The nature of nonlinear effects in ship wave making
Conference/JournalShip Technology Research / Schiffstechnik
Date1 Feb 1997
This paper reconsiders the validity of linearised wave resistance theories and studies "nonlinear effects", which we here define as those effects that are disregarded in methods imposing linearised free surface boundary conditions but 'exact' hull boundary conditions (Neumann-Kelvin or slow-ship theories, not thin-ship theory). Such a study is facilitated today by the availability of solution methods for the nonlinear wave resistance problem. The method applied here is the RAPID code, (Raven 1993, 1996). Its solutions satisfy the exact (inviscid) boundary conditions at the true location of the free surface, the hull boundary condition at the actually wetted part of the hull surface, and include the dynamic trim and sinkage. The predicted wave patterns generally are quite close to those measured, (Raven 1996), and will therefore be used as a reference here. Differences between nonlinear and linearised methods are found both in the wave pattern and in the resistance. The latter may be substantial, but are hard to explain directly due to their global character. The differences in wave pattern are physically more meaningful, and it is those that we discuss in this paper.