bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Advances in Flexible Riser Monitoring Techniques Using Optical Fiber Sensors
Authors: Morikawa Sérgio R. K. , Braga Arthur M. B. , Camerini Claudio S. , Kato Carla C. , Llerena Roberth A. , Camerini Murilo G. , Simões Tiago B. 
Published: August 2013

Petrobras oil and gas production in the deep and ultra deepwater fields in Campos Basin and other provinces off the Brazilian coast heavily relies on flexible pipes. Maximizing the availability and reliability of an extensive offshore pipeline network poses innumerous challenges to the Company, which is steadily moving towards a condition based approach to maintenance of their flexible risers. In this context, Petrobras, in cooperation with its academic partners, has launched a comprehensive R&D program named MONFLEX, focusing on novel techniques for structural monitoring of flexible risers.
Years of field experience have demonstrated that one of the most frequent failure modes of flexible pipes is the sequential rupture of wires in their tensile armor layers [1]. The MONFLEX Program has explored a range of different technologies in order to timely detect and monitor the growth of this class of progressive structural damage. Some of the proposed approaches have relied on video cameras pointed towards fixedly mounted targets on the riser outer sheath, vibration and acoustic methods, these in a wide frequency range, and techniques based on fiber optic strain sensors. All three have been experimentally deployed in the field and are currently being evaluated. Among those, fiber optic monitoring is the one that has shown the better promise of becoming the chosen method for detecting wire ruptures in the riser’s armor layers.
The fiber optic based monitoring system developed in the MONFLEX R&D Program has been named MODA, which, in Portuguese, stands for Direct Wire Optical Monitoring. The MODA system consists in instrumenting all the wires of the riser’s external tensile armor layer with fiber Bragg grating strain sensors. In flexible risers already in operation, a window in the polymeric outer sheath of the pipe is temporarily opened in order to allow the sensors installation, and then repaired with a protective, anticorrosive layer. Even though in MODA the strain sensors are installed in the external armor layer, full scale laboratory tests have demonstrated that the algorithm employed to treat and analyze the real time data provided by the system is capable of instantaneously detecting ruptures of wires either in the external or internal layers of the tensile armor. The proposed contribution will report the later results of extensive laboratory tests and field trials performed with the MODA system.
Fatigue Analysis of Tether Chain in Hybrid Risers
Authors: Cerkovnik Mark , Chang S. , Griffin Cary 
Published: August 2013

Hybrid risers represent an excellent way to isolate the riser from most of the host vessel motions and thereby limit riser fatigue. A common arrangement features the riser supported by a buoyancy can via a tether chain. The tether chain is a cheap simple way to make the connection while providing flexibility for installation. However, in service the tether is under very high tension, and the chain is not really flexible in the face of small amplitude fatigue loads. The friction effectively “welds” the chain together. Moment and torque input to the system by first order vessel motions and vortex induced vibrations are carried through the chain and induce fatigue loading in the links.
Analysis of the chain can be problematic because the determination of the detailed stress in the chain requires a refined FEA model with contact element between the links. From the global sense the analysis may require running hundreds of sea-state realizations in the time domain and the vortex induced vibration (VIV) assessment of thousands of current profiles. In this paper an efficient numerical method is described to rigorously determine fatigue damage at locations throughout the chain.
Influence of Iceberg Geometry and Scour Depth on Drag Force in Sand
Authors: Ivanović Ana , Banimahd Meysam , Oliphant John 
Published: August 2013

The seabed disturbance in Arctic regions comes predominently through horizontal cutting mechanisms induced by natural processes such as iceberg scour. The zone of soil being disturbed by the iceberg and the soil resistance to the object movement is of interest to the geotechnical engineer. The influence of the iceberg on potential movement of the pipeline buried in the seabed has been of concern recently with recovery of the oil and gas assets situated in Arctic region.
Despite the significant developments in recent years in numerical modelling the ice gouging process still remains a challenge and further work is required to obtain a fully calibrated and validated numerical model. This paper therefore aims at developing a validated numerical model of the interaction between the iceberg and seabed through a series of laboratory tests undertaken at the University of Aberdeen.
This paper reports on a preliminary study focusing primarily on the comparison between laboratory and finite element (FE) modelling of the interaction between an iceberg and the seabed in terms of drag force and disturbance of the sediment. The FE model and experimental rig are described. The effect of the shape of the iceberg and the depth at which it penetrates has been investigated. Outputs of drag force from FE calculations showed a good agreement with the results obtained from the laboratory model giving the confidence to move to the next stage where both the inclusion of a pipeline segment and sand with different densities will be considered.
Vortex Shedding From a Bilge Keel in a Transient Turbulent Flow
Authors: Piehl Henry , el Moctar Bettar Ould 
Published: August 2013

