基于SuperSAP的有限元前处理接口程序设计

基于ＳｕｐｅｒＳＡＰ软件的前处理功能,提出了两种有限元前处理的数据文件接口程序设计方法,一种是从ＡｕｔｏＣＡＤ中调入模型的接口设计方法,另一种是直接生成有限元分析数据文件的接口设计方法。采用该接口程序可以方便地进行结构、材料、边界复杂的工程问题的有限元前处理。     

基于数字单元法的三维正交织物微观几何结构建模

为了反映织物内部纱线的空间构型和微观几何结构,针对在织物建模过程中,因忽略纤维间的相互作用而引起的纱线截面形状变化的问题,基于数字单元法理论,提出了一种计算纤维间摩擦力的方法。通过纱线纤维化离散,用数值模拟和仿真方法模拟三维正交织物成型过程,建立了5种精度递进的微观几何结构数值模型。5种模型中的每根纱线分别由4、7、12、19和37根数字纤维表征。研究结果表明:随着纱线纤维化离散程度的提高,仿真时间延长,织物厚度减小,纤维体积分数增大,节点平均作用力下降速度变缓,势能变小;当每根纱线由19根数字纤维组成时,所建织物的微观几何结构数值模型与真实织物样本在显微镜下的内部切片图像较为吻合。     

煤灰结渣特性的粗集评判

基于粗集理论,提出了煤灰结渣特性的粗集评判模型,由于直接来源于实际观测数据,可靠性高,与其它判别方法相比,能更有效地判别结渣特性。     

Accurate computation of design sensitivities for structures under transient dynamic loads using time marching scheme

Design sensitivities for structures under transient dynamic loads with constraints on displacements and stresses are sensitive to proper space and time discretization. Accuracy within acceptable error limit is feasible when an appropriate time increment coupled with an optimal mesh is used. In this paper, we handle this problem by systematically achieving an adaptive mesh for a reasonably fine but constant time step. Design sensitivities calculated for a good number of examples demonstrate the behaviour of this integrated approach. Comparison is made in terms of total computational time between time-marching scheme and modal superposition method in the context of design sensitivity calculation. Optimal meshes are also obtained corresponding to adaptive time stepping and accurate values of design sensitivities are computed using the optimal mesh and the values of the time increment obtained adaptively. © 1998 John Wiley & Sons, Ltd.     

Complementary 2-D finite element procedures for the magnetic field analysis using a vector hysteresis model

The main purpose of this paper is to incorporate a refined hysteresis model, viz., a vector Preisach model, in 2-D magnetic field computations. Two complementary formulations, based either on the scalar or on the vector potential, are considered. The governing Maxwell equations are rewritten in a suitable way, that allows to take into account the proper magnetic material parameters and, moreover, to pass to a variational formulation. The variational problems are solved numerically by a Finite Element approximation, using a quadratic mesh, followed by a time discretization method based upon a modified Cranck–Nicholson algorithm. Finally, the effectiveness of the presented mathematical tools have been confirmed by several numerical experiments, comparing the complementarity of the two procedures. © 1998 John Wiley & Sons, Ltd.     

模拟脆性材料动态裂纹扩展的非连续变形分析方法

非连续变形分析方法(DDA)属于隐式离散元法,通过引入虚拟节理可以模拟材料从连续到破坏全过程.尝试将DDA方法应用于脆性材料动态裂纹扩展问题.采用基于Voronoi多边形离散的DDA方法进行模拟.由于Voronoi多边形会存在较多短边,采用原始DDA程序计算时短边会优先发生破坏.针对该问题通过引入均布弹簧算法,在一定程...     

Transient algorithms for heat transfer: general developments and approaches for theoretically generating Nth‐order time‐accurate operators including practically useful second‐order forms

New theoretical ideas and developments describing the fundamental underlying basis for formulating a general family of time discretization operators for first‐order parabolic systems emanating from the framework of a generalized time weighted philosophy are first presented which can be broadly classified as pertaining to Type 1, Type 2 and Type 3 family of time discretization operators. As a consequence, the evolution including the clear distinction and the bridging of the relationships between time operators termed as integral operators to the so‐called integration operators in time are theoretically developed and demonstrated. The present developments seem to not only provide avenues leading to new algorithms for transient analysis but also provide generalizations and framework to recover a wide variety of existing algorithms. Consequently, under the umbrella of the present framework, a variety of plausible new approaches for generating Nth‐order accurate time discretization operators from approximations introduced to Type 1 integral operators in time are first described followed by the developments systematically leading to Type 2 time discretization operators, and subsequently to a wide class of Type 3 time integration operators including the recovery of a variety of known existing time integration operators which can be uniquely identified by Discrete Numerically Assigned (DNA) algorithmic markers. Of the various developments, of noteworthy mention and emphasis here are a new family of L‐stable Nth‐order Integration Operators (LNInO) of Type 2 for transient computations. Subsequently, some practically useful second‐order forms are specifically illustrated and highlighted. The stability and accuracy characteristics are also described for a variety of generated algorithms applicable for transient heat transfer computations. Although the primary focus is on the theoretical developments encompassing linear operators, some simple numerical examples are finally demonstrated to merely illustrate the salient features of the proposed developments. Copyright © 1999 John Wiley & Sons, Ltd.     

螺旋曲面加工刀位轨迹数值算法研究与应用

为了提高复杂螺旋面的加工精度,对其刀位轨迹算法进行研究,提出了基于最小有向距离的刀位轨迹数值计算方法。建立了刀具与工件曲面的三维数值几何模型,并通过坐标变换矩阵来建立与实际加工情况一致的数值计算模型。采用空间离散化思想将刀具与工件两空间曲面的最小有向距离的求解问题简化为一个二维求解问题,保证了求解效率和精度。根据阿基米德插补曲线原理,建立了刀位轨迹的数值计算方法。实例加工结果证明,基于该方法得到的刀位轨迹编制的数控加工程序能够加工出满足精度要求的螺旋面。     

复杂工件夹紧力作用区域的规划算法

在机械加工过程中,工件受到切削力、切削扭矩等外载的作用,这将破坏工件定位时所获得的合理位置,甚至会导致生产事故的发生。因而必须对工件施加合理的夹紧力以保证其在整个加工过程中具有稳定性。为此,以工件稳定性为核心,提出了复杂形状工件的夹紧力作用区域确定算法。基于虚功原理和线性规划技术,建立了工件稳定性的判定算法;基于表面网格离散化方法,按照一定方向逐次分析各个节点处的工件稳定性,建立了夹紧力作用区域的确定算法。该方法不仅能够验证夹紧力大小的可行性,而且还能够用来指导夹紧力作用点位置的合理设计。     

A New Fourth-Order Compact Off-Step Discretization for the System of 2D Nonlinear Elliptic Partial Differential Equations

This paper discusses a new fourth-order compact off-step discretization for the solution of a system of two-dimensional nonlinear elliptic partial differential equations subject to Dirichlet boundary conditions. New methods to obtain the fourth-order accurate numerical solution of the first order normal derivatives of the solution are also derived. In all cases, we use only nine grid points to compute the solution. The proposed methods are directly applicable to singular problems and problems in polar coordinates, which is a main attraction. The convergence analysis of the derived method is discussed in detail. Several physical problems are solved to demonstrate the usefulness of the proposed methods.