Step Based Experiment Design and System Identification for AeroElastic Dynamic Modeling

This paper gives an overview of the main ideas behind a new estimation technique that is able to deliver a consistent estimate of (poorly-damped) structural resonance modes induced by aeroservoelastic interaction without user intervention. Instead of using broadband sinusoidal or sine-sweep excitation signals, the new estimation method proposed in this paper uses simple step-based excitation signals that can be applied to any of the control surfaces to formulate a model of the aerodynamically-induced structural vibration modes. Simple step-based excitation signals address the issue of broadband excitation while allowing a reasonable (short-time) excitation signal on the control surfaces. The proposed estimation method has been tailored to find consistent model estimates on the basis of step-based input signals. The estimation method uses a modified version of the well-known realization algorithm that is extended to arbitrary input signals to formulate a discrete-time model directly on the basis of step-based experiments. Since the numerical implementation only requires a singular value decomposition and a standard least-squares estimation, robust numerical algorithms can be put in place to formulate a dynamical model with little or no user intervention. The procedure is illustrated on time-domain data obtained from a high fidelity model of an F/A-18 to find a low-order model that captures the structural parameters, such as damping and location of the first main resonance modes.