Flutter instability of a fluid-conveying fluid-immersed pipe affixed to a rigid body

A set of simplified boundary conditions for a flexible beam connected to a rigid body at one end and free at the other end is presented and applied to the case of a fluid-conveying, fluid-immersed pipe. These boundary conditions represent an analytically tractable approximation to those of a submersible which uses a combination of jet action and flutter instability induced tail motion to produce thrust. The boundary conditions are made non-dimensional, and the effect of the non-dimensional mass of the rigid body on system stability is assessed. The neutral stability of this system is determined within a two-parameter space consisting of the velocity of the fluid within the tail, and the forward speed of the submersible. Equations in the literature, derived using slender-body theory, were used to compute the sign of the thrust produced by the tail and the tail's Froude efficiency for the neutrally stable waveforms of the beam.

► We investigated the dynamics of underwater fluid-conveying pipes with a new boundary condition. ► The boundary conditions approximate a submersible propulsion by a fluid jet and fluttering tail. ► We obtained two-parameter neutral stability curves for various values of rigid body mass. ► We determined thrust and efficiency of the tail over the internal and external fluid velocity ranges.