Second Order Wave Generation Technique in the Laboratory

Abstract

Correct generation of the primary waves and the reproduction of the group-induced second-order low and high frequency waves have been considered essential for physical model test in the laboratory to understand the effects of the wave-action phenomena on, for instance, offshore structures, mooring system, LNG, other floating vessels, harbor resonance, etc. When natural waves are reproduced, the primary waves and their locked bounded waves are generated along with some unwanted free waves. Those free waves are evidently generated and propagate towards the test model and reflect from the boundaries. The free waves, having the same frequency of the bounded wave are reproduced due to mismatch of the boundary conditions at the wave paddle. The other two types of free waves are due to the wave paddle displacement and the local disturbances. The so-called second-order wave generation technique could eliminate these alleged free waves. In this experiment second-order wave generation technique is successfully used to reproduce the correct bounded waves along with elimination of the unwanted free waves from the wave profiles. This experiment is implemented by means of compensating free waves imposed on the system by second-order paddle motion. The control signal for this motion has to be introduced along with the primary waves. An extensive experimental works are carried out in the Offshore Engineering wave Basin (OEB) at the Institute of Ocean Technology (IOT), NRC to investigate the quality and the characteristics of the generated primary waves and their locked bounded waves when the unwanted free waves are eliminated. The measured results are then compared with the predicted results. Two different water depths are used within the shallow water limit. The obtained results are also compared with the numerical predictions.