풍력터빈 전산유체역학해석에서 비균일 그리드 무차원 연직거리의 난류모델에 대한 영향특성

이경수,하크 지아올,한상을 한국공간구조학회 2015 한국공간구조학회지 Vol.15 No.1

This paper presents the dimensionless wall distance, y+ effect on SST turbulent model for wind turbine blade. TheNational Renewable Energy Laboratory (NREL) Phase VI wind turbine was used for the study, which the wind tunnel andstructural test data has publicly available. The near wall treatment and turbulent characteristics have important role forproper CFD simulation. Most of the CFD development in this area is focused on advanced turbulence model closuresincluding second moment closure models, and so called Low-Reynolds (low-Re) number and two-layer turbulence models. However, in many cases CFD aerodynamic predictions based on these standard models still show a large degree ofuncertainty, which can be attributed to the use of the  -equation as the turbulence scale equation and the associated limitations of the near wall treatment. The present paper demonstrates the y+ definition effect on SST (Shear Stress Transport) turbulent model with advanced automatic near wall treatment model and Gamma theta transitional model for transition from lamina to turbulent flow using commercial ANSYS-CFX. In all cases the SST model shows to be superior, as it gives more accurate predictions and is less sensitive to grid variations.

미사일-타깃해석법에 의한 콘크리트돔의 항공기 충돌해석에 관한 연구

이경수,하크 지아올,한상을 대한건축학회 2014 大韓建築學會論文集 : 構造系 Vol.30 No.6

In this paper, the authors performed the missile-target interaction analysis for B747 airplane against prestressed concrete dome structure. The aircraft model was developed and verified from the previous researches that were done by the authors. Therefore, the FE aircraft model can be used for the aircraft impact loading case. The development of aircraft FE model is theoretically based on the Riera function which was proposed by Riera derived from the rigid wall impact hypothesis. When the aircraft impact to the freeform or circular section shaped structure, the resulting impact force and it's integral impulse force may be different from the theoretical values. In this paper, the authors developed the artificial prestress concrete dome structure which has circular section shape and usually using for the nuclear power plant containment building structure. And the aircraft impact analyses were performed using missile-target interaction method. The commercial Hydrocode AUTODYN was used for FE modelling and simulations. From the comprehensive numerical studies, the shape of target structure significantly affects the aircraft impact load and decreases it compared to the Riera function and rigid wall impact simulation.

미사일-타깃해석법에 의한 콘크리트돔의 항공기 충돌해석에 관한 연구

이경수,하크 지아올,한상을,Lee, Kyoung-Soo,Huque, Ziaul,Han, Sang-Eul 大韓建築學會 2014 大韓建築學會論文集 : 構造系 Vol.30 No.6

In this paper, the authors performed the missile-target interaction analysis for B747 airplane against prestressed concrete dome structure. The aircraft model was developed and verified from the previous researches that were done by the authors. Therefore, the FE aircraft model can be used for the aircraft impact loading case. The development of aircraft FE model is theoretically based on the Riera function which was proposed by Riera derived from the rigid wall impact hypothesis. When the aircraft impact to the freeform or circular section shaped structure, the resulting impact force and it's integral impulse force may be different from the theoretical values. In this paper, the authors developed the artificial prestress concrete dome structure which has circular section shape and usually using for the nuclear power plant containment building structure. And the aircraft impact analyses were performed using missile-target interaction method. The commercial Hydrocode AUTODYN was used for FE modelling and simulations. From the comprehensive numerical studies, the shape of target structure significantly affects the aircraft impact load and decreases it compared to the Riera function and rigid wall impact simulation.

풍력터빈의 구조특성 평가에 관한 연구-Part2

이경수,하크 지아올,Kommalapati, Raghava,한상을 한국공간구조학회 2015 한국공간구조학회지 Vol.15 No.1

This paper presents the structural model verification process of whole wind turbine blade including blade model which proposed in Part1 paper. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine which the wind tunnel and structural test data has publicly available is used for the study. In the Part1 of this paper, the processes of structural model development and verification process of blade only are introduced. The whole wind turbine composed by blade, rotor, nacelle and tower. Even though NREL has reported the measured values, the material properties of blade and machinery parts are not clear but should be tested. Compared with the other parts, the tower which made by steel pipe is rather simple. Since it does not need any considerations. By the help of simple eigen-value analysis, the accuracy of structural stiffness and mass value of whole wind turbine system was verified by comparing with NREL's reported value. NREL has reported the natural frequency of blade, whole turbine, turbine without blade and tower only models. According to the comparative studies, the proposed material and mass properties are within acceptable range, but need to be discussing in future studies, because our material properties of blade does not match with NREL's measured values.

