness and performance of the mining industry. In the literature, a wide range of techniques have been developed to cope with these challenges. However, a structured methodology to integrate solutions of diverse nature considering PAM perspectives has not been developed in depth. In this work we introduce a continuous improvement methodology based on prioritizing and optimizing the best opportunities in different asset management areas to achieve throughput targets. The proposed procedure, called Throughput Oriented System Improvement Methodology (TOSIM), starts with a criticality analysis to identify the bottleneck components. It is followed by the application of an optimization technique, finishing with the implementation and evaluation of policy changes. The aforementioned steps have to be applied cyclically until the production target is reached. We illustrate its use in a case study from a mining company in northern Chile. Results show that the operational efficiency can be significantly improved by optimally changing the maintenance policy and the plant layout.

Keywords: Physical Asset Management, Performance Improvement, Criticality Analysis, Production Target, Production Lines.


25

A methodology for integrated critical spare parts and insurance management

Applied Stochastic Models in Business and Industry,  32(1), 90-98, 2016

DOI: 10.1002/asmb.2125

A. Martínez, R. Pascual, Sergio Maturana
Mining Engineering Department, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, Chile.
Industrial and Systems Engineering Department, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Santiago, Chile.

Critical spare parts stock optimization has become a relevant topic for academy and industry. In most articles the problem has been stated as a trade-off between economic risks of shortages, and financial costs. Risk optimization in this context has been mainly studied from a logistics point of view. The most common decision variables have been stock levels, stock location, and reorder points. In this context, buying insurance to cover shortage cost can be a complementary (or exclusive) measure for risk mitigation. Insurance optimization traditionally has been studied from a microeconomic and financial perspective. The main decision variable has been the indemnity function, and occasionally, the insurance premium. Its use in the context of physical asset management has not been observed to the best of our knowledge. This creates an opportunity to link inventory optimization techniques with insurance optimization for shortage losses.
In this work we present a novel approach to jointly manage the shortage risk of a critical non-repairable component in a unique critical system. We develop an original model to integrate critical spare parts stock optimization with insurance optimization techniques. The result is a decision model to select the optimal stock and insurance policy that maximizes the decision maker's expected utility. This allows for a business-centered integrated perspective in critical parts decisions. We present a case study representative of the mining industry, illustrating the complementary nature of selecting optimal stock levels and contracting an optimal insurance. Our results shows that contracting an insurance can lead to policies preferred by a risk-averse decision maker. The case study shows this may even occur lowering stock levels and increasing profits.


Keywords: spares management, insurance management, critical spares, asset management, multicriteria analysis




24
Optimal failure-finding intervals for heat shields in a gas turbine combustion chamber using a multi-criteria approach

Journal of Engineering for Gas Turbines and Power, 137(7), 072501, 2015.

doi:10.1115/1.4029202

Alejandro Martínez*, Gloria Lara*, Rodrigo Pascual*, Enrique Lopez**

*Department of Mining Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile. 
**Center for Risk and Reliability University of Maryland, MD, USA.


Abstract


When a component, as heat shields, degrade, two stages can be distinguished. First, a potential failure appears which could evolve to the second stage and become a functional failure. The time between these two stages is called delay time, which has been widely studied in literature to deter- mine when to inspect to avoid breakdown. These studies have shown only single analysis criteria to find FFI. In order to overcome this limitation, we developed a novel strategy to apply multi-criteria methodology to optimize FFI. Our ap- proach considers availability, system breakdown risk and re- liability analysis from a systemic perspective, studying heat shields as groups, according to their location in the combus- tion chamber, regardless of age defect. Hence is not neces- sary to check every one of the shields. Our results show an optimal FFI policy subject to a determined breakdown risk level. This analysis may be adaptable to other components that can be grouped together.


23

A Multi-Objective Genetic Algorithm for Determining Efficient Risk-Based Inspection Programs

M.C. Moura, I. Lins, E.L. Droguett, R.F. Soares, R. Pascual
Reliability Engineering & System Safety, 133, 253–265, 2015.

http://dx.doi.org/10.1016/j.ress.2014.09.018


Abstract

This paper proposes a coupling between Risk-Based Inspection (RBI) methodology and Multi-Objective Genetic Algorithm (MOGA) for defining efficient inspection programs in terms of inspection costs and risk level, which also comply with restrictions imposed by international standards and/or local government regulations. The proposed RBI + MOGA approach has the following advantages: (i) a user-defined risk target is not required; (ii) it is not necessary estimating the consequences of failures; (iii) the inspection expenditures become more manageable, which allows assessing the impact of prevention investments on the risk level; (iv) the proposed framework directly provides, as part of the solution, the information on how the inspection budget should be efficiently spent. Then, genetic operators are tailored for solving this problem given the huge size of the search space. The ability of the proposed RBI + MOGA in providing efficient solutions is evaluated by means of two examples, one of them involving an oil and gas separator vessel subject to internal and external corrosion that cause thinning. The obtained results indicate that the proposed genetic operators significantly reduce the search space to be explored and RBI + MOGA is a valuable method to support decisions concerning the mechanical integrity of plant equipment.





22

A decision-making framework to integrate maintenance contract conditions with critical spares management

D.R. Godoy, R. Pascual, P. Knights
Reliability Engineering & System Safety, 131, 102-108, 2014.

http://dx.doi.org/10.1016/j.ress.2014.06.022

Abstract

Maintenance outsourcing is a strategic driver for asset intensive industries pursuing to enhance supply chain performance. Spare parts management plays a relevant role in this premise since its significant impact on equipment availability, and hence on business success. Designing critical spares policies might therefore seriously affect maintenance contracts profitability, yet service receivers and external providers traditionally attempt to benefit separately. To coordinate both chain parties, we investigated whether the spare components pool should be managed in-house or contracted out. This paper provides a decision-making framework to efficiently integrate contractual conditions with critical spares stockholding. Using an imperfect maintenance strategy over a finite horizon, such scheme maximizes chain returns while evaluates the impact of an additional part to stock. As result, an original joint value -preventive interval and stock level- sets the optimal agreement to profitably allocate the components pool within the service contract. Subsidization bonuses on preventive interventions and pooling costs are also estimated to induce the service provider to adjust its policy when needed. The proposed contractual conditions motivate stakeholders to continuously improve maintenance performance and supply practices, thus obtaining higher joint benefits.




21

Scheduling production for a Sawmill: A robust optimization approach

M. Varas, S. Maturana, R. Pascual, I. Vargas, J. Vera

International Journal of Production Economics, 150, 37–51, 2014

https://doi.org/10.1016/j.ijpe.2013.11.028

Abstract

Optimization models are increasingly being used for planning natural resources operations. However, the inherent uncertainty present in natural resources makes it difficult to directly apply their results. In particular, production scheduling for sawmills presents several challenges since the supply of logs and the finished product orders are often unknown at scheduling time. In this paper we consider the problem of scheduling production under uncertainty in a sawmill, where the deterministic model proposed by Maturana et al. (2010) was extended to account for uncertainties in product demand and availability of raw materials. The robust optimization methodology of Bertsimas and Sim (2004) and Bertsimas and Thiele (2006) was applied to develop three robust models: one that considers only uncertainty in the product demand, the second considers only uncertainty in the raw material supply, and the third considers both uncertainties simultaneously. For each of these models we carried out an experiment to evaluate the robustness of the solutions and the effect of the conservatism level on the solutions. This allowed us to determine the impact of both sources of uncertainty separately, and the combined effect on the production schedules. In each experiment we defined several levels of variability for the uncertain parameters, and for each of them, we changed the level of conservatism through the manipulation of budgets of uncertainty. We analyzed the behavior of the robust solutions and their average performance with respect to uncertainty using Monte Carlo simulation. This analysis allowed us to provide several managerial insights that could help schedulers choose the appropriate level of conservatism with respect to each source of uncertainty according to their preferences.

Keywords: Optimization, Forestry, Sawmill scheduling, Robust optimization



20

Critical spare parts ordering decisions using conditional reliability and stochastic lead time

Reliability Engineering & System Safety, 119 (2013) 199–206

https://doi.org/10.1016/j.ress.2013.05.026



David Godoy, Rodrigo Pascual, Peter Knights
Physical Asset Management Lab, Department of Mining Engineering, Pontificia
Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile

School of Mechanical and Mining Engineering, The University of Queensland, QLD
4072, St. Lucia, Brisbane, Australia

Abstract
Asset-intensive companies face great pressure to reduce operation costs and increase utilization. This scenario often leads to over-stress on critical equipment and its spare parts associated, affecting availability, reliability, and system performance. As these resources impact considerably on financial and operational structures, the opportunity is given by demand for decision making methods for the management of spare parts processes. We proposed an ordering decision-aid technique which uses a measurement of spare performance, based on the Stress-Strength Interference Theory; which we have called Condition-Based Service Level (CBSL). We focus on Condition Managed Critical Spares (CMS), namely, spares which are expensive, highly reliable with higher lead times, and are not available in store. As a mitigation measure, CMS are under condition monitoring. The aim of the paper is orienting the decision time for CMS ordering or just continuing the operation.
The paper presents a graphic technique which considers a rule for decision based on both condition-based reliability function and a stochastic/fixed lead time. For the stochastic lead time case, results show that technique is effective to determine the time when the system operation is reliable and can withstand the lead time variability, satisfying a desired service level. Additionally, for the constant lead time case, the technique helps to define insurance spares. In conclusion, presented ordering decision rule is useful to asset managers for enhancing the operational continuity affected by spare parts.

Keywords: Critical spare parts, Condition-Based spares ordering, Proportional Hazards Model, Lead time, Condition-Based Service Level, Stress-Strength Interference models, Ordering process.




