One key design variable that has largely been neglected in control-structure design is passive structural damping. Passive damping improves nominal performance by eliminating degrading structural vibrations resulting in improved control characteristics and lowered required effort. A great advantage of added passive damping in SISO controlled structures is the improved stability and performance robustness characteristics given plant uncertainties. Theoretical formulations verifying the improved stability robustness characteristics on simple controlled structures are derived based on phase margin, gain margin and root locus properties of the structures. Numerical studies performed on more complicated systems verify the improved design characteristics for passively damped controlled structures. The theory is expanded to include MIMO controlled structures where the robustness properties of these systems are greatly affected by uncertainties in plant directions. Numerical studies verify the improved performance and robustness characteristics of passively damped MIMO controlled structures. Thesis Supervisor: Prof. Andreas H. von Flotow Title: Associate Professor _1^~~.1.-11_11_1 -.1~11-1_-111--1 11-_---_ I ~IILI

The virtues of passive damping for feedback controlled flexible structures

: There exists a need to remotely monitor the structural integrity of large space structures without costly manned missions. This work focused on further damage detection characterization of the Air Force Institute of Technology's Flexible Truss Experiment (FTE). The FTE is intended to be representative of a large space structure. Several damage detection algorithms were developed and tested for the FTE using 112 different damage conditions and the one undamaged condition. The algorithms were trained using two frequency response functions (FRFs) from each damage case and then tested using the same two FRFs, but from newly acquired data. A data reduction technique from the field of speech recognition was adapted for this damage detection application. The data was reduced by greater than an order of magnitude, via a discrete, point-by-point, integration process in both training and testing. As shifts in both the resonant and anti-resonant frequencies were caused by the damage, another damage detection algorithm was developed that extracted the resonant and anti-resonant frequencies from the two FRFs. This algorithm vectorized the frequencies of the peaks and valleys in the FRFs for comparison. Over 99% accuracy was obtained using both the adapted speech recognition method and the resonant and anti-resonant frequencies method. However, only 44% accuracy was achieved by training the resonant and anti-resonant frequencies method with synthetic, Finite Element Model generated data, and testing it with measured data.

/pdf/damage-identification-in-a-real-structure-using-resonant-and-nkafvobzva.pdf

Damage Identification in a Real Structure: Using Resonant and Anti-Resonant Frequencies

The objective of this research was to test vibration suppression (settling time and jitter) of a large space structure (LSS) characterized by low frequency high global vibration modes. Five percent passive damping in a large truss was analyzed, tested and correlated. A representative system article re-target analysis shows that modest levels of passive damping dramatically reduce the control energy required. LSS must incorporate passive damping from the outset. The LSS system performance will not be met by either active or passive damping alone.

https://ntrs.nasa.gov/api/citations/19870013281/downloads/19870013281.pdf

Lynn Rogers

Papers

Optimum mix of passive and active control of space structures