Wave Energy Flashcards
How are waves formed?
From winds, wind storms.
Wind creates small ripples, ripples turn into wind waves, and leaving the storm area as swells.
What parameters are wave height and period dependent on?
Wind speeds, fetch length, duration of storm.
What parameters are used to describe a wave?
height: H Wavelength: lambda Period: T phase velocity: c zero crossing period: To
What kind of statistical parameters are used in wave description?
mean wave height: Hs = average of largest 1/3
mean wave period: Tm = average of all wave periods
peak wave period: Tp = period of waves representing the highest energy in the wave spectrum
What kind of distribution are used for waves?
Rayleigh distribution
How are deep water waves classified?
depth > 1/2lamda
What is the phase velocity of deep water waves?
see slide 153 for formula
How is the transitional regional waves classified?
1/2 lamda > depth > 1/20 lamda
What is the phase velocity in the transitional region?
see slide 153 for formula
How are shallow water waves classified?
depth
what is the phase velocity of shallow water waves?
see slide 153 for formula
mention three things that happens to waves when they run ashore.
- wavelenght decreases
- wave height decreases
- waves are getting steeper
What path does the water molecules follow?
deep water - orbital
gets more and more elliptical as the depth decreases.
What is the critical wave steepness before a wave breaks?
H/L = 1/7
What happens to the energy of a breaking wave?
Dissipated
What types of sea waves do we have?
capillary waves wind waves swells tsunami storm floods
What is the energy flux density of waves?
see slide 156
Where is the largest wave energy potential on the earth?
northern and southern west wind belts. Formed from the westerlies.
When did the first wave energy utilization patent dated?
1799
List soe epros and cons for wave energy utilization in comparison with other renewable resources.
+ high energy concentration
+ offshore, no land mass required
+ ecologically and aesthetically unproblematic
+/- potential comparable to biomass, wind and hydro power
- extremely hostile environments for engineering structures
- offshore, difficult to maintain
- high number of load cycles
- storm loads can be as high as 50-100 times the avg. load.
Santa cruz’s West Cliff Drive Wave Motor
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What does WEC stand for?
Wave Energy Converter
What are the three main categories of wave energy converters?
- Floating Body Converters
- Oscillating Water Column Converters (OWC)
- Overtopping Converters
What’s the principle of a floating body converter?
A floating body is moved up and down by the waves. The work resulting from the movements is exploited via high pressure hydraulics or electric linear generators.
Explain the principle Power Takeoff system (PTO) of a floating body converter.
see slide 166-167.
What kind of different PTO systems do we have?
Oil Hydraulic PTO, Water Hydraulic PTO, Pneumatic PTO, Mechanic PTO
List efficiency, and some pros and cons for each of the PTO systems for Floating Body Converters.
see slides 168 - 171.
Linear Electric generator PTO system, pros and cons, efficiency.
+ 85%
- waterproofing
- costly power electronics
How does the Floating Body Converter from CETO, Australia work?
Floating bodies creates high pressure salt water which is taken ashore to drive a pelton turbine.
List a few wave energy project that has emerged over the recent years.
PELAMIS
Salter’s Duck (succesful lab test)
Aqua BuOY (pelton)
Fred Olsen FO3
Wave Star
Archimedes Wave Swing
Searev, high pressure oil hydraulics, inner pendulum
Circular Wave Energy Converter, CWEC
- floater mounted on crank, circular motion
The Oyster, util. circ. motion of water molecules, oil hydr.
The Anaconda, high pressure waves, water turbine
What is the working principle of a Oscillating Water Column (OWC)?
- Waves are exciting oscillations of an enclosed water col.
- Air displaced is driving an air turbine
- On shore or floating offshore device
What is the main advantage of an OWC?
slow movement of big water surface results in high air velocity. Small turbine with high energy density.
Problems with the OWC?
reciprocating air stream –> continuos rotary motion of the generator. One turbine reversing twice during every wave period. most of the energy is lost in acceleration and deceleration of the turbine.
Explain the power takeoff on an OWC.
Wells turbine. symmetrical blade, thick leading edge. Turbine moves in same direction irrespectively of the flow direction.
Projects using OWS?
Mighty Whale, Japan
Pico Plant, Onshore, damaged by storm flood
LIMPET: WaveGen and Voith Siemens
Explain the principle of Overtopping Converters
Waves run up a slope and overtop into a reservoir situated above the mean sea water level.
Potential energy in the reservoir exploited usin low head hydrturbines.
Shape and slope is optimized for maximum energy capture –> capturing the biggest volume possible.
What are some adv. with the overtopping system?
+ no moving parts except for the turbine offcorse
+ proven to be a durable technology for power takeoff
+ steady
Some restrictionswit overtopping system?
Only onshore
Only feasible with small tidal range.
Examples of overtopping Converters?
Tapchan, Norway -> planned installation on Java
WaveSSG, Norway
Explain the WaveSSG system
Overtopping in three stages with separate turbines for each stage –> utilizing the whole wave spectrum
++++ can be combined with wave breakers in harbours
WaveSSG project:
Kvitsøy, Norway --> Kvitsøy project 2005 Wave climate survey from Aalborg Uni Power Simulation from TUM Turbine layout, TUM Project stopped 2007 - still looking for a new site!
Explain the Wave Dragon functional principle + project history.
see slides 199 - 229 (lots of pictures)!
