bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lateral Buckling Induced by Trawl Gears Pull-Over Loads on High Temperature/High Pressure Subsea Pipeline
Authors: Herlianto Iswan , Chen Qiang , Karunakaran Daniel 
Published: August 2013

Lateral buckling has become a challenge to deep water and high pressure/high temperature (HP/HT) flowlines. In areas that support major commercial fishing industries (e.g. the North Sea in Norway and Atlantic Margin in UK), there is high possibility of interaction between flowlines and fishing trawl gears. This interaction can expose the flowlines to substantial loads and induce lateral buckling.
This paper presents global response of subsea pipeline as a result of trawl gear pull-over loads. The external interference from trawl gear pull-over loads can create substantial imperfection or out-of-straightness on the pipeline and may also generate global lateral buckling. The pull-over loads can also induce excessive bending moments and strains in the buckle region.
To be able to understand the global response of the pipeline under pull-over loading conditions, a Finite Element (FE) analysis is carried out based on DNV OS F101 [1], DNV RP F110 [2] and DNV RP F111 [3] using general FE analysis software ANSYS v13. Non-linear transient analysis is used to incorporate the non-linear effects, such as the pipeline material nonlinearity, and the response of a structure under the action of pull-over time-dependent loads [8].
The FE analysis covers two periods of duration, i.e. during pull-over duration and post pull-over duration. The analysis during pull-over duration deals with the pipeline global response as a result of trawl gear pull-over loads. The pipeline is subjected to substantial horizontal and vertical pull-over forces from the trawl gear. For post pull-over duration, the FE analysis was carried out for an additional five seconds. In this period, the pull-over loads are no longer applied. However, the pipeline may expand further due to temperature and pressure loads on pipeline.
The FE analysis result shows that the pull-over loads induce out-of-straightness on the pipeline and may cause lateral buckling. The pipeline deforms laterally at the pull-over location. The DNV displacement condition code check is used to check the integrity of the pipeline. The pipeline may in the risk under the trawl gears pull-over loads.
This paper also shows the development of lateral buckling on the pipeline under different magnitudes of trawl gear pullover loads and lateral soil frictions. Further work should also take into account different dimension of pipeline, as the variation of operating temperature and pressure and variation of lateral and axial soil friction combinations to obtain better conclusions.
Wellhead Fatigue Analysis Method: The Effect of Variation of Lower Boundary Conditions in Global Riser Load Analysis
Authors: Reinås Lorents , Russo Massimiliano , Grytøyr Guttorm 
Published: August 2013

Subsea wellhead mechanical fatigue can potentially result in a gross structural failure of barrier elements in the upper part of the well, potentially resulting in loss of well control. Several major E&P operators have acknowledged the importance of wellhead fatigue and are participating in the JIP “Structural Well Integrity”. It is within the scope of this JIP to develop a recommended practice for wellhead fatigue analysis methodology. The analysis methodology currently being investigated by the JIP is a decoupled approach, with modifications of the lower boundary to account for the stiffness of the conductor, soil and template interface. A detailed local wellhead model is used to generate the lower boundary condition for a decoupled global riser load analysis model. This lower boundary condition definition is intended to capture the overall non-linear stiffness of a site specific well in order to achieve best possible global riser loads estimate.
In this article the effect of varying the lower boundary conditions on a global load estimate is studied. Global load estimates are generated from a typical North Sea case and various lower boundary conditions are introduced as the only change to the global riser model. A fixed lower boundary condition is used as a reference and load estimates generated from riser models with various lower boundary conditions are compared.
The different lower boundary conditions selected for comparison in this study has been derived from the following cases:
1. Fixed at WH
2. As per ISO 13624-2
3. As per JIP “Structural Well Integrity” -Current
4. As per JIP “Structural Well Integrity” -Modified
Comparing the analysis results gives indications that the lower boundary condition modelling approach affect global riser load estimate. The fixed lower end boundary conditions did not yielded the most conservative load history in a fatigue context. Modelling well specific flexibility at the riser lower end increased the total number of wellhead fatigue load cycles. This finding support the current approach suggested by the works of the JIP “Structural Well Integrity”. Ensuring that riser load results are still conservative places a higher importance on precise local modelling of the well system.
On the Dynamic Response of Flexible Risers Caused by Internal Slug Flow
Authors: Ortega Arturo , Rivera Ausberto , Nydal Ole Jørgen , Larsen Carl M. 
Published: August 2013

