Compressible Navier--Stokes System with General Inflow-Outflow Boundary Data

Chang, T.,Jin, B.J.,Novotný,, A. Society for Industrial and Applied Mathematics 2019 SIAM journal on mathematical analysis Vol.51 No.2

<P>We prove existence of weak solutions to the compressible Navier--Stokes equations in a barotropic regime (adiabatic coefficient <TEX>$\gamma>3/2$</TEX> in three dimensions, <TEX>$\gamma>1$</TEX> in two dimensions) with large velocity prescribed at the boundary and large density prescribed at the inflow boundary of a bounded sufficiently smooth domain, without any restriction on either the shape of the inflow/outflow boundaries or the shape of the domain. The result applies also to pressure laws that are nonmonotone on a compact portion of the interval <TEX>$[0,\infty)$</TEX>.</P>

A combination method to generate fluctuating boundary conditions for large eddy simulation

Dayang Wang,Y. Zhou,X.J. Yu,K.T. Tse 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.4

A Combination Random Flow Generation (CRFG) technique for obtaining the fluctuatinginflow boundary conditions for Large Eddy Simulation (LES) is proposed. The CRFG technique wasdeveloped by combining the typical RFG technique with a novel calculation of k and  to estimate thelength- and time-scales (l, τ) of the target fluctuating turbulence field used as the inflow boundary conditions. Through comparatively analyzing the CRFG technique and other existing numerical/experimental results,the CRFG technique was verified for the generation of turbulent wind velocity fields with prescribedturbulent statistics. Using the turbulent velocity fluctuations generated by the CRFG technique, a series ofLESs were conducted to investigate the wind flow around S-, R-, L- and U-shaped building models. As thepressures of the models were also measured in wind tunnel tests, the validity of the LES, and theeffectiveness of the inflow boundary generated by the CRFG techniques were evaluated through comparingthe simulation results to the wind tunnel measurements. The comparison showed that the LES accuratelyand reliably simulates the wind-induced pressure distributions on the building surfaces, which indirectlyvalidates the CRFG technique in generating realistic fluctuating wind velocities for use in the LES. Inaddition to the pressure distribution, the LES results were investigated in terms of wind velocity profilesaround the building models to reveal the wind flow dynamics around bluff bodies. The LES resultsquantitatively showed the decay of the bluff body influence when the flow moves away from the buildingmodel.

On the prescribed inlet boundary condition with no buffer zone for the subsonic compressible laminar boundary layer with hybrid application of equations

권현진,장세명 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1

In the computation of compressible Navier-Stokes equations for viscous flows, if a uniform boundary condition is enforced at the inlet of computational domain without buffer zone, the thickness of boundary layer is underestimated while the inner-layer velocity is overestimated since the pressure is artificially added due to the growth of shear velocity at the surface of a flat plate. This results in unstable and inaccurate numerical solutions, and to solve this problem, a novel hybrid method is proposed to obtain an aligned prescribed inlet boundary condition. With a solution of perturbed velocity potential equation for compressible flow and the consideration of displacement thickness of laminar boundary layer at the earlier stage, the whole domain is solved rapidly to prescribe the modified velocity profile at the inlet boundary as a next step for the main solution of full Navier-Stokes equations. For faster convergence and better numerical stability, 2D-NSCBC(two-dimensional Navier-Stokes characteristics boundary condition) is applied in the solution of full Navier-Stokes equations. The results overall give a complete success for Ma < 0.9 at least, and are even improved remarkably for the numerical stability with adoption of specified velocity despite of considerable error in the transonic flow regime above the critical Mach number 0.9. With the present method, we succeeded to remove the whole buffer zone for the inlet boundary condition of subsonic compressible flow.

