Anisotropic Material value

Pearse

Hello all,

I'm trying to create a simple muscle with a long tendon, something like you would have in the hand or foot. This is just a test to see if we can use Ziva for some medical illustrations and animations

I have set up my muscle fibers and materials (based on the numbers in the docs), and I would like the "tendon" part of my muscle to work like a pully. I'm sing the recommended youngs Modulus for tendons but the mesh is just holding it shape, as you can see:

The docs mention Anisotropic Material
"The anisotropic direction can vary spatially, and is specified via the muscle fiber field."

This looks like exactly what i need to change but I don't seem to have the option to change anisotropic material properties in my muscle or fiber objects.

Has it been renamed or moved?

Would really appreciate any help anyone can give me with this.

Cheers,
Pearse

Pearse

Just going to put this here incase someone else is looking for the same thing.
I found it in the OUTPUTS of my tissue object.

But I'm still not getting the result I was hoping for.

If any one can give me some idea of hoe to make my tendons bendy but not stretchy I would really appreciate it.

jamesj

Pearse Here is an example that I hope will help to answer your questions:

The simulation in the above video has the following components:

a single Tissue object for the belly of the muscle, and the tendon
a bone object that the top to attach the muscle to (the cube)
a bone object to collide the muscle with (the cylinder)
a tissue object attached to the end of the "tendon"
a tissue object for the "belly" of the muscle, with a fiber
a tissue object for the "tendon" with a fiber

The "belly" and the "tendon" object are added to the "muscle" object as subtissues
For the fiber on the "tendon" - set the contraction limit to 1.0 increase the fiber strength to something like 10⁶ and set the muscle excitation to 1.0 (this will have the effect of making the muscle "stiff" only in the direction of the muscle fiber)
for the fiber on the "belly" - set the contraction limit to 0.2 increase the fiber strength to something like 10⁵ and animate the muscle excitation when you want to contract the muscle.
turn on collisions and animate the cube so that the tendon collides with the cylinder.

I hope this helps!
-jj

Pearse

Hey jamesj,
Thanks so much for getting back to me so quickly. That looks great and it's working for me.

I just have one more question now: Is there any way of countering the sag of the muscle tissue under gravity? I would like to keep appearance of my tendons being under tension and not lose the shape of my muscles once the simulation begins.

I understand that I can use a rest shape to counter the effects of gravity. When I do that for a structure like with a long sagging tail - I inherit the changes to the tendon which makes my simulation budge and warp in unwanted ways.

I was hoping to add a rest shape to the sub tissue, and Ziva lets me do that but I don't see any results in the simulation. Is it possible to do that?
or is it possible to paint weights of a rest shape similar to how I can for fiber?

Or perhaps I'm thinking about this the wrong way...

The reason I'm asking is that I want to simulate muscles like the flexors and extensors in the forearm, for a medical animation. You can see them here;

I would like to be able to start the simulation without loosing the shape of the muscles. I need to go from a static mesh to an animated one without too much of a jump, and have the tendons behave correctly as the muscles contract.

I am starting to thing I am approaching this all wrong.
Can I ask, how would you go about doing that?

Thanks again,
Pearse

Pearse

Managed to prevent the sag by brining gravity to 0 – I have a feeling that's not a great idea though?
It gave me a lot of jittering but I was able to counter most of that by upping the mass dampening on the ziva node to 30, again I have no idea if that's best practise.

Getting some lovely shapes now and only a little wobble. Would love to hear if there is an alternative way of approaching this.

jamesj

Pearse alternatively, you could run a sim with gravity oriented in the opposite direction, wait until the tissues settle, stop the sim and then duplicate off the tissue meshes.
Then, in your normal scene (with gravity pointing down), add the duplicated meshes as Art Directable Rest Shapes (ADRS)
As gravity ramps up during your runup, blend on your ADRS to counter the effect of gravity.

I hope this helps!
-jj

Pearse

Hey James and Co.

Sorry to dig this up again I am just trying your suggestion using ADRS to correct for the effect of gravity but I don't seem to be able to get them to behave with any long muscles that only have attachments at either end.
Here is my set up right now, I'm rigging some eye muscles. on the left you can see the corrective shape I am using, I created from a blend shape of the muscle under gravity set to -1.
You can also see how the muscle is supposed to sit against the bottom of the eye.

Here is the result of my simulation with the ADRS

and here it is without any ADRS

Here is the comparison, red is no rest shape, green is with a rest shape and the textured muscle is what I'm aiming for. Below is the rest shape. You can see it's doing something but it's nowhere near where I would need it to be.

Would appreciate any help you can give on this.
Thanks,
Pearse

kishchris

hi Pearse !
Here is an example using zFiber to hold the shape.

zFiber Excitation is keyed 0-1 after full gravity act on it. Just to show before and After effect.

hope this will be Helpful.

Pearse

Hey @kishchris,
Sorry for the late reply and thank you for getting back to me.

Can you tell me are the rest shapes computed before everything else? If I did the above and added a rest shape would it bring the muscle back to it's original shape? or would the fiber override the rest shape

I think the simplest solution might be to just work with gravity set to .1

kishchris

hey Pearse !!
In the above screen capture I have not used rest shape at all. Just added zFiber with its default value and excitation is triggered.
Muscles is long , thin and with just two attachments which is not enough to hold its shape. In this case zFiber forces help to keep it intact.
I rarely use rest shape when gravity and all are involved.