19

Joint optimization of fleet size and maintenance capacity in a fork-join cyclical transportation system

Journal of the Operational Research Society, 2013, 64, 982–994

https://doi.org/10.1057/jors.2012.103

R. Pascual, A. Martínez


Department of Mining Engineering,
Pontificia Universidad Católica de Chile, Santiago, Chile
R. Giesen
Department of Transport Engineering and Logistics
Pontificia Universidad Católica de Chile, Santiago, Chile

Abstract

This article presents an asset-management oriented multi-criteria methodology for the joint estimation of a mobile equipment fleet size, and the maintenance capacity to be allocated in a productive system. Using a business-centered life-cycle perspective, we propose an integrated analytical model and evaluate it using global cost rate, availability and throughput as performance indicators. The global cost components include: (i) opportunity costs associated to lost production, (ii) vehicle idle time costs, and (iii) maintenance resources idle time costs. This multi-criteria approach allows to build a balanced scorecard that identifies the main trade-offs in the system. The methodology uses an improved closed network queueing model approach to describe the production and maintenance areas. We test the proposed methodology using an underground mining operation case study. The decision variables are the size of a load-haul-dump (LHD) fleet and specialized maintenance crew levels. Our model achieves savings of 20.6% in global cost terms with respect to a benchmark case. We also optimize the system to achieve desired targets of vehicle availability and system throughput (based on system utilization). Results show increments of 7.1% in vehicle availability and 13.5% in system throughput with respect to baseline case. For the case studied, these criteria also have a maximum, which allow for further improvement if desired. Results also show the importance of using balanced performance measures in the decision process. A multi-criteria optimization was also performed, showing the Pareto front of considered indicators. We discuss the trade-offs among different criteria, and the implications in finding balanced solutions. The proposed analytical approach is easy to implement and requires low computational effort. It also allows for an easy reevaluation of resources when the business cycle changes and relevant exogenous factor vary.

Full paper



18

Optimizing Maintenance Service Contracts under Imperfect Maintenance and a Finite Time Horizon

Applied Stochastic Models in Business and Industry, 29(5), 564-577, 2013


DOI: 10.1002/asmb.1943


R. Pascual, D. Godoy
Department of Mining Engineering, Pontificia Universidad Católica de Chile
Av. Vicuña Mackenna 4860, Santiago, Chile

H. Figueroa
Department of Mechanical Engineering, Universidad de Chile
Beauchef 850, Santiago, Chile

Abstract
When companies decide to outsource its services, the most important arguments usually are: focus on the core business, ability to access high-quality services at lower costs, and improved risk sharing. However, contractual agreements have typically followed structures in which both the manufacturer and the contractor attempt to maximize its own expected profits in a non-coordinated way. Although previous research have considered supply chain coordination by means of contracts, they included unrealistic hypotheses, such as perfect maintenance and/or infinite time-span contracts. Overcoming these limitations, this work studies contractual conditions to coordinate the supply chain through a preventive maintenance strategy that maximizes the total expected profit for both parties in a finite time-span contract. This paper presents a model to establish such conditions when maintenance is imperfect and the contract duration is fixed through a number of preventive maintenance actions along a significant part of the asset life-cycle under consideration. We also study cases where the owner is profit-centered or service-centered, while the contractor is profit-centered. Results show that players can achieve a greater benefit together than what could be obtained separately. The formulation leads to a win-win coordination under a set of restrictions that can be evaluated a priori. The proposed contract conditions motivate stakeholders to continually improve its maintenance services in order to reach channel coordination, where both parties obtain higher rewards.

Keywords: Maintenance; Service contracts; Imperfect maintenance; Finite time horizon.

Full paper

17

Condition-based Spares Ordering for Critical Components

Mechanical Systems & Signal Processing, 25 (2011) 1837–1848


https://doi.org/10.1016/j.ymssp.2011.01.004


Darko Louit, Rodrigo Pascual
Centro de Minería, Pontificia Universidad Católica de Chile
Av. Vicuña Mackenna 4860, Santiago, Chile

Dragan Banjevic, Andrew K.S. Jardine
Department of Mechanical and Industrial Engineering, University of Toronto
5 King's College Road,  Toronto, Ontario, Canada M5S 3G8, Canada


It is widely accepted that one of the potential benefits of Condition-Based Maintenance (CBM) is the expected decrease in inventory as the procurement of parts can be triggered by the identification of a potential failure. For this to be possible, the interval between the identification of the potential failure and the occurrence of a functional failure (P-F interval) needs to be longer than the lead time for the required part. In this paper we present a model directed to the determination of the ordering decision for a spare part when the component in operation is subject to a condition monitoring program. In our model the ordering decision depends on the Remaining Useful Life (RUL) estimation obtained through (i) the assessment of component age and (ii) condition indicators (covariates) that are indicative of the state of health of the component, at every inspection time. We consider a random lead time for spares, and a single-component, single-spare configuration that is not uncommon for very expensive and highly critical equipment.

Full paper


16

Throughput Centered Prioritization of Machines in Transfer Lines
Reliability engineering and system safety, 96 (2011), 1396-1401
doi:10.1016/j.ress.2011.05.006

R. Pascual , D. Godoy
Physical Asset Management Lab
Centro de Minería, Pontificia Universidad Católica de Chile
Av. Vicuña Mackenna 4860, Santiago, Chile
D.M. Louit
Komatsu Chile S.A., Av. Americo Vespucio 0631, Quilicura, Santiago, Chile
Abstract
In an environment of scarce resources and complex production systems, prioritizing is key to confront the challenge of managing physical assets. In the literature, there exist a number of techniques to prioritize maintenance decisions that consider safety, technical and business perspectives. However, the effect of risk mitigating elements -such as intermediate buffers in production lines- on prioritization has not yet been investigated in depth. In this line,
the work proposes a user-friendly graphical technique called the System Efficiency Influence Diagram (SEID). Asset managers may use SEID to identify machines that have a greater impact on the system throughput, and thus set prioritized maintenance policies and/or redesign of buffer capacities. The tool provides insight to the analyst as it decomposes the influence of a given machine on the system throughput as a product of two elements: (1) system influence efficiency factor and (2) machine unavailability factor. We illustrate its applicability using three case studies: a four-machine transfer line, a vehicle assembly line, and an open-pit mining conveyor system. The results confirm that the machines with greater unavailability factors are not necessarily the most important for the efficiency of the production line, as it is the case when no intermediate buffers exist. As a decision aid tool, SEIDem emphasizes the need to move from a maintenance vision focused on machine availability, to a systems engineering perspective.

Keywords: prioritization, production line, throughput analysis


15

Optimal inspection intervals for safety systems
with partial inspections

Journal of the Operational Research Society, 62, 2051-2062, 2011.

doi: 10.1057/jors.2010.173


R. Pascual, D. Louit
Centro de Minería
Pontificia Universidad Católica de Chile, Santiago, Chile
A.K.S. Jardine
Department of Mechanical and Industrial Engineering
University of Toronto, Toronto, Ontario, Canada

Abstract
The introduction of International Standard IEC 61508 and its industry-specific derivatives sets demanding requirements for the de.nition and implementation of lifecycle strategies for safety systems. Compliance with the Standard is important for human safety and environmental perspectives as well as for potential adverse economic effects (e.g. damage to critical downstream equipment or a clause for an insurance or warranty contract). This situation encourages the use of reliability models to attain the recommended safety integrity levels using credible assumptions. During the operation phase of the safety system life-cycle, a key decision is the de.nition of an inspection program, namely its frequency and the maintenance activities to be performed. These may vary from minimal checks to complete renewals. This work presents a model (which we called rho-beta model) to fi.nd optimal inspection intervals for a safety system, considering that it degrades in time, even when it is inspected at regular intervals. Such situation occurs because most inspections are partial, that is, not all potential failure modes are observable through inspections. Possible reasons for this are the nature and the extent of the inspection, or potential risks generated by the inspection itself. The optimization criterion considered here is the mean overall availability Ao, but also taking into account the requirements for the safety availability As. We consider several conditions that ensure coherent modeling for these systems: sub-systems decomposition, k-out-of-n architectures, diagnostics coverage (observable/total amount of failure modes), dependent and independent failures, and non-negligible inspection times. The model requires an estimation for the coverage and dependent-failure ratios for each component, global failure rates, and inspection times. We illustrate its use through case studies and compare results with those obtained by applying previously published methodologies.


Full paper



14
An integrated model for optimizing strategic overhaul planning of distributed pump stations

ASCE Journal of Computing in Civil Engineering, 25(4), 2011.

DOI: 10.1061/(ASCE)CP.1943-5487.0000085

R. Pascual1, P.A. Rey2, M. Hodkiewicz3 and C. Cruz4

1
Centro de Minería, Pontifícia Universidad Católica de Chile
Av. Vicuña Mackenna 4860, Santiago, Chile.
2 Escuela de Ingeniera Industrial, Universidad Diego Portales
Ejercito 441, Santiago, Chile.
3 School of Mechanical Engineering, University of Western Australia
35 Stirling Highway, Perth, Australia.
4 Department of Mechanical Engineering, Universidad de Chile
Beauchef 850, Santiago, Chile.

Abstract

An important part of the lifecycle costs for pump stations are the support costs associated with energy and preventive maintenance of the pumps. Both cost terms are interrelated as there exists a trade-off  between maintaining pumps frequently (with increased pump efficiency, reduced energy costs and increasing maintenance costs and pump unavailability) and extending the intervals between the overhauls (and increased loss of efficiency, increased energy costs and decreased maintenance costs). The planner needs to forecast pump overhaul demands in order to determine budget levels, as economic resources are limited. This process is assisted by the use of mathematical programming methods to prioritize funding for equipment requiring renewal considering limited resources in a strategic time horizon (several years). This work proposes a novel model to define an overhaul maintenance program for a pump network with a large number of pumps (a few hundreds in the case study). The model minimizes the discounted total (energy + overhaul) cost by selecting and scheduling pumps for overhaul subject to budget constraints. The formulation uses 0-1 integer programming.


Full paper



13

Optimization Models For Critical Spare Parts Inventories - A Reliability Approach

Journal of the Operational Research Society, (2011) 62, 992 --1004

 

Darko Louit and Rodrigo Pascual

Centro de Minería

Pontificia Universidad Católica de Chile

 

Dragan Banjevic and Andrew K.S. Jardine

Department of Mechanical and Industrial Engineering

University of Toronto

 In industries characterized by heavy utilization of equipment and machinery, such as mining, oil & gas, utilities, transportation, adequate stockholding of critical spare parts becomes essential. Insufficient stocks affect overall performance of physical assets, as lack of spares may result in gross penalties, lower availability or increased operational risks. On the other hand, oversized inventories lead to inefficient use of capital and may imply severe expenditures. This paper presents various approaches for the determination of the optimal stock size, when the stock is composed of (i) non-repairable or (ii) repairable parts. The paper is focused on spares for relatively expensive, highly reliable components, rather than on fast-moving spare parts. Optimization criteria considered are minimization of costs, maximization of equipment availability, and the achievement of a desired stock reliability (probability that a spare part request will not be rejected due to lack of spares in stock). For stock reliability, instantaneous and interval reliability calculations are considered. In addition, models directed to the estimation of the remaining life of a given stock of spare parts (at a certain stock reliability level) are introduced. The paper describes several models subject to practical industrial application, and presents case studies from utilities and mining to illustrate their use.

