Development of a Simplified Three Degrees of Freedom Model to Represent the Installation of a Subsea Manifold

Abstract

Due to risks involved during the installation of subsea equipment, it is necessary to simulate the installation process to determine a safe operating window. However, most of the software capable of running these kinds of simulations are very expensive, and these simulations usually take a long time to be made. It is then very convenient to develop a simplified model, capable of running these analyses in a short period of time while still providing us with reliable results. This model was developed using the Python programming language, where a fourth-order Runge Kutta method was implemented to solve the equation of motions that governs the manifold’s installation process. The assumptions are that the wave forces are applied to the ship executing the manifold installation. The ship’s motions were applied at the top of the cable, connected to the crane, so the manifold motions underwater and the cable tension could be calculated. Previously, a simplified one-degree of freedom (1DoF) model was developed and compared to other numerical models and experimental data. In this present work, the model was then expanded to motions in a vertical plane, that is, three degrees of freedom (3 DoF), in order to better represent the physics of the real problem. Its results were then compared to the ones obtained by the 1 DoF model and to the experimental results. The 3 DoF model resulted in a dynamic response closer to the ones observed in the experiments, which shows that it is a better representation of the problem.