Ocean waves are a huge, large untapped energy source, which is a considerable renewable energy source that can generate the useable energy forms. This review introduce the general status of wave energy and evaluate the device types that represent current wave energy converter (WEC) technology which defer according to the location, type and the modes of operation, power take off (PTO) methods Benefits and the challenges that have to face during the ocean wave power generation. Ocean wave energy power can contribute to the Sri Lanka power crisis. Wave climate and geographical construction around the country and best places to establish the wave energy power plant in the Sri Lanka and available technologies. Social and environmental impact of wave power plant.

1. ME 6213 RESEARCH METHODOLOGY AND ETICS
Review of journal articles of Wave Energy Converters and their Impact on
Power Systems in Sri Lanka
Submitted to
Department of Mechanical and Manufacturing Engineering
University of Ruhuna
Hapugala
Dinusha GLN
EG/2014/2392
24/10/2017

2. 1
Abstract
Ocean waves are a huge, large untapped energy source, which is a considerable
renewable energy source that can generate the useable energy forms. This review introduce
the general status of wave energy and evaluate the device types that represent current wave
energy converter (WEC) technology which defer according to the location, type and the modes
of operation, power take off (PTO) methods Benefits and the challenges that have to face
during the ocean wave power generation. Ocean wave energy power can contribute to the Sri
Lanka power crisis. Wave climate and geographical construction around the country and best
places to establish the wave energy power plant in the Sri Lanka and available technologies.
Social and environmental impact of wave power plant [1-2].
Introduction
Since industrialization, the use of fossil fuel energy has increased with the large
amount of side effects like global warming, environmental pollution, decreasing the life
expectation of the living beings. As a result, the importance of renewable energy is on the rise,
and energy sources that use wind, sun, ocean wave and geothermal heat. Among these energy
sources wave energy have a unique energy flow, which reciprocation motion, high energy
density with slow speed and seasonal variations in heights and periods [2-4].
1. Ocean wave energy
Wave power is the transport of energy by wind waves and a unlimited renewable energy source
that can get free, and the capture of that energy to do useful work for example, electricity
generation, water desalination, or the pumping of water (into reservoirs). A machine able to
exploit wave power is generally known as a wave energy converter (WEC).
2. Benefits and Challengers
Sea waves offer the highest energy density among renewable energy sources. Limited negative
environmental impact in use. Natural seasonal variability of wave energy, which follows the
electricity demand in temperate climates. Waves can travel large distances with little energy
loss. Storms on the western side of the Atlantic Ocean will travel to the western coast of
Europe, supported by prevailing westerly winds. It is reported that wave power devices can
generate power up to 90 per cent of the time, compared to ∼20–30 per cent for wind and solar
power devices. When considering the challengers that occur working with the ocean wave is
conversion of the slow, random and high force oscillatory motion into useful motion to drive

3. 2
a generator with output quality acceptable to the utility network. This variable input has to be
converted into smooth electrical output, for that some energy storage system or an array of
devices is required. There are also design challenges in order to mitigate the highly corrosive
environment of devices operating at the water surface [2].
3. Wave energy converters (WEC)
There are over 1000 wave energy converting concepts and method all over the world. Despite
this large variation in design, WECs are generally categorized by location, type and the modes
of the operation. There are three type of locations in the oceans according to the establishment
of the wav energy power plant. Shoreline devices which can be placed on sea bottom in
shallow water, Near to shore devices which can be deployment in approximately 10 -20 meters
of water depth, hundreds of meters or up to some kilometers away from shore and the offshore
devices which Floating or submerged devices in deep waters, moored to the sea floor. The
advantage of siting a WEC in deep water is that it can harvest and generate greater amount of
energy because of the higher energy content in the deep water waves but it is difficult to
construct and maintain because of the greater wave height and energy content in the waves,
need to be designed with high strength and non-corrosive materials. But, floating devices in
deep water offer greater structural economy. It is useful to note that wave energy occurs in the
movements of water near the surface of the sea. Up to 95% of the energy in a wave is located
between the water surface and one-quarter of a wave length below it. From the large variation
in designs and concepts, WECs can be classified into three predominant types. Which are
point absorber (Figure 1), attenuator (Figure 2) and the terminator (Figure 3) [2-5].
Methods of operation also can be divided in to the three main four main categories,
which are submerged pressure differential (Figure 3), oscillating wave surge converter,
oscillating water column (Figure 4) and the over topping device [2,6-7,9,12].
Figure 1: Point absorber
device: OPT Powerbuoy [3].
Figure 2: Attenuator device:
Pelamis wave farm [6].
Figure 3: Terminator device:
Salter’s Duck [7].

4. 3
4. Power take off methods
The method of energy capture varies from device to device, but the general method of
producing electrical power is through conventional high-speed rotary electrical generators is
slightly different same concept for all devices. Let’s consider different types generator which
are rotary generator type, turbine transfer and electrical linear generation [1, 2].
Rotary generator type
Electricity generated through the magnetically interaction between the stator and rotary. This
can be divided sub models according to the behavior and the type of the stator and the rotary
(permanent magnet or a field winding).
 Double fed induction generator
 Squirrel cage induction generator
 Permanent magnet synchronous generator
 Field wound synchronous generator
Figure 3: Submerged pressure differential [8]. Figure 4: OWC: the Limpet [10].
Figure 5: Overview of different wave energy extraction systems [1].

