Forums Anyscript.org  

Go Back   Forums Anyscript.org > Professional Forum > AnyBody Managed Model Repository

Notices

Reply
 
Thread Tools Display Modes
  #1  
Old 09-11-2018, 11:36 PM
johnwu johnwu is offline
Junior Member
 
Join Date: Nov 2011
Posts: 29
Default Patellar tendon stiffness

Hi AnyBody,

I have a model based on AMMR.v2.0.0. I am interested in the knee joint loading. The predicted femur/tibia contact forces are in a reasonable range. However, the predicted patella/femur contact forces are nearly two times of the experimental data. The reason is likely the patella tendon stiffness in the existing (AMMR.v2.0.0) model is too high. My question is how to adjust the patella tendon stiffness?

Thanks,

John
Reply With Quote
  #2  
Old 09-12-2018, 11:32 AM
toerholm's Avatar
toerholm toerholm is offline
AnyBody Support
 
Join Date: Feb 2009
Posts: 924
Default

Hi John,

Which AMMR model are you referring to?

The normal knee model do not have a patella/femur stiffness implemented, it is made with kinematic constraints.

Are you sure you are looking at the right property in the modeltree and that the coordinate system these forces are given in corresponds to the value you are comparing with.

If on the other hand you are running an FDK model for the knee it is a different story, then the stiffness will influence results.

Best regards
Søren
__________________
TIP: How to save and load results.
http://wiki.anyscript.org/index.php/All_about_AnyBody_Modeling_System#Save_Load_and_Re play_Results

Subscribe to the forums, click the 'Forum Tools' link above the list of threads then select 'Subscribe to Forum'. You will then have the option to choose the subscription mode for this forum and get an email automatically.
Reply With Quote
  #3  
Old 09-12-2018, 04:03 PM
johnwu johnwu is offline
Junior Member
 
Join Date: Nov 2011
Posts: 29
Default

Søren,

Thanks for the quick response. I mean the tendon pulling the patella to the tibia, as shown in red line of the attached picture. The stiffness of the patella tendon should have a big effect on the patella/femur contact force. I need adjust the stiffness of this tendon.

John
Attached Images
File Type: jpg patella tendon_0006.jpg (36.0 KB, 1 views)
Reply With Quote
  #4  
Old 09-12-2018, 04:14 PM
johnwu johnwu is offline
Junior Member
 
Join Date: Nov 2011
Posts: 29
Default

I have used AMMR.v2.0.0 and defined the model as:

......
#define BM_LEG_MODEL _LEG_MODEL_TLEM_

#define BM_LEG_MUSCLES_BOTH _MUSCLES_3E_HILL_

#define BM_SCALING _SCALING_LENGTHMASSFAT_
....

This is equivalent to "Twente Lower Extremity Model v.1.2" in AMMR.v2.1.0

John
Reply With Quote
  #5  
Old 09-13-2018, 02:14 PM
toerholm's Avatar
toerholm toerholm is offline
AnyBody Support
 
Join Date: Feb 2009
Posts: 924
Default

Hi John,

The connection between patella and tibia is a kinematic constraint made as a AnyKinPLine, so it do not have a stiffness… but as i wrote earlier if you are running an application which replaces the knee with an FDK model then the kinematic constraint is replaced by a ligament with a stiffness.

Best regards
Søren
__________________
TIP: How to save and load results.
http://wiki.anyscript.org/index.php/All_about_AnyBody_Modeling_System#Save_Load_and_Re play_Results

Subscribe to the forums, click the 'Forum Tools' link above the list of threads then select 'Subscribe to Forum'. You will then have the option to choose the subscription mode for this forum and get an email automatically.
Reply With Quote
  #6  
Old 09-13-2018, 04:06 PM
johnwu johnwu is offline
Junior Member
 
Join Date: Nov 2011
Posts: 29
Default

Søren,

Thanks.

Do you know a good existing model that applied FDK to knee joint, which I can adopt and modify? The only model I found in AMMR.v2.1.0 is THA-KneeBendDemo, which applied FDK to a hip joint.

John
Reply With Quote
  #7  
Old 09-13-2018, 11:44 PM
johnwu johnwu is offline
Junior Member
 
Join Date: Nov 2011
Posts: 29
Default AMMR.v2.0.0. FDK knee model.

Søren,

I tried to include the FDK into knee patellar/femur joint, according to "THA-KneeBendDemo" (see attachment). I got a error message: some DOFs have not been constrained. Do you have time to look at my model and give me some suggestions? When FDK is switched off, the model works.

Thanks,

John
Attached Files
File Type: zip SquattingModel_Sept13_18.zip (14.19 MB, 0 views)
Reply With Quote
  #8  
Old 09-14-2018, 09:07 AM
toerholm's Avatar
toerholm toerholm is offline
AnyBody Support
 
Join Date: Feb 2009
Posts: 924
Default

Hi John,

Please have a look in the Beta folder there is a TKA_kneebenddemo model.

Replacing joints in the model with FDK driven joints requires some experience and may lead to models errors on the way until the proper stiffness in the model has been established.

Please see this section of the wiki https://github.com/AnyBody/support/w...ent-Kinematics

Among other things you need to:
  1. ensure proper stiffness applied on the DOF you ask FDK to solve for.
  2. use a reasonable starting guess on the position for the FDK dof


Best regards
Søren
__________________
TIP: How to save and load results.
http://wiki.anyscript.org/index.php/All_about_AnyBody_Modeling_System#Save_Load_and_Re play_Results

Subscribe to the forums, click the 'Forum Tools' link above the list of threads then select 'Subscribe to Forum'. You will then have the option to choose the subscription mode for this forum and get an email automatically.
Reply With Quote
  #9  
Old 09-14-2018, 10:01 PM
johnwu johnwu is offline
Junior Member
 
Join Date: Nov 2011
Posts: 29
Default Knee TKA

Søren,

Thanks for your help.

The TKA-kneebenddemo model in Beta folder is not available. Is it possible that you send it to me or put it github?

John
Reply With Quote
  #10  
Old 09-15-2018, 12:56 AM
johnwu johnwu is offline
Junior Member
 
Join Date: Nov 2011
Posts: 29
Default Knee TKD

Søren,

I found the Beta-TKA-kneebenddemo model, which you mentioned, in the older AnyBody version v6.1. I can start from there.

Thanks,

John
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +2. The time now is 07:56 AM.