• Tribology and Lubricants
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• 제39권3호
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• pp.102-110
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• 2023

This study aims to quantify the variation in the performance of a tilting pad journal bearing (TPJB) owing to the elastic deformation of its pad. To this end, we first defined a parameter, "elastic preload", and predicted the changes in the performance of the TPJB, as a function of the preload amount. We used the iso-viscosity Reynolds equation, which ignores the temperature rise due to viscous shear in thin films, and the resultant thermal deformation of the bearing structure. We employed a three-dimensional finite element model to predict the elastic deformation of the bearing pad, and a transient analysis, to converge to a static equilibrium condition of the flexible pads and journal. Conducting a modal coordinate transformation helped us avoid heavy computational issues arising from a mesh refinement in the three-dimensional finite element pad model. Moreover, we adopted the Hertzian contact model to predict the elastic deformation at the pivot location. With the aforementioned overall strategy, we predicted the performance changes owing to the elastic deformation of the pad under varying load conditions. From the results, we observed an increase in the preload due to the pad elastic deformation.

• Tribology and Lubricants
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• 제5권1호
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• pp.64-68
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• 1989

The dynamic characteristics of the annular pressure seal employed in pump have been theoretically deduced with consideration of the effects of elastic deformation due to the centrifugal stress. The deformation of the shaft is governed by the linear theory of elasticity. The results derived herein considering the elastic deformation are compared with the previously published author's results in the stiffness and damping coefficients.

• 한국지진공학회논문집
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• 제3권4호
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• pp.95-100
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• 1999

암석 코아의탄성계수 측정에 동적방법은 잘 사용되지 않을뿐만아니라 그 값은 설계에 많이 사용되지 않는다 그이유는 동적으로 결정한 탄성계수 값이 정적으로 결정된 값보다 매우 큰 것 (약 10배)으로 인식되기 때문이다. 이논문에서는 암석 코아의 동적과 정적 시험결과를 제시하였다 도출괸 결과는 :1) 실내탄성파시험으로 매우 일관성 있는 탄성계수가 결정되고 2) 변형율에 따른 암석 코아의 비선형 변형특성의 잠정적 모델이 제시되었다.

• Journal of Welding and Joining
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• 제21권3호
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• pp.68-77
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• 2003

It is important to understand the characteristics of material strength and fracture under the dynamic loading like as earthquakes to assure the integrity of welded structures. The characteristics of dynamic strength and fracture in structural steels and their welded joints should be evaluated based on the effects of the strain rate and the service temperature. It is difficult to predict or measure temperature rise history with the corresponding stress-strain behavior. In particular, material behaviors beyond the uniform elongation can not be precisely evaluated, though the behavior at large strain region after the maximum loading point is much important for the evaluation of fracture. In this paper, the coupling phenomena of temperature and stress-strain fields under the dynamic loading was simulated by using the finite element method. The modified rate-temperature parameter was defined by accounting for the effect of temperature rise under the dynamic deformation, and it was applied to the fully-coupled analysis between heat conduction and thermal elastic-plastic behavior. Temperature rise and stress-strain behavior including complicated phenomena were studies after the maximum loading point in structural steels and their undermatched joints and compared with the measured values.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.353-360
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• 1998

Dynamic measurements are used rather sparingly to determine the elastic moduli of rock cores and modulus values are not much utilized in design practice. The reason seems to result from the general perception that values obtained by dynamic measurement are much higher (about 10 times) than those determined statically. This paper presents results from dynamic and static tests on rock cores. The findings are : 1) elastic moduli can be consistently determined by laboratory seismic testing. 2) nonlear deformation characteristic of rock cores was tentatively proposed with variation in elastic modulus with strain.

• 한국정밀공학회지
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• 제10권3호
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• pp.107-116
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• 1993

In the design and operation of robitic arm with flexible links, the equation of motion are required to exactly model the interaction between rigid body motion and elastic motion and to be formulated efficientlyl. In this paper, the flexible link is represented by applying the D-H rigid link representation method to measure the elestic deformation. And the equations of motion of robotic arm, which are configured by the generalized coordinates of elastic and rigid degrees of freedom, are formulated from the principle of virtual power. Dynamic characteristics due to elastic deformation of each link are obtained by using F. E. M to model complex shaped link acurately and by eliminating elastic modes of higher order that do not largely affect motion to reduce the number of elastic degrees of freedom. Also presented is the result of simulation of flexible robotic arms whose joints are controlled by direct or PD control.

