Physical Experimental Investigation On The Resonance In Rectangular Harbors

Harbor resonance refers to a phenomenon that when the frequency of the incident wave from the open sea is the same as or close to that of the harbor,it will cause violent oscillation of the water body in the harbor.When the harbor resonance is occurred in a harbor,it will affect the normal loading and unloading operation of the ships.For some severe instances,it will break the mooring lines of the ships,cause serious collision between the ships and the wharf,and cause huge loss of life and property.Therefore,in order to reduce the harm of harbor resonance,this paper studies the mechanism of harbor resonance induced by different steady and transient waves through a series of physical model experiments.It begins with introducing the background and significance of the investigation on the resonance of harbor,and reviews and summarizes the previous research results on this problem.On this basis,the following further studies are made.Firstly,the influence of the distortion rate of the model on the accuracy of the low-frequency oscillation of the regular shape narrow-long harbor and square harbor are studied through a physical model experiment.The experimental results show that the experimental results of both narrow-long and square harbor are in good agreement with the numerical results.When the distortion rate of the model is in the range of less than 4.0,the distortion rate of the model has little effect on the resonance frequency of the narrow-long harbor,but has a great effect on the amplification factor.When the distortion rate is 4.0,the error of amplification factor,R_f,is more than fifty percent.The distortion rate of the model has a great influence on the resonance frequency and amplification factor of the square,and the error increases with the increase of the distortion rate.Both the horizontal velocity distribution and the vertical velocity distribution of different distortion models are similar.Secondly,the influence factor of wave group?bichromatic waves and bimodal spectrum waves?on the low-frequency oscillation in the narrow-long harbor basin in the harbor is studied by physical model experiment.The results show that when the frequency of the short wave in the bichromatic waves is close to or consistent with the resonance frequency of the harbor,the second-order long wave oscillation in the harbor is more violent.The energy sources of different frequency components in the response wave can be analyzed in detail by the normalized wavelet-based bispectrum.The closer the low-frequency spectral peak frequency(f_p1)in the bichromatic spectrum is to the first resonance frequency of the harbor,the more obvious the low-frequency wave oscillation is inside harbor.With the increase of f_p1and significant wave height(H_S1)of low-frequency spectral,the nonlinear wave interaction in the harbor increases gradually.Finally,the physical model experiments are carried out to study the influence factors of the low-frequency oscillation induced by the solitary wave?transient wave?in the square harbor.The results show that the maximum response coefficient of wave height at different positions in the harbor is between 2.0-2.5.So it can be reasonably inferred that the upper limit of the maximum response wave height in the harbor is 2.5 times of the incident wave height.By comparing the amplification factor curves of the solitary wave wake and the regular wave,it is found that the solitary wave wake can induce the oscillations of the first five resonance modes of the square harbor,and the oscillations of the five resonance modes become more obvious with the increase of the incident wave height.The strong non-linear interaction between waves mainly occurs in the low-frequency region,and the number of wave involved in the wave non-linear interaction increases with the increase of incident wave height.The non-linear interaction in the high-frequency wave region decreases with the increase of incident wave height.