Handbook of Railway Vehicle Dynamics

Field Testing and Instrumentation of Railway Vehicles 455
Psd g*g/Hz (E-3)
2.00
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
4. Body Modes Tests
Such tests are generally commissioned toprovide the dynamics engineer with confirmation of the
fundamental vibration modes of various parts of the vehicle. They are useful for comparison with
the eigenvalue analysis used at the model checking stage as they will include the effects of all the
parasitic stiffnesses. Tests are usually performed by disconnecting the vehicle dampers and then
applying asine sweep displacement signal in the direction of interest via an electric or hydraulic
actuator. The response of the vehicle body is measured using both vertical and lateral
accelerometers mounted at various positions along the length of the vehicle. These tests may
also be used to confirm the first body bending mode.
B. D YNAMIC T ESTS
0.00 0.00 5.00 10.00 15.00 20.00
25.00 30.00 35.00 40.00 45.00 50.00
FREQUENCY (Hz)
FIGURE 13.33 PSD of body vertical acceleration, mainline diesel locomotive.
Vehicle ride tests providethe means to validate the dynamic behaviour of amodel. The vehicle will
typically beinstrumented with accelerometers at various positions on the body, bogie frame, and
axle boxes, and this may be complemented with displacement transducers to measure primary and
secondary suspension displacements. To be of maximum value for model validation purposes, the
data should also include the vehicle speed and location and be accompanied by recent track
recording coach data for the test route and measured wheel profiles from the vehicle at the time
of the test.
Raw acceleration data from ride tests is normally expressed interms of the power spectral
density (p.s.d.) of the signal vs. its frequency range, asshown inthe example in Figure 13.33.
The test data p.s.d. plots are likely toinclude peaks representing the rigid body modes, flexible
modes, and rail length passing frequencies. They may also include peaks associated with the
traction unit, originating from vibration of the engine or driveline.The results may be further sorted
into speed banded p.s.d. to assist in identifying speed dependent effects such as excitation of various
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