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Ansys Learning Forum › Forums › Discuss Simulation › General Mechanical › Natural frequency in Transient Structural › Reply To: Natural frequency in Transient Structural

May 9, 2024 at 12:00 am
peteroznewman
Subscriber

The natural frequency of the bridge is 2.5 Hz.

You set the damping ratio to be 1% at 2.5 Hz which affects the rate at which the envelope of the amplitude of vibration reduces over time. Try a much larger damping ratio like 10% to see the envelope reducing over time.

Then you changed the damping ratio to be 1% at 10 Hz, but that does not change the natural frequency of the bridge, it affects the rate at which the envelope of the amplitude of vibration reduces over time.

Do some research on Rayleigh Damping and you will find an equation that converts a Damping Ratio into a Stiffness Coefficient and an equation to plot Damping Ratio as a function of frequency. That equation will show you what the new damping ratio is at 2.5 Hz when you changed it to be 1% at 10 Hz.

If you want to change the natural frequency of the bridge, you need to reduce the mass and/or increase the stiffness of the structure.