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Numerical Investigations of Pumpkin Balloon DeploymentStability

机译：南瓜气球部署能力的数值研究

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The application of geometric and materially non-linear finite element analysis techniques to the NASA Ultra Long Duration Balloon (ULDB) Program has been driven by the need to understand and overcome deployment problems that have shadowed the chosen #pumpkin' design. Tensys have been involved in this effort since 2004, alongside parallel investigations into material characterization, fabrication techniques and a program of model and prototype testing. The S-cleft, a stable but asymmetric geometric anomaly that develops during the ascent and pressurization, has been recently identified as the principal design problem. This is a different instability to the overall geometric issues previously identified both numerically and physically. As for these problems, the likely solution to the S-cleft requires the minimization of excess material in the lobes of the pumpkin design. Achieving this will test the structural performance of the film to its limits and make full use of the strain arresting feature of the much stiffer tendons. A full numerical model that takes account of the non-linear visco-elastic response of the film is required to properly judge these design issues over the whole duration of a flight. Stress concentrations must be considered, along with the influence of shape change though film creep on the maintenance of stability. This paper summarizes the numerical paths that have been followed en route to the current situation, and details the implementation of the latest visco-elastic formulation. A foundation is set for `whole flight' analyses of balloon stresses and stability.
机译：几何和物质非线性有限元分析技术对NASA超长持续时间气球（ULDB）程序的应用是由理解和克服所选择的#Pumpkin'设计的部署问题的需求驱动的。自2004年以来，张力已经参与了这项努力，并将平行调查与模型表征，制造技术和模型和原型测试程序相同。 S-CLEFT，稳定但不对称的几何异常在上升和加压期间开发，已被确定为主要设计问题。这是对以前和物理上的先前识别的整体几何问题的不同不稳定性。至于这些问题，S-CLEFT的可能解决方案需要最小化南瓜设计的裂片中的过剩材料。实现这将测试薄膜的结构性，并充分利用肌腱筋的应变滞留特征。考虑到薄膜的非线性粘弹性响应的完整数值模型是在飞行的整个持续时间内妥善判断这些设计问题。必须考虑应力浓度，并且由于薄膜蠕变对维持稳定性的影响，因此形状变化的影响。本文总结了在通往当前情况的路线上进行的数值路径，并详细了解最新的粘弹性配方。为“全程”分析气球应力和稳定性分析。

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