Uncertainty Analysis Of Ship Model Resistance Measurement In Circulating Water Channel

Experimental fluid dynamics EFD and computational fluid dynamics CFD are two main methods to study fluid mechanics problems,both of which have uncertainty analysis problems.The uncertainty of resistance test of ship model in circulating water channel is studied under three working conditions of low speed,medium speed and high speed and the uncertainty caused by precision limit,balance calibration and data acquisition process are analyzed respectively.It is difficult to solve the sensitivity coefficient of uncertainty by EFD method for the specific inflow unevenness and turbulence intensity of circulating water channel.According to the actual situation of circulating water channel in Shanghai Jiao Tong University,the related mathematical model is established,and the influence of inflow unevenness and turbulence intensity on total resistance is obtained by CFD simulation.The corresponding uncertainty component is obtained by applying the uncertainty theory,and the uncertainty of CFD calculation is also specially analyzed.In addition,the free surface fluctuation is not obvious at low and medium speed,and the wave-making resistance can be almost ignored.On the premise that the feasibility of CFD calculation is verified,the superposition method is adopted in the CFD calculation.The free surface fluctuation is obvious at high speed,and the wave-making resistance cannot be ignored.In this paper,the wave-making resistance is calculated by combining the superposition method and the VOF method,and the total resistance of the ship model after considering the influence of the free surface is finally obtained.The research shows that in the uncertainty analysis of CFD,the corrected and uncorrected calculation results are effectively confirmed,which indicates the feasibility of using CFD simulation to carry out research.The relative uncertainty of ship model resistance test in circulating water channel is 0.42%,1.91% and 3.91% respectively at low,medium and high speeds.The higher the speed,the greater the relative uncertainty.Under the three working conditions,the turbulence intensity has the greatest influence on the resistance and plays a leading role.Therefore,it should be considered to reduce the turbulence intensity as much as possible when designing the circulating water channel.The second is the uncertainty component caused by unevenness.The uncertainty components caused by precision limit,balance calibration and data acquisition process are not large.This paper shows that CFD method is feasible and useful for analyzing some components of EFD uncertainty.Indirect method is used to calculate wave-making resistance,which has certain economic practicability.