Dissertations / Theses: 'Contact forces'

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Metzger, Philip. "DERIVING THE DENSITY OF STATES FOR GRANULAR CONTACT FORCES." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2809.

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The density of single grain states in static granular packings is derived from first principles for an idealized yet fundamental case. This produces the distribution of contact forces P_f(f) in the packing. Because there has been some controversy in the published literature over the exact form of the distribution, this dissertation begins by reviewing the existing empirical observations to resolve those controversies. A method is then developed to analyze Edwards' granular contact force probability functional from first principles. The derivation assumes Edwards' flat measure -- a density of states (DOS) that is uniform within the metastable regions of phase space. A further assumption, supported by physical arguments and empirical evidence, is that contact force correlations arising through the closure of loops of grains may be neglected. Then, maximizing a state-counting entropy results in a transport equation that can be solved numerically. For the present it has been solved using the "Mean Structure Approximation," projecting the DOS across all angular coordinates to more clearly identify its predominant features in the remaining stress coordinates. These features are: (1) the Grain Factor related to grain stability and strong correlation between the contact forces on the same grain, and (2) the Structure Factor related to Newton's third law and strong correlation between neighboring grains. Numerical simulations were then performed for idealized granular packings to permit a direct comparison with the theory, and the data including P_f(f) were found to be in excellent agreement. Where the simulations and theory disagree, it is primarily due to the coordination number Z because the theory assumes Z to be a constant whereas in disordered packings it is not. The form of the empirical DOS is discovered to have an elegant, underlying pattern related to Z. This pattern consists entirely of the functional forms correctly predicted by the theory, but with only slight parameter changes as a function of Z. This produces significant physical insight and suggests how the theory may be generalized in the future.
Ph.D.
Department of Physics
Arts and Sciences
Physics

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Osman, Mohammad Shahril. "Measurement of granular contact forces using frequency scanning interferometry." Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/7025.

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The propagation of stress within a granular material has been studied for many years, but only recently have models and theories focused on the micromechanical (single grain) level. Experiments at this level are still rather limited in number. For this reason, a system using optical techniques has been developed. The substrate on which the granular bed is assembled is a double layer elastic substrate with high modulus epoxy constituting the top layer and silicone rubber as the bottom layer. In between the two layers, gold is coated which acts as a reflective film. To design the substrate, a Finite Element Analysis package called LUSAS was used. By performing a non-linear contact analysis, the design of the substrate was optimised so as to give a linear response, high stiffness, deflection in the measurable range, and negligible cross-talk between neighbouring grains. Fabrication and inspection techniques were developed to enable samples to be manufactured to this design. The deformation of the gold interface layer is measured using interferometry. The interferometer utilised a frequency tunable laser which acts both as the light source and the phase shifting device. The optical arrangement is based on the Fizeau set-up. This has removed several problems such as multiple reflections and sensitivity to vibration that occurred when using a Mach-Zehnder configuration. A fifteen-frame phase shifting algorithm, was developed based on a Hanning window, which allows the phase difference map to be obtained. This is then unwrapped in order to obtain the indentation profile. The deflection profile is then converted to a single indentation depth value by fitting a Lorentzian curve to the measured data. Calibration of the substrate is carried out by loading at 9 different locations simultaneously. Spatial and temporal variations of the calibration constants are found to be of order 10-15%. Results are presents showing contact force distributions under both piles of sand and under face-centred cubic arrangements of stainless steel balls. Reasonable agreement was obtained in the latter case with both the expected mean force and the probability density function predicted by the so-called 'q' model. The experimental techniques are able to measure small displacements down to a few nanometers. To the best of my knowledge these experiments are the first to employ the interferometer method in attempting to measure the contact force distribution at the base of a granular bed.

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Troaca-Luchici, L. A. "The role of forces during contact inhibition of locomotion." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1553415/.

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Contact Inhibition of Locomotion (CIL), a process where migrating cells repel upon collision, was first observed in cultured cells more than 60 years ago. Previous work investigating Drosophila hemocyte collisions in vivo revealed that precise CIL interactions are required for hemocytes to acquire their developmental patterning. Kinematics analysis of the exact velocity and acceleration changes surrounding the contact inhibition process revealed that rapid and synchronous kinematic changes take place during collisions. To understand the cause of such intriguing CIL kinematics I examined the actin network dynamics surrounding collisions. Pseudo-speckle microscopy tracking the actin retrograde flow dynamics during collisions revealed that the actin flow un¬dergoes synchronous temporal and spatial reorganization across the entire lamella of both colliding partners. Also, a region of low retrograde flow develops perpen¬dicular to the leading edge spanning colliding cells. Upon repulsion, retrograde flow simultaneously spikes in both lamellae. Further experimental investigations revealed that as hemocytes collide, an inter-cellular adhesion develops at the site of cell-cell contact which leads to the formation of an actin stress-fibre like structure transiently coupling the cells through an actin clutch-like mechanism analogous to the integrin clutch encountered in migrating cells. I subsequently modelled the cytoskeletal stresses in freely moving and colliding cells using a linear viscoelastic model. Upon collision, lamellar stress redistributes from the cell body to the leading edge along the region of low retrograde flow. Direct laser abscission of the actin stress-fibre like structure spanning colliding cells confirmed that lamellar tension is increasing during CIL and showed that the release of this excess tension is sufficient to cause cells to migrate away from the collision. It is this haptic feedback mechanism, and the subsequent release of lamellar tension, that allows CIL to act as a productive migratory cue for the hemocyte developmental patterning.

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Lundberg, Oskar. "On the influence of surface roughness on rolling contact forces." Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193935.

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Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.

QC 20161013

Centre for Eco2 Vehicle Design

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Lyons, Percie Jewell. "Effects of Hip Osteoarthritis on Lower Extremity Joint Contact Forces." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/104968.

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People with osteoarthritis (OA) suffer from joint degeneration and pain as well as difficulty performing daily activities. Joint contact forces (JCF) are important for understanding individual joint loading, however, these contact force cannot be directly measured without instrumented implants. Musculoskeletal modeling is a tool for estimating JCF without the need for surgery. The results from these models can be very different due to different approaches used in the development of a model that was used for simulation. Therefore, the first purpose of this study was to develop and validate a musculoskeletal model in which lower extremity JCF were calculated at the hip, knee, and ankle in 10 participants with hip OA (H-OA) and 10 healthy control participants using OpenSim 4.0 [simtk.org, 23]. The generic gait2392 model was scaled to participant demographics, then the inverse kinematics (IK) solution and kinetic data were input into the Residual Reduction Algorithm (RRA) to reduce modeling errors. Kinematic solutions from RRA were used in the Computed Muscle Control (CMC) tool to compute muscle forces, then JCF were estimated using the Joint Reaction Analysis tool. Validation included JCF comparisons to published data of similar participant samples during level walking, and movement simulation quality was assessed with residual forces and moments applied at the pelvis, joint reserve actuators, and kinematic tracking errors. The computed JCFs were similar to the overall trends of published JCF results from similar participant samples, however the values of the computed JCFs were anywhere from 0.5 times body weight (BW) to 3BW larger than those in published studies. Simulation quality assessment resulted in low residual forces and moments, and low tracking errors. Most of the reserve actuators were small as well, besides pelvis rotation and hip rotation. The computed JCF were then used in the second portion of this study to determine the effect of group and side on JCF during both the weight acceptance and push-off phases of level walking. It was determined that there was a significant difference in the knee and ankle JCF during the weight acceptance portion of stance phase and at all joints during the push-off phase when comparing the H-OA and control groups on the affected limb. A significant interaction between group and limb was found for the peak hip JCF timing (% stance) during the push-off portion of the stance phase (p=0.009). These results demonstrate that H-OA participants experience an earlier peak hip JCF during propulsion on their affected limb. Based on previous research in OA that has examined spatiotemporal measures, this finding suggests that H-OA participants may use step or stride length changes as a strategy to decrease or limit pain and loading on the affected limb. Knowledge of potential JCF differences in H-OA participants, such as timing of the peaks in either portion of the stance phase, could provide useful insight to clinicians and therapists to make decisions on how to proceed with treatment or rehabilitation programs.
Master of Science
People with osteoarthritis suffer from joint degeneration and pain as well as difficulty performing daily activities, like walking. It is important to understand the forces and loading within individual joints. Musculoskeletal modeling is one way that researchers can estimate these joint contact forces (JCF) without needing a joint replacement implant that can measure these forces. When it comes to modeling simulations, there is a wide variety of results. Therefore, the first purpose of this study was to develop and validate a musculoskeletal model in which JCFs were calculated at the hip, knee, and ankle in 10 participants with hip osteoarthritis and 10 healthy adults. Validation of the model was completed through a comparison between computed results and published data of similar participant samples during level walking. The computed results were similar to the overall trends of published JCF results, however the numerical values themselves were larger than those in published studies. The computed JCFs were then used in the second portion of this study to determine how the two groups and limbs differ during level walking. There was a significant difference in the knee and ankle JCF during the first half of the stance phase and in all joints during the second half of stance when comparing the two groups. The hip osteoarthritis participants also experience an earlier peak hip JCF during the second half of stance phase on their affected limb. This finding suggests that hip osteoarthritis participants may change the way they take a step as a strategy to decrease or limit pain and loading on the affected limb. Knowledge of potential JCF differences, such as timing of the peaks in either portion of the stance phase, could provide useful insight to clinicians and therapists to make decisions on how to proceed with treatment or rehabilitation programs.

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Alvarellos, Jose. "Fundamental Studies of Capillary Forces in Porous Media." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5314.

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The contact angle defined by Young's equation depends on the ratio between solid and liquid surface energies. Young's contact angle is constant for a given system, and cannot explain the stability of fluid droplets in capillary tubes. Within this framework, large variations in contact angle and explained aassuming surface roughness, heterogeneity or contamination. This research explores the static and dynamic behavior of fluid droplets within capillary tubes and the variations in contact angle among interacting menisci. Various cases are considered including wetting and non-wetting gluids, droplets in inclined capillary tubes or subjected to a pressure difference, within one-dimensional and three-dimensional capillary systems, and under static or dynamic conditions (either harmonic fluid pressure or tube oscillation). The research approach is based on complementary analytical modeling (total energy formulation) and experimental techniques (microscopic observations). The evolution of meniscus curvatures and droplet displacements are studied in all cases. Analytical and experimental results show that droplets can be stable within capillary tubes even under the influence of an external force, the resulting contact angles are not constant, and bariations from Young's contact angle aare extensively justified as menisci interaction. Menisci introduce stiffness, therefore two immiscible Newtonian fluids behave as a Maxwellian fluid, and droplets can exhibit resonance or relaxation spectral features.

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Andrews, Sheldon. "Measurement-based modeling of contact forces and textures for haptic rendering." Thesis, University of Ottawa (Canada), 2007. http://hdl.handle.net/10393/27570.

