Mar. Res. 2023/12
Vol.3. Iss.2 :61-75
Numerical Study on the Evolution of Internal and Surface Waves Propagating over a Permeable Trapezoidal Obstacle

Ming-Hung Cheng 1*, Chih-Min Hsieh 2 and Robert R. Hwang 3
1Marine Industry and Engineering Research Center, National Academy of Marine Research, Kaohsiung City, Taiwan
2Department of Maritime Information and Technology, National Kaohsiung University of Science and Technology, Kaohsiung City, Taiwan
3Department of System Engineering and Naval Architecture, National Taiwan Ocean University, Keelung City, Taiwan; Institute of Physics, Academia Sinica, Nankang, Taipei City, Taiwan

Abstract: Although interesting phenomena associated with the interactions between internal waves (IWs) and surface waves (SWs) over impermeable submerged obstacles have been observed in laboratory experiments and numerical models, less research has explored the effects of permeable beds on wave evolution. In this study, we employed a numerical model to solve the Navier-Stokes equations using the Improved Delayed Detached Eddy Simulation (IDDES) model for turbulence closure, investigating the evolution of internal and surface waves propagating over a permeable trapezoidal obstacle. The porous media equation was adopted to further explore the evolution of the flow field during this process. A plunger-type wavemaker was utilized to create surface pressure differences, generating both surface and internal waves. Additionally, air, water, and brine were used to simulate the complete process. The numerical simulations revealed that the amplitude and wave period of SWs are affected by the propagation of IWs over submerged obstacles. While both SWs and IWs propagate over the trapezoidal obstacle, the wave amplitude decreases significantly, but the fundamental frequency remains constant, regardless of whether the obstacle is impermeable or permeable. In the case of the impermeable obstacle, the strength of the fundamental wave period of IWs decreases as IWs propagate over the plateau. In the case of the permeable obstacle, porous effects cause the amplitude and strength of the fundamental frequency of both SWs and IWs to decrease significantly during this process. Based on the numerical simulations, the interaction mechanisms between these two waves and obstacles have been elucidated, providing essential insights for future coastal and ocean engineering endeavors.

Keywords:  Internal waves, surface waves, permeable trapezoidal obstacle, wave-obstacle interaction, numerical simulations.

*Corresponding author; e-mail: chengminghung@gmail.com
© 2023  Marine Research , ISSN 2709-6629 

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