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Academic literature on the topic 'Contact forces'

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Published: 4 June 2021
Last updated: 20 February 2023

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Journal articles on the topic "Contact forces"

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Anglin, C., U. P. Wyss, and D. R. Pichora. "Glenohumeral contact forces." Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 214, no. 6 (June 2000): 637–44. http://dx.doi.org/10.1243/0954411001535660.

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Adams, G. G., and M. Nosonovsky. "Contact modeling — forces." Tribology International 33, no. 5-6 (May 2000): 431–42. http://dx.doi.org/10.1016/s0301-679x(00)00063-3.

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Hao, Huang Wen. "Electrostatic and contact forces in force microscopy." Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures 9, no. 2 (March 1991): 1323. http://dx.doi.org/10.1116/1.585188.

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Yang, R., R. Miller, and P. J. Bryant. "Atomic force profiling by utilizing contact forces." Journal of Applied Physics 63, no. 2 (January 15, 1988): 570–72. http://dx.doi.org/10.1063/1.340089.

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Petrov, E. P., and D. J. Ewins. "Effects of Damping and Varying Contact Area at Blade-Disk Joints in Forced Response Analysis of Bladed Disk Assemblies." Journal of Turbomachinery 128, no. 2 (September 28, 2005): 403–10. http://dx.doi.org/10.1115/1.2181998.

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An approach is developed to analyze the multiharmonic forced response of large-scale finite element models of bladed disks taking account of the nonlinear forces acting at the contact interfaces of blade roots. Area contact interaction is modeled by area friction contact elements which allow for friction stresses under variable normal load, unilateral contacts, clearances, and interferences. Examples of application of the new approach to the analysis of root damping and forced response levels are given and numerical investigations of effects of contact conditions at root joints and excitation levels are explored for practical bladed disks.
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Ahmed, Rizwan, Christian Maria Firrone, and Stefano Zucca. "Design and Calibration of a Tri-Directional Contact Force Measurement System." Applied Sciences 11, no. 2 (January 19, 2021): 877. http://dx.doi.org/10.3390/app11020877.

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In low pressure turbine stages, adjacent blades are coupled to each other at their tip by covers, called shrouds. Three-dimensional periodic contact forces at shrouds strongly affect the blade vibration level as energy is dissipated by friction. To validate contact models developed for the prediction of nonlinear forced response of shrouded blades, direct contact force measurement during dynamic tests is mandatory. In case of shrouded blades, the existing unidirectional and bi-directional contact force measurement methods need to be improved and extended to a tri-directional measurement of shroud contact forces for a comprehensive and more reliable validation of the shroud contact models. This demands an accurate and robust measurement solution that is compatible with the nature and orientation of the contact forces at blade shrouds. This study presents a cost effective and adaptable tri-directional force measurement system to measure static and dynamic contact forces simultaneously in three directions at blade shrouds during forced response tests. The system is based on three orthogonal force transducers connected to a reference block that will eventually be put in contact with the blade shroud in the test rig. A calibration process is outlined to define a decoupling matrix and its subsequent validation is demonstrated in order to evaluate the effectiveness of the measurement system to measure the actual contact forces acting on the contact.
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McClelland, John A. "Contact and field forces." Physics Teacher 37, no. 9 (December 1999): 516. http://dx.doi.org/10.1119/1.880385.

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8

Yang, B. D., and C. H. Menq. "Modeling of Friction Contact and Its Application to the Design of Shroud Contact." Journal of Engineering for Gas Turbines and Power 119, no. 4 (October 1, 1997): 958–63. http://dx.doi.org/10.1115/1.2817082.

