Hi

I have successfully modeled a simple 2d dc discharge between two electrodes in comsol 5.2 and now I want to calculate the force applied by the discharge in the domain.

I chose "Force Calculation" from the domains and set a name for it but didn't change "torque axis" and "torque rotation point".

after computing, I tried to plot the force on a surface with the expression: DC Discharge(Electrostatics) >Mechanical >Electromagnetic force>z component

and i received the following errors:

Undefined variable.

- Variable: comp1.dc.unTz

- Geometry: geom1

- Boundaries: 1, 3-4

Failed to evaluate variable.

- Variable: comp1.dc.nTz_force

- Defined as: comp1.dc.unTz

Failed to evaluate expression.

- Expression: r*(pi*(2*comp1.dc.nTz_force))

Failed to evaluate expression.

- Expression: comp1.dc.intfcal1(r*(pi*(2*comp1.dc.nTz_force)))

Failed to evaluate variable.

- Variable: comp1.dc.Forcez_force

- Defined as: comp1.dc.intfcal1(r*(pi*(2*comp1.dc.nTz_force)))

Failed to evaluate expression.

- Expression: comp1.dc.Forcez_force

- Plot: surf1 (Surface)

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Can anyone please help me?