1,256 research outputs found
Finite element analysis of fretting crack propagation
In this work, the finite elements method (FEM) is used to analyse the growth
of fretting cracks. FEM can be favourably used to extract the stress intensity
factors in mixed mode, a typical situation for cracks growing in the vicinity
of a fretting contact. The present study is limited to straight cracks which is
a simple system chosen to develop and validate the FEM analysis. The FEM model
is tested and validated against popular weight functions for straight cracks
perpendicular to the surface. The model is then used to study fretting crack
growth and understand the effect of key parameters such as the crack angle and
the friction between crack faces. Predictions achieved by this analysis match
the essential features of former experimental fretting results, in particular
the average crack arrest length can be predicted accurately
Subspace Instability Monitoring for Linear Periodically Time-Varying Systems
Most subspace-based methods enabling instability monitoring are restricted to the linear time-invariant (LTI) systems. In this paper, a new subspace method of instability monitoring is proposed for the linear periodically time-varying (LPTV) case. For some LPTV systems, the system transition matrices may depend on some parameter and are also periodic in time. A certain range of values for the parameter leads to an unstable transition matrix. Early warning should be given when the system gets close to that region, taking into account the time variation of the system. Using the theory of Floquet, some symptom parameter of stability- or residual- is defined. Then, the parameter variation is tracked by performing a set of parallel cumulative sum (CUSUM) tests. Finally, the method is tested on a simulated model of a helicopter with hinged blades, for monitoring the ground resonance phenomenon
Real-Time Predictive Modeling and Robust Avoidance of Pedestrians with Uncertain, Changing Intentions
To plan safe trajectories in urban environments, autonomous vehicles must be
able to quickly assess the future intentions of dynamic agents. Pedestrians are
particularly challenging to model, as their motion patterns are often uncertain
and/or unknown a priori. This paper presents a novel changepoint detection and
clustering algorithm that, when coupled with offline unsupervised learning of a
Gaussian process mixture model (DPGP), enables quick detection of changes in
intent and online learning of motion patterns not seen in prior training data.
The resulting long-term movement predictions demonstrate improved accuracy
relative to offline learning alone, in terms of both intent and trajectory
prediction. By embedding these predictions within a chance-constrained motion
planner, trajectories which are probabilistically safe to pedestrian motions
can be identified in real-time. Hardware experiments demonstrate that this
approach can accurately predict pedestrian motion patterns from onboard
sensor/perception data and facilitate robust navigation within a dynamic
environment.Comment: Submitted to 2014 International Workshop on the Algorithmic
Foundations of Robotic
Robust curvature extrema detection based on new numerical derivation
International audienceExtrema of curvature are useful key points for different image analysis tasks. Indeed, polygonal approximation or arc decomposition methods used often these points to initialize or to improve their algorithms. Several shape-based image retrieval methods focus also their descriptors on key points. This paper is focused on the detection of extrema of curvature points for a raster-to-vector-conversion framework. We propose an original adaptation of an approach used into nonlinear control for fault-diagnosis and fault-tolerant control based on algebraic derivation and which is robust to noise. The experimental results are promising and show the robustness of the approach when the contours are bathed into a high level speckled noise
Existence and uniqueness for dynamical unilateral contact with coulomb friction : a model problem.
International audienceA simple dynamical problem involving unilateral contact and dry friction of Coulomb type is considered as an archetype. We are concerned with the existence and uniqueness of solutions of the system with Cauchy data. In the frictionless case, it is known [Schatzman, Nonlinear Anal. Theory, Methods Appl.2 (1978) 355–373] that pathologies of non-uniqueness can exist, even if all the data are of class . However, uniqueness is recovered provided that the data are analytic [Ballard]. Under this analyticity hypothesis, we prove the existence and uniqueness of solutions for the dynamical problem with unilateral contact and Coulomb friction, extending [Ballard] to the case where Coulomb friction is added to unilateral contact
A Methodology for the Diagnostic of Aircraft Engine Based on Indicators Aggregation
Aircraft engine manufacturers collect large amount of engine related data
during flights. These data are used to detect anomalies in the engines in order
to help companies optimize their maintenance costs. This article introduces and
studies a generic methodology that allows one to build automatic early signs of
anomaly detection in a way that is understandable by human operators who make
the final maintenance decision. The main idea of the method is to generate a
very large number of binary indicators based on parametric anomaly scores
designed by experts, complemented by simple aggregations of those scores. The
best indicators are selected via a classical forward scheme, leading to a much
reduced number of indicators that are tuned to a data set. We illustrate the
interest of the method on simulated data which contain realistic early signs of
anomalies.Comment: Proceedings of the 14th Industrial Conference, ICDM 2014, St.
Petersburg : Russian Federation (2014
Model changes in signal processing: state of the art and results of GRECO SARTA
The purpose of this paper is to outline the interest of the so-called "model changes" approach for solving Signal Processing
problems. We describe what we think to be the state of the art in this field together with the remaining open problems, and we
present the results of the CNRS GRECO SARTA working group on this topic.
After an introduction to the change detection and estimation problem, we present three typical examples of situations in which
change detection techniques can be used . We then give the state of the art together with the main existing references and we
list the open problems . Finally, we describe the contribution of the GRECO SARTA in this area and conclude with some future
research works.Le but de ce bref article est de mettre en évidence l'intérêt de l'approche dite « ruptures de modèles » en Traitement du
Signal, de présenter ce que l'auteur considère comme étant l'état de l'art ainsi que les problèmes ouverts qui demeurent, et
d'indiquer le bilan du GRECO SARTA pour ce thème .
Après une introduction au problème, on présente trois exemples typiques de situations qui peuvent être abordées à l'aide de
techniques de ruptures de modèles . On précise ensuite l'état de l'art avec les principales références existantes, et on indique
les problèmes ouverts . Enfin, on décrit l'apport du GRECO SARTA et en conclusion on propose des perspectives
Analyse de textes sur les femmes d'origine maghrébine de France liés au féminisme émancipateur
Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal
Fault detection and isolation on a noisy nonlinear circuit
In this paper fault detection and isolation (FDI) schemes are applied in the context of the surveillance of emerging faults in an electrical circuit. The FDI problem is studied on a noisy nonlinear circuit, where both abrupt and incipient faults in the voltage source are considered. A rigorous analysis of fault detectability precedes the application of the fault detection (FD) scheme; then, the fault isolation (FI) phase is accomplished with two alternative FI approaches, proposed as new extensions of that FD approach. Numerical simulations illustrate the applicability of the mentioned schemes
Aircraft engine fleet monitoring using Self-Organizing Maps and Edit Distance
International audienceAircraft engines are designed to be used during several tens of years. Ensuring a proper operation of engines over their lifetime is therefore an important and difficult task. The maintenance can be improved if efficient procedures for the understanding of data flows produced by sensors for monitoring purposes are implemented. This paper details such a procedure aiming at visualizing in a meaningful way successive data measured on aircraft engines and finding for every possible request sequence of data measurement similar behaviour already observed in the past which may help to anticipate failures. The core of the procedure is based on Self-Organizing Maps (SOM) which are used to visualize the evolution of the data measured on the engines. Rough measurements can not be directly used as inputs, because they are influenced by external conditions. A preprocessing procedure is set up to extract meaningful information and remove uninteresting variations due to change of environmental conditions. The proposed procedure contains four main modules to tackle these difficulties: environmental conditions normalization (ECN), change detection and adaptive signal modeling (CD), visualization with Self-Organizing Maps (SOM) and finally minimal Edit Distance search (SEARCH). The architecture of the procedure and of its modules is described in this paper and results on real data are also supplied
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