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Designers of aircraft engines frequently employ shrouds in turbine design. In this paper, a variable normal load friction force model is proposed to investigate the influence of shroudlike contact kinematics on the forced response of frictionally constrained turbine blades. Analytical criteria are formulated to predict the transitions between stick, slip, and separation of the interface so as to assess the induced friction forces. When considering cyclic loading, the induced friction forces are combined with the variable normal load so as to determine the effective stiffness and damping of the friction joint over a cycle of motion. The harmonic balance method is then used to impose the effective stiffness and damping of the friction joint on the linear structure. The solution procedure for the nonlinear response of a two-degree-of-freedom oscillator is demonstrated. As an application, this procedure is used to study the coupling effect of two constrained forces, friction force and variable normal load, on the optimization of the shroud contact design.
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Xiong, Cai-Hua, Michael Yu Wang, Yong Tang, and You-Lun Xiong. "On the prediction of passive contact forces of workpiece-fixture systems." Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 219, no. 3 (March 1, 2005): 309–24. http://dx.doi.org/10.1243/095440505x30159.

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The prediction of passive forces in a frictional workpiece-fixture system is an important problem, since the contact forces have a strong influence on clamp design and on workpiece accuracy during machining. This paper presents a general method for the computation of passive contact forces. Firstly, an indeterminate system of static equilibrium is defined, in which the passive, frictional contact forces cannot be determined arbitrarily as in an actively controlled robotic multifinger grasp. Then, a locally elastic contact model is used to describe the non-linear coupling between the contact forces and elastic deformations at the contact point. This model captures the essence of the passive contact. Further, a set of ‘compatibility’ equations is given so that the relationship can be developed between the elastic deformations at all contacts and the displacement of the workpiece. Finally, combining the force equilibrium, the locally elastic contact model and the ‘compatibility’ conditions, the passive force computation problem is transformed into a determinate system of non-linear equations governing all of the elastic deformations at all of the passive contacts. By solving the resulting non-linear equations, all passive contact forces can be accurately predicted in the frictional workpiece-fixture system. This method is illustrated with example cases. The method presented here may also have an application to other passive, indeterminate problems such as power grasps in robotics.
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Petrov, E. P. "Method for Direct Parametric Analysis of Nonlinear Forced Response of Bladed Disks With Friction Contact Interfaces." Journal of Turbomachinery 126, no. 4 (October 1, 2004): 654–62. http://dx.doi.org/10.1115/1.1776588.

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An effective method for direct parametric analysis of periodic nonlinear forced response of bladed disks with friction contact interfaces has been developed. The method allows, forced response levels to be calculated directly as a function of contact interface parameters such as the friction coefficient, contact surface stiffness (normal and tangential coefficients), clearances, interferences, and the normal stresses at the contact interfaces. The method is based on exact expressions for sensitivities of the multiharmonic interaction forces with respect to variation of all parameters of the friction contact interfaces. These novel expressions are derived in the paper for a friction contact model, accounting for the normal load variation and the possibility of separation-contact transitions. Numerical analysis of effects of the contact parameters on forced response levels has been performed using large-scale finite element models of a practical bladed turbine disk with underplatform dampers and with shroud contacts.
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Dissertations / Theses on the topic "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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Books on the topic "Contact forces"

1

Stears, J. H. Roof truss contact forces. Pittsburgh, Pa: U.S. Dept. of the Interior, Bureau of Mines, 1988.

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McAulay, Lex. Contact: Australians in Vietnam. Milsons Point, N.S.W: Hutchinson Australia, 1989.

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Ultimate risk: SAS contact Al Queda. London: Macmillan, 2003.

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Baghbanan, Mohammad reza. Contact forces and surface characterization of aluminum alloys in a vibratory surface finishing process. Ottawa: National Library of Canada, 2002.

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J, Willke Richard, and Center for Health Policy Research (American Medical Association), eds. Physicians and the military: A study of contact, awareness, and interest. Chicago, Ill: American Medical Association, 1987.

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M, Peers Douglas, ed. Warfare and empires: Contact and conflict between European and non-European military and maritime forces and cultures. Aldershot, Great Britain: Ashgate/Variorum, 1997.

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Becqué-Ickowicz, Solange. Le parallélisme des formes en droit privé. Paris: Éditions Panthéon-Assas, 2004.

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Flores, Paulo, and Hamid M. Lankarani. Contact Force Models for Multibody Dynamics. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-30897-5.

