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Ocean & Wind Energy > Wave Energy > Flashcards

Wave Energy Flashcards

1
Q

How are waves formed?

A

From winds, wind storms.

Wind creates small ripples, ripples turn into wind waves, and leaving the storm area as swells.

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2
Q

What parameters are wave height and period dependent on?

A

Wind speeds, fetch length, duration of storm.

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3
Q

What parameters are used to describe a wave?

A 
height: H
Wavelength: lambda
Period: T
phase velocity: c
zero crossing period: To
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4
Q

What kind of statistical parameters are used in wave description?

A

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

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5
Q

What kind of distribution are used for waves?

A

Rayleigh distribution

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6
Q

How are deep water waves classified?

A

depth > 1/2lamda

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7
Q

What is the phase velocity of deep water waves?

A

see slide 153 for formula

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8
Q

How is the transitional regional waves classified?

A

1/2 lamda > depth > 1/20 lamda

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9
Q

What is the phase velocity in the transitional region?

A

see slide 153 for formula

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10
Q

How are shallow water waves classified?

A

depth

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11
Q

what is the phase velocity of shallow water waves?

A

see slide 153 for formula

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12
Q

mention three things that happens to waves when they run ashore.

A
  • wavelenght decreases
  • wave height decreases
  • waves are getting steeper
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13
Q

What path does the water molecules follow?

A

deep water - orbital

gets more and more elliptical as the depth decreases.

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14
Q

What is the critical wave steepness before a wave breaks?

A

H/L = 1/7

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15
Q

What happens to the energy of a breaking wave?

A

Dissipated

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16
Q

What types of sea waves do we have?

A 
capillary waves
wind waves
swells
tsunami
storm floods
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17
Q

What is the energy flux density of waves?

A

see slide 156

18
Q

Where is the largest wave energy potential on the earth?

A

northern and southern west wind belts. Formed from the westerlies.

19
Q

When did the first wave energy utilization patent dated?

A

1799

20
Q

List soe epros and cons for wave energy utilization in comparison with other renewable resources.

A

+ 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.

21
Q

Santa cruz’s West Cliff Drive Wave Motor

A

-

22
Q

What does WEC stand for?

A

Wave Energy Converter

23
Q

What are the three main categories of wave energy converters?

A
  1. Floating Body Converters
  2. Oscillating Water Column Converters (OWC)
  3. Overtopping Converters
24
Q

What’s the principle of a floating body converter?

A

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.

25
Q

Explain the principle Power Takeoff system (PTO) of a floating body converter.

A

see slide 166-167.

26
Q

What kind of different PTO systems do we have?

A

Oil Hydraulic PTO, Water Hydraulic PTO, Pneumatic PTO, Mechanic PTO

27
Q

List efficiency, and some pros and cons for each of the PTO systems for Floating Body Converters.

A

see slides 168 - 171.

28
Q

Linear Electric generator PTO system, pros and cons, efficiency.

A

+ 85%

  • waterproofing
  • costly power electronics
29
Q

How does the Floating Body Converter from CETO, Australia work?

A

Floating bodies creates high pressure salt water which is taken ashore to drive a pelton turbine.

30
Q

List a few wave energy project that has emerged over the recent years.

A

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

31
Q

What is the working principle of a Oscillating Water Column (OWC)?

A
  • Waves are exciting oscillations of an enclosed water col.
  • Air displaced is driving an air turbine
  • On shore or floating offshore device
32
Q

What is the main advantage of an OWC?

A

slow movement of big water surface results in high air velocity. Small turbine with high energy density.

33
Q

Problems with the OWC?

A

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.

34
Q

Explain the power takeoff on an OWC.

A

Wells turbine. symmetrical blade, thick leading edge. Turbine moves in same direction irrespectively of the flow direction.

35
Q

Projects using OWS?

A

Mighty Whale, Japan
Pico Plant, Onshore, damaged by storm flood
LIMPET: WaveGen and Voith Siemens

36
Q

Explain the principle of Overtopping Converters

A

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.

37
Q

What are some adv. with the overtopping system?

A

+ no moving parts except for the turbine offcorse
+ proven to be a durable technology for power takeoff
+ steady

38
Q

Some restrictionswit overtopping system?

A

Only onshore

Only feasible with small tidal range.

39
Q

Examples of overtopping Converters?

A

Tapchan, Norway -> planned installation on Java

WaveSSG, Norway

40
Q

Explain the WaveSSG system

A

Overtopping in three stages with separate turbines for each stage –> utilizing the whole wave spectrum
++++ can be combined with wave breakers in harbours

41
Q

WaveSSG project:

A 
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!
42
Q

Explain the Wave Dragon functional principle + project history.

A

see slides 199 - 229 (lots of pictures)!

Ocean & Wind Energy (3 decks)

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