This paper proposes a structure of energy harvester that is used to scavenge environment energy to power wireless sensor nodes. The ambient energy usually is from sunlight, wind, vibration, and so on. As the size of a sensor node is limited, the energy converted is normally small and has a prodigious random fluctuation. In order to improve the conversion efficiency of energy harvester, the paper proposes a power conversion circuit to collect rapidly paroxysmal energy generated by external environment. The circuit, as a power conditioner, bridges between energy transducers and the load of a wireless sensor node, and the power output of transducers are either AC or DC. The power conditioner implements AC-DC conversion, voltage adjusting and energy storage. A design model is developed to describe the dynamic behavior of the power conditioner under the different excitation from ambient energy sources, and energy conversion efficiency can be evaluated with the model. The proposed system architecture can be applied in the design of solar, wind or stochastic vibration energy harvesters.

The dynamic performance of automotive vehicles is influenced by the suspension system design. Suspensions owing damping elements with a wide range of non-linear behaviour can provide higher mobility and better ride comfort performances. Pneumatic suspensions due to their inherent nonlinear behaviour can provide high mobility performance while suspensions with MR dampers can provide this nonlinearity through the controllable damping force produced by the control of the MR fluid. The pneumatic and MR suspension models are usually developed from experimental force-displacement and force-velocity characteristics. The purpose of this paper is to measure and compare the dynamic characteristics of pneumatic, magnetorheological, and hydraulic shock absorbers. The study is carried out through measuring the characteristics of the different types of dampers at different frequencies and amplitudes using an Electro-Servo Hydraulic (ESH) testing machine. The shock absorber is subjected to sinusoidal excitation of frequency varying from 0 to 10 Hz, and amplitude varying from 0 to 10 mm. In the case of the MR damper, the tests are also done at different current levels of between 0 and 2 amp. The input displacement and acceleration to the shock absorber were measured using an LVDT (Linear Voltage Displacement Transducer) and an accelerometer, respectively while the input velocity was derived from the measured displacement and acceleration. This dual identification of the input velocity was done in order to ensure accurate representation of the velocity. The output force response of the shock absorber was measured by means of a force transducer. The force-displacement and force-velocity characteristics of each shock absorber were subsequently derived from the measured data. The results show the tunability of the MR damper characteristics in comparison to those of the pneumatic and hydraulic dampers.

The use of acoustic finite element modal analysis for simulating and identifying blockage in a pipe network is presented in this paper. The analysis commences with a straight fluid-filled pipe without any flaw. The natural frequencies of the acoustic modes of the fluid in the pipe are computed. Blockages of different magnitudes are introduced at different locations along the length of the pipe. The corresponding natural frequencies of the acoustic modes of the fluid in the pipe are again computed by finite element technique. From these results, the modal characteristics of partially blocked pipes are established and compared with simulation results of defect-free fluid-filled pipes in order to ascertain the defect location and sizes.

The finite element method is used to analyse the through-the-width stress distribution characteristics of single and multiple delaminated cantilevered composite beams. Single delaminations of fixed length, which are located at different through-the-thickness locations, and multiple delaminations of sequential and diagonal configurations are investigated. The total length of multiple delaminations in a beam was made equal to the fixed length of a single delamination. The results show that the configurations and spatial distributions of multiple delaminations have significant effects on the magnitude of the maximum stresses induced in the beams. Beams in which most of the delaminations are concentrated around the mid-plane of the beam show higher stresses than beams in which most of the delaminations are concentrated close to the surface of the laminate. However, delaminations close to the surfaces of the beams exhibit higher stresses at the tips of the delaminations.

The present paper further develops The Fractal-like Finite Element Method (FFEM) to compute the stress intensity factors (SIFs) for non-symmetrical configurations of sharp V-notched plates. The use of global interpolation functions (GIFs) in the FFEM significantly reduces the number of unknown variables (nodal displacements) in a singular region surrounding a singular point to a small set of generalised coordinates. The same exact analytical solutions of the notch tip asymptotic field derived for a symmetrical notch case can be used as GIFs when the notch is non-symmetrical. However, appropriate local coordinate transformation in the singular region is required to obtain the correct global stiffness matrix. Neither post-processing technique to extract SIFs nor special singular elements to model the singular region are required. Any conventional finite elements can be used to model the singular region. The SIFs are directly computed because of the use of exact analytical solutions as GIFs whose coefficients (generalised coordinates) are the unknowns in the singular region. To demonstrate the accuracy and efficiency of the FFEM to compute the SIFs and model the singularity at a notch tip of non-symmetrical configurations of notched plates, various numerical examples are presented and results are validated via available published data.

