Laboratory experiments were conducted to examine an internal solitary wave (ISW) propagating over a ridge terrain and its interaction with a submerged slender body in a large-type gravity stratified fluid tank. It is shown that when the ISW of depress propagates over the ridge terrain its wave configuration will be changed markedly. Meanwhile this change of the ISW configuration will affect obviously characteristics of the acting force on a slender body. According to those characteristics the representative movement of the slender body will be deduced roughly so that the uncertain factors threatening the safety of marine architecture or submerged vehicle from the nonstationary ISW can be predicted.


The ridge terrain is one kind of typical structures at the ocean bottom extending from the margin of continental shelf to the deep ocean and also an important environmental factor that affects the formation and propagation of internal solitary waves (ISW) (Fang, 2005; Feng, 1982). The spatial and temporal characteristics such as waveform, amplitude and propagating velocity of the ISW over a ridge can result in the broken ISWs of large amplitude and the strong mixing density near the pycnocline, which will significantly increase the uncertain factors threatening the safety for both marine architectures and submerged vehicles (Cai, 2011; Huang, 2015; Wang, 2016).

A lot of numerical and laboratory researches (Song, 2011; Si, 2012; Zhang, 2016) on interactions between the ISW and structural objects such as ocean platform, submarine cable and underwater cylinder etc. have played an important role in cognizing varieties of the ISW forces exerted on those structural objects. Therefore it is one of the more noteworthy issues that the characteristics of the forces exerted on a slender body can be changed by the ISW and its effect cannot be ignored. For instance, the variation regulation of the additional load on a slender body has been obtained by simulating the interaction process of the ISW with it in their numerical tank of internal wave (Fu,2009).

The characteristics of the maximum ISW load have been verified by quantitatively measuring the force exerted on a slender body in a large-type stratified fluid tank (Wei, 2014). The preliminary results about effects of the nonstationary ISW on the force characteristics have been given by means of the laboratory experiments on the evolution of the ISW over a gentle slope and its action on a slender body (Du, 2016). Obviously the spatial and temporal variation of the ISW structure due to the ocean bottom topography will result in the more complicated characteristics of forces on a submerged slender body. So far, it is not clear that the effect of complex topography such as a ridge terrain on the characteristics of ISW forces exerted on the slender body.

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