 Keywords: Inventory, spare parts, stochastic processes, non-repairable parts, repairable parts.


Full paper


12
Dynamic Optimization Model for Mining Equipment Repair by Using the Spare-Parts Inventory
D. Louit, R. Pascual, A. Jardine,
Journal of Mining Science, 46(4), 394-403, 2010

We present the dynamic control system for the service rate in an M/M/1 queuing system, to optimize the inventory of critical repairable spare components for a fleet of mobile equipment in presence of an adjustable single server repair facility, namely, the repair rate can be expedited or slowed down. We consider the normal and expedited rates, when the faster repair rate implies higher repair costs. The repair rate selection depends on the number of units in operational condition; actual operating units plus stock on hand is generated at the moment of demand for a spare. The resulting optimal policy is to minimize the expected cost per unit time for the inventory system in the long run.

Keywords: Stochastic processes, dynamic control, spare parts, expedited repair, inventory, queueing

full paper




11

Optimal interval for major maintenance actions in electricity distribution networks

International Journal of Electrical Power and Energy Systems, 31 (2009) 396–401

Darko Louit, Rodrigo Pascual

 Centro de Minería, Pontificia Universidad Católica de Chile

Av. Vicuña MacKenna 4860, Santiago, Chile

 

Dragan Banjevic

Centre for Maintenance Optimization & Reliability Engineering

University of Toronto,5 King’s College Rd.,Toronto, Ontario M5S 3G8,Canada

 

ABSTRACT

 Many systems require the periodic undertaking of major (preventive) maintenance actions (MMAs) such as overhauls in mechanical equipment, reconditioning of train lines, resurfacing of roads, etc. In the long term, these actions contribute to achieving a lower rate of occurrence of failures, though in many cases they increase the intensity of the failure process shortly after performed, resulting in a non-monotonic trend for failure intensity. Also, in the special case of distributed assets such as communications and energy networks, pipelines, etc., it is likely that the maintenance action takes place sequentially over an extended period of time, implying that different sections of the network underwent the MMAs at different periods. This forces the development of a model based on a relative time scale (i.e. time since last major maintenance event) and the combination of data from different sections of a grid, under a normalization scheme. Additionally, extended maintenance times and sequential execution of the MMAs make it difficult to identify failures occurring before and after the preventive maintenance action. This results in the loss of important information for the characterization of the failure process. A simple model is introduced to determine the optimal MMA interval considering such restrictions. Furthermore, a case study illustrates the optimal tree trimming interval around an electricity distribution network.

 

Full paper


10

 

Business-oriented prioritization:A novel graphical technique

R. Pascuala, G.Del Castilloc, D. Louitb, P.Knightsd

Reliability Engineering and System Safety 94 (2009) 1308–1313

a Centro de Minería, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
b Komatsu Chile, Av. Americo Vespucio 0631, Quilicura, Santiago, Chile
c Department of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile
d Division of Mining Engineering, Faculty of Engineering, Architecture and Information Technology, The University of Queensland, St. Lucia, Brisbane, 4072, Australia

 

Abstract

Traditionally, Pareto analysis has been used to select the most critical components and failure modes of a system. A clear disadvantage of this technique is that it requires preselecting a single criterion to establish priorities.

More recently, a graphical log-scatter diagram technique has been proposed. It considers 3 key performance indicators simultaneously: reliability (MTBF), maintainability (MTTR) and unavailability (D). This technique only considers times and does not include economical effects explicitly. This article extends both techniques to explicitly consider both direct and indirect costs to prioritize from the point of view of an asset manager or from a maintenance decision-maker, as required. Due to the economic-based approach of this article, cost discounting is also considered inside financial costs such as -but not limited to- reliability-related investments. Also, the results are displayed on simple and accessible graphs which make them particularly useful for conveying results to non-technical managers. The methodology is illustrated by analyzing a shovel from the copper mine industry, and it clearly shows how the proposed technique facilitates business oriented decisions and how they should change under different market conditions.

 

Key words: prioritization, physical asset management, maintenance decision-making, resource assignment, criticality, subset selection, multicriteria analysis

 

full paper


9

 

A Practical Procedure for the Selection of Time to Failure Models Based on The Assessment of Trends in Maintenance Data

Reliability Engineering and System Safety 94 (2009) 1618–1628

 D.M. Louit


Komatsu Chile, Av.AmericoVespucio 0631, Quilicura, Santiago, Chile

R. Pascual

Centro de Minería, Pontificia Universidad Católica de Chile

Av.Vicuña Mackenna 4860, Santiago, Chile

A.K.S. Jardine

Department of Mechanical and Industrial Engineering, University of Toronto

5 King’s College Road, Toronto, Ont., Canada M5S 3G8

 

Abstract

Many times, reliability studies rely on false premises such as the independent andidentically distributed time between failures assumption (renewal process). This can lead to erroneous model selection for the time to failure of a particular component or system,which can in turn lead to wrong conclusions and decisions. A strong statistical focus, a lackof a systematic approach, and sometimes inadequate theoretical background seem to have made it difficult for maintenance analysts to adopt the necessary stage of data testing before the selection of a suitable model. In this paper, a framework for model election to represent the failure process for a component or system is presented, based on a review of available trend tests. The paper focuses only on single time variable models and is primarily directed to analysts responsible for reliability analyses in an industrialmaintenance environment. The model selection framework is directed towards the discrimination between the use of statistical distributions to represent the time to failure(“renewal approach”); and the use of stochastic point processes (“repairable systems approach”), when there may be the presence of system ageing or reliability growth. An illustrative example based on failure data from a fleet of backhoes is included.

 

Keywords: trend testing; time to failure; model selection; repairable systems; NHPP

 

Full paper

 


8

 

Identification of nonlinear dynamic coefficients

in plain journal bearings

V. Meruane and R. Pascual

Mechanical Engineering Department, Universidad de Chile, Beauchef 850,

Santiago, Chile

 

Tribology International 41 (2008) 743–754

Abstract

This work proposes a framework to the numerical identification of nonlinear fluidfilm bearing parameters from large journal orbital motion (20%-60% bearing clearance).Nonlinear coefficients are obtain from a third order Taylor expansion of oil film forces, and are estimated by means of a time domain technique from journal orbit. The journal orbit is obtain from a CFD (Computational Fluid Dynamics) model of a plain journal bearing on high dynamic loading conditions. The model considers Fluid Structure Interaction (FSI) between the fluid flow and journal. The case study considers a laboratory test rig. Results indicate that nonlinear coefficients have an important effect on stiffness. It was found a change on nonlinear behaviour when oil whirl phenomenon starts, which is not seen in classical linear models.

 

Key words: journal bearing, Computational Fluid Dynamics, transient, identification, large orbital motion, nonlinear

 

full paper

 

 


7

 

Optimal Maintenance Service Contract Negotiation with Aging Equipment

European Journal of Operational Research, 189, 387-398, 2008

 

Canek Jackson, Rodrigo Pascual

Departament of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile

 

Abstract

In recent years, there has been a growing trend to out-source service operations in which the equipment maintenance is carried out by an external agent rather than in-house. Often, the agent (service provider) offers more than one option and the owners of equipment (customers) are faced to the problem of selecting the optimal option, under the terms of a contract. In the current work, we develop a model and report results to determine the agent’s optimal strategy for a given type of contract. The model derives in a non-cooperative game formulation in which the decisions are taken by maximizing expected profits. This work extends previous models by considering the realistic case of equipments having an increasing failure intensity due to imperfect maintenance, instead of the standard assumption that considers failure times are exponentially distributed (constant failure intensity). We develop a model using a linear function of time to characterize the failure intensity. The main goal, for the agent, is to determine the pricing structure in the contract and the number of customers to service. On the other hand, for the clients, the main goal is to define the period between planned actions for preventive maintenance and the time to replace equipments. In order to give a complete characterization of the results, we also carry out a sensitivity analysis over some of the factors that would influence over the failure intensity.

 

Full paper

 

 


6

On the effect of downtime costs and budget constraint on preventive and replacement policies

 

Reliability Engineering and System Safety Safety 93 (2008) 144–151

 

R. Pascual

V. Meruane

Department of Mechanical Engineering, Universidad de Chile, Casilla 2777,

Santiago, Chile

P.A. Rey

Department of Industrial Engineering, Universidad de Chile, Casilla 2777,

Santiago, Chile

 

Abstract

This work proposes a general approach to study and improve the effectiveness of the system with respect to its expected life-cycle cost rate. The model we propose considers a production system which is protected against demand fluctuations andfailure occurrences with elements like stock piles, line and equipment redundancy,and the use of alternative production methods. These design policies allow to keep orminimize the effect on the nominal throughput, while corrective measures are taken.The system is also subject to an aging process which depends on the frequency andquality of preventive actions. Making decisions is difficult because of discontinuitiesin intervention and downtime costs and the limited budget. We present a nonlinearmixed integer formulation that minimizes the expected overall cost rate withrespect to repair, overhaul and replacement times and the overhaul improvementfactor proposed in the literature. The model is deterministic and considers minimalrepairs and imperfect overhauls. We illustrate its application with a case based ona known benchmark example.

Keywords: decision-making, downtime cost, maintenance policies, repair rate,replacement,imperfect maintenance, decision support systems, consequential cost,budget constraint

 

full paper


5

 

Robust parameter identification using forced responses

Mechanical Systems and Signal Processing 21 (2007) 1008–1025

 

R. Pascual, R. Schalchli, M. Razeto

 

Department of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile

Department of Mechanical Engineering, Universidad de Concepción, Casilla 53-C, Concepción, Chile

 

Abstract

In this paper, a new model updating scheme is introduced to adjust the system matrices of a finite-element model by using experimental operating deflection shapes (ODS). An ODS is defined here as the response vector when the system is driven at a given degree of freedom with a unit force of fixed frequency. The proposed algorithm adjusts the numerical model in an iterative way. The matrix equilibrium equation is solved by first taking into account the frequency shift that appears between the non-updated finite element model and the experimental structure. In this way, numerical instabilities observed in state-of-the-art methods are avoided. We present results on two well-known numerical and experimental benchmark cases. They show the good convergence properties of the proposed approach.

