Abstract:
This paper addresses the modeling of the thick uniform or general composite laminate and sandwich structures commonly used for helicopter construction to support the fast and accurate modelling of such structures for high frequencies using SEA. For laminated composites, each layer of the lamina is described by a Reissner-Mindlin displacement field leading to equilibrium relations accounting for membrane, transverse shearing, bending and full inertial terms. The sandwich model adheres to the sandwich panels' assumptions and uses a discrete displacement field for each layer, also allowing for out-of-plane displacements and shearing rotations. For applied use with an SEA methodology, an accurate wave-based approach formulation is developed where each subsystem is modeled as a superposition of waves travelling within the subsystem. The validity of this modeling approach is confirmed through comparison to measured test data and alternate validated theoretical approaches are confirmed for several simplified test structures comprised of "thick" uniform-layer structures, laminate composite sandwich structures with composite skins and general laminated viscoelastic structures. Representative examples of helicopter interior noise predictions for typical load cases are shown and the use of SEA models as a tool for guiding construction of multi-layer lightweight structures to meet acoustic performance and weight targets and optimize designs are presented. Conclusions about the overall applications and improvements offered by this approach, current limitations, and future work to extend and improve this approach are given.