OPTIMUM DESIGN OF A GEARBOX FOR LOW VIBRATION

A computer program was developed for designing a low vibration gearbox . The code is based on a finite element shell analysis, a modal analys is, and a structural optimization method. In the finite element analys is, a triangular shell element with 18 degrees-of-freedom is used. In the optimization method, the overall vibration energy of the gearbox i s used as the objective function and is minimized at the exciting freq uency by varying the finite element thickness. Modal analysis is used to derive the sensitivity of the vibration energy with respect to the design variable. The sensitivity is representative of both eigenvalues and eigenvectors. The optimum value is computed by the gradient proje ction method and a unidimensional search procedure under the constrain t condition of constant weight. The computer code is applied to a desi gn problem derived from an experimental gearbox in use at the NASA Lew is Research Center. The top plate and two side plates of the gearbox a re redesigned and the contribution of each surface to the total vibrat ion is determined. Results show that even the optimization of the top plate alone is effective in reducing total gearbox vibration.