Version 2 boundary conditions

[Todd Pataky]

Hi Ahmet,

I have a question about the boundary conditions as implemented in Version 2 of the Generation 1 model. From what I can see in the FEB file (tf_joint_FEBio_v2.feb), it appears that the prescribed kinematics are applied over the interval 0 to 1 s, but in version 1 this was done over the interval 1 to 2 s. Also, in Version 2 it appears that neither kinematic nor force constraints are changing between the interval 1 to 2 s.

Here are the relevant sections of the FEB file:

Code: Select all

<rigid_body mat="1">
         <prescribed bc="Rx" lc="2">0.785</prescribed>
</rigid_body>

<loadcurve id="2" type="smooth">
        <point>0,0</point>
        <point>0.1,0.1</point>
        <point>0.9,0.9</point>
        <point>1,1</point>
        <point>1.1,1</point>
        <point>1.9,1</point>
        <point>2,1</point>
</loadcurve>

Since the force constraints all have zero magnitude it appears that everything is constant between 1 and 2 s.

I assume that this means simply that the new version's boundary conditions do not precisely replicate the previous version's?

Please confirm at your convenience.


Cheers,

Todd

[Ahmet Erdemir]

Hi Todd,

I changed the prescription of boundary conditions and loads in the new version slightly, mostly for convenience. With the newer version, we are applying a passive flexion from 0 to 0.785 radians in 1 second and holding the joint at that angle for the remainder of the simulation, which ends at 2 s. We also defined another load curve, which is set to 0 for t=0-1s and ramps up to 1 in t=1-2s. Using this load curve we apply loads to remainder degrees of freedom of the joint. Right now, these loads are set to 0 but can be changed to any desirable load by the user.

Best,

Ahmet

[Todd Pataky]

Understood, thanks for clarifying.

Just curious: is that flexed-posture loading meant to relate to a particular in vitro loading experiment or a particular in vivo task?

[Ahmet Erdemir]

That is how we do the in vitro loading in our specimens. Nonetheless you should be able to change load curves and magnitudes to any that you would like.

ahm.

[Todd Pataky]

Great, thanks for that Ahmet.
And thanks again for sharing this fabulous resource with the community!
Todd