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axisymmetric material coordinate (R, Z) vs. spatial coordinate (r, z) in moving mesh

Posted 2011/12/21 3:07 GMT-5 7 Replies

Abbie
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Dear all,

I am confused about the capital (R, Z) and small letter (r, z) coordinates which I was told that R,Z is material coordinate while r,z is spatial coordinate.

I tried to understand the underlying meaning of these two sets of coordinates by applying them in moving mesh (in attached .mph file),

I defined deformation velocity of the model (in ellipse geometry) as follow:
prescribed r velocity, Vr: 0.01*(R/0.5)
prescribed z velocity, Vr: 0.01*(Z/0.25)

and also in other set,
prescribed r velocity, Vr: 0.01*(r/0.5)
prescribed z velocity, Vr: 0.01*(z/0.25)

I found that the volumes that obtained (defined as Vol_s and Vol_m in attached .mph file) are slightly different for these two sets of implementation.

May i ask what does these coordinates represent in the moving ellipse geometry?

Thanks so much.
7 Replies Last Post 2011/12/23 9:32 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2011/12/21 4:57 GMT-5
Hi

it's rather important to understand the differences.
I would suggest to use structural and test the deformations of a soft solids to illustrate the difference of the spatial (deformed) frame and the material (initial) frame

--
Good luck
Ivar
Hi it's rather important to understand the differences. I would suggest to use structural and test the deformations of a soft solids to illustrate the difference of the spatial (deformed) frame and the material (initial) frame -- Good luck Ivar
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 2011/12/21 23:40 GMT-5
Variables r, z refer to spatial coordinates that move with the solid (in the case of solid mechanics). Variables R, Z refer to the reference coordinates which are independent of deformation/displacement. If a point starts at z=Z=1 and moves by 0.1, then Z remains 1.0 but z becomes 1.1. Your integrals are different because they integrate over different areas.

Nagi Elabbasi
Veryst Engineering
Variables r, z refer to spatial coordinates that move with the solid (in the case of solid mechanics). Variables R, Z refer to the reference coordinates which are independent of deformation/displacement. If a point starts at z=Z=1 and moves by 0.1, then Z remains 1.0 but z becomes 1.1. Your integrals are different because they integrate over different areas. Nagi Elabbasi Veryst Engineering
Abbie
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Posted: 1 decade ago 2011/12/22 12:00 GMT-5
Thanks Ivar and Nagi!

I implemented a simple model in solid mechanics. By applying force to a elastic rectangle over time, it deformed and coordinate of its points was plotted. Indeed R and Z always remain at the same coordinate (reference coordinates: static) while r and z change over time (spatial coordinates: moving). I think this is what have told by Nagi.

Thanks for your help. :)

Thanks Ivar and Nagi! I implemented a simple model in solid mechanics. By applying force to a elastic rectangle over time, it deformed and coordinate of its points was plotted. Indeed R and Z always remain at the same coordinate (reference coordinates: static) while r and z change over time (spatial coordinates: moving). I think this is what have told by Nagi. Thanks for your help. :)
Abbie
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Posted: 1 decade ago 2011/12/22 22:50 GMT-5
Hi, another thing i am would like to ask:

By plotting the deformation result in 2D plot group>surface (total deformation) and deformation (displacemnt field), I found that plot data set edge (black border line: in spatial frame) does not match with the edge of colour plot deformation (as shown in attached solid_displacement.png). I thought they should match each other?

Hi, another thing i am would like to ask: By plotting the deformation result in 2D plot group>surface (total deformation) and deformation (displacemnt field), I found that plot data set edge (black border line: in spatial frame) does not match with the edge of colour plot deformation (as shown in attached solid_displacement.png). I thought they should match each other?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2011/12/23 4:11 GMT-5
Hi

well if you add the displacement ot an already "displaced" deformation you get it double up, this was an issue in 3.5 as you needed to uncheck the disp when turning on the spatial frame, but normally it's treated correctly in v4 (apart if you are tweaking the equations such that COMSOL does not understand)

--
Good luck
Ivar
Hi well if you add the displacement ot an already "displaced" deformation you get it double up, this was an issue in 3.5 as you needed to uncheck the disp when turning on the spatial frame, but normally it's treated correctly in v4 (apart if you are tweaking the equations such that COMSOL does not understand) -- Good luck Ivar
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago 2011/12/23 8:06 GMT-5
It’s either what Ivar just described above or you are scaling the deformation field in this plot. In that case, setting the deformation scaling factor to 1.0 should match the two plots.
It’s either what Ivar just described above or you are scaling the deformation field in this plot. In that case, setting the deformation scaling factor to 1.0 should match the two plots.
Abbie
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Posted: 1 decade ago 2011/12/23 9:32 GMT-5
Yea, it works after changing the deformation scale factor to 1.0! Thank you again, Ivar and Nagi!
Yea, it works after changing the deformation scale factor to 1.0! Thank you again, Ivar and Nagi!

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