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Ken123456

Eddy current in a stream

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For an application with an eddy current not moving in an stream and the following condition exist. The stream bottom is concreted and at an angle, will the eddy's bottom move mostly downhill the concrete.  

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37 minutes ago, Ken123456 said:

For an application with an eddy current not moving in an stream and the following condition exist. The stream bottom is concreted and at an angle, will the eddy's bottom move mostly downhill the concrete.  

Your question will become much  more understandable when you set out all the details.

The biggest question at the moment is : Why is there an eddy ? Eddies do not just appear, something causes them.

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Posted (edited)

Thanks or the comment. There are eddies in the Mississippi River above the new control structure which flows to the Atchafalaya River and they travel upstream from the Mississippi about 1 mile to the structure. A friend said there was a video showing marine concrete was being pumped into the new structure, is undercutting happening with eddies at this structure location. I wonder about the eddies and if it's bottom would mostly stay closer to the structure if upstream concrete was sloped down to the structure. If so then there should be less undercutting. If the structure is undercut then the Mississippi River will divert to the Atchafalaya River. All videos, If did happen, are not found on the internet and may have been deleted. May need to give more please see link.  https://www.google.com/search?q=old+river+control+structure&rlz=1C1CHBF_enUS867US867&oq=old+river+control+structure&aqs=chrome..69i57j0l7.8791j0j8&sourceid=chrome&ie=UTF-8

Edited by Ken123456

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1 hour ago, Ken123456 said:

Thanks or the comment.

Interesting topic to raise. +1

Just a small question for a Tuesday huh  ?

I will do some investigation, hopefully others with information might chip in here.

Meanwhile can you say if the concrete being poured was foaming or aerated (lightweight) concrete?

That is what I would recommend for filling (scour) voids in soft ground like there is there.

I have done this on the Somerset levels.
I seem to remember a discussion thread about the Mississippi before.

Was that yours also?

 

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Supposedly the CORPS were using marine concrete and this will hopefully prevent undercutting the structure, kind of scary.

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Are 'eddies' not an example of turbulent flow, which is extremely hard to model ?
Would this be a good tie-in with the other thread on chaotic conditions, Studiot ?

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Posted (edited)

I suspect a water flow lab can model an eddie but keeping the eddie in essentially a location would be a challenge. This is what happened when the old structure right wing fell in the 1973 flood. Roll down below 50% for the eddy which undercut the structure. America's Achilles' Heel: the Mississippi River's Old River Control Structure https://www.wunderground.com/cat6/Americas-Achilles-Heel-Mississippi-Rivers-Old-River-Control-Structure

I call it an eddie but not sure, I am only an hobbyist on this subject.

Edited by Ken123456

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17 hours ago, MigL said:

Are 'eddies' not an example of turbulent flow, which is extremely hard to model ?
Would this be a good tie-in with the other thread on chaotic conditions, Studiot ?

Yes and no and yes , but I will come back to this.

11 hours ago, Ken123456 said:

I suspect a water flow lab can model an eddie but keeping the eddie in essentially a location would be a challenge. This is what happened when the old structure right wing fell in the 1973 flood. Roll down below 50% for the eddy which undercut the structure. America's Achilles' Heel: the Mississippi River's Old River Control Structure https://www.wunderground.com/cat6/Americas-Achilles-Heel-Mississippi-Rivers-Old-River-Control-Structure

I call it an eddie but not sure, I am only an hobbyist on this subject.

 

I have done some investigation as I said it is interesting but the Mississippi is rather out of my Bailiwick.

Anyway here is a list of references I have been looking at.

http://onlinemanuals.txdot.gov/txdotmanuals/hyd/bridge_hydraulic_considerations.htm

https://www.google.co.uk/search?q=failure+of+old+river+control+structure&tbm=isch&source=iu&ictx=1&fir=ftZcfe0bK17l7M%2CRRxDk-YnG3761M%2C_&vet=1&usg=AI4_-kTt_zi0s8YadwIFHcgXfndAvIoFOA&sa=X&ved=2ahUKEwjCiKyRmaLqAhVyVBUIHUVIDbgQ_h0wAHoECAUQBA&biw=1366&bih=646#imgrc=yJo1u-GB9q7rDM&imgdii=RRciLzxOFVVPIM

http://www.americaswetlandresources.com/background_facts/detailedstory/LouisianaRiverControl.html

https://www.mvn.usace.army.mil/Portals/56/docs/PAO/Brochures/OldRiverControlBrochure.pdf

https://www.amazon.com/Beyond-Control-Mississippi-Channel-Americas/dp/1496811135

Please confirm which of the control structures is is currently causing concern and requiring concrete.
The 1973 scour damage at the low sill structure seems well documented.

