Non-linear Vibration of Beam Immersed in Fluid

Abstract

In space launch vehicles with liquid propulsion system, various sub-systems like gas bottles, anti-slosh baffles and fluid lines are placed inside the propellant tanks which become partially filled over time during flight. In this context, the dynamic response of a structure immersed in a fluid becomes complex as the force exerted by the fluid on the structure during vibration is very sever. Several theoretical models have been reported in literature to solve this type of fluid-structure interaction problems. However, the selection of a suitable model depends on the realistic physical condition and the numerical accuracy with which the solution has to be analyzed. The theoretical models considered here are based on (1) a loosely coupled fluid-structure interaction model, (2) a strongly coupled fluid-structure interaction model with large deformation and (3) a phenomenological fluid-structure interaction model, all of them including the effect of large deformation. The commercial code ANSYS CFX is used to study the first two models. Computational performance and accuracy aspects are discussed in detail with reference to experimental measurements. In order to apply the detailed understandings further in efficient simulation study, particularly those requiring iterative design optimization of the structural system, it is desired to have a much faster computational speed of simulation without compromising on the numerical accuracy. Model order reduction with phenomenology based mathematical models is one such approach considered further. A phenomenological fluid-structure interaction model is formulated and implemented in a new code. Data generated from an experimental study of internal fluid conveying a beam immersed partially in an external fluid environment is used to fit phenomenological model parameters. In this the problem is sub-divided into two parts. In the first part, a database is generated for the inertial force and the drag forces induced on the beam by the external fluid, and a parametric relationship is incorporated in the phenomenological model. Next a blind transient simulation of this phenomenological model is carried out with base excitation. Simulation results are compared with the experimental results which are found to be in good agreement. Potential application of the developed approach is discussed