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

Experimental and numerical validation of guided wave phased arrays integrated within standard data acquisition systems for structural health monitoring

A three-dimensional, six-degree-of-freedom hypersonic vehicle model is being developed that more accurately characterizes vehicle dynamics for control studies. The main focus areas for this paper are the development of the rigid body dynamics equations of motion, the parametrization of the vehicle geometry, the formulation of the three-dimensional aerodynamic loads, and the adaptation of an existing 1D propulsion model. The aerodynamic loads are calculated by using or combining two-dimensional shock/expansion theory and the Taylor-Maccoll equations for conical flow. Comparisons with computational results show good agreement of resultant force and moment for the top and bottom vehicle surfaces and for most trials for the side surfaces. Using these models, the vehicle is trimmed for steady cruise conditions, and its flight dynamics are linearized about that state. This analysis provides information regarding the stability and controllability of a generic hypersonic vehicle in three-dimensional flight.

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Six-Degree-of-Freedom Simulation of Hypersonic Vehicles

High-Altitude Long-Endurance (HALE) aircraft have wings with high aspect ratios. During operations of these aircraft, the wings can undergo large de∞ections. These large de∞ections can change the natural frequencies of the wing which, in turn, can produce noticeable changes in its aeroelastic behavior. This behavior can be accounted for only by using a rigorous nonlinear aeroelastic analysis. Results are obtained from such an analysis for aeroelastic behavior as well as overall ∞ight dynamic characteristics of a complete aircraft model representative of HALE aircraft. When the nonlinear ∞exibility efiects are taken into account in the calculation of trim and ∞ight dynamics characteristics, the predicted aeroelastic behavior of the complete aircraft turns out to be very difierent from what it would be without such efiects. The overall ∞ight dynamic characteristics of the aircraft also change due to wing ∞exibility. For example, the results show that the trim solution as well as the short-period and phugoid modes are afiected by wing ∞exibility.

Nonlinear aeroelasticity and flight dynamics of High-Altitude Long-Endurance aircraft

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A Computational and Experimental Studies of Flexible Wing Aerodynamics

This paper addresses modeling of guided-wave excitation by surface-bonded piezoelectric wafer transducers in multi-layered composite plate structures. Each of the individual layers is assumed to have unidirectional fibers in an epoxy matrix and is modeled as being transversely isotropic. The piezoelectric actuators are modeled as causing shear traction along their edges on the plate surface and uncoupled actuator-substrate dynamics are assumed. The formulation is generic enough to accommodate arbitrary shape actuators, and specific expressions are derived for the cases of rectangular and ring-shapes. The surface and interfacial conditions are implemented using the global matrix approach. Since the three-dimensional guided-wave field is modeled without using reduced structural formulations, all possible guided-wave modes are captured. The two-dimensional spatial Fourier transform is used to solve the problem, and a rigorous inversion procedure is outlined. These models are implemented numerically and results in the form of harmonic radiation plots are presented for various configurations.

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Carlos E. S. Cesnik

Papers

Experimental and numerical validation of guided wave phased arrays integrated within standard data acquisition systems for structural health monitoring

Six-Degree-of-Freedom Simulation of Hypersonic Vehicles

Nonlinear aeroelasticity and flight dynamics of High-Altitude Long-Endurance aircraft

A Computational and Experimental Studies of Flexible Wing Aerodynamics

Modeling of Guided-wave Excitation by Finite-dimensional Piezoelectric Transducers in Composite Plates