Accurate predictions of the annual energy yield from wave energy converters are essential to the development of the wave industry. The current method based on power matrices uses only a small part of the data available from sea state estimations and it is consequently prone to inaccuracies. The research presented in this work investigates the issue of energy yield prediction and questions the power matrix method. This is accomplished by quantifying the influence of several directional sea states parameters on the performances of wave energy converters. The approach taken was to test several wave energy converters in the Edinburgh Curved tank with a large set of sea states. The selected wave energy converters are a fix OWC, a set of two OWCs acting as a weak directional device and the desalination duck model. Uni-modal and bi-modal sea states were used. For the uni-modal sea states, parameters related to the wave system shape were considered. For the bi-modal sea states, the relative position of the wave system peaks was investigated and the uni-modality index was introduced to quantify the degree to which sea states could be considered bi-modal. For all sea states, the significant wave height was kept constant. The experimental work required good spectral estimates. The MLM and MMLM were adapted to deterministic waves to improve their stability and accuracy. A routine to isolate wave systems was also developed in order to estimate parameters with respect to each wave systems. For uni-modal spectra, parametric models of the observed performances of the devices could be devised. The frequency spreading and its interaction with the energy period proved to be as important as the energy period itself, which suggests that the frequency spreading should be used for energy production prediction. For bi-modal spectra, evidence of the duck sensitivity to directionality was found while the OWCs were not affected.

The basis of the study lies with a newly patented gearbox by cardiologist and inventor Stig Lundbäck. Stig founded CorPower Ocean AB to further develop the gearbox to be used in a wave energy device. The purpose of this project is to develop a concept of a lifting system with CorPower Oceans gearbox that is more energy efficient than a hydraulic lifting system. The goal is to use technology from CorPower Oceans gearbox inversely to perform heavy lifting as an alternative to hydraulics. The project is limited to applying the gearbox and gear rack on a forklift with a lifting capacity of ten tons.The main tool in this project will be the product development process Systems Engineering where only the most relevant parts will be used to develop a concept. Calculations of the strength and dimensions of the gear racks are made to ensure the possibility of this solution.

A prototype point absorber style wave energy converter has been proposed for deployment off the West coast of Vancouver Island near the remote village of Hotsprings Cove in Hesquiaht Sound; a site identified as having significant wave energy potential. The proposed design consists of two components, a long unique cylindrical spar and a concentric toroid float. To serve ongoing wave energy converter (WEC) dynamics modelling and control research in support of that project, an experimental facility for small scale physical model testing is desired at UVIC. In the immediate term, the facility could be used to determine the hydrodynamic coefficients over a range of wave frequencies. Refined estimates of the hydrodynamic coefficients would be exploited in the optimisation of the WEC geometry. To date, WEC research at UVIC has neglected the frequency dependence of the hydrodynamic coefficients, relying on limited experimental results to provide a single frequency invariant set of coefficient estimates. / Graduate / 0791 / 0547 / 0548 / mercedes.baylis@hotmail.com

This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Diode bridge rectifiers are considered for rectification to avoid the complex linear generator control at the input side. To reduce the size and the cost of energy storage elements, DC voltage regulation is done using a DC/DC converter. To achieve smooth and high power, many WECs need to be connected to a common DC link. A neutral point clamped inverter is considered for the DC/AC conversion due to its advantages over conventional topologies. Various pulse width modulation schemes are tested for the inverter to choose the optimum PWM method. The harmonics in the inverter output voltage is derived numerically and compared with simulation and experiment to understand the effect of dead-time in the inverter operation. Depending on the load current drawn from the inverter, the voltages in the two input capacitors of a three-level neutral point clamped inverter deviates from equilibrium unless the neutral point is grounded. To avoid this voltage imbalance as well as to regulate the DC link voltage a dual output boost converter with pulse delay control is proposed. The modeling, simulation and experiments show an improvement in the compensation voltage using pulse delay control compared to the previously proposed methods in the literature. The synchronous current control and the grid connection of the three-level converter have been accomplished in the laboratory.  Finally, the three-level power converter system has been tested with a linear permanent magnet generator at Lysekil to analyze the controller requirements.

Abstract     In this project, I present a design of a scale model of a linear generator (LG) similar to a full size Wave Energy Converter (WEC) being developed at Uppsala University since 2002 and commercialized by Seabased AB. The purpose of a WEC is to convert the energy from ocean waves into electrical energy. In order to implement the behaviour of the prototype design, a preliminary study has been done to further build it for use in education, laboratory tests and research. The challenge with this project is to scale down the WEC but maintain the shape, appearance and characteristics of the generator for educational purposes. A miniature version of a WEC, previously developed by Uppsala University in collaboration with Seabased Industry AB, has been designed with scaling rate 1:14 of the linear dimensions. In this case, the value of the output power is not important- it has simply been calculated. The electrical rated parameters of the three phase generator are power  26 W,  peak line-line voltage  13 V and  rated armature current  2 A. The mechanical parameters utilized in the design are the total length and the diameter of the miniature WEC, 50 cm and 25 cm, respectively. The simulated prototype model (described in Section 5.4) has been validated with an experimental setup comprising translator and stator (described in Section 5.1), where the translator is moved by a programmed industrial robot. The experimental results have shown good agreement with the simulations.

