• Journal of Communications and Networks
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• 제15권6호
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• pp.547-558
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• 2013

Ultra broadband communication systems operated at THz frequencies will require the thorough knowledge of the propagation channel. Therefore, an extensive measurement campaign of 50 GHz wide indoor radio channels is presented for the frequencies between 275 and 325 GHz. Individual ray paths are resolved spatially according to angle of arrival and departure. A MIMO channel is recorded in a $2{\times}2$ configuration. An advanced frequency domain ray tracing approach is used to deterministically simulate the THz indoor propagation channel. The ray tracing results are validated with the measurement data. Moreover, the measurements are utilized for the calibration of the ray tracing algorithm. Resulting ray tracing accuracies are discussed.

• 한국광학회지
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• 제17권1호
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• pp.89-93
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• 2006

방향성 결합기의 소멸비 특성 개선을 위해 입사도파로의 접근각도를 조절하는 방안의 가능성과 오차한계를 살펴보았다. 입사도파로의 접근각도가 크면 단순한 모드분석 이론의 틀에 오차를 유발하게 되지만 적절하게 조절하면 오차를 극소화하면서도 입사되는 광모드의 결합계수를 미세 조절함으로써 소멸비를 개선하는 효과가 있었다. 급격한 접근각도의 설정 시에는 비록 그 각도가 작아서 유출모드(leak mode)에 의한 손실이 있기 전이더라도 광모드의 과잉쏠림(field-profile overshooting)에 의해 각종 특성의 열화가 생기기 시작하는 것을 발견하고 그 영향을 분석하였다. 진행 광모드의 변화는 BPM(Beam Propagation Method)으로 전산 모사하였으며, 직선형 및 곡선형의 두 가지 입사도파로 구조에 대해 특성변화를 비교하여 소멸비 특성을 최적화하는 조건을 얻어내었다.

• Journal of Welding and Joining
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• 제6권3호
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• pp.43-55
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• 1988

An experimental study was carried out to identify the fatigue fractue behavior of weld zone in generally rolled steel for marine structure. The bending an shear loads were applied simultaneously on the specimens to simulate real load condition for marine structure. The effect of the stress intensity factor under mode I with II loading condition on the initiation and the propagation of a crack were investigated, with particular emphaiss on mode II. When the $K_{II}$ stress intensiy factor in mode II was applied under mode I load condition, the growth behavior of a crack seems to be affected mainly by the anisotropic characteristic of materials. Especially, when the crack was located in and near the weld zone and parallel to th weld line, the propagation behaviour was turned out to be quite different from that of the base metal along the direction transverse to the weld line. In general, the propagation veiocity of the cracks in and near the weld zone was found to be slower that the velocity in base metal.

• Structural Engineering and Mechanics
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• 제92권1호
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• pp.99-110
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• 2024

The crack propagation path can be considered as a boundary problem in which the crack advances towards the interior of the domain. Consequently, this poses an optimization problem wherein the local crack-growth direction angle can be treated as a design variable. The advantage of this approach is that the continuous minimization of strain energy naturally leads to the mode I propagation path. Furthermore, this procedure does not rely on the precise characterization of the stress field at the crack tip and is independent of stress intensity factors. This paper proposes an algorithm based on internal point exploration as well as shape sensitivity optimization and strain energy minimization to determine the crack propagation direction. To implement this methodology, the algorithm utilizes a modeling GUI associated with an academic analysis program based on the Dual Boundary Elements Method and determines the propagation path by exploiting the elastic strain energy at points in the domain that are candidates to be included in the boundary. The sensitivity of the optimal solution is also assessed in the vicinity of the optimum point, ensuring the stability and robustness of the solution. The results obtained demonstrate that the proposed methodology accurately predicts the crack propagation direction in Mode I opening for a single crack (lateral and central). Furthermore, robust optimal solutions were achieved in all cases, indicating that the optimal solution was not highly sensitive to changes in the design variable in the vicinity of the optimal point.

