# Joule heating analysis - no degrees of freedom in the model

Hi,

I’m trying to perform a Joule heating analysis in CalculiX. The geometry and problem definition are simple - a cylindrical bar is grounded (0 electric potential) at one end and subjected to a current at the other end. The analysis must be transient and I’m interested in the temperature increase due to the current flow in the conductor after a given time. I don’t know if it can be done in CalculiX since the documentation doesn’t mention such cases (only inductive heating) but Mecway supports this type of analyses so maybe CalculiX itself can handle them too.

The first problem is that I’m not sure which type of step I should use. Unlike Abaqus, CalculiX doesn’t have a coupled thermal-electrical step so I have to perform the analysis with sequential coupling (an electrical step followed by a thermal step). However, there’s no step type that could be used directly for electric current flow simulation. The electromagnetic analysis types mentioned in the documentation are:

• electrostatics
• magnetostatics
• magnetic induction

The first one is steady-state so it won’t help. The second one also won’t work here. So I tried the last one, hoping that the magnetic part can be ignored. I defined only the first step for now (no heat transfer) to check if it works. Here’s a piece of my input file:

``````*Material, Name=Steel
*Density
7.85E-09
*Conductivity
16
*Specific heat
490000000
*Electrical conductivity
1450
*Magnetic permeability
0.002, 2
*Solid section, Elset=eall, Material=Steel
*Initial conditions, type=temperature
nall, 293.15
*Step, Inc=100
*Electromagnetics
1, 50, 1E-05, 1E+30
*Boundary
ground, 8, 8, 0
*Dflux
current_source, S, 2419.35483871
*Node file
POT
*El file
ECD, EMFE
*End step
``````

I applied the 0 electric potential as a boundary condition with DOF 8 (according to documentation) but I also tried with DOF 11 (since the documentation says that it should be applied like a temperature BC). On the other hand, the current was applied as *Dflux (value in A/mm^2), also following the documentation.

Unfortunately, the analysis gives empty results but there are also no errors. However, there’s a warning message: no degrees of freedom in the model.

I also tried with `no heat transfer` parameter and temperature dependency for all materials (with just one data point) but it didn’t help.

Do you know what can be wrong here ? Is it possible to perform such analysis in CalculiX ?

I checked in Mecway and unfortunately, internal solver is used in place of CalculiX for DC current flow (and thus also Joule heating) analyses. So maybe CalculiX can’t simulate this.