Modeling and Control of Offshore Pipelay Operations Based on a Finite Strain Pipe Model

This paper deals with modeling and control of offshore pipelay operations from a dynamically positioned surface vessel where a nonlinear dynamic beam formulation in three dimensions capable of undergoing shearing, twist and bending is used to model the pipe. This pipe model is coupled with a nonlinear vessel model that has been adopted as a standard for vessel control design and analysis purposes. The complete pipelay system is shown to be input-output passive taking the thruster force as the input and the vessel velocity as the output. A nonlinear controller is applied, and using the passivity condition of feedback connection of two passive systems, the closed loop system is stable. Numerical simulations using both PD and PID controllers illustrate the theoretical results.