1. IN SITU AND REAL TIME X-RAY COMPUTED TOMOGRAPHY FOR THE
MICROMECHANICS BASED CONSTITUTIVE MODELLING OF THE UNBONDED
FLEXIBLE RISER
Ketan Pancholi
Aquaterra Energy Limited
2 Alkamaar Way, Norwich, NR6 6BF
United Kingdom
Vineet Jha
GE Oil and Gas UK
Wellstream Flexibles, Subsea Systems,
Newcastle upon Tyne, NE6 3PF, United Kingdom
Neville Dodds
GE Oil and Gas UK
Wellstream Flexibles, Subsea
Systems, Newcastle upon Tyne,
NE6 3PF, United Kingdom
Mehul Pancholi
City University
London,
EC1V 0HB,
United Kingdom
James Latto
GE Oil and Gas UK
Wellstream Flexibles, Subsea
Systems, Newcastle upon Tyne,
NE6 3PF, United Kingdom
ABSTRACT
The failure mechanism of the composite flexible riser,
comprising a pipe with melt fused carbon fiber tape or
pultruded composite rods, is not well understood. As there is
change in the configuration of the composite layers and its
manufacturing methods, so the bulk material property also
changes significantly. To capture the correct material model for
global FE analysis, real time x-ray computed tomography was
performed while the flexible pipe was being compressed. For
developing a constitutive model for the composites, a time
series of 3D volume images were analyzed quantifying the
local strains responsible for the debonding of the layers and the
crack development. These values were then used to understand
the inter-layer adhesion leading to correlation between the FE
global modelling and experiments capable of capturing the
progressive delamination. The resulting global modelling was
used to determine the area under compressive loading. The
effect of global sea conditions and cumulative damage was
noted. A correlation between the global model and experiments
can be used to optimize riser performance. This method hopes
to capture the overall behavior of flexible pipe under
compressive loading.
1. INTRODUCTION
Lightweight materials like carbon fiber reinforced polymer
(CFRP) composites are increasingly in demand for various
industries, such as aerospace, oil and gas, automotive,
bioengineering, etc. Special applications include deepwater
flexible risers, panels for satellites, ailerons, to name but a few.
The main interest of using CFRP composites is based on
weight reduction, durability, and low thermal expansion.
Global analysis using Orcaflex has been used to study the
response of wave loading on flexible pipes made from both
composite and metallic materials (1, 2, 3, 4). Most of these
papers study the global response and some studies compare the
behavior with scaled flexible pipe structures (5). It is known
that shallow water risers experience a more dynamic response;
both at connection to top infrastructure and at the touchdown
point (6, 7). For deeper water conditions, dynamic responses
are equally important. These effects are seen at the connection
to top infrastructure, bend in pipe, buoyancy attachment and in
the vicinity of the touchdown point (8, 9, and 10). Parameters
such as installation methods, top tension, curvature, material
model, hysteresis, mudline/sea bed contact point, shear
strength and local stress can greatly influence the behaviors
and overall performance of the riser system (1, 6, 11, 12).
CFRP composites can offer high specific tensile strength,
however the strength is relatively low in compression, as the
fiber in particular is sensitive to compressive loading (8,14).
For deepwater flexible risers, the compressive loads can be
experienced by these layers under external hydrostatic
pressure, bending and inter-layer interaction (13, 14). So far
the failure mechanism, especially at micro scale level, has not
been fully understood. To understand its failure mechanism,
both global modelling (as discussed) and experimental work
are needed to identify the failure modes of the CFRP composite
pipes under radially compressive loads.
Among several non-destructive testing (NDT) methods,
the X-ray computed tomography (CT) as an imaging test
procedure has many advantages over other NDT methods for
applications involving defect analysis at the micro scale. This
is attributed to its good spatial resolution and fast 3D scanning
capability. Our previous work has demonstrated that the
capability of using X-ray CT techniques in detecting and
quantifying the development of micro-cracks in the composite
layers during in-situ compression testing (13). Obtained results
have clearly shown the possibility of using this technique
further; especially to investigate the detailed failure
mechanism of the composite pipe. Crack propagation and
delamination have been observed in testing, and delamination
was identified as a source of the crack initiation. The crack
also formed a continuous connection with the delamination
within the volume. More interestingly, such a crack initiation
1

2. and delamination was observed at stresses less than previously
thought. However, a time step for the obtaining of such 3D
images was too large to determine the exact reason of the crack
initiations. Additionally, due to the relatively large diameter
test rings used, early crack initiation can be attributed to the
stress concentration caused by the application of loads on the
smaller area.
