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Статті в журналах з теми "Frictional contact model":
1
Chang, L., and H. Zhang. "A Mathematical Model for Frictional Elastic-Plastic Sphere-on-Flat Contacts at Sliding Incipient." Journal of Applied Mechanics 74, no. 1 (December 9, 2005): 100–106. http://dx.doi.org/10.1115/1.2178838.
Анотація:
This paper presents a mathematical model for frictional elastic-plastic sphere-on-flat contacts at sliding incipient. The model is developed based on theoretical work on contact mechanics in conjunction with finite-element results. It incorporates the effects of friction loading on the contact pressure, the mode of deformation, and the area of contact. The shear strength of the contact interface is, in this paper, assumed to be proportional to the contact pressure with a limiting value that is below the bulk shear strength of the sphere. Other plausible interfacial-shear-strength characteristics may also be implemented into the contact model in a similar manner. The model is used to analyze the frictional behavior of a sphere-on-flat contact where the experimental data suggest that the interfacial shear strength is similar in nature to the one implemented in the model. The theoretical results are consistent with the experimental data in all key aspects. This sphere-on-flat contact model may be used as a building block to develop an asperity-based contact model of rough surfaces with friction loading. It may also serve in the modeling of boundary-lubricated sliding contacts where the interfacial shear strength in each micro-contact is coupled with its flash temperature and related to the lubricant/surface physical-chemical behavior.
2
Yu, Chunxiao, Dinghui Jing, Chang Fu, and Yanfang Yang. "A Kind of FM-BEM Penalty Function Method for a 3D Elastic Frictional Contact Nonlinear System." Journal of Mathematics 2021 (January 13, 2021): 1–11. http://dx.doi.org/10.1155/2021/6626647.
Анотація:
In this paper, a kind of node_face frictional contact FM-BEM penalty function method is presented for 3D elastic frictional contact nonlinear problems. According to the principle of minimum potential energy, nonpenetrating constraints are introduced into the elastic frictional contact system as a penalty term. By using the least square method and penalty function method, an optimization mathematical model and a mathematical programming model with a penalty factor are established for the node_face frictional contact nonlinear system. For the two models, a penalty optimization IGMRES (m) algorithm is proposed, and the influences of different penalty factors on the solution of the whole system are analyzed. Finally, a numerical simulation is carried out for two elastic frictional contact objects, and some important results including displacements, pressures, friction forces, and friction slips in the contact area are presented. Theoretical analysis and numerical experiment show that the newly presented FM-BEM penalty function method not only is efficient and practical but also has much superiority. It is easy to implement, and it is fast convergent with good stability.
3
Li, Zheng, and Ken Mao. "Frictional Effects on Gear Tooth Contact Analysis." Advances in Tribology 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/181048.
Анотація:
The present paper concentrates on the investigations regarding the situations of frictional shear stress of gear teeth and the relevant frictional effects on bending stresses and transmission error in gear meshing. Sliding friction is one of the major reasons causing gear failure and vibration; the adequate consideration of frictional effects is essential for understanding gear contact behavior accurately. An analysis of tooth frictional effect on gear performance in spur gear is presented using finite element method. Nonlinear finite element model for gear tooth contact with rolling/sliding is then developed. The contact zones for multiple tooth pairs are identified and the associated integration situation is derived. The illustrated bending stress and transmission error results with static and dynamic boundary conditions indicate the significant effects due to the sliding friction between the surfaces of contacted gear teeth, and the friction effect can not be ignored. To understand the particular static and dynamic frictional effects on gear tooth contact analysis, some significant phenomena of gained results will also be discussed. The potentially significant contribution of tooth frictional shear stress is presented, particularly in the case of gear tooth contact analysis with both static and dynamic boundary conditions.
4
Wingertszahn, Patrick, Oliver Koch, Lorenzo Maccioni, Franco Concli, and Bernd Sauer. "Predicting Friction of Tapered Roller Bearings with Detailed Multi-Body Simulation Models." Lubricants 11, no. 9 (September 1, 2023): 369. http://dx.doi.org/10.3390/lubricants11090369.
Анотація:
In the presented work, a parametric multibody simulation model is presented that is capable of predicting the friction torque and kinematics of tapered roller bearings. For a highly accurate prediction of bearing friction, consideration of solid and lubricant friction is mandatory. For tapered roller bearings in particular, the friction in the contact between the rolling element and raceway is of importance. Friction forces in the contact between the rolling element end face and inner ring rib as well as roller cage pocket contacts are also considered in the model. A large number of tests were carried out to validate the model in terms of the simulated frictional torque. Influencing variables such as speed, axial load, radial load, and temperature were investigated. The simulation results show good agreement with the measured friction torque, which confirms that the model is well suited to predict frictional torques and therefore the kinematics of tapered roller bearings.
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BAJKOWSKI, J., J. R. FERNÁNDEZW, K. L. KUTTLER, and M. SHILLOR. "A thermoviscoelastic beam model for brakes." European Journal of Applied Mathematics 15, no. 2 (April 2004): 181–202. http://dx.doi.org/10.1017/s0956792503005370.
Анотація:
A model for the dynamic thermomechanical behavior of a viscoelastic beam which is in frictional contact with a rigid rotating wheel is presented. It describes a simple braking system in which the wheel comes to a stop as a result of the frictional traction generated by the beam. Friction is modelled with a temperature and slip rate dependent coefficient of friction. Frictional heat generation is taken into account as well as the wheel temperature evolution, and the wear of the beam's contacting end. The model is formulated as a variational inequality. A FEM numerical scheme for the model is described, implemented, and the results of numerical simulations are shown.
6
ABDALLA, W. S., S. S. ALI-ELDIN, and M. R. GHAZY. "ADAPTIVE INCREMENTAL FINITE ELEMENT PROCEDURE FOR SOLVING ELASTOPLASTIC FRICTIONAL CONTACT PROBLEMS SUBJECTED TO NORMAL AND TANGENTIAL LOADS." International Journal of Applied Mechanics 06, no. 03 (May 6, 2014): 1450031. http://dx.doi.org/10.1142/s1758825114500318.
Анотація:
This paper presents a numerical model for analyzing the stresses and displacements of deformable bodies in contact with the presence of friction and material nonlinearity. Based on the finite element method (FEM), the elastoplastic frictional contact problem is formulated as an incremental convex programming model (ICPM) under inequality contact constraints and friction conditions. The classical Coulomb's friction law and the Prandtl–Reuss flow rule with the von Mises yield criterion are used to simulate the interface friction conditions and the elastoplastic behavior of the contacting bodies, respectively. The Lagrange multiplier approach is adopted for imposing the contact constraints. Furthermore, an effective adaptive incremental procedure is developed for solving the elastoplastic frictional contact problems. Examples for the frictional contact having advancing and receding nature are analyzed. The obtained results prove the ability of the developed procedure to investigate the sequence of different events during monotonic application of external loads. In addition, the results elucidate the effect of external side force on the friction behavior in the presence of plastic deformation. Good agreement has been found with published results.
