A discussion is given on practical aspects of digital representation in time of the slowly oscillatory second-order wave drift force from a known force spectrum. The emphasis is placed on the computational efficiency and on the suitability of the simulation to a numerical integration of an equation of motion using a variable integration step size, where the force acts as the excitation of motion. The effect of approximating the original spectrum by a white spectrum is discussed. A sensitivity analysis is made to the range of frequencies of the spectra. The force time record is obtained by first generating at equal time intervals a discrete time series which possesses the desired random characteristics, and then by extending the discrete series into a continuously available digital record using a sin(x)/ x-type interpolation. Various numerical tests are illustrated with plots. Superiority of the fast Fourier transform over the cosine series is demonstrated in terms of the spectral contents preservation.
Reprinted with the permission of the Society of Naval Architects and Marine Engineers (SNAME). Materials originally appearing in SNAME publications cannot be reprinted without written permission from the Society, 601 Pavonia Ave., Jersey City, JY 07306 or email@example.com.
Oppenheim, B.W. and Wilson, P.A. (1980) Continuous digital simulation of the second-order slowly varying wave drift force. Journal of Ship Research, 24, (3), 181-189.