HAL Portal UTC Université de Technologie de Compiègne
Not a member yet
11652 research outputs found
Sort by
An adaptive modeling method with a local choice of optimal displacement fields for finite element analysis of structures
No full textInternational audienceIn the standard finite element procedure, the user chooses himself which mechanical theory will be used for a given application. To this end, he relies on some rules acquired through experience or some theoretical consideration. But choosing an appropriate theory may be a difficult task when geometry, boundary conditions, loadings, and materials are complex. This paper aims to define an adaptive methodology to identify, in the context of linear static analysis, optimal finite element models from a theory choice point of view. A criterion is defined to choose, in each part of the structure, the relevant mechanical theory: solid, shell or beam. A solid mesh is defined for the whole structure while specific solid-shell or solid-beam approaches are used in shell or beam areas respectively. This avoids the construction of mid-surface or mid-axis geometries from solid ones, which is a complicated task, in particular for industrial applications. Kinematic relations between nodes are imposed to apply the displacement fields of shell or beam theories. This leads to a set of linear equations which are used for eliminating slave degrees of freedom. The methodology proposed can also be interpreted as a model size reduction method, compared to a complete solid approach. The effectiveness of this approach is demonstrated through two numerical examples, including academic cantilever structures and an industrial multilayered composite structure
Adaptive modeling methodology with a local choice of displacement field for finite element analysis - application to multilayered timber structures
No full textInternational audienceIn the standard finite element procedure, the user chooses himself which mechanical theory willbe used for a given application. To this end, he relies on some rules acquired through experience or sometheoretical consideration. But choosing an appropriate theory may be a difficult task when geometry, boundaryconditions, loadings, and materials are complex. This study aims to define an adaptive methodology to identify,in the context of linear static analysis, optimal finite element models from a theory choice point of view. Acriterion is defined to choose, in each part of the structure, the relevant mechanical theory: solid, shell or beam.A solid mesh is defined for the whole structure while specific solid-shell or solid-beam approaches are used inshell or beam areas respectively. This avoids the construction of mid-surface or mid-axis geometries from solidones, which is a complicated task, in particular for industrial applications. Kinematic relations between nodesare imposed to apply the displacement fields of shell or beam theories. This leads to a set of linear equationswhich are used for eliminating slave degrees of freedom. The methodology proposed can also be interpreted asa model size reduction method, compared to a complete solid approach. The effectiveness of this approach isdemonstrated through two numerical examples, including academic cantilever structures and a multilayeredcomposite structure
Aerial Transportation Control of Suspended Payloads with Multiple Agents
No full textInternational audienceIn this paper we address the control problem of aerial cable suspended load transportation, using multiple Unmanned Aerial Vehicles (UAVs). First, the dynamical model of the coupled system is obtained using the Newton-Euler formalism, for n UAVs transporting a load, where the cables are supposed to be rigid and massless. The control problem is stated as a trajectory tracking directly on the load. To do so, a hierarchical control scheme is proposed based on the attractive ellipsoid method, where a virtual controller is calculated for tracking the position of the load, with this, the desired position for each vehicle along with their desired cable tensions are estimated, and used to compute the virtual controller for the position of each vehicle. This results in an underdetermined system, where an infinite number of drones' configurations comply with the desired load position, thus additional constrains can be imposed to obtain a unique solution. Furthermore, this information is used to compute the attitude reference for the vehicles, which are feed to a quaternion based attitude control. The stability analysis, using an energy-like function, demonstrated the practical stability of the system, it is that all the error signals are attracted and contained in an invariant set. Hence, the proposed scheme assures that, given well posed initial conditions, the closed-loop</div
r-ERBFN : an Extension of the Evidential RBFN Accounting for the Dependence Between Positive and Negative Evidence
