Engineering Computations: International Journal for Computer-Aided Engineering and Software

Ali Soua; Maurice Touratier; Laurent Polac

doi: 10.1108/02644409910251184pmid: N/A

The aim of the research work presented here is to control the geometric distortions of engine cylinders, which involve both noise and oil consumption. The final goal is then to limit pollution from engines. The simulation deals initially with the cold stamping and crushing operations of a cylinder head gasket; based on using solid finite element models from the Abaqus computer code (version 5.3) for large deformation with plasticity and contact, including friction. In addition, experiments have been carried out to identify the plasticity rule for the materials used in order to simulate the crushing of the cylinder head gasket under a given normal pressure representing the clamping operation. The main difficulty of this work is to correlate the cylinder head gasket behaviour and cylinder distortions with the main function of the gasket, i.e. pressurized gas sealing. The cylinder head gasket is a complex multilayered structure made of three spot welded metal sheets. This assembly has many holes of different shapes. Around the cylinder hole on both outer layers of the gasket, there is a small size embossment to ensure gas sealing between the engine block and cylinder head. This rib is not circular because of the combustion chamber shape.

J.E. Akin

doi: 10.1108/02644409910251210pmid: N/A

There is a widely available object oriented (OO) programming language that is usually overlooked in the OO analysis, OO design, OO programming literature. It was designed with most of the features of languages like C++, Eiffel, and Smalltalk. It has extensive and efficient numerical abilities including concise array and matrix handling, like Matlab®. In addition, it is readily extended to massively parallel machines and is backed by an international ISO and ANSI standard. The language is Fortran 90 (and Fortran 95). When the explosion of books and articles on OOP began appearing in the early 1990s many of them correctly disparaged Fortran 77 (F77) for its lack of object oriented abilities and data structures. However, then and now many authors fail to realize that the then new Fortran 90 (F90) standard established a well‐planned object oriented programming language while maintaining a full backward compatibility with the old F77 standard. F90 offers strong typing, encapsulation, inheritance, multiple inheritance, polymorphism, and other features important to object oriented programming. This paper will illustrate several of these features that are important to engineering computation using OOP.

A.F. Marcon; E. Bittencourt; G.J. Creus

doi: 10.1108/02644409910251229pmid: N/A

Discusses an alternative formulation for the incremental determination of stresses in strain measures that can be used to replace the stress rates currently employed. The formulation is based on Doyle‐Hill generalized definition of strain, the corresponding conjugate stresses and an isotropic hyperelastic constitutive equation. When used to analyze the simple shear deformation, the proposed formulation avoids the pathologies usually observed (oscillations, pressure build up, path dependence). The origin and importance of these pathologies is then discussed in relation to different materials behavior. It is shown that the incremental procedure used together with the logarithmic definition of strain is the most convenient, but that other approximations may be used in well defined particular situations. The numerical algorithms proposed are detailed in an Appendix.

O.M. Heeres; R. de Borst

doi: 10.1108/02644409910251283pmid: N/A

An important characteristic of many soil models is a volume change during plastic flow. In computations, this plastic volume change is expressed via a kinematic constraint on the possible deformations. Due to this constraint the plane‐strain three‐noded triangular element exhibits locking when plastic deformations occur, under dilatant, contractant and isochoric conditions. It is demonstrated that using the method of enhanced assumed strains by Simol this locking cannot be remedied. For six‐noded wedges and four‐noded and five‐noded pyramids the same conclusion is obtained.

G. Zavarise; P. Wriggers

doi: 10.1108/02644409910251292pmid: N/A

The numerical solution of contact problems via the penalty method yields approximate satisfaction of contact constraints. The solution can be improved using augmentation schemes. However their efficiency is strongly dependent on the value of the penalty parameter and usually results in a poor rate of convergence to the exact solution. In this paper we propose a new method to perform the augmentations. It is based on estimated values of the augmented Lagrangians. At each augmentation the converged state is used to extract some data. Such information updates a database used for the Lagrangian estimation. The prediction is primarily based on the evolution of the constraint violation with respect to the evolution of the contact forces. The proposed method is characterised by a noticeable efficiency in detecting nearly exact contact forces, and by superlinear convergence for the subsequent minimisation of the residual of constraints. Remarkably, the method is relatively insensitive to the penalty parameter. This allows a solution which fulfils the constraints very rapidly, even when using penalty values close to zero.

G.P. Nikishkov; A. Makinouchi; G. Yagawa; S. Yoshimura

doi: 10.1108/02644409910251300pmid: N/A

An algorithm for domain partitioning with iterative load balancing is presented. A recursive graph labeling scheme is used to distribute elements among subdomains at each iteration. Both graph distance information and information about neighbor vertices are employed during the labeling process. Element quantities for balanced subdomains are predicted, solving the algebraic load balancing problem after each iteration. The same graph labeling scheme with slight modifications is applied to node renumbering inside subdomains. The proposed algorithm is especially suitable for load balancing when a direct method is used for subdomain condensation and the evaluation of cost function is time consuming. Several examples of optimized partitioning of irregular and regular meshes show that load balancing can be achieved with one to three iterations.