ssc-367 - Ship Structure Committee

influence on the applied loading. However, a linear theory can
still be used in a harsh environmentto produce approximateloadings
as harsh environment generally contributes very little to the
cumulative fatigue damage.
If an appreciable portion of fatigue damage is due to harsh
environment loading, some of the important variables not accounted
for in linear theory should be evaluated:
●
●
●
●
●
Wave steepness
Wave slamming
Viscous effects
Hydrostatic effects (due to flaring ship sections)
Hydrodynamic effects (due to flaring ship sections)
These primary and other secondary nonlinearity effects on ship
loading can be accounted for by perturbation and simulation
methods. Second-order perturbation methods are relatively simple
and they are used to solve the wave action/ship motion problem in
the frequency domain. A detailed discussion of second order
perturbationmethods is presented in References 5.3 and 5.4.
Another approach to determine the non-linear effects is the
integration over time of the applied forces on the structure. A
detaileddiscussionofsuchsimul ationmethods, includingprinciples
of effective computer simulations, is presentedby Hooft (Reference
5.5).
Motions Model and Anal.vsisTechniques
Since the linear ship motion theory is considered appropriate for
large majority of spectral fatigue analyses, the modeling and
analysis technique is further discussed.
Typically, a standard ship or a tanker has two distinct drafts, one
for laden and another for ballast condition. The pre-analyses
effort usually covers the following:
5-7