Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

density variable

Angela Pallone
how to define a variable density in the same piece? I give 100% at the center of the piece and the edges 70, 80!

10 Replies Last Post 03/10/2012, 12:47 GMT-04:00
Nagi Elabbasi Certified Consultant
Posted: 5 years ago 02/10/2012, 08:10 GMT-04:00
Specify the density to be a function of the spatial coordinates, X, Y and/or Z.
Specify the density to be a function of the spatial coordinates, X, Y and/or Z.

Angela Pallone
Posted: 5 years ago 02/10/2012, 09:26 GMT-04:00
I define a function variable analytic form? or assign material at certain points thus giving the coordinates?


thanks for reply!!!
I define a function variable analytic form? or assign material at certain points thus giving the coordinates? thanks for reply!!!

Angela Pallone
Posted: 5 years ago 02/10/2012, 11:34 GMT-04:00
if I had a cylinder, assuming that I know the radius and the radius max min and the density to 100% and the density to 80! how should I define this variability?
if I had a cylinder, assuming that I know the radius and the radius max min and the density to 100% and the density to 80! how should I define this variability?

Posted: 5 years ago 02/10/2012, 14:39 GMT-04:00
Hi

what about a density of something like (assuming rho is a scalar)

"rho*(0.8+0.2*2*(r-rmin)*(rmax-r) / (rmax-rmin))"

this should make a nice parabola, non ?

--
Good luck
Ivar
Hi what about a density of something like (assuming rho is a scalar) "rho*(0.8+0.2*2*(r-rmin)*(rmax-r) / (rmax-rmin))" this should make a nice parabola, non ? -- Good luck Ivar

Nagi Elabbasi Certified Consultant
Posted: 5 years ago 02/10/2012, 16:02 GMT-04:00
Thank Ivar, that gives 100% at the middle and 80% at the extremes. I want to fix a type though: "rho*(0.8+0.2*4*(r-rmin)*(rmax-r) / (rmax-rmin)^2)".
Thank Ivar, that gives 100% at the middle and 80% at the extremes. I want to fix a type though: "rho*(0.8+0.2*4*(r-rmin)*(rmax-r) / (rmax-rmin)^2)".

Posted: 5 years ago 02/10/2012, 17:08 GMT-04:00
Hi Nagi

Très perspicace I see ;) As often I read through the question a bit too quickly ;)
Thanks for the correction, with COMSOL I check the units, but I'm not by my WS, and obviously getting lazy ...

--
Having fun COMSLing,
but only from tomorrow morning off
Ivar
Hi Nagi Très perspicace I see ;) As often I read through the question a bit too quickly ;) Thanks for the correction, with COMSOL I check the units, but I'm not by my WS, and obviously getting lazy ... -- Having fun COMSLing, but only from tomorrow morning off Ivar

Angela Pallone
Posted: 5 years ago 03/10/2012, 06:08 GMT-04:00
can I define a vector in which the distance from the center varies between 0 and R? cause the problem is to vary the r small!
Thanks
can I define a vector in which the distance from the center varies between 0 and R? cause the problem is to vary the r small! Thanks

Posted: 5 years ago 03/10/2012, 07:41 GMT-04:00
Hi

I'm not sure we understand us all correctly, but if you select an Edge in 2D then you have access to a variable "s" that goes from 0 to 1 along the edge in the direction of the "edge" arrow, you can use this to define a variable along an edge.

If it is for a domain in 2D (surface) then by selecting this entity, you implicitly define an "(x,y)" coordinate and if you define a variable on this entity it can be seen as a field i.e "rho(x,y)", with the trivial case "rho" is a scalar hence independent of (x,y)

This is why and how material properties are dependent in T and pA ...

--
Good luck
Ivar
Hi I'm not sure we understand us all correctly, but if you select an Edge in 2D then you have access to a variable "s" that goes from 0 to 1 along the edge in the direction of the "edge" arrow, you can use this to define a variable along an edge. If it is for a domain in 2D (surface) then by selecting this entity, you implicitly define an "(x,y)" coordinate and if you define a variable on this entity it can be seen as a field i.e "rho(x,y)", with the trivial case "rho" is a scalar hence independent of (x,y) This is why and how material properties are dependent in T and pA ... -- Good luck Ivar

Angela Pallone
Posted: 5 years ago 03/10/2012, 09:08 GMT-04:00
I applied from the center to the outside of all the geometry,a material with a density that varies linearly with a decreasing from the center towards the outside of it!So my geometry is in 3D! I can, however, define this edge in 2D? I can not understand under which entry you can do this!
I can not find a tutorial to provide guidance

thanks
I applied from the center to the outside of all the geometry,a material with a density that varies linearly with a decreasing from the center towards the outside of it!So my geometry is in 3D! I can, however, define this edge in 2D? I can not understand under which entry you can do this! I can not find a tutorial to provide guidance thanks

Posted: 5 years ago 03/10/2012, 12:47 GMT-04:00
Hi

you can then "define" a cylindrical coordinate and refer to sys2.r or whatever your radial vector name is ;)

--
Good luck
Ivar
Hi you can then "define" a cylindrical coordinate and refer to sys2.r or whatever your radial vector name is ;) -- Good luck Ivar

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.