Forces on a submerged object due to currents in the ocean

[Higgs_world]

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

 

[phlegmy]

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 equivalent 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 textbook).
[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 won't break away from an anchoring. note that where the anchoring is attached will be very important as some members may experiece disproportionate forces.

i don't understand the setup very well but essentially for the force exerted by a moving fluid on a submerged stationary body your looking at drag.

 

[astrokreng]

I would first like to commend you for your curiosity and interest in understanding the forces acting on a submerged object in the ocean. This is a complex topic and requires a thorough understanding of fluid mechanics and hydrodynamics.

To answer your first question, the forces acting on the surface of the collector (umbrella looking part) will depend on several factors such as the size and shape of the collector, the angle at the base, and the flow rate of the current. The main forces acting on the surface of the collector are drag force and lift force.

Drag force is the force acting in the opposite direction of the flow of the current. It is calculated using the drag equation: Fd = 0.5 * ρ * v^2 * Cd * A, where ρ is the density of the fluid, v is the velocity of the current, Cd is the drag coefficient, and A is the surface area of the collector. The drag coefficient depends on the shape and surface roughness of the collector and can be determined experimentally.

Lift force, on the other hand, is the force acting perpendicular to the direction of the flow. It is caused by the pressure difference between the top and bottom surfaces of the collector. The lift force can be calculated using the lift equation: Fl = 0.5 * ρ * v^2 * Cl * A, where ρ is the density of the fluid, v is the velocity of the current, Cl is the lift coefficient, and A is the surface area of the collector. The lift coefficient also depends on the shape and surface roughness of the collector and can be determined experimentally.

To calculate the forces in foot pounds and pounds per square inch, you would need to convert the units using appropriate conversion factors. However, it is important to note that these forces will vary depending on the angle at the base and the diameter of the collector. The larger the angle and diameter, the higher the forces acting on the surface of the collector.

For your second question, the anchor weight needed to keep the collector stable will also depend on the size and shape of the collector, the angle at the base, and the flow rate of the current. The main purpose of the anchors is to counteract the drag and lift forces acting on the collector. The number and position of the anchors will also play a significant role in the stability of the collector.

In conclusion, the forces acting on a submerged object due to currents