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Haptics is a topic which, in recent years, has gained significant attention from several research fields, including computer graphics, robotics, human-computer interfaces, and virtual environments. Through the use of computer controlled forces, a user is given tactile and kinesthetic cues about the underlying application. These cues enhance the overall quality of the application, or possibly add a new dimension, by allowing the user to experience first-hand some previously unavailable phenomena (e.g., hardness, softness, mass, inertia). In this thesis, we introduce an interactive and mobile system for the acquisition and synthesis of haptic textures, which includes the surface profile and compliance. Texture represents the attributes at the surface of an object and is related to physical characteristics such as roughness and friction. By texturing objects in a 3D virtual application, the realism of the simulation is greatly increased. Our system is cost effective, simple, and adaptable to a number of workspace environments. We demonstrate how surface features may be acquired by scanning an object using a hand-held touch probe. Sensor data is processed and used to generate haptic textures of sufficient quality to allow for haptic rendering. We also introduce a method to assign 2D texture coordinates based on registration of scanning trajectory with 3D geometry.

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Pang, Tao, and tony_pang@hotmail com. "Studies on Wheel/Rail Contact Impact Forces at Insulated Rail Joints." Central Queensland University. Centre for Railway Engineering, 2008. http://library-resources.cqu.edu.au./thesis/adt-QCQU/public/adt-QCQU20080410.154708.

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To investigate the wheel/rail contact impact forces at insulated rail joints (IRJs), a three-dimensional finite element model and strain gauged experiments are employed and reported in this thesis. The 3D wheel/rail contact-impact FE model adopts a two-stage analysis strategy in which the wheel-IRJ railhead contact is first established in the static analysis and the results transferred to dynamic analysis for impact simulations. The explicit FE method was employed in the dynamic analysis. The Lagrange Multiplier method and the Penalty method for contact constraint enforcement were adopted for the static and dynamic analyses respectively. The wheel/rail contact-impact in the vicinity of the end post is exhibited via numerical examples from the FE modelling. The wheel/rail contact impact mechanism is investigated. The strain gauged experiments which consist of a lab test and a field test are reported. The signature of the strain time series from the field test demonstrates a plausible record of the dynamic responses due to the wheel/rail contact impact. By using the experimental data, both the static and the dynamic FE models are validated. It is found that the stiffness discontinuity of the IRJ structure causes a running surface geometry discontinuity during the wheel passages which then causes the impact in the vicinity of the end post. Through a series of sensitivity studies of several IRJ design parameters, it is shown that the IRJ performance can be effectively improved with optimised design parameters.

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Hurtado, José Francisco. "Experimental study of workpiece-fixture contact forces and friction during machining." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16096.

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Tolomeo, Mathias. "Estimation des forces de contact intergranulaires par mesures de champs cinématiques." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI074/document.

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Dans les études expérimentales de la micromécanique des matériaux granulaires, la mesure des forces de contact entre particules est de nos jours toujours un challenge en comparaison avec les outils et techniques bien mieux établis pour la caractérisation cinématique à l'échelle des particules. Cette thèse de doctorat s'attaque à cet ambitieux problème. L'approche proposée implique deux aspects : (i) la caractérisation expérimentale du réseau de contact et de la cinématique à l'échelle des particules, qui peut être réalisée avec des techniques d'imagerie standards ; (ii) une approche numérique capable d'exploiter ces mesures afin de déduire les forces de contact.L'une des contraintes qu'on s'était imposée était de ne s'appuyer que sur la connaissance de la géométrie des particules ainsi que du réseau de contacts pour réaliser la déduction des forces de contact. Trois techniques numériques différentes ont été proposées à cet effet : une méthode basée sur l'élasticité des contacts (CEM), une méthode basée sur la dynamique de contact (CDM) et une méthode basée sur l'équilibre élasto-plastique de l'assemblage granulaire (QSM). Chacune de ces techniques repose sur une approche de la famille des méthodes en éléments discrets ; il s'agit respectivement de le DEM de type Cundall, la dynamique des contacts non régulière, et une approche de calcul statique élastoplastique. La non-unicité de la solution est le principal problème avec les techniques choisies, et elles sont étroitement liées à l’indétermination des forces dans le système.Les trois méthodes sont d'abord présentées et validées en les appliquant à l'estimation des forces dans les systèmes granulaires 2D générés au moyen de simulations DEM explicites. Nous prenons ces simulations comme des expériences "idéales" dans le sens où elles fournissent des données similaires à celles extraites des expériences, mais dépourvues d'erreurs de mesure. Un avantage évident de cette stratégie est d’obtenir des ensembles de forces faisant office de référence faisant foi. Sur cette base, les principaux aspects affectant la détermination des forces peuvent être étudiés. En particulier, le rôle crucial de l'histoire du chargement est mis en évidence et certaines solutions pour les prendre en compte dans la détermination des forces ont été prospectées. Une évaluation de l'influence de l'erreur de mesure a également été réalisée pour prédire l'applicabilité de chaque méthode à des expériences réelles. Une brève analyse de la variabilité des solutions est également fournie.Finalement, des tentatives ont été faites pour déduire des forces issues d’expériences effectuées dans le dispositif 1gamma2epsilon. La cinématique des particules et la connectivité ont été évaluées au moyen de la technique de corrélation d'image numérique. Les avantages et inconvénients des trois méthodes ont été éclaircis. Ils nous conduisent à envisager une utilisation combinée des trois méthodes pour tirer parti de leurs atouts respectifs. À l'avenir, il conviendra de réfléchir à la prise en compte de la stabilité de la solution -- dans l'algorithme de convergence vers une solution -- avec l'espoir de limiter la variabilité des solutions
In the experimental study of the micro-mechanics of granular materials, measuring inter-particle contact forces is still a challenging task, if compared to the well-established tools and techniques for the kinematic characterisation at particle scale. This doctoral thesis addresses this problem. The proposed approach consists of two parts: an experimental characterisation of the granular network geometry and of particle-scale kinematics, which can be carried out with common imaging techniques such as Digital Image Correlation; a numerical approach aiming to exploit these measurements for the estimation of forces.One imposed constraint was to only make use of the rigid motions of particles, together with the knowledge of the contact network, to infer contact forces. Three different numerical techniques have been proposed to this purpose, referred to as Contact Elasticity Method (CEM), Contact Dynamics-based Method (CDM) and Quasi-Static Method (QSM). Each of these techniques is based on the formulation of common approaches in the family of Discrete Element Methods, respectively the classical Cundall-like DEM, the Non Smooth Contact Dynamics and a quasi-static approach accounting for both contact elasticity and plasticity. It is shown that memory of the history of the packing is the main concern with all the chosen techniques.The three methods are first presented and validated by applying them to the estimation of forces in 2D granular systems generated by means of explicit-time DEM simulations. We refer to these simulations as "ideal" experiments since they are meant to provide the same information that can be extracted from experiments, but without any measurement error. An obvious benefit of this strategy is to get reference force sets that are taken as ground truth. Based on this, the main aspects that affect the determination of forces can be investigated. In particular, the crucial role of history is emphasised here, and some solutions to take it into account in the force inference have been investigated.An assessment of the influence of measurement error has also been carried out, to predict the applicability of each method to real experiments. A short analysis of the variability of the solutions is also provided.Finally, some attempts have been made to infer forces from experiments carried out in the 1gamma2epsilon device. Particle kinematics and connectivity have been assessed by means of the Digital Image Correlation technique.The benefits and drawbacks of the three methods have been demonstrated. They conduct us to envision a combined usage of the three methods. In the future, studying the stability of equilibrium might help reducing the variability of the solutions

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Racine, Jean-Olivier. "Estimation de l'effet d'une force virtuelle sur les forces de contact lors de la transition assis-debout." Mémoire, École de technologie supérieure, 2010. http://espace.etsmtl.ca/313/1/RACINE_Jean%2DOlivier.pdf.

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Introduction : Près de 31% des gens de plus de 55 ans disent avoir certaines difficultés à se lever. Les forces de contact articulaires sont considérées comme une source importante de douleurs favorisant les difficultés à la transition assis-debout. L’effet d’aides techniques à la transition assis-debout sur ces forces a été très peu étudié. Objectifs : 1) Développer un modèle permettant d’estimer les forces de contact durant la transition assis-debout 2) Simuler l’effet d’une force virtuelle sur le modèle. Méthodologie : Un modèle ayant 7 segments et 70 muscles, piloté par des données de l’Institut de Réadaptation Gingras-Lindsay de Montréal a été développé grâce à l’Anybody Modeling System. Deux forces virtuelles dont on a varié l’angle, l’amplitude et la position du point d’application ont été introduites sur les fémurs afin de simuler l’effet qu’aurait une aide technique. Résultats : Les forces de contact ont été estimées, à la hanche, à 2.95±0.74 fois le poids du corps à droite et 2.97±0.54 fois à gauche et, aux genoux, à 4.61 ±0.85 fois le poids du corps à droite et 4.73±0.75 fois à gauche. En modifiant uniquement les moments articulaires sur la trajectoire formée sur la chaîne cinématique par les deux forces, la force virtuelle s’est déplacée vers la force résiduelle. Discussion : Le problème de dynamique inverse est traditionnellement mal posé. Une reformulation du problème, en incorporant des coefficients de distribution des forces de réaction au sol, plutôt que l’introduction directe de celles-ci, devrait permettre une meilleure adaptabilité du modèle à l’ajout de forces virtuelles.

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Essa, Irfan A. (Irfan Aziz). "Contact detection, collision forces and friction for physically based virtual world modeling." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14054.

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Zhang, Yuanfang. "Étude sur banc d'essai des forces de contact dynamique pneumatique/chaussée à l'origine du bruit de roulement." Thesis, Ecole centrale de Nantes, 2016. http://www.theses.fr/2016ECDN0026.

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Les modèles de contact dynamique pour le bruit de roulement reposent souvent sur une hypothèse quasistatique et une approximation de massif semi-infini pour le pneu. L’objectif de la thèse est de vérifier ces hypothèses par la mesure de forces de contact sur un banc d’essai constitué d’un pneu lisse de taille réduite roulant sur un bâti cylindrique. Au préalable, l’analyse modale expérimentale du pneu permet d’identifier des modes propres de formes classiques. Bien qu’un modèle éléments finis basé sur une section de pneu homogène élastique donne des modes satisfaisants, une section hétérogène hyper-viscoélastique permet d’obtenir un bon compromis entre vibrations et contact statique. La force de contact dynamique lors du roulement du pneu sur une seule aspérité sphérique ou conique est ensuite mesurée. La relation entre la force maximale et la hauteur de l’aspérité est conforme aux lois de contact théoriques. La durée de contact sur l’aspérité est inversement proportionnelle à la vitesse. Les calculs de contact basés sur un massif semi-infini élastique permettent d’approcher correctement la force maximale mesurée pour les fortes hauteurs d’aspérités, mais pas pour les faibles. La dissymétrie du signal temporel de force est bien modélisée en introduisant la viscoélasticité dans le modèle. Les forces de contact dynamique mesurées entre le pneu et plusieurs aspérités de formes simples confirment les résultats précédents, démontrant dans l’ensemble la nature quasi-statique du contact roulant. Toutefois, les forces calculées sont sous-estimées sur les bords de l’aire de contact, montrant une limitation de l’hypothèse de massif semi-infini pour décrire la structure du pneu
The dynamic contact models for tyre/road noise are often based on a quasi-static assumption and a half-space approximation for the tyre. The aim of the thesis is to assess these assumptions by measuring contact forces on a test rig composed of a smooth reduced-sized tyre rolling on a cylindrical basis. Beforehand, the experimental modal analysis of the tyre allows the identification of eigenmodes of classical shapes. Although a finite element model based on a homogeneous elastic tyre section yields satisfactory modes, a hyper-viscoelastic heterogeneous section provides a good compromise between vibrations and static contact. The dynamic contact force on a single spherical or conical asperity during rolling of the tyre is then measured. The relationship between the maximum force and the height of the asperity is consistent with theoretical contact laws. The contact duration on the asperity is inversely proportional to the speed. The contact calculations based on an elastic half-space assumption lead to a proper estimation of the maximum force measured on high asperity heights, but not on low asperity heights. The dissymmetry of the force time signal is well modelled by introducing the viscoelasticity in the model. The dynamic contact forces measured between the tyre and several asperities of simple shapes confirm the previous results, demonstrating the quasistatic nature of the rolling contact. However, the calculated forces are underestimated at the edges of the contact area, showing a limitation of the half-space assumption to describe the tyre structure

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Baffet, Guillaume. "Développement et validation expérimentale d’observateurs des forces du contact pneumatique/chaussée d’une automobile." Compiègne, 2007. http://www.theses.fr/2007COMP1695.