5. 4
Turbine transform
Turbine transfer’ is the term used here to represent the method employed in devices where the
flow of fluid (either sea water or air) drives a turbine, which is directly coupled to a generator.
The types of devices using direct transfer include OWCs and overtopping devices and the air
transfer through the oscillation water column method. Propeller-type turbines are often used
for the turbines generators.
Electrical linear generator
A linear synchronous generator offers the possibility of directly converting mechanical energy
into electrical energy. The electrical direct drive PTO alternative. This method is much simpler
than other methods, with no intermediate steps between the primary interface and the electrical
machine. Conventional electrical machines are designed to be driven with high-speed rotary
motion. The air gap speed between the rotor and stator in these machines can be high (upwards
of 60 m/s) allowing for easy conversion into a rapid change in flux [2, 3].
5. Ocean wave energy machine control
In regular waves, energy is captured most efficiently in a point-absorber-type WEC when the
undammed natural frequency of the device is close to the dominant frequency of the incident
wave. At resonance, the velocity of the oscillator is in phase with the dynamic pressure (and
hence force) of the incoming wave, resulting in a substantial transfer of energy from the wave
to the oscillator. The behavior of the device therefore is dependent on the damping. For most
power extraction, damping must be adjusted to achieve maximum energy conversion
efficiency. If the damping is too high then the motions are limited and little power is produced.
If the damping is too light, then the damper absorbs little power and little power is taken off.
With any PTO system, the correct damping is vital for an efficient system. Control can be
divided in to three main categories, which are latching control, reactive loading control and
the simulation for controller development.
6. Research and Development
Modeling and Simulation of wave Energy converter INWAVE
INGINE Inc. developed its own wave energy converter (WEC) named INWAVE and has
currently installed three prototype modules in Jeju Island, Korea. This device is an on shore
type WEC that consists of a buoy, pulleys fixed to the sea-floor and a power take off module

6. 1
(PTO). Three ropes are moored tightly on the bottom of the buoy and connected to the PTO
via the pulleys, which are moving back and forth according to the motion of the buy.
Since the device can harness wave energy from all six degrees of movement of the
buoy, it is possible to extract energy efficiently even under low energy density conditions
provided in the coastal areas [8]. In the PTO module, the ratchet gears convert the
reciprocating movement of the rope drum into a uni-directional rotation and determine the
transmission of power from the relation of the angular velocities between the rope drum and
the generator. In this process, the discontinuity of the power transmission occurs and causes
the modeling divergence [8]. The concept of the virtual torsion spring is used in order to
prevent the impact error in the ratchet gear module, thereby completing the PTO modeling.
The generator uses a 20-kW permanent magnet synchronous generator (Yaskawa, Tokyo,
Japan) and is linked to the grid through an AC/DC converter (LSIS, Gyeonggi-do, Korea) and
a DC/AC inverter [8].
Impact of Generator Stroke Length on Energy Production for a direct drive
wave Energy Converter
The Lysekil wave energy converter (WEC), developed by the wave energy research groupof
Uppsala University, has evolved through a variety of mechanical designs since the first
prototype was installed in 2006 (Figure 07). The WEC model consists of two parts, a buoy
floating on the surface and a linear generator at the seabed. The floating buoy is connected to
the generator via a line. Electrical power is converted by the relative motion between a fixed
stator and a movable translator, as illustrated in Figure 7. There are two end stops installed
Figure 6: Schematics of the INWAVE device model configuration [8].

7. 2
inside the generator, with the purpose to protect the generator from damage during rough wave
conditions [9].
7. Impact of ocean wave energy for Sri Lanka
Wave climate in Sri Lanka
Lots of analyzed data are needed to investigate the most suitable place to establish a Wave
Energy Power Plant (WEPP). There is no any ocean wave power plant in the Sri Lanka since
it covered all around the ocean. There isn’t any detailed information available, in this study,
alternative solutions such as wave data prediction based on wind data have been investigated.
Using the geographical location of Sri Lanka, a first estimation was made to find where the
most energetic waves hit the coast. The north western part of Sri Lanka is in the shadow of
India and the east side is relatively closer to Malaysia, Indonesia and Burma (see Figure 1). It
is more difficult to get larger swells due to the restricted fetch in North West and north east
areas. Therefore, it restricts the energy content in the waves. On the other hand, southern part
of Sri Lanka opens all the way to Antarctica, which enables a long fetch to have good waves.
By considering the two monsoon that effect to the Sri Lanka which are the north east monsoon
and the south west monsoon, southwest part of the Sri Lanka is full of strong large waves [1].
Figure7: illustration of the wave energy converter (WEC) device developed in Lysekil Project: (a)
one of the WEC prototypes L12 was assembled at the harbour; and (b) a simplified mechanical
structure of a direct-drive type WEC device.

8. 3
Figure 6: Wind patterns around Sri Lanka during two monsoon periods: (a) North east, (b)
South west [1].
According to the above details following cities are the most suitable for establish the ocean
wave power plant.
1. Matugama 2. Galle/Unawatuna 3.Matara
4. Hambantota 5. Bundala 6. Palatupana
8. Social and Environmental Concerns
Social and environmental concerns have to be considered before establishing the wave energy
power plant. This can effect to the costal activities, marine biology, water pollution, visual
effects and land uses. These environmental impacts and other problems can be avoided by
selecting and design the eave energy power plants in proper places.
Conclusion
The potential for generating electricity from wave energy is considerable. The ocean is a huge
resource, and harnessing the energy in ocean waves represents an important step towards
meeting renewable energy targets. This review introduces the current status of WEC
technology. The different device types are established and evaluated. Future research should
take a systems engineering approach, as the individual subsystems of a WEC are all intimately
related and any one should not be optimized without considering the other subsystems.
Furthermore, individual WECs will often operate as part of a wave farm, so future systems
analysis must include the interaction between devices.

9. 4
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