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. ...

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

This paper presents studies about aerodynamic modeling for aeroelastic analyses of composite laminated flexible wings subjected to large displacements. An unsteady vortexlattice method (UVLM) is used, aiming reduction in computational costs when comparing with higher order CFD solutions. The UVLM has the advantage of being computationally simple, especially for complex configurations and for incompressible flow. Lifting surfaces subject to large angle of attack are very common in rotary wings area, but can also be important in the case of flapping wings in forward flight, where local fluid velocity components can lead to an effective angle of attack larger than the profile static stall limit. Since the vortex-lattice method is a potential method, without viscous effects, the boundary layer separation can not be captured. An engineering approach is then used to modify directly the pressure distribution based on an effective angle of attack calculated at each vortex-ring element. Applications to flat plate surfaces show good agreement with theory, and can predict hysteretic behavior in time response analyses. Application examples showing the ability to deal with multiple surfaces in rotary motion are also presented.

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An object-oriented unsteady vortex lattice method for aeroelastic analyses of highly flexible wings.

Nonlinear Multibay Panel Flutter Evaluation of Composite Laminates with Curvilinear Fibers

This paper studies roll maneuvers of a very flexible, high-aspect-ratio-wing transport aircraft with free flared folding wingtips. The maneuvers are commanded by different control surfaces inboard or outboard of the hinge. The computational study is conducted using a fully coupled nonlinear aeroelastic-flight dynamics framework---the University of Michigan's Nonlinear Aeroelastic Simulation Toolbox. Flared folding wingtips make the aircraft roll faster only when deflecting outboard-of-hinge leading-edge control surfaces. However, the achieved roll angles and rates are much lower than when deflecting inboard-of-hinge trailing-edge control surfaces, for which flared folding wingtips do not impact or even degrade the roll maneuver. Higher wing out-of-plane bending stiffness increases the ability of flared folding wingtips to enhance roll maneuvers at low dynamic pressure but plays only a small role in cruise conditions. 

Roll Maneuvers of Very Flexible Aircraft with Flared Folding Wingtips

This paper considers the nonlinear and unsteady loads environment of an agile high-speed vehicle with reaction control jets and structural degrees of freedom to account for the flexibility of the s...

Carlos E. S. Cesnik

Papers

An object-oriented unsteady vortex lattice method for aeroelastic analyses of highly flexible wings.

Nonlinear Multibay Panel Flutter Evaluation of Composite Laminates with Curvilinear Fibers

Roll Maneuvers of Very Flexible Aircraft with Flared Folding Wingtips

Unsteady Fluid-Structure-Jet Interactions of Agile High-Speed Vehicles

New Strategy for Design of Composite Rotor Blade with Active Flaps