Classical Mechanics : Forces and Torques

[praneeth ratna]

Hey!

While going through the GSOC 2022 ideas I have come across the idea of Implementing Specific Forces and Torque objects which i found interesting. There are many possible examples mentioned by Jason K. Moore. And I'm able to find a resource for contact force models : https://www.researchgate.net/publication/299604992_Contact_Force_Models_for_Multibody_Dynamics which i found useful. Are there any resources for the examples mentioned in issue which can helpful for understanding the implementation of concept other than contact force models?

I'm thinking of adding different classes for different type of force models and torques and that can be used to create a force object or torque object of that type also numerical methods can be added to individual classes.

I would request Jason K. Moore to guide me on how to move forward in this project, regarding the implementation and about what all kinds of forces and torques should be implemented so that i can start working on my proposal.

Thanks, 

Praneeth 

[praneeth ratna]

Hi all,

I have already posted regarding my interest in the idea Implementing Specific Forces and Torque objects but have not recieved any reply yet,Could the potential mentor please guide me on what has to be done in this project and some resources, so that I can start working on my proposal since there isn't much time left.

Thanks, 

Praneeth

[Jason Moore]

Hi Praneeth,

I recommend looking at force types in various physics engines to get ideas. The rest would really come from academic papers and text books.

Jason

moorepants.info
+01 530-601-9791

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[Peter Stahlecker]

Stupid question from me:

I thought a force was a force and a torque was a torque.

Are there differentforces?

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Best regards,

Peter Stahlecker

[praneeth ratna]

Hi Jason,

Thanks for the reply,

I have searched for physics engines which have implemented forces and torques but could not find one. Could you suggest any physics engines which has forces implemented so that i can get an idea regarding the implementation?

Thanks,

Praneeth

[Jason Moore]

Praneeth,

Checking out examples in pydy, sympy, and my various courses (MAE 223, ENG122, ME41055) are also good locations.

Jason

moorepants.info
+01 530-601-9791

[Jason Moore]

Peter,

Yes a force is a force and a torque is a torque, but there are specific mathematical descriptions of specific forces and torques. For example, what is the mathematical (analytic and computational) representation of two forces that contact each other. There are many models of contact forces and if we provide popular implementations in sympy mechanics, then it will save users time on defining these from scratch (which can be very tedious). Newton's law of gravitation is another simple force that we could encode or even a simple spring (or a complex nonlinear spring).

Jason

moorepants.info
+01 530-601-9791

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[Peter Stahlecker]

Dear Jason,

Thanks!

If I understood correctly, this refers to, how forces may be ‚created‘, such as e.g. by gravitation, or by friction or by an electric field or…..

NB: 

I tried a nonlinear spring one time in one of my play programs.

‚Kane‘ worked fine, but numeric integration was a mess….

Peter

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[praneeth ratna]

Hi jason,

I have gone through the examples of pydy and your courses that you have mentioned. For example: Here https://pydy.readthedocs.io/en/stable/examples/mass-spring-damper.html, the plan is to implement the same thing in a class so that user can call the linear spring damper object whenever it is required and use numerical methods that can operate on force objects, is it the right thing? Also is there any priority for forces that should be implemented first since there many kinds of forces to be implemented.

Thanks,

Praneeth

[Jason Moore]

Praneeth,

Yes we should have a linear spring and damper force that is premade, but that is really just a trivial case. The GSoC project should be focused primarily on adding non-trivial forces.

Jason

moorepants.info
+01 530-601-9791

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[praneeth ratna]

Hi jason,

I have at present written down the following models:

1. Linear hooke contact model
2. Non linear hertz model
3. Linear Kelvin-Voigt Contact Model
4. Nonlinear Hunt and Crossley Contact Model
5. Nonlinear Hunt and Crossley Contact Model
6. Nonlinear Flores et al. Contact Model
7. multi_mass_spring_damper()
   
8. n_link_pendulum_on_cart()
   

7 and 8 are taken from pydy, are they non trivial cases? Also could you suggest any resources for muscle force, actuator force and aerodynamic force models which are useful for the user?

I have taken 1 to 6 from the here https://www.researchgate.net/publication/299604992_Contact_Force_Models_for_Multibody_Dynamics, are they useful cases?

Thanks,

Praneeth

[praneeth ratna]

Jason,

Regarding the implementation, do you suggest similar to pydy engine? So we also need to  create a System class similar to the one pydy has? Also could you suggest any sources for some trivial cases of muscle force, actuator force and aerodynamic force models, could you provide feedback on whether the model specified in my previous mail are useful or not, so that i can include them in my proposal.

Thanks,

Praneeth

[praneeth ratna]

Hi jason,

Could you please provide your feedback on my previous two emails, So that I can start writing my proposal and since there isn't much time left for proposal deadline.

Thanks,

Praneeth

[Jason Moore]

Praneeth,

We volunteer our time and will reply when and if we can.

Your list of forces looks interesting and useful. I recommend reading the force related sections of Kane & Levinson 1985, as those would be obvious places to take forces ideas from. I'm currently writing a force chapter in my book that has some examples (these are still in draft form and likely incorrect): https://github.com/moorepants/learn-multibody-dynamics/pull/57

There should be no need for a system or anything from pydy. We need valid mathematical descriptions of a variety of common forces that will work nicely with our code generators for efficient numerical implementations.

Jason

moorepants.info
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[praneeth ratna]

Jason,

Thanks for the reply,

I have started writing my proposal, But have some queries regarding the implementation.

I have created a new submodule forces.py in sympy.mechanics module and create force definitons in forces.py. I have included code for one of the model here:

def linear_hooke_contact_model(stiffness, penetration):

    stiffness = sm.sympify(stiffness)

    penetration = sm.sympify(penetration)

    force = stiffness * penetration

    return [force]

Is this the write way of creating the force models, or do we need to create classes for individual force model? Please correct me here if I'm wrong

Thanks, 

Praneeth

[praneeth ratna]

Jason,

I'm sorry for mailing again but I am not yet sure of the implementation - 'We need valid mathematical descriptions of a variety of common forces that will work nicely with our code generators for efficient numerical implementations'. I do not have a clear understanding of how force should be implemented as mentioned by you, could you please help me out here?

Thanks,

Praneeth

[praneeth ratna]

Hi Jason,

I have made a draft of my proposal https://docs.google.com/document/d/13hmPNM2JdEhnMhctH5hsbuTOnA0916WUvrFOzvb98ig/edit?pli=1, Most of examples were added from here:   https://github.com/moorepants/learn-multibody-dynamics/pull/57, could you please provide your feedback on my proposal since there is only 4 days left for deadline.

Thanks,

Praneeth