The Laboratory Experiment Study Of Propagation Of Internal Beams And Energy Dissipation Of Internal Solitary Waves Passing Periodic Topography

The internal waves, common phenomena in the density stratified ocean, arevery worthy of being studied, which are the intermediate process of energytransfer from large scale to small scale phenomena. There are three methods tostudy oceanic internal waves, including theory study, field survey andlaboratory experiments. It’s the laboratory experiments that are repeatable andmore economical than field survey, and that are comprehensive to study theprocess of generation and evolution of the internal waves. The data of thelaboratory experiments can also be used to test the results of the numericalmodels.The density of the fluid, in which the internal waves can be generated, mustbe stratified, so that the preparation of density stratified fluid is necessaryfor all the internal waves experiments. The two layers fluid is used in theexperiments of internal solitary waves, whereas the internal tides experimentsmust be conducted in the continuous density stratified fluid. There is a limitin conventional “double-tank” method which can only prepare uniformly densitystratified fluid, however the density profile in the ocean has the characteristicof thermocline. In order to study the characteristics of the propagation of theinternal waves in the non-uniformly stratified fluid, this paper improves the“double-tank” method by controlling the quantity of flow with two peristalticpumps. The improved "double-tank" method is tested to be feasible by experiments.With this method, this paper studied the phenomena of propagation of internalbeams in the uniformly stratified fluid and the non-uniformly stratified fluid.The velocity field of the internal waves is measured by the method of ParticleImage Velocimetry (PIV), whereas the density disturbance field is measured by the technique of synthetic Schlieren. It is known from the linear theory thatthe phrase velocity of the internal waves is perpendicular with the groupvelocity. Combined with the experiment results, it’s obvious that the internalbeams are parallel to the direction of the group velocity. The reflectionphenomena occurred simultaneously when the internal beam is refracted at theinterface of the bottom layer and the middle layer. The internal waves will onlypropagate in the middle layer when their circular frequencies are lager thatbuoyancy frequency of the top and bottom layers yet less than that of the middlelayer. There will be eddies at the interface of two layers when the two beamsare reflected at that areas, and the eddies are generated and disappearcircularly.In order to study the reflection of the beam encountering the slopetopography, a slope is put in the tank. The internal beams narrow down when theyare reflected on the slop in the experiments. The energy dissipation is strongwhen the beams are reflected on the slope.In the chapter of experiments of solitary waves passing periodic topography,the formula calculating the kinetic energy and potential energy is derived. Thereis an approximate linear relationship between the energy dissipation of internalsolitary waves and their amplitudes when they pass periodic topography.