The United Kingdom recently committed to reducing emissions by the fastest rate of any major economy. In line with the ambitious goals announced by the Prime Minister, investors have started to show considerable interest in innovative renewable technologies.
Wave energy converters are renewable energy harvesters that capture the vast energy in waves. They have the potential to be a principal competitor to offshore wind, but the capturing and utilisation of wave energy remains a largely unsuccessful endeavour due to, paradoxically, the immense amount of energy in waves, as well as other engineering challenges such as the corrosive salt water and large variations in wave profiles.
This project aims to change that track record. We present a small-scale proof of concept oscillating water column wave energy converter prototype. The device is divided into three subassemblies, namely anchor and frame (06A), energy converter (06B), and energy transmission (06C). The anchor and frame subassembly consists of a rigidly secured cylindrical section to house and protect energy generation components, whilst accelerating internal airflow for turbine efficiency. An accompanying testing rig is designed to facilitate more effective testing. The energy converter subassembly is based around a Wells turbine design, a turbine blade profile that allows for unidirectional rotation from bi-directional fluid flow, which has been optimised from extensive wind tunnel testing. Lastly, the energy transmission subassembly transmits and conditions the mechanical energy from the energy converter to a generator, converting it into useful electrical energy.
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DMT06A Anchor and Frame
A great challenge faced by society today is meeting humanities energy needs without compromising the climate in an irreversible manner. Much effort has been spent developing renewable energies in recent decades to prevent such a scenario. Wind and solar technologies have been the main area of focus, seeing widespread adoption. However, wave power also presents a dense energy source with a potentially stable and predictable power output.
The super-project aims to create an oscillating wave column or OWC generator, a point absorber designed to harness the energy due to the relative motion of a body to a wave. Our team was tasked with creating a frame and anchor that would survive the harsh conditions experienced at sea and protect energy generation components housed within. The frame features a clear pipe to allow for observation of the turbine within; nozzles at the top and bottom to accelerate and diffuse airflow for turbine efficiency; and a shared exterior fixing method/layout to optimise rigidity and airflow. A testing rig is designed to facilitate more effective testing, constraining the frame's oscillation to the vertical direction.
Ocean waves contain large quantities of renewable, pollutant-free energy and utilising this energy is an attractive idea for nations with substantial coastlines. However, a method for extracting the energy in ocean waves has not yet been standardised and therefore the feasibility of the idea has been questioned. One category of possible designs is called an Oscillating Wave Column which floats on the surface of the water. An incoming wave raises the water level in an enclosed chamber, forcing air out through a hole at the top which turns a turbine attached to an electric generator. The aim of this project was to develop a turbine for use in this type of Wave Energy Converter.
The design utilised a Wells turbine which is symmetrical and thus turns the shaft in the same direction regardless of whether the air is entering or exiting the air chamber. It uses NACA0021 blade profiles, which are relatively thick blades, to increase the performance of the turbine at low air velocities and decrease the likelihood of stall. The turbine is also self-starting which is a critical characteristic due to the intermittent nature of ocean waves. A full-scale implementation of this design could reliably power an underwater data centre.
We present a novel energy transmission device built for use in an oscillating water column wave energy converter. The device performs multiple functions simultaneously, including mechanical energy transmission and conversion from turbine to generator with minimal frictional losses, structural interfacing between turbine and frame, and turbine speed control.
In an elegant solution, the entire design, including the generator, is integrated within the hub of the turbine, isolating it from the environment. It further benefits from a compact build, minimal mass imbalance for the general assembly, and low frictional losses.
The driving philosophy of the design is simplicity through multifunctionality, exemplified by the bottom bearing housing which also functions as a drive shaft and a vacuum seal boundary. Similarly, the generator casing also functions as a stationary support shaft that resists both axial and radial forces. The centrepiece of the design is an innovative, mechanical, instantaneous energy storage system used for turbine speed control, coined the axial variable inertia flywheel (AVIF). The highly efficient AVIF stores energy by changing its rotational inertia rather than rotational speed. It can therefore maintain a steady shaft speed whilst absorbing the transient energy of waves. In line with the design philosophy, the AVIF also acts as a self-stabiliser for any eccentricity in the rotating subassembly through its free flymasses.
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