• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.119-128
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• 1999

본 연구는 등방탄성체에 고속충격하중이 작용하는 경우에 대한 유한요소해석에 관한 것으로 대상구조는 여러 가지 모양의 2차원 평면구조를 택하였다. Galerkin 방법을 이용하여 유한요소 정식화하였으며 직접시간적분법에 의해 수치해를 구하였다. 본 해석에서는 균열이 없는 평판으로 수치해와 이론해를 비교하여 수치해의 신뢰성을 확인하였으며, 0°, 30°, 45°경사 균열이 없는 평판에 적용한 3가지 예를 분석하였다. 수치해석 결과는 이론해의 결과와 상호 잘 일치하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06d
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• pp.9-12
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• 1998

공기경계층을 갖는 유리평판에서 힘의 크기가 10N이고 상승시간이 약 280ns 인 경사 점하중이 인가된 경우에 대하여 진앙점에서 입자 변위와 입자 속도를 계산하였다. 이론적으로 계산된 수직성분이 입자속도가 PZT변환자에 입사한다고 가정하여 PZT 변환자의 과도 응답특성을 Mason 등가회로와 격자점을 이용하여 계산하였다. 유리모세관의 파과시에 방출괴는 과도탄성파를 이용하여 유리평판의 진앙점에서 PZT 변환기의 응답을 조사하였고, 이론과 비교한 결과 상당히 일치하였다. 이를 이용하여 음향방출 시스템인 발생원, 전파매질, 변환자 및 신호분석시스템을 수학적으로 모형화할 수 있는 기초를 마련하였다.

• KDI Journal of Economic Policy
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• v.34 no.2
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• pp.1-15
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• 2012

We develop an identity choice model within the context of a stereotyping-cum-signaling framework. The model allows us to explore implications of the fact that, when individuals can choose identity, then the distribution of abilities within distinct identity groups becomes endogenous. This is significant because, when identity is exogenous and if the ability distributions within groups are the same, then inequality of group reputations in equilibrium can only arise if there is a positive feedback between group reputation and individual human capital investment activities (Arrow, 1973; Coate and Loury, 1993). Here we show that when group membership is endogenous then the logic of individuals' identity choices leads there to be a positive selection of higher ability individuals into the group with a better reputation. This happens because those for whom human-capital-investment is less costly are also those who stand to gain more from joining the favored group. As a result, ability distributions within distinct groups can endogenously diverge, reinforcing incentive-feedbacks. We develop the theoretical framework that can examine the positive selection and the endogenous group formation. The model implies that inequality deriving from stereotyping of endogenously constructed social groups is at least as great as the inequality that can emerge between exogenously given groups.

• Computational Structural Engineering
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• v.3 no.3
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• pp.101-111
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• 1990

The elastic analysis of floor slabs using the p-version of finite element method encounters stress singularities at certain types of reentrant corners, openings and cut-outs. Results obtained using the computer code based on C.deg. - hierarchic plate element formulated by Reissner-Mindlin theory are compared with theoretical predictions and with computational results reported in the literature. The convergence rate of h-, p- and hp-version can be estimated on the basis of the energy norm in global sense. If accuracy in terms of the number of degree-of-freedom is used as a criterion, the solutions presented here are the most efficient that have been published up to date. Examples are the rhombic plate with the obtuse angle of 150.deg. and the square plate with cut-outs.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.800-809
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• 1987

For precise stress analysis of pressure vessel nozzle junction area, it should be modelized as a cylindrical shell with a cylindrical outlet attached on it, but because of its geometrical complexity, exact analysis and solution is very difficult to obtain. So, when the nozzle diameter is small compared to that of vessel, it is general to simplify the model as a flat plate with a cylinder. As the current nozzle shape is manufactured as "Through Type" to reduce the stress concentration around the nozzle junction part of pressure vessel, a theoretical analysis on the cylinder with finite length should be performed to accomodate this fact. In this paper, the general solutions which were obtained by applying Fulgge's theory to the finite length cylinder, membrane and bending theory to the flat plate were superposed to analyze the model. Each theoretical optimal values were obtained through the analysis of stress concentration caused by the variation of cylinder length and thickness, and these results were estimated by performing model experimentation.mentation.

