• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.66-72
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• 2000

Aerodynamic sensitivity analysis is performed for the Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method and a direct differentiation method respectively. Like the mean flow equations, the turbulence model equations are also hand-differentiated to accurately calculate the sensitivity derivatives of flow quantities with respect to design variables in turbulent viscous flows. Both the direct differentiation code and the adjoint variable code adopt the same time integration scheme with the flow solver to efficiently solve the differentiated equations. The sensitivity codes are then compared with the flow solver in terms of solution accuracy, computing time and computer memory requirements. The sensitivity derivatives obtained from the sensitivity codes with different turbulence models are compared with each other. Using two-equation turbulence models, it is observed that a usual assumption of constant turbulent eddy viscosity in adjoint methods may lead to seriously inaccurate results in highly turbulent flows.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.64-69
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• 1995

A computer code for solving the Reynolds averaged full Navier-Stokes equations has bent developed for analysis of gas and steam turbine cascade flows with the option of using one of two types of turbulence model. One is the Baldwin-Lomax model and the other is standard $k-{\varepsilon}$ model. The numerical integration is based on the explicit four stage Runge-Kutta scheme and finite volume method. To be verified, the resulting code is applied to VKI turbine cascade and compared with the previous experimental results. Finally, the flowfield around a steam turbine cascade is analyzed. Comparisons with experimental data show that present numerical scheme is an accurate Navier-Stokes solver and can give very good predictions for both gas and steam turbine cascade flow.

• 한국소음진동공학회논문집
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• 제12권11호
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• pp.864-872
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• 2002

In this study, the effect of planform curvature on the stability of coupled flow/structure vibration is examined in transonic and supersonic flow regions. The aeroelastic analysis for the frequency and time domain is performed to obtain the flutter solution. The doublet lattice method(DLM) in subsonic flow is used to calculate unsteady aerodynamics in the frequency domain. For all speed range, the time domain nonlinear unsteady transonic small disturbance code has been incorporated into the coupled-time integration aeroelastic analysis (CTIA). Two curved wings with experimental data have been considered in this paper MSC/NASTRAN is used for natural free vibration analyses of wing models. Predicted flutter dynamic pressures and frequencies are compared with experimental data in subsonic and transonic flow regions.

• 한국철도학회논문집
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• 제8권5호
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• pp.425-433
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• 2005

For the design of welded bogie frame, the concept of multidisciplinary engineering activities, i.e. static, fatigue and dynamic analysis, has been applied, in which the sharing of design parameters related with each analysis and the collaboration of the working parts in charge should be fulfilled. However, in spite of these necessities, the multi-disciplinary engineering activities couldn't be performed in practice due to tack of the automation of the required analysis. In this paper, an automation of fatigue durability analysis of welded bogie frame according to UIC-Code was proposed by using the Model Center, which enables to integrate the several tools for the fatigue durability analysis, i.e. I-DEAS, ANSYS and BFAP, and to perform iterative analysis works in relation to the geometrical change of transom support bracket. Besides, the wrapping programs to control I/O-data and interfaces of these tools were developed. The developed automation technique brings not only significant decreasing man-hour required in the durability analysis, but also providing a platform of the multidisciplinary engineering activities.

• 경영과학
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• 제15권2호
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• pp.109-124
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• 1998

Recently, as the importance placed on the design phase of system development has increased, the use of diagrams to design the overall system before implementing the actual program code has seen a proportionate increase. This study focuses on the diverse diagrams depicting organizational processes when integrating multiple processes of individual organizations to form an Inter-Organizational System(IOS). In this study, we attempt to identify the critical representation features of process diagrams that enable the effective integration of Inter-Organizational processes. In particular, the effect of the mapping relationship between the representation features of different diagrams to be integrated was tested empirically in a laboratory setting. The experimental task consisted of integrating the processes of two organization based upon the given process diagrams. Actual business processes were selected from real world cases and process diagrams were formulated based upon existing object-oriented notation. An analysis of the errors committed by the subjects during the integration process indicated that the mapping relationship between the diagram features representing the respective organizational processes had a significant impact upon the final integration outcome. Based upon these results, the present study provides a guideline for process diagrams that are crucial to effective Inter-Organizational process implementation and maintenance.

