In the last few years, internal waves have been extensively studied by many scholars, mostly focused on the physical property and the effect on ecology and geochemistry. The geological influence, however, was rarely discussed. By EK500 and 3.5 kHz sub-bottom sonar system, it is reported that many sand waves exist in the South China Sea at 600 meter water depth. Internal waves are a very important driving mechanism in the South China Sea. Its movement over the marine bed causes unsteady flow field disturbance. In order to clarify whether the internal wave is the main factor to form sand wave, we conduct a series of numerical simulations. Most studies on the formation of sand waves are mainly in the nearshore area. Due to the difficulty in observation, only very few special discussions consider depth of 500 meters or deeper. First of all, in this thesis, we use the Korteweg de Vries (KdV) equation to derive wave and current in an internal soliton. Then, the flow field is substituted into the Regional Ocean Modeling System (ROMS) numerical model to simulate the three-dimensional movement of internal waves and the associated movement of suspended sediment in order to discuss the mechanism of sand wave formation. Finally, the variation of wavelengths of sand wave is analyzed and compared with in-situ measurement. From the simulation result, the internal wave causes the formation of sand waves. After the passage of dozens of internal waves, a flat sea floor will gradually form sand wave topography. Different depth and slope of the sea bottom will affect the sand wave wavelength also.

Thesis (M. Eng.)--Carleton University, 1988. / Also available in electronic format on the Internet.

Thesis (Ph.D.) in Mechanical Engineering--University of Maine, 2004. / Includes vita. Includes bibliographical references (leaves 91-94).

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It is not a coincidence that over half the world‟s population live in coastal areas using the sea as a mean to develop its industry, thus the sea is present in most aspects of daily life. Because of the vital relationship with the marine environment, for many years mankind is aware of the high energy potential contained in waves. During the last hundred years, thousands patents of devices for the extraction of the energy from waves have been published. However, the researching still faces the challenge of develop the optimal wave energy converter that matches robustness, to withstand extreme marine conditions, and sensitivity, to respond the different sea states. In this thesis a scale model of a wave overtopping converter has been designed, built and tested. In this type of wave electricity converter the waves ascend a ramp, filling a reservoir located at a certain height above sea level. The stored water in the reservoir is discharged back into the sea, powering a turbine, thus generating electricity. The system is composed of a wave energy converter, at a scale of 1:100 without turbine, a test channel and a plunger type wave maker. Different sea conditions have been simulated, to assess how the different configurations of the device influence the obtained hydraulic power and flow. It has been concluded that there is an appropriate configuration of the wave electricity converter for each wave period and height. The simulated sea conditions were composed of wave periods of around a second and wave heights of about two centimeters. Finally by applying scale transformations, an estimation of the hydraulic power that the wave electricity converter would extract with this configuration in the deep waters of Tenerife South has been calculated. Summarizing, in this thesis the methodology of testing and the comparison with real conditions has been developed.

Cross-waves generated by an oscillating wavemaker in a rectangular wave tank are examined when two or more modes are simultaneously unstable. The partial differential equations governing the evolution of the complex amplitude of inviscid cross-waves are shown to be two coupled nonlinear Schrodinger equations with transverse modulations. Energy dissipation in the system is taken into account by the inclusion of a linear viscous damping term into the amplitude equations. A linearized stability analysis is performed on these equations to determine the critical modes, the growth rates and the stability curves. A center manifold analysis is used to reduce the PDE's to a system of ODE's in the neighborhood of a codimension two point where two adjacent spanwise modes are simultaneously nearly marginal. Four possible steady states of the system are found, one of which is a mixed mode state. A Hopf bifurcation from the mixed mode is predicted for a certain region of the parameter plane, suggesting the possibility of energy interchange between the two modes. The stability of the Hopf bifurcation is determined by studying a fifth order problem, where the quintic contributions come from the higher modes as well as the perturbations of damping and detuning.

Function generator has been widely used in each electronics fields recent years. In this thesis, the authors will introduce some basic structure and working principles of a function generator, moreover a function generator which can create three kinds of wave: sine wave, square wave and triangle wave has been implemented. There are many ways to build the function generator; a method of combine the operational amplifier and discrete components is introduced in this thesis. First use the RC Wien bridge oscillator to achieve sinusoidal wave; and convert it into square wave by using the shaping circuit. Lastly, use the integrating circuit to obtain triangle wave. The basic simulation software Multisim has been used to simulate the circuit.

Two problems in mesoscale wave dynamics are addressed: (i) wave-turbulence interaction in a breaking mountain wave and (ii) gravity wave generation associated with coastal heating gradients. The mean and turbulent structures in a breaking mountain wave are considered using an ensemble of high-resolution (essentially LES) wave-breaking calculations. A turbulent kinetic energy budget for the wave shows that the turbulence production is almost entirely due to the mean shear. Most of the production is at the top of the leeside shooting ow, where the mean- ow Richardson number is persistently less than 0:25. Computation of the turbulent heat and momentum uxes shows that the dissipation of mean- ow wave energy is due primarily to the momentum uxes. The resulting drag on the leeside shooting ow leads to a loss of mean ow Bernoulli function as well as a cross-stream PV ux. The dependence of both the resolved-scale and subgrid turbulent uxes on the grid spacings is examined by computing a series of ensembles with varying grid spacings. The subgrid parameterization is shown to produce an overestimate of the PV ux at low grid resolution. The generation of gravity waves by coastal heating gradients is explored using linear theory calculations and idealized numerical modeling. The linear theory for ow without terrain shows that the solution depends on two parameters: a nondimensional coastal width L and a nondimensional wind speed U. For U 6= 0 the solution is composed of three distinct wave branches. Two of these branches correspond to the no-wind solution of Rotunno, except with Doppler shifting and dispersion. The third branch exists only for U 6= 0 and is shown to be broadly similar to ow past a steady heat source or a topographic obstacle. The relative importance of this third branch is determined largely by the parameter combination U=L. The e ect of terrain is explored in the linear context using an idealized linear model and associated diagnostic computations. These results are then extended to the nonlinear problem using idealized nonlinear model runs.

Laboratory experiments were conducted in an internal wave flume ( m), at the National Sun Yat-Sen University, Kaohsiung, Taiwan. A series of fundamental experiments on wave generation, propagation and interaction with obstacles were carried out using stratified two-layer fresh/brine water with a total depth of 50 cm in the flume. Factors governing the experiments included the thickness ratio of the upper and lower layer H1/H2, interface difference

This thesis studies the target identified by analyzed scattering signal which is from active sonar impinged under water. In general, the specular reflected waves and corner waves provide the information of target profile in scattering signal. The resonance scattering waves and surface waves submit the material properties of target by analysis signal. The Rayleigh wave is a candidate for target identified in surface wave analysis. Since then, the theorem focuses on Rayleigh wave propagation on solid sphere and cylinder in this thesis. To analyze the problem of scattering wave, if the normal mode methed is applied to solve it, the character of reflected surface wave can not appear on the solution. So the Sommerfeld-Watson transform(SWT) method is used to solve it. This method can convege the infinite partial-wave series rapidly and the physical property of acoustic wave can be elucidated easily. In experiment, the reduced scale experiment is setup for Rayleigh wave measurement using ultrasonic wave. For Rayleigh wave discussion, the individual profile, sizes and material of target is applied respectively in this experiment. The beam pattern is also measured in the Rayleigh wave filed. The result appears the target identified by analytical Rayleigh wave obviously.