Hydrodynamic Forces on a Body Moving Arbitrary in Time on a Free Surface

Abstract

In order to predict theoretically the motions and mooring forces of a body moored by the non-linear mooring system in irregular sea waves, we have to use the equation of motion in the time domain. Therefore the hydrodynamic coefficients involved in that equation must be ones in the time domain. This paper presents a calculation method of the hydrodynamic coefficients in the time domain. The hydrodynamic boundary-value problem on a two-dimensional body is formulated on the basis of the linear potential theory, using the impulse response function which Cummins first proposed, and the problem is solved making use of the Green's function. A numerical example for a circular cylinder is presented. And in order to confirm the validity of the present method, the calculations of the force of forced oscillation and the hydrodynamic coefficients in the frequency domain for the same cylinder using the hydrodynamic coefficients by the method have been carried out and the results were compared with those by the established method in the frequency domain. It is found that the results are quite satisfactory.