A linearized reduced-order model approach for sloshing to be used for aerospace design

This paper proposes Reduced-Order Models (ROMs) based on data provided by Computational Fluid Dynamics (CFD) simulations for generally flexible tanks to be embedded in a larger aerospace structure. A commercial off-the-shelf CFD code addressed to sloshing analyses is employed to generate data set to be used for the synthesis of the sloshing system ROM. The developed sloshing ROM, based on a Linearized Frequency Domain (LFD) approach, makes use of an Input/Output system identification technique from CFD transient simulations to construct an unsteady Generalized Sloshing Force (GSF) transfer function (or frequency response function) matrix. This is done in analogy with the Generalized Aerodynamic Force (GAF) matrix used to model the aircraft unsteady aerodynamics for linearized aeroelastic analyses. The obtained GSF frequency response function data are suitably fitted via a rational polynomial form in the frequency domain so achieving a state-space representation for the sloshing system. Although the formulation is applicable for any 3D tanks of arbitrary shape, a parallelepiped tank is used as benchmark in order to compare the obtained GSF frequency response matrix with that available in the literature for simple tank geometries. The prediction capability of such method is also assessed by comparing the sloshing forces provided by the ROM and those obtained via direct CFD simulations even using unsteady boundary motions different than those used for ROM identification. The obtained linearized ROM of flexible tank with sloshing fluid seems suitable for aerospace applications for perspective integrated stability and response analyses and design of the aircraft/spacecraft structures.