No full textLecture Notes in Computer ScienceInternational audienceRecently, it was shown that a radial basis function network (RBFN) with a softmax output layer amounts to pooling by Dempster's rule positive and negative evidence for each class, and approximating the resulting belief function by a probability distribution using the plausibility transform. This so-called latent belief function offers a richer uncertainty quantification than the probabilistic output of the RBFN. In this paper, we show that there exists actually a set of latent belief functions for a RBFN. This set is obtained by considering all possible dependence structures, which are described by correlations, between the positive and negative evidence for each class. Furthermore, we show that performance can be enhanced by optimizing the correlations brought to light
Unraveling the Adsorption Mechanism of Rhodamine B onto Conjugated Polymeric Nanoparticles Using Isothermal Calorimetry and Monte Carlo Simulations
No full textInternational audienceWe present herein a comprehensive study on the thermodynamics of rhodamine B (RhB) adsorption onto poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) nanoparticles (NPs) dispersed in water using the isothermal calorimetric titration (ITC) technique. ITC experiments were carried out over a wide temperature range (5-65 degrees C), and the resulting thermograms were subjected to a detailed thermodynamic analysis using different adsorption models. For this purpose, we developed a versatile computational code based on the Monte Carlo method. We found that the thermograms obtained at the different temperatures cannot be interpreted using the Langmuir, bi-Langmuir, or Brunauer, Emmet, Teller (BET) models. However, excellent thermogram fits were attained by applying the Langmuir model coupled with the formation of a RhB dimer on the surface of F8BT NPs. Using this model, the best fit to the experimental data at 25 degrees C yielded the following parameters for direct RhB adsorption on the F8BT NPs surface: equilibrium constant (K-l) of similar to 2 x 10(7) M-1, enthalpy change (Delta H-l) of similar to 1 kJ mol(-1), and entropy change (Delta S-l) of similar to 140 J K-1 mol(-1). These results indicate that dye adsorption is predominantly an entropy-controlled process. The fit also provided parameters associated with the formation of a second dye adsorption layer, i.e., the formation of the RhB dimer on the F8BT NPs surface, revealing values of similar to 1.7 x 10(5) M-1, ca. -20 kJ mol(-1), and similar to 30 J K-1 mol(-1) for K-m, Delta H-m, and Delta S-m, respectively. The latter two parameters are similar to those previously reported for RhB dimer formation in water (Delta H-d = -12 kJ mol(-1) and Delta S-d = 22 J K-1 mol(-1)) supporting the chosen Langmuir-dimer model. The analysis of the thermograms also suggests that the NPs surface available for RhB adsorption is small, as compared to the total surface, and that it decreases with decreasing temperature. The latter observation is intriguing, especially since the F8BT NPs hydrodynamic diameter shows only a small decrease with decreasing temperature. To explain these results, we propose that the surface of the NPs harbors highly hydrated polar groups that reduce the accessibility of the dye for adsorption
Paving the way for social touch sonification: behavioral studies and applications in virtual reality
No full textInternational audienceWith the increase of social isolation and distant communication, it appears timely to allow distant socio-affective interactions. To do so, we developed a methodology combining the use of a novel sonification technique that considers skin as a singular sonic texture and prototypical social touch gestures. Three studies explored the feasibility of this technique, its core components, and its potential applications in virtual reality. In the first study, the vibratory signals from prototypical skin-to-skin touches were recorded with a piezoelectric transducer, allowing their conversion into sounds. The resulting sonified signals were presented to participants who were able to accurately categorize both the different gestures (stroking, rubbing, tapping, hitting) and their underlying emotional intentions (love, empathy, joy, impatience, fear, anger). The second study investigated the respective roles of rhythm and textural properties on participants’ abilities to recognize social touch through sounds. The same tactile gestures as in the first study were reproduced in two different surface conditions: skin-on-skin and object-on-object. The results revealed that the dynamics of the surface involved in the touch are crucial, and that skin-on-skin interactions bear information that sets them apart from object-on-object movements. The third study was conducted with the platform of virtual agents Greta, which allows simulating 3D touch gestures between the user and the virtual agent. Participants performed a virtual reality game during which they received socio-affective touch from the agent, or not. We then quantitatively investigated participants’ perception of the virtual agent depending on their tactile behavior and the emotional intentions conveyed this way. These results pave the way for allowing social touch at a distance, through multisensory channels, with both humans and virtual agents
