Experiment On Three-dimensional Characteristics For Internal Solitary Waves Past An Island

Internal waves is a common phenomenon of fluctuation in the ocean with stablestratification of density and can be observed in all regions of the coastal region withcontinental shelf and so on.Internal solitary waves(ISW) is a special kind of internal waves with stronglynonlinearity and generated randomly. One of the main mechanism of generation is theinteraction between tide and complicated topography and the other is the lee-wavemechanism. There are two forms of ISW in the ocean, ISW trains and single pattern.ISWs propagate along a single direction after be generated from the source with largeamplitudes and speed and in the propagation ISWs remain stable form and carryenergy from the deep to the coastal region. As a result, ISWs play an important role inpropagation of energy, environment, development of energy, military marine and theoffshore engineering. The South China Sea (SCS) is a region where internal solitarywaves (ISWs) are very active. The ISWs will propagate westward after they form inthe northern SCS. During the propagation process of the ISWs past the DongShaIsland, their shapes and amplitudes will change accordingly. Therefore, the study ofthe three-dimensional evolution of ISWs are of great significance.In situ measurements, satellite observations, numerical simulations and laboratoryresearch are used in the study of ISWs. The applications of remote sensingobservation make it possible to not only catch the group of ISWs but also get thephysical distribution of the global information directly.Spaceborne and airborne synthetic aperture radar(SAR) is an effective method tostudy the generation, propogation, evolution and dissipation of internal wavesbecause of that they provide a wealth of in-situ information. The characteristic ofinternal waves on images captured by SAR present dark and bright strips whichcorrespond with the convergence and divergence area. The study under certainconditions apply the theoretical theory(KdV) to research the parameters of internalwaves by the distance between the dark and bright strips which correspond with theconvergence and divergence area. The results of previous laboratory studies show thatunder conditions of certain water depth, the form of waves in lab are not consistentwith the form in theory. Therefore, deviations locate in the process of researching theparameters of internal waves by the distance between the dark and bright strips.In this paper, the process of internal solitary waves past an island was examined inlaboratory using the method of gravitational collapse to generate the ISW whichpropagated in a two-layer fluid with the pure water in the upper and the salt water ofconstant density in the lower. Dying technique, particle image velocimetry(PIV) andfluorescence technique were used in this experiment and got the relationship about thedistance between convergence and divergence and amplitude of ISW in thetwo-dimension tank. At the same time, the relationship between the characteristic wave width and amplitude of ISW was used to the error existed in the theory of KdV.The evolution of ISWs past an island were focused using the fixed relationship in thethree-dimension tank. The results in this experiment provided not only method ofdealing with in-situ data but also evidence to fix the parameters in the numericalsimulation of ISW. As a result of that,they played an important role on application ofthe ocean dynamics and military oceanography.In this paper, the process of research was divided into four steps:The first step, the introduction of the method of building system of equipment tostudy ISWs, including two-dimension tank and three-dimension tank, PIV andcatching images.The second step, experiment of ISWs in two-dimension tank, using technique ofdyeing and PIV. CCD was one kind of cameras which catched the wave form andfield of velocity. Each set of experiments were conducted12groups. With the use oftime series and field of velocity other parameters for example amplitude, phasevelocity, characteristic width and defined width obtained to fix the relationship in thetheory.The third step, experiment of ISWs in three-dimension tank, using technique offluorescence and PIV. CCD was one kind of cameras which catched the wave formand field of velocity. In the experiment of ISW past an island, combining the data ofthree-dimension experiment with the relationship obtained in two-dimensionexperiment to describe the evolution of the ISWs.In this paper, with the combination of PIV advanced in the world and technique offluorescence in two-dimension tank and three-dimension tank, not only fixed therelationship in the theory but also calculate the parameters after ISWs past an island.In terms of experimental technique and research questions had some innovation.