• Structural Engineering and Mechanics
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• 제60권3호
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• pp.489-505
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• 2016

Sinusoidal shear deformation theory (SSDT) is developed here for dynamic buckling of functionally graded (FG) nano-plates. The material properties of plate are assumed to vary according to power law distribution of the volume fraction of the constituents. In order to present a realistic model, the structural damping of nano-structure is considered using Kelvin-Voigt model. The surrounding elastic medium is modeled with a novel foundation namely as orthotropic visco-Pasternak medium. Size effects are incorporated based on Eringen'n nonlocal theory. Equations of motion are derived from the Hamilton's principle. The differential quadrature method (DQM) in conjunction with Bolotin method is applied for obtaining the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the nonlocal parameter, orthotropic visco-Pasternak foundation, power index of FG plate, structural damping and boundary conditions on the dynamic instability of system. The results are compared with those of first order shear deformation theory and higher-order shear deformation theory. It can be concluded that the proposed theory is accurate and efficient in predicting the dynamic buckling responses of system.

• Tribology and Lubricants
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• 제12권3호
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• pp.63-71
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• 1996

The connecting rod bearing, which is subjected to periodical dynamic loading, is an impoRant component of the reciprocating engine. In the operation of this bearing, significant parameters are the oil film thickness and the film pressure. Peak film pressures of 20-30 MPa are not uncommon. So the elastic deformation of the bearing housing can have a significant effect on the bearing performance. In this study, a numerical analysis of connecting rod bearing is investigated. Elastic deformation of the bearing housing is considered in the analysis. Separate hydrodynamic and structural analysis are coupled through a direct iterative process. It is shown that as the result of the elastic deformation of the bearing housing, the eccentricity ratio is increased, and the minimum value of the minimum film thickness and the maximum value of the maximum film pressure are decreased. The variations of rotational speed and cylinder pressure affect the minimum film thickness and the maximum film pressure variations of the connecting rod bearing.

• 대한기계학회논문집
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• 제16권4호
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• pp.737-752
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• 1992

본 연구에서는 링크를 여러개의 2절점 6자유도의 보 요소로 이상화하고 링크 의 운동을 평면 운동으로 한정하며 링크의 지지부의 강성은 무한대이고 회전 대우 부 분의 간극은 없는 것으로 가정하여 링크의 탄성 변형에 관한 운동 반정식을 유도하였 다. 즉, 변위법에 기초한 정적 변위 해석에 관한 유한 요소법에서 관성력, 중력 그 리고 외력을 외부 부하로 간주하여 동적인 운동 방정식을 유도하였다. 여기에, 회전 대우의 베어링을 선형 스프링으로 이상화하여 유연성 링크의 일부분으로 고려함으로써 베어링의 탄성 변형이 유연성 링크의 동적 변형에 미치는 영향에 대하여 고찰하였다. 베어링의 탄성 변형이 고려된 유연성 링크에 관한 운동 방정식을 모우드 중첩법에 근 거를 둔 수치해법으로 그 해를 구하였다.

• 대한기계학회논문집A
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• 제38권1호
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• pp.79-88
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• 2014

제품 정밀도와 생산성 향상을 위해 고속프레스의 초고속화 및 초정밀화 기술이 더욱 중요해지고 있다. 그러나 고속프레스는 작동 속도 증가에 따라 슬라이드의 반복 위치 정밀도가 저하되고 프레스 구조 부품의 파손 위험성은 증가하는 것으로 알려져 있다. 따라서 고속프레스의 설계 정밀도를 향상시키기 위해서는 이런 문제점을 해석적으로 예측하고 설계에 미리 반영하는 것이 필요하다. 이번 연구에서는 편심 질량을 갖는 프레스 구동부 부품의 회전에 따른 동적 탄성 변형을 유한요소해석과 실험을 통해 분석하였다. 이를 통해 고속의 작동 조건에서 프레스의 정밀도와 파손 위험성 변화를 평가하였다.