基于ANSYS的拱形闸门自振特性研究

拱形闸门属轻型壳体结构,在水流作用下易发生共振,甚至引起振动破坏。本文结合某控制闸工程实例,建立了拱形闸门的三维有限元模型,考虑流固耦合引起的附加质量对闸门自振特性的影响,利用有限元分析软件ANSYS进行模态分析,揭示了拱形闸门的自振频率和振型等自振特性。研究结果为最终设计方案的选定提供了理论依据,对同类闸门结构的设计具有参考意义。     

规则波浪中舰船操纵运动计算

当船舶在波浪中处于尾斜浪或顺浪航行时,可能出现稳性丧失和横甩等现象,所以船舶在波浪中的操纵性问题已引起人们的关注.目前,关于该问题的大多数研究往往局限在有限的浪向角范围内.本文在船舶静水操纵性基础上,直接迭加高频的波浪力,建立一个波浪中高频运动响应的操纵性预报方法.用二维Frank源汇分布法计算船舶随摇荡频率变化的附加质量———波浪的辐射力,以及规则波浪的扰动力———Froud Krylov力,在六自由度运动方程上直接迭加所计算的波浪力,并引用静水操纵中船、桨、舵水动力的计算模型,建立了规则波浪中船舶操纵运动预报模型,并数值计算了一条高速方尾船舶在不同规则波浪的波长、波高和浪向角下的操纵舵回转运动和Z形操纵舵运动,附加质量和波浪扰动力根据运动中的遭遇频率和浪向角确定.数值计算的回转角速度、横倾角和纵倾角的变化规律与文献中单桨单舵船模试验有着相似结果.     

Added-mass estimation of flat membranes vibrating in still air

It is widely known that added mass has a significant influence on the natural frequency of membrane structures. Previously, the total added mass of a one-dimensional membrane has been investigated with theoretical analysis. However, no test result has been applied to verify results of the theoretical analysis. Furthermore, the distribution of the added mass is still unclear. In this study, first, thin-airfoil theory was applied to analyze the distribution of the added mass. The distribution of the added mass was found to be basically uniform for the first vibration mode of a one-dimensional membrane. Then, it was assumed that the added mass of one vibration region is independent of the added mass of another vibration region for higher vibration modes, where the vibration regions are the parts of the membrane separated by the nodal points (nodal lines for two-dimensional membranes) of the vibration mode. Based on the above analysis, a simplified added-mass model was proposed; i.e., for every vibration mode, the added mass of each vibration region is equivalent to the uniformly distributed air with a height of α_ml, where α_m is the added mass coefficient and l is the diameter of the inscribed circle of the corresponding vibration region. To ascertain the added-mass coefficient and verify the simplified added-mass model, a vacuum chamber was designed to test the vibration of a circular flat membrane in still air with varying air pressures. The results showed that the simplified added-mass model was accurate when the added-mass coefficient was taken as 0.65. The efficiency of the proposed simplified added-mass model was further verified by an existing test of a three-sided membrane.