Experimental Study Of Internal Waves Generation And Evolution In Laboratory With Visualization Measurement

Experimental study of the generation and evolution of internal waves in stratified fluid (or ocean) is carried out by means of many optical visualization and imaginary techniques in the present paper. Based on the scientific and applying significance of internal wave in physical oceanography, ocean engineering and related subjects, its research is paid a considerable attention by oceanographers, researchers of oceanic engineering etc. Due to high cost and impossibility of synchronous in–situ observation of internal waves in the ocean, the experimental study of internal waves is one of important research methods. Recently, with progress in science and technique, especially the progress in visualization technique, data acquisition technique and digital imagery processing, and appearance of some new techniques, the visualization of the internal waves under condition of laboratory can be achieved.In the visualization study of internal waves, the optical technique is an important method based on its no interferences, non-contact and instant recording for 2D- even 3D-wave fields. In past decade, with the fast development of optical technology, imaging techniques and computer science, some existing optical method, such as schlieren and particle image velocimeter grow up and some new optical methods such as digital synthetic schlieren (DSS) etc. emerge and have been put into application. The study of visualization measurement applying in internal wave field has an early start abroad and now an advanced development, while generally it is not well developed in land.For theoretical study of internal wave, the experimental study is an important reference; and for numerical simulation study, it can provide some data to validate the results from the numerical calculation. Therefore, for some applying study, experimental study combining optical visualization measurement and internal wave modeling has significant importance and value for promoting the application and industrialization of inland fluid measurement technology.Experiments are carried out in 2D- and 3D- internal wave and stratified fluid tanks in the Physical Oceanography Lab in Ocean University of China. The modeling experiments of internal waves cover two main aspects: 1) internal waves generated by a moving spheroid in stratified fluids; 2) propagation and evolution of internal solitary waves generated by gravity collapse. All the experiments are performed by analogue criterions, so the experimental results have certain value for physical oceanography, military oceanography and oceanic environmental science et al., at the same times the results can also provide valuable data for ocean remote sensing, mathematical inversion model and for validity of theoretical study and numerical simulation of internal waves.The methodology of our research mainly concerns combing optical visualization measurement with experimental modeling of internal waves, according to specific measurement requirement. First step: set up experiment devices including water tank, towing system, model moving velocity control and measuring system, terrain model etc.. Second step: start experiment and recording the digital image of the internal wave field. Third step: according the image and circumstances data of the experiment, program to obtain information and build wave field image including velocity field and vorticity field. Fourth step: based on data obtained optimize the experimental system. Fifth step: comparing experimental result with existing theoretic and numerical simulation result.In order to measure the internal wave field fully and accurately, not only traditional optical measurement method but also novel techniques including large scale vertical laser schlieren, digital synthetic schlieren (DSS) and particle image velocimeter (PIV) are studied and applied in the research of the transaction and vertical section of internal wave field. Basic principles and physics mechanisms of related technology and equipment are studied, according to which the technology and equipment can be divided into two main types: one type is measuring the relative density distribution of internal wave field via recording and analyzing image distortion caused by change of the refractive index. This type includes large scale vertical laser schlieren and DSS; the other type is measuring velocity and vorticity distribution of internal wave field by analyzing the images of fluid motion while light scattering particles, illuminated by laser slice during experiments, are added in and then move with fluid. This type includes PIV technology. What is emphasized on our realization measurement study is the designing of the large scale vertical laser schlieren and independently developing of Argon-Ion Laser Slice Large Area PIV System with its information processing method. These two equipments are of advanced international level. The specific work of mine is participating in designing large scale vertical laser schlieren, independently setting up DSS and PIV systems, and furthermore integrating the latter two equipment to a DSS & PIV system for internal waves visualization measurement.The results of our research are in several forms including the following: original image of internal wave field recorded by digital camera, intensity distribution of internal wave field acquired by schlieren, cross-section velocity field and vorticity field. The results of our work, for the first time inland, acquired whole and accurate internal wave fields in the gross, and compare experimental measurement with theoretic and numerical simulation result concerning the internal wave problem studied, the result of which shows that they are well identical. The result improved that optical visualization measurement that being studied and applied in our internal wave field research, also for the first time inland, are reliable and efficient.