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

Abstract

AtSTRACTA 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.

WEC prototype advancement with consideration of a real-time damage accumulation algorithm

“…• Finding a balance between capturing as much energy as possible from a given wave and mitigating the damage incurred by the main drive train components in real-time seems to be a very beneficial endeavour. • It would appear that a Life Extending Control algorithm would provide a significant increase in service life for the WEC drive train bearing under consideration, with a small reduction in overall energy capture (as shown in [6]). …”

“…The final bearing life equation, (6), is plotted in Fig. 10, with all of the parameters entered from Table I One of the most important things to notice from Fig.…”

“…As mentioned above, since O & M costs have proven to be a very significant part of the overall cost of energy in the wind industry, it seems to make sense to include these parameters in the governing equations for wave energy devices as well. The main concept proposed is that this new type of damage mitigating control could increase the service life of the main drive train components, while maintaining a relatively small reduction in the WEC's total energy capture [6].…”

“…They termed it "damage mitigation" and the authors of [5] re-worded the term to "Life Extending Control" or LEC. However, over the past 20 years, LEC has received very little attention from the controls community at large, not because the concept or resulting test data were poor, but most likely because of the strong contribution of both, very different disciplines [4] - [6].…”

Optimal life-extending control of a boiler system

“…LEC is an area of research involving the integration of two distinct disciplines: system science and mechanics of materials. Although a significant amount of research has been conducted in each of the individual areas of control and diagnostics, and analysis and prediction of damage to materials, integration of these two areas has not received much attention [7].…”