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 …

I and i

Vibration based condition monitoring refers to the use of in situ non-destructive sensing and analysis of system characteristics –in the time, frequency or modal domains –for the purpose of detecting changes, which may indicate damage or degradation. In the field of civil engineering, monitoring systems have the potential to facilitate the more economical management and maintenance of modern infrastructure. This paper reviews the state of the art in vibration based condition monitoring with particular emphasis on structural engineering applications.

Vibration Based Condition Monitoring: A Review:

Aircraft wings are a compromise that allows the aircraft to fly at a range of flight conditions, but the performance at each condition is sub-optimal. The ability of a wing surface to change its geometry during flight has interested researchers and designers over the years as this reduces the design compromises required. Morphing is the short form for metamorphose; however, there is neither an exact definition nor an agreement between the researchers about the type or the extent of the geometrical changes necessary to qualify an aircraft for the title ‘shape morphing.’ Geometrical parameters that can be affected by morphing solutions can be categorized into: planform alteration (span, sweep, and chord), out-of-plane transformation (twist, dihedral/gull, and span-wise bending), and airfoil adjustment (camber and thickness). Changing the wing shape or geometry is not new. Historically, morphing solutions always led to penalties in terms of cost, complexity, or weight, although in certain circumstances, thes...

A Review of Morphing Aircraft

This book focuses on structural health monitoring in the context of machine learning. The authors review the technical literature and include case studies. Chapters include: operational evaluation, sensing and data acquisition, introduction to probability and statistics, machine learning and statistical pattern recognition, and data prognosis.

Structural Health Monitoring: A Machine Learning Perspective

The capability of embedded piezoelectric wafer active sensors (PWAS) to excite and detect tuned Lamb waves for structural health monitoring is explored. First, a brief review of Lamb waves theory is presented. Second, the PWAS operating principles and their structural coupling through a thin adhesive layer are analyzed. Then, a model of the Lamb waves tuning mechanism with PWAS transducers is described. The model uses the space domain Fourier transform. The analysis is performed in the wavenumber space. The inverse Fourier transform is used to return into the physical space. The integrals are evaluated with the residues theorem. A general solution is obtained for a generic expression of the interface shear stress distribution. The general solution is reduced to a closed-form expression for the case of ideal bonding which admits a closed-form Fourier transform of the interfacial shear stress. It is shown that the strain wave response varies like sin a, whereas the displacement response varies like sinc a. ...

/pdf/tuned-lamb-wave-excitation-and-detection-with-piezoelectric-1s8tzaji61.pdf

Tuned Lamb-Wave Excitation and Detection with Piezoelectric Wafer Active Sensors for Structural Health Monitoring

Application of the variational-asymptotical method to static and dynamic behavior of elastic beams

This paper presents a new method to measure wing deflections in flight for small UAVs. It employs a pair of high resolution stereo cameras and LED wing markers, as well as a small form factor computer for control and storage. Post-processing of all the data is done off-line. Accuracy benchmark tests are conducted. Finally, theoretical discussion of wing shape reconstruction is presented. The method employs numerical optimization by minimizing the difference between numerical geometrically nonlinear slender beam equations and observed markers points with associated uncertainties.

/pdf/in-flight-wing-deformation-measurement-system-for-small-5cgfsavhrs.pdf

In-Flight Wing Deformation Measurement System for Small Unmanned Aerial Vehicles

This paper presents the initial development of an optimization framework for designing active twist helicopter rotor blade cross sections with embedded anisotropic piezocomposite actuators. Optimum design of active twist blades is a complex task, since it involves a rich design space with tightly coupled design variables, e.g., the simple orientation of the actuators aects the blade natural frequencies. Therefore, it becomes advantageous to apply the principle of mathematical optimization to the design task. In the proposed framework, the blade cross-sectional internal layout is designed to maximize the static twist actuation while satisfying a series of blade requirements. These requirements are associated with locations of the center of gravity and elastic axis, blade mass per unit span, fundamental rotating blade frequencies, and the blade strength based on local threedimensional stress and strain fields under worst loading conditions. An active composite cross-sectional analysis and a geometrically exact one-dimensional beam analysis, along with other related analysis routines, are combined with a gradient-based optimizer within MATLAB. The developed optimization framework is exemplified by using the NASA/Army/MIT Active Twist Rotor blade and its baseline design.

/pdf/optimum-design-framework-for-integrally-twisted-helicopter-20w39vdir2.pdf

Optimum Design Framework for Integrally Twisted Helicopter Blades

Presented at the 6th AIAA/USAF/NASA/ISSMO Symposium on Multidisciplinary Analysis and Optimization, Bellevue, WA, September 4-6, 1996.

A new approach to integrated wing design in conceptual synthesis and optimization

An experimental, remotely-piloted aircraft has been designed and fabricated at University of Michigan that is aeroelastically representative of very flexible aircraft. Known as X-HALE, this Experimental High-Altitude Long-Endurance aircraft exhibits geometrically nonlinear behaviour and displays specific aeroelastic characteristics designed into the experiment. This paper presents the data from the initial flight tests of the lightly instrumented X-HALE Risk Reduction Vehicle that confirm the expected aeroelastic characteristics. This opens the way for future flight tests with a fully-instrumented platform which will provide data to support validation of coupled, nonlinear aeroelastic/flight dynamic codes.

Carlos E. S. Cesnik

Papers

Application of the variational-asymptotical method to static and dynamic behavior of elastic beams

In-Flight Wing Deformation Measurement System for Small Unmanned Aerial Vehicles

Optimum Design Framework for Integrally Twisted Helicopter Blades

A new approach to integrated wing design in conceptual synthesis and optimization

Preliminary flight test correlations of the X-hale aeroelastic experiment