Experimental Study On The Evolution Of Internal Solitary Wave And The Interaction With Topography

With the continuous development of ocean exploration and deep-sea equipment technology,ocean movement in deep-sea has attracted more attention,internal wave is one of the typical motions.Internal solitary wave is a special internal wave,which can carry enormous energy,occur very frequently and distribute widely in the ocean,and has an important impact on the marine environment.Therefore,domestic and foreign scholars have done lots of work on internal solitary wave.But in the experiment field,most of the experiments carried out are to construct two-layer flow system by using water and saline water.However,due to the mixing of water and saltwater,when internal solitary waves pass through underwater topography,there are obvious diffusion between the two layers of fluids due to the influence of topography.At this time,the flow field information cannot be accurately captured.Therefore,the use of two-layer fluid with strong stratification,which could avoid the problem of diffusion between fluids,is helpful to accurately measure the flow field information of internal solitary waves passing through underwater topography.It has important guiding significance for understanding the propagation and evolution characteristics of internal solitary wave and improving the theoretical model.In this paper,the construction of internal solitary wave flume independently carried out by Shipbuilding Engineering of DUT.The two-layer fluid system under strong stratification conditions is constructed by using completely immiscible dimethyl silicone oil and water.Method of generating internal solitary waves by gravity collapse is used and improved in our research.CCD(Charge coupled Device)camera is applied to collect data.An image processing method based on morphological closed operation and adaptive threshold segmentation is developed to extract the wave surface features of internal solitary wave.PIV(Particle Image Velocimetry)technology is used and improved in our research to obtain flow field under strictly two-layer fluid conditions.Through the improved test method,the repeatability and accuracy of the experiment are improved,and a high quality internal solitary wave fine flow field is obtained.The influence of gravity collapse wave-making method on the characteristics of internal solitary wave is studied.The experimental results are compared with the typical theoretical solutions of internal solitary wave.The structure of flow field,the evolution characteristics of velocity field and vorticity field and their spatial distribution are analyzed.Three typical topographies are arranged in the lower fluid to study the evolution of flow field of internal solitary waves passing through different topographies.The effects of underwater topography on some key physical quantities(horizontal velocity and vorticity)are discussed.Changes of amplitude and wave surface of internal solitary wave before and after passing through topography are studied.The researches show that the experimental results are closest to the MCC theory considering free surface condition.The height and width of collapse area have obvious influence on the waveform and amplitude of internal solitary wave.The flow field structure with different amplitudes is similar.When internal solitary waves pass through different underwater topography,the velocity field and vorticity field have different evolution laws.Large eddies will be formed in front of the terrain,and the motion law of the eddies will be different under different terrain.Topography has a strong influence on the horizontal velocity and vorticity of upper and lower fluid.After the internal solitary waves pass through the terrain,the wave surface will evolve and the amplitude will obviously attenuate.The internal solitary wave characteristics obtained in this paper under the strong stratification condition have important guiding significance for the improvement of the theoretical model in the future.The characteristics obtained on the flow field of internal solitary wave passing through topography in a strictly two-layer flow system has important reference value for understanding the propagation and evolution mechanism of internal solitary wave.