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Energy is needed to make the spray. The proposed scheme will draw all the energy from the wind. Numbers of remotely controlled spray vessels will sail back and forth, perpendicular to the local prevailing wind. The motion through the water will drive underwater 'propellers' acting in reverse as turbines to generate electrical energy needed for spray production. Each unmanned spray vessel will have a global positioning system, a list of required positions and satellite communications to allow the list to be modified from time to time, allowing them to follow suitable cloud fields, migrate with the seasons and return to port for maintenance.

The problems of remotely operating and maintaining ropes, sails and reefing gear will be avoided if the vessels use Flettner rotors instead of sails. These are vertical

Figure 11.5 Anton Flettner's first rotor ship, the Baden-Baden, crossed the Atlantic in 1926.

spinning cylinders that use the Magnus effect to produce forces perpendicular to the wind direction. Anton Flettner built two sea-going ships. The first, named Buckau, then renamed Baden-Baden (Figure 11.5), crossed the Atlantic in 1926 (Seufert & Seufert 1983).

The rotors allow a sailing vessel to turn about its own axis, apply 'brakes' and go directly into reverse. They even allow self-reefing at a chosen wind speed. Flettner's rotor system weighed only one-quarter of the conventional sailing rig which it replaced. The rotor ships could sail 20° closer to the wind than unconverted sister ships. The heeling moment on the rotor flattened out in high wind speeds and was less than the previous bare rigging. With a wind on her quarter, the ship would heel into the wind. The only disadvantage of these vessels is that they have to tack to move downwind. Energy has to be provided for electric motors to spin the rotors, but this was typically 5-10 per cent of the engine power for a conventional ship of the same thrust. (After the Atlantic crossing, Flettner obtained orders for six more. He built one, Barbara, but had the rest cancelled as a result of the 1929 depression.) Flettner used drums of steel and, later, aluminium. Today much lighter ones could be built with Kevlar or carbon-reinforced epoxy materials. His main problem seems to have been to find bearings capable of taking the large aerodynamic forces at quite high velocities despite the geometric distortions of heavily loaded structures. The development by SKF of geometrically tolerant rolling bearings will have removed many of the difficulties. A major wind-turbine

Spin ralio rotor surface to wind

Figure 11.6 A collection of measured and calculated lift and drag coefficients for spinning cylinders.

Spin ralio rotor surface to wind

Figure 11.6 A collection of measured and calculated lift and drag coefficients for spinning cylinders.

manufacturer, Enercon, commissioned a Flettner rotor ship which was launched in August 2008. The launch design showed propulsion by four rotors, 4 m in diameter and 27 m tall.

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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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