Modeling of a heaving buoy wave energy converter with stacked dielectric elastomer generator

This paper introduces a novel architecture of Wave Energy Converter (WEC) provided with a Dielectric Elastomer (DE) Power Take-Off (PTO) system. The device, named Poly-Buoy, includes a heaving buoy as primary interface, that captures the mechanical energy from waves, and a DE Generator (DEG), made by stacked layers of silicone elastomer, that converts mechanical energy into electricity. A mathematical model of the Poly-Buoy is proposed, which includes analytical electro-hyperlastic equations for the DEG and a linear model for wave-buoy hydrodynamics. Procedures for the design and optimization of different layouts and control strategies for the DE-PTO are introduced that specifically consider single-DEG and dual-DEG architectures. A numerical case study is also reported for specific geometrical dimensions of the buoy and specific wave climate data

Modelling and Control of Lozenge-Shaped Dielectric Elastomer Generators

none3noDielectric Elastomers (DEs) are a very promising technology for the development of energy harvesting devices based on the variable-capacitance electrostatic generator principle. As compared to other technologies, DE Generators (DEGs) are solid-state energy conversion systems which potentially feature: 1) large energy densities, 2) good energy conversion efficiency that is rather independent of cycle frequency, 3) easiness of manufacturing and assembling, 4) high shock resistance, 5) silent operation, 6) low cost. Envisioned applications for DEGs are in devices that convert ocean wave energy into usable electricity.This paper introduces the Lozenge-Shaped DEG (LS-DEG) that is a specific type of planar DE transducer with one degree of freedom. A LS-DEG consists of a planar DE membrane that is connected along its perimeter to the links of a parallelogram four-bar mechanism. As the mechanism is put into reciprocal motion, the DE membrane varies its capacitance that is then employed as a charge pump to convert external mechanical work into usable electricity.Specifically, this paper describes the functioning principle of LS-DEGs, and provides a comparison between different hyper-elastic models that can be used to predict the energy harvesting performances of realistic prototypes. Case studies are presented which address the constrained optimization of LS-DEGs subjected to failure criteria and practical design constraints.nonenoneMoretti, G; Fontana, M; Vertechy, RMoretti, G; Fontana, M; Vertechy,

Experimental characterization of a Circular Diaphragm Dielectric Elastomer Generators

Inflated Circular Diaphragm Dielectric Elastomer Generators (CD-DEGs) are a special embodiment of polymeric transducer that can be used to convert pneumatic energy into high-voltage direct-current electricity. Potential application of CD-DEGs is as power take-off system for wave energy converters that are based on the oscillating water column principle. Optimal usage of CD-DEGs requires the adequate knowledge of their dynamic electro-mechanical response. This paper presents a test-rig for the experimental study of the dynamic response of CD-DEGs under different programmable electro-mechanical loading conditions. Experimental results acquired on the test-rig are also presented, which highlight the dynamic performances of CD-DEGs that are based on acrylic elastomer membranes and carbon conductive grease electrodes

Simplified model of offshore Airborne Wind Energy Converters

Airborne Wind Energy Converters (AWECs) are promising devices that, thanks to tethered airborne systems, are able to harvest energy of winds blowing at an altitude which is not reachable by traditional wind turbines. This paper is meant to provide an analysis and a preliminary evaluation of an AWEC installed on a floating offshore platform. A minimum complexity dynamic model is developed including a moored heaving platform coupled with the dynamics of an AWEC in steady crosswind flight. A numerical case study is presented through the analysis of different geometrical sizes for the platform and for the airborne components. The results show that offshore AWECs are theoretically viable and they may also be more efficient than grounded devices by taking advantage of a small amount of additionally harvested power from ocean waves

Parallelogram-shaped dielectric elastomer generators: Analytical model and experimental validation

