Page 52 - ENGINEERING REVIEW NOVEMBER 2022_Neat

ENGINEERING
REVIEW INSIGHT

through dynamic structural modification
of the suspension assembly after
detailed evaluations of the strain energy
and their density distributions. The
modified suspension assembly with the
cooling fan accounted for the gyroscopic
stiffening and was designed and verified
through mobility transfer function
Fig. a) Fundamental Mode shapes -12Hz & 18Hz b) Measured Mobility measurements for effectiveness.
Verification trials indicated that the
Deep dive diagnostics in dynamic amplification causing high vibration response levels were found to
The unbalanced excitation frequency vibrations. The bouncing mode remains be significantly lesser, ensuring smooth
of the fan at 22.5Hz was far from the constant at 12Hz, whereas the tilting and safe operation of the fan motor
fundamental structural modes to cause frequency increases from 18Hz to 22Hz. subassembly, eliminating stator-rotor
dynamic amplification. Hence, it was While operating on approaching the rub, and leading to the continuous and
anticipated that the residual unbalance fan’s rated operating speed, this resulted safe operation of the plant.
might be abnormally higher, resulting in dynamic amplification of the vibration
in higher vibration levels. Hence, the due to the gyroscopic stiffening of the Conclusion
fan motor assembly was driven by a assembly. The stator-rotor rub failure of a fan
standalone variable frequency drive to motor in the cooling system assembly
analyse residual unbalance behaviour Optimal Solution through Structural that led to the shutdown of the 250 kW
during the coast up and coast down Dynamic Modification compressor was investigated in detail.
operation. Despite having adequate Subsequent to the identification of The application of engineering know-
safety margins, the system resulted the root cause, solutions were sought how aided by a systemic approach
and tools led to sustainable solutions
to the real-world engineering problem.
This structured approach resulted in
a comprehensive resolution, thereby
reassuring the customers of the promise
of a reliable product and an assured
uptime.
A complete version of this technical
content was presented at the 28th
International Congress on Sound and
Figure a) Strain energy distribution of tilting mode b) Vibration response Vibration (ICSV28), held in Singapore
comparison (Black - original configuration, Grey – improved configuration) during July 24-28, 2022.

Figure 8 a) Vibration velocity response in coast up b) Time frequency analysis (Contour map)

48 | NOVEMBER 2022