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# Frequency Response studies to compare models

Pioneer

Hi!
I want to compare two models which represent the same structure. The eigenvalues of both models are identical but I want to do also a frequency response study to provide an additional comparison.

The structure has 6 RBE3 elements which shall be basis for this study. The behaviour on the DOF of the RBE midnodes represent the focus.

I already tried running a frequency response calculation with XYplot etc but I am still missing some knowledge or basic understanding of the frequency response function.

My "dream"/objective is to generated two frequency response functions like this :

for both comparison models in order to say that they are both identical.

Could you please help me here? Where shall I put my harmonic forces and which which DOF displacements shall i set as XYout?

Thank you very much

4 REPLIES

# Re: Frequency Response studies to compare models

Phenom

assume you vibrate in 1 direction say X

Attach all the nodes where you have all the constraints (normally) - (fixed to the ground) to an RBE2 (with independant node 999 say)

fixed all the directions but X at node 999

input vibration (1g sine or random) on node 999

output the accelerations of all the nodes of interest in Tx,Ty,Tz or only 1 directin if you want to. Always good practice to get the accel of your input node

Production: NX9.0.3.4, NX10.0.2.6
Development: VB.NET (amateur level !)

# Re: Frequency Response studies to compare models

Legend

selex_ct wrote:

assume you vibrate in 1 direction say X

Attach all the nodes where you have all the constraints (normally) - (fixed to the ground) to an RBE2 (with independant node 999 say)

fixed all the directions but X at node 999

input vibration (1g sine or random) on node 999

output the accelerations of all the nodes of interest in Tx,Ty,Tz or only 1 directin if you want to. Always good practice to get the accel of your input node

I concur with Dr selex_ct

# Re: Frequency Response studies to compare models

Pioneer
Thank you for your response. I will test that !

# Re: Frequency Response studies to compare models

Pioneer

I am still not managing to achieve the result.

In the picture below, I tried it using a simple "cone" shell model. I have 4 RBE3 spiders for each circumference.

Now I want to generate a frequency response for it, lets say vibrate on the right RBE3 midnode in radial direction and show the influence.

could you please help me here? I could provide the corresponding .dat file as well if required.

Thank you