How to change the number of load cases available in a .h3d file?

Bastien Dacqui

Good morning,

I am currently working on a Non-Linear analysis, using Optistruct.
The analysis completes and the results seem fine, however I would like to increase the number of load cases available in the .h3d file.
I already adjusted the number of incrementations during the NL analysis but it didn't change anything to my problem. I still have only 10 load cases for each subcase.

I noticed that the .nl.h3d file had more load cases available, unfortunately this kind of file only supports displacement results, so it is not very useful to me.

Any piece of advice would be much appreciated.

Sincerely,

Bastien Dacqui

I spent some time looking for an answer to this problem, so I will share the solution I came up with.
It may not be the best, but it worked for me and I hope it can help whoever will encounter the same issue.

I had to use two Bulk Data Entry, "NLOUT" and "NLADAPT".

NLOUT defines incremental result output parameters for Nonlinear Analysis, but it will not always be enough to have the load cases you want the results for. For example, with a value of 10 in the NINT field, I expected to have a load case every 0.1, which was not the case as you can see on the picture I posted in the original post.

That is because in NL Analysis, Optistruct increases progressively the load you specified, using load increments. Then NLOUT specifies which of these load increments must be available as load cases in the .h3d file. The selected load increments are those that verify the condition (Current Load Increment - Previous Load Case >= 1/NINT). If like me, you let the solver handle the load increments automatically, then something like this might happen.

Load increments          Load cases
0.00                             0.00
0.01                              0.14
0.02                              0.25
0.05                              0.36
0.09                              0.47
0.14                             0.60
0.20                              0.70
0.25                             0.82
0.30                              0.92
0.36                             1.00
0.41
0.47
0.60
0.70
0.82
0.92
1.00

To prevent this, you have to control the load increments precisely, using NLADAPT. For example, you can set the maximum or the minimum difference between two load increments. You can also use NLPARM-->NINC to set the value of the first load increment. But be careful to keep enough load increments to let your NL Analysis converge.

I will also share with you the Altair documentation on NLOUT and NLADAPT, in case you need further details.

Good luck and have a nice day.

NLADAPT.pdf

NLOUT.pdf