Search found 14 matches

by Simone Hendriks
Fri Sep 06, 2024 10:43 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Integrate over short transients
Replies: 4
Views: 6095

Re: Integrate over short transients

Hi Sherm,

It's all clear now, thank you for your help! :)

Best regards,
Simone
by Simone Hendriks
Wed Sep 04, 2024 9:29 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Integrate over short transients
Replies: 4
Views: 6095

Re: Integrate over short transients

Hi Sherm, Thanks for the feedback. With sufficiently tight accuracy values (1e-6 in my case), the integrator takes enough steps during the transition. Regarding question (b), if the reporting period is much smaller than the average step size, is the system solved at the reporting step, or is interpo...
by Simone Hendriks
Fri Aug 02, 2024 3:55 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Integrate over short transients
Replies: 4
Views: 6095

Integrate over short transients

Hi, I have a system upon which a force of the following type is exerted: Screenshot 2024-08-02 123917.png That is, at a certain point, the force smoothly increases from 0 to its peak during a very short transient of a few milliseconds. In most scenarios, I guess this transient is irrelevant, but in ...
by Simone Hendriks
Sat Jul 27, 2024 2:20 pm
Forum: Simbody: SimTK multibody dynamics API
Topic: Fixed step size and end-of-step event
Replies: 3
Views: 8093

Re: Fixed step size and end-of-step event

Hi, I just wanted to post a summary of the results/thoughts I got using different methods, in case it might help anyone. I tried the following to model a Coulomb-like friction force (with a sign function discontinuity and depending on a reaction force): a) Using an auto-update state variable to calc...
by Simone Hendriks
Wed Jul 03, 2024 2:22 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Fixed step size and end-of-step event
Replies: 3
Views: 8093

Re: Fixed step size and end-of-step event

Hi Sherm, Thank you very much for the reply, and apologies for my late reply as well. (b) I'm not yet confident about extending Simbody, but please if anyone reading interested in this feature wants to submit a PR, it would certainly come in handy. (a) Clay's approach is indeed very interesting! Whi...
by Simone Hendriks
Tue Jun 18, 2024 3:47 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Fixed step size and end-of-step event
Replies: 3
Views: 8093

Fixed step size and end-of-step event

Hi, I have two questions about the integration of the EOM: a) The system under study implements a force F=-A*sign(v), where A is a constant and v is the speed of the point where the force acts. The actual implementation smoothes the sign() function to avoid integration issues. The problem of the lat...
by Simone Hendriks
Wed Nov 22, 2023 10:28 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Get internal forces for a MobilizedBody
Replies: 14
Views: 20990

Re: Get internal forces for a MobilizedBody

Hi Sherm,

I am connecting the dots now, many thanks for your valuable help!

Best regards,
Simone
by Simone Hendriks
Wed Nov 22, 2023 3:20 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Get internal forces for a MobilizedBody
Replies: 14
Views: 20990

Re: Get internal forces for a MobilizedBody

Hi Sherm, Yes, I will apply it as body forces! The mobilizers are actually following a unit speed trajectory, so the equivalent body force should be along the tangent to the trajectory, with the same magnitude as the mobility force. Moreover, I noticed (for example in a system with 1 slider along th...
by Simone Hendriks
Tue Nov 21, 2023 6:08 am
Forum: Simbody: SimTK multibody dynamics API
Topic: Get internal forces for a MobilizedBody
Replies: 14
Views: 20990

Re: Get internal forces for a MobilizedBody

Hi Sherm, Thank you, with the documentation and the example I could create a minimal system that allocates an auto-update variable. Now I am still trying to find a way to compute the needed reactions. Let me explain it again with the following basic system: diagram.PNG The system consists of two sli...
by Simone Hendriks
Mon Nov 20, 2023 3:10 pm
Forum: Simbody: SimTK multibody dynamics API
Topic: Get internal forces for a MobilizedBody
Replies: 14
Views: 20990

Re: Get internal forces for a MobilizedBody

Hi Sherm, Regarding the reaction force, where should I be setting the allocated auto-update discrete variables? And by auto-update does it mean that, no matter when I set the value, it will be updated only after a step finishes? As for the actual friction force calculation, it does not directly depe...