The hydrodynamic damping of a bilge keel during the roll motion of a ship is fairly well understood and its basic principle can be summarized as follows: The larger the bilge keel attached to the hull, the stronger is its roll damping effect.
The geometric limitations regarding the size of the bilge keel are set by class regulations mainly dependent on the ship’s length, breadth and draft. Most bilge keel shapes are simple flat bars attached to the center of the bilge radius. While the added resistance of the bilge keel has to be kept as low as possible, the effective area for the cross flow generated by the roll motion should be maximized. Therefore the bilge keel’s cross section has to be kept small and its camber line parallel to the streamlines. In more sophisticated designs L-shaped bilge keels are applied in order to increase the damping effect on the roll motion. The aspects above need to be considered when defining the geometric limits of a bilge keel, however to further optimize the design of bilge keels numerical simulations are needed.
Even with today’s computing power, the costs of simulating a full ship hull with a sufficiently high mesh resolution to capture viscous vortex shedding effects would be prohibitive. To address and overcome this restriction a numerical test setup was developed that simulates the flow only in the near vicinity of the bilge keel. By further neglecting the influence of the free surface, it was possible to use a standard single-phase, incompressible, turbulent, transient solver. The open source FVM code OpenFOAM was used for all three stages of the simulation: mesh generation, solution process and post-processing.
With this simplified simulation model a systematic investigation of the turbulence model, the temporal and spacial discretization, as well as the principles of vortex shedding was carried out. The damping efficiency of the bilge keels was evaluated on basis of the mechanical work — by moving the hull through a viscous fluid — and the kinetic energy transported within the vortices. The findings from these flow simulations provide insights into the principles of bilge keel vortex shedding and their interaction with the hull and enable the development of bilge keel design guidelines.
A Method for the Prediction of Design Space for a Bend Stiffener Cone
Authors: Drobyshevski Y. 
Published: August 2013

Bend stiffeners are commonly used to protect flexible flow-lines and dynamic risers from over-bending, especially in the areas where they interface with fixed or floating structures. Sizing of bend stiffeners and confirmation of their feasibility is an important step in the design of the complete riser system.
The objective of this paper is to develop a method for the prediction of the design space for the bend stiffener cone, which is defined in terms of its length and diameter at the base. The analysis method is based on the analytical formulation for an elastic cone consisting of the main pipe and the hollow bend stiffener. A “marching” technique is developed which is based on combining linear solutions for several conical segments. The analysis method requires a small number of segments, and is efficient in dealing with large deflections. It is shown that even a linear solution alone for the bend stiffener cone provides good accuracy for moderate deviation angles.
Criteria for setting the design space boundaries for the bend stiffener cone are discussed. The selection of load cases from the tension-angle curve is discussed and its effect on the shape of the design space is demonstrated. The method is illustrated by developing a design space for the bend stiffener of a typical flexible riser connected to the turret of an FPSO.
Modeling Oscillatory Behavior of ESP Wells Under Two-Phase Flow Conditions
Authors: Vieira Rinaldo Antonio de Melo , Prado Mauricio Gargaglione 
Published: August 2013

The effect of free gas on the Electrical Submersible Pump (ESP) performance is well known. At a constant rotational speed and constant liquid flowrate, small amount of gas causes a mild head reduction when compared to the single phase liquid head. However, at higher gas rates, a drastic reduction in the head is observed. This critical condition, known as surging point, is a combination of liquid and gas flow rates that cause a maximum in the head performance curve. The first derivative of the head with respect to the liquid flow rate change sign as the liquid flow rate crosses the surging point. In several works on ESP two-phase flow performance, production conditions to the left of the surging region are described or reported as unstable operational conditions.
This paper reviews basic concepts on stability of dynamical systems and shows through simulation that ESP oscillatory behavior may result from two-phase flow conditions. A specific drift flux computation code was developed to simulate the dynamic behavior of ESP wells producing without packer.
WindFloat Contraption: From Conception to Reproduction
Authors: Aubault Alexia , Cermelli Christian , Lahijanian Alireza , Lum Alan , Peiffer Antoine , Roddier Dominique 
Published: August 2013