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La connaissance de la dynamique d'un véhicule et de son environnement est un enjeu majeur. L'objectif de cette thèse est de développer des observateurs d'état permettant d'estimer des variables liées à l'adhérence du contact pneumatique/chaussée. Différentes méthodes d'observation sont proposées afin de reconstruire les efforts des pneumatiques et l'angle de dérive d'une automobile. Ces algorithmes d'estimation sont conçus pour être fonctionnels en cas de situation de conduite critique, notamment lors de fortes accélérations latérales ou lorsque l'adhérence de la chaussée varie. Outre une description des techniques d'observation mises en oeuvre, cette étude présente d'importantes phases de validation par la simulation et l'expérimentation. Ce travail a abouti à la conception d'un module temps réel embarqué qui a pu être évalué relativement à des mesures des forces des roues
Estimation of vehicle-dynamic variables is essential for safety enhancement, in particular for braking and trajectory-control systems. The aim of this thesis is to develop state observers for the estimation of variables linked to tire-road friction. Different estimation methods are proposed in order to reconstruct tire-road forces and vehicle sideslip angle. The estimation algorithms are constructed so as to be functional in critical driving situations, notably for weak lateral accelerations and road friction changes. In addition to estimation methods, this thesis presents a substantial number of observer evaluations, performed in simulations and in experiments. The estimation process was integrated in an experimental vehicle, and was tested in real time, particularly in relation to wheel force measurements

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Jones, Logan. "Modélisation des forces de contact entre le pneu d’un avion et la piste." Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0019/document.

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Lorsqu’un avion atterrit, la force principale nécessaire pour arrêter l’avion est obtenue par le freinage. Par une réduction de la vitesse de rotation des roues, les freins provoquent une vitesse de glissement entre les pneus et la piste. C’est cette différence de vitesse qui génère la force de freinage capable de stopper l’avion. La modélisation de cette force est essentielle pour l’estimation de la longueur de piste à l’atterrissage. Les modèles classiques utilisés par les avionneurs sont assez simplistes et dérivent expérimentalement des modèles de frictions les plus simples. De sorte que ces modèles sont dans l’incapacité d’estimer l’influence de paramètres clefs influençant la force de freinage. Il s’agit, en particulier de la pression des pneus, de la nature de la gomme, de la température ambiante et de celle de la gomme, de l’état de la piste, de sa texture, etc. L’objectif de la thèse a été de développer un modèle de contact pneu-piste capable d’estimer la force de freinage. C’est le « Brush Model » qui a servi de base à cette modélisation. En phase de freinage la zone de contact est constituée d’une première zone de déformation de la gomme qui crée une force résistante en suivant la loi de Hooke, puis d’une seconde zone de glissement dont la force de résistance suit la loi de Coulomb. Ce modèle a été amélioré grâce aux résultats de la mécanique des structures pour la loi de Hooke et grâce aux résultats de la tribologie pour la loi de Coulomb. Ces deux modélisations faisant appel aux données issues de la science des matériaux. L’ensemble de ces modélisations a été enrichi par une coopération avec plusieurs centres de recherches ayant fourni de nombreux résultats expérimentaux. Le modèle obtenu a ensuite été confronté avec des résultats d’essais en vol obtenus avec « Airbus Operations S.A.S ». La thèse a validé le prétraitement des données d’essais ainsi que le processus d’identification qui a permis de montrer l’accord du modèle avec les résultats expérimentaux obtenus lors des essais en vol. Cette modélisation donne des résultats très encourageants, elle permet une compréhension beaucoup plus approfondie des effets de l’environnement sur les forces de freinage. De sorte que cette thèse a permis d’améliorer très sensiblement la compréhension fondamentale des phénomènes en jeu lors du freinage, au contact entre le pneu et la piste. Chez Airbus, les résultats obtenus vont servir de base pour les travaux à venir sur ce thème
As an aircraft lands on a runway, the principal force acting to stop the aircraft within the confines of the runway is generated by the brakes. The brakes cause the tire’s rotational speed to slow down with regards to the aircraft’s speed over the ground. This difference in speed causes friction and it is this friction that is the principal force to stop the aircraft. In order to be able to estimate the stopping distance of an aircraft an understanding of this friction is essential. Traditionally, aircraft manufactures have relied on simplistic, empirically derived friction models. However, these empirical models cannot estimate the influence of several key factors that are known (scientifically) to affect friction such as the rubber temperature, the runway texture, the ambient air temperature and the rubber composition to name a few. This PhD work aims to develop a frictional model that can be used to estimate the friction developed between an aircraft tire and the runway. A model commonly known as the Brush Model, is derived for usewith aircraft tires and runways. The underlying physics of this model are developed using the established scientific theories of tribology, material science and strength of materials. Coordination with several research institutes provides experimental results to reinforce the model. The model is then compared with flight test results obtained from a partnership with Airbus OperationsS.A.S. The PhD works demonstrates the entire validation process from flight test data cleaning, the derivation of a curve-fitting algorithm and the matching of derived model with the flight test data. The modeling has shown very encouraging results. It allows for a much deeper understanding of the environmental effects on friction. This PhD work has greatly improved the fundamental understanding of friction and will serve as a base for future works with Airbus

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Huang, Kaiwu. "Surface Forces in Thin Liquid Films." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/104111.

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Thin liquid films (TLFs) of water are ubiquitous in daily lives as well as in many industrial processes. They can be formed between two identical phases, as in colloid films between two macroscopic surfaces and foam films between two air bubbles; and between two dissimilar phases, as in wetting films. Stability of the colloids, foams, and wetting films is determined by the surface forces in the TLFs. Depending on the nature of the surfaces involved, the stabilities can be predicted using combinations of three different forces, i.e., the van der Waals, electrical double layer (EDL), and hydrophobic forces. The objective of the present work is to study the roles of these forces in determining the stabilities of the TLFs of water confined between i) an air bubble and a hydrophobic surface and ii) an oil drop and a hydrophobic surface, with particular interest in studying the role of the hydrophobic force. The first part of the study involves the measurement of the surface forces in the TLFs confined between bitumen drops and mineral surfaces. Deformation of bitumen drops has been monitored by interferometry while it approaches a flat surface. By analyzing the spatiotemporal film profiles, both the capillary and hydrodynamic forces have been calculated using the Young-Laplace equation and the Reynolds lubrication approximation, respectively, with the surface forces being determined by subtracting the latter from the former. The results are useful for better understanding the effects of electrolyte and pH on bitumen liberation and recovery by flotation and for developing a filtration model from first principles. The second part of the study involves the surface force measurement in wetting (flotation) films. Surface forces in the TLFs of water on silica surfaces have been measured using the force apparatus for deformable surfaces (FADS) using an air bubble as a force sensor. The measurements have been conducted in the presence of various cationic surfactants such as dodecylamine hydrochloride (DAH), and alkyltrimethylammonium chloride (CnTACl), electrolytes, and polymers. The results show that film stability and hence the kinetics of film thinning can be greatly improved by the control of bubble ζ-potentials, whose role in flotation has long been neglected in flotation studies. Force measurements have also been conducted in the TLFs of water confined between oil drops and hydrophobic surfaces. Stability of this type of film plays an important role in a process of using oil drops rather than air bubbles to collect hydrophobic particles from aqueous phase. The force measurements conducted in the present work show that hydrophobic forces are much stronger in water films formed between oil drops and hydrophobic surfaces than in water films formed between air bubbles and hydrophobic surfaces, which can be attributed to the differences in the Hamaker constants involved.
Doctor of Philosophy
When two macroscopic surfaces in water are brought to a close proximity, a thin liquid film (TLF) is formed in between, with its stability being determined by the surface forces present in the film. TLFs are ubiquitous in daily lives and play a decisive role in many industrial processes such as mineral flotation, food processing, oil extraction, heat transfer, etc. In the present work, the surface forces present in wetting films have been measured by approaching an air bubble (or an oil drop) slowly toward a flat surface while monitoring the curvature changes during film thinning by interferometry and calculating the capillary forces using the Young-Laplace equations. By analyzing the results in view of the Frumkin-Derjaguin isotherm and the extended DLVO theory, it was possible to determine the changes in the van der Waals, electrical double-layer (EDL), and hydrophobic forces during film thinning. The results show that both the EDL and the long-range component of the hydrophobic force control the kinetics of film thinning and rupture while the contact angle formation is controlled by the van der Waals force and the short-range hydrophobic force. It has been found also that n-alkane drops form substantially larger contact angles than air bubbles on a hydrophobic surface due to the fact that the van der Waals force is attractive in the drop-surface interactions while the same is repulsive in the bubble-surface interactions. These observations have a profound implication in flotation, that is, oil drops can recover hydrophobic particles from an aqueous phase better than air bubbles.

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Wood, Peter Edwin. "An investigation of contact forces, flow, pressure, hysteresis and frictional effects in brush seals." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393118.

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Wang, Andrew Eric. "Driving Forces for the Triboelectric Charging of Well-Defined Insulating Material Surfaces." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1588612948239934.

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Singh, Harmeet. "Discontinuities, Balance Laws, and Material Momentum." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/86664.

