Investigation of Internal Generation of Waves and Currents for 3D Navier-Stokes Equations Model

• Main Authors: Yen-LungChen, 陳彥龍
• Other Authors: Shih-Chun Hsiao
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/mw5d66

博士 === 國立成功大學 === 水利及海洋工程學系 === 106 === This dissertation presented an investigation on the method of internal generation of waves and currents for three-dimensional (3D) Navier-Stokes equations models to enhance the model's capacity to simulate wave-current-structure interaction issues. The development of the proposed method could be divided into four steps: wave generation and absorption for two-dimensional (2D) wave tank, generation of directional waves for 3D wave flume, generation of wave-current, and applications for coastal/ocean engineering. The 3D numerical model FLOW-3D which solves the Navier-Stokes type equations and captures the water surface elevation by the volume of fluid method was utilized in this study. FLOW-3D was employed to investigate the mass source internal wavemaker and the numerical sponge layer. Besides, the wave-generating and-absorbing method was extended to generate currents. The problems of wave-structure interactions and wave-current interactions were considered to evaluate the ability of the proposed method. Finally, a buoyant round jet in a wave environment was studied in detail as a topic for the application. The methodology of a directional wave-current numerical tank for a 3D Navier-Stokes equations model was established. To start with, a mass source wavemaker and a numerical sponge layer were embedded. The capability of the numerical sponge layer was first examined and an optimal layout of the sponge layer was determined based on a series of 2D numerical experiments. The scheme was successfully extended to 3D geometry. Nest, an approach for designing the mass source function was developed. Regular, irregular, and solitary waves were examined. The numerical results were compared with the analytical solutions and some numerical results obtained using the momentum source method, with good agreements observed for a wide range of relative water depths. The proposed method was applied to directional wave cases and various layouts of the source line were discussed. Also, the wave-current generation method is proposed by including the idea of the relaxation method. Finally, the proposed model was applied to simulate 2D and 3D wave-structure interaction problems. Model-data comparisons showed that the proposed method is potentially useful and efficient for examining wave-structure interactions. The numerical study on the kinematics of buoyant round jets in a wave environment was presented. A buoyant round jet was horizontally discharged at the mid-depth in regular waves. Three kinds of effluent with various densities were used for the jets. The numerical results were compared with the experimental data, with reasonable agreement observed. The mechanism of the jet oscillation under different wave-to-jet momentum ratios was presented. The effects of relative water depth, the ratio of the wave height to the water depth, and buoyancy on jet diffusion were considered. Among them, the ratio of the wave height to the water depth appeared to be the most critical factor on jet diffusion processes under the conditions being considered. Finally, the variations of the jet cross-sectional profiles in the potential core region and the near field region were studied.