| Similar to the ship navigation on the surface of ocean,the underwater vehicle often encounters the oblique propagating internal solitary wave(ISW),whose intrinsic typical nonlinearity and coupling effect of wave-flow fields make it more complex the hydrodynamic characteristics for a submerged slender body.In present paper,the experimental investigations on the interaction of the oblique ISW with a submerged slender body are carried out by means of changing the inclined angle between the body length and the ISW propagation directions.The fine structure for the wave-induced flow field and its influenced factors have been analyzed quantitatively.Both flow field and force for the interaction between the ISW and the submerged slender body have been measured experimentally,and also the characteristics of the ISW force exerted on the body for its different oblique propagating angles has been analyzed.The present studies can provide some important assistance for the navigation safety of underwater vehicle in the complicated ocean environments.The novel points and the main conclusions of the paper are as follows:1.The fine structure of flow field induced by an ISW have been studied systematically in a large-type gravity stratified fluid tank.The experimental results have shown that the structure of three-dimensional flow field of the ISW can be cognized by means of the two-dimensional particle image velocimetry(PIV)technique.According to the measuring flow field for the increasing amplitudes,the applicative range of amplitudes for three theoretical models of KdV,eKdV and MCC has been given.Moreover,experimental results shows that the velocity fields for same ISW amplitude will be enhanced with the increase of the density difference or the decrease of thickness ratio between the upper and lower layers,which verifies the relevant numerical simulation results.2.The measurement of velocity field for the interaction between oblique propagating ISW and submerged slender body has been carried out in the large-type gravity stratified fluid tank.By use of the two-dimensional PIV and the auxiliary dye displaying image techniques,the three dimensional velocity field and its variation have been analyzed quantitatively.It has been shown that with the increase of the encountering angle,the influence of the submerged body on the wave-induced flow field will be enhanced.When the slender body encounters the oblique propagating ISW,its different parts will be located in different locations of the ISW wave profile.It will lead to the different intensity of flow fields along the body length,as a result,the velocity around the body’s tail is 2 to 3 times than the one around its head.So that a torque exerted on the slender that affects its movement characteristics greatly will been generated,which can threaten the safety of the underwater vehicles.3.For the first time the force exerted on the submerged slender body by the oblique propagating ISW has been measured quantitatively in the large-type gravity stratified fluid tank by use of the three-component micro-force measuring system,and the attempt to explain its action mechanism has been accomplished based on the obtained characteristics of wave-flow fields.It shows that the horizontal force of the submerged body will be enhanced significantly with the increase of the encountering angle,as a result,the horizontal force for the angle of 90 degree will reach several times than the one for the zero degree.Moreover,the vertical force of the body presents the variation of W-type in process of the oblique propagating ISW evolution and its maximum value is reached at the position when the body is among the ISW packet.Consequently when the slender body encounters the oblique propagating ISW,the second action along the vertical direction must be concerned beside the submerged depth. |
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