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United States. Defense Logistics Agency. [Military Standard Contract Administration Procedures]. Ft. Belvoir, Va. (8725 John J. Kingman Rd., Ste. 2533, Ft. Belvoir 22060-6221): Dense Logistics Agency, Headquarters, 1999.

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A contract officer in the Oman. Tunbridge Wells: Costello, 1988.

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Book chapters on the topic "Contact forces"

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Popov, Valentin L. "Capillary Forces." In Contact Mechanics and Friction, 41–54. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10803-7_4.

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Popov, Valentin L. "Capillary Forces." In Contact Mechanics and Friction, 43–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-53081-8_4.

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Ramtal, Dev, and Adrian Dobre. "Contact and Fluid Forces." In The Essential Guide to Physics for Flash Games, Animation, and Simulations, 181–220. Berkeley, CA: Apress, 2011. http://dx.doi.org/10.1007/978-1-4302-3675-7_7.

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Ramtal, Dev, and Adrian Dobre. "Contact and Fluid Forces." In Physics for JavaScript Games, Animation, and Simulations, 155–86. Berkeley, CA: Apress, 2014. http://dx.doi.org/10.1007/978-1-4302-6338-8_7.

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Goloshchapov, Nikolay. "Method of the Differential Specific Forces (MDSF)." In Contact Dynamics, 23–91. Oakville, ON ; Waretown, NJ : Apple Academic Press, 2018.: Apple Academic Press, 2019. http://dx.doi.org/10.1201/9781351166522-2.

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Borovac, B., L. Nagy, and M. Sabli. "Contact Tasks Realization by Sensing Contact Forces." In ROMANSY 11, 381–88. Vienna: Springer Vienna, 1997. http://dx.doi.org/10.1007/978-3-7091-2666-0_44.

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Goloshchapov, Nikolay. "Method of The Differential Specific Forces in Dynamics of Elastoplastic Contacts." In Contact Dynamics, 203–62. Oakville, ON ; Waretown, NJ : Apple Academic Press, 2018.: Apple Academic Press, 2019. http://dx.doi.org/10.1201/9781351166522-4.

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Knoll, Johannes, Frank Rhein, and Hermann Nirschl. "Determination of the Adhesion Forces of Magnetic Composite Particles." In Particles in Contact, 359–84. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-15899-6_12.

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Schmid, Hans-Joachim, Guido Grundmeier, Michael Dörmann, Alejandro González Orive, Teresa de los Arcos, and Boray Torun. "Understanding and Manipulation of Nanoparticle Contact Forces by Capillary Bridges." In Particles in Contact, 31–65. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-15899-6_2.

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Chien, Chi-Hui, George A. Costello, and Liang-Chaang Chang. "Contact Forces and Stresses in Cables." In Computational Mechanics ’86, 399–406. Tokyo: Springer Japan, 1986. http://dx.doi.org/10.1007/978-4-431-68042-0_53.

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Conference papers on the topic "Contact forces"

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Hotz, G., A. Kerzmann, C. Lennerz, R. Schmid, E. Schömer, and T. Warken. "Calculation of contact forces." In the ACM symposium. New York, New York, USA: ACM Press, 1999. http://dx.doi.org/10.1145/323663.323701.

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Magrini, Emanuele, Fabrizio Flacco, and Alessandro De Luca. "Estimation of contact forces using a virtual force sensor." In 2014 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2014). IEEE, 2014. http://dx.doi.org/10.1109/iros.2014.6942848.

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Kirchenkamp, Svenja, and Dirk So¨ffker. "Reconstruction of the Dynamic Rail-Wheel Contact Forces." In ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/detc2003/vib-48356.

