Analysis Of Factors Affecting Ship CFD Simulation And Study Of Methods Improving Calculation Of Trimaran Hull Resistance

In the last few decades, CFD technology has been widely applied in the research of ship performance as a result of rapid development of computer technology and computational fluid dynamics theory and technology. In comparison with traditional tank towing methods and potential methods, the CFD method displays an advantage of flow field simulation in the study of ship performance, and has been accepted as an effective method to deal with ship performance study of resistance, propulsion and maneuverability. The defects of CFD method are that when it is applied the numerical results are affected by various kinds of simulation errors and uncertainties, and these errors and uncertainties will decrease the reliability and credibility of numerical results. So it's important and meaningful to analyze factors affecting ship CFD simulation, and study methods improving numerical calculation of ship performance.In this dissertation, in order to improve the numerical calculation of ship performance all the main sources of errors and uncertainties influencing the ship performance calculation have been particularly studied and the feasibility and effectiveness of the methods used to improve the numerical calculation are discussed based on the calculation of ship resistance. Finally a new improving method is brought up and shown. Because all the fators affecting the calculation of ship resistance will also affect, in more or less the same manner, the application of CFD technology in the calculation for other performance, the conclusions in this dissertation can be applied in the study of other performance.In order to ascertain the influence of grid on the calculation precision of ship resistance, the simple Wigley hull and a mathematical trimaran hull were chosen as examples of study and grid convergence study was carried out to analyze the effect of grid error and uncertainty on ship resistance calculation. The study showed that grid convergence study can improve the reliability and credibility of resistance calculation of ship hulls.In order to ascertain the influence of turbulence closure theory on the calculation precision of ship resistance, the Wigley hull and mathematical trimaran hull were chosen as examples of study, and resistance calculation of the two hulls based on different turbulence models were performed, and the sensitivity study of model coefficients and constants were performed, too. The study showed that existing turbulence models could result in the different model errors and uncertainties in the resistance calculation of ship hull. The sensitivity study showed that the model coefficients and constants of two common turbulence models were suitable for the hull resistance calculation. The more suitable turbulence models for the resistance calculation of trimaran hull were pointed out, too.In order to ascertain the influence of advection discretization schemes on the calculation precision of ship resistance, the Wigley hull and mathematical trimaran hull were chosen as examples of study and resistance calculation of the two hulls using different advection discretization schemes were performed. The study showed that different advection schemes could cause the variation of results of hull resistance calculation. Compared with grid and turbulence model, the effects of advection discretization schemes were relatively small.According to the conclusions drawn from the study of resistance performance of Wigley hull and mathematical trimaran hull, the effects on improving the trimaran hull resistance calculation by modifying grid, turbulence models or advection discretization schemes respectively were not very pronounced.Analysis of simulation results showed that the errors and uncertainties caused by grid, turbulence models, discretization schemes and other factors could not be removed completely. The errors affected the magnitude of discrepancy between simulation results and experiment data. On the premise that errors and uncertainties can not be avoided in the present numerical calculation, one new method based on the idea of errors cancellation was brought out. The calculation and validation study showed that this method could improve the resistance calculation of trimaran hulls with complex configuration, although it is newly proposed which needs to be developed and matured.