宽带密排平面阵声辐射分析

应用声有限元-边界元法计算了宽带基阵声场分布.建立了平面9元阵有限元-边界元模型,给出了阵元之间互阻抗数值计算方法,分析了阵元间互辐射对声性能影响的变化规律,计算了9元阵3个谐振频率点处指向性和波束宽度.利用3谐振换能器研制出一种宽带密排平面9元阵,并在消声水池中对其输入阻抗和指向性进行了实验测量.研究结果表明,按阵元...     

天线振子作为初值问题求解

根据计算实践和物理考虑,指出电磁场基本方程作为一阶双曲型偏微分方程组的初值问题,可以成为有效的天线振子数值计算方法。对于隐式差分格式,建议了一种交替方向追赶和外边界插值相结合的办法。讨论了圆柱对称振子的数值结果。     

在二维叶栅势流计算中边界元法的应用

一、前言 边界元法是近年来兴起的一种新的基于边界积分方程的数值计算方法.Brebbia将其归之为加权剩余法的一个分支,但该法比有限元和有限差分法更具有解析——数值计算特点.有别于区域计算法,边界元法通过引入一个满足场方程的奇异函数作为权函数,将问题的区域计算转化为边界计算.由于所获得的一组边界积分方程仅联系边界上各个     

有限元-边界法在光电目标散射计算中的应用

为了解决三维目标电磁散射计算中准确性与有效性的矛盾,建立了有限元-边界法的计算模型,对三维腔体目标的电磁散射计算方法进行了研究。首先,分析了针对三维电磁腔体目标的电磁散射计算边界积分方法,引入了矢量格林函数,利用麦克斯韦方程得到电磁场形式与三维腔体形式的关系,建立了三维开口腔体边界模型;然后,结合光电目标曲面建模方法及高阶基函数的方法,建立了三维光电目标的有限元泛函,完成了有限元-边界法在三维腔体目标电磁散射计算中的应用;最后,进行了实例验证。分析显示,当三维腔体内部为空或为各向异性物质时,角度吻合非常理想,与传统模式匹配法所得结果的吻合度达90%以上。结果表明,采用本方法对三维腔体目标进行电磁散射计算,准确度、效率均有所提高。     

抛物方程基于自然边界归化的耦合法

将冯康和余德浩提出的自然边界归化方法^[1~4]应用于求解抛物方程初边值外区域问题,提出一种自然边界元与有限元耦合算法。先将控制方程对时间进行离散化,得到关于时间步长的离散化格式,给出圆外域上的自然积分方程,基于此研究抛物方程无界区域问题的自然边界元与有限元耦合法,最后给出相应的数值例子。     

超导悬浮系统悬浮力磁滞性质数值分析

利用矢量电位法建立了NdFeB永磁铁和超导体相互作用的电磁场数学模型方程。在求解过程中采用磁通流动蠕动模型,通过伽辽金有限元离散,解出超导体电流密度分布,计算磁悬浮力并分析磁悬浮力磁滞性质。     

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将等离子体作为磁流体,考虑其流体属性和电磁属性,介绍了利用FLUENT软件包并将其进行二次开发,解算电磁场方程、质量连续性方程、动量守恒方程、以及能量守恒方程的数值模拟方法,得到了以磁矢势为表达形式的电磁场分布、温度分布和速度分布.数值模拟了粉末球化所用的感应耦合等离子体炬电磁场分布、温度分布、速度分布.分析了温度分布、速度分布产生的物理原因,为感应耦合等离子体炬球化粉末颗粒提供理论性指导.     

Navier-Stokes方程的有限元边界元耦合方法

主要研究了三维外部区域上具有Dirichlet边界条件的非定常Navier-Stokes方程的有限元边界元耦合方法,并分析了这一数值解的收敛速度.     

