Minggang Tang

Residual Stress Evaluation and Buckling Analysis of Carcass Layers in Flexible Pipes Using 3D Finite Element Model

A carcass layer plays an important role in unbonded flexible pipes to resist the high level of external pressure without buckling collapse. The layer is made of an interlocked helically wound metal wire of profiled section that cold-deformed by a series of rollers. In typical design and analysis process of the carcass layer, the initial stress is always assumed to be zero. During the carcass layer manufacturing (a cold forming process), the metal strap is however subjected to varies of squeezing and bending and deformations to take “S” shape, and then the profiled wire to a cycling sequence of bending, squeezing and twisting deformations, which take it beyond its material elastic limit. The residual stress is therefore introduced and could has effect on the critical pressure of the carcass layer.This paper presents a 3D finite element model to investigate the detailed residual stress distribution and variation during the forming process of the carcass layer. A study case using a 3D ring model is presented to systemically study the influence of imperfections, especially the residual stress, on the critical pressure of carcass layers.Copyright

Collapse Estimation of Interlocked Armour of Flexible Pipe With Strain Energy Equivalence

Deepwater environment brings unbonded flexible pipelines with collapse risk of interlocked armours, such as pressure armour and carcass. An effective and accurate prediction for collapse is required in design process.This paper presents a theoretical approach for estimating collapse of the interlocked armours based on strain energy equivalence principle of representative volume method. The strain energy with Dirichlet boundary is calculated using FEA software for the armours, which usually have complex cross-section. Meanwhile, an equivalent ring model is established as the representative volume, of which strain energy is acquired analytically. Equivalent thickness can be obtained by equivalence of both the two energys. And then the resistance to collapse of the flexible pipe can be carried out directly.Theoretical results from the approach presented in the paper are compared with numerical results proved by experimental ones from reference, which verifies the equivalence approach. This approach provides a new angle to process parametric design for critical collapse of the flexible pipe.Copyright

Reinforced Design of an Unbonded Flexible Flowline for Shallow Water

Flexible pipeline has been widely used in offshore engineering. Comparing to steel pipe, flexible subsea pipeline has some merits such as anti-corrosive, easy laying and recycling. So it is suitable to be used as flowline in shallow water. Especially there are lots of marginal oil fields in shallow water of China. Different from deepwater dynamic riser, flexible pipe for shallow water applications has a low requirement of resisting external pressure. On the other hand, Flexible pipe need to satisfy the requirement of tensile property during installation. Therefore, a kind of simple and economical flexible pipe can be developed to meet the requirement of shallow water application. This paper presents an economical unbonded flexible pipeline, which is helically wound by steel wires. In order to guarantee the safety of the economical flexible pipeline under the laying, installation and working loads, a reinforced design of tensile property is necessary. A helically wounded flat-steel layer is introduced to constrain the steel wire radial deformation and strengthen the axial tensile stiffness of the pipeline. A theoretical model is established to analyze the tension behavior of the flexible pipes and some suggestions are proposed to strengthen the flexible pipe design. Additionally, tensile experiments are carried out for the original and reinforced flexible pipes, which verify the theoretical model and the effectiveness of the reinforced design. The results show that the reinforced pipeline not only meets the tensile requirement during installation for shallow-water applications, but also meets requirements of the minimum bend radius as well as hydrostatic collapse (resistance of the external pressure) with low cost.Copyright

Multidisciplinary Optimization Design for Section Layout of Complex Umbilical Cables Based on Intelligent Algorithm

Umbilical which links the top floater and the subsea devices provides control functions through electrical cables and hydraulic remote transmission. They are treated as the “lifeline” of the subsea production system for offshore oil and gas exploitation. During operation, umbilical needs to undertake self-weight and periodical load due to the ocean environment. Meanwhile, the heat during power transmission in electric cable is released to the umbilical body, which influences the mechanical properties and optical transmission in the cable. However, there are a number of components and many kinds of sectional arrangement for the umbilical. So the sectional design with multiple components needs to be solved as a multidisciplinary optimization problem. From the mechanical point of view, the umbilical structure should be designed with more compacted and symmetric layout to obtain even probability of resistance to loads and reduce structural stress to improve its fatigue performance. Concerning thermal effect, these units should be arranged to dissipate the heat easily to avoid the influence on the functional and structural components. In this paper, compactedness, symmetry and temperature distribution are quantified through introducing corresponding indices. Then multidisciplinary optimization framework is established. Particle Swarm Optimization (PSO) intelligent algorithm is adopted to carry out the optimization to obtain the optimal solution, which is far superior to the initial design. The optimization design strategy is proved to be effective and efficient by some numerical examples, which provides reference for design of umbilical cables.© 2015 ASME

Riser Configuration Design for Extreme Shallow Water With Surrogate Model Based Optimization

The aim of this paper is to study the optimization design of a steep wave riser for extreme shallow water based on radial basis function (RBF) surrogate model approach. As the design of riser configuration is rather time consuming and exhaustive due to the nonlinear time domain analysis and large quantities of load cases, it would be more difficult when we need to deal with some extreme design such as in extreme shallow water. The surrogate model in this paper is constructed with RBF networks from the samples obtained by optimal Latin hyper cubic sampling and time domain analysis in a given design space. Then, a hybrid optimization is performed based on the established surrogate model. An optimized design is finally found to meet the design criterion with high accuracy and efficiency, even all the samples fail to meet the curvature criterion.Copyright