항공연료 질량을 고려한 대형항공기 충돌하중모델의 개발

이경수,하크 지아올,전두진,한상을,Lee, Kyoung-Soo,Huque, Ziau,Jeon, Doo-Jin,Han, Sang-Eul 大韓建築學會 2014 大韓建築學會論文集 : 構造系 Vol.30 No.8

In this paper, the aircraft impact force models of large commercial B747 aircraft were developed by using so called Missile-Target Interaction Method. The Lagrangian meshfree SPH concept was adopted to the fuel mass for impact force calculation. 240ton, 320ton, 420ton of aircraft mass were considered to meet with the previously proposed aircraft impact force model by OECE/NEA(2002) and Arros & Doumbalski(2007). The model of present studies are based on the model of OECE/NEA originally, and extended to the model of Arros & Doumbalski. To calculate and evaluate the aircraft impact force, the impact analyses were simulated by using commercial Hydrocde AUTODYN considering the fuel mass effect. The resultant reaction force of symmetric rigid wall is considered as the impact force of aircraft. The preparation of refined FE mesh and impact simulation were done by using AUTODYN. The aircraft and fuel debris and secondary trajectory effects were considered by the eroding effect on the FE shell element and the explicitly modeled fuel mass. To evaluate and verify the impact force of aircraft, the Riera approach were used for the reference impact time history graph. The rigid wall impact test shows that the finite element model of a B747 which considering the explicit fuel mass effect is good agreement with reference values and the applicability of fuel modelling approaches of this study.

전산유체역학을 이용한 풍력 터빈 블레이드의 풍력평가

이경수,한상을,하크 지아올,김효진 한국풍공학회 2014 한국풍공학회지 Vol.18 No.2

본 연구에서는 풍력터빈 블레이드에 대한 전산유체해석(CFD)을 수행하였다. 이를 위해서 National RenewableEnergy Laboratory(NREL)에서 수행하였으며, 다양한 실험 및 해석결과가 공개된 실물크기 풍력터빈 블레이드인 NRELPhase VI를 해석대상으로 하였다. 상업용 범용 전산유체해석코드인 ANSYS-CFX와 파라매트릭 3D CAD 모델을 이용하여 해석을 수행하였으며, 실험결과와 비교하여 연구결과의 타당성을 검토하였다. 다양한 난류모델에 대한 비교연구를통하여 Shear Stress Transport(SST) k − ω 난류모델의 정확성을 검증하였으며, 유동의 비정상상태를 최소화하기 위해서0-각도 요(yaw)각을 고려하였다. NREL Phse VI 풍력터빈 블레이드는 2개의 날개를 가졌으며, 비선형 비틀림각과 선형테이퍼가 고려되었다. 풍력터빈 블레이드가 주축에 대해서 회전하기 때문에 상대속도는 스팬에 대해서 비선형의 관계를가진다. 따라서 받음각(angle of attack)을 최소화하기 위해서 비선형 비틀림각이 고려되었다. 해석결과의 3차원 풍력특성을 분석하기 위해서, 각 단면의 압력계수 및 이를 적분하여 풍력계수(수직, 접선, 추력, 회전력)를 계산하였다. 풍력터빈 블레이드의 회전속도는 72 RPM으로 고정한 상태에서 다양한 풍속(5m/s, 7m/s, 10m/s, 13m/s, 15m/s, 20m/s, 25m/s) 상태를 해석하였다. 해석결과와 풍동실험결과는 모든 풍속에 대해서 근사한 수치를 나타냈으며, 높은 풍속에서의 풍하면 박리현상에 대한 정확한 유동특성을 해석할 수 있었다. This paper presents the aerodynamic force evaluation of wind turbine blade. The National Renewable EnergyLaboratory (NREL) Phase VI wind blade profile is used for the analysis. It has comprehensive available wind tunnel testdata that performed by NREL at NASA Ames Research Center. The aerodynamic forces around flow field are evaluatedusing 3D Computational Fluid Dynamics (CFD) simulation. The commercial Ansys-CFX and parameterized 3D CAD modelof NREL Phase VI are used for the analyses. The Shear stress transport (SST) k-ω turbulence model and 0-degree yaw anglecondition are adopted for CFD analysis from the comparative studies for various turbulence models . Nonlinear twist angleswere adopted for the effects of nonlinear resultant wind speed. The linearly tapered shape was made by reducing thechord length linearly to the tip region. To find out the 3D aerodynamic effects, sectional pressure coefficient andintegrated forces about primary axis, which are normal, tangent, thrust and torque, are evaluated. 7 wind speed cases(5m/s, 7m/s, 10m/s, 13m/s, 15m/s, 20m/s, 25m/s) with constant blade rotating speed (72 RPM) are considered. Thenumerical difference on wind blade surface between this study's CFD and wind tunnel test are negligible and shown in goodagreement for the all wind speed cases. The massive separation occurred due to the high angle of attack created by the higherwind speed could be analyzed successfully.