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This dissertation presents an analytical study of a class of problems involving discontinuities, also referred to as shocks, propagating through one dimensional flexible objects such as strings and rods. The study entails interrogation of the classical balance laws of momentum, angular momentum, and energy across propagating discontinuities. A major part of this dissertation also concerns itself with a non-classical entity called the ``material momentum''. The balance of material momentum is studied in a variational context, where both the local and singular forms of it are derived from an action principle. A distinguishing aspect of discontinuities propagating in continua is that, unlike in the bulk, the balance of momentum and angular momentum are not sufficient to describe their mechanics, even when the discontinuities are energy conserving. In this work, it is shown that the additional information required to close the system of equations at propagating discontinuities can be obtained from the singular form of energy balance across them. This entails splitting of the energy balance by its invariance properties, and identifying the non-invariant and invariant part of the source term with the power input and energy dissipation respectively at the shock. This approach is in contrast with other treatments of such problems in the literature, where additional non-classical concepts such as ``material momentum'' and ``configurational force'' have been invoked. To further our understanding of the connections between the classical and non-classical approaches to problems involving discontinuities, a detailed exposition of the concept of material momentum is presented. The balance and conservation laws associated with material momentum are derived from an action principle. It is shown that the conservation of material momentum is associated with the material symmetry of the continuum, and that the conditions for the conservation of physical and material momentum are independent of each other. A new classification of the deformed configurations of the planar Euler elastica based on conserved quantities associated with the spatial and material symmetry of the rod is proposed. The manifestation of the balance of material momentum in seemingly unrelated fields of research, such as fracture mechanics, ideal fluids, and the mechanics of rods with discontinuities, is also discussed.
Ph. D.
One dimensional flexible bodies such as strings and rods can exhibit fascinating and counterintuitive behavior when they interact with rigid obstacles. For instance, a chain falling on a rigid surface falls faster than it would have if it were falling freely. When one end of a long chain piled up in a container placed at an elevation is pulled across the rim and let go, the chain flows out of the container like a water fountain. Discontinuities in the cross-sectional properties of an elastic rod contained in a curved frictionless channel can result in the generation of forces that propel the rod along the channel. Such counterintuitive phenomena are a consequence of the physics taking place at the point of partial contact where the flexible body comes in contact with a rigid surface. The purpose of this dissertation is to study the mechanics of such points of discontinuity. Several such phenomena where effectively one dimensional bodies interact with rigid surfaces are all around us. A familiar example is the peeling of an adhesive tape, where the peeling front qualifies as a point of discontinuity propagating through the tape as the peeling progresses. A good understanding of the mechanics of the peeling front is crucial in estimating the strength of the adhesive. Another such example of practical importance is a mooring line being placed on the seabed. In such situations, the existence of a reaction force acting at the touchdown point depends on whether or not the cable develops a kink at that point. Similar questions of importance can be asked in the context of deployment and unspooling of space tethers. In this dissertation, an analytical study of the general physics of the phenomena described above is presented. Standard theoretical tools of classical physics are employed to understand the mechanics of points of partial contact between flexible and rigid bodies. The conditions under which a flexible body could experience sharp changes in its geometry (e.g. a kink) at such points are investigated. In addition to that, we explore the implications of a nonclassical law of physics called the balance of “material momentum” in the context of such problems.

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Raoof, Mohammed. "Interwire contact forces and the static, hysteretic and fatigue properties of multi-layer structural strands." Thesis, University of London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339423.

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Moas, Eduardo. "Investigation of the finite element method for computing wheel/rail contact forces in steady curving." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/50064.

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The understanding of rail vehicle steady-state and dynamic curving has increased substantially in the last few years. Contemporary curving models include such nonlinear effects as two-point contact, creep force saturation, and rail flexibility. The usual approximation concerning the contact geometry is that the Iocalized wheel and rail curvatures at the center of the contact patch are constant throughout the contact patch. This approximation allows computation of contact stresses using Hertzian theory, and it allows the computation of contact patch forces using one of Kalker’s theories. ln vehicle curving, contact usually occurs at or near the wheel flange, where the wheel/rail contact geometry is non·Hertzian. Furthermore, after being in service for some time, the wheel and rail profiles provide non·Hertzian geometry due to wear. Both of these effects tend to invalidate the assumption of Hertzian contact geometry in the contact region. This work uses a generic wheelset model which is the basic component of any rail vehicle model. The wheel/rail interaction is modelled using the finite element method. The wheel is generated as a surface of revolution of its tread profile, and the rail is generated as an extrusion of the rail head profile. Three—dimensional contact elements are used to characterize the wheel/rail interface. A simple stick/slip friction model is used wherein relative motion is permitted if the tangential force exceeds the adhesion limit, and no relative motion occurs otherwise. The results show that the finite element method was successfully used to solve the static contact problem. Both Hertzian and non-Hertzian contact problems were ana- Iyzed correctly. However, the application of the finite element method to the rolling contact problem was not completely successful. The finite element method results for tangential contact forces were about 25 percent lower than forces predicted by Kalker’s theory. Recommendations for extending the analysis to solve the rolling contact problem are made. The report includes a derivation of the wheelset steadystate equations of motion, as well as a solution algorithm for the nonlinear, algebraic equations.
Master of Science
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Barhale, Koushik R. "Design and testing of a prototype gripper for a wheelchair mounted robot." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000564.

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Vu, Trong Dai. "Modélisation des effets tournants du pneumatique et des forces decontact pour le bruit de roulement basses fréquences." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1051/document.

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Le bruit de roulement contribue fortement au bruit perçu à l'intérieur de l'habitacle des automobiles. Ce bruit a pour origine le contact du pneumatique sur une chaussée rugueuse. En basses fréquences (0-400 Hz), il est transmis dans l'habitacle du véhicule essentiellement par la voie solidienne. La méthode actuelle de prévision de ce bruit chez PSA Peugeot Citroën repose sur une approche mixte calcul-mesure longue, coûteuse et pas suffisamment prédictive. Pour contourner ces limitations, une filière purement numérique est envisagée. Elle demande de modéliser le comportement vibro-acoustique du pneumatique en prenant en compte les effets liés à la rotation et de résoudre le problème de contact avec une chaussée rugueuse. Concernant la modélisation d'un pneumatique en rotation, des formulations des effets tournants d'un solide déformable sont établies en utilisant une approche Arbitrairement Lagrangienne Eulérienne (ALE). Ces formulations sont validées par une application sur un nouveau modèle simplifié du pneumatique. Il s'agit d'un modèle d'anneau circulaire incluant les effets de cisaillement soumis localement à une charge représentative de la masse du véhicule. Un modèle plus complexe d'ensemble monté pneu/roue/cavité intégrant l'ensemble des effets liés à la rotation est également validé par une comparaison avec des essais. Ensuite, le contact avec une chaussée réelle est formulé par différentes approches permettant de réduire le temps de calcul pour une utilisation industrielle. En particulier, le calcul du contact est décomposé en un calcul statique non linéaire suivi d'un calcul dynamique linéaire. La validation du modèle de contact est réalisée par une comparaison calcul/essai. Les résultats sont très satisfaisants
The rolling noise contributes significantly to the noise inside cars. This noise comes from the tire/road contact. In low frequencies (0-400 Hz), it is mainly transmitted into the cabin through structural vibration. The current method used at PSA Peugeot Citroen to predict this noise, is a mixed simulation/experimental approach which is long, expensive and not sufficiently predictive. In order to overcome these difficult, a full numerical approach is considered. It requires modeling the tire vibration by taking into account the rotating effects and the contact with the rough surface. Concerning the model of rotating tire, a formulation of a deformable solid is constructed by using an Arbitrary Lagrangian Eulerian approach (ALE). This formulation is validated by an application on a new simplified tire model which is a circular ring including the shear stresses and the non linear effects due to the vehicle weight. A more complex model composed of tire/wheel/cavity including all the rotating effects is also validated by comparison with experiments. Then the contact with a real road is calculated by different approaches to get the acceptable computing time for industrial uses. In particular, the calculation of the contact is divided into a non-linear static analysis followed by a linear dynamic calculation. The validation of this model is successfully achieved by comparison test results

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Moghadam, Ali. "Capillary Forces in Partially Saturated Thin Fibrous Media." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6110.

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Capillarity is often exploited in self-cleaning, drag reducing and fluid absorption/storage (sanitary products) purposes just to name a few. Formulating the underlying physics of capillarity helps future design and development of optimized structures. This work reports on developing computational models to quantify the capillary pressure and capillary forces on the fibrous surfaces. To this end, the current study utilizes a novel mass-spring-damper approach to incorporate the mechanical properties of the fibers in generating virtual fibrous structures that can best represent fibrous membranes. Such virtual fibrous structures are then subjected to a pressure estimation model, developed for the first time in this work, to estimate the liquid entry pressure (LEP) for a hydrophobic fibrous membrane. As for accurate prediction (and not just estimation) of the capillary pressure, this work also presents an energy minimization method, implemented in the Surface Evolver code, for tracking the air–water interface intrusion in a hydrophobic fibrous membrane comprised of orthogonally oriented fibers. This novel interface tracking algorithm is used to investigate the effects of the membrane’s microstructure and wetting properties on its resistance to water intrusion (i.e., LEP). The simulation method developed in this work is computationally affordable and it is accurate in its predictions of the air–water interface shape and position inside the membrane as a function of pressure. Application of the simulation method in studying effects of fiber diameter or contact angle heterogeneity on water intrusion pressure is reported for demonstration purposes. Capillary forces between fibrous surfaces are also studied experimentally and numerically via the liquid bridge between two parallel plates coated with electrospun fibers. In the experiment, a droplet was placed on one of the polystyrene- or polyurethane-coated plates and then compressed, stretched, or sheared using the other plate and the force was measured using a sensitive scale. In the simulation, the liquid bridge was mathematically defined for the Surface Evolver finite element code to predict its 3-D shape and resistance to normal and shearing forces, respectively, in presence of the contact angle hysteresis effect. Despite the inherent non-uniformity of the fibrous surfaces used in the experiments and the simplifying assumptions considered for the simulations, reasonable agreement was observed between the experiments and simulations. Results reveal that both normal and shear force on the plates increase by increasing the liquid volume, or decreasing the spacing between the plates.

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Barre, Arnaud. "Estimation des forces de contact fémoro-tibiales lors de la marche : comparaison de trois modèles réductionnistes." Mémoire, École de technologie supérieure, 2007. http://espace.etsmtl.ca/551/1/BARR%C3%89_Arnaud.pdf.

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La détermination des forces de contact fémoro-tibiales (FCFT) nécessite l'utilisation d'une modélisation biomécanique du membre inférieur. En se focalisant sur la méthode de réduction, trois modèles estimant les FCFT ont été recensés dans la littérature. La présente étude propose de comparer ces trois modèles et de calculer leurs incertitudes pour déterminer le modèle le plus adapté à l'analyse des FCFT lors de la marche. L'estimation des FCFT est basée sur les essais de marche de sept participants asymptomatiques (27.6 (4.3) ans, 1.71 (0.10) m, 73.5 (15.0) kg), marchant à vitesse confortable (4.0 (0.4) km/h) sur un tapis roulant. Les éléments de la modélisation influençant significativement les résultats sont les bras de levier musculaires, l'ajout des gastrocnémiens et le contrôle musculaire. L'incertitude demeure pour chaque modèle inférieure à 10%. Cette étude identifie le modèle de Devita et Hortobayi (2001) comme le plus adapté à l'analyse des FCFT lors de la marche.

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Barre, Arnaud. "Estimation des forces de contact fémoro-tibiales lors de la marche : comparaison de trois modèles réductionnistes /." Thèse, Montréal : École de technologie supérieure, 2007. http://proquest.umi.com/pqdweb?did=1407500661&sid=6&Fmt=2&clientId=46962&RQT=309&VName=PQD.

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Thèse (M.Ing.) -- École de technologie supérieure, Montréal, 2007.
"Mémoire présenté à l'École de technologie supérieure comme exigence partielle à l'obtention de la maîtrise en génie". Bibliogr.: f. [185]-196. Également disponible en version électronique. CaQMUQET

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Feldman, Jonathan. "Dynamic refinement and boundary contact forces in smoothed particle hydrodynamics with applications in fluid flow problems." Thesis, Swansea University, 2006. https://cronfa.swan.ac.uk/Record/cronfa42459.

