楔形发射体真空微三极管性能的有限元分析

楔形发射体的有效发射面积较大，能够随较大的发射电流，并产生较高的跨导，因而更适用于大功率微波放大器。用有限元法对器件的性能进行了分析，计算出了器件内部电场和电势分布，用Ｆｏｗｌｅｒ－Ｎｏｒｄｈｅｉｍ公式计算出场致发射电流，得到了楔形发射体真空策三极管的电流发射特性，所得结果对器件的设计和制造有重要的参考价值。     

金属楔形发射体电子场发射理论研究

提出楔形发射体的电子场发射理论并给出计算实例。该公单原子发射点假设为基础，用经典动力学方法计算出楔形发射体的隧道势垒，然后用Ｎｕｍｅｒｏｖ方法计算其透射比，最后得到楔形发射体的场发射伏安特性，还分析了几何结构参数对楔形发射体场发射特性的影响。     

金属楔形发射体电子场发射理论研究

提出楔形发射体的电子场发射理论并给出计算实例。该理论以单原子发射点假设为基础，用经典电动力学方法计算出楔形发射体的隧道势垒，然后用Numerov方法计算其透射比，最后得到楔形发射体的场发射伏安特性，还分析了几何结构参数对楔形发射体场发射特性的影响。     

圆锥形阴极真空微三极管的计算机模拟

利用有限元法对圆锥形场致发射阴极的真空微三极管进行了计算机模拟。改变真空微三极管的各项结构参数及阳极和栅极电压 ,得到一系列模拟数据。然后对模拟结果进行分析讨论 ,总结出圆锥形阴极有效发射、阳极电流与真空微三极管的结构尺寸、阳极电压和栅极电压之间的关系 ,对于真空微三极管的实际设计和制作有一定的参考价值     

圆锥形阴极真空微三极管的计算机模拟

利用有限元法对圆锥形场致发射阴极的真空微三极管进行了计算机模拟。改变真空微三极管的各项结构参数及阳极和栅极电压,得到一系列模拟数据。然后对模拟结果进行分析讨论,总结出圆锥形阴极有效发射、阳极电流与真空微三极管的结构尺寸、阳极电压和栅极电压之间的关系,对于真空微三极管的实际设计和制作有一定的参考价值。     

面向21世纪的真空微电子学

本文概述了真空微电子学的研究领域、基本特点、冷阴极发射源、真空微电子器件与电路、真空微电子学的应用前景及发展趋势。     

边缘场发射体的非正交有限差分算法模拟

对边缘场致发射三极管进行了模拟，采用的模型为“鸡尾酒怀”结构。在静电分析中引入了一种新的数值计算方法－非正交曲线坐标系下的有限差分算法。由于取的坐标轴与边界重合，所以该方法能有效地处理任间形状的场致发射体。     

硅场致发射阵列的工艺研究

介绍了硅场致发射阵列工艺研究的初步结果。应用湿法化学腐蚀、硅锥切削及介质平坦化技术成功地制备出了理想形状的场致发射阵列。     

边缘场致发射体的非正交有限差分算法模拟

对边缘切致发射三极管进行了模拟，采用的模型为“鸡尾酒杯”结构。在静电分析中引入了一种新的数值计算方法──非正交曲线坐标系下的有限差分算法。由于取的坐标轴与边界重合。所以该方法能有效地处理任意形状的场致发射体。给出了电场强度和发射电流与几何因子的关系及I－U特性曲线。     

10kV户外真空断路器绝缘性能分析

本文采用电磁场理论以及有限元分析方法,利用电磁场数值分析软件平台,对三相分立敞开式10kV户外高压交流真空断路器进行了电场绝缘结构的分析校核。获得触头分别在不同开距下,真空断路器的整体和真空灭弧室的电位及电场强度分布云图,分析其绝缘的薄弱环节,所得分析结果及理论数据为产品样机的绝缘结构设计提供了可靠依据。     

Finite Element Simulation on Thermal Fatigue of a Turbine Blade with Thermal Barrier Coatings

In this paper, a finite element model was developed for a turbine blade with thermal barrier coatings to investigate its failure behavior under cyclic thermal loading. Based on temperature and stress fields obtained from finite element simulations, dangerous regions in ceramic coating were determined in terms of the maximum principal stress criterion. The results show that damage preferentially occurs in the chamfer and rabbet of a turbine blade with thermal barrier coatings and its thermal fatigue life decreases with the increase of thermal stress induced by high service temperature.     

