Abstract

Assemblies containing fluid filled reservoirs are present in space launch vehicles and their satellite payloads, automotive structures, ship containers and rail transportation to name just a few. When the reservoirs contain a liquid, or heavy fluid, they are strongly affected by the motion of the structure and the heavy fluid adds significant mass to that of the structure. Dynamic response analysis with the finite element method using direct solutions of the coupled fluid-structure assembly are expensive and provide no means to obtain the coupled modes of the fluid-structure assembly. A new real coupled modes capability was first introduced into MSC Nastran 2019 and has since been extended. The new method delivers the accuracy of direct methods with a significant gain in elapsed time allowing the engineer to perform fast and accurate design studies. Rigid body and constant pressure modes are handled correctly, and the modal basis is available for vibro-acoustic response analysis. Traditional damping models (modal, structural, wmodal, Rayleigh) may be used and the capability is available for interior and exterior acoustics with or without strong coupling (ACOWEAK) to the infinite domain. Excellent agreement is obtained when compared with the modal basis computed using a complex eigenvalue solution and dynamic responses computed using the direct method. In the later versions, external superelements may be generated that contain one or more heavy fluid cavities where the additional mass of the fluid, and the effects of the heavy fluid in the modal basis, are captured. This naturally also makes the capability available for Adams MNF, as well as AVL Excite, generation where the flexible body component may now contain heavy fluid filled reservoirs. In this talk you will learn from the core MSC Software development staff about the latest advancements with MSC Nastran's vibro-acoustic capabilities and how to apply that to your structures application.