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

Ground Vibration Testing on Very Flexible Aircraft

A simulation framework is developed for assessing the eect of control surface inertial loads on hypersonic vehicle response. The framework is based on a partitioned, timemarching approach in which the fuselage and control surface equations of motion are integrated independently and forces/motion at the interface are exchanged between the two systems at pre-determined time intervals. This approach is advantageous in that it does not require direct coupling of the fuselage and control surface models, and therefore allows for the models to be of dissimilar form. Equations of motion for both the fuselage and control surface are presented and a formulation for coupling the two systems is outlined which includes iterations within each aeroelastic time step. The methodology is applied to a representative hypersonic vehicle elevator control surface model which includes aerothermoelastic eects and is attached to a single degree of freedom oscillator representing the fuselage. Results show that control surface inertial eects lead to a departure of the instantaneous control surface lift force by up to a factor of eight with respect to the static value. Investigation of the system response under a commanded change in control surface deection angle shows that control surface inertia results in departure of the instantaneous control surface pitching moment by up to a factor of 500 with respect to the static value.

/pdf/effect-of-control-surface-fuselage-inertial-coupling-on-3s21obclxy.pdf

Effect of Control Surface-Fuselage Inertial Coupling on Hypersonic Vehicle Flight Dynamics

This paper demonstrates an adaptive approach for solving fluid–structure interaction problems using high-fidelity numerical methods along with a detailed analysis of mesh-motion errors. A high-orde...

Adaptive High-Order Fluid-Structure Interaction Simulations with Reduced Mesh-Motion Errors

This paper presents results for the aeroelastic stability and LCO behavior for a complete aircraft. Comparison are presented between the results predicted by a cantilevered wing model, an untrimmed aircraft model (no gravity or drag) and a trimmed aircraft model. It is seen that the stability behavior is predicted accurately only if the correct trim loads are applied to the wing. The LCO behavior of the untrimmed aircraft was similar to that of the cantilevered wing. On the other hand, the LCO behavior of the trimmed aircraft configuration was complicated due to the presence of flight dynamic instabilities.

http://www.dept.aoe.vt.edu/~mpatil/conference/SDM00LCO.pdf

Limit Cycle Oscillations of a Complete Aircraft

This paper considers the performance and stability of high-speed vehicles due to 7changes in the vehicle configuration that introduce the interaction of multiple physics. A conventional vehicle mod...

Carlos E. S. Cesnik

Papers

Ground Vibration Testing on Very Flexible Aircraft

Effect of Control Surface-Fuselage Inertial Coupling on Hypersonic Vehicle Flight Dynamics

Adaptive High-Order Fluid-Structure Interaction Simulations with Reduced Mesh-Motion Errors

Limit Cycle Oscillations of a Complete Aircraft

Fluid-Structure-Jet Interaction Effects on High-Speed Vehicle Performance and Stability