Osteoarthritis is a degenerative joint disease that affects millions of people worldwide. The aims of this study were (1) to quantitatively characterise the boundary and surface features of wear particles present in t...
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Osteoarthritis is a degenerative joint disease that affects millions of people worldwide. The aims of this study were (1) to quantitatively characterise the boundary and surface features of wear particles present in the synovial fluid of patients, (2) to select key numerical parameters that describe distinctive particle features and enable osteoarthritis assessment and (3) to develop a model to assess osteoarthritis conditions using comprehensive wear debris information. Discriminant analysis was used to statistically group particles based on differences in their numerical parameters. The analysis methods agreed with the clinical osteoarthritis grades in 63%, 50% and 61% of particles for no osteoarthritis, mild osteoarthritis and severe osteoarthritis, respectively. This study has revealed particle features specific to different osteoarthritis grades and provided further understanding of the cartilage degradation process through wear particle analysis - the technique that has the potential to be developed as an objective and minimally invasive method for osteoarthritis diagnosis.
This study presents a fast-efficient error concealment method for recovering information related to shape. The proposed technique comprises block classification, edge direction interpolation and filtering interpolatio...
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This study presents a fast-efficient error concealment method for recovering information related to shape. The proposed technique comprises block classification, edge direction interpolation and filtering interpolation. Missing blocks are classified into four categories: transparent, opaque, edge and isolated blocks. Most of the computation is spent on edge blocks and isolated blocks to maximise the cost and performance tradeoff. For the recovery of edge blocks, the edge slope is computed by referring to the nearest available block, from which the missing shape is interpolated parallel to the edge. Isolated blocks are dealt with using a cascade filter to approximate the actual shape. Experimental results show that the proposed method provides better cost performance in the restoration of shapes than that afforded by comparable algorithms, both in numerical parameters and the resulting shapes. The processing speed is approximately two to three times faster than previous methods and low computational load makes the proposed technique applicable to real-time MPEG-4 systems.
Significant springback occurs after tube rotary-draw-bending （RDB）, especially for a high-strength Ti-3A1-2.5V tube （HSTT） due to its high ratio of yield strength to Young＇s modulus. The combination scheme of exp...
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Significant springback occurs after tube rotary-draw-bending （RDB）, especially for a high-strength Ti-3A1-2.5V tube （HSTT） due to its high ratio of yield strength to Young＇s modulus. The combination scheme of explicit and implicit is preferred to predict the springback. This simulation strategy includes several numerical parameters, such as element type, number of elements through thickness （NEL）, element size, etc. However, the influences of these parameters on spring- back prediction accuracy are not fully understood. Thus, taking the geometrical specification 9.525 mm × 0.508 mm ofa HSTT as the objective, the effects of numerical parameters on prediction accuracy and computation efficiency of springback simulation of HSTT RDB are investigated. The simulated springback results are compared with experimental ones. The main results are： （1） solid and continuum-shell elements predict the experimental results well; （2） for C3DSR elements, NEL of at least 3 is required to obtain reliable results and a relative error of 29% can occur as NEL is varied in the range of 1-3; （3） specifying damping factor typically works well in Abaqus/Emplicit simulation of springback and the springback results are sensitive to the magnitude of damping factor. In addition, the explanations of the effect rules are given and a guideline is added.
We examine the connection between the variational multiscale (VMS) formulation and the variational counterpart of the Germano identity (VGI). We note that they are both based on the same multiscale construct of a give...
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We examine the connection between the variational multiscale (VMS) formulation and the variational counterpart of the Germano identity (VGI). We note that they are both based on the same multiscale construct of a given coarse scale space and a user-defined projector into this space, which defines the desired numerical solution. By utilizing this connection we demonstrate how the VGI may be used to determine parameters for the models derived using the VMS formulation. Copyright (C) 2010 John Wiley & Sons, Ltd.
The validity of three-dimensional discontinuous deformation analysis(3-D DDA) is examined by comparing its solution for dynamic block displacement with an analytical. Displacement of a single block on inclined planes ...
