G.L. Kuiper,
A.V. Metrikine

Experimental investigation of
dynamic stability of a cantilever pipe aspirating fluid 
International Journal of Fluids and Structures 
Summary. The dynamic stability of a submerged
cantilever pipe conveying fluid upwards is considered as one of the
unresolved issues in the area of fluidstructure interaction. There is a
contradiction between theoretical predictions and experiments. Reported
experiments did not show any instability, while theory predicts instability
beyond a critical fluid velocity. Recently, several papers appeared,
improving the theoretical modeling of the
cantilever pipe conveying fluid. All theories predict unstable behaviour,
either oscillatory instability or static instability, denoted here as flutter
and divergence, respectively. To investigate whether
the previous experimental setups did not allow to observe
the instability or the pipe aspirating water is unconditionally stable, a new
test setup was built which could attain a higher internal fluid velocity than
the predicted critical velocities. A cantilever pipe of about 5 m length was
partly submerged in water. The free open end of the pipe was in the water,
whereas the fixed end was above the waterline. The experiments clearly
showed that the cantilever pipe aspirating water becomes unstable by flutter
beyond a critical velocity of water convection through the pipe. Below this
velocity the pipe is stable, whereas above it, the pipe shows a complex
motion that consists of two alternating types of motion. The first type is a
nearly periodic orbital motion with the amplitude of a few pipe diameters and
the second one is a quasichaotic motion with very small amplitude.
Increasing the internal fluid velocity results in a larger
amplitude of the orbital motion. 