Dual-Mode Vibration Isolator/Absorber System

Analysis and Design of a Nonholonomic, Impact-Based, Dual-Mode Vibration Isolator/Absorber System

Sponsor: National Science Foundation (NSF CMMI-1663376)

Role: Harvey (PI)

Duration: 08/2017 - 07/2020

Students: Skylar Calhoun (MS), Corey Casey (MS), Mohammad Tehrani (PhD), Thomas Cain (MS), Puthynan Bin (MS), Mehrun Nisa (MS)

Abstract:

The objective of this project is to insulate sensitive contents of a building from disruptions due to vibration, while also preventing severe damage to the structure of the building from large motions, such as from an earthquake. This will be achieved by advancing and combining the techniques of vibration isolation and vibration absorption, which have previously only been applied independently or in parallel. An effective method of protecting sensitive equipment from small amplitude building motion is a vibration isolation platform, supported by rollers. However, when the building motion is sufficiently large, as in an earthquake, the overriding concern becomes preventing the possible collapse of the structure. In this case a vibration absorber can be used to transfer mechanical energy out of the structure. This project uses the same system to act as a vibration isolator when the building motion is small, and as a vibration absorber when the building motion is large. The hybrid device is created using purely passive mechanical elements, each consisting of a ball rolling between two concave plates, with a restraining wall or similar structure at the boundary of the concave region. When the amplitude of motion is small, the ball remains near the center of the plates. As the motion becomes large, the ball will eventually impact the restraining structure, marking the transition from vibration isolator to vibration absorber. This project will relate parameters such as the curvature of the concave plates, the size of the concave region, and the materials of the plates and restraining boundary to the isolation and absorbing properties of the device. The results of this work will be used to minimize disruption to business operations, damage to structures, and injury to building occupants. Web-based demonstration of the concept will facilitate education and outreach to building owners, structural engineers, and future professionals.

This project aims to answer the ongoing question: How can systems and their subsystems be designed to achieve synergistic interactions and enhanced system-level resilience? To answer this question, the research will: (a) develop a framework to model complex nonholonomic dynamical systems; (b) extend nonlinear vibration absorption theory; (c) optimize impact mechanisms for enhancing multi-level hazard mitigation; and (d) experimentally verify the predicted performance. Rolling isolation platforms are the primary means of equipment isolation. A new mathematical framework will be created to model the three-dimensional dynamics of these systems incorporating the nonholonomic constraints described by the kinematics of rolling balls, loss of contact, and impacts with displacement limits. At low-to-moderate disturbance levels, the platforms are to function primarily as isolators, and they will passively adapt under strong disturbances to function as essentially nonlinear (vibro-impact) dynamic vibration absorbers to protect the primary building system from collapse. In order to achieve the desired multi-functional dynamic behavior, this research will establish new algorithms for determining optimal control strategies satisfying inequality constraints on state and control trajectories. Ultimately, the methodologies developed in this project will help to understand the fundamental limitations and achievable performance of multi-functional isolation systems.

RII Track-4: Quantifying Seismic Resilience of Multi-Functional Floor Isolation Systems through Cyber-Physical Testing

Sponsor: National Science Foundation (NSF EPSCoR-RII 1929151)

Role: Harvey (PI)

Duration: 12/2019 - 11/2021

Students: Braulio Covarrubias Vargas (MS) and Esteban Villalobos Vega (PhD)

Abstract:

Damage caused by seismic events to buildings and their contents can impact life safety and disrupt business operations following an earthquake. The resulting social and economic losses can be minimized, or even eliminated, by reducing the seismic forces on building contents through vibration isolation. Floor isolation systems (FISs), in particular, are a promising retrofit strategy for protecting vital building contents and enhancing a community's seismic resilience. This project will establish an experimental testbed and test protocol for FISs, utilizing the state-of-the-art NSF-funded Natural Hazards Engineering Research Infrastructure (NHERI) Experimental Facility at Lehigh University. Through the tests conducted during extended research visits, the PI and a graduate student will assess the performance of FISs and advance the understanding of their underlying physics, while also receiving hands-on training on the unique cyber-physical testing capabilities at Lehigh called real-time hybrid simulation. The new techniques and knowledge learned through these visits will transform the way the PI conducts research at the University of Oklahoma through the integration of real-time hybrid testing on existing facilities. This will have a lasting impact on the training of undergraduate and graduate students and researchers at the PI's home institution.

A community's resilience to seismic hazards is defined by its ability to absorb an extreme event and maintain an acceptable level of functionality following the event. To help ensure a more resilient community and a safer environment, the proposed research will rigorously evaluate a design methodology developed in the PI's lab for multi-functional FISs incorporating building-FIS interactions. This will be achieved by utilizing a cyber-physical systems based approach, namely real-time hybrid simulation, leveraging the state-of-the-art facilities at Lehigh University. The overall aim of these tests is to: (a) extend real-time hybrid simulation algorithms to seismic isolation systems; (b) experimentally validate physics-based mathematical models for resilient FISs; (c) advance the understanding of the underlying nonlinear dynamics of these systems; and (d) quantify the performance of these systems incorporating multi-scale (building-FIS) interactions. The cyber-physical tests conducted during the extended research visits will help to clarify the fundamental limitations of resilient isolation systems and quantify their achievable performance with respect to resilience goals. These tests constitute the first ever real-time hybrid simulation of FISs, in particular, and multi-axial hybrid testing of seismic isolation devices, in general. This research has the potential to lower the repair and demolition costs of post-earthquake recovery, including damage to non-structural elements/contents, save lives, and provide immediate operation for critical facilities.

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