齿轮边界元强度计算的单元自动生成

本文提出一种专用于齿轮边界元强度计算的单元自动生成办法，只需输入端截面内一半数据，便可自动生成空间四边形8节点等参元的全部数据，也适合于其它螺旋体的边界元计算．     

齿轮边界元强度计算的单元自动生成

本文提出一种专用于齿轮边界元强度计算的单元自动生成办法，只需输入端截面内一半数据，便可自动生成空间四边形８节点等参元的全部数据，也适合于其它螺旋体的边界元计算。     

微型机网格自动生成和显示软件MESHG

划分有限元网格、计算节点坐标、准备单元编号及节点坐标等原始数据是有限元计算中工作量很大的一部分。本软件旨在极大地减轻这一类劳动,给有限元计算人员带来方便。 本软件利用用户提供的少量描写结构形状的原始数据,自动生成有限元分析所需网格,自动计算节点坐标、形成单元编号及近似优序编排节点号。可自动划分网格的结构有:(1)二维平面或轴对称问题;(2)板和空间壳体;(3)三维块体;结构可以在直角坐标系、球坐标系、柱(极)坐标系中描写;生成的单元类型有三点、四点及八点等参元(平面情形),八     

直接基于单元平衡的变截面梁反应分析方法

固定形状的单元位移插值函数不能合理地近似变截面梁内部的位移变化,从而影响了传统梁单元用于计算变截面梁的精度.采用直接基于单元平衡的思想给出了计算变截面梁反应的有限元方法,解决了单元位移插值函数局限性所带来的问题.导出了变截面梁单元的单元刚度矩阵、单元等效节点荷载和单元一致质量矩阵.在此基础上,利用编制的程序进行了算例验证与分析.算例验证了本文理论的正确性,表明本文方法具有很高的计算精度.     

梯形截面直齿零件挤压过程变形力规律的数值模拟

本文采用上限单元技术(UBET),对非完全轴对称单元、推导出梯形截面直齿零件的挤压速度场公式,并成功地模拟了挤压过程中变形力的变化规律,理论计算结果与实验结果比较吻合.     

海洋平台导管架结构分析中管节点局部柔度的等效单元

本文建立了一种在海洋平台导管架有限元分析中代表管节点局部柔度的等效单元,可有效地反映管节点在轴力和弯矩作用下的局部变形性质,并导出了T型、Y型以及K型管节点的局部柔度等效单元的刚度矩阵。本文建立的等效单元可方便地与通用结构分析有限元程序(如SAP5)配合,对海洋平台导管架进行计及管节点局部柔度的精确静动力分析。作者编制了与SAP5配合使用的前处理程序,可自动生成符合SAP5输入格式的等效单元读入刚度矩阵的数据。文中给出了说明等效单元应用方法的简单算例。与有限元法计算的结果比较表明,用等效单元模拟管节点的局部柔度是必要的和准确可行的。     

三角形截面梁柱构件的三维等效弹簧计算模型

传统有限元在分析梁柱构件时一般采用常应变单元和双线性单元,但此类单元在梁柱构件受弯分析中计算精度不是很高.本文根据梁柱构件的力学性能,在三维连续介质体受到轴向变形和弯曲变形的状态下,利用其轴向变形和弯曲挠度相同,得到具有相同宽度和高度且刚度等效的超静定桁架力学模型.然后,通过桁架杆的截面参数求得弹簧的刚度系数,从而得等效弹簧元模型.本文提出的等效弹簧模型计算方法简单,便于扩展到更为复杂的构件分析中.     

大型空间结构的热-动力学耦合问题及其有限元分析

论文对辐射换热条件下闭口薄壁杆件与单枝开口薄壁杆件的瞬态温度场问题,提出了一种一维傅立叶温度有限元,克服了传统一维温度单元只能计算薄壁杆截面平均温度的缺点,通过增加结点摄动温度自由度的方法,该一维单元能计算杆截面的温度分布.在此一维温度单元与梁位移单元相协调的基础上,进一步发展了大型空间结构热诱发振动稳定性判据与热颤振响应有限元计算方法.对于柔性空间结构发展了考虑几何非线性的热-结构动力学耦合有限元计算方法,成功地对这类结构的热动力屈曲问题进行了数值模拟.     

