# Possible Bug in Section Print Flux and Anisotropic Materials

**URL:** <https://calculix.discourse.group/t/possible-bug-in-section-print-flux-and-anisotropic-materials/1528>\
**Category:** Uncategorized\
**Created:** [March 9, 2023, 2:26pm UTC](https://calculix.discourse.group/t/possible-bug-in-section-print-flux-and-anisotropic-materials/1528 "2023-03-09T14:26:20Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![cmcclellan](https://avatars.discourse-cdn.com/v4/letter/c/77aa72/32.png) [@cmcclellan](https://calculix.discourse.group/u/cmcclellan)\
**Post date:** [March 9, 2023, 2:26pm UTC](https://calculix.discourse.group/t/possible-bug-in-section-print-flux-and-anisotropic-materials/1528/1 "2023-03-09T14:26:20Z")

</div>

Hi all,  
I am using Calculix 2.20 and ran into an error when running a heat transfer simulation and trying to record the heat flux through a defined surface. If I use an ORTHO solid material and add the line:  
\*SECTION PRINT, SURFACE=surface1, NAME=nsurface  
FLUX

I get the error “\*ERROR in materialdata\_cond conductivity for fluids must be isotropic”, even though there are no fluids in my simulation file. If I make the solid material isotropic, the simulation runs fine. However, I need to have anisotropic materials for my simulations and need the heat flux through a defined surface.

Any advice on how to fix this issue would be greatly appreciated, thanks!

---

<div class="post-metadata">

**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [March 9, 2023, 3:11pm UTC](https://calculix.discourse.group/t/possible-bug-in-section-print-flux-and-anisotropic-materials/1528/2 "2023-03-09T15:11:09Z")

</div>

> [@cmcclellan](#):
>
> and add the line:  
> \*SECTION PRINT, SURFACE=surface1, NAME=nsurface  
> FLUX

What if you remove that line - does it work ?

Can you share the input file for tests ?

---

<div class="post-metadata">

**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\
**Post date:** [February 15, 2025, 9:12pm UTC](https://calculix.discourse.group/t/possible-bug-in-section-print-flux-and-anisotropic-materials/1528/4 "2025-02-15T21:12:12Z")

</div>

> [@Calc\_em](#):
>
> Can you share the input file for tests ?

Activating Section Print the analisys fails.  
Example.

```auto
*NODE
1,0,0,0
2,1,0,0
3,1,1,0
4,0,1,0
5,0,0,1
6,1,0,1
7,1,1,1
8,0,1,1
9,0.5,0,0
10,0.5,0,1
11,0.5,1,0
12,0.5,1,1
*ELEMENT,TYPE=DC3D8
1,9,2,3,11,10,6,7,12
2,1,9,11,4,5,10,12,8
*NSET,NSET=OUT_N
2
3
6
7
*ELSET,ELSET=DEFAULT
1
2
*SURFACE,NAME=SURFACE_OUT
1,S4
*SURFACE,NAME=SURFACE_IN
2,S6
*MATERIAL,NAME=MATERIAL
*CONDUCTIVITY,TYPE=ORTHO
0.01,0.01,0.01,0
*SOLID SECTION,ELSET=DEFAULT,MATERIAL=MATERIAL
*STEP
*HEAT TRANSFER,STEADYSTATE
1,1,0,0
*CFLUX
4,11,0.25
1,11,0.25
5,11,0.25
8,11,0.25
*FILM
1,F4,272.15,1
*NODE FILE,GLOBAL=YES
NT
*EL FILE
HFL
*Node file
RFL
*El file
HFL,ENER

**SECTION PRINT,SURFACE=SURFACE_OUT,NAME=Heat_Flow2
**FLUX
*END STEP

```

---

<div class="post-metadata">

**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [February 17, 2025, 11:47am UTC](https://calculix.discourse.group/t/possible-bug-in-section-print-flux-and-anisotropic-materials/1528/5 "2025-02-17T11:47:33Z")

</div>

Yes, it’s reported on GitHub: [Error with \*CONDUCTIVITY,TYPE=ORTHO and \*SECTION PRINT · Issue #70 · Dhondtguido/CalculiX · GitHub](https://github.com/Dhondtguido/CalculiX/issues/70)

---

<div class="post-metadata">

**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\
**Post date:** [February 17, 2025, 5:30pm UTC](https://calculix.discourse.group/t/possible-bug-in-section-print-flux-and-anisotropic-materials/1528/6 "2025-02-17T17:30:54Z")

</div>

I don’t remember that bug post at all and I comment about it. 😬