| Aircraft structure subjected to elevated temperature and acoustic loading present a challenging design environment. Thermal stress in a structural component has typically been alleviated by allowing thermal expansion. However, very little work has been done which directly addresses the situation where such a prescription is not possible. When a structural component has failed due to thermally-induced tensile stresses, the answer to the question of how best to stiffen the structure is far from trivial. In this work, we demonstrate that conventional stiffening techniques, for example, those which add material to the thickness of a failing panel, may actually increase the rate of damage as well as increasing load into sub- and surrounding structure. The typical compliance minimization topology optimization formulation is applied to a thermally-loaded panel resulting in extremely nonoptimal configurations. To generate successful thermal stress designs where the objectives are to lower the tensile stresses while simultaneously limiting the amount of additional load into sub- and surrounding structures, a well-known characteristic of topology optimization for a single-load case mechanical loading is exploited which by construction limits additional load into surrounding structure. Acoustic loading is also a major concern as exhaust gases with random frequency content impinge on aircraft structure in the vicinity of the engines. An evolutionary structural optimization algorithm is developed which addresses both the maximum von-Mises stress and minimum natural frequency for a generic thermal protection system. The similarities between the two approaches are demonstrated. |