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Dickrell, P. L., W. G. Sawyer, and A. Erdemir. "Fractional Coverage Model for the Adsorption and Removal of Gas Species and Application to Superlow Friction Diamond-Like Carbon." Journal of Tribology 126, no. 3 (June 28, 2004): 615–19. http://dx.doi.org/10.1115/1.1739408.
Анотація:
The frictional behavior of diamond-like carbon (DLC) films varies with environmental condition. One theory asserts that the cause of variations in the frictional performance is environmental contaminants adsorbing onto the DLC film surface. Testing of the frictional performance of DLC films in a pin-on-disk contact has mapped the transient behavior of the friction coefficient. A model for fractional coverage, based on the adsorption of environmental contaminants and their removal through the pin contact, is developed. The rate of adsorption is taken from Langmuir’s model [17], which is combined with the removal ratio from Blanchet and Sawyer [18]. The coefficient of friction is based on the average fractional coverage under the pin contact. The model also gives a closed-form expression for the steady-state fractional coverage. Model calculations compared favorably to the time progression of the friction coefficient for a series of earlier experiments on a superlow friction DLC coating [7], when the fractional removal term was allowed to increase with increasing sliding speed.
8
Murphey, Todd D. "Kinematic reductions for uncertain mechanical contact." Robotica 25, no. 6 (November 2007): 751–64. http://dx.doi.org/10.1017/s0263574707003827.
Анотація:
SUMMARYThis paper describes the methods applicable to the modeling and control of mechanical contact, particularly those systems that experience uncertain stick/slip phenomena. Geometric kinematic reductions are used to reduce a system's description from a second-order dynamic model with frictional disturbances coming from a function space to a first-order model with frictional disturbances coming from a space of finite automata over a finite set. As a result, modeling for purposes of control is made more straight-forward by getting rid of some dependencies on low-level mechanics (in particular, the details of friction modeling). Moreover, the online estimation of the uncertain, discrete-valued variables has reduced sensing requirements. The primary contributions of this paper are the introduction of a simplifying representation of friction and formal tests for kinematic reducibility. Results are illustrated using a slip-steered vehicle model and an actuator array model.
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Chang, L., Yongwu Zhao, P. B. Hall, R. Thom, and C. Moore. "On Heat Generation in Rolling Contacts Under Boundary and Mixed Lubrication." Journal of Tribology 123, no. 1 (August 17, 2000): 61–66. http://dx.doi.org/10.1115/1.1330733.
Анотація:
This paper reports on experiments and theoretical analyses of heat generation and scuffing failure in rolling contacts. The experiments were conducted with dry contacts, and the theoretical analyses were carried out using a deterministic thermal contact model. The research reveals that heat generated by asperity plastic deformation in the direction normal to the contact can be significant in high-load, high-speed contacts under boundary and mixed lubrication conditions. Under near rolling conditions, heat generated by the plastic deformation largely dominates that by the friction and is the main source leading to contact scuffing. This heat generation is shown to be significant compared to frictional heating even at relatively large slide-to-roll ratios. Parametric studies show that the ratio of asperity-plastic-deformation heating to frictional heating is sensitive to slide-to-roll ratio, hardness and surface finish but insensitive to contact load, rolling velocity and fluid/asperity load sharing.
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Heß, Markus, and Valentin L. Popov. "Voltage-Induced Friction with Application to Electrovibration." Lubricants 7, no. 12 (November 20, 2019): 102. http://dx.doi.org/10.3390/lubricants7120102.
Анотація:
Due to the growing interest in robotic and haptic applications, voltage-induced friction has rapidly gained in importance in recent years. However, despite extensive experimental investigations, the underlying principles are still not sufficiently understood, which complicates reliable modeling. We present a macroscopic model for solving electroadhesive frictional contacts which exploits the close analogy to classical adhesion theories, like Johnson-Kendall-Roberts (JKR) and Maugis, valid for electrically neutral bodies. For this purpose, we recalculate the adhesion force per unit area and the relative surface energy from electrostatics. Under the assumption of Coulomb friction in the contact interface, a closed form equation for the friction force is derived. As an application, we consider the frictional contact between the fingertip and touchscreen under electrovibration in more detail. The results obtained with the new model agree well with available experimental data of the recent literature. The strengths and limitations of the model are clearly discussed.
Дисертації з теми "Frictional contact model":
1
Do, Nguyen Ba. "Modeling of Frictional Contact Conditions in Structures." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7123.
Анотація:
This thesis explores two aspects of modeling the behavior of joint friction in structures. The first aspect deals with the accurate and efficient simulation of a simple system that incorporates the LuGre friction law. Energy transfer and dissipation in a structural joint model is the second topic of this thesis. It is hypothesized that friction could serve to pump energy from one frequency to higher frequencies where it might be dissipated more quickly. Motivation for this study stems from the need to have accurate models of high-precision space structures. Because friction at connecting joints plays a major role in the damping capacity of the structure, a good understanding of this mechanism is necessary to predict the vibratory response and enhance the energy dissipation of the structure.
Simulation results of a dynamic system with LuGre friction show that the system is relatively well-conditioned when the slip velocity is small, and ill-conditioned for large slip velocities. Furthermore, the most efficient numerical method to simulate this system is determined to be an implicit integration scheme. To study the energy transfer and dissipation, two models of a jointed structure with friction are considered. Results from the steady-state forced responses of the two structural systems indicate that friction converted low frequency, single harmonic excitation to multi-harmonic response through internal resonances. However, differences in energy dissipation results between the models show that the response of a frictional system is highly sensitive to system parameters and friction laws. Conclusions and suggestions for future research are also discussed.
2
de, Carufel Jean. "Model predictive control of a manipulator arm with frictional/unilateral contact." Thesis, University of Ottawa (Canada), 1998. http://hdl.handle.net/10393/4114.
