Damage-mitigating control: an interdisciplinary thrust between controls and material science

A major goal in the control of complex mechanical systems such as rocket engines, advanced aircraft, and power plants is to achieve high performance with increased reliability, availability, component durability, and maintainability. The current state-of-the-art of control systems synthesis focuses on improving dynamic performance and stability under constraints that often do not adequately represent the dynamics of material degradation. The reason is that traditional design is usually based upon the assumption of conventional materials with invariant characteristics. In view of high performance requirements and availability of improved materials, the lack of appropriate knowledge about the properties of these materials will lead to either less than achievable performance due to overly conservative design, or over-straining of the structure leading to unexpected failures and drastic reduction of the service life. The key idea of this research concept is that a significant improvement in service life can be achieved by a small reduction in the system dynamic performance. This requires augmentation of the current system-theoretic techniques for synthesis of decision and control laws with governing equations and inequality constraints that would model the properties of the materials for the purpose of damage representation. The major challenge in this research is to characterize the damage generation process in the continuous-time setting, and then utilize this information for synthesizing algorithms of robust control, diagnostics, and risk assessment in complex mechanical systems. This paper presents the concept of damage mitigation for control applications, and explains the potential benefits for life extension of a reusable rocket engine.