Modal characteristics of a scaling stratospheric airship in still air

Abstract

As one of the most crucial and intrinsic characteristics of structural systems, modal analysis has received considerable attention in aerospace, mechanical, and civil engineering. A traditional approach of modal identification involves linear perturbation of the solid structure alone. However, the modal behaviors of flexible stratospheric airships are greatly influenced by surrounding air and prestress, and the accurate modal identification remains a challenge. In this paper, the modal characteristics of a scaling stratospheric airship in still air are thoroughly investigated by experimental and numerical methods. The 3D testing comprehensively revealed the full-field modal characteristics, while the 1D testing served as a supplement and validation for the frequency results. The global vibration contours stitched by four regions indicate that the first four modes of the airship under 2∼10 kPa pressure are all breathing modes. Furthermore, a refined fluid-structure interaction (FSI) model based on the potential fluid theory was built with ADINA software. It is found that the numerical model can give satisfactory results for the first mode with a 1.05% error, but errors for higher-order modes may exceed 10%. Besides, the air domain significantly decreases the modal frequency of the airship. The maximum error of the first-order frequency neglecting the air amounts to 32.25%.