Improved Discontinuity-capturing Finite Element Techniques for Reaction Effects in Turbulence Computation

Recent advances in turbulence modeling brought more and more sophisticated turbulence closures (e.g. k-ɛ, k-ɛ -v ²-f, Second Moment Closures), where the governing equations for the model parameters involve advection, diffusion and reaction terms. Numerical instabilities can be generated by the dominant advection or reaction terms. Classical stabilized formulations such as the Streamline–Upwind/Petrov–Galerkin (SUPG) formulation (Brook and Hughes, comput methods Appl Mech Eng 32:199–255, 1982; Hughes and Tezduyar, comput methods Appl Mech Eng 45: 217–284, 1984) are very well suited for preventing the numerical instabilities generated by the dominant advection terms. A different stabilization however is needed for instabilities due to the dominant reaction terms. An additional stabilization term, called the diffusion for reaction-dominated (DRD) term, was introduced by Tezduyar and Park (comput methods Appl Mech Eng 59:307–325, 1986) for that purpose and improves the SUPG performance. In recent years a new class of variational multi-scale (VMS) stabilization (Hughes, comput methods Appl Mech Eng 127:387–401, 1995) has been introduced, and this approach, in principle, can deal with advection–diffusion–reaction equations. However, it was pointed out in Hanke (comput methods Appl Mech Eng 191:2925–2947) that this class of methods also need some improvement in the presence of high reaction rates. In this work we show the benefits of using the DRD operator to enhance the core stabilization techniques such as the SUPG and VMS formulations. We also propose a new operator called the DRDJ (DRD with the local variation jump) term, targeting the reduction of numerical oscillations in the presence of both high reaction rates and sharp solution gradients. The methods are evaluated in the context of two stabilized methods: the classical SUPG formulation and a recently-developed VMS formulation called the V-SGS (Corsini et al. comput methods Appl Mech Eng 194:4797–4823, 2005). Model problems and industrial test cases are computed to show the potential of the proposed methods in simulation of turbulent flows.     

A Smoothed Finite Element Method for Mechanics Problems

In the finite element method (FEM), a necessary condition for a four-node isoparametric element is that no interior angle is greater than 180° and the positivity of Jacobian determinant should be ensured in numerical implementation. In this paper, we incorporate cell-wise strain smoothing operations into conventional finite elements and propose the smoothed finite element method (SFEM) for 2D elastic problems. It is found that a quadrilateral element divided into four smoothing cells can avoid spurious modes and gives stable results for integration over the element. Compared with original FEM, the SFEM achieves more accurate results and generally higher convergence rate in energy without increasing computational cost. More importantly, as no mapping or coordinate transformation is involved in the SFEM, its element is allowed to be of arbitrary shape. Hence the restriction on the shape bilinear isoparametric elements can be removed and problem domain can be discretized in more flexible ways, as demonstrated in the example problems.     

Finite Element Simulation on the Spin-forming of the 3D Non-axisymmetric Thin-Walled Tubes

The roller movement trace for the 3D non-axisymmetric thin-walled tubes is a complex space curve. Besides the roller rotation caused by contact with the blank, the roller rotates around the workpiece together with the main spindle, and also moves simultaneously along the direction of the revolution radius. The method to correctly establish the finite element (FE) models of the metal spinning is based on the MSC. MARC software was introduced. The calculation formulas considering both the revolution and rotation of the roller were obtained by the mathematical deduction. The saving calculation points m should be a multiple of 4 for one revolution of the roller around the workpiece to obtain the maximum forming force for the spinning of the 3D non-axisymmetric thin-walled tubes. The simulation results conform well to the experimental ones for several spinning methods; the maximum error is less than ±15%.     

Interval Finite Element Analysis using Interval Factor Method

A new method called the interval factor method for the finite element analysis of truss structures with interval parameters is presented in this paper. The structural parameters and applied forces can be considered as interval variables by using the interval factor method, the structural stiffness matrix can then be divided into the product of two parts corresponding to the interval factors and the deterministic value. From the static governing equations of interval finite element method of structures, the structural displacement and stress responses are expressed as the functions of the interval factors. The computational expressions for lower and upper bounds, mean value and interval change ratio of structural static responses are derived by means of the interval operations. The effect of the uncertainty of the structural parameters and applied forces on the structural displacement and stress responses is demonstrated by truss structures.     

