A novel ellipsoidal acoustic infinite element

A novel ellipsoidal acoustic infinite element is proposed. It is based a new pressure representation, which can describe and solve the eUipsoidal acoustic field more exactly. The shape functions of this novel acoustic infinite element are similar .to the Burnett‘s method, while the weight functions are defined as the product of the complex conjugates of the shaped functions and an additional weighting factor. The code of this method is cheap to generate as for 1-D element because only 1-D integral needs to be numerical. Coupling with the standard finite element, this method provides a capability for very efficiently modeling acoustic fields surrounding structures of virtually any practical shape. This novel method was deduced in brief and the conclusion was kept in detail. To test the feasibility of this novel method efficiently, in the examples the infinite elements were considered, excluding the finite elements relative. This novel eUipsoidal acoustic infinite element can deduce the analytic solution of an oscillating sphere. The example of a prolate spheroid shows that the novel infinite element is superior to the boundary element and other acoustic infinite elements. Analytical and numerical results of these examples show that this novel method is feasible.     

船舶螺旋桨空化噪声预报初步

本文介绍基于能量观点的原型螺旋桨空化噪声基本预报公式以及经过空泡空气含量修正的预报公式,并提供了预报结果。模型桨空化噪声谱是在上海交通大学空泡水筒中测得,其原型桨的谱在实海中测得。预报实例证实,基本预报公式是适用的,经过空气含量修正的预报公式可获得比较精确的预报结果。     

边界元法计算已知振速封闭面的声辐射

采用边界元法求解封闭面在无限域声媒质中的辐射声场具有内存小、计算精度高、速度快等优点。但需处理被积函数在边界面上的奇异积分及表面Helmholtz方程在特征频率下无唯一解的问题。本文提出把内部Helmholtz方程与它关于内点坐标取导后的式子构成补充方程式,经与表面Helmholtz方程相结合,可求解任意频率下的声辐射问题;而在奇点附近区域,则提出用极坐标变换消除积分的奇异性。文中以轴对称形封闭面为例,计算了具有已知表面振速分布下的辐射声场。     

一种新的声椭球无限单元

提出了一种新的声椭球无限单元．这种声无限单元基于一种新的声压表达式,这种声压表达式能够更准确地代表着椭球声场的声传播模式．这种新方法的形函数类似于Burnett方法,而权函数定义为形函数和一个附加因子的乘积．因为仅需要一维的数值积分,这种新方法的代码生成十分容易,就像处理一维单元一样．耦合标准的有限元程序,这种声无限单元理论上能够高效地求解任何形状的声源的声辐射和声散射现象．简要地推导了这种新方法,并给出了这种方法详尽的推导结果．为更有效地检验该无限元方法的可行性,文中例子仅考虑无限元求解的精度,而不包括相应的有限元．使用这种新方法,精确地推导出了摆动球的理论计算公式．而长旋转椭球的例子则表明了这种方法优于边界元方法和其他声椭球无限元方法．这些例子表明了这种新方法是切实可行的．     

PRELIMINARY RESULTS ON THE PREDICTION OF SHIP PROPELLER CAVITATION NOISE POWER SPECTRA FROM THE MEASUREMENT OF ITS MODEL IN A CAVITATION TUNNEL

Propeller cavitation noise spectra were measured in the cavitation tunnel of Shanghai JiaotongUniversity as well as in actual ship.Formulae of prediction for prototype propeller cavitation noisespectra in a ship are derived on the basis of energy relations.The formula with correction of aircontent of bubble gives more accurate results.