Edward F. Crawley

Bio: Edward F. Crawley is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: CDIO & Engineering education. The author has an hindex of 43, co-authored 344 publications receiving 12716 citations. Previous affiliations of Edward F. Crawley include George Washington University & Marathon Oil.

Use of piezoelectric actuators as elements of intelligent structures

Abstract: This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.

Rethinking Engineering Education: The CDIO Approach

Abstract: In the past ten years, leaders in engineering industries have identified specific knowledge, skills, and attitudes required of their workforce if they want to be innovative and competitive in a glo

Detailed Models of Piezoceramic Actuation of Beams

Abstract: In this paper, techniques for modeling induced strain actuation of beam-like components of intelligent structures are developed. Two analytical models and one numer ical model describing the detailed mechanics of induced strain actuators bonded to and embedded in one-dimensional structures are presented. The models illustrate the exten sion, bending, and localized shearing deformations induced. The range of parameters for which the simpler analytic models are valid is also established. The specific characteris tics of one type of induced strain actuator, piezoceramic materials, are discussed, and im plications for practical use of piezoceramic actuators are outlined. Experimental results are used to validate the beam actuation models presented.

Induced strain actuation of isotropic and anisotropic plates

Abstract: The development and experimental verification of the induced strain actuation of plate components of an intelligent structure is presented. Equations relating the actuation strains, created by induced strain actuators, to the strains induced in the actuator/substrate system are derived for isotropic and anisotropic plates. Plate strain energy relations are also developed. Several exact solutions are found for simple actuator/substrate systems, and a general procedure for solving the strain energy equations with a Rayleigh-Ritz procedure is formulated. Approximate Ritz solutions lead to both an understanding of the system design parameters, and to detailed models of cantilever plate systems. Simple test articles were used to verify the accuracy of the basic induced strain actuator/substrate system models, and cantilever plate test articles were built and tested to verify the ability of the models to predict the strains induced in systems with extensive stiffness coupling and complicated boundary conditions.

A technical comparison of three low earth orbit satellite constellation systems to provide global broadband

Abstract: The idea of providing Internet access from space has made a strong comeback in recent years. After a relatively quiet period following the setbacks suffered by the projects proposed in the ’90s, a new wave of proposals for large constellations of low Earth orbit (LEO) satellites to provide global broadband access emerged between 2014 and 2016. Compared to their predecessors, the main differences of these systems are: increased performance that results from the use of digital communication payloads, advanced modulation schemes, multi-beam antennas, and more sophisticated frequency reuse schemes, as well as the cost reductions from advanced manufacturing processes (such as assembly line, highly automated, and continuous testing) and reduced launch costs. This paper compares three such large LEO satellite constellations, namely SpaceX's 4425 satellites Ku-Ka-band system, OneWeb's 720 satellites Ku-Ka-band system, and Telesat's 117 satellites Ka-band system. First, we present the system architecture of each of the constellations (as described in their respective FCC filings as of September 2018), highlighting the similarities and differences amongst the three systems. Following that, we develop a statistical method to estimate the total system throughput (sellable capacity), considering both the orbital dynamics of the space-segment and the variability in performance induced by atmospheric conditions both for the user and feeder links. Given that the location and number of ground stations play a major role in determining the total system throughput, and since the characteristics of the ground segment are not described in the FCC applications, we then run an optimization procedure to minimize the total number of stations required to support the system throughput. Finally, we conclude by identifying some of the major technical challenges that the three systems will have to overcome before becoming operational.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

Multimedia in Learning

Abstract: A wide variety of media can be used in learning, including distance learning, such as print, lectures, conference sections, tutors, pictures, video, sound, and computers. Any one instance of distance learning will make choices among these media, perhaps using several.