筒形件温差拉深数值模拟研究

温差拉深时,温度是影响成形的重要因素。用PAM STAMP对不锈钢筒形件的温差拉深工艺进行了模拟,分析了温度对温差拉深的影响,为筒形件温差拉深工艺的制定提供了依据。     

铝合金盒形件充液成形法兰变形特性及其失稳影响分析

通过有限元模拟和实验对铝合金盒形件充液成形过程进行研究,分析了铝合金盒形件充液成形法兰直边区和圆角区的变形特性,以及法兰变形对起皱和破裂等失稳形式的影响.结果表明:法兰圆角区变形复杂,存在径向压应力,根据变形特征可分为五个变形区;长直边法兰抗皱能力比短直边法兰小,容易起皱;短直边侧壁变薄量大,在与凸模圆角相切处的板料容易破裂;合理的压边间隙可以有效控制长直边法兰起皱和短直边侧壁破裂,实验结果证明了数值模拟结果的准确性.     

A priori evaluation of dynamic subgrid models of turbulence in square duct flow

A priori tests of two dynamic subgrid-scale (SGS) turbulence models have been performed using a highly resolved direct numerical simulation database for the case of turbulent incompressible flow in a straight duct of square cross-section. The model testing is applied only to the homogeneous flow direction where grid filtering can be applied without the introduction of commutation errors. The first SGS model is the dynamic (Smagorinsky/eddy viscosity) SGS model (DSM) developed by Germano et al. [1] while the second is the dynamic two parameter (mixed) model (DTM) developed by Salvetti and Banerjee [2]. For the Smagorinsky model we have used both the Fourier cut-off filter and a modified Gaussian filter which has the property that it removes aliasing errors in consistent a priori model-testing for spectral-based datasets. Results largely consistent with those found for plane channel flow are observed but with some slight differences in the corner regions. As found in prior studies of this sort, there is a very poor correlation of the modelled and exact subgrid-scale dissipation in the case of the DSM. The DSM over-predicts subgrid-scale dissipation on average. Instantaneously, the model provides an inaccurate representation of subgrid-scale dissipation, in general underestimating the magnitude by approximately one order of magnitude. On the other hand, the DTM shows excellent agreement with the exact SGS dissipation over most of the duct cross-section with a correlation coefficient of approximately 09.     

B550CL高强钢轮辐反拉深-翻边复合成形损伤开裂研究

针对高强钢汽车轮辐在实际生产过程中经常出现反拉深-翻边复合工序中中心孔翻边开裂这一问题,采用有限元数值模拟的方法,建立了有限元模型,并通过试制轮辐验证其可靠性.模拟获得了新型高强钢材料B550CL在用于轮辐翻边成形时的应力应变的分布和变化规律,并进一步对轮辐的损伤和壁厚分布情况进行了分析.研究表明:反拉深-翻边复合工序中翻边区在成形过程中应力应变集中明显,变形量较大;同时,材料的损伤和壁厚减薄在翻边区域也比较严重,导致实际成形中翻边区可能出现开裂等缺陷.     

多点成形中压痕的数值模拟及极限成形力的分析

压痕是多点成形中特有的成形缺陷之一,对压痕形成过程进行模拟时,采用实体单元比壳单元计算更准确.但是板料较薄时,采用实体单元划分的有限元很多,计算时间极长.为获得最佳的计算效率及模拟结果,对不同材料和不同厚度的球面和马鞍面样件进行了对比的数值模拟.结果表明,当板厚与板宽的比值小于0.015时,采用壳单元模拟压痕也能得到比较准确的结果,而当比值大于0.015时,则应采用实体单元.在此基础上,对不同板厚、不同曲率半径下的马鞍面和球面件出现压痕时的极限成形力进行分析,得到了厚向压应变为1%和5%的压痕对应的成形力极限图.     

