• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.697-700
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• 2011

본 논문에서는 X-FEM을 사용하여 혼합모드 하중 상태에서의 이차원 선형탄성체의 균열문제에 대한 형상 설계민감도 해석을 수행하였다. X-FEM이란 균열과 같은 특수한 해를 근사하는 방법으로써, 확장함수를 도입하여 FEM의 한계를 극복하는 방법론이다. X-FEM 하에서 해를 근사하는 데 쓰이는 확장함수들은 불연속성과 특이성을 포함하고 있어 물리적 영역에 의존한다. 이는 설계민감도 해석을 수행하는 과정에서 그러한 의존성을 고려해주는 것이 필요하다. 따라서 본 논문에서는 X-FEM 기반의 형상 설계민감도 해석해를 제안하고자 한다. 식의 유도는 전 미분 공식에 기초하고 있으며, 형상함수의 설계변분에 대한 의존성에 관한 항을 추가시켰다. 또한, 균열 주위의 국부적인 공간에서의 확장된 자유도에 설계속도를 가한다. 이에 대한 몇 가지 수치 예제를 통하여 개발된 방법론의 타당성을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.537-543
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• 1991

In this study, the strain rate effects are considered in the formulation by introducing the constitutive equation of the strain rate sensitive materials and rigid-viscoplastic finite element program is developed for axisymmtric extrusion. The effect of strain rate sensitivity on the flow characteristics and forming pressure are investigated and the experiments are carried out for extrusion with pure lead specimens. The theoretically predicted forming pressure showed reasonably good agreement with the experimental values.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.176-177
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• 2005

PDMS는 생명공학 분야에서 중요한 기술적 폴리머이다. Nd:YAG레이저의 4고조파 ($\lambda$=266nm, pulse) 레이저를 사용하여 표면 처리를 하여 PDMS 표면의 습윤성과 접착성의 향상됨을 확인하였다. 식각한 PDMS는 샘물체의 미세회로에 사용될 수 있다. 본 논문은 레이저 빔의 주사속도를 변화시키며 PDMS를 레이저로 식각하며 PDMS의 식각 특성을 연구한다 식각 특성을 의존성이 가장 효과적인 주사 속도에 대한 의존성을 규명하고자 스테이지 컨트롤러의 속도를 변화시키며 실험하였다. 그리고 최적의 레이저 출력값을 알아내려고 레이저 출력값을 조절하며 실험 하였다. 단차측정기(알파스템)을 이용하여 식각형상과 식각 효율 등을 분석하였다.

• Korean Journal of Materials Research
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• v.2 no.1
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• pp.76-82
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• 1992

Deposition of $TEOS-O_3$ oxide film as inter-metal dielectric layer shows the substrate dependency according to the substrate material and pattern density and pitch size. To minimize substrate and Pattern dependency, TEOS-base and $SiH_4-base$ Plasma oxide were predeposited as underlying material on the substrate. The substrate dependency of $TEOS-O_3$ oxide film was more significant on TEOS-base plasma oxide than on $SiH_4-base$ plasma oxide. The dependency of $TEOS-O_3$ oxide film was remarkably reduced, or nearly eliminated, by $N_2$plasma treatment on TEOS-base plasma oxide, which appears to be caused by the O-Si-N structure, observed on the the surface of TEOS-base plasma oxide.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.509-517
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• 2012

In the present study, temperature and frequency dependences of ultrasonic properties such as attenuation coefficient and phase velocity was investigated for six kinds of commercial MC-Nylon polymer samples. The ultrasonic properties of the samples were measured by using a pulse transmission method in water over a broadband frequency range of 2 to 8 MHz. Water temperature was varied from 10 to $60^{\circ}C$ with the $10^{\circ}C$ interval. The attenuation coefficients of the samples increased with the frequency and the exponent n of frequency dependence ranged within 1.16 to 1.44, slightly deviating from the linear dependence (n=1). The phase velocities of the samples exhibited negative dispersion, i.e., decreasing velocity with increasing frequency, except for ivory sample at $60^{\circ}C$. The frequency-dependent phase velocities of the samples showed the decreasing tendency with increasing temperature.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.5
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• pp.437-445
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• 2016

Recently, polyurethane foam has been used in various industry fields to preserve temperature environment of structures, and a wide range of loads from the static to the dynamic are imposed on the material during a life period. The biggest characteristic of polyurethane foam is porosity as being polymeric material, and it is generally known that insulation performance of the material strongly depends on internal void size. In addition, polyurethane foam's mechanical behavior has high dependence on strain rate and temperature as well as being highly non-linear ductile for compression. In the non-linear compressive behavior, volume fraction of voids and elastic modulus decrease as strain increases. Therefore, in this study, temperature-dependent viscoplastic-damage constitutive model was developed to describe the non-linear compressive behavior with the aforementioned features of polyurethane foam.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.112-118
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• 2008

In the present study, the dependence of ultrasonic phase velocity on porosity and frequency in cancellous bone was predicted using the Biot model and the modified Biot-Attenborough (MBA) model for propagation in fluid-saturated porous media. It was also compared with previously published measurements in human and bovine cancellous bones in vitro. It was shown that the phase velocity in cancellous bone decreased with increasing porosity and frequency The dependence of phase velocity on propagation angle in cancellous bone as predicted using the Schoenberg model together with the Biot model and tile MBA model which were modified to include the effect of angle. The theoretical models used in the present study advance our understanding of the interaction between ultrasound and cancellous bone and can be expected to be usefully employed for the diagnosis of osteoporosis.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.681-687
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• 2000

Ideograph is a truly unifies data and procedural dependencies, Ideograph can be used to assist various program optimization, such as common expression elimination, code motion, constant folding etc. In this paper, we design and implementation of the optimized abstract syntax tree using Ideograph. Ideograph has control flow information and data flow information for source program. So we use a Ideograph in order to produce a optimized Ideograph with control flow information and data flow information.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.91-93
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• 1991

DARBS는 저널베어링 및 구름베어링에 지지되어 있는 회전체-베어링계에 대한 동력학적 해석을 수행하는 프로그램이다. 해석에는 유한요소법(finite element method)을 이용하며 선회속도(whirl speed), 모우드 형성(mode shape), 임계속도(ciritical speed) 그리고 비동기 가진응답(asynchronous response)등에 대한 해석결과를 제공한다. 본 프로그램의 주된 특징은 람다 행렬(lambda matrices)의 개념을 도입하여 비동기 가진응답의 해석에 적용하 고, 베어링 상수와 자이로 효과와 같은 회전속도 의존성에 대하여 체계적인 접근방법을 사용했다는 점이다. 본 프로그램은 IBM PC 및 호환 기종에 적 합하도록 개발되었으며 기본적인 출력장치를 지원하는 S/W가 포함되어 있 다. 또한 대화식 데이타 입력과 메뉴처리방식을 채택하여 사용하기 편리하게 하였으며, 오류발생시 메세지가 나타나 오류수정을 용이하게 하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.5
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• pp.340-346
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• 1999

Minimum reflection and backward radiation methods on liquid/solid interrace were used to determine the velocity dispersion relation of acoustical surface wave for brass and aluminum substrates and copper/stainless steel nickel/brass, and nickel/aluminum layered substrates. Dispersion data agreed to dispersion characteristics of a generalized Lamb wave. The difference between velocities determined by two phenomena was closely related to the dispersion characteristics. This correspondence was explained by considering the generation mechanism of surface waves and the concept of group velocity.