Research On Numerical Method For A Paraboloid Entering Water Surface Under Fully Nonlinear Boundary Conditions

With the further development of the national marine development strategy,the development of Marine resources and competition for space will be the focus of the world.Improving the design and manufacturing level of marine engineering structures is the key factor to enhance international competitiveness.With the continuous increase of new ships and Marine structures in the ocean development,the research on the problem of water slamming is becoming more and more critical.For instance,during the voyage,the ship's bow and the surface of the water will collide frequently,causing a great slam load to cause structural damage;the plane landing on the water in aviation;the water entry and out of water of the boat and so on.When the slam occurs,it is often accompanied by drastic changes in the wet surface of the structure,the deformation of free surface,and fluid-solid coupling.The impact of the slamming is a big bang.The impact time is short but the peak is large enough to cause damage to the structure in a short period of time,or the repeated slamming can cause fatigue damage to the structure.It is necessary to study the prediction method of slamming load in order to effectively deal with the hazards caused by fluid-solid slamming.The main research content of this paper is to simulate and track the parameters change in the water entry process of a paraboloid.In this paper,based on the three-dimensional potential flow theory,the water entry problem of curved surface is numerically simulated by imposing the impenetrable condition and the fully non-linear boundary conditions on the object and the free surface respectively.In the process of numerical simulation,the free surface is discretized into quadrilateral meshes,the unknown velocity potential and its normal derivative on the boundary are sloved by using the boundary element method on each time step.In order to avoid the multi-value problem of free surface function,the local cylindrical coordinate system is established on any ? section plane which passing through the paraboloid axis,mesh reconstruction and smoothing can also be carried out on the intersection line between each ?plane and free surface in the simulation process.The node information of the new mesh is obtained by interpolation method on the basis of the node information of the old mesh.Fully nonlinear free surface kinematics and dynamics boundary conditions satisfy Euler equations.Mesh reconstruction and smoothing are performed every few time steps to ensure the stability of numerical computation.In this paper,the convergence of the numerical method is verified,and the high-precision convergence analysis based on different time steps and mesh sizes is completed.The numerical method is used to simulate the process of vertical and oblique costant velocity of curved objects entering water,the influences of structure shape and transverse velocity were analyzed in detail.Then,the distribution of flow field under different working conditions,the variation of free surface,the distribution of pressure on the surface of the body and the characteristics of hydrodynamic load under water entrying are discussed.At the same time,numerical simulation method is used to study the slamming load characteristics of free entry of paraboloid,and the effects of gravity and initial velocity on the freefall process of a paraboloid were analyzed.