Evaluation of the Performance of a Taut-moored Dual-body Direct-drive Wave Energy Converter Through Numerical Modeling and Physical Testing

Evaluation of the Performance of a Taut-moored Dual-body Direct-drive Wave Energy Converter Through Numerical Modeling and Physical Testing
Author: David E. Elwood
Publisher:
Total Pages: 196
Release: 2009
Genre: Electric current converters
ISBN:

With energy prices rising and increasing concern about the influence of fossil fuels on climate change, wave energy systems are on the verge of commercial implementation. These first generation wave energy converters utilize either pneumatics or hydraulics to convert the mechanical energy of waves into electricity. For the last several years, the wave energy research group at Oregon State University has focused on increasing the efficiency of wave energy conversion systems by developing direct drive power take-off systems. Beginning in the fall of 2006 an interdisciplinary team was tasked with designing and building a 1kW direct drive wave energy converter to be tested in the open ocean. Their device, the SeaBeavI, provided a proof of concept for a taught moored, dual body, wave energy conversion system using a linear generator for power take-off. To evaluate the performance of the SeBeavI system a method was developed to incorporate measured forces from the linear generator into a coupled model of the system. This thesis is comprised of one conference paper and two journal papers. The conference paper provides an overview of the design and construction of the SeaBeavI. The first journal paper presents an in-depth description of the physical testing and numerical modeling of the system. The second journal paper provides performance predictions for the device based on the combined numerical and experimental results.

Modelling and Optimization of Wave Energy Converters

Modelling and Optimization of Wave Energy Converters
Author: Dezhi Ning
Publisher: CRC Press
Total Pages: 384
Release: 2022-07-28
Genre: Technology & Engineering
ISBN: 1000629112

Wave energy offers a promising renewable energy source, however, technologies converting wave energy into useful electricity face many design challenges. This guide presents numerical modelling and optimization methods for the development of wave energy converter technologies, from principles to applications. It covers the development status and perspectives of wave energy converter systems; the fundamental theories on wave power absorption; the modern wave energy converter concepts including oscillating bodies in single and multiple degree of freedom and oscillating water column technologies; and the relatively hitherto unexplored topic of wave energy harvesting farms. It can be used as a specialist student textbook as well as a reference book for the design of wave energy harvesting systems, across a broad range of disciplines, including renewable energy, marine engineering, infrastructure engineering, hydrodynamics, ocean science, and mechatronics engineering. The Open Access version of this book, available at www.routledge.com has been made available under a Creative Commons Attribution-Non Commercial-No Derivatives 4.0 license.

Analysis and Development of a Three Body Heaving Wave Energy Converter

Analysis and Development of a Three Body Heaving Wave Energy Converter
Author: Scott J. Beatty
Publisher:
Total Pages:
Release: 2009
Genre:
ISBN:

A relative motion based heaving point absorber wave energy converter is being co-developed by researchers at the University of Victoria and SyncWave Systems Inc. To that end--this thesis represents a multi-faceted contribution to the development effort. A small scale two-body prototype wave energy converter was developed and tested in a wave tank. Although experimental problems were encountered, the results compare reasonably well to the output of a two degree of freedom linear dynamics model in the frequency domain. A two-body wave energy converter design is parameterized as a basis for an optimization and sensitivity study undertaken to illustrate the potential benefits of frequency response tuning. Further, a mechanical system concept for frequency response tuning is presented. The two degree of freedom model is expanded to three degrees of freedom to account for the tuning system. An optimization procedure, utilizing a Sequential Quadratic Programming algorithm, is developed to establish control schedules to maximize power capture as a function of the control variables. A spectral approach is developed to estimate WEC power capture in irregular waves. Finally, as a case study, the modeling, optimization, and spectral methods are applied to predict performance for a large scale wave energy converter deployed offshore of a remote Alaskan island. Using archived sea-state data and community electrical load profiles, a wave/diesel hybrid integration with the remote Alaskan community power system is assessed to be technologically feasible.

Ocean Wave Energy

Ocean Wave Energy
Author: Joao Cruz
Publisher: Springer Science & Business Media
Total Pages: 435
Release: 2007-12-22
Genre: Technology & Engineering
ISBN: 3540748954

The authors of this timely reference provide an updated and global view on ocean wave energy conversion – and they do so for wave energy developers as well as for students and professors. The book is orientated to the practical solutions that this new industry has found so far and the problems that any device needs to face. It describes the actual principles applied to machines that convert wave power to electricity and examines state-of-the-art modern systems.

