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Muller A.,French Institute for Research in Computer Science and Automation | Pontonnier C.,Ecoles de Saint-Cyr Coetquidan | Dumont G.,French Institute for Research in Computer Science and Automation
Multibody System Dynamics | Year: 2017

In biomechanics, calibration of body segment inertial parameters (BSIP) is crucial to take into account subject morphological specificities. To avoid strenuous protocols, identification methods based on rigid body dynamics laws have been proposed. Thanks to a motion capture system and force platforms, these methods optimize BSIP by minimizing errors in the equations of motion. These errors can be defined as the dynamic residuals reflecting inaccuracies arising from estimated BSIP, as well as from kinematics and force plate measurements. The current study aims at evaluating the part of uncertainty on the dynamic residuals directly related to kinematics and force plate measurements. To answer this question, we captured the movements of 10 participants performing a standardized motion. We then applied a Monte Carlo-based approach to introduce variations in the kinematics and force plate measurements, and evaluated the reconstructed difference on the dynamic residuals. Results show that, first, the BSIP evaluation using a regression method seemed to be an acceptable estimate for the studied subjects. Second, the part of uncertainty in the dynamic residuals was significantly higher than the dynamic residuals obtained. In conclusion, a subject-specific calibration of the BSIP based on dynamic residuals, for this model and protocol, seems irrelevant and prone to overfitting of BSIP. © 2017 Springer Science+Business Media Dordrecht

Cadou J.M.,University of Southern Brittany | Guevel Y.,University of Southern Brittany | Girault G.,University of Southern Brittany | Girault G.,Ecoles de Saint-Cyr Coetquidan
Fluid Dynamics Research | Year: 2012

This paper deals with the numerical study of bifurcations in the two-dimensional (2D) lid-driven cavity (LDC). Two specific geometries are considered. The first geometry is the two-sided non-facing (2SNF) cavity: the velocity is imposed on the upper and the left side of the cavity. The second geometry is the four-sided (4S) cavity where all the sides have a prescribed motion. For the first time, the linear stability analysis is performed by coupling two specific algorithms. The first one is dedicated to the computation of the stationary bifurcations and the bifurcated branches. Then, a second algorithm is dedicated to the computation of Hopf bifurcations. In this study, for both problems, it is shown that the flow becomes asymmetric via a stationary bifurcation. The critical Reynolds numbers are close to 1070 and 130, respectively, for the 2SNF and the 4S cavity. Following the stationary bifurcated branches, supplementary results concerning the stability are found. Firstly, for both examples, a second stationary bifurcation appears on the unstable solution, for a Reynolds number equal to 1890 and 360, respectively, for the 2NSF and the 4S cavity. Secondly, a second stationary bifurcation is found on the stable solutions of the 4S LDC for a critical Reynolds number close to 860. Nevertheless, no Hopf bifurcation has been found on this stable bifurcated branch for Reynolds numbers between 130 and 1000. Concerning the 2SNF LDC, Hopf bifurcation points have been determined on these stable bifurcated solutions. The first bifurcation occurs for a Reynolds number close to 3000 and a Strouhal number equal to 0.47. © 2012 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.

Brezillon A.,University of Southern Brittany | Girault G.,Ecoles de Saint-Cyr Coetquidan | Cadou J.M.,University of Southern Brittany
Computers and Fluids | Year: 2010

This paper deals with the computation of Hopf bifurcation points in fluid mechanics. This computation is done by coupling a bifurcation indicator proposed recently (Cadou et al., 2006) [1] and a direct method (Jackson, 1987; Jepson, 1981) [2,3] which consists in solving an augmented system whose solutions are Hopf bifurcation points. The bifurcation indicator gives initial critical values (Reynolds number, Strouhal frequency) for the direct method iterations. Some classical numerical examples from fluid mechanics, in two dimensions, are studied to demonstrate the efficiency and the reliability of such an algorithm. © 2010 Elsevier Ltd.

De Boisboissel G.,Ecoles de Saint-Cyr Coetquidan
ICMT 2015 - International Conference on Military Technologies 2015 | Year: 2015

This paper is a prospective view on how Lethal Autonomous Weapon Systems (LAWS) could be used by Armed Forces. It addresses the operational benefits and ethical issues in the use of such systems. Several scenarios are also presented on the future deployment of such systems on a battlefield. © 2015 University of Defence.