 

Keywords: Model updating; Forced response; Structural dynamics

 

Full paper


4

 

Optimal replacement and overhaul decisions with imperfect maintenance and warranty contracts

Reliability Engineering and System Safety Safety 91 (2006) 241–248

R. Pascual*, J.H. Ortega**

*Department of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile

**Departamento de Ciencias Básicas, Universidad del Bío–Bío, Casilla 447, Campus Fernando May, Chillán, Chile

Centro de Modelamiento Matemático UMR 2071 CNRS-UChile, Universidad de Chile, Casilla 170/3, Correo 3, Santiago, Chile

Received 15 March 2004; accepted 13 January 2005

 

Abstract

In this article, we develop a model to help a maintenance decision making situation of a given equipment. We propose a novel model to determine optimal life-cycle duration and intervals between overhauls by minimizing global maintenance costs. We consider a situation where the costumer, which owns the equipment, may negotiate a better warranty contract by offering an improved preventive maintenance program for the equipment. The equipment receives three kind of actions: repairs, overhauls, and replacement. An overhaul represents an imperfect maintenance action, that is, the failure rate is improved but not a point that the equipment is as good as new. Corrective maintenance actions are minimal, in the sense that the failure rate after each repair is the same as before the failure. The proposed strategy surpasses others seen in the literature since it considers at the same time the warranty negotiation situation and the optimal life-cycle duration under imperfect preventive actions. We also propose a simplified approach that facilitates the task of implementing the method in standard solvers.

 

Keywords: Imperfect maintenance; Warranty; Management; Life-cycle cost

 

Full paper

 

 


3

Improvement of Damage-Assessment Results using

High-Spatial Density Measurements

R.Pascual

Department of Mechanical Engineering, Universidad de Chile, Casilla 2777,

Santiago, Chile

R.Schalchli  M.Razeto

Department of Mechanical Engineering, Universidad de Concepci´on, Casilla

53-C, Concepcion, Chile

 

Mechanical Systems and Signal Processing, 19(1), 123–138, 2005.

 

Abstract

Model based damage assessment is based on measuring the distance between experimental and analytical results. In practice, measurements yield only partial mode shapes with respect to the total degrees of freedom present in the corresponding finite element model. Thus, before any damage detection method is implemented, the experimental mode shape has to be expanded to the same dimension of the numerical mode shape. Mode shapes expansion is a key point in the damage localization process, since actual defects of the structure may be hidden by expansion errors.This paper introduces a new general procedure to the expansion/damage assessment process using an optimized choice for: the size of the expansion basis, the number of experimental degrees of freedom (DOFs) and the sensor placement. We introduce a new indicator to evaluate the problems inherent to the expansion/damage detection process using the Minimization of Error on Constitutive Equations (MECE) technique. It provides insight of the inherent limitations of MECE and helps the decision making process on how many degrees of freedom should be measured and how many mode shapes should be used in the expansion basis. The procedure is illustrated using a finite element model of a plate-like structure, where the damage state is simulated as a reduction of the local stiffness.

 

Full paper

 


2

Optimal procurement decisions in the presence of total quantity discounts

and alternative product recipes

Y. Crama1 , R. Pascual 2 and A. Torres3

 

European Journal of Operations Research, 159 (2), 364-378, 2004

 

1 University of Liège, Boulevard du Rectorat 7 (B31), 4000 Liège, Belgium,y.crama@ulg.ac.be

2 Department of Mechanical Engineering, Universidad de Chile, Beauche¤ 850, Santiago, Chile, rpascual@cec.uchile.cl

3 FEPASA, La Concepcion 331, Providencia, Santiago, Chile

 

Abstract

We describe the cost-minimization problem faced by the purchasing department of a multi-plant company when its suppliers offer discounts based simultaneously on plant and on corporate purchases, when discount schedules depend on the total quantity (rather than cost) of ingredients purchased, and when alternative production recipes exist for each final product. We formulate the problem as a nonlinear mixed 0-1 programming problem and we propose various ways to linearize this formulation.

The quality of these models is evaluated on real-world data.

 

Keywords: supply chain management, purchasing, supplier selection, quantity discounts, flexible recipes, mixed 0-1 programming.

 

Full paper

 


1

DESCRIPTION OF THE STEELQUAKE BENCHMARK

Mechanical Systems and Signal Processing. 17(1), 77-82, 2003

 

J. MOLINA

ELSA-JRC Ispra, Italy

 

R. PASCUAL

Departamento de Ingeniería Mecánica, Universidad de Chile,

Beaucheff 850, Casilla 2777, Correo 21, Santiago, Chile

 

J.-C. GOLINVAL

Université de Liège, LTAS – Vibrations et identification des structures,

Chemin des chevreuils, 1 (Bât. B52/3), B-4000 Liège 1, Belgium

 

 Abstract

The two-storey frame depicted in Fig. 1 and called the “Steelquake” structure was proposed as benchmark for damage detection by the European Laboratory for Structural Assessment (ELSA) of the  Joint Research Centre (JRC) in Ispra, Italy. Originally this structure was designed to assess steel buildings performance during earthquakes.

The definition of the measurement set-up and the experimental modal analysis were performed on the undamaged structure by R. Pascual during his short term scientific mission at ELSA-JRC in July 1998. After damage testing of the structure, a new modal analysis was conducted by J. Molina. All the data were collected and made available to the COST F3 WG2 participants [1].

Full paper

 

Artículos en proceso de revisión en revistas ISI

 

Optimal negotiation of maintenance contracts under several failure processes

 

Canek Jackson, Rodrigo Pascual

cjackson@ing.uchile.cl, rpascual@ing.uchile.cl

Departament of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile

 

(Submitted to the European Journal of Operations Research)

 

Abstract

Nowadays, we observe a dramatic increase of maintenance outsourcing. This is specially true for heavy industries such as mining in which focus in core business, increasing technological complexity and scale economies appear as some of the main reasons to outsource maintenance. In this work, the authors propose an analysis for the optimal negotiation of maintenance service contracts in which the parties involved (service provider and equipment owner) have shared long-run goals in order to maximize their own profits. In these models we study how different type of planned maintenance actions affect aspects of the reliability of equipments having an increasing failure rate. The results show a maximum reduction of about 95% in the surplus generated by the parties, when the aging of the equipment is taken into account. It has been predicted the optimal period between equipment replacements and preventive overhauls, showing the relevant influence of the type of planned actions over the decisions making associated to the settling of the terms and conditions of the maintenance service contract. The model improves previous works by reporting some misconceptions related to the evaluation of the expected number of failure times occurring during a contract horizon. The results show a loss of about 10% in the surplus generated by the parties, due to mistaken decisions arising from such misconceptions. The models are validated by simulations over a test case carried out in a commercial software.

 

Working paper

 

Capitulos de libros


Negotiation of extended warranties for medical equipment

B.N. Guedes, M. Moura, I.D. Lins, H.P.S. Zaidan & D. Morais
Federal University of Pernambuco, Recife, Pernambuco, Brazil
E. López Droguett
University of Maryland, College Park, Maryland, USA
R. Pascual
Pontificia Universidad Católica de Chile, Santiago, Chile

In: Safety and Reliability of Complex Engineered Systems – Podofillini et al. (Eds)
2015 Taylor & Francis Group, London.


ABSTRACT

A growing trend in hiring maintenance services has been observed in companies in general in order to enhance competition and reduce costs. This practice becomes even more evident in the context of health institutions, as they strongly employ technology-intensive equipment that must follow tight quality standards that intend to ensure the continuity of the service and the safety of patients. These characteristics contribute in allowing the maintenance to be executed by the Original Equipment Manufacturer (OEM), since several pre-established procedures must be attended during maintenance. Thus, it is necessary to determine the best option between hiring an extended warranty, offered by the OEM, or simply paying for each maintenance intervention when necessary. In this paper we develop a mathematical model in which the manufacturer (leader) and the customer (follower) interact in a Stackelberg game formulation with incomplete information.


Chapter


Optimization of distribution networks resilience based on costs and design changes


H.H.L. Diniz, M. Moura, B. Cunha & I.D. Lins
Federal University of Pernambuco (UFPE), Recife, Pernambuco, Brazil
E. Lopez Droguett
Center for Risk and Reliability, Mechanical Engineering Department, University of Maryland, USA
R. Pascual
Mining Engineering Department, Pontificia Universidad Católica de Chile, Santiago, Chile

In: Safety and Reliability of Complex Engineered Systems – Podofillini et al. (Eds)
2015 Taylor & Francis Group, London.


ABSTRACT

This paper deals with the optimization of distribution networks resilience based on costs of performance reduction, restoration actions and project design changes. Resilience can be considered as the capacity of an entity to recover from an external disturbing event, involving the ability to reduce effectively both magnitude and duration of the deviation from the nominal performance. Although preevent resilience actions are faster in recovering the system, most of research papers about resilience have focused on post-event policies. Therefore, in this work, in addition to post-event recovery actions, we also consider pre-event actions so as to reduce recovery costs and increase recovery speed. Thus, this paper applies an optimization model for resilience in the context of the system design of a logistics network by
minimizing the overall cost associated with the occurrence of disturbing events. Finally, the paper presents a practical example using available data from a logistics company.

Chapter



 

Artículos y presentaciones en conferencias (Conference articles)


REDISEÑO DE UN SISTEMA DE MANEJO DE MINERAL DE COBRE CON CRITERIO DE NEGOCIO

REDESIGNING A COPPER MINERAL PROCESSING SYSTEM FROM A BUSINESS PERSPECTIVE

Rodrigo Madariaga
Universidad de Chile
Rodrigo Pascual
Pontificia Universidad Católica de Chile

MAPLA 2009. Antofagasta, Chile

RESUMEN
Este trabajo propone una metodología para optimizar el diseño de un sistema de manejo de material con pilas intermedias. El método minimiza el costo global esperado y estima la tasa de producción esperada del sistema. Un modelo económico es desarrollado para cuantificar el beneficio del aumento de producción. El estudio de caso considera un sistema de manejo de mineral de cobre que transporta una distancia de 10 km. Los resultados muestran que la introducción de pilas intermedias aumenta notoriamente la productividad y genera un beneficio significativo para el negocio.
Al considerar 3 pilas intermedias, el criterio económico señala que la configuración óptima de stockpiles genera un aumento de productividad de un 19 % equivalente a 4,5 MTon/año. A un precio 2,2 USD/lb Cu, los beneficios se estiman en 110 Millones USD/año.

ABSTRACT
This work presents a methodology that optimizes the capacity of intermediate stockpiles of a bulk handling system by minimizing the expected global cost rate. The proposed methodology estimates the expected system throughput. An economic model is developed to quantify the increase of the system profit. The case study considers a copper ore handling system 10 km long. Results show the increased productivity and profit obtained with the buffers. When considering 3 buffers, the economic criterion predicts a 19 % productivity increase, equivalent to 4.5 MTon/year, or 110 Million USD/year when the cooper price is 2,2 USD/lb Cu.