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Smoothed Particle Hydrodynamics (SPH) is a relatively new, simple and effective numerical method that can be used to solve a variety of difficult problems in computational mechanics. It is a fully Lagrangian meshless method ideal for solving large deformation problems such as complex free surface fluid flows. This research was carried out with the support of BAE Systems and falls into two distinct areas. Firstly to investigate new methods for treating fixed boundaries and secondly to investigate refinement algorithms which allow for both sparsely and densely populated regions of particles within the same computational domain. Much work has been done in the modelling of particle-boundary interactions in SPH since the governing equations do not naturally incorporate essential boundary conditions. In this research a new technique for calculating boundary contact forces is developed. The forces are obtained from a variational principle and as such conserve both the linear and angular momentum of the system. The boundaries are explicitly defined using this new approach and so the need for additional boundary particles is removed. In the past most SPH derivations have been based on a uniform distribution of particles of equal mass. This leads to large simulations with many particles and long run times. In other mesh based schemes it has become common place to use mesh adaptivity to improve numerical results and reduce computation times. With a corresponding refinement strategy SPH can gain these same advantages. In this research a refinement strategy based upon particle splitting is developed. Candidate particles are split into several 'daughter' particles according to a given refinement pattern centred about the original particle position. Through the solution of a non-linear minimisation problem the optimal mass distribution for the daughter particles is obtained so as to reduce the errors introduced into the underlying density field. This procedure necessarily conserves the mass of the system. The unique daughter particle velocity configuration that conserves the linear and angular momentum of the system is also identified. The conclusion of the research was the successful implementation of these improvements into the existing SPH framework. As a result the capability and flexibility of the code is greatly increased and the computational expense needed for running large simulations has been reduced.

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Zhang, Yi. "Static and Dynamic Behaviour of Inter-granular Liquid Bridges: Hysteresis of Contact Angle and Capillary Forces." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16151.

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The wet granular material, a mixture of solid grains, liquid and air, has been studied in many industrial applications. Understanding the mechanical properties of wet granular materials is extremely important in geotechnical engineering. The cohesion in these materials arising from a liquid bridge between a pair of grains is produced by the capillary force and the viscous force. Thus, investigating the behaviour of liquid bridges between grains helps people obtain a better understanding of the factors influencing the cohesion, including the geometry and topological distribution of liquid bridges, the size of grains, or the liquid flow rate. This thesis focuses on the static and dynamic behaviour of liquid bridges connecting two solid substrates. The aims of our study are to (1) explore the quasi-static and dynamic force arising from liquid bridges when two substrates move at various speeds and (2) established an analytical model to describe and predict the behaviour of liquid bridge when it moves at different speeds. Our work can be divided into three parts: parallel plates experiments, analytical modelling and extended experiments. The working content and the main results are presented in the below. 1. A series of parallel plates experiments are conducted to systematically investigate the capillary force and the contact angle hysteresis of a liquid bridge which forms between two moveable parallel plates under the quasi-static and dynamic conditions. The experimental results show that the contact angle hysteresis can be divided into pinning and slipping stages in both of the extension and compression processes. With the increase of plate moving speeds, it is observed that in the slipping stage, the receding angle becomes smaller and the advancing angle becomes larger. The capillary force hysteresis also changes correspondently. The liquid bridge hysteresis can be used to predict the cohesion behaviour of wet granular material during the wetting and drying processes. Moreover, in some geotechnical events such as the seepage in soil or the shear movement of the grains, the rate effect on the contact angle and the force between grains can provide a potential direction to investigate the failure criterion of soils and their dynamic behaviour. 2. In the quasi-static regime, an analytical model has been first established based on the geometrical shape of liquid bridges. According to the pinning and slipping stages of liquid bridge hysteresis, the proposed model describes the geometrical characteristics of a liquid bridge being extended and compressed under the quasi-static condition. The models have been compared to the experimental results and the analytical model can particularly predict the quasi-static contact angle and contact radius hysteresis. In the dynamic regime, an empirical rate-dependent contact angle fitting function has been established to capture the change of dynamic contact angle with respect to the loading rate. Furthermore, the dynamic analytical model has been established to predict the variation of viscous force and dynamic contact angle hysteresis with the increase of plate moving speeds. The model predictions are in a good agreement with the experiments. 3. Moreover, to consider the effects of surface curvature and roughness, we extended the experiments forming liquid bridges between various substrates: (1) two plates with different surface roughness; (2) two spheres; (3) a sphere and a plate. The influence of surface properties and curvatures on the behaviour of liquid bridges has been discussed and possible future research directions are provided. As the cohesion between gains is influence by many factors such as the volume, size, contact angle of a liquid bridge, as well as the flow speeds and the grain movement, this study provides a good start to investigate the capillary force and the contact angle hysteresis under the quasi-static and dynamic conditions. In this work, the experimental observation of liquid bridge hysteresis is presented and the analytical models are established to predict the force and contact angle hysteresis at a given moving speed. This study demonstrates potential to use this microscopic information towards the macro scale properties of wet granular materials, such as the soil-water retention hysteresis under different wetting and drainage rates.

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Ferguson, Jeremy Lee. "A Moving Load Finite Element-Based Approach To Determining Blade Tip Forces During A Blade-On-Casing Incursion In A Gas Turbine Engine." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204131916.

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Shah, Palak V. "A Comparative Study of Treadmill Walking/Jogging and Mini-trampoline Jogging for Metabolic Cost and Contact Forces." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1195077861.

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Karlborg, Lisa. "Enforcing Legitimacy : Perspectives on the Relationship between Intervening Armed Forces and the Local Population in Afghanistan." Doctoral thesis, Uppsala universitet, Institutionen för freds- och konfliktforskning, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-263061.

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Bolstering local perceptions of legitimacy in armed intervention has emerged as an important feature of increasingly complex international peace and statebuilding efforts. Yet, previous research has only begun to explore what local legitimacy entails to those involved in, and affected by, armed intervention. This dissertation advances an understanding of local legitimacy as a perception-based, relational phenomenon. Through this lens, it examines armed intervention in Afghanistan (2001-2014). In particular, this dissertation studies how the relationship between Afghan citizens and intervening armed forces interacts with, and shapes, perspectives on local legitimacy held by the main 'interveners' and those 'intervened upon'. This dissertation consists of an introduction, which situates the study in a wider context, and four essays. Beginning with the organizational perspectives of the main intervening actors in Afghanistan, Essay I finds that the UN and NATO initially conceptualized problems of local legitimacy as principally the consequence of a fragile Afghan state, and not as failings of the intervention. When negative dimensions of intervention became increasingly recognized, principal responsibility for the legitimacy process shifted away from intervening authorities and onto the Afghan state. Similarly, Essay II shows how key U.S. military doctrine, over time, reconceptualized the formal duty of intervening forces in the local legitimacy process, ultimately considering it contingent on, and subordinate to, the will and capabilities of host-state authorities and the local population. Turning thereafter to firsthand accounts from the field, Essay III and Essay IV together contrast personal perspectives on the intervention held by U.S. Army Officers and Afghan citizens. Essay III finds that personal experiences of noncombat contact with Afghans reinforced the Officers' sense of duty toward the local population. Conversely, Essay IV suggests that the local legitimacy of intervening forces became increasingly contested among Afghans, due largely to the perceived intensification of foreign intrusion on 'everyday' life. Taken together, the findings of this dissertation lay the foundation for the development of a new concept, the host-citizen contract. In so doing, it provides a social contract framework to better understand the complex dynamics of local legitimacy in Afghanistan, and beyond.

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Delventhal, Brooke. "Simulation-Based Stability Tests in Total Knee Arthroplasty: Are Component Alignment, KneeLaxity, and Tibiofemoral Contact Forces Related?" The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574422948246589.

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Hansson, Petra M. "Hydrophobic surfaces: Effect of surface structure on wetting and interaction forces." Doctoral thesis, KTH, Yt- och korrosionsvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103409.

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The use of hydrophobic surfaces is important for many processes both in nature and industry. Interactions between hydrophobic species play a key role in industrial applications such as water-cleaning procedures and pitch control during papermaking but they also give information on how to design surfaces like hydrophobic mineral pigments. In this thesis, the influence of surface properties on wetting and interaction forces has been studied. Surfaces with close-packed particles, pore arrays, randomly deposited nanoparticles as well as reference surfaces were prepared. The atomic force microscope (AFM) was utilized for force and friction measurements while contact angles and confocal Raman microscopy experiments were mainly used for wetting studies. The deposition of silica particles in the size range of nano- to micrometers using the Langmuir-Blodgett (LB) technique resulted in particle coated surfaces exhibiting hexagonal close-packing and close to Wenzel state wetting after hydrophobization. Force measurements displayed long-range interaction forces assigned to be a consequence of air cavitation. Smaller roughness features provided larger forces and interaction distances interpreted as being due to fewer restrictions of capillary growth. Friction measurements proved both the surface structure and chemistry to be important for the observed forces. On hydrophobic pore array surfaces, the three-phase contact line of water droplets avoided the pores which created a jagged interface. The influence of the pores was evident in the force curves, both in terms of the shape, in which the three-phase contact line movements around the pores could be detected, as well as the depth of the pores providing different access and amount of air. When water/ethanol mixtures were used, the interactions were concluded to be due to ethanol condensation. Confocal Raman microscopy experiments with water and water/ethanol mixtures on superhydrophobic surfaces gave evidence for water depletion and ethanol/air accumulation close to the surface. Force measurements using superhydrophobic surfaces showed extremely long-range interaction distances. This work has provided evidence for air cavitation between hydrophobic surfaces in aqueous solution. It was also shown that the range and magnitude of interaction forces could, to some extent, be predicted by looking at certain surface features like structure,roughness and the overall length scales.

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Schuind, Frederic. "Transmission des forces au niveau du poignet: application d'une technique analytique de calcul des pressions articulaires de contact." Doctoral thesis, Universite Libre de Bruxelles, 1991. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212978.

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Hoang, Hoa. "Calibrated EMG-Informed Neuromusculoskeletal Modelling to Estimate Physiologically Plausible Hip Joint Contact Forces in People with Hip Osteoarthritis." Thesis, Griffith University, 2017. http://hdl.handle.net/10072/371909.

