• 한국소음진동공학회논문집
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• 제17권7호
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• pp.649-661
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• 2007

Friction-type reinforcing members(FRM) to enhance the resistance to wind loads of a transmission tower through both stiffness strengthening and damping increase are energy dissipation devices that utilize bending deflection of a tower leg. In this paper, the hysteretic behavior of the transmission tower structure with FRMs was experimentally investigated through cyclic loading tests on a half scale substructure model. Firstly, the variation of friction forces and durability of the FRM depending on the type of friction-inducing materials used in the FRM were examined by performing the cyclic loading tests on the FRM. Secondly, cyclic loading tests of a half-scale two-dimensional substructure model of a transmission tower with FRMs were conducted. Test results show that the FRM, of which desired maximum friction force is easily regulated by adjusting the amplitude of the torque applied to the bolts, have stable hysteretic behaviors and it is found that there exists the optimum torque depending on a design load by investigating the amount of energy dissipation of the FRMs according to the increase of torque.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.568-577
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• 2007

Friction-type reinforcing members (FRM) to enhance the resistance to wind loads of a transmission tower through both stiffness strengthening and damping increase are energy dissipation devices that utilize bending deflection of a tower leg. In this paper, the hysteretic behavior of the transmission tower structure with FRMs was experimentally investigated through cyclic loading tests on a half scale substructure model. Firstly, the variation of friction forces and durability of the FRM depending on the type of Friction-inducing materials used in the FRM were examined by performing the cyclic loading tests on the FRM. Secondly, Cyclic loading tests of a half-scale two-dimensional substructure model of a transmission tower with FRMs were conducted. Test results show that the FRM, of which desired maximum friction force is easily regulated by adjusting the amplitude of the torque applied to the bolts, have stable hysteretic behaviors and it is found that there exists the optimum torque depending on a design load by investigating the amount of energy dissipation of the FRMs according to the increase of torque.

• Tribology and Lubricants
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• 제25권4호
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• pp.207-216
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• 2009

Friction tests were carried out in order to investigate the effects of temperature on the friction and wear behaviors between a PMMA film and a fused silica lens using a microtribometer. The friction forces on the PMMA film were measured under atmospheric condition as the temperature of the film was increased from 300 K to 443 K. The contact area between the film and the lens was observed. The tribological characteristics of the film were significantly changed as the temperature increased. The changes were discussed with the change of the film state from glassy to viscous flow. In addition, the results showed that the friction behavior can be varied with the thermal history of the PMMA film. Residual solvent in the PMMA film could emerge to the PMMA surface due to an additional heating and the solvent on the film surface decreased the friction force.

• Structural Engineering and Mechanics
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• 제82권4호
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• pp.435-444
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• 2022

This study proposes a novel longitudinal self-centering earthquake resistant system for reinforced concrete (RC) continuous bridges by using superelastic shape memory alloy (SMA) reinforcement and friction dissipation mechanism. The SMA reinforcing bars are implemented in the fixed piers to provide self-recentering forces, while the friction dampers are used at the movable substructures like end abutments to enhance the energy dissipation of the bridge system. A reasonable balance between self-centering and energy dissipation capacities should be well achieved by properly selecting the parameters of the SMA rebars and friction dampers. A two-span continuous bridge with one fixed pier and two abutments is chosen as a prototype for illustration. Different longitudinal earthquake resistant systems including the proposed one in this study are investigated and compared. The results indicate that compared with the designs of over-dissipation (e.g., excessive friction) and over-self-centering (e.g., pure SMAs), the proposed system with balanced design between self-centering and energy dissipation would perform satisfactorily in controlling both the peak and residual displacement ratios of the bridge system.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.63-64
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• 2002

In a micro-scale contact, surface forces such as capillary force and van der Waals Interaction significantly Influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (hydrophilicity), relative humidity and deformation of asperities In the real area of contact. A better understanding of these surface forces is of great necessity in order to find an optimal solution for reducing friction and adhesion of micro surfaces. We proposed an effective method to analyze capillary and van der Waals forces In nano-scale contact. In this method, Winklerian foundation model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height Images. Self-mated contact of diamond-like-carbon (DLC) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidify and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• 소음진동
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• 제7권5호
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• pp.861-869
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• 1997