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This contribution introduces a virtual measurement device for the reconstruction of the in practice unmeasureable railwheel contact forces. For this aim the Proportional-Integral (PI)-Observer is used. Then, the concept of a measurement sleeve at the axle bearing is shown. With the displacement measurements resulting from the sleeve using the PI-Observer, an estimation of the tangential contact force and the dynamic normal force is possible. Using the simulation of the rail-wheel contact, the feasibility of the estimation of the contact force behavior is shown. As an outlook for further applications of the PI-Observer in the context of rail-wheel contact force estimation, the reconstruction of contact forces by using acceleration measurements is demonstrated by an example of an elastic beam for the first time.
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Yang, Been-Der, and Chia-Hsiang Menq. "Modeling of Friction Contact and its Application to the Design of Shroud Contact." In ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-gt-472.

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Designers of aircraft engines frequently employ shrouds in turbine design. In this paper, a variable normal load friction force model is proposed to investigate the influence of shroud-like contact kinematics on the forced response of frictionally constrained turbine blades. Analytical criteria are formulated to predict the transitions between slick, slip, and separation of the interface so as to assess the induced friction forces. When considering cyclic loading, the induced friction forces are combined with the variable normal load so as to determine the effective stiffness and damping of the friction joint over a cycle of motion. The harmonic balance method is then used to impose the effective stiffness and damping of the friction joint on the linear structure. The solution procedure for the nonlinear response nf a two-degree-of-freedom oscillator is demonstrated. As an application, this procedure is used to study the coupling effect of two constrained forces, friction force and variable normal load, on the optimization of the shroud contact design.
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Brocker, Richard, Frederik Vits, Patrick Mattfeld, and Fritz Klocke. "Contact Forces in Unguided Vibratory Finishing." In ASME 2015 International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/msec2015-9220.

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In vibratory finishing the material removal rate is influenced by the contact forces between work piece and media. In this paper a measurement system is presented which is capable of measuring the contact forces between work piece and media in unguided vibratory finishing. The unique feature of the measurement system is its completely wireless construction. The measurement results are not influenced by wires of the force sensor system including the electrical power supply and the data logging. By means of this measurement system, contact forces can be measured in unguided vibratory finishing processes for the first time. Furthermore, the influence of media size and adjustment of the unbalance motor like revolution speed, phase angle and mass distribution between the upper and the lower eccentric weight was investigated.
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Siewert, Christian, Lars Panning, Jo¨rg Wallaschek, and Christoph Richter. "Multiharmonic Forced Response Analysis of a Turbine Blading Coupled by Nonlinear Contact Forces." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-59201.

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The rotor blades of a low pressure (LP) steam turbine stage are subjected to high static and dynamic loads during operation. The static loads are mainly due to the centrifugal force and thermal strains, whereas the dynamic loads are caused by fluctuating gas forces resulting in forced vibrations of the blades. The forced vibrations can lead to high cycle fatigue (HCF) failures causing substantial damage and high maintenance effort. Thus, one of the main tasks in the design of LP steam turbine blading is the vibration amplitude reduction in order to avoid high dynamic stresses that could damage the blading. The vibration amplitudes of the blades in a LP steam turbine stage can be reduced significantly to a reasonable amount if adjacent blades are coupled by shroud contacts that reinforce the blading, see Fig. 1. Furthermore, in the case of blade vibrations, relative displacements between neighboring blades occur in the contacts and friction forces are generated that provide additional damping to the structure due to the energy dissipation caused by micro- and macroslip effects. Therefore, the coupling of the blades increases the overall mechanical damping. A three-dimensional structural dynamics model including an appropriate spatial contact model is necessary to predict the contact forces generated by the shroud contacts and to describe the vibrational behavior of the blading with sufficient accuracy. To compute the nonlinear forced vibrations of the coupled blading, the nonlinear equations of motion are solved in the frequency domain owing to the high computational efficiency of this approach. The transformation of the nonlinear equations of motion into the frequency domain can be carried out by representing the steady-state displacement in terms of its harmonic components. After that transformation, the nonlinear forced response is computed as a function of the excitation frequency in the frequency domain.
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Xiongand, Cai-Hua, You-Lun Xiong, and Michael Yu Wang. "On Prediction of Passive Contact Forces of Workpiece-Fixture Systems." In ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/detc2003/dfm-48158.

