船用螺旋桨振动特性数值计算与分析

Numerical analysis on vibration of marine propeller

为了降低螺旋桨结构振动产生的水下辐射噪声,采用结构有限元耦合流体边界元的虚拟质量法,运用通用有限元软件MSC.NASTRAN计算了螺旋桨在空气中和水中的固有频率和振型,分析了流体与结构之间的相互作用对螺旋桨振动特性的影响。研究结果表明:虚拟质量法能够准确计算螺旋桨在水中的固有频率;螺旋桨在水中的固有频率要显著低于空气中的固有频率,且在水中的振动位移也比空气中小;无论在空气中还是水中,螺旋桨都存在三类基本的桨叶振型;螺旋桨在空气中和水中的振型存在差异,且随着频率的升高二者差异明显;对于不同阶桨叶振型,固有频率随模态阶数的变化显著,而对于同一阶桨叶振型,这种变化并不明显;对于同一阶桨叶振型而言,随着频率的升高,频率缩减比呈递增趋势,相应的附连水质量依次减小。

To reduce underwater radiated noise generated by vibrating propellers,an approach to combining finite element with boundary element is adopted to calculate the natural frequencies and mode shapes of marine propeller in the air and in the water by using common finite element analysis software MSC.NASTRAN.The effects on the natural frequencies and mode shapes of marine propeller caused by interactions between fluid and structure are investigated.The results show that the natural frequencies of marine propeller in the water can be obtained accurately by the virtual mass method.The natural frequencies and vibration displacements of marine propeller in the water are smaller than those in the air.There are three kinds of essential blade mode shapes of propeller whether in the air or in the water.The mode shapes of marine propeller in the air are different from those in the water.The difference of mode shapes of marine propeller is more notable with the increase in frequency.For the different rank blade mode shapes the larger the mode number is,the more remarkably the natural frequencies change,while the natural frequencies are less variable for the same rank.With the increase in frequency,frequency reduction ratio is enhanced and converse trend appears for added mass in terms of the same rank blade mode shapes.