This paper focuses on showing how one could identify a component by using acoustic waves within the audible frequency range. The purpose of this study is to incorporate the findings from this paper in concealed weapon detection (CWD) where objects hidden behind a person’s clothing could be detected using acoustic or ultrasonic sound waves. Experimental trials are carried out using a directional speaker which generates a highly directional acoustic beam. This can then be pointed at any target and the sound reflected from it analyzed. Initially, a sound source is selected based on the maximum frequency range. The characteristic of the acoustic signal produced by the source is then recorded to be used as reference. Different objects are selected to be used as targets. The sound reflected from these objects is recorded. The spectrograms from these targets reveal that the incident sound waves have been modulated. By taking the ratio of the reflected and the incident sound signals one could obtain the natural frequencies of the object and the spectrogram of the reflected acoustic signal could give indication of the object’s shape.

The energy harvesting for wireless sensor nodes is one of the effective methods to extend the lifespan of wireless sensor networks. The paper firstly analyzes the power requirement of a sensor node, and surveys the energy output for typical energy transducers working indoor. In general, energy harvested from the indoor environment is not matched with the power requirement of wireless sensor nodes. The harvested energy indoor is generally less than the required energy. Therefore, we propose a solution to design a middleware for the dynamic power management of a wireless sensor node. The implementation and performance evaluation of the middleware are investigated. It is shown that the proposed middleware is an effective way of solving the challenge problem above.

The free vibration characteristics of a rotating tapered Rayleigh beam is analysed in this study. First, the strain-displacement relationship for the rotating beam is formulated and used to derive the kinetic and strain energies in explicit analytical form. Second, Hamilton’s variational principle is used to derive the governing differential equation of motion and the associated boundary conditions. Third, the Differential Transformation Method (DTM) is applied to reduce the governing differential equations of motion and the boundary conditions to a set of algebraic equations from which the frequency equation is derived. Next, a numerical algorithm implemented in the software package Mathematica is used to compute the natural frequencies of vibration for a few paired combinations of clamped, pinned and free end conditions of the beam. Also, the variation of the natural frequencies of vibration with respect to variations in the rotational speed, hub radius, taper ratio and the slenderness ratio is studied. The results obtained from the Bresse-Rayleigh theory are compared with results obtained from the Bernoulli-Euler and Timoshenko theories to demonstrate the accuracy and relevance of their application.

The Dynamic Stiffness Method (DSM) is used to analyse the free vibration characteristics of a rotating uniform Shear beam. Starting from the kinetic and strain energy expressions, the Hamilton’s principle is used to obtain the governing differential equations of motion and the natural boundary conditions. The two equations are solved simultaneously and expressed each in terms of displacement and slope only. The Frobenius power series solution is applied to solve the equations and the resulting solutions are also expressed in terms of four independent solutions. Applying the appropriate boundary conditions, the Dynamic Stiffness Matrix is assembled. The natural frequencies of vibration using the DSM are computed by employing the in-built root finding algorithm in Mathematica as well as by implementing the Wittrick-Williams algorithm in a numerical routine in Mathematica. The results obtained using the DSM are presented in tabular and graphical forms and are compared with results obtained using the Timoshenko and the Bernoulli-Euler theories.

This paper proposes a response-only method in frequency domain for structural damage detection by using the derivative of natural frequency curve of beam-like structures with a traversing auxiliary mass. The approach just uses the response time history of beam-like structures and does not need the external source of force excitation. The natural frequencies of a damaged beam with a traversing auxiliary mass change due to change in flexibility and inertia of the beam as the auxiliary mass is traversed along the beam. Therefore the auxiliary mass can enhance the effects of the crack on the dynamics of the beam and, therefore, facilitating locating the damage in the beam. That is, the auxiliary mass can be used to probe the dynamic characteristic of the beam by traversing the mass from one end of the beam to the other. However, it is impossible to obtain accurate modal frequencies by the direct operation of the Fast Fourier Transform of the response data of the structure because the frequency spectrum can be only calculated from limited sampled time data which results in the well-known leakage effect. A spectrum correction method is employed to estimate high accurate frequencies of structures with a traversing auxiliary mass. In the present work, the modal responses of damaged simply supported beams with auxiliary mass are computed using the Finite Element Analysis. The graphical plots of the natural frequencies versus axial location of auxiliary mass are obtained. The derivatives of natural frequency curve can provide crack information for damage detection of beam-like structures. However, it is suggested that the derivative do not go beyond the third derivative of natural frequency curves to avoid the difference approximation error which will be magnified at higher derivative. The sensitivity of crack index for different noise, crack depth, auxiliary mass and damping ratio are also investigated. The simulated result demonstrated the efficiency and precision of the response-only frequency-domain method which can be recommended for the real application in structural damage detection.

Energy harvesting is the process of converting low level ambient energy into usable electrical energy, so that remote electronic instruments can be powered without the need for batteries or other supplies. Piezoelectric material has the ability to convert mechanical energy into electrical energy, and cantilever type harvesters using this material are being intensely investigated. The typical single cantilever energy harvester design has a limited bandwidth, and is restricted in ability for converting environmental vibration occurring over a wide range of frequencies. A multiple cantilever piezoelectric generator that works over a range of frequencies, yet has only one Piezo element, is being investigated. The design and testing of this novel harvester is described.