A combination method to generate fluctuating boundary conditions for large eddy simulation

Wang, Dayang,Yu, X.J.,Zhou, Y.,Tse, K.T. Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.20 No.4

A Combination Random Flow Generation (CRFG) technique for obtaining the fluctuating inflow boundary conditions for Large Eddy Simulation (LES) is proposed. The CRFG technique was developed by combining the typical RFG technique with a novel calculation of k and ${\varepsilon}$ to estimate the length- and time-scales (l, ${\tau}$) of the target fluctuating turbulence field used as the inflow boundary conditions. Through comparatively analyzing the CRFG technique and other existing numerical/experimental results, the CRFG technique was verified for the generation of turbulent wind velocity fields with prescribed turbulent statistics. Using the turbulent velocity fluctuations generated by the CRFG technique, a series of LESs were conducted to investigate the wind flow around S-, R-, L- and U-shaped building models. As the pressures of the models were also measured in wind tunnel tests, the validity of the LES, and the effectiveness of the inflow boundary generated by the CRFG techniques were evaluated through comparing the simulation results to the wind tunnel measurements. The comparison showed that the LES accurately and reliably simulates the wind-induced pressure distributions on the building surfaces, which indirectly validates the CRFG technique in generating realistic fluctuating wind velocities for use in the LES. In addition to the pressure distribution, the LES results were investigated in terms of wind velocity profiles around the building models to reveal the wind flow dynamics around bluff bodies. The LES results quantitatively showed the decay of the bluff body influence when the flow moves away from the building model.

Inflow Conditions for Modelling the Neutral Equilibrium ABL Based on Standard k-ε Model

Jinghan Wang,Chao Li,Yiqing Xiao,Jinping ou Council on Tall Building and Urban Habitat Korea 2022 International journal of high-rise buildings Vol.11 No.4

Reproducing the horizontally homogeneous atmospheric boundary layer in computational wind engineering is essential for predicting the wind loads on structures. One of the important issues is to use fully developed inflow conditions, which will lead to the consistence problem between inflow condition and internal roughness. Thus, by analyzing the previous results of computational fluid dynamic modeling turbulent horizontally homogeneous atmospheric boundary layer, we modify the past hypotheses, detailly derive a new type of inflow condition for standard k-ε turbulence model. A group of remedial approaches including formulation for wall shear stress and fixing the values of turbulent kinetic energy and turbulent dissipation rate in first wall adjacent layer cells, are also derived to realize the consistence of inflow condition and internal roughness. By combing the approaches with four different sets of inflow conditions, the well-maintained atmospheric boundary layer flow verifies the feasibility and capability of the proposed inflow conditions and remedial approaches.

신흥유럽의 외국인투자여건 분석

조양현 한국외국어대학교 국제지역연구센터 2019 국제지역연구 Vol.23 No.3

This paper aims to analyze conditions of foreign direct investment (FDI) toward Emerging Europe after negotiation of Brexit, and suggest its implication. In this regard, it reviews major advanced research of environment of FDI, and selects business management conditions (institutional changes) toward five major Emerging Europe such as Czech, Hungary, Poland, Russia and Turkey. Accordingly, it reflects four important fields including registration procedures and time (starting business), minimum wage and unemployment (labour conditions), corporate tax and VAT (taxation level), exchange rate and policy interest rate (exchange control) as policy indicators for institutional changes during 2016-2018. Since negotiation of Brexit, FDI inflows to Czech and Russia as well as the United Kingdom have reduced after 2017, whilst FDI inflows to Hungary, Poland and Turkey have fluctuated with their different patterns. Overall, it has been analyzed that institutional changes based on increase (or decrease) of registration time, minimum wage, corporate tax rate and policy interest rate have influenced on increase (or decrease) of FDI inflows during 2016-2018. On the other hands, country and/or sovereign risk ratings such OECD, S&P and Moody’s have insufficiently explicated on the FDI inflows due to bias by year of the ratings in the perspectives of risk perception. As a result, it implies that conditions of FDI in the major Emerging Europe depend on FDI-friendly policies and markets as well as the institutional changes and relevances in the fields of starting business, labour conditions, taxation level and exchange control on the process of FDI. 본고의 연구목적은 최근 영국의 유럽연합(EU) 탈퇴(브렉시트) 협상 이후 신흥유럽의 외국인투자여건을 분석하고 그 시사점을 도출하는 데 있다. 따라서 외국인투자환경에 대한 주요선행연구 및 분석대상을 검토하고, 신흥유럽 주요국(체코·헝가리·폴란드·러시아·터키 5 개국)의 기업경영여건(제도변화)에 대해 분석했다. 2016~2018년 기간 신흥유럽 주요국의제도변화에 대한 정책지표의 경우 현지법인 설립을 위한 단계 및 소요시간(사업등록 분야), 최저임금 인상률 및 실업률(노동여건 분야), 표준 법인세율 및 부가가치세율(조세부과 분야), 연평균 환율 및 기준금리(외환통제 분야)의 변동내역을 살펴보았다. 브렉시트 협상 이후 2016~2018년 기간 영국에 대한 외국인직접투자(FDI) 유입실적은2017년부터 감소추세를 보였고, 신흥유럽 주요국에서 체코·러시아는 영국과 유사한 경향을나타냈지만, 헝가리·폴란드·터키에 대한 FDI 유입실적은 국가별로 다른 양상을 보였다. 동기간 중 사업등록의 소요시간 증가(단축), 최저임금(단위노동비용 포함) 인상, 법인세율 인상(인하) 및 기준금리 인상 등의 제도변화(정책지표 포함)가 FDI 유입실적의 감소(증가)에 대체적으로 영향을 미친 것으로 분석된다. 그러나 스탠더드앤드푸어스(S&P) 및 무디스(Moody’s) 등의 정부채권 평가등급은 국가별 FDI 유입실적과는 연도별 편차를 보이고 있어신흥유럽 주요국의 FDI 유입실적과는 일치된 패턴을 형성하지 않고 있다. 요컨대, 신흥유럽의 외국인투자여건은 현지법인 설립과정에서 나타난 사업등록, 노동여건, 조세부과 및 외환통제의 모든 분야에 대한 제도적 (규제)완화와 더불어, 기업 우호적인 (시장)여건조성에 따라변동(개선 또는 악화)될 수 있다는 것을 시사한다.

