• Title, Summary, Keyword: Sliding velocity

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Seismic Performance Evaluation of Seismically Isolated Nuclear Power Plants Considering Various Velocity-Dependent Friction Coefficient of Friction Pendulum System (마찰진자시스템의 마찰계수 변화에 따른 면진된 원전구조물의 거동특성 비교)

  • Seok, Cheol-Geun;Song, Jong-Keol
    • Journal of the Earthquake Engineering Society of Korea
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    • v.20 no.2
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    • pp.125-134
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    • 2016
  • In order to improve seismic safety of nuclear power plant (NPP) structures in high seismicity area, seismic isolation system can be adapted. In this study, friction pendulum system (FPS) is used as the seismic isolation system. According to Coulomb's friction theory, friction coefficient is constant regardless of bearing pressure and sliding velocity. However, friction coefficient under actual situation can be changed according to bearing pressure, sliding velocity and temperature. Seismic responses of friction pendulum system with constant friction and various velocity-dependent friction are compared. The velocity-dependent friction coefficients of FPS are varied between low-and fast-velocity friction coefficients according to sliding velocity. From the results of seismic analysis of FPS with various cases of friction coefficient, it can be observed that the yield force of FPS becomes larger as the fast-velocity friction coefficient becomes larger. Also, the displacement response of FPS becomes smaller as the fast-velocity coefficient becomes larger.

경사진 고체 표면 위를 내려가는 액적의 미글림 유동

  • 김진호;김호영;강병하;이재헌
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.10
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    • pp.1025-1033
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    • 2001
  • A scaling analysis is provided which predicts the sliding velocity of a liquid drop down an inclined surface. The analysis is based on the balance of the gravitational work rate that drives the drop sliding and the resistances by capillary and viscous forces. The capillary resistance is accounted for via the contact angle hysteresis, which is quantified by measuring the critical inclination causing the drop to start sliding. The sliding of the drop is governed by the rate of the viscous dissipation of the Stokes flow. The analysis result in its limit form for small contact angles is consistent with previous results. In the experiments to verify the analysis results, the measured sliding velocity of various liquid drops are shown to obey the predictions made in this study.

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Turbulent Drag Reduction Using the Sliding-Belt Device (미끄러지는 벨트 장치를 이용한 난류 항력 감소)

  • Choi, Byunggui;Choi, Haecheon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.11
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    • pp.1481-1489
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    • 1999
  • The sliding-belt concept introduced by Bechert et al. (AIAA J., Vol. 34, pp. 1072~1074) is numerically applied to a turbulent boundary layer flow for the skin-friction reduction. The sliding belt is moved by the shear force exerted on the exposed surface of the belt without other dynamic energy input. The boundary condition at the sliding belt is developed from the force balance. Direct numerical simulations are performed for a few cases of belt configuration. In the ideal case where the mechanical losses associated with the belt can be ignored, the belt velocity increases until the integration of the shear stress over the belt surface becomes zero, resulting in zero skin friction on the belt. From practical consideration of losses occurred In the belt device, a few different belt velocities are given to the sliding belt. It is found that the amount of drag reduction is proportional to the belt velocity.

Friction Characteristics of Magnetic Clutch Used in Automobiles (차량용 마그네틱 클러치의 마찰 특성)

  • Kim, Dong-Wook;Kim, Kyung-Woong
    • Tribology and Lubricants
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    • v.25 no.4
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    • pp.243-249
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    • 2009
  • A magnetic clutch consists of pulley and disk. It delivers and isolates the power needed for the operation of the compressor used in automotive air conditioning system. To improve the performance, efficiency and durability of automotive air conditioning system, appropriate design of pulley, disk and system working parameters(the magnitude of magnetic force, and so on) is necessary. For that goal, it is required to understand the friction characteristics of magnetic clutch for the initial operating time. In this study, friction tests were carried out in order to investigate the effect of sliding velocity on the friction characteristics of magnetic clutch using pin-on-disk type friction and wear tester. For experiments, pulley and disk used in real automotive air conditioning system were considered. Friction experiments were conducted under various sliding velocities, and coefficients of kinetic friction were obtained. Under the experimental conditions considered in this study, the coefficients of kinetic friction increased with the increase of test number(sliding distance) and decreased with the increase of sliding velocity.

Precise Control for Servo Systems Using Sliding Mode Observer and Controller (슬라이딩 모드 관측기와 제어기를 이용한 서보시스템의 정밀제어)

  • Han, Seong-Ik;Gong, Jun-Hui;Sin, Dae-Wang;Kim, Jong-Sik
    • Journal of the Korean Society for Precision Engineering
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    • v.19 no.7
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    • pp.154-162
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    • 2002
  • The effect of nonlinear friction in the low velocity is dominant in precise controlled mechanisms and it is difficult to model. This paper is concerned with the compensation for friction using the variable structure system approach as nonmodel based method. The problem of chattering in the sliding mode controller is suppressed by the implementation of the boundary layer concept. And the estimation for friction using sliding mode observer makes the upper bound of matched uncertainty reduced. Accordingly, the effect of chattering can be more suppressed. And the sliding surface is constructed by adding an integral component to the switching function that is made by using error dynamics. This sliding surface guarantees the good tracking performance. Experimental results for a XY table system show that the proposed method has a good performance especially in the low velocity.

