The finite element method for hydroelastic instability of underwater towedcylindrical structures

The dynamics of underwater towing of flexible cylindrical structures belong s to the class of fluid-structure interaction problems commonly referred to as "cylinders in axial flow". The serious concern in such towing operation s is the various types of hydroelastic instabilities exhibited by the struc ture at certain critical tow speeds. In practice, reliable prediction of to w configurations and stability characteristics of such towed systems can le ad to optimum deployment of cable scope and control of tow speed. The prese nt investigation is concerned with the development of a comprehensive linea r finite element method for the dynamics of the flexible towed cylinder wit h focus on the stability behaviour. The finite element approximation is der ived from a variational statement of the problem based on Hamilton's princi ple. The various structure- and fluid-related matrices as well as matrices resulting from boundary terms have been derived, resulting in a complex uns ymmetric eigenvalue problem. Exhaustive validation and convergence studies show that the comparisons between finite element and analytical results are almost exact. Using the finite element code, the hydroelastic instability of a ship-towed array system has been analyzed. The effect of cable scope a nd shape of the downstream end on stability have been examined. (C) 2000 Ac ademic Press.