Experimental studies have been carried out on the dynamics and stability of thin cylindrical shells fluid-coupled by means of a narrow liquid-filled annulus with a concentric outer rigid cylinder. Eleven aluminium shells, with radius 277.5 mm, thickness 0.8 mm and height 268 mm were tested. The shell-liquid system was excited by assigning to the outer cylinder a horizontal harmonic rigid-body motion with small amplitude. With this type of dynamic load it was found that an unexpected dynamic instability, with non-stationary large vibrations of the shell and exponential amplification of the dynamic pressure in the liquid, could occur. In some cases it even resulted in the permanent buckling of the shell. This phenomenon appears not to have previously been observed in similar systems. Such instability was observed whatever the frequency of excitation in the testing range 10 to 45 Hz, provided the amplitude of the excitation reached a threshold value. Systematic investigations allowed the stable region in the frequency versus amplitude plane to be clearly defined. The influence of the superimposition of a static pressure in the liquid annulus was also investigated.
1. Introduction
FLUID STRUCTURE COUPLING has become a topic of increased interest in the petrochemical and power industry mainly to improve the design of structural members operating in a fluid environment against flow-and seismic-induced failures.
In particular, the dynamics of circular coaxial cylindrical shells coupled by a fluid-filled gap has been widely investigated over the past few years. Some recent review papers have accounted for the extensive effort devoted to some aspects of this problem in both experimental and theoretical areas. Brown [1, 2] and Au-Yang [3] reviewed the studies on the hydrodynamic response of fluid-coupled coaxial cylindrical shells. In these studies the emphasis was on the effect of the fluid virtual mass on the vibrational behaviour of the shells. On the other hand, Pa'idoussis [4] considered the dynamics and stability of coaxial cylindrical shells conveying a fluid. For shells supported at both ends, stability was found to be lost, at sufficiently high flow, by divergence. More details on this issue can also be found in References [5,6].
However, the stability of fluid-coupled shells under the dynamic pressure induced by their own vibration has only recently received attention. The need for information on the behaviour of thin shells of revolution interacting with a narrow liquid annulus and subjected to an earthquake led to the study of fluid-structure interaction problems from this fresh point of view.
As a matter of fact, the reactor block of some liquid metal fast breeder reactors contain several axisymmetric shells separated by narrow liquid gaps. The design of such systems should take into account the response to seismic excitation and the 0889-9746/89/030211