파워 효과를 고려한 덕티드 팬 시스템의 공력 해석

강형민(H. M. Kang),김철완(C. W. Kim) 한국전산유체공학회 2014 한국전산유체공학회 학술대회논문집 Vol.2014 No.5

The aerodynamic analysis of ducted fan system was performed with the consideration of the power effect. To do this, 3D Computational Fluid Dynamics (CFD) analysis was applied according to 6 tilting angles. The propeller rotation was reproduced by Multiple Reference Frame (MRF) and Sliding Mesh (SM) techniques. From the comparison, the SM technique presented more accurate results at some tilting angles, however, the MRF was more efficient than SM because the it performs steady state calculations. Also, the duct generated more pitch up moment and drag during the tilting process in spite of the improvement of thrust.

공기역학적 불확실성을 고려한 CX 팬터그래프의 접촉력 안정성 평가

강형민(H.M. Kang),이상아(S.A. Lee) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.1

The stability of the contact force of CX pantograph was assessed with considering aerodynamic uncertainties of the angle of attack(AOA) and velocity of the inflow(V<SUB>i</SUB>). At first, the aerodynamic modeling of pan head of CX pantograph was performed. And the standard deviation of the contact force of the simulation results were calculated with changing AOA and V<SUB>i</SUB>; the range of AOA was from –10° to 10° at intervals of 2° and that of V<SUB>i</SUB> was from 200㎞/h to 400㎞/h at intervals of 50㎞/h. From the results, the response surface model was constructed using the 8<SUP>th</SUP> order regression equation. Then, Monte Carlo Simulation (MCS) was performed to assess the probabilitic charateristics of uncertainties of AOA and V<SUB>i</SUB>. Therefore, it became possible to statistically evaluate the change in contact force due to the aerodynamic uncertainties of the AOA and V<SUB>i</SUB>.

하이퍼루프 차량 공력 해석을 위한 적합직교분해 기법 연구

강형민(H.M. Kang) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.2

The Proper Orthogonal Decomposition (POD) method was applied for enhancing the computational efficiency of aerodynamic simulations of hyperloop vehicle. At first, two dimensional axisymmetric computations of hyperloop vehicle were performed according to the vehicle speed and pressure inside tube in order to construct a snapshot dataset. Then, a reduced order model (ROM) was constructed through the POD method. For improvement of the accuracy of reconstructed dataset from ROM, POD basis weight coefficients were calculated by the artificial neural network. (ANN) By the comparison of original CFD data and reconstructed POD data, it was confirmed that the POD data follow the features of CFD data; the flow contours and pressure distributions of the POD data showed good agreement with CFD data. After ROM and POD basis weight coefficients by ANN are obtained, it can reconstruct the flow field data with new set of flow conditions quickly. Therefore, the POD method can be sufficiently used for the aerodynamic computations of hyperloop vehicle and ultimately design optimization problem of hyperloop system.

고속철도차량 개활지 주행 시 공기역학적 불확실성을 고려한 팬터그래프의 접촉력 안정성 분석

강형민(H.M. Kang),이상아(S.A. Lee) 한국전산유체공학회 2022 한국전산유체공학회지 Vol.27 No.1

The stability of pantograph concerning the contact force was investigated with considering aerodynamic uncertainties of the flow during the high speed train’s running in open field. For this, three dimensional flow around the train was calculated in open field. It was convinced that the growth of the boundary layer reduced the velocity of the inflow (V<SUB>i</SUB>) to the pantograph pan head to 92% of the train’s speed. Then, the standard deviation of contact force (σ) was calculated with changing the angle of attack (AOA) and V<SUB>i</SUB>. From the simulation results with taking account of boundary layer effect, the response surface model (RSM) was constructed. Then Monte Carlo Simulation (MCS) was applied to investigate the effect of uncertainties of AOA and V<SUB>i</SUB>. As a result, statistical evaluation of the stability of became possible with the uncertainties of the AOA and V<SUB>i</SUB> and the probability of violating the stability condition of was greatly reduced when the boundary layer effect was considered.

