Ming-Hung Cheng

Potential hazards and dynamical analysis of interfacial solitary wave interactions

Over the last few decades, a lot of attention has been concentrated on the consequences of marine impacts, especially those caused by the tsunami wave train. Internal solitary waves are similar to the surface waves that commonly occur in the waters of the ocean or large lakes and can have significant effects on oceanic mixing, climate change, the movement of submerged plankton, and the weathering of geological structures. This motion can be severe enough to create natural hazards, such as submarine tsunamis in the ocean. These could also even occur in large lakes. Numerical modeling has shown that the waveform of a soliton that interacts with others of a similar kind would emerge unchanged from the collision, except for a phase shift. However, the results from laboratory experiments are rather limited, despite the successful generation of ISWs using a collapse mechanism in a wave flume. This paper reports on some interesting facts compiled from the results of a series of laboratory experiments on the investigation of the head-on collision of two ISWs. Our results confirm that the waveforms of two depression ISWs will more or less retain their initial shape after a head-on collision. However, the transmitted wavelength will broaden when two elevation ISWs collide, perhaps affected by bottom friction. Overall, the resulting waveforms induced by such head-on collisions agree well with the theoretical predictions for depression ISWs, regardless of their scale of amplitude, but the results are only valid for elevated waveforms of large amplitude.

Effects of initial amplitude and pycnocline thickness on the evolution of mode-2 internal solitary waves

Numerical simulations are performed to investigate the effects of the initial amplitude and pycnocline thickness on the evolutions of convex mode-2 internal solitary waves propagating on the flat bottom. A finite volume method based on a Cartesian grid system is adopted to solve the Navier-Stokes equations using the improved delayed detached eddy simulation turbulent closure model. Mode-2 internal solitary waves (ISWs) are found to become stable at t = 15 s after lifting a vertical sluice gate by a gravity collapse mechanism. Numerical results from three cases of pycnocline thickness reveal the following: (1) the occurrence of a smooth mode-2 ISW when the wave amplitude is small; (2) the PacMan phenomenon for large amplitude waves; and (3) pseudo vortex shedding in the case of very large amplitudes. In general, basic wave properties (wave amplitude, wave speed, vorticity, and wave energy) increase as the wave amplitude increases for a specific value of the pycnocline thickness. Moreover, the pycnocline th...

Effect of Plateau Length on the Transformation of Internal Solitary Waves

Abstract—The propagation and dissipation of internal waves over continental shelf bathymetry are complex phenomenon. The waveform would be re-generated while transmitting a submerged deep-shallow-deep topography. To study the effect of the marine topography on the evolution of an internal wave, numerical simulation is utilized to perform the flow evolution and waveform inversion of a large depression internal wave over a trapezoidal obstacle with different plateau. A finite volume based Cartesian grid method is adopted to solve the Reynolds averaged Navier-Stokes equations using a k-ε model for the turbulence closure. Numerical results reveal that the re-generated waveform does not occur due to baroclinic wave. The shorter plateau length would induce strong vortex in back of the obstacle. Moreover, the wave amplitude, vorticity and turbulent kinetic energy are dissipated significantly. However, the level of the phenomenon decreases as the plateau length is larger than the wavelength.