Parallel cylinders in contact

NotOsborneReynolds · November 19, 2020, 16:33

What's the recommended approach for modeling cases where there are cylindrical objects that are parallel and are touching? Common physically, but the mathematical model is that they have line contact and vanishing separation approaching the contact. Numerical methods don't like singularities generally.

I have one case where the cylinders are solids in external contact, a bundle of rods tied together. I have another case where a smaller solid cylinder is inside a larger tube, so a rod lying in and supported by a pipe (cylinder diameter is maybe 0.9 of the pipe ID).

Does everybody normally just sketch it up, hold their nose, and hit go? Or is there something more... I dunno, elegant? respectable maybe? Use some solid deformation analysis to figure a reasonable finite width stripe of contact?

Thank you!

bluebase · November 25, 2020, 12:05

Quote:

Originally Posted by NotOsborneReynolds

sketch it up

A sketch could help to understand what you actually want to do. Are you interested into some bearing simulation, or do you just happen to have circular geometries in your domain and are interested in flow around such geometries?

NotOsborneReynolds · November 30, 2020, 14:45

[IMG]file:///A:/IllustrationForPosting.png[/IMG]

NotOsborneReynolds · November 30, 2020, 14:50

Great, that didn't work. I take it I have to find a web site for hosting images before I can post a sketch here. Will go off and search for one, but meanwhile...
I have several cases but the most urgent is this: a jacketed cable with multiple straight (untwisted) wires inside. At a glance you might mistake it for Ethernet cable. The wires touch each other, and the jacket touches the wires on the outside of the bunch. I need to estimate how the wires heat up as the outside of the jacket is exposed to high temperature. I am analyzing it as a 2D domain. It may be sufficient to only simulate the conductive transfer from part to part, but it the result is close to our go/nogo condition I may have to add the small air spaces as well as radiation transfer.

NotOsborneReynolds · November 30, 2020, 14:55

NotOsborneReynolds · November 30, 2020, 14:57

Aw, heck. What's the trick? I posted my image publicly on imgur and put the url into the "Insert Image" dialog, but still nothing. How do I post an image?

NotOsborneReynolds · November 30, 2020, 15:06

I hope you can use the text of the URL to see the 2D sketch:

https://imgur.com/gallery/VMwe3ho

My construction is a cable with six wires of nearly the same size. There are more details but they're not relevant to my question.

The circles represent wires that are in contact with one another. I think mathematically they touch at a single point in the sketch, or in 3D they touch along a line. If we are talking mathematical idealizations in the sketch, there is a singularity at the contact point, which numerical methods struggle with. In the red shaded area (which I shaded in MS Paint), there are three sharp edges which get infinitely thin as we approach the contact point. Likewise in the green area, with two infinitely thin edges as we approach the tangency point of the jacket. Also, do the red and green areas touch each other? The distance between them is zero or infinitely small.

I'm trying stuff and it may go well, but even I think what I'm asking it to do is not a well posed question. What is the best way to do sims with these kinds of singularities in the problem definition?

November 19, 2020, 16:33	Parallel cylinders in contact	#1
NotOsborneReynolds New Member Chris Bailey Join Date: Dec 2019 Posts: 16 Rep Power: 6	What's the recommended approach for modeling cases where there are cylindrical objects that are parallel and are touching? Common physically, but the mathematical model is that they have line contact and vanishing separation approaching the contact. Numerical methods don't like singularities generally. I have one case where the cylinders are solids in external contact, a bundle of rods tied together. I have another case where a smaller solid cylinder is inside a larger tube, so a rod lying in and supported by a pipe (cylinder diameter is maybe 0.9 of the pipe ID). Does everybody normally just sketch it up, hold their nose, and hit go? Or is there something more... I dunno, elegant? respectable maybe? Use some solid deformation analysis to figure a reasonable finite width stripe of contact? Thank you!

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November 30, 2020, 14:45		#3
NotOsborneReynolds New Member Chris Bailey Join Date: Dec 2019 Posts: 16 Rep Power: 6	[IMG]file:///A:/IllustrationForPosting.png[/IMG]

November 30, 2020, 14:50		#4
NotOsborneReynolds New Member Chris Bailey Join Date: Dec 2019 Posts: 16 Rep Power: 6	Great, that didn't work. I take it I have to find a web site for hosting images before I can post a sketch here. Will go off and search for one, but meanwhile... I have several cases but the most urgent is this: a jacketed cable with multiple straight (untwisted) wires inside. At a glance you might mistake it for Ethernet cable. The wires touch each other, and the jacket touches the wires on the outside of the bunch. I need to estimate how the wires heat up as the outside of the jacket is exposed to high temperature. I am analyzing it as a 2D domain. It may be sufficient to only simulate the conductive transfer from part to part, but it the result is close to our go/nogo condition I may have to add the small air spaces as well as radiation transfer.

November 30, 2020, 14:55		#5
NotOsborneReynolds New Member Chris Bailey Join Date: Dec 2019 Posts: 16 Rep Power: 6

November 30, 2020, 14:57		#6
NotOsborneReynolds New Member Chris Bailey Join Date: Dec 2019 Posts: 16 Rep Power: 6	Aw, heck. What's the trick? I posted my image publicly on imgur and put the url into the "Insert Image" dialog, but still nothing. How do I post an image?

November 30, 2020, 15:06		#7
NotOsborneReynolds New Member Chris Bailey Join Date: Dec 2019 Posts: 16 Rep Power: 6	I hope you can use the text of the URL to see the 2D sketch: https://imgur.com/gallery/VMwe3ho My construction is a cable with six wires of nearly the same size. There are more details but they're not relevant to my question. The circles represent wires that are in contact with one another. I think mathematically they touch at a single point in the sketch, or in 3D they touch along a line. If we are talking mathematical idealizations in the sketch, there is a singularity at the contact point, which numerical methods struggle with. In the red shaded area (which I shaded in MS Paint), there are three sharp edges which get infinitely thin as we approach the contact point. Likewise in the green area, with two infinitely thin edges as we approach the tangency point of the jacket. Also, do the red and green areas touch each other? The distance between them is zero or infinitely small. I'm trying stuff and it may go well, but even I think what I'm asking it to do is not a well posed question. What is the best way to do sims with these kinds of singularities in the problem definition?