커버 형상을 고려한 고속전철 팬터그래프 공력특성의 수치해석적 연구

강형민(H.M. Kang),김철완(C.W. Kim),조태환(T.H. Cho),김동하(D.H. Kim),윤수환(S.H. Yoon),권혁빈(H.B. Kwon) 한국전산유체공학회 2012 한국전산유체공학회지 Vol.17 No.3

The aerodynamic performance of the pantograph on a high speed train was compared for different pantograph covers which are designed to block the aero-acoustic noise from the pantograph. For the study, two types of cover are designed: wedge and cone types. The lift force of pantograph with cover was compared with the force of pantograph only. The comparison clarified that the cone type cover increases the sideslip angle of the flow and decreases the lift force considerably. However, the wedge type cover changes the flow direction upward and increases the lift force of the pan head. This increment of lift force compensates the decrement of lift force caused by the blocking of the flow into the pantograph lower frame due to cover. Therefore, in case of the wedge type cover, the overall lift force changes slightly compared with the cone type cover.

적합직교분해기법을 활용한 속도 및 압력에 따른 하이퍼루프 차량의 유동 해석 데이터 복원

강형민(H.M. Kang) 한국전산유체공학회 2021 한국전산유체공학회 학술대회논문집 Vol.2021 No.5

적합직교분해 기법에서의 효율적인 스냅샷 선정을 위한 고유값 분석

강형민(H.M. Kang),전상욱(S.O. Jun),이관중(K. Yee) 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.1

The guideline of selecting the number of snapshot dataset, N<SUB>s</SUB> in proper orthogonal decomposition(POD) was presented via the analysis of Eigen values based on the singular value decomposition(SVD). In POD, snapshot datasets from the solutions of Euler or Navier-Stokes equations are utilized to SVD and a reduced order model(ROM) is constructed as the combination of Eigen vectors. The ROM is subsequently applied to reconstruct the flowfield data with new set of flow conditions, thereby enhancing the computational efficiency. The overall computational efficiency and accuracy of POD is dependent on the number of snapshot dataset; however, there is no reliable guideline of determining N<SUB>s</SUB>. In order to resolve this problem, the order of maximum to minimum Eigen value ratio, O(R)from SVD was analyzed and presented for the decision of N<SUB>s</SUB>: in case of steady flow, N<SUB>s</SUB> should be determined to make O(R) be 10<SUP>9</SUP>. For unsteady flow, N<SUB>s</SUB> should be increased to make O(R) be 10<SUP>11~12</SUP>. This strategy of selecting the snapshot dataset was applied to two dimensional NACA0012 airfoil and vortex flow problems including steady and unsteady cases and the numerical accuracies according to N<SUB>s</SUB> and O(R) were discussed.

경계면 처리 개선을 통한 다중해상도 유동해석 기법 개선 연구

강형민(H.M. Kang) 한국전산유체공학회 2015 한국전산유체공학회지 Vol.20 No.4

The computational efficiency of flow simulations with Multi-resolution analysis (MRA) was enhanced via the boundary treatment of the computational domain. In MRA, an adaptive dataset to a solution is constructed through data decomposition with interpolating polynomial and thresholding. During the decomposition process, the basis points of interpolation should exceed the boundary of the computational domain. In order to resolve this problem, the weight coefficients of interpolating polynomial were adjusted near the boundaries. By this boundary treatment, the computational efficiency of MRA was enhanced while the numerical accuracy of a solution was unchanged. This modified MRA was applied to two-dimensional steady Euler equations and the enhancement of computational efficiency and the maintenance of numerical accuracy were assessed.

전산유체해석 및 인공신경망을 활용한 고속철도차량의 터널 내부 주행 프레임워크 개발

강형민(H.M. Kang) 한국전산유체공학회 2024 한국전산유체공학회 학술대회논문집 Vol.2024 No.10

공기역학적 성능 향상을 위한 플랩의 최적 위치 선정

강형민(H.M. Kang),박영민(Y.M. Park),김철완(C.W. Kim),이창호(C.H. Lee) 한국전산유체공학회 2013 한국전산유체공학회지 Vol.18 No.4

The selection of the optimal position of the flap was performed in order to improve the aerodynamic performance during the take-off and landing processes of aircraft. For this, the existing airfoils of the main wing and flap are selected as the baseline model and the lift coefficients (cl) according to angle of attacks (AOA) were calculated with the change of the position of flap airfoil. The objective function was defined as the consideration of the maximum cl, lift to drag ratio and cl at certain AOA. Then, at 121 experimental points within 20mm×20mm domain, two dimensional flow simulations with Spalart-Allmaras turbulence model were performed concerning the AOA from 0 to 15 degree. If the optimal position was located at the domain boundary, the domain moved to the optimal position. These processes were iterated until the position was included in the inside of the domain. From these processes, the flow separation at low AOA was removed and cl increased linearly comparing with that of the baseline model.