• Advanced Composite Materials
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• 제17권4호
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• pp.359-372
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• 2008

The moisture absorption behavior of carbon fiber-reinforced plastic (CFRP) and its effect on dimensional stability were examined. Moisture diffusivity in CFRP was determined by measuring a specimen's weight during the moisture absorption test. Three types of CFRP specimens were prepared: a unidirectionally reinforced laminate, a quasi-isotropic laminate and woven fabric. Each CFRP was processed into two geometries - a thin plate for determination of diffusivity and a rod with a square cross-section for the discussion of two-dimensional diffusion behavior. By solving Fick's law expanded to 3 dimensions, the diffusivities in the three orthogonal directions were obtained and analyzed in terms of the anisotropy of CFRP moisture diffusion. Coefficients of moisture expansion (CMEs) were also obtained from specimen deformation caused by moisture absorption. During moisture absorption, the specimen surfaces showed larger deformation near the edges due to the distribution of moisture contents. This deformation was reasonably predicted by the finite element analysis using experimentally determined diffusivities and CMEs. For unidirectional CFRP, the effect of the fiber alignment on CME was analyzed by micromechanical finite element analysis (FEA) and discussed.

• Imaging Science in Dentistry
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• 제38권2호
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• pp.81-87
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• 2008

Purpose: To investigate the relationship between 3D bone architectural parameters and direction-related elastic moduli of cancellous bone of mandibular condyle. Materials and Methods: Two micro-pigs (Micro-$pig^R$, PWG Genetics Korea) were used. Each pig was about 12 months old and weighing around 44 kg. 31 cylindrical bone specimen were obtained from cancellous bone of condyles for 3D analysis and measured by micro-computed tomography. Six parameters were trabecular thickness (Tb. Th), bone specific surface (BS/BV), percent bone volume (BV/TV), structure model index (SMI), degree of anisotropy (DA) and 3-dimensional fractal dimension (3DFD). Elastic moduli of three orthogonal directions (superior-inferior (SI), medial-lateral (ML), andterior-posterior (AP) direction) were calculated through finite element analysis. Results: Elastic modulus of superior-inferior direction was higher than those of other directions. Elastic moduli of 3 orthogonal directions showed different correlation with 3D architectural parameters. Elastic moduli of SI and ML directions showed significant strong to moderate correlation with BV/TV, SMI and 3DFD. Conclusion: Elastic modulus of cancellous bone of pig mandibular condyle was highest in the SI direction and it was supposed that the change into plate-like structure of trabeculae was mainly affected by increase of trabeculae of SI and ML directions.

• 한국정밀공학회지
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• 제18권2호
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• pp.177-185
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• 2001

This study shows the process design and forming analysis of permalloy shielding can that support the automobile multi-display parts to indicate the accurate information of car. This study is particularly important, since the strain and thickness of permalloy shielding can is known to affect the magnetic properties such as coercivity and permeability quite thickness of permalloy shielding can is known to affect the magnetic properties such as coercivity and permeability quite sensitively. The objective functions are strain and thickness deviation. The punch radius, die radius and blank holding force are considered as design parameters. Orthogonal array (OA) table and characteristics are applied to neural network (NN) as train data. After training, the optimal and robust condition of design parameters is selected. This study shows the correlation between the design methodology of NN and the statistical design of experiments (DOE) approach.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.331-349
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• 2016

Stiff and light fibre reinforced composites as used in air- and space-craft applications tend to high sound emission. Therefore, the damping properties are essential for the entire structural and acoustic engineering. Viscous damping is an established and reasonably linear model of the dissipation behaviour. Commonly, it is assumed to be isotropic and constant over all modes. For anisotropic materials it depends on the fibre orientation as well as the elastic and thermal material properties. To portray the orthogonal anisotropic behaviour, a model for unidirectional fibre reinforced plastics (frp) has been developed based on the classical laminate theory by ADAMS and BACON starting in 1973. Their approach includes three damping coefficients - for longitudinal damping in fibre direction, damping transversal to the fibres and shear based dissipation. The damping of a laminate is then accumulated layer wise including the anisotropic stiffness. So far, the model has been applied mainly to thermoset matrix materials. In this study, an experimental parameter estimation for different thermoplastic frp with angle ply and cross ply layups was carried out by measuring free vibrations of cantilever beams. The results show potential and limits of the ADAMS/BACON damping criterion. In addition, a possibility of modelling the anisotropic damping is shown. The implementation in standard FEA software is used to study the influence of boundary conditions on the damping properties and numerically estimate the radiated sound power of thin-walled frp parts.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.65-73
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• 2004

