A Wave Energy Converter (WEC) is a device designed to harness the ocean wave energy to generate electricity. The commercial viability of WECs depends largely on reducing the cost per kWh to make it competitive against other sources of renewable energy. This thesis proposes a novel WEC. Simplicity is a key feature of the proposed design with the objective of reducing the manufacturing costs and circumventing issues associated with current WECs, such as installation complexity. impact on marine life, survivability and navegability of vessels. The performance of the proposed unidirectional Flow Collective Air Pumps (UFCAP) WEC has been evaluated using analytical and computational models for a variety of operating conditions. A parametric design study has been carried out to evaluate the proposed design in operation off the coast of Vancouver Island.

A new concept, extracting energy from sea waves by parametric pendulor, has been explored in this project. It is based on the conversion of vertical oscillations to rotational motion by means of a parametrically-excited pendulor, i.e. a pendulum operating in rotational mode. The main advantage of this concept lies in a direct conversion from vertical oscillations to rotations of the pendulum pivot. This thesis, firstly, reviewed a number of well established linear and nonlinear theories of sea waves and Airy’s sea wave model has been used in the modelling of the sea waves and a parametric pendulum excited by sea waves. The third or fifth order Stokes’s models can be potentially implemented in the future studies. The equation of motion obtained for a parametric pendulum excited by sea waves has the same form as for a simple parametrically-excited pendulum. Then, to deepen the fundamental understanding, an extensive theoretical analysis has been conducted on a parametrically-excited pendulum by using both numerical and analytical methods. The numerical investigations focused on the bifurcation scenarios and resonance structures, particularly, for the rotational motions. Analytical analysis of the system has been performed by applying the perturbation techniques. The approximate solutions, resonance boundary and existing boundary of rotations have been obtained with a good correspondence to numerical results. The experimental study has been carried out by exploring oscillations, rotations and chaotic motions of the pendulum.

The performance of the power take-off (PTO) system for a wave energy converter (WEC) depends largely on its control algorithm. This paper presents an adaptive damping control algorithm that improves power capture across a range of sea states. Validation for the numerical model was performed using data from two sources; sea trail data of a 1:7 scaled model and tank testing data from a 1:33 scaled model. The comparison between this control algorithm and other active control approaches such as linear damping is presented. Short term wave elevation forecasting methods and wave period determination methods are also discussed as requirements for this method. This research is conducted for a novel point absorber WEC, developed by Columbia Power Technologies (COLUMBIA POWER). / Graduation date: 2012

Thesis (MOcE)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 52-54). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaves 115-116). Also available on the World Wide Web.

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on July, 1 2009). Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 96-97). Also available on the World Wide Web.

In order to increase energy security and meet carbon emission reduction targets set by the EU and UK government, the UK energy sector has increased its reliance on renewable energy. The marine renewable sector is set to become a major contributor to the UK's energy portfolio but incumbent on the offshore renewable sector are the high development, operation and maintenance costs. Prevailing metocean conditions at an offshore energy site contribute significantly to the life-cycle costs of an offshore energy project. Where access to a site is limited by a lack of suitable weather-windows, leading to high instances of downtime, weather-induced costs increase. Determination of suitable metocean weather-windows, defined by maximum operating thresholds and the length of time required to perform a task can assist with the risk management of a project and the reduction of downtimes, thus reducing costs. Metocean weather-windows are determined using 31 years (the “climatological norm”) of ECMWF ERA-40 reanalysis data. The annual, seasonal and monthly distribution parameters for wind and wave regimes at three sites are derived, using three different distribution parameter estimation models. Probabilities of defined weather-windows are determined using the derived distribution parameters and compared with empirical probabilities, based on the frequentist approach. Wind regimes fit a Weibull distribution and wave regimes fit a 3P gamma distribution and unique annual, seasonal and monthly distribution parameters are required for accurate weather-window determination. When fitted to appropriate PDFs, the shape and scale values determined by the different estimation techniques result in significantly different probabilities. Empirical probabilities converge with those determined using the MLE model but both significantly differ from those derived using the LSM and MoM derived parameters. In the absence of a dataset spanning the climatological norm, this suggests that the MLE method of parameter estimation is more accurate for the successful determination of weather-windows.

Marine renewable energy developments (MRED) will result in large quantities of infrastructure being deployed in coastal habitats, and the localised exclusion of fishing. The ecological consequences of this scale of deployment are largely unknown, particularly for benthic species. Infrastructure has the capacity to act as artificial reefs (ARs), providing novel habitat, and this may viewed as a benefit of MRED, or a means to mitigate the exclusion of fishing. At present, the functioning of AR ecosystems remains poorly understood. As a measure of ecosystem function, secondary productivity can be used to assess the implications of MRED. The lack of suitable methodology, deployable at relevant scales within time and/or cost constraints, has limited benthic secondary productivity (BSP) quantifications on ARs. Techniques to measure potential BSP and particle flux were developed and applied to the Loch Linnhe Artificial Reef (functionally similar to scour protection material). Variations in BSP and mobile epifaunal densities on, and between, structures in different environments were quantified. Reefs exposed to intermediate current had the highest potential productivity. The BSP on internal areas of structures contributed to the total productive output, but the relative contribution varied according to reef location and design. BSP was primarily determined by particle supply, but the response was not consistent among locations. Mobile epifaunal densities related to reef location, but not reef design, and were highest on reefs in the deepest water and exposed to the fastest currents. The evidence presented in this thesis highlights the need to account for the receiving environment when predicting the ecological consequences of MRED, or when modelling the productive capacity of structures. Such information can be used to suggest modifications to proposed or existing structures in order to maximise their benefit to coastal ecosystems.

Surface gravity waves carry enormous amounts of energy over our oceans, and if their energy could be harvested to generate electricity, it could make a significant contribution to the worlds power demand. But the survivability of wave energy devices in harsh operating conditions has proven challenging, and for wave energy to be a possibility, peak forces during storms and extreme waves must be studied and the devices behaviour understood. Although the wave power industry has benefited from research and development in traditional offshore industries, there are important differences. Traditional offshore structures are designed to minimize power absorption and to have small motion response, while wave power devices are designed to maximize power absorption and to have a high motion response. This increase the difficulty of the already challenging survivability issue. Further, nonlinear effects such as turbulence and overtopping can not be neglected in harsh operating conditions. In contrast to traditional offshore structures, it is also important to correctly account for the power take off system in a wave energy converter (WEC), as it is strongly coupled to the devices behaviour. The focus in this thesis is the wave loads and the peak forces that occur when a WEC with a limited stroke length is operated in waves higher than the maximum stroke length. The studied WEC is developed at Uppsala University, Sweden, and consists of a linear generator at the seabed that is directly driven by a surface buoy. A fully nonlinear CFD model is developed in the finite volume software OpenFOAM, and validated with physical wave tank experiments. It is then used to study the motion and the forces on the WEC in extreme waves; high regular waves and during tsunami events, and how the WECs behaviour is influenced by different generator parameters, such as generator damping, friction and the length of the connection line. Further, physical experiments are performed on full scale linear generators, measuring the total speed dependent damping force that can be expected for different loads. The OpenFOAM model is used to study how the measured generator behaviour affects the force in the connection line.