Static Acceleration

[Anonymous]

Hi, 

a static acceleration of 5 g will be applied on my model ,which type of analysis and type of load should i be choosing?

I tried using explicit dynamics and enforced motion-acceleration as a load but i am getting unreasonable results. should i put the enforced motion on the whole model and then constrain it ? or only at 1 face and also constraining the same face?

Also my model is a part of a bigger model that connected to it using bolts , so the 5 g acceleration will be applied to the model but the hold points are at another model connected by bolts. should i only add constraints at the location of the bolts?

What i am trying to calculate is if the bolts will withstand such an acceleration or not.

Best Regards,

Omar Nimer

[John_Holtz]

Hi @Anonymous . Welcome to the Nastran forum.

You asked "which type of analysis and type of load should i be choosing?"

What type of result do you want? Normally, a "static" load would create a static result, so a linear static analysis would be fine. However, I think it is rare to have a static acceleration of 5G. (Maybe a rocket launch can cause a 5G load for a long enough duration that the results are "static". Or a centrifuge or similar rotating machinery could cause a 5G rotational acceleration.) If the results are dynamic, then you should use one of the many dynamic analysis types available (explicit dynamic if the duration is really short, transient response for durations that are longer than really short.)

The load that apply should mimic the real load. It sounds like your model is bolted to something that is accelerating at 5G. In this case, the bolt holes could be constrained to represent that they are not moving relative to the something, and the load is gravity/acceleration with a magnitude equal to 5G.

[Anonymous]

Hi,

So yea actually I am trying to simulate a rocket launch load , the issue that in Inventor Nastran 2021 there no option of enforced motion-acceleration in linear static analysis. Only translational and rotational motion are available , so i went for explicit dynamics .

I read somewhere that the older versions of Inventor Nastran had that option(enforced motion-acceleration) , i am not sure why it got removed. Is there a trick to do it in 2021 Version or something? Can i use for example gravity load as static acceleration in the required direction?

[John_Holtz · Accepted solution]

Acceleration implies that displacement changes over time. It does not make sense to apply an acceleration to a fraction of a model in an analysis that does not involve time. Therefore, it does not make sense to apply an enforced acceleration to a model in a static analysis. (If the interface allowed that load to be applied in the past, then it was proper to remove it.)

Gravity load is not forcing the model to accelerate: it applies a force that causes a displacement. If the rocket accelerates upward at 5G for at a steady rate for a period of time, the parts connected to it reach a steady state deflection that is equal to a 5G gravity load pointed downward. That is the type of analysis that you want to do.

[Anonymous]

Thanks that helped