Design and Control of a Floating Wave-Energy Converter Utilizing a Permanent Magnet Linear Generator

Design and Control of a Floating Wave-Energy Converter Utilizing a Permanent Magnet Linear Generator
Author: Nathan Michael Tom
Publisher:
Total Pages: 160
Release: 2013
Genre:
ISBN:

This thesis considers the design, optimization, and control of a coupled cylindrical floater and permanent magnet linear generator for wave-energy conversion. The investigation begins with the construction of the time-domain equation of motion for a generic floating body. The construction of a physical cylindrical floater is followed by a description of the experiments completed to verify free-motion and wave-exciting force predictions. The time-domain equation of motion was compared against experiments where it was found that corrective terms needed to be added due to the presence of viscosity. Initial low motion amplitudes lead to evaluation of the hydrodynamic performance between a floater with a flat and rounded-hemispherical bottom. Experimental results demonstrated that motion amplitudes can be over predicted by a factor of 2 when neglecting the effects of viscosity. Second, modifications to the design, fabrication process, and material of a permanent magnet linear generator (PMLG) will be discussed with the aim of increasing both power output and mechanical-to-electrical conversion efficiency. In order to evaluate the performance of the power-take-off unit a dry-bench test was completed which consisted of driving the armature of the PMLG at various frequencies with a fixed motion amplitude. The force signature from the bench test was used to extract the spring, damping, and inertia force coefficients due to the influence of the PMLG. The force coefficients were obtained for various speeds, resistive loads, and magnet coil gap widths. The floater equation of motion was modified to accommodate the influence of the PMLG to predict the coupled system performance. As the damping coefficient was the dominant contribution to the PMLG reaction force, the optimum non time-varying damping values were presented for all frequencies, recovering the well known impedance matching at the coupled resonance frequency. Model-scale tests of the coupled floater-generator system were performed at the UC-Berkeley Model Testing Facility to verify the optimum conditions for energy extraction. In an effort to further maximize power absorption, nonlinear model predictive control (NMPC) was applied to the model-scale point absorber. The NMPC strategy was set up as a nonlinear optimization problem utilizing the Interior Point OPTimizer (IPOPT) package to obtain the optimal time-varying generator damping from the PMLG. This was accompanied by a latching damper that was allowed to periodically slow the floater velocity in an effort to increase power absorption. The emphasis on this work has been on sub-optimal strategies that limit the power-take-off unit to behave as a generator, thereby minimizing energy return to the waves. It was found that the ideal NMPC strategy required a PTO unit that could be turned on and off instantaneously, leading to sequences where the generator would be inactive for up to 60% of the wave period. Experimental validation of the NMPC included repeating the dry bench test in order to characterize the time-varying performance of the PMLG. This was achieved through the use of mechanical relays to control when the electromagnetic conversion process would be active. After the time-varying performance of the PMLG was characterized the experimental set-up was transferred to the wave tank. The on/off sequencing of the PMLG was tested under regular and irregular wave excitation to validate NMPC simulations using the control inputs obtained from running the controller offline. Experimental results indicate that successful implementation was achieved and the absorbed power was indeed maximized.

Self-reacting Point Absorber Wave Energy Converters

Self-reacting Point Absorber Wave Energy Converters
Author: Scott J. Beatty
Publisher:
Total Pages:
Release: 2015
Genre:
ISBN:

A comprehensive set of experimental and numerical comparisons of the performance of two self-reacting point absorber wave energy converter (WEC) designs is undertaken in typical operating conditions. The designs are either currently, or have recently been, under development for commercialization. The experiments consist of a series of 1:25 scale model tests to quantify hydrodynamic parameters, motion dynamics, and power conversion. Each WEC is given a uniquely optimized power take off damping level. For hydrodynamic parameter identification, an optimization based method to simultaneously extract Morison drag and Coulomb friction coefficients from decay tests of under-damped, floating bodies is developed. The physical model features a re-configurable reacting body shape, a feedback controlled power take-off, a heave motion constraint system, and a mooring apparatus. A theoretical upper bound on power conversion for single body WECs, called Budal's upper bound, is extended to two body WECs.

Handbook of Ocean Wave Energy

Handbook of Ocean Wave Energy
Author: Arthur Pecher
Publisher: Springer
Total Pages: 305
Release: 2016-12-07
Genre: Technology & Engineering
ISBN: 331939889X

This book is open access under a CC BY-NC 2.5 license. This book offers a concise, practice-oriented reference-guide to the field of ocean wave energy. The ten chapters highlight the key rules of thumb, address all the main technical engineering aspects and describe in detail all the key aspects to be considered in the techno-economic assessment of wave energy converters. Written in an easy-to-understand style, the book answers questions relevant to readers of different backgrounds, from developers, private and public investors, to students and researchers. It is thereby a valuable resource for both newcomers and experienced practitioners in the wave energy sector.

Wave Energy Converter Design Via a Time-domain Rankine Panel Method

Wave Energy Converter Design Via a Time-domain Rankine Panel Method
Author: João Seixas de Medeiros
Publisher:
Total Pages: 115
Release: 2017
Genre:
ISBN:

Efficient design of energy converters heavily depends on the capacity of the designer to accurately predict the device's dynamic, which ultimately leads to the power extraction. This is specially true for wave energy converters (WEC), which usually present a high cost per kWh generated. In this thesis a particular WEC which uses a rotating mass for power extraction is studied. A numerical model for the prediction of its motion and power extraction is presented. The nonlinear dynamic model consists of a time-domain three dimensional Rankine panel method coupled, in the time integration, with a MATLAB algorithm which solves for the equations of the gyroscope and Power Take-Off (PTO). The former acts as a force block, calculating the forces due to the waves on the hull, which is then sent to the latter through TCP/IP, which couples the external dynamics and performs the time-integration using a 4th order Runge-Kutta method. With the proposed code, two case studies are examined. The first consists of two gyroscopes, rotating in opposite directions, to negate undesirable yaw effects on the WEC's hull. The device's optimum PTO damping value and flywheel spin are then shown, which change for different sea states. The second is a comparison against results from experimental testing of a 1:50 model at the Davidson Laboratory during the Wave Energy Prize.

Design and Analysis of a Novel Wave Energy Converter with a Tension Leg Platform and Oscillating Proof Masses

Design and Analysis of a Novel Wave Energy Converter with a Tension Leg Platform and Oscillating Proof Masses
Author: Franklin J. Zhang
Publisher:
Total Pages: 0
Release: 2022
Genre:
ISBN:

A design of novel wave energy converter with an oscillating proof mass and an electromagnetic power takeoff mechanism was considered. The wave energy converter has two parts, a tension leg platform connected by tether lines to the sea floor and inside of it, proof mass oscillators with motions which are coupled to those of the tension leg platform. In order to simplify the analysis, the system was constrained to only oscillate in the direction of surge. Complex hydrodynamic forces caused by ocean waves will excite the system and the surge motion of the proof mass relative to the tension leg platform will generate power via the electromagnetic power takeoff mechanism. First a model of the system with a linear restoring force exerted on the proof mass is analyzed using linear theory. Following the development of the linear theory, a more complex model with a nonlinear restoring force was considered. Using both a frequency-domain approach and a time-domain simulation, the average power of these systems were calculated. To further maximize power, a control circuit and control law are introduced which increase the average power by multiple factors. By introducing nonlinear restoring force and a control law, the performance of the system was shown to be further improved.

Comparison of Direct Drive Hydraulic and Dual-Stator Spoke Array Vernier Permanent Magnet Machines For Ocean Wave Energy Conversion

Comparison of Direct Drive Hydraulic and Dual-Stator Spoke Array Vernier Permanent Magnet Machines For Ocean Wave Energy Conversion
Author: Ridwan Azam
Publisher:
Total Pages: 26
Release: 2017
Genre: Ocean wave power
ISBN:

Recently, there has been peaked interest in developing high energy producing and optimized power take-off topologies for Wave Energy Converters (WEC). As large as the potential of the oceans may seem, harnessing that energy and effectively converting it to electricity in significant amounts is a challenge. Currently, there are no single devices that satisfy this sufficiently. In this thesis we compare two promising Power Take-Off (PTO) units; the Dual-Stator Spoke Array Vernier Permanent Magnet machine (DSSA VPM) and the Direct Drive Hydraulic Power Take-Off (DDHPTO). A steady state and transient analysis is done to compare the efficiencies of the two machines. The results will show that the DSSA VPM has the higher efficiency and a greater Annual Energy Production (AEP) over the DDHPTO.