Research On Ship Performance Numerical Tank Based On CFD

With the improvement of computer hardware level and modern numerical algorithm, the technic of ship performance numerical tank has become an indispensable method of ship research and design. Compared with the physical experimental pool, on the one hand, numerical tank has the advantages of short period, less consumption of resources and low cost, which meets the social requirements of low carbon; on the other hand, the application of numerical tank can promote ship design from the traditional experience design pattern gradually to the new knowledge-based design pattern, so as to get rid of the strong dependence on ship design experience, parent ship etc.. Meanwhile ship numerical tank can integrate performance prediction and evaluation into the design of a new style of ship, and realize the optimization design, which is the envy of physics experiment tank.The research progress of ship numerical tank has been systematically and thoroughly expounded. Based on Viscosity solution of the RANS equations, the key difficult problems of accurate prediction of ship resistance, Seakeeping and maneuverability are innovatively studied. The main work of the paper lies in:(1) There are many difficulties in the accurate prediction of the flow field around the ship of CFD numerical simulation method, and taking a certain type of marine environmental monitoring ship(0.1<Fr<0.4) as the research object, reasonable solutions are put forward to the difficulties in the process of numerical simulation. Based on dynamic equilibrium method, Numerical simulation accurately predicte the flow field around the ship with considering variation of ship navigation attitude; Advanced body to surface mesh generation and octree structure mesh splitting methods are applied, which are suitable for the numerical simulation of the flow field around the ship; With the method of actuator disk propeller, a virtual torque is added behind numerical ship model, which makes the sailing condition of numerical hull model more close to ship model experiment. Compared the numerical simulation results with experimental data, it indicates that the maximum error of the hull total resistance is less than 1.7%, and the information about the flow field around the ship is also very close.(2) When ship is sailing at high speed, its equilibrium position differs greatly from that of hydrostatic floating state. During numerical simulation, great change of hull attitude will result in large mesh distortion and eventually lowers the simulation accuracy. This paper applies numerical analysis step by step to forecast the hull equilibrium position and resistance successively based on CFD two phase flow theory and dynamic mesh method. First of all, the hull equilibrium position is estimated roughly. Then the hull attitude in equilibrium of step one will be taken as initial state, allowing for fluid viscosity and hull voyage attitude effect, numerical simulation is applied again to accurately forecast hull resistance. The hull initial posture is close to the final equilibrium posture, thus when utilizing dynamic mesh technique, problems due to large grid distortion such as numerical calculation accuracy reduction or numerical divergence, etc. will not be caused. This paper studies on a certain type of wave piercing catamaran to obtain the hull resistance in a range of length Froude number 0.6~1.0 by applying step-by-step calculation, and compared numerical results with experimental data. Results indicates a maximum error less than 2.5% with satisfying accuracy. Numerical method put forward in this paper can provide a new way for accurate prediction of high speed and ultra-high speed ship resistance.(3) In present, ship seakeeping numerical simulation is based on potential flow theory, and specify the ship movement in advance, which does not realize hull motion and flow field coupling. To predict the motions of ship in regular waves, it solves the RANS equations and the kinematics equations of rigid body simultaneity, and uses moving grid method during the simulation. On this basis, it carries out a group of simulations and obtains the heave and pitch transfer functions for ship model Wigley-III.(4) Regarding the KVLCC2 as research subject, hydrodynamic model is established by plane motion of small amplitude assumptions and Abkowitz’s third-order nonlinear mathematical model of maneuvering motion. Based on two phase flow theory and dynamic mesh method, ship PMM performance numerical tank is built. Comparing the numerical simulation results with experimental data, it verified the feasibility and effectiveness of the numerical method. This method will provide support for the ship maneuvering numerical simulation and promote the use of numerical method into practical application.