Random Vibration PSD input

Altair Forum User

Hi,

I am doing random vibration, my model is in metric units (mm, tonne, seconds).

i have input of vibration profile which is in g^2/Hz, generally i use input of vibration profile in G^2/Hz, following the image below so that my results will be metric units.

 

 

how to convert g^2/Hz PSD- input to standard G^2/Hz input in optistruct using TableRND card.

Kindly help me with this.

Thank you in advance.

Rahul Rajan_21763

PSD value 0.1 G^2/Hz and want the results in MPa, simply convert it to (mm/s^2)^2/Hz =>  0.1*(9810*9810)=9623610 (mm/s^2)^2/Hz)

If you use mm and mass = tonnes (Mg), a psd in g^2/Hz then you stress should be in MPa^2/Hz, disp in mm^2/Hz, accel in (mm/s^2)/Hz 

 

Altair Forum User

Hi Rahul,

 

Thank you for your response.

 

PSD value 0.1 G^2/Hz and want the results in MPa, simply convert it to (mm/s^2)^2/Hz =>  0.1*(9810*9810)=9623610 (mm/s^2)^2/Hz)

when i have value in 0.1 G^2/Hz,  i don't have to convert the values to (mm/s^2)^2/Hz since i follow the stranded table which i mentioned below.

 

If you use mm and mass = tonnes (Mg), a psd in g^2/Hz then you stress should be in MPa^2/Hz, disp in mm^2/Hz, accel in (mm/s^2)/Hz.

Yes when my model is in mm, mass in tonnes, and psd in g^2/Hz, then what should i do to get results, Stress in MPa, Disp in mm?

 

Let me put a table,

I need output to be displacement in mm, stress in MPa.

when the psd input changes, what conversion factor to be used to get output, displacement in mm, stress in MPa.

 

 

PSD-Input	Model-Units	SPCD- Excitation	Conversion (If any)	RMS Output-disp	RMS Output-stress
G^2/Hz	mm, tonnes, seconds	1	?	mm	MPa
G^2/Hz	mm, tonnes, seconds	9810	?	mm	MPa
g^2/Hz	mm, tonnes, seconds	1	?	mm	MPa
g^2/Hz	mm, tonnes, seconds	9810	?	mm	MPa
G (peak)	mm, tonnes, seconds	1	?	mm	MPa
G (peak)	mm, tonnes, seconds	9810	?	mm	MPa

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Correct me if i am wrong,

G^2/Hz=(m/s^2)^2/Hz

g^2/Hz=(mm/s^2)^2/Hz

 

Regards,

Kishore.

 

 

Rahul Rajan_21763

 

Please refer attached pdf for random response analysis which should clear most of your doubts.

Altair Forum User

 

Thank you for the document provided Rahul.

 

Attached document clarified most of the doubts, still need small clarification as shown below.

 

And I have attached PPT of my understanding, Kindly review.

 

Thank you in advance,

 

Regards,

Kishore.

Rahul Rajan_21763

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berk luleci

Rahul Rajan_21763 said:

 

Please refer attached pdf for random response analysis which should clear most of your doubts.

Hi, thank you for sharing this document. I was wondering, if we can access the rest of it?