A Study On Water Entry Problems By Numerical And Experimental Method

Water entry problem is ubiquitous in engineering situations,such as planing of sea plane or the interaction process of the bow part of a ship when leaving and then hitting the free surface.Meanwhile,it is also a classical problem in science research and has drawn many researchers' attention.A significant aspect needed to focus is to capture the movement of the free surface since it usually moves with large deformation and even with breaking and splashing.Theoretical or mesh methods are hard to deal with it.Thanks to the meshless Lagrangian property,the smoothed particle hydrodynamics(SPH)method is easy to deal with free surface flow problem and has become more and more popular.The core of the SPH method is to use a set of particles with physical quantities to denote the fluid field and move the particles with Lagrangian governing equations.The physical quantity of each individual particle is approximated by nearby particles.Because of meshless charachter,it can save amounts of researchers' time to deal with the mesh with mesh methods.The thesis is to research on the water entry problem by the SPH mehod.First of all,the SPH method is validated by experiments.Two cases of a constant velocity water entry and a free fall motion water entry are simulated respectively and the numerical results are compared with published experimental results.Good agreements are achieved.Afterwards,the thesis analyses the zero-horizontal-velocity wedge water entry problem.The problem is discussed from two perspectives,namely the fluid part and the wedge part.For the fluid part,it puts the common 2D simulation forward to 3D simulation and shows the results of the movement of the free surface,the movement of the fluid particles on the free surface and the affected splash-out region.Also,we conduct experiment to research on the transformation of the spray and compare it with the numerical method.As for the wedge part,we develop a new analytical method which improves the accuracy compared with classical method.Both analytical and numerical method are used to compute the forces exerted on the wedge.The thesis gives the relationship between the maximum acceleration and the entry velocity and deadrise angle.The result can give some guidance in both engineering practise and everyday life.Lastly,the thesis analyses the water entry problem with initial horizontal velocity,and picks the classical one-stone skipping-to present the results.The thesis uses both the analytical and numerical method to do the research.The analytical method is based on the Second Law of Newton and Momentum Theorem and it only serves as a qualitative assistant.The purpose of the numerical method is to find out the effects of initial horizontal velocity and rotational velocity on successful stone skipping.We adopt the variable control method to analyses the action of the two aspects and give suggestions on how to skipping further.