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One of the drivers for our software development process is to keep pace with the ever changing portfolio of design rules applicable to the wide range of vessels that are designed using Maxsurf each year.

In the version 15 release our focus has been on the new probabilistic methods for assessing damage stability. To this end we have added a new version of Hydromax to our Maxsurf suite. Hydromax Ultimate is the most capable version of that module and includes all of the capabilities of Hydromax Pro, plus the new probabilistic damage stability functions. Hydromax Ultimate is available for purchase by existing Hydromax owners by paying the difference in price between the two versions. 

As well as adding Hydromax Ultimate, we have also upgraded many of the Maxsurf modules with new capabilities. The details of those changes follow below. All members of the Maxsurf subscription program will be sent Maxsurf version 15 over the coming weeks. Contact your local distributor or FormSys directly for a price quotation to add Hydromax Ultimate to your suite of software.

Probabilistic Damage Stability

Hydromax Ultimate supports checking probabilistic damage requirements as defined in IMO Resolution MSC.216(82) as well as the older formulation of MSC.19(58). MSC.216(82) applies to all cargo ships of 80m or more in length and to all passenger ships regardless of length, built from 1 January 2009 onwards.

The International Maritime Organisation (IMO) summarises the probabilistic approach to damage stability as follows:

“The probabilistic concept was originally developed in 1973 through study of data relating to collisions collected by IMO and adopted by resolution A.265 (VIII). This showed a pattern in accidents which could be used in improving the design of ships.

Most damage, for example, is sustained in the forward part of ships and it seemed logical, therefore, to improve the standard of subdivision there rather than towards the stern. The probabilistic concept is based on statistical evidence concerning what actually happens when ships collide, in terms of sea state and weather conditions; extent and location of damage; speed and course of ship; and whether the ship survived or sank.

Therefore, the probabilistic concept is believed to be far more realistic than the earlier “deterministic” method, in which ships’ subdivision is based on theoretical principles.

The probabilistic concept was introduced into SOLAS regulations for passenger ships in 1978 in the 1978 SOLAS Protocol. The probabilistic concept was introduced into SOLAS for cargo ships in 1990, applicable to cargo ships of 100 metres or more in length built on or after 1 February 1992; and in 1996 to cargo ships between 80 metres and 100 metres.”

Key Concepts

The fundamental approach of the probabilistic damage analysis is to first assume that the vessel has been damaged, then to assign a probability (p) that the damage will occur in a certain area of the ship. Given that the damage has occurred, a probability that the vessel will survive (s) is then calculated from certain parameters of the GZ curve calculated for the vessel in that damage condition. The conditional probability that the vessel will sustain certain damage and survive is then given by the product p.s; by summing this probability for a range of different damage scenarios, the total probability of the vessel surviving a damage incident is calculated – this is the attained index (A). The attained index can then be compared with a required index (R) to determine if the vessel is sufficiently safe.

Probabilistic damage workflow in Hydromax

It is useful to illustrate how it is envisaged that a user would use Hydromax to perform a probabilistic damage analysis:

1. The vessel is modelled in Maxsurf and tank and compartment definition is performed in Hydromax as usual.
2. The user defines other ship data required for the probabilistic damage analysis. This data includes the vessel type, which load cases to consider, and the number of adjacent damage zones to consider.
3. The user defines the boundaries of the damage zones
4. Longitudinal bulkhead and deck locations are defined for each zone and groups of adjacent zones.
5. Once steps 2 and 3 have been completed, the p-factors are automatically calculated and displayed as the zone data is modified. With the bulkheads and decks defined in step 4, the r- and v-factors are also calculated.
6. When the zones have been defined the user can then define which tanks are damaged in each zone and sub-zone. A first pass at this can be automatically generated using the Extent of Damage command which automatically detects which compartments would be breached by the corresponding damage (sub) zone.
7. The user can then perform a probabilistic damage analysis. Hydromax runs a large angle stability analysis for each combination of loadcase and damage and collates the results to calculate the attained index. This index (A) is then compared with the required index R to determine a pass or fail.

Main parameters, subdivision and calculation of required subdivision index

Hydromax Ultimate is able to perform probabilistic damage analysis according to MSC.216(82) and MSC.19(58). Several new sheets have been added to the Damage window where the user can specify the relevant parameters required for the analysis. This includes: global hull parameters; loadcases that define the different loading conditions; longitudinal, transverse and vertical subdivision to be used; etc. Once these main parameters have been specified, the required index and probability factors (p, r and v) are automatically calculated. At this stage the user can decide whether further subdivision might be appropriate: a finer subdivision will potentially increase the attained index but at the cost of longer analysis time.