含裂纹弹性结构声相互作用研究

应用分形有限元和边界元相结合的方法研究了含裂纹的结构声的耦合作用问题。利用二级分形有限元方法离散含裂纹结构,这将使得自由度大为减少;使用边界元方法计算外域辐射声场,这将自动满足无限远辐射边界条件。数值结果初步表明:(1)随着裂纹深度的增加,结构声耦合系统的共振频率将下降;(2)裂纹附近的声场所受的影响更为明显。     

势问题的径向基函数——局部边界积分方程方法

将基于径向基函数构造的具有插值特性的近似函数和局部边界积分方程方法相结合，建立了求解势问题的径向基函数——局部边界积分方程方法，推导了相应离散方程.与其他边界积分方程的无网格方法相比，本文方法具有数值实现过程简单、计算量小、精度高的优点，并可直接施加边界条件.最后通过算例说明了该方法的有效性. 关键词： 径向基函数 无网格方法 局部边界积分方程 势问题     

边界元素法在集成电路CAD中的应用

本文采用边界元素法(BEM)计算任意多边形的二维电阻和复杂结构的二维电容。同一计算程序既能计算电阻又能计算电容,而只需作微小不同的后处理。对于边界元素法,由于仅需计算边界上的积分方程,其离散边界上的网格点数大大少于有限差分法及有限元素法所需的网格点数,使CPU执行时间显著减少,并简化了网格划分工作。此外,计算结果还指出边界元素法具有精度高和处理复杂边界能力强的优点。     

FINITE ELEMENT AND BOUNDARY ELEMENT MODELLING FOR THE ACOUSTIC WAVE TRANSMISSION IN MEAN FLOW MEDIUM

The frequency characteristics of the acoustic wave transmission in a medium with mean flow are considered. One approach is to solve the Helmholtz equation with mean flow medium in original co-ordinates, which is directly discretized for the one-dimensional and the axisymmetric FEM. Another approach is to transform the equation into the standard Helmholtz equation, which is discretized for the axisymmetric FEM and the three-dimensional BEM. The numerical models are examined first for a straight circular duct. The solutions by the numerical approaches are compared with the analytical solution. The examination is then extended to the case when the mean flow is locally present in the muffler with expansion chamber. To model the spatial mean flow in the BEM model, the partitioned domain approach is also developed. No shear effect between the two regions are included.     

微波元件与加速结构的有限元分析

研究了有限元方法在二维均匀结构和轴对称加速结构中的应用,采用了带宽优化技术和子空间求解特征值方法,并给出了部分例子,结果表明该方法精度高、速度快.这些方法可直接用于三维程序、并行计算.     

A regularised boundary element formulation for contactless SAR evaluations within homogeneous and inhomogeneous head phantoms

This work presents a Boundary Element Method (BEM) formulation for contactless electromagnetic field assessments. The new scheme is based on a regularised BEM approach that requires the use of electric measurements only. The regularisation is obtained by leveraging on an extension of Calderón techniques to rectangular systems leading to well-conditioned problems independent of the discretisation density. This enables the use of highly discretized Huygens surfaces that can be consequently placed very near to the radiating source. In addition, the new regularised scheme is hybridised with both surfacic homogeneous and volumetric inhomogeneous forward BEM solvers accelerated with fast matrix–vector multiplication schemes. This allows for rapid and effective dosimetric assessments and permits the use of inhomogeneous and realistic head phantoms. Numerical results corroborate the theory and confirms the practical effectiveness of all newly proposed formulations.     

Application of convolution perfectly matched layer in finite element method calculation for 2D acoustic wave

A method was presented to extend the Convolution Perfectly Matched Layer(CPML), which bases on the complex coordinates transformation and complex frequency shifted stretched-coordinate metrics,to the 2D acoustic equation calculated with the method of Finite Element Method(FEM).This non-physical layer is used at the computational edge of a FEM as an Absorbing Boundary Condition(ABC) to truncate unbounded media.In this paper,the CPML equations have been presented in frequency domain and in time domain,respectively,and the calculations have been realized in the FEM software of COMSOL.The main advantage of CPML over the classical PML layer is that it is based on the unsplit components of the wave field leading to a more stable,highly effective absorption and a more facility to realize.The results of numerical simulation demonstrate that CPML has better absorbability than PML and it absorbs the outgoing energy more effectively.     