In Vivo mechanical properties of bulk tissue have not been yet investigated sufficiently. One of the major problems the researchers confront is the lack of agreement for the constitutive models and standardized methodology for experimental studies (1). Despite the fact that the tissue properties are non-linear, many modeling studies preferred to adopt linear isotropic models. The object of this study was to obtain bulk modulus of the upper arm under relax and controlled contraction that was 25% of the maximum voluntary contraction (MVC).

In this paper, vibration analysis of through-width single- and multi-delaminated cantilevered composite beams is carried out using Finite Element Analysis (FEA) approach. Different configurations of multiple delaminations are considered. The FEA results for single delaminations are validated via experimental testing. It is found that changes in the natural frequencies of delaminated cantilevered beams are related to the number, type and distributions of delaminations within a beam. Also, the natural frequency shifts due to single or multiple delaminations are influenced by the thickness-wise locations of the delaminations. As the delamination is moved from the outermost inter-laminar layer towards the mid-plane of the beam, the natural frequency decreases and reaches a minimum value when the delamination is located at the midplane. Single delaminations have a more significant effect on natural frequencies than multiple delaminations of the same overall dimension as the single delamination. Furthermore, it is found that there is a greater reduction in natural frequency when multiple delaminations are close together than when they are spread out. However, where the locations of multiple delaminations coincide with nodal or antinodal vibration points, the effect is significantly altered.

The fractal-like finite element method (FFEM) has been proved to be an accurate and efficient method to analyse the stress singularity of crack tips. The FFEM is a semi-analytical method. It divides the cracked body into singular and regular regions. Conventional finite elements are used to model both near field and far field regions. However, a very fine mesh of conventional finite elements is used within the singular regions. This mesh is generated layer by layer in a self-similar fractal process. The corresponding large number of degrees of freedom in the singular region is reduced extremely to a small set of global variables, called generalised co-ordinates, after performing a global transformation. The global transformation is performed using global interpolation functions. The Concept of these functions is similar to that of local interpolation functions (i.e. element shape functions.) The stress intensity factors are directly related to the generalised co-ordinates, and therefore no post-processing is necessary to extract them. In this paper, we apply this method to analyse the singularity problems of sharp notched plates. Following the work of Williams, the exact stress and displacement fields of a plate with a notch of general angle are derived for plane stress and plane strain conditions. These exact solutions which are eigenfunction expansion series are used as the global interpolation functions to perform the global transformation of the large number of local variables in the singular region around the notch tip to a few set of global co-ordinates and in the determination of the stress intensity factors. The numerical examples demonstrate the accuracy and efficiency of the FFEM for sharp notched problems.

Optical sensor offers remarkable advantage compared with traditional sensor, such as electromagnetic immunity, small size, and light weight. A low-cost intensity-based plastic optical fibre (POF) sensor is presented in this paper to measure both static and dynamic strain on a cantilevered beam. The principle of measurement is that the intensity of transmitted light changes as strain changes. By detecting the transmitted light intensity, the change of strain can be measured. First, the principle and design of the sensor are presented. Three POF sensors made using three types of housings (silicon rubber tube, rubber tube and PTFE tube) are evaluated to compare their performance, such as sensitivity, resolution and linearity. A comparison of the strain response of these sensors in static test shows that the soft material (silicon rubber and rubber tube) offers better sensitivity than that of hard material (PTFE tube). However, in dynamic test, PFTE tube gives faster response time compared with rubber tube which is not suitable for high speed test (1k Hz). Both static and dynamic test results have shown that all sensors offer excellent agreement with electrical strain gauge readings and the sensitivity of POF sensor can be up to 20 μ strain. Strain transfer function is also conducted to examine the ability of optical sensors in detection of vibration modes of a cantilevered beam. A PCB piezoelectric accelerometer sensor is attached to the beam as well to measure the acceleration transfer function of the beam, which is used as a reference signal. The results also showed the possibility that POF sensors can be used for structural health monitoring.

In this paper, the application of MR damper in structure control using PID tuning based on genetic algorithms and fuzzy logic is developed and used to control the vibrations of based-excited linear and nonlinear single degree-of freedom-systems, which represent building structures subjected to earthquake loading and are excited by means of the El Centro earthquake. For GA method, the fitness function, which is based on these three constraint conditions: the control variable, the error and the rise-time, is chosen in order to apply genetic algorithms to optimize the coefficients of a PID controller. For the fuzzy control, the PID parameters are found using fuzzy self-tuning for the fuzzy logic relationship between the parameters of PID control and the controller input variables e and ec . The adaptive fuzzy PID control, which uses the error e and the change of the error ec as the input variables, modifies the three PID parameters on line based on the fuzzy control principle. The Bouc-Wen model of MR damper is used to simulate the MR damper characteristics. The simulation results demonstrate that the MR damper, used in conjunction with PID tuning control is effective for controlling the vibration of the structure.