A procedure for reduced-order model based robust aeroelastic control
Brüderlin, Manuel Pedro; Behr, Marek (Thesis advisor); Schröder, Kai-Uwe (Thesis advisor)
Aachen (2019) [Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (xxii, 125 Seiten) : Illustrationen
Due to the increase in computer performance coupled CFD-CSM (Computational Fluid Dynamics - Computational Structural Mechanics) tools are state of the art for aeroelastic simulation of aircraft. Such a coupled CFD-CSM tool allows very accurate computations of aeroelastic phenomena. However, due to its complexity and computational expense, it is not suited for control law design. Suitable control parameters can only be determined with computationally expensive trial and error attempts. For designing a control system, a simplified model of the aeroelastic system, which still captures the essential system behavior, is required. Therefore, in the present work a Reduced-Order Model (ROM) derived from the CFD-CSM simulation environment is used. Based on the CFD-CSM input-output relation, system identification methods are used to identify a ROM. Mathematically the ROM is a linearization of the CFD-CSM simulation around the steady state equilibrium. The linearization enables using common control design methods. The designed controller should be robust across a range of sub- and transonic flow conditions. Therefore a collection of ROMs, which span the desired operational envelope, is considered. For each condition the stability region for a three-term controller is determined with the parameter space approach. The intersection area of all conditions is the area of robust stability. Out of this area, a set of control parameters is computed with an optimization approach, where all ROMs conditions contribute to the cost function. The objective of this optimization is to increase the damping of the aeroelastic system and thus accelerate the vibration decay. For the implementation of the ROM as well as for control design Matlab is used. The resulting controller is then exported from Matlab to the CFD-CSM environment and validated. The procedure is successfully applied to three test cases in sub- to transonic flow: an airfoil section, an elastically suspended winglet, and a complete wing configuration. The focus of the first test case is flutter control while the remaining cases focus on tailoring the dynamic response. The control structure is chosen in such a way that the three control parameters correlate with displacement, velocity, and acceleration. The impact of each can change significantly with the Mach number. Most effective in all test cases is the velocity parameter. However, for a maximum gain, all three parameters are necessary. For all test cases, the comparison between ROM and CFD-CSM revealed that the linear ROM is able to predict the response very accurately, despite nonlinearities due to shocks and flow separation. This justifies the ROM based control design.