• 한국군사과학기술학회지
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• 제13권6호
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• pp.1034-1042
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• 2010

This study investigates effects of three different parameterizations of vertical mixing scheme on upper ocean simulation of the East Sea, focusing on the seasonal variations of the sea surface temperature(SST) and the mixed layer depth(MLD) using an ocean general circulation model(GFDL MOM1.1). The considered vertical mixing schemes are the Laplacian scheme(L scheme) that use a constant eddy coefficient, the Mellor-Yamada scheme(MY scheme), and a new scheme(Noh scheme). The Noh scheme, a second-order turbulence closure, was developed considering recent observational evidences such as the enhancement of turbulent kinetic energy near the sea surface. During summer L scheme underestimates the SST, while MY scheme overestimates the SST, compared to climatological SST. Noh scheme produces the SST in better agreement with climatological one. During winter all schemes overestimate the SST up to $4^{\circ}C$ compared to climatological SST. Vertical profiles of the basin-mean temperature show that L scheme produces higher temperature below the thermocline than those of other schemes. The winter MLD simulated from L scheme is rather large compared to that from other schemes, but the differences in MLD during summer are not significant.

• 한국환경과학회지
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• 제19권2호
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• pp.137-148
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• 2010

This paper investigates the characteristics of turbulence schemes. Turbulence closures are fundamental for modeling the atmospheric diffusion, transport and dispersion in the boundary layer. In particular, in non-homogeneous conditions, a proper description of turbulent transport in planetary boundary layer is fundamental aspect. This study is based on the Regional Atmospheric Modeling System (RAMS) and combines four different turbulence schemes to assess if the different schemes have a impact on simulation results of vertical profiles. Two of these schemes are Isotropc Deformation scheme (I.Def) and Anisotropic deformation scheme (A.Def) that are simple local scheme based on Smagorinsky scheme. The other two are Mellor-Yamada scheme (MY2.5) and Deardorff TKE scheme (D.TKE) that are more complex non-local schemes that include a prognostic equation for turbulence kinetic energy. The simulated potential temperature, wind speed and mixing ratio are compared against radiosonde observations from the study region. MY2.5 shows consistently reasonable vertical profile and closet to observation. D.TKE shows good results under relatively strong synoptic condition especially, mixing ratio simulation. Validation results show that all schemes consistently underestimated wind speed and mixing ratio but, potential temperature was somewhat overestimated.

• Environmental Engineering Research
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• 제21권4호
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• pp.365-372
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• 2016

The effects of hydrodynamics and alum dose on particle growth were investigated by monitoring particle counts in a rapid mixing process. Experiments were performed to measure the particle growth and breakup under various conditions. The rapid mixing scheme consisted of the following operating parameters: Velocity gradient (G) ($200-300s^{-1}$), alum dose (10-50 mg/L) and mixing time (30-180 s). The Poisson regression model was applied to assess the effects of the doses and velocity gradient with mixing time. The mechanism for the growth and breakup of particles was elucidated. An increase in alum dose was found to accelerate the particle count reduction. The particle count at a G value of $200s^{-1}$ decreased more rapidly than those at $300s^{-1}$. The growth and breakup of larger particles were more clearly observed at higher alum doses. Variations of particles due to aggregation and breakup of micro-flocs in rapid mixing step were interactively affected by G, mixing time and alum dose. Micro-flocculation played an important role in a rapid mixing process.

• Ocean and Polar Research
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• 제35권3호
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• pp.249-258
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• 2013