一种新的准结构网格生成方法

在有限元分析中,高质量的结构网格可以有效地提高有限元分析的精度,但结构网格的几何适应性差,针对复杂边界的二维计算模型,现有的方法很难自动生成高质量的结构网格;而非结构网格几何适应性很好,但存在计算效率低和精度差等问题。提出了一种新的准结构网格生成方法,能够实现复杂区域的网格自动生成并且具有高网格质量。该方法首先对计算区域运用Delaunay三角剖分技术生成粗背景网格;然后利用背景网格,使用优化的Voronoi图生成过渡的蜂巢网格;最后,通过中心圆方法对蜂巢网格单元进行结构网格剖分。分析NACA0012翼型数值模拟结果表明,提出的新准结构网格生成方法能够对边界复杂的模型自动生成高质量的网格,并且通过三种不同拓扑类型网格计算结果相互对比及与实验结果对比,证明准结构网格具有高计算精度。     

一种新的准结构网格生成方法

在有限元分析中,高质量的结构网格可以有效地提高有限元分析的精度,但结构网格的几何适应性差,针对复杂边界的二维计算模型,现有的方法很难自动生成高质量的结构网格;而非结构网格几何适应性很好,但存在计算效率低和精度差等问题。提出了一种新的准结构网格生成方法,能够实现复杂区域的网格自动生成并且具有高网格质量。该方法首先对计算区域运用Delaunay三角剖分技术生成粗背景网格;然后利用背景网格,使用优化的Voronoi图生成过渡的蜂巢网格;最后,通过中心圆方法对蜂巢网格单元进行结构网格剖分。分析NACA0012翼型数值模拟结果表明,提出的新准结构网格生成方法能够对边界复杂的模型自动生成高质量的网格,并且通过三种不同拓扑类型网格计算结果相互对比及与实验结果对比,证明准结构网格具有高计算精度。     

An Experimental-Numerical Hybrid Method for Elastic Contact Problems*

ABSTRACT

An experimental-numerical hybrid technique for determining the contact stress distribution between two elastic bodies having both frictionless as well as bonded contact is discussed in this paper. The hybrid method makes use of experimental data collected at a section far from the contact surface and the numerically generated influence coefficients, in terms of the applied unit normal and shear stresses. The experimental data, i.e., the differences in normal stresses and the shear stress, are obtained using photoelastic analysis for the examples illustrated in this paper. When substituted into equations corresponding to the unit normal and shear stress applied in the contact region, this results in a set of algebraic equations which, when solved, allow the contact stress distribution to be obtained. This method is illustrated with examples involving simple and complex geometries of the contacting bodies.     

Reliability for design of planetary gear drive units

Gear drive units are important components of technical systems (TS) and need to be of high quality. Planetary gear units are very compact and efficient mechanical power transformers, but further increase of operating quality level requires the application and development of the new design methodology. The subject of this contribution is presentation of Reliability for design as the new approach of reliability modelling suitable for the new design methodology application, especially for planetary gear units using various kinds of experimental and exploitation data. The methodology follows V-model for TS design which is in this work adapted for gear units design and for presentation of the new methodology based on property based design, axiomatic design and robust design methodology. To this end, the procedure for total reliability of TS decomposition, and methodology for elementary reliability for design of structure components calculation is developed and presented. The reliability for design is established in reverse form of reliability for maintenance which presents common perception of the “reliability” term. This approach is intended to provide further increase of planetary gear unit’s quality and efficient usability of gear unit component resources. The design directions are oriented to providing equal level of elementary reliability of components.     

Free transverse vibration analysis of a toothed gear

Analysis of transverse vibration of the gear found in a high-speed gearbox considered as an annular plate reflecting gear geometry is the subject of this paper. How gear angular velocity affects the deformation of normal modes of transverse vibration of the system under consideration is analysed. Models considered were discretized by the finite elements method. Numerical computations have been performed in the ANSYS environment. The algorithm to identify the proper distorted mode shapes is presented. The Campbell diagram for the system under consideration is elaborated. The problems discussed here can be useful for engineers dealing with dynamics of rotating machine systems.     

Method for detecting fatigue crack in gears

The most undesirable damage that can occur in gear units is crack in the tooth root as it often makes gear unit operation impossible. Monitoring vibrations can be used to detect defects. Time signals are acquired experimentally and afterwards. Different methods can be used to analyse them. The changes in tooth stiffness caused by a fatigue crack in the tooth root are of significance. The dynamic response of a gear unit with a damaged tooth differs from the one of an undamaged tooth. Amplitudes of time signal are, by time–frequency analysis, presented as a function of frequencies in spectrum.     