Composites are a material class for which nondestructive material property characterization is as important as flaw detection. Laminates of fiber reinforced composites often possess strong in-plane elastic anisotropy attributable to the specific fiber orientation and layup sequence when waves are propagating in the thickness direction of composite laminates. So the layup orientation greatly influences its properties in a composite laminate. It could result in the part being .ejected and discarded if the layup orientation of a ply is misaligned. A nondestructive technique would be very beneficial, which could be used to test the part after curing and requires less time than the optical test. Therefore a ply-by-ply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. This model decomposes the transmission of a linearly polarized ultrasound wave into orthogonal components through each ply of a laminate. Also in order to develop these methods into practical inspection tools, motorized system have been developed for different measurement modalities for acquiring ultrasonic signals as a function of in-plane angle. It is found that high probability shows between the model and tests developed in characterizing cured layups of the laminates.

• 천문학회보
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• 제36권2호
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• pp.86.1-86.1
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• 2011

We are developing a new universal spectropolarimeter on the Domeless Solar Telescope (DST) at the Hida Observatory to realize precise spectropolarimetric observations in a wide range of wavelength in visible and near infrared. The system aims to open a new window of plasma diagnostics by using Zeeman effect, Hanle effect, Stark effect, impact polarization, and atomic polarization for measuring the external magnetic field, electric field, or an anisotropy in the excitation of the atoms. The polarimeter is a successor of formerly developed polarimeter on DST, which make possible to observe a polarization in a photospheric spectral line with polarimetric accuracy of 10-2 (Kiyohara et al. 2004). The new system consists of a 60cm aperture vacuum telescope, a high dispersion vacuum spectrograph, polarization modulator / analyzer composed of a rotating waveplate whose retardation is constant for a wide range of wavelength and Wallaston prism, and a fast and large format CCD camera or IR camera. Spectral images in both orthogonal polarizations are taken simultaneously with a frame rate of ~20Hz while the waveplate rotates continuously in a rate of 1rev./sec. Thus It takes 5 ~ 60 sec to observe polarization with accuracy of 10-3 in a wide wavelength range (400 - 1100nm). We also examined a polarimetric model of the telescope with accuracy of 10-3 to calibrate instrumental polarization on some wavelengths. In this talk, I will focus on the performance of the instrument.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2022년도 학술발표회
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• pp.281-281
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• 2022

바닥에서 생성되는 난류는 순간적으로 강한 모멘텀을 바닥에 전달함과 동시에 바닥에 있는 입자를 움직이게 한다. 경계층 내 난류 운동에 대한 분석은 다양한 유사 이송 문제를 이해하기 위해 필수적이며 이에 따라 많은 선행 연구들은 실험실 실험을 통해 해당 연구를 수행하였다. 본 연구에서는 선행 연구에서 사용하지 못했던 진보된 실험 방법을 활용하여 바닥 경계층 내의 난류 운동에 대해 확인하고 해당 운동에 의해 관성 입자의 움직임이 어떻게 발생하는지에 대하여 물리적으로 설명하고자 한다. 다양한 흐름 조건에서 3가지의 입경 크기를 가지는 모래 입자를 가지고 실험을 수행하였으며, 실험 조건별 고해상도 유속장 및 관성 입자의 움직임은 3차원 입자 영상 유속계 (Particle Image Velocimetry; 이하 PIV)와 입자 추적 유속계 (Particle Tracking Velocimetry; 이하 PTV)를 동시에 적용하여 파악하였다. 취득된 3차원 유속장과 입자 궤적을 기반으로 실험 조건별 흐름 및 입자 거동 특성에 대해 분석하였으며, 관성 입자의 움직임을 발생시키는 3차원 난류 운동은 측정된 유속장에서 산정한 Q-criterion 값을 기반으로 도식화하였다. 측정값 내에는 난류 운동에 대한 정보와 더불어 잡음이 포함되어 있으므로 이를 제거하고자 적합 직교 분해 (Proper Orthogonal Decomposition; 이하 POD) 방법을 적용하였다. 그리고 POD로 추출한 유속장을 통해 바닥면 부근에 존재하는 헤어핀 와류 운동 혹은 와류 묶음과 같은 난류 고유 구조를 파악하였다. 해당 와류 운동들의 3차원 난류 특성을 확인하고자 비등방성 불변 지도(anisotropy invariant map)를 활용하였으며 경계층 내부에서 난류의 형태가 흐름 방향으로 늘어진 럭비공 형태임을 확인하였다. 마지막으로, 입자의 움직임을 발생시키는 난류 이벤트를 결정하고자 사방구 분석 (Quadrant analysis) 기법을 적용하였으며 흐름 조건별로 입자를 움직이게 하는 난류 이벤트는 달라짐을 확인하였다.

