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DISCUSSION

G.Schlachter

MTG, Germany

The authors should be thanked for their effective contribution to more reliable design loads on ships in a seaway. Different from the approach of Meyerhoff/Schlachter (1980), the present method contains a clear separation of linear and nonlinear loads neglecting the frequency influence only with impact, i.e., slamming effects. The approach of Schlachter (1989) is different because it is based on frequency-independent hydrodynamic coefficients. All three methods calculate the elastic response of the hull girder by superposition of eigenmodes. However, the present approach is based on “dry” modes, whereas the other two mentioned use “wet” modes assuming that orthogonality is still given.

In order to make the present method even more attractive for practical use, the future development of it should aim at the solution of the following problems:

  • Wet-deck slamming: The figure below shows how wet-deck slamming dominates the hull girder loads of a 700 t SES in higher sea states (from calculations verified by tank tests).

  • Deformation of incoming waves by the ship: It can have a considerable impact on local pressures on the shell.

Furthermore, a statistical evaluation should be part of the computer program which enables the user to extrapolate extreme, i.e., design loads.

AUTHORS' REPLY

Thank you for your kind comments. The purpose of the current paper was to verify our nonlinear simulation method which did not take into account the wet-deck slamming. We agree that the whipping response due to wet-deck slamming might be significant as you suggested in your figure and therefore deserves a thorough investigation on its own. We have been working on this problem for some time. Parts of the results will be published in the near future.

Also, statistical analysis of extreme responses is beyond the scope of the current paper. This issue was, however, touched upon in an accompanying paper (Wu and Moan, 1996). But the activity in this area will be emphasized in order to establish results for probability-based design of advanced vessels.

We totally agree with you that the pile-up water should be taken into consideration as far as local pressure and local structure are concerned.



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