水面比降对船舶航行阻力影响的数值研究

Numerical Study on the Influence of Water Surface Gradient on Ship Sailing Resistance

水面比降是影响船舶水动力性能的重要因素之一。为了揭示船舶航行遭遇有比降水面时的水动力特性,采用计算流体力学(CFD)方法,以某集装箱船为研究对象,基于RANS方程,利用VOF方法捕捉自由液面,放开船体升沉和纵倾两个自由度,分析了水面比降对船舶航行阻力与浮态的影响。首先进行船舶在不同纵倾角时的阻力计算,并与试验对比,验证仿真方法计算船舶浮态和阻力关系的准确性。然后通过改变河道断面纵向收缩角和入口流速,获得了水面比降变化引起的船舶阻力、浮态、伴流等参数的变化规律。结果表明:计算流体力学(CFD)方法可以用来模拟船舶遭遇比降水面时的阻力变化和航行特性,评估船舶航行能力;船舶的总阻力随着比降的增大而增大;比降对摩擦阻力的影响较小,在高流速下,摩擦阻力随着比降的增大还有一定程度的减小;总阻力增大的原因主要是压阻力在总阻力中的占比随着水面比降的增大而增大,这将增大船舶航行难度。研究结果可为船舶航行于带有比降水面时的安全决策提供一定的参考。

The water surface gradient is one of the important factors that affect the hydrodynamic performance of ships.In order to reveal the hydrodynamic characteristics of the ship when it encountered the water surface with slopes,the computational fluid dynamics(CFD)method was used to analyze the influence of water surface gradient on the ship sailing resistance and floating state.Based on RANS equation,VOF method was used to capture the free surface and release the two degrees of freedom of heave and trim.Firstly,the resistance of the ship at different trim angles was calculated and compared with the test,to verify the accuracy of the simulation method to calculate the relationship between ship floating state and resistance.Then,by changing the longitudinal contraction angle and inlet velocity of the river section,the variation rules of ship resistance,floating state,wake and other parameters caused by the change of water surface gradient were obtained.The results show that:the computational fluid dynamics(CFD)method can be used to simulate the change of resistance and navigation characteristics when the ship encounters the water surface gradient,and to evaluate the navigation ability of the ship.The total resistance of the ship increases with the increase of the gradient.The gradient has little effect on the friction resistance.At high flow velocity,the friction resistance decreases to a certain extent with the increase of gradient.The main cause of the increase of the total resistance is that the proportion of the pressure resistance in the total resistance increases with the increase of the water surface gradient,which will increase the difficulty of ship navigation.The relevant research results can provide some reference for the safety decision-making of ships sailing on the surface with gradient.