| Abstract: | Two methods are presented for analysis of second order waves in a wave tank. The first method is by placing three wave probes in a line parallel to the line of propagation of long-crested irregular waves. By correlation analysis the spectra of set-down, parasitic waves and reflected waves of the second order are separated. The second method is to apply the square-law operation as proposed by Bendat and Piersol, to the spectral analysis of this particular non-linear system. The results of the two methods seem to agree reasonably well. A practical application of the present analysis is to analyse low frequency responses of a moored structure in a wave tank, where it is recognized that simulation of second order waves and the structure's responses are often accompanied by parasitic second order waves and reflected waves in the tank. These adulterations may be regarded as noises, and the proper information regarding non-linear second order responses extracted from the raw output. |
