A finite element analysis of parallel-coupled acoustic systems using subsystems

A Lagrangian energy expression is presented that is suitable for finite element analysis of parallel-coupled acoustic systems, as a series of subsystems. The analysis can proceed in small stages, thereby being versatile and economic in computing costs. The technique has been applied to automotive muffler configurations and has been verified experimentally.     

Free vibration analysis of a flat plate using the hierarchical finite element method

The hierarchical finite element method is used to determined the natural frequencies and modes of a flat, rectangular plate. Ten different boundary conditions—including free edges and point supports—are considered in this paper. Extensive results are presented for each case (including the variation of frequency with the aspect ratio and the Poisson ratio), and these are shown to be in very good agreement with the work of other investigators. This confirms both the applicability and accuracy of solution of the HFEM to problem of this type.     

Design and analysis of coplanar waveguide optical modulator using finite element method

An analysis is given on the finite element method (FEM) for calculating the various parameters of optical modulators and a computer program is written to solve the finite element equation. Based on this method, a Mach-Zehnder type electro-optic modulator with coplanar waveguide (CPW) electrode is designed and fabricated. When compared with the Fourier series method, small differences on the 3-dB bandwidth, characteristic impedance and half-wave voltage, etc. are obtained.     

Characterization of silicon nanophotonic devices using the finite element method

The Poynting vector and the full-vectorial H and E-field profiles are considered for use in nanoscale silicon waveguides in this article. This paper reveals that the mode profile of a circular silicon nanowire is not circular and also has a strong axial field component. From the analysis, the characteristics of single mode operation and the vector field profiles of both circular and planar silicon nanowires are presented. The modal birefringence of rectangular silicon nanowires and power density in low-index region of a slot-type waveguide and designs of a compact polarization rotator are also presented in this work.     

A finite element analysis of perforated component acoustic systems

A Lagrangian energy expression is presented that is suitable for finite element analysis of perforated component acoustic systems. This technique can be applied to systems with complex shaped boundaries and is not restricted to the limited geometry that inhibits the traditional one-dimensional techniques. The technique has been applied to automotive muffler component configurations and has been verified experimentally. Perforate flow effects have also been included.     

Numerical analysis of partially molten splat during thermal spray process using the finite element method

A finite element method is used to simulate the deposition of the thermal spray coating process. A set of governing equations is solving by a volume of fluid method. For the solidification phenomenon, we use the specific heat method (SHM). We begin by comparing the present model with experimental and numerical model available in the literature. In this study, completely molten or semi-molten aluminum particle impacts a H13 tool steel substrate is considered. Next we investigate the effect of inclination of impact of a partially molten particle on flat substrate. It was found that the melting state of the particle has great effects on the morphologies of the splat.     

反射声波成像测井的有限元模拟

应用有限元法对新兴的反射声波成像测井进行了数值模拟研究，计算了井旁附近存在不同倾角声阻抗不连续界面对声波的反射，使用的井内激励源为幅度加权相控线阵声波辐射器。从计算出的声全波波形上可以清楚地看到沿井壁传播的折射波和来自井旁界面的反射纵波。应用偏移叠加等数据处理技术对数值模拟波形进行了处理，从偏移剖面上反演出的反射界面的尺寸、位置和倾角等几何特性与数值模拟输入参数基本一致。     

应用声有限元素法模拟坐席吸声低谷效应

本文给出了应用声有限元素法模拟坐席吸声低谷效应的计算模型。该模型首先在时间域计算房间脉冲响应,再通过傅立叶变换得到声压频谱特性。将有限元分析结果与已有的模型实验及大厅实测数据相比较,证明该方法是研究坐席吸声低谷效应的有效手段。     

Super-FRS超导磁体失超瞬态热应力分析

国际反质子与离子大科学工程(FAIR)项目是一个大型的国际合作项目,其中Super-FRS超导二极磁体由中国科学院近代物理研究所研制。利用ADINA有限元程序对项目中的超导Super-FRS磁体线圈的失超过程进行了模拟分析。利用C程序对ADINA程序进行二次开发以便对有限元求解器的调用和载荷的控制。分析结果显示:在失超过程中产生的最大热应力为26 MPa,可能产生的声波频率在35 Hz左右。     

Non-linear dynamic analysis of rotors by finite element method

Non-linear natural vibration characteristics and the dynamic response of hingeless and fully articulated rotors of rectangular cross-section are studied by using the finite element method. In the formulation of response problems, the global variables are augmented with appropriate additional variables, facilitating direct determination of sub-harmonic response. Numerical results are given showing the effect of the geometric non-linearity on the first three natural frequencies. Response analysis of typical rotors indicates a possibility of substantial sub-harmonic response especially in the fully articulated rotors widely adopted in helicopters.     

Simulation of residual stresses and their effects on thermal barrier coating systems using finite element method

Thermal barrier coating(TBC)systems are widely used in industrial gas-turbine engines.However,premature failures have impaired the use of TBCs and cut down their lifetime,which requires a better understanding of their failure mechanisms.In the present study,experimental studies of isothermal cycling are firstly carried out with the observation and estimation of microstructures.According to the experimental results,a finite element model is established for the analysis of stress perpendicular to the TBC/BC interface.Detailed residual stress distributions in TBC are obtained to reflect the influence of mechanical properties,oxidation,and interfacial roughness.The calculated results show that the maximum tensile stress concentration appears at the peak of TBC and continues to increase with thermal cycles.Because of the microstructural characteristics of plasma-sprayed TBCs,cracks initialize in tensile stress concentration(TSC)regions at the peaks of TBC and propagate along the TBC/BC interface resulting in the spallation of TBC.Also,the inclusion of creep is crucial to failure prediction and is more important than the inclusion of sintering in the simulation.     

