Flow Field Characteristics And Motion Prediction Of High Speed Planing Hull Based On CFD Method

With the deepening of the strategy of maritime power,the focus of China’s development has gradually shifted from land to sea,from offshore to deep sea and open sea.Due to its small size,fast speed and other advantages,unmanned aerial vehicle is widely used.It can not only achieve the functions of hydrogeographical environment and energy exploration,but also complete the combat tasks of target strike,mine sweeping,anti submarine,etc.,playing an irreplaceable role in the front position of civil military integration.Scholars in China and abroad have done many extensive and in-depth researches on the unmanned vehicle development,but the researches on the seakeeping performance of unmanned vehicles are less conducted,and most of them are conducted based on the traditional potential flow method.The potential flow method has high efficiency,but it is difficult to solve the strong nonlinear problems such as fluid flow separation and bow splash,which leads to low accuracy of calculation results.Computational fluid dynamics(CFD)method considers the influence of fluid viscosity and directly solves the N-S equation,which greatly improves the calculation accuracy.Therefore,based on the CFD method,this paper carried out the research on the motion prediction of the speed and seakeeping of planing hull.Firstly,based on the actual hydrodynamic performance requirements of planing hull,the research status in China and abroad and currently existing shortcoming are systematically summarized.Then,we respectively studied the questions regarding to the planing hull’s mobility performance in still water and regular wave conditions.The specific research work of this paper is as followed:1)In the question of resistance performance and the motion posture of unmanned aerial vehicle in still water,through the pool test of single-surfaced unmanned aerial vehicle,the motion postures of the unmanned aerial vehicle in still water and facing waves are obtained.We validated The CFD method on the basis of the pool test data,and we analysized the accuracy of the simulation based on the effects of different grid types,grid thickness near the wall,hull surface grid,time step and other parameters.Finally,the static water resistance,heave and trim attitude of the planing hull are obtained by simulations under different speeds and different longitudinal positions of the gravity center.According to the simulation data,the influence of the gravity center on the motion attitude of the planing hull in still water is analyzed;and according to fluid field features,the mechanism of the influence on the hydrodynamic performance of the planing hull is analyzed.2)In the question of planing hull mobility characteristics in regular wave,in this paper,we firstly introduced the numerical wave making technique,and analyze the convergence of the grids number and time step in the numerical wave making process.Then,combined with the two parts of numerical simulation and numerical wave-making simulation in still water,the question of regular wave head-on is further studied.In this paper,we further studied the effects of speed and wave length on the heave motion response,pitch motion response and vertical acceleration motion response at the gravity center of the planing hull,and we compared the change of the motion posture in still water attitude and in the regular wave attitude.At the same time,the influence of the longitudinal position of the gravity center on the three aspects of motion response is also analyzed.Then,the accuracy of CFD method and potential flow method is compared by using the pool data.Finally,through the bottom pressure and flow field details and other parameters,we analyzed the reasons that changed the planing hull motion posture.The research work of this paper can provide a certain reference for the design and manufacture of unmanned aerial vehicle,and also has a certain reference significance for the relevant simulation work of planing hull.