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'intop' function in variable : Error due to Surface Integral of FaceLoad that doesn't exist (yet) (SOLVED)

Posted Aug 3, 2021, 12:06 p.m. EDT General, Parameters, Variables, & Functions, Studies & Solvers Version 5.6 1 Reply

Jan
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I want to use the surface integral of a face load as a variable by using intop(mbrn.F_A_Mag). The problem is: at the beginning of the time dependent study, that face load doesn't exist yet, because the face load depends on a contact pressure, which hasn't been esablished at t=0s

When I calculate intop(mbrn.F_A_Mag) for t=0 as a global evaluation in the results, the result is simply 0. For the data evalutation, Comsol doesn't seem to have a problem with calculating the integral of a non-existing face load. When I use the same expression as a variable, comsol stops the study with the following error:

Attempt to evaluate negative power of zero. - Function: ^ Failed to evaluate temporary symbolic derivative variable. - Variable: comp1.mbrn.F_A_Mag@VDN${real@10} - Defined as: (2real(comp1.mbrn.F_Ay))(0.5*((((real(comp1.mbrn.F_Ax)^2)+(real(comp1.mbrn.F_Ay)^2))+(real(comp1.mbrn.F_Az)^2))^(-0.5)))

How can I bypass that problem? thanks, Jan

1 Reply Last Post Aug 9, 2021, 10:27 a.m. EDT
Jan
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Posted: 3 years ago Aug 9, 2021, 10:27 a.m. EDT

COMSOL-Support kindly helped me on this one. As the equation states, the error occurs when the face load is equal to zero in all directions. Support told me this issue will be fixed in the upcoming version of the software.

For a workaround one may edit the equation of 'mbrn.F_A_Mag' by adding a small value (eps) to ensure it is non-zero:

  • Make sure Equation View is enabled in COMSOL Multiphysics. This is controlled via the Show More Options button at the top of the Model Builder Tree Window.

  • Go to the Equation View node under Face Load 1 in the Membrane interface.

  • In the list of variables, locate the variable mbrn.F_A_Mag.

  • In the expression field for this variable, add +eps inside the square root, to add a small value and avoid getting zero inside the square root.

COMSOL-Support kindly helped me on this one. As the equation states, the error occurs when the face load is equal to zero in all directions. Support told me this issue will be fixed in the upcoming version of the software. For a workaround one may edit the equation of 'mbrn.F_A_Mag' by adding a small value (eps) to ensure it is non-zero: > - Make sure Equation View is enabled in COMSOL Multiphysics. This is controlled via the Show More Options button at the top of the Model Builder Tree Window. > > - Go to the Equation View node under Face Load 1 in the Membrane interface. > > - In the list of variables, locate the variable mbrn.F_A_Mag. > > - In the expression field for this variable, add +eps inside the square root, to add a small value and avoid getting zero inside the square root.

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