Learning Forum

[remi.gerard-marzan]

Hi all,

I am performing a transient thermal analysis modelling a laser beam over a surface. For this, I am using the Moving Heat Flux ACT to model a gaussian spot of heat flux input that can move along a line. Said line is crossing three different solids, thus being decomposed into three "sub-lines", one on each solid. Due to the way the ACT works, this means I need to instantiate three times the ACT, defining its trajectory on each of the sub-lines in turn.

The following screenshot displays how the green line cuts three different solids.

And there, we can see how the first three Moving Heat Flux ACTs each are defined around a different surface (in blue). They each handle the part of the green line that touches said surface.

 

The transient analysis then shows that while the ACT works perfectly fine on the first two instances, it fails to input any power for the third one. I'm having trouble figuring out why exactly. The following screenshot shows that the maximum temperature in the model abruptly falls off starting near 512s, when the third instance of the ACT should kick in.

 

[Ashish Khemka]

Hi,

I have not used this ACT but can you check the solver filer files directory (right click on solution information) and check the input file (ds.dat file) and solver output to see what is going around at this time?

Regards,

Ashish Khemka

[ashutosh]

Do you have your 'Start point' and 'End point' defined correctly? 

[remi.gerard-marzan]

I have, but there's nothing unusual in that file. It says the same thing for the instance that's failing than for all the others.

Would you know if the ACT creator is still around? Ashutosh Srivastava.

[Ashish Khemka]

Hi,

Yes, let me check if Ashutosh can comment on this query.

 

Regards,

Ashish Khemka

[Sampat Kumar]

Hi Remi,
Can you check the following points ?
1. The start and end times of all three moving heat sources should be correctly defined. 
2. The last patch should be “NO” in the second moving heat source. 
2. Please ensure that the last moving heat source is set to The first patch is “no,” and the last patch is ”yes.”. 

Best Regards,
Sampat

 

 

[remi.gerard-marzan]

Hello Sampat, Ashish and Ashtutosh. First off, thank you all for helping me sort out this problem.

The following image shows another one of my projects, where I have instanciated the module 13 times.

The following picture shows that the "Start Time" and "End Time" of instance 13 have been correctly defined. First patch is "no" and last patch is "yes" since it is the last one, and the start time and end time have been precisely computed so that, given the velocity of the beam and the length of the path, the ACT is active just long enough for the beam to travel the whole path without overflowing. Past experiences have shown me that this was a source of errors. And, as you can see, the injected flux is of the order of 2e5 W/m² (downwards, which means it takes negative values when projected onto axis Z).

The following picture displays the directional along Z heat flux during the transient thermal analysis. What is of interest here is the red line, which shows the minimum value attained anywhere in the model, at each time step. Of course, since the beam injects 2e5 W/m² in the -Z direction, the beam location itself makes up for that minimum heat flux value most of the time. You can see how the red line hovers around -0.8~1.6e-5 W/m² between 0 and 3000s.

But then, it abruptly falls off starting from 3511s - right when instance 13 of the ACT should kick in. Which, to me, indicates that all previous ACT instances have worked just fine, and then the 13th fails for some reason.

And to answer your three questions, Sampat:

1. All start and end times for all 13 instances are correctly defined. It so happens that they do not overlap, though for previous works I have been able to make several ACTs activate at the same time without any issue.
2. The following picture displays that for all instances that are neither the first nor the last, "First" and "Last" are set to No. For the first one however, it is "Yes" and "No" respectively.

This raises another question from me, however: what does "correctly defined" mean exactly, for you?