Slug flow through flexible risers is a frequent phenomenon which occurs during production of a mixture of oil and gas. The dynamic nature of the slug pattern induces time varying forces, which leads to structural vibrations of the riser. These vibrations can produce large deflections and stresses, which can leave it to fail by fatigue, excessive bending or local buckling.
In this work the influence from slug flow on the structural dynamic response of a lazy wave flexible riser is analyzed using a computational tool consisting of one program for calculation of slug flow dynamics, and another program for structural dynamic response. Both programs apply a time integration method, and since slug flow will lead to dynamic motion response of the riser, and riser motion dynamics will influence slug flow dynamics, the two codes need to exchange information during the integration process. Information exchange is established by making a federation based on High Level Architecture (HLA).
The federation is composed of SLUGIT and RISANANL. SLUGGIT is a two-phase flow code written in C++ which simulates dynamic slug flow through pipes and riser using a Lagrangian tracking model. RISANANL is a FORTRAN program for static and dynamic structural analysis of slender marine structures based on a finite element formulation. Using the HLA standard these two programs can carry out synchronized time integration and exchange information for each time step.
In this work the structural analysis code accomplishes the dynamic response using a linear finite element (FE) formulation. Hence, forces from centripetal acceleration of the internal flow, relative velocity between the riser and surrounding water, and varying gravity of the pipe and content will be accounted for in the dynamic analysis. Displacements, stresses, internal pressure, and outlet flow rates of liquid and gas will be accounted for. The results encourage us to carry out a fully non-linear finite element analysis, in order to have a better understanding of the dynamic behaviour of flexible risers undergoing an unsteady internal two-phase flow.
The Use of Flexible Pipe for CO2 Enhanced Oil Recovery Applications
Authors: Taravel-Condat C. , Epsztein T. 
Published: August 2013

The use of CO2 rich gas mixtures as injection fluid is nowadays considered in order to enhance the oil recovery process. Flexible pipes, which have been used to transport oil and gas in offshore applications for more than 35 years, are attractive products for the transportations of such fluids. The CO2 content encountered for these applications can be higher than 90%. This value being superior to what is found in standard applications (<15%), and CO2 being known to behave as a supercritical fluid as soon as the temperature and the pressure are higher than 31.1°C, 72.8 atm, the compatibility of the pipe materials with the CO2 rich gas mixture had to be verified.
This paper will present the qualification work carried out so far on several thermoplastic materials used for flexible pipe pressure sheathes and stainless steel carcasses. This qualification work covers application as high as 90°C/600bar/100%CO2.
The formation of blisters (blistering) is known as a possible degradation mode of thermoplastic materials when subjected to rapid gas decompression. This phenomenon is directly linked to the fluid solubility in the polymer. Different materials have been tested for their ability to withstand rapid gas decompression in CO2 rich gas mixtures.
Long time exposure tests have been carried out. The objectives of these tests were to check the impact of CO2 on the physical, mechanical and chemical properties of the polymer grades. A special attention has been brought to the plasticizer effect of CO2. The impact of supercritical CO2 on the hydrolysis degradation mode has also been assessed.
Finally, CO2 being a small molecule, it will permeate through the pressure sheath to reach the annulus. The metallic layers which are constitutive of this annulus are potentially sensitive to corrosion phenomenon in acidic conditions. A good knowledge of the permeation properties of the polymer materials when subjected to high pressure CO2 is necessary in order to assess the severity of this annulus and to select the appropriate steel grade. The results of such tests will also be presented.
The Effect of a Fatigue Failure on the Wellhead Ultimate Load Capacity
Authors: Reinås Lorents , Sæther Morten , Aadnøy Bernt Sigve 
Published: August 2013

A subsea well will experience external loading during drilling operations that can lead to the development of a fatigue fracture in the primary load bearing structural members of the upper well construction. Such a fatigue fracture can occur at several fatigue hotspots which all are located in the upper part of a subsea well. There are two main load sharing structural members; the outer tubular string named the conductor (structural) casing and the next tubular string named the surface casing. Both these strings have a circumferential load bearing weld close to the top. The load sharing between these 2 tubular strings are affected by the supported weight from further tubular strings placed inside the well.
This paper discusses the residual ultimate load capacity of a typical North Sea subsea well assuming that a fatigue fracture has developed. The discussion is based on FEM analysis results where a fully developed fatigue fracture has been introduced to the analytical model of a typical well either to the conductor part of the well or to the surface casing string. Then the residual ultimate load capacity is evaluated assuming a fully developed fatigue fracture. Evaluations presented herein can be important and necessary tools in considering the consequences of a possible fatigue failure of a subsea well.
A reduction in ultimate load capacity due to a fatigue fracture may reduce the safety margin should an accidental or extreme loading occur. The results indicate that the location of the potential fatigue failure is important when assessing the residual ultimate load capacity. If the factored fatigue life of a subsea well is approaching its limit the presence of a fatigue fracture should be assumed. The most prudent approach would then be to perform a permanent P&A operation of the well. Planning of such operations should comprehend the possibility of reduced structural capacity of the well due to a fatigue fracture. This paper also discusses the results in an operational context. The applied methodology is outlined and illustrative results are presented from a typical North Sea well.
An Optical Tool for Measuring Vortex-Induced Vibrations of Long Flexible Cylinders
Authors: Huera-Huarte Francisco J. 
Published: August 2013

