响应面法的杆式超声电机有限元模型修正

现有杆式超声电机的有限元模型大都采用连续复合材料的简化结构形式,忽略了实际超声电机各部件间的接触特性,导致计算结果与实验结果具有较大偏差。针对该问题,提出了一种采用响应面法的杆式超声电机有限元模型修正方法,来获得高精度的有限元模型。该方法考虑了超声电机螺栓预紧力及各部件接触界面的法向接触刚度和摩擦系数,筛选出显著影响电机工作模态的参数,建立响应面模型替代超声电机的有限元模型实现快速计算结构响应的目的,并以实验模态分析结果为目标对模型进行修正。修正结果表明,修正后的模型模态频率的平均误差由修正前的1.20%降到0.21%,模型精度得到明显改善,表明以响应面的有限元模型修正方法对杆式超声电机以及类似夹心式压电振子的设计具有应用价值。      

Nonlinear Study on FEM Amplifier with a Novel Elliptic-Groove Guide

FEM amplifier with a novel elliptic-groove guide is proposed and three-dimensional nonlinear theory for the elliptic-groove guide FEM amplifier is developed. A set of coupled nonlinear differential equations is derived and the characteristics of this FEM amplifier are numerically analyzed in detail including the evolution of power, efficiency and bandwidth. The effects on saturation efficiency due to electron momentum spread and wiggler taper are also studied.     

A finite-element method using dispersion reduced spline elements for room acoustics simulation

This paper presents a finite element method (FEM) using hexahedral 27-node spline acoustic elements (Spl27) with low numerical dispersion for room acoustics simulation in both the frequency and time domains, especially at higher frequencies. Dispersion error analysis in one dimension is performed to increase the accuracy of FEM using Spl27 by modifying the numerical integration points of element stiffness and mass matrices. The basic accuracy and efficiency of the FEM using the improved Spl27, which uses modified integration points, are presented through numerical experiments using benchmark problems in both the frequency and time domains, revealing that FEM using the improved Spl27 in both domains provides more accurate results than the conventional method does, and with fewer degrees of freedom. Moreover, the effectiveness of FEM using the improved Spl27 over that using hexahedral 27-node Lagrange elements is shown for time domain analysis of the sound field in a practical sized room.     

Dynamic behavior and sound transmission analysis of a fluid-structure coupled system using the direct-BEM/FEM

A direct-BEM/Fem method was proposed to analyze the vibration and acoustic radiation characteristics of a submerged structure. Model parameters of the structure and the fluid-structure interaction due to surrounding water were analyzed by using FEM and direct BEM. Vibration velocity of the outer hull surface and underwater sound pressure were computed through modal superposition technique. The direct-BEM/FEM method was first validated by analyzing a submerged cylindrical shell, then was used to analyze the vibro-acoustic behavior of a submarine stern structure. The results have demonstrated the direct-BEM/FEM method is more effective than FEM in computing the underwater sound radiation of the stern structure.     

有限元与无网格伽辽金耦合法分析二相连续多孔介质

将有限元法和无网格伽辽金法相结合,创造出一种新的数值计算方法,该法既能利用有限元法的优点,又能发挥无网格伽辽金法局部化技术的无单元特性,使其具有计算优势.推导了二相多孔介质的有限元法与无网格伽辽金法耦合的离散方法.给出了两个算例,在计算二维固结方程时,精度较高且处理液体流量准确,是有限元法的有力补充.     

FEM calculation and the effects of hydrogen diffusion in fabrication processes of long-period fiber gratings

The wavelength shift of a long-period fiber grating (LPG) related to re-distribution of hydrogen molecules was studied by the finite-element method (FEM) calculation and by the experiment. The FEM calculation was performed solving a diffusion equation of hydrogen in glass fiber, and the wavelength of an LPG was calculated. In the experiment, the hydrogen-loaded fiber was out-diffused before laser exposure, and the resonance wavelengths of LPGs fabricated by exposure were measured. The wavelength depended on the duration of out-diffusion, and the variation was up to 114 nm. The FEM calculation considering the hydrogen re-distribution by out-diffusion agreed with the experiment. After the laser exposure, the wavelength of an LPG shifted towards the long wavelength without any exposure. The FEM calculation assuming hydrogen depletion in the core and its recovery agreed with the measured wavelength shift. Extension of the FEM to fibers with more complicated structures has been discussed.     

