E09: Natural Frequencies of a Torsional System

Owned by Gokhan Alkan (Unlicensed)
Last updated: Jul 05, 2019 by Harika Inanc (Unlicensed)

A simple torsional system has two torsional springs with stiffness K = 100.0 lb-in/rad and two mass elements with rotary inertia of 1.0 lb-in-sec2. Determine the lowest two natural frequencies and mode shapes of the system.

The system is modeled using 2-node torsional spring elements and mass elements. Joint 1 is fixed and all degrees of freedom except rotation about the Global X are restrained at joints 2 and 3.

App 

Object Link : https://openbrim.org/objidvlfpe7b1ewl4dwjsika6nt.project

Library 

Object Link : https://openbrim.org/objidwer35svkx680kvtn4cv3ct.libobj

Solution Comparison


OpenBrIMLARSAThomsonEMRC

Percent Difference

OpenBrIM-LARSA

Mode 1 f= 0.9836 (Hz)
6.1801
6.186.186.180%
Mode 2 f= 2.5752 (Hz)
16.1804
16.1816.1816.180%



Tested Features


Sources

  • W.T. Thomson, "Theory of Vibration with Applications", Prentice-Hall Inc., Englewood Cliffs, NJ, 2nd Edition (1981).
  • EMRC, "NISA II Verification Problems Manual", 1991.
  • LARSA 4D