"Visualizing The Future- HARVESTING ENERGY FROM TIDES"

My Theory on Structural Design and Mathematical Modelling of a Revolutionary  Uni-Directional Tidal Flap Turbine with Advanced Sea Bed Installation Methodology.

The oceans have long been recognized as a potential source of energy. The ocean's motion carries energy in the form of tides, currents, and waves. The interest in tidal power is constantly increasing thanks to its high predictability, the huge potential of tides and the actual need for renewable energy. It explains the emergence of many tidal turbine designs, especially in Coastal Countries like India, often inspired from wind turbines. All of them are at a more or less early stage of development. But because of the high density of water, environmental drag forces are very large compared with wind  turbines of the same capacity. Therefore the knowledge acquired by the wind industry is certainly qualitatively useful, but it has to be reconsidered to be applicable to tidal turbines. The aim of the project presented in this paper is to create a 1 MW Uni-directional flap tidal turbine, The tests focused on estimation of torque, which are an important reason of failure, and thus will help tidal turbine designers in their work by gaining valuable experience in turbine performance in various operating conditions. The designed  turbine has a vertical axis and four  blades, which have been  designed using the blade element momentum theory for a diameter of 1 m. This blog describes the structural design of a  Uni-  directional flap tidal turbine blade. The structural design is preceded by two steps:   Drag base  hydrodynamic design and determination of extreme loads. The  Drag base hydrodynamic design provides the chord and twist distributions  along the blade  length that  result in  optimal performance of the Uni Directional flap tidal turbine. The extreme loads, i.e. the extreme flap and edgewise loads that the blade  would likely encounter over its lifetime, are associated with extreme tidal flow conditions and are  obtained  using a computational fluid dynamics (CFD) software.

General Arrangement of Flap turbine:  

The turbine has four blades with flaps in them. Basically, the flaps are valves designed to operate in one direction. The four blades are placed at right angles to each other. These blades are rigidly attached to the central rod, and hence rotate it.

As shown, when the flow is towards north the flap opens. When the flow is towards south, the flap closes. A pair of such flaps (at least) is placed on either side of the central pivot as shown in later diagrams.  

The flow of waves direction is Northwards on the page. With  left  flap  closed  and  right  flap  open; more torque is generated on the  left  causing a  clockwise  rotation when viewed from the top. 

The flow direction is Southwards on the page.

With left flap open and right flap closed; more torque is generated on the right causing a clockwise rotation when viewed from the top. 

Thus the rotation is clockwise irrespective of flow direction. This is how the turbine looks to the wave or the view of the turbine from the lower drawing in colour is a slightly enlarged version of the one above with the colour added to make the dotted lines of the edges and flaps clearer.

It can be seen that after rotation the left flap (brown) comes to the right side. With flow into page, this opens while the blue one now on the left closes. i.e. no matter what, the flap on the right always opens to flow into the page. Thus the direction of rotation is clockwise when viewed from the top

It can also be seen that when flow is directed outwards from the page (for example when the wave goes back into the ocean) the right flap (blue) closes while the left flap (brown) opens. Thus the force exerted by the receding wave is also such that the rotation is clockwise when viewed from the top.

If we term the brown and blue pair together as a flap arm, with more such arms (say one normal to the plane of the paper) the rotation would be clockwise irrespective of flow direction.

Analysis and Estimation of Turbine Parameters:

The torque, specified with regard to the axis of rotation, is equal to the magnitude of the component of the force vector lying in the plane perpendicular to the axis, multiplied by the shortest distance between the axis and the direction of the force component. Regardless of its orientation in space, the force vector F can always be located in a plane parallel to the axis.

Force Acting on the single blade

   So in short, torque is the combination of force applied at a point with the right angle (perpendicular) distance from that point to the axis of rotation (in our case, this'll be an axle). The formula to compute torque is simply this:

T = F * d, where 

T = Torque 

F = Force (here, the force applied perpendicular to the axis)

d = Distance

The force vector F lies in the plane parallel to the line OL; the component FL, being parallel to OL, has no moment about OL, while the component FP, lying in the plane perpendicular to OL, has a moment, or torque, about OL equal to FP * d, in which d, the shortest distance between FP and OL, is the moment arm or lever arm.

You can visualize this simply:

Two dimensions View of the Flap turbine

So, if you had a pulley of 1 meter radius and a Blade fixed to it with a 1 ounce weight Attached to it and hanging down through the axis, it would produce 1 inch-ounce of torque on the its axis:

T = F * d = (1 oz.) * (1 mt.) = 1 meter-ounce

Bear in mind that we can also turn this all around. Given a value of torque, and the value of d (generally called the moment arm), we can also compute the tangential force that would be generated. Take our torque equation (T = F * d), and divide both sides of the equation by d:

T / d = (F * d) / d 

T / d = F 

So we're now armed with two powerful equations to follow torque through a system 

Before we get too far, you should be aware that we're making a few assumptions to simplify things:

a) Torque stays constant along a shaft (so we're neglecting any friction in bearings that hold the shaft in place). 

b) We're neglecting friction in our gears; a fairly accurate simplification for our applications. In particular, this means that force is the same on each gear at the contact point of two meshed gears (you'll see where this comes in later).

c) We can neglect the mass of any gears (the mass of gears only comes into play when they are particularly large, or particularly heavy -- both unlikely for BEAM bots).

 This equation has certain assumptions:

· The force has been calculated assuming that the wave has completely transferred its momentum to the turbine blade and the wave has stopped completely.

· Due to this, the actual torque generated will be less than this value.

· The force is expressed as the rate of change of momentum.

· Frictional losses in the rotating shaft have been neglected.

· Wave is assumed to be striking continuously.

· The already existing rpm of the blade has been neglected.

· The wave has been assumed to hit all parts of the blade equally i.e. uniform load distribution.

Installation Foundation Diagram

The research paper was published in International l Journal of Applied Research in n Mechanical Engineering (IJARME) ISSN: 223 31 –5950, Volume-2, Issue-1, 2012.

And The Short paper was published in International Conference on Energy Water and Environment (ICEWE '2011).

For more details you may please visit the Journal link. 

Paper Link: interscience.in/IJARME_Vol2Iss1/paper3.pdf