We describe the design and performance of a novel optical measurement system that can be used for measuring vortex-induced vibrations (VIV) of long flexible cylinders. We believe this is the first time this technology has been used to measure VIV in a long flexible cylinder. The emphasis is given to the measurement technique itself. It can be used either in air or in water and we believe it is a better alternative to other traditional vibration response measurement techniques used to study VIV in the laboratory. The measurement system is based on the Defocusing Digital Image Particle Velocimetry (DDPIV) concept, proposed by Willert and Gharib in [1] for measuring velocity flow fields.
A set-up, which was built to conduct vortex-induced vibration measurements in a wind tunnel facility with a cross-section of 1.8 × 1.2 m, has been used in a laboratory to demonstrate the capabilities of the optical measurement system when known displacements are produced in the mappable or measurement volume. The same supporting structure designed to provide suport for the cylinder models inside the wind tunnel test section, has been used to hold a target which has been move to different known locations to measure the performance of the system. The design, description and performance of the measurement technique are discussed.
Power Performance and Environmental Footprint of High-Speed Vessels in Calm Deep Water
Authors: Skejic Renato , Jullumstrø Egil 
Published: August 2013

This paper reports a theoretical study of the power performance and environmental footprint of high-speed vessels in calm deep water, paying particular attention to a high-speed catamaran cargo vessel Faltinsen [1]. The power analysis uses a modified version of the method of Doctors and Day [2]. One modification to their approach is that the wave resistance and free surface wave profiles, have been numerically predicted using two different linear potential flow field theories; Michell thin-ship theory (Yeung and Wan [3]) and the 3D Rankine panel method (Hess and Smith [4]), respectively. We have based the latter method on the combination of the Dawson [5] upstream finite difference operator and the ‘staggered grid’ technique (Jensen et al. [6]). In addition, this paper shows how the viscosity effects modeled on the free surface layer influence the behavior of the wave resistance curves as predicted by Michell’s thin ship theory. This was done by adopting the approaches described by Tuck [7] and Lazauskas [8].
The wave resistance models were verified and validated using the examples of Wigley monohull (Lazauskas [8], Tarafder and Suzuki [9]) and catamaran (Yeung and Wan [3], Tarafder and Suzuki [10]) analytical forms, as well as on the Tuck parabolic strut (Tuck [7]). Furthermore, the resistance models were extended using free surface profile estimates at selected Froude numbers and applied to the case of a high-speed catamaran cargo vessel. The numerical results obtained were compared with published results and their accuracy and application feasibility is discussed from the perspective of preliminary high-speed vessel design.
Based on the discussion above, suitable wave resistance models were selected and combined with the modified Doctors and Day [2] method giving the total resistance of the high-speed catamaran cargo vessel in the interval of Froude numbers. Having the estimates of total resistance, enables the effective power to be found. The results were compared with known results and were found to be in good agreement. Through combination of the effective power and propulsion factors, the brake power of the generic propulsion system is predicted. Taking into account the type of vessel being analyzed, the most common type of the propulsion diesel engine was selected. Finally, knowing the indicative environmental footprint of the selected engine, emission levels of Green House Gases (GHG) and solid particles were obtained. The emission results are further discussed in an ecologically friendly high-speed vessel design perspective (IMO [11, 19]).
Influence of Incoming Flow Direction on Spacing Between Vertical Axis Marine Current Turbines Placed in a Row
Authors: Dyachuk Eduard , Goude Anders , Lalander Emilia , Bernhoff Hans 
Published: August 2013

From the commercial point of view it may be beneficial to install a set of marine current turbines forming a park, by analogy with wind parks. Consequently, this motivates research on park configurations.
An array of ten vertical axis marine current turbines is simulated to study how the distance between the turbines affects the performance of the park for different flow directions. The simulations are performed using a two-dimensional vortex method. An array of identical turbines is created, where all turbines are on a single line. The turbines are operated at the tip speed ratio, which corresponds to the highest power coefficient for a single turbine. The distance between the turbines is varied and the total power from the array is compared to the turbine spacing for different flow directions.
Additionally, flow data from a real site is used to find an optimal orientation of the line of turbines. The performance of the array is estimated for the site as a function of turbine spacing.
DP Ice Model Test of Arctic Drillship and Polar Research Vessel
Authors: Hals Torbjørn , Jenssen Nils Albert 
Published: August 2013

