Time-domain aeroservoelastic modeling using weighted unsteady aerodynamic forces

A modeling method for constructing a state-space aeroservoelastic mathematical model for time-domain analysis with a low number of aerodynamic lag states is presented. The modeling method employs the minimumstate method for rational approximation of tabulated unsteady aerodynamic force coefficients at various reduced-frequency values. The approximation method is modified to deal with weighted aerodynamic data and with alternative constraint combinations. Two weighting types are analyzed and discussed. The first weighting is normalizing the aerodynamic data to maximum unit value of each aerodynamic coefficient. The second weighting is one in which each tabulated coefficient, at each reduced-frequency value, is weighted according to the effect of an incremental error of this coefficient on aeroelastic characteristics of the system. This weighting yields a better fit of the more important terms at the expense of less important ones. The analytical developments are presented and numerical examples, which demonstrate various features of this method, are shown to yield significant reduction in model size per given accuracy relative to other rational approximation methods.

[1]  M. Karpel.  Sensitivity derivatives of flutter characteristics and stability margins for aeroservoelastic design , 1990 .

[2]  J. R. Newson.  A method for obtaining practical flutter-suppression control laws using results of optimal control theory , 1979 .

[3]  Peretz P. Friedmann,et al.  Towards integrated multidisciplinary synthesis of actively controlled fiber composite wings , 1990 .

[4]  R. Vepa.  Finite state modeling of aeroelastic systems , 1977 .

[5]  J. Edwards.  Unsteady aerodynamic modeling and active aeroelastic control , 1977 .

[6]  H. Dunn.  An analytical technique for approximating unsteady aerodynamics in the time domain , 1980 .

[7]  Thomas A. Zeiler,et al.  A new simulation model building process for use in dynamic systems integration research , 1987 .

[8]  W. M. Adams,et al.  A Digital Program for Calculating the Interaction Between Flexible Structures, Unsteady Aerodynamics and Active Controls , 1979 .

[9]  Mordechay Karpel.  Design for Active Flutter Suppression and Gust Alleviation Using State-Space Aeroelastic Modeling , 1982 .

[10]  Sherwood H. Tiffany,et al.  Nonlinear programming extensions to rational function approximations of unsteady aerodynamics , 1987 .

[11]  Hugh L. Dryden,et al.  A review of the statistical theory of turbulence. , 1943 .

[12]  E. Nissim,et al.  Reduction of aerodynamic augmented states in active flutter suppression systems , 1991 .

[13]  M. Karpel,et al.  Design for active and passive flutter suppression and gust alleviation. Ph.D. Thesis , 1981 .

[14]  K. L. Roger,et al.  Airplane Math Modeling Methods for Active Control Design , 1977 .

[15]  Kenneth L. Roger,et al.  Active Flutter Suppression—A Flight Test Demonstration , 1975 .

[16]  Mordechay Karpel,et al.  Application of aeroservoelastic modeling using minimum-state unsteady aerodynamic approximations , 1991 .

[17]  Gene F. Franklin,et al.  Digital control of dynamic systems , 1980 .

[18]  Martin Goland,et al.  Principles of aeroelasticity , 1975 .

[19]  W. M. Adams,et al.  Fitting aerodynamic forces in the Laplace domain: An application of a nonlinear nongradient technique to multilevel constrained optimization , 1984 .

[20]  M. Karpel,et al.  Reduced-order aeroelastic models via dynamic residualization , 1990 .