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Osteoarthritis (OA) is a common and progressive joint disease with a prevalence of 3.6-4.1% of the global population in 2010 and one of the leading causes of worldwide disability. Hip OA is less common than knee OA; although the prevalence of hip OA is 8% in people aged 85 years and over. There is no cure for hip OA, and pain and disability can be only managed through conservative therapies, or finally total hip replacement. Inappropriate hip joint loading, measured as hip joint contact forces (HJCF), during daily activities is believed to be a factor in hip OA initiation and progression. Neuromusculoskeletal (NMS) models, which are anatomical and physiological mathematical representations of an individual, can be used to estimate muscle-tendon and internal joint contact forces (JCF) during human movement. However, the musculoskeletal system is inherently indeterminant and there are infinite combinations of muscle-tendon forces that can produce the same external joint loads. Two main neural control solutions that have been employed to solve this muscle-tendon force distribution problem: optimisation and electromyography (EMG)-informed solutions. Although static optimisation is commonly used, an EMG-informed NMS approach may offer more physiologically plausible HJCF estimates, since it accounts for an individual’s unique muscle activation patterns. Indeed, individuals with hip OA have abnormal muscle activation, which may influence the HJCF. Calibration, or tuning, of the neuromuscular parameters in EMG-informed NMS modelling is required to create subject-specific models. There are various cost functions used for calibration and their selection is crucial for obtaining physiological plausible estimates of JCF. EMG-informed NMS modelling is driven by EMG signals experimentally measured with surface electrodes. However, surface electrodes cannot record deep muscles important for hip function, which limits this application of EMG-informed modelling. Recently, EMG-hybrid and EMG-assisted modes have been developed to address this limitation, although, to date, there have been only two limited studies using these EMG-informed approaches for the hip, and only in healthy individuals. Furthermore, no studies have assessed how different calibrations cost functions and EMG-informed neural control solutions affect HJCF estimates. Subsequently, this thesis aimed to assess the use of calibrated EMG-informed NMS modelling, available in the Calibrated EMG-informed Neuromusculoskeletal Modelling toolbox (CEINMS), to explore the HJCF from healthy individuals and patients with mild-to-moderate hip OA during walking. The first study compared how different calibration cost functions and EMG-informed neural solution modes affected the estimated HJCF from a healthy population. Calibrating with a cost function to minimise joint moments prediction errors and peak HJCF, used together with the EMG-assisted neural solution mode well tracked the external joint moments and measured EMGs, and was the recommended approach to calculate physiologically plausible HJCF. The study has been submitted to the Journal of Biomechanics with following author order and title: Hoang, H.X., Pizzolato, C., Diamond, L.E., Lloyd, D.G., 2017. “Subject-specific calibration of neuromuscular parameters enables neuromusculoskeletal models to estimate physiologically plausible hip joint contact forces in healthy adults.” The second study compared estimated HJCF in people with mild-to-moderate hip OA obtained with the calibrated EMG-assisted pipeline in CEINMS (recommendation from the first study) and the static optimisation pipeline in OpenSim. The results showed that EMG-assisted mode and static optimisation both well tracked lower limb joint moments. However, the EMG-assisted mode was able to track hip muscle co-contraction patterns, whereas static optimisation did not. The associated manuscript is in preparation for submission to the Journal of Biomechanics as: Hoang, H.X., Diamond, L.E., Lloyd, D.G., Pizzolato, C., 2017. “A calibrated EMG-informed neuromusculoskeletal modelling method can appropriately account for muscle co-contraction to estimate hip joint contact forces in people with hip osteoarthritis.” The third study assessed the hip muscle co-contraction and HJCF in people with mild-to-moderate hip OA and healthy individuals using the calibrated EMG-informed NMS modelling approach as recommended in the previous two studies. Higher hip muscle co-contraction and lower HJCF were observed in individuals with hip OA compared to controls. These findings challenge previous beliefs of over-loading due to muscle co-contraction in people with hip OA. The associated manuscript is in preparation for submission to Osteoarthritis and Cartilage as: Hoang H.X., Loureiro, A., Constantinou, M.,Barrett, R., Pizzolato C., Lloyd D.G., Diamond L.E., 2017. “People with symptomatic mild-to-moderate hip osteoarthritis exhibit higher muscle co-contraction and walk with lower hip joint contact forces compared to healthy people.” The findings of this thesis showed that (i) the neural solution control is essential when estimating muscle-tendon forces and HJCF with NMS models and, therefore, subject-specific muscle activation patterns should be included in any modelling framework, (ii) calibration through tracking of joint moments and peak HJCF in conjunction with the EMG-assisted neural solution mode resulted in more physiologically plausible HJCF compared to other methods, and (iii) people with mild-to-moderate hip OA walk with more hip muscle co-contraction and lower HJCF compared to healthy people.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School Allied Health Sciences
Griffith Health
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Jourdan, Guillaume. "Vers un microscope de force de Casimir : mesure quantitative de forces faibles et nanopositionnement absolu." Phd thesis, Université Joseph Fourier (Grenoble), 2007. http://tel.archives-ouvertes.fr/tel-00273933.

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Les fluctuations quantiques de point zéro du champ électromagnétique (EM) produisent un effet mécanique remarquable entre deux objets macroscopiques, quelles que soient la forme et la nature de leurs matériaux : la force de Casimir, du nom du physicien hollandais qui en 1948 prédit l'existence d'une force attractive dans la configuration idéale de deux miroirs plans parfaits, neutres et parallèles.
Depuis sa mise en évidence théorique, cet effet attire l'intérêt de communautés scientifiques d'horizons tous azimuts, des cosmologistes aux concepteurs de micro/nanosystèmes mécaniques en passant par les physiciens de la théorie quantique des champs et de la gravitation. Cette force qui se situe au coeur de nombreux problèmes actuels de physique théoriques, à l'interface de la physique de la gravitation et de la théorie quantique des champs (divergence de l'énergie du vide), joue en effet un rôle majeur dans le fonctionnement de nanosystèmes mécaniques en cours de développement, qui sont appelés dans les années futures à révolutionner toute l'industrie de la microélectronique. Les effets des conditions aux limites imposées au champ EM soulèvent en particulier de nombreuses interrogations sur le comportement de ce phénomène quantique. Son contrôle, par ce biais, constitue ainsi l'une des principales motivations du travail expérimental développé durant cette thèse : la conception d'un appareil de mesure de forces faibles entre deux surfaces de tailles micrométriques présentant une structuration à l'échelle du nanomètre en vue de l'étude de la force de Casimir. La sonde de force, développée au cours de la thèse de Gauthier Torricelli qui a lancé cette activité dans l'équipe Piconewton, est constituée d'une micropoutre au bout de laquelle est collée une sphère de quelques dizaines de micromètres de rayon et recouverte d'or.
Cette thèse propose tout d'abord une caractérisation expérimentale et théorique de son comportement mécanique en présence de son environnement et des appareils de mesure qui l'entourent. La mise au point d'une procédure de calibration de force constitue ensuite une étape incontournable pour obtenir des mesures de forces absolues et ainsi réaliser des comparaisons théorie/expérience significatives.

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Saxby, David John. "The Tibiofemoral Contact Forces in Human Anterior Cruciate Ligament Reconstructed and Healthy Knees and their Association with Articular Tissue Degeneration." Thesis, Griffith University, 2016. http://hdl.handle.net/10072/367609.

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Osteoarthritis is a prevalent and debilitating joint disease. The global prevalence of osteoarthritis is estimated to be 3.6-4.1% of the global population, making it the 11th highest contributor to global disability. Osteoarthritis most commonly occurs in the medial tibiofemoral compartment of the knee. Inappropriate knee loading, during daily activities, is believed to be a principle cause of knee osteoarthritis. Moreover, individuals who have sustained anterior cruciate ligament (ACL) rupture and reconstruction (ACLR) are at particularly high risk of onset of knee OA in the near future. Within 12 years following ACL injury approximately 50% of people will develop knee OA. Worse still, many individuals who have sustained an ACL injury show signs of early knee degeneration as little as 4-5 years post- surgery. The question arises, what is it about ACL injury that results in such high risk of future OA onset? Individuals with ACLR have abnormal gait biomechanics and muscle activation patterns, which may influence the knee contact forces. As well, the autograft donor muscles are often impaired following harvesting. This muscle impairment also likely influences the knee contact forces. However, what links exist between the altered knee contact forces and degeneration of the articular tissues have not been established. To date, there are no literature reports of the knee contact forces during both daily gait tasks and sporting movements. Likewise, an investigation of the differences in the knee contact forces between ACLR and healthy individuals during different movement tasks has not been performed. Finally, the literature lacks an assessment of the relationships between the tibiofemoral contact forces that arise during daily activity and the structural health of the articular tissues in the knees of ACLR individuals.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Allied Health
Griffith Health
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Bacchetta, Hervé. "Une nouvelle technique d'étude des diélectriques par mesure de forces électrostatiques et sans contact : analyse théorique, développement expérimental et premiers résultats." Dijon, 1998. http://www.theses.fr/1998DIJOS027.

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Pouvoir accéder de manière fiable aux propriétés électriques des matériaux isolants permet à la fois d'améliorer leurs performances et de développer une connaissance théorique de leur comportement, étroitement lié à leurs caractéristiques physico-chimiques et microstructurales. Parmi les nombreuses méthodes développées à ce jour afin d'étudier des isolants soumis à un champ électrique et, ce, jusqu'à leurs ultimes limites de résistance a la rupture diélectrique, les mesures de forces électrostatiques ont été peu utilisées. Pourtant, l'utilisation des forces comme moyen de mesure sans contact du champ électrique présent au voisinage d'un isolant représente une voie instrumentale prometteuse que cette thèse a explorée. Deux prototypes originaux ont été conçus, réalisés et mis au point. Les géométries de la zone d'interaction électrique avec l'isolant ont été choisies afin de permettre une modélisation précise de la réponse des dispositifs. L'accent a été porté principalement sur le dispositif dont la sonde de mesure est une électrode sphérique submillimétrique polarisée, et déplaçable au voisinage de la surface du diélectrique. Son étude instrumentale détaillée a permis de vérifier la précision des mesures des forces mises en jeu et de définir les conditions d'application des modèles d'interprétation. La limite de détection de charges électriques atteint 10-14 c avec une résolution latérale submillimétrique. A l'issue de cette étude statique, a été ébauchée l'investigation de la dynamique de réponse de quelques isolants soumis à un champ électrique quasi statique et inhomogène. S'appuyant sur l'extrême sensibilité de l'appareil, les études de conductivité ne nécessitent pas de recourir à une implantation préliminaire de charges excédentaires. Des comportements non-ohmiques sont clairement mis en évidence.

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Aumatell, Gomez Guillem [Verfasser], and Gerhard [Akademischer Betreuer] Wurm. "Experiments on sublimation and contact forces of water ice particles and their application on planet formation / Guillem Aumatell Gomez. Betreuer: Gerhard Wurm." Duisburg, 2015. http://d-nb.info/1077986742/34.

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Kunze, Christian [Verfasser]. "Influence of oxygen and water adsorption on the surface chemistry and contact forces of defect rich metaloxide and nitride surfaces / Christian Kunze." Paderborn : Universitätsbibliothek, 2014. http://d-nb.info/1058406426/34.

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Vijaywargiya, Raghvendra. "A finite element investigation of the deformations, forces, stress formations, and energy lossses in elasto-plastic sliding contacts." Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-05132006-131833/.

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Bande, Gianluca. "Formes de contact généralisé, couples de contact et couples contacto-symplectiques." Mulhouse, 2000. http://www.theses.fr/2000MULH0621.

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On introduit trois types de structures géométriques nouvelles sur des variétés différentiables : formes de contact généralisé, couples de contact et couples contacto-symplectiques. Une forme de contact généralisé sur M est une 2k + 1-forme ω telle que ω∧dω soit une forme volume. Plusieurs exemples sont construits et on donne un critère local qui permet de montrer que tous ces exemples ne sont pas triviaux dans le sens qu'ils ne sont pas de la forme α ∧ dαk (où α est une forme de contact). Un couple de contact sur M est un couple (α, β) de formes de Pfaff de classe constante 2k + 1 et 2h + 1 respectivement et telles que la forme α ∧ dαk ∧ β ∧ dβh soit une forme volume. Chacune de ces formes détermine un feuilletage caractéristique dont les feuilles sont des variétés de contact. Ces feuilletages sont transverses et supplémentaires. La géométrie de tels objets est très riche car on peut naturellement leur associer deux champs de Reeb qui commutent, deux types de courbes de Legendre et deux crochets de Poisson. D'une manière similaire on définit un couple contacto-symplectique. Pour les deux dernières structure on démontre qu'il y a un unique modèle local et on construit plusieurs exemples non triviaux dans les groupes de Lie et dans les fibrés principaux en tores. Comme conséquence de la théorie des couples contacto-symplectiques on construit des exemples de champs de vecteurs (sur des variétés de contact) sans transversale fermée et qui ne sont le champ de Reeb d'aucune forme de contact. Ce qui répond à un célèbre problème de Reeb.

