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Analysis Problems (analysis + problem)

Distribution by Scientific Domains

Engineering	77%

Kinds of Analysis Problems

limit analysis problem

Selected Abstracts

Solving limit analysis problems: an interior-point method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2005
F. Pastor
Abstract This paper exposes an interior-point method used to solve convex programming problems raised by limit analysis in mechanics. First we explain the main features of this method, describing in particular its typical iteration. Secondly, we show and study the results of its application to a concrete limit analysis problem, for a large range of sizes, and we compare them for validation with existing results and with those of linearized versions of the problem. As one of the objectives of the work, another classical problem is analysed for a Gurson material, to which linearization or conic programming does not apply. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A practical large-strain solid finite element for sheet forming

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2005
Jue Wang
Abstract An alternative approach for developing practical large-strain finite elements has been introduced and used to create a three-dimensional solid element that exhibits no locking or hourglassing, but which is more easily and reliably derived and implemented than typical reduced-integration schemes with hourglassing control. Typical large-strain elements for forming applications rely on reduced integration to remove locking modes that occur with the coarse meshes that are necessary for practical use. This procedure introduces spurious zero-energy deformation modes that lead to hourglassing, which in turn is controlled by complex implementations that involve lengthy derivations, knowledge of the material model, and/or undetermined parameters. Thus, for a new material or new computer program, implementation of such elements is a daunting task. Wang,Wagoner-3-dimensions (WW3D), a mixed, hexahedral, three-dimensional solid element, was derived from the standard linear brick element by ignoring the strain components corresponding to locking modes while maintaining full integration (8 Gauss points). Thus, WW3D is easily implemented for any material law, with little chance of programming error, starting from programming for a readily available linear brick element. Surprisingly, this approach and resulting element perform similarly or better than standard solid elements in a series of numerical tests appearing in the literature. The element was also tested successfully for an applied sheet-forming analysis problem. Many variations on the scheme are also possible for deriving special-purpose elements. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A general non-linear optimization algorithm for lower bound limit analysis

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2003
Kristian Krabbenhoft
Abstract The non-linear programming problem associated with the discrete lower bound limit analysis problem is treated by means of an algorithm where the need to linearize the yield criteria is avoided. The algorithm is an interior point method and is completely general in the sense that no particular finite element discretization or yield criterion is required. As with interior point methods for linear programming the number of iterations is affected only little by the problem size. Some practical implementation issues are discussed with reference to the special structure of the common lower bound load optimization problem, and finally the efficiency and accuracy of the method is demonstrated by means of examples of plate and slab structures obeying different non-linear yield criteria. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Nonlinear regression checking via local polynomial smoothing with applications to thermogravimetric analysis

JOURNAL OF CHEMOMETRICS, Issue 6 2009
Ricardo Cao
Abstract A goodness-of-fit test statistic for nonlinear regression models based on local polynomial estimation is proposed in this paper. The criterion used to construct the test is the distance between the parametric fit and the nonparametric regression estimation. The good performance of the test is shown via a simulation study. The method is applied to check a logistic mixture regression model for real data coming from a thermal analysis problem. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Using pulsed gradient spin echo NMR for chemical mixture analysis: How to obtain optimum results

CONCEPTS IN MAGNETIC RESONANCE, Issue 4 2002
Brian Antalek
Abstract Pulsed gradient spin echo NMR is a powerful technique for measuring diffusion coefficients. When coupled with appropriate data processing schemes, the technique becomes an exceptionally valuable tool for mixture analysis, the separation of which is based on the molecular size. Extremely fine differentiation may be possible in the diffusion dimension but only with high-quality data. For fully resolved resonances, components with diffusion coefficients that differ by less than 2% may be distinguished in mixtures. For highly overlapped resonances, the resolved spectra of pure components with diffusion coefficients that differ by less than 30% may be obtained. In order to achieve the best possible data quality one must be aware of the primary sources of artifacts and incorporate the necessary means to alleviate them. The origin of these artifacts are described, along with the methods necessary to observe them. Practical solutions are presented. Examples are shown that demonstrate the effects of the artifacts on the acquired data set. Many mixture analysis problems may be addressed with conventional high resolution pulsed field gradient probe technology delivering less than 0.5 T m,1 (50 G cm,1). © 2002 Wiley Periodicals, Inc. Concepts Magn Reson 14: 225,258, 2002. [source]

