• Title, Summary, Keyword: Viscous Friction

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Dynamic Analysis of the Small Reciprocating Compressors Considering Viscous Frictional Force of a Piston (피스톤의 점성 마찰력을 고려한 소형 왕복동 압축기의 동적 해석)

  • 김태종
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.11
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    • pp.904-913
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    • 2002
  • In this study, a dynamic analysis of the reciprocating compression mechanism considering viscous friction force of a piston used in small refrigeration compressors is performed. The length of cylinder in this class of compressors is shortening to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder liner is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the compression mechanism dynamics, the change in bearing length of the piston and all corresponding viscous forces and moments are considered in order to determine the trajectories of piston and crankshaft. The piston orbits for viscous friction model and Coulomb friction model were used to compare the effect of the friction forces of piston on the dynamic trajectories of piston. To investigate the effect of friction force acting on the piston for the dynamic characteristics of crankshaft, comparison of the crankshaft loci is given in both viscous model and Coulomb model. Results show that the viscous friction force of piston must be considered in calculating for the accurate dynamic characteristics of the reciprocating compression mechanism.

Identification of Viscous and Friction Damping Using Free Vibration Response to SDOF System (단자유도계의 자유진동응답을 이용한 점성 및 마찰감쇠의 식별)

  • Lee, Sung-Kyung;Lee, Woong-Gu
    • The Journal of the Convergence on Culture Technology
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    • v.5 no.3
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    • pp.305-310
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    • 2019
  • This paper proposes the method of exactly identifying both viscous and friction damping from free vibration response to SDOF structure. Both displacement and acceleration free vibration responses to SDOF system, in which both viscous and friction damping are considered as its damping mechanism, are discussed to verify the proposed method. The relationship for identifying both viscous and friction damping is derived from two consecutive amplitudes of displacement or acceleration peak response. The proposed method is verified through the numerical simulation for an assumed SDOF system consisting of mass, both viscous and friction damping and spring components.

Effect of Friction Force on the Dynamic Characteristics of a Flow Divider Valve (Flow Divider Valve의 동특성에 미치는 마찰력의 영향)

  • 박태조;황태영
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.1
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    • pp.198-203
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    • 2000
  • In this paper, a numerical analysis is carried out to show the effect of friction farce on the dynamic characteristics of a flow divider valve. The continuity equations and the equation of motion fur spool are numerically solved. The viscous friction force acting on the spool is considered analyzing the Reynolds equation which governs the viscous flow in the clearance gap between the spool and sleeve. Dynamic characteristics are highly affected by the viscous friction farce whose magnitude is relatively small compare with other fluid forces. Therefore present theoretical formulation and numerical scheme can be used generally in designing and performance evaluation of all the hydraulic spool valve.

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Impulse Response Analysis of an Amplitude Proportional Friction Damper System (변위비례식 마찰댐퍼 시스템의 임펄스 가진 응답해석)

  • 최명진;박동훈
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.14 no.5
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    • pp.377-384
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    • 2004
  • An Amplitude Proportional Friction Damper (APFD), in which the friction force is proportional to the system displacement, has been introduced and mathematically modeled. To understand the damping characteristics of APFD, analytical solutions for the impulse response has been derivedand compared to the viscous damper. It is found that APFD system has very similar damping characteristics to viscous damper even though it is a friction damper. APFD may be used as a cost-effective substitution for the viscous damper and could also be used to improve the simple friction or Coulomb dampersince APFD works with no stick-slip and always returns to original position when external disturbance is disappeared.

Equivalent Viscous Damping Ratio of a Friction Damper Installed in a SDOF Building (단자유도 건물에 설치된 마찰감쇠기의 등가점성감쇠비)

  • Seong, Ji-Young;Min, Kyung-Won
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.23 no.2
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    • pp.199-208
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    • 2010
  • A friction damper installed at a building shows nonlinear behavior since its stick and slip states are occurred repeatedly depending on the amplitude of external loadings to dissipate input energy. Friction damping is existed for the building with a friction damper. In additionally viscous one is inherently included. Therefore, the building installed in such combined damping is quite involved to find the analytical solution. In this study, first, displacement and acceleration characteristics are identified based on the exact solution for a single-degree-freedom building with a friction damper having both friction and viscous damping. Second, in free vibration, the equivalent viscous damping ratio is obtained by the energy dissipation. Third, numerical analysis is carried out to find response configuration with various friction force ratios. Fourth, corresponding equivalent viscous damping ratio is derived with the finding that the response reaches into steady-state for both friction and viscous damped structure. It is deduced using balance of input external energy and output dissipation energy for steady-state response. Finally, the equivalent viscous damping ratios of free or harmonic vibration are verified through nonlinear analysis.

