• Tribology and Lubricants
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• 제39권6호
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• pp.273-277
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• 2023

This paper presents a molecular dynamics simulation-based numerical investigation of the influence of surface energy on water lubrication. Models composed of a crystalline substrate, half cylindrical tip, and cluster of water molecules are prepared for a tribological-characteristic evaluation. To determine the effect of surface energy on lubrication, the surface energy between the substrate and water molecules as well as that between the tip and water molecules are controlled by changing the interatomic potential parameters. Simulations are conducted to investigate the indentation and sliding processes. Three different normal forces are applied to the system by controlling the indentation depth to examine the influence of normal force on the lubrication of the system. The simulation results reveal that the solid surface's surface energy and normal force significantly affect the behavior of the water molecules and lubrication characteristics. The lubrication characteristics of the water molecules deteriorate with the increasing magnitude of the normal force. At a low surface energy, the water molecules are readily squeezed out of the interface under a load, thus increasing the frictional force. Contrarily, a moderate surface energy prevents expulsion of the water molecules due to squeezing, resulting in a low frictional force. At a high surface energy, although squeezing of the water molecules is restricted, similar to the case of moderate surface energy, dragging occurs at the soil surface-water molecule interface, and the frictional force increases.

• Journal of Mechanical Science and Technology
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• 제20권1호
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• pp.125-132
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• 2006

To understand fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Stratified steady and unsteady two-phase flows between two parallel plates have been studied to investigate the general characteristics of the flow related to flow-induced vibration. Based on the spectral collocation method, a numerical approach has been developed for the unsteady two-phase flow. The method is validated by comparing numerical result to analytical one given for a simple harmonic two-phase flow. The flow parameters for the steady two-phase flow, such as void fraction and two-phase frictional multiplier, are evaluated. The dynamic characteristics of the unsteady two-phase flow, including the void fraction effect on the complex unsteady pressure, are illustrated.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.78-87
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• 1998

A dynamic model of direct-acting OHC valve train system has been used to determine the load conditions in the system. The modified equations for calculating the friction forces between cam and HLA, and at a camshaft bearing have been defined considering the lubrication conditions. Then, to understand the frictional characteristics in the system, a parameter study has been performed. As the results of the analysis, valve spring stiffness and preload have great effects on the friction in the system, but the effects of other parameters are negligible. So, how to design the valve train system with respect to the reduction of friction is to minimize the valve spring stiffness and preload in the limit of satisfying the dynamic constraints.

• 한국정밀공학회지
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• 제18권7호
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• pp.91-97
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• 2001

When a body including a crack inside is subjected to the compressive forces, the crack is closed and sliding occurs on the crack surfaces. In this work, a subsurface crack subjected to a static compressive load is analyzed with the finite element method considering friction on the crack surface. The friction on the crack surface is assumed to follow the Coulomb friction law, and a numerical method based on the finite element method and iterative method is applied in this work. The result is compared with those of ANSYS and references.

• Structural Engineering and Mechanics
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• 제21권1호
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• pp.1-18
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• 2005

Foschi's connector model is used as a basic component in the development of nonlinear analysis programs for timber structures. This paper presents the extension of the model to include the effect of shaft frictional forces. The wood medium is modeled using the Foschi embedment model, while shaft friction is modeled using an elastic Coulomb-type friction model. The initial confining pressure for the case of driven fasteners is accounted for by a lateral shift of the load-embedment curve. The model is used to compute the cyclic response of both driven and inserted fasteners. The results obtained from the cases studied indicate that initial confining pressure and friction do not have a significant effect on the computed hysteretic response, however, they significantly affect the computed amount of fastener withdrawal. This model is particularly well-suited for modeling the hysteretic response of shear walls with moderate fastener withdrawal under lateral cyclic or earthquake loading.

• Tribology and Lubricants
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• 제11권3호
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• pp.48-53
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• 1995

In this paper, the friction characteristics of contact region between vane tip and camring is studied using a modeled experimental device. The contact region is under the influence of variable loads with the amplitude of hundreds of Newton and frequency of tens of Hz. The condition of lubrication between vane and disk is modeled after the actual condition between vane and camring. The coefficient of friction is obtained by measuring the frictional forces in the contact region between camring and vane. The friction characteristics of the actual oil hydraulic vane pump is estimated on the basis of coefficient of friction. The analysis of frictional characteristics shows us that the lubrication condition of vane tip is that of transition regime between hydrodynamic lubrication and mixed lubrication.

• 한국공간구조학회논문집
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• 제15권3호
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• pp.103-110
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• 2015

Various hybrid dampers have been developed as increasing tall buildings in Korea. To minimize the installment space and cost, the new hybrid friction damper was developed using friction components. It is composed of two one-nodal rotary frictional components and a slotted bolted frictional connection. Because of these components, hybrid friction damper can be activated by building movements due to lateral forces such as a wind and earthquake. In this paper, displacement amplitude dependency tests were carried out to evaluate on the structural performance and the multi-slip mechanism of the hybrid damper. Test results show that the multi-slip mechanism is verified and friction coefficients are increasing as displacement amplitudes are increasing.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.517-522
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• 2000

When a body including a crack inside is subjected to the compressive forces, the crack is closed and sliding occurs on the crack surfaces. In this work, a subsurface crack subjected to a static or moving compressive load is analyzed with the finite element method considering friction on the crack surface. The friction on the crack surface is assumed to follow the Coulomb friction law. A numerical method based on the finite element method and iterative method is applied in this work. And the result is compared with the frictional contact of crack by ANSYS using contact 12 element. The numerical results of two methods are compared with the wellknown analytical solutions, and the accuracy of iterative method is checked..

• 한국정밀공학회지
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• 제30권8호
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• pp.847-853
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• 2013

Micro-dimples on sliding surfaces have been investigated to reduce the frictional forces on metal bearing surfaces; however, for an elastomer, such as thermoplastic polyurethane (TPU), this has not been studied. The material properties of an elastomer are affected by temperature, and this can shorten the life of the elastomer. In this paper, micro-dimples were applied on the surface of an elastomer in order to reduce the frictional heating, which was experimentally investigated using pin-on-disk apparatus while the surface temperature was measured. To obtain optimal design parameters, the design of the experiment was applied, and the shape of the section, size, depth and density of micro-dimples were selected as the design parameters. The results show that the size of the dimple is the most important design parameter.

• 유공압시스템학회논문집
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• 제8권3호
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• pp.21-26
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• 2011

Nonlinear seal friction in pneumatic cylinders can impede the performance of pneumatic systems designed for high precision positioning with favorable high speed actuation. The behaviour of an elastomeric piston seals in high speed pneumatic cylinders is analyzed by nonlinear finite element analysis using ABAQUS. The contact pressures, stress and strain distributions and frictional forces of the squeeze type piston seal are simulated with variation of the seal radial installed interference, the operating pressures, friction coefficients and piston rod velocities. The nonlinear finite element model of the squeeze type piston seal is used to predict deformation of a seal, friction force and contact pressure distributions.