ssc-367 - Ship Structure Committee

The ship motion and wave action result in truly complicated
interaction of variables affecting the loading on the hull
structure. Theloads dueto incident,diffractedand radiatedwaves
and due to ship forward motions may be approximated for various
sections of the hull by the use of strip theory. Loads due to
diffraction and radiation can be also directly obtained from a
three-dimensional flow solution. Work carried out by Liapis and
Beck (Reference5.2) provides a very good comparison of various 3-D
flow solutions, strip theorysolutionand experimentalresults. The
added mass and damping coefficients plotted against frequency on
Figure 5-1 indqcate that the coefficients obtained by Liapis and
Beck are quite close to those obtained based on both strip theory
and experimental work. Actually, over the range of applicable
frequencies,the three sets of coefficients based on 3-D solutions
show larger scatter.
Considering the difficulties of applying 3-D solutions and the
proven reliability of good strip methods, a strip method is 1ikely
to remain the preferred approach to determine the applied loads in
most ships. Ships with special characteristicCS, including
supertankers, navy vessels, drillships, etc., are the likely
candidates for application of 3-D flow solutions. It should be
emphasized that whichever solution method is chosen, substantially
greater inaccuraciesare introduced into the hull loading due to:
●
Uncertaintieson wave height and period (wave statistics)
●
Uncertaintiesregarding ship routing and the correlationwith
wave environment
●
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The variable nature of ship cargo and ballasting
Inaccuraciesin hull response to applied loads
The precedingdiscussioncoverswave loadingon ships susceptibleto
cumulative fatigue damage. A linear theory is applicable to
determine the applied loading for fatigue analyses and design. In
an extremelyharshenvironment,wave nonlinearitieshave substantial
5-6