Moonpool Effect Assessment During Structure Installation

Heerema Marine Contractors (HMC) is entering a new era of pipe laying with the new Deep water Construction Vessel (DCV) Aegir, which is designed to be able to reel/J-lay pipelines for a wide range of pipe dimension and water depth combinations. The DCV Aegir has a moonpool close to the center of the vessel in which the Hang Off Module (HOM) for pipeline installation is positioned. The HOM is utilized to hold the pipeline and its structures during installation [1]. Pipelines and its structures will be lowered through the moonpool. When a pipeline structure is lowered through the moonpool the HOM is retracted, thus clearing the moonpool to allow the free pass of the structure.The behavior of the water in the moonpool will induce loads on the structures when these are being lowered. These loads will induce motions and bending moments on the attached pipeline. The effect of the moonpool on the structure has to be known in order to assess the integrity of the pipe (fatigue and local buckling limit state) and the optimal procedure for structure installation.The assessment of the moonpool effect on the structure during the lowering through the splash zone is complex because it is governed on one side by the motions of the vessel and on the other side by the motion of the water inside the moonpool.This paper will focus on the moonpool effect assessment in a Pipe Line End Termination (PLET) installation analysis. Two different software packages are utilized; Flexcom of MCSKenny and STAR-CCM+ of CD-Adapco.Flexcom is used to reproduce the vessel motions which affect the PLET motion behavior. Pipe properties (OD, WT and length) and PLET together with pipelay equipment; such as Upper Tensioner (UT), HOM, Pipe Wire Centralizer (PWC) and winch, are modelled.To assess the hydrodynamic loads on the PLET inside the moonpool a Computational Fluid Dynamics (CFD) approach is required. STAR-CCM+ is a CFD program which uses Finite Volume Method (FVM) to solve the flow field motion equations. With this software it is possible to accurately model the geometry of the PLET and simulate the interaction between water in the moonpool and the PLET.The paper will present an overview of the models and the analyses performed, together with the methodology used to combine the outcome of both software packages.Copyright © 2014 by ASME