Passive control of vibration of thin-walled gears: advanced modelling of ring dampers

Vibrations on gears are mainly induced by the gear mesh contact. Resonance conditions of the gear may occur during service if the mesh frequency is close to the natural frequencies of the system at the designed speed of the shaft. Since detuning is not always possible in gears, the response level must be reduced by increasing the damping of the system. In this paper, a passive approach based on the application of a ring damper to reduce the vibration level is presented. The ring damper is placed in a groove underneath the outer rim of the gear. The contact is guaranteed by the preload due to the elasticity of the ring damper itself and above all by the centrifugal force that presses the damper against the groove during rotation. The relative motion of the two components at the contact interface dissipates energy by friction, and hence damping is generated. The vibration amplitude is reduced by optimizing the material and geometrical properties of the ring damper. One of the most important parameters in the determination of the amount of damping due to friction phenomena is the static normal load at the contact, which depends on the mass, the shape, and the material of the ring damper. A numerical method is presented, which couples the static and dynamic equilibrium equations of the assembly. The core of the proposed method is the contact element that takes into account local stick–slip–lift off of the contact and determines the contact forces in terms of static and dynamic loads, which are then used to solve the coupled static and dynamic equilibrium. Since the ring damper has a cut that breaks its continuous circular shape in order to be fitted on the groove, the hypothesis of cyclic symmetry for the gear/ring–damper assembly fails. As a consequence, an appropriate reduced-order modeling is presented to allow the forced response calculations. The algorithm is applied to a dummy bevel gear and to a ring damper having a flat punch contact area. The forced response calculations are performed to highlight the nonlinear interaction between the gear and damper by varying the parameters that mainly affect the amount and distribution of the contact forces and therefore the response level.     

Experimental research for robust design of power transmission components

In the future progress of technical systems it is impossible to avoid the power transmission (PT) components. Mechatronical technical systems will include the innovated PT components with high-level quality indicators. The article proposes the application of the new approaches to those components design in order to challenge innovation and inventions. The main objective is to define the design parameters in terms of reliability, vibration and noise as design constraints in the stage of the Embodiment design of PT components. Robust design is provided by using the axiomatic method in this way. Reliability as the design constraint of PT components is defined and modeled in a specific way suitable for this purpose and application. Also, the model of gear vibrations and gear units noise generation is presented in a new way suitable for applying as the design constraint. Those design constraints provide design parameters definition in an efficient way, with high-level service quality indicators. The presented models are based on a great volume of experimental data about service conditions probability, gear and bearing failure probability, gear units vibration and modal behavior etc. Theoretical knowledge and models are insufficient yet to provide the necessary data. The article contains presentation of testing methods and data processing oriented to provide data necessary for the application in the suggested approach to PT components design.     

Analysis of multi-layered microelectronic packaging under uniformly distributed loading

An accurate estimate of interfacial stresses in multi-layered microelectronic packaging is very important for design and prediction of delamination-related failures. An analytical model for stress analysis of multi-layered stacks, which is based on an extension of Valisetty’s model (Bending of Beams, Plates and Laminates: Refined Theories and Comparative Studies, Ph.D. thesis, Georgia Institute of Technology, Atlanta, March 1983), is proposed in this paper. This analytical approach considers each layer as a beam-type plate with orthotropic material properties. A new miniature material testing unit is developed. High sensitive Moiré interferometry was used to measure the strain field in the bi-material interfaces. The test data is in good agreement with the proposed analytical solution. The problem is also analyzed by a finite element analysis. Comparison of all three results indicates that the analytical procedure is far superior to finite element analysis for this problem.     

外啮合齿轮泵随机内泄漏模型的研究

为了获得更加精确的外啮合齿轮泵内泄漏数学模型,将不确定性理论引入齿轮泵传统内泄漏模型中进行研究。将齿轮泵的轴向间隙、径向间隙、液压油温度、工作压力和输入转速作为随机变量,运用随机因子法和代数综合法建立齿轮泵随机内泄漏模型,进而获得在不确定性下的齿轮泵容积效率。将随机内泄漏模型研究结果和传统模型的计算结果分别与实验结果进行比较,证明随机内泄漏模型的正确性和优越性。     

Solve a contact problem by optimization method—to calculate the stresses for the softwheel in a harmonic gear

It is difficult to solve the contact problem by usual finite element program. In this paper, we express the contact problem as an optimization problem. In this form we do not need to know all boundary condition in advance. We only need to know the constraint conditions. This method is especially good for solving contact problem. Using this method, we calculate the stresses of the softwheel in the harmonic gear given by Shanghai Jiaotong University, and the results are in good agreement with the experimental results.     

二维类桁架材料结构弹塑性分析

类桁架材料所构成结构的弹塑性行为的精确建模分析保证非常耗时, 为了 在保证精度的前提下提高此类问题的求解效率, 本文利用类桁架材料基本构件长细比 较大的特点,将材料单胞简化为桁架模型. 考虑到微单胞空间分布的周期性,基于 数值均匀化理论提出了类桁架材料结构的宏微观两 级弹塑性求解格式. 原问题转化为宏观上一个非线性弹性连续体计算问题和微观上多个小规 模桁架系统的弹塑性计算问题. 两个数值算例分别考虑了简单加载,非单调加载,规则宏观 结构和具有非完整单胞的较复杂宏观结构等问题. 与实际结构计算结果在精度和时间等方面 的比较验证了求解格式的有效性. 最后还探讨了算法的适用范围.