| Summary: | 碩士 === 國立高雄海洋科技大學 === 海事資訊科技研究所 === 105 === In nature, internal solitary waves (ISWs) exist a stratified fluid. When the wave propagates in the ocean, the wave-obstacle interaction causes strong shear effect to generate acute converging water and abrupt strong currents. It also effects the human actives in the marine, therefore, we need to study its mechanisms. As promoting the field instruments, the researchers found the mode-2 ISWs in the ocean and focused on the mode-2 ISW transformations in the physical oceanography field. Because of limited literatures about mode-2 ISW propagating over variable topography, this study adopted numerical simulations to discuss the evolutions of mode-2 ISW propagating over a submerged ridge.
In this study, a finite volume method solving the Navier-Stokes equations using Improved Delayed Detached Eddy Simulation turbulence model is adopted to discuss the evolution as a mode-2 ISW passes through a submerged ridge. The pressure-velocity coupling is obtained by a PISO algorithm (Pressure Implicit with Splitting of Operator). In order to update the interface capturing with every time step, the volume of fluid method is implemented. The six kinds of initial amplitudes and two types of obstacle heights are employed in this numerical simulations. Moreover, the equal depths of upper and lower layers is adopted in initial condition and this study employs the so-called gravity collapse mechanism to generate a mode-2 ISW. Based on the numerical results, the evolutions of mode-2 ISW’s generation, propagation and wave-obstacle interaction are shown by density field, vorticity filed, dimensionless analysis and trajectories of the fluid particles.
The numerical results reveal that two wave-obstacle interactions are found and can be classified as strong and middle interaction. For strong interaction, the lead trough almost dissipates in front of the submerged ridge and the deformed waveform is investigated after the mode-2 ISW pass through the ridge; for middle interaction, the obstacle has weak effect on wave propagation and the waveform almost is similar during this process. For example, the open mouth is found as the symmetric large mode-2 ISW propagates on flat bottom. And then, two small mode-2 ISWs are generated and trail after leading wave. When the wave encounters the front slope of the submerged obstacle, the leading crest and leading trough deform slightly due to shoaling effect. The velocity on front slope becomes fast because the width between the leading trough and front slope decreases. After the wave passes through the ridge, the amplitude of leading trough increases weakly. Asymmetric waveform becomes unstable due to reorganization until the wave propagates on flat bottom in rear of the obstacle. Finally, this study can present the spatiotemporal evolutions of mode-2 propagating over a ridge in order to understand further its mechanisms.
Keywords: Mode-2 ISW; IDDES-SA model; submerged ridge; OpenFOAM.
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