Development and evaluation of ANFIS-based conditional dam inflow prediction method using flow regime

Moon Geon-Ho,Kim Seon-Ho,Bae Deg-Hyo 한국수자원학회 2018 한국수자원학회논문집 Vol.51 No.7

본 연구에서는 ANFIS 기반의 유황별 댐 예측유입량 산정 기법(Flow regime-based ANFIS Dam Inflow Prediction, FADIP)을 개발하고, 이를 단 순 ANFIS 기반 댐 예측유입량 산정 기법(ANFIS Dam Inflow Prediction, ADIP)과 비교 평가하였다. 대상유역은 국내 주요 다목적댐인 충주댐 유역과 소양강댐 유역을 선정하였으며, 입력자료로 댐 유입량, 강수량, 장기기상예보 자료를 사용하였다. 모델의 훈련 및 보정기간으로 충주댐 유역은 1987~2010년, 소양강댐 유역은 1984~2010년을 선정하였다. 검정기간은 두 유역 모두 2011~2016년을 활용하였다. 훈련 및 보정결과 FADIP 는 ADIP에 비해 평수기, 저수기에 훈련이 개선되는 것으로 나타났다. 검정결과 ADIP는 통계모델의 학습방법 특성상 일반적인 사상에 학습이 이루어져, 저수기에 예측성이 떨어지는 것으로 나타났다. 반면 FADIP는 ADIP에 비해 전기간의 정확도가 향상되었으며, 특히 평수기와 저수기에 예측성이 우수하였다. 따라서 FADIP는 다목적댐 이수관리에 활용성이 높을 것으로 판단된다. Flow regime-based ANFIS Dam Inflow Prediction (FADIP) model is developed and compared with ANFIS Dam Inflow Prediction (ADIP) model in this study. The selected study area is the Chungju and Soyang multi-purpose dam watersheds in South Korea. The dam inflow, precipitation and monthly weather forecast information are used as input variables of the models. The training and validation periods of the models are 1987~2010 for Chungju and 1984~2010 for Soyang dam watershed. The testing periods for both watersheds are 2011~2016. The results of training and validation indicate that FADIP has better training ability than ADIP for predicting dam inflow in normal and low flow regimes. In the result of testing, ADIP shows low predictability of dam inflow in the low flow regime due to the model tuning on all flow regime together. However, FADIP demonstrates the improved accuracy over the entire period compared to ADIP, especially during the normal and low flow seasons. It is concluded that FADIP is valuable for the prediction of dam inflow in the case of drought years, and useful for water supply management of the multi-purpose dam.

