Numerical Simulation of Strongly Non-linear Internal Wave in Northern South Cnina Sea
Date Issued
2008
Date
2008
Author(s)
Fu, Yung-Ching
Abstract
Nonlinear internal waves (NLIWs) are very active in the northern South China Sea (SCS). Historical satellite images show that NLIWs appear often between Luzon Strait in the east and the continental shelf at northwest of SCS. Most of the researches of NLIW concentrate over the shelf of SCS, but not much on the propagation and the generation process of NLIW in the deep sea region of SCS. So far, lots of researches suggest that the source of NLIW is in the Luzon Strait, but there is no definitive conclusion about how it happens and where the locations of source regions are.In the field experiment to find the source of NLIWs in 2005 and 2006, total 5 T-strings were deployed in Luzon Strait for a week long observation. By the record of isotherm displacement during the passage of NLIW at different locations, we derived information on the evolution of NLIW (from single wave front to wave packets) west of HengChun Ridge, and found maximum amplitude about 140 m. In 2007 experiment, the focus was closer to HengChun Ridge and the NLIWs again have big amplitude (η) and large half-length from surface down to 500 m depth. The ratio of η to upper layer thickness (h) was nearly 1. They are categorized as strongly NLIWs, while KdV theory can only simulate the wave form and propagation of a weakly NLIW, i.e. η/h < 0.4 (Grue, 1999). From the analysis of field data and satellite images of these NLIWs, we found that the width between points of vertical displacement equal to half amplitude, is about 5.5 km, that is equivalent to half-width of 2.9 km, according to KdV theory. To account for the strong non-linearity of NLIWs, a fully non-linear Navier-Stokes equation, along with diffusion and continuity equations, are used to construct a numerical model studying strong NLIWs. Simulation starts with a solitary wave at the left side of the model that represents the source of NLIW and the location of HengChun Ridge (Liu et al, 2006). The model-simulated propagation of NLIW looks similar to that observed in the field, in the sense of (1) the propagation speed, amplitude and half-width of NLIWS, (2) the number of wave packets that increases with the distance of propagation, or the evolution of NLIW. With the advancement of computer technology and the improvement of numerical method, this numerical model may imitate the NLIW evolution with details and become a more powerful tool in studying the generation process of NLIW.
Subjects
Strongly nonlinear internal wave
numerical model
half amplitude,Navier-Stokes equation
Type
thesis
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