Papers by Keyword: Stiffened Shell

Abstract: Frequency-aimed optimal structural design of stiffened shell is concerned. It is a reverse design problem for the first several modal frequencies to converge to a set of target value. A design method combined modified bi-directional evolutionary structural optimization (BESO) and size optimization is presented. Optimization model consists of skin and regular grid frame structure. To solve irregular branches and holes that often exist in ordinary topology optimization results, instead of elements, the existence states of ribs in the frame are used as design variables and sensitivity of the rib is discussed. Detailed design is conducted by size optimization. Example shows that frequency requirements are achieved. And the optimum structure is regular and clear, the localized modes problem is avoid. This is very suitable for designing airplane wind tunnel flutter test models.

Abstract: A method to predict the modal density and radiation efficiency of orthogonally stiffened cylindrical shell is presented in this paper. The modal density is derived using energy method from the undamped natural frequencies of stiffened shell by treating the stiffeners as discrete elements. The band averaged radiation efficiency is estimated by categorizing the structural modes into acoustically fast and acoustically slow modes. The predicted parameters are compared with experimental results using laser vibrometer measurements. Phase-roll off has been observed in laser vibrometer measurements for which a correction procedure is applied. This prediction method can be easily extended to shells with stiffeners having different size, orientation etc.