35개국 패널자료를 이용한 자본유입통제의 실효성 분석

홍서희(Seohee Hong),조하현(Ha-hyun Jo),임형우(Hyungwoo Lim) 한국경제통상학회 2020 경제연구 Vol.38 No.1

본 연구는 자본유입통제 시행의 효과를 분석하고, 자본유입통제의 효과를 높이기 위한 조건을 제안하였다. 1995~2013년 기간에 대한 35개 국가 자료를 이용하여 패널 VAR 모형을 구축하였으며, 자본유입통제에 따른 환율변동성 및 경제성장률의 효과를 충격반응함수를 통해 분석하였다. 그 결과 특정조건이 만족될 때 자본유입통제의 효과가 커지는 것을 확인하였다. 즉, ① OECD에 속할 경우, ② 제도의 질이 우수할 경우, ③ 자본유입통제 지속성 높을 경우, ④ 금융 효율성이 높을 경우 자본유입통제를 통해 환율변동성을 낮추거나 경제성장률을 높일 수 있음을 확인했다. 더 나아가 복수 조건이 만족될 때 자본유입통제의 효과가 더 큼을 발견했다. 특히 자본통제 지속성이 높다는 조건을 중심으로 결합할 때 효과가 개선되었다. 한국은 대부분의 실효성 조건을 충족했기에 자본유입통제 정책의 유지가 효과적일 수 있음을 확인하였다. This study analyzed the effect of implementing capital inflow control and explored the conditions for enhancing the effect of control. We structured a 3-variable panel VAR model using 35 national data for the period 1995-2013. The responses of exchange rate volatility and economic growth to capital inflow control were observed through the Impulse Response Function. We also found that the effect of capital inflow control increased when certain conditions were met. We found that if the nation belongs to the OECD, if the system is of good quality, if the capital inflow control is sustained, and if the financial efficiency is high, the exchange rate volatility can be reduced or the economic growth can be increased through capital inflow control. South Korea has met most of the conditions for effectiveness. This means that the maintenance of the capital inflow control policy can be effective.

An Investigation of the Aerodynamic Characteristics of a Helicopter Rotor in Hover by the Variety of Inflow Conditions using Blade Element Momentum Theory (BEMT)

Joon-yong Yoon(윤준용),Woo Chul Kwon(권우철),Youn-hwan Kim(김윤환) 한국유체기계학회 2009 유체기계 연구개발 발표회 논문집 Vol.2009 No.-

In this paper, the aerodynamic characteristics of a helicopter rotor in hover were compared based on a variety of inflow conditions using Blade Element Momentum Theory (BEMT). BEMT has been widely used as an aerodynamic analysis method for helicopter rotors because of its simpler code and shorter calculating time than computational fluid dynamics (CFD) analysis. In order to verify the validity of inflow models, we applied the conventional inflow conditions and Madsen's inflow condition to the helicopter rotor in hover. The results were compared with Caradonna and Tung's data.

Scale Effect of the Model Extent on Seepage Analysis of Circular Tunnels under Drained Conditions

Jian Wu,Zhifang Zhou 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.12

Numerical simulations have been widely used to predict groundwater inflow into tunnels during excavations. An appropriate geometric size of a numerical model is crucial for reducing the simulation time and ensuring the accuracy of numerical results. However, to the best of our knowledge, no information concerning the scale effect of the model extent on the seepage characteristics of tunnels under drained conditions has been published. This study evaluates how the model extent affects the tunnel inflow, drawdown, and water pressure via the Signorini type variational inequality formulation. A series of two-dimensional finite element models are conducted with various combinations of tunnel parameters, including tunnel radius, initial groundwater level, lining thickness, and relative permeability. Subsequently, a comprehensive function to yield the optimum model extent within an allowable error is proposed. Interestingly, the optimum model extent for both tunnel inflow and water pressure decreases with an increase in the relative permeability, whereas that of the drawdown exhibits the opposite pattern. A model extent of no less than 200 times the tunnel radius is recommended to acquire accurate model results and is verified with existing analytical methods. This study therefore not only highlights the drainage effect of the tunnel but also provides universal suggestions for engineering practice.