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Barelli, Floran. "Développement d'une méthodologie d'optimisation des conditions d'usinage : application au fraisage de l'alliage de titane TA6V." Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/15684/1/Barelli.pdf.

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Les travaux présentés dans cette thèse s’inscrivent dans le contexte de l’identification de l’influence des paramètres de coupe et géométries d’outil sur l’usinabilité de l’alliage de titane Ti-6Al-4V sous deux états cristallographiques : alpha\beta et beta et s’insèrent dans le projet TiMaS, en partenariat avec Airbus et Figeac Aéro. La première partie consiste donc en une identification des différents critères d’usinabilité considérés dans la bibliographie pour l’usinage des titanes et la modélisation des actions thermomécaniques régissant la coupe. Dans une deuxième partie, l’usinabilité des deux matériaux a été étudiée pour deux outils coupants, utilisés par les industriels, constituant ainsi nos deux couples outil matière. Aussi, suivant la démarche du Couple Outil-Matière (COM) un espace de fonctionnement des conditions de coupe a été défini pour les deux couples considérés, afin de déterminer les paramètres de coupe garantissant une amélioration de la productivité. Les efforts de coupe, ainsi que la durée de vie des outils ont de ce fait été sélectionnés comme critère d’usinabilité. Egalement, l’observation de la morphologie des copeaux et de leur état de déformation a permis de voir les singularités de comportement existantes entre les deux microstructures. Ces singularités ayant un impact sur la géométrie même du copeau et les actions thermomécaniques exercées par ce dernier sur les outils coupants, dans la troisième partie, des essais de coupe orthogonale (pour les deux matériaux) ont été effectués afin d’évaluer l’impact des géométries d’outil, des conditions de coupe et de la microstructure du matériau sur la thermomécanique de la coupe et les longueurs de contact entre la face de coupe des outils coupant et le copeau. La visualisation de l’écoulement du copeau par caméras rapides a permis de constater une certaine variabilité des longueurs de contact, influencée en partie par les paramètres de coupe et majoritairement par l’état cristallographique du matériau. L’analyse EDX des faces de coupe des outils coupant a montré que cette variabilité a une influence marquée sur l’usure en diffusion des plaquettes. Enfin, dans une dernière partie, un dernier critère d’usinabilité est étudié, reposant sur l’analyse des contraintes résiduelles générées par la coupe en surface de la pièce usinée. En se basant sur les essais de coupe orthogonale réalisés dans la partie précédente, une modélisation numérique basée sur un couplage thermomécanique faible a été développée afin de déterminer l’effet des conditions de coupe et des géométries d’outil sur les actions thermomécaniques et donc la génération de contraintes résiduelles, pour le cas du matériau à structure cristallographique bimodale. Les résultats de la modélisation ont ensuite étés comparés à des mesures de diffractométrie à rayons X effectués sur les pièces.

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Lauzier, Nicolas. "Mécanismes de sécurité pour l'interaction physique humain-robot : réduction des forces de contact par l'utilisation de limiteurs de couple dans la conception de robots manipulateurs." Thesis, Université Laval, 2011. http://www.theses.ulaval.ca/2011/28505/28505.pdf.

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Cette thèse présente l'analyse, la synthèse, l'optimisation, le design et la validation expérimentale de mécanismes de sécurité dans le contexte de l'interaction physique humain-robot. Afin d'améliorer la sécurité, une condition essentielle à la coexistence d'humains et de robots, une approche basée sur la conception de manipulateurs intrinsèquement sécuritaires est préférée à des systèmes d'évitement et de détection de collision, pour des raisons de fiabilité. La force maximale de contact survenant lors d'une collision est utilisée comme critère de sécurité pour sa simplicité et sa validité dans le contexte de la robotique. Pour les robots sériels, il est proposé de placer un limiteur de couple en série avec chaque actionneur tandis que pour les robots suspendus, on opte pour la séparation de la base et de l'effecteur par un mécanisme parallèle dont certains pivots sont remplacés par des limiteurs de couple --- formant ainsi un \emph{limiteur de force cartésien}. L'utilisation de ces mécanismes permet de réduire l'inertie effective du manipulateur lorsqu'une collision survient sans nuire aux performances du robot en situation normale. Un modèle est d'abord créé afin de comparer par simulation les gains de sécurité obtenus par des limiteurs de couple et d'autres mécanismes de sécurité articulaires utilisés seuls ou en combinaison avec d'autres dispositifs. Des méthodes de commande optimale des seuils de limiteurs de couple ajustables placés en série avec chaque actionneur d'un robot sériel sont ensuite développées. Un indice de performance cinématique est proposé afin d'optimiser la pose et l'architecture d'un tel robot. L'approche et les méthodes développées sont validées expérimentalement à l'aide de prototypes de limiteurs de couple ajustables basés sur la friction placés en série avec les actionneurs d'un robot sériel à quatre degrés de liberté. Finalement, des architectures de limiteurs de force cartésiens sont proposées et optimisées et leur efficacité dans le contexte des robots suspendus est validée expérimentalement.
This thesis presents the analysis, synthesis, optimization, design and experimental validation of safety mechanisms in the context of physical human-robot interaction. In order to improve safety, which is essential to allow the coexistence of humans and robots, an approach based on the design of intrinsically safe manipulators is preferred to collision avoidance and detection systems for reliability reasons. The maximum contact force occuring during a collision is used as a safety criterion due to its simplicity and validity in the context of robotics. For serial robots, it is proposed to place a torque limiter in series with each actuator whereas for suspended robots, it is preferable to separate the base and the effector with a parallel mechanism in which some joints are replaced with torque limiters --- thereby forming a \emph{Cartesian force limiting device}. The use of such mechanisms allows the reduction of the effective manipulator inertia during a collision without affecting the performances under normal conditions. A model is first created in order to compare --- using simulations --- the safety gains obtained with torque limiters with the ones obtained with other articular safety mechanisms when they are implemented alone or in combination with other safety devices. Methods to optimally control the thresholds of adjustable torque limiters placed in series with each actuator of a serial robot are developed. A kinematic performance index is proposed in order to optimize the pose and architecture of such a robot. The approach and the developed methods are experimentally validated using prototypes of adjustable torque limiters based on friction which are placed in series with each actuator of a four-degree-of-freedom robot. Finally, architectures of Cartesian force limiting devices are proposed and optimized and their effectiveness in the context of suspended robots is experimentally validated.

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Bala, Srujeeth Khanna. "Estimation of Blocked Forces in an Assembly with Rear Drive Unit as a Source." Thesis, KTH, Maskinkonstruktion (Inst.), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302780.

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Experimental validations are widely used for studying dynamic structural behaviors and these studies involve defining the structures completely as being used in real time. While in numerical simulations such detailed features are not specified to ease the computation, thereby deviating from accurate results. Hence experimental validations are more desired in product developments process. Applications of experimental verification for noise and vibration (referred to as NVH inautomotive industry) are expanding over the last few decades. Researchers are exploring ways to predict the responses on the new receiver using receiver independent forces, which led to evolution of component based TPA (Transfer Path Analysis) concept. The Component based TPA concept is an important development in automotive industry. It allows the auto manufacturers to make use of their available subsystems (like motor or a gearbox) in their newly developing vehicles. This has been made possible by defining the dynamic forces exerted by the source independent of receiving structure, which are then used to predict the responses on the new receiver. Evaluation of such receiver independent forces allows measurements to be made in a test rig rather than in the vehicle. This indeed helps in better communication between different departments or between suppliers and vehicle manufacturers, saves design iterations and time, and would help vehicle manufactures to predict the vehicle structural behaviors much before the first prototype is made. The method is based on the international standard ISO 20270:2019 (en) Acoustics – Characterization of sources of structure-borne sound and vibration – indirect measurement of blocked forces. The thesis is based on evaluating the source characterized forces that are used for predicting responses on a new receiving structure. For this, different methods in TPA are explored and for the rear drive unit application, in-situ method is chosen. The source characterized forces also termed as blocked forces are computed in different test set up and a validation check is performed. The obtained results are also compared with FEM and useful conclusions are drawn. And finally contact forces evaluated by integrating the subsystems are compared to the contact forces derived from the source characterized forces.
Experimentell verifiering av dynamiska krafter och vibrationer som uppkommer i fordon innebär mätning av tids-, frekvens- och/eller varvtalsberoende kvantiteter. Numeriska beräkningar har utvecklats till en hög nivå, men kan ännu inte beskriva alla förlopp och detaljer som förekommer i de verkliga processerna. På grund av detta krävs det fortfarande mätningar som en del av produktionsutvecklingen. Valideringsmetoder för ljud och vibrationer har utvecklats mycket desenaste decennierna, och ett mål har varit att utveckla mätmetoder där de uppmätta krafterna från en komponent som bidrar till buller kan mätas på ett sätt som inte beror på den testrigg eller det fordon den mäts i. Komponentbaserad TPA Transfer Path Analysis är en analysmetod som är viktig inom fordonsindustrin. Den gör det möjligt för en tillverkare att använda modeller av existerande komponenter (t.ex. motorer eller växellådor) i modeller för nya fordon. En grundläggande förutsättning är att de krafter som mäts är oberoende av den mottagande strukturen, det vill säga fordonet. Om krafterna är oberoende av strukturen där de mäts innebär det att komponenten kan mätas i en test rigg på ett annat ställe (till exempel hos en underleverantör) och att tillgång till fordon inte krävs för karaktäriseringen. Det underlättar kommunikationen mellan olika delar av organisationen och mellan underleveratörer och tillverkare och bidrar till att prediktera ljud och vibrationer innan den första prototypen är tillgänglig. Den föreslagna metoden är baserad på den internationella normen ISO 20270:2019 (en) Acoustics – Characterization of sources of structure-borne sound and vibration – indirect measurement of blocked forces. Examensarbetet handlar om att utveckla en mätmetod för att kunna ta fram krafter genererade av komponenter som är oberoende av testriggens egenskaper. De framtagna krafterna kan då användas i en virtuell fordonsmodell för att se ljud och vibrationsbidragen på fordonsnivå. Källan som har studerats är en slutväxel (rear drive unit) för fyrhjulsdrift i bil. Flera olikametoder för TPA har undersöks, och för karaktärisering av slutväxeln har in-situ metoden valts. Krafter som är oberoende av den mottagande strukturen kallas även ‘blocked forces’. Krafterna beräknas baserat på resultaten från flera olika delmätningar. Validering och även jämförelse medFEM beräkningar har gjorts liksom jämförelser mellan mätningar på enbart komponenten och av hela systemet.

