Numerical Study Of Hydrodynamic Interaction Between Two Submerged Moving Objects

In the flow field, when two or more objects in close proximity are in relativemotion, they will interfere with each other, which is widespread in the enginering. Tosolve these problems, it is necessary to deeply research the characteristics of theinteraction among two or more objects in the flow field.In this dissertation, the hydrodynamic characteristics of two objects approachingto each other in viscous flow were studied using the Computational Fluid Dynamics(CFD) tool based on dynamic mesh technology and some results are obtained.In the two-dimensional (2D) viscid flow, the cylinder force characteristics in theviscid flow were firstly compared with that in the inviscid flow. Then, thecharacteristics of forces acting on the cylinders in viscid flow under differentinterstice ratios, different approaching velocities and different background flows wereanalyzed. The numerical results show that when the background flow velocity is zero,the drag coefficient increases with the decrease of interstice ratio and the increase ofapproaching velocity. As the background flow velocity is not zero, the drag coefficientincreases with the increase of background flow velocity. While the ratio of thebackground flow velocity to the approaching velocity is large, the force acting on thecylinder vibrates obviously.Further on, the force of the two objects close to each other in thethree-dimensional (3D) flow field was analyzed based on the method in the2D flowfield. Compared with the2D case, the repulsion significantly reduced when thecylinders approached to each other in the3D case, which shows that the wall effect ofcylinders approaching to each other in the3D case is less than that in the2D case. Wealso verify that the calculation method used to simulate rotation ellipsoid problem isreliable. When simulating the situation that underwater ellipsoid was close to thestructures and performing rotational movement, we find that the torque exerted on theellipsoid changes greatly when the ellipsoid rotates around itself and the structures. Itshould be noticed when the ellipsoid is controlled to perform the precise motion.