Laboratory wave generation: A second-order theory for regular and irregular waves in wave channels

TLDR: In this article, expressions for the motion of a waveboard to generate a correct second-order wave field were found for both regular and irregular waves, and two important features of the procedure adopted here are that the computing time for the waveboard is signifcantly smaller compared to a method based on the frequency domain and the accuracy of the physical representation increases with decreasing spectral width.

Abstract: The correct generation of a second order wave field in a laboratory wave tank is of importance in several experimental investigations, particularly those of nonlinear evolutions and sediment transport. In the present work, which was carried out under the MLTP (medium long-term planning) of DELFT HYDRAULICS for improving experimental techniques, expressions are found for the motion of a waveboard to generate a correct second order wave field. These expressions are valid for both regular and irregular waves. Two important features of the procedure adopted here are that the computing time for the motion of the waveboard is signifcantly smaller compared to a method based on the frequency domain and that the accuracy of the physical representation increases with decreasing spectral width. The assumption of a narrow band spectrum is sufficient for realistic sea states described by spectral shapes of JONSWAP and Pierson-Moskowitz types. Results of some experimental investigations into the performance of the software based on the wave generation theory are also included in the report. Although the overall agreement between the theory and the experiment is good, some discrepancies are apparent from the limited analysis carried out so far, all of which cannot be attributed to the wave generation theory. Further analysis (and possibly a set of new experiments) is required in order to resolve aH the discrepancies.