A mixed differential quadrature and finite element free vibration and buckling analysis of thick beams on two-parameter elastic foundations

As a first endeavor, a mixed differential quadrature (DQ) and finite element (FE) method for boundary value structural problems in the context of free vibration and buckling analysis of thick beams supported on two-parameter elastic foundations is presented. The formulations are based on the two-dimensional theory of elasticity. The problem domain along axial direction is discretized using finite elements. The resulting system of equations and the related boundary conditions are discretized in the thickness direction and in strong-form using DQM. The method benefits from low computational efforts of the DQ in conjunction with the effectiveness of the FE method in general geometry and systematic boundary treatment resulting in highly accurate and fast convergence behavior solution. The boundary conditions at the top and bottom surface of the beams are implemented accurately. The presented formulations provide an effective analysis tool for beams free of shear locking. Comparisons are made with results from elasticity solutions as well as higher-order beam theory.     

Topology optimization of microfluidic mixers

This paper demonstrates the application of the topology optimization method as a general and systematic approach for microfluidic mixer design. The mixing process is modeled as convection dominated transport in low Reynolds number incompressible flow. The mixer performance is maximized by altering the layout of flow/non‐flow regions subject to a constraint on the pressure drop between inlet and outlet. For a square cross‐sectioned pipe the mixing is increased by 70% compared with a straight pipe at the cost of a 2.5 fold increase in pressure drop. Another example where only the bottom profile of the channel is a design domain results in intricate herring bone patterns that confirm findings from the literature. Copyright © 2008 John Wiley & Sons, Ltd.     

具有双模特性的大模场面积微结构光纤的设计

本文提出了一种具有双模特性大模场面积的微结构光纤,通过有限元法计算其模场分布、基模有效模场面积及弯曲损耗特性,并分析了不同结构参量对限制损耗及有效模场面积的影响.计算结果表明:通过合理地改变光纤结构参量,可以使二阶模LP11、三阶模EH11截止,实现基模LP01、三阶模HE31双模传输,其中基模的有效模场面积可达700μm2.这种结构的光纤制作简单,在大容量光纤传输系统中具有重要应用.     

集成芯片LED场地照明灯新型叠片散热器热分析

针对大功率LED场地照明集成芯片散热问题,提出了一种新型散热器结构。该散热器利用高导热纯铝材料,采用叠片的方式成型。采用实验和有限元模拟相结合的研究方法,对包括直流电源的新型叠片式LED散热器的散热性能进行了研究。结果表明：LED电源达到稳态所需时间较长,最终能够稳定在一个较低的温度范围。叠片式纯铝散热器通过增加散热面积和提高散热器材料的导热系数能有效降低LED结温。所设计的散热器和选择的电源在自然对流条件下能够很好地满足250 W大功率LED散热要求。     

FEM simulation of Rayleigh waves for CMOS compatible SAW devices based on AlN/SiO2/Si(1 0 0)

A simulation study of Rayleigh wave devices based on a stacked AlN/SiO₂/Si(1 0 0) device was carried out. Dispersion curves with respect to acoustic phase velocity, reflectivity and electromechanical coupling efficiency for tungsten W and aluminium Al electrodes and different layer thicknesses were quantified by 2D FEM COMSOL simulations. Simulated acoustic mode shapes are presented. The impact of these parameters on the observed Rayleigh wave modes was discussed. High coupling factors of 2% and high velocities up to 5000 m/s were obtained by optimizing the AlN/SiO₂ thickness ratio.     

混合法分析平面应变橡胶材料的大变形

基于混合法 (以位移和静水压力为基本未知量 ) ,引入 Penn[1 ]建议的不变量分解的 Mooney型 [2 ]本构形式 ,针对混合法建立起总刚元素的特点 ,分析平面应变不可压缩橡胶材料的大变形 ,克服以前在处理不可压缩时 ,计算易失稳等缺点 ,算例表明 :有限元计算稳定并与解析解[4] 吻合。     

机械密封焊接金属波纹管膜片结构的有限元分析

在Linux操作平台下应用FAST_wmg有限元前后处理软件对机械密封焊接金属波纹管膜片建立了有限元模型并进行了非线性有限元分析．在同等条件下对焊接金属波纹管采用了S型膜片和V型膜片，并分别进行了有限元强度评价和对比分析．结果表明，两种膜片最大应力集中都在膜片两端周围发生．这与文献所叙述的波纹管的主要失效发生在膜片两端与焊谷接近的部位非常吻合，但是，在同样边界条件下，在同样位移量时S型膜片最大应力值比V型膜片最大应力值小，压缩量大．     

BELENE nuclear power plant numerical and experimental bedrock,layers and surface signals

An investigation of BELENE Nuclear Power Plant (NPP) free field signal is presented in the current study. An SH wave propagation trough multilayer geological media in the region is considered. An original structural model of the geological column has been developed. The investigated layers are isotropic, with constant depth and skyline parallel. The SH rays are with an arbitrary angle as far as the layers are concerned. The seismic SH waves have been generated by a special detonation device. The main results of the study are graphically illustrated. A comparison between the original BELENE NPP experimental and the numerical surface (free field) signals (obtained by the formulated direct problem) for the investigated geological column has been carried out and its results are hereby shown.     

Lyapunov spectrum determination from the FEM simulation of a chaotic advecting flow

The problem of the determination of the Lyapunov spectrum in chaotic advection using approximated velocity fields resulting from a standard FEM method is investigated. A fourth order Runge–Kutta scheme for trajectory integration is combined with a third order Jacobian matrix method with QR ‐factorization. After checking the algorithm on the standard Lorenz and coupled quartic oscillator systems, the method is applied to a model 3‐D steady flow for which an analytical expression is known. Both linear and quadratic approximated velocity fields succeed in predicting the Lyapunov exponents as well as describing the chaotic or regular regions inside the flow with satisfactory accuracy. A more realistic flow is then studied in order to delineate the possible limitations of the approach. Copyright © 2005 John Wiley & Sons, Ltd.