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# Element Force Evaluation in Response Dynamics

Pioneer

Dear all,

I am running Response Simulation on a model and want to evaluate the element forces. I am having a problem interpreting the curve. I attached an acceleration and a force response graph for comparison. The first response freqeuency is at about 350 Hz. But why does the force evaluation graph show a peak right at the beginning at 20 Hz? Is this a valid force peak? It is not possible that the element force has the highest peak right at 20 Hz, is it?

Best,

Jintin

8 REPLIES 8
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# Re: Element Force Evaluation in Response Dynamics

Gears Phenom

What are normal modes of structure? Maybe there is a peak at 20Hz. Also does other peaks correspond to normal modes values?

If you use modal frequency response, then do you request all modes, maybe you also request rigid body modes that affect results (but they produce high values only at near zero freq).

Try to request modes not from zero, but from 0,1 Hz.

# Re: Element Force Evaluation in Response Dynamics

Pioneer

First EF is at 390 Hz. Yes, all other peaks correspond to its normal modes. But there is no mode at 20 Hz. This is just the lower limit of the graph. Maybe it has a relation to that?

# Re: Element Force Evaluation in Response Dynamics

Gears Phenom

Also do you have functional dependent damping or stiffness, maybe near 20 Hz it become near zero.

# Re: Element Force Evaluation in Response Dynamics

Pioneer

No, I used a global damping factor for all modes. As you can see in the acceleration response plot, there is no acceleration response at 20 Hz for the same elements.

# Re: Element Force Evaluation in Response Dynamics

Gears Phenom

And stress at this elements are ok or they also have peak at 20 Hz.

# Re: Element Force Evaluation in Response Dynamics

Pioneer

Element stresses do show a peak at 20 Hz as well. The difference between acceleration and force/stress evaluation is that for acceleration I evaluate nodes, and for stresses and forces I evaluate elements. Does that make a difference?

# Re: Element Force Evaluation in Response Dynamics

Gears Phenom

Hmm... Maybe element forces oriented in element CSys and element CSys dont align global CSys.

# Re: Element Force Evaluation in Response Dynamics

Pioneer

Somehow it disappeared when I evaluated force on a simplified model. When I returned to my inital model it was not there anymore as well. I think it was a bug. Sorry for bothering.