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Prediction of passive forces in a frictional workpiece-fixture system is an important problem, since the contact forces have a strong influence on clamp design and on workpiece accuracy during machining. This paper presents a general method for the computation of the contact forces. First, based on the rigid-body kinematics, an indeterminate system of static equilibrium is defined, in which the passive, frictional contact forces cannot be determined arbitrarily as in an actively controlled robotic multi-finger grasp. Then, we define a locally elastic contact model to describe the nonlinear coupling between the contact forces and elastic deformations at the contact point. This model captures the essence of the passive contact. Further, a set of “compatibility” equations are given so that the elastic deformations among all passive contacts in the workpiece-fixture system result in a consistent set of rigid-body displacement of the workpiece in its global system. Finally, combining the locally elastic contact model and the “compatibility” conditions, we transform the force computation problem into a determinate system of nonlinear equations governing all of the elastic deformations at all of the passive contacts. By solving the resulting nonlinear equations with frictional constraints, we can accurately predict all contact forces in the frictional workpiece-fixtures system. This method is illustrated with example cases. The method presented here may also have an application to other passive, indeterminate problems such as power grasps in robotics.
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Yusuke Maeda, Koutarou Oda, and Satoshi Makita. "Analysis of indeterminate contact forces in robotic grasping and contact tasks." In 2007 IEEE/RSJ International Conference on Intelligent Robots and Systems. IEEE, 2007. http://dx.doi.org/10.1109/iros.2007.4399022.

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Mohtat, Arash, and Jozsef Kovecses. "Energy-consistent haptic rendering of contact forces." In 2013 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2013). IEEE, 2013. http://dx.doi.org/10.1109/iros.2013.6697005.

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Dahl, Markus, Håkan Wettergren, and Henrik Tidefelt. "Modelica Spur Gears with Hertzian Contact Forces." In The 12th International Modelica Conference, Prague, Czech Republic, May 15-17, 2017. Linköping University Electronic Press, 2017. http://dx.doi.org/10.3384/ecp17132755.

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Reports on the topic "Contact forces"

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Shmulevich, Itzhak, Shrini Upadhyaya, Dror Rubinstein, Zvika Asaf, and Jeffrey P. Mitchell. Developing Simulation Tool for the Prediction of Cohesive Behavior Agricultural Materials Using Discrete Element Modeling. United States Department of Agriculture, October 2011. http://dx.doi.org/10.32747/2011.7697108.bard.

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The underlying similarity between soils, grains, fertilizers, concentrated animal feed, pellets, and mixtures is that they are all granular materials used in agriculture. Modeling such materials is a complex process due to the spatial variability of such media, the origin of the material (natural or biological), the nonlinearity of these materials, the contact phenomenon and flow that occur at the interface zone and between these granular materials, as well as the dynamic effect of the interaction process. The lack of a tool for studying such materials has limited the understanding of the phenomena relevant to them, which in turn has led to energy loss and poor quality products. The objective of this study was to develop a reliable prediction simulation tool for cohesive agricultural particle materials using Discrete Element Modeling (DEM). The specific objectives of this study were (1) to develop and verify a 3D cohesionless agricultural soil-tillage tool interaction model that enables the prediction of displacement and flow in the soil media, as well as forces acting on various tillage tools, using the discrete element method; (2) to develop a micro model for the DEM formulation by creating a cohesive contact model based on liquid bridge forces for various agriculture materials; (3) to extend the model to include both plastic and cohesive behavior of various materials, such as grain and soil structures (e.g., compaction level), textures (e.g., clay, loam, several grains), and moisture contents; (4) to develop a method to obtain the parameters for the cohesion contact model to represent specific materials. A DEM model was developed that can represent both plastic and cohesive behavior of soil. Soil cohesive behavior was achieved by considering tensile force between elements. The developed DEM model well represented the effect of wedge shape on soil behavior and reaction force. Laboratory test results showed that wedge penetration resistance in highly compacted soil was two times greater than that in low compacted soil, whereas DEM simulation with parameters obtained from the test of low compacted soil could not simply be extended to that of high compacted soil. The modified model took into account soil failure strength that could be changed with soil compaction. A three dimensional representation composed of normal displacement, shear failure strength and tensile failure strength was proposed to design mechanical properties between elements. The model based on the liquid bridge theory. An inter particle tension force measurement tool was developed and calibrated A comprehensive study of the parameters of the contact model for the DEM taking into account the cohesive/water-bridge was performed on various agricultural grains using this measurement tool. The modified DEM model was compared and validated against the test results. With the newly developed model and procedure for determination of DEM parameters, we could reproduce the high compacted soil behavior and reaction forces both qualitatively and quantitatively for the soil conditions and wedge shapes used in this study. Moreover, the effect of wedge shape on soil behavior and reaction force was well represented with the same parameters. During the research we made use of the commercial PFC3D to analyze soil tillage implements. An investigation was made of three different head drillers. A comparison of three commonly used soil tillage systems was completed, such as moldboard plow, disc plow and chisel plow. It can be concluded that the soil condition after plowing by the specific implement can be predicted by the DEM model. The chisel plow is the most economic tool for increasing soil porosity. The moldboard is the best tool for soil manipulation. It can be concluded that the discrete element simulation can be used as a reliable engineering tool for soil-implement interaction quantitatively and qualitatively.
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Houston, J. E., and J. G. Fleming. Non-contact atomic-level interfacial force microscopy. Office of Scientific and Technical Information (OSTI), February 1997. http://dx.doi.org/10.2172/453500.

