Laboratory Study on the Interaction Between Internal and Surface Waves Over a Submerged Ridge

Cheng, Ming-Hung (National Taiwan Ocean University) | Hsieh, Chih-Min (National Kaohsiung University of Science and Technology) | Hwang, Robert R. (National Taiwan Ocean University) | Hsu, Tai Wen (National Taiwan Ocean University)

OnePetro 

ABSTRACT

Surface waves (SWs) and internal waves (IWs) are the most common natural phenomena in the ocean. Some oceanographers believe that internal solitary waves have significant influence over the surface waves. In order to observe the interaction between IWs and SWs with different periods over a submerged ridge, laboratory experiments by using plunging wavemaker are run in the study. Laboratory results reveal that the amplitude of SWs decreases as the fluid changes from homogeneous into stratified. At the slow wavemaker speed, the wave period of SWs has a significant decrease when the wave propagates over a ridge; at fast wavemaker speed, the wave period of SWs keep the same value. For the evolution of IWs in strong breaking cases, the wave transmitted amplitude increases as the wave approaches to the ridge. The wave fundamental period of IWs also shorten in slow wavemaker speed but is fixed in fast wavemaker speed. Moreover, the oscillation noises in long period is significant than that in short period.

INTRODUCTION

In a stratified fluid, external forces (ex., wind or flow etc.,) produce the barotropic waves in surface layer (i.e., Surface waves; SWs) and then induce baroclinic waves in interface (i.e., Internal waves; IWs) due to the different pressure variations. In the ocean, the IWs generation is induced by the interaction between flow and submerged topography (Hsu et. al., 2000); in the lake, the wind plays an important role on producing the surface pressure difference and then internal waves are generated indirectly (Pannard et. al., 2011); at the estuary, the internal waves are generated by the interaction between waves and flow. Internal waves have significant effect on ecology, environment and engineering when they propagate over varied topography (Bourgault et al., 2014; Lamb, 2014). Internal solitary wave (ISW), which is a special type of internal waves, has been studied in previous literature about its generation, transport and dissipation (Grimshaw and Helfrich, 2018; Hsieh et al. 2016, Lamb, 2014). Due to the short flow induced by its larger amplitude of ISW, surface waves becomes small and can be ignored during the interaction.