 PRIORIZACIÓN DESDE UNA PERSPECTIVA DE NEGOCIOS: EL DIAGRAMA DE INFLUENCIA PARA LA EFICIENCIA DE SISTEMA

PRIORITIZATION FROM A BUSINESS PERSPECTIVE: THE SYSTEM EFFICIENCY INFLUENCE DIAGRAM
David Godoy & Rodrigo Pascual
Pontificia Universidad Católica de Chile

MAPLA 2009. Antofagasta, Chile


RESUMEN

En un ambiente de escasez de recursos, la priorización es clave para enfrentar los desafíos en la administración de activos mineros. En este contexto, existen técnicas tradicionales para priorizar equipos, a las que se han sumado herramientas que incorporan una visión económica. Sin embargo, la presencia de elementos mitigadores de riesgo -por ejemplo, las pilas- aún no ha sido investigada. Este trabajo propone una técnica gráfica de fácil interpretación para solucionar esta dificultad, llamada Diagrama de Influencia para la Eficiencia de Sistema (SEID, System Efficiency Influence Diagram). El artículo presenta el modelo que describe al SEID e ilustra su uso en tres casos de estudio: una línea de producción de cuatro máquinas, una línea de ensamblaje de vehículos, y una línea de chancado-molienda en una faena minera. Los resultados indican que los equipos con mayor indisponibilidad inherente no son necesariamente los más importantes para la eficiencia de la línea de producción. La priorización según un simple criterio de inversión es cuestionable, puesto que un equipo de bajo costo puede ser el determinante para la tasa de producción efectiva (throughput) y, por tanto, el más crítico a priorizar si se piensa en la eficiencia y en el negocio. Se revela así, la necesidad de pasar desde una visión de gestión de mantenimiento centrada en equipos y sus disponibilidades, a una perspectiva global de gestión de activos mineros.


ABSTRACT

In an environment of scarce resources, prioritizing is key to confront the management challenges of mining assets. In this context, techniques exist to prioritize equipment to which tools have been added to incorporate an economic vision. However, the presence of risk mitigating elements, such as stock piles, has not yet been investigated. This work proposes a user-friendly graphical technique to solve this problem called the System Efficiency Influence Diagram (SEID). The paper presents a model that describes the SEID and illustrates its use in three study cases: a four-machine transfer line, a vehicle assembly line, and a crushing-milling line in a mining operation. The results show that equipment with greater inherent downtime are not necessarily the most important for the efficiency of the transfer line. Prioritization using capital costs is criticizable, as low cost equipment may be the determinant for the throughput, and thus the most critical to prioritize if the efficiency and the business are considered. The work demonstrates the need to switch from a maintenance management vision focused on equipment and their availabilities to a global perspective of mining asset management.


Full paper


OPTIMIZACIÓN DE RECURSOS PARA CONTRATOS M&R DE FLOTAS DE CAMIONES MINEROS

RESOURCE OPTIMISATION FOR M&R CONTRACTS OF MINING TRUCK FLEET
Gonzalo Navarro
Departamento de Ingeniería Mecánica, Universidad de Chile
Francisco Aguirre
Komatsu Chile S.A., Chile
Rodrigo Pascual
Laboratorio de Gestión de Activos Físicos, Centro de Minería, Pontificia Universidad Católica de Chile

MANTEMIN 2009. Antofagasta, Chile

RESUMEN

Los recursos de taller son factores importantes que afectan a la disponibilidad de camiones mineros. Para el mantenedor es crucial verificar la sensibilidad de este indicador al modificar estos recursos, especialmente para los contratos basados en el desempeño. Este trabajo muestra un modelo de simulación del taller. El estudio de caso considera una flota con dos tipos de camiones. Para validar el modelo, el taller se simula considerando los recursos actuales. Los resultados muestran que el modelo es muy similar a la situación actual. A partir del análisis de sensibilidad se propone una lista de mejoras. Se observa que la disponibilidad aumenta bastante al agregar una bahía. El modelo es genérico y se puede aplicar a otras faenas mineras, así también como a otros tipos de maquinarias.


ABSTRACT

Workshop resources are key factors that affect mining trucks’ availability. For the maintenance contractor, it is crucial to verify the sensitivity of this indicator when the resources vary, especially for performance-based service contracts. This work presents a workshop simulation model. The study case considers a fleet with two types of trucks. In order to validate the model, the workshop was simulated considering current resources. Results show a close agreement between the simulation and the actual situation. A list of improvements is proposed from sensitivity analysis. It is observed that significant availability can be gained by adding an extra maintenance bay. The modeling approach is generic and can be applied to other mining contracts, as well as to other kinds of machinery.

ANÁLISIS DE PRODUCTIVIDAD DE TRANSPORTE DE CARGA EN UNA MINA DE COBRE RAJO ABIERTO

PRODUCTIVITY ANALYSIS OF A HAUL-TRANSPORT SYSTEM IN AN OPEN PIT COPPER MINE

Javier Rebolledo, Sebastián Silva & Walter Tejada
Departamento de Ingeniería Mecánica, Facultad de Ciencias Físicas y Matemáticas,
Universidad de Chile


Rodrigo Pascual
Centro de Minería, Pontificia Universidad Católica de Chile

MANTEMIN 2009. Antofagasta, Chile

RESUMEN

Este artículo describe el modelo usado para estimar el rendimiento esperado para diferentes configuraciones de un sistema carguío-transporte. El estudio de caso toma lugar en una mina de rajo abierto en Chile. Se desarrolla una simulación y análisis de sensibilidad para estimar la importancia de incrementos en la disponibilidad de flota. Resultados muestran que un incremento en la disponibilidad de los camiones de 82 a 87% implicaría sólo un 2% de incremento en el rendimiento del sistema.


ABSTRACT

This paper describes the model used to estimate the expected system throughput for different design configurations of a mining haul-transport system. The case study takes place in an open pit copper mine in Chile. Simulation and sensitivity analyses are developed to estimate the effect of truck availability gains. Results suggest that increasing truck availability from 82% to 87% would only indicate a 2% system throughput increase.



ANÁLISIS INTEGRADO DE CONFIABILIDAD PARA LA NEGOCIACIÓN ÓPTIMA DE CONTRATOS DE MANTENIMIENTO

Mapla 2007, 5-7 Sept. 2007, Viña del Mar

 

Canek Jackson y Rodrigo Pascual

Universidad de Chile

 

RESUMEN

En la actualidad, existe una gran tendencia en subcontratar operaciones en las que el mantenimiento de un equipo se realiza de manera externa a la empresa propietaria de la unidad. De esta manera, existe un proveedor del servicio (contratista) que ofrece un contrato de mantenimiento al propietario de la máquina (mandante), y cuyos términos incluyen la estructura tarifaria de pago, así como posibles cláusulas de penalización en caso de incumplimientos.

En el presente trabajo se desarrolla un modelo para la determinación óptima de las es­trategias de mantenimiento a establecer en un contrato de estructura tarifaria dada, cuyo valor es definido mediante negociación entre las partes. El modelo permite la integración de los resultados en diferentes planos de confiabilidad: equipos sin envejecimiento, man­tenimiento imperfecto, reparaciones mínimas y procesos de renovación. Los resultados muestran reducciones de hasta más de un 95% en las utilidades generadas por las partes, sólo por el hecho de considerar que el equipo envejece en el tiempo. La implementación nu­mérica del modelo permite entonces, dependiendo del tipo de intervenciones preventivas a las que se someta el equipo, determinar las variables de decisión relevantes involucradas en un contrato para servicios de mantenimiento, como lo son: el período de reemplazo del equipo y el período entre overhauls.

 

 

 

El Eslabon Roto: Educación en Gestión de Activos Físicos

Mapla 2007, 5-7 Sept. 2007, Viña del Mar

R. Pascual

 

Abstract

La presentación incluye un marco para comprender la brecha que existe entre la educación y la practica de la ingeniera en lo que se refiere a la gestión de activos físicos. Se hace énfasis en la necesidad de orientar los programas a alcanzar competencias que sean de real aplicación en nuestro entorno.

 

Presentación

 

 

 

 

 

Maintenance and replacement policies for protective

devices with imperfect repairs

A. Pak (1), R. Pascual (2), A.K.S. Jardine (1)

(1) Department of Mechanical and Industrial Engineering,

University of Toronto, Toronto, Canada

(2) Department of Mechanical Engineering,

Universidad de Chile, Santiago, Chile

 

Maintenance and Reliability Conference

MARCON 2007

May 8-11, 2007

Knoxville Tennessee

 

Abstract



This work considers setting an optimal policy for inspection, repair, and replacement (IRR) of a protective system. Failures of protective systems are hidden and can only be discovered during inspections or an actual case of emergency. The model proposed here considers maximization of expected interval availability of a protective system during a given interval of time. In this model, at any decision epoch we use dynamic programming to determine the optimal time to next inspection, and the type of action to be undertaken, depending on the observed state of the device. During a perfect inspection (all failures can be detected) and in case failure was detected, an immediate repair or replacement is performed and optimal time to next inspection is determined. In case when the system was found in operating condition, immediate repair or replacement can be performed or an optimal time to next action found. It is assumed that repairs are imperfect, i.e. they change the distribution of times to failure. The IRR policy is constrained by a maximum number of repairs and a maximum operating age limit. The proposed model has been applied to a set of real industrial data. Results and discussion are included.

Keywords: protective device, inspection interval, non-periodic inspection, imperfect repair, dormant failures

 

full paper

 

 

 

Optimization of Inspection Decisions of Safety Related Systems

R. Pascual

2nd International Maintenance Excellence Conference

Toronto, November 1-3, 2006.

Abstract

The recent introduction of International Standard IEC 61508:2004 and its industry-specific derivatives sets demanding requirements for the definition and implementation of lifecycle strategies for safety systems. Compliance with the Standard is important for human safety and environmental perspectives as well as for potential adverse economic effects (e.g. damage to critical downstream equipment or a clause for an insurance or warranty contract). This situation encourages the use of reliability models to attain the recommended safety integrity levels using credible assumptions.During the operation phase of the safety system life-cycle, a key decision is the definition of an inspection program, namely its frequency and the maintenance activities to be performed. These may vary from minimal checks to complete renewals. This work presents a model (which we called rho-beta  model) to find optimal inspection intervals for a safety system,considering that it degrades in time, even when it is inspected at regular intervals. Such situation occurs because most inspections are partial, that is, not all potential failure modes are observable through inspections.