An approximate analytical method has been developed for estimating hydrodynamic forces acting on oscillating inner cylinder in concentric annulus. When the rigid inner cylinder executes translational oscillation, fluid inertia and damping forces on the oscillating cylinder are generated by unsteady pressure and viscous skin friction. Considering the dynamic-characteristics of unsteady viscous flow and the added mass coefficient of inviscid fluid, these hydrodynamic forces including viscous effect are dramatically simplified and expressed in terms of oscillatory Reynolds number and the geometry of annular configuration. Thus, the viscous effect on the forces can be estimated very easily compared to an existing theory. The forces are calculated by two models developed for relatively high and low oscillatory Reynolds numbers. The model for low oscillatory Reynolds number is suitable for relatively high ratio of the penetration depth to annular space while the model for high oscillatory Reynolds number is applicable to the case of relatively low ratio. It is found that the transient ratio between two models is approximately 0.2~0.25 and the forcea are expressed in terms of oscillatory Reynolds number, explicity. The present results show good agreements with an existing numerical results, especially for high and low penetration ratios to annular gap.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2180-2186
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• 2002

In a micro-scale contact, capillary force and van der Waals interaction significantly influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (wet angle), relative humidity and deformation of asperities in the real area of contact. A better understanding of these surface forces is of great necessity in order to find a solution for reducing friction and adhesion of micro surfaces. The objective of this study is to investigate the surface forces in micro-scale rough surface contact. We proposed an effective method to analyze capillary and van der Waals forces in micro-scale contact. In this method, Winkler spring model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height images. Self-mated contact of DLC(diamond like carbon) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidity and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• Korean Journal of Acupuncture
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• 제35권3호
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• pp.149-158
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• 2018

Objectives : In this study, we quantitatively evaluated the needle forces using needle insertion-measurement system and compared the needle sensation of each acupuncture practical model. Methods : After inserting acupuncture with a sensor to six models, a lifting-thrusting motion was implemented using the needle insertion-measurement system. The needle force was measured repeatedly, and the measurement was analyzed based on the modified Karnopp friction model for a comparison of friction coefficients. After the insertion, practitioners did lifting-thrusting manipulations. They quantified the similarity of needle sensation with VAS (Visual Analogue Scale). Results : When friction force and coefficients of friction in five different models were compared with a porcine shank model, all five models were significantly different from a porcine shank model, cotton and apple showing the closest frictional values to that of a porcine shank model. In the Cp and Cn values of cotton and in the Cp values of IM injection pad, there was no statistically significant difference. The similarity of the needle sensation between the porcine shank and five models was the highest in the apple, and overlapping papers was the lowest. Conclusions : This study quantitatively compared the physical forces in the practical model when implementing lifting-thrusting manipulations, using a needle insertion-measurement system. We suggest that a reproducible exercise model that reflects the characteristics of various human tissues, such as viscoelasticity or strength, needs to be further developed. This will contribute to establishing standardized acupuncture practice training.

• 한국구조물진단유지관리공학회 논문집
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• 제20권2호
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• pp.34-39
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• 2016

경부 고속철 40 m 단경간 PSC 교량을 대상으로 38 자유도 KTX 동력차를 주행속도 500 km/h까지 12 단계 불규칙 궤도형상과 상호 작용력을 고려하여 해석하였다. 차량의 윤축하중과 중심회전각을 평가하기 위하여 170 m 일반도상을 교량과 조합하여 횡압과 탈선계수 그리고 윤중감소율을 허용기준과 비교하였다. 단순교와 연속교의 교량받침 최대 변위와 누적이동거리를 주행속도별로 해석하였다. PTFE 마찰판과 DP-mate의 EN-1337-2 기준의 장기마찰시험을 수행하였다. 수행된 장기마찰시험은 차세대 고속철의 증가되는 주행속도를 고려하여 개선 방안을 제안하였다.

• 드라이브 ㆍ 컨트롤
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• 제18권4호
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• pp.77-83
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• 2021

With the progress in virtual reality technology, various virtual objects can be displayed using head-mounted displays (HMD). However, force feedback sensations such as pushing against a virtual object are not possible with an HMD only. Focusing on force feedback, desktop-type devices are generally used, but the user cannot move in a virtual space because such devices are fixed on a desk. With a wearable force feedback device, users can move around while experiencing force feedback. Therefore, the authors have developed a wearable force feedback device using a magnetorheological fluid clutch and pneumatic rubber artificial muscle, aiming at presenting the elasticity, friction, and viscosity of an object. To date, we have developed a wearable four-degree-of-freedom (4-DOF) force feedback device and have quantitatively evaluated that it can present commanded elastic, frictional, and viscous forces to the end effector. However, sensory evaluation with a human has not been performed. In this paper, therefore, we conduct a sensory evaluation of the proposed method. In the experiment, frictional and viscous forces are rendered in a virtual space using a 4-DOF force feedback device. Subjects are asked to answer questions on a 1- to 7-point scale, from 1 (not at all) to 4 (neither) to 7 (strongly). The Wilcoxon signed rank test was used for all data, and answer 4 (neither) was used as compared standard data. The experimental results confirmed that the user could feel the presence or absence of viscous and frictional forces. However, the magnitude of those forces was not sensed correctly.