Current Density Calc/Plot in DC Conduction Model

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Current Density Calc/Plot in DC Conduction Model

randress
Does the FEATool equation and post processing flexibility in the DC Conduction model allow for the current density (A/m^2) to be calculated and/or plotted?

-Randal

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Re: Current Density Calc/Plot in DC Conduction Model

Precise Simulation
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If an expression is not pre-defined you can most often enter and evaluate the expression manually as explained previously.

randress wrote
Does the FEATool equation and post processing flexibility in the DC Conduction model allow for the current density (A/m^2) to be calculated and/or plotted?

-Randal
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Re: Current Density Calc/Plot in DC Conduction Model

randress
Ok.
Current density, J = (conductivity)*E.  
E = sqrt(Vx^2+Vy^2+Vz^2).
How can I represent conductivity/sigma since it is not a constant for all materials but is dependent upon location (x,y,z) within the model?

-Randal
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Re: Current Density Calc/Plot in DC Conduction Model

Precise Simulation
Administrator

If you are using the "Conductive Media DC" physics mode you can use the global variable name 's_dc' (short for sigma_DC). When evaluating the expression the software will take what ever value you have entered in the "Subdomain/Equation Settings" dialgo box depending on location/subdomain. You can try just plotting 's_dc' and see how it varies.


randress wrote
Ok.
Current density, J = (conductivity)*E.  
E = sqrt(Vx^2+Vy^2+Vz^2).
How can I represent conductivity/sigma since it is not a constant for all materials but is dependent upon location (x,y,z) within the model?

-Randal
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Re: Current Density Calc/Plot in DC Conduction Model

randress
Precise Simulation wrote
 you can use the global variable name 's_dc' (short for sigma_DC). When evaluating the expression the software will take what ever value you have entered in the "Subdomain/Equation Settings" dialgo box depending on location/subdomain.
Great.  Thanks for digging that up for me!   Just where is that found - that s_dc is the symbol for sigma_DC?  Sounds like I need to be spending some time studying there :-).

-Randal
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Re: Current Density Calc/Plot in DC Conduction Model

Precise Simulation
Administrator
There are currently no explicit listings or documentation of boundary or equation variables. However, if you are familiar with the equations/PDEs you can click on the "edit" button in the "Equation Settings" dialog box and then see that for example the partial differential equation for the Conductive Media DC physics mode written in the FEATool Multiphysics PDE syntax looks like:

    dts_dc*V' - s_dc*(Vx_x + Vy_y + Vz_z) = q_dc

where "s_dc" can be identified as the conductivity, "q_dc" the current source term, and "dts_dc" time scaling coefficient (V, and Vx is the potential / derivative).

Alternatively, if you have a registered verison you can export the finite element data struct 'fea' to the Matlab workspace and inspect the 'fea.coef' field which lists the coefficients, for example here the DC mode again for two subdomains:

>> fea.coef

ans =

    'dts_dc'         [1x34 char]         [1x24 char]    {1x2 cell}
    's_dc'           [1x20 char]         [1x21 char]    {1x2 cell}
    'q_dc'      '<html>Q</html>'    'Current source'    {1x2 cell}
    'V0_dc'          [1x68 char]         [1x23 char]    {1x2 cell}

>> fea.coef{2,end}

ans =

    's_dc coefficient for subdomain 1'    's_dc coefficient for subdomain 2'

So that effectively the the first colum in "fea.coef" contains the coefficient name, and last colum the coefficient values or expressions for each subdomain (so that when it is evaluated with the function evalexpr it will take the correct value).


randress wrote
Precise Simulation wrote
 you can use the global variable name 's_dc' (short for sigma_DC). When evaluating the expression the software will take what ever value you have entered in the "Subdomain/Equation Settings" dialgo box depending on location/subdomain.
Great.  Thanks for digging that up for me!   Just where is that found - that s_dc is the symbol for sigma_DC?  Sounds like I need to be spending some time studying there :-).

-Randal