Proper Orthogonal Decomposition을 이용한 고고도 장기체공 항공기 날개의 정적 공탄성 해석에 관한 연구

이상아,박경현,김정화,전상욱,이동호 한국항공우주학회 2011 한국항공우주학회 학술발표회 논문집 Vol.2011 No.4

본 연구에서는 고고도 장기체공 항공기 날개 모델에 대해 공력 축소모델(Reduced Order Model;ROM)의 정확성을 검증하고 Proper Orthogonal Decomposition(POD)를 이용한 정적공탄성 해석을 수행하였다. Full order 공력해석을 통한 Snapshot을 추출하기 위해 3D Euler Solver를 이용하였으며, 이들 Snapshot들을 통해 날개 주위 유동장의 거동을 모사하는 POD의 기저벡터를 계산 하였다. 계산된 기저벡터는 POD의 공력해석 검증과 정적 공탄성 해석을 위한 공력-구조 연계해석에 적용 하였다. 해석대상이 된 날개는 구조적 대변형이 발생하는 유연날개 구조를 가지므로 비선형성이 고려된 정적 공탄성 해석을 수행하였으며 해석 결과는 full order 3D Euler Solver와 유한요소법을 이용한 결과와 비교하였다. 이를 통해 POD를 이용한 정적 공탄성 해석의 정확성 및 효율성을 확인하였다. In this Study, static aeroelasticity analysis using Proper orthogonal decomposition(POD) is performed for HALE aircraft wing. Three dimensional Euler equation is solved to exclude snapshot data of the full order aerodynamic analysis, and then a set of POD basis vectors reproducing the flow field around the wing is calculated from these snapshots. The POD basis is applied to validation of POD and fluid-structure interaction analysis for static aeroelasticity. Because the wing analysed in this study has characteristic of flexibility of large deflection, the study has performed with nonlinear Finite Element Method(FEM) analysis. Results are compared with full order analysis and accuracy and efficiency of POD are confirmed.

Proper Orthogonal Decomposition을 이용한 천음속 날개/동체 모델의 최적 설계

박경현(Kyung-Hyun Park),전상욱(Sang-Ook Jun),조맹효(Maeng-Hyo Cho),이동호(Dong-Ho Lee) 한국항공우주학회 2010 韓國航空宇宙學會誌 Vol.38 No.5

본 연구에서는 천음속 날개/동체 모델에 대한 축소모델(Reduced Order Model; ROM)의 정확성을 검증하고, Proper Orthogonal Decomposition(POD)을 이용한 최적설계를 통해 그 효율성을 검토하였다. full order 공력해석을 통한 Snapshot을 추출하기 위해 삼차원 오일러 방정식을 이용하였으며, 이들 snapshot들을 통해 날개/동체 모델 주위 유동장의 거동을 모사하는 POD의 기저벡터를 계산 하였다. 이러한 과정을 거쳐 구축된 축소모델은 6개의 Case 들로 검증하였으며, 그 결과 ROM을 이용해 관심영역에 대한 유동장의 예측을 할 수 있다는 것을 확인하였다. 그리고 ROM을 통한 날개/동체 모델의 최적설계를 수행 하였으며, 그 결과는 반응면모델(Response Surface Model; RSM)을 이용한 최적설계 결과와 비교 하였다. 이를 통해 ROM을 바탕으로한 최적설계가RSM을 이용한 것보다 효율적임을 확인하였다. This paper presents a validation of the accuracy of a reduced order model(ROM) and the efficiency of the design optimization using a Proper Orthogonal Decomposition(POD) to transonic wing/fuselage system. Three dimensional Euler equations are solved to extrude snapshot data of the full order aerodynamic analysis, and then a set of POD basis vectors reproducing the behavior of flow around the wing/fuselage system is calculated from these snapshots. In this study, reduced order model constructed through this procedure is applied to several validation cases, and then it is confirmed that the ROM has the capability of the prediction of flow field in the space of interest. Additionally, after the design optimization of the wing/fuselage system with the ROM is performed, results of the ROM are compared with results of the design optimization using response surface model(RSM). From these, it can be confirmed that the design optimization with the ROM is more efficient than RSM.

Proper Orthogonal Decomposition을 활용한 극저온 수직 평판의 열전달 예측

류익현(Ikhyun Ryu),류동흠(Dongheum Ryu),이용빈(Yongbin Lee) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11

In this research, heat transfer prediction of cryogenic vertical flat plate subject to frosting was conducted using Proper Orthogonal Decomposition (POD). Experiments were conducted using a heat flux sensor from varying the air temperature, air humidity, air velocity, and wall temperature. With POD, one of the popular Reduced Order Modeling (ROM) techniques, dominant behaviors of the heat flux variation were extracted to generate a predictive model together with Polynomial Regression (PR). To compare with the previous work of the correlation equation built from the common heat transfer characteristics, two performance metrics were calculated: Mean Absolute Error (MAE) and the relative error of the total heat transfer prediction. As a result, the predictive model built using POD showed better prediction performance compared to the correlation equations, showing great potential in predicting time-series outputs of the heat transfer of cryogenic vertical flat plate under forced convection.

