Controlled extreme wave generation using an improved focusing method

Abstract

Dispersive focusing technology is one of the most widely used methods to simulate extreme waves in the laboratory. However, such methods that are based on the linear dispersion relation are not robust. The focusing waves are always generated at unexpected positions owing to nonlinear effects. Hence, in this paper, an improved focusing method named the All Phase Correction Method (APCM) is developed to produce accurate focusing waves at a predefined position. An improved phase estimation algorithm and second-order wavemaker theory is employed to iteratively correct the phases and amplitudes of the generated waves. Different types of experiments were conducted in a wave flume using this method. The results indicate that the present method works well for accurately generating extreme events. Both the component phases and the focal positions match well with the target values. The influences of wave steepness, spectral bandwidth and spectral type on the correction procedure were investigated extensively. The analysis revealed that with the increase in wave steepness and narrowness of spectral width, the phase deviation increased. Thus, more correction iterations are needed to achieve convergence of iteration. In addition, the spectral type also influences the wave correction procedure. The focal position deviations for the constant-steepness spectrum and the constant-amplitude spectrum are significantly smaller than that of the JONSWAP spectrum, and the correlation coefficient converges faster.