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Transverse tensile armour buckling of flexible pipes
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2014 (English)MasteroppgaveStudent thesis
Abstract [en]

During the installation and operation process, the empty flexible pipe will experience a large end fitting load which is the compression load at the ends of the pipe. At the same time, the dynamic load from wave and current will force the pipe to bend cyclically which will cause the transverse buckling within the tensile layers. The end of pipe will rotate due to the transverse buckling mechanism during each cycle, resulting in a serious end rotation to make the pipe collapse. This thesis will study transverse buckling behaviour under different loading conditions and performthe sensitivity analysis to study the influence of the relevant characteristic parameters. This section will briefly summarize the main contents and conclusions in the thesis. • INTRODUCTION Chapter 1 is the introduction of the master thesis, including the study motivation, previous literature overview about this topic, the main contributions of this thesis and the structure of the rest thesis. • LITERATURE STUDY Chapter 2 and Chapter 3 are the literature study, focusing on the flexible pipe technology, failure modes and design criteria. Chapter 2 includes an introduction to the flexible pipe applications in the offshore industry, flexible pipe structure and termination of riser. Chapter 3 is a brief introduction of failure modes and design criteria. • THEORY AND METHOD Chapter 4 is an introduction to the linear finite element methods and non-linear finite element methods and the relevant non-linear code used in FEM software, Bflex2010 andMarc. The theory background of the finite element model established in Bflex2010 and the analytical methods for stress and buckling analysis in tensile armour are also shown in this chapter. The physical interpretation of the lateral buckling failure mode is shown as well. • MODEL ESTABLISHMENT Chapter 5 is an introduction of the model establishment, including the simplified model(one tendon without friction) and the full model(all the layers including anti-buckling tape). The determination of loading conditions, boundary conditions and relevant important parameters are also introduced. • BUCKLING PERFORMANCE STUDY OF SIMPLIFIED MODEL Chapter 6 is the lateral buckling study of the simplified model, including the influence of lay angle, start angle and imperfection. Three sensitivity studies for the time interval, axisymmetric interaction and start procedure in Bflex2010 are also carried out. Lay angle will have a big influence on the buckling occurring positions during the process of loading, but it is hard to predict. However, the buckling load capacity will be increased due to the decrease of lay angle, which is testified by the analytical solution and tests in Bflex2010. The start angle will have no influence on the buckling load capacity except the buckling occurring positions. The imperfection will lead to a sudden axial force increase in the tendon which is shown as a snap in the realistic physical issues. This phenomenon will be presented and explained in the thesis. For the sensitivity study, the following conclusions can be obtained: 1) The length of time interval will decide the accuracy of the test in Bflex2010. The smaller time interval will capture the buckling behavior at the beginning of the process. 2) The axisymmetric interaction and start procedure will not have a significant influence on the test results. • BUCKLING PERFORMANCE STUDY OF FULLMODEL Chapter 7 is the lateral buckling study of the full model, including the comparison with the simplified model under the same load conditions, the detail study of the lateral buckling of tendons and the end rotation of riser caused by lateral buckling due to the cyclic bending. The results of full model are also close to the analytical solution and a little more conservative than the simplified model. The end rotation behaviour due to transverse buckling is studied by full model, which can simulate the failure modes in a right way and the results will be close to the experimental results if the additional axial stiffness of pipes in experiments is provided. The sensitivity study is performed to study the effect of anti-buckling tape. The results show that the anti-buckling tape has a large effect to prevent the transverse buckling and the lay angle direction of the anti-buckling tapewill also affect the transverse buckling behaviour and prevent the buckling process to a great extent.

Place, publisher, year, edition, pages
Institutt for marin teknikk , 2014. , 107 p.
URN: urn:nbn:no:ntnu:diva-26276Local ID: ntnudaim:11888OAI: diva2:746125
Available from: 2014-09-11 Created: 2014-09-11 Last updated: 2014-09-11Bibliographically approved

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