POD에 의한 하이브리드 로켓 모터의 진동 특성 해석

박차렴(Charyeom Park),이창진(Changjin Lee) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.5

본 논문에서는 Proper Orthogonal Decomposition(POD)를 이용하여 Large Eddy Simulation(LES) 을 통해 계산한 하이브리드 로켓 모터 내부 유동을 분석하였다. 하이브리드 로켓 모터 내부의 에너 지 분포 및 거동을 분석하기 위해서는, 주요한 에너지 준위를 각각 모드 개념으로 분할하고 그 분포 를 나타내는 POD 해석 기법이 필요하다. 본 과제의 목적을 달성하기 위해, POD 기법 중 Snapshot 을 활용하여 하이브리드 로켓 모터 내부 유동장의 시간 흐름에 의한 에너지 거동을 모드별로 나누어 살펴보았다. 특히, 점성력에 의해 벽면을 기준으로 발생하는 에너지 형상을 살펴보기 위해 상대적으 로 낮은 에너지 준위를 갖는 POD 모드를 분석하였다. 그리고 그 결과, 상대적으로 큰 에너지 준위 를 갖는 거동이 중심축을 기준으로 발생하며, 작은 에너지 준위를 갖는 거동이 벽면에서 나타남을 확인하였다. In this paper, analysis of internal flow of hybrid rocket motor calculated by Large Eddy Simulation is executed using Proper Orthogonal Decomposition. To analyse the distribution and motion of energy in hybrid rocket motor, POD process that divides flow structure by each mode and shows the distribution is needed. For achieving of the object, the energy behavior of internal flow of hybrid rocket motor is analysed by dividing modes using snapshot POD. Especially, to look energy behavior near the wall that occurs by viscous stress, POD modes that hold relatively low energy are analysed. As a result, the high-energy behaviors are proceeded based on the center axis, but relatively low-energy behaviors are appeared near the wall.

적합직교분해 기법을 통한 하이퍼루프 차량의 공력 해석

강형민 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.2

A framework for aerodynamic analysis of hyperloop vehicle was constructed by using Proper Orthogonal Decomposition (POD) method. The overall processes were as following; at first, an aerodynamic analysis of a hyperloop vehicle according to the vehicle speed was performed with varying the vehicle speed in order to construct a snapshot dataset. Then, a reduced order model was constructed through a combination of Eigen vectors calculated from Singular Value Decomposition. At this time, an Artificial Neural Network was used to predict the POD basis weight to reflect the nonlinear characteristics of the dataset. The reduced order model is subsequently applied to reconstruct the flowfield data with new set of flow conditions, thereby enhancing the numerical efficiency of the computation. The constructed POD framework was applied to the hyperloop vehicle flow analysis problem. As a result, it was confirmed that the difference in drag was calculated to be about 0.1%, so that the constructed POD framework can be sufficiently used for hyperloop flow analysis problems.

Modal parameter identification with compressed samples by sparse decomposition using the free vibration function as dictionary

Jie Kang,Zhongdong Duan 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.25 No.2

Compressive sensing (CS) is a newly developed data acquisition and processing technique that takes advantage of the sparse structure in signals. Normally signals in their primitive space or format are reconstructed from their compressed measurements for further treatments, such as modal analysis for vibration data. This approach causes problems such as leakage, loss of fidelity, etc., and the computation of reconstruction itself is costly as well. Therefore, it is appealing to directly work on the compressed data without prior reconstruction of the original data. In this paper, a direct approach for modal analysis of damped systems is proposed by decomposing the compressed measurements with an appropriate dictionary. The damped free vibration function is adopted to form atoms in the dictionary for the following sparse decomposition. Compared with the normally used Fourier bases, the damped free vibration function spans a space with both the frequency and damping as the control variables. In order to efficiently search the enormous two-dimension dictionary with frequency and damping as variables, a two-step strategy is implemented combined with the Orthogonal Matching Pursuit (OMP) to determine the optimal atom in the dictionary, which greatly reduces the computation of the sparse decomposition. The performance of the proposed method is demonstrated by a numerical and an experimental example, and advantages of the method are revealed by comparison with another such kind method using POD technique.

The change in flow dynamics inside the post chamber of hybrid rocket

최고은,이창진 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.11

Visualization of the flow field inside the post chamber of hybrid rocket has been conducted with direct imaging technique. It has beensuggested that the flow dynamics inside the post chamber of hybrid rocket strongly affects the occurrence of Low frequency instability(LFI). Conventional observations of pressure and temperature measurements are insufficient to investigate the flow dynamics, therebythe visualization was applied. Direct imaging was used and the simple inexpensive method showed its capability of capturing interestingflow dynamics at reduced accuracy. First of all, in-phase like behavior between the unsteady heat release approximated by luminosityfluctuation and pressure oscillation has been confirmed. The coupling mechanism between local heat release and pressure oscillation ofnon-acoustic instability would lie in the hydrodynamics. Further analysis was done on visualized flow field with Proper orthogonal decomposition. The difference due to the existence of LFI was repeatedly appeared in mode 3 analysis. As a result, it is suggested thatmode 2 and 3 interaction generates a rotating motion. The frequency characteristic of the rotating motion is found to be at a higher frequencythan the most dominant frequency in the vicinity of 20 Hz. It is suspected that this rotating motion is closely related to vortexgeneration and is seemed to share similar characteristics to the Benard-von Karman instability found in bluff-body combustions. Investigationswill be extended to the previously found cases of instability occurred experiments to understand the change in flow dynamics dueto LFI.

