ISSN:0029-5981    

DOI:10.1002/nme.1620371302

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620371303

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn such local phenomena as shocks and boundary layers, etc, the discretization errors are directional and the use of elongated elements is obvious if economy is to be achieved. Although facilities for local mesh elongation have been incorporated into earlier codes in generating unstructured meshes, these do not permit the use of very high stretch ratios required for the analysis of such problems as boundary layers. Here the use of locally introduced structured meshes has been practised involving much manual interaction and loss of error control. In the paper we present a procedure which achieves the combination of such locally structured meshes with a general unstructured mesh generator in an automatic and fully adaptive manner. The procedure is illustrated in the context of compressible, viscous and inviscid, flows but has obvious applications in other (solid mechanics) problems involving localization.

ISSN:0029-5981    

DOI:10.1002/nme.1620371304

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractFinite element modelling of three‐dimensional elasticity problems give rise to large sparse matrices. Various preconditioning methods are developed for use in preconditioned conjugate gradient iterative solution techniques. Incomplete factorizations based on levels of fill, drop tolerance, and a two‐level hierarchical basis are developed. Various techniques for ensuring that the incomplete factors have positive pivots are presented. Computational tests are carried out for problems generated using unstructured tetrahedral meshes. Quadratic basis functions are used. The performance of the iterative methods is compared to a standard direct sparse matrix solver. Problems with up to 70 000 degrees of freedom and small (≪1) element aspect ratio are consi

ISSN:0029-5981    

DOI:10.1002/nme.1620371305

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn this paper, control of spurious mechanisms for sub‐integrated 20‐node and transition hexahedral elements is devised by an assumed stress approach. The higher‐order stress modes for stabilizing the sub‐integrated elements are identified by examining the spurious mechanisms. With an admissible simplification of the flexibility matrix, row vectors of the leverage matrix can be used as stabilization vectors. Numerical examples for the stabilized 20‐node element are presented. Accuracy of the derived element is far better than the fully integrated displacement elements. Meanwhile, the former also consumes marginally less CPU time than t

ISSN:0029-5981    

DOI:10.1002/nme.1620371306

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIntensive research and development in Computational Fluid Dynamics (CFD) has recently produced many powerful CFD codes to simulate complex aerodynamic phenomena. However, in order to enhance the usefulness of these CFD codes for design practice, development of design sensitivity equations compatible to these codes becomes very important. This paper represents a part of such an effort to develop a sensitivity analysts methodology that enables the sensitivity equations to be implemented into existing CFD codes with minimal code modification. The methodology is based upon a pre‐elimination procedure which accounts for consistently linearized boundary conditions. Formulations of both the direct differentiation and the adjoint variable methods will be presented in the pape

ISSN:0029-5981    

DOI:10.1002/nme.1620371307

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe focus of the present work is directed towards the one‐dimensional non‐linear analysis of space‐curved and twisted beams undergoing large displacements and finite rotations. According to Cosserat's model, a beam is intended here as a continuum generated by the rigid motion of a cross‐section along a curve. The novelty of the proposed methodology is implied in the assumption that the reference line of the beam, both in the undeformed and in the deformed configurations, is a helicoid in space.This formulation radically departs from the classical beam models based on polynomial interpolations of the independent fields. In fact, within the framework of helicoidal geometry, a powerful description of space‐curved beam kinematics with large displacements and finite rotations can be developed. Furthermore, the beam model developed herein can be proved to enjoy several invariance properties that make it particularly attractive for non‐linear analysis. The formulation discussed in this work adheres to a mixed variational principle, the independent fields being the generalized displacements and the sectional stress resultants.In a companion paper, we address the linearization of the governing weak form, the finite element implementation of the proposed methodology with a novel incremental treatment of finite rotations, and the development of a helicoidal model for rigid body dynamics using finite eleme

ISSN:0029-5981    

DOI:10.1002/nme.1620371308

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe helicoidal beam model developed in the first part of this work is applied here to the development of a mixed finite element for space‐curved and twisted beams undergoing large displacements and finite rotations. Starting from the governing weak form expressed by the principle of virtual work, a consistent linearization is obtained in the following and a novel updated Lagrangian finite element implementation is thoroughly discussed.The unique features and the distinguishing properties previously claimed for the helicoidal model are shown here to imply remarkable numerical consequences. For this purpose, meaningful example problems regarding the non‐linear static response of beams are addressed in the following and the results are compared with those available from the literature.Furthermore, a finite element in time for the rigid body dynamic problem is developed within the framework of the helicoidal geometry. The underlying philosophy of this novel finite element for dynamics is the realization of the helicoidal decomposition of the rigid body motion within a time s

ISSN:0029-5981    

DOI:10.1002/nme.1620371309

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA finite element approach for shape optimization in two‐dimensional (2‐D) frictionless contact problems is presented in this work. The goal is to find the shape that gives a constant distribution of stresses along the contact boundary.The whole formulation, including mathematical model for the unilateral problem, sensitivity analysis and geometry definition is treated in a continuous form, independently of the discretization in finite elements. Shape optimization is performed by direct modification of geometry through B‐spline curves and an automatic mesh generator is used at each new configuration to provide the finite element input data for numerical analysis and sensitivity computations. Using augmented‐Lagrangian techniques (to solve the contact problem) and an interior‐point mathematical‐programming algorithm (for shape optimization), we obtain several results reported at the end of

ISSN:0029-5981    

DOI:10.1002/nme.1620371310

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620371311

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY