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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.

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.

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 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
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.

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