# Structural integrity and partial vacuums

1. May 8, 2013

### Havoko_o

I have several questions that are related to something I am designing. I am having a hard time finding the correct formulas I need, so I am here :D

Anything will be helpful, from general topics/ideas to get me in the right direction, to specific formulas. I do not mind abstract ideas, this is a hobby and learning everything is more fun than the actual project :)

1. I am creating a hollow torus (circular pipe) that is a partial vacuum. I need to be able to calculate the failure point of any material used to create the torus (steel, acrylic, etc). I would imagine this to be the structural integrity of a circle, given that a torus is a series of circles.

2. Inside the torus will be an object that will be nearly the same diameter as the inside that moves and is lubricated. I need to calculate the friction/drag between the object and the inside of the torus. Ideally, this would be a formula that I could use with any given area so that I can chart the change in friction with the change in size.

3. A variation of this that would also be helpful is to calculate the friction of wheel-object or wheel-wheel contact on a tracked system.

4. I would like to be able to calculate the gain in pressure from leaks. For instance, if the inside of the torus is 0.02 atm, and the outside is 1 atm, how many atm per second would enter into a hole that is 1 square mm.

5. Last but not least, how do you calculate the change in boiling point in relation to pressure deviating from 1 atm? The only thing I can find is calculators do to it for me, and I want to calculate it myself.

Edit: One more thing - Are there any free CAD programs that would do structural calculations for me? I'm using sketchup currently.

2. May 9, 2013

### Danger

Hi.
I don't have much to offer, but I'll mention a couple of things. Regarding failure points, my main concern would be your welds (or other attachment methods).
As for free software, I always recommend Source Forge. Just make sure that you check the system requirements before downloading, and don't take an Alpha version.

3. May 10, 2013

### 256bits

Your torus could fail along the hoop, but also along the inner radius.
You need knowledge of strength of materials, stress loading, falure ..... .

The friction will be complicated. Try fluid dynamics.
I doubt if one simple formula can be formulated to calculate the friction/size.

Change in pressure from a leak would depend on the volume of your torus.

Look up vapour pressure for a liquid.
I did the Wiki one for you:
http://www.motivate.maths.org/content/wonderful-world-gyroscopes/gyroscopic-effect

If someone else adds more then great, but since you are asking "how is it done" then I am assuming your project might be overloading your present level of understanding of strength of materials, fluid dynamics, ....... You will have to plug away and do some research and learning on several topics.

4. May 11, 2013

### Havoko_o

hmm

This project is completely beyond my knowledge, but only because I choose it to be. I'm purposely using this project to learn. I could do this by trial and error, but I would prefer to know why something works. For instance, I didn't know much about thermodynamics, so I spent quite some time looking that up. By doing so, I realized there is a large amount of bad information out on the web. My last question about heat of vaporization is a good example. I came here hoping for some guidance, not asking how it is done. I only included some specifics so that readers know which direction to point me.
Thank you for giving me a topic name, that is what I need :)

I haven't had the time to look it up yet, but as for the drag, the amount of drag should be directly proportional to the touching surface area. A leak should not be volume dependent, it should be pressure dependent. Volume should only effect the rate of exchange when at equilibrium. I'm slowly working through teaching myself, but it never hurts to ask for help :)