Ferreira A.,Prisme Institute |
Aphale S.S.,University of Aberdeen
IEEE Transactions on Systems, Man and Cybernetics Part C: Applications and Reviews | Year: 2011
In the current times, microelectromechanical systems and nanoelectromechanical systems form a major interdisciplinary area of research involving science, engineering, and technology. A lot of work has been reported in the area of modeling and control of these devices, with the aim of better understanding their behavior and improving their performance. This paper presents a review of the emerging advances in the modeling and control of these micro- and nanoscale devices and converges on the exciting research in on-chip control , with a mechatronics and controls perspective and concludes by projecting future trends. © 2010 IEEE.
Bouvet N.,French National Center for Scientific Research |
Chauveau C.,French National Center for Scientific Research |
Gokalp I.,French National Center for Scientific Research |
Halter F.,Prisme Institute
Proceedings of the Combustion Institute | Year: 2011
Syngas laminar flame speed measurements have been carried out at atmospheric pressure and ambient temperature using spherically expanding flames. Mixture compositions ranging from 5/95% to 50/50% H2/CO and equivalence ratios from 0.4 to 5.0 have been investigated. Both state-of-the-art linear and non-linear extrapolation methodologies have been tested and extracted laminar flame speeds have been compared to datasets available in the literature as well as computations using two leading kinetic mechanisms for syngas combustion. Syngas flame sensitivities to stretch have been characterized by extracting the corresponding Markstein lengths. In order to explain important disparities found for rich syngas flames among datasets of the literature, computations have been performed to quantify the possible extent of velocity reduction corresponding to small contents of iron pentacarbonyl. © 2010 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.
Mazellier N.,Imperial College London |
Mazellier N.,Prisme Institute |
Vassilicos J.C.,Imperial College London
Physics of Fluids | Year: 2010
We investigate experimentally wind tunnel turbulence generated by multiscale/fractal grids pertaining to the same class of low-blockage space-filling fractal square grids. These grids are not active but nevertheless produce very much higher turbulence intensities u′/U and Reynolds numbers Reλ than higher blockage regular grids. Our hot wire anemometry confirms the existence of a protracted production region where turbulence intensity grows followed by a decay region where it decreases, as first reported by Hurst and Vassilicos ["Scalings and decay of fractal-generated turbulence," Phys. Fluids19, 035103 (2007)]. We introduce the wake-interaction length scale x* and show that the peak of turbulence intensity demarcating these two regions along the centerline is positioned at about 0.5x*. The streamwise evolutions on the centerline of the streamwise mean flow and of various statistics of the streamwise fluctuating velocity all scale with x*. Mean flow and turbulence intensity profiles are inhomogeneous at streamwise distances from the fractal grid smaller than 0.5x*, but appear quite homogeneous beyond 0.5x*. The velocity fluctuations are highly non-Gaussian in the production region but approximately Gaussian in the decay region. Our results confirm the finding of Seoud and Vassilicos ["Dissipation and decay of fractal-generated turbulence," Phys. Fluids19, 105108 (2007)] that the ratio of the integral length-scale Lu to the Taylor microscale λ remains constant even though the Reynolds number Reλ decreases during turbulence decay in the region beyond 0.5x*. As a result, the scaling Lu/λ∼Reλ, which follows from the u′3/Lu scaling of the dissipation rate in boundary-free shear flows and in usual grid-generated turbulence, does not hold here. This extraordinary decoupling is consistent with a noncascading and instead self-preserving single-length scale type of decaying homogeneous turbulence proposed by George and Wang ["The exponential decay of homogeneous turbulence," Phys. Fluids21, 025108 (2009)], but we also show that Lu/λ is nevertheless an increasing function of the inlet Reynolds number Re0. Finally, we offer a detailed comparison of the main assumption and consequences of the George and Wang theory against our fractal-generated turbulence data. © 2010 American Institute of Physics.
Hambli R.,Prisme Institute
Bone | Year: 2013
Most micro-CT finite element modeling of human trabecular bone has focused on linear and non-linear analysis to evaluate bone failure properties. However, prediction of the apparent failure properties of trabecular bone specimens under compressive load, including the damage initiation and its progressive propagation until complete bone failure into consideration, is still lacking. In the present work, an isotropic micro-CT FE model at bone tissue level coupled to a damage law was developed in order to simulate the failure of human trabecular bone specimens under quasi-static compressive load and predict the apparent stress and strain. The element deletion technique was applied in order to simulate the progressive fracturing process of bone tissue. To prevent mesh-dependence that generally affects the damage propagation rate, regularization technique was applied in the current work. The model was validated with experimental results performed on twenty-three human trabecular specimens. In addition, a sensitivity analysis was performed to investigate the impact of the model factors' sensitivities on the predicted ultimate stress and strain of the trabecular specimens. It was found that the predicted failure properties agreed very well with the experimental ones. © 2013 Elsevier Inc.
Hambli R.,Prisme Institute
Journal of biomechanical engineering | Year: 2010
In this paper, a novel multiscale hierarchical model based on finite element analysis and neural network computation was developed to link mesoscopic and macroscopic scales to simulate the bone remodeling process. The finite element calculation is performed at the macroscopic level, and trained neural networks are employed as numerical devices for substituting the finite element computation needed for the mesoscale prediction. Based on a set of mesoscale simulations of representative volume elements of bones taken from different bone sites, a neural network is trained to approximate the responses at the meso level and transferred at the macro level.
