A well-known engineering company involved in energy and environment got a requirement of optimizing its cooling tower structural components along with resolving its noise and vibration issues. The current design was a frame made up of I beams which were used to support a fan weighing about 1 tonne and Motor gearbox weighing another 2 tonnes. The client had extracted field data of vibration (velocities and displacements) for an existing installation of such frame in a working cooling tower. This data was used as a benchmark for developing a new optimized design.
At analyzer, we used this field data to validate our FEA model of the existing system. As this structure was part of a bigger assembly of a cooling tower, we adjusted different parameters in the FEA model to tune the model with field data.
The Frame structure was subjected to simultaneous vibratory forces at different frequencies. Doing a transient dynamic analysis to capture all the loads was time consuming owing to a high range of frequencies. We worked out a faster option of combining various harmonic analysis at different frequencies and accordingly validated the model. Since the operating frequency of Fan was very much near to the natural frequencies of fan-forced response analysis was conducted on a validated model for the new optimized frame. ISO 1940 was followed to calculate dynamic excitation forces due to Motors, Fan, and gearbox as per balancing grade of the same.
The weight of the Frame structure was reduced by about 30% with a better estimated NVH characteristic than that of the original frame by using analysis-based design modifications.