Energy Harvesting Using Flextensional Piezoelectric Energy Harvesters in Resonance and Off-Resonance Modes

Energy harvesting technologies are integrated into various modern devices and systems. These systems include Artificial Intelligence (AI) systems, Internet of Things (IoT), various types of energy harvesters are integrated in many engineering applications such as automotive, aerospace and ocean engineering. In order to develop a fully functioning stand-alone system, it is essential to integrate it with a built in power source such as a battery or a power generator. Also, in many situations, city power sources might not be available. Therefore, reliable, renewable and sustainable local power generators are desired. Piezoelectric energy harvesting (PEH) technologies, which are piezoelectric material-based devices, are one of the best candidates for this job. Piezoelectric energy harvesters convert mechanical energy from vibrating or moving objects to electrical energy. These devices have the highest capability of designing self-powered systems as they are not weather dependent and they are capable of harvesting both small or large mechanical movements into electrical energy. The piezoelectric materials are materials that generate electrical charges when mechanical stress or force is exerted on them. On the other hand, they deform when an electric voltage is applied to them. The piezoelectric-based energy harvesters are small and effective devices that promise future engineering systems to be more intelligent, reliable and environmentally friendly. Designing a piezoelectric device is cumbersome, and it is indispensable to have a comprehensive understating of many engineering disciplines before delving into designing a new device or redesigning an existing device. These disciplines include mechanical engineering, electrical engineering, materials sciences, and device physics. In this thesis, comprehensive mathematical and experimental investigations were done for modeling piezoelectric multi-later stacks and Flextensional Energy Harvesters in resonance and in off- resonance modes. For the resonance mode, mathematical and variational approaches were used to modeling a selected piezoelectric multi-layer stack found in the market; the models are a static model, single degree of freedom model (SDOF), a distributed parameter model and a finite element model for the resonance mode, a finite element model (using ANSYS) was used to model a single and a multiple stage Flexteisonal Energy Harvester. To validate off-resonance results, previously published experimental results were used; however, for the resonance mode an experiment was carried out to validate the numerical model\u27s results for the multi-stage Energy Harvester. As for the single stage Flextensional Energy Harvester, previously published experimental results were used to validate the finite element model. The advantages and disadvantages of different models and approaches are compared and discussed

Dynamic modeling of the motions of variable-shape wave energy converters

In the recently introduced Variable-Shape heaving wave energy converters, the buoy changes its shape actively in response to changing incident waves. In this study, a Lagrangian approach for the dynamic modeling of a spherical Variable-Shape Wave Energy Converter is described. The classical bending theory is used to write the stress-strain equations for the flexible body using Love's approximation. The elastic spherical shell is assumed to have an axisymmetric vibrational behavior. The Rayleigh-Ritz discretization method is adopted to find an approximate solution for the vibration model of the spherical shell. A novel equation of motion is presented that serves as a substitute for Cummins equation for flexible buoys. Also, novel hydrodynamic coefficients that account for the buoy mode shapes are proposed. The developed dynamic model is coupled with the open-source boundary element method software NEMOH. Two-way and one-way Fluid-Structure Interaction simulations are performed using MATLAB to study the effect of using a flexible shape buoy in the wave energy converter on its trajectory and power production. Finally, the variable shape buoy was able to harvest more energy for all the tested wave conditions.Comment: 29 pages, 13 figures; Renewable and Sustainable Energy Reviews, v173 (2023) in progress. arXiv admin note: substantial text overlap with arXiv:2201.0894

Dynamic Modeling Of Spherical Variable-Shape Wave Energy Converters

In the recently introduced Variable-Shape heaving wave energy converters, the buoy changes its shape in response to changing incident waves actively. In this study, the dynamic model for a spherical Variable-Shape Wave Energy Converter is developed using the Lagrangian approach. The classical bending theory is used to write the stress-strain equations for the flexible body using Love's first approximation. The elastic spherical shell is assumed to have an axisymmetric vibration behavior. The Rayleigh-Ritz discretization method is adopted to find an approximate solution for the vibration model of the spherical shell. One-way Fluid-Structure Interaction simulations are performed using MATLAB to validate the developed dynamic model and to study the effect of using a flexible buoy in the wave energy converter on its trajectory and power production.Comment: 24 pages, 8 figures, and 2 tables, the paper is currently under review (journal

