• 제목/요약/키워드: dynamic eccentric motion

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Dynamic analysis of a beam subjected to an eccentric rolling disk

  • Wu, Jia-Jang
    • Structural Engineering and Mechanics
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    • 제47권4호
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    • pp.455-470
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    • 2013
  • This paper presents a theory concerning the beam element subjected to an eccentric rolling disk (or simply called the eccentric-disk-loaded beam element) such that the dynamic responses of a beam subjected to an eccentric rolling disk with its inertia force, Coriolis force and centrifugal force considered can be easily determined. To this end, the property matrices of an eccentric-disk-loaded beam element are firstly derived by means of the Lagrange's equations. Then, the overall property matrices of the entire vibrating system are determined by directly adding the property matrices of the eccentric-disk-loaded beam element to the overall ones of the entire beam itself. Finally, the Newmark direct integration method is used to solve the equations of motion for the dynamic responses of a beam subjected to an eccentric rolling disk. Some factors relating to the title problem, such as the eccentricity, radius and rotating speed of the rolling disk, and the Coriolis force and centrifugal force induced by the rolling disk are investigated. Numerical results reveal that the influence of last factors on the dynamic responses of the pinned-pinned beam is significant except the centrifugal force.

등장성 수축 결합기법의 특성에 대한 고찰 - 원심성 훈련의 중요성 - (Review of characteristics of the isotonic combination: Importance of eccentric training)

  • 김미현;배성수
    • PNF and Movement
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    • 제2권1호
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    • pp.25-33
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    • 2004
  • Purpose : The purpose of this article is to summarize the characteristics of isotonic combination. Method : Some studies of the motor unit activation patterns during isometric, concentric, and eccentric actions, neural strategies in the control of muscle force, and concentric versus combined concentric-eccentric training were reviewed. Results & Conclusions : Eccentric torque may be relatively higher than concentric torque for two potential reasons: 1) stretch responses in the antagonist are not elicited to restrain the motion as can occur concentrically and 2) stretch responses in the agonist may augment eccentric torque production. Concentric-eccentric training has a greater influence on functional capacity than that of concentric training. Both maximal force and average force throughout the motion were significantly higher when the dynamic action was started with preactivation as compared to the mode without preactivation. The peak torques observed during the concentric phase of the eccentric-concentric muscle actions were higher than those noted in the pure concentric contraction.

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저강도 원심성 운동과 동적 스트레칭이 지연성 근육통에 미치는 효과 비교 (The Comparison of Low Intensity Eccentric Exercise and Dynamic Stretching on Delayed Onset Muscle Soreness)

  • 이수영;김지윤
    • 한국산학기술학회논문지
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    • 제13권10호
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    • pp.4676-4685
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    • 2012
  • 본 연구는 저강도 원심성 운동과 동적 스트레칭이 지연성 근육통에 미치는 효과를 비교하고자 시행하였다. 본 연구의 대상자는 연구에 참여하기 5개월 전부터 하지에 규칙적인 운동을 하지 않았던 18명의 20대 건강한 여성을 대상으로 하였다. 대상자들은 전체 3그룹인 대조군, 저강도 원심성 운동군 그리고 동적 스트레칭군에 무작위로 배정되었다. 측정변수로는 최대 수의적 등척성 수축력, 초음파 영상을 통한 근 두께, 근 통증 척도, 무릎관절 가동범위이며 지연성 근육통 유발 전, 유발 후 24시간, 48시간, 72시간에 각각 측정되었다. 저강도 원심성 운동군과 동적 스트레칭군의 운동 프로그램은 지연성 근육통 유발 4주 전에 일주일에 3회씩 각각 시행되었다. 본 연구의 결과 최대 수의적 등척성 수축력과 근 통증 척도에서만 그룹간 유의한 차이가 있었으며(p<.05), 저강도 원심성 운동은 동적 스트레칭에 비해 근 통증 척도가 유의하게 감소하였다(p<.05). 그러므로 저강도 원심성 운동과 동적 스트레칭이 지연성 근육통의 증상 중 근 통증에 효과적임을 제시하며 또한 저강도 원심성 운동이 동적 스트레칭보다 근 통증을 빠르게 감소시킴으로써 근 통증에 더 효과적임을 제시하고자 한다.