Анотація:
Controlling mechanisms whose equations of motion involve nonlinear discontinuous terms is difficult. A robot manipulator doing a task requiring intermittent contacts with the environment is such a system. Historically, the difficulty was avoided by splitting the global control problem into subproblems defined by the smooth structures of the piecewise discontinuous model. As a result, algorithms for controlling robot manipulators in free motion, transition to contact (impact control) and force/motion in contact were obtained separately and implementation was done using a switching law. In this thesis, nonlinear Model Predictive Control (MPC) is proposed as a unified solution for controlling robot manipulators with intermittent contacts. The use of a model-based prediction over a receding horizon allows MPC to foresee discontinuous changes in the dynamics and smoothly adjust the control command. Therefore, it was used extensively in the process industry where state and control command saturations are often present. The first contribution in this thesis lies in the use of MPC for controlling systems with discontinuities in the equations of motion. Through analysis and simulation, the ability of the nonlinear MPC approach to provide a unifying solution is demonstrated. The literature on nonlinear MPC being almost inexistent, the work presented herein also contributes to the understanding of how MPC can be applied to nonlinear systems. Because the complete analytical solution of the nonlinear MPC problem is not prone to real-time applications, two implementation alternatives are also proposed. Both use the operational space information about the task to perform to reduce considerably how much computation is necessary for a solution. The first approach is similar to the resolved-acceleration algorithm with the resolved acceleration being computed from a reduced MPC problem. The second is called the predictive impedance algorithm since its formulation is similar to impedance control with the impedance being replaced by the output of a reduced MPC problem. The applicability of both algorithms has been demonstrated through simulation. Experimental results were also obtained for the predictive impedance solution.
3
De, Carufel Jean. "Model predictive control of a manipulator arm with frictional/unilateral contact." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0002/NQ32441.pdf.
4
Nykänen, Robin. "Simulation of Bolted Joint with Frictional Contacts." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-74490.
Анотація:
An easy and reliable way to join two or more components is to use a bolted joint. When torque is applied on the bolt head, a clamp force is achieved. However about 90% of this torque will be used just to overcome the friction in the interfaces. To be able to fasten these in an ecient and precise manner the friction in the bolt threads and underhead area is important to understand. This is currently investigated at Atlas Copco by using a friction test rig, FTR, which measures the clamp force, the total torque and the shank torque. To evaluate the test rig and also to be able to evaluate dierent friction models, a parameterised simulation model of a bolted joint is built. This is a 3D-model of the joint containing a bolt, a nut and a test specimen. The stiness and frictional behaviour of the FTR is used in the model to get a good comparison between these two. Dierent contact formulations and settings are tested to achieve a good model. Also, mesh size, step size and material models are evaluated to see the eect of these. The results show a good correlation between the FTR data and the simulation model. For the total torque to clamp force ratio a dierence of about 1% is achieved. The average dierence in shank torque and underhead torque is at 3.1% and -1.6% respectively. The pressure distribution for this model is shown to be unevenly distributed along the threads. This is minimized by softening the contact, but this instead increases the error between the FTR data and the simulation model. For the evaluation of friction models that are based on the contact pressure this needs to be investigated further to nd a good compromise between the contact pressure and the frictional behaviour.
5
DESHMUKH, DINAR V. "PHYSICS BASED REDUCED ORDER MODELS FOR FRICTIONAL CONTACTS." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1115997302.
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Giacoma, Anthony. "Efficient acceleration techniques for non-linear analysis of structures with frictional contact." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0095.
Анотація:
La mécanique computationnelle est un outil incontournable pour le monde de l’ingénierie mécanique. Motivé par un désir de réalisme et soumis à un perpétuel gigantisme, les modèles numériques doivent aujourd’hui inclure des phénomènes physiques de plus en plus complexes. Par conséquence, d’importantes capacités calculatoires sont requises afin de traiter des problèmes à la fois non-linéaires mais aussi de grande taille. Pour atteindre cet objectif, il convient de développer les stations de calculs mais aussi les méthodes algorithmiques utilisées afin de résoudre efficacement ces types de problèmes. Récemment, les méthodes de réduction de modèle se révèlent comme d’excellentes options au développement d’algorithmes de résolution performants. Le problème du contact frottant entre solides élastiques est particulièrement bien connu pour sa complexité et dont les temps de calcul peuvent devenir prohibitifs. En effet, les lois qui le régissent sont très hautement non-linéaires (non différentiables). Dans ce mémoire, nous nous proposons d’appliquer différentes méthodes de réduction de modèle (a posteriori et a priori) à ce type de problème afin de développer des méthodes de calculs accélérées dans le cadre de la méthode des éléments finis. Tout d’abord, en se plaçant dans le cadre des petites perturbations en évolution quasistatique, la réductibilité de diverses solutions impliquant du contact frottant est mise en évidence via leur décomposition en valeur singulière. De plus, leur contenu à échelle séparée est exhibé. La méthode non-incrémentale et non-linéaire à large incrément de temps (LATIN) est par la suite présentée. Dans un second temps et à partir des observations faites précédemment, une méthode LATIN accélérée est proposée en s’inspirant des méthodes multigrilles non-linéaires de type “full approximation scheme” (FAS). Cette méthode s’apparente en partie aux méthodes de réduction de modèle de type a posteriori. De plus, une stratégie de calcul de modes à partir d’un modèle de substitution est proposée. Par la suite, la décomposition propre généralisée (PGD) est utilisée afin de développer une méthode de résolution non-linéaire efficace reposant fondamentalement sur une approche de réduction de modèle de type a priori. Enfin, quelques extensions sont proposées telle que la résolution de problème faisant intervenir des études paramétriques, ou encore la prise en charge de non-linéarités supplémentaires telle que la plasticitéComputational mechanics is an essential tool for mechanical engineering purposes. Nowadays, numerical models have to take into account complex physical phenomenons to be even more realistic and become larger and larger. As a consequence, more and more computing capacities are required in order to tackle not only non-linear problems but also large scale problems. For that purpose, both computers and numerical methods have to be developed in order to solve them efficiently. In the last decades, model reduction methods show great abilities to assign such challenges. The frictional contact problem between elastic solids is particularly well-known for its difficulty. Because its governing laws are highly non-linear (non-smooth), prohibitive computational time can occur. In this dissertation, model reduction methods (both a posteriori and a priori approaches) are deployed in order to implement efficient numerical methods to solve frictional contact problem in the finite element framework. First, small perturbations hypothesis with a quasi-static evolution are assumed. Then, reducibility of some frictional solutions is emphasized and discussed using the singular value decomposition. In addition, a scale separability phenomenon is enlightened. Then, the non-linear large time increment method (LATIN) is introduced. Secondly, an accelerated LATIN method is suggested by drawing an analogy between previous scale separability observations and the non-linear multigrid full approximation scheme (FAS). This accelerated non-linear solver relies essentially on the a posteriori model reduction approach. A precomputation strategy for modes relying on surrogate models is also suggested. Next, the proper generalized decomposition (PGD) is used to implement a non-linear solver relying fundamentally on an a priori model reduction method. Finally, some extensions are given to assign parametric studies and to take into account an additional non-linearity such as elastoplastic constitutive laws
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Filippis, Hugo de. "Dynamique non linéaire du contact inter-aubes de turbine : caractérisation expérimentale et simulation numérique." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2023. http://www.theses.fr/2023ECDL0056.