In order to establish better understanding of the crack
development during compressive loading of the ring, it is
necessary to reduce the time between two consecutive imaging
scans. This will allows detection of the initial, smallest crack
in composite materials at a much finer time step than previous
work. Fast scanning of the ring during in-situ compression
gives a detailed picture of the failure modes and crack growth
in relation to the applied stress and strain. Furthermore, the
role of interlayer bonding strength in failure of the composite
can clearly be established if crack growth is observed in a
slower time frame. In order to capture the details of crack
growth at a finer time scale, a compression testing rig was
used to initiate a crack and it was placed inside the imaging
area during compression. The compression test was repeated to
observe the crack development. The data was stored in the data
logger attached to a testing rig.
Further, small diameter test rings were used for the
current work and hence the compressive load was applied to a
larger area depicting uniform loading from all directions. This
solves the problem of stress concentration and, therefore, it is
likely that it provides a more accurate correlation of failure
with the acquired stress-strain data.
This work employed a method based on advanced CT
technology to facilitate the precise evaluation of the micro-
mechanical failure, manufacturing defects and interaction of
various micro-failure modes with such defects. The distinctive
objectives of the work included:
a) Using the best resolution to investigate the minimal
initial crack size
b) Revealing the failure mode, i.e. the crack propagation
modes (e.g. along or across the layers)
c) Investigating the correlation between micro local
stress/strain, crack initiation and global analysis
d) Investigating the influence of pre-existing defects on
the crack initiation and propagation.
2. Materials and Experimental Method
2.1. The test ring
The compression test ring used in the X-ray CT
experiment is carbon fiber reinforced polymer (CFRP)
composite. Laser processing was used to improve the bonding
strength between layers. The test ring has an outer diameter of
40 mm, an inner diameter of 30 mm and a length of 20 mm.
Figure 1 shows a test ring siting on the compression rig on the
machine before loading.
Figure 1: X-ray computed tomography facility
A 3D non-destructive technique using high-resolution X-
ray tomography was applied in the current experiment to
investigate the damage during the compression tests. The
Nikon Metris Custom Bay (Figure 1 & 2) is the most
frequently used imaging machine at the Manchester X-ray
Imaging Facility (MXIF) due to its multi-functionality. There
are many advantages to this machine such as the large bay
area, heavy-duty manipulator, and its ability to perform serial
scans enabling the Custom Bay to be used to scan large
samples such as turbine blades or geological core samples. The
system is adopted to scan specimens between 5 mm and 230
mm in cross-section, and higher resolution scanning for the
interest region. During tomography scanning, the X-ray
generator and detector remain stationary. The specimen
remains stationary relative to the turntable and is placed in the
origin of the virtual coordinate system. The X-ray generator
scans a slice of the object as a very high precision turntable
rotates 360˚. All images were taken at 200-220 amp current
and 185-200 kVA voltage. Sufficient care was taken to avoid
the metal parts being seen in the field of view as metal parts
have a very high density compared to polymer-based
composites and appear dark, blocking the details of the
specimen. The ring specimen with a metal clamp capable of
applying the compression load in-situ is designed in such a
way that its jaw will not interfere in the imaging of the ring.
The plates that are in direct contact with the ring are made of a
polymer matching the composite ring’s density (as shown in
Figure 1). This helps to prevent the high density material
appearing in the field of the view.