Hambli R.,Prisme Institute
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2011
In this paper, a neural network model is developed to simulate the accumulation of apparent fatigue damage of 3D trabecular bone architecture at a given bone site during cyclic loading. The method is based on five steps: (i) performing suitable numerical experiments to simulate fatigue accumulation of a 3D micro-CT trabecular bone samples taken from proximal femur for different combinations of loading conditions; (ii) averaging the sample outputs in terms of apparent damage at whole specimen level based on local tissue damage; (iii) preparation of a proper set of corresponding input-output data to train the network to identify apparent damage evolution; (iv) training the neural network based on the results of step (iii); (v) application of the neural network as a tool to estimate rapidly the apparent damage evolution at a given bone site. The proposed NN model can be incorporated into finite element codes to perform fatigue damage simulation at continuum level including some morphological factors and some bone material properties. The proposed neural network based multiscale approach is the first model, to the author's knowledge, that incorporates both finite element analysis and neural network computation to rapidly simulate multilevel fatigue of bone. This is beneficial to develop enhanced finite element models to investigate the role of damage accumulation on bone damage repair during remodelling. © 2011 Elsevier Ltd.
Hambli R.,Prisme Institute
Medical and Biological Engineering and Computing | Year: 2013
In this paper, a simple and practical finite element (FE) model coupled to a quasi-brittle damage law to describe the initiation and progressive propagation of multiple cracks based on element deletion is developed to predict the complete force-displacement curve and the fracture pattern of a human proximal femur under quasi-static load. The motivation of this work was to propose a FE model for possible clinical use with a good compromise between complexity and capability of the simulation. The model considers a limited number of parameters that can predict proximal femur fracture in more adequate physical terms than criteria-based fracture models. Based on experimental results, different damage laws for cortical and trabecular bone are proposed to describe inelastic damage accumulation under excessive load. When the damage parameter reaches its critical value inside an element of the mesh, its stiffness matrix is set to zero, leading to the redistribution of the stress state in the vicinity of the damaged zone (crack initiation). Once a crack is initiated, the propagation direction is simulated by the propagation of the broken elements of the mesh. To illustrate the potential of the proposed approach, the left femur of a male (age 61) previously investigated by Keyak and Falkinstein  (Model B: male, age 61) was simulated till complete fracture under one-legged stance quasi-static load. The proposed finite element model leads to more physical results concerning the shape of the force-displacement curve (yielding and fracturing) and the profile of the fractured edge. © 2012 International Federation for Medical and Biological Engineering.
Hambli R.,Prisme Institute
International Journal for Numerical Methods in Biomedical Engineering | Year: 2011
In this paper, a novel multiscale algorithm to simulate accumulation of trabecular bone crack density and crack length at macroscopic scale during cyclic loading is developed. The method is based on finite element analysis and neural network computation to link mesoscopic (trabecular level) and macroscopic (whole femur) scales. The finite element calculation is performed at the macroscopic level and a trained neural network incorporated into the finite element code Abaqus is employed as a numerical device to perform the local mesoscopic computation. Based on a set of mesoscale simulations of representative volume elements obtained by digital image-based modeling technique using μ-CT and voxel finite element, a neural network is trained to approximate the local finite element responses. The input data for the artificial neural network are the applied stress, the stress orientation and the cycle frequency. The output data are the averaged crack density and crack length at a given site of the bone. © 2010 John Wiley & Sons, Ltd.
Hambli R.,Prisme Institute |
Rieger R.,Prisme Institute
Biomechanics and Modeling in Mechanobiology | Year: 2012
Developing mathematical models describing the bone transduction mechanisms, including mechanical and metabolic regulations, has a clear practical applications in bone tissue engineering. The current study attempts to develop a plausible physiologically based mathematical model to describe the mechanotransduction in bone by an osteocyte mediated by the calcium-parathyroid hormone regulation and incorporating the nitric oxide (NO) and prostaglandin E2 (PGE2) effects in early responses to mechanical stimulation. The inputs are mechanical stress and calcium concentration, and the output is a stimulus function corresponding to the stimulatory signal to osteoblasts. The focus will be on the development of the mechanotransduction model rather than investigating the bone remodeling process that is beyond the scope of this study. The different components of the model were based on both experimental and theoretical previously published results describing some observed physiological events in bone mechanotransduction. Current model is a dynamical system expressing the mechanotransduction response of a given osteocytewith zero explicit space dimensions, but with a dependent variable that records signal amplitude as a function of mechanical stress, some metabolic factors release, and time. We then investigated the model response in term of stimulus signal variation versus the model inputs. Despite the limitations of themodel, predicted and experimental results from literature have the same trends. © Springer-Verlag 2011.
Hambli R.,Prisme Institute
Finite Elements in Analysis and Design | Year: 2011
A human femur is composed of cortical and trabecular bone organized in a hierarchical way. In this paper, a multiscale procedure based on finite element simulation and neural network computation was developed to link mesoscopic and macroscopic scales to simulate trabecular bone adaptation process. The finite element calculation is performed at macroscopic level and trained neural networks are employed as numerical devices for substituting the finite element computation needed for the mesoscale prediction. Based on a set of mesoscale simulations of representative volume element of bone, a neural network is trained to approximate the responses. The input data for the artificial neural network are boundary conditions and the applied stress. The output data are some averaged bone properties. A macroscale constitutive model is obtained by homogenization of the mesoscale responses. The proposed approach is able to predict in rapid way some relevant outputs related to bone adaptation process such as trabecular bone density, elastic modulus and accumulation of apparent fatigue damage of 3D trabecular bone architecture at a given bone site. The proposed rapid multiscale method was able to predict final proximal femur trabecular bone adaption similar to the patterns observed in a human proximal femur. © 2011 Elsevier B.V.