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Vibration analysis

Hi Vijay

I have been given the following Project and they have put a tight dead line on this. So I really appreciate if you reply me as soon as you can.

This is a fan shroud. When this fan shroud is installed on the engine and starts to vibrate, one of the following happens

1. Those purple pieces which are made of steel start to craking

2. The soft shot (green piece) become separated from the hard shot ( yellow piece)

The customer is going to give us two more version of revised design of this to see if they work better than their current model

<?xml version="1.0" encoding="UTF-8"?>

Here is the material stress strain curve and its data point for the the yellow piece, the purple pieces are made of stain less steel and we don't have the material data for the green piece (the soft shot) yet.

The inner surface of all those steel pieces and a surface all around the soft shot are constrained in all DOF. The customer has provide us the attached Excel file which shows the frequency range and acceleration at each point (please see the attached file)

I appreciate if you guide me about type of analysis for this project.
What should I consider in the current model to be compared with revised design to say if the revised ones are better or worse?
I have sent you the model via your drop box link too.

<?xml version="1.0" encoding="UTF-8"?>

Unable to find an attachment - read this blog

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Altair Forum User

Hi Bita,

What the customer wants out of this (objective)?

Why the customer has provided you the stress-strain curve?

Vibrational analysis (FRF) doesn't require non-linear material (linear dynamic analysis)

You can do a FRF analysis based on the input freq-acceleration and compare the stress, displacement, etc.. for different models (maybe)

Altair Forum User

I have't done frequency before. Can you give me an example of frequency response analysis whin the inputs are frequency and acceleration?

In which load collector should I define my inputs ( acceleration and frequency)??

How can I define that for all 4 nodes? the frequency is the same but the acceleration is different for each node

Do I have to do 3 different type of analysis? one in X direction, one in Y and one in Z direction??

Please answer my question and give me any guidance that you think is required for this analysis . I have no idea of this frequency response analysis

it would be great id you can put a similar example here where the inputs are frequency and acceleration Thanks alot

Altair Forum User

Hi bita,

PFA, tutorial on FRF analysis

Unable to find an attachment - read this blog

Altair Forum User

In which load collector should I define my inputs ( acceleration and frequency)??

Go through the tutorial and you will get the idea about load collector

How can I define that for all 4 nodes? the frequency is the same but the acceleration is different for each node

You can use 4 different load collectors and combine using DLOAD (Dynamic load combination)

Do I have to do 3 different type of analysis? one in X direction, one in Y and one in Z direction??

So you have four nodes and you will apply acceleration on all four in same direction at a time, correct? In that case you can run different analysis for different directions.

Altair Forum User

Hi Prakash

Thank you very much for your help. I did this tutorial. In the tutorial a unit load is applied to the model via DAREA but in my case I have acceleration for each point I have 17 different values of acceleration in each direction which shoud be defined via SPCD I guess. My question is how to input these acceleraton data point please guide me. Thanks

Altair Forum User

Hi Bita,

Yes, you need SPCD and in RLOAD1 card change the type of loading to acceleration.

17 different Acceleration Vs Freq can be applied via TableD1 card.

Altair Forum User

Hi Prakash

One more question. which outputs are usually considered in frequency response analysis ? I want to know which outputs I can consider to be compared in current design with modified design to say the modified design works better or worse under the same loading.

for instance Von Mises stress of elements at each frequency should be considered and compared or what?

I appreciate if you can elaborate this

Altair Forum User

Hi Prakash

I got this error. I searched but I couldn't find anything

*** ERROR # 5408 ***
Aborting analysis because no structural modes have been
computed in the modal dynamic subcase 1.

*** PROGRAM STOPPED: FATAL ERROR(s) ENCOUNTERED.

Altair Forum User

Hi Bita,

You can compare displacements, stress strain etc.. and depends on your client's interest at a particular frequency or frequencies.

Can you check if the density for any material is missing in your model?

Altair Forum User

Thanks a lot Prakash

Altair Forum User

Hi all,

can i ask one question here?

does any body explain to me more about unit load? almost example i saw is 1 but sometime it is another value.

Thanks so much,

Altair Forum User

Hi @Doan Ba Do

Maybe it is associated with any load Vs time/freq table and this unit load acts as a factor.