2

3. Figure 2: Nikon custom bay X-ray tomography facility
set-up
2.2. The in-situ loading rig
The loading rig produced by Deben UK Ltd is available
for in-situ deformation studies in either tension or compression
modes, and is specifically for use with the Nikon Custom
320kV bay. The rig can operate in displacement and load
control and with 4 different load cells depending on the
material/sample under investigation. The available load cells
are 1.25 kN, 2.5 kN, 10 kN and 25 kN. The top grips with load
cell are supported on a polycarbonate tube to allow a clear
view through the sample around a 360° rotation during
tomography scanning. The loading platens (for compression
mode) have a maximum diameter of 30 mm and the maximum
sample height is 80 mm. Figure 3. Shows the Deben loading
rig used in the experiment.
2.3. Procedures
The experiments in this work include specimen centring,
loading tube material correction, initial crack identification,
full rotation CT scanning, post processing of the images, etc.
The detailed procedures are as follows:
1. The CFRP composite test ring was placed between a
pair of parallel transparent PMMA blocks, as shown in Figure
1 and 3. The PMMA blocks are placed between the steel
parallel plates of the loading rig. The benefit of using
transparent PMMA blocks is to avoid steel plates appearing in
the field of view, as the metal parts have a higher density
compared with polymer-based materials and are displayed as a
dark area in the imaging field, thus blocking the details of the
specimen to be measured.
2. To increase the grip between the specimen and the
PMMA blocks, the PMMA block surface was filed with sand
paper to deliberately reduce its surface roughness.
Figure 3: The Deben loading rig
3. The test ring specimen was carefully positioned in the
centre of both X and Y coordinates to allow 360° rotation
tomography scanning.
4. Set the Z position to allow the test ring is in the centre
of Z direction.
5. Since the density of the Deben loading rig (its
cylindrical tube is made of transparent polycarbonate, as
shown in Figure. 3) is similar to that of the test ring specimen,
the imaging quality will be reduced. A correction process is
therefore conducted before imaging the test ring. A full
rotation X-ray CT scanning was conducted on the
polycarbonate tube, i.e. Without the test ring inside. The
image data was then stored and used to correct the images to
be taken with the test ring later on.
6. Set the time step size and resolution, based on the size
of the test ring (the whole ring needs to be imaged) and other
parameter settings, the best resolution was determined to be a
voxel size of 6 μm and a spatial resolution of 12 μm.
7. Set other parameters – X-ray power (current 55
µAmp, 150 kV)
8. Before applying any compression load, a full
revolution scan was first performed using the above parameter
settings on the test ring. The purpose of this scan is to set the
reference images and identify any pre-existing defects in the
materials which could be introduced by the manufacturing
process.
9. Apply initial load, there are two methods to apply
loads, one is applying constant force and the other is applying
constant displacement. The latter method was used to apply
load on the test ring. The deformation was controlled, but the
varying forces were also recorded for later analysis.
10. Observe initial crack initiation, if no cracks are found,
increase loads and repeat the above step until cracks are found.
11. With the cracks observed in the test ring, adjust the
display (zoom in to a certain region), use the best spatial
resolution, and then perform a 360° rotation tomography
scanning.
12. Further, increase the loading, adjust the interested
area, and perform a new 360° rotation tomography scanning.
13. Apply incremental loads, until the test ring is broken.
14. Data were stored for the above operations, and
analyzed by the 3D image processing software
3. Global modelling
3

4. Global analysis was carried out using Orcaflex to
understanding the effect of wave loading on flexible composite
pipe. The operating condition was assumed to be the Gulf of
Mexico Deepwater field having a depth of 3000 m. The pipe
size was 8-inches having a pressure rating 40 MPa, operating
temperature of 120°C and life of 25 years. Weather data used
for analysis is shown below in the Table 1. This includes wave
current speed data.
Table 1: 1000 year wave hurricane data
Parameter Sector
Compass direction Omni-directional
Hs (ft.) 57.7
Tp (s) 14 ±1.4
Hmax (ft.) 101.3
Crest elevation 56.2
Spectral shape Jon-swap
Current speed (kt)
Surface 2.9
200 (ft.) 2.9
300(ft.) 0.2
Mud-line 0.1
Table 2: Vessel parameter
Parameter Units Ballaste
d
Loaded
LOA M 292.2
LPP M 277.0
Breadth M 45.5
Depth M 28.0
Draft(at turret) M 12.34 18.31
LCG( aft of turret centerline) M 65.98 69.23
VCG(above keel) M 17.76 13.38
Turret center position (aft
FP)
M 74.0
Environmental condition and input vessel data (RAO) was
used as provided for GOM conditions. In the present case,
varied vessel offset between 8%-10% of water depth was used.
