Issue link: https://cp.revolio.com/i/854494
22 ista views • July 2017 • www.ista.org Vibration Analysis of Motor Coach Buses Used in the Transport of Goods > CONTINUED FROM PAGE 20 A PSD profile of the vertical axis for each trip compares all four trips, Fig. 5. Trips 1, 2 and 3 all shared similar shapes in vertical vibration. Trip 4 varied in shape due to the use of a different bus model. All trips indicate vehicle input peaks between 7-21 Hz, Fig. 5. While PSD profiles of the trips shared similar shapes, some variation existed. Trip 2 experienced a peak at 21 Hz that coincided with a lower level peak in Trip 3 at 19 Hz. Neither Trip 1 or 4 had a visible peak in this 19-21 Hz range. Trip 1 data was recorded at low speeds primarily on poorly maintained secondary roads, which could have contributed to its dominate peak occurring at the lowest frequency of the different trips, 8 Hz. While each of these trips had some individual difference, they combined to provide significant information about the vibration of motor coach buses. Utilizing the vertical axis data from trips 1, 2, and 3, excluding trip 4 due to variance in bus, a smoothed composite envelope PSD was constructed, Fig. 7. Using the event intensity of each 2 second, timer triggered event analyzed, a distribution plot event intensities was plotted, Fig. 8. Referencing an ISTA document from the 2009 Field Data Workshop, specific break points for an envelope PSD were estimated using the vertical PSD plots from Trips 1, 2, and 3. These points were selected as an envelope of the three trip's vibratory response, Table 2. In instances where one trip's PSD profile values exceeded the other, the higher PSD value was favored [Kipp]. The data collected in this motor coach study is uncompressed data, meaning it has not been artificially scaled to enable reducing test time. In order to accurately compare this data to other industry plots, it must be compared to uncompressed data. Figure 9 was constructed using uncompressed seed data from ISTA Procedure 4AB. Using this data ensures the profiles are commensurable. Figure 9 shows a comparison of the motor coach composite envelope PSD, Fig.7, to industry standard PSD profiles for truck, rail, and air [ISTA]. It can be seen that the bus composite envelope PSD is not as intense as the truck, rail, 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1 10 100 PSD (g2/Hz) Frequency (Hz) Trip 1 Trip 2 Trip 3 Trip 4 Figure 5: Graph comparing vertical PSD profiles for Trips 1, 2, 3, and 4. 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1 10 100 PSD (g2/Hz) Frequency (Hz) Trip 1 Trip 2 Trip 3 Trip 4 Figure 6: Graph comparing longitudinal PSD profiles for Trips 1, 2, 3 and 4. 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1 10 100 PSD (g 2 /Hz) Frequency (Hz) Trip 1 Trip 2 Trip 3 Composite Figure 7: Composite envelope PSD summarizing vertical vibration of Trips 1, 2, and 3. > MORE ON PAGE 24