Spectral analysis

[tony.ridley]

Hi,

When running spectral analysis;

I go to Spectral --------->direction definition---------->Resolution of a force into directions--------->Newmark Combination.  I'm only checking X and Y directions, so I choose Group 1 and Group 2.  

Robot then automatically assigns 4 CQC combinations as shown in the next picture.  

Questions:

1. Why is only Y direction given a negative sign.  I would expect to see negative X somewhere too.  
2. When the spectral analysis is run (say X direction only), does the active mass act on the structure in both +X and -X?
3. If the mass in X acts both positive and negative, then I guess it's the same for the Y direction too.  So why the need for a neg Y case?
4. If I double click on the generated combinations, I can choose "signed".  I guess this automatically runs the combination for a variety of -ve and +ve signs for X and Y.  If I guess coreectly, then I only need two linear signed combinations and not four, no? (+- 100%x +- 30%y, +-30%x +- 100%y).  If I guess wrong please can you explain it to me.  
5. I read from help menu that combination sign "main mode" defaults to zero and thus all signs for all modes are taken into account.  By nominating a main mode, am I still getting +ve and -ve signing?
6. Have I missed something and am completey on the wrong track here?

Tony

[Artur.Kosakowski]

Hi @joverac

The ones where you define the loads manually rather than have them generated by Robot itself.

[joverac]

Thank you but, when do i have to choose a mode in combination sign and when not?

[Artur.Kosakowski]

Hi @joverac

There is no harm to do this at all times but I'd definitely do so when I wantto run the design of elements of a model.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[joverac]

thank you so much. Could you explain the difference in results?. What does Robot do different? Does Robot utilize only the results of that mode?

[nomanhaider09]

Hi @Artur.Kosakowski .
I have been trying to run spectral analysis in robot using a given file. I have imported the data successfully nut I am not sure if data is exchanged as only first 50 points are being considered. Is their limit for data points for spectral analysis. See the images below.