摘要:

AbstractIt is known that when two springs are connected in series, the stiffness coefficient of an equivalent system that consists of one spring is less than the stiffness coefficients of the original springs. Experimental observations indicate that this fact can be very useful in determining the overall vibration characteristics of tracked vehicles. This simple fact is used in this investigation to develop a computer aided analysis procedure for the dynamic simulation of large‐scale tracked vehicles. The track is considered as a closed kinematic chain that consists of rigid bodies connected by revolute joints. The contacts between the track links and the rollers, the sprocket, and the idler are represented by non‐linear continuous force models. The stiffness and damping coefficients in these contact force models are determined by studying the viberation characteristics of the tracked vehicle. The tooth of the sprocket is defined using three surfaces. These are the left, the bottom, and the fight surfaces. Three successive transformations are used to define the contact kinematic relationships between the sprocket teeth and the pins of the track links. The equations of motions of the vehicle are formulated using theLagrangian approach. Non‐linear constraint equations that describe mechanical joints and specified motion trajectories in the system are adjoined to the differential equations of motion using the technique ofLagrange multipliers. The resulting mixed system of differential and algebraic equations is solved numerically using a direct numerical integration method. ANewton–Raphson algorithmis used to check on the violations in the kinematic constraints. The results presented in this paper are obtained using a 54 body planer tracked vehicle in which the track consists of 42 rigid links connected by revolute

ISSN:0029-5981    

DOI:10.1002/nme.1620370802

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractWithin the context of the consistent tangent update, this paper outlines a stress update algorithm for combined creep and plasticity. The algorithm is implicit, providing unconditional stability, and utilizes local Newton iteration to solve SCALAR forms of the coupled constitutive equations for the creep and plastic strain increments. The tangent for the local iteration is obtained accurately providing quadratic convergence at the Gauss point level. Quadratic convergence of the global iteration procedure is also maintained using an explicitly derived consistent tangent for combined plasticity and creep. Further, combination with an automatic time‐stepping scheme provides an efficient, stable, accurate and robust computational algorithm. The algorithm has been implemented in the general purpose FE package LUSAS

ISSN:0029-5981    

DOI:10.1002/nme.1620370803

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA finite element model is developed on the basis of a variational formulation of the perturbed Lagrange type and the classical Coulomb law of friction, for the analysis of frictional contact problems in two dimensions. The model accounts for all geometric/kinematic non‐linearities associated with large sliding motions as well as arbitrary contact‐surface curvatures. Explicit forms for the contact force and tangent stiffness operators and a penalty‐type format is utilized in the implementation. An extensive number of numerical simulations are used to demonstrate the effectiveness and practical usefulness of the

ISSN:0029-5981    

DOI:10.1002/nme.1620370804

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSignificant performance improvements can be obtained if the topology of an elastic structure is allowed to vary in shape optimization problems. We study the optimal shape design of a two‐dimensional elastic continuum for minimum compliance subject to a constraint on the total volume of material. The macroscopic version of this problem is not well‐posed if no restrictions are placed on the structure topoiogy; relaxation of the optimization problem via quasiconvexification or homogenization methods is required. The effect of relaxation is to introduce a perforated microstructure that must be optimized simultaneously with the macroscopic distribution of material.A combined analytical‐computational approach is proposed to solve the relaxed optimization problem. Both stress and displacement analysis methods are presented. Since rank‐2 layered composites are known to achieve optimal energy bounds, we restrict the design space to this class of microstructures whose effective properties can easily be determined in explicit form. We develop a series of reduced problems by sequentially interchanging extremization operators and analytically optimizing the microstructural design fields. This results in optimization problems involving the distribution of an adaptive material that continuously optimizes its microstructure in response to the current state of stress or strain. A further reduced problem, involving only the response field, can be obtained in the stress‐based approach, but the requisite interchange of extremization operators is not valid in the case of the displacement‐based model.Finite element optimization procedures based on the reduced displacement formulation are developed and numerical solutions are presented. Care must be taken in selecting the discrete function spaces for the design density and displacement response, since the reduced problem is a two‐field, mixed variational problem. An improper choice for the solution space leads to instabilities in the optimal design similar to those encountered in mixed formulations of the S