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Nordick, Glenn D. Exploring the Psychological Contract of the Canadian Forces. Fort Belvoir, VA: Defense Technical Information Center, March 1999. http://dx.doi.org/10.21236/ada363948.

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Whitehead, Martha, Dale Askey, Donna Bourne-Tyson, Karen Estlund, Susan Haigh, Claire Stewart, Kornelia Tancheva, Tyler Walters, Jennifer Muilenburg, and Judy Ruttenberg. ARL/CARL Joint Task Force on Research Data Services: Final Report. Association of Research Libraries and Canadian Association of Research Libraries, July 2021. http://dx.doi.org/10.29242/report.arlcarlrdstaskforce2021.

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The Association of Research Libraries (ARL)/Canadian Association of Research Libraries (CARL) Joint Task Force on Research Data Services formed in 2020 with a two-fold purpose: (1) to demonstrate and commit to the roles research libraries have in stewarding research data and as part of institution-wide research support services and (2) to guide the development of resources for the ARL and CARL memberships in advancing their organizations as collaborative partners with respect to research data services in the context of FAIR (findable, accessible, interoperable, and reusable) data principles and the US National Academies’ Open Science by Design framework. Research libraries will be successful in meeting these objectives if they act collectively and are deeply engaged with disciplinary communities. The task force formed three working groups of data practitioners, representing a wealth of expertise, to research the institutional landscape and policy environment in both the US and Canada. This report presents the task force’s recommendations for the roles of research libraries with regard to research data principles, policies, and approaches to managing research data. The report also offers strategies for discipline-specific research data approaches, priorities for automation of processes, economic models to scale and sustain shared resources, prioritization of research data to steward, and decision-making rubrics.
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Law, Edward, Samuel Gan-Mor, Hazel Wetzstein, and Dan Eisikowitch. Electrostatic Processes Underlying Natural and Mechanized Transfer of Pollen. United States Department of Agriculture, May 1998. http://dx.doi.org/10.32747/1998.7613035.bard.

