Showing papers on "Vortex-induced vibration published in 2022"

Recent advancement of flow-induced piezoelectric vibration energy harvesting techniques: principles, structures, and nonlinear designs

Abstract: Abstract Energy harvesting induced from flowing fluids (e.g., air and water flows) is a well-known process, which can be regarded as a sustainable and renewable energy source. In addition to traditional high-efficiency devices (e.g., turbines and watermills), the micro-power extracting technologies based on the flow-induced vibration (FIV) effect have sparked great concerns by virtue of their prospective applications as a self-power source for the microelectronic devices in recent years. This article aims to conduct a comprehensive review for the FIV working principle and their potential applications for energy harvesting. First, various classifications of the FIV effect for energy harvesting are briefly introduced, such as vortex-induced vibration (VIV), galloping, flutter, and wake-induced vibration (WIV). Next, the development of FIV energy harvesting techniques is reviewed to discuss the research works in the past three years. The application of hybrid FIV energy harvesting techniques that can enhance the harvesting performance is also presented. Furthermore, the nonlinear designs of FIV-based energy harvesters are reported in this study, e.g., multi-stability and limit-cycle oscillation (LCO) phenomena. Moreover, advanced FIV-based energy harvesting studies for fluid engineering applications are briefly mentioned. Finally, conclusions and future outlook are summarized.

A Novel Magnetic-Coupling Non-Contact Piezoelectric Wind Energy Harvester With a Compound-Embedded Structure

Abstract: Herein, we propose a magnetic-coupling non-contact piezoelectric wind energy harvester with a compound-embedded structure to improve the power generation performance, environmental adaptability, and reliability. It is mainly composed of a cylinder, a fixed square plate, and a generator which is embedded inside a square shell and indirectly excited by the magnetic force. Unlike most existing harvesters where the performance improvement was achieved by changing cylinder geometry, this harvester realized the enhancement and suppression of the power generation performance via the interference effect of the square plate on the cylinder. The feasibility of the structure and principle of the harvester was proved through simulations and experiments. At the distance-diameter ratio of 2 and the width-diameter ratio of 3, the corresponding Strouhal number of the cylinder varied from 0.223 to 0.113, realizing the conversion from vortex-induced vibration to galloping vibration with larger amplitude. Thus, the maximum voltage of the proposed harvester increased from 7.5 V to 14.8 V, and the corresponding excitation wind speed was reduced by 10.5 m/s. Besides, according to two evaluation indicators proposed in this paper, the performance improvements on the proposed harvester could be characterized as 201.57% and 97.33%, respectively. As a result, the proposed harvester could output a maximum power density of 2.139 mW/cm3, which was 289.62 % higher than the 0.549 mW/cm3of the harvester with a single cylinder.

Comprehensive Experimental Study on Bluff Body Shapes for Vortex-Induced Vibration Piezoelectric Energy Harvesting Mechanisms

Abstract: Vortex-induced vibration (VIV) is an appropriate mechanism to harvest energy from the low-speed wind energy by flexible piezoelectric flags as transducers. To enhance the low-speed wind energy harvesting, this work proposes a novel study on finding the best possible combination of bluff body shape and flag configuration. This study considered several bluff body shapes in different cross sections and flag configurations as two crucial parameters for finding an appropriate combination. In high flexible piezoelectric flag, zero strain or electrical canceling point along the length of the flag is an important parameter that could be considered in energy harvester design. To this purpose, wind tunnel experiments were conducted to investigate the combination of proper bluff body shape and flag configuration to improve the harvester performance. The proposed bluff body shapes are classified by drag and lift coefficients which are calculated by a computational fluid dynamics (CFD) analysis. Then, several flag configurations in different active area length were clamped to these bluff bodies and tested in the wind tunnel in low wind speed range. The analysis in time and frequency domain of the acquired voltage lead to the conclusion that in low wind speed the bluff body with higher drag coefficients can excite more the longer full active piezoelectric flags, consequently generating more energy. However, for the same bluff body shapes, short full active flags generate more energy in higher wind speed. This study could develop a new experimental approach on finding the most favorable combination of bluff body shape and flag configuration which is as important as just considering bluff body shape to improve the efficiency of the low-speed wind piezoelectric energy harvesting system.

Numerical investigations of the flow-induced vibration of a three-dimensional circular cylinder with various symmetric strips attached

Abstract: For a cylinder immersed in a uniform incoming flow, changes to the surface morphology affect the surrounding flow characteristics. This paper first analyzes the effects of 22 types of symmetric strips on the three dimensional (3D) flows around a fixed cylinder. Then, the P5-60-20 cylinder (location , coverage , thickness ) is selected to investigate the transverse flow-induced vibration (FIV) response numerically. Within the range of reduced velocities of , four types of FIV phenomena are recognized: initial and passive upper branches in vortex-induced vibration (VIV), the transition region from VIV to galloping, and pure galloping region. The passive upper branch, caused by the symmetrical strips, differs from the traditional upper branch because of the improved spanwise correlation, reduced nonlinear flow, and in-phase feature between lift and displacement. With the increasing reduced velocities, the symmetric strips trigger the FIV mode transition from VIV to galloping. This region exhibits the properties with unstable vibration amplitude, low spanwise lift correlation, and flow nonlinearity. Until , the pure galloping occurs, replacing the desynchronization region of the smooth cylinder.

Optimization of the Wake Oscillator for Transversal VIV

Abstract: Vibrations of slender structures associated with the external flow present a design challenge for the energy production systems placed in the marine environment. The current study explores the accuracy of the semi-empirical wake oscillator models for vortex-induced vibrations (VIV) based on the optimization of (a) the damping term and (b) empirical coefficients in the fluid equation. This work investigates the effect of ten fluid damping variations, from the classic van der Pol to more sophisticated fifth-order terms, and prediction of the simplified case of the VIV of transversally oscillating rigid structures provides an opportunity for an extended, comprehensive comparison of the performance of tuned models. A constrained nonlinear minimization algorithm in MATLAB is applied to calibrate considered models using the published experimental data, and the weighted objective function is formulated for three different mass ratios. Comparison with several sources of published experimental data for cross-flow oscillations confirms the model accuracy in the mass ratio range. The study indicates the advantageous performance of the models tuned with the medium mass ratio data and highlights some advantages of the Krenk–Nielsen wake oscillator.