Possible reasons for this are the nature and the extent of the inspection, or potential risks generated by the inspection itself. The optimization criterion considered here is the mean overall availability Ao, but also taking into account the requirements for the safety availability As. We consider several conditions that ensure coherent modelling for these systems: sub-systems decomposition, k-out-of-n architectures, diagnostics coverage (observable/total amount of failure modes), dependent and independent failures, and non-negligible inspection times. The model requires an estimation for the coverage and dependent-failure ratios for each component, global failure rates, and inspection times. We illustrate its use through case studies and compare results with those obtained by applying previously published methodologies.

 

Keywords: safety system, inspection program, availability, IEC 61508, redundancy, coverage ratio, non-periodic inspection, partial inspection.

 

Presentation

 

Optimización en la toma de decisiones de gestión de activos físicos en minería

R.Pascual

1er Encuentro de Mantenedores de Equipos Mina

MANTEMIN

Iquique, 25-27 Octubre 2006.

 

La presentación entrega un marco general para establecer una estrategia de gestión objetiva y basada en evidencia. Así mismo se  presentan varios modelos matemáticos para el apoyo a la toma de decisiones.

   

Presentación

 


 

OPTIMAL MAINTENANCE SERVICE CONTRACT NEGOTIATION WITH AGING EQUIPMENT

Canek Jackson, Rodrigo Pascual

Departamento de Ingeniería Mecánica, Universidad de Chile

Beauchef 850, Santiago

 

XII Congreso Chileno de Ingeniería Mecánica (COCIM’06)

8-10 Noviembre 2006, Talca

 

Abstract: In recent years, there has been a growing trend to out-source service operations in which the equipment maintenance is carried out by an external agent rather than in-house. Often, the agent (service provider) offers more than one option and the owners of equipment (customers) are faced to the problem of selecting the optimal option, under the terms of a contract. In the current work, we develop a model and report results to determine the agent’s optimal strategy for a given type of contract. The model derives in a non-cooperative game formulation in which the decisions are taken by maximizing expected profits. This work extends previous models to consider the realistic case of equipments having an increasing failure intensity due to imperfect maintenance, instead of the standard assumption that considers failure times are exponentially distributed (constant failure intensity). We develop the model using a linear function with time to characterize the failure intensity. The main goal, for the agent, is to determine the pricing structure in the contract and the number of customers to service. In the other hand, for the clients, the main goal is to define the period between planned actions for preventive maintenance and the time to replace equipments. In order to give a complete characterization of the results, we also carry out a sensitivity analysis over some of the factors that would influence over the failure intensity.

 

 

 

Link programa

 

 

 

PLANIFICACIÓN ÓPTIMA DE MANTENIMIENTO

EN INFRAESTRUCTURAS CIVILES

Sergio Courtin V., Rodrigo Pascual J.

Departamento de Ingeniería Mecánica, Universidad de Chile

Beauchef 850, Santiago

 

XII Congreso Chileno de Ingeniería Mecánica (COCIM’06)

8-10 Noviembre 2006, Talca

 

Resumen. En el presente trabajo se presenta un modelo de optimización para planificar las actividades de mantenimiento en infraestructuras civiles. En un primer análisis la función objetivo considera los costos en un periodo estratégico. Las restricciones son el presupuesto y la capacidad de reacondicionamiento. El modelo propuesto permite examinar numerosos escenarios presupuestarios. Se presenta un caso numérico para mostrar el uso del modelo, además se realiza un análisis de sensibilidad de las variables.

   

Link programa

 

 

 

 

Repair, overhaul and replacement policies

with buffers and alternative production

methods

 

1st International Maintenance Excellence Conference, Toronto

November 2005

 

R. Pascual

 

Department of Mechanical Engineering, Universidad de Chile, Casilla 2777,

Santiago, Chile

 

Abstract

This work proposes a general framework to study and improve the effectiveness of a production system with respect to its expected life-cycle cost rate. The model that we propose considers that the system is protected against demand fluctuations and failure occurrence with elements like stock piles, line and equipment redundancy, and the use of alternative production methods. These design elements allow us to keep or minimize the effect of equipment downtime on the nominal throughput, while palliative measures are taken. The system is also subjected to an aging process which depends on the frequency and quality of preventive actions. Decisions are diffcult because there exist discontinuities in direct and downtime costs and there is a limited budget. We present a non-linear mixed integer formulation that minimizes the expected global cost rate with respect to repair, overhaul and replacement times and overhaul improvement factor. The model is deterministic and considers minimal repairs and imperfect overhauls.We illustrate its application using a known example from the literature.

 

Key words: decision-making, downtime cost, maintenance policies, repair rate,

replacement,imperfect maintenance, decision support systems, consequential cost,

budget constraint

full paper (working version)

presentation

 

ANALYSIS OF TRANSIENT LOADS ON CABLE-REINFORCED CONVEYOR

BELTS WITH DAMPING CONSIDERATION

 

XXVI Iberian Latin-American Congress on Computational Methods in Engineering CILAMCE 2005

 

R. Pascual

V. Meruane

rpascual@ing.uchile.cl

vmeruane@ing.uchile.cl

Mechanical Engineering Department, Universidad de Chile, Beauchef 850, Santiago, Chile

G. Barrientos

gbarrien@udec.cl

Mechanical Engineering Department, Universidad de Concepci´on, Concepci´on, Chile

Abstract. This work presents a methodology to compute dynamic stress distributions on large conveyor belts considering a viscous-damping model. Results could be very useful at the conveyor design stage since at starts and stops of the system, large dynamic loads may be encountered. Such loads may produce a catastrophic failure of the conveyor, with important direct and downtime costs. We present a finite- element based methodology and use the Newmark time-integration method to solve the transient responses. Our scheme includes the effects of damping. A real-life industrial case is analyzed and three critical situations are considered: normal stop, sudden stop, suddenly aborted start. Results are shown in terms of dynamic loads at critical points of the system. The simulations show that the damping effects are negligible in the analysis of real-life designs, thus allowing the use of the analytical solution. For the analized case, maximum loads obtained with the present methodology are smaller in 5% than those obtained with the conservative approach.

Keywords: Structural dynamics, large conveyor belts, finite element, transient analysis.

 

Full paper

 

 

OPTIMAL PREVENTIVE AND REPLACEMENT POLICIES FOR

INDUSTRIAL SYSTEMS WITH BUFFERS

 

XXVI Iberian Latin-American Congress on Computational Methods in Engineering CILAMCE 2005

 

R. Pascual

rpascual@ing.uchile.cl

Department of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile

P. Rey

preyy@dii.uchile.cl

Department of Industrial Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile

Abstract.

This work proposes a general framework to study and improve the effectiveness of a production system with respect to its expected life-cycle cost rate. The model that we propose considers that the system is protected against demand fluctuations and failure occurrence with elements like stock piles, line and equipment redundancy, and the use of alternative production methods. These design elements allow us to keep or minimize the effect of equipment downtime on the nominal throughput, while palliative measures are taken. The system is also subjected to an aging process which depends on the frequency and quality of preventive actions. Decisions are difficult because there exist discontinuities in direct and downtime costs and there is a limited budget. We present a non-linear mixed integer formulation that minimizes the expected global cost rate with respect to repair, overhaul and replacement times and overhaul improvement factor. The model is deterministic and considers minimal repairs and imperfect overhauls. We illustrate its application using a known example from the literature.

Keywords: decision-making, downtime cost, maintenance policies, repair rate, replacement,

imperfect maintenance, decision support systems, consequential cost, budget constraint

 

full paper

 

 

El Método Proyecto: una estrategia en la Enseñanza de Ingeniería Civil Mecánica

R. Pascual

Departamento de Ingeniería Mecánica, Universidad de Chile

Beauchef 850, Santiago, rpascual@ing.uchile.cl

 

R. Uribe

Escuela de Ingeniería, Universidad de Chile

Beauchef 850, Santiago, rouribe@ing.uchile.cl

Agosto 2005

 

XIX Congreso Chileno de Educación en Ingeniería

Pucon, 5-7 Octubre 2005

 

Abstract

Este trabajo presenta la aplicación y evaluación del método proyecto (MP), en un curso de especialidad de la carrera de Ingenieraıa Civil Mecánica. Esta metodología permitió desarrollar habilidades pertinentes y significativas para los ingenieros en formación tales como: toma de decisiones, trabajoen equipo, presentar y defender ideas, aprendizaje autónomo, manejode conflictos, entre otros. La evaluación de la iniciativa fue medida a través de una encuesta de satisfacción a los alumnos y una evaluación de los ingenieros responsablesdel mantenimiento en las empresas analizadas en el proyecto. Los resultados muestran que la experiencia fue exitosa pues el aprendizaje logradofue de carácter significativo.

 

Working paper

 

 

 

 

ASSESSING STRUCTURAL DAMAGE USING HIGH-SPATIAL DENSITY

MEASUREMENTS

CILAMCE 2004, Recife, Pernambuco, November, 2004.

R. Pascual

rpascual@ing.uchile.cl

Departamento de Ingeniería Mecánica, Universidad de Chile

Beauchef 850, Casilla 2777, Santiago, Chile

M. Razeto

R. Schalchli

mrazeto@udec.cl

rschalchli@udec.cl

Departamento de Ingeniería Mecánica, Universidad de Concepción

Casilla 53-C, Concepción, Chile

Abstract.

We study some limitations that appear when using the Minimization of Error on Constitutive Equations (MECE) technique for damage identification purposes. The proposed strategy is based on measuring the distance between experimental and numerical vibration data. In practice, measurements yield only partial mode shapes with respect to the total degrees of freedom present in the corresponding finite element model. Thus, before any damage detection method is implemented, the experimental mode shape has to be expanded to the same dimension of the numerical mode shape. We discuss the expansion/damage assessment process and we use an optimized choice for the size of the expansion basis, the number of experimental degrees of freedom (DOFs) and the sensor placement. We introduce an indicator to evaluate the problems inherent to the expansion/damage detection process using MECE. It provides insight of the inherent limitations of MECE and helps the decision making process on how many degrees of freedom should be measured and how many mode shapes should be used in the expansion basis. The procedure is illustrated using a finite element model of a plate-like structure, where the damage state is simulated as a reduction of the local stiffness.

