Author(s): Stig E. Sand Ph.D.; Bjarne Donslund M.Sc.

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Abstract: The long wave energy attached to the grouping of natural waves has been shown to play a very important role in the design of mooring systems, offshore terminals, floating structures, harbours, etc. Therefore, in model testing, efforts should be made to reproduce only the correct amount of long wave energy present in nature. However, when only traditional first-order control signals are applied to the wave generator errors will be introduced. Hence, a second-order signal has to be calculated and imposed in order to obtain satisfactory long wave conditions in the physical model. The necessary signal and transfer functions are outlined below for all common types of wave boards. It is demonstrated that dependent on the type (piston, hinged, etc.) considerable differences can be found in the amplitude of the required second-order control signal. Also the erroneous longwave energy is assessed in case of only first-order wave generation. The results indicate that in such situations significant deviations from the correct long waves may appear, but it turns out that these errors are to a certain extent independent of the actual type of wave board used for the wave generation. The typical range of the deviations is shown to be from − 100% to about + 300% if second-order (compensation) signals are not applied.

DOI: https://doi.org/10.1080/00221688509499362

Year: 1985