Research On Numerical Prediction And Optimization Of Resistance And Propulsion Performance Of Waterjet Propelled Ships

Waterjet system is a kind of special propeller which uses the reaction force of waterjet to push the ship forward.It has many advantages such as high propulsion efficiency,good maneuverability,anti cavitation and low noise at high speed.With these advantages,it has been used as propulsion device by some highspeed displacement monohull,catamarans,trimarans,planning boats,hydrofoil boats patrol boats,cruise ships and air cushion ships.Waterjet system has a wide prospect in high-performance ships.Speedability performance has always been one of the most important issues in ship industry,so in this thesis the speedability optimization of waterjet propelled ship is taken as the researchment.This thesis focuses on the grid auto-generation technology in the optimization system and the high-precision numerical prediction method of the speediness of the water jet propulsion ships.The speedability optimization system is built by adopting the hull geometry reconstruction,grid auto-generation,numerical calculation,surrogate model and optimal algorithm,and the speedability optimization of waterjet propelled ships,a luxury cruise ship,a planning boat and a trimaran,are completed by using the optimization system.The optimization can provide guidance for the rapid optimization design of waterjet propelled ships.The main research works of this thesis are as follows:Based on the general commercial grid generation software GAMBIT,a structured grid generation software SUGOT V2.0 for ships with bulbous bow and without skeg is developed by writing in C++.The operation of importing model,blocking calculational domain,generating grids and setting boundary conditions are all completed automatically.A luxury cruise ship model is taken as an example to verify the software,and the dependence of resistance performance and free surface wave pattern on grids is investigated.The results show that the software can save the grid generation time significantly,and the coarse grid has enough accuracy for resistance prediction.On this basis,the resistance performance optimization of the luxury cruise ship is carried out.Through modifying the hull shape of the bulbous bow and aft-body by free-form deformation method,the pressure resistance of the hull is reduced by 4.14% and the total resistance of the hull is reduced by 0.45%.The purpose of resistance reduction at the design speed is achieved.Self-propulsion numerical prediction of the waterjet propelled ship is carried out by using STAR-CCM+.First of all,the self-propulsion numerical calculation of a planning boat with the waterjet system is carried out.The results show that the pressure resistance of the planning boat accounts for the majority of the total resistance,and the total resistance coefficient of the planning boat has a resistance peak near Fr = 0.964.Then self-propulsion calculation of a trimaran is simulated,and the interaction between the hull and the waterjet is studied.The numerical results are in good agreement with the experimental results,which shows that the numerical calculation method proposed in this thesis can accurately and effectively predict the self-propulsion performance of the waterjet propelled ships.The installation of the waterjet system can increase the hull sinkage and trim,which results in the resistance increase.The hull boundary layer leads to the gross thrust of the waterjet system less than the net thrust.The method of obtaining the capture area of the waterjet system required by the momentum flux method is studied.The method is based on the streamline method,and a program is developed by MATLAB language,which can greatly simplify the process of obtaining the capture area and improve the efficiency of thrust calculation and resistance and propulsion analysis of the waterjet system.The resistance and propulsion characteristics of the waterjet propelled trimaran are analyzed by the momentum flux method.The duct efficiency and the pump efficiency do not change too much with the hull speed,and the overall efficiency of the waterjet system mainly depends on the ideal jet efficiency and pump efficiency.Two kinds of typical waterjet propelled ships are optimized for their speedability.Firstly,the optimization of the stern interceptor is carried out,and the optimization scheme of the stern interceptor is given at the bare hull and selfpropulsion condition at the sailing speeds.The results show that the installation of the stern interceptor can reduce the total resistance of the planning boat by changing the attitude of the hull,especially reduce the sinkage and trim.The optimal scheme of the stern interceptor can reduce the peak of resistance coefficient at the bare hull and self-propulsion condition by 35.24% and 34.51%respectively.Then,the multi-objective optimization of the speedability performance of a waterjet propelled trimaran is carried out by using the speedability optimization system.The whole optimization process is divided into three parts: the optimization of the waterjet system,the optimization of the global hull shape,the optimization of the local hull shape and the arrangement of the waterjet system.The shape of duct and nozzle is parametrically modified by using geometric reconstruction method.The global and local hull shape is modified by using Lackenby and free-form deformation method.The results show that the propulsion performance of the waterjer system can be improved by modifying the angle of the duct,and the flow separation phenomenon at the root of the guide vanes can be improved by reducing the angle of the hub.The hull shape at the inlet of the duct becomes flat and the hull shape at aft-body changes to the extreme U-shape,which can reduce the total resistance of the hull and improve the propulsion performance of the waterjet system.The waterjet system arranged near to the longitudinal section can increase the propulsion performance of the waterjet system.After the optimization,at the design speed,the resistance of the hull is reduced by 3.85%,the resistance and propulsion of the waterjet system is reduced by 10.39%,and the propulsion efficiency is increased by 7.03%,which realizes the purpose of reducing the resistance and resistance and propulsion consumption.