Comparison of wave forces computed by linear and stream function methods

Two previously-published deterministic methods which have been employed to compute the water particle kinematics required to predict hurricane-generated water wave forces on piles by the Morison equation are (1) the linear filter technique and (2) the stream function representation. "Exact comparisons between these previous studies have not been possible because the linear filter technique utilized continuous time data records of nonperiodic water waves while the stream function representation utilized only single waves from the continuous data records with water surface profiles which were assumed to be permanent, periodic forms traveling with a speed equal to the wave celerity. In order to compare these two methods, forty two single waves with well defined (but asymmetric) crests and troughs were selected from the four continuous data files recorded during Hurricane Carla by Wave Force Project II. In addition, thirteen single waves recorded by Wave Force Project I were utilized in a phase averaged form for comparison by the two methods. Based on the same data sets, comparisons of the normalized mean square differences between measured and predicted forces computed using the previously published force coefficients indicate generally better results from the stream function method using Dean-Aagaard coefficients. Under certain conditions, results obtained using the linear filter technique may be improved when used with the Dean-Aagaard coefficients.