This paper will discuss the very serious topic of the design of the WindFloat, a full-scale floating wind turbine. The importance of the fundamentals of hydrodynamics in achieving the desired performance cannot be overstressed. These will be discussed in this paper, together with some of the key considerations that entered into the design process. At the time of writing of this manuscript, a full-scale WindFloat prototype has been spinning for a few months, and the electricity it generated powered all the Christmas lights of Pòvoa de Varzim, a small town in the north of Portugal — whose inhabitants are not seeing a reduction in their electricity bill.
The authors have chosen to disassociate the presentation — a progress report — from this manuscript, which should discuss a topic more appropriate to the permanent literature.
Oil Transfer Between DP Shuttle and Conventional Tankers in Tandem Configuration: A Numerical Evaluation of Alternatives
Authors: Tannuri Eduardo A. , Morishita Helio M. , Miyazaki Michel R. , Moratelli Lazaro , Madureira Rafael M. L. 
Published: August 2013

The recent Pre-Salt oil fields discovered in Brazil are imposing some new logistical challenges concerning distribution in the internal and external markets. In order to reduce the demand in the on-shore terminals, the export oil could be directly transferred from the platforms to the export tankers. However, internal regulations define that the offloading operation must be carried out by DP Shuttle Tankers (ST). Due to this definition, since 1994, the DP-ST fleet has been increased, and the safety and uptime of the offloading operations are improving. The utilization of a DP-ST to navigate across the oceans for exportation is not economically advantageous, since the day-rates of those vessels are significantly higher than conventional (non-DP) STs. Hence, a possible solution is to transfer the oil from the DP-ST to the conventional ST in the offshore waters. Several alternatives were proposed, considering stationary tandem configuration, ship-to-ship or tandem with advance speed.
This paper is focused on the stationary tandem configurations, considering the aid of offshore tugboats and/or monobuoys. The alternatives comprehend the conventional ST connected to the DP-ST or vice-versa, with the position being held by the DP system, a tugboat or a monobuoy. The numerical time-domain simulations were used for predicting the safety under typical environmental conditions, with crossed-bimodal sea states and sudden wave-wind changes. The relative motions of the vessels, hawser force, DP or tugboat utilization and loads on the vessels mooring equipment were verified in order to define the limiting environmental window for a safe operation, for each one of the alternatives. This comparative analysis was used to support the decision about this topic, since the advantages and problems of each solution could be identified.
Microbiologically Influenced Corrosion of Gulf of Mexico Mooring Chain at 6,000 Feet Depths
Authors: Miller Jonathon D. , Warren Brett J. , Chabot Luc G. 
Published: August 2013

During a post-installation inspection of a polyester and chain mooring system in water depths of approximately 6,000 ft, evidence of microbiologically influenced corrosion (MIC) was found in the form of rust tubercles known as rusticles. These porous concretions commonly form on submerged steel shipwrecks and provide evidence that subsea corrosion occurs in a hypoxic environment. Iron and sulfate-reducing bacteria cause corrosion in marine environments.
This paper will discuss one form of MIC found on submerged steel structures, analyze the ambient conditions required for MIC to occur, and compare rusticles found during the mooring inspection to those found on other subsea shipwrecks such as the RMS Titanic. An analysis of the type of iron used in mooring chains and the rate of rusticle formation will be presented. Possible remedies to prevent rusticle growth on mooring chains will be summarized.
Aero-Hydro-Elastic Simulation of a Semi-Submersible Floating Wind Turbine
Authors: Philippe Maxime , Babarit Aurélien , Ferrant Pierre 
Published: August 2013

This paper presents an aero-hydro-elastic model of a semi-submersible floating wind turbine. A specific attention is drawn to hydrodynamic modelling options and its effect on the dynamic response of the platform.
The NREL 5MW reference wind turbine mounted on the historical concept of semi-submersible platform Dutch Tri-floater is considered. A specific hydrodynamic model of loads on semi-submersible platform is used within the wind turbine design code FAST from NREL. This hydrodynamic model includes non linear hydrostatic and Froude-Krylov forces, diffraction/radiation forces obtained from linear potential theory, and Morison forces to take into account viscous effects on the braces and damping plates. The effect of the different hydrodynamic modelling options is investigated. As one could have expected, it is found that the effect of viscous drag and non linear Froude-Krylov loads, becomes larger with increasing wave height. Simulations are run with directional wave spectrum, it is found that wave directionality induces larger transverse motions.
Theoretical Prediction of Tension-Stroke Relationship of Hydro-Pneumatic Tension Systems
Authors: Zhang Hanqing , Song Ruxin 
Published: August 2013

