Week 2 - Class Test Flashcards
Give a brief description of a terminator wave energy device
Wave energy devices oriented perpendicular to the direction of the wave.
These terminators include a stationary component and a component that moves in response to the wave.
The “stationary” part could be fixed to the sea floor or shore. An oscillating water column (OWC) is, for example, a terminator
Give a brief description of an attenuator wave energy device
These devices are oriented parallel to the direction of the wave. One of the most well-known examples of this is the Pelamis.
The devices send the electricity through cables to the sea floor where it then travels through a cable to shore
What is a point absorber? Give an example of one such device.
Point absorbers work by drawing wave energy from the water beyond their physical dimensions, but they have small dimensions relative to the incident wavelength.
Tethered buoy systems, such as the aquabuoy for example, act as point absorbers.
Give some advantages and disadvantages of Fixed devices (usually terminators)
Advantage - Having a fixed frame of reference
and with good access for maintenance purposes
Disadvantages - they generally operate in shallow water and hence at reduced wave
power levels. In addition, there appears to be a limited number of sites for future deployment.
How does an oscillating water column (OWC) produce energy?
An air chamber pierces the surface of the water and the contained air is forced out of and then into the chamber by the approaching wave crests and troughs. On its
passage from and to the chamber, the air passes through an air turbine generator and so produces energy
Name an alternative to an OWC fixed wave energy device. Briefly describe how this device works.
Pendulor.
The Pendulor is a gate, hinged at the top, which
is fitted one-quarter of a wavelength from the back wall of a caisson. This is at the first antinode (i.e. a point of maximum amplitude of a series of waves) and so the gate is subjected to maximum movements resulting from the wave.
Name some floating wave energy conversion devices.
Duck Clam Pelamis Whale Backward Bent Duct Buoy (BBDB) Floating Wave Power Vessels (FWPV)
Discuss some of the advantages of floating wave energy devices in comparison to fixed devices
These devices should be able to harvest more energy than fixed, on-shore devices, since the wave power density is greater in offshore than in shallow water and there is little restriction to the deployment of large arrays of such devices
Discuss the basic premise of a Floating Wave Power Bessel (FWPV)
The device has been anchored at around 50-8om depth in practice. This device functions by capturing the water from waves that run up its sloping front face. The captured water is returned to the sea via a standard Kaplan hydroelectric turbine.
Describe how a ‘clam’ device works
The circular Clam consists of twelve interconnected air chambers, or cells, arranged around the circumference of a toroid, with Wells turbines in each cell.
At full scale this would be 60 metres or so in diameter, and would be deployed in deep water (40-100 water).
Each cell is sealed against the sea by a flexible reinforced rubber membrane. Waves cause the movement of air between cells. Air, pushed from one cell by the incident wave, passes through at least one of the twelve Wells turbines on its way to fill other cells. As the air system is sealed, this flow of air will be reversed as the positions of wave crest and trough on the circle change.
Describe a Pelamis device.
The Pelamis, or ‘sea snake’, is a device consisting of a number of cylindrical sections hinged together, though in this case these are arranged as an attenuator device and are therefore the active components. The wave-induced motion of the cylinders is resisted at the joints by hydraulic rams that pump high-pressure oil through hydraulic motors via smoothing accumulators, and the hydraulic motors drive electrical generators to produce electricity.
Other than fixed and floating devices; name another type of wave energy device
Tethered devices: Float systems, with the main body of the structure floating on the surface, but moored to the seabed via a pump
Which technology bears similarities to the premise behind Tidal Energy Converter Devices? What advantages do these have over the alternative technology.
Wind Turbines.
Due to the higher density of water, this means
that the blades can be smaller and turn more slowly, but they still deliver a significant amount of power.
What are the six main types of Tidal Energy Converters (TEC)? Briefly describe each of them.
- Horizontal Axis Turbine - extract energy from moving water in much the same way as wind turbines extract energy from moving air. The
tidal stream causes the rotors to rotate around the horizontal axis and generate
power. - Vertical Axis Turbine - similar to 1. however the turbine is mounted on a
vertical axis. The tidal stream causes the rotors to rotate around the vertical axis and
generate power - Oscillating hydrofoil - A hydrofoil is attached to an oscillating arm. The tidal current flowing either side of a wing results in lift. This motion then drives fluid in a hydraulic system to be converted into electricity
- Enclosed Tips (venturi) - Venturi Effect devices house the device in a duct which concentrates the tidal flow
passing through the turbine. The funnel-like collecting device sits submerged in the tidal current. The flow of water can drive a turbine directly or the induced pressure differential in the system can drive an airturbine - Archimedes Screw - a helical corkscrewshaped
device (a helical surface surrounding a central cylindrical shaft). The device draws power from the tidal stream as the water moves up/through the spiral turning the turbines. - Tidal Kite - tethered to the sea bed and carries a turbine below the wing. The kite
‘flies’ in the tidal stream, swooping in a figure-of-eight shape to increase the speed
of the water flowing through the turbine.
Name four horizontal axis wind turbine types
Multi-bladed wind pump
Two-bladed horizontal-axis wind turbine
Single-bladed horizontal-axis wind turbine
Three bladed horizontal axis wind turbine
