Abstracts of Journal Articles - Accepted for Publication

A Feasibility Study on Piezoelectric Energy Harvesting from the Operational Vibration of a Highway Bridge

M Infantes (Universidad de Granada, Spain), R Castro-Triguero, RR Sola-Guirado, D Bullejos (Universidad de Cordoba, Spain) & MI Friswell (Swansea University)

Advances in Structural Engineering

Vibration-based energy harvesting represents a clean power technology that can be of interest for application in civil engineering structures. This study focuses on energy harvesting using cantilever piezoelectric devices excited by operational and ambient bridge vibration. The optimal design and analysis of energy harvesters is usually performed using the mean and standard deviation of a response quantity of interest (i.e. voltage) under broadband Gaussian white noise excitation. In this paper, a novel holistic approach to the problem is proposed through the statistics of the voltage of piezoelectric energy harvesters under real measured bridge vibration base excitation. A new semi-analytic expression of the expected power is developed. The solution is based on the closed-form of the frequency response function between the harvester output voltage and the base excitation, and the experimentally measured spectral density of the latter. A study on the influence of the electromechanical coupling of the problem equations is first conducted. Then, a sensitivity analysis of the piezoelectric energy harvester parameters is performed. The critical analysis is developed through a case study of the measured long-term vibrations of a bowstring-arch highway bridge. Both operational and ambient vibration records are considered in the feasibility study. The results show the potential of the semi-analytic expression to evaluate the harvested power of piezoelectric harvesters under operational structural vibration. This is a promising approach to confidently develop future analyses on the power requirements of wireless sensor networks for SHM.

Improving Wind Tunnel '1-cos' Gust Profiles

D Balatti, H Haddad Khodaparast, MI Friswell (Swansea University) & M Manolesos (City University, London)

Journal of Aircraft

A vane type gust generator has been designed and characterized in the Swansea University wind tunnel to enable the validation of the response of aircraft models to gust loads. The experimental results reveal the complexity of the flow between the gust vanes and the aircraft model location. Previous studies have shown that generating a predetermined gust profile at the desired location in the wind tunnel is a challenging problem. In this work, two techniques to improve the '1-cos' gust have been considered. In the first case, the transfer functions between the vane rotation and the gust produced at the aircraft model location have been identified, and its inverse has been used to calculate the vane rotation. The strong aerodynamics nonlinearity limits the improvements of this method. A parametric study on vane rotation has shown that a more complicated vane rotation function made it possible to obtain '1-cos' gusts at the aircraft model location with a mean square error two orders of magnitude smaller than the initial case. Creating '1-cos' gusts with similar frequency content as the regulations require will help design more efficient gust load alleviation systems.

Nonlinear Modal Interactions during Rub-Impact of a Rotating Flexible Shaft

A Kartheek, K Vijayan (Indian Institute of Technology Kharagpur, India) & MI Friswell (Swansea University)

Journal of Vibration and Control

An understating on interaction between a rotating flexible member and a stationary element has wide range of industrial application. The focus of this study was to understand the modal interactions using a conceptual model. The conceptual model of the system consists of multiple disc rotor with a localised conduit. A theoretical model of the system was developed using finite element analysis. An eigenvalue analysis was carried out on the system and a Campbell diagram of the system was developed. The Campbell diagram provided information about the rotor speed wherein synchronization with the whirling modes occur. Further a reduced order non-linear contact model was developed. A numerical bifurcation analysis with rotor speed as parameter was carried out on the reduced model. Analysis was carried out using randomized initial condition for each rotation speed. During the bifurcation study certain rotation speed produced high whirling response at speeds different from the critical speed. The increase in response was associated with the internal resonance of whirling modes and rotor speed. The participating modes were identified using the Campbell diagram and full spectrum. The results from the theoretical model was validated using an experimental test rig. The identification of these internal resonance rotor speed can be useful in identifying the rotor speed exclusion zone and thereby improve the rotor life.

Eringen's Nonlocal and Modified Couple Stress Theories Applied to Vibrating Rotating Nanobeams with Temperature Effects

A Rahmani, S Faroughi (Urmia University of Technology, Iran), MI Friswell (Swansea University) & A Babaei (University of Kentucky, USA)

Mechanics of Advanced Materials and Structures

This study develops a comprehensive vibrational analysis of rotating nanobeams on visco-elastic foundations with thermal effects based on the modified couple stress and Eringen's nonlocal elasticity theories. This approach accurately simulates the nonlocal stress and size effects. Higher-order shear deformation beam theory and the generalized differential quadrature method are used to obtain the numerical results. The effects of nonlocal parameters, length scale, Winkler-Pasternak coefficients, thermal gradient, slenderness ratios, rotating velocity and viscoelastic coefficient are demonstrated and discussed in detail. Mode switching and the importance of the correct choice of theory and associated size effect parameters are highlighted.