Experimental investigation on the three-dimensional oblique interaction of an internal solitary wave with a horizontal finite-length cylinder

Abstract

An experiment on the oblique interaction of an internal solitary wave (ISW) with a horizontal finite-length cylinder was conducted in a gravitationally stratified fluid flume. The multi-measuring technique, which was composed of the multichannel conductivity-probe array, dyeing identification and particle image velocimeter (PIV), was used to study the coupling wave–flow structure, and the three-component micro-amplitude force sensor was used to measure the horizontal longitudinal, horizontal transverse and vertical forces on the cylinder. Based on the experimental observations and measurements, a theoretical analysis method of the three-dimensional force on the cylinder interacting with an ISW at any angle was established for the experimental analysis. The ISW force on the cylinder is composed of the wave force, the friction force and the disturbance force, in which three components of the wave force in the horizontal longitudinal, horizontal transverse and vertical directions can be estimated by the Morison formulas corresponding to those component velocities perpendicular to their respective directions, the dynamic friction force depends on the tangential velocity at the surface of the cylinder, additionally the disturbance force composed of the reduced gravity and the vortex shedding lift is considered in the vertical direction. Furthermore, it is found that the wave–flow structure of the ISW at its windward side, leeward side and inside its wave profile dominates the three-dimensional force on the horizontal finite-length cylinder, of which its characteristics change with key factors such as the interaction angle between the cylinder and the ISW, the incident ISW amplitude and the cylinder-submerged depth. When the interaction angle increases, the same order of the horizontal transverse force at a certain angle as the increasing horizontal longitudinal force can be gotten, and the ”double peak” of the vertical force can be made. With the increase of the incident amplitude, the magnitude of the three-dimensional force always increases, but its direction is unchanged. For different submerged depths, the vertical force depends on the ratio of the reduced gravity or the vortex shedding lift or their resultant force to the vertical disturbance pressure. However, the understanding of the oblique interaction mechanism of an ISW with a horizontal finite-length cylinder provides direct insight into the intrinsic characteristics of the damage to the safety of marine and offshore structures in the actual ocean.