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항공기 날개 형상 최적화를 위한 distributed design의 적용
김태희(TaeHee Kim),최성임(Seongim Choi) 한국전산유체공학회 2013 한국전산유체공학회 학술대회논문집 Vol.2013 No.5
Aircraft design is very difficult because aircraft is composed of many subsystems which are highly coupled. Therefore, aircraft design with decoupled analysis at subsystems is meaningless and it is important to perform an integrated analysis. Designers revise existing design methods or find a new design method for satisfying the complex design requirement, one of them is a Multidisciplinary Design Optimization(MDO) which is methodology that tries to slove those issues and many study is performed recently. A distributed design divides the aircraft system into system and subspace levels and distributes independent role to each discipline. Collaborative Optimization(CO) and Concurrent Sub-Space Optimization(CSSO) are kinds of distributed design which have different formulations and different characteristics. CSSO carries out system analysis and solves a series of sensitivity equations. Also CSSO contains concept of responsible coefficient and trade-off coefficient. In contrast, CO doesn’t has system analysis and sensitivity equation and uses concept of auxiliary variables and compatibility condition. In current study, we compare Collaborative Optimization(CO) and Concurrent Sub-Space Optimization(CSSO) methods about their advantages and weaknesses through their application to aircraft wing shape design problem.
Mapped Chebyshev Pseudo-Spectral Method for Dynamic Aero-Elastic Problem of Limit Cycle Oscillation
Im, Dong Kyun,Kim, Hyun Soon,Choi, Seongim The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2
A mapped Chebyshev pseudo-spectral method is developed as one of the Fourier-spectral approaches and solves nonlinear PDE systems for unsteady flows and dynamic aero-elastic problem in a given time interval, where the flows or elastic motions can be periodic, nonperiodic, or periodic with an unknown frequency. The method uses the Chebyshev polynomials of the first kind for the basis function and redistributes the standard Chebyshev-Gauss-Lobatto collocation points more evenly by a conformal mapping function for improved numerical stability. Contributions of the method are several. It can be an order of magnitude more efficient than the conventional finite difference-based, time-accurate computation, depending on the complexity of solutions and the number of collocation points. The method reformulates the dynamic aero-elastic problem in spectral form for coupled analysis of aerodynamics and structures, which can be effective for design optimization of unsteady and dynamic problems. A limit cycle oscillation (LCO) is chosen for the validation and a new method to determine the LCO frequency is introduced based on the minimization of a second derivative of the aero-elastic formulation. Two examples of the limit cycle oscillation are tested: nonlinear, one degree-of-freedom mass-spring-damper system and two degrees-of-freedom oscillating airfoil under pitch and plunge motions. Results show good agreements with those of the conventional time-accurate simulations and wind tunnel experiments.