Previous work has demonstrated how the number and spacing of ribs could be optimized to minimize the noise radiated from rib-stiffened panels in specified frequency bands. This paper demonstrates the application to constant speed gearboxes, where the radiated noise is usually dominated by harmonics of a small number of gearmesh frequencies, their harmonics and sidebands. It is assumed that a good finite element (FE) model of the gearbox exists, updated by experimental modal analysis. With some experience, it is likely that a reasonably accurate model could be obtained from an earlier model but modified to represent a new design. It is assumed that the forces at the bearing blocks will be little affected by the detailed casing design, so that they can be determined from measurements of surface velocity and the original updated modal model of the gearbox. They can then be applied to the new design, modified in such a way as to minimize the radiation in bands around the specified frequencies. These bands must be sufficiently wide to allow for typical errors in the model, or different realizations of a gearbox made to the same drawings. This procedure has been applied to a single stage pump drive gearbox, by minimizing the vibration energy in bands around the first two harmonics of the gearmesh frequency. The vibration energy was weighted both by the radiation efficiency and A-weighting, and final prediction of the radiated noise from the optimal gearbox configuration showed the same improvement. The optimization moved resonance peaks outside the specified bands. The optimization procedure was much more onerous computationally than for the previous plate studies, but it was found that a combination of genetic algorithms (to get good initial estimates of the optimal design) and the Zero-Order Subproblem Approximation method (provided by FE language ANSYS) gave acceptable results.
展开▼
