Learning Forum

[AhmedCfx]

Hi all
I have mass spring system, and I need to find the damping ratio, settling time, and the rise time. How can find it or plot it in ansys?

Best regards

[peteroznewman]

Is damping defined in the same element that defines the spring stiffness?

Which spring element are you using?

[AhmedCfx]

I have mass 500 g put on a spring its stiffness 0.400 kN/mm without damaging coefficient .
I used ground contact spring in workbench, but I didn’t know how to show the above requirements.

Thanks in advance

[peteroznewman]

If you have a physical mass-spring system, you can drive the spring support with a step function and use sensors to record the displacement-time history of the mass. You can analyze that recording to determine the damping ratio, settling time and rise time.

You can build a simulation of that physical system, but the damping ratio is an input to the system. Once you have set that, you can simulate a step function input on the ground side of the spring and watch the response of the mass.

You don't even need to use ANSYS, you can just numerically integrate the equations of motion for a mass-spring-damper system in matlab or python, or whatever.

[AhmedCfx]

Thank you sir for your support, your information were really helpful. Please how can I create a graph like that ?

[peteroznewman]

Attached is an ANSYS 2019 R3 model that provides a damped spring-mass system with an input force to disturb it.

I did not use 500 g of mass or a spring rate of 0.4 N/mm, you will need to edit the system to set that up.  You can add a Point Mass to body 1 to make up the difference between the current mass and the desired mass.

[AhmedCfx]

Dear peteroznewman

How can I get such graph in ansys 18.2?

Best regards

[peteroznewman]

Is your goal to learn ANSYS or is it to obtain a graph of the damped response of a mass-spring system?

You don't need to use ANSYS to get the graph. You can use this website. Below is the solution to your problem.

You can type in the equation into a program such as MathCAD or Excel to plot the time response.

[AhmedCfx]

Dear
My goal is how to obtain such graphs in ansys and find some results like settling time and rise time

[peteroznewman]

Do you have a second computer that you can install the free ANSYS 2019 R3 Student software?  If so, you can open the attachment above to see how I did that.  Don't install a Student license on a computer with a permanent license, it might mess up the permanent license.

What is your definition of settling time and rise time?

 

[AhmedCfx]

Dear peteroznewman

Settling time means how long it takes to system be stable ? And rise time is the the first peak on graph its the maximum amplitude (displacement vs time)

[peteroznewman]

You see the equation of motion has an exponential decay times the oscillating component, so mathematically, the motion never stops. You need a definition of settling time that has some non-zero value relative to the equilibrium position.

[AhmedCfx]

Dear peteroznewman

Thank you sir I really appreciate your effort.

Best regards