Vibration Energy Harvester Based on Torsionally Oscillating Magnet

Most of the miniaturized electromagnetic vibrational energy harvesters (EVEHs) are based on oscillating proof mass suspended by several springs or a cantilever structure. Such structural feature limits the miniaturization of the device’s footprint. This paper presents an EVEH device based on a torsional vibrating magnet over a stack of flexible planar coils. The torsional movement of the magnet is enabled by microfabricated silicon torsional springs, which effectively reduce the footprint of the device. With a size of 1 cm × 1 cm × 1.08 cm, the proposed EVEH is capable of generating an open-circuit peak-to-peak voltage of 169 mV and a power of 6.9 μW, under a sinusoidal excitation of ±0.5 g (g = 9.8 m/s2) and frequency of 96 Hz. At elevated acceleration levels, the maximum peak-to-peak output voltage is 222 mV under the acceleration of 7 g (±3.5 g).

Non-Linear Response of Cable-Mass-Spring System in High-Rise Buildings under Stochastic Seismic Excitation

In high-rise buildings earthquake ground motions induce bending deformation of the host structure. Large dynamic displacements at the top of the building can be observed which in turn lead to the excitation of the cables/ropes within lift installations. In this paper, the stochastic dynamics of a cable with a spring-damper and a mass system deployed in a tall cantilever structure under earthquake excitation is considered. The non-linear system is developed to describe lateral displacements of a vertical cable with a concentrated mass attached at its lower end. The system is moving slowly in the vertical direction. The horizontal displacements of the main mass are constrained by a spring-viscous damping element. The earthquake ground motions are modelled as a filtered Gaussian white noise stochastic process. The equivalent linearization technique is then used to replace the original non-linear system with a linear one with the coefficients determined by utilising the minimization of the mean-square error between both systems. Mean values, variances and covariances of particular random state variables have been obtained by using the numerical calculation. The received results were compared with the deterministic response of the system to the harmonic process and were verified against results obtained by Monte Carlo simulation.

A speed measurement method for underwater robots using an artificial lateral line sensor

Underwater robot technology has made considerable progress in recent years. However, due to the harsh environment and noise in the flow field near the underwater robots, it is difficult to measure some basic parameters, including swimming speed. The traditional speed measurement methods for underwater robots have the disadvantages of being limited by the environment and bulky. In order to overcome these shortcomings, an artificial lateral line sensor based on cantilever structure was developed in this paper. According to the deformation of cantilever beam under water impact, the swimming speed of underwater robots can be measured. In addition, an "end-to-end" calibration algorithm was proposed to calibrate the artificial lateral line sensor in the noisy environment, avoiding the complicated noise modeling and filter design process. To reduce the risk of overfitting, a hybrid loss function based on physical model was adopted. Compared with the classical calibration method, our method can reduce the error by 47.8%. Our sensor achieved an average absolute error of 0.07897 m/s, and can measure water speed up to 3 m/s.

Flexural–Torsional Free Vibration Analysis of a Double-Cantilever Structure

This paper aims to investigate the free coupled flexural–torsional vibrations of a double-cantilever structure. The structure consists of two identical Euler–Bernoulli cantilever beams with a piezoelectric layer on top. The beams are connected by a rigid tip connection at their free ends. The double-cantilever structure in this study vibrates in two distinct modes: flexural mode or coupled flexural–torsional mode. The flexural mode refers to the in-phase flexural vibrations of the two cantilever beams resulting in translation of the tip connection, while the coupled flexural–torsional mode refers to the coupled flexural–torsional vibrations of the cantilever beams resulting in rotation of the tip connection. The latter is the main interest of this research. The governing equations of motion and boundary conditions are developed using Hamilton’s principle. Two uncoupled equations are realized for each beam: one corresponding to the flexural vibrations and the other one corresponding to the torsional vibrations. The characteristic equations for both the flexural and the coupled flexural–torsional vibration modes are derived and solved to find the natural frequencies corresponding to each mode of vibration. The orthogonality condition among the mode shapes is derived and utilized to determine the modal coefficients corresponding to each mode of vibration. Moreover, the analytical and experimental investigations show that the coupled flexural–torsional fundamental frequency of the structure is dependent on dimensional parameters including the length of the cantilever beams and the length of the tip connection.

Surface contour error model of five-axis machining considering multifactor coupling effects

During five-axis flank milling procedure, the static deflection of workpiece and cutter creates surface errors that lead to defects in projects with strict requirements, especially in thin-walled parts industry. Focusing on the mentioned issues, the surface contour error is predicted in this paper considering the coupling between the deflection and cutting force. First, an efficient calculation method of the cutting force is presented in five-axis flank milling. This method accounts for the impact of cutter runout on cutter/workpiece engagement (CWE) and the instantaneous undeformed chip thickness (IUCT). Then, a cutter is modelled as a cantilever structure and thus an analytical solution for the deflection of the end mill can be obtained. Next, the flexible cutting force is distributed on a finite element (FE) model of workpiece, while the workpiece stiffness keeps varying with the material removal. Subsequently, a flexible iterative calculation method for achieving deflection prediction is established. Finally, the prediction model is proven by machining tests of an S-shaped specimen in which predicted values of the surface error match with the experimental results.

