• Aerospace Engineering and Technology
• /
• v.2 no.1
• /
• pp.1-10
• /
• 2003

Methodology of predicting steady performance of gas turbine engine from transient test data was explored to develop an economic performance test technique. Discrepancy of transient performance from steady performance was categorized as dynamic, thermal and aerodynamic transient effects. Each effect was mathematically modeled and quantified to provide correction factors for calculating steady performance. The influence of engine inlet/outlet condition change on engine performance was corrected firstly, and then steady performance was predicted from the correction factors. The result was compared with steady performance test data. This correction method showed an acceptable level of precision, 3.68% difference of fuel flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.5
• /
• pp.62-70
• /
• 2002

Methodology of predicting steady performance of gas turbine engine from transient test data was explored to develop an economic performance test technique. Discrepancy of transient performance from steady performance was categorized as dynamic, thermal and aerodynamic transient effects. Each effect was mathematically modeled and quantified to provide correction factors for calculating steady performance. Engine performance tests were conducted at Altitude Engine Test Facility of KARI. The influence of engine inlet/outlet condition change on engine performance was corrected firstly, and then steady performance was predicted from the correction factors. The result was compared with steady performance test data. This correction method showed an acceptable level of precision, 3.68% difference of fuel flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.3
• /
• pp.202-211
• /
• 2017

In this study, numerical simulations were performed using the ${\gamma}-Re_{\theta}$ transition model of KFLOW for the transitional flow over the KARI-11-180 airfoil. Numerical results of KFLOW were compared with experimental data and two other numerical results of XFoil and MSES. Fully turbulence model was predicted high skin friction drag than transition model because fully turbulence model could not solve the transitional flow. Numerical predictions using the ${\gamma}-Re_{\theta}$ model of KFLOW show a good agreement with experimental data and other numerical results. Present numerical results were confirmed the state of drag bucket due to dramatic changing of the transition location on the airfoil surface.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.5
• /
• pp.407-419
• /
• 2008

In this study, the transition Reynolds number of compressible axi-symmetric sharp cone boundary layer is predicted by using a linear stability theory and the -method. The compressible linear stability equation for sharp cone boundary layer was derived from the governing equations on the body-intrinsic axi-symmetric coordinate system. The numerical analysis code for the stability equation was developed based on a second-order accurate finite-difference method. Stability characteristics and amplification rate of two-dimensional second mode disturbance for the sharp cone boundary layer were calculated from the analysis code and the numerical code was validated by comparing the results with experimental data. Transition prediction was performed by application of the -method with N=10. From comparison with wind tunnel experiments and flight tests data, capability of the transition prediction of this study is confirmed for the sharp cone boundary layers which have an edge Mach number between 4 and 8. In addition, effect of wall cooling on the stability of disturbance in the boundary layer and transition position is investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.5
• /
• pp.403-413
• /
• 2010

Transition location of boundary layers over airfoils is predicted by using PSE(Parabolized Stability Equations) and $e^N$-method. Growth rates of disturbances are obtained from the PSE analysis and the N-factor curves are calculated by integrating the growth rates. The computational code developed in the present study is validated by comparing the computed results with the well known data for the cases of flat plate boundary layers and airfoils. Predictions of transition location are made for the boundary layers over NACA0012, NLF(1)-0414F, and NLF(1)-0416 airfoil. Predicted transition locations are found to be in good agreement with the experimental data.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2004.05a
• /
• pp.523-526
• /
• 2004

가입자단에서의 병목현상 해결과 통신방송융합서비스의 제공을 위해 가입자망 기술은 디지털화된 HFC와 상하향 100Mbps이상의 속도를 제공하는 FTTH(Fiber To The Home)로 진화될 것으로 예측되며, 궁극적으로는 FTTH로 수렴될 것으로 전망되고 있다. FTTH는 통신과 방송이 융합된 다양한 신규서비스로 새로운 수익을 창출할 것으로 기대되나, 대규모 투자가 필요한 상황에서 정확한 수요 예측은 통신 회사들의 네트워크 구축 관련 의사결정에 필수적인 요인이다. 이를 위해 본 논문에서는 경쟁서비스로 천이가 용이한 통신서비스의 특징을 고려하여 FTTH의 수요예측을 실시하였다. 1차 전문가 설문을 통해 서비스간 전이형태를 모형화하였으며, 이를 토대로 FTTH 서비스로의 천이에 의해 추가적인 확산이 일어나는 변형된 Bass모형을 제안하였다. FTTH 서비스의 확산요인을 분석한 후 이를 토대로 2차 전문가 설문을 통해 각 계수를 추정하였다.

