Bulging Instabilities and Zero-Stiffness Behavior in Hyperelastic Shells for Flow Stabilization

We present the development of a soft damper designed to reduce flow fluctuations by utilizing the zero-stiffness region during the nonlinear deformation of hyperelastic spherical and cylindrical shells. In these structures, the volumetric stiffness becomes zero within certain strain regions, allowing the internal pressure to remain constant despite changes in volume. This passive stabilization mechanism allows the damper to inflate and deflate in response to flow fluctuations, effectively storing and releasing fluid to maintain a consistent discharge rate. In cylindrical shells, a localized bulging instability occurs beyond a critical strain, and the bulged region propagates along the shell while maintaining constant internal pressure, thereby defining the zero-stiffness region. Furthermore, applying axial tension lowers the pressure threshold for zero stiffness, enabling the structure to exhibit this behavior across a wider range of pressures. We experimentally evaluate the performance of the damper in reducing flow fluctuations and develop a hydrodynamic model to describe the interplay between inflow, outflow, and volume changes within the soft damper. Our results show that the soft damper effectively stabilizes flow across a wide range of frequencies, providing uniform discharges, which makes it suitable for precise fluid control applications.