In the field of ocean wave energy converters (WECs), active areas of research are on a priori or in situ methods for power production estimates and on control system design. Linear potential flow theory modelling techniques often underpin these studies; however, such models rely upon small wave and body motion amplitude assumptions and therefore cannot be applied to all wave conditions. Nonlinear extensions can be applied to the fluid loads upon the structure to extend the range of wave conditions for which these models can provide accurate predictions. However, careful consideration of the thresholds of wave height and periods to which these models can be applied is still required. Experimental modelling in wave tank facilities can be used for this purpose by comparing experimental observations to numerical predictions using the experimental wave field as an input. This study establishes a recommended time domain numerical modeling approach for power production assessments of oscillating wave surge converters (OWSCs), a class of WEC designed to operate in shallow and intermediate water depths. Three candidate models were developed based on nonlinear numerical modelling techniques in literature, each with varying levels of complexity. Numerical predictions provided by each model were found to be very similar for small wave amplitudes, but divergence between the models was observed as wave height increased. Experimental data collected with a scale model OWSC for a variety of wave conditions was used to evaluate the accuracy of the candidate models. These experiments were conducted in a small-scale wave flume at the University of Victoria. A challenge with this experimental work was managing wave reflections from the boundaries of the tank, which were significant and impacted the dynamics of the scale model OWSC. To resolve this challenge, a modified reflection algorithm based upon the Mansard and Funke method was created to identify the incident and reflected wave amplitudes while the OWSC model is in the tank. Both incident and reflected wave amplitudes are then input to the candidate models to compare numerical predictions with experimental observations. The candidate models agreed reasonably well with the experimental data, and demonstrated the utility of the modified wave reflection algorithm for future experiments. However, the maximum wave height generated in the wave tank was found to be limited by the stroke length of the wavemaker. As a result, no significant divergence of the candidate model predictions from the experimental data could be observed for the limited range of wave conditions, and therefore a recommended model could not be selected based solely on the experimental/numerical model comparisons. Preliminary assessments of the annual power production (APP) for the OWSC were obtained for a potential deployment site on the west coast of Vancouver Island. Optimal power take-off (PTO) settings for the candidate models were identified using a least-squares optimization to maximize power production for a given set of wave conditions. The power production of the OWSC at full scale was then simulated for each bin of a wave histogram representing one year of sea states at the deployment site. Of the three candidate models, APP estimates were only obtained for Model 1, which has the lowest computational requirements, and Model 3, which implements the most accurate algorithm for computing the fluid loads upon the OWSC device. Model 2 was not considered as it provides neither advantages of Models 1 and 3. The APP estimates from Models 1 and 3 were 337 and 361 MWh per year. For future power production assessments, Model 3 is recommended due to its more accurate model of the fluid loads upon the OWSC. However, if the high computational requirements of Model 3 are problematic, then Model 1 can be used to obtain a slightly conservative estimate of APP with a much lower computational effort. / Graduate

Multiple wave energy devices supported by a common structure represent one possible method of efficiently converting ocean wave energy into electricity. In this study, experimental measurements of multiple small-scale wave energy devices are reported to assist the development and validation of numerical models. Through observation and measurement, the response of two float geometries subjected to a range of wave conditions and device settings were determined. A range of regular wave conditions were identified that caused a linear relationship to occur between the heave displacement amplitude of the float and the incident wave amplitude. These test cases will enable comparisons to be made with linear simulations of response. Tests conducted in various wave conditions have highlighted the capability of altering the device response by changing the equilibrium draft of one float geometry. Additional damping on the upper surface of the float, due to wave overtopping, could be exploited as a method of limiting the heave response of the device in large amplitude waves. The influence of hydrodynamic interactions on arrays of closely spaced devices has been experimentally investigated for devices subjected to regular and irregular wave conditions. The magnitude and occurrence of interactions and their affect on the individual device response is demonstrably dependent on the incident wave frequency and device separation distance. Compared to an isolated device, positive interactions result in higher average power outputs for an array of devices at certain wave frequencies. Positive interactions occuring at particular wave frequencies are balanced by negative interactions at other wave frequencies, in agreement with published numerical studies of array performance. Varying the level of mechanical damping applied to the float through the power take-off system results in a frequency shift of the calculated power transfer function and alters the motion path of the float. This finding implies that the level of generator torque could be used as an alternative method to tune the response of the device based on the measured incident wave-field. Several time-averaged and time-varying approaches to simulating the response of a wave energy device subjected to wave-field forcing and undergoing free response have been studied. By comparing the simulated and measured responses, the feasibility of using linear and non-linear force terms in a time-varying model has been assessed. In general, single degree-of-freedom simulations based on linear hydrodynamic parameters tend to over-predict device response amplitudes, requiring the application of additional damping. The simulation approach which resulted in the closest agreement with measured responses required the combination of linear diffraction force and radiation added mass terms with non-linear drag and buoyancy force terms, as well as body inertia and gravity forces. This approach goes part way to simulating the complex time-varying hydrodynamics associated with a wave energy device subjected to wave-field forcing.