Numerical study for the use of different nozzle shapes in microscale channels for producing clean energy

Nowadays, most rural and hilly areas use the small and microscale plants to produce electricity; it is cheap, available and effective. Utilizing hydrokinetic turbines in flow of rivers, canal or channel to produce power has been a topic of considerable interest to researchers for past years. Many countries that are surrounded by irrigation or rainy channels have a great potential for developing this technology. Development of open flow microchannels that suit these countries has a main problem, which is low velocity of current appears, hence deploying nozzle in-stream open channels flow is the brilliant method for increasing the channels current flow systems’ efficiency. The nozzle is believed to have an ability of concentrating the flow direction whilst increasing the flow velocity. In this study, the effects of nozzle geometrical parameters such as diameter ratio, nozzle configuration and nozzle edges shape on the characteristics of the flow in the microscale rectangular channels have been investigated numerically, using a finite volume RANSE code ANSYS CFX. The physical parameters were reported for a range of diameter ratio (d2/d1) from 5/6 to 1/6 and nozzle length (Ln) of 0.8 m for various nozzle shapes. We also proposed a new approach which is the use of NACA 0025 aerofoils as a deploying nozzle in channels. The results of the current study showed that, although the decrease in the nozzle diameter ratio led to an increase of the flow velocity through the channel but it can affect drastically on the flow pattern, especially the free surface, at the nozzle area, which may reduce the amount of the generated power, thus the study concluded with optimum diameter ratio, which was 2/3. The flow patterns improved with the curved edges shape; the NACA shape gave the most preferable results

Modeling and optimal control of flexible wave energy converters

Wave energy converters are devices used to harvest energy from ocean waves. This thesis focuses on a particular type of wave energy converter called flexible buoy wave energy converters (FWECs), also called the variable-shape wave energy converters (VSB WECs). Both names will be used interchangeably in this thesis. This is one of the earliest theses to address flexible buoy wave energy converters' modeling and optimal control problems. For a conventional fixed-shape buoy (FSB) WEC, the power take-off unit (PTO) usually needs to apply a spring-like force on the buoy in order to harvest energy in some optimal sense. This results in a bidirectional power flow in the PTO. The FWECs were recently introduced to eliminate the need for this bidirectional power flow. By eliminating the bidirectional power flow when using FWECs, the cost, and complexity of the PTO are significantly reduced while still harvesting energy at a level comparable to that of a conventional FSB WEC that uses bidirectional power flow. This concept can be conceived as obtaining the spring-like force from the waves rather than relying on the PTO. It is inspired by how marine animals employ rapid shape change for propulsion and maneuvering. The motion of the proposed FWEC would resemble that of a jellyfish, continuously changing its shape to favorably alter the wave field around it, and harvest more energy using a relatively simple PTO unit. This work presents low-fidelity and high-fidelity modeling for FWECs, and derives the optimal control laws for actively and passively controlled buoy shapes. This thesis uses Lagrangian mechanics to derive a low-fidelity Fluid-Structure Interactions (FSI) model for spherical buoys. This model describes shell deformations, the expression for hydrodynamic/hydrostatic coefficients, and can handle constraints applied to the shell deformations and the center of gravity (c.g.) motions. Additionally, the optimal control laws are derived using the Pontryagin minimum principle, and these laws are valid for both passively and actively controlled shells. Although these control laws are derived for FWECs (VSB WECs) and tested on spherical buoys, they can also be applied to any buoy shape, FSB WECs with multiple degrees of freedom, and wave energy converter arrays. Furthermore, this thesis presents the first high-fidelity FSI model for FWECs, where a numerical wave tank is developed using computational fluid dynamics (CFD) and utilizes finite element analysis to simulate the hyperelastic buoy. The FSI model is developed using ANSYS Workbench, where the pressures on the buoy obtained in the fluid solver are mapped to the buoy mesh in the structural solver. For this model, a passively controlled PTO unit shell is used, and internal pressure is applied inside the buoy to prevent excessive deformation of the shell. The results presented in this thesis demonstrate the energy harvesting capabilities of FWECs are superior to the conventional wave energy converters