• Proceedings of the Korean Institute of Intelligent Systems Conference
• /
• 2007.11a
• /
• pp.205-209
• /
• 2007

생산 현장에서 기기의 운영과 관리는 제품의 품질 및 기업의 수익성과 직결된다. 그러나 정상적인 작동을 하고 있는 시스템에서 고장의 시점과 고장의 종류를 예측하기 곤란하며 따라서 잔여 가동 시간이 얼마인지도 예측하기 힘들다. 본 논문에서는 산업용 기계, 공정과 의료기기 등 신뢰성이 요구되는 Brushless DC 모터의 상태 변화의 추이를 관찰하여 진단의 특징점으로 사용한다. 본 논문에서 제안한 상태천이 모텔은 고장의 시점과 고장의 종류를 예측할 수 있으며 유지보수의사결정에 도움을 줄 수 있다.

• Nuclear Engineering and Technology
• /
• v.27 no.6
• /
• pp.853-858
• /
• 1995

The initial condition of a core transient should be consistent with real core state for the simulation of the core tansient. The initial xenon distribution, which can not be measured in the core, has a significant effect on the transient with xenon dynamics. In the simulation of the transient starting from non-equilibrium xenon state, the accurate initialization of the non-equilibrium xenon distribution is essential for the prediction of the core transient behavior. In this study, a xenon initialization method to predict the core transient more accurately was developed through the equivalent pre-xenon-oscillation which represents the tenon oscillation before the transient and verified by the application of the simulation for a startup test of Yonggwang Unit 3.

• Proceedings of the IEEK Conference
• /
• 2001.09a
• /
• pp.349-352
• /
• 2001

일반적인 동영상 압축 부호화 방법에서 시간적 중복 정보를 줄이기 위해 움직임 예측과 움직임 보상 방법을 이용한다. 웨이블릿 변환을 이용한 동영상 압축 부호화 기법 중에는 기존의 공간 영역에서의 움직임을 예측하는 대신에 웨이블릿 변환 영역에서 움직임을 예측하기도 한다. 이러한 방법은 움직임 예측 시간을 줄이는 장점이 있지만, 웨이블릿 변환에서 추림(Desimation)하는 과정에서 천이-변동 문제 (Shift-Variant Problem)를 일으켜 좋지 않은 성능을 나타낸다. 본 논문에서는 웨이블릿 영역에서의 다중 해상도 움직임 예측에서 천이-변동 문제를 해결하기 위한 새로운 움직임 예측과 움직임 보상 방법을 제안한다. 제안된 방법은, 기존의 공간 영역에서의 블록 정합 방법과 비교하여, 더 높은 화질을 나타낼 뿐 아니라, 주관적 화질에도 개선된 결과를 보인다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.287-293
• /
• 2010

본 연구에서는 개방형 로켓엔진시스템의 제어시스템을 구성하기 위한 선행연구로서, 시동특성을 예측하기위해 Simulink 모델을 구성하였다. 구성품별 동특성 모델을 바탕으로 로켓엔진시스템의 예측 프로그램을 구성하였으며, 대상으로 하는 시스템의 천이 작동상태에서의 동특성 변화의 예측과 더불어 그 모델링의 타당성 검증을 위하여 실제 개방형 로켓엔진 상사모델의 수류실험을 통해 실험적으로 측정하여 비교하였다. 또한 Simulink모델이 제어시스템을 구성하기위해 적합한지를 판단하기위해 기 수행된 천이 동특성 예측 프로그램의 결과와 비교하였고 검증하였다.