Force on submerged plate perpendicular to flow

In summary: This might be a good place to mention the importance of rigidity in any system with moving parts. If the wall is not rigid, the animal will cause the lip to deflect, and the pressure and force on the plate will increase.There is a lot of engineering involved in designing traps for submerged objects.
  • #1
tjosan
33
2
Hey,

I wonder how I can calculate the force of a plate that is submerged in water.

I thought maybe the drag equation would be suitable for this with the drag coefficient set to 1.28 (https://www.grc.nasa.gov/www/k-12/airplane/shaped.html). But is implies the flow is according to the image (bottom part, https://en.wikipedia.org/wiki/Drag_coefficient#Background):
Cd_flat_plate.svg

But in my case, I only have a flow under the plate, not on both sides:
force.png

I want to calculate the force at the bottom of the wall. The wall is attached in place. Can anyone assist me how to proceed? Thank you.
 
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  • #2
The magnitude of the ram pressure against the plate will be about;
P = ½⋅ρ⋅v2 ; pascal.
Where ρ is the density of the water in kg/m3
and v is the water velocity in m/s.
 
  • #3
There is no good way to calculate the force on the plate working from dimensions and flow rate. There are ways to make a rough estimate. The post above by @Baluncore is one such way. Another way is to treat the gap under the plate as an orifice, and use Bernoulli's equation. The pressure difference to create the velocity increase under the plate is the pressure on the plate.

Or you can measure the pressure drop. Your diagram appears to show that the water has a free surface. Measure the difference in water height before and after the plate. That height difference multiplied by the water density is the pressure difference across the plate. The pressure difference times the plate area is the total force on the plate.
 
  • #4
I agree with @jrmichler.
There is really no simple way to analyse the typical operation.

However there are a number of conceivable worst case fault situations that would require consideration during the design process. You are building a "trap".

“The body of an animal falls into the trap and blocks the h * w aperture”. Water on the supply side then overflows. Water on the outlet side falls to the height of the outlet, but is then pumped out by the contractor sent to identify and rectify the problem.

First, you can evaluate the pressure on the area of the plate, by considering the plate as part of a static dam wall, with a hydrostatic pressure differential.

But the body rolls along the bottom surface of the trap, until stopped by the bottom edge of the wall. Half the hydrostatic pressure on the body, ( at a depth = H + h/2 ), appears as a force on the bottom lip of the wall. (It is actually a directed vector dependent on the size, in terms of h, of the cylindrical animal model). That mechanical force against the lip, must be added to the pressure force on the plate.
 

Related to Force on submerged plate perpendicular to flow

1. What is the force on a submerged plate perpendicular to flow?

The force on a submerged plate perpendicular to flow is the force exerted by a fluid on a plate that is placed at a right angle to the direction of flow. This force is known as the drag force and is caused by the pressure difference between the front and back of the plate.

2. How is the force on a submerged plate perpendicular to flow calculated?

The force on a submerged plate perpendicular to flow can be calculated using the equation F = ½ρu²CdA, where ρ is the density of the fluid, u is the velocity of the fluid, Cd is the drag coefficient, and A is the area of the plate perpendicular to the flow.

3. What factors affect the force on a submerged plate perpendicular to flow?

The force on a submerged plate perpendicular to flow is affected by several factors, including the density and velocity of the fluid, the size and shape of the plate, and the roughness of the plate's surface. The angle of the plate with respect to the flow direction also plays a role in determining the force.

4. How does the force on a submerged plate perpendicular to flow impact the design of structures?

The force on a submerged plate perpendicular to flow is an important consideration in the design of structures such as dams, bridges, and offshore platforms. Engineers must take into account the magnitude of this force when determining the size and shape of these structures to ensure they can withstand the pressure and avoid damage.

5. Can the force on a submerged plate perpendicular to flow be reduced?

Yes, the force on a submerged plate perpendicular to flow can be reduced by changing the shape or angle of the plate, or by adding surface features such as dimples or grooves. These alterations can help to reduce drag and decrease the force on the plate, making it more efficient in the flow of fluid.

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