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The setting is as follows. A hollow pipe (flooded) with radius R-pipe is being lifted from below the water surface (totally submerged) to above the water surface with a speed of v1. The pipe is closed at the top and the bottom. The crane that is lifting the pipe does not want to lift the water that is inside the pipe as well. What size holes (how many) do you have to drill at the top of the pipe and the bottom of the pipe so natural flow through the pipe occurs (if this even does occur)?

enter image description here

Also, when the pipe is being lifted from the water (so while a part is still in the water) you don't want the water level in the pipe to be higher than the level of the water surface (you don't want to lift the extra kilo's). I thought this was the case:

enter image description here

But I think there is something wrong. So how big should the hole at the top and bottom be related to the lift speed and the height between the two holes so water flows through the pipe? Does water even flow through when the holes are in the side of the pipe?

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closed as off-topic by sammy gerbil, Jon Custer, Kyle Kanos, Asher, Rory Alsop Nov 25 '17 at 20:47

This question appears to be off-topic. The users who voted to close gave this specific reason:

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If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ -1. Not clear what you are asking. What does "so natural flow through the pipe occurs" mean? Natural flow occurs when the pipe has no top or bottom at all, and does not restrict the free movement of water. Any top or bottom will affect natural flow to some extent. $\endgroup$ – sammy gerbil Nov 23 '17 at 12:49
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    $\begingroup$ @sammygerbil: I disagree somewhat. It could have been formulated better but it's quite clear what the question means. $\endgroup$ – Gert Nov 23 '17 at 13:08
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Does water even flow through when the holes are in the side of the pipe?

Only if the surface of the water in the pipe is higher than the surface of the water in the reservoir. And this is precisely what you don't want:

Also, when the pipe is being lifted from the water (so while a part is still in the water) you don't want the water level in the pipe to be higher than the level of the water surface (you don't want to lift the extra kilos).

As long as the water levels are the same, no flow occurs because the hydrostatic pressure on both sides of the submerged holes is exactly the same. Bernoulli then tells us no flow will occur.

So in order for flow to occur from the pipe into the reservoir, the levels in pipe and reservoir must effectively be different, violating your condition.

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  • $\begingroup$ That's true, but a tiny difference in water levels would have contributed to a flow while barely increasing the load. Hope op would clarify further, as tiny difference wouldn't matter in real life situations but mean the world in homework assignments. $\endgroup$ – See Jian Shin Nov 23 '17 at 14:19

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