FEM study of NOW and NO2W adsorption system

Nitric oxide adsorption on tungsten and nitric dioxide adsorption on tungsten have been investigated by the FEM method. When NO or NO₂ adsorbs gradually on W at 300 K and at 80 K, the FEM patterns which appear at first are found to be similar to those which appear in N₂ adsorption on W. In the case of NO adsorption on W at 80 K, with further exposure, no further change of the FEM patterns is observed. However, in the cases of NO adsorption on W at 300 K, NO₂ adsorption on W at 300 K, and NO₂ adsorption on W at 80 K, further changes of the FEM patterns are observed with further exposure, and the FEM pattern which is obtained at the saturated state is found to be similar to the FEM pattern which appears at the saturated state of O₂ adsorption on W. From the above results it is suggested that NO and NO₂ dissociate on W at 300 and at 80 K.     

激光辐照受拉铝板破坏行为的时空多尺度数值模拟

推导耦合过渡区内参变量信息交换的元/网格动量传递多尺度算法,建立离散元与有限元耦合时空多尺度计算模型,并应用于激光辐照下受拉铝板破坏行为的数值模拟中.通过对比有限元计算模型、空间多尺度计算模型与时空多尺度计算模型在激光辐照下受拉铝板破坏算例的模拟结果,验证离散元与有限元耦合时空多尺度计算模型的准确性和数值计算高效率优势.使用该多尺度计算模型从宏观和细观尺度对铝板破坏行为进行数值模拟,模拟结果与实验结果基本一致.     

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 novel Galerkin-like weakform and a superconvergent alpha finite element method (SαFEM) for mechanics problems using triangular meshes

A carefully designed procedure is presented to modify the piecewise constant strain field of linear triangular FEM models, and to reconstruct a strain field with an adjustable parameter α. A novel Galerkin-like weakform derived from the Hellinger–Reissner variational principle is proposed for establishing the discretized system equations. The new weak form is very simple, possesses the same good properties of the standard Galerkin weakform, and works particularly well for strain construction methods. A superconvergent alpha finite element method (SαFEM) is then formulated by using the constructed strain field and the Galerkin-like weakform for solid mechanics problems. The implementation of the SαFEM is straightforward and no additional parameters are used. We prove theoretically and show numerically that the SαFEM always achieves more accurate and higher convergence rate than the standard FEM of triangular elements (T3) and even more accurate than the four-node quadrilateral elements (Q4) when the same sets of nodes are used. The SαFEM can always produce both lower and upper bounds to the exact solution in the energy norm for all elasticity problems by properly choosing an α. In addition, a preferable-α approach has also been devised to produce very accurate solutions for both displacement and energy norms and a superconvergent rate in the energy error norm. Furthermore, a model-based selective scheme is proposed to formulate a combined SαFEM/NS-FEM model that handily overcomes the volumetric locking problems. Intensive numerical studies including singularity problems have been conducted to confirm the theory and properties of the SαFEM.     

Finite element model updating of a rod-type ultrasonicmotor based on response surface method

The conventional finite element model(FEM) of a rod-type ultrasonic motor is usually simplified by means of continuous composite structure. Because the actual contact characteristics between the parts of the ultrasonic motor is ignored, there is bigger error between the calculated values and experimental results. Aiming at solving problem, a new modeling method of a rod-type ultrasonic motor is presented to obtain a high-accuracy FEM. The bolt pretension and the normal contact stiffness and friction coefficient of the contact surface of ultrasonic motor are all considered in this method, and the significant parameters of working mode of the motor are selected by the response surface method, and the goal of calculating the structural response rapidly is realized by building the response surface model to replace the FEM. The result of finite element model updating shows that the average error of modal frequencies of updated model drops to 0.21% from 1.20%. The accuracy of FEM is obviously improved, which indicates that the FEM updating based on response surface method is of great application value on the design for a rod-type ultrasonic motor.     

应用有限元和边界元法计算方坯软接触结晶器的电磁场

给出了用有限元和边界元相结合的方法计算方坯软接触结晶器内钢液电磁场分布的全过程,并对4面体单元基础上的Whitney边元素,H-Φ方程及边界积分方程的离散方法作了重点解释.采用有限元和边界元相结合的方法来计算电磁场的分布可以大大减少计算工作量和计算时间.自行开发了三维电磁场计算程序,将数值模拟结果与物理实际进行了比较.     