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The project objective was to more fully understand how the motion of pollen grains may be controlled by electrostatic forces, and to develop a reliable mechanized pollination system based upon sound electrostatic and aerodynamic principles. Theoretical and experimental analyses and computer simulation methods which investigated electrostatic aspects of natural pollen transfer by insects found that: a) actively flying honeybees accumulate ~ 23 pC average charge (93 pC max.) which elevates their bodies to ~ 47 V likely by triboelectrification, inducing ~ 10 fC of opposite charge onto nearby pollen grains, and overcoming their typically 0.3-3.9 nN detachment force resulting in non-contact electrostatic pollen transfer across a 5 mm or greater air gap from anther-to-bee, thus providing a theoretical basis for earlier experimental observations and "buzz pollination" events; b) charge-relaxation characteristics measured for flower structural components (viz., 3 ns and 25 ns time constants, respectively, for the stigma-style vs. waxy petal surfaces) ensure them to be electrically appropriate targets for electrodeposition of charged pollen grains but not differing sufficiently to facilitate electrodynamic focusing onto the stigma; c) conventional electrostatic focusing beneficially concentrates pollen-deposition electric fields onto the pistill tip by 3-fold as compared to that onto underlying flower structures; and d) pollen viability is adequately maintained following exposure to particulate charging/management fields exceeding 2 MV/m. Laboratory- and field-scale processes/prototype machines for electrostatic application of pollen were successfully developed to dispense pollen in both a dry-powder phase and in a liquid-carried phase utilizing corona, triboelectric, and induction particulate-charging methods; pollen-charge levels attained (~ 1-10 mC/kg) provide pollen-deposition forces 10-, 77-, and 100-fold greater than gravity, respectively, for such charged pollen grains subjected to a 1 kV/cm electric field. Lab and field evaluations have documented charged vs. ukncharged pollen deposition to be significantly (a = 0.01-0.05) increased by 3.9-5.6 times. Orchard trials showed initial fruit set on branches individually treated with electrostatically applied pollen to typically increase up to ~ 2-fold vs. uncharged pollen applications; however, whole-tree applications have not significantly shown similar levels of benefit and corrective measures continue. Project results thus contribute important basic knowledge and applied electrostatics technology which will provide agriculture with alternative/supplemental mechanized pollination systems as tranditional pollen-transfer vectors are further endangered by natural and man-fade factors.
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Johansen, William A. Contract versus Military Pilot Training in Today's Air Force. Fort Belvoir, VA: Defense Technical Information Center, May 1987. http://dx.doi.org/10.21236/ada202155.

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Westphal, Lynne M., Michael J. Dockry, Lincoln Bramwell, Hutch Brown, Jim Lootens-White, Laura S. Kenefic, Sonya S. Sachdeva, Dexter H. Locke, Cherie L. Fisher, and Karl Hess. Forest Service Diversity in Context. Madison, WI: U.S. Department of Agriculture, Forest Service, Northern Research Station, 2022. http://dx.doi.org/10.2737/fs-diversity-inclusion-timeline.

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Cairney, John T. Considerations in Working With Partner Air Forces - Context and Culture. Fort Belvoir, VA: Defense Technical Information Center, March 2010. http://dx.doi.org/10.21236/ada519920.

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Dolado, Juan J., Etienne Lalé, and Hélène Turon. Zero-hours Contracts in a Frictional Labor Market. CIRANO, January 2022. http://dx.doi.org/10.54932/hvdc9170.

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We propose a model to evaluate the U.K.’s zero-hours contract (ZHC) – a contract that exempts employers from the requirement to provide any minimum working hours, and allows workers to decline any workload. We find quantitatively mixed welfare effects of ZHCs. On one hand they unlock job creation among firms that face highly volatile business conditions and increase labor force participation of individuals who prefer flexible work schedules. On the other hand, the use of ZHCs by less volatile firms, where jobs are otherwise viable under regular contracts, reduces welfare and likely explains negative employee reactions to this contract.
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Ertanowska, Delfina. Media offer for Ukrainian children and teenagers in former Yugoslavia countries. Ivan Franko National University of Lviv, February 2022. http://dx.doi.org/10.30970/vjo.2022.51.11403.

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The article discusses the media offer addressed to children and youth from the Ukrainian national minority in the former Yugoslavia countries. The content, languages of publications and forms of publication were analyzed. In addition to traditional paper press and periodicals, the content published in digital form, in social media such as Facebook, Instagram, were also analyzed.
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