The vessel direction was varied between ±30° and all load
cases were analyzed under conservative 1000 year omni-
directional wave conditions. The declination angle at the hang-
off point was varied between 4°and 16°. The density of the
inside fluid was varied between no fluid and 800 kg/m.3 The
motion of the vessel was prescribed by the RAO and tension
was applied from the top of the flexible riser. Static analysis
was first carried out with inside fluid to perform effective
tension optimization in relation to declination angle of pipe
and applied top tension.
Figure4: Schematic of model used for global analysis
Table 3: Pipe data used for Global modeling
Pressure :
40MPa
Temp :
120°C
Water
Depth :
3000m
ID : 8"
Composite Bonded Liner
Weight in air (kg/m) 152.45
Weight in seawater
(kg/m)
189.12
4
Buoyancy
section 1
Buoyancy
section 2
Mid section
Bottom section
Front section

5. Figure 5: Effective tension vs Pipe length for various design
cases
Figure 6: Bend radius vs Pipe length for various design
cases
Figure 7: RZ stress vs pipe length for various design cases
Figure 8: CZ stress vs pipe length for various design cases
Figure 9: Max Shear vs Pipe length for various design cases
The material was modelled using the Saevik stick-slip
model (15) in an area where large bending curvature was
expected. The stiffness of the remaining section of the
composite pipe was calculated by considering the stiffness of
each individual layer. The friction model for the seabed-pipe
interaction was used to match the seabed soil condition at the
GOM. Dynamic analysis was performed to study the sensitivity
to buoyancy and buoyancy length in many cases. In this work,
four different cases are explained to study this effect. For each
case effective tension, bend radius and shear stress have been
studied and co-related with experimental results.
4. Results and Discussion:
Many configurations for the flexible pipe were studied to
find the effect of the parameters such as buoyancy, length,
vessel offset and its location on the pipe. The buoyancy
modules with different buoyancy values, buoyancy module
length were modelled and parameters such as effective tension
and bending radius were extracted. These values were used as
a selection criterion for determining the flexible riser
configuration. After selecting the favorable configuration, the
5

6. shear stress and compressive stress were extracted or
calculated to check whether flexible pipe fails under the
compressive or shear load at the critical location such as the
touchdown point. Furthermore, the obtained results were
compared with the conventional pipe results to observe
deviation in stresses due to the use of lighter composite pipe.
After taking the water depth (3000 m) and 1000 year
environmental condition of the location into account, the steep
riser configuration is considered for further numerical
experimentation. Since the new pipe with low mass per length
was used instead of the conventional heavier pipe, the effect on
the choice of buoys, its length and finding out the stresses
under compression was the main aim of the work.
4.1. Optimization of Effective tension and Bending Radius:
During the analysis, it was found that achieving
acceptable effective tension whilst not exceeding the maximum
allowable bending radius is relatively easy compared with the
conventional pipe (Figure 5). As seen in Figure 5, the
maximum effective tension value was observed at the hang-off
point. With installation of the buoys one section away from the
hang-off point, the tension in the section of the flexible pipe
between the hang-off point and starting of the buoys will
decrease. However, as we move away from the curvature (and
buoys, towards the touchdown point), the effective tension
along the length of buoy section 1 gradually increases
depending upon the radius of the curvature (Figure 6). Because
of the high depth, shallow curvature is difficult to achieve with
the amount of buoyancy required to lift the pipe.
