NUMERICAL-CALCULATIONS OF LARGE TRANSIENT WATER-WAVES

This paper concerns the description of a two-dimensional irregular sea state in which a large transient wave is generated through the constr uctive interference (or focusing) of the component waves. A numerical model is presented and comparisons are made with recent laboratory dat a. This includes measurements of the horizontal kinematics within the crest to trough region. The proposed solution is based upon a Fourier series expansion in space and time, in which the amplitude of the indi vidual harmonics are determined by a least squares fit to the non-line ar free surface boundary conditions. This approach allows for a realis tic mix of free waves (with differing phase velocities) and their asso ciated bound waves. The solution, which is not assumed to be either lo cally or globally steady, can be used to predict the kinematics beneat h a recorded (or predicted) water surface elevation. The numerical res ults are in excellent agreement with the laboratory data, and the solu tion is robust in the sense that convergence is always achieved from s imple initial conditions. The proposed model is not computationally in tensive and may thus be suitable for design calculations.