• 한국통신학회논문지
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• 제21권1호
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• pp.161-174
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• 1996

CDMA 역방향 링크에서 슬롯 모드로 전송되는 프리엠블을 탐색하기 위한 최대우도 동기획득 방식의 성능을 분석한다. CDMA 복조기 출력의 통계적 특성에 기초하여 신호검출 성능을 주파수 선택성 레일라이 페이딩 채널에서 다중 $H_1$ 셀의 경우에 대해 이론적으로 분석한다. 복조기 출력으로 구성되는 판정 변수의 확률밀도 함수를 수신신호의 페이딩 특성을 고려하여 단일 및 이중 안테나 시스템의 경우에 대해 유도하고 후치 적분의 수. 페이딩 율 및 안테나 다이버시티에 따른 효과를 고려하여 성능을 분석한다.

• 한국전산유체공학회지
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• 제4권1호
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• pp.53-61
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• 1999

Two-dimensional, unsteady, incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. The compressible code involves a conventional upwind-differenced scheme for the convective terms and LU-SGS scheme for temporal integration. The incompressible code with pseudo-compressibility method also adopts the same schemes as the compressible code. Three two-equation turbulence models are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by predicting the flow around the RAE 2822 transonic airfoil and the NACA 4412 airfoil, respectively. In addition, both the incompressible and compressible code are used to compute the flow over the NLR 7301 airfoil with flap to study the compressible effect near the high-loaded leading edge. The grid systems are efficiently generated using Chimera overlapping grid scheme. Overall, the κ-ω SST model shows closer agreement with experiment results, especially in the prediction of adverse pressure gradient region on the suction surfaces of high-lift airfoils.

• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1961-1971
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• 2006

A soft recovery system (SRS) is a device that stops a high speed projectile without damaging the projectile. The SRS is necessary to verify the shock resistant requirements of microelectronics and electro-optic sensors in smart munitions, where the projectiles experience over 20,000 g acceleration inside the barrel. In this study, a computer code for the performance evaluation of a SRS based on ballistic compression decelerator concept has been developed. It consists of a time accurate compressible one-dimensional Euler code with use of deforming grid and a projectile motion analysis code. The Euler code employs Roe's approximate Riemann solver with a total variation diminishing (TVD) method. A fully implicit dual time stepping method is used to advance the solution in time. In addition, the geometric conservation law (GCL) is applied to predict the solutions accurately on the deforming mesh. The equation of motion for the projectile is solved with the four-stage Runge-Kutta time integration method. A small scale SRS to catch a 20 mm bullet fired at 500 m/s within 1,600 g-limit has been designed with the proposed method.

• 한국지반공학회논문집
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• 제18권4호
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• pp.207-214
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• 2002

미소변형에서 대변형에 이르는 전체 변형도 영역의 구성모델을 ABAQUS 코드에 구현하였다. 구성모델은 비등방경화규칙에 근거한 전응력 개념의 탄소성 모델이다. 사용된 정식화 및 알고리즘은 (1) Jaumann 응력속도를 이용한 대변형도 조건 정식화 (2) 내재적 인 응력적분 (3) 일관된 접선계수를 포함하고 있다. 이를 통하여 비등방경화 구성관계를 적용한 대변형 해석을 정확하고 효율적으로 수행할 수 있는 토대를 구축하였다. 동반논문(전병곤 등, 2002)에서는 예제해석을 통하여 새로운 구성모델과 ABAQUS 코드를 이용한 대변형 해석결과를 기술하였다.

• 터널과지하공간
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• 제17권6호
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• pp.493-502
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• 2007

암반의 수리적 특성 및 지하수 유동 양상을 파악하는데 요구되는 수리전도도맵 작성시, 투수시험 자료의 자료수 한계를 극복하고 수리전도도맵의 신뢰도 향상을 목적으로 물리탐사 결과 자료와의 병합툴을 개발하고 현장 적용해 보았다. 개발된 병합툴은 지구통계학적 최적화 시뮬레이션 기법 중의 하나인 모의 담금질 기법(Simulated Annealing)을 활용하였으며, 시뮬레이션에 필요한 전처리 과정과 후처리 과정을 포함한 4개의 모듈로 구성되었다. 파쇄대 수리특성의 파악 및 가시화를 위한 현장 적용 결과, 시추공 사이의 비조사 영역에서의 투수특성의 변화를 파악하는데 유용하게 적용될 수 있음을 확인하였다.