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Question by kobal · Oct 15, 2012 at 09:25 PM · physics

Help with hose physics

I hope someone here can help me.

I am trying to simulate dynamic hoses that are attached to a set of gauges. I am using Interactive Cloth with some success, but I have a few issues. I have attached an image showing the Gauges I am attempting to simulate.

alt text

  1. The hose is a bit to flexible. Is there a way to stiffen up the cloth so it acts more like a rubber hose rather than a cloth hose?

  2. The end of the hose has to have a brass connector. If I attach the brass connector to the end of the hose as a ridged body, it will stretch the hose indefinitely when gravity takes over. If I make the brass connector as part of the hose mesh, it deforms as if made of cloth.

Is there a better way of going about this? Any help would be greatly appreciated as I have been trying to figure this out on my own for some time with not much luck.

gauges-manifold.jpg (18.4 kB)
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avatar image kobal · Oct 16, 2012 at 12:09 AM 0
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Anyone? Am I attempting to do something that is extremely difficult? I was hoping someone would have at least a tip to point me down the right path.

avatar image kobal · Oct 16, 2012 at 02:55 AM 0
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(sorry for replying in the Answer box. I just wanted to add another pic)

Hey Sparkzarca, Thank you so much for trying to help me. I have been at this for a while now with little luck.

I have tried to set the brass fitting to use no gravity, but it does not act right. When gravity is disable the fitting does not move. It does not swing with the hose, if that makes since. I should note that the way I am attempting to attach the brass end is with the "Attached Colliders" element. $$anonymous$$aybe this is where I am going wrong?

I have also played with the "bending Stiffness" and "Stretching Stiffness" numbers. The hose has some stretch to it no matter how high I set the numbers. I have attached another screen shot showing my issue when gravity is disabled on the brass fitting. The Blue Hose stretches a bit, but bunches up due to the fact that the brass fitting is not moving.

Note: I am not too worried about the stiffness of the hose at this moment. I think it is something I can play around with and get to work. The big issue is getting the hose to act realistically with the brass fitting. If it helps, I can build the Scene and upload it so you can see it in action.

alt text

gauge-hoses.jpg (22.2 kB)
avatar image sparkzbarca · Oct 16, 2012 at 06:47 AM 0
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hmmm yea you might want to load up the project so I can try to play around with it right now i'm thinking maybe playing with the mass of the hose (which is the density value) or the mass of the brass fitting might fix it.

Since force = mass times acceleration you should apply less force to stretch if the brass has less mass because its accelerating at the speed of gravity but with less force.

$$anonymous$$ass also increases inertia on the side of the hose, since inertia basically says the more mass the harder it is to start you moving the vertexes might not move if they are more massive.

Lastly maybe friction on the hose, again increases inertia.

This strecthing thing you said it would stretch forever but are you sure about that, see I don't think it works like that i think it stretches each vertice out to a maximum amount one would think.

I for example just ran this test

One cube position locked, rigid body fix jointed to hose one cube below it called hose with interactive cloth as the type and a rigid body one cube below hose a fixed jointed cube that is affected by gravity.

That doesnt stretch at all, I can tell you that stretching and bending are related to the number of vertices in a poly.

The more you have the more you stretch and bend.

I think you need to make sure you stretch forever and not just for awhile. If you stretch for awhile to fix to stretch issues and bending is to remove the number of vertices in your model.

reply back. :)

avatar image sparkzbarca · Oct 16, 2012 at 06:50 AM 0
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yea if you can, create your hose in blender but subdivide a time or two less to get the vertices, just extrude to the same length and start subdividing but make it maybe 1/4th the amount (2 less subdivides assu$$anonymous$$g thats how you made it) and see if the stretching gets less, the bending definately will.

avatar image kobal · Oct 16, 2012 at 07:16 AM 0
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I am pretty sure it stretches forever. However you gave me a thought. I think it is stretching forever because the bottom fitting is attached as an "attacked collider" (as if it was a flag attached at the flag pole). Because I gave that attached point physics, it pulls the cloth with it (forever). If that makes since.

You said you attached it with a hinge joint. This could be the tip I needed.

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Answer by sparkzbarca · Oct 16, 2012 at 01:50 AM

you can disable the use of gravity on a rigidbody. That solves that.

its a checkbox in rigidbody or scriptwise by

rigidbody.usegravity = false;

im confused by your question to increase bending stiffness. I mean its an option in the editor box.

http://docs.unity3d.com/Documentation/Components/class-InteractiveCloth.html

i mean bending stiffness, stretching stiffness, thickness, friction its all there.

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avatar image sparkzbarca · Oct 16, 2012 at 01:50 AM 0
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mark if answered comment if not

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