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The validity of three-dimensional discontinuous deformation analysis(3-D DDA) is examined by comparing its solution for dynamic block displacement with an analytical. Displacement of a single block on inclined planes subjected to dynamic loadings is studied for analytical solutions derived with respect to the frictional resistance offered by the planes. 3-D DDA predicts accurately the analytical displacements, and the results were found sensitive to the maximum displacement ratio, and the size of the time step, which are defined by the user. Best results were achieved when the actual displacements were approximately equal to the assumed maximum displacements per time step. Furthermore, edge-to-edge contact constraints have been improved by using the augmented Lagrangian method instead of the penalty method. Using the augmented Lagrangian method to enforce contact restraints retains the simplicity of the penalty method, and reduces its disadvantages. The new formulation of edge-to-edge contact using the augmented Lagrangian method is implemented in 3-D DDA and has been programmed in VC++. Finally two illustrative examples are presented for demonstrating this new approach. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.
numerical studies play a major role in the understanding and prediction of plasticity induced crack closure (PICC). However, the available numerical models can be considered simplifications of reality as they consider...
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numerical studies play a major role in the understanding and prediction of plasticity induced crack closure (PICC). However, the available numerical models can be considered simplifications of reality as they consider discrete crack propagations, relatively high fatigue crack growth rates (FCGR), sharp cracks, and propagation occurring at well-defined loads. Besides, there are a great number of numerical and physical parameters affecting the predictions of PICC. The aim of this paper is to discuss the numerical study of PICC. The numerical parameters affecting the accuracy of the numerical simulations, and the dependent parameters used to characterise the plastic wake and the closure level, are identified. The influence of the radial size of crack front elements and crack propagation is analysed. Ail extrapolation model is proposed, with excellent results. An intrinsic uncertainty is associated with the number of load cycles between crack increments and the definition of crack closure level. Finally, the effect of the stress ratio (R) oil crack closure level is analysed. (c) 2007 Elsevier Ltd. All rights reserved.
The variational Germano identity (VGI) is a condition that must be satisfied if the variational approximation to a partial differential equation is optimal in a user-defined metric. The VGI is useful as it can be util...
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The variational Germano identity (VGI) is a condition that must be satisfied if the variational approximation to a partial differential equation is optimal in a user-defined metric. The VGI is useful as it can be utilized to dynamically determine unknown parameters in the variational approximation without any a-priori knowledge of the exact solution. With these values it yields solutions that are close to the optimal solution. In this manuscript we examine the relation between the definition of an optimal solution and the parameters computed using the VGI. We demonstrate that this relation is made precise by a so-called truncated restriction operator that appears in the final expression for the model parameters and is sensitive to the criterion used for selecting the optimal solution. In order to facilitate the use of the VGI for determining model parameters, we derive explicit expressions for this operator when three distinct approaches are used for defining the optimal solution. Through numerical examples that make use of these expressions, we confirm that the VGI does indeed yield model parameters and numerical solutions that are consistent with the choice of the optimal solution. We also observe that the numerical solutions obtained using the VGI are close to the best numerical solution that can be obtained from a given variational approximation, indicating that it yields nearly optimal values for the parameters. (C) 2008 Elsevier B.V. All rights reserved.
Osteoarthritis (OA), the most prevalent form of arthritis, is a degenerative joint disease affecting millions of people worldwide. The overall aims of the project were: (i) to gain a better understanding of the wear p...
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Osteoarthritis (OA), the most prevalent form of arthritis, is a degenerative joint disease affecting millions of people worldwide. The overall aims of the project were: (i) to gain a better understanding of the wear processes occurring in human joints during a walking process, particularly in relation to osteoarthritic degeneration and (ii) to develop effective, minimally intrusive tools to assess OA activity and progression. Based on existing developments, this project, using three-dimensional numerical descriptors, further investigated correlation between the cartilage surface subjected and particle generated in the walking process. This is a critical step in developing and utilizing wear particle analysis techniques for OA assessment. With further study and development along with this study, it is possible to develop better diagnostic and prognostic procedures for clinic OA assessment using wear debris analysis techniques. (c) 2006 Elsevier B.V. All rights reserved.
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