Modeling of the added mass of air on ETFE cushions vibrating in still air

摘要

ETFE (Ethylene-Tetra-Fluoro-Ethylene) cushions are popularly used in civil engineering structures. A vibrating ETFE cushion will drive the surrounding still air in motion and the inertia of air produces an action on the cushion which is known as the added mass. This effect is usually significant due to the light weight of ETFE cushions. This paper proposes a new model on the added mass effect for a close-type ETFE cushion vibrating in still air with improved accuracy compared with other existing models. The fluid velocity along the z-direction of the enveloping membrane from perturbation of the vibrating cushion is assumed to vary in the form of a quartic function. The added mass is analytically obtained from the Laplace equation. This new formulation is then validated by comparing the dynamic responses of square ETFE cushions with those from the fluid- structure interaction (FSI) analysis and other methods in the literature. The accuracy of the proposed approach is further investigated for different rise-span ratio, initial inner pressure, side length, Young's modulus and membrane thickness of the ETFE cushion. It may be concluded that the proposed approach is more accurate than existing methods with more realistic predictions on the actual variation of the fluid velocity along the z-direction above the cushion and the errors are less than 4% for practical ranges of influencing parameters studied.