Dielectric elastomers are smart materials that can be used to conceive solid-state electromechanical transducers such as actuators, sensors, and generators. Dielectric elastomer generators, in particular, are very promising for energy harvesting applications because they potentially feature large energy densities, good conversion efficiencies, good shock and corrosion resistance, and low cost. In this article, a novel concept of parallelogram-shaped dielectric elastomer generator is presented and analyzed. Parallelogram-shaped dielectric elastomer generators are rotary variable capacitance transducers, which are made by planar dielectric elastomer membranes that are covered with compliant electrodes and clamped along their perimeter to the links of a parallelogram four-bar mechanism. First, an analytical model for the electro-hyperelastic response of the parallelogram-shaped dielectric elastomer generator is described and used to assess the maximum theoretical performances of the device. Then, an experimental case study with a parallelogram-shaped dielectric elastomer generator prototype featuring a natural rubber dielectric elastomer membrane and carbon conductive grease electrodes is presented. Simulation and experimental results demonstrate the practical feasibility of the parallelogram-shaped dielectric elastomer generator concept

Model-based design and optimization of a dielectric elastomer power take-off for oscillating wave surge energy converters

This paper investigates a new kind of device for producing electricity from the mechanical energy carried by ocean waves. The proposed machine, named poly-surge, is based on an existing sea-bottom hinged surging-flap concept that is equipped with a new power take-off (PTO) system based on a novel soft dielectric elastomer (DE) transducer. DEs are highly deformable polymeric materials that can be used to conceive electrostatic generators relying on capacitance variation. This kind of generators shows a number of features that well match the requirements of a wave energy converter since they are light-weight, low-cost, tolerant to salty/aggressive marine environment, noise-free during operation, and easy to manufacture and install. The considered poly-surge converter employs a parallelogram-shaped DE generator (PS-DEG) arranged in a dual agonist–antagonist configuration, which makes it possible to provide the flap with controllable bidirectional torques. In this paper, first a complete wave-to-wire multiphysics model of the overall system is described that assumes a simplified hydrodynamic response for the hinged-flap and an electro-hyperelastic behaviour of the PS-DEG. Second, a procedure is presented for the dimensioning and optimization of the PS-DEG for given sets of poly-surge flap dimensions, wave-climate information and constraints on both design and operational variables. Finally, simulation results are provided to demonstrate that the poly-surge can achieve quasi-optimal power production with a properly designed agonist–antagonist DEG PTO system

Experimental characterization of a new class of polymeric-wire coiled transducers

The recent discovery of a new kind of thermo-Active coiled polymeric wires has opened new perspectives for the implementation of a novel class of actuators that can be easily and effectively manufactured using low-cost materials such as sewing threads or finishing lines. These new devices feature large displacements in response to temperature variations and show very promising performance in terms of energy and power densities. With the aim of providing information and data useful for the future engineering applications of polymeric coiled actuators, a custom experimental test-bench and procedure have been developed and employed to characterise their thermo-mechanical response. Such a test-bench has been designed to run isothermal and isometric tensile tests on a set of sample actuators that are fabricated with a repeatable process. This paper provides technical details on the manufacturing process of such sample actuators and on the design and operation of the test-bench. Preliminary experimental results are finally reported

A new class of variable capacitance generators based on the dielectric fluid transducer

This paper introduces the novel concept of dielectric fluid transducer (DFT), which is an electrostatic variable capacitance transducer made by compliant electrodes, solid dielectrics and a dielectric fluid with variable volume and/or shape. The DFT can be employed in actuator mode and generator mode. In this work, DFTs are studied as electromechanical generators able to convert oscillating mechanical energy into direct current electricity. Beside illustrating the working principle of dielectric fluid generators (DFGs), we introduce different architectural implementations and provide considerations on limitations and best practices for their design. Additionally, the proposed concept is demonstrated in a preliminary experimental test campaign conducted on a first DFG prototype. During experimental tests a maximum energy per cycle of and maximum power of has been converted, with a conversion efficiency up to 30%. These figures correspond to converted energy densities of with respect to the displaced dielectric fluid and with respect to the mass of the solid dielectric. This promising performance can be largely improved through the optimization of device topology and dimensions, as well as by the adoption of more performing conductive and dielectric materials