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Acoustic fatigue procedure validation and application on cavity wall

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2019
Küden, Zeynep
Acoustic loading formed due to boundary layer fluctuation, engine efflux and separated aerodynamic flow cause vibration that may result in fatigue failure of the structure. The subject of this thesis deals with the analytical acoustic fatigue procedure composition and validation in addition to critical wall stress analysis of representative weapon bay. It is aimed to feed the design process of the projects during its preliminary stages from structural point of view. The thesis can be discussed into two section. Firstly, analytical procedure on acoustic fatigue is composed by Engineering Science Data Unit documents. Verification is achieved via Finite Element Method by assuming single degree of freedom theory; since, fatigue damage is usually dominated by one mode, although acoustically induced vibration usually consists of several response modes. Analytical method covers the extraction of dynamic characteristics, response under unit loading, acoustic loading generation and dynamic stress response of the simple-geometry structures. Obtained stress levels are used to predict endurance life of the structure with simplified equations. Secondly, critical wall stress response analysis of cavity shape structure, represents weapon bay of an aircraft, with different boundary conditions is carried out. These boundary conditions arise from different housing cases of the internal members of the aircraft. Effects of changes in the internal rib structures’ location on the structural response is investigated for different Mach numbers and controlling methods, spoiler and swept rear wall alike, applied to reduce the pressure fluctuation generated due to the flow over cavity.