• 한국자동차공학회논문집
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• 제9권3호
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• pp.210-220
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• 2001

This paper aims at the evaluation on the characterization of CFRP laminate plates using falling weight impact tester. The experimentation was conducted on several laminates of different fiber and ply orientation. A system was built for the impact strength of CFRP laminates in consideration of stress wave propagation with using drop-weight impact tester as one of impact test. Absorbed energy of orthotropic composites with using T300 fiber, which are composed of the same fiber and stacking number is higher than that or quasi-isotropic specimen over impact energy 7J, but in case or using T700 fiber, much difference does not show. Also, absorbed energy of orthotropic composites with using T300 fiber, which are composed or stacking number and orientation became more than that of T700 fiber specimen; however great change doesn't show in case of quasi-isotropic specimens. It is found that influence was confirmed between impact energy and absorbed energy as the impact energy is increased with adding the falling weight.

• Carbon letters
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• 제6권1호
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• pp.1-5
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• 2005

Isotropic pitch based carbon fibers were exposed to isothermal oxidation in carbon dioxide gas to study the activation kinetics under the temperature of 800~$1100^{\circ}C$. The kinetic equation $f=1-{\exp}(-at^b)$ was introduced and the constant b was obtained in the range of 0.92~1.25. It was shown that the activated carbon fiber shows the highly specific surface area (SSA) when the constant b comes close to 1. The activation kinetics were evaluated by the reaction-controlling regime (RCR) according to changes of the apparent activation energy with changes of the conversion. It was observed that the activation energies increase from 47.6 to 51.2 kcal/mole with the conversion increasing from 0.2 to 0.8. It was found that the pores of the activated carbon fiber under the chemical reaction were developed well through the fiber.

• Transactions on Control, Automation and Systems Engineering
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• 제3권4호
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• pp.210-216
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• 2001

In this paper, design of a 3-degree-of-freedom mobile robot with three caster wheels is performed. Initially, kinematic modeling and singularity analysis of the mobile robot is performed. It is found that the singularity can be avoided when the robot has more than two wheels on which two active joints are located. Optimal kinematic parameters of mobile robots with three active joint variables and with four active joint variables are obtained and compared with respect to kinematic isotropic index of the Jacobian matrix of the mobile robot which is functions of the wheel radius and the length of steering link.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2162-2167
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• 2003

It is well-known that high anisotropic characteristic of turbulent flow field is dominant inside tip leakage vortex. This anisotropic nature of turbulence invalidates the use of the conventional isotropic eddy viscosity turbulence model based on the Boussinesq assumption. In this study, to check whether an anisotropic turbulence model is superior to the isotropic ones or not, the results obtained from steady-state Reynolds averaged Navier-Stokes simulations based on the RNG ${\kappa}-{\varepsilon}$ and the Reynolds stress model in two test cases, such as a linear compressor cascade and a forward-swept axial-flow fan, are compared with experimental data. Through the comparative study of turbulence models, it is clearly shown that the Reynolds stress model, which can express the production term and body-force term induced by system rotation without any modeling, should be used to predict the complex tip leakage flow, including the locus of tip leakage vortex center, quantitatively.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.687-694
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• 1997

The anisotropy and shape of distributed piezopolymer actuator have advantages over isotropic piezo ceramic materials, since these features of PVDF can be utilized as another design variable in control application. This study is interested in the reduction of sound transmission through elastic plate into interior space by using the PVDF actuator. The plate-cavity system is adopted as a test problem. The vibration of composite plate and the sound fields through plate are analyzed by using the coupled finite element and boundary element method. Some numerical simulations are performed on sound transmission through elastic plates. To investigate the effects of anisotropy and shape of distributed piezopolymer actuator, various kinds of distributed PVDF actuators are applied in sound control simulation for isotropic and anisotropic plates. The PVDF actuators applied are different from each other in their shapes and laminate angles. The results of control simulation show that the control effectiveness of distributed PYDF actuator can be enhanced by using the coupling between shape of actuator and vibration modes of structure and the anisotropy of piezoelectric properties of PVDF.

• 한국의학물리학회지:의학물리
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• 제9권1호
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• pp.55-64
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• 1998

고선량률 원격 강내조사 선원은 전량 외국에서 수입되어 왔으며, 최근 Co-60 소선원의 공급부진으로 초기 도입시의 치료시간에 비해 4내지 5배의 시간을 조사하게 되어 대체용 선원의 개발이 크게 요구되고 있다. 이 연구는 국내 하나로 원자로의 중성자를 이용하여 $^{191}$ Ir(n,Υ)$^{192}$ Ir 핵반응을 일으켜 Ir-192 선원 2.87 Ci (밀봉 1.012 Ci)를 생산하고, 고선량률 원격 강내조사선원의 선량특성을 조사하였다. 제작선원에 대한 조사선량률은 아크릴 지지체의 중앙에 아크릴 아프리케이터를 고정하고 선원의 중심으로부터 각각 5, 10, 20 cm 거리에 전리함을 설치하여 일정시간 선원을 노출시켜 측정한 결과 6.36 $\pm$ 0.147 Rm$^2$/GBq-hr (2.350 $\pm$ 0.054 R$cm^2$/mCi-hr)을 결정하였으며, 측정오차는 1$\sigma$ 는 2.2% 였다. 계산선량은 조사선량률 상수 4.69 R$cm^2$/h-mCi 와 Ir-192 에너지 스펙트럼을 이용한 선원자체 및 철에 대한 질량흡수계수를 통해 구했으며, 실제 측정선량과 평균 3.8 % 오차범위에서 일치하였다. 선량 등방성은 선원의 측방향과 축 및 대각선방향으로 전리함을 이용하여 측정한 결과 3 % 이내 균등한 선량을 나타내었으며, 필름선량에서도 균등선량분포를 확인할 수 있었으며, Co-60 선원과 유사한 선량분포를 얻었을 수 있었다. 특히 본 연구의 선량특성조사는 강내조사선량선원 대체용의 선원개발과 선량계획 전산화의 근거가 될 것으로 믿는다.