Simulation of Lumbar Spinal Stenosis Using the Finite Element Method

Lumbar spine stenosis (LSS) is a narrowing of the spinal canal that results in pressure on the spinal nerves. This orthopedic disorder can cause severe pain and dysfunction. LSS is a common disabling problem amongst elderly people. In this paper, we developed a finite element model (FEM) to study the forces and the von Mises stress acting on the spine when people bend down. An artificial lumbar spine (L3) was generated from CT data by using the FEM, which is a powerful tool to study biomechanics. The proposed model is able to predict the effect of forces which apply to the lumbar spine. In addition, FEM allows us to investigate the tests into the lumbar spine instead of applying the tests to the real spine in humans. The proposed model is highly accurate and provides precise information about the lumbar spine (L3). We investigate the behavior of humans in daily life which effects to the lumbar spine in a normal person and a patient with LSS. The computational results revealed high displacement levels around the spinal canal and lower displacement levels in the spinal body when bending down. The total displacement of the axial load in a normal person was higher when compared with patients with LSS. Higher degree bends resulted in a lower total displacement when compared with lower degree bends, while the von Mises stress decreased as the bending degree increased.     

ANSYS有限元法在测长绝热真空腔二维热分析中的应用

针对测长绝热真空腔内温度场测量困难的特点,提出应用ANSYS有限元仿真与实验研究相结合的方法进行二维热分析。详细介绍了真空腔的ANSYS有限元建模、参数确定、网格划分、施加载荷和求解过程。仿真结果表明外界环境温度变化1℃,绝热真空腔内温度将变化0.085℃。对仿真结果进行了实验验证,实验结果证明利用该仿真技术可准确、可靠地分析绝热真空腔内的温度场,并且提高实验效率的同时降低了实验成本。     

联合载荷下无裂纹DLC薄膜的内应力有限元分析

本文用有限元分析的方法,对受法向和切向联合载荷作用下的无裂纹类金刚石(DLC)薄膜系统内部应力进行了模拟计算,分析了不同摩擦系数和膜厚比对于内部应力的影响,数值模拟结果表明:较大的摩擦系数可以使得界面处剪切应力和Mises等效应力以及y轴Mises等效应力显著增大,而对于界面处的y向压应力影响不是很大。在一定的范围内(0相似文献   

蜂窝纸板振动传递特性的有限元仿真分析

目的针对蜂窝纸板的振动防护性能,研究不同结构和材料参数的蜂窝纸板振动传递特性的有限元仿真分析方法。方法利用有限元软件Abaqus/Standard建立蜂窝纸板-质量系统模型,设定2种蜂窝纸板,分别具有不同的面纸材料参数和蜂窝胞元边长。仿真分析蜂窝纸板的振动传递特性,并对其进行实验验证。结果通过仿真和实验得到了蜂窝纸板的振动传递率-频率曲线,共振频率的仿真结果与实验值误差小于3.43%,共振时振动传递率的仿真结果与实验值误差小于11.31%。结论利用该有限元仿真方法,能够获得不同结构和材料参数的蜂窝纸板的振动传递特性。仿真分析结果表明,面纸定量对蜂窝纸板振动传递特性的影响不大,而蜂窝胞元边长较大的蜂窝纸板,其系统共振频率较小,振动传递率变化不明显。     

3D Finite Element Numerical Simulation of Residual Stresses on Electron Beam Welded BT20 Plates

A three-dimensional finite-element model (FEM) used for calculating electron beam (EB) welding temperature and stresses fields of thin plates of BT20 titanium has been developed in which the nonlinear thermophysical and thermo-mechanical properties of the material has been considered. The welding temperature field, the distributions of residual stresses in as-welded (AW) and electron beam local post-weld heat treatment (EBLPWHT) conditions have been successfully simulated. The results show that: (1) In the weld center, the maximum magnitude of residual tensile stresses of BT20 thin plates of Ti alloy is equal to 60%- 70% of its yield strength σs. (2) The residual tensile stresses in weld center can be even decreased after EBLPWHT and the longitudinal tensile stresses are decreased about 50% compared to joints in AW conditions. (3) The numerical calculating results of residual stresses by using FEM are basically in agreement with the experimental results. Combined with numerical calculating results, the