# Ansys 2D - Spring system

1. Nov 18, 2015

### Jayaram12391

Hi friends,

I am working on a model of linear generator. I have modeled the linear generator in Ansys 2D. Now I want to attach a spring to one end of the rotor and see how it works with the spring attached to it. How do I model the spring?

Also is there any proper way to determine the damping co-efficient of the system

Any help or suggestions will be highly appreciated. Thanks

2. Nov 18, 2015

### Hesch

First of all you have to determine what the input/output is to be in the model. Say that the input is some force, F, that affects the rotor, and that x is the position of the rotor, you will get a model like this:

m = mass of rotor
a(s) = acceleration
v(s) = velocity
x(s) = position
K = spring coefficient

Using Masons rule, you will get a transfer function: x(s)/F(s) = 1 / ( m*s2 + K ) = ( 1/m) / ( s2 + K/m ).

which can be rewritten

x(s)/F(s) = ( 1/m ) / ( s2 + 2ζωns + ωn2 )

Here the damping ratio, ζ = 0 , because the coefficient to s = 0. So in this model no damping takes places, but that's because there is no friction and no power loss due to the generator included in this model.
So to calculate a realistic damping coefficient, ζ > 0, you must introduce friction/power loss in the model.

Last edited: Nov 18, 2015
3. Nov 19, 2015

### Jayaram12391

Thank you very much for your answer. I know the stiffness of the spring to be attached to be 750pounds/inch. But i am not sure how I can introduce it into the ansys model.

Thanks for your explanation on damping co-efficient. I know the efficiency of the generator. I will try to calculate the damping co-efficient of the system.