ssc-367 - Ship Structure Committee

‘Thereare numerous finite element programswell-suited for detailed
analyses and design of continuous structures such as ships,
semisubmersibles and TLPs. The best known of these programs in
public-domain are ANSYS, NASTRAN, SAPIV, DAISY and SESAM. Mansour
and Thayamballi (Reference 4.26) provide a survey of computer
software and they discuss programs specifically developed for the
marine industry.
4.5.3
Fatique Versus Other Desiqn and Scheduling Requirements
Fatigue analysis and design is only one of many aspects of the
overall analysis and design effort. Because the final as-designed
structure must meet many varied pre-service and in-service
requirements, the fatigue design effort reflects the necessary
interactions among various activities. The design criteria
typically includespecific assumptionsand procedures to coordinate
such activities. As an example, some of these interactions for a
fixed offshore platform design project are as follows:
●
A computermodel used to generateextreme environment loads is
also used for fatigue analysis,with changes in hydrodynamics
coefficients and foundationmatrix as necessary.
●
A computer analysis model used for stiffness analysis should
not account for the effect of thickened brace stubs, but the
stress ranges used for fatigueanalysis should account for the
increased thickness.
The overall design schedule often dictates that fatigue design and
analysis be carried out inunediatelyafter the structure’s general
configurationis finalized. But the fatiguedesign must incorporate
flexibility,to allowfor significantconfigurationrevisionsduring
the detailed design, which will affect both the applied loads and
the stress ranges. The desired flexibility is often obtained by
carrying out parametric studies to identifythe effects of changes,
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