• Radiation Oncology Journal
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• 제20권3호
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• pp.283-293
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• 2002

목적 : 고선량률의 Ir-192 선원을 이용한 근접조사의 모의촬영 영상을 개인컴퓨터(PC)에 입력하여 해부학적 영상에 선량분포를 구현하고 히스토그램, 선량-용적히스토그램 및 3차원 선량분포를 전산화하였다. 대상 및 방법 : 선량전산화에 이용된 선원은 원격근접조사장치(Buchler 3K, 독일)의 Co-60 대체선원으로 한국원자력 연구소와 공동으로 개발한 Ir-192이다. 선원 모양에 의존하는 선량분포의 비등방성은 선원을 미소 분할하여 구한 선량과 선원 중심에서 측방 기준점의 공중선량을 기준으로 규격화한 값을 이용하였다. 선원 주위의 조직선량은 선원 중심에서 측방으로 실측된 조직감쇠와 산란에 의한 보정계수와 에너지에 따른 공기 저지능에 대한 조직의 저지능 비로 공중-조직선량 변환계수를 적용하고 기준점에 대해 규격화한 선량률표를 검색하여 얻도록 하였다. 선량계획 전산화 과정에 모의촬영 영상입력, 선원입력과 선원의 축면 결정과 해부학적 영상을 이용한 선량분포와 점선량, 히스토그램 및 선량-용적 히스토그램을 구현하였다. 결과 : 저자들이 개발한 근접조사 선량계획시스템에는 선원모의촬영 영상을 스켄하여 비트맵 파일로 저장하고, 좌표원점과 확대율을 정해, 선원위치를 결정하고 선량분포와 선량분석 프로그램을 포함한 선량전산화를 구현하였다. 실험에 이용된 Ir-192 선원의 조직내 선량은 공중선량율과 조직에 의한 감쇠 및 산란에 의한 실험식을 이용하였다. 선원 중심에서 축상의 거리와 축에서 떨어진 거리에 따른 선량률표에서 행렬 검색하여 얻도록 하였다. 근접조사선량계획은 선원좌표 입력과 선원의 축면(principal plane)을 결정하여 선원이 포함된 평면상의 선량을 구현하였으며, 시뮬레이션 영상인 관상면과 시상면에 선량분포를 구현하였다. 선량-히스토그램에 의한 선량분포 분석은 임의의 해부학적 영상면 위에 커서가 놓인 위치의 선량 스켓치로 얻었다. 임상에 필요한 선량분석은 선원의 축에서 면의깊이를 이동하여 선량분포를 구할 수 있게 하였으며, 선량-용적 히스토그램과 3차원 선량분포를 구현하였다. 결론 : 고선량률 Ir-192를 이용하여 근접조사선량계획을 전산화하였으며, 선량분포의 분석에는 해부학적 영상의 선량분포와 선량-히스토그램, 선량-용적히스토그램을 구현하였으며, 선량분포의 면을 임의 선택할 수 있고 3차원 선량분포를 포함한 선량계획시스템을 준비하였다.