Keywords: mode shape expansion, high spatial density measurements, damage detection, finite

Element

 

Full paper

 

 

Optimal replacement and overhaul decisions with imperfect maintenance

and warranty contracts

International Conference on Intelligent Maintenance Systems

Arles, France, 2004

R. Pascual

Department of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile

Phone: +56-2-6784591 Fax:+56-2-6896057

rpascual@ing.uchile.cl

Abstract

In this article we develop a model to help a maintenance decision-making situation of a given equipment. We propose a novel model to determine optimal life-cycle duration and intervals between overhauls by minimizing global maintenance costs. We consider a situation where the customer, which owns the equipment, may negotiate a better warranty contract by offering an improved preventive maintenance program for the equipment. The equipment receives three kind of actions: repairs, overhauls, and replacement. An overhaul represents an imperfect maintenance action, that is, the failure rate is improved but not a point that the equipment is as good as new. Corrective maintenance actions are minimal, in the sense that the failure rate after each repair is the same as before the failure. The proposed strategy surpasses others seen in the literature since it considers at the same time the warranty negotiation situation and the optimal life-cycle duration under imperfect preventive actions. We also propose a simplified approach that facilitates the task of implementing the method in standard spreadsheet solvers.

 

Full paper

 

 

Damage Identification in Composite Plates by Dynamic

Displacement Measurements

G. Coppotelli, R. Di Conza, F. Mastroddi, R. Pascual, M.A. Caponero

Dipartimento di Ingegneria Aerospaziale e Astronautica,

Universit`a degli Studi di Roma “La Sapienza”, Rome, Italy

e-mail: giuliano.coppotelli@uniroma1.it

Departamento de Ingenier´ýa Mec´anica

Universidad de Chile, Santiago, Chile

e-mail: rpascual@ing.uchile.cl

Centro Ricerche Frascati

Ente Nazionale Energie Alternative, Frascati, Italy

e-mail: caponero@frascati.enea.it

Abstract

Assessing structural health from vibration measurements appears as an advantageous approach to monitorthe conditions and performances of mechanical systems. An accurate knowledge of the dynamic behavior of the structure can be considered as a prime source of basic information for the detection of possible damages occurring in the structure and, above all, the evaluation of this behavior from operating conditions represents the potential gain this approach can offer since structures can be monitored continuously during their operative life. In this paper, two different experimental techniques for structural damage identification, based both on the changes of modal and response characteristics, have been considered and compared. The identification of an “acceptance criterion” to be considered not only when the structure is being manufactured, but

also during its working life, represent the main topics of this work, together with an investigation among the different approaches considered in evaluating the health of the structure via dynamic measurements.

 

Full paper

 

 

 

EXPLOITING HIGH-SPATIAL DENSITY VIBRATION MEASUREMENTS AND FE MODELS FOR DAMAGE IDENTIFICATION

8th Pan American Congress of Applied Mechanics (PACAM), La   Habana, Cuba, 2004

 

R. Pascual, R. Schälchli, M. Razeto

Mechanical Engineering Department, Universidad de Chile

Casilla 2777, Santiago, Chile

e-mail:  rpascual@ing.uchile.cl

 

Abstract

Model based damage assessment is based on measuring the distance between experimental and analytical results. In practice, measurements yield only partial mode shapes with respect to the total degrees of freedom (DOFs) present in the corresponding finite element model. Thus, before any damage detection method is implemented, the experimental mode shape have to be expanded to the same dimension of the numerical mode shape. Mode shapes expansion is a key point in the damage localization process, since actual defects of the structure may be hidden by expansion errors. This paper introduces a new general procedure to the expansion/damage assessment process using an optimal choice for: the size of the expansion basis, the number of experimental DOFs and the sensor placement. We introduce a new indicator to evaluate the problems inherent to the expansion/damage detection process using the Minimization of Error on Constitutive Equations (MECE) technique [1]. It provides insight of the inherent limitations of MECE and helps the decision making process on how many degrees of freedom should be measured and how many mode shapes should be used in the expansion basis. The procedure is illustrated using a finite element model of a plate-like structure, where the damage state is simulated as a reduction of the local stiffness.

 

full paper

 

 

DAMPING IDENTIFICATION USING A ROBUST FRF-BASED MODEL

UPDATING TECHNIQUE

International Modal Analysis Conference, Florida, USA, 2003.

 

Rodrigo Pascual, Roberto Schalchli and Mario Razeto

Department of Mechanical Engineering

Universidad de Chile, Beauchef 850

Santiago, Chile. E-mail: rpascual@ing.uchile.cl

 

ABSTRACT

Frequency Response Functions (FRFs) residues have been widely used in time to update Finite Element models. The main reasons for this are that FRFs are very sensitive to modal properties such as damping, local modes influence is included, and no modal analysis is strictly required. Nevertheless, it is well known that due to the nature of the FRFs, model updating strategies may suffer serious discontinuities in the topology of the objective function, causing the updating procedure to diverge or to find a local non-physical minimum. This paper addresses the situation by presenting a residue that avoids such numerical instabilities. In particular we concentrate on damping  identification. A benchmark from a European group is used to assess the goodness of the method compared to other well known techniques.

 

Full paper

 

 

A Robust FRF-based technique for Model Updating

International Conference on Noise & Vibration Engineering ISMA27, Leuven Belgium

September 2002

R. Pascual, M. Razeto, J.C. Golinval, R. Schalchli

Mechanical Engineering Department, Universidad de Chile

Casilla 2777, Santiago, Chile

LTAS, Universit´ e de Li` ege

Chemin des chevreuils, 1, B-4000, Li` ege, Belgium

e-mail: rpascual@ing.uchile.cl

 

full paper

Abstract

Frequency Response Functions (FRFs) residues have been widely used in time to update Finite Element models [2, 3, 4, 5, 6, 11, 12, 14, 15, 16]. Major reasons for this is that FRFs are very sensitive to damping properties at resonance peaks, local modes influence is included and no modal analysis is required. Nevertheless, it is well known that due to their nature, the frequency responses may change its order of magnitude very rapidly for small parameter or frequency changes. This situation may cause serious discontinuities in the topology of the objective function, causing the updating strategy to diverge or to find a local non-physical minimum

[5, 15, 18]. A primary tool for the correlation of FRFs is the Frequency Domain Assurance Criterion [19].This technique introduces the concept of frequency shift between the frequency response shapes of a reference model (the experimental structure) and a perturbed model (an initial non-updated FE model). Such a concept

opens the way for using residues at different frequencies. For instance, in reference [6] the residue is composed by point FRFs at anti-resonances. This paper introduces a general FRF-based model-updating technique, which is focused in using stable residues during the interactive optimization procedure. A benchmark case from the Cost F3 action is used to assess the goodness of the method compared to other well known methods.

 

 

NUMERICAL AND EXPERIMENTAL ANALYSIS ON THE DYNAMIC BEHAVIOUR OF THE VIOLIN PLATES

International Conference on Noise & Vibration Engineering ISMA27, Leuven Belgium

September 2002



Claudia Staforelli C*., Mario Razeto M.*, Rodrigo Pascual**

*Mechanical Engineering Department, Universidad de Concepción, Chile

Casilla 160 C – Concepción, Chile. E-mail mrazeto@udec.cl.

** Mechanical Engineering Department, Universidad de Chile, Chile

Casilla 2777, Santiago, Chile. E-mail: rpascual@ing.uchile.cl




Abstract



The study of dynamic and vibratory behavior of violins consider the effect of the different parts that compose it for the resulting sound. The top and back plates have great importance in the transmission of vibrations and the timbre characteristic of the violin, centering the study in their vibratory behavior. Experimental tests determine the vibrational modes with their resonant frequencies of the top of a violin. A numerical model of the plate is made by means of the finite elements method, to determine the influence of the different mechanical and geometric properties on its main vibrational modes and natural frequencies; different methods are found to make changes in their structure with the objective to obtain the expected acoustic answers. The distribution of thicknesses or the height in the arch is modified to obtain different effects on the frequencies and the vibrational modes.

 

Full paper

 

NUMERICAL AND EXPERIMENTAL ANALYSIS OF THE VIOLIN

DYNAMICS BEHAVIOUR

 

Seventh Pan American Congress of Applied Mechanics, PACAM VII

Universidad de La Frontera, Temuco,Chile, 2 - 5 January, 2002

 

Claudia Staforelli1, Mario Razeto1, Rodrigo Pascual2

1Departamento de Ingeniería Mecánica, Universidad de Concepción, Chile

Casilla 160 C – Concepción, Chile. E-mail mrazeto@udec.cl.

2Departamento de Ingeniería Mecánica, Universidad de Chile,

Beaucheff 850, Casilla 2777, Correo 21, Santiago, Chile

 

Abstract

Famous luthiers have studied the importance of geometry properties of the wood in the acoustic qualities of the violins. Later works developed by scientists have given varied bibliographical information on the acoustic characteristics of the great violins, centering attention in the mechanical and acoustic properties of their main components (its covers and bottom). With the objective to study the influence of these different physical and geometric parameters, in the present work a model was made by means of finite elements to analyze the dynamic behavior of his main parts.

 

Full paper

 

ANÁLISIS NUMÉRICO Y EXPERIMENTAL DEL COMPORTAMIENTO DINÁMICO DE UN VIOLÍN

 

XII Congress on Numerical Methods and their Applications
October 30th - November 2nd, 2001, Córdoba - Argentina

http://www.efn.uncor.edu/otros/enief/

 

Claudia Staforelli, Mario Razeto, Rodrigo Pascual

1Departamento de Ingeniería Mecánica, Universidad de Concepción, Chile

Casilla 160 C – Concepción, Chile. E-mail mrazeto@udec.cl.

2Departamento de Ingeniería Mecánica, Universidad de Chile,

Beaucheff 850, Casilla 2777, Correo 21, Santiago, Chile

ABSTRACT

A numerical and experimental study of the plates of a violin was made, taking into account the effect that different physical and mechanical factors produce on their dynamic response.

Experimental tests were conducted to determine the eigenmodes, along with the resonant frequencies, of the cover of a violin. A numerical model of the board by means of the finite element method was made, to determine the influence of the different mechanical and geometric properties on its eigenmodes and frequencies; finding methods that allow to make changes in their structure with the purpose of obtaining the expected acoustic response. Modifying the distribution of thicknesses or varying the arching, different effects were obtained on the frequencies and the eigenmodes.


Full paper

 

ASSESSMENT OF A RESIDUAL ENERGY ERROR

INDICATOR FOR MODEL UPDATING

 

International Conference on Structural System Identification, Kassel, Alemania, 2001.