• The Journal of the Acoustical Society of Korea
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• v.11 no.3
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• pp.25-39
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• 1992

Undesired vibratory motion of a simply supported plate is controlled with piezoelectric sensors and actuators. Appropriate dynamic equations of the sensor and actuator are derived and coupled with the dynamic equation of the plate for the construction of an active feedback vibration control system. Analytic solutions are obtained for amplitude response of the plate, reflecting the combined effect of external driving forces and piezoelectric control moments. Numerical examples are presented to illustrate the effectiveness of this approach for two types of external forces, i.e. a concentrated point load and a piezoelectric plate driver. Calculation results show that the sensors and actuators can be efficient tools to mitigate the sensitivity of the structure to external sources of vibration. The method investigated in this work is applicable to arbitrary external loading conditions and control algorithms.

• Computational Structural Engineering
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• v.10 no.2
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• pp.179-188
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• 1997

A 4-node element for efficient finite element analysis of plate bending is presented in this paper. This element is formulated based on Mindlin plate theory to take account of shear deformation. To overcome the overestimation of shear stiffness in thin Mindlin plate element, especially in the lower order element, five nonconforming displacement modes are added to the original displacement fields. The proposed nonconforming element does not possess spurious zero-energy mode and does not show shear locking phenomena in very thin plate even for distorted mesh shapes. It was recognized from benchmark numerical tests that the displacement converges to the analytical solutions rapidly and the stress distributions are very smooth. The element also provides good results for the case of high aspect ratio.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1485-1492
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• 1992

While the vibration of circular plates were considered by many researchers, rather less attention is given to elliptical plates. In the present paper, the Rayleigh-Ritz mothod is used to obtain an eigenvalue equation for the free flexural vibration of thin elliptical plates having the classical free, simply suported or clmped boundary condition. Circular plates are included as a special case of the elliptical plates. Products of simple polynomials are used as the admissible functions and a recurrence relationship facilitates the evaluation of the necessary integrals. The analysis is developed for rectilinear orthotropic plates but the numerical results are given for isotropic plates with various aspect ratios.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.113-117
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• 1996

구조물의 진동에 의해 소음이 방사되는 현상은 기계에서 소음의 발생원으로 볼 수 있기 때문에 기게류의 소음을 예측하거나 저감방안을 제시하기 위해서는 구조물의 동특성과 방사특성을 이해하고 있어야 한다. 특히, 엔진블럭, 펀치프레스, 배의 갑판구조물등과 같은 대다수의 소음 발생기계는 평판의 형상을 가진 구조물로서 기계적인 충격 등에 의해 그 표면에서 소음이 발생되므로 강성을 증가시키고, 소음저감을 목적으로 빔과 같은 보강재를 통해 보강되어 있다. 그런데, 해석적인 방법으로는 평판이나 원판 또는 구와 같은 단순한 형태의 특정구조물에 대해서만 그 결과를 얻을 수 있으므로 이와 같은 불연속 평판구조물의 진동 및 방사특성은 평판에 대한 순수 이론으로는 해석이 곤란하여 따라서 본 연구에서는 수치해석적인 방법을 통해 이를 해결하고자 하였다. 수치해석적인 방법으로는 유한요소법(FEM)과 경계요소법(BEM), 및 통계적 에너지 해석기법(SEA)등이 있으며 구조물의 진동-소음연성문제의 경우에 있어서는, 진동해석을 FEM과 SEA으로, 공기 중에서의 방사현상은 BEM으로 예측하고 있다. 본 연구에서는 재질이 균일한 얇은 2차원 평판구조와 보강평판에 대해서 진동특성은 유한요소해석 프로그램을 사용하여 해석하였으며 이때의 진동특성값을 입력데이터로 사용하여 경계요소해석 프로그램으로 방사효율 등을 예측하였다. 또한 이 과정에서 2차원 평판구조의 모우드 밀도와 가진점 모빌리티의 실수값이 가지는 평균치의 물리적 특성을 분석하였으며, 추후 실험을 통해 이를 검증코자 한다.

• Journal of Labour Economics
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• v.32 no.1
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• pp.1-29
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• 2009

This paper exploited the data reported in BK21 program of professors' research performances and analyzed the effects of reputational concerns on professors' research performances. According to the established theory of reputation effects in incentive provision, a professor's research incentive gets stronger if one's ability is less known, and one's colleagues' abilities are better known. We confirmed this theoretical hypothesis of reputation effects. Moreover, we found that a professor's research incentive was larger under inter-generational grouping in terms of age distribution and homogeneous grouping in terms of ability uncertainty.