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Presented Procedure (presented + procedure)

Distribution by Scientific Domains
Engineering42%

Selected Abstracts

A computerized procedure for long-life fatigue assessment under complex multiaxial loading

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2001
B. Li
A computerized procedure is presented and evaluated for application examples of long-life fatigue analyses of metallic materials under complex multiaxial loading. The method is based on the stress invariants and uses the minimum circumscribed ellipse approach for evaluating the effective shear stress amplitude under complex multiaxial loading. The applicability of the procedure for handling non-proportional loading is examined through typical examples such as combined normal/shear stresses and combined bi-axial normal stresses with complex stress time histories. The effects of phase shift angles, frequency ratios and waveforms on fatigue endurance were re-analysed and compared with available experimental results from the literature. The comparison shows that the presented procedure based on stress invariants is a potential conservative engineering approach, very suitable for fast fatigue evaluation in the integrated computer aided fatigue design. [source]

A back-tracking procedure for optimization of simplex meshes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2005
Joaquim B. Cavalcante-Neto
Abstract This work presents a back-tracking procedure for the optimization of meshes. It can be applied to all ill-shaped elements in a mesh in order to improve quality in mesh optimization. Basically, the original mesh is reconstructed in regions around the ill-shaped elements by means of a set of deletion and reconstruction operations based on visibility tests. The back-tracking procedure fixes problems related to the quality of generated meshes in general and can be applied in two or three dimensions. The procedure works by deleting elements ranked below a predefined shape quality measure. It is important to mention that, although the presented procedure was devised for advancing-front algorithms, it can also be used in meshes generated by different approaches, such as Delaunay and others, requiring no modification. The proposed procedure is applicable to simplex elements (triangles and tetrahedra), although ideally it could be extended to other types of elements. Examples of improved meshes using the back-tracking procedure are presented, in which the quality of these meshes is assessed in order to validate the procedure proposed in this work. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Development of the DYNA3D simulation code with automated fracture procedure for brick elements

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2003
Ala Tabiei
Abstract Numerical simulation of cracked structures is an important aspect in structural safety assessment. In recent years, there has been an increasing rate of development of numerical codes for modelling fracture procedure. The subject of this investigation is implementing automated fracture models in the DYNA3D non-linear explicit finite element code to simulate pseudo 3D crack growth procedure. The implemented models have the capabilities of simulating automatic crack propagation without user intervention. The implementation is carried on solid elements. The methodology of implementing fracture models is described. An element deletion-and-replacement remeshing procedure is proposed for updating the explicit geometric description of evolving cracks. Fracture parameters such as stress intensity factors, energy release rates and crack tip opening angle are evaluated. The maximum circumferential stress criterion is used to predict the direction of crack advancement. Seven crack problems are presented to verify the effectiveness of the methodology. Mesh sensitivity and loading rate effects are studied in the validation of the presented procedure. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Coherent superposition of resonance wave function in terms of weighted orthogonalized natural localized configurations

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2008
A. H. Pakiari
Abstract In this research, the projection technique has been applied in order to decompose the electronic wave function into its weighted orthogonalized resonance components. These components have been constructed by determinants whose orbitals are selected among natural bond orbitals. However, the procedure is general and any other localized orbitals can be used as well. Both , and , delocalize systems have been considered in order to check the reliability of the calculated resonance weights. For ,-systems, the presented procedure could predict significant decrease of weight of certain resonance structures when the molecular planarity was destroyed. Water cyclic clusters were also tested and the results confirmed the existence of strong ,-delocalization in the clusters. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Profile-based push models in manpower planning

APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 1 2008
Marie-Anne Guerry
Abstract A methodology is presented to deal with heterogeneity due to observable variables in modeling personnel systems. For a manpower system, a model based on personnel profiles is introduced. The proposed algorithm concerns an analysis of the evolution of personnel profiles under time-discrete Markov assumptions. In this way, based on an historical personnel database, the estimation of transition probabilities of profiles as well as the computation of forecasts on the evolution of the manpower system can be found. Based on the presented procedure, a policy supporting software package has been developed for the Belgian Federal Government (research project financed by Federaal Wetenschapsbeleid). Copyright © 2007 John Wiley & Sons, Ltd. [source]

A robust method for the joint estimation of yield coefficients and kinetic parameters in bioprocess models

BIOTECHNOLOGY PROGRESS, Issue 3 2009
V. Vastemans
Abstract Bioprocess model structures that require nonlinear parameter estimation, thus initialization values, are often subject to poor identification performances because of the uncertainty on those initialization values. Under some conditions on the model structure, it is possible to partially circumvent this problem by an appropriate decoupling of the linear part of the model from the nonlinear part of it. This article provides a procedure to be followed when these structural conditions are not satisfied. An original method for decoupling two sets of parameters, namely, kinetic parameters from maximum growth, production, decay rates, and yield coefficients, is presented. It exhibits the advantage of requiring only initialization of the first subset of parameters. In comparison with a classical nonlinear estimation procedure, in which all the parameters are freed, results show enhanced robustness of model identification with regard to parameter initialization errors. This is illustrated by means of three simulation case studies: a fed-batch Human Embryo Kidney cell cultivation process using a macroscopic reaction scheme description, a process of cyclodextrin-glucanotransferase production by Bacillus circulans, and a process of simultaneous starch saccharification and glucose fermentation to lactic acid by Lactobacillus delbrückii, both based on a Luedeking-Piret model structure. Additionally, perspectives of the presented procedure in the context of systematic bioprocess modeling are promising. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]

Optimal design and optimal control of structures undergoing finite rotations and elastic deformations

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2004
A. Ibrahimbegovic
Abstract In this work, we deal with the optimal design and optimal control of structures undergoing large rotations and large elastic deformations. In other words, we show how to find the corresponding initial configuration through optimal design or the corresponding set of multiple load parameters through optimal control, in order to recover a desired deformed configuration or some desirable features of the deformed configuration as specified more precisely by the objective or cost function. The model problem chosen to illustrate the proposed optimal design and optimal control methodologies is the one of geometrically exact beam. First, we present a non-standard formulation of the optimal design and optimal control problems, relying on the method of Lagrange multipliers in order to make the mechanics state variables independent from either design or control variables and thus provide the most general basis for developing the best possible solution procedure. Two different solution procedures are then explored, one based on the diffuse approximation of response function and gradient method and the other one based on genetic algorithm. A number of numerical examples are given in order to illustrate both the advantages and potential drawbacks of each of the presented procedures. Copyright © 2004 John Wiley & Sons, Ltd. [source]