트윈 빌딩의 적합 직교 분해 기법을 이용한 풍하중 및 풍응답 평가

김법렬 한국전산구조공학회 2018 한국전산구조공학회논문집 Vol.31 No.6

트윈 빌딩의 풍하중의 특성과 구조적 특성은 일반 고층건물보다 복잡하다. 이러한 특성을 조사하기 위해서 풍동실험을 통해서 트윈 빌딩의 풍압을 계측하였다. 계측된 데이터와 적합 직교 분해 기법을 이용하여 풍압의 패턴을 파악하였다. 1차 모드에서는 채널링 효과가 2차 모드에서는 와류 효과가 나타났다. 또한, 두 빌딩의 하중의 상관관계를 파악하였는데, 풍 방향 하중은 양의 상관관계를 가지며, 풍 직각 방향의 하중은 명확한 상관관계가 나타나지 않았다. 이러한 상관관계는 횡 방향 변위에도 영향을 미쳤다. 양의 상관관계를 가지면 트윈 빌딩을 연결하는 구조부재의 영향이 적게 작용한 반면에 음의 상관관계를 가지면 연결 구조부재의 영향이 횡 방향의 변위를 줄이는데 큰 영향을 미치게 되었다. The wind load and structural characteristics of a twin building are more complex than those of conventional high-rise buildings. The pressure load due to wind on a twin building was therefore measured via wind tunnel experiments to analyze such characteristics. The wind pressure pattern was then deduced from measured data using proper orthogonal decomposition. Channeling and vortex shedding were observed in the first and second modes, respectively. The along-wind loads on the two buildings featured a positive correlation and the cross-wind loads featured no correlation. Such a correlation affected the wind-induced displacement. The structural member connecting the two buildings had an insignificant effect on the positive correlation, but it notably reduced the wind-induced displacement with a negative correlation.

Simulation of nonstationary wind in one-spatial dimension with time-varying coherence by wavenumber-frequency spectrum and application to transmission line

Xiongjun Yang,Ying Lei,Lijun Liu,Jinshan Huang 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.4

Practical non-synoptic fluctuating wind often exhibits nonstationary features and should be modeled as nonstationary random processes. Generally, the coherence function of the fluctuating wind field has time-varying characteristics. Some studies have shown that there is a big difference between the fluctuating wind field of the coherent function model with and without time variability. Therefore, it is of significance to simulate nonstationary fluctuating wind field with time-varying coherent function. However, current studies on the numerical simulation of nonstationary fluctuating wind field with time-varying coherence are very limited, and the proposed approaches are usually based on the traditional spectral representation method with low simulation efficiency. Especially, for the simulation of multi-variable wind field of large span structures such as transmission tower-line, not only the simulation is inefficient but also the matrix decomposition may have singularity problem. In this paper, it is proposed to conduct the numerical simulation of nonstationary fluctuating wind field in one-spatial dimension with time-varying coherence based on the wavenumber-frequency spectrum. The simulated multivariable nonstationary wind field with time-varying coherence is transformed into one-dimensional nonstationary random waves in the simulated spatial domain, and the simulation by wavenumber frequency spectrum is derived. So, the proposed simulation method can avoid the complicated Cholesky decomposition. Then, the proper orthogonal decomposition is employed to decompose the time-space dependent evolutionary power spectral density and the Fourier transform of time-varying coherent function, simultaneously, so that the two-dimensional Fast Fourier transform can be applied to further improve the simulation efficiency. Finally, the proposed method is applied to simulate the longitudinal nonstationary fluctuating wind velocity field along the transmission line to illustrate its performances.

국한 충돌 슬롯 제트의 비정상 거동에 대한 실험적 연구

김경천(Kyung Chun Kim),오성진(Sung Jin Oh),이인원(In Won Lee) 한국가시화정보학회 2005 한국가시화정보학회지 Vol.3 No.2

The flow characteristics in a confined slot jet impinging on a flat plate were investigated by using cinematic Particle Image Velocimetry technique. The jet Reynolds number was varied from 250 to 1000 for a fixed jet-to-plate spacing of H/W=5. We found that the vortical structures in the shear layer are developed with increase of Reynolds number and that the jet becomes unsteady by the interaction of vortex pairs between 500 and 750 of Reynolds number. Vortical structures and their temporal evolution are verified by using proper orthogonal decomposition.