Study on unsaturated shapes of helium ballonet of rigid airship during ascent process.

Airship has a good application prospect in tourism, material transportation, emergency rescue, communication relay, early warning, environmental protection and other fields. Airships can be classified into non-rigid types, semi-rigid types and rigid types. The rigid airship relies on the external skeleton to maintain its overall stiffness and shape, and the internal helium ballonet provides buoyancy. The helium ballonet is always in unsaturated state during ascent process, which will affect the center of gravity and buoyancy and the stress in wrinkle area, so it is great significance to study the unsaturated shape of the helium ballonet during ascent process. In this paper, the principal stress-principal strain principal is used to judge the stress state of the membrane. The modified constitutive matrix method and the pressure gradient method are used to obtain the shape of the helium ballonet under different saturation by the dynamic explicit FEM (Finite Element Method). When the pressure gradient method is used to apply the pressure difference internal and external of the ballonet, the change of unsaturated shape of the ballonet can be interpreted as the change of zero pressure level of the ballonet. The modified constitutive matrix method can effectively avoid the problem of non-convergence in the process of programming. The simulation results are in good agreement with the experimental results, which shows that the analysis method is reasonable and correct. [ABSTRACT FROM AUTHOR]