Decision-making method using a visual approach for cluster analysis problems; indicative classification algorithms and grouping scope

EXPERT SYSTEMS, Issue 3 2007
Ran M. Bittmann
Abstract: Currently, classifying samples into a fixed number of clusters (i.e. supervised cluster analysis) as well as unsupervised cluster analysis are limited in their ability to support ,cross-algorithms' analysis. It is well known that each cluster analysis algorithm yields different results (i.e. a different classification); even running the same algorithm with two different similarity measures commonly yields different results. Researchers usually choose the preferred algorithm and similarity measure according to analysis objectives and data set features, but they have neither a formal method nor tool that supports comparisons and evaluations of the different classifications that result from the diverse algorithms. Current research development and prototype decisions support a methodology based upon formal quantitative measures and a visual approach, enabling presentation, comparison and evaluation of multiple classification suggestions resulting from diverse algorithms. This methodology and tool were used in two basic scenarios: (I) a classification problem in which a ,true result' is known, using the Fisher iris data set; (II) a classification problem in which there is no ,true result' to compare with. In this case, we used a small data set from a user profile study (a study that tries to relate users to a set of stereotypes based on sociological aspects and interests). In each scenario, ten diverse algorithms were executed. The suggested methodology and decision support system produced a cross-algorithms presentation; all ten resultant classifications are presented together in a ,Tetris-like' format. Each column represents a specific classification algorithm, each line represents a specific sample, and formal quantitative measures analyse the ,Tetris blocks', arranging them according to their best structures, i.e. best classification. [source]

Solving limit analysis problems: an interior-point method

Topology optimization for stationary fluid,structure interaction problems using a new monolithic formulation

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2010
Gil Ho Yoon
Abstract This paper outlines a new procedure for topology optimization in the steady-state fluid,structure interaction (FSI) problem. A review of current topology optimization methods highlights the difficulties in alternating between the two distinct sets of governing equations for fluid and structure dynamics (hereafter, the fluid and structural equations, respectively) and in imposing coupling boundary conditions between the separated fluid and solid domains. To overcome these difficulties, we propose an alternative monolithic procedure employing a unified domain rather than separated domains, which is not computationally efficient. In the proposed analysis procedure, the spatial differential operator of the fluid and structural equations for a deformed configuration is transformed into that for an undeformed configuration with the help of the deformation gradient tensor. For the coupling boundary conditions, the divergence of the pressure and the Darcy damping force are inserted into the solid and fluid equations, respectively. The proposed method is validated in several benchmark analysis problems. Topology optimization in the FSI problem is then made possible by interpolating Young's modulus, the fluid pressure of the modified solid equation, and the inverse permeability from the damping force with respect to the design variables. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Convergence analysis and validation of sequential limit analysis of plane-strain problems of the von Mises model with non-linear isotropic hardening

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2005
S.-Y. Leu
Abstract The paper presents sequential limit analysis of plane-strain problems of the von Mises model with non-linear isotropic hardening by using a general algorithm. The general algorithm is a combined smoothing and successive approximation (CSSA) method. In the paper, emphasis is placed on its convergence analysis and validation applied to sequential limit analysis involving materials with isotropic hardening. By sequential limit analysis, the paper treats deforming problems as a sequence of limit analysis problems stated in the upper bound formulation. Especially, the CSSA algorithm was proved to be unconditionally convergent by utilizing the Cauchy,Schwarz inequality. Finally, rigorous validation was conducted by numerical and analytical studies of a thick-walled cylinder under pressure. It is found that the computed limit loads are rigorous upper bounds and agree very well with the analytical solutions. Copyright © 2005 John Wiley & Sons, Ltd. [source]