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Kubisch, Jörg. "Developing of a device for measuring the areal distribution of the forces in the contact zone of foot and underground for the use in leg prostheses." Master's thesis, Pontificia Universidad Católica del Perú, 2020. http://hdl.handle.net/20.500.12404/17068.

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The presented work demonstrates the process of designing a cheap, low cost three axis force sensor. Further it describes its integration in an array of multiple sensors to measure the distribution of forces acting on the sole of a prosthetic foot. The focus will be on easy manufacturing and common materials since the sensor will be integrated in a low cost prosthesis for lower limp amputees. Using the knowledge from bio mechanics and some basic assumptions for the later use, requirements for the project are derived. After a presentation of some state of the art sensor principles, suitable concepts are collected. Than, the concepts are compared using a comparison table to find the one the fits the requirements the best. A very compelling concept using barometers casted in silicone rubber is tested using a simple prototype to try out whether it is a good candidate or not. The tests show that the concept is capable of measuring forces but due to its disadvantageous susceptibility for temperature changes it is rejected for the further development process. The concepts are reevaluated and a new concept is chosen. Afterwards the design process is described. Beginning with the mechanical design explaining the working principle. The calculation of the dimensions is presented. After that a circuit to work with a capacitive measurement as well as a version for resitive measurement is developed and a layout for a prototype board using capacitive measurement is proposed. To prove the functionality, the capacitive system is built up as a prototype. To try the measurement behavior and to measure its repeatability a test stand is designed. It uses commercial available load cells to conduct a reference measurement. The output of the sensor is compared to the reference measurement. With various different test procedures the curves mapping the measured values to the force for normal and shear force measurement are determined. During the tests, different aspects of performance like creep behavior or hysteresis are investigated. Also the repeatability is measured various times under different loads to make reliable estimations of the precision of the measurement. Further on, a resistive force sensor which could be used instead of the capacitive sensing elements is tested regarding its curve and performance to have a comparison of the advantages and disadvantages of either designing the future sensor with resistive or capacitive sensing elements. With both concepts a repeatability of a few percent uncertainty can be achieved. Further on ways to improve future versions of the sensor are described based on the experiences made during the work with the prototype. Finally a possible way to integrate multiple sensors into a sensing array is proposed. The design as well as possible electrics to acquire the data are discussed. This way a solid basis for further developments of a sensing array measuring the force distribution is given.
Die vorgestellte Arbeit zeigt den Prozess der Konstruktion eines preiswerten, kostengünstigen Dreiachs-Kraftsensors. Weiterhin wird eine Integration der Sensoren in ein Array, zur Messung der Verteilung von Kräften auf der Fußsohle besprochen. Der Schwerpunkt soll dabei auf einer einfachen und günstigen Herstellung, sowie der Verwendung handelsüblicher Materialien liegen, da der Sensor in ein kostengünstiges Prothesenkonzept integriert werden soll. Ausgehend von den Erkenntnissen der Biomechanik und einigen grundlegenden Annahmen für die Nutzung des Sensors, werden verschiedene Anforderungen abgeleitet. Im Folgenden wird der Stand der Technik anhand einiger aktueller Forschungsarbeiten und Sensorprinzipien vorgestellt. Daraufhin werden geeignete Konzepte gesammelt, die zur Entwicklung des Sensors eingesetzt werden können. Anschließend werden die Konzepte anhand einer Vergleichstabelle verglichen, um das bestgeeignetste Konzept zu finden. Eine sehr überzeugende Variante, bei der Barometerchips in Silikon eingegossen werden, wird mit einem einfachen Prototyp getestet, um herauszufinden, ob es sich um einen guten Kandidaten für die weitere Entwicklung handelt, oder nicht. Die Versuche zeigen, dass der Prototyp in der Lage ist, Kräfte zu messen, jedoch zeigt sich eine große Anfälligkeit für Temperaturschwankungen. Das Konzept wird deshalb nicht weiter verfolgt. Die Konzepte werden neu bewertet und anschließend ein Neues ausgewählt. Daraufhin wird der Entwurfsprozess beschrieben. Das Funktionsprinzip und die Auslegung der Abmessungen werden erläutert. Anschließend wird eine Schaltung zum Arbeiten mit einer kapazitiven Messung, sowie eine Schaltung für eine resitive Messung entwickelt und ein Layout für eine Platine zur kapazitiven Kraftmessung vorgeschlagen. Zum Nachweis der Funktionalität wird das kapazitive System als Prototyp aufgebaut. Um das Messverhalten zu testen und seine Wiederholbarkeit nachzuweisen, wird ein Prüfstand entworfen. Zur Durchführung einer Referenzmessung werden handelsübliche Wägezellen verwendet. Der Ausgang des Sensors wird mit der Referenzmessung verglichen. Mit verschiedenen Prüfverfahren werden die Kurven bestimmt, die die Messwerte der Normalund Querkraft zuordnen. Während des Tests werden verschiedene Leistungsaspekte wie Kriechverhalten oder Hysterese untersucht. Auch die Wiederholbarkeit wird mehrmals unter verschiedenen Belastungen gemessen, um zuverlässige Schätzungen der Genauigkeit der Messung vorzunehmen. Weiterhin wird ein resistiver Kraftsensor, der anstelle der kapazitiven Sensorelemente verwendet werden könnte, hinsichtlich seiner Kurve und Leistung getestet, um einen Vergleich der Vor- und Nachteile der Konstruktion des zukünftigen Sensors mit resistiven oder kapazitiven Sensorelementen zu erhalten. Mit beiden Konzepten kann eine gute Wiederholgenauigkeit mit nur wenigen Prozent Unsicherheit erreicht werden. Weiterhin werden Möglichkeiten zur Verbesserung der zukünftigen Version des Sensors auf Grundlage der gesammelten Erfahrungen beschrieben. Schließlich wird ein möglicher Weg zur Integration mehrerer Sensoren in eine Sensoranordnung vorgeschlagen. Das Design, sowie die mögliche Elektrik zur Erfassung der Daten werden diskutiert. Damit wird eine solide Grundlage für die Weiterentwicklung einer Sensoranordnung zur Messung der Kraftverteilung geschaffen.
Tesis

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47

Costa, Luca. "The Force Feedback Microscope : an AFM for soft condensed matter." Phd thesis, Université de Grenoble, 2014. http://tel.archives-ouvertes.fr/tel-01063820.

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Depuis son invention en 1986, les microscopes à force atomique (AFM) ont été des puissants outils pour la caractérisation des matériaux et des propriétés des matériaux à l'échelle nanométrique. Cette thèse est entièrement dédiée à la mesure de l'interaction entre une sonde AFM et une surface avec une nouvelle technique AFM appelée Force Feedback Microscopy (FFM). La technique a été développée et utilisée pour l'étude d'échantillons biologiques. Le principe central de la technologie FFM est que la force totale moyenne appliquée à la pointe est égal à zéro. En conséquence, en présence d'une interaction pointe-échantillon, une force égale et contraire doit être appliquée à la pointe par une boucle de rétroaction. La force de réaction est ici appliquée à la pointe à travers le déplacement d'un petit élément piézoélectrique positionné à la base du levier AFM. La boucle de rétroaction permet d'éviter instabilités mécaniques tels que le saut au contact, permettant la mesure complète de la courbe d'interaction. En plus, il donne la possibilité de mesurer simultanément les parties élastique et inélastique de l'interaction. La technique a été appliquée à l'étude des interactions à l'interface solide/gaz, avec un intérêt particulier pour l'observation de la formation et de la rupture des ponts capillaires entre pointe et échantillon. Ensuite, on a focalisé notre attention aux interfaces solide/liquide. Dans ce contexte, courbes complètes de type DLVO sont caractérisées d'un point de vue élastique et dissipatif. Nous avons développé des nouveaux modes d'imagerie AFM pour l'étude des biomolécules. Images de phospholipides et de l'ADN à force constante ont été réalisées et certaines propriétés mécaniques comme le module de Young des échantillons ont été évaluées. En plus, nous avons réalisé une étude spectroscopique de l'élasticité et du coeffcient d'amortissement de l'interaction entre des cellules vivantes de type PC12 et une pointe AFM en nitrure de silicium. L'étude montre que le FFM est un instrument capable de mesurer l'interaction à des fréquences qui ne sont pas nécessairement liées aux résonances caractéristiques du levier. L'étude spectroscopique pourrait avoir dans le futur des applications importantes pour l'étude des biomolécules et des polymères.

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48

Pathak, Saurabh. "A Dynamic Model of the Magnetic Head Slider with Contact and Off-Track Motion Due to a Thermally Actuated Protrusion or a Moving Bump Involving Intermolecular Forces." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1468408012.

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49

Pustoc'H, Audrey. "Elaboration d'un modèle mécanique de l'articulation de la hanche sous sollicitations dynamiques – Application à l'étude de l'influence d'une orthèse podale sur une hanche arthrosique." Phd thesis, Université Claude Bernard - Lyon I, 2007. http://tel.archives-ouvertes.fr/tel-00261947.

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L'objectif de ce travail est d'élaborer un modèle mécanique de la hanche saine susceptible d'être utilisé comme référence pour pouvoir ensuite analyser le comportement de hanches pathologiques en évaluant l'effet des traitements préconisés par comparaison des différents comportements simulés. Dans ce contexte, un modèle éléments finis générique de l'articulation de la hanche est développé. Il est également nécessaire de déterminer l'état de chargement de l'articulation de la hanche pour notre simulation. L'analyse du mouvement permet le calcul des données cinématiques et dynamiques à partir des mesures expérimentales. A partir de ces données, un modèle musculo-squelettique associant une méthode de dynamique inverse et d'optimisation statique, permet de déterminer les efforts musculaires mis en jeu par les muscles croisant l'articulation de la hanche. L'évaluation des forces développées par les muscles de la hanche permet de calculer la réaction de contact articulaire exercée par le fémur sur le bassin. C'est cette réaction que nous implémentons dans le modèle éléments finis. Ainsi, les simulations du comportement de la hanche saine sont réalisées pour la phase d'appui de la marche et la phase d'appui de la montée d'escaliers. Nous traitons ensuite d'une application clinique visant à évaluer l'influence du port d'une orthèse podale sur le comportement mécanique d'une hanche arthrosique. La démarche suivie est la même que celle mise en place pour l'étude du comportement de la hanche saine. L'état de chargement de la hanche arthrosique est déterminé chez le patient pendant la marche et la montée d'escaliers évoluant successivement avec puis sans orthèses.

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50

Nony, Laurent. "Applications de la microscopie de force dynamique en mode non-contact : structures supramoléculaires sur surfaces isolantes et microscopie de sonde de Kelvin." Habilitation à diriger des recherches, Aix-Marseille Université, 2013. http://tel.archives-ouvertes.fr/tel-00861989.

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Ce manuscrit d'HDR comprend trois parties comprenant pour certaines plusieurs chapitres. Mes travaux de recherche depuis le post-dosctorat (2001) jusqu'à 2012 y sont présentés synthétiquement. Ceux-ci concernent les thématiques de microscopie à force atomique en mode non-contact et de microscopie de sonde de Kelvin appliquées à la caractérisation structurale et à la mesure des propriétés électroniques de phases de molécules organiques adsorbées sur des surfaces de sels alcalins sous ultra-vide.

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Dissertations / Theses on the topic 'Contact forces'

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