Snap loading of marine cable systems

Abstract

This study presents a general two-part analysis procedure for the investigation of snap load behavior of marine cable systems in regular seas. A simple dynamic model of a package suspended from a multi-cable configuration is presented. It is used as the basis to develop dimensionless curves which are useful for the preliminary assessment of the susceptibility of a design to snap load behavior. For cases where this model indicates a strong possibility of snap load behavior, the designer must use a more complex dynamic model. A deepwater marine cable system, similar to that designed for scientific coring studies of the Mid-Atlantic Ridge, is used as the basis for the illustrative examples. The packages to be placed on the seafloor had complicated geometrical shapes with openings through which fluid could pass. Experiments to determine the hydrodynamic added-mass were performed and the results compared to common hydrodynamic approximations. The numerical examples illustrate the sensitivity of these dynamic response predictions to hydrodynamic approximations, ship heading and design wave conditions. They also show that it may be possible to avoid snap loading through proper design, and that if snap loading occurs it is possible to mitigate its effects without complete failure of the system.