A sequential linear least square algorithm for tracking dynamic shapes of smart structures

This paper presents a sequential linear least square algorithm for tracking dynamic shapes of piezoelectric smart structures. The dynamic shape discussed in this paper is defined as a host structural shape varying with time, and the tracking technique is to find an electric voltage history for each piezoelectric device over a time period so that the desired structural movements can be achieved. In the theoretical formulation, dynamic equations of piezoelectric smart structures are introduced by finite element analysis, and then a solution procedure for a set of time‐dependent electric voltages is derived by combining the linear least square method and the Houbolt numerical integration scheme. The formulation indicates that this algorithm can be used to find the time‐dependent voltages for tracking structural movements of piezoelectric smart structures. The present novel formulation is then demonstrated through numerical examples for tracking dynamic shapes of piezoelectric smart beams and plates. The numerical results for the smart beam are compared with the experimental ones. It is shown that the present sequential linear least square algorithm is capable of efficiently simulating dynamic shape tracking for smart structures. Copyright © 2006 John Wiley & Sons, Ltd.     

排水型方尾船加装尾板前后振动性能分析

采用大型通用有限元分析软件和流体边界元方法，对某排水型方尾船加装尾板前后的总体振动特性和尾部振动响应进行了分析计算和比较，得出了加装尾板对该型船总体振动特性和尾部振动响应影响很小的结论．     

Investigation into the wrinkling behaviour of thin sheets in the cylindrical cup deep drawing process using bifurcation theory

The initiation and growth of wrinkles are influenced by many factors such as stress ratios, the mechanical properties of the sheet material, the geometry of the workpiece, and contact condition. It is difficult to analyse wrinkling initiation and growth while considering all the factors because the effects of the factors are very complex and studies of wrinkling behaviour may show a wide scattering of data even for small deviations in factors. In the present study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element method. Wrinkling initiation is found by checking the determinant of the stiffness matrix and wrinkling behaviour is analysed by successive iteration with the perturbed guess along the eigenvector. Wrinkling initiation and growth in the cylindrical cup deep drawing process are analysed by using the proposed bifurcation algorithm. The mechanism of wrinkling initiation and growth in the cylindrical cup deep drawing process is investigated in detail. The results of the finite element analysis are compared with the experimental results. Through the finite element analyses of wrinkling growth for various material constants, the effects of plastic anisotropy and the strain hardening coefficient on the wrinkling behaviour of sheet metal are investigated. Copyright © 2003 John Wiley & Sons, Ltd.     

纸杯中有机模拟污染物分配系数的研究

以3种纸杯样品为研究对象,使用微量点滴样法研究了有机模拟污染物邻苯二甲酸二丁酯(DBP)、二苯甲酮在纸杯样品和空气间的分配系数(Kpaper/air)。研究发现,分配系数值随着温度的升高而减小。70℃时,DBP、二苯甲酮的Kpaper/air值范围分别为105.723~1638.894和67.469~991.849;而100℃时Kpaper/air值范围分别为28.661~360.978和7.506~407.225。Kpaper/air值不仅与污染物的沸点有关,还与纸杯样品的厚度、定量及紧度有很大的关系,厚度、定量、紧度越大,分配系数越大,纸杯样品中的DBP越不易发生迁移。     

A finite‐volume method for deformation analysis of woven fabrics

Efficient numerical methods for simulating cloth deformations have been identified as the key to the development of successful Computer‐Aided Design systems for clothing products. This paper presents the formulation of a new finite‐volume method for the simulation of complex deformations of initially flat woven fabric sheets under self‐weight or externally applied loading. The fabric sheet is assumed to undergo very large displacements and rotations but small strains during the process of deformation. The fabric material is assumed to be linear elastic and orthotropic. The fabric sheet is discretized into many small structured patches called finite volumes (or control volumes), each containing one grid node and several face nodes. The bending and membrane deformations of a typical volume can be defined using the global co‐ordinates of its grid node and surrounding face nodes. The equilibrium equations governing the complex deformations are derived employing the principle of stationary total potential energy. These equations are solved using a single‐step full Newton–Raphson method which is found to be capable of predicting the final deformed shape, the only result of interest in a fabric drape analysis. To speed up convergence, the line search technique is adopted with good effect. This single‐step approach is more efficient than the step‐by‐step incremental approach employed in conventional non‐linear finite element analysis of load‐bearing structures. A number of example simulations of fabric drape/buckling deformations are included in the paper, which demonstrate the efficiency and validity of the proposed method. Copyright © 1999 John Wiley & Sons, Ltd.