Tunable Stiffness and Damping Study on Flexible PVC Cantilever Structure Embedded with MR Fluid

The stiffness and damping of a flexible smart cantilever structure controlled by a magnetic field is investigated in this research. The cantilever structure is fabricated by using flexible polyvinyl chloride as a host structure of rectangular cross-section embedded with magnetorheological (MR) fluid. The deflection of the cantilever structure at the free end is used to analyze the stiffness change of the cantilever structure. The stiffness of the specimen with MR fluid at magnetic flux density of 0.171T is greater than that of the specimen without subjected to magnetic field. The strength of the applied magnetic field is directly related to the structure’s stiffness. Under the influence of a magnetic field, the MR fluid embedded inside the flexible PVC cantilever structure significantly dampens the vibrations of the structure.

Bandwidth Broadening of Piezoelectric Energy Harvesters Using Arrays of a Proposed Piezoelectric Cantilever Structure

One of the most important challenges in the design of the piezoelectric energy harvester is its narrow bandwidth. Most of the input vibration sources are exposed to frequency variation during their operation. The piezoelectric energy harvester’s narrow bandwidth makes it difficult for the harvester to track the variations of the input vibration source frequency. Thus, the harvester’s output power and overall performance is expected to decline from the designed value. This current study aims to solve the problem of the piezoelectric energy harvester’s narrow bandwidth. The main objective is to achieve bandwidth broadening which is carried out by segmenting the piezoelectric material of the energy harvester into n segments; where n could be more than one. Three arrays with two, four, and six beams are shaped with two piezoelectric segments. The effect of changing the length of the piezoelectric material segment on the resonant frequency, output power, and bandwidth, as well as the frequency response is investigated. The proposed piezoelectric energy harvesters were implemented utilizing a finite element method (FEM) simulation in a MATLAB environment. The results show that increasing the number of array beams increases the output power and bandwidth. For the three-beam arrays, at n equals 2, 6 mW output power and a 9 Hz bandwidth were obtained. Moreover, the bandwidth of such arrays covered around 5% deviation from its resonant frequency. All structures were designed to operate as a steel wheel safety sensor which could be used in train tracks.

Design and simulation of piezoelectric nano cylindrical hollow structure for energy harnessing applications

This article investigates piezoelectric materials for harnessing vibrational energy. A nano hollow cylindrical structure based on various piezoelectric materials was designed and utilised to generate the voltage. An accurate and efficient model is developed here, so as to optimized the efficiency of the piezoelectric energy harvester. This work analyses the piezoelectric actuator deflection and involves the Eigen frequency computation. A measurement methodology for investigating the mechanical and electrical behaviour of vibrational harvester's was modelled and analysed by finite element method using COMSOL software. The energy harvesting structure was developed and tested with different piezoelectric materials to attain appreciable voltage through a small deflection. The Simulated results predicts that for the same pressure range, different piezoelectric materials have the different output voltage and Eigen frequencies. The maximum voltage was observed for Barium Titanate (3.0847 V at 250 µm), along with poled Polyvinylidene fluoride. In addition, a comparison was made with different piezoelectric materials ideally suited to intelligent cantilever structure. For optimizing the performance of the piezoelectric energy harvester an accurate and efficient model is required, which was developed in this simulation study. A high voltage value with a small deflection through a cylindrical hollow structure was designed and tested using various piezoelectric materials in this study.

Dynamic Behavior of a Simplified Cantilever With Progressive Static Loading due to Ratchet Deformation

The importance of the severe accident mitigation under beyond design-basis events (BDBEs) was realized to achieve the nuclear safety through the Fukushima accident. Failure mode estimation of essential components in nuclear facilities is necessary to take appropriate measures against the severe accident conditions. The failure mode of piping systems exposed to excessive seismic loading was found to be ratchet deformation followed by fatigue failure through many experimental tests in the past, whereas the failure of Test #37 of Pipe-fitting dynamic reliability program (PFDRP) conducted by EPRI was unexpected and its failure mechanism remains unclear, as it was often suspected to have been failed in plastic collapse. In the past research, the constant stress on the structure such as a dead-weight was revealed to significantly affect the failure mode and failure level of structures under seismic excitation. In this study, the constant stress components which can increase due to the ratchet deformation during a seismic excitation is focused and is analytically examined to clarify the effects on the failure mode of structures by using a cantilever structure with various dead-weight conditions and a constant cycles of sinusoidal waves which essentially represents the seismic loading with specific frequency ratios to establish the failure estimation of a structure exposed to seismic loading.