ISSN:0029-5981    

DOI:10.1002/nme.1620370805

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThea posteriorierror estimates based on the post‐processing approach are introduced for elastoplastic solids. The standard energy norm error estimate established for linear elliptic problems is generalized here to account for the presence of internal variables through the norm associated with the complementary free energy. This is known to represent a natural metric for the class of elastoplastic problems of evolution. In addition, the intrinsic dissipation functional is utilized as a basis for a complementarya posteriorierror estimates.A posteriorierror estimates and adaptive refinement techniques are applied to the finite element analysis of a strain localization problem. As a model problem, the constitutive equations describing a generalization of standardJ2‐elastoplasticity within the Cosserat continuum are used to overcome serious limitations exhibited by classical continuum models in the post‐instability region. The proposeda posteriorierror estimates are appropriately modified to account for the Cosserat continuum model and linked with adaptive techniques in order to simulate strain localization problems. Superior behaviour of the Cosserat continuum model in comparison to the classical continuum model is demonstrated through the finite element simulation of the localization in a plane strain tensile test for an elastopiastic softening material, resulting in convergent solutions with anh‐refinement and almost uniform error distribution in all considered erro

ISSN:0029-5981    

DOI:10.1002/nme.1620370806

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractHydraulic jump on a straight horizontal channel with supercritical Froude numbers 2·0 and 4·0 is numerically simulated by solving the Reynolds averaged Navier–Stokes equations. Turbulence is modelled through thek–ϵ closure equations and the mixed Eulerian–Lagrangian description of flow is utilized to overcome the problem posed by moving free boundary. Time stepping is done via fractional step method and pressure is determined from Poisson's equation. Galerkin finite element method with three‐noded triangular elements is used for spatial discretization. A detailed study of the internal and external characteristics of hydraulic jump is done and compared with experimental values where possible. Surface roller and recirculation zone are found to play a dominant role in turbulence generation and d

ISSN:0029-5981    

DOI:10.1002/nme.1620370807

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn this paper an iterative scheme of first order is developed for the purpose of solving linear systems of equations. In particular, systems that are derived from boundary integral equations are investigated. The iterative schemes to be considered are of the formEx(k+1)=Dx(k)+d, whereEandDare square matrices. It will be assumed thatEis a lower matrix, i.e. the coefficients above the central diagonal are zero. It will be shown that by considering matrixDembedded in a vector space and reducing its size with respect to a chosen metric, that convergence rates can be substantially improved. Equation ordering and parameter matrices are used to reduce the magnitude ofD. A number of examples are tested to illustrate the importance of the choice of metric, equation ordering and the parameter matrix. Computation times are determined for both the iterative procedure and Gauss elimination indicating the usefulness of iteration which can be orders of magnitude faster.

ISSN:0029-5981    

DOI:10.1002/nme.1620370808

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper investigates the performance of a class of methods based on the Preconditioned Conjugate Gradient (PCG) method for the solution of large and sparse systems of linear equations which arise from thep‐version of the adaptive finite element method. The hierarchical type of preconditioning used in the past is extended to the SSOR and incomplete factorization type preconditioning and applied with a global handling of the stiffness matrix. The paper also presents some new ideas on Domain Decomposition (DD) matrix‐handling techniques, whereby the explicit formulation of the resulting Schur complement is avoided by utilizing the PCG method with efficient preconditioners and by processing separately on the coarse and the fine mesh. The suitability of the methods to thep‐version of the adaptive finite element method is demonstrated through extensive numerical tests in two dimen

ISSN:0029-5981    

DOI:10.1002/nme.1620370809

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620370810

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620370811

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY