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.

Numerical Modelling of Wave Energy Converters

Numerical Modelling of Wave Energy Converters
Author: Matt Folley
Publisher: Academic Press
Total Pages: 308
Release: 2016-06-14
Genre: Technology & Engineering
ISBN: 0128032111

Numerical Modelling of Wave Energy Converters: State-of-the Art Techniques for Single WEC and Converter Arrays presents all the information and techniques required for the numerical modelling of a wave energy converter together with a comparative review of the different available techniques. The authors provide clear details on the subject and guidance on its use for WEC design, covering topics such as boundary element methods, frequency domain models, spectral domain models, time domain models, non linear potential flow models, CFD models, semi analytical models, phase resolving wave propagation models, phase averaging wave propagation models, parametric design and control optimization, mean annual energy yield, hydrodynamic loads assessment, and environmental impact assessment. Each chapter starts by defining the fundamental principles underlying the numerical modelling technique and finishes with a discussion of the technique’s limitations and a summary of the main points in the chapter. The contents of the chapters are not limited to a description of the mathematics, but also include details and discussion of the current available tools, examples available in the literature, and verification, validation, and computational requirements. In this way, the key points of each modelling technique can be identified without having to get deeply involved in the mathematical representation that is at the core of each chapter. The book is separated into four parts. The first two parts deal with modelling single wave energy converters; the third part considers the modelling of arrays; and the final part looks at the application of the different modelling techniques to the four most common uses of numerical models. It is ideal for graduate engineers and scientists interested in numerical modelling of wave energy converters, and decision-makers who must review different modelling techniques and assess their suitability and output. Consolidates in one volume information and techniques for the numerical modelling of wave energy converters and converter arrays, which has, up until now, been spread around multiple academic journals and conference proceedings making it difficult to access Presents a comparative review of the different numerical modelling techniques applied to wave energy converters, discussing their limitations, current available tools, examples, and verification, validation, and computational requirements Includes practical examples and simulations available for download at the book’s companion website Identifies key points of each modelling technique without getting deeply involved in the mathematical representation

Wave Energy Potential, Behavior and Extraction

Wave Energy Potential, Behavior and Extraction
Author: Hua Li
Publisher: MDPI
Total Pages: 238
Release: 2020-03-27
Genre: Technology & Engineering
ISBN: 3039283960

Wave energy has a higher potential than most of the available ocean energy resources; however, it fluctuates dramatically depending on geographical and temporal baselines. The complexity of wave energy is only exacerbated by that fact that the cycle of creation, transport, and disappearance of wave energy is influenced by a wide variety of factors. This Special Issue of Energies explores the latest developments in wave energy potential, behavior, and extraction. This Special Issue introduces 1) thorough reviews on the status of wave energy development, 2) novel technologies to extract wave energy including wave energy converter design, and 3) latest methodologies applied in analyzing wave energy potentials.

A New Methodology for Frequency Domain Analysis of Wave Energy Converters with Periodically Varying Physical Parameters

A New Methodology for Frequency Domain Analysis of Wave Energy Converters with Periodically Varying Physical Parameters
Author: Mark Mosher
Publisher:
Total Pages:
Release: 2012
Genre:
ISBN:

Within a wave energy converter's operational bandwidth, device operation tends tobe optimal in converting mechanical energy into a more useful form at an incidentwave period that is proximal to that of a power-producing mode of motion. Pointabsorbers, a particular classification of wave energy converters, tend to have a relativenarrow optimal bandwidth. When not operating within the narrow optimal bandwidth, a point absorber's response and efficiency is attenuated. Given the wide rangeof sea-states that can be expected during a point absorber's operational life, thesedevices require a means to adjust, or control, their natural response to maximize theamount of energy absorbed in the large population of non-optimal conditions. In thefield of wave energy research, there is considerable interest in the use of non-linearcontrol techniques to this end. Non-linear control techniques introduce time-varying and state dependent controlparameters into the point absorber motion equations, which usually motivates a computationallyexpensive numerical integration to determine the response of the device- important metrics such as gross converted power and relative travels of the device'spieces are extracted through post processing of the time series data. As an alternative, the work presented in this thesis was based on a closed form perturbation basedapproach for analysis of the response of a device with periodically-varying controlparameters, subject to regular wave forcing, in the frequency domain. The proposed perturbation based method provides significant savings in computationaltime and enables the device's response to be represented in a closed formmanner with a relatively small number of solution components - each component iscomprised of a complex amplitude and oscillation frequency. This representation ofthe solution was found to be very concise and descriptive, and to lend itself to the calculationof gross absorbed power and travel constraint violations, making it extremelyuseful in the automated design optimization process; the methodology allows largenumber of design iterations, including both physical design and control variables, tobe evaluated and conclusively compared. In the development of the perturbation method, it was discovered that the device'smotion response can be calculated from an in nite series of second order ordinary differentialequations that can be truncated without destroying the solution accuracy. It was found that the response amplitude operator for the generic form of a solutioncomponent provides a means to gauge the device's response to a given wave input andcontrol parameter variation, including a gauge of the solution process stability. It isunclear as of yet if this is physical, a result of the solution process, or both. However, for a given control parameter set resulting in an unstable solution, the instability wasshown to be, at least in part, a result of the device's dynamics. If the stability concerns can be addressed through additional constraints and updatesto the wave energy converter hydrodynamic parameters, the methodology willexpand on the commonly accepted boundaries for wave energy converter frequency domainanalysis methods and be of much practical importance in the evaluation ofcontrol techniques in the field of wave energy converter technology.

