• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1503-1511
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• 1991

본 연구에서는 곡면을 포함할 수도 있는 얇은 물체를 모델링하기 위해 새로운 기법을 도입했는데, 그 기본 개념은 다음과 같다. Fig.(a)에서와 같이 먼저 사용자 는 박판으로 불리는 두께가 없는 얇은 판을 여러장 가지고 이들을 접거나, 오려내거나, 붙이는 등의 작업을 통해서 원하는 형상으로 모델링한다.각각의 박판의 형상의 입 력은 거의 모두 2차원 좌표계에서 이루어지기 때문에, 사용자는 마치 철판위에 선을 긋는 것과 같이 쉽게 박판의 형상을 입력할 수 있다. 또한 박판에서 임의의 부분을 오려내거나 임의의 박판을 붙이는 등의 작업을 통해서 원하는 형상으로 모델링한다. 각각의 박판의 형상의 입력은 거의 모두 2차원 좌표계에서 이루어지기 때문에, 사용자 는 마치 철판위에 선을 긋는 것과 같이 쉽게 박판의 형상을 입력할 수 있다. 또한 박판에서 임의의 부분을 오려내거나 임의의 박판을 붙이는 등의 작업이 기존의 시스템 에서와는 달리 복잡한 입력이나, 수행과정을 거치지 않기 때문에, 보다 편리한 모델링 을 할 수 있다. 또한 곡면으로 된 박판 형상의 경우는 해당되는 모서리들을 곡선으 로 바꿈으로써 모델링 되도록 하였다. 박판의 모델링이 끝나면, 입력된 박판에 일정 한 두께를 부여하여 Fig.2(b)에서와 같이 부피를 갖는 입체(솔리드)로 변환하게 되는 데 이 작업은 Stroud에 의한 것과 같이 시스템에서 자동으로 이루어진다.

• Computational Structural Engineering
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• v.16 no.2
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• pp.71-78
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• 2003

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.2
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• pp.138-149
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• 2000

Various modeling techniques for ultrasonic wave propagation and scattering problems in finite solid media are presented. Elastodynamic boundary value problems in inhomogeneous multi-layered plate-like structures are set up for modal analysis of guided wave propagation and numerically solved to obtain dispersion curves which show propagation characteristics of guided waves. As a powerful modeling tool to overcome such numerical difficulties in wave scattering problems as the geometrical complexity and mode conversion, the Boundary Element Method(BEM) is introduced and is combined with the normal mode expansion technique to develop the hybrid BEM, an efficient technique for modeling multi mode conversion of guided wave scattering problems. Time dependent wave forms are obtained through the inverse Fourier transformation of the numerical solutions in the frequency domain. 3D BEM program development is underway to model more practical ultrasonic wave signals. Some encouraging numerical results have recently been obtained in comparison with the analytical solutions for wave propagation in a bar subjected to time harmonic longitudinal excitation. It is expected that the presented modeling techniques for elastic wave propagation and scattering can be applied to establish quantitative nondestructive evaluation techniques in various ways.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.7-14
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• 2018

In this study, a new check valve was studied to improve the load pressure of a brake system with a small piezoelectric-hydraulic pump. During the pressurization process, the steady-state pressure at the load is affected by the ratio of the cross-sectional area of the check valve the chamber pressure and load pressure. Since the flow path cover of the check valve is made wider than the cross-sectional area of the output flow to prevent backflow, a method of reducing the area ratio is proposed for a higher load pressure by mounting an additional mass to a thin plate spring type check valve. To identify the effect of mounting an additional mass to the existing check valve on the load pressure, a simple brake system with a small piezoelectric-hydraulic pump was modeled using a commercial code AMESim. The AMESim modeling was verified by comparing the simulation results with the experimental results of the pump the existing check valve. The additional mass was added to the verified AMESim modeling and higher load pressure was able to be obtained through simulation. The 35% performance improvement in load pressure identified by carrying out pressurization test of the brake system after adopting the new check valve the small piezoelectric-hydraulic pump.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.509-516
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• 2007

Mathematical modeling and vibration control of a tiltrotor aircraft composite wing-rotor system are investigated in this study. A wing-mounted rotor can be tilted from the vertical position to a horizontal one, and vice versa. Effect of vibration control of the wing-rotor system via piezoelectricity is studied as a function of tilt angle, ply angle of composite wing and rotor's spin speed. Composite wing is modeled as a thin-walled box beam having a circumferentially uniform stiffness configuration that produces elastic coupling between flap-lag and between extension-twist behavior. Numerical simulations are provided and pertinent conclusions are outlined.