다물체 모델링을 이용한 2단 유성식 외륜 고정형 사이클로이드 감속기의 진동특성분석 (Vibration Analysis of Planetary Fixed Outer-ring Type Cycloidal Speed Reducer by using Multi-body Modeling)

  • 김홍기;이기복;유홍희
    • 한국소음진동공학회논문집
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    • 제23권3호
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    • pp.234-239
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    • 2013
  • There are many types of speed reducer for industrial uses. However the cycloid speed reducer is widely used in manipulators based on excellent performance of low backlash, high reduction ratio and compact size. It is essential to use precision speed reducer for accuracy of position controls on robot systems and electric vehicles. The cycloid speed reducer has a eccentric rotating motion and offset to avoid some problem of assembly, so it has a disadvantage for vibration. In this paper, a multi-body dynamic model is developed for a cycloid speed reducer and the dynamic behaviors of the reducer are investigated. The cycloid speed reducer consists of cycloidal plate gears, housing gear, input shaft, output pin and shaft, and eccentric bearings. Using a CAD program, each component of cycloid reducer is modeled based on the offset and eccentric. Multi-body simulations using Recurdyn and test using a rig tester are performed. As a result, the pin reaction force and the amplitude of housing displacement are increased by the larger offset and smaller eccentric value of cycloid reducer.

Mathieu stability of offshore Buoyant Leg Storage & Regasification Platform

  • Chandrasekaran, S.;Kiran, P.A.
    • Ocean Systems Engineering
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    • 제8권3호
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    • pp.345-360
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    • 2018
  • Increasing demand for large-sized Floating, Storage and Regasification Units (FSRUs) for oil and gas industries led to the development of novel geometric form of Buoyant Leg Storage and Regasification Platform (BLSRP). Six buoyant legs support the deck and are placed symmetric with respect to wave direction. Circular deck is connected to buoyant legs using hinged joints, which restrain transfer of rotation from the legs to deck and vice-versa. Buoyant legs are connected to seabed using taut-moored system with high initial pretension, enabling rigid body motion in vertical plane. Encountered environmental loads induce dynamic tether tension variations, which in turn affect stability of the platform. Postulated failure cases, created by placing eccentric loads at different locations resulted in dynamic tether tension variation; chaotic nature of tension variation is also observed in few cases. A detailed numerical analysis is carried out for BLSRP using Mathieu equation of stability. Increase in the magnitude of eccentric load and its position influences fatigue life of tethers significantly. Fatigue life decreases with the increase in the amplitude of tension variation in tethers. Very low fatigue life of tethers under Mathieu instability proves the severity of instability.

외팔보형 구조물의 편심축 회전운동 해석 (Analysis of Cantilevered Structure Rotating on an Eccentric Axis)

  • 조지현;윤신일;한상보
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2001년도 춘계학술대회논문집
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    • pp.115-120
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    • 2001
  • A gyroscope is a rotating body possessing one axis of symmetry and whose rotation about the symmetry axis is relatively large compared with the rotation about any other axis. Tuning fork is this type of structure that various modem gyro-sensors are based on. In this paper, dynamic behavior of a cantilevered beam subjected ta a base rotation with respect to the eccentric axis that is parallel to the beam axis is analyzed. The final equations of motion in terms of generalized coordinates can be solved with numerical scheme with various values of angular velocities and angular accelerations of the rotating axis. In contrast to the case of rotating cantilever beam like helicopter blade, the rotational motion with respect to the beam axis has effect to decrease the stiffness of the beam and has unstable region depending on the magnitude of the rotational angular velocity and angular acceleration.