Study of the effect of low profile vortex generators on ship viscous resistance

A study of the effect of the well-known aerodynamic device low profile vortex generators (VGs) on the viscous resistance of the DTMB 5415 ship hull form through the control of the ship boundary layer separation is performed using the finite volume code Ansys CFX. The tetrahedral unstructural grids have been used for meshing the different cases. Different types of VGs have been tested, but the study has forced on two main types of VGs. The effects of VGs on the ship viscous resistance and its components have been investigated for the different cases in this study, and comparisons between the various results have been made

Effect of adding trunk core training exercise to conventional therapy on patients with chronic mechanical neck pain

Background: One of the most frequent causes of musculoskeletal pain in the general population is cervicalgia, sometimes known as neck pain. Its estimated prevalence ranges from 16.7% to 71.5 percent, and it should be noted that up to 50% of these cases may develop into chronic conditions. In this study, patients with persistent mechanical neck pain were examined to determine the effectiveness of trunk core training exercises on pain, range of motion, functional impairment, and muscle activity. Purpose: The goal of the study was to determine the impact of adding core training to patients' existing conventional treatments for chronic mechanical neck pain. Methods: Twenty male and twenty female patients with persistent mechanical neck pain, ranging in age from 18 to 40, participated in this study. The cases were classified into two equal groups randomly (A and B). Group A has got standard physiotherapy program (Passive stretching of the upper fibers of trapezius, sternocleidomastoid, and scalene muscles, Isometric strengthening exercises of neck muscles, hot pack). Group B has obtained standard physiotherapy program in addition to trunk core training program.&nbsp

Numerical investigation of curvature and torsion effects on water flow field in helical rectangular channels

Helical channels have a wide range of applications in petroleum engineering, nuclear, heat exchanger, chemical, mineral and polymer industries. They are used in the separation processes for fluids of different densities. The centrifugal force, free surface and geometrical effects of the helical channel make the flow pattern more complicated; hence it is very difficult to perform physical experiment to predict channel performance. Computational Fluid Dynamics (CFD) can be suitable alternative for studying the flow pattern characteristics in helical channels. The different ranges of dimensional parameters, such as curvature and torsion, often cause various flow regimes in the helical channels. In this study, the effects of physical parameters such as curvature, torsion, Reynolds number, Froude number and Dean Number on the characteristics of the turbulent flow in helical rectangular channels have been investigated numerically, using a finite volume RANSE code Fluent of Ansys workbench 10.1 UTM licensed. The physical parameters were reported for range of curvature (d) of 0.16 to 0.51 and torsion (?) of 0.032 to 0.1 .The numerical results of this study showed that the decrease in the channel curvature and the increase in the channel torsion numbers led to the increase of the flow velocity inside the channel and the change in the shape of water free surface at given Dean, Reynolds and Froude numbers

Operation, performance and economic analysis of low head micro-hydropower turbines for rural and remote areas: A review

Electrical power is essential in commercial, economic and social investments especially in emergent countries. Hydropower energy has become one of the most suitable and efficient sources of renewable energy, though it has taken more than a century of experience to actually generate efficient electricity for supply. Nowadays, most rural areas in developed and developing countries use cheap and effective micro-hydropower plants for producing electricity. To achieve more efficiency, researchers are looking forward to using simple turbines for achieving good performance with minimum initial and running cost, for utilization especially in poor countries. This paper presents a review of low head micro-hydropower turbines; focusing on categories, performance, operation and cost