Edward F. Crawley

INTELLIGENT STRUCTURES FOR AEROSPACE - A TECHNOLOGY OVERVIEW AND ASSESSMENT

HIS article presents an overview and assessment of the technology leading to the development of intelligent structures. Intelligent structures are those which incorporate actuators and sensors that are highly integrated into the structure and have structural functionality, as well as highly integrated control logic, signal conditioning, and power amplification electronics. Such actuating, sensing, and signal processing elements are incorporated into a structure for the purpose of influencing its states or characteristics, be they mechanical, thermal, optical, chemical, electrical, or magnetic. For example, a mechanically intelligent structure is capable of altering both its mechanical states (its position or velocity) or its mechanical characteristics (its stiffness or damping). An optically intelligent structure could, for example, change color to match its background.17 Definition of Intelligent Structures Intelligent structures are a subset of a much larger field of research, as shown in Fig. I.123 Those structures which have actuators distributed throughout are defined as adaptive or, alternatively, actuated. Classical examples of such mechanically adaptive structures are conventional aircraft wings with articulated leading- and trailing-edge control surfaces and robotic systems with articulated manipulators and end effectors. More advanced examples currently in research include highly articulated adaptive space cranes. Structures which have sensors distributed throughout are a subset referred to as sensory. These structures have sensors which might detect displacements, strains or other mechanical states or properties, electromagnetic states or properties, temperature or heat flow, or the presence or accumulation of damage. Applications of this technology might include damage detection in long life structures, or embedded or conformal RF antennas within a structure. The overlap structures which contain both actuators and sensors (implicitly linked by closed-loop control) are referred to as controlled structures. Any structure whose properties or states can be influenced by the presence of a closed-loop control system is included in this category. A subset of controlled structures are active structures, distinguished from controlled structures by highly distributed actuators which have structural functionality and are part of the load bearing system.

Rethinking Engineering Education

© Springer International Publishing Switzerland 2007, 2014. This book describes an approach to engineering education that integrates a comprehensive set of personal, interpersonal, and professional engineering skills with engineering disciplinary knowledge in order to prepare innovative and entrepreneurial engineers. The education of engineers is set in the context of engineering practice, that is, Conceiving, Designing, Implementing, and Operating (CDIO) through the entire lifecycle of engineering processes, products, and systems. The book is both a description of the development and implementation of the CDIO model and a guide to engineering programs worldwide that seek to improve the education of young engineers.

Open- and closed-loop results of a strain-actuated active aeroelastic wing

Open- and closed-loop tests for a strain-actuated active aeroelastic wing are summarized. Linear quadratic Gaussian (LQG) control laws as well as robust control laws are designed using sensitivity weighted LQG, classical rationalization, and multiple models. Significant vibration suppression and load alleviation are demonstrated, reducing the power spectral density of the first modes response by an order of magnitude. The flutter dynamic pressure is increased by 12%. The three major performance limitations are the saturation limit of the piezoelectrics, the choice of performance metric or output sensor, and the changes in the dynamic response of the test article. T

Multivariable high-authority control of plate-like active structures

A dynamic modeling capability for plate-like structures with integrated strain actuators is developed using the Rayleigh-Ritz assumed-mode method. The analytical model is utilized to design multi-input, multi-output (MIMO) controllers for active plate-like test articles. High control authority linear quadratic Gaussian (LQG) and optimal projection compensators are designed using a control-law development procedure that combines performance objectives, physical measurements, and LQG design variables in a consistent manner. The control laws are implemented using a real-time digital-control computer. In addition, a stability robustness guideline is developed to predict, a priori, the amount of control authority that can be applied to the test articles without destabilizing high-frequency modes. Closed-loop benchtop experiments are performed to verify the open-loop analytical model, the stability robustness predictions, and the control-law development procedure; the experiments demonstrate the ability of integrated strain actuators to effect high-authority MIMO control on flexible plate-like structures. The results show that considerable disturbance attenuation can be achieved both in the quasi-steady response and over large bandwidths spanning many flexible modes.

Rethinking engineering education - The CDIO approach, 2nd ed

© Springer International Publishing Switzerland 2007, 2014. This book describes an approach to engineering education that integrates a comprehensive set of personal, interpersonal, and professional engineering skills with engineering disciplinary knowledge in order to prepare innovative and entrepreneurial engineers. The education of engineers is set in the context of engineering practice, that is, Conceiving, Designing, Implementing, and Operating (CDIO) through the entire lifecycle of engineering processes, products, and systems. The book is both a description of the development and implementation of the CDIO model and a guide to engineering programs worldwide that seek to improve the education of young engineers.

Measurement of the modal parameters of a space structure in zero gravity

An analytic and experimental study of the changes in the modal parameters of space structural test articles from 1 to 0 g is presented. Deployable, erectable, and rotary modules were assembled to form three one- and two-dimensional structures in which variations in bracing wire and rotary joint preload could be introduced. The structures were modeled as if hanging from a suspension system in 1 g, and unconstrained, as if free floating in 0 g. The analysis is compared with ground experimental measurements made on a spring/wire suspension system with a nominal plunge frequency of 1 Hz and with measurements made on the Shuttle middeck. The degree of change in linear modal parameters, as well as the change in nonlinear nature of the response, is examined. Trends in modal parameters are presented as a function of force amplitude, joint preload, and ambient gravity level.

The CDIO Approach

The objective of engineering education is to educate students who are “ready to engineer,” that is, broadly prepared with both pre-professional engineering skills and deep knowledge of the technical fundamentals. It is the task of engineering educators to continuously improve the quality of undergraduate engineering education in order to meet this objective. Over the past 30 years, many in industry and government have tried to describe these desired outcomes in terms of attributes of engineering graduates. By examining these views, we identified an underlying need: to educate students to understand how to Conceive-Design-Implement-Operate complex value-added engineering products, processes and systems in a modern, team-based environment.

Nonlinear forced-response characteristics of contained fluids in microgravity

An experimental study of the change in the lateral slosh behavior of contained fluids between earth and space is presented. The experimental apparatus used to determine the slosh characteristics is described and a nonlinear analytic model of a coupled fluid/spacecraft system is outlined. The forced response characteristics of silicon oil and distilled water in cylinder tanks with either a flat or spherical bottom are reported and discussed. A comparison of the measured earth and space results identifies and highlights the effects of gravity on the linear and nonlinear slosh behavior of these fluids.

Adapting and Implementing a CDIO Approach

Adapting and implementing a CDIO approach can be of great value to educational programs and the students they serve. However, that means change—an inherently challenging endeavor, especially at a university. Program leaders are more likely to succeed in this change process if faculty are equipped with an understanding of how to bring about change and provided with relevant guidance and resources.

Classically Rationalized Low-Order, Robust Structural Controllers

An experimental and analytical comparison of classically rationalized and optimal control design techniques is conducted. Classically rationalized compensators blend the loop assignments, complex topological design, and robustness of optimal controllers and the lower order, robustness, and practical insight of classical controllers. The single-input/single-output disturbance rejection problem for controlled structures is divided into four distinct topologies, and optimal controllers aredesignedand interpreted classically.Theobservationsarethen summarized into a set of design rules forthedesign oflow-order robustcontrollers. Classically rationalized and robust compensators are experimentally implemented on the Middeck Active Control Experiment, a Shuttle e ight experiment