Dear Kostas,
Thank you for your response. As my intuition is not as sharp as yours, I
might need a few explanations:
- md.add_nonlinear_term(mim, "(u-rot(phi)*(X-[xc;yc])).mult", HoleZone)
--> This order zero term seems pretty straightforward and much more
readable than in my code
- md.add_linear_term(mim, "Fy/area*Test_yc", HoleZone) --> No multiplier
is involved in your formulation. Is this because we need to combine this
term with the previous order 0 term -((rot(phi)*([0;1])).mult)*Test_yc
(and check the sign) ?
- md.add_linear_term(mim,
"([Fx/area,0]*rot_der(phi))*(X-[xc;yc])*Test_phi", HoleZone) --> Could
you explain how do you come up with this term ?
- A more general question: Is it possible to formulate the whole
condition as an order 0 term ?
Thanks in advance,
Best regards
Raphaël
Le mer. 6 avr. 2022 à 23:14, Konstantinos Poulios <logar...@googlemail.com>
a écrit :
> Dear Raphaël,
>
> Interesting question. Prescribing Fx is a bit strange condition. I haven't
> checked it, but I think something like this should work:
>
> md.add_initialized_data("Fx", 10.)
> md.add_initialized_data("Fy", 100.)
>
> md.add_initialized_data("xc", 0.)
> md.add_variable("yc", 1)
> md.set_variable("yc", yc)
> md.add_variable("phi",1)
> md.set_variable("phi", 0.)
> md.add_fem_variable("u", mfu)
> md.add_filtered_fem_variable("mult", mfu, HoleZone)
>
> md.add_macro("rot(x)", "[cos(x)-1,sin(x);-sin(x),cos(x)-1]")
> md.add_macro("rot_der(x)", "[-sin(x),cos(x);-cos(x),-sin(x)]")
>
> md.add_initialized_data("area", gf.asm_generic(mim, 0, "1", HoleZone)) #
> Calculate the area of the region
> md.add_nonlinear_term(mim, "(u-rot(phi)*(X-[xc;yc])).mult", HoleZone)
> md.add_linear_term(mim, "Fy/area*Test_yc", HoleZone)
> # check if a minus sign is needed
> md.add_linear_term(mim, "([Fx/area,0]*rot_der(phi))*(X-[xc;yc])*Test_phi",
> HoleZone) # check if a minus sign is needed
>
> for time in [0,0.1,0.3,0.6,0.9]:
> md.set_variable("xc", speed*time)
> md.solve("noisy")
>
> A bit based on intuition but you can certainly learn something from
> analyzing this suggestion. Let us discuss it further if you cannot get it
> to work and have more questions. Try to avoid expressions like "speed*time"
> and "alpha*time" in your expressions, they seem too specific to constant
> velocities, they make the code more difficult to read, and they will not
> help you to generalize the code later. Just solve for positions/angles
> directly if that's what you want.
>
> FYI, the expression
> (u-rot(phi)*(X-[xc;yc])).mult
> will expand internally to something like
> (u-rot(phi)*(X-[xc;yc])).Test_mult
> +Test_u.mult
> -((rot_der(phi)*(X-[xc;yc])).mult)*Test_phi
> -((rot(phi)*([0;1])).mult)*Test_yc
>
> BR
> Kostas
>
>
> On Wed, Apr 6, 2022 at 4:54 PM Raphaël Meunier <raphael.meuni...@gmail.com>
> wrote:
>
>> Dear Getfem-Users,
>>
>> I am trying to impose a rolling condition on a "tire". My work is
>> directly inspired from the "Example of wheel in contact" tutorial
>> <https://getfem.org/tutorial/wheel.html>. In this tutorial, one wants to
>> prescribe the rim rigidity and the vertical force. From this, I just have
>> to add a rolling condition. Specifically I want to find the rotation speed
>> "alpha_rot" that enables me to impose some force Fx:
>>
>> gwfl_rot='-lambda_D.Test_u +
>> ([cos(alpha_rot*time),sin(alpha_rot*time);-sin(alpha_rot*time),cos(alpha_rot*time)]*(X-[0;y_c])-(X-[0;y_c])\
>> + [speed*time;alpha_y] - u).Test_lambda_D +(lambda_D.[1;0] +
>> Fx)*Test_alpha_rot + 1E-6*alpha_rot*Test_alpha_rot'
>> gwfl_y='(lambda_D.[0;1] + Fy)*Test_alpha_y + 1E-6*alpha_y*Test_alpha_y'
>> roll_gwfl=gwfl_y+gwfl_rot
>>
>> idBrick = model.add_nonlinear_term(mim, roll_gwfl, HoleZone)
>>
>>
>> Where alpha_rot and alpha_y are the "parameters" I am trying to find.
>> This works for up to ten timesteps but then it diverges... I tried to use
>> two multipliers instead of one which leads to worse results.
>> Am I on the right track ? Is there a better way to achieve this ?
>>
>> Thanks in advance,
>>
>> Best regards,
>>
>> Raphaël
>>
>