Анотація:
Dans la perspective d’une amélioration des performances et de l’efficacité de la génération future des turboréacteurs, et afin de respecter les réglementations environnementales évolutives concernant les pollutions diverses émises par ces machines, les industriels du secteur de l’aéronautique cherchent des solutions technologiques adaptées. Parmi l’ensemble des pistes étudiées par les fabricants, l’augmentation de la vitesse de rotation de la turbine basse pression au sein du turboréacteur est envisagée pour augmenter le rendement global, en contrepartie du renforcement des phénomènes vibratoires complexes, dont il est nécessaire de maîtriser en phase de conception. En effet, la turbine basse pression qui compose les turboréacteurs de la génération LEAP a la particularité d’être constituée d’un assemblage d’aubes dont la géométrie intègre un talon à l’extrémité supérieure de celles-ci. L’ensemble des talons vient alors s’emboîter les uns avec les autres lors du montage des aubes sur le disque, appliquant de ce fait une précharge statique sur celles-ci, grâce à un angle de prétorsion prévu dès la phase de conception. La fonctionnalité de ce talon est double : d’une part il sert à garantir l’étanchéité de la veine aérodynamique en limitant les pertes fluides du flux d’air traversant les aubes, et d’autre part il introduit un amortissement par frottement par le biais du contact entre les talons des aubes fixées sur le disque, permettant ainsi de réduire l’amplitude de vibration de celles-ci. L’objectif de cette thèse est alors de pouvoir reproduire le comportement dynamique non-linéaire d’une aube de turbine basse pression sur un modèle numérique, et de valider les résultats obtenus à l’aide d’un banc d’essai expérimental académique. Pour ce faire, une étude bibliographique est menée afin d’établir un état de l’art des bancs d’essai expérimentaux existant, leurs spécificités, les observations réalisées, le matériel employé, etc., afin de positionner par rapport à la littérature le banc d’essai académique conçu dans le cadre de cette thèse, compte-tenu des spécifications souhaitées. Une fois la conception et la fabrication du banc d’essai abouties, des essais préliminaires nécessaires au déverminage de celui-ci sont réalisés, notamment des analyses modales des aubes ainsi que des essais de torsion pour la calibration de jauges de déformation afin de mesurer la précharge statique lors de l’assemblage des aubes sur le banc d’essai. Des réponses forcées sur la plage de fréquence du premier mode de flexion de la structure ont été réalisées à l’aide d’une excitation par un sinus pas à pas pour différence configurations de précharge statique. De même, la construction du modèle numérique ainsi que la réalisation de calculs de réponses fréquentielles non-linéaires implique la compréhension et le maniement de méthodologies spécifiques, notamment pour traiter les forces non-linéaires liées au contact avec frottement entre les talons des aubes. Par ailleurs, une problématique supplémentaire, intrinsèque à la construction du modèle éléments finis reproduisant la précharge statique par prétorsion des aubes, est la non-coïncidence des maillages des interfaces de contact, nécessitant dans un premier temps de les contraindre pour les rendre suffisamment réguliers afin de conserver la construction d’éléments de contact nœud à nœud. Dans un second temps, une méthode permettant de traiter cette problématique est proposée, à partir d’une courte bibliographie et en prenant en compte les différentes méthodologies de calcul, des réponses fréquentielles supplémentaires sont alors calculéesWith a view of improving the performance and efficiency of the future generation of turbojet engines, and in order to comply with evolving environmental regulations concerning the various pollutants emitted by these machines, aerospace manufacturers are looking for suitable technological solutions. Among all the avenues studied by the manufacturers, increasing the rotational speed of the low-pressure turbine within the turbojet engine is envisaged to increase overall efficiency, in return for the reinforcement of complex vibratory phenomena which need to be taken into account during the design phase. In fact, the low-pressure turbine used in the LEAP generation of jet engines has the particularity of being made up of an assembly of blades whose geometry incorporates a shroud at the upper end of them. All the shrouds interlock with each other when the blades are mounted on the disc, thereby applying a static pre-load to the blades, thanks to a pre-twist angle provided for at the design stage. The function of this shroud is twofold: on the one hand, it serves to guarantee the tightness of the airfoil by limiting the fluid losses of th airflow passing through the blades, and on the other hand, it introduces frictional damping through contact between each blade fixed on the disc, thus reducing their vibration amplitude. The aim of this thesis is to reproduce the non-linear dynamic behavior of a low-pressure turbine blade on a numerical model, and to validate the results obtained using an academic experimental test bench. To this end, a bibliographical study is carried out to establish the state of the art of existing experimental test benches, their specific features, the observations made, the equipment used, etc., in order to position the academic test bench designed as part of this thesis in relation to the literature, taking into account the desired specifications. Once the design and manufacture of the test bench have been completed, the preliminary tests required for its debugging are carried out, including modal analysis of the blades and torsion tests for the calibration of strain gauges to measure the static pre-load when the blades are assembled on the test bench. Forced responses over the frequency range of the structure’s first bending mode have been achieved using step sinus excitation for different static pre-load configurations. Similarly, building the numerical model and calculating non-linear frequency responses requires an understanding and handling of specific methodologies, particularly for dealing with the non-linear forces associated with the frictional contact between the blades shrouds. An additional problem, intrinsic to the construction of the finite element model reproducing the static pre-loading by blade pre-twisting, is the non-coincidence of the meshes of the contact interfaces, necessitating firstly to constrain them to make them sufficiently regular in order to preserve the construction of node-to-node contact elements. Secondly, a method for dealing with this problem is proposed, based on a short bibliography, and taking into account the various calculation methodologies, additional frequency responses are then calculated
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Cazier, Olivier. "Instabilités dynamiques de systèmes frottants en présence de variabilités paramétriques - Application au phénomène de crissement." Phd thesis, Université de Valenciennes et du Hainaut-Cambresis, 2012. http://tel.archives-ouvertes.fr/tel-00830950.
