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Too high stress result for random vibration simulation

Creator
Creator

Hi, I am doing a random vibration simulation on NX 10 with a PSD data of

 

Hz/g^2Hz^-1

20/0.001

110/0.001

250/0.015

1000/0.015

2000/0.015

 

My constraints are as follows:

- Sliders on all 4 sides, restricting the model to movements only in the Z direction

- 1d connectors from the bottom centre to the bottom 4 corners (to mimic a spring at the bottom)

- a fixed point at the bottom centre of the 1d connectors

- Enforced motion location at the bottom centre, with enforceed motion in DOF3 (Z-direction)

 

Loads:

- A 18.4N load acting downwards at the top of the model

 

I created a random event from response simulation as post-processing but the stress values i have gotten is in the range of 1000Mpa, which is too high to be realistic in my opinion. I would like to know which part of the simulation I had made a mistake in or if my constraints are not correct.

 

I have attached a few pictures of the constraints below and a gif to show how the constrained mode of the model is. I thought that the constrained mode looks pretty accurate to what the model would actually experience.

 

Thanks for the assistance!

constraints.PNGspring_enforced.PNG

2 REPLIES

Re: Too high stress result for random vibration simulation

Legend
Legend

Hi felchen,

You didn't mention any damping, so my assumption is the stresses are very high because you didn't specify any, i.e. you're looking at an undamped response. If you add 2%-5% modal damping, your results should be more reasonable...

Re: Too high stress result for random vibration simulation

Creator
Creator

Hi, yup that did lowered my stress to about 10MPa, which is a reasonable value. Smiley Very Happy Thanks for the help!