Hello AnyBody forum members,
I would like to modify the standing human model by inserting an stl file of an intervertebral disc into the lumbar spine. Any pointers on how to go about this?
Thank you,
Victor.
Hi Victor,
Here are some possible steps, that will create a visual representation of the disc.
[ol]
[li] Locate a node on the vertebra which can be used as attachment point for the disc
[/li][li] Use the AnyDrawSurf object inside the node of the first step. This will draw the surface visually
[/li][/ol]
the STL file will be static so it will not bend and it will not change model results because it is graphics only.
It would be possible to make it bend dynamically using the object AnyFunTransform3Ddyn. In principle this object works exactly like AnyFunTransform3D except that Point0 and Point1 can be posvar. So it can be used to bend the Disc visually while the model is running, again this is just graphics and it will not change the results, only appearance.
Unfortunately AnyFunTransfor3Ddyn is not well documented in the manual, but please refer to the AnyFunTransfor3D object for the details, only difference is that this object accepts dynamic data as point0 and point1.
Best regards
Søren
Hi Soren,
I got as far as inserting the disc. Thank you very much.
If I understand you correctly, I cannot make the disc a segment so that I can study the forces and torques acting on it during the body’s motion? Because I intend to use the same disc in finite element analysis and I was hoping to transfer the boundary conditions directly from the disc I have inserted into the AnyBody model into the one in the FEA software.
If the inserted disc is only visual and doesn’t affect the results, is there a way of doing this without having to insert a disc into AnyBody’s model?
Best regards,
Victor
Hi Victor,
There are two ways if you want to export forces on the disc segment for FE
[ol]
[li] Make a disc as a virtual segment… create a disc segment which is placed right in the middle between the two vertebraes… having springs to both sides . Then when exporting the disc seg forces to fe you would see the spring forces.
[/li][li] Do not model the disc as a segment, keep the current approach where the disc is created a rotational springs, and export forces to the vertebraes separately .
[/li][li] in principle both approached would be possible to obtain same results seen form the muscles “perspective” they would not feel the difference. The requires careful calibration of the springs though.
[/li][/ol]
Hope it made sense.
Best regards
Søren
Hi Soren,
Thank you, it makes sense …Could you explain further about the springs? I have an stl file of an intervertebral disc but I don’t have any spring data. Is the spring a feature in AnyBody or I am to get that from a different source? An example would really help make it clear.
Best regards,
Victor
Hi Victor,
In AnyBody springs are made using the measures and then applying a force, in this tutorial there is an example on a rotational spring.
http://www.anybodytech.com/fileadmin/AnyBody/Docs/Tutorials/A_Getting_started_modeling/lesson4.html
Note that you can do the same on linear measures.
I would try to make an a small example of a three segments, two vertebraes, and a disc segment for an approach see sketch below… also note that it would be significantly easier to define the springs between the existing vertebraes in the model and export the forces for each segment separately this is option 2 from last post.
[ol]
[li] Make thee segments
[/li][li] Lock one seg to ground all six dof using a AnyStdJoint
[/li][li] Create nodes on verbraes to use for joint attachments
[/li][li] make two spherical joints vertebra1->disc and disc->vertebra2
[/li][li] Add drivers to the spherical joints make sure the model run kinematically
[/li][li] now add nodes on vertebra and disc to use for springs
[/li][li] Make linear measures between the nodes
[/li][li] Add AnyForce object to the linear measures… this is the springs…
[/li][li] play around with stiffness… evaluate results.
[/li][/ol]
I would use option 2 from last post and if you want to refine the springs in the model use some of the steps (6-8) above to do this.
Best regards
Søren
Hi Soren,
Thank you for the outline. I will implement this workflow and hope it works (you’ll know if it doesn’t because I’ll be back :D).
Best Regards,
Victor