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.

Identifications of Spurious Waves in the Wave Tank With Shallow Water

“…So the generation of spurious waves free primary waves and the reproduction of the group-induced second-order low frequency and high frequency components are essential for physical model tests in the laboratory. Please see Zaman and Mak (2007) for high frequency second-order wave components, not be discussed here.…”

Second-order wave maker theory using force-feedback control. Part I: A new theory for regular wave generation

“…This has been discussed extensively (Flick & Guza (1980), Sulisz & Hudspeth (1993), van Leeuwen & Klopman (1996), Schäffer (1996) and Zaman & Mak (2007)) and will not be repeated herein. Indeed, throughout this paper the notation and solution as presented by Schäffer (1996) will be adopted.…”

Spurious Waves During Generation of Multi-Chromatic Waves in the Wave Tank in Shallow Water

“…Hansen (1978), Sand (1982), Barthel et al (1983), Sand and Mansard (1986a, b), Mansard (1991), Mansard et al (1987), Schaffer (1993), Stansberg (2006), Zaman and Mak (2007), Zaman et al (2010), Spinneken and Swan (2009) are a few who described the methods to curtailing these unavoidable free waves from the resulting surface elevations in the wave basin.…”

“…So it is essential to reduce or eliminate the unwanted free waves components for physical model tests and to ensure the reproduction of the group-induced second-order low frequency and high frequency components in the laboratory. Please see Zaman and Mak (2007) for high frequency second-order wave components and Zaman et al (2010) for mono-and bichromatic waves, not to be discussed here.…”