hydro-elasticity presentation
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WAVE ENERGY CONVERTERSHydro-elastic perspective
GIRISH DEV KUMAR CHAURASIYA (10NA10011)AVEEK GIRGOSWAMI (10NA30007)
The policy
To utilize the energy in waves to produce electricity
Why offshore? The waves on the open sea have great
energy potential Negligible environmental impacts Minimize the use of fossil fuels in the long
run
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Topics
What causes waves? Wave energy converters Offshore devices Hydroelastic perspective on WECs Advantages/disadvantages
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What causes waves?
The wave energy resource is a concentrated form of solar energy
Winds generated by the differential heating of the earth pass over open bodies of water
The wind pushes surface water particles along with it, setting up a rolling motion in the water and moving the water particles in a vertical, circular path
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Wave energy densities
The power in a wave is proportional to the square of the amplitude and to the period of the motion
Large amplitude (~2 m), long period (~7-10 s) waves have energy fluxes commonly exceeding 40-50 kW/m width of oncoming wave
Wave energy is unevenly distributed over the globe
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Wave energy densities around the globe
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Wave climate in Europe The wave climate along the western coast of
Europe is characterized by particularly high energy. The UK has over half the wave energy potential in Europe, up to 75 kW/m off Ireland and Scotland
Wave climate in the US The West Coast is the most promising area
with wave energy densities in the 25 – 40 kW/m range
Wave energy converters
Four different types of WECs: Oscillating water columns Overtopping devices Point absorbers Surging devices
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Wave energy converters The oscillating water
column Partly submerged
structure with an opening to the sea below the water line
Waves cause the water column to rise and fall, which alternately compresses and depressurizes the air column
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~ This air flows through a turbine which drives an electric generator
Overtopping device mechanism
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Wave energy converters Point absorbers
They provide a heave motion that is converted by mechanical/ hydraulic systems in linear or rotational motion for driving electrical generators
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Wave energy converters
Surging devices Surging devices exploit
the horizontal particle velocity in a wave to drive a deflector or to generate pumping effect of a flexible bag facing the wave front
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Placement of wave energy converters
Three locations Shore Near shore Offshore
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Placement of WECs
Shore/Near shore vs. offshore The potential energy
The power available in the waves is much greater offshore
Near the coastline the average energy intensity of a wave decreases due to interaction with the seabed
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Placement of WECs
Other factors Engineering challenges Construction costs Maintenance and/or installation costs Transmission costs and losses Environmental impacts The scale of electricity production
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Offshore devices
The Pelamis Is a semi-submerged structure composed of
cylindrical sections linked by hinged joints
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Offshore devices
The Pelamis 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
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Offshore devices The Pelamis
Several devices can be connected together and linked to shore through a single seabed cable
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Offshore devices The Pelamis
A typical 30MW installation would occupy a square kilometer of ocean and provide sufficient electricity for 20,000 homes
Ocean Power Delivery has won a bid for a 750kW project off Islay, Scotland and has recently signed a memorandum of understanding with BC Hydro to develop a 2 MW project off the coast of Vancouver Island, Canada
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Hydro elastic overview
Hydroelastic response of a floating structure can be improved to enhance the safety, serviceabilty, efficiency levels of a wave energy converter.
However, there are some limitations :
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Hydro elastic Limitations
Increasing the structural stiffness. But this approach is not cost effective since larger
structural stiffness translates to need of more and more material.
Surround by breakwaters.Not suitable when the water depth is large.
Disrupted water flow because of the breakwater might result in environmental issues.
Use of air cushion (low frequency incident waves)Sloshing problems might arise because presence of
air columns. Interior space is unnecessarily wasted.
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Reducing hydroelastic response:
Installation of anti motion devicesHowever these devices must have large draft to be
purposeful. They might obstruct incoming ships. Attaching another floating structureExtensive parametric study is reqd. to find
appropriate properties of attachment as well as the connection.
Wave energy converters are usually built by connecting modules of smaller size. So investigation can be done on them to reduce the hydroelastic response.
21Hydro elastic LimitationsReducing hydroelastic response:
In case wave induced response is used to generate electricity which is the case here in our wave energy converter, an increase is response is also desirable
It is important to examine the possibility of maximizing the wave capturing efficiency of the machine by introducing the ability to adjust not only the rotational stiffness(pelamis case) but also the locations connections to the machine.
22Hydro elastic LimitationsIncreasing the hydroelastic response:
Two approaches
First approach objective is to study the effects of length, flexural rigidity and mass of attachments, as well as rotational stiffness of the connections on the hydroelastic response of the main floating structure.
Second approach is to seek for an optimum connection design for a multi-module wave energy converter. This approach will maximize he efficiency of a large floating beam used as a wave energy converter.
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Advantages
Advantages of offshore wave energy Sea waves have high energy densities, the
highest among renewable energy sources Wave energy is generally considered to
provide a clean source of renewable energy with limited negative environmental impacts
It could become a significant source of energy not involving CO2 emissions
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Advantages
The natural seasonal variability of wave energy follows the electricity demand in temperate climates
Negligible demand on land use Could secure energy supplies in remote
regions Large-scale implementation of wave power
technologies will stimulate declining industries, e.g. shipbuilding
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Disadvantages
Disadvantages of offshore wave energy The main wave energy barriers result from
the energy carrier itself: The sea The peak-to-average load ratio in the sea is
very high and difficult to predict The structural loading in the event of
extreme weather conditions, such as hurricanes, may be as high as 100 times the average loading
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Disadvantages
High construction costs induce high power generation costs, thus making the technology uncompetitive
The incidence of wave power at deep ocean sites is three to eight times the wave power at adjacent coastal sites, but the cost of electricity transmission from deep ocean sites is often prohibitively high
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Environmental impacts
Offshore wave energy devices may be a potential navigation hazard to ships
Near shore devices will have a visual impact Wave energy devices could have an effect on
some forms of recreation Impacts on the marine environment
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Thank You
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