Pneumatic system

A typical pneumatic system for a WEC, known as an Oscillating Water Column (OWC), consists of a partially submerged air compartment with one end open to the ocean and the other open to the atmosphere. As the water level inside the chamber oscillates with incoming waves, so too must the air above it, which is hence periodically expelled to and drawn from the atmosphere. The energy in the waves is thus converted into an oscillating column of air with a velocity greater than that of the waves, Figure 2.1, which may then be converted to high speed rotary motion by an air turbine.

low force, high low force, high velocity

velocity high force, low velocity

♦ waler/ air interface

Figure 2.1: Pneumatic gearing in an OWC

In the 1970's Professor A Wells of Queens University Belfast proposed a form of self rectifying axial flow air turbine which rotates in the same direction irrespective of the direction of airflow. The Wells' Turbine became part of the standard power take off system for any OWC proposed as it provides a simple method of rectifying the movement of the air into high speed rotary motion. Further research, however, has highlighted its inherent disadvantages such as low efficiency (<40%), poor starting, high noise and high axial thrust when compared with a traditional turbine [47]. Variable pitch turbines, either externally controlled with hydraulics [48] or with self pitch control [49], have since been proposed. Both of these offset slightly the Wells' turbine disadvantages. It should be noted that the requirement for this type of unidirectional turbine technology is specific to WECs, which implies that research into efficiency improvements will only be carried out within the wave energy community.

The entire pneumatic system and turbine acts as a mechanical linkage both increasing and rectifying the motion contained within a wave. Furthermore, the resonant frequency of such a device and the power extracted from the ocean may be controlled by restricting the airflow through the turbine or by venting directly to the atmosphere.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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