Search found 46 matches
- Mon Oct 23, 2017 10:53 am
- Forum: 2017 Fall OpenSim Virtual Workshop
- Topic: Accessing to equilibrium equations
- Replies: 6
- Views: 1181
Re: Accessing to equilibrium equations
Hi Mohammadhossein, I'm not sure if this helps but if you download OpenSim's source code, you can view and replicate the equilibrium equations that OpenSim uses by accessing the muscle model of interest and then looking for the compute functions. For example, the equilibrium equations for the Millar...
- Fri Sep 29, 2017 8:23 am
- Forum: OpenSim
- Topic: Change objective function in static optimization or CMC?
- Replies: 3
- Views: 2819
Re: Change objective function in static optimization or CMC?
Hi Xiao, I also wanted to change the cost function in OpenSim but unfortunately, it is embedded in source code. A possible alternative method, which I have got to work in Matlab, is to use an optimal control approach such as direct collocation to run the optimisation outside of the OpenSim framework...
- Fri Sep 29, 2017 8:17 am
- Forum: OpenSim
- Topic: How to check passive muscle forces?
- Replies: 4
- Views: 1889
Re: How to check passive muscle forces?
To my knowledge, I don't believe static optimisation include the passive force-length curve of the muscle fibre so what you're predicting using static optimisation is active fibre force only.
Hope that helps!
Hope that helps!
- Tue Jul 12, 2016 7:45 pm
- Forum: OpenSim
- Topic: Passive fiber force without exceeding optimal fiber length
- Replies: 6
- Views: 1053
Re: Passive fiber force without exceeding optimal fiber length
Oh perfect. Thanks Tom!
Adrian
Adrian
- Tue Jul 12, 2016 5:15 pm
- Forum: OpenSim
- Topic: Passive fiber force without exceeding optimal fiber length
- Replies: 6
- Views: 1053
Re: Passive fiber force without exceeding optimal fiber length
Hi Tom, Thanks for the advice about the flags. I didn't know that the fiber damping value could affect the passive forces. After relaxing this value a bit, I was able to get rid of the passive forces (when the lengths were below the optimal fiber length) as well as negative passive force values (whi...
- Mon Jul 11, 2016 9:15 am
- Forum: OpenSim
- Topic: Passive fiber force without exceeding optimal fiber length
- Replies: 6
- Views: 1053
Re: Passive fiber force without exceeding optimal fiber length
Hi Jim, Thanks for the reply. According to the outputs from muscle analysis using CMC (i.e. PassiveFiberForce and ActiveFiberForce), the muscle does develop active force (due to the constraints of the activation levels) but has passive forces as well so the accumulated force is shown in the ForceRep...
- Fri Jul 08, 2016 1:17 pm
- Forum: OpenSim
- Topic: Passive fiber force without exceeding optimal fiber length
- Replies: 6
- Views: 1053
Passive fiber force without exceeding optimal fiber length
Hi all, I was just wondering if anyone has come across the problem of obtaining passive fiber forces without the normalised muscle fiber lengths exceeding optimal fiber length. The only way I feel this could happen would be that the normalised passive muscle fiber F-L curve has been skewed left such...
- Wed Mar 09, 2016 10:56 pm
- Forum: OpenSim
- Topic: Active fibre force in a muscle with no activation
- Replies: 8
- Views: 1072
Re: Active fibre force in a muscle with no activation
I just wanted to let people following this thread that I found the issue. Similar to the thread that Brad referred to, it was not the default activation that was set incorrectly but a minimum activation value that I didn't have in my Millard model. The default value for this variable is set to 0.01....
- Mon Mar 07, 2016 1:04 am
- Forum: OpenSim
- Topic: Active fibre force in a muscle with no activation
- Replies: 8
- Views: 1072
Re: Active fibre force in a muscle with no activation
Hi Brad, For now, I'm applying excitations through the standard forward dynamics tool. I've set all the default activations for all the actuators to 0 but it unfortunately made no difference. Thanks for the heads up. I'm hoping to transfer my whole workflow into the matlab API in the future. Adrian
- Thu Mar 03, 2016 3:28 pm
- Forum: OpenSim
- Topic: Active fibre force in a muscle with no activation
- Replies: 8
- Views: 1072
Re: Active fibre force in a muscle with no activation
Hi Brad, Which muscles are these (Millard, Thelen, Schutte)? I'm using the Millard2012EquilibriumMuscle model. Just a thought, but have you looked at the force in the tendon (series elastic element)? If your active element is initially too short and the tendon is not near slack, it could still produ...