Transverse tensile armour buckling of flexible pipes
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.
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
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.
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.
IdentifiersURN: urn:nbn:no:ntnu:diva-26276Local ID: ntnudaim:11888OAI: oai:DiVA.org:ntnu-26276DiVA: diva2:746125
Sævik, Svein, ProfessorYe, Naiquan