SOL109 Shock Input Problems

[PG8911]

Hello everyone

I am having problems with a shock input into a SOL 109 analysis. So far I have managed to get my model running with some dummy loads whilst I waited on the correct loading from a supplier. When I came to add the correct loads I get the following error:

*** USER FATAL MESSAGE 3046 (TRD1)
THIS TRANSIENT RESPONSE ANALYSIS HAS NO EXCITATION SPECIFIED FOR IT.
APPLIED LOADS, ENFORCED MOTION, INITIAL CONDITION AND NON-LINEAR FORCES
ARE ALL NULL.
THE RESULT WILL THEREFORE BE A ZERO SOLUTION.
0FATAL ERROR

The load that I am inputting is a shown below and is prescribed within a single TABLED1 card. As you can see, the load is not zero.

What I have managed to do is to run the model with only the first triangle - but not the second. So it appears that my problem is to do with the negative load part.I would imagine that if the problem was with the TABLED1 it would have given a different error.

Is there anyone that can help me out with the loading of the model?

Just to recap:
[ul]
[li]The model runs in a SOL109 with dummy step input[/li]
[li]The model runs in the SOL109 with just the positive triangle load defined[/li]
[li]The model will NOT run in the SOL109 with both the positive and negative triangles of the load[/li]
[/ul]

Load Graph:

 

[JBlack68]

Would be surprised if it's related to the negative values. There is no restriction in the manual for the TABLED1 card. If your input was say a acceleration vs. time (shock) then Nastran would not have a problem accelerating your "body" in the positive direction then the other way (i.e. the negative). you may want to double check the LOAD cards. You might be calling the wrong LOAD ID.

 

[PG8911]

Thanks for the reply. The LOAD cards were my first check, and are definitely calling correctly because I simply change the TABLED1 and get a result. The input is indeed an acceleration-time input, so I don't see why there would be a problem.

I managed to get it to run with just a negative load so it appears to have a problem with the combination.

Having said that I have currently got a run that has been solving for the past few hours and is likely to finish soon that includes the whole load profile. Which is odd because at the moment I can't see why this particular run is any different to the other runs I tried.... But if it is successful I will post my finding just in case anyone else gets this issue.

 

[PG8911]

I have found my error to be simply that the TSTEP didn't line up exactly with the TABLED1 that defined the load input.