Feedback on a cross-curricular health technology teaching for undergraduate students at the Bordeaux Institute of Technology
No full textInternational audienceThis paper introduces a new cross-disciplinary curriculum teaching in Health Technology (HT) for undergraduate students involved in five different disciplines, which are computer sciences, materials engineering, mechanics, electronics, and applied physics. The major insight is based on the integration of University Degrees (UDs) to educational programs of Bordeaux Institute of Technology (BIT) to empower students to customize their educational paths based on their individual projects and interests. To the best of authors knowledge, such personalized pathway opening up learning practices and breaking down preconceived stereotypes is unique in a French institute of technology. Focusing on the UD dedicated to HT, the new cross-curricular syllabus is introduced. Highlights are i) a project-based learning to promote student success and the development of soft and hard skills, and ii) the establishment of a partnership to bring together healthcare professionals and local authorities on identified needs in HT. Students' feedback, lessons learnt and on-going discussions finally conclude the paper
Evaluation of HD-sEMG descriptor sensitivity to changes of anatomical and neural properties with aging : A simulation study
No full textBackground and objectives: A reliable evaluation of anatomical and neural muscle properties and its effects on the electrical signals measured at the skin surface aims to develop a medical non-invasive aid-diagnosis tool assisted by model and personalized to the patient. This tool will be dedicated to understand and evaluate muscle diseases and aging. Methods: We perform a new Robust Morris Screening Method: RMSM in Douania et al. (2023), to assess the impact of muscle anatomy (model inputs) uncertainties and variations on a simulated HD-sEMG signals (model outputs). The model describes a complex neuromuscular system simulating HD-sEMG (high density surface electromyography) signals generated from motor units electrical sources of a striated muscle: the Biceps Brachii (BB). Two subjects categories and two contractions levels are studied: young men (YM) and old men (OM) at low and high contraction (LC = 20% of MVC and HC = 60% of MVC). A 33 features in time and frequency domains are used as model outputs. Results: We have demonstrated that the neuromuscular model is able to deliver HD-sEMG signals sensitive to the same anatomical and neural muscle factors as in real cases. Time domain features are mainly sensitive to muscle thickness, conduction velocity of fibers, electrode locations (at HC), number of motor units, and to the number of slow and fast fibers for young and aged categories respectively. Frequency domain feature are sensitive mainly to the conduction velocity of fibers and muscle conductivities (no significant differences between YM and OM are observed). Conclusion: This result is important, it allows to obtain simulated HD-sEMG signals close to experimental ones with low cost and in reduced time. However, for a reliable evaluation of muscle aging, the neuromuscular model should be enhanced to better describe structural, morphological, and functional age-related phenomena
Enhancing Multifunctionality: Optimal Properties of Iron-Oxide-Reinforced Polyvinylidene Difluoride Unveiled Through Full Atom Molecular Dynamics Simulations
No full textInternational audienceNanocomposites made of magnetite (Fe3O4) nanoparticles (NP)s with different surface chemistry and Polyvinyl difluoride (PVDF) polymer were investigated using full atom molecular dynamics (MD) simulation. NPs with hydroxyl (OH), hexanoic, and oleic acid terminations were considered in this study. The effect of each surface chemistry was investigated in terms of the mechanical properties, the distribution of the internal energy around the NP, and the chain polarization gradient from the interface to the bulk. From this investigation, we find that oleic acid termination although the most popular, is less favorable for interfacial interaction and local polarization. The OH-terminated NP results in the best configuration for the properties investigated. The hexanoic acid-grafted NP presents a good compromise. Hydrogen bonding governs the induced response of the nanocomposites.Although the hexanoic acid grafted NP presents less hydrogen bonding than the OH-terminated case, the conformation of the hexanoic acid acts as a mobility flow inhibitor, leading to performance comparable to the OH-terminated NP composite. This work led to investigating routes to make nanocomposite materials with optimized properties. These results shed light on the multiple combinations offered by nanocomposites that go beyond the conventional effects of size</p