Vertical and horizontal mixing processes in the ocean mixed layer determine sea surface temperature and temperature variability. Accordingly, simulating these processes properly is crucial in order to obtain more accurate climate simulations and more reliable future projections using an ocean general circulation model (OGCM). In this study, by using Modular Ocean Model version 4 (MOM4) developed by Geophysical Fluid Dynamics Laboratory, the upper ocean temperature and mixed layer depth were simulated with two different vertical mixing schemes that are most widely used and then compared. The resultant differences were analyzed to understand the underlying mechanism, especially in the Tropical Pacific Ocean where the differences appeared to be the greatest. One of the schemes was the so-called KPP scheme that uses K-Profile parameterization with nonlocal vertical mixing and the other was the N scheme that was rather recently developed based on a second-order turbulence closure. In the equatorial Pacific, the N scheme simulates the mixed layer at a deeper level than the KPP scheme. One of the reasons is that the total vertical diffusivity coefficient simulated with the N scheme is ten times larger, at maximum, in the surface layer compared to the KPP scheme. Another reason is that the zonal current simulated with the N scheme peaks at a deeper ocean level than the KPP scheme, which indicates that the vertical shear was simulated on a larger scale by the N scheme and it enhanced the mixed layer depth. It is notable that while the N scheme simulates a deeper mixed layer in the equatorial Pacific compared to the KPP scheme, the sea surface temperature (SST) simulated with the N scheme was cooler in the central Pacific and warmer in the eastern Pacific. We postulated that the reason for this is that in the central Pacific atmospheric forcing plays an important role in determining SST and so does a strong upwelling in the eastern Pacific. In conclusion, what determines SST is crucial in interpreting the relationship between SST and mixed layer depth.

• 한국해양학회지:바다
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• 제18권3호
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• pp.111-121
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• 2013

지역규모의 정확한 일기예보와 해양생태계 변화 이해에 있어서 수온 예측은 매우 중요하다. 황해는 조류가 매우 빠르고 탁도가 높다. 이러한 해역에서는 수치 모델의 수직 혼합 기법 및 해수의 탁도에 따른 수형(water type)이 수온 구조 결정에 많은 영향을 미친다. 수직 혼합 기법 변화와 탁도의 변화에 따른 황해 수온 모사의 민감도를 알아보기 위해 3차원 해양 순환 모델인 Regional Ocean Modeling System (ROMS)을 사용하여 수치 실험을 수행하였다. 수직 혼합 기법은 해양 순환 모델에서 많이 사용되는 Mellor-Yamada level 2.5 closure(M-Y)와 K-Profile parameterization (KPP)을 사용하고, 탁도는 Jerlov의 분류에 따른 수형 1, 3, 5를 사용하여 수치 실험을 수행하고 그 결과를 국립수산과학원에서 제공하는 정선 해양 관측 자료와 비교, 분석하였다. M-Y 기법은 수직적 혼합을 상대적으로 강하게 모의하였으며 그 결과로 저층수온이 높게 형성되었다. 높은 저층 수온은 탁도를 높게 설정하면 완화되지만 표층 수온이 높아지는 단점이 있다. KPP 기법은 M-Y 기법보다는 수직 혼합을 약하게 모의하고 이 약한 수직 혼합 때문에 황해 연안을 따라 형성되는 조석전선을 잘 재현하지 못하였으나, 저층 수온은 관측 수온에 더 가깝게 재현하였다. 결과적으로 황해 3차원 해양순환 모델실험에서 M-Y 기법은 수직 혼합이 잘 되어 표층과 저층의 수온 차이가 작게 나타나고, KPP 기법은 이와 반대로 모의하였다. 탁도의 영향을 표현하는 Jerlov 수형은 높을수록 일사량이 낮은 수심까지만 투과되어 성층을 잘 표현하였고, 낮을수록 깊은 수심까지 일사량이 투과되어 표층과 저층의 수온차를 작게 모의하였다.

• Journal of Theoretical and Applied Mechanics
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• 제3권1호
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• pp.45-65
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• 2002

A constitutive model on oorthotropic thermo-elasto-viscoplasticity for fiber-reinforced composite materials Is illustrated, and their thermomechanical responses are predicted with the fully-coupled finite element formulation. The unmixing-mixing scheme can be adopted with the multipartite matrix method as the constitutive model. Basic assumptions based upon the composite micromechanics are postulated, and the strain components of thermal expansion due to temperature change are included In the formulation. Also. more than two sets of mechanical variables, which represent the deformation states of multipartite matrix can be introduced arbitrarily. In particular, the unmixing-mixing scheme can be used with any well-known isotropic viscoplastic theory of the matrix material. The scheme unnecessitates the complex processes for developing an orthotropic viscoplastic theory. The governing equations based on fully-coupled thermomechanics are derived with constitutive arrangement by the unmixing-mixing concept. By considering some auxiliary conditions, the Initial-boundary value problem Is completely set up. As a tool of numerical analyses, the finite element method Is used with isoparametric Interpolation fer the displacement and the temperature fields. The equation of mutton and the energy conservation equation are spatially discretized, and then the time marching techniques such as the Newmark method and the Crank-Nicolson technique are applied. To solve the ultimate nonlinear simultaneous equations, a successive iteration algorithm is constructed with subincrementing technique. As a numerical study, a series of analyses are performed with the main focus on the thermomechanical coupling effect in composite materials. The progress of viscoplastic deformation, the stress-strain relation, and the temperature History are careful1y examined when composite laminates are subjected to repeated cyclic loading.