• Transactions of Materials Processing
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• v.7 no.1
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• pp.12-22
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• 1998

An expert drawbead model is developed for the finite element analysis of stamping processes. The expert model calculates drawbead restraining forces and bead-exit thinnings with the forming condi-tions and drawbead size. The drawbead restraining forces and bead-exit thinnings of a circular draw-bead and stepped drawbead are computed by mathematical models and corrected by the multiple lin-ear regression method based on experimental measurements. The squared drawbead preventing the sheet from drawing-in inside die cavity is assumed to have a very huge drawbead restraining force and no pre-strain just after drawbead. The combined beads are considered as a combination of basic draw-beads such as circular a drawbead stepped drawbead and squared drawbead so that the drawbead restraining forces and bead-exit thinnigs are basically sum of those of basic drawbeads.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.400-404
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• 1997

This paper presents spatial relationshaps and engineering features for the feature based modeling of Sheet Metal Weld Assemblies (SMWA) that are made of sheet metal components through are welding processes. Spatial relationships in ProMod-S, a sheet metal product modeler,are further extended for the SMWA modeling. Some spatial relationships for special weld joint types are newly introduced. The geometrical and topological relations between spatial reationship, mating features, and assembly features are defined. Finally, assembly data stucturess for the product modeling of SMWA are proposed. They are an engineering relation to represent the constraints between component features, and a mating bond to integrate component design information.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.163-168
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• 2000

In this paper, a 3-D computer-aided die design process was developed for automobile rear frame with drawing, trimming, flanging, cam-piercing and piercing for tool design. The tool design has been done using Pro/Engineer on a personal computer. It is composed of four stations. The goal of this research is to apply each of stations for the standard tool specification to each station.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1992.10a
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• pp.124-129
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• 1992

이동 집중력 및 집중질량에 의한 이동하중을 받는 직사각형 보강판에 대하 여 보강재효과집중 모델링방법에 의거하여 보강판을 등방성 박판 및 보강재 효과를 반영한 등가보요소로 이루어진 판-보 조합체로 유한요소 모델링하고 Newmark의 직접 시간적분법을 이용한 동응답 해석방법을 정식화하였다. 일 련의 수치계산 예를 통하여 본 연구에서 제시한 방법이 이동하중을 받는 보 강판의 동응답 해석문제에 효과적으로 적용될 수 있음을 확인하였다. 아울러 parametric study를 통하여 이동하중이 작용하는 보강판의 동응답특성은 이 동하중의 질량효과를 고려하는 경우와 고려하지 않는 경우 매우 달라지며, 이동하중에 의한 동적응답은 이동속도가 증가할수록 정하중에 의한 응답보 다 증폭되어 나타나고 증폭비율이 질량효과를 고려할 경우 훨씬 더 커짐을 확인하였다.

• Journal of Korea Foundry Society
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• v.20 no.2
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• pp.129-140
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• 2000

This study aims at the phase-field modeling of the phase transformation in graphitization of the cast iron. As the first step, we constructed a phase-field model including the phases with negligible solubility. Under the dilute regular solution approximation, a simplified version of the phase-field model was obtained, which can be used for the phase transformation related with the stoichiometric phases. The results from the numerical calculation of the phase-field model was in good agreement with the exact analytic solution. The compositional shift due to Gibbs-Thomson effect can be reproduced within 0.5% error in the numerical calculation. The interface velocity, whereas, in numerical calculation of phase-field model appeared to be 15% larger than that from the analytic solution. This error is due to the shift of the interface position in phase-field model from the position with ${\phi}=0.5$.