Wave Energy

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Wave Energy
2013-12-07 13:44:19
Wave Energy

Wave Energy
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  1. Wave movement
    • Cause by surface winds
    • Period of about 6 seconds
  2. Cause of waves
    Transfer of energy from wind to sea
  3. Wells Turbine Diagram
  4. Force Diagram
  5. Types of velocity
    • Vc - absolute velocity
    • Vu - peripheral velocity
    • Vw - relative velocity
  6. Force Equations

  7. FT
    • Forward component of FL
    • Produces the thrust which drives the blade forward
  8. Wave Diagram
  9. Phase Velocity (c)
    The rate at which the phase of the wave propagates in space
  10. Wave energy and power (eqn)
    • A water particle whose mean position below the surface z moves in a circle of radius:
  11. Wave number (k)
  12. Oscillating water column diagram
  13. Oscillating water column
    • Wave motion induces pressure changes beneath the column
    • Pressure changes cause the water level in the chamber to oscillate
    • Oscillating water level cause airflow changes in the chamber
  14. Wells Turbine
    Consists of aerofoils whose symmetry directs the air in the same direction -> allows turbine to power generator regardless of airflow direction
  15. Water density
    Water is 800 times denser than air
  16. Why offshore
    • The waves on the open sea have great energy potential
    • Negligible environmental impacts
  17. Three locations of wave energy converters
    • Shore
    • Near shore
    • Offshore
  18. Shore downside
    Nearer the coastline the average energy intensity of a wave decreases due to interaction with the seabed.
  19. Offshore sdvantage
    Greater power available in the waves
  20. Factors in Placement (6)
    • Engineering challenges
    • Construction costs
    • Maintenance and/or installation costs
    • Transmission costs and losses
    • Environmental impacts
    • The scale of electricity production
  21. Basic methods for converting wave energy
    • Fixed (TAPCHAN and OWC)
    • Floating (floating devices and wave profile devices)
  22. Fixed WEC Devices
    Fixed WEC devices are either built into the shoreline or fixed to the seabed 

    The number of suitable sites is limited.
  23. TAPCHAN Diagram
    • tapered channel systems
    • consist of a tapered channel feeding into a reservoir that is constructed on a cliff
    • The narrowing of the channel causes the waves to increase their amplitude (wave height) as they move towards the cliff face
    • The kinetic energy of the moving wave is converted into potential energy as the water is stored in the reservoir
    • The stored water is then fed through a water turbine to generate electricity.
  25. TAPCHAN Advantages
    • Low maintenance costs
    • Reliable
    • Power on demand
  26. TAPCHAN Disadvantages
    Not suitable for all costal regions
  27. TAPCHAN suitable locations:
    • COnsistent waves
    • Good average wave energy
    • Tidal range less than 1m
    • Deep water near shore
    • Location for a reservoir
  28. OWC Advantages
    Air velocity can be increased by reducing channel cross sectional area
  29. Floating WEC Devices
    systems that are floating in the ocean, either close to shore or offshore
  30. Types of floating WEC devices
    • Powerbuoy
    • Wave Profile WEC devices (The Whale device, Pelamis, Salter duck)
  31. PowerBuoy Diagram
  32. PowerBuoy
    • Mechanical power is obtained by floats making use of the motion of water
    • Float moves up and down with the water
    • An air turbine is run by the compressed air which in turn drives an electrical generator producing electricity
    • The generated electricity is then transmitted to the shore through an underwater cable.
  33. Wave Profile Devices
    They float on or near the sea surface and move in response to the shape water rather than just the vertical displacement of water
  34. Mighty Whale Device
    • OWC based device for offshore operation
    • A 120 kW prototype with 3 OWCs in a row has been operating since 1998 1.5 km off Nansei Town, Japan at 40 m depth
  35. Pelamis (Sea Snake)
    • The Pelamis is a semi-submerged, articulated structure composed of sections linked by hinged joints
    • The wave induced motion of these joints is resisted by hydraulic rams which pump high pressure oil through hydraulic motors via smoothing accumulators
    • The hydraulic motors drive electrical generators to produce electricity
  36. Salter Duck
    • Generates electricity through the harmonic motion of the floating part of the device
    • The devices rise and fall according to the motion of the wave and electricity is generated through the motion.
  37. Salter Duck working principle
    The Duck rotates with a nodding motion as the wave passes. This motion pumps a hydraulic fluid that drives a hydraulic motor, which in turn, drives an electrical generator
  38. Advantages of offshore wave energy (6)
    • Sea waves have high energy densities
    • Clean source of renewable energy
    • Natural seasonal variability of wave energy follows the electricity demand
    • Negligible land use demand
    • Secure energy in remote regions
    • Stimulate declining industries
  39. Disadvantages of offshore wave energy (4)
    • The peak-to-average load ratio in the sea is very high and difficult to predict
    • The structural loading in extreme weather conditions may be as high as 100 times the average loading
    • High construction costs
    • Cost of electricity transmission from deep ocean sites
  40. Environmental Impacts
    • Navigation hazard to ships
    • Visual impact
    • Effect recreation
    • Marine environment
  41. Wave Equation Diagram
  42. Radius Equation (r)
  43. dV
    dV=dx dz
  44. dm
  45. Ek
  46. E
  47. Power carried forward in the wave (P')
  48. Group velocity (u)
    u = c/2