The paper presents the results from a series of ice model tests performed as part of the DYPIC (Dynamic Positioning in Ice Conditions) research program. DYPIC is a research and development project within the EU’s ERA NET MARTEC project. The major purpose of the DYPIC project is development of equipment and methods for DP Ice Model testing which allows the prediction of station keeping capability of different vessel types and offshore structures under various ice conditions.
The first DYPIC model tests performed in 2011 was conducted with two significantly different vessel sizes, a 68.0000 m3 volume displacement arctic drillship and an 8.600 m3 polar research vessel. The model scale was 1/30 for the arctic drillship and 1/18.6 for the Polar Research Vessel.
The model tests were performed in the ice model basin at HSVA using vessel models equipped with thruster capacity similar to full scale operation according to DP class 2 / 3 operations. The DP control system was also modified from normal open water DP operations in order to cope with the highly varying ice drift loads acting on the vessel.
The test program gave data supporting the development of numerical models of ice loads from managed ice, see reference [6]. The main focus in this paper is on the station keeping performance and associated thrust utilization as a function of varying ice drift loads.
The results and data collected in the first year of the DYPIC program demonstrates that DP ice model tests will be a valuable tool for evaluation of vessel performance prior to moving on to full scale arctic DP operations.
Pipeline Walking Interaction With Buckle Formations Along Routes With Significant Seabed Features
Authors: Wang Yunxiao Nick , Maschner Emil , McKinnon Colin 
Published: August 2013

In the last few years some ‘long’ HPHT (high pressure high temperature) offshore pipelines have been required to be routed across challenging seabed terrains such as salt diapirs and deep trenches with relatively large OOS (out of straightness) and steep slopes. This has given rise to a combined design concern of lateral buckling with pipeline walking. Typically anchor points in the form of caisson piles as well as buckle sites in the form of sleepers or buoyancy modules maybe required in the vicinity of the seabed features to release the compressive forces associated with the high pressure and temperature loads in a controlled manner and to prevent the pipelines from migrating down slope during operation. The instigation of buckle sites can essentially divide any ‘long’ pipelines into a number of short sections with different walking behaviour due to varying seabed slopes and varying pressure and temperature gradients at locations along the route. In addition pipeline anchors influence the development of any planned buckle site and thus limit the extent of cyclic feed-in and/or pull-out. This integrated mechanism is termed buckling walking interaction within this paper.
The prevailing methodology and numerical modelling of pipeline walking usually evaluates ratcheting end expansions by means of ‘short’ and overall ‘long’ pipe lengths which ignore or consider the existence of buckle sites along any pipeline route respectively. This paper presents a general-purpose study on the phenomenon of buckling walking interaction considering a typical pipe route configuration with anchors and buckles along its length. Aspects such as the cyclic evolution of mode shapes of buckles and the effect of soil berm resistance on buckling walking interaction are explored. Finally the design application of buckling walking interaction for ‘long’ cyclically constrained pipelines with buckles and anchors is discussed.
Effect of Polyester Mooring Stiffness on SCR Design for Semi Applications
Authors: Cao Peimin , Thompson Hugh , Kwan Tom 
Published: August 2013

Polyester rope mooring system has been widely accepted as a reliable and cost effective choice for deepwater mobile offshore drilling and floating production units in recent years. Polyester rope is made of a visco-elastic material and its stiffness is affected by mean tension, tension amplitude, loading period, and loading history. This creates complexity and uncertainty in the design of hull, mooring and riser systems.
This paper summarizes the results of a JIP study investigating the effect of polyester rope stiffness on the SCR design of a semi-submersible FPU at two water depths in the Gulf of Mexico (GoM). A two-slope static-dynamic stiffness model proposed in the recently issued ABS “Guidance Notes on The Application of Fiber Rope for Offshore Mooring”[1] is used in the global motion analysis to provide input for the riser analysis. Parametric studies of SCR extreme analysis, wave fatigue analysis, and VIM fatigue analysis have been performed. Based on the results, recommendations on the impact of rope stiffness to the riser design are presented.
Combination of Multiple Extreme Bending Moment Components
Authors: Leira Bernt J. 
Published: August 2013

A procedure for estimating the combined load effect for processes with different zero-crossing periods is described. The procedure is illustrated by application to the combination of wave-induced bending moments. The basic formulations related to the distribution of maxima and extremes for a scalar Gaussian process are first reviewed. Subsequently, an outline of the procedure for multi-component processes is given. The developed formulation is then applied for analysis of the combined bending moment load effect.
Two cases of such combinations are addressed (i) A case with widely different velocity variances (ii) A case involving a non-linear combination of the bending moments. A geometric approach to the interpretation and derivation of associated load effect combination factors is also demonstrated.