structure design for a vibration test
structure design for a vibration test
(OP)
Hello to all,
Recently we have acquired a shaker test bench and we need to design a support structure to make a vibration test of a part. We had an internal discussion about this matter but i wonder if you could let me know if we are working in the right direction.
Firstly we think that we should calculate the maximum mass of the whole part taking into account the test specifications and the vibration shaker limits.
As the acceleration in the test is constant i was able to calculate the mechanic power necessary to move a given mass in a frequency:
Pm=(M*a^2)/(2*(2*Pi)^2*f) Is this formula correct or am i missing something else?
Many thanks in advance.
Recently we have acquired a shaker test bench and we need to design a support structure to make a vibration test of a part. We had an internal discussion about this matter but i wonder if you could let me know if we are working in the right direction.
Firstly we think that we should calculate the maximum mass of the whole part taking into account the test specifications and the vibration shaker limits.
As the acceleration in the test is constant i was able to calculate the mechanic power necessary to move a given mass in a frequency:
Pm=(M*a^2)/(2*(2*Pi)^2*f) Is this formula correct or am i missing something else?
Many thanks in advance.





RE: structure design for a vibration test
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: structure design for a vibration test
Thanks for your reply. You're right, that formula gives low power consumption at high frequencies, that is the reason why i am not sure about that.
I will try to explain the way i got it:
Assuming that the displacement is sinusoidal
x=X*Sin(w*t)
(where w=2*Pi*f)
then velocity and acceleration
v=dx/dt= X*w*Cos(w*t)
a=dv/dt= -X*w^2*Sin(w*t)
In our test we must apply constant acceleration, so then the amplitude of the displacement=
a=X*w^2 => X=a/w^2
Hence, the higher the frequency the less the displacement we need to achieve a constant acceleration and less the power necessary.
The force necessary to move the structure should be F=m*a, and the mechanical work W=F*deltaX.
So then, taking root mean square values of the force and the displacement, I obtain that the Energy= 1/2* F * X and Power(Pm)= 1/2*F*X*f (F=force, f=frequency)
And expanding the equation:
Pm=1/2*m*a*X*f=1/2*m*a*(a/(w^2))*f=1/2*m*a^2/((2*Pi)^2*f)
( In case of a constant displacement is required i get other equation:
Pm=1/2*m*(X*Pi)^2*f^3 )
Am I missing something?
Many thanks in advance
RE: structure design for a vibration test
RE: structure design for a vibration test
Consider the case where you are testinga shock absorber with a mass of 2 kg and a c of say 1000 N/m/s
or a spring mass system with no damping and a steel spring.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: structure design for a vibration test
That is why i consider important to do a modal analysis of the assembly. Theoretically, if the natural frequencies are far from our study range, could we avoid those effects of mass / damping?
RE: structure design for a vibration test
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: structure design for a vibration test
Does it make sense to me. In fact, in the specifications of the shaker it appears the maximum force we can apply.
Thank you very much for your help.