Zone and Sub-Zone Damage Specification

The damage for each zone and sub-zone is defined in a similar way to damage cases - that is by the selection of tanks and compartments. This defines which tanks and compartments are damaged for each zone or sub zone; from this Hydromax can work out the damage for each of the damage cases to be computed. The damage can be automatically generated and/or edited manually.

When in the Probabilistic Damage analysis mode the damaged compartments for the currently selected zone or sub-zone are displayed in the design view. Again this facilitates verification of the input data.

S-factor calculation

The calculation of the s-factors is done from the GZ curve calculated for each combination of loadcase and damage condition. The parameters for the GZ curve analysis may be set up in the same way as for a Large Angle Stability analysis and the parameters for calculation of the s-factors are defined in stability criteria (these same criteria are also available in Large Angle Stability analysis mode should manual verification of any of the individual Probabilistic Damage conditions be required).

Analysis

Once all the parameters have been specified, the analysis may then be run. Large angle stability analyses are  computed for each combination of loadcase and zone damage up to either the specified maximum number of adjacent zones or minimum specified p-factor. As this analysis can be time consuming, Hydromax Ultimate adds support for calculations on multi-core processors. This can speed up analysis on a quad-core machine by 50%.

On completion, basic data pertinent to calculation of the s-factor is presented as well as a total attained subdivision index at the bottom of the table.

IMO MSC.267(85)

The library of stability critieria in Hydromax continues to grow. The latest addition is IMO resolution MSC.267(85) “Adoption of the international code on intact stability”.

Simplifying Design Management

As our Maxsurf users use more surfaces, more trimming and larger numbers of tanks and compartments, managing the objects in the design becomes more of an issue. Two new capabilities help with this process. In Maxsurf, a new command to automatically show all of the surfaces which intersect the selected surface is very useful when managing trimming.

In Hydromax, the extension of the assembly tree to this program helps both with the management of surface visibility and also with managing tanks and compartments.

In addition Hydromax adds a new property sheet for tanks and compartments. This sheet is similar to the property sheet for control points and markers in Maxsurf and allows quick modification of tank properties from a graphical selection.

Hullspeed - Blount & Fox for Planing Craft

A new resistance prediction method based on the paper “Small–Craft Power Prediction” by Donald Blount and David Fox has been included into Hullspeed. This method is used for estimating the resistance of planing hulls when in the planing speed regime.  The algorithm is based on the Savitsky planing method with improvements to the algorithm at “hump speed” - the speed at which the vessel just begins to plane.  The method is considered superior to the Savitsky planning method (which is based on prismatic hullforms) for vessels with variable deadrise and/or beam in the afterbody.

Project Profile - EAS Brazil

After many decades of up and down economic growth, Brazil is emerging as a real powerhouse in the world economy. Much of the current growth is being driven by a massive expansion in offshore oil exploration and production. Estaleiro Atlântico Sul (EAS) Brazil is a new shipyard which is beginning to produce many of the vessels required for this development.

Construction of the EAS Shipyard on Brazil’s east coast began in mid-2007 and on completion it will be the largest shipyard in the southern hemisphere. It will have a drydock measuring 400 metres long and 73 metres wide and have a ship production capacity of 160,000 tons.  The shipyard is nearing completion but EAS has already received orders to design and build ten Suezmax tankers.

The Suezmax vessels are part of a batch of 26 ships to be built in the first phase of the Program of Modernization and expansion the Transpetro fleet. Transpetro is a subsidiary of Petrobras, the national oil company of Brazil.

The use of Maxsurf and ShipConstructor by EAS is being supported by our new Brazilian partner, Sincronia. Developers of the IFM engineering document management system, Sincronia are specialists in enterprise IT systems for offshore and shipbuilding companies.

EAS are using Maxsurf, Rhino, Hydromax, Hullspeed and Seakeeper for their design work.

Maxsurf Subscription Program

The Maxsurf subscription program has been adopted by the majority of our users to ensure that they automatically receive any updates to Maxsurf as soon as they become available. The subscription program also makes you eligible to receive an unlimited amount of technical support via email, telephone or fax. When renewal time comes around, the subscription lets you pay one annual fee for all of the programs you own and will normally give you a major upgrade as well as any minor updates during the year. Upgrades are delivered online and minor updates are are also occasionally available for download.

Tips and Tricks

When dragging the Assembly or Properties views, if you drag and drop them on to the centre blue icon, then both views are displayed in the same location with a tab at the bottom to switch between views. This maximises the screen space to display your assembly tree.

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