Spring, Mass , Dumper system. Dumper Value.

[Bluesky1]

1. The problem statement, all variables and given/known data

Hi,

I have a problem with first question from site below:
http://engineeronadisk.com/V2/notes_courses/engineeronadisk-91.html#pgfId-521824




3. The attempt at a solution

I was trying to solve it using transmissibility equation but there is no mass so I cant find a natural frequency.

Transmissibility is in this case 0.01% because the isolation required is 99.9%.

T= sqrt {[1+4*d^2*(f/f0)^2]/[(1-(f/f0)^2)^2 + 4*d^2*(f/f0)^2]}

d- damper value
f- frequency which is 100Hz
f0- natural frequency

The other way is to use dynamic equation and then find transfer function:

dynamic equation: cx' + kx = M x''

but the Mass is unknown and it's the problem.

Please help

[Gokul43201]

I believe you are correct - you need the mass, and there is no way to absorb it into the value of the damping coefficient. I guess you could proceed by assuming some convenient value for the mass.

[Bluesky1]

I believe you are correct - you need the mass, and there is no way to absorb it into the value of the damping coefficient. I guess you could proceed by assuming some convenient value for the mass.

Thanks for answer,

The other way that i was trying to assume that system is in resonance because of low damper value, but 100Hz of forcing frequency doesn't need to be natural frequency.:(

First question when I have started to practice and I found without enough data.

Ehhh I'm lucky :cool: