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Bolt preloads in Response Dynamics process

Experimenter
Experimenter

  Hi,
This is a problem about NX Nastran and more precisely: the bolt preloads in the SOL 103 Response Dynamics solution and in the Response Dynamics process (or Response Simulation process).

In SOL 103, I created a BOLTFOR card with the Bolt Preload procedure. I put it in Loads in the Subcase - Dynamics.
Consequence : the screw preloads are well taken into account in the eigenmodes calculation.

 

Then, in Response Simulation process, I simulate the structure with sinus excitation functions in the frequency domain. I evaluate Contour Results in order to get Peak Von-Mises Stress Results.

Consequence : the stress levels in bolt elements are far from the expected values (very low with respect to the results obtained with a static analysis with an equivalent acceleration).

 

So I don't understand why bolt preloads cannot be included in Response Dynamics calculations... I don't find any explanation in the NX Nastran User's Guide.

Ideas from advanced users ? Thanks.

3 REPLIES

Re: Bolt preloads in Response Dynamics process

Solution Partner Pioneer Solution Partner Pioneer
Solution Partner Pioneer

Hi,

Maybe I have similar problem. I want to include preload (not only bolt preload, but also force etc.) in frequency response analysis and I also see almost no difference between solution with and without preload.

Re: Bolt preloads in Response Dynamics process

Creator
Creator

Hello,

 

I afraid you can't simple use external loading for modal analysis.

If you focus on motion equetion for natural frequencies, you can see that force vector is zero...

 

If you wish include preload effect for modal analysis and frequency response, I would reccomend to focus on STATSUB instruction. It will have some effect on stiffness matrix.

 

But especially in you case, it seems to me reasonable to apply two analyses:

static analysis (f.e. in SOL 101), define bolt preload, and other loadings if neccesary

frequency response (SOL 111 if it is suitable for you), loading by specific amplitude

 

and then combine both results in Result Manipulation module.

You just need to be careful to pick just real part of results becase SOL 111 give you results in complex format (real and imaginary part).

 

Hope it helps,

regards Jan

 

 

 

Re: Bolt preloads in Response Dynamics process

Experimenter
Experimenter

Hi,

I found an explanation (thanks to a Siemens expert) to this problem. When you want to calculate solutions for Response Dynamics, you know that you need to create an event node on the Navigator bar. At that level, the Static Offset node appears only for Transient events and allows you to enable or disable the static offset from the event evaluation.

So, static offset is applied only within Transient events. But requests already exist to have this functionality in future releases of NX Nastran for Frequency, Random, or Response Spectrum events.

  Christophe