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

Chongbin Zhao; B.E. Hobbs; H.B. Mühlhaus; A. Ord; Ge Lin

2000 Engineering Computations: International Journal for Computer-Aided Engineering and Software

doi: 10.1108/02644400010334801

Numerical methods are used to solve double diffusion driven reactive flow transport problems in deformable fluid‐saturated porous media. In particular, the temperature dependent reaction rate in the non‐equilibrium chemical reactions is considered. A general numerical solution method, which is a combination of the finite difference method in FLAC and the finite element method in FIDAP, to solve the fully coupled problem involving material deformation, pore‐fluid flow, heat transfer and species transport/chemical reactions in deformable fluid‐saturated porous media has been developed. The coupled problem is divided into two sub‐problems which are solved interactively until the convergence requirement is met. Owing to the approximate nature of the numerical method, it is essential to justify the numerical solutions through some kind of theoretical analysis. This has been highlighted in this paper. The related numerical results, which are justified by the theoretical analysis, have demonstrated that the proposed solution method is useful for and applicable to a wide range of fully coupled problems in the field of science and engineering.

R.V.N. Melnik

2000 Engineering Computations: International Journal for Computer-Aided Engineering and Software

doi: 10.1108/02644400010334810

The dynamics of coupling between spectrum and resolvent under ॉ‐perturbations of operator and matrix spectra are studied both theoretically and numerically. The phenomenon of non‐trivial pseudospectra encountered in these dynamics is treated by relating information in the complex plane to the behaviour of operators and matrices. On a number of numerical results we show how an intrinsic blend of theory with symbolic and numerical computations can be used effectively for the analysis of spectral problems arising from engineering applications.

W. Gutkowski; J. Bauer ; J. Zawidzka

2000 Engineering Computations: International Journal for Computer-Aided Engineering and Software

doi: 10.1108/02644400010334829

Deals with an approximate, but very simple, method of finding the minimum of structural weight under static loads. The design consists of assigning an appropriate rolled profile, from a given catalogue, to each structural member. The design is then formulated as a discrete structural optimization problem. The structure may be subjected to an arbitrary number of constraints imposed on stresses and structural material from members with the least stress. Presented examples are showing that the problems with k0 catalogue elements, and j0 structural members, including k0 to the power j0 combinations, can be solved with k0j0 analyses only. The knowledge needed to solve the problem is limited to structural analysis.

H. Kim; M.J. Garcia; O.M. Querin ; G.P. Steven; Y.M. Xie

2000 Engineering Computations: International Journal for Computer-Aided Engineering and Software

doi: 10.1108/02644400010334838

Introduces a faster and improved structural optimisation method which combines fixed grid finite element analysis (FG FEA) and evolutionary structural optimisation (ESO). ESO optimises a structure by removing a few elements at every iteration. FG methods allow fast mesh generation, fast solution and fast re‐evaluation of the modified meshes. The implementation of FG into the ESO process eliminates the need for regenerating the mesh and a few arithmetic calculations replace the full regeneration of the stiffness matrix every time the structure is modified. This greatly reduces the solution time, and the examples presented in this paper demonstrate and validate the method.

S. Rizzo; R. Spallino; G. Giambanco

2000 Engineering Computations: International Journal for Computer-Aided Engineering and Software

doi: 10.1108/02644400010334847

Approaches the shakedown optimal design of reinforced concrete (RC) structures, subjected to variable and repeated external quasi-static actions which may generate the well-known shakedown or adaptation phenomenon, when constraints are imposed on deflection and/or deformation parameters, in order to simulate the limited flexural ductility of the material, in the presence of combined axial stress and bending. Within this context, the classical shakedown optimal design problem is revisited, using a weak upper bound theorem on the effective plastic deformations. For this problem a new computational algorithm, termed evolution strategy, is herein presented. This algorithm, derived from analogy with the biological evolution, is based on random operators which allow one to treat the areas of steel reinforcements at each RC cross-section of the structure as design variables of discrete type, and to use refined non-linear approximations of the effective bending moment - axial force M-N interaction diagrams of each RC cross-section. The results obtained from case studies available in the literature show the advantages of the method and its effectiveness.

Andrea P. Assanelli; Rita G. Toscano; Daniel H. Johnson; Eduardo N. Dvorkin

2000 Engineering Computations: International Journal for Computer-Aided Engineering and Software

doi: 10.1108/02644400010334856

The production of steel pipes with guaranteed external collapse pressure (e.g. high collapse casings for oil wells) requires the implementation of an accurate process control. To develop that process control it is necessary to investigate how different parameters affect the external collapse pressure of the pipes. Experimental/numerical techniques implemented to investigate the collapse behavior of steel pipes are presented. The discussion of the experimental techniques includes the description of the facilities for performing external pressure collapse tests and the description of an imperfections measuring system. The numerical techniques include 2D and 3D finite element models. The effects on the value of the pipes' external collapse pressure of their shape, residual stresses and material properties are discussed.

C.A.N. Dias; J.R.D. Petreche

2000 Engineering Computations: International Journal for Computer-Aided Engineering and Software

doi: 10.1108/02644400010334865

In marine structures, the long-term non-stationary response of flexible lines, due to random environmental loads, may be regarded as successive short-term stationary processes in which current, wind and ocean wave conditions remain constant. The power spectrum of each stationary process can be characterized by its linear and non-linear energy components: the linear energy defines a Gaussian process, and the additional nonlinear energy characterizes a non-Gaussian process. Within this scope, digital bispectral analysis has enabled one to describe non-linear stationary response of flexible lines in the frequency domain, so that the complex coefficients of a quadratic model, in the frequency domain, can be estimated. The real and symmetrical matrix constructed from these coefficients has eigenvalues and eigenvectors useful to describe the characteristic function of the response from where the probability density function can be obtained by using a fast Fourier transform algorithm. The bases of the method presented here have already been treated, in a similar but pure algebraic method, to obtain the asymptotic probability function applicable to the response of non-linear systems in closed form.