• 한국대기환경학회지
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• 제8권3호
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• pp.162-168
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• 1992

Numerical solutions to the advection equations used for long-range transport air pollution models are calculated using three numerical methods; Antidiffusion correction method(Smolarkiewicz, 1983), Positive definite advecton scheme obtained by nonlinear renormalization of the advective fluxes(Bott, 1989), and Positive definite pseudospectral method(Bartnicki, 1989). Accuracy, numerical diffusion and computational time requirement are compared for two-dimensional transport calculations in a uniform rotational flow field. The solutions from three methods are positive definite. Bartnicki(1989)'s method is most conservative but requires approximately 10 times as much computational time as Smolarkiewicz(1983)'s method of which numerical diffusion is the largest. All three methods are more conservative for a cone shape initial condition than for a rectangular block initial condition with a steep gradient.

• 전자공학회논문지
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• 제52권5호
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• pp.155-164
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• 2015

본 연구에서는 다양한 HEVC 구문요소들을 적응적으로 파이프라인 및 병렬 처리할 수 있는 CABAC 복호화기 아키텍처를 설계 및 구현하였다. CABAC는 높은 압축률을 제공하지만, 구문요소 단위 순차적 복호화와 문맥간 강한 데이터 종속성, 빈 단위 복호화 과정 때문에 고성능 복호화 처리를 어렵게 한다. CABAC의 복호화 처리 성능을 높이기 위하여 연속된 flag 타입의 구문요소에 대해서는 다음에 복호될 구문요소들을 선행 연산하여 적응적으로 파이프라인 처리하였고, 멀티빈으로 구성된 구문요소는 최대 3개 빈까지 병렬 처리하는 고성능 구조를 설계하였다. 또한 이진산술복호기를 가속화하기 위해 문맥모델 업데이트와 재정규화를 선행 병렬 연산하고, 복호화 결과값에 따라 선택해서, 이진산술복호기의 임계 지연시간을 개선하였다. 제안하는 HEVC CABAC 아키텍처는 최대 1.01bins/cycle의 처리 성능으로 기존 구조대비 약 2배의 가속화 성능을 갖는다. 65nm ASIC 합성 결과 224M bins/sec.의 복호화 성능을 보이며, QFHD영상의 실시간 처리를 가능하게 하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.125.1-125.1
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• 2016

The excitonic insulator (EI), which is one of fundamental insulators, was theoretically proposed in 1967 but its material realization has not been established well. Only a few materials were proposed as EIs but their experimental evidences were indirect such as the renormalization of band dispersions or an anomaly in electrical resistivity. We conducted scanning tunneling microscopy / spectroscopy measurements and found out that $Ta_2$ $NiSe_5$, which was the most recently proposed as an EI, had a metal-insulator phase transition with the energy gap of 700 meV at 78 K. Moreover, the spatially delocalized excitonic energy level was observed within the energy gap, which could be the direct evidence of the EI ground state. Our theoretical model calculation with the order parameter of 150 meV reproduces the spectral function and the excitonic energy gap very well. In addition, experimental data shows that the band character is inverted at the valence and conduction band edges by the exciton formation, indicating that the mechanism of exciton condensation is similar to the Bardeen-Cooper-Schrieffer (BCS) mechanism of cooper pairs in superconductors.

• 한국대기환경학회지
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• 제21권5호
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• pp.525-535
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• 2005

Using a three-dimensional computational fluid dynamics (CFD) model with the $k-{\varepsilon}$ turbulence closure scheme based on the renormalization group theory, flow regimes in urban street canyons are classified according to the building and street aspect ratios. The transition between skimming flow (SF) and wake interference flow (WIF) is determined with the size of double-eddy circulation generated behind the upwind building. The transition between WIF and isolated roughness flow (IRF) is determined with the flow reattachment distance from the upwind building. The critical aspect ratios at which the flow transition occurs are found and compared with those in previous studies. The results show that the flow-regime classification method used in this study is quite reasonable and that the values of the critical aspect ratios are generally consistent with those in fluid experiments or large-eddy simulation. The regression equation describing a relation between the building and street aspect ratios at the flow-regime transition is presented.

• 태양에너지
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• 제12권1호
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• pp.72-80
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• 1992

본 연구에서는 건물의 축열 질량이 실내 온도의 변화에 미치는 영향을 조사하였다. 건물의 열적 성능 분석과 관련하여 사용된 기법은 미국 신에너지 연구소에서 개발된 PSTAR(Primary and Secondary Terms Analysis and Ronormalization)방법이다. 얻어진 결과는 축열질량과 관련하여 매우 대조적인 두 경우를 대변하는데, 특히 실내의 열환경과 건물의 전체적인 열적 성능에 미치는 영향을 잘 보여주고 있다. 재표준화된 모델을 이용한 월별 냉난방 부하와 이의 최대 요구치는 건물에 있어서 냉난방 시스템의 설계에 유용한 자료를 제시하고 있다.

