Modal analysis just providing 5 modes

[lucmartzz]

Hi,

I'm running a modal analysis, on the setup I'm requestion 10 modes without specifying the lower and the highest frequency but the analysis just provide 5 modes on the results. Looking a the percent modal effective mass, most of the values are high but the one in X direction is very low so I need mode modes specially because that's one of the most important based on the deflection direction of interest (check the attached image). 

The problem is, no matter how many modes are requested, I always obtain 5 modes.

Thanks in advance for the help.

Esteban.

[John_Holtz]

Hi Esteban,

Here is the only thought I have. Sometimes the input entered in a dialog will set Parameters. These parameters can remain set even when you change the analysis type or duplicate the analysis. Perhaps the lower and upper frequency were set a previous time and they need to be cleared out? Here's how to check:

1. Open the Nastran file (.nas) with Notepad, or in Inventor click in a blank area of the model tree and choose "Generate Nastran File".
2. Just below the BEGIN BULK and the comments that give the version, model name, analysis name, date, there may be some PARAM commands. Is there anything other than the Units?

Portion of Nastran file showing two parameters set that control the lowest and highest natural frequencies calculated. There may be other parameters in your file that are set that control the frequency range that is calculated.

If the problem is not caused by the parameters, I suggest that you attach your model.

• The Inventor file is best provided by following the steps in this post: What files to provide when the model is needed - Autodesk Community - Inventor Nastran.
• The Nastran file may be sufficient in this situation. Zip the .nas file and attach it. (The Nastran file is only useful in this type of situation where "something" is happening in the analysis, and the "something" is not set by the user interface.)

John