Steady-State Configuration of an Underwater Suspended Bipod Cable System

Underwater suspended bipod cable systems are utilized to moor oceanographic instrumentation. An analysis to determine the steady-state configuration of an underwater-suspended bipod cable system subject to buoyant lift forces as well as current drag forces is presented. It is assumed that the cables are neutrally buoyant or can be made neutrally buoyant by the addition of buoyancy and that the effects of tangential drag on each cable are negligible. The equations used to find the equilibrium position of the buoyed joint and also the tensions in each mooring cable are of two kinds: three force equilibrium equations at the buoyed joint and two compatibility equations for the displaced bipod system. These equations are sufficient to solve for the five unknowns, namely, the displacement of the buoyed end in three directions and the two cable tensions. A computer program was developed to solve the system of equations. Iterations are performed until a convergence is obtained on an equilibrium position and cable tensions. As an example, a bipod system 10,000 ft high with a 20,000 Ib buoyant force under installed conditions was considered. The flow direction was taken at an angle of 30 deg with the normal of the plane containing the system. A linear velocity profile ranging from 1 ft/s at the top to 0 at the bottom was found to cause a 670 ft horizontal and 153 ft vertical deflection of the buoyed joint.