Mathematical Modeling of Friction Force in LM Ball Guides (LM 볼가이드 마찰력의 수학적 모델링)

  • Oh, Kwang-Je;Khim, Gyungho;Park, Chun-Hong;Chung, Sung-Chong
    • Journal of the Korean Society for Precision Engineering
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    • v.32 no.5
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    • pp.423-429
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    • 2015
  • Linear motion (LM) ball guides have good accuracy and high efficiency. They are widely applied for precision machinery such as machine tools, semiconductor fabrication machines and robots. However, friction force incurs heat between the balls and grooves. Thermal expansion due to the heat deteriorates stiffness and accuracy of the LM ball guides. For accurate estimation of stiffness and accuracy during the linear motion, friction models of LM ball guides are required. To formulate accurate frictional models of LM ball guides according to load and preload conditions, rolling and viscous frictional analyses have been performed in this paper. Contact loads between balls and grooves are derived from Hertzian contact analysis. Contact angle variation is incorporated for the precision modeling. Viscous friction model is formulated from the shear stress of lubricant and the contact area between balls and grooves. Experiments confirm validity of the developed friction model for various external load and feedrate conditions.

Effect of viscous Damping on the Stability of Beam Resting on an Elastic Foundation Subjected to Dry friction force (점성감쇠가 건성마찰력을 받는 탄성지지 보의 안정성에 미치는 효과)

  • 장탁순;고준빈;류시웅
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.11
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    • pp.179-185
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    • 2004
  • The effect of viscous damping on stability of beam resting on an elastic foundation subjected to a dry friction force is analytically studied. The beam resting on an elastic foundation subjected to dry friction force is modeled for simplicity into a beam resting on Kelvin-Voigt type foundation subjected to distributed follower load. In particular, the effects of four boundary conditions (clamped-free, clamped-pinned, pinned-pinned, clamped-clamped) on the system stability are considered. The critical value and instability type of columns on the elastic foundation subjected to a distributed follower load is investigated by means of finite element method for four boundary conditions. The elastic foundation modulus, viscous damping coefficient and boundary conditions affect greatly both the instability type and critical load. Also, the increase of damping coefficient raises the critical flutter load (stabilizing effect) but reduces the critical divergence load (destabilizing effect).

Friction Characteristics of Piston Assembly (II) -Experiment- (피스톤계 마찰 특성 (II) -실험적 연구-)

  • Cho, Myung-Rae;Ha, Kyoung-Pyo;Kim, Joong-Soo;Oh, Dae-Yoon;Han, Dong-Chul
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.1
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    • pp.88-93
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    • 2003
  • The aim of this paper is to investigate the friction characteristics of piston assembly, which composed of ring pack and piston skirt. The friction force of piston assembly was measured by using the movable liner in the single cylinder engine, and the various parameters were tested. The friction force was suddenly increased at the expansion stroke due to higher cylinder pressure. The viscous friction was dominant at the mid stroke, but the boundary friction was dominant at the top and bottom dead centers. Through the experiment, we could validate previous theoretical study, and confirm that th e radial clearance and ring tension were very effective to reduce friction loss of piston assembly.

Friction Torque Analysis of a Hydraulic Motor-Load System using Proportional Control Valve (비례제어밸브를 이용한 유압모터 부하계의 마찰토크 해석)

  • Yu, Hwan-Shin;Park, Hyung-Bae
    • The Journal of Advanced Navigation Technology
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    • v.14 no.5
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    • pp.760-766
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    • 2010
  • In this paper, The static friction torque and viscous friction torque including hydraulic motor-load system driven by hydraulic proportional control valve analysis. The basic experimental was performed toward characteristic in pressure and flow rate in hydraulic system energy. The variable of friction torque was experiment on brake pressure variable using pneumatic brake system. The analysis of nonlinear friction and linear friction was perform ed toward friction characteristic of hydraulic system.

A Study on the Characteristics of an Amplitude Proportional Friction Damper (변위비례식 마찰댐퍼의 특성에 관한 연구)

  • 박동훈;최명진
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.717-720
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    • 2002
  • An Amplitude Proportional Friction Damper (APFD) system is considered in order to improve the stick-slip characteristics of Coulomb friction damper. The frictional force is proportional to the amplitude in APFD system and the system is non-linear as is Coulomb damper system. The free vibration analysis on an 1-DOF system has conducted to demonstrate the characteristics of the APFD system and the results show that the APFD system has similar damping characteristics to the viscous damper system. It is concluded that the APFD system may become a cost effective substitution for the viscous damper and it also has certain advantages over Coulomb damper system since the APFD system can be designed to work with no stick-slip.

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