Stresses in the frigate type hull structure obtained with the STRUC tool

Free running experiments with a model having 10 segments in the bow area (WHIP-2 project)

can then be evaluated using CFD. In this way the probability of the event is determined by the approximate method, while the magnitude of the impact (and its consequences) are determined by CFD results.

Structural response Once there was a tool available that could calculate pressures on the hull of a ship, the STRUC-1 working group was started up in 2001. The goal of this working group was to provide the link between the hydrodynamic calculations and the structural calculations. The approach taken was a one-way coupling. Unit panel pressure load cases were defined to be calculated by different finite element solvers. Combined with transfer functions of the calculated pressures, this results in transfer functions of stresses.

The developed tool STRUC takes care of the necessary interfacing between the two

26 report

programs and determines the long-term fatigue damage and extreme load assessment. The basis for the structural CRS tool was ready. As nonlinearities in the loads have an important contribution to fatigue and ultimate load assessment, these were addressed as part of STRUC-2. This working group also changed the way the loads were translated from the unit pressure to the unit wave method. Once the number of hydrodynamic panels exceeds the number of load cases, the latter is a more efficient method.

SANE to SIINE The SANE working group that followed collaborated closely with the PRETTI-2 working group. As a result of PRETTI-2’s activities, the hull bending modes were included in PRECAL. The STRUC software now served not only as a post-processor for PRECAL, but also as a pre-processor in which the global bending modes were determined. Additionally, the

SANE working group carried out more extensive validation work of the tool and its robustness. The most recent group SIINE finished this work in 2018.

An important topic within the working groups was the user-friendliness of the tool. The operational profile used in the long- term assessment has a clear and significant effect on the analysis. Its definition is therefore very important. As such it should be clear to the user of the tools how this definition is properly done. Nonlinear work performed in STRUC-2 was revisited and is now an integral part of STRUC. Finally, the testing and validation of these state-of-the-art tools and their capabilities was completed.

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