 

 

Rodrigo Pascual1, Jean-Claude Golinval2, Mario Razeto3

1Departamento de Ingeniería Mecánica, Universidad de Chile,

Beaucheff 850, Casilla 2777, Correo 21, Santiago, Chile

2Université de Liège, LTAS - Vibrations et Identification des Structures,

Chemin des Chevreuils, 1 (Bât. B52), 4000 Liège, Belgium

3Departamento de Ingeniería Mecánica, Universidad de Concepción,

Casilla 53-C, Concepción, Chile

 

SUMMARY: Error localization techniques for model updating from test data seek the regions where damage or model errors may be present, being these places responsible for the discrepancies between the analytical and experimental results. The aim of this paper is to analyze the limitations of the indicator proposed by the Minimization of Errors in the Constitutive Equation (MECE) to locate model errors. This indicator is based on a residual strain energy result of the unbalance in the finite element model equilibrium equation. To perform the analysis, first a brief explanation of the expansion methods is presented, then the error localization technique is explained. Numerical examples verify the ability of the MECE indicator to produce good localization results. Beyond that, the work highlights several problems related to the use of the indicator and several techniques are here proposed to avoid these difficulties. These techniques allow the analysis of confidence in the damage detection procedure and appear to be valuable tools to evaluate localization results.

 

KEYWORDS: model updating, damage assessment, error localization.

Full paper

 

DAMAGE DETECTION USING MODEL UPDATING AND

IDENTIFICATION TECHNIQUES

R.Pascual

Université de Liège, Vibrations et Identification des Structures,

rue E. Solvay, 21-C3, B-4000 Liège, Belgium (R.Pascual@ulg.ac.be)

I.Trendafilova

Department of Mechanical Engineering, PMA, KULeuven, Celestijnenlaan

300 B, B-3001 Heverlee, Belgium (Irina.Trendafilova@mech.kuleuven.ac.be)

J.C.Golinval

Université de Liège, Vibrations et Identification des Structures,

rue E. Solvay, 21-C3, B-4000 Liège, Belgium (JC.Golinval@ulg.ac.be)

W. Heylen

Department of Mechanical Engineering, PMA, KULeuven, Celestijnenlaan

300 B, B-3001 Heverlee, Belgium (Ward.Heylen@mech.kuleuven.ac.be)

 

2nd International Conference on Identification

in Engineering Systems,  Swansea, UK, 1999.

 

ABSTRACT

The problem for damage detection and localisation is approached employing two different techniques for fault localisation and quantification. A case study on a reinforced concrete beam with distributed damage of crack accumulation is studied. The measured frequency response functions are used as vibration data for the structure, on the basis of which the localisation procedures are performed. The considered localisation procedures are model based and use a FE model of the structure. One of the approaches suggests the use of a residual energy criterion for the fault localisation, followed by an updating procedure for an eventual quantification of the defect. The other procedure employs pattern recognition techniques for a primary localisation of the damage in a part of the structure, followed by an identification procedure for more accurate localisation and quantification. A comparison of the results and performance of both techniques is provided.

 

Full paper

 

 

Model based Structural Damage Assessment Using Vibration Measurements

Ph.D. Thesis, Université de Liège, 1999.

Outline

The objective of this work is to introduce the developments made in several steps of the updating/damage assessment procedure. Except for the chapter on correlation techniques and the second part of the chapter on model updating methods, the thesis is guided by the method of Minimization of Errors on Constitutive Equations (MECE). Thus, instead of following the time-descendent line in schema (2), We will link chapters 2 to 5 in a common framework.

In the first place, a study of the correlation techniques in the three domains (time, frequency, modal) is done. In particular we focus on the correlation in the frequency domain that did not, up to the present, consider the shift in frequency caused by the errors of the model. TWO techniques are introduced for measuring the correlation between the experimental operating deflection shapes and those of the numerical model. They indicate the range of frequencies where the model matches the experimental responses and help in the decision of the best frequencies to build residues for the model updating based on operating deflection shapes.

In chapter 2, the problem of expansion of the measured mode shapes is discussed. Emphasis is put on the comparison of the different expansion methods. It Will be seen that they can al be expressed as optimization problems whose objectives are similar:

find an expanded shape that fits the measurements and that minimizes the error of equilibrium in the equation of motion of the model. The differences appear from the weights used to solve the problem and the confidence given to the measurements. The approaches considered in this work are compared to previous works, and their limitations are also discussed. Based on reference [22] We propose three implementations of the expansion based on the MECE. The first version fits exactly the measured mode shapes but provides biased results When the effects of noise are not negligible. The second version uses a quadratic inequality constraint for the fitting term. Thus, it is able to hand the presence of noise, but it is necessary to determine a good bound parameter for the constraint. The third version considers expanded mode shapes obtained through a projection in the modal basis of the model. Again in this case, noise is handled but the expanded vector may be too smooth if the basis is not large enough.

At the error localization level (chapter 3), e concentrate on the limitations of the MECE error indicator. As result of the analysis We propose two indicators that quantify the limitations inherent to the localization using MECE. They appear to be valuable tools in deciding the performance of the expansion step before testing is done and allow an optimal choice for the modal basis for expansion and the placement of the sensors. In order to estimate the influence of noise on the expanded vector (Which is the input of the localization technique) a Monte Carlo simulation [103] is proposed.

The problem of sensor placement is treated in chapter 4 and presents several techniques to optimize the limited numbers of sensors that are available. Emphasis is put on the strong relationship between the step of expansion and the one of sensor placement. We show that a well known sensor placement [63] oriented initially towards modal analysis, also produces optimal configurations for the MECE localization.

Updating of the finite element model is treated in chapter 5. We develop two recent ideas: the first one considers the implicit coupling [ that exists between the process of expansion (which uses a model with errors) and the process of updating (Which uses the expanded vector) and We propose an improved method considering the MECE updating problem. The second idea is to consider the concepts of shift in the frequency domain

(treated in chapter 1) in the adjustment process using operating deflection shapes. The method that will be proposed produces a more balanced residue in the updating equations.

Several application examples are presented in chapter 6 to validate the proposed techniques.

 

 

Full document

 

 

On-line damage assessment using Operating Deflection Shapes

R. Pascual, J. C. Golinval, M. Razeto

IMAC XVII : 17th international modal analysis conference  (Kissimmee FL, 8-11 February 1999)

 

Abstract

Structural health monitoring using measured vibration data may (or not) be based on a numerical model. If a structural model is not available, the measurements of the nominally healthy structure have to be used as the baseline for comparison. In this way, alterations of the behavior may be tracked. This approach can be considered as a reactive way to handle the problem since the engineer will detect that the characteristics of the structure changed, but he will not know if the modification(s) render(s) the structure unreliable. The exploitation of a numerical model allows the application of a more rich, proactive strategy. In some conditions, the analyst may even be able to diagnose the remaining lifetime of the structure. A common approach to health monitoring is to use identified modal data. In this paper, the direct use of operating deflection shapes (ODS) is considered The main advantage of this approach is that ODS are more sensitive to structure modifications than mode shapes which have to be identified; moreover, the modal analysis efforts (and errors) are avoided. In this paper, a two level approach for damage assessment is presented. In the reactive level, current experimental ODS are compared to the healthy measured ODS. The Frequency Domain Assurance Criterion -FDAC- is used to track a global evolution and the shifted residual ODS technique is used to obtain a first damage localization. If changes in the ODS are significant, the proactive level of damage assessment is activated. It uses a FE model and is based on the theory of Minimization of Errors on Constitutive Equations -MECE- to locate and quantify damage in terms of physical parameters. The proposed methods are applied on the example of an actual civil engineering structure on which the time evolution of damage is known.

 

Full paper

 

 

MODEL UPDATING USING

OPERATING DEFLECTION SHAPES

R. Pascual, J. C. Golinval, M. Razeto

International Modal Analysis Conference 1998

 

 

ABSTRACT

Model updating using a structural model is based on the analysis of the discrepancies between analytical and experimental results. In order to compare these quantities, a matching process is necessary.The updating procedure can be based on mode shapes or on operating deflection shapes. The operating deflection shapes correspond to the deformations that the structure suffers when it is excited with an harmonic force. The direct use of operating deflection shapes for model updating is interesting since they contain information on all the excited mode shapes. Moreover, their reliability can be evaluated by the coherence function. Thus the errors associated to modal identification are avoided. The local error indicator considered in this paper is an extension of a technique already used with expanded mode shapes. Physical insight is straightforward since the error measure corresponds to a local strain energy. Then, model correction can be performed by minimizing energy residuals.

 

Full paper

 

UPDATING INDUSTRIAL MODELS UNDER

A GENERAL OPTIMIZATION ENVIRONMENT

R. Pascual , J.C. Golinval,  M. Berthillier, T. Després

 

ABSTRACT

Model updating techniques are widely used by analysts in order toverify and eventually improve the correlation between analytical and experimental results.The application of such techniques in large scale models is made difficult by the inverse nature of the problem which allows multiple solutions. Also the increasing computational power of computers and theimprovement of analytic algorithms to manage large problems generates an accelerated tendency to over-discretize the FE models, which reduces even more the ratio between measured and analytical degrees of freedom, and increase substantially thenumbers of potential adjusting parameters. Thus, the situation points towards the use of reduction techniques to solve the matching incompatibility without loosing accuracy of the analytical results. This paper deals with the tuning of FE models using experimentalmeasures. It considers the use of appropriate cost functions that express the discrepancies between the analytical and experimental models in the modal space. The technique is successfully implemented in a general purpose optimization package used for industrial applications. This environment allows an open choice of the design parameters, and to perform easily parametric studies, statistical analyses, multi-objective optimizations.

 

Full paper

 

 

A Frequency Domain Correlation Technique

for Model Correlation and Updating

R. Pascual, J. C. Golinval, M. Razeto

International Modal Analysis Conference 1997

Up to now, existent FRF based model updating methods use the differences between measured and analytical FRFs at a fixed frequency, as residual to minimize. This approach does not take into account that FRFs between a reference model (experimental) and a perturbed one (a finite elements model not yet updated), displace in two axes : amplitude and frequency. A more physical correlation, then, uses also the frequency shift . The problem is how to find it.Taking as base the well known Modal Assurance Criterion (MAC), the Modal Scale Factor (MSF), and the concept of frequency shift, two correlation techniques, the Frequency Domain Assurance Criterion (FDAC) and the Frequency Response Scale Factor (FRSF), are presented. They help to quantify the level of correlation between responses coming from the two models, determine the frequency shift at all measured frequencies, and establish a suitable set of frequencies to use during the updating procedure.

 

Full paper

 

Adaptación de modelos basada en las respuestas dinámicas: Una comparación de métodos

R.Pascual, M.Razeto

Universidad de Concepción

 

9 Congreso sobre métodos numéricos y sus aplicaciones (ENIEF’95)

Centro Atómico de Bariloche, Argentina, 1995.

 

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