Hydro-pneumatic tension systems have been widely used to support production and drilling risers on floating production systems (such as Spars and TLPs). A hydro-pneumatic tension system utilizes several hydro-pneumatic piston-cylinders (typically four) filled with a working gas (such as nitrogen) to provide the riser it supports with a tension. When the riser experiences strokes with respect to its supporting vessel caused by vessel motion (e.g. due to environmental change), the tensioner will accommodate most of the strokes by changing the volume and pressure of the cylinders. The riser tension will accordingly fluctuate with the pressure change about its design value. Such tension variation directly affects riser design and the vessel’s performance. Therefore, in the design of a hydro-pneumatic tension system, the stiffness of the tensioner, which describes the tension and stroke relationship of the tensioner, is one of the key design parameters to be concerned of. Since it is difficult to perform full-scale tests to determine the relationship for a tensioner, a theoretical model, which considers the tension’s stroke motion as a polytropic process, has been used to simulate the tension-stroke behavior of the tensioners. A polytropic process is well defined by a single parameter, the exponent. For nitrogen as the working gas, an exponent of 1.1 to 1.3 has been adopted in the offshore industry without theoretical or experimental verification.
The objective of this study is to theoretically predict the pressure-stroke relationship of the hydro-pneumatic tension systems and to determine proper values of the exponent for the polytropic process used in the offshore industry. The study uses the first law of thermodynamics and the knowledge of heat transfer to predict status change of the working gas with piston stroke and then to calculate the pressure-stroke relationship of the tensioner. The status of the gas is determined from the work exchange induced by piston strokes and heat transfer through the outer surfaces of piston rods and cylinder barrels. As a numerical example, a tension system similar to those used in the Gulf of Mexico is analyzed for 100-year hurricane environments. The predicted pressure time traces are compared with those given by a polytropic process with a series of exponents (or gas constants). The comparisons show that an exponent of 1.3 or 1.4 is a proper value for the polytropic process.
Effects of Second-Order Extreme Waves on the Dynamics of a Non-Linear Floating Body
Authors: Nava Vincenzo , Arena Felice 
Published: August 2013

Nowadays technical and scientific communities are increasingly interested in the development of technologies for floating devices which can serve different purposes both in coastal and offshore environment. Thus, strong effort is required in the development of correct and efficient algorithms for studying the behavior of such structures under the action of sea wave loadings. At this purpose, in the past few years several approaches were investigated, both in frequency and in time domains, using linear and non-linear structural models and linear and non-linear wave theories.
In this note, the effects of nonlinearities in the wave model on the dynamics of a non-linear floating rigid body model are calculated using the second-order Quasi-Determinism (QD) theory (see [1], [2]; [3]) under the action of extremely high waves. Structural nonlinearities consist essentially in non linear damping and nonlinear stiffness due to mooring lines, following the model shown in Nava & Arena, [4]. Numerical nonlinear simulations were performed by means of an algorithm based on the approach showed in Zheng et al. [5], and the results compared to those provided by the nonlinear QD theory.
The purpose of this note is to show not only the effects of nonlinearities in the behavior of a floating body and to compare them with those obtained from a linear approach, but also to estimate them through non linear QD theory under the occurrence of a large wave in order to evaluate the reliability of the proposed approach.
Optimized Operations and Integrity Management Through Instrumentation
Authors: Jenkins Peter , Pytte Trond , Holden Harald , Marre Ignacio , Rønningen Jo Espen , Johnstone Les , Berg Ole Johan 
Published: August 2013

During drilling and well intervention (DWI) operations today operating limits are normally given as limiting wave height, and sometimes wave periods. The resulting diagrams are often not directly comparable with weather information received on the rig and the final decisions are often based on subjective assessment of wave height and period.
The paper will present how BP, on the newly developed Skarv field in the Norwegian Sea, through thorough planning in the engineering phase has implemented a system where operating limits are specified based on directly measurable parameters such as rig heave and upper and lower flexjoint angles. How weather forecasting can be translated to give the rig crew direct forecasting of the limiting vessel or riser responses (e.g. flexjoint angles or heave), will also be presented. It will be shown how this allows for improved operational planning and support from onshore.
Over the last years requirements for oil companies to be able to document the structural integrity of their subsea assets, including wells, has increased. On the Norwegian Continental Shelf (NCS) there has been a particular focus on fatigue loading in the wellhead structure, including the upper sections of casing and conductor, due to loads induced by the riser and BOP during DWI operations. There have been cases where the design fatigue life of a wellhead system limits the number of days one can perform operations with a rig on a given well. This in term affects future oil recovery rates as the well fatigue life may not be sufficient to allow for side step drilling or intervention work required to maintain an optimal production from the well.
The paper continues to present how BP on the Skarv field, stores and utilizes the measured lower flexjoint response to track and document well integrity. It will be demonstrated how the return on investment of a drilled well can be improved by documenting actual fatigue loading from each operation on a well compared to conservative design calculations.
BP has addressed the above issues in a way that is likely to set a new standard for drilling and intervention operations in the North Sea in the future.
4Subsea AS has provided the engineering and instrumentation services that formed the basis for this paper.