This document presents a novel active magnetic levitation system. In the pursued of this endeavour different topics related with wave energy were explore. Climate change and energy security are the main motivation to pursued new options for non-fossil fuels energy generation. An overview of renewable energy and specifically of wave energy was presented. The potential for wave energy in The United Kingdom turn out to be 75 TWh/year from wave energy, 3 times more of what wind energy has produced in 2013. This means a massive impact on the energy market and emission reduction. In order to achieve this, improvements on wave energy devices have to be done. An overview of wave energy converters was covered selecting the C-Gen as the generator topology this document will base its studies. Linear generator bearings are desired to have long lifespan with long maintenance intervals. The objective is to come with an active magnetic levitation design that can replace traditional bearings augmenting the reliability of the system. Therefore magnetic bearings option have been reviewed and simulation experimentations has resulted in a novel active magnetic levitation system using an air-cored coils Halbach array acting over a levitation track. The configuration would generate bi directional repulsion forces with respect of the levitating body. Different software were used to analyse the magnetic field and forces generation. Additionally a prototype was built and tested to corroborate the results. As part of the modelling a mathematical model was explored and robust control implementation was also realised. Finally a scalability study of the device as well as a reliability analysis was done. Although the reliability studies shows an increase of ten times of the mean time to failure, the concept is not able to endure the loads acting on the generator unless the magnetic bearings became bigger than the generator and therefore economically unfeasible.

The interaction between water waves and a floating or fixed body is bi-directional: wave forces act on and cause motion in the body, and the body alters the wave field. The impact of the body on its wave field is important to understand because: 1) it may have positive or negative consequences on the natural or built environment; 2) multiple bodies in proximity interact via the waves that are scattered and radiated by them; and 3) in ocean wave energy conversion, by conservation of energy, as a device absorbs energy, so too must the energy be removed from the wave field. Herein, the cylindrical solutions to the linear wave boundary-value problem are used to analyze the floating body wave field. These solutions describe small-amplitude, harmonic, potential-flow waves in the form of a Fourier summation of incoming and outgoing, partial, cylindrical, wave components. For a given geometry and mode of motion, the scattered or radiated waves are characterized by a particular set of complex cylindrical coefficients. A novel method is developed for finding the cylindrical coefficients of a scattered or radiated wave field by making measurements, either computationally or experimentally, over a circular-cylindrical surface that circumscribes the body and taking a Fourier transform as a function of spatial direction. To isolate evanescent modes, measurements are made on the free-surface and as a function of depth. The technique is demonstrated computationally with the boundary-element method software, WAMIT. The resulting analytical wave fields are compared with those computed directly by WAMIT and the match is found to be within 0.1%. A similar measurement and comparisons are made with experimental results. Because of the difficulty in making depth-dependent measurements, only free-surface measurements were made with a circular wave gauge array, where the gauges were positioned far from the body in order to neglect evanescent modes. The experimental results are also very good. However, both high-order harmonics and wave reflections led to difficulties. To compute efficiently the wave interactions between multiple bodies, a well-known multiple-scattering theory is employed, in which waves that are scattered and radiated by one body are considered incident to another body, which in turn radiates and scatters waves, sending energy back to the first. Wave fields are given by their cylindrical representations and unknown scattered wave amplitudes are formulated into a linear system to solve the problem. Critical to the approach is the characterization of, for each unique geometry, the cylindrical forces, the radiated wave coefficients, and the scattered waves in the form of the diffraction transfer matrix. The method developed herein for determining cylindrical coefficients is extended to new methods for finding the quantities necessary to solve the interaction problem. The approach is demonstrated computationally with WAMIT for a simple cylinder and a more complex wave energy converter (WEC). Multiple-scattering computations are verified against direct computations from WAMIT and are performed for spectral seas and a very large array of 101 WECs. The multiple-scattering computation is 1,000- 10,000 times faster than a direct computation because each body is represented by 10s of wave coefficients, rather than 100s to 1,000s of panels. A new expression for wave energy absorption using cylindrical coefficients is derived, leading to a formulation of wave energy absorption efficiency, which is extended to a nondimensional parameter that relates to efficiency, capture width and gain. Cylindrical wave energy absorption analysis allows classical results of heaving and surging point absorbers to be easily reproduced and enables interesting computations of a WEC in three-dimensions. A Bristol Cylinder type WEC is examined and it is found that its performance can be improved by flaring its ends to reduce "end effects". Finally, a computation of 100% wave absorption is demonstrated using a generalized incident wave. Cylindrical representations of linear water waves are shown to be effective for the computations of wave-body wave fields, multi-body interactions, and wave power absorption, and novel methods are presented for determining cylindrical quantities. One of the approach's greatest attributes is that once the cylindrical coefficients are found, complex representations of waves in three dimensions are stored in vectors and matrices and are manipulated with linear algebra. Further research in cylindrical water waves will likely yield useful applications such as: efficient computations of bodies interacting with short-crested seas, and continued progress in the understanding of wave energy absorption efficiency.

