Experimental Study On Extreme Waves Impact On A Vertical Cylinder In Shear Flow

Extreme waves is a kind of special situation of waves,which has strong destructive effect.However,lots of previous studies have found that the influence of waves on offshore structures,pile caps,columns and other foundations are often accompanied by water flow.The actual ocean water flow is not uniform flow but shear flow with a certain velocity gradient.There are many physical experiments and numerical simulation of wave-flow interaction in the past researches.However,few studies have been done on the effects of waves on structures in shear flow.This article through the shear flow under the action of wave action of physical model experiment to explore the role of to simulate the real waves to buildings,the experiment to the actual ocean engineering to deal with the corresponding wave action.It can also be slightly to fill the domestic blank of shear flow fields of wave action.At the same time,it will be good for the future in the field of scientific research.And people can also take it to continue to study with great convenience.In this paper,the wave characteristics and their effects on the vertical cylindrical structures are studied through physical experiments,and the wave surface propagation and hydrodynamic characteristics of the focused wave are numerically analyzed.The specific steps are as follows:Firstly,the scheme design of the experiment was carried out to explore the generation methods of regular wave,uniform flow and shear flow.The actual physical model experiment was carried out in the PIV tank of the state key laboratory of coastal engineering to generate regular wave under different parameters,and the uniform flow and shear flow with different flow rates were generated by the laboratory and the self-made diversion device;Then the regular wave focusing wave and its hydrodynamic characteristics are analyzed and studied by combining the theoretical formula calculation with the wave physics experiment;After that,in the second chapter,the instruments used in the experiment and the preparation before the experiment are introduced in detail,including checking whether the instruments are normal and the calibration of related experimental instruments.In the case of shear flow and uniform flow,it is improved on the basis of Morrison equation,where the velocity of uniform flow is treated as a constant and the velocity of shear flow is treated as a function.As for the focused wave part,first of all,the focused wave is pooled.The pooled wave uses the pooled wave pooled program of the wave generator.By modifying the parameters and using the wave height acquisition instrument to collect the wave height data of the pooled wave,the focused wave condition required by the experiment is analyzed.For the focusing wave condition of superimposed uniform flow shear flow,firstly,the position change of the focus was tested,and then the focusing wave under different flow conditions was obtained,and Morrison's formula was still used for calculation.For regular waves,the theoretical calculation results are in good agreement with the actual measured values.Under the condition of increasing counter-current,the water flow has a similar buffering effect on the waves,so that the wave force is relatively small.At the same time,the counter-current also has an effect on the waves themselves.Under the circumstances of excessive flow velocity,the regular wave appears unstable or even broken.The time course and energy spectrum of the total positive force on an upright cylinder under the action of focused wave vary with the wave parameters.It is also consistent with the trend of focusing wave surface.The maximum positive total force under the action of regular waves is higher than the theoretical result of Morison formula,while the maximum positive total force under the action of focused waves is higher than the result of regular waves.Meanwhile,the maximum total positive force increases with the increase of relative column diameter.The transfer function of the total positive force under the action of the focusing wave has the same change trend as the result of the action of regular wave and the theoretical transfer function,that is,the transfer function increases with the increase of frequency.Wave parameters also have little effect on the frequency response function of the total forward force of the focused wave.Under the counter-current condition,the wave peak degree and skewness increase,but the wave force on the cylinder decreases.