• 한국전산유체공학회지
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• 제10권1호
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• pp.99-106
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• 2005

Performance of first, second and third order accurate methods for calculation of in viscid fluxes in fluid flow governing equations are investigated here. For the purpose, an upwind method based on Roe's scheme is used to solve 2-dimensional Euler equations. To increase the accuracy of the method two different schemes are applied. The first one is a second and third order upwind-based algorithm with the MUSCL extrapolation Van Leer (1979), based on primitive variables. The other one is an upwind-based algorithm with the Chakravarthy extrapolation to the fluxes of mass, momentum and energy. The results show that the thickness of shock layer in the third order accuracy is less than its value in second order. Moreover, applying limiter eliminates the oscillations near the shock while increases the thickness of shock layer especially in MUSCL method using Van Albada limiter.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.153-158
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• 2000

For the analysis of compressible flow with real gas effect, characteristic form of Roe's Riemann solver was derived again using real gas equation of state and variable specific heal and it was extended to multi component reactive system. From this study, it is known that some correction should be made for the use of existing numerical algorithm. 1) Sonic speed and characteristic variable should be corrected with real gas effect. 2) Roe's average was applicable only with the assumption of constant properties. 3) Artificial damping term and characteristic variables should be corrected but their influence may not be significant.

• 한국항공우주학회지
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• 제35권12호
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• pp.1067-1074
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• 2007

예조건화 오일러 방정식의 수렴특성을 개선하기 위하여 밀도에 대한 온도의 미분항의 크기를 조절하는 온도예조건화 방법을 제시하고자 한다. 다양한 마하수의 원형 턱이 있는 이차원 관내 유동을 계산하였다. 온도예조건화에 맞는 새로운 Roe의 FDS 기법의 수치 소산항을 유도하여 사용하였다. 온도예조건화는 예조건화 오일러 방정식의 수렴 속도를 증가시키는 것으로 나타났다

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제30회 춘계학술대회논문집
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• pp.332-335
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• 2008

본 연구의 목적은 수소 및 탄화수소를 이용한 bluff-body 화염 안정화 및 hyper-mixer와 같은 초음속 연소기 연료 분사기 주변의 유동해석 이다. 대규모 박리영역을 갖는 후방단 형상의 초음속 주변 유동을 해석하기 위한 검증 단계로 다양한 수치기법을 평가해 보았다. 고차 공간 정확도로 확장된 5차 TVD-MUSCL기법, Roe FDS, S-A DES/DDES 조합이 기저유동과 기저유출 유동에 좋은 결과를 보여 주었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.19-26
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• 2008

From numerical point of view on flow network system analyses, stagnation properties are not preserved along streamlines across geometric discontinuities. Hence, GJM and DTM using ghost cell and thermodynamic relations are developed to preserve the stagnation enthalpy for the boundaries, such as the interfaces between junction and branches and the interface between two pipes of different cross-sections in serial pipelines. Additionally, the resolving power and efficiencies of the 2nd order Godunov type FV schemes are investigated and estimated by the tracing of the total mechanical energy during calculating rapid transients. Among the approximate Riemann solvers, RoeM is more suitable with the proposed boundary treatments especially for junction than Roe's FDS because of its conservativeness of stagnation enthalpy across geometric discontinuities.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.19-26
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• 2008

From numerical point of view on flow network system analyses, stagnation properties are not preserved along streamlines across geometric discontinuities. Hence, GJM and DTM using ghost cell and thermodynamic relations are developed to preserve the stagnation enthalpy for the boundaries, such as the interfaces between junction and branches and the interface between two pipes of different cross-sections in serial pipelines. Additionally, the resolving power and efficiencies of the 2nd order Godunov type FV schemes are investigated and estimated by the tracing of the total mechanical energy during calculating rapid transients. Among the approximate Riemann solvers, RoeM is more suitable with the proposed boundary treatments especially for junction than Roe's FDS because of its conservativeness of stagnation enthalpy across geometric discontinuities.

• 한국병원경영학회지
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• 제2권1호
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• pp.80-95
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• 1997

It has been an issue in the field of hospital management to develope a systematic and comprehensive analysis frame for financial position. This study developed a return on equity(ROE) model that includes the components of financial profitability, activity, stability and growth with reference to that developed in the USA The application of the model was attempted to assess its feasibility using data collected from a general hospital that has long been in the red. The hospital's financial ratio were compared to those of another private hospital in the black and also to the average ratios values of the similar bed-sized hospitals. Factors that cause the financial deficit and the strategies that can help to reorient the management's financial decision-making together with requisite conditions for effective use of the model, were identified. This study concludes that the ROE model can be usefull when effective financial strategies of the private hospitals are to be formulated.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 추계 학술대회논문집
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• pp.48-58
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• 1999

The Characteristic Flux Difference Splitting (CFDS) scheme designed to adapt the characteristic boundary conditions at the wall and inflow/outflow boundary planes satisfies Roe's property U, although the CFDS Jacobian matrix is decomposed by a product of elaborate transformation matrices and explicit eigenvalue matrix. When the CFDS algorithm, thus a variant of Roe's scheme, is applied straightforwardly to hypersonic flows over a blunt body, the strong bow shock gradually breaks down near the stagnation point. This numerical instability is widely observed by many researchers employing flux-difference method, known in the literature as the carbuncle phenomenon. Many remedies have been proposed and resulted in partial cures. When the idea of Sanders et al. which identifies the minimum eigenvalues near the discontinuity present is applied to CFDS method, it is shown that the instability problem can be controlled successfully. A few flux splitting methods have also been tested and results are compared against the Nakamori's Mach 8 blunt body flow.

• 경영과학
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• 제30권2호
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• pp.1-10
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• 2013

Case studies are made to investigate the relationship between the accuracy of energy production estimation and project feasibility indicators such as rate of return on equity (ROE) and debt service coverage ratio (DSCR) for three wind farm projects. It is found out that 1% improvement in the accuracy of energy production estimation may enhance the ROE by more than 0.5% in the case of P95, thanks to improved financing terms. AHP survey shows that MCP correlation of measured in situ wind data with long term wind speed distribution and hands-on experiences of flow analysis are more important than other factors for more precise annual energy production estimation.

• 한국항공운항학회:학술대회논문집
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• 한국항공운항학회 2004년도 추계학술발표대회 논문집
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• pp.240-246
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• 2004

For the prediction on the onset of oblique shock wave-induced vortex breakdown, computational studies on the Oblique Shock wave/Vortex Interaction (OSVI) are conducted and compared with both experimental results and analytic model. A Shock-stable numerical scheme, the Roe scheme with Mach number-based function (RoeM), and a two-equation eddy viscosity-transport approach are used for three-dimensional turbulent flow computations. The computational configuration is identical to available experiment, and we attempt to ascertain the effect of parameters such as a vertex strength, streamwise velocity deficit, and shock strength at a freestream Mach number of 2.49. Numerical simulations using the ${\kappa}-{\omega}SST$ turbulence model and suitably modeled vortex profiles are able to accurately reproduce many fine features through a direct comparison with experimental observations. The present computational approach to determine the criterion on the onset of oblique shock wave-induced vortex breakdown is found to be in good agreement with both the experimental result and the analytic prediction.