טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAginsky Ziv
SubjectNonlinear Spatio-Temporal Acoustic-Fluid-Structure
Interaction of Panels in a Compressible Inviscid
Fluid
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Oded Gottlieb
Full Thesis textFull thesis text - English Version


Abstract

Acoustic fluid-structure interaction is defined as structural response to excitation by sound and sound scattering due to structural fluctuations, respectively. This interaction is due to the coupling between the acoustic fluid pressure and an elastic structure where the fluid field and the moving structure mutually transfer information. The fluid transfers loads to the structure resulting in its deformation which in-turn causes a change in the near fluid field from which acoustic radiation is generated to the far field. In many cases the acoustic pressure fluctuations are small, and linear analysis is suitable. However, when structures such as aircraft panels, are exposed to significant acoustic excitation, such as in vicinity of engine outlets, linear assumptions are no longer valid and a nonlinear analysis is required. Thus, the focus of this research is on the asymptotic and numerical investigation of a nonlinear fluid-structure interaction of an acoustically excited clamped panel immersed in an inviscid compressible fluid. A multiple-scale asymptotic analysis of the corresponding two and three-dimensional initial-boundary-value-problem was employed to investigate primary, secondary and internal resonances. A two-dimensional numerical validation of the asymptotic structural response and the far field pressure was conducted and showed good agreement. The weakly nonlinear analysis revealed coexistence of symmetric and asymmetric, periodic and period-doubled solutions culminating with chaotic-like slowly varying plate evolution. The latter correspond to fast qusiperiodic torus-doubling and non-stationary plate response and scattered pressure. The resulting bifurcation structure enabled discovery of an intricate scattered pressure field due to complex and non-stationary symmetric and asymmetric panel surface pattern formation. The numerical investigation of the strongly nonlinear spatio-temporal acoustic fluid-structure interaction of a two dimensional panel in an Euler fluid field also revealed an intricate bifurcation structure near the fifth mode panel resonance. This structure includes coexisting symmetric and asymmetric periodic, quasiperiodic and chaotic-like non-stationary response which evolved from an orbital loss of stability of an m/n=3/2 ultrasubharmonic solution. We note that panel response to two-frequency acoustic excitation reveled combination resonances incorporating multiple spatial modes culminating with an irregular pattern corresponding to spatio-temporal chaos. The investigation reveals the need for a consistent nonlinear acoustic fluid-structure interaction analysis of a panel that is exposed to a high source pressure level. Furthermore, the coexistence of multiple periodic and non-stationary solutions may be a crucial factor for design of high integrity structural systems required for aviation or space where light structures are exposed to intensive acoustic pressure fluctuations.