• 한국항행학회논문지
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• 제8권2호
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• pp.120-128
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• 2004

일반적인 OFDM/QAM 변조 방식은 연속된 심볼 사이에 보호구간 (guard interval)을 삽입함으로서 시간 영역에서 다중경로채널에 강한 특성을 가지지만, 도플러 효과에 의한 주파수 영역에서의 채널 간 간섭에 약한 특성을 보인다. 이에 반해 OFDM/OQAM 변조 방식은 시간과 주파수 영역에서 직교성을 가지는 IOTA (Isotropic Orthogonal Transform Algorithm) 필터를 사용하여 이동 환경에서 지연 확산(delay spread)과 도플러 효과(doppler effect) 에 강한 특성을 보이며, 보호구간을 사용하지 않아 OFDM/QAM 시스템에 비하여 주파수 효율을 현저하게 높일 수 있다. 본 논문에서는 OFDM/OQAM-IOTA 시스템의 물리 구조 및 OFDM/OQAM-IOTA 시스템을 위한 perfect channel estimation 방식을 제시하고, AWGN 및 1-path Rayleigh fading 채널 환경에서 OFDM/OQAM-IOTA 시스템과 일반적인 OFDM/QAM 시스템의 성능을 비교하였다. 시뮬레이션 결과에 의하면, OFDM/OQAM-IOTA 방식이 OFDM/QAM 방식보다 성능이 우수함을 알 수 있다.

• Tribology and Lubricants
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• 제39권6호
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• pp.221-227
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• 2023

A rotordynamic system consists of components that undergo rotational motion. These components include shafts, impellers, thrust collars, and components that support rotation, such as bearings and seals. The motion of this type of rotating system can be modeled as two-dimensional motion and, accordingly, the equation of motion for the rotordynamic system can be represented using complex coordinates. The directional frequency response function (dFRF) can be derived from this complex coordinate system and used as an effective analytical tool for rotating machinery. However, the dFRF is not widely used in the field because most previous studies and commercial software are based on real coordinate systems. The objective of the current study is to introduce the dFRF and show that it can be an effective tool in rotordynamic analysis. In this study, the normal frequency response function (nFRF) and dFRF are compared under rotordynamic analysis for isotropic and unisotropic rotors. Results show that in the nFRF, the magnitude of the response is the same for both positive and negative frequencies, and the response is similar under all modes. Consequently, the severity of the mode cannot be identified. However, in the dFRF, the forward and backward modes are clearly distinguishable in the frequency domain of the isotropic rotor, and the severity of the mode can be identified for the unisotropic rotor.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1997년도 제8회 학술강연회논문집
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• pp.121-129
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• 1997

Wave propagation was studied for an unidirectionally reinforced composite materials. The velocities, the particle directions and the amplitudes of reflected and transmitted waves were obtained. This analysis involves an immersion C-scan procedure. Snell's law was modified to get the velocities of waves. This analysis could be applied to the detection of flaws in a transversely isotropic composite motor case.

• 한국지진공학회논문집
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• 제13권6호
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• pp.67-86
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• 2009

이 연구에서는 u-w 정식화에 근거하여 일반적인 3차원 문제에 적용할 수 있는 지하수로 포화된 가로등방성 층상지반에서의 3차원 전달경계를 개발하였다. 지반 원역에서의 동적거동을 Fourier 급수로 전개하고, 각 항에 대한 동적강성을 u-w 정식화에 근거하여 유도하였다. 그리고 이를 Cartesian 좌표계에서 표현된 지반 근역의 3차원 유한요소와 결합할 수 있도록 변형하여 일반적인 3차원문제에도 적용할 수 있는 방법을 개발하였다. 개발된 방법을 강체 원형 기초의 동적거동 해석에 적용하고 기존의 해석 결과와 비교하여, 이 연구에서 개발된 전달경계가 정확함을 확인하였다. 또한 다양한 형태의 강체 기초 동적거동 해석에 개발된 전달경계를 적용하였고, 지하수로 포화된 가로등방성 층상지반에서 지하수위에 따라 강체 기초 동적거동의 변화 양상을 조사하여, 이 연구에서 개발된 방법의 활용성을 입증하였다.