quick-release

[mn06rj]

Hy,
Im trying to simulate quick release experiments on a muscle, my aim is to create a force-velocity curve.
To do this I need to simulate mass for the the stretched muscle to "lift", when excited,
any ideas how I would go about doing this?
Regards,
Rhodri

[maas]

Hi Rhodri,

I'm not sure I completely understand what you need. Are you saying you need to be able to run your models dynamically, instead of the default quasi-static response? If that is case, you can turn on dynamics by adding the following tag to your control section:

<analysis type="dynamic"></analysis>

The density of the material is specified as a material parameter. Please keep in mind that currently FEBio does not include damping for dynamic simulations. Let me know if this answers your question or not.

Cheers,

Steve.

[mn06rj]

oh ok, i was also wondering, il try and explain this as simply as possible, if when the muscle material has been stretched to a prescribed displacement that it could then attach to a rigid body, the muscle then being stimulated to pull the rigid body back with the muscle it's original shape so to speak,
regards,
Rhodri

[maas]

Hi Rhodri,

I suggest you checkout Chapter five in the FEBio user's manual: Multi-step analysis. If I understand you correctly, the multi-stepping feature is what you need. This feature allows you to modify boundary conditions during a simulation. I'd be more than happy to help you set up this problem if you run into any problems.

Cheers,

Steve.

[mn06rj]

Thankyou very much with your help, I will have a go and see how if i succeed,
Rhodri

[mn06rj]

Hy steve, this is my attempt at a quick release experiment, I'm guessing the contact is not right, was wondering if you knew an alternative method of simulating this,
regards,
Rhodri

[maas]

Hi Rhodri,

My first recommendation is not to use the muscle material. In our experience, this material performs very poorly and will be most likely seriously revised or entirely removed in the future. I would recommend staying with the trans iso Mooney-Rivlin material.

I also modified your boundary conditions a little bit to create a uni-axial tension case. I have attached my input files and results. Hopefully this will help. Let me know if you have any questions.

Cheers,

Steve.

[mn06rj]

Thankyou very much for your help,
Rhodri

[mn06rj]

Thankyou for the feb file, was just wondering, im tryin to get the muscle element to stretch towards another element with density, it then to connect to it so that it is like a dead weight so then the muscle element is pulling it when contracted, hope you understand what im tryin to say,
Rhodri

[maas]

Hi Rhodri,

I think I understand what you are trying to do. The way to do this would be to attach your muscle to a rigid body, as you had originally done. I removed the rigid body since I cannot yet remove the rigid body constraints at the beginning of the dynamic part. I still need to add that feature to FEBio. I will add it to my todo-list and keep you posted on the progress. We are planning to release the next version on 1st april, and I will try to add this feature by then. Let me know if this time frame would pose any inconvenience for you.

Cheers,

Steve.

[mn06rj]

thanyou very much for the reply,
my project is in for the beginning of april, if you could add it sooner that would be fantastic but if not no worries,
Rhodri

[maas]

Hi Rhodri,

I finished the implementation. If you tell me what version you work with (Windows, Mac, Linux) I will upload the executable to the website.

Cheers,

Steve.

[mn06rj]

Thankyou very much,
working on mac os,
Rhodri