Desensitizing structural-control design

A method for targeted robustness optimization is presented. This method allows the analyst to target the most critical performance parameter for enhanced protection from uncertainties in the model. To create this protection, this method uses statistical data about the uncertainties in the parameters of the model. The power of the targeted robustness method is demonstrated numerically for the active damping of two truss examples. The results show that the sensitivity of the most critical damping ratio to uncertainties is far below those of noncritical damping ratios. ARGE civil and space structures planned for the next century are expected to depend on active control systems to achieve a variety of structural response objectives. Exam- ples include tall buildings whose response to wind loads and earthquakes is actively controlled and large space antennas designed to achieve precise pointing using active shape and vibration control. Control systems are designed based on models of both the structure to be controlled and the control hardware, which includes sensors, actuators, and analog or digital computers. There may be significant differences between the models and the real systems. One reason is modeling deficiencies such as neglect of nonlinearitie s'or truncation of the model. Another reason is variability in material properties, geometrical dimen- sions, and the construction and assembly processes. Accuracy of structural models is often improved in an itera- tive process that involves testing the structure and comparing the response to a numerical simulation based on the model. There are three problems associated with this approach. First, it is difficult to test large civil and space structures due to their size. Second, it is difficult to predict actual in-orbit perfor- mance of large space structures based on ground tests. Finally, testing the structure to improve the model is costly due to the actual expense of the tests as well as the cost associated with delays in the design process while the structure is being tested. There are several approaches to developing active control systems based on inaccurate models. One solution is to use

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