• Tribology and Lubricants
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• 제39권2호
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• pp.35-42
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• 2023

Bearing is a mechanical component that supports loads and transmits rotation. As the application of high-value-added products such as semiconductors, aviation, and robots have recently become diverse and more precise, an accurate bearing performance prediction and evaluation technology is required. Bearing performance evaluation can be divided into evaluations based on bearing theory and on numerical analysis. An evaluation based on numerical analysis is a technique that has been highlighted because the problems that remained unsolved owing to time problems can be solved through recent developments in computers. However, current studies have the disadvantage of not considering the essential changes over time and bearing rotation. In this study, bearing performance evaluation based on rigid body dynamic analysis considering rotation and load over time is performed. Rigid body dynamic analysis is performed for deep groove ball bearing to calculate the load applied by the ball. The reliability of the analysis is verified by comparing it with the results calculated using bearing theory. In addition, rigid body dynamic analysis is performed for automotive wheel bearings to calculate the contact angle and load applied by the ball for cases where axial load and radial load are applied, respectively. The effect of rotation and load over time is evaluated from these results.

• Structural Engineering and Mechanics
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• 제2권3호
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• pp.257-267
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• 1994

Motions of an unsymmetric rigid body on a rigid floor subjected to earthquake excitations with special attention to coefficient of friction are investigated. Motions of a body in a plane are classified (Ishiyama 1980) into six types, i.e. (1) rest, (2) slide, (3) rotation, (4) slide rotation, (5) translation jump, (6) rotation jump. Based upon the theoretical and experimental research work special attention is paid to the sliding of a body. The equations of motions and the behavior of coefficient of friction in the time of floor excitation are studied. One of the features of this investigation is the introduction and estimation of the "time dependent" coefficient of friction. It has been established that the constant kinetic coefficient of friction $${\mu}(kin){\sim_\sim}0.8{\mu}(stat)$$ does not give the appropriate results. The method for the estimation of the friction coefficient variation during the time is given.

• 한국기계가공학회지
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• 제18권1호
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• pp.1-8
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• 2019

The optimal design parameters of a dynamic absorber (DA) in a machine body (that is considered as a rigid body) are discussed in this paper. The bounce and rotation motions of the rigid body have been controlled passively by a DA, which consists of a mass and a spring. The rigid body is subjected to a harmonically excited force and supported by linear springs at both ends. To define the motion of a rigid body with a DA, the equation of motion was expressed in the third-order matrix form. To define the optimal design conditions of a DA, the reduction of dynamic characteristics, represented by the amplitudes of bounce and rotation, and the transmitted powers, were evaluated and discussed. The level of reduction was found to be highly dependent on the location and spring stiffness of the DA.

• 대한기계학회논문집B
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• 제25권3호
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• pp.339-346
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• 2001

The impulsive spin-up flow in a shallow rectangular container is analyzed numerically by quasi 3-D unsteady laminar flow. In the non-inertia coordinates, the flow is generated by the virtual forces as Coriolis force, etc.. After the boundary layers grow up near sidewalls, primary vortexes separate from the sidewalls. As the Reynolds number increases, the subsidiary vortexes take place in the boundary layer. The rigid body rotation is started from the inner region and propagated to the outer region, finally all the fluid reaches the rigid body rotation. According to the Reynolds number and the aspect ratio, the development of vortex pattern is symmetric or asymmetric.

• 대한기계학회논문집
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• 제17권7호
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• pp.1719-1730
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• 1993

This paper presents the theoretical natural frequencies of out-of-plane deformable ring based on the variables such as out-of-plane deflection, torsional rotation and shear rotation. Based on the same variables, a finite element eigen analysis is carried out by using the $C^0$-continuous, isoparametric element which has three nodes per element and three degrees-of-freedom at each node. Numerical experiments are peformed to find the integration scheme which produces accurate natural frequencies, natural modes and correct rigid body motion. The uniformly reduced integration and the selective reduced integration give more accurate numerical frequencies than the uniformly full integration, but the uniformly reduced integration produces incorrect rigid body motion while selective reduced integration does correct one. Therefore, the ring element based on the three variables which employes selective reduced integration is recommended to avoid spurious modes, to alleviate the error due to shear locking and to produce correct rigid body motion, simultaneously.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.546-551
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• 1997

New typology of failure mechanisms for uniform compression fields are presented based on the classical theory of plasticity, in particular th normality rule, and the limit theorem. The concrete is assumed as a rigid-perfectly plastic material obeying the modified Coulomb failure criteria with zero tension cut-off. The failure mechanisms are capable of explaining flexural types of crushing failure in uniaxial uniform compression stress fields which are called struts in truss models. The failure mechanisms consist of sliding failure along straight failure lines or hyperbolic failure curves and rigid body rotation. The failure mechanisms involving straight failure lines are explained by constant strain expansion in the first principal direction and rigid body rotation motion. The failure mechanisms presented are applied to the explanation of bond failure of bar combined with concrete crushing failure and flexural crushing failure of concrete.