During the optimization process, the length and buoyancy
was varied to understand its effect. In this study, it is
considered that the highest point of curvature formed due to
buoys acts as a new hang-off point for the bottom pipe section
going towards the mudline. However, it also reduces the
tension in the front section of pipe preceding the installed
buoy. If the cumulative buoyancy of the entire length of buoy
section 1 is 1.5-2 times the cumulative buoyancy of the front
pipe section preceding it, the maximum effective tension drops
considerably. However, considerably longer pipe in this
configuration requires two sections of buoys installed to reduce
the tension and control the bending radius at the touchdown
point. The length of mid-section of the pipe between the front
and bottom sections of the buoyancy modules has to be
relatively smaller than the front and bottom sections of the
pipe. It is found that the length of this middle section of pipe
should approximately be 0.5 times the other section of the
pipe. If the rule of thumb (1.5 time buoyancy) is followed for
buoyancy sections, the effective tension peak can be brought
down further to a desirable level.
Instead of two separate sections of buoyancy modules, if
single large sections (~800m) of buoyancy modules are
installed at the midspan of the pipe (case 4), the maximum
effective tension reaches 1.7 times the effective tension
observed in configuration with two buoyancy sections. Before
recording this observation, many configurations with single
modules of different buoyancy were tested to obtain the best
possible results.
Installing buoyancy section 2 with buoyancy more than 2
times the buoyancy of the mid pipe section also increases the
effective tension along the length. The similar buoyancy
relation also found to be important for the bottom section of
the pipe (at mudline) and buoyancy section 2 module attached
at the length preceding bottom pipe section.
In all cases, it is desirable to make sure that the buoyancy
modules are located where the maximum of the current is not
present. Additionally, longer front and bottom pipe (1000 m
approx.) is required to be available for the larger offset (300 m)
of the vessel. With shorter front pipe sections and larger offset
of the vessel, the effective tension due to lateral pull and
dynamic wave loading tends to increase. This also affects the
bending radius.
Figures 7, 8 and 9 show shear stress at different pipe lengths
for four different cases (each case having a different buoyancy
ratio). It is clear from graphs shears RZ, CZ and Max shear
are reasonably low in strength varying between 140KPa to 350
KPa. It should be noted the highest shear stress value occurs at
zero, the highest curvature point and the touchdown point.
These areas of pipe are therefore more prone to delamination
or material compressive failure. Later, these values have been
correlated with experimental shear stress values.
4.2. Comparison between conventional and lighter pipe
The study suggests that effective tension can be reduced to
the desired level with the buoyancy module alone while
keeping the bending radius below the maximum allowable
limit. To reduce the amount of buoyancy and bending radius, it
is advisable to apply external tension. For a conventional pipe,
(with similar configuration as the lighter pipe) results in
effective tension being more than the allowable (without safety
factor). Moreover, the lighter pipe does not exceed its limit
under compressive load at the touchdown point.
5. Micro scale testing Imaging
6

7. Figure 10: An image showing cross-section of the composite
pipe before compression testing.
The images were acquired in real time during the
compression test. Approximately ¼ of the bottom and top of
the composite pipe section was subjected to compressive load
at a rate of 4 mm/min. Thus, it was not considered as the point
load for the purpose of the analysis. The strain values were
obtained using image analysis in Imagej plotted along the
thickness of the layers. The above figure shows the
development of the strain at layers during the compression.
The strain increased at 26 mm radius from the center of the
ring section. At 2.2 minutes, the strain starts to appear at the
middle of the composite section layers.
After an additional 2.1 minutes, the location of the strain
shifted with further increases. The shift in the location was
observed due to the physical deformation of the ring during the
compression.
Resulting strains were measured and used to calculate the
bonding strength of the layers. It was considered that the
applied compression load was 3 times higher in the area where
stresses are concentrated. These geometrical nonlinearities can
be fed into the 2D model to predict any micro-shearing in the
composite section. This can also confirm the suitability of the
lighter pipe for the deepwater application without
apprehensive compression failure.
Figure 11: The typical temporal lapsed images showing
the composite ring section under compressive load at
different time step. All images were taken in real time
while compression load is being applied to the composite
ring at a constant speed of 4 mm/minutes. The image (i)
depicts the state of the composite ring at 1.7 m after the test
was initiated. Subsequent images were obtained at (ii) 2.2
minutes (iii) 3.7 minutes (iv) 4.3 minutes
During the ring compression test, no material compressive
failure was observed before delamination (a function of shear
stress; in the present case a thermoplastic composite material
was tested) which occurs at the strain shown in Figure 12, in
which micro strain varies from 0-70 (overall difference of
images under consideration). This trend was consistent with
shear testing performed later and in-situ ring testing confirmed
overall trend and details of failure mechanism.
