• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.29-37
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• 1997

An implicit viscous turbulent flow solver is developed for two-dimensional geometries on unstructured triangular meshes. The flux terms are discretized based on a cell-centered finite-volume formulation with the Roe's flux-difference splitting. The solution is advanced in time using an implicit backward-Euler time-stepping scheme. At each time step, the linear system of equations is approximately solved with the Gauss-Seidel relaxation scheme. The effect of turbulence effects is approximated with a standard $k-{\varepsilon}$ two-equation model which is solved separately from the mean flow equations using the same backward-Euler time integration scheme. The triangular meshes are generated using an advancing-front/layer technique. Validations are made for flows over the NACA0012 airfoil and the Douglas 3-element airfoil. Good agreements are obtained between the numerical results and the experiment.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.258-261
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• 2007

Simulations of the thermally-induced residual stresses and birefringence in freely quenched plates of polycarbonate were performed by using the linear viscoelastic and photoviscoelastic constitutive equations for the mechanical and optical properties, respectively, and the first order rate equation for volume relaxation. The predictions for the birefringence showed good agreement with experimental measurements. Based on the simulation, the influences of various cooling conditions on the residual stress and birefringence in plates were investigated. The residual stress and birefringence increased with increasing initial temperature, decreasing coolant temperature and increasing heat transfer coefficient of coolants.

• Structural Engineering and Mechanics
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• 제76권5호
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• pp.579-590
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• 2020

This paper's objective is to investigate the effect of gravity on a micropolar thermoelastic medium with voids. The problem is assessed according to the three-phase-lag model. An analysis of the resulting non-dimensional displacement, temperature variation, and internal stress of the study material is carried out and presented graphically. The non-dimensional displacement, temperature, micro-rotation, the change in the volume fraction field and stress of the material are obtained and illustrated graphically. Comparisons are made with the results predicted by different theories for different values of gravity, the phase-lag of the heat flux and the phase-lag of the temperature gradient. The numerical results reveal that gravity and relaxation times have a significant influence on the distribution of the field quantities. Some notable insights of interest are deduced from the investigation.

• Journal of Korean Vacuum Science & Technology
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• 제3권2호
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• pp.116-120
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• 1999

Possible role of hydrogen atoms on the formation of microcrystalline silicon films was schematically investigated using a plasma enhanced chemical vapor deposition system. A layer-by-layer technique that can alternate deposition of ${\alpha}$-Si thin film and then exposure of H2 plasma was used for this end. The experimental process was extensively carried out under different hydrogen plasma times (t2) at a fixed number of 20 cycles in the deposition. structural properties, such as crystalline volume fractions and grain shapes were analyzed by using a Raman spectroscopy and a scanning electron microscopy. Electrical transports were characterized by the temperature dependence of the dark conductivity that gives rise to the calculation of activation energy (Ea). Optical absorption was measured using an ultra violet spectrophotometer, resulting in the optical energy gap (Eopt). Our experimental results indicate that both of the hydrogen etching and the structural relaxation effects on the film surface seem to be responsible for the growth mechanism of the crystallites in the ${\mu}$c-si films.

• 대한수학회보
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• 제60권1호
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• pp.93-111
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• 2023

In this paper we study a nudging continuous data assimilation algorithm for the three-dimensional Leray-α model, where measurement errors are represented by stochastic noise. First, we show that the stochastic data assimilation equations are well-posed. Then we provide explicit conditions on the observation density (resolution) and the relaxation (nudging) parameter which guarantee explicit asymptotic bounds, as the time tends to infinity, on the error between the approximate solution and the actual solution which is corresponding to these measurements, in terms of the variance of the noise in the measurements.

• 한국생산제조학회지
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• 제7권6호
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• pp.117-125
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• 1998

The paper attempts to estimate the incubation time of a cavity in the interface between a power law creep particle and an elastic matrix subjected to a uniaxial stress. Since the power law creep particle is time dependent, the stresses in the interface relax. The volume free energy associated with Helmholtz free energy includes strain energies caused by applied stress and dislocations piled up in interface(DPI). The energy due to DPI is found by modifying the result of Dundurs and Mura[4]. The volume free energies caused by both applied stress and DPI are a function of the cavity size(r) and elapsed time(t) and arise from stress relaxation in the interface. Critical radius $r^*$ and incubation time $t^*$ to maximise Helmholtz free energy is found in present analysis. Also, kinetics of cavity formation are investigated using the results obtained by Riede [7]. The incubation time is defined in the analysis as the time required to satisfy both the thermodynamic and kinetic conditions. Through the analysis it is found that 1) strain energy caused by the applied stress does not contribute significantly to the thermodynamic and kinetic conditions of a cavity formation, 2) in order to satisfy both thermodynamic and kinetic conditions, critical radius $r^*$ decreases or holds constant with increase of the time until the kinetic condition(eq. 2.3) is satisfied. there for the cavity may not grow right after it is formed, as postulated by Harris [15], and Ishida and Mclean [16], 3) the effects of strain rate exponent (m), material constant $\sigma$0, volume fraction of the particle to matrix(f)and particle size on the incubation time are estimated using material constants of the copper as matrix.