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.

Design and Analysis for a Floating Oscillating Surge Wave Energy Converter

Design and Analysis for a Floating Oscillating Surge Wave Energy Converter
Author:
Publisher:
Total Pages: 11
Release: 2014
Genre:
ISBN:

This paper presents a recent study on the design and analysis of an oscillating surge wave energy converter. A successful wave energy conversion design requires the balance between the design performance and cost. The cost of energy is often used as the metric to judge the design of the wave energy conversion system. It is often determined based on the device power performance, the cost for manufacturing, deployment, operation and maintenance, as well as the effort to ensure the environmental compliance. The objective of this study is to demonstrate the importance of a cost driven design strategy and how it can affect a WEC design. Three oscillating surge wave energy converter (OSWEC) designs were used as the example. The power generation performance of the design was modeled using a time-domain numerical simulation tool, and the mass properties of the design were determined based on a simple structure analysis. The results of those power performance simulations, the structure analysis and a simple economic assessment were then used to determine the cost-efficiency of selected OSWEC designs. Finally, a discussion on the environmental barrier, integrated design strategy and the key areas that need further investigation is also presented.

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.

Conceptual Design of Wave Energy Converters

Conceptual Design of Wave Energy Converters
Author: Kush Bubbar
Publisher:
Total Pages:
Release: 2018
Genre:
ISBN:

Despite presenting a vast opportunity as a renewable energy resource, ocean wave energy has yet to gain commercial success due to the design space being divergent. To facilitate convergence, this dissertation has proposed a method using the mechanical circuit framework to transform a linear representation of any wave energy converter into an equivalent single body absorber, or canonical form, through the systematic application of Thévenin's theorem. Once the canonical form for a WEC has been established, criteria originally derived to maximize power capture in single body absorbers is then applied. Through this process, a master-slave relationship was introduced that relates the geometry and PTO parameters of a wave energy converter device to one another and presents a new method to establish the best possible power capture in analytical form based on dynamic response. This method has been applied to reprove the power capture limits derived by Falnes and Korde for their point absorber devices, and proceeds to introduce a new analytical power capture limit for the self-reacting point absorber architecture, while concurrently establishing design criteria required to achieve the limit. A new technology, the inerter, has been introduced as a means to implement the design criteria. The method has been further developed to establish the generic optimal phase control conditions for complex WEC architectures. In doing so, generic equations have been derived that describe how a geometry control feature set is used to satisfy the required optimal phase criteria. Finally, this dissertation has demonstrated that applying this method with a generic reactive force source enacting the geometry control establishes analytical optimal conditions on the force source to achieve optimal power capture. This work revealed how the analytical equations defining the optimal force source reactance derived in this dissertation for self-reacting point absorbers represents a tangible design constraint prior to specifying how that constraint must be satisfied. As the force source is generic and conceptual, substitution with a physical embodiment must adhere to this constraint thus, steering technology innovation.

WEC3: Wave Energy Converter Code Comparison Project: Preprint

WEC3: Wave Energy Converter Code Comparison Project: Preprint
Author:
Publisher:
Total Pages: 0
Release: 2017
Genre:
ISBN:

This paper describes the recently launched Wave Energy Converter Code Comparison (WEC3) project and present preliminary results from this effort. The objectives of WEC3 are to verify and validate numerical modelling tools that have been developed specifically to simulate wave energy conversion devices and to inform the upcoming IEA OES Annex VI Ocean Energy Modelling Verification and Validation project. WEC3 is divided into two phases. Phase 1 consists of a code-to-code verification and Phase II entails code-to-experiment validation. WEC3 focuses on mid-fidelity codes that simulate WECs using time-domain multibody dynamics methods to model device motions and hydrodynamic coefficients to model hydrodynamic forces. Consequently, high-fidelity numerical modelling tools, such as Navier-Stokes computational fluid dynamics simulation, and simple frequency domain modelling tools were not included in the WEC3 project.