Divergence instability in an air-conveying soft tube: Analysis of static zig-zag shapes

This work is devoted to the characterization and modeling of surprising stable states appearing in air-conveying soft tubes. A tube differs from a flexible by its very thin walls which allows it fold with sharp angle. When upper end fixed an air pump while bottom left free, system exhibits divergence instability develops under form “zig-zag” shapes constituted three roughly straight segments. We characterize each shape lengths angles these observe, for example, that intermediate segment limited short because inclined direction respect vertical increases gravitational torque on fold. In order theoretically reproduce zig-zag shapes, we use model articulated rigid tubes conveying airflow. The exerted pressurized folded part pipe modeled nonlinear torsional spring. shows can stabilize into qualitatively similar experimental observations.