Анотація:
Lors de la conception d'un frein, le confort et le bien-être du consommateur font partie des critères principaux. En effet, les instabilités de crissement, qui engendrent une des pollutions acoustiques les plus importantes, représentent un challenge actuel pour la communauté scientifique et les industriels du domaine. Dans le cadre de cette thèse, nous nous sommes intéressés à la mise en évidence du caractère variable du crissement, observé pour deux systèmes de freinage d'un même véhicule, grâce à des plans d'expériences, expérimental et numérique. Pour être représentatif d'une famille de structures, il est désormais indéniable qu'il faille prendre en compte les variabilités observées sur de multiples paramètres liés au système étudié dès la phase de conception. L'enrichissement des simulations déterministes actuelles nécessite la mise en place d'outils non déterministes rapides et respectant le conservatisme des solutions étudiées. Pour ce faire, nous avons contribué au développement de méthodes numériques dédiées à la propagation des données floues dans le cas des graphes de coalescence, à la détermination des positions d'équilibre de corps en contact frottant à partir d'une méthode de régulation basée sur la logique floue. Cette solution permet d'appliquer une technique de projection pour réduire le coût numérique en utilisant des bases modales des composants réanalysées par un développement homotopique.
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wu, yunxian, and yiyun wang. "A Drucker-Prager model for elastic contact with friction." Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-16693.
Анотація:
In mumerical contact simulations with friction, the simple Coloumb law is usually employed. Standard plasticity models are difficult to use since the balance enforced on the contact surface typically only involves balance of traction vectors, and does not use the full stress tensor on the interface. In this work we describe an approach that allows for the use of the stress tensor, thus opening up the possibility of using more advanced plasticity models. We exemplify this approach by implementing the Drucker-Prager pressure sensitive plasticity model.
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Vadakkeveetil, Sunish. "Analytical Modeling for Sliding Friction of Rubber-Road Contact." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/79596.
Анотація:
Rubber friction is an important aspect to tire engineers, material developers and pavement engineers because of its importance in the estimation of forces generated at the contact, which further helps in optimizing tire and vehicle performances, and to estimate tire wear. It mainly depends on the material properties, contact mechanics and operating condition. There are two major contributions to rubber friction, due to repeated viscoelastic deformation from undulations of surface called hysteresis and due to Vander Waals interaction of the molecules called adhesion. The study focuses on analytical modeling of friction for stationary sliding of rubber block on rough surfaces. Two novel approaches are discussed and compared. Frictional shear stress is obtained from the energy dissipated at the contact interface due to the elastic deformations of rubber block at different length scales. Contact mechanics theories based on continuity approach combined with stochastic processes to estimate the real contact area, mean penetration depth and true stresses at contact depending on operating conditions. Rubber properties are highly temperature dependent. Temperature model developed based on heat diffusion relation is integrated to consider the effects of temperature rise due to frictional heating.
Model results are validated with theoretical results of literature. Simulation results of friction model is obtained for Compound A sliding on rough surface. Material properties are obtained using Dynamic Mechanical Analysis and Time temperature superposition. Influence of the friction models under different conditions are discussed. Model results are validated with experimental data from Dynamic friction tester on a 120-grit surface followed by future works.Master of Science
Книги з теми "Frictional contact model":
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Tanner, John A. Computational methods for frictional contact with applications to the space shuttle orbiter nose-gear tire: Development of frictional contact algorithm. Hampton, Va: Langley Research Center, 1996.
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Tanner, John A. Computational methods for frictional contact with applications to the space shuttle orbiter nose-gear tire: Comparisons of experimental measurements and analytical predictions. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1996.
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Antràs, Pol. Contractual frictions and global sourcing. Cambridge, Mass: National Bureau of Economic Research, 2006.
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Eck, Christof. Unilateral contact problems: Variational methods and existence theorems. Boca Raton: Chapman & Hall/CRC Press, 2005.
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Awrejcewicz, J. Nonsmooth dynamics of contacting thermoelastic bodies. New York, NY: Springer, 2009.
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Awrejcewicz, J. Nonsmooth dynamics of contacting thermoelastic bodies. New York, NY: Springer, 2009.
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Awrejcewicz, J. Nonsmooth dynamics of contacting thermoelastic bodies. New York, NY: Springer, 2009.
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Sextro, Walter. Dynamical Contact Problems with Friction: Models, Methods, Experiments and Applications. 2nd ed. Springer, 2007.
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Sextro, Walter. Dynamical Contact Problems with Friction: Models, Methods, Experiments and Applications. Springer, 2010.
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Sextro, Walter. Dynamical Contact Problems with Friction: Models, Methods, Experiments and Applications. Springer, 2013.
Частини книг з теми "Frictional contact model":
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Barboteu, Mikael, David Danan, and Mircea Sofonea. "A Hyperelastic Dynamic Frictional Contact Model with Energy-Consistent Properties." In Advances in Mechanics and Mathematics, 249–75. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-14490-0_10.
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Maiba, I. A., V. V. Maiba, and D. V. Glazunov. "Mathematical Model of Railway Vehicle Moving Along Track with Nonlinear Variable Characteristic of Friction Ratio in Zone of Wheel Frictional Contact with Rail." In Lecture Notes in Mechanical Engineering, 1254–62. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-54814-8_145.
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Sextro, Walter. "Point Contact Model." In Dynamical Contact Problems with Friction, 29–75. Berlin, Heidelberg: Springer Berlin Heidelberg, 2002. http://dx.doi.org/10.1007/978-3-540-46871-4_3.
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Goedecke, Andreas. "The MIMEAC Contact Model." In Transient Effects in Friction, 119–62. Vienna: Springer Vienna, 2013. http://dx.doi.org/10.1007/978-3-7091-1506-0_6.
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Popov, Valentin L. "The Prandtl-Tomlinson Model for Dry Friction." In Contact Mechanics and Friction, 155–74. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10803-7_11.
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Popov, Valentin L. "The Prandtl-Tomlinson Model for Dry Friction." In Contact Mechanics and Friction, 173–92. Berlin, Heidelberg: Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-53081-8_11.
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Shillor, Meir, Mircea Sofonea, and Józef Joachim Telega. "10 Slip or Temperature Dependent Frictional Contact." In Models and Analysis of Quasistatic Contact, 163–82. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-540-44643-9_10.
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Mróz, Zenon. "Contact Friction Models and Stability Problems." In Friction and Instabilities, 179–232. Vienna: Springer Vienna, 2002. http://dx.doi.org/10.1007/978-3-7091-2534-2_5.
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Strömberg, Niclas, Lars Johansson, and Anders Klarbring. "A Generalised Standard Model for Contact, Friction and Wear." In Contact Mechanics, 327–34. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1983-6_44.
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Konyukhov, Alexander, and Karl Schweizerhof. "Experimental Validations of the Coupled Anistropic Adhesion-Friction Model." In Computational Contact Mechanics, 367–80. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-31531-2_12.
Тези доповідей конференцій з теми "Frictional contact model":
1
Song, Peng, and Vijay Kumar. "Distributed Compliant Model for Efficient Dynamic Simulation of Systems With Frictional Contacts." In ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/detc2003/dac-48809.