• Composites Research
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• 제25권2호
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• pp.34-39
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• 2012

본 논문에서는 일방향 섬유강화 복합재료의 열-기공-탄성 거동을 효과적으로 기술하기 위하여 미시역학에 기반을 둔 분리-혼합 기법을 적용하였다. 온도 증가에 따른 열팽창, 내부 기공에서의 가스 압력, 열분해 과정의 수축 변형 효과를 정식화 과정에 모두 포함하였다. 유도된 구성 방정식을 검증하기 위한 비교 대상으로서 복합재료 이차원 단층의 대표 체적 요소를 유한요소법으로 모델링하고, 다양한 하중 조건에 대하여 해석하였다. 즉, 대표 체적 요소에 분포된 전체 평균 응력과 변형도 등을 구하여, 분리-혼합 기법에 의해 예측된 해당 결과 값을 서로 비교하였다. 도출된 수치 결과를 분석함으로써 제안된 복합재료의 열-기공-탄성 거동 예측 기법의 유용성을 확인하였다.

• 정보학연구
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• 제2권2호
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• pp.89-105
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• 1999

본 논문은 컴퓨터를 이용한 문서 화상의 보안 통신에서 요구되는 문서 화상의 보안, 위조, 인증 등의 제반 분쟁에 대처하기 위한 연구이다. 문서 화상의 보안을 위해서 기존에 연구되어온 각종 암호화 방식 및 스크램블 방식과 같이 정보의 보안 여부를 노출시키고 비도에 의지하는 방식과 달리 정보의 보안여부를 제3자가 판독하기 어렵도록 하여 일상의 문서 교환으로 인식하게 함으로써 1차적으로 이의 해독에 따른 위험을 감소시키고 2차적으로는 해독이 가해진다 하여도 알고리즘 자체의 비도에 의해 해독을 용이하지 않도록 하는 방식의 보안 체계를 제안한다.

• 한국공작기계학회논문집
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• 제16권1호
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• pp.47-52
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• 2007

A material mixing method to obtain an optimal topology for a structure in a thermal environment was suggested. This method is based on Evolutionary Structural Optimization(ESO). The proposed material mixing method extends the ESO method to a mixing several materials for a structure in the multicriteria optimization of thermal flux and thermal stress. To do this, the multiobjective optimization technique was implemented. The overall efficiency of material usage was measured in terms of the combination of thermal stress levels and heat flux densities by using a combination strategy with weighting factors. Also, a smoothing scheme was implemented to suppress the checkerboard pattern in the procedure of topology optimization. It is concluded that ESO method with a smoothing scheme is effectively applied to topology optimization. Optimal topologies having multiple thermal criteria for a printed circuit board(PCB) substrate were presented to illustrate validity of the suggested material mixing method. It was found that the suggested method works very well for the multicriteria topology optimization.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1758-1760
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• 2008

Under typical operating conditions, flows in microfluidic devices are laminar and molecular diffusion across the channels is slow, which makes an efficient mixing in microfluidic devices difficult to achieve. The mechanism to achieve effective mixing in laminar flows is that of repetitive stretching and folding. Essential is to generate spatially periodic flows with crossing cross sectional streamlines. A mapping method is employed to analyze mixing in micromixers, enabling us to investigate the progress of mixing both qualitatively and quantitatively. The progress of mixing is characterized by a measure of mixing, called the discrete intensity of segregation. The mapping method is applied to mixing in such micromixers as the staggered herringbone mixer, the barrier embedded micromixer, and the three-dimensional serpentine channel to demonstrate the capability of the numerical scheme to tackle general mixing problems in microfluidic devices.