In the last decade, an enormous amount of attention has been paid to piezoelectric harvesters due to their flexibility in design and the increasing need for small-scale energy generation. As a result, various energy review papers have been presented by many researchers to cover different aspects of piezoelectric-based energy harvesting, including piezo-materials, modeling approaches, and design points for various applications. Most of these papers have tried to shed light on recent progress in related interdisciplinary fields, and to pave the road for future prospects in the development of these technologies. However, there are some missing parts, overlaps, and even some contradictions in these review papers. In the present review of these review articles, recommendations for future research directions suggested by the review papers have been systematically summed up under one umbrella. In the final section, topics for missing review papers, concluding remarks on outlooks and possible research topics, as well as potentially misleading strategies, have been presented. The review papers have been evaluated based on their merits and subcategories and the authors’ choice papers have been presented for each section based on clear classification criteria.
Fracture of blades is usually catastrophic and creates serious damages in the turbomachines. Blades are subjected to high centrifugal force, oscillating stresses, and high temperature which makes their life limited. Therefore, blades should be checked and replaced at specified intervals or utilize a health monitoring method for them. Crack detection by nondestructive tests can only be performed during machine overhaul which is not suitable for monitoring purposes. Blade tip timing (BTT) method as a noncontact monitoring technique is spreading for health monitoring of the turbine blades. One of the main challenges of BTT method is identification of vibration parameters from one per revolution samples which is quite below Nyquist sampling rate. In this study, a new method for derivation of blade asynchronous vibration parameters from BTT data is proposed. The proposed method requires only two BTT sensors and applies least mean square algorithm to identify frequency and amplitude of blade vibration. These parameters can be further used as blade health indicators to predict defect growth in the blades. Robustness of the proposed method against measurement noise which is an important factor has been examined by numerical simulation. An experimental test was conducted on a bladed disk to show efficiency of the proposed method.
Wind‐induced ground vibrations are a source of noise in seismic surveys. In a previous study, a wind‐ground coupling theory was developed to predict the power spectral density of ground motions caused by wind perturbations on the ground surface. The prediction was developed using a superposition of the point source response of an elastic isotropic homogeneous medium deforming quasi‐statically with the statistical description of the wind‐induced pressure fluctuations on the ground. Model predictions and field measurements were in agreement for the normal component of the displacement but underpredicted the horizontal component. In this paper, two generalizations are investigated to see if they lead to increased horizontal displacement predictions: (1) First, the dynamic point source response is calculated and incorporated into the ground displacement calculation. Measured ground responses are used to incorporate losses into the dynamic calculation. (2) The quasi‐static response function for three different types of nonuniform grounds are calculated and used in the seismic wind noise superposition. The dynamic point source response and the three more realistic ground models result in larger horizontal displacements for the point source at distances on the order of 1 m or greater from the source. However, the superposition to predict the seismic wind noise is dominated by the displacements very close to the point source where the prediction is unchanged. This research indicates that the modeling of the wind‐induced pressure source distribution must be improved to predict the observed equivalency of the vertical and horizontal displacements.
Lumped element (LE) modeling is one of the simplest and fastest tools for designing and predicting the performance of miniature speakers. Tweeters are being incorporated more frequently to extend the high-frequency range of earphones in the commercial earphone market with balanced armature (BA) receivers being commonly used as tweeters. To support this trend, it is necessary to develop LE models of BAs that are accurate at high frequencies. Developing accurate models has been challenging due to several mechanical and acoustic modes interacting at frequencies over 10 kHz. Based on the work of Sun and Hu [“Lumped element multimode modeling of balanced-armature receiver using modal analysis,” J. Vib. Acoust. 2016 Dec 1;138(6)], a multimode LE modeling method using finite element (FE) modal analysis is implemented and compared with older LE models. The simulation results are compared with experimental data for several production models of BA. The multimode LE method shows significant improvements compared to the old single-mode LE models in predicting BA receiver acoustic response, especially at frequencies above 10 kHz.
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