Dynamic behavior of the sheave installation process of the large subsea cluster manifold

Abstract

The sheave installation method is an unconventional, reliable engineering technique to safely lower large cluster manifolds to a water depth of over 1500 m. This paper established a numerical model for the sheave installation system dynamics based on the finite-element principle. The analysis first considered the subsea structure mass, while the hydrodynamic forces were calculated using Morison's equation. Furthermore, it accounted for the sensitivity of the critical parameters to the dynamic responses of the entire system, including the amplitude and phase differences between two excitations and the ocean current velocities. The results showed that the finite-element model in OrcaFlex provided accurate solutions compared with the mathematical model, while a practical water depth for the second stage could be obtained by analyzing all the depths. Additionally, an asynchronous rise in the amplitude of two excitations placed more tension on the top of the steel cable than a simultaneous increase in the amplitudes and phase differences of the excitations, as well as the current speed. A series of sensitivity analyses were performed to evaluate the influencing factors on the dynamic response of the manifold, offering guidance for ocean engineers on deploying the large equipment.