I think an especial difficulty with this system is that water seems to be able to flow in either direction according to circumstance.

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It is the Auxiliary Structure (linked from your link) in the first picture and in the background is the failed low sill structure in 1973.https://www.wunderground.com/cat6/If-Old-River-Control-Structure-Fails-Catastrophe-Global-Impact

Your link https://www.google.co.uk/search?q=failure+of+old+river+control+structure&tbm=isch&source=iu&ictx=1&fir=ftZcfe0bK17l7M%2CRRxDk-YnG3761M%2C_&vet=1&usg=AI4_-kTt_zi0s8YadwIFHcgXfndAvIoFOA&sa=X&ved=2ahUKEwjCiKyRmaLqAhVyVBUIHUVIDbgQ_h0wAHoECAUQBA&biw=1366&bih=646#imgrc=wdhLniFoa9rB9M

There may be reverse flow if the river is low but there is little energy because the river is low. At high river low, flow thru the auxiliary structure is 10 times flow of Niagara falls

My buddy said the eddy currents in the river travels the mile to the Aux structure and is undercutting the structure but as mentioned  can't find the video. Did my buddy dream this or did the government delete all documents and videos as to not scare the public?

Attached picture of the Low Sill before it failed. 

 

bRed Line Plot.jpg

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I, as a dumb college student, went there and walked on the wing, the next week it collapsed.

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On 6/27/2020 at 4:12 PM, studiot said:
On 6/26/2020 at 10:50 PM, MigL said:

Are 'eddies' not an example of turbulent flow, which is extremely hard to model ?
Would this be a good tie-in with the other thread on chaotic conditions, Studiot ?

Yes and no and yes , but I will come back to this.

 

Quote

Sir Horace Lamb  -  Physicist & Applied Mathematician  -  author of many famous Physics texts.

I am an old man now and when I die and go to Heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, the other is turbulent motion of fluids. About the former I am really rather optimistic.

So to Eddies and Chaos.

In a normal  flow eddies form when there is a physical obstruction in the flow or the direction of part of the flow  is diverted.

This second option is what happened at the wing wall in the 'low sill structure' when the floodwate floded out to the side of the structure, beyond the wing wall.
Here water is travelling sideways, ralative to the main flow and therefore being left behind.
Eventually some of the water is flooding backwards in the opposite direction to the main flow.
This formally contitutes the eddy and can form a complete loop of flow circulation.

The same effect can be seen in the Texas manual I linked to around big obstructions like bridge piers and little ones like sticks held in the water.

Kelvin's theorem tells us that these eddies come in pairs to maintain the non circulatory property of the main flow.
This is well known in the phenomenon of vortex (eddy) shedding from the tips of aircraft wings and tail planes.
The shed vortices alternate rotation direction.

This is what I meant by

On 6/23/2020 at 3:43 PM, studiot said:

 

The biggest question at the moment is : Why is there an eddy ? Eddies do not just appear, something causes them.

Now it is tempting to think that the 'right conditions' might induce 'little eddies' as opposed to the  'big eddies' so far described.
And that would lead to Chaos.

Several factors mitigate against this, suggesting there is more to consider.

1) Big eddies are persistent and consistent in their orientation. Little eddies start and stop, and form in every direction.

2) Big eddies can form in both turbulent and laminar flow regimes, as occurred at the low sill structure.

3) It is normally found that turbulence start to occur below and above lower and upper limit critical Reynolds numbers. But more careful experiments , even some by Reynolds himself.
show that these critical values can be substantially exceeded without turbulence forming.

A final factor is that of specific energy.

If the flow speed is altered slowly and smoothly the flow regime has time to adjust to the new conditions.
But if the change is too fast the energy of the incoming flow builds up the specific energy in the water until it is greater than the flow can sustain.
So the flow regime makes a sudden transition to turbulent flow, which has a higher intrinisc specific energy to accomodate this extra energy in the only way it can.
This effect was used in the stilling basin of the low sill structure in normal operation to dissipate the energy of the emerging water.
The purpose of the wing walls was to direct the water in a safe manner.

But the water with the higher specific energy could wash away the material between the piles as a self regenerating process.
The more it washed away, the greater the scour effect.

 

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Thanks but far over my head (I am an engineer but did not have fluid mechanics). Back to my original question, I probably have resigned to there is not an answer as you have shared.

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