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# Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

## Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

(OP)
Dear Friends...

Due to sudden drawdown of hydraulic turbine, the static water stored in vertical shaft steel cylinder will have drawdown. I am trying to find the drag effect (along vertical pipe direc) and lift effect (on radial direc).

Supposing the steel cylindrical tank is unsupported radially from outside, will the lift effect cause a wrapping of steel plate Like when we suck the folded circular paper roll, it wraps from the other end.

Is it worth thinking on that line...
Then I can explain how I want to calculate...

Thanks
Raj

### RE: Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

I don't actually understand your terminology in terms of drag and lift. This is more like an aerofoil.
~A drawing or sketch would help hugely here to explain what you're after.

Any large diameter thin cylinder is very vulnerable to a lower pressure inside than outside. If your cylinder can get any free water between it and the concrete outer shell then you're potentially in a lot of trouble.

I await further info.

LI

Remember - More details = better answers
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### RE: Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

"...will the lift effect cause a wrapping of steel plate Like when we suck the folded circular paper roll...? If understand the question because your OP is a little fuzzy to me, then my answer would be it depends on the wall thickness of the cylinder.

### RE: Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

(OP)
@LittleInch thank you for your quick response.

Now i explain to you about the problem. The is related to a hydro electric system water conductor system where a surge shaft is provided to take the transient pressure due to sudden closing or opening of the turbine.
The operational plant is having a huge concrete lined vertical shaft of dia 16 m for the lower half and 23 m upper half.
Now the problem... due to the crack in lining, water is seeping from inside to outside,though quantity is very less 1 m3/s out of design in flow of 400 m3/s.
At this someone has come up with a wild idea of lower ing down a vertical steel cylinder to stop the seepage.about 30 m high and 22.5 m dia steel cylinder of thin plate will be lowered down in water as plant will not be shut down and to be placed just above the small er dia.
What will be the practical and design issue...
I guess..
1. What ever may be the weight of the cylinder or what may be the capacity of crane, due to buyonacy effect, it is impossible to lowered in water with accurate vertical alignment, thereby causing tilting.
2. Surge analysis will certainly show due to constriction of area and damping surface replaceed by steel in place of concrete will increase the upsurge.
3. Due to sudden draw down or sudden puruse of water in the shaft, a force will ve exerted due to change in momentum.I am not sure its effect on plate surface and whether it can be equated to drag force 0.5 Cd n A v2.
I still not sure whether this drag force dan have a radikal component like lift, which will try to pull or push the plate radially.

Please give your views on the above three points and what other problem may crop up hydraulically if you assamese theoritically the arrangement is erection wise possible.
Thanks
Raj

### RE: Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

This really could do with a drawing....

I get the idea, but to do it as a retrofit, especially if you can't drain the shaft you really need to design this internal liner as a free standing cylinder with the potential for water on the outside and not on the inside if the level suddenly drops. This will mean a degree of internal rings of channel and probably internal bracing, which will increase the weight, but will then be strong enough to work.

What I don't get is this lift and drag stuff nor why the minor reduction in ID or the change in surface roughness between concrete and steel has any impact.

As I said we really need a drawing and some explanation of where the water comes in and out, but this whole drag thing is the major puzzle ( at least for me).

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

The magnitude of the drag & lift forces (your terminology) on a tank liner will be minimal because of the conduit diameter. The static pressures will be large.

However, the concept of fabricating and installing such a thin liner inside such a large diameter conduit does not seem to be practical.

### RE: Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

So, if you do pre-fabricate it, then lift it into place, how will you hold it there permanently?
A 16 meter dia liner will not be "perfectly" nor nominally round - It needs to be fabricated in place, which requires you shut down the downcomer. And, if you do that, repair it properly.

### RE: Drag & Lift Force for sudden drawdown of water column in vertical steel cylindical

(OP)
Hello racookpe1978

Idea is to self standing tank..though impracticable, the prefabricated tank is to be lowered from top.

Regards

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