Girault G.,Ecoles de Saint-Cyr Coetquidan | Girault G.,University of Southern Brittany | Guevel Y.,University of Southern Brittany | Cadou J.M.,University of Southern Brittany
International Journal for Numerical Methods in Fluids | Year: 2012

Recently, a numerical method was proposed to compute a Hopf bifurcation point in fluid mechanics. This numerical method associates a bifurcation indicator and a Newton method. The former gives initial guesses to the iterative method. These initial values are the minima of the bifurcation indicator. However, sometimes, these minima do not lead to the convergence of the Newton method. Moreover, as only a single initial guess is obtained for each computation of the indicator, the computational time to obtain a Hopf bifurcation point can be quite long. The present algorithm is an enhancement of the previous one. It consists in automatically computing several initial guesses for each indicator curve. The majority of these initial values leads to the convergence of the Newton method. This method is evaluated through the problem of the lid-driven cavity with several aspect ratios in the framework of the finite element analysis of the 2D Navier-Stokes equations. The results prove the efficiency and the robustness of the proposed algorithm. © 2011 John Wiley & Sons, Ltd.

Bartheye O.,Ecoles de Saint-Cyr Coetquidan
2nd International Conference on Communications Computing and Control Applications, CCCA 2012 | Year: 2012

In this paper, we try to precise what should be relevant algebraic, topological and axiomatic properties of self-orientation systems. Thanks to a formal apparatus one expects to measure the complexity of self-orientation computation process, to gain accuracy and ultimately to find new algorithms as corollaries of this modeling attempt. The main issue can be depicted as follows : assume that candidate self-orientations form a set S or a vector space V or more generally an algebraic structure A (e.g. a partially ordered set P, a monoid M, a semi-group S,...); if the computation of a self-orientation refers to a motivated choice among possible orientations inside an algebraic structure, one should be able in this structure to separate 'good' and 'bad' self-orientations. That is, consistency is required and as such needs to be defined. Take a cognitive entity e; a 'good' valuation is called a e-model and is noted e and a 'bad' valuation is called e-counter-model and is noted e. Therefore, consistent self-orientations can be called formal actions provided that the algebraic structure must agree with the separable property which in terms of polynomial algebra corresponds to the reducible property. This paper try to connect algebraic and geometrical representations of actions and axiomatic consistent representations using deductive systems and Hopf Algebras. © 2012 IEEE.

Guevel Y.,University of Southern Brittany | Girault G.,Ecoles de Saint-Cyr Coetquidan | Cadou J.M.,University of Southern Brittany
Computers and Fluids | Year: 2014

This work deals with the computation of steady bifurcation points in 2D incompressible Newtonian fluid flows. The problem is modeled with the Navier-Stokes equations with an evolving geometric parameter. The aim of the present study is to propose a reliable and efficient numerical method for parametric steady bifurcation calculations. The numerical algorithm is based on the coupling of a continuation method with a homotopy technique. The continuation method lies on the asymptotic numerical method with Padé approximants for an initial linear stability analysis with an initial geometric configuration. The homotopy technique completes the calculation with the computation of critical Reynolds numbers for different discrete values of the geometric parameter. Two classical numerical problems are approached. The first one is the flow in sudden expansion. The geometric parameter is the height of the expansion inlet. The second problem is the flow in a divergent/convergent channel. In this case, the geometric parameter is the length of the channel. Comparisons of results with those obtained from the literature are performed, showing the efficiency of the proposed algorithm. The aim of this study is to determine the critical Reynolds numbers of the flow using few computations for each geometric parameter. © 2014 Elsevier Ltd.

Jacopin E.,Ecoles de Saint-Cyr Coetquidan
Proceedings of the 10th AAAI Conference on Artificial Intelligence and Interactive Digital Entertainment, AIIDE 2014 | Year: 2014

We present a general framework for Game Artificial Intelligence Planning (AIP) Analytics. The objective is to provide analytic tools to study and improve AIP components and their use in video-games. Extraction and formatting of AI data is first described and discussed. Then AIP metrics are listed with examples and illustrations from three popular First-Person Shooters: F.E.A.R. (2005), Zone 3 (2011) and Transformers 3: Fall of Cybertron (2012). The patterns we discovered in our study clearly show the AIP component is called more often by the game over the years. Copyright © 2014, Association for the Advancement of Artificial Intelligence ( All rights reserved.

Maheo L.,Arts et Metiers ParisTech | Maheo L.,Ecoles de Saint-Cyr Coetquidan | Grolleau V.,University of Southern Brittany | Rio G.,University of Southern Brittany
Computational Mechanics | Year: 2013

The use of Finite Element and Finite Difference methods of spatial and temporal discretization for solving structural dynamics problems gives rise to purely numerical errors. Among the many numerical methods used to damp out the spurious oscillations occurring in the high frequency domain, it is proposed here to analyse and compare the Bulk Viscosity method, which involves calculating the stresses, and a method recently presented by Tchamwa and Wielgosz, which is based on an explicit time integration algorithm. The 1-D study and the 2-D axisymmetric study on a bar subjected to compression and impact loads presented here show that the former method is insensitive to meshing irregularities, whereas the latter method is not. The Bulk Viscosity method was found to be sensitive, however, to the behavior of the material, contrary to the Tchamwa-Wielgosz method. Since comparisons of this kind are rather complex, a specific method of analysis was developed. © 2012 Springer-Verlag.

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