1,721,001 research outputs found
Active control for flutter suppression: an experimental investigation
No full textThis paper describes an experimental study involving the implementation of the method of receptances to control binary flutter in a wind-tunnel aerofoil rig. The aerofoil and its suspension were designed as part of the project. The advantage of the receptance method over conventional state-space approaches is that it is based entirely on frequency response function measurements, so that there is no need to know or to evaluate the system matrices describing structural mass, aeroelastic and structural damping and aeroelastic and structural stiffness. There is no need for model reduction or the estimation of unmeasured states, for example by the use of an observer. It is demonstrated experimentally that a significant increase in the flutter margin can be achieved by separating the frequencies of the heave and pitch modes. Preliminary results from a complementary numerical programme using a reduced-order model, based on linear unsteady aerodynamics, are also presente
Complex-damped dynamic systems in the time and frequency domains
Full text linkThe fact that a complex-damped model may represent the dynamic behaviour of elasto-mechanical systems when acted upon by a magnetic field was brought to the attention of the structural dynamics community very recently by Professor Bruno A. D. Piombo and his colleagues at the Politecnico di Torino. In this paper a thorough analysis of the single degree-of-freedom complex-damped mass-spring system is presented. The analysis includes the root locus, the (non-causal) impulse response, the frequency response and the transmissibility. Regions of different behaviour in the frequency response and transmissibility are described in detail. The stiffening behaviour observed in Prof. Piombo's experiments and known as the "phantom effect" is demonstrated by the complex-damped model
Stabilised Layer Method for linear and nonlinear spatial non classical damping identification
No full textIn the Layer Method the damping matrix is written as a sum of several layers characterised by a semidefinite positive elementary matrix. Each layer is modulated by an unknown damping coefficient and finally expanded to the system total dimensions, using a localisation matrix based on the system topology. The linear and nonlinear spatial damping distribution most close to the real dissipations can be identified directly from experimental FRFs combining the Stabilised Layer Method approach with the inverse receptance method. In this paper the Stabilised Layer Method is experimentally applied to a simple nonclassically viscous damping system and to a quite complex industrial example as a body in white chassis. Finally a nonlinear system with a localised magnetic eddy-current damping is numerically investigated. The nonlinear damping coefficients are identified from numerical nonlinear frequency response functions with additional random noise
An assessment of damping identification methods
No full textA study is carried out into the philosophy and performance of different approaches for the determination of linear viscous damping in elasto-mechanical systems. The methods studied include a closed-form solution, identification methods based on inverting the matrix of receptances, energy expressions developed from single-frequency excitation and responses
as well as first-order perturbation methods. The work is concentrated particularly up on modal truncation and how this affects the distribution of matrix terms and the ability of the identified damping (together with known mass and stiffness
terms) to reproduce the complex eigenvalues and eigenvectors of the full-order system. A simulated example is used to illustrate various points covered in the theoretical discussion of the methods considered
Damping identification in multiple degree-of-freedom systems using an energy balance approach
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Experimental partial feedback linearisation: comparison between two active control strategies on a non-smooth nonlinear system
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