The Cetus Technology
• Understanding the true nature of the Energy source
The notion that the energy contained in wave motion is expressed in its up-and-down movement is as erroneous as it is prolific. Adherence to that notion has resulted in a plethora of devices designed to exploit the vertical oscillatory motion of the sea surface, nearly all of which extract only a small proportion of the total energy contained in the wave system. This is because such systems only harness a proportion of the POTENTIAL energy represented by the wave section that is above ambient sea-level, whereas the full energy quotient of the wave is represented by the KINETIC energy of its participating particles. To illustrate this anomaly, we can hypothesise about an imaginary Oscillating Water Column device (OWC generator) placed on one of the shores recently devastated by the Indonesian Tsunami. In most of the sites that suffered such destruction, the device would have registered and collected energy from one or two wave cycles of two or three metres height, producing barely enough energy to light a few dozen light bulbs for a minute or so. Yet, as we all know, the total energy contained in those waves was enough to destroy whole towns and kill thousands of people with its unstoppable power. The first indicator and expression of that power was not the wall of water approaching the beaches, but the retreat of the water from those beaches as it was sucked to seaward as part of the wave motion. The KINETIC energy contained in that first movement was many times more than could be extracted by any device utilising just the variation in surface height of the approaching wave. It is the fundamental understanding of this kinetic energy that defines the first rules in the design process for Cetus. Such an understanding determines that: (a). The Particulate flows exist within the wave system, and represent the highest energy source. (b). Such flows will be essentially chaotic in nature, although there must be a determined flow 'cell' size, dictated by the operating volume of an individual bladehead. (c). Each flow 'cell' is assumed to have a predominately linear flow within its boundaries, even though in reality there will be further turbulences contained within. (d). The linear flow vector of any cell will constantly vary, requiring that the common axes of a single blade's sub-blades self-rectify in response to this variance to increase thrust and reduce stall turbulence. (e). The highest particle velocities are to be found at the surface, and diminish with depth. This requires that the swept volume of the energy extraction device be contained within a shallow depth. The Design Solution (a). The propulsion device has to exhibit multiple lifting surfaces to respond to the variation of flow directions. The minimum number of these is two, arranged at right angles to each other. (b). This 'sub-assembly' of blades must be flexibly mounted to respond to changes in flow directions. (c). A large number of small blades is preferable to a small number of large blades since a greater conformity to the variance in flow vectors is achieved, with the added benefit that opposing forces on the overall mounting of the device tend to cancel each other out, allowing a lighter tethering or mounting solution. (d). Design must include weed-shedding characteristic. (e). The Primary Component (the Blade Assemblies) must be simple in operation, robust enough to achieve realistic life-cycles, cost-effective in terms of power output, and be environmentally friendly. |
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