• Proceedings of the KSME Conference
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• 2000.04a
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• pp.304-308
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• 2000

In this work, an equation of J-integral for a penny-shaped crack at the end of the cord embedded in rubber matrix is proposed. The dimensional analysis is applied to derived to the equation of J-integral. We assume that the energy Parameter J is separated into the deformation and the geometry function, and which is proved using by separation parameter.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.215-222
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• 1993

A general method is proposed for stiffness analysis of the leaf springs only using the geometric data and Young's modulus of the leaf springs. In this method, an engineering beam theory and Castigliano's theory are applied for the derivation of the stiffness of the leaf springs. To show realiability and effectiveness of this method, the stiffness from the proposed method is compared with the results for various types of leaf springs. From these comparisons the proposed method has been proved to be effective and reliable to estimate the stiffness of the leaf springs.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.304-309
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• 2001

In this paper, we consider the dynamic electromechanical behavior of an eccentric Yoffe permeable crack in a piezoelectric ceramic strip sandwiched between two elastic materials under the combined anti-plane mechanical shear and in-plane electrical loadings. Fourier transforms are used to reduce the problem to the solution of two pairs of dual integral equations, which are then expressed to a Fredholm integral equation of the second kind. The initial crack propagation orientation for PZT-5H piezoceramics is predicted by maximum energy release rate criterion.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.710-715
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• 2001

Rubber is used extensively in many industries because of its large reversible elastic deformation, excellent damping and energy absorption characteristics, and wide availability. It becomes very important to predict the fatigue life of rubber components. But a great deal of time and cost are necessary for the fatigue test of rubber components. In this study the fatigue life of rubber components is evaluated by performing the fatigue test of a specimen and FE analysis. The fatigue life of Jang-gu type specimen which is considered as a simple rubber component is predicted and compared with experimental results. Its material is natural rubber of which hardness is 60 and used for the engine mount of commercial vehicles.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.395-401
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• 2000

Rubber is used extensively in many industries because of its large reversible elastic deformation, excellent damping and energy absorption characteristics, and wide availability. Therefore it becomes very important to evaluate fracture characteristics of rubber. Tearing energy and J-integral have been used as fracture parameters of rubber. The J-integral values for pure shear and single edge specimen are calculated by finite element analysis and compare with theoretical values. Finite element analysis is performed by ABAQUS.

• Computational Structural Engineering
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• v.11 no.4
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• pp.239-251
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• 1998

본 연구에서는 비대칭 박벽단면을 갖는 곡선보의 안정성해석을 수행할 수 있는 이론 및 엄밀해를 제시하기 위하여, 3차원 연속체로부터 유도된 평형방정식으로부터 선형화된 가상일의 원리를 적용하였다. 박벽단면의 구속된 ？(warping)과 곡률효과를 고려하고 유한한 회전각의 2차항을 포함하는 곡선보의 변위장을 도입하여 단면에 대해 적분함으로써 도심축에 대한 박벽 곡선보의 총포텐셜에너지를 유도하였다. 또한, 단순지지되고 일축대칭 단면을 갖는 박벽원형 곡선보의 면내 및 면외좌굴에 대한 엄밀해를 유도하기 위하여, 면내에 대해서는 균일압축을 받는 원형아치의 역대칭 좌굴모드에 대한 좌굴하중을 유도하고 면외좌굴에 대해서는 균일압축 및 순수휨을 받는 아치의 처짐함수를 가정하여 곡선보의 횡좌굴하중에 대한 일반해를 제시하였다.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.12
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• pp.629-637
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• 2005

This paper proposes a new anti-windup strategy to suppress integrator windup for PI speed controller and to be implemented on the existing system with minimal modification. When the speed control mode is changed from P controller to PI controller. an appropriate initial value for integrator is assigned. This value restricts overshoot and high settling time. Also, the proposed method guarantees the designed performance independent on operating conditions, i.e. different set-point change and load torque. Simulation and experimental results for PMSM speed controller have shown its superior performance compared with the conditional integration and tracking back calculation.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.169-170
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• 2015

본 논문에서는 고효율 에너지 저장 시스템에 적합한 양방향 단일 전력변환 AC-DC 컨버터를 제안한다. 제안하는 컨버터는 단일 전력변환을 통해 저가격, 고효율 특성을 가지며, 기존 양방향 전력변환 시스템에 비해 소형화되었다. 본 논문에서는 양방향 단일 전력변환 AC-DC 컨버터를 능동 클램프를 가지는 플라이백 컨버터로 구현하였다. 전력 용량과 효율을 높이기 위해 연속전류모드를 채택하였으며, 양방향 전류 제어를 위해 분할 적분 제어기를 이용하였다. 최종적으로 시제품을 제작하여 제안하는 양방향 컨버터의 타당성을 검증하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1167-1173
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• 2013

This study aimed to calculate the CFFs (critical flow functions) of a sonic nozzle bank with a 12-nozzle package within 1 s. Toward this end, the Helmholtz free energy of natural gas was formulated by using the AGA8-dc equation of state in a form without integral terms, and thereafter, thermodynamic properties such as the enthalpy, entropy, speed of sound, and heat capacity, which are used in CFF calculation, were derived in analytical form. As a result, the calculation time of CFFs was improved from 6.7 s in a previous study to 0.6 s per 12-nozzle package and kept almost constant regardless of the number of components in natural gas. Furthermore, it was confirmed that the calculated CFF values were in agreement with the results of a CFF international comparison test carried out under ISO management in 1998-1999.

• Journal of the Korean Geotechnical Society
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• v.29 no.8
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• pp.65-73
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• 2013

Ground-coupled heat pump system has attracted attention as a promising renewable energy technology due to its improving energy efficiency and eco-friendly mechanism for space cooling and heating. Pipes buried in the ground play a role of direct thermal interaction between circulating fluid inside the pipe and surrounding soils in the geothermal exchange system. However, both complexities of turbulent flow coupling thermal-hydraulic phenomena and very long aspect ratio of the pipe make it difficult to model the heat exchange system directly. Energy balance for fluid flow inside the pipe was derived to model thermal-hydraulic phenomena, and one-dimensional pipe element was proposed through Galerkin formation and time integration of the equation. Developed element is combined to pre-developed FEM code for THM phenomena in porous media. Numerical results of Thermal Response Test showed that line-source model overestimates equivalent thermal conductivity of surrounding soils due to thermal interaction between adjacent pipes and finite length of the pipe. Thus, inverse analysis for the TRT simulation was conducted to present optimal transformation matrix with utmost convergence.