Figure 12: Micro strains as function of radial distance from
center of ring
Combining Global and Micro-scale testing: Shear stress as
a predictor
Specimens were cut out based on ASTM D2344. The
testing fixture used is shown in Figure 13. Results of the
experiments are shown in Figure 14. It can be seen from the
results of ILSS that the tests are repeatable. All specimens
show a maximum shear stress of 25 – 27 MPa and
displacement at maximum shear stress: ≈ 2000 μm. To get a
broad overview of the failure mechanism, microscopic was
first carried out. This was followed by detailed 3D tomography
7

8. testing. Figure 15 and Figure 16 show a microscopic cross-
section of the tested specimen. This shows fiber fractures occur
along a detectable line, beginning from the outer surface
ending at the middle of the specimen.
There were no fiber fractures between the middle of the
tape and the inner surface. Changing fiber direction was
caused by the bending test in the area of fiber fractures. Micro
buckling of fibers occurs under compression. Surface
deformation of the thermoplastic matrix was also observed.
Multiple fiber fractures were seen in the same fiber at two
different positions (typical shear fracture for FRPs). Local
inception fiber cracking was seen. The specimen was nearly
free of delamination in microscopic testing or showed only
small areas of delamination. However, 3D tomography was
performed to check for delamination in the 3D volume of the
specimen.
Figure 13: Short beam shear fixture
Figure 14: Shear stress vs displacement
Figure 15: Microscopy of cross-section
Figure 16: Micro-buckling of fiber under compression
Figure 17: 3D Tomography images of short beam shear
before and after testing showing area of delamination
8
Outer surface
Inner surface
Surface deformation due
to application of force
Black spots
are artefacts
Micro buckling

9. Figure 18: Showing Delamination (occurs first) and
material compressive failure
Figure 17 and Figure 18 show 3D tomography images. This
shows minor pores could be present showing as white points
occurring in the CT scan. Clear delamination can be observed
in the top-right area which lies in the 3D volume of this
particular specimen. It seems the delamination starts at the
line of fiber fractions. In the present case delamination occurs
before the fiber fracture, or fiber fracture (material
compressive failure) occurs just after or at point of
delamination. Delamination is strongly related to the shear
stress value shown in Figure 14. Delamination occurs at the
top end to experimental shear stress value or 25 MPa- 27 MPa.
This value of shear stress is much higher than RZ,CZ or max
shear reported in earlier Figures 7, 8, and 9.
Therefore:
1. Delamination occurs before material compression
failure
2. Shear stress is more important when relating bulk
stress to micro failure
3. Shear stress in global modelling is much lower than
experimentally observed (Figures 7, 8, 9 and 14). However,
shear stress value in global modelling is strongly related to
effective tension, curvature and buoyancy location. It must be
noted, as previously mentioned, the areas of pipe more prone
to failure include the top connection point, highest curvature
point and touchdown point.
4. As long as the shear stress value of the produced
composite is high, material compressive failure is unlikely to
occur or will occur very close to the point of delamination. It
must be noted this observation is related to softer thermoplastic
material and might not be applicable for all composite
materials.
Therefore shear stress value combined with global
modelling is recommended as a good predictor for compressive
failure. This can be followed by the relevant mid-scale bend or
compression test as final verification (and 2D FE modelling).
It is hoped this can be carried out in the near term for the
present sample and product.
4. Conclusions
Composite material offers to expand the working design
envelope of flexible pipes. Local and global analysis is key for
understanding the overall performance of the proposed
composite flexible riser. Overall effective tension, buoyancy
selection, buoyancy distribution, and bend radius are key
parameters that can influence the local behavior.
3D Image analysis has shown the ability to capture details
of the failure mechanism which is normally not visible in
microscopy analysis. It has been shown that micro-strain can
be worked out and correlated with the failure mechanism.