Анотація:
The use of Coulomb’s friction law with the principles of classical rigid body dynamics introduces mathematical inconsistencies. Specifically, the forward dynamics problem can have no solutions or multiple solutions. In these situations an explicit model of the contact compliance at the contact point can resolve these difficulties. In this paper, we introduce a distributed compliant model for dynamic simulation. In contrast to the rigid body model and the lumped model, our approach models each contact as a finite patch and uses half space approximation to derive solutions for the small deformations and force distributions in the contact patch. This approach leads to a linear complementarity problem formulation for the contact dynamics. The existence of an unique solution can be proved for both the lumped model in the point contact case and the more accurate, distributed model. Simulation algorithm that incorporates compliant contact models and linear complementarity theory are created and demonstrated through numerical examples.
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Ma, Ou, Jianxun Liang, and Steven Fillmore. "A 2D Bristle Friction Force Model for Contact Dynamics Simulation." In ASME 2009 Dynamic Systems and Control Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/dscc2009-2600.
Анотація:
This paper describes a 2D bristle contact friction model which is capable of modeling and simulating frictional behavior in both sliding and sticking regimes occurring in general 3D rigid-body contact. The model extends the 1D integrated bristle friction model to a 2D space by allowing the “bristle spring” to not only stretch along the direction of the relative velocity but also rotate due to the direction change of the velocity or motion trend in the common tangential plane of the contacting surfaces involved at the contact point of interest. With such an extension, the resulting friction model can be readily used to compute 3D contact friction forces in both sticking and sliding regimes for a general 3D contact dynamics model working with a multibody dynamics simulation application. Several simulation examples are provided to demonstrate the effectiveness of the model for predicting the experimentally seen frictional behavior such as sticking, stickslip, and sliding.
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Janko, Marco, Zhengqiao Zhao, Moshe Kam, and Yon Visell. "A partial contact frictional force model for finger-surface interactions." In 2018 IEEE Haptics Symposium (HAPTICS). IEEE, 2018. http://dx.doi.org/10.1109/haptics.2018.8357185.
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Fillmore, Steven, Jianxun Liang, and Ou Ma. "Experimental Validation of a 2D Bristle Friction Force Model." In ASME 2010 Dynamic Systems and Control Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/dscc2010-4031.
Анотація:
This paper describes an experimental effort designed to validate a general 2D bristle contact friction model. The model extends the 1D integrated bristle friction model to a 2D space by allowing the “bristle spring” to not only stretch along the direction of the bristle displacement but also rotate due to the instantaneous direction change of the velocity or motion trend in the common tangential plane of the contacting surfaces involved at the point of interest. The model is capable of simulating frictional behaviour in both sliding and sticking regimes occurring in general 3D rigid-body contact. With such an extension, the resulting friction model can be readily used to compute 3D contact friction forces in both sticking and sliding regimes. Two experiments were designed and implemented to validate the new 2D bristle model. The experiments were able to passively produce common frictional phenomena such as sliding, sticking, and stick-slip.
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Liu, Geng, Tianxiang Liu, Qin Xie, and Fanghui Shi. "Thermal Elasto-Plastic Contact Model of Rough Surfaces." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63810.
Анотація:
A thermal elasto-plastic contact model is developed in this paper to investigate the influences of steady-state frictional heating on the contact performance of surface asperities and subsurface stress fields. This model takes into account the asperity distortion caused by temperature variation in a tribological process, micro plastic flow of surface asperities, and the coupled thermo-elasto-plastic behavior of materials, with and without considering the strain-hardening property of the materials. The model is verified through the contact analysis between a rigid, isolated cylinder and a plane. Furthermore, the thermal effects on the contact pressure, real contact area, and average gap of rough surfaces in contact with different frictional coefficients and heat inputs under the thermal elasto-plastic contact conditions are studied.
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Provasi, Rodrigo, Fernando Geremias Toni, and Clovis de Arruda Martins. "Frictional Flexible Pipe Model Using Macroelements." In ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/omae2020-18005.
Анотація:
Abstract Flexible pipes are structures composed by many layers varying in composition and shapes, in which the structural behavior is defined by the role it must play. Flexible pipes construction is such that layers are unbounded, allowing relative movement between them and modifying its behavior. Many approaches are used to model such cables, both analytical and numerical, such as the macroelements model. This sort of model consists in finite elements where geometrical characteristics are taken into account by the formulation and is under development by the authors. Previous works have shown in detail the modeled cylindrical and helical elements, as well node-to-node connection elements (bounded, frictionless and frictional), which have allowed simplified flexible pipe with bonded elements simulations. This article will focus on modeling a simplified cable consisting in an external sheath, two armor layers and a polymeric core, since recent advances in the contact formulation opens the possibility to incorporate friction between the layers. Taking into consideration accuracy, computational time and memory usage, results from macroelements are compared to commercial finite element software.
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Li, Dongwu, and Chao Xu. "Modelling of Mechanical Systems With Friction Interfaces Considering Variable Normal Contact Load and Tangential Micro/Macro Slip." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-65995.
Анотація:
Mechanical structures with frictionally constrained interfaces often involve complex contact kinematics induced by tangential and normal relative motions. The tangential motion induces stick-micro/macro slip friction and causes energy dissipation. The normal motion induces normal load variation and possible separation of the joint interfaces. For effective analysis of dynamics of jointed structures, a reduced friction contact model is needed to characterize the nonlinear, coupled normal and tangential contact behaviors precisely. However, most developed microslip friction contact models considers only constant normal load. In this paper, an improved microslip friction model with normal load variation induced by normal motion is proposed. The tangential stick-micro/macro slip friction is modeled by continuous Iwan hysteretic model. This model is characterized by a slippage uniform distribution density function and a linear stiffness at stick state. The coupling relationship between tangential nonlinear restoring force and normal load variation is built. This leads to generalization of the original Iwan hysteretic friction model to consider the effect of variable normal load. The proposed model is applied to model a 7-dofs frictional damping experimental system. The results show that normal load variation and tangential microslip motion exert an important effect on prediction of friction contact behaviors. The proposed model is capable of generating asymmetric hysteresis loops and intermittent normal separation. The numerical simulation fit well with the experimental results for the 7-dofs frictional damping system, which validates the effectiveness and accuracy of the proposed model.
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Nacivet, Samuel, Christophe Pierre, Fabrice Thouverez, and Louis Jezequel. "Analysis of Periodic Frictional Contact in Finite Elements Problems." In ASME 2001 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/detc2001/vib-21735.