Medium range order of bulk metallic glasses determined by variable resolution fluctuation electron microscopy

Variable resolution fluctuation electron microscopy (FEM) experiments are implemented with hollow-cone dark-field transmission electron microscopy. Medium range order lengths of zirconium and iron based bulk metallic glasses and amorphous silicon nitride are determined from the FEM results. It shows that maximum normalized intensity variances of FEM images occur when their nominal resolution approaches the correlation length Λ of the amorphous materials. Additionally, differences in the length and magnitude of medium range order are compared between metallic and covalent bond amorphous materials.     

On Scientific Data and Image Compression Based on Adaptive Higher-Order FEM

We present a novel compression algorithm for 2D scientific data and images based on exponentially-convergent adaptive higher-order finite element methods (FEM). So far, FEM has been used mainly for the solution of partial differential equations (PDE), but we show that it can be applied to data and image compression easily. The adaptive compression algorithm is trivial compared to adaptive FEM algorithms for PDE since the error estimation step is not present. The method attains extremely high compression rates and is able to compress a data set or an image with any prescribed error tolerance. Compressed data and images are stored in the standard FEM format, which makes it possible to analyze them using standard PDE visualization software. Numerical examples are shown. The method is presented in such a way that it can be understood by readers who may not be experts of the finite element method.     

A combined three-dimensional finite element and scattering matrix method for the analysis of plane wave diffraction by bi-periodic,multilayered structures

A three-dimensional finite element method (FEM) for the analysis of plane wave diffraction by a bi-periodic slab is described and implemented. A scattering matrix formalism based on the FEM allows the efficient treatment of light reflection and transmission by multilayer bi-periodic structures, and the computation of Bloch modes of three-dimensional arrays. Numerical simulations, which show the accuracy and flexibility of the FEM, are presented.     

直接冷却的高温超导磁体热稳定性有限元仿真

制冷机直接冷却超导磁体是一门新兴技术,研究超导磁体在直接冷却下的热稳定性具有重要意义。用有限元方法解决复杂边界问题的热力学问题非常有效,而有限元分析软件ANSYS能使得用有限元法解决问题更加方便。该文用有限元方法对直接冷却高温超导磁体进行了热稳定性数值仿真。仿真结果表明,在设定热负荷作用下,直接冷却的B i2223系高温超导磁体具有较好的热稳定性,磁体温度低于其临界温度。     

Investigation of field electron microscope tips bombarded with microparticles at limited field emission currents

Mo, Ta, W, and Re field electron microscope (FEM) tips, bombarded with microparticles at limited field emission currents (400 MΩ resistor in series with the FEM tip) were investigated by means of FEM, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Two groups of tips could be distinguished: One group had a slight tip radius increase to a maximum of 2.5 μm and microcraters were formed along the tip shank. The other group had no detectable tip radius change; however, there was microcrater formation near the tip apex area. FEM patterns showed surface contamination clearly. Heating such contaminated tips and tips where phosphorescent material (Zn:Cd)S had been deposited in less than monolayer concentration by evaporation from a heating coil, resulted in similar sequences of FEM patterns. A new type of microcrater with smooth crater lips could be detected in both groups. These results support the combined microparticle-field emission mechanism [1], which was proposed earlier to be responsible for melting cap and microcrater formation. Excerpts were presented at the 19th Field Emission Symposium, Urbana, Illinois (USA), August 1972.     

Study on Combined Method Based on 3-D ESPI

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Study on Combined Method Based on 3-D ESPI

The finite element method (FEM),whether the calculation is accurate or not,depends closely on object boundary condition.If the three dimensional displacement of the object obtained in experiment is regarded as its boundary condition,a new method combining the results of experiment and calculation,called combined method (CM),is formed.The combined method possess advantages of experiment and calculation.It can correct calculation and improve the accuracy of FEM.Accordingly it has more practicability.In this paper,the three dimensional displacement fields of a typical beam loaded at three points are tested by using 3-D electric speckle pattern interferometry (ESPI).Using the experimental results as boundary condition the whole three-dimensional displacement fields can be calculated by FEM.The beam′s three-dimensional displacement fields obtained by FEM agree very well with those obtained by experiment.This proves that the combined method is effective and practicable.