A Feasibility Study - Aaltodoc - Aalto-yliopisto

Analyzing waves and their movement in a defined and thorough way would require a
thesis or a dissertation of their own due to the complexity of the phenomenon. This,
however, is not the purpose of this thesis, and therefore only references to sources are
given, from which an inspired reader may find additional information from this field.
Excellent sources to begin with are Flügge (1960), Le Méhauté (1976), McCormick
(1973), Puolakka (2011) and Tucker (1991), but it has to be noted that literature is
ample with good sources.
2.2 Wave energy converters
In order to harness the power of the waves, there needs to be a device that transforms
the wave energy to a more useful type, usually to mechanical energy, from which e.g.
electricity can be made (McCormick 2007). At present, there are a great number of
different concepts for wave energy utilization (Polinder, Scuotto 2005), but not one
universally accepted configuration, like the three bladed turbine in wind energy industry
(Folley, Whittaker & Henry 2007). Also there does not exist one single agreed way of
classification of the different concepts (Polinder, Scuotto 2005).
Wave Energy Converters (WECs) can be classified e.g. by their position (on-shore, near
shore or offshore), by their size (point absorbers versus large absorbers) or by their
operating principle (Falcão 2010). In this thesis the classification based on the operating
principle is adopted and the main types shortly presented. A more detailed description
will be given of the WEC that will be used as part of the AaltoRO system.
Figure 5 represents eight operating principles that cover the majority of WEC types:
Figure 5a expresses an attenuator, which captures energy as the waves move the two
arms in relation to each other. Figure 5b is bulge wave, in which water travels through a
tube, gathering energy which can be utilized e.g. in a turbine at the other end of the
tube. Figure 5c is an oscillating water column (OWC), in which air is
compressed/decompressed according to the movement of the waves and energy
produced via a Wells turbine. Figure 5d is an oscillating wave surge converter (OWSC),
which utilizes wave surges near the shore.
Figure 5e is an overtopping device, in which waves wash in to a reservoir and are let out
through a turbine at the bottom. Figure 5f is a rotating mass, in which an eccentric mass
collects energy as it rotates in the waves. Figure 5g is a point absorber, which acquires
energy from the up/down movement of the buoy. Figure 5h is a submerged pressure
differential, which utilizes the pressure variations due to changes in the sea level (Aqua-
RET 2012, EMEC 2012).
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