• 한국정밀공학회지
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• 제14권8호
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• pp.108-114
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• 1997

A simple and efficient method is presented for the dynamics of interconnected flexible beams having large rigid body rotations. A simple mass matrix is obtained by interpolating the displacements in the global inertia frame, and the elastic force is also simply computed by using linear finite element technique with the moving frame attached to the beam. For the beams connected by revolute joints, kinematic constraints and relative rotations between the beans are not required and the equations of motions are time integrated by a simple ODE technique. Numerical simulations are conducted to demonstrate the accuracy and efficiency of the present technique.

• 대한전기학회논문지:시스템및제어부문D
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• 제52권8호
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• pp.500-505
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• 2003

In this paper, the method to register multiple sets of skull CT images to absolute coordinate system is proposed. Contrary to correspondence paired mapping of previous techniques, four anatomical landmark points, three coplanar points and one non-coplanar point, compose three principal axes simple and unique for efficient registration by means of rigid body transformation. Throughout the numerical simulation with added random noises, the error performances in terms of different rotation and rounding-off of landmark points, and incorrect localization of anatomical landmark and target points are quantitatively analyzed to generalize the proposed technique. Experiments using real skull CT images demonstrate the feasibility for an efficient use in clinical practice.

• Journal of Astronomy and Space Sciences
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• 제15권1호
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• pp.209-220
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• 1998

The stability problem of steady motion of a rigid body with multi-elastic appendages and multi-liquid-filled cavities, in the presence of no external forces or torque, is considered in this paper. The flexible appendages are modeled as the clamped -free-free-free rectangular plates, or/and as the discrete mass- spring sub-system. The motion of liquid in every single ellipsoidal cavity is modeled as the uniform vortex motion with a finite number of degrees of freedom. Assuming that stationary holonomic constraints imposed on the body allow its rotation about a spatially fixed axis, the equation of motion for such a systematic configuration can be very complex. It consists of a set of ordinary differential equations for the motion of the rigid body, the uniform rotation of the contained liquids, the motion of discrete elastic parts, and a set of partial differential equations for the elastic appendages supplemented by appropriate initial and boundary conditions. In addition, for such a hybrid system, under suitable assumptions, their equations of motion have four types of first integrals, i.e., energy and area, Helmholtz' constancy of liquid - vortexes, and the constant of the Poisson equation of motion. Chetaev's effective method for constructing Liapunov functions in the form of a set of first integrals of the equations of the perturbed motion is employed to investigate the sufficient stability conditions of steady motions of the complete system in the sense of Liapunov, i.e., with respect to the variables determining the motion of the solid body and to some quantities which define integrally the motion of flexible appendages. These sufficient conditions take into account the vortexes of the contained liquids, the vibration of the flexible components, and coupling among the liquid-elasticity solid.

• 한국멀티미디어학회논문지
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• 제13권9호
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• pp.1382-1390
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• 2010

우리는 일상에서 유체와 강체 사이에서 일어나는 상호작용을 흔히 볼 수 있다. 하지만 이를 시뮬레이션하는 것은 많은 계산량이 필요한 어려운 작업이다. 본 논문에서는 유체와 강체 사이의 상호작용 현상 중 하나인 물수제비 현상을 실시간으로 시뮬레이션 할 수 있는 역학적 모델을 제안한다. 이를 위해 실시간에 계산 가능하면서도 이전 연구에서 고려하지 않았던 돌멩이의 회전운동을 포함하는 개선된 역학적 모델을 사용하며 공기와의 마찰로 생기는 힘들도 포함한 수식을 제안한다. 제안하는 모델을 사용하면 사용자의 다양한 입력에 대해 사실적인 물수제비 현상을 시뮬레이션 할 수 있다. 또한 이전 결과에 비해 보다 원에 가까운 파장을 만들면서 실시간 처리가 가능한 수면 모델도 제시한다. 본 논문에서 제안하는 방법은 상호작용 역학 시스템이나 게임 엔진들에 쉽게 적용할 수 있다.