| dc.description.abstract | Umbilical is a hardware element that connects the subsea systems to the top side systems of a floating production unit. During its manufacture, storage and installation, sometimes it shows behaviour like snake as found in three of the Aker Solution s umbilical Agbami, Droshky and kipper in three different situations.
An umbilical passes through many operations in the manufacturing plant like bundling, extrusion, reeling on and off the storage drum, transfer into installation vessel from storage reel. Different types of loading phenomenon may appear in these stages of operation. And from these loads even before being in the operation field, umbilical can experience different type of deformation in the manufacturing plant.
Curvature is the main source of umbilical deformation in the manufacturing field. Curvature may introduce directly in the umbilical from operation loads of straightener, creeping or squeezing effect in tensioner. Curvature may also arise from internal friction and unbalanced bending moment which arises from design i.e. orientation, geometry and material property of the internal structural components.
To find the solutions of avoiding different deformations at the different stages of the manufacturing plant and to ensure desire comfortable handling, it is necessary to predict their behaviours correctly at different loading conditions. Exact analytical and numerical modelling is needed to find and predict the exact behaviours. In this thesis work, number of modelling and simulations have been done in software USAP and BFLEX to investigate the reason of snaking behaviour of three umbilicals, occurred in the manufacturing plant of Aker Solutions.
From the results of simulations it has found that umbilical Agbami experienced snaking when it was transferring from storage reel for installation work, due to having residual curvature from storage reel, gravity load and twisting rotation. The reason of residual curvature is creeping of its outersheath.
Umbilical Droshky showed snaking deformation because of having residual curvature in its component steel tubes. And, in umbilical Kipper snaking deformation arose because of developing internal friction in it.
In the different modelling of this work, PIPE31 element is used for the modelling of umbilical core pipe or outersheath and to model the inside helix elements HELIX231 element is used in USAP and HSHEAR353 element in BFLEX. The contact between pipe and helix element in BFLEX is modelled by HCONT453 element.
The software USAP and BFLEX has showed convergence problem in some cases of modelling. Improvement is needed to overcome these problems. | |