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진원도 오차를 고려한 스핀들 시스템의 동적 특성 해석 (Dynamic Analysis of a Tilted HDD Spindle System due to Roundness)

  • 곽규열;장건희
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2007년도 추계학술대회논문집
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    • pp.840-846
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    • 2007
  • This paper investigates the dynamic behavior of a HDD spindle system due to the imperfect roundness of a rotating shaft. The shaft of a spindle motor rotates with eccentricity by the unbalanced mass of the rotating part. The eccentricity generates the run-out of a spindle motor which results in the eccentric motion of a rotating part. Roundness of a shaft affects this motion which limits the memory capacity of a HDD. This research proposes a modified Reynolds equation for the coupled journal and thrust FDBs to include the variable film thickness due to the roundness. Finite element method is used to solve the Reynolds equation for the pressure distribution. Reaction forces and friction torque are obtained by integrating the pressure and shear stress, respectively. The dynamic behavior is determined by solving the equations of a motion of a HDD spindle system in six degrees of freedom with the Runge-Kutta method to characterize the motion of a rotating part. This research shows that the roundness of a rotating shaft causes the excitation frequency with integer multiple of a rotating frequency.

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소형 회전식 압축기의 동수압적 윤활해석 (Hydrodynamic Lubrication Analysis of a Small Rotary Compressor)

  • 송기선;장시열;한동철
    • Tribology and Lubricants
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    • 제4권1호
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    • pp.74-80
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    • 1988
  • For an analytic investigation on the dynamic behaviour of the eccentric piston and roller in the cylinder of small rotary vane compressors the hydrodynamic lubrication theory is opplied, analogous to the dynamic analysis of a engine bearing. An adequate modification of the equation of journal motion permits stable convergencies of the numeric calculation of the journal orbits. The increase of the outer diameter of the roller and the eccentricity of the piston gives a relative large decrease of the minimum gap between the roller and cylinder.

On triply coupled vibration of eccentrically loaded thin-walled beam using dynamic stiffness matrix method

  • Ghandi, Elham;Shiri, Babak
    • Structural Engineering and Mechanics
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    • 제62권6호
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    • pp.759-769
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    • 2017
  • The effect of central axial load on natural frequencies of various thin-walled beams, are investigated by some researchers using different methods such as finite element, transfer matrix and dynamic stiffness matrix methods. However, there are situations that the load will be off centre. This type of loading is called eccentric load. The effect of the eccentricity of axial load on the natural frequencies of asymmetric thin-walled beams is a subject that has not been investigated so far. In this paper, the mentioned effect is studied using exact dynamic stiffness matrix method. Flexure and torsion of the aforesaid thin-walled beam is based on the Bernoulli-Euler and Vlasov theories, respectively. Therefore, the intended thin-walled beam has flexural rigidity, saint-venant torsional rigidity and warping rigidity. In this paper, the Hamilton‟s principle is used for deriving governing partial differential equations of motion and force boundary conditions. Throughout the process, the uniform distribution of mass in the member is accounted for exactly and thus necessitates the solution of a transcendental eigenvalue problem. This is accomplished using the Wittrick-Williams algorithm. Finally, in order to verify the accuracy of the presented theory, the numerical solutions are given and compared with the results that are available in the literature and finite element solutions using ABAQUS software.

다물체 모델링을 이용한 외륜 고정형 Cycloid 감속기의 Offset에 의한 핀반력 및 진동차이 분석 (Multibody modeling and Analysis on Difference of Pin-reaction Force and Vibration caused by Offset in Fixed Outer Ring Type Cycloidal Speed Reducer)

  • 김홍기;이기복;유홍희
    • 한국소음진동공학회논문집
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    • 제22권11호
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    • pp.1057-1063
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    • 2012
  • A cycloid speed reducer is a type of the speed reducers. The cycloid speed reducer has a eccentric rotating motion and offset to avoid some problem of assembly, so it has a disadvantage for vibration. In this paper, a multi-body dynamic model is developed for a cycloid speed reducer and the dynamic behaviors of the reducer are investigated. The cycloid speed reducer consists of cycloidal plate gears, housing gear, input shaft, output pin and shaft, and eccentric bearings. Using a CAD program, each component of cycloid reducer is modeled based on the offset and multi-body simulations are performed using Recurdyn. As a result, the pin reaction force and the amplitude of bearing displacement are increased by the offset.