Анотація:
Abstract This paper considers the dynamics of structural systems modeled using the finite element method and subject to dry friction damping, using Coulomb’s law for the friction force model. A new frequency-time domain method, the Dynamic Lagrangian mixed Frequency-Time method (DLFT), is developed to calculate the steady-state forced response. The dynamic Lagrangians formulation introduced herein, when used in conjunction with a nonlinear solver in the frequency domain, is better suited to handling dry friction nonlinearities than the traditional augmented Lagrangians method. Namely, the use of dynamic Lagrangians allows one to solve for the nonlinear forces between two finite element nodes of the structure without using artifacts such as a spring. Hence the finite element model does not have to be degraded at the contact interface. Furthermore, a new reduction of the nonlinear system is proposed to decrease the required computation time. Finally, a set of numerical examples is presented for a beam in contact with a flexible dry friction element connected to ground, for frictional constraints that feature two-dimensional relative motion, and for a large-scale structural system with many friction dampers.
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Huang, Jianmeng, Chenghui Gao, Youxi Lin, and Xiezhao Lin. "Analysis of Contact Area Between an Elasto-Plastic Rough Body and a Flat Body Under Different Working Mode." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37443.
Анотація:
A thermo-mechanical coupling contact model between a fractal rough body and a flat body is established. In the model, the heat flux coupling between the sliding surfaces and the effect of elasto-plastic deformation of the rough body are considered. To obtain the transient microcontact process between the rough body and the flat body during rotating sliding friction, the thermo-mechanical problem under this three-dimensional model is solved by the nonlinear finite element multi-physical methods. The comparisons of the real contact area are analyzed under two different working modes, including loading processes with and without frictional rotating. During the loading and rotating process, the shear stress and the total frictional force on the frictional rough interface, and the equivalent plastic strain of the contact asperity are larger. All these including the thermal expansion make the real contact area increase with the applied normal load much faster under the working mode of loading and rotating than it does under the only loading mode.
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Ghafoor, Abdul, Jian S. Dai, and Joseph Duffy. "Grasp Stiffness Matrix for Soft Finger Contact Model in Robotic Applications." In ASME 2000 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/detc2000/mech-14110.
Анотація:
Abstract This paper proposes a practical and analytical model for soft finger grasp. It presents a contact stiffness matrix by applying congruence transformation and mapping stiffnesses from a line spring model onto translational and rotational stiffnesses. The contact that is realised in this paper is in the form of a patch contact with evenly distributed finite number of equivalent point contacts. An analytical approach is hence proposed based on line springs and screw representation of the frictional elastic point contacts that provides a direct correlation between the equivalent point contact and soft finger contact of a rigid object and gives a procedure to complete the analysis. The grasp achieved with the analysis provides both translational and rotational restraint. The approach and its use for finite manipulation are supported by a case study.
Звіти організацій з теми "Frictional contact model":
1
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.
Анотація:
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.
2
Lever, James, Susan Taylor, Arnold Song, Zoe Courville, Ross Lieblappen, and Jason Weale. The mechanics of snow friction as revealed by micro-scale interface observations. Engineer Research and Development Center (U.S.), December 2021. http://dx.doi.org/10.21079/11681/42761.
Анотація:
The mechanics of snow friction are central to competitive skiing, safe winter driving and efficient polar sleds. For nearly 80 years, prevailing theory has postulated that self-lubrication accounts for low kinetic friction on snow: dry-contact sliding warms snow grains to the melting point, and further sliding produces meltwater layers that lubricate the interface. We sought to verify that self-lubrication occurs at the grain scale and to quantify the evolution of real contact area to aid modeling. We used high-resolution (15 μm) infrared thermography to observe the warming of stationary snow under a rotating polyethylene slider. Surprisingly, we did not observe melting at contacting snow grains despite low friction values. In some cases, slider shear failed inter-granular bonds and produced widespread snow movement with no persistent contacts to melt (μ < 0.03). When the snow grains did not move and persistent contacts evolved, the slider abraded rather than melted the grains at low resistance (μ < 0.05). Optical microscopy revealed that the abraded particles deposited in air pockets between grains and thereby carried heat away from the interface, a process not included in current models. Overall, our results challenge whether self-lubrication is indeed the dominant mechanism underlying low snow kinetic friction.
3
Fernández Martín, Andrés, and Adam Gulan. Interest Rates and Business Cycles in Emerging Economies: The Role of Financial Frictions. Inter-American Development Bank, November 2012. http://dx.doi.org/10.18235/0011424.
Анотація:
Countercyclical country interest rates have been shown to be both a distinctive characteristic and an important driving force of business cycles in emerging market economies. In order to account for this, most business cycle models of emerging market economies have relied on ad hoc and exogenous countercyclical interest rate processes. This paper embeds a financial contract à la Bernanke et al. (1999) in a standard small open economy business cycle model that endogenously delivers countercyclical interest rates. The model is then applied to the data, drawn from a novel panel dataset for emerging economies that includes financial data, namely sovereign and corporate interest rates as well as leverage. It is shown that the model accounts well not only for countercyclical interest rates, but also for other stylized facts of emerging economies` business cycles, including the dynamics of leverage.
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Blyde, Juan S., and José Pineda. Microeconomic Flexibility, Creative Destruction and Trade. Inter-American Development Bank, December 2009. http://dx.doi.org/10.18235/0011076.
Анотація:
We investigate whether greater microeconomic flexibility facilitates the process of creative destruction in the context of new trade models with heterogeneous firms (Bernard et al., 2003 and Melitz, 2003). In these models, freer trade increases aggregate productivity because high-efficiency firms expand through exporting and low-efficiency firms exit the market. However, factor reallocation could be negatively affected by the presence of microeconomic frictions. We use these insights of the theory to analyze whether a reduction in trade costs increases the probability of becoming an exporter relatively more in industries with greater microeconomic flexibility and whether plant exit driven by trade costs declines is more likely in industries with lower frictions. Using plant level data from Venezuela, we report results supporting these predictions.
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Altinok, Ahmet, and Diana E. Mac Donald. Designing the Menu of Licenses for Foster Care. Banco de México, December 2023. http://dx.doi.org/10.36095/banxico/di.2023.19.
Анотація:
In the United States, prospective foster parents must become licensed by a child welfare agency before a foster child can be placed in their care. This paper contributes by developing a theoretical matching model to study the optimal menu of licenses designed to screen foster parents. We construct a two-sided matching model with heterogeneous agents, adverse selection, search frictions, and a designer who coordinates match formation through a menu of contracts. We focus on incentive compatible contracts, examine optimal allocations and transfers, and analyze equilibrium sorting patterns. There are three main results: (i) optimal allocation calls for a segregation of the market, (ii) a simple transfer schedule does the job, (iii) complementarities do not ensure that Positive Assortative Matching (PAM) will arise in equilibrium, thus we provide an additional condition that guarantees it. Our results suggests that the menu of licenses used in practice, exhibits some of the properties of the optimal solution. However, the menu might not be reaching its screening objective.
