Difference between single and multiple loadcases in simulation

[thomas.ruest.1]

Hi everyone,

I'm having some problems with Fusion 360 simulation.

I have multiple loadcases that are different and 1 is critical.

I've designed my part suppressing the other load cases for rapidity purpose.

The problem I'm having is : When I unsuppressed the other load cases, the stress change in the critical load case.

Same mesh, same constraint, just more load cases

With all the loadcases active :

With only the critical loadcase active :

Same load applied, same everything, the only thing that changes was the active load cases.

I don't understand why the stress change in the part.

Thank you for your help!

[John_Holtz]

Hi @thomas.ruest.1 

Sorry for the delay in responding.

You are correct that for a linear static stress analysis, the result of each subcase is independent of every other subcase. Therefore you would expect the results of the load case "beam 40" to be the same regardless of how many other subcases were analyzed.

I just tried to reproduce the problem with a test model, but I was unsuccessful. My results were the same why my model had 2 load cases A & B compared to the model with just load case A compared to the model with just load case B.

Here are some things to check:

1) This is a long shot, but the controls over the legend also show which load case is used for the results. Is this how you selected the load case to display? Or if you activated it from the browser, did this control also update?

2) Was Fusion updated in between the runs? That could happen if you ran the two analyses on different days, or if you closed Fusion after the first run and started Fusion again.

3) Check the output files. You may need to clone the study so that you have the two output files available, or save the output file after to each run. To access the output file,

1. From the Results, choose "Inspect > Solver Data" from the menu.
2. On the dialog that appears, changed "Solver Data" to "Solver Output" at the top.
3. If you want to save the output (making it easier to compare), click the "Save" button on the bottom left of the dialog.
4. These are the main things to compare. Are they the same in each analysis?

On page 1:

PROGRAM VERSION:  17.0.0.21
CPU VERSION:      Intel Pentium
OS VERSION:       Linux x64

Around page 4:

 MODEL DATABASE SIZE
 
 SUBCASES                     =        2
 GRID POINTS                  =      539
 ELEMENTS                     =      256
 ELEMENT PROPERTIES           =        1
 MATERIAL PROPERTIES          =        1
 SINGLE POINT CONSTRAINTS     =       21
 GRAVITY LOADS                =        1
 ELEMENT PRESSURES            =      120
 SETS                         =        1
 SURFACES                     =        1
 VOLUMES                      =        1

4) If everything looks consistent  but the results are still different, feel free to export the model to an archive ("File > Export") and attach the .f3d/.f3z file to the forum.

John