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

A refined composite beam theory based on the variational-asymptotical method

Nonlinear aeroelasticity of a flapping wing Micro Air Vehicle (MAV) is analyzed in this paper. The geometrically nonlinear deformations are modeled by a nonlinear strain-based beam formulation, coupled with six rigid-body degrees of freedom of the aircraft. Wing flapping kinematics is described using a set of Euler angles. Two types of unsteady aerodynamic formulations are incorporated for loads on all lifting surfaces. One is Peters’ finitestate inflow formulation and the other is developed in Cranfield University, which considers the effects of vortex shedding from both the airfoil’s leading- and trailing-edges on lift generation. All these formulations are implemented in an integrated numerical frame-work, where coupled aeroelastic and flight dynamic simulations can be performed. The two aerodynamic formulations are prototyped within this framework and their applicability is assessed. Nomenclature A1 ~ A11 = coefficients computed from the airfoil degrees of freedom a = distance of beam reference axis (pitching axis) in front of mid-chord, m a0 = local aerodynamic frame, with a0y axis aligned with zero lift line of airfoil a1 = local aerodynamic frame, with a1y axis aligned with airfoil motion velocity B = body reference frame b = positions and orientations of the B frame, as time integral of β; semi-chord of airfoil, m BF, BM = influence matrices for the distributed forces and moments c = airfoil chord length, m CFF, CFB, CBF, CBB = components of the generalized damping matrix C GB = rotation matrix from the B frame to the G frame d

/pdf/nonlinear-aeroelastic-simulations-of-a-flapping-wing-micro-3t2wupg2c0.pdf

Nonlinear Aeroelastic Simulations of a Flapping Wing Micro Air Vehicle Using Two Unsteady Aerodynamic Formulations

Large thermal variations can cause significant changes in guided-wave (GW) propagation and transduction for
structural health monitoring (SHM). This work focuses on GW SHM using surface-bonded piezoelectric wafer
transducers in metallic plates for the temperature range encountered in internal spacecraft structures (20°C to 150°C).
First, studies done to determine a suitable bonding agent are documented. That was then used in controlled experiments
to examine changes in GW propagation and transduction using PZT-5A piezoelectric wafers under quasi-statically
varying temperature (also from 20°C to 150°C). Modeling efforts to explain the experimentally observed increase in
time-of-flight and change in sensor response amplitude with increasing temperature are detailed. Finally, these results
are used in detection and location of mild and moderate damage using the pulse-echo GW testing approach within the
temperature range.

Studies on effects of elevated temperature for guided-wave structural health monitoring

The flutter behavior of tow steered composite panels, in which the fiber placement follow curvilinear trajectory, is evaluated. A simple structural model based on Ritz method combined with supersonic aerodynamic piston theory is used to analyze the aeroelastic behavior. Classical lamination plate theory and symmetric stacking sequence are used and the fiber trajectories are defined by Lagrange interpolation functions. The flutter stability boundaries for optimal conventional (constant stiffness laminates) layups and nonconventional (variable stiffness laminates) steered panels are numerically compared. The effect of in-plane loads is also accounted for in the aeroelastic analyses.

/pdf/panel-flutter-analysis-and-optimization-of-composite-tow-9d5rknebfn.pdf

Panel flutter analysis and optimization of composite tow steered plates

Hypersonic vehicle simulation is complicated due to coupling between aerodynamics, the propulsion system, heat transfer due to aerodynamic heating, and structural deformations. The high speed involved in hypersonic flight results in the existence of a large heat flux at the vehicle surface. Heat transfer through the internal structure leads to temperature gradients that load the structure due to differential thermal expansion. Additionally, the structure is loaded by aerodynamic pressure. Of particular interest in this study is the extent to which structural deformation alters aerodynamic performance as it relates to vehicle control. As the control surfaces are expected to produce a significant portion of the aerodynamic forces and moments on the vehicle, this paper will focus on the integrated aerothermoelastic modeling of such a structure with the goal of evaluating the effect of structural elasticity on flight dynamics and control system performance. The Eckert reference temperature method is used to calculate the aerodynamic heat flux boundary condition at the surface and finite element representations are used to calculate the temperature distribution and structural displacements. The aerodynamic pressures over the deformed configuration are found using the analytical oblique shock/expansion fan relations. The resulting pressures are integrated over the surfaces to calculate the total lift and drag. For the trajectory points considered, the maximum relative change in lift and drag were found to be 2% and 6%, respectively. A lift-based trim routine is outlined for use in assessing the control surface deflections required to account for the change in aerodynamic lift and drag.

/pdf/thermoelastic-formulation-of-a-hypersonic-vehicle-control-3kfvis7bbk.pdf

Carlos E. S. Cesnik

Papers

A refined composite beam theory based on the variational-asymptotical method

Nonlinear Aeroelastic Simulations of a Flapping Wing Micro Air Vehicle Using Two Unsteady Aerodynamic Formulations

Studies on effects of elevated temperature for guided-wave structural health monitoring

Panel flutter analysis and optimization of composite tow steered plates

Thermoelastic Formulation of a Hypersonic Vehicle Control Surface for Control-Oriented Simulation