In the present paper shear stress, calculated form global
analysis, was correlated with shear testing resulting and local
material compressive failure. It has been shown as long as
shear stress remains within the limit, material compressive
failure is not expected. Therefore, shear stress can be used as a
predictor for failure. Shear stress value strongly depends on the
production quality of the manufactured composite material.
Thus, careful consideration must be given to ensure a
functional quality assurance system is implemented whilst
producing long lengths of composite riser systems.
References
(1) Tan Z., Quiggin P., and Sheldrake T., ‘Time Domain
Simulation of the 3D Bending Hysteresis Behavior of an
Unbonded Flexible Riser’ J. Offshore Mech. Arct. Eng. 131(3),
031301, May 29, 2009.
(2) Do Anh T., Legeay S. Pere J., M. Charliac D., Roques Jean
P., K Alexandre. ‘New Design Of Lightweight Flexible Pipe
For Offshore Oil Offloading’ Offshore Technology Conference,
Houston, Texas, 05-08 May, 2014.
(3) Onna M. v., Kanter J. and Steuten B. ‘Advancements in
Thermoplastic Composite Riser Development’ ,ASME 2012
31st International Conference on Ocean, Offshore and Arctic
Engineering Rio de Janeiro, Brazil, July 1–6, 2012
Engineering Cancun, Mexico, June 8–13, 2003
(5) Ruskin A., Tahana Z., Chai S., Balash C., Morand H.,and
Izarn C. ‘On the Effects of Bending Stiffness for Flexible Riser
Model Tests, ASME 2014 33rd International Conference on
Ocean, Offshore and Arctic Engineering San Francisco,
California, USA, June 8–13, 2014
(6) Sadjad K., ‘Flexible riser global analysis for very shallow
water’ Master thesis, University of Stavanger, Norway 2013.
(7) Hanonge, D., Technip; and Luppi, A., SEAL Engineering
SA.,’Challenges of Flexible Riser Systems in Shallow Waters’,
OTC 20578, Texas ,May 3-6, 2010
(8) Jha V., Dodds N., Finch D. and. Latto J.R., Anderson T.A.
and Vermilyea M.E., ‘Qualification of Flexible Fibre-
Reinforced Pipe for 10,000-Foot Water Depths’, Offshore
Technology Conference, Houston, Texas, USA, 6–9 May 2013.
(9) Masturi L. M., ‘Comparison Study of Selected Uncoupled
Riser Concepts in Deep Water and Harsh Environment’,
Master thesis, University of Stavanger, Norway 2014
(10) Ismail, N., Nilsen, R.and Kanarellis, M., Wellsream
corporation, ”Design Considerations for Selecting of Flexible
Risers Configuration”, ASME, PD-Vol. 42, Offshore and
Arctic Operations, Panama City, Florida ,1992
9

10. (11) Randolph M. and Quiggin P. ‘Non-Linear Hysteretic
Seabed Model for Catenary Pipeline Contact’ 28th
International Conference on Ocean, Offshore and Arctic
Engineering, Honolulu, Hawaii, USA, May 31–June 5, 2009
(12) Janssen E. F. ‘Comparison study of deepwater
installation methods’ Master thesis, University of Stavanger,
Norway 2014
(13) Jha V., Dodds N., Finch D. and. Latto J.R., Anderson
T.A. and Vermilyea M.E., RPSEA UDW ‘Research Efforts -
Floaters and Risers: Flexible Fibre-Reinforced Pipe for 10,000
Foot Water Depths: Performance Assessments and Future
Challenges’, Offshore Technology Conference, Houston,
Texas, USA, 6–9 May 2014.
(14) N. Dodds, K. Pancholi, N.Dodds, V.Jha et al. , In Situ
Investigation of Microstructural Changes In Thermoplastic
Composite Pipe under Compressive Load, 33rd International
Conference on Ocean, Offshore and Arctic Engineering,
OMAE, 2014.
(15) Saevik, S. ‘A finite element model for predicting stresses
and slip in flexible pipe armouring tendons’, Computers &
Structures, 46, 2 219-230,1993.
10