This master thesis is done within the Energy Systems Engineering program at Uppsala University and performed for CorPower Ocean. Wave energy converters (WECs) are devices that utilize ocean waves for generation of electricity. The WEC developed by CorPower Ocean is small and intended to be deployed in an array. Placed in an array the different WECs will interact hydrodynamically and the combined power output is altered. The aim of this thesis is to model and investigate how the array configuration affects the electric power output. The goal is to target an optimal array layout for CorPower Ocean WECs, considering both average power and power smoothness in the optimization.   In this thesis multiple buoys have been implemented in the time-domain model at CorPower Ocean. The hydrodynamic interactions are computed using an analytical interactions theory together with a recently developed calibration method able of handling WEC bodies of complicated shapes. The array behavior in regular waves is analyzed and it is identified how the beneficial separation distances vary with wave length. It is observed that the best separation distances for high average power does not exactly correspond to the best for minimizing the peak-to-average power. Simulation results show that it is possible to obtain both high average array power as well as increased power smoothening in a regular wave. A genetic algorithm for optimizing the array configuration is designed and tested for two different array patterns. Initial simulations are conducted in realistic multi-directional irregular waves. The power smoothening capacity of the array remains even in these conditions but the exact extent of it is still uncertain.   This thesis delivers a WEC array simulation model as well as an initial view on the array characteristics of the phase controlled CorPower Ocean WEC. Additionally, it demonstrates an optimization algorithm taking both average power and power smoothness into account.

In this project, the wave energy converter (WEC) designed at Seabased AB and Uppsala University was modelled in the program MATLAB. In order to increase the average output power, the WEC should be controlled. Therefore, the simulation tool was used to investigate damping strategies where the damping coefficient was changed at different times of the wave period. The tests showed that a suitable damping strategy, matched to the sea state at the specific location of the site and the overall WEC design, increases the average output power, as well as may protect the WEC from damages. This can lead to a more sustainable WEC system, which may contribute to the increasing demand of renewable energy solutions.

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

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 quest to diversify the renewable energy producing systems has led to the development of wave energy converters. To get to a viable commercial wave energy converter system it is very crucial to have a levelized cost to energy for the system. This is done driving forward the system level optimization and upgradation for the whole wave energy converter. In this thesis, the focus was the support for the development of a full scaled composite pretension cylinder. Different predictive models were identified and studied to characterize the effects due to the cyclic reciprocating contacts on the composite pretension cylinder. The results of which, gave an early input to move forward towards more accurate testing leading to the development of a test rig. The test rig once developed could provide with the long term required data so that the actual composite pretension cylinder be designed and integrated onto the wave energy converter. / Strävan efter att diversifiera de system som producerar förnybar energi har lett till utvecklingen av vågenergiomvandlare. För att komma till ett livskraftigt kommersiellt vågenergiomvandlingssystem är det mycket viktigt att ha en nivåiserad energikostnad för systemet. Detta görs för att förbättra systemnivåoptimeringen och uppgraderingen för hela vågenergiomvandlaren. I denna avhandling var fokus stödet för utvecklingen av en fullskalad komposit förspänningscylinder. Olika prediktiva modeller identifierades och studerades för att karakterisera effekterna på grund av de cykliska fram- och återgående kontakterna på den sammansatta förspänningscylindern. Resultaten gav en tidig input för att gå vidare mot mer exakta tester, vilket ledde till utvecklingen av en testrigg. Den testrigg som en gång utvecklats kan ge långsiktigt erforderliga data så att den faktiska sammansatta förspänningscylindern kan utformas och integreras i vågenergiomvandlaren.

About 3/4th percentage of Earth’s surface is covered with water, the demand for harnessing energy from the ocean is increasing periodically. This form of energy conversion is Wave Energy. This method is practised all around the world, Novi-Ocean by Novige AB is one of its kind where they aim to build a wave energy converter. The main component of the device is the oating platform above the sea level and powertake-o (cylinder) below the sea level. The motion of waves makes the platform to move vertically up and down thus creating a lift force 450 tons. The force is experienced at the interface of platform and cylinder attachment. Therefore, a conceptual design for distributing the force along the length of the shaft is necessary. Also, suitable bearing for the marine application needs to be selected. For the application mentioned relevant research is made on understanding the types of the wave energy converter and their working principles. The product development methodology is carried out to generate a conceptual design. Next, simulations were performed to decide the diameter of the shaft at the interface. A numerical and FEA model analysis of press- t is performed to check the contact pressure. / Cirka 3/4 procent av jordens yta är täckt med vatten, efterfrågan på att utnyttja energi från havet ökar periodvis. Denna form av energiomvandling är Wave Energy. Denna metod utövas över hela världen, Novi-Ocean av Novige AB är ett i sitt slag där de syftar till att bygga en vågenergikonverterare. Huvudkomponenten i enheten är den ytande plattformen över havsnivån och kraftuttaget (cylinder) under havsnivån. Vågens rörelse gör att plattformen rör sig vertikalt upp och ner och skapar en lyftkraft 450 ton. Kraften upplevs vid gränssnittet mellan plattform och cylinderfäste. Därfor är en konceptuell design för fördelning av kraften längs axelns längd nödvändig. Dessutom måste lämpligt läger för den marina applikationen väljas. För den nämnda applikationen görs relevant forskning for att förstå typerna av vågenergikonverteraren och deras arbetsprinciper. Produktutvecklingsmetodiken genomförs för att generera en konceptuell design. Därefter utfördes simuleringar för att bestämma axelns diameter vid gränssnittet. En numerisk och FEA-modellanalys av presspassning utförs för att kontrollera kontakttrycket.