• 한국가스학회지
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• 제19권5호
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• pp.13-19
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• 2015

본 연구에서는 보다 현실적인 파쇄균열 전파를 묘사하기 위해 수압파쇄균열 전파 모델을 개발하였다. 이 모델에서는 두 가지 균열 전파 기준을 적용하였다. 첫 번째는 균열의 발생각을 결정하기 위한 최대 접선응력 기준과 두 번째는 파쇄균열의 자연균열 통과 여부 기준이다. 본 모델의 검증 결과, 수압파쇄균열이 자연균열을 통과하는 양상이 실험값과 동일함을 확인하였다. 균열의 전파에 직접적인 영향을 미치는 요소인 최대수평응력 방향, 균열면의 마찰계수, 자연균열의 방향성에 대한 민감도 분석 결과, 이론적 기준에 적합하게 균열의 전파 방향과 통과 여부가 결정되는 것으로 나타났다. 기존의 수직 판형 균열 전파 모델과 본 모델을 비교하여 균열의 연결성과 유정 자극부피 측면에서 차이가 있음을 확인하였다.

• 한국항행학회논문지
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• 제28권3호
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• pp.278-287
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• 2024

본 논문에서는 소형 발사체의 원격측정시스템 링크 버짓 모델을 제안하고, 제안한 링크 버짓 모델을 바탕으로 링크 버짓 시뮬레이터를 구현하였다. 제안하는 링크 버짓 모델은 기하학적 모델과 전파 손실 모델로 구성되어 있다. 기하학적 모델은 지상국과 소형 발사체 사이의 시선각을 계산하기 위한 모델이다. 전파 손실 모델은 소형 발사체 비행 환경에 적합하도록 자유공간 손실과 소형 발사체의 시선각 및 안테나 방사 패턴 기반의 편파 손실, 지향 손실로 구성되어 있어, 복잡한 전파 환경에 대한 계산 없이 전파 손실을 계산 할 수 있다. 링크 버짓 시뮬레이터는 제안하는 링크 버짓 모델을 기반으로 MATLAB으로 구현하였으며, 지상국 위치 및 소형 발사체의 궤적, 안테나의 방사 패턴 등을 기반으로, 소형 발사체의 시선각, 자유공간 손실, 편파 손실 파라미터, 지향 손실, 지상국에서의 수신 신호 레벨 등을 계산한다.

• Geomechanics and Engineering
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• 제12권3호
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• pp.541-560
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• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.234-237
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• 2001

In this study, efforts were made to understand the propagation of electromagnetic wave through the foam core sandwich structure by the analytical model. Foam core sandwich structure is composed of glass/epoxy composite skins and foam core. Transmittance and reflectance of the arbitrary linearly polarized incident TEM waves through the unidirectional composites, foam and foam core sandwich structures were determined as functions of thickness, fiber orientation of composites, incident angle and polarization angle by the analytical model. From the results of the analysis, the general tendency of transmittance and reflectance of electromagnetic wave through composites, foam and foam core sandwich structures was obtained.

• 비파괴검사학회지
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• 제25권3호
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• pp.163-170
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• 2005

A modular Gaussian beam model is developed to simulate some ultrasonic testing configurations where multiple interfaces are involved. A general formulation is given in a modular matrix form to represent the Gaussian beam propagation with multiple interfaces. The ultrasonic transducer fields are modeled by a multi-Gaussian beam model which is formed by superposing 10 single Gaussian beams. The proposed model, referred to as "MMGB" (modular multi-Gaussian beam) model, is then applied to a typical contact and angle beam testing configuration to predict the output signal reflected from the corner of a vertical crack. The resulting expressions given in a modular matrix form are implemented in a personal computer using the MATLAB program. Simulation results are presented and compared with available experimental results.

• 한국정밀공학회지
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• 제12권11호
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• pp.36-44
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• 1995

When sliding a hard cylinder along the surface of glass, periodic surface cracks appear on the flat surface due to tensile stresses induced by the slider. These cracks propagate into the substrate and will affect the fracture properties of a body. Crack spacings and the directions of crack propagation into glass were calculated numerically by applying the finite element method and linear elastic fracture mechanics. The calculated crack spacings were in the range of the experimental results. Stress intensity factors and crack extension angles depended on the radius of slider and the load, and from these two factors the possible directions of crack propagation were calculated. The calculated propagation directions were in good agreement with real crack propagation.