Natural Frequencies

Natural Frequency analysis often used in structural dynamic investigate the resonant frequencies of a design. This analysis type helps users ensure that the natural modes of vibration are well away from environmental forcing frequencies that a design might encounter during service. For geotechnical engineering, the analysis is useful when designing a foundation for a vibration source such as machinery equipment, rocket launch base, etc. Another important use of the analysis type is to be used to determine appropriate Rayleigh damping parameter.

To compute natural frequencies:

1. Enter the Minimum and Maximum Frequencies as range limits.
2. Set the Interval for natural frequency computation.
3. Select Compute.
4. When computation completes, select Save and view results. Frequency (Hz) vs. Damping ratio (%) under specific Rayleigh damping parameters (alpha and beta) will be displayed in the pop up dialog. Results are stored and can be accessed by selecting View Results from the Natural Frequencies sub-menu of the Dynamic menu.

Interval

Interval can be set to improve the performance of the server. Amid computation, the range of natural frequencies will be divided into several equally distributed districts. The Interval for each district can be user defined (default value is 1). Reducing the Interval value will speed up the computation.

See the Dynamic Slope Analysis Part C: Rayleigh Damping tutorial for an example of the use of the Natural Frequencies option.