For the present field observations, mode-2 internal solitary waves (ISWs) have been found in many ocean, especially at South China Sea and are important issues in physical oceanography. In order to study the spatiotemporal variations while a mode-2 ISW propagates over a submerged ridge, a finite volume is employed to solve the Navier-Stokes equations using IDDES model for the turbulent closure. Numerical results reveal a symmetric waveform of a mode-2 ISW propagates in deep water. At the same time, second and third mode-2 ISWs trailed after leading wave can be observed during wave transmission. The leading crest and leading trough deform slightly due to shoaling effect when the wave passes on the front slope of the submerged obstacle. As the wave approaches the front slope, the flow in lower layer increases because of the narrow width between the leading trough and front slope. And then, the amplitude of leading decreases significantly but that of leading crest almost maintains the original value when the wave encounters the submerged ridge. After the wave leaves the ridge, the amplitude of leading trough increases weakly and asymmetric waveform becomes unstable due to restructured effect. By comparing with different obstacle shapes, the decrease of transmitted amplitude and vorticity in trapezoid is larger than that in ridge.


Internal solitary waves (ISWs) are the important phenomenon in the ocean with density stratified fluid. They usually generated by tide- current-topography interaction. In the South China Sea (SCS), its amplitude of a mode-1 ISW usually reaches 170 m with strong velocity difference exceeding 2.4 ms−1 between its upper and lower water layers (Chang et al., 2008), therefore, an ISW could have significant ramification not only in marine ecology but also on engineering works in the ocean (Bourgault et al., 2014; Lamb, 2014). Based on the filed observations, mode-1 and mode-2 types of ISWs have been found in the ocean. Mode-1 ISW includes depression and elevated waveform and is available in abundant literature on the physical mechanisms that generate the mode-1 ISW and the wave transformation on variable topography, arising from field observations (Bai et al., 2017; Alford et al., 2015), laboratory experiments (Chen et al., 2017; Cheng and Hsu 2014) and numerical simulations (Grimshaw and Helfrich; 2018; Sutherland et al., 2015).

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