卷积完全匹配层在两维声波有限元计算中的应用

将基于复坐标变换和复频移扩展坐标变量的卷积完全匹配层Convolution Perfectly Machted Layer(CPML)引入到两维声波方程的有限元(FEM)计算中,该匹配层作为一种吸收边界条件Absorbing Boundary Condition(ABC)应用在有限元计算的边界截断上。文中分别给出了频域和时域的CPML方程的表达形式,并在有限元计算软件COMSOL中完成数值计算。相对于经典的PML,CPML最大的优势在于它不需要把场分裂开,这使其具有更好的稳定性和更高的吸收性能,且更易于实现。数值计算结果表明,CPML边界层有着比PML更好的吸收效果,其更有效的吸收了进入其中的声场能量。      

Energy flow model considering near field energy for predictions of acoustic energy in low damping medium

The Acoustic Energy Flow Boundary Element Method (AEFBEM) is developed to predict the acoustic energy density and intensity of an engineering system. Up to now, the acoustic energy flow model has been used only for analysis of high frequencies or radiation noise because of plane wave and far-field assumptions. In this research, a new energy flow governing equation that can consider the near field acoustic energy term and spherical wave characteristics is derived successfully to predict the acoustic energy density and intensity of a system in the medium-to-high frequency range. A near field term of acoustic energy in spherical coordinate is added to the relationship between energy density and energy flow. But with the far-field assumption, this term vanishes, so the relationship between energy density and energy flow becomes the same as that of the plane wave. By considering the near field energy term without far-field assumption, the energy density at medium frequencies can be estimated. However, the governing equation has to be numerically manipulated for use in the analysis of complex structures; therefore, the Boundary Element Method (BEM) is implemented. AEFBEM is a numerical analysis method formulated by applying the boundary element method to an acoustic energy flow governing equation. It is very powerful in predicting the acoustic energy density and intensity of complex structures in medium-to-high frequency ranges, and can analyze interior noise and radiating sound. To verify its validity, several numerical results are provided. BEM and AEFBEM were compared with respect to energy density, and the results from both methods were similar.     

多量子阱平面光波导的有限元分析

本文利用有限元法分析了多量子阱平面光波导的传播特性,给出了任意阱数多量子阱光波导_TE模和TM模的有效折射率和TE模的强度分布.结果表明:γ(势阱与势垒的厚度比)值的改变,影响波导中导模的模式数目、有效折射率、双折射和强度分布;并发现在某些情况下,均方根近似是不适用的.     

COMBINATION OF FINITE AND BOUNDARY ELEMENT METHODS IN INVESTIGATION AND PREDICTION OF LOAD-CONTROLLED NOISE OF POWER TRANSFORMERS

A recently developed calculation scheme for the computer modelling of the load-controlled noise of oil-insulated three-phase power transformers is presented. This modelling scheme allows the precise and efficient computation of the coupled electromagnetic, mechanical and acoustic fields. The equations are solved using the finite element method (FEM) as well as the boundary element method (BEM), resulting in a separation of the calculation of the winding and tank surface vibrations (using FEM) and the computation of the acoustic free-field radiation (using BEM). The complex dynamic behaviour of the loaded transformer can then be studied and, furthermore, an appropriate computer-aided design including an investigation and optimization of design parameters can be established.The validity of the computer simulations has been verified by means of appropriate measurements. Simulated and measured values for winding and tank surface vibrations as well as sound power levels of the loaded transformer are found to be in good agreement. The applicability of the calculation scheme with respect to the computer-aided design of power transformers is demonstrated by reporting two practical applications: the influence of the stiffness of winding supports and the influence of the tap changer positions.     

半导体激光器列阵的有限元分析

本文利用有限元法对四种半导体激光器列阵进行了分析,得到了超模的近场强度分布,为实现最低阶超模的均匀强度分布提供了一些可能的结构.