• 한국해안해양공학회지
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• 제16권4
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• pp.241-257
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• 2004

전구해양순환모형인 Bryan-Cox-Semtner모형에서 파생된 NCAR의 NCOM모형을 이용하여 한반도 주변해역의 해수순환을 가능한 세밀하게 해상시킨 예단적 전구해양순환모형을 수립하였다. 모형영역은 남북방향으로 $80.6{^\circ}S~88.6{^\circ}N$의 범위로서 북극해가 제외되었으며, 한반도 주변이 약 $0.3^\circ$로 해상된 수평 가변격자와 연직방향으로 15층으로 구성하였다. 섬 주변해안의 순환을 적절히 재현하기 위한 구멍완화법(Hole-relaxation method)을 적용하여 22개의 섬처리가 고려되었으며, NCAR에서 CSM(Climate System Model)운용을 위해 300년동안 spin-up 계산된 결과를 초기자료로 하고, Choi et al.(2002)의 접합 대기해양모형의 결과로부터 얻은 바람응력자료가 사용되었다. 모형결과로부터, 전구와 북서태평양 해역의 순환패턴을 살펴보았으며, 한반도 주변의 5개해협에서의 용적수송량을 Choi et al.(2002)의 결과 및 관측치와 비교하였다.

• 약학회지
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• 제41권2호
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• pp.247-254
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• 1997

The proteinase-activated receptor (PAR-2) belongs to the family of seven transmembrane region receptors, like the thrombin receptor, it is activated by specific proteolytic clea vage of its extracellular amino terminus and a synthetic peptide (SLIGRL). The earthworm protein fraction (EPF) extracted from Lumbricus rubellus elicted dose- and endothelium-dependent relaxations in phenylephrine-contracted rat thoracic aorta, whereas heat inactivated EPF (0.5 ${\mu}g$ /ml) had no effect. In the presence of the nitric oxide synthase inhibitor NG-methyl-L-arginine (1.8 micro M), EPF (0.5 ${\mu}g$ /ml)-induced relaxations were partially inhibited. Furthermore, EPF (0.5 ${\mu}g$ /ml) dramatically caused relaxation of thrombin-desenstized rat thoracic aorta. These results indicate that EPF activates PAR-2 in vascular endothelial cell. Intravenous injection of EPF (20 mg/kg, bolus) into anesthetized rats produced a marked depressor response. EPF (0 ~ 80 ${\mu}g$ /ml, gradient) was very effective on increasing of perfusion volume in rabbit ear vessel preparations. These results imply the usefulness of EPF as a vascular smooth muscle relaxant and indicate that the activation of PAR-2 may be a mechanism of EPF on hemokinetic improvement.

• 한국재료학회지
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• 제3권2호
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• pp.197-204
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• 1993

Plastic기 복합재료의 파괴거동에 미치는 원공크기오 판폭의 영향을 검토하기 위하여 단축인장시험을 행하였다. 점응력파손조건에서의 특성길이 $d_o$는 원공크기 및 판폭에 의존하며, 이를 기초로 파손강도를 예측하기 위한 수정 점응력 파손조건식을 제안하였다. 이 파손조건의 예측값은 실험값과 잘 일치하였다. 파손 강도는 원공선단의 손상비의 증가에 따라 증가하며, 이는 손상영역의 형성으로 인한 응력완화현상으로 설명되어 진다. 또한 불안정 파괴시의 최대균열길이 $a_c$는 특성길이 $d_o$의 약 2배의 값을 나타낸다. 파괴인성에 대응하는 한계에너지해방율 $G_c$의 변화는 원공선단의 손상영역의 증가에 의한 응력완화가 주요한 원인이라고 할 수 있다.

• 한국재난정보학회 논문집
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• 제16권2호
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• pp.267-275
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• 2020

연구목적: 본 연구에서는 공동 영역의 변화를 규명하기 위해 GPR 탐사장비, 유량계, 천공기, 공내 촬영장비, 공동 형상화 장비 등을 사용하여 공동 체적에 비례한 일정량의 물을 주입하고, 주입한 물이 빠짐에 따라 확대되는 공동 영역 변화를 정량적으로 평가하였다. 연구방법: 지하수 주입에 의한 공동 체적변화를 살펴보기 위해 실험공 2개소에 대한 주입시간-주입유량-체적증가량을 측정하였다. 연구결과: 주입시간이 증가할수록 체적증가량은 감소하고 있으며 1시간 정도 주입하면 더 이상의 체적증가가 없음을 알 수 있었다. 결론: 주입실험을 통해 체적변화 양상을 분석하여 공동생성의 원인이 주변 지중 매설물에 대한 영향 유무를 판단할 수 있었다. 그리고 지하수 주입 시, 공동이 확장되는 과정에서 주변의 이완된 지반이 일부 붕괴되거나 세립토가 주변 지반의 간극을 채우기 때문이며, 지하수 주입 유량이 증가할수록 체적변화가 증가하는 것으로 미루어, 공동의 확장은 지하수 유동에 큰 영향이 있음을 알 수 있었다.