미사일-타깃해석법에 의한 콘크리트돔의 항공기 충돌해석에 관한 연구

이경수(Lee, Kyoung-Soo),하크 지아올(Huque, Ziaul),한상을(Han, Sang-Eul) 대한건축학회 2014 大韓建築學會論文集 : 構造系 Vol.30 No.6

In this paper, the authors performed the missile-target interaction analysis for B747 airplane against prestressed concrete dome structure. The aircraft model was developed and verified from the previous researches that were done by the authors. Therefore, the FE aircraft model can be used for the aircraft impact loading case. The development of aircraft FE model is theoretically based on the Riera function which was proposed by Riera derived from the rigid wall impact hypothesis. When the aircraft impact to the freeform or circular section shaped structure, the resulting impact force and it"s integral impulse force may be different from the theoretical values. In this paper, the authors developed the artificial prestress concrete dome structure which has circular section shape and usually using for the nuclear power plant containment building structure. And the aircraft impact analyses were performed using missile-target interaction method. The commercial Hydrocode AUTODYN was used for FE modelling and simulations. From the comprehensive numerical studies, the shape of target structure significantly affects the aircraft impact load and decreases it compared to the Riera function and rigid wall impact simulation.

항공연료 질량을 고려한 대형항공기 충돌하중모델의 개발

이경수(Lee, Kyoung-Soo),하크 지아올(Huque, Ziau),전두진(Jeon, Doo-Jin),한상을(Han, Sang-Eul) 대한건축학회 2014 大韓建築學會論文集 : 構造系 Vol.30 No.8

In this paper, the aircraft impact force models of large commercial B747 aircraft were developed by using so called Missile-Target Interaction Method. The Lagrangian meshfree SPH concept was adopted to the fuel mass for impact force calculation. 240ton, 320ton, 420ton of aircraft mass were considered to meet with the previously proposed aircraft impact force model by OECE/NEA(2002) and Arros & Doumbalski(2007). The model of present studies are based on the model of OECE/NEA originally, and extended to the model of Arros & Doumbalski. To calculate and evaluate the aircraft impact force, the impact analyses were simulated by using commercial Hydrocde AUTODYN considering the fuel mass effect. The resultant reaction force of symmetric rigid wall is considered as the impact force of aircraft. The preparation of refined FE mesh and impact simulation were done by using AUTODYN. The aircraft and fuel debris and secondary trajectory effects were considered by the eroding effect on the FE shell element and the explicitly modeled fuel mass. To evaluate and verify the impact force of aircraft, the Riera approach were used for the reference impact time history graph. The rigid wall impact test shows that the finite element model of a B747 which considering the explicit fuel mass effect is good agreement with reference values and the applicability of fuel modelling approaches of this study.

전산유체역학을 이용한 포인트 팁이 고려된 풍력터빈 블레이드의 공력평가에 관한 연구

이경수(Lee, Kyoung-Soo),하크 지아올(Huque Ziaul),한상을(Han, Sang-Eul) 대한건축학회 2014 大韓建築學會論文集 : 構造系 Vol.30 No.7

This paper presents the pointed tip effects on the aerodynamic load of The National Renewable Energy Laboratory (NREL) Phase VI wind blade rotor. The aerodynamic loads around flow field are evaluated using 3D CFD simulation. The commercial ANSYS CFX and parameterized 3D cad models of NREL Phase VI are used for the analyses. The Shear Stress Transport (SST) turbulence model and 0-degree yaw angle condition are adopted for CFD analysis. Nonlinear twist angles were adopted for the effects of nonlinear resultant wind speed. The linearly tapered shape was made by reducing the chord length linearly to the tip region. To find out the 3D aerodynamic effects, sectional pressure coefficient and integrated forces about primary axis, which are normal, tangent, thrust and torque, are evaluated. 7 wind speed cases (5m/s, 7m/s, 10m/s, 13m/s, 15m/s, 20m/s, 25m/s) with constant blade rotating speed (72 RPM) are considered. The pointed tip shape was made by reducing the original NREL chord length gradually near the tip region. The numerical difference of Cp on wind blade surface between original and modified pointed tip models is negligible except near tip region, and also shown good agreement with experimental result in low wind speed case. From the CFD simulation for pointed tip shape, the decreased value of surface integrated torque about primary axis are obtained because of the reduced surface area in pointed tip region, but it is negligible compared to total values. Rather it can help to increase the structural stability and reduce the vortex because of the reduced force coefficient on near the tip region