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Pullammanappallil, Pratap, Haim Kalman, and Jennifer Curtis. Investigation of particulate flow behavior in a continuous, high solids, leach-bed biogasification system. United States Department of Agriculture, January 2015. http://dx.doi.org/10.32747/2015.7600038.bard.
Анотація:
Recent concerns regarding global warming and energy security have accelerated research and developmental efforts to produce biofuels from agricultural and forestry residues, and energy crops. Anaerobic digestion is a promising process for producing biogas-biofuel from biomass feedstocks. However, there is a need for new reactor designs and operating considerations to process fibrous biomass feedstocks. In this research project, the multiphase flow behavior of biomass particles was investigated. The objective was accomplished through both simulation and experimentation. The simulations included both particle-level and bulk flow simulations. Successful computational fluid dynamics (CFD) simulation of multiphase flow in the digester is dependent on the accuracy of constitutive models which describe (1) the particle phase stress due to particle interactions, (2) the particle phase dissipation due to inelastic interactions between particles and (3) the drag force between the fibres and the digester fluid. Discrete Element Method (DEM) simulations of Homogeneous Cooling Systems (HCS) were used to develop a particle phase dissipation rate model for non-spherical particle systems that was incorporated in a two-fluid CFDmultiphase flow model framework. Two types of frictionless, elongated particle models were compared in the HCS simulations: glued-sphere and true cylinder. A new model for drag for elongated fibres was developed which depends on Reynolds number, solids fraction, and fibre aspect ratio. Schulze shear test results could be used to calibrate particle-particle friction for DEM simulations. Several experimental measurements were taken for biomass particles like olive pulp, orange peels, wheat straw, semolina, and wheat grains. Using a compression tester, the breakage force, breakage energy, yield force, elastic stiffness and Young’s modulus were measured. Measurements were made in a shear tester to determine unconfined yield stress, major principal stress, effective angle of internal friction and internal friction angle. A liquid fludized bed system was used to determine critical velocity of fluidization for these materials. Transport measurements for pneumatic conveying were also assessed. Anaerobic digestion experiments were conducted using orange peel waste, olive pulp and wheat straw. Orange peel waste and olive pulp could be anaerobically digested to produce high methane yields. Wheat straw was not digestible. In a packed bed reactor, anaerobic digestion was not initiated above bulk densities of 100 kg/m³ for peel waste and 75 kg/m³ for olive pulp. Interestingly, after the digestion has been initiated and balanced methanogenesis established, the decomposing biomass could be packed to higher densities and successfully digested. These observations provided useful insights for high throughput reactor designs. Another outcome from this project was the development of low cost devices to measure methane content of biogas for off-line (US$37), field (US$50), and online (US$107) applications.
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Carrasco, Alex, and David Florián Hoyle. External Shocks and FX Intervention Policy in Emerging Economies. Inter-American Development Bank, August 2021. http://dx.doi.org/10.18235/0003457.
Анотація:
This paper discusses the role of sterilized foreign exchange (FX) interventions as a monetary policy instrument for emerging market economies in response to external shocks. We develop a model for a commodity-exporting small open economy in which FX intervention is considered as a balance sheet policy induced by a financial friction in the form of an agency problem between banks and their creditors. The severity of banks agency problem depends directly on a bank-level measure of currency mismatch. Endogenous deviations from the standard UIP condition arise at equilibrium. In this context, FX interventions moderate the response of financial and macroeconomic variables to external shocks by leaning against the wind with respect to real exchange rate pressures. Our quantitative results indicate that, conditional on external shocks, the FX intervention policy successfully reduces credit, investment, and output volatility, along with substantial welfare gains when compared to a free-floating exchange rate regime. Finally, we explore distinct generalizations of the model that eliminate the presence of endogenous UIP deviations. In those cases, FX intervention operations are considerably less effective for the aggregate equilibrium.
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Palkovic, Steven, Yasamin Salamat, Brendon Willey, and Simon Bellemare. PR-610-183867-R01 Fracture Toughness via In-ditch Non-destructive Testing - Validation. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), September 2020. http://dx.doi.org/10.55274/r0011802.
Анотація:
A challenge for many pipeline operators is missing or incomplete records for sections of their transmission pipeline networks, especially regarding fracture toughness properties. These toughness values are necessary for performing fitness for service calculations and engineering critical assessment. New regulations for gas transmission pipelines stipulate conservative default values for applicable assets when traceable, verifiable, and complete (TVC) records are not available. The new rules allow for the use of nondestructive techniques within material verification programs to measure the actual steel properties in lieu of conventional destructive cut-outs. However, the nondestructive technique must be validated, and the measurement must account for error and uncertainty of the nondestructive process. The aim of this research program is to assess the capabilities and limitations of the Nondestructive Toughness Tester (NDTT) to meet the requirements of a material verification process for measuring fracture toughness properties. The NDTT is a new approach for measuring the toughness of steel pipelines through the application of a contact mechanics technique known as frictional sliding. This project consists of testing on 41 vintage steel pipe joints to compare the NDTT measurement of the tensile fracture response in a superficial volume of surface material with conventional laboratory measurements of toughness on the same sample. The outcomes include the development and assessment of nondestructive prediction models for the initiation fracture toughness from compact tension (CT) testing and the upper shelf Charpy V-Notch (CVN) impact energy. This report summarizes the testing procedures and analysis methodologies used, and the prediction performance of models based on NDTT measurements.
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ROTATIONAL RESISTANCE TEST OF A NEW ALUMINUM ALLOY PENETRATING (AAP) JOINT SYSTEM. The Hong Kong Institute of Steel Construction, June 2023. http://dx.doi.org/10.18057/ijasc.2023.19.2.4.
Анотація:
Aluminum alloy penetrating (AAP) joint is an improved form of the Aluminum Alloy Temcor (AAT) joint system consisting of one penetrating member, four short members, gussets, bolts and a U-shaped connector. The rotational resistance performance of AAP joints is investigated by a static out-of-plane flexural test. The specific experimental parameters include the gusset thickness (6 mm and 12 mm) and shape (circular and X-shaped). The differences between penetrating and short members in AAP joints are analyzed, and the influence of thicknesses and shapes of gusset on rotational resistance behavior of the joints is analyzed. The establishment of the finite element model of the AAP joint system in this paper considers the effects of bolt pre-tightening force, installation gap and friction between contact surfaces. The M-Φ curves and damage patterns are obtained by numerical simulation. The detailed comparative analysis between AAP joint numerical simulation and test results verifies the accuracy of the numerical model.