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Hi, I would like to know if it is possible to get the tangential effort on a contact point between two solids from a subroutine ? Thanks you

aurelien.chevallier
Hi,
I would like to know if it is possible to get the tangential effort on a contact point between two solids from a subroutine ?
Thanks you
  • 0
    Hello Aurelien,
     
    I suppose by the tangential effort, you are referring to the contact friction force. If so, in the post processor, we do report friction under each contact track.
     
    Using the CFFSUB routine, you can also compute the friction force but for the whole contact patch.
     
    Thank you,
    Maziar Rostamian
    MSC Software
  • 0
    Hello Maziar, Thanks for your answer.
     
    Actually, it is not the friction force I am looking for but a tangential force which is indeed the projection of ​the force applied on a contact point onto the direction of movement (while the normal force is the projection of this force on the contact section normal). For instance, in the case of man pushing a cube on a plane area, I would like to get the force applied by the man on the cube when I am studying the contact between the cube and the ground. I don't know if this information is accessible from a subroutine (maybe thanks to SYSARY or a similar function) or  the only parameter accessible is the normal force.
     
    Please have a good day
  • 0
    The "force applied by the man on the cube" is a modeling object that you can query using the SYSFNC utility routine.
  • 0
    I don't understand... If there is no friction, there is no force along the direction of movement. If you have a man pushing the cube (with an applied force) the only reaction force you will get in the direction of motion is the friction force. If friction coefficient is set to zero, there is no reaction force and the cube will accelerate according to acc=mass/applied_force.
    The contact element only handles reaction forces. As Maziar points out, any applied force should be measured in the applied force element.
  • 0
    Thank you for both your answers
     
    I ​though friction force was created in response of the force applied by the man in order to compensate for it so the system can be static. My objective is to apply a friction force equal in magnitude but opposite in sign to the "force applied by the man on the cube" thanks to a subroutine but without using CFFSUB.
     
    Unfortunately, as Maziar said, it will be difficult for me to get this parameter if it is not accessible from SYSFNC.
    I will try to find a solution to this issue or change my strategy.
     
    Thank you for your help
  • 0
    Aurelien,
     
    If your objective is to "apply a friction force equal in magnitude but opposite in sign to the force applied by the man on the cube", then you can use a CONTACT object in Adams View with the provided Coulomb friction. Please check out the attached model as a starting point.
     
    However, please note that the Coulomb friction model in Adams is a velocity based model where friction is only present for non-zero velocities. Therefore, tweaking the transition velocity knobs in the friction section can help approach the ideal behavior. If the above (statement in bold) is absolutely NOT an option, then you would need to build your own/other friction models through CFFSUB. This Contact Friction Force Subroutine gives you the advantage of introducing your own friction model while you can still access information from the Adams Solver during run time using SYSFNC, SYSARY.
     
    Please note that you can also simplify this by using a translational joint with friction, in case contact is not really what you are interested in. The friction model for JOINTs is the same velocity-based friction model as in CONTACTs.
     
    Finally, please note that even in reality of the cube example, there are very minute imperfections on the surface (asperities) that are the root cause of the friction force. These imperfections will have lateral deformations when the force is applied.
     
    friction_asperities
    These lateral deformation cause the cube to translate minutely! Therefore, the velocity-based friction model present in Adams is not very different than the reality in my opinion.
     
    Hope this helps.
     
    Thank you,
    Maziar
     
     
    Attached Files (1)
  • 0
    Hello Maziar,
     
    Thank you for your explonation, it helped me a lot to understand how friction is implemented, especially the friction model you joined. I will try as you said to tweak the transition velocity in order to approach the ideal behavior.
    Thank you again for your help and your support,
     
    Regards,
     
    Aurélien
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