The collector of an oscillating water column system (OWC) for wave energy utilization requires a bidirectional turbine that copes with pneumatic power while providing specified impedance or, in terms of an OWC designer, “damping”. Damping is realized by keeping to a specific flow rate through the turbine at a given pressure head due to the individual performance characteristic of the turbine. With the number of turbine designs increasing designers of OWC systems are facing more options to select and dimension a bidirectional turbine. Energy yield, size and hence cost of the turbine and electric generator, operational behaviour, envisaged control strategy and noise emitted by the turbine are possible criteria for selection. The primary objective of this paper is to describe a simple procedure for making a first choice of a turbine for a particular OWC application. Here we confine ourselves to a family of reaction type of turbines (axial-flow Wells and mixed-flow turbines by Moisel) with their approximately linear pressure head/volume flow rate characteristics. Starting point is the set of non-dimensional steady-state characteristics of each turbine in the family. Utilizing standard scaling laws and a very simple time domain model for the cyclic turbine operation (i.e. based one single sea state and turbine operation assumed to be fixed rotational speed), first estimates of turbine size and rotor speed, number for stages or flows, and performance curves can be determined. The resulting turbine may also serve as a starting configuration for a refined analysis, e.g. the optimization of the turbine and the complete OWC system, utilizing more complex stochastic models. Three case studies illustrate the application of the method: selection and scaling of turbines, effect of collector parameters, turbines in series and parallel.

Numerous studies have identified the west coast of Canada as an attractive place for the development of wave energy projects. To evaluate the viability of these projects, an accurate description of the wave resource is crucial. Most of the previous efforts to characterize the wave climate in B.C. at shallower waters, where wave energy converters (WECs) are most likely to be deployed, lack the necessary nearshore spatial resolution, and were driven by overly simplistic wave boundary conditions. In addition, none of the previous studies have included the effect of tidal currents, which have been proven to be significant in wave resource characterizations in other locations. This work increased the fidelity of the wave resource characterization and developed an understanding of the impact of tidal currents on the wave conditions in this region by generating two most accurate, long-term (14 years, 2004 to 2017), high resolution (in space and time) datasets of the wave resource for the west coast of Canada. The two datasets were generated using nearly identical SWAN wave models, which their only difference was that one of them (V5), did not incorporate the effect of currents, while the other (V6) included tidal currents as forcing. Thus, the pure influence of the tidal currents on the wave characteristics was able to be identified when comparing the two wave model results. This study developed simple, robust, and objective metrics to support the calibration process and to evaluate the performance of the models. Utilizing these metrics, the V5 and V6 models presented substantial improvements in reproducing the wave conditions of about 18% and 20%, respectively and in relation to the previous most complete and accurate wave model of the region (V4). Their better performance was largely achieved by a significant increment in their ability to reproduce the significant wave height (H_m0) and energy period (T_e). The inclusion of tidal currents in the wave model increased the accuracy of the wave resource characterization, mainly by improving the model’s ability in simulating T_e by 5.1%. The most sensitive wave parameter to the tidal currents was the peakedness of the wave spectrum (Q_p), which was consistently and significantly reduced by values even larger than 2.5. In some regions, directions characterized by the mean wave direction (D_m) and the directional spreading (D_spr) were also noticeably very sensitive to the currents, which even deflected D_m to its opposite direction and drove changes in D_spr that reached values of up to 40°. However, these significant transformations were less frequent and reduced in magnitude at exposed (to swell-waves) sites, where strong currents have affected waves in a reduced part of their trajectory. Typically, tidal currents had the effect of reducing the wave power density (P), but in a relatively small amount, however, during rare events, tidal currents were able to induce changes in this parameter ranging -140 kW/m to 75 kW/m. At these extreme events, it was observed that the peak of the wave spectra became flatter, with some of its wave height variance redistributed to near increasing and decreasing frequencies and directions, regardless to the magnitude and direction of the local tidal currents. Impacts of the tidal currents on P were largely attributed to the induced changes in H_m0 and T_e. Although D_spr and Q_p were greatly transformed by the action the tidal currents, they account very little in explaining the variations in P. These four wave parameters together, and how they are transformed under the presence of currents, can explain a large part of the changes in P, however, other transformations of the wave spectrum due to the currents, not investigated in this study, must account for a considerable part of the changes in P. / Graduate

This research paper was submitted to the Department of Geography in fulfillment of the requirements of Geography 4C6. / This study reports on the relationship between the foreshore slopes, grain size characteristics and the wave height on the Hamilton-Burlington Beach. This beach is a non-tidal, low-energy beach. At five stations along the beach, profiles were taken, sediment samples were collected and the average wave heights determined. The slopes were plotted against the mean grain size, the median grain size and the wave heights. There was no clear relationship between the variables tested. It was determined, however, that there existed three areas along this beach. The first area was he one affected only by the wave energy, the second are was affected by both the wave energy and the grain size characteristics, and the third region was affected by the grain size characteristics. / Thesis / Bachelor of Arts (BA)