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The Surf Turbine

This is the Subwave turbine turned sideways and put on a stand. It's for deployment near land where the waves start to "feel" the bottom. When the depth is substantially less than half the wavelength, the movement of the water particles becomes more and more flattened and the oscillation becomes increasingly horizontal . This is shown in more detail below.

Credit: Kraaiennest / CC BY-SA. Wikimedia Commons.

Here we see shallow water waves, with a wave length much longer than the water depth. The red circles are the present positions of massless particles, moving with the flow velocity. The light-blue line gives the path of these particles, and the light-blue circles the particle position after each wave period. The white dots are fluid particles, also followed in time. In the case shown here, the mean horizontal velocity below the wave trough is zero. We can clearly see that there is a marked water transport in the upper layer in the direction of the waves. In this case the bottom is flat.

Credit: J. Buhr Hansen & I.A. Svendsen. Wikimedia Commons.

However, if the bottom slopes upwards towards land, as it often does, this water must flow back again. This happens close to the bottom, as this figure shows. It is called "undertow". Incoming waves transport water in the upper part of the profile, while it flows out again along the bottom. The boundary zone between the two opposite flows fluctuates constantly, so that at a given point the flow will soon go in, soon outward from land. It is in this area the surf turbine will be located.

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