• 한국대기환경학회지
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• 제23권2호
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• pp.214-224
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• 2007

A three-dimensional computational fluid dynamics (CFD) model with the renormalization group (RNG) $k-{\varepsilon}$ turbulence model is used to examine the effects of difference in building height on flow and pollutant dispersion in asymmetric street canyons. Three numerical experiments with different street canyons formed by two isolated buildings are performed. In the experiment with equal building height, a portal vortex is formed in the street canyon and a typical recirculation zone is formed behind the downwind building. In the experiment with the downwind building being higher than the upwind building, the ambient flow comes into the street canyon at the front of the downwind building and incoming flow diverges strongly in the street canyon. Hence, pollutants released therein are strongly dispersed through the lateral sides of the street canyon. In the experiment with the upwind building being higher than the downwind building, a large recirculation zone is formed behind the upwind building, which is disturbed by the downwind building. Pollutants are weakly dispersed from the street canyon and the residue concentration ratio is largest among the three experiments. This study shows that the difference in upwind and downwind building height significantly influences flow and pollutant dispersion in and around the street canyon.

• 한국환경과학회지
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• 제23권7호
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• pp.1223-1232
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• 2014

Density currents have been easily observed in environmental flows, for instance turbidity currents and pollutant plumes in the oceans and rivers. In this study, we explored the propagation dynamics of density currents using the FLOW-3D computational fluid dynamics code. The renormalization group (RNG) $k-{\varepsilon}$ scheme, a turbulence numerical technique, is employed in a Reynold-averaged Navier-Stokes framework (RANS). The numerical simulations focused on two different types of intrusive density flows: (1) propagating into a two-layer ambient fluid; (2) propagating into a linearly stratified fluid. In the study of intrusive density flows into a two-layer ambient fluid, intrusive speeds were compared with laboratory experiments and analytical solutions. The numerical model shows good quantitative agreement for predicting propagation speed of the density currents. We also numerically reproduced the effect of the ratio of current depth to the overall depth of fluid. The numerical model provided excellent agreement with the analytical values. It was also clearly demonstrated that RNG $k-{\varepsilon}$ scheme within RANS framework is able to accurately simulate the dynamics of density currents. Simulations intruding into a continuously stratified fluid with the various buoyancy frequencies are carried out. These simulations demonstrate that three different propagation patterns can be developed according to the value of $h_n/H$ : (1) underflows developed with $h_n/H=0$ ; (2) overflows developed when $h_n/H=1$ ; (3) intrusive interflow occurred with the condition of 0 < $h_n/H$ < 1.

• 한국자동차공학회논문집
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• 제5권1호
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• pp.87-100
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• 1997

The ability of turbulence model to accurately describe the complex characteristics of the flow field and the fuel spray is of great importance in the optimum design of diesel engine. The numerical simulations of the flow field and the spray characteristics within the combustion chamber of direct injection model entgine are performed to examine the applicability of turbulence model. The turbulence models used are the RNG $\varepsilon$ model and the modified $\varepsilon$ model which included the compressibility effect due to the compression/expansion of the charges. In this study, the predicted results in the quiescent condition of direct injection model engine show reasonable trends comparing with the experimental data of spray characteristics, i. e., spray tip penetration, spray tip velocity. The results of eddy viscosity obtained using the $\varepsilon$ model in the spray region is significantly larger than that obtained using the RNG $\varepsilon$ model. The application of the RNG model seems to have some potential for the simulations of the spray characteristics, e. g., spray tip penetration, spray tip velocity, droplets distribution over the $\varepsilon$ model.

• 대기
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• 제21권1호
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• pp.95-108
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• 2011

The effects of an apartment complex on flow and pollutant dispersion in an urban area are numerically investigated using a computational fluid dynamics (CFD) model. The CFD model is based on the Reynolds-averaged Navier-Stokes equations and includes the renormalization group k-${\varepsilon}$ turbulence model. The geographic information system (GIS) data is used as an input data of the CFD model. Eight numerical simulations are carried out for different inflow directions and, for each inflow direction, the effects of an apartment complex are investigated, comparing the characteristics of flow and dispersion before and after construction of the apartment complex in detail. The observation data of automatic weather system (AWS) is analyzed. The windrose analysis shows that the wind speed and direction after the construction of the complex are quite different from those before the construction. The construction of the apartment complex resulted in the decrease in wind speed at the downwind region. It is also shown that the wind speed increased partially inside the apartment complex due to the channeling effect to satisfy the mass continuity. On the whole, the wind speed decreased at the downwind region due to the drag effect by the apartment complex. As a result, the passive pollutant concentration increased (decreased) near the downwind region of (within) the apartment complex compared with that before the construction.

• 태양에너지
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• 제11권2호
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• pp.3-8
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• 1991

본 연구는 미국의 태양에너지 연구소(Solar Energy Research Institute)에서 최근에 개발한 건물 열 성능 측정 기법인 PSTAR(Primary and Secondary Terms Analysis and Renormalization) 방법에 따라 대전에 위치한 한 자연형 주택의 열성능 측정 결과를 분석하고 이를 토대로 건물의 종합적인 Thermal Analysis를 수행하였다. 실험 주택은 $156m^2$의 주거 면적을 가지고 있으며 3개의 침실과, 거실 그리고 부엌으로 구성되었으며 아울러 다양한 자연형 시스템을 갖추었다. 본 연구의 목적은 PSTAR 방법을 적용하여 열적으로 massive한 건물의 실제 동적 열성능을 정확히 측정하는 데에 있다. 결과를 분석하여 보면 측정치와 검정치(Renormalized Values)는 대부분의 경우에 있어 잘 일치하나 순수한 도면에 의거한 시뮬레이션치(Audit Values)는 다소 차이를 나타내었다.