Forces on a submerged object due to currents in the ocean

  • #1

Main Question or Discussion Point

Attached is a picture of the object that I am trying to figure out the forces due to currents that will be acted on it.

Here are the questions I have ( I really just need some direction in the area of appropriate formulas)

1) what are the force againts the surface of the collector in foot pounds and pounds per square inches(umbrella looking part) when the angle at the base is 20 and 30 degrees and the total diameter is is 20', 30' 40', 50', and 60' at a current flow rate of 5 mph, 7mph, and 15, mph
2) Based on the above information what is the anchor weight if there are 4, 6 and 8 anchors deployed to keep it at a stable position for the various degress of the octogon (shape of the collector) and is position important.


I appreciate any help. I have not taken a class fluid mechanics and from everything I have read on the internet shear stress seems really important and I could be wrong but it seems that it will be the majority of the forces acting on it by a current.

Thanks
 

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  • #2
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well if you havnt taken any fluid mechanics and your just looking for a pointer:
what [i think] your looking at is the DRAG force.
current moving against the sationary object is equivalant to the object moving through a stationary fluid. it will be resisted by drag.
the formula iirc is
[.5]*[fluid density]*[[velociy]^2]*[drag coefficient]*[frontal area]

the drag coefficient is the achilles heel. its pretty hard to determine mathmatically and may need to be experimentally determined in wind or water tunnell testing. there are tables of drag coefficinets for common geometry available (any fluid mech text book).
[as well as geometry,it will also depend on the flow regieme, laminar/turbulant]

also if your worried about it remaining "stable" i presume this means that it wont break away from an anchoring. note that where the anchoring is attached will be very important as some members may experiece disproportionate forces.

i dont understand the setup very well but essentially for the force exerted by a moving fluid on a submerged stationary body your looking at drag.
 

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