How to model Vibration of Machine

[SantoZoo]

Dear All,

I want to ask about the vibration of machine.

As far as I know, we need to input as sine function. Am I right?

I assumed the weight of machine is 110 kN and assumed that 10% of weight will be placed as the vibration.

I use Time History Definitions - Harmonic Function.

Sine function and frequency machine is 37.233 cps.

Amplitude, what should I input in Amplitude?

Cause I have assumed that 10% of machine weight will be used as vibration, I input Amplitude as Force 11 kN

Then cycles, I input 372 (I think its like 10 second of vibration)

Step = 0 second

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Then after define Type 1 Force, I define Arrival Time

I used Time Step 0.05

Damping 0.05

0 Arrival Time

For Load Cases, I used DEAD and MACHINE

DEAD is only selfweight

MACHINE is

SELFWEIGHT X 1
SELFWEIGHT Y 1
SELFWEIGHT Z 1
TIME LOAD
77 78 117 118 FX 1 1 1.000000
JOINT LOAD
77 78 117 118 FY -110


Please your kindly advice whether my modelling is correct or not.
What should MACHINE be assigned as DEAD or LIVE load? cause it will affect the load combination

Please your help.
I have attached my Staad.

Thanks a lot.

 

[hanxi]

SantoZoo:

Good day.
I hope my response is not yet late.
Amplitude for machine vibration problem can be computed by:

F=mew^2
F=amplitude
m=mass of rotating element of your machine (rotor), you can have this value from vendor data
e= eccentricity (can be given or provided by vendor)
w=machine frequency

However, if some data like eccentricity are not provide by vendor:, you can rearrange above formula into:
F=m(ew)w
m=mass
ew=balance quality grade of your machine (you can search ISO 1940, if my memory is correct, and choose what grade level does your machine qualify, like G2.5 for turbine/generator as an example)
w=machine frequency

Kindly follow below steps for typical calculation:
F=m(ew)w F : amplitude (vertical), N
m : mass of machine rotor, kg
(eω) : balance quality grade (G2.5 for for turbine/generator = 2.5mm/s)
but the next critical grade/level is selected for design
(G6.3 = 6.3mm/s)
ω : machine frequency

Cheers.