Long time series of wave field are experimentally simulated by JONSWAP spectra with random phases in a 2D wave flume.Statistic properties of wave surface,such as significant wave height,skewness and kurtosis,are analyzed,and the freak wave occurrence probability and its relations with Benjamin Feir index(BFI)are also investigated.The results show that the skewness and the kurtosis are significantly dependent on the wave steepness,and the kurtosis increases along the flume when BFI is large.The freak waves are observed in random wave groups.They occur more frequently than expected,especially for the wave groups with large BFI.
Physical model tests with highly reflective structures often encounter a problem of multiple reflections between the structures and the wavemaker. This paper presents a piston-type active absorbing wavemaker system which can absorb most of the reflections. Based on the first-order wavemaker theory, a frequency domain absorption transfer function is modeled. Its time realization can be achieved by designing an IIR digital filter, which is used to control the absorbing wavemaker system. In a real system, time delays often exist in the wave making process. Thus a delay compensation term to the transfer function is proposed. Experimental results show that the system performs well for both regular and irregular waves with periods from 0.6 s to 2.0 s, and the absorption capability is larger than 96.5% at target wave fields.
