Muscle solver vellum issue
1165 8 1- SEGAS
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Hi,
I have been trying to research and learn how to create a muscle system in Houdini.
I looked at the tutorials and scenes ( like the dinosaur setup ).
I have found a weird behavior. I'm trying to make one tissue stiffer than the other but no matter how I change Shape Stiffness the behavior is the same. I have tried multiple scenes and different Houdini versions. It was the same.
Then I tried to use a regular vellum solver and changing stiffness works well.
To me, it looks like there is something wrong with the muscle solver or maybe I'm missing something.
I would appreciate some help here.
Thank you.
I have been trying to research and learn how to create a muscle system in Houdini.
I looked at the tutorials and scenes ( like the dinosaur setup ).
I have found a weird behavior. I'm trying to make one tissue stiffer than the other but no matter how I change Shape Stiffness the behavior is the same. I have tried multiple scenes and different Houdini versions. It was the same.
Then I tried to use a regular vellum solver and changing stiffness works well.
To me, it looks like there is something wrong with the muscle solver or maybe I'm missing something.
I would appreciate some help here.
Thank you.
- johm
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- SEGAS
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Hi John,
You can use the dinosaur file from here https://www.sidefx.com/contentlibrary/muscle-and-tissue/ [www.sidefx.com]
If you change the stiffness of the muscles it will not affect the simulation results
You can use the dinosaur file from here https://www.sidefx.com/contentlibrary/muscle-and-tissue/ [www.sidefx.com]
If you change the stiffness of the muscles it will not affect the simulation results
- johm
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That example file uses some significant Fiber Strength, and the muscles have a boosted lower end to the Fiber Scale range. (meaning that at their minimum muscletension, they still have fiber stiffness applied.) Fiber stiffness can make the muscles stiffer. Once you reach a high stiffness value, there may not be much visible difference. So maybe that's what you're seeing?
Edited by johm - April 18, 2024 11:58:28
- SEGAS
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Hi, I tried to disable fiber stiffness the results of low and high muscle stiffness still match
Here is a simple example to show what I mean. There are 2 outputs for each muscle solver and regular vellum solver. For muscle solver shape stiffness is 10 and 1e+07 and results are the same. For the vellum solver same values ( as for the muscle solver ) for stiffness but the results are different.
Here is a simple example to show what I mean. There are 2 outputs for each muscle solver and regular vellum solver. For muscle solver shape stiffness is 10 and 1e+07 and results are the same. For the vellum solver same values ( as for the muscle solver ) for stiffness but the results are different.
Edited by SEGAS - April 18, 2024 16:03:36
- johm
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Thanks for the example SEGAS. The key difference is in your regular Vellum setup, you are using the stiffness parameters without a Scale by modifier. In the MuscleSolver, we use attributes to scale constraint stiffness values.
The Scale By factoring is not a linear scale.
If you look at a geometry spreadsheet for the Constraint Primitives, and watch what happens to the stiffness attribute for tetrahedral stretch, (Scale By Value behaves just like Scale By Attribute):
Stiffness: 1 x 1000
No Scaling yields a stiffness of 1000.0
Scale By Value: 1.0 yields stiffness = 1000.0
Scale By Value: 1.5 yields stiffness = 31669.0
Scale By Value: 2.0 yields stiffness = 1e6
Scale By Value: 10.0 yields stiffness = 1e30
Scale By Value: 100.0 yields stiffness = 1e37
So getting back to your original question, try using much lower stiffness values to see a difference. Once you start getting into higher Muscle Properties Stiffness values, the constraint stiffness starts to max out.
The Scale By factoring is not a linear scale.
If you look at a geometry spreadsheet for the Constraint Primitives, and watch what happens to the stiffness attribute for tetrahedral stretch, (Scale By Value behaves just like Scale By Attribute):
Stiffness: 1 x 1000
No Scaling yields a stiffness of 1000.0
Scale By Value: 1.0 yields stiffness = 1000.0
Scale By Value: 1.5 yields stiffness = 31669.0
Scale By Value: 2.0 yields stiffness = 1e6
Scale By Value: 10.0 yields stiffness = 1e30
Scale By Value: 100.0 yields stiffness = 1e37
So getting back to your original question, try using much lower stiffness values to see a difference. Once you start getting into higher Muscle Properties Stiffness values, the constraint stiffness starts to max out.
- SEGAS
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- johm
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- SEGAS
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