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 The information provided may be out of date.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.

Interpretation of results

Please login with a confirmed email address before reporting spam

Hi,

what is the difference between "Line Integration", "Line Maximum/Minimum" and "Line Average" under subnode "Derived Values"?
What is calculated specifically? How to interpret the results?
For example, if I want to calculate the reaction forces?

When to choose the linear and when to choose the quadratic discretization as displacement field for Solid Mechanics Model?

2 Replies Last Post 22 janv. 2013, 10:26 UTC−5
Josh Thomas Certified Consultant

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 22 janv. 2013, 09:57 UTC−5
Yasemin,

Line integration - integrates the expression over the line
Line max/min - returns the maximum or minimum of the expression over the line
Line average - integrates the expression over the line and divides by the length of the line

The simplest way to calculate reaction forces is to use the predefined reaction force variables that can be found by clicking on the "Replace Expression" icon and browsing under the Solid Mechanics section. In 3D with cartesian coordinates the names will be solid.RFx, solid.RFy, and solid.RFz. If you want the total reaction force along a line for example, then use the Line integration to integrate the reactions force variables over the line. COMSOL will automatically detect that the reaction forces are discrete nodal values and apply a summation instead of an integration. The same holds true for integrating over a surface.

As far as when to choose linear or quadratic discretization, it depends. The discretization refers to the order of the approximation functions used to approximate the solution variable (disp.) across each element. If you expect the displacement field to vary linearly across each element use linear. If you expect a quadratic variation of displacement across each element use quadratic, etc. In beam bending problems, strains vary linearly through the thickness of beams which means that displacements vary quadratically. So, if you expect bending, it's a good idea to use quad. discretization. Although, you can always just use a large number of linear elements to capture the variation of your dependent variables. If you doing contact modeling, linear elements can be more stable during the solution process.

Hope this helps.

Regards,
Josh Thomas
AltaSim Technologies
Yasemin, Line integration - integrates the expression over the line Line max/min - returns the maximum or minimum of the expression over the line Line average - integrates the expression over the line and divides by the length of the line The simplest way to calculate reaction forces is to use the predefined reaction force variables that can be found by clicking on the "Replace Expression" icon and browsing under the Solid Mechanics section. In 3D with cartesian coordinates the names will be solid.RFx, solid.RFy, and solid.RFz. If you want the total reaction force along a line for example, then use the Line integration to integrate the reactions force variables over the line. COMSOL will automatically detect that the reaction forces are discrete nodal values and apply a summation instead of an integration. The same holds true for integrating over a surface. As far as when to choose linear or quadratic discretization, it depends. The discretization refers to the order of the approximation functions used to approximate the solution variable (disp.) across each element. If you expect the displacement field to vary linearly across each element use linear. If you expect a quadratic variation of displacement across each element use quadratic, etc. In beam bending problems, strains vary linearly through the thickness of beams which means that displacements vary quadratically. So, if you expect bending, it's a good idea to use quad. discretization. Although, you can always just use a large number of linear elements to capture the variation of your dependent variables. If you doing contact modeling, linear elements can be more stable during the solution process. Hope this helps. Regards, Josh Thomas AltaSim Technologies

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 22 janv. 2013, 10:26 UTC−5
Many thanks.

The answer is very helpful.
Many thanks. The answer is very helpful.

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.