FIRST ORDER WAVE LOADS IN BEAM WAVES

In may cases, the simple strip-theory method with the classic relative motion approach delivers a poor prediction of the first order wave loads for sway, heave and roll of a cross section of a ship in beam waves. A better prediction is given by the diffraction theory, which calculates the diffracted wave system by using Green's second identity and the known incident wave potential. A disadvantage of this method is that the wave load calculations are relatively time consuming, because these calculations have to be repeated for each wave direction. Therefore a simple calculation method to obtain the wave loads, without solving the diffraction problem itself for each wave direction, would be welcome. As a first attempt for beam waves only, this paper presents a very quick, simple and accurate method to obtain the wave loads from the potential coefficients and the radiated wave energy. Results of this method have been compared with computational results of the diffraction theory and a perfect fit in beam waves was found. Also the radiated damping waves, produced by the oscillating ship, have been used to account for the amplification of the incoming wave system. Calculated vertical relative motions have been compared with experimental data and a fair agreement was found.