Example 19 - Features of Eigenvalues and Eigenvectors - System with Mixed Modes#

This example is based on Example 5.9.3 from [Friswell, 2010].

System with Mixed Modes. Analyze the system o f Example 5.9.2
with bearing stiffnesses of l MN/ m in the x direction and 0.2 MN/m in the y
direction. Calculate the eigenvalues and mode shapes at 4,000 rev/min and show
that some modes contain both forward and backward whirling components.
import ross as rs
import numpy as np
import plotly.graph_objects as go
from IPython.display import display
Q_ = rs.Q_
steel = rs.Material("steel", E=211e9, G_s=81.2e9, rho=7810)
L = 0.25
N = 6
idl = 0
odl = 0.05

shaft = [rs.ShaftElement(L=L, idl=idl, odl=odl, material=steel) for i in range(N)]
bearings = [
    rs.BearingElement(n=0, kxx=1e6, kyy=0.2e6, cxx=0, scale_factor=2),
    rs.BearingElement(n=len(shaft), kxx=1e6, kyy=0.2e6, cxx=0, scale_factor=2),
disks = [
        n=2, material=steel, width=0.07, i_d=odl, o_d=0.28, scale_factor="mass"
        n=4, material=steel, width=0.07, i_d=odl, o_d=0.35, scale_factor="mass"

rotor = rs.Rotor(shaft_elements=shaft, disk_elements=disks, bearing_elements=bearings)
campbell = rotor.run_campbell(speed_range=Q_(list(range(0, 4500, 50)), "RPM"))
modal = rotor.run_modal(speed=Q_(4000, "RPM"))
for mode in range(6):
    display(modal.plot_mode_3d(mode, frequency_units="Hz"))
for mode in range(6):
    display(modal.plot_orbit(mode, nodes=[2, 4]))



MichaelĀ I Friswell. Dynamics of rotating machines. Cambridge University Press, 2010.