Calculation of waveguides by the finite element method using the Bunch-Kaufman procedure

An algorithm for the numerical solution of the problem for eigenvalues in a waveguide in the complete vector statement using the finite-element method and the Bunch-Kaufman procedure for the factorization of the matrix of the derived set of linear algebraic equations was built and implemented.     

Three-dimensional radiative transfer modeling using the control volume finite element method

In the present study, a three-dimensional algorithm for the treatment of radiative heat transfer in emitting, absorbing and scattering media is developed. The approach is based on the utilization of control volume finite element method (CVFEM) which, to the knowledge of the authors, is applied at the first time to 3D radiative heat transfer in participating media. The accuracy of the present algorithm is tested by comparing its predictions to other published works. Comparisons show that CVFEM produces good results. Moreover, this approach permits compatibility with other numerical methods used for computational fluids mechanics problems.     

Approximation of the inductionless MHD problem using a stabilized finite element method

In this work, we present a stabilized formulation to solve the inductionless magnetohydrodynamic (MHD) problem using the finite element (FE) method. The MHD problem couples the Navier–Stokes equations and a Darcy-type system for the electric potential via Lorentz’s force in the momentum equation of the Navier–Stokes equations and the currents generated by the moving fluid in Ohm’s law. The key feature of the FE formulation resides in the design of the stabilization terms, which serve several purposes. First, the formulation is suitable for convection dominated flows. Second, there is no need to use interpolation spaces constrained to a compatibility condition in both sub-problems and therefore, equal-order interpolation spaces can be used for all the unknowns. Finally, this formulation leads to a coupled linear system; this monolithic approach is effective, since the coupling can be dealt by effective preconditioning and iterative solvers that allows to deal with high Hartmann numbers.     

柔性铰链的有限元法设计与分析

大变形、小应力、小中心漂移的柔性铰链的研制一直是柔性铰链研究的难题。本文在参考国外某款柔性铰链的基础上,利用V型结构设计、叠加理论和对称布置方法设计了一种新型的柔性铰链。针对这种柔性铰链的设计进行了概念性研究,建立了铰链的数学模型,研究了这种新型柔性铰链的性能。有限元方法分析表明,该设计方法增加了铰链柔性部分的长度,降低了它的中心漂移和最大应力,得到其最大转角约为16°,最大中心漂移为3.557μm,最大应力为499.8 MPa,满足了最初的设计指标要求。结果证明该铰链具有一定的实用价值。     

柔性铰链的有限元法设计与分析

大变形、小应力、小中心漂移的柔性铰链的研制一直是柔性铰链研究的难题。本文在参考国外某款柔性铰链的基础上,利用V型结构设计、叠加理论和对称布置方法设计了一种新型的柔性铰链。针对这种柔性铰链的设计进行了概念性研究,建立了铰链的数学模型,研究了这种新型柔性铰链的性能。有限元方法分析表明,该设计方法增加了铰链柔性部分的长度,降低了它的中心漂移和最大应力,得到其最大转角约为16°,最大中心漂移为3.557μm,最大应力为499.8 MPa,满足了最初的设计指标要求。结果证明该铰链具有一定的实用价值。     

On the forced response of waveguides using the wave and finite element method

The forced response of waveguides subjected to time harmonic loading is treated. The approach starts with the wave and finite element (WFE) method where a segment of the waveguide is modeled using traditional finite element methods. The mass and stiffness matrices of the segment are used to formulate an eigenvalue problem whose solution yields the wave properties of the waveguide. The WFE formulation is used to obtain the response of the waveguide to a convected harmonic pressure (CHP). Since the Fourier transform of the response to a general excitation is a linear combination of the responses to CHPs, the response to a general excitation can be obtained via an inverse Fourier transform process. This is evaluated analytically using contour integration and the residue theorem. Hence, the approach presented herein enables the response of a waveguide to general loading to be found by: (a) modeling a segment of the waveguide using finite element methods and post-processing it to obtain the wave characteristics, (b) using Fourier transform and contour integration to obtain the wave amplitudes and (c) using the wave amplitudes to find the response at any point in the waveguide. Numerical examples are presented.     

Numerical simulation of premixed combustion using an enriched finite element method

In this paper we present a novel discretization technique for the simulation of premixed combustion based on a locally enriched finite element method (FEM). Use is made of the G-function approach to premixed combustion in which the domain is divided into two parts, one part containing the burned and another containing the unburned gases. A level-set or G-function is used to define the flame interface separating burned from unburned gases. The eXtended finite element method (X-FEM) is employed, which allows for velocity and pressure fields that are discontinuous across the flame interface. Lagrange multipliers are used to enforce the correct essential interface conditions in the form of jump conditions across the embedded flame interface. A persisting problem with the use of Lagrange multipliers in X-FEM has been the discretization of the Lagrange multipliers. In this paper the distributed Lagrange multiplier technique is adopted. We will provide results from a spatial convergence analysis showing good convergence. However, a small modification of the interface is required to ensure a unique solution. Finally, results are presented from the application of the method to the problems of moving flame fronts, the Darrieus–Landau instability and a piloted Bunsen burner flame.