Menu

Discussion Forum

New Discussion
查找

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.

What exactly is a point probe (3D) measuring?

Posted 2015年4月19日 GMT-4 15:41 Chemical Reaction Engineering, Geometry, Mesh 2 Replies

Gerardo Felix
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

I'm solving a reaction-diffusion model in a 3D geometry consisting in a simple sphere (radius 10 mm) with some point sources in its surface. I've configured a point probe right in front of one of those point sources, exactly 0.05 mm (50 um) away from it. However, the mesh I'm using consists of elements with a minimum size of 0.1 mm. When I plot the location of the point probe it seems it is located where I wanted (0.05 mm away from the point source) and I'm getting some results (the concentration) in real time as well.

The question is: Are the results that I'm getting an estimation of the concentration where I put the point probe? or COMSOL is giving me the concentration at 0.1 mm (the minimum element size) or how does COMSOL "measures" the concentration at the point probes??

Thanks a lot....
2 Replies Last Post 2015年4月20日 GMT-4 02:20
Daniel Connelly
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 2015年4月19日 GMT-4 16:01
Assuming concentration is defined at the nodes, and assuming linear discritization, it SHOULD be interpolating the values of the concentration linearly onto the point in question. If there's tetrahedral elements than there's only one way to do this (4 points bound the element, the values at these 4 points defining a mean value and the gradients along each of three dimensions: in 1D you need 2 points, in 2D you need 3 points, and in 3D you need 4 points). If there's more than 4 points, for example a prismatic element, then the problem may be overconstrained, and so the interpolation must proceed with certain assumptions.
Assuming concentration is defined at the nodes, and assuming linear discritization, it SHOULD be interpolating the values of the concentration linearly onto the point in question. If there's tetrahedral elements than there's only one way to do this (4 points bound the element, the values at these 4 points defining a mean value and the gradients along each of three dimensions: in 1D you need 2 points, in 2D you need 3 points, and in 3D you need 4 points). If there's more than 4 points, for example a prismatic element, then the problem may be overconstrained, and so the interpolation must proceed with certain assumptions.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 9 years ago 2015年4月20日 GMT-4 02:20
Hi

I'm not sure the interpolation is linear, as most operations in COMSOL uses higher order integrations/interpolations, see the operator and plot definition nodes.
I'm not behind my WS, but I seem to remember you can define the order for the "probe" point integration/averaging

--
Good luck
Ivar
Hi I'm not sure the interpolation is linear, as most operations in COMSOL uses higher order integrations/interpolations, see the operator and plot definition nodes. I'm not behind my WS, but I seem to remember you can define the order for the "probe" point integration/averaging -- 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.

Suggested Content