Friction and Wear at Dry Sliding Low Carbon Steel Surfaces Under Vacuum Conditions (진공분위기 내에서 건조마찰 미끄럼운동을 하는 저탄소강 표면의 마찰마모 특성)

  • 공호성;윤의성;권오관
    • Tribology and Lubricants
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    • v.10 no.3
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    • pp.29-38
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    • 1994
  • The friction and wear of mild steel at dry sliding surfaces under different vacuum conditions have been investigated to understand the wear mechanisms. For the test, a ball-ondisk typed wear-rig has been built and implemented, allowing control of sliding speed, load and vacuum. Results show that, at a high sliding velocity, friction of low carbon steel (SS41) under a high vacuum is much higher than that of ambient condition and wear is much severer. It is due to lack of effective oxidation film formation on which steel surfaces could protect themselves against the severe wear. It has been shown, however, that there is a critical regime with contact conditions (at a low sliding velocity, a low load, and under a medium vacuum) at which effective, protective films of low carbon steel have been built on the surfaces in a friction process with a self-regulating way, resulting in both very low coefficients of friction (about 0.3) and mild wear. In order to investigate the protective films on steel surfaces, the worn surfaces and the wear debris have been experimentally analyzed with SEM, AES/SAM and XRD. A theoretical analysis of frictional heating at sliding surfaces, and an experimental analysis of the influence of oxidation wear under various vacuum conditions are described. The important variables on which self-formations of protective films at dry sliding surfaces depend, and the wear mechanisms are also investigated.

A New Velocity Measurement Method using Linear Type Hall-effect Sensor for Electro-mechanical Fin Actuator (선형홀센서를 이용한 전기식 구동장치의 속도 신호 구현)

  • Gu, Jeong-Hoi;Song, Chi-Young
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.59 no.1
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    • pp.70-75
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    • 2010
  • The objective of this paper is to propose a new velocity measurement method for an electro-mechanical fin actuator. The model of the electro-mechanical fin actuator includes uncertainties such as unknown disturbances and parameter variations in flight condition. So, an electro-mechanical fin actuator system needs robust control algorithm which requires not only position information but also velocity information. Usually, analog tachometers have been used for velocity feedback in an electro-mechanical fin actuator. However, using these types of sensors have problems such as the cost, space, and malfunction. These problems lead to propose a new velocity measurement method using linear type Hall-effect sensor. In order to verify the proposed method, several experiments are performed using Model Following Sliding Mode Controller(MFSMC). It is shown that the MFSMC with a new velocity measurement method using linear type Hall-effect sensor can satisfy the requirements without using of velocity sensor.

Forward Velocity Estimation Algorithm for Planar Mobile Robots

  • Lee, Seung-Eun;Kim, Wheekuk;Yi, Byung-Ju;You, Bum-Jae
    • 제어로봇시스템학회:학술대회논문집
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    • pp.51.5-51
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    • 2001
  • The sliding and/or skidding motions generally occur to a car - like planar mobile robot consisting of four conventional fixed wheels attached on two parallel axles. Thus, the kinematic model of such mobile robot should include the description of skidding and sliding frictional motions. However, most of previous kinematic models do not take these frictional motions into account the kinematic model, as the work done by Muir and Newman [1]. Thus, does it result in least square solution in estimating sensed forward velocity. In this paper, the sensed forward velocity estimation algorithm for mobile robots is proposed, which not only includes those skidding and sliding frictional motions into kinematic model but also utilizes only the minimal set of dependent internal kinematic variables of the mobile robot. Then, ...

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Precise Control of Ball-Screw Systems with Friction (마찰을 고려한 볼-스크류 시스템의 정밀 제어)

  • 김종식;한성익;공준희;신대왕
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.11 no.3
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    • pp.93-101
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    • 2002
  • The effect of nonlinear friction in the low velocity is dominant in precise controlled mechanisms and it is difficult to identify the friction effect. The friction model which Canudas suggested so called, LuGre model is well expressed the friction effect as Streibeck in the law velocity. But it\`s model parameters were estimated continuously in operation for precise control. This paper suggests the sliding mode controller and observer for compensating the friction effect. Experimental results for a ball-screw system show that the proposed method has a good performance especially in the low velocity.

Velocity Control of Permanent Magnet Synchronous Motors using Model Predictive and Sliding Mode Cascade Controller (슬라이딩 모드 및 모델 예측 직렬형 제어기를 이용한 영구자석형 동기전동기의 속도제어)

  • Lee, Ilro;Lee, Youngwoo;Shin, Donghoon;Chung, Chung Choo
    • Journal of Institute of Control, Robotics and Systems
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    • v.21 no.9
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    • pp.801-806
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    • 2015
  • In this paper, we propose cascade-form velocity controller for a permanent magnet synchronous motor (PMSM). The proposed controller consists of a sliding-mode controller (SMC) for the inner current control loop and a model-predictive controller (MPC) for the outer velocity control loop. With SMC, we can ensure that the current tracking error always converges to zero in finite time. The SMC is designed to track the desired currents. Additionally, with MPC, we can obtain the optimal velocity control input which minimizes the cost function. Constraint conditions for input and input variation are included in the MPC design. The simulation results are included to validate the performance of the proposed controller.