bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimisation of Conductor System Design to Minimise Wellhead Fatigue Issues
Authors: Williams Dara , Purcell Kevin 
Published: November 2013

Current market trends in the construction of newbuild drilling rigs indicate that the market is driven by demand for ultra-deepwater capacity semi-submersible rigs and drillships. These drilling vessels have capacity to drill in water depths of up to 12,000ft and possibly beyond in the near future. With increase in water depth capacity, more complex and heavier BOP stacks are required. Many modern drilling vessels are now incorporating BOPs with capacities of 20ksi pressure and up to 7 shear/seal rams incorporated. This leads to increased height and weight in the BOP. Whilst newbuild drilling vessels will be required to operate in water depths from 1,500ft to 12,000ft whilst on DP mode, deepwater semi-submersible drilling rigs will also have capability for operation in water depths <1,500ft using conventional mooring. Recent experience with modern deepwater rigs with large BOP stacks in water depth of 1,500ft or less suggests increased risk of fatigue when compared to 3rd generation rigs. If future trends continue with larger BOP stacks being designed then the problem of wellhead fatigue with modern deepwater drilling vessels is likely to become more acute.
As noted in previous studies the water depth at drillsite has a major impact on the level of fatigue accumulated in the wellhead system. The main driver for this has been found to be the height and weight of the BOP. With requirements for newbuild drilling rigs for 12,000ft water depth capacity being the industry norm, and with increased requirements for BOP functionality, the gap between wellhead loading from 3rd generation and 6th generation rigs is widening. Given that many 3rd generation rigs will likely be decommissioned in the coming years then the usage of 6th generation rigs for shallow water operations will only become more commonplace due to rig availability. Thus, unless market conditions dictate the construction of smaller and lighter BOP stacks, the design of shallow water wells will be critical to ensure fatigue loading on the wellhead and conductor is kept to a minimum.
This paper presents a summary of the results of a series of parameter studies carried out to assess a range of options for optimisation of casing and conductor design for 6th generation rigs in shallow water. Various recommendations are made as part of this study as to the addition of supplemental casing and conductor strings of varying sizes and wall thickness to ensure a robust conductor system design for fatigue performance.
Preliminary Cross-Validation of Wave Energy Converter Array Interactions
Authors: Folley Matt , Whittaker Trevor 
Published: November 2013

The development of wave energy for utility-scale electricity production requires an understanding of how wave energy converters will interact with each other when part of a wave farm. Without this understanding it is difficult to calculate the energy yield from a wave farm and consequently the optimal wave farm layout and configuration cannot be determined. In addition, the uncertainty in a wave farm’s energy yield will increase the cost of finance for the project, which ultimately increases the cost of energy.
Numerical modelling of wave energy converter arrays, based on potential flow, has provided some initial indications of the strength of array interactions and optimal array configurations; however, there has been limited validation of these numerical models. Moreover, the cross-validation that has been completed has been for relatively small arrays of wave energy converters. To provide some validation for large array interactions wave basin testing of three different configurations of up to 24 wave energy converters has been completed. All tests used polychromatic (irregular) sea-states, with a range of long-crested and short-crested seas, to provide validation in realistic conditions.
The physical model array interactions are compared to those predicted by a numerical model and the suitability of the numerical and physical models analysed. The results are analysed at three different levels and all provide support for the cross-validation of the two models. The differences between the physical and numerical model are also identified and the implications for improving the modelling discussed.
Optimisation of Resistance and Towed Stability of an Offshore Going Barge With CFD
Authors: Toxopeus Serge , Stroo Ko , Muller Bart 
Published: November 2013

For the transport of large structures over sea, offshore going barges are one of the preferred means of transportation. The resistance and towed stability of these vessels are of prime importance with respect to the economic feasibility of transport. To ensure acceptable towed stability behaviour, side skegs are generally placed under the aft ship of the barge. However, these skegs give additional resistance and thus undesired fuel consumption.
SMIT and MARIN joined forces with the intention of designing a new ocean going barge with sufficient towed stability and superior resistance characteristics compared to the already low drag Giant 4 barge. The Giant 4, for which favourable tow characteristics were observed during its service, was used as a reference vessel. The first step was to modify the hull form in order to fulfil SMIT’s design requirements. Subsequently, a detailed CFD study into the flow around the barge and the size, shape and positioning of the side skegs was performed leading to a significant resistance reduction. However, this reduction in resistance led to a degradation of the towed stability of the vessel, which was compensated for by adding a centreline skeg. The final design has a 14% percent reduction in resistance compared to the existing barge, with comparable towed stability.
A model testing program was performed in order to validate the CFD computations. The agreement between the CFD and experimental results was found to be very good, demonstrating that CFD tools can be used to optimise the resistance and towed stability of barges.
Fatigue of Risers and Pipeline Girth Welds
Authors: Horn Agnes Marie , Wästberg Stig , Cordes Rogers 
Published: November 2013

Deep-water tendon and riser systems are often subjected to severe fatigue loading from waves, currents and vessel movements. The girth welds between successive lengths of pipe or at pipe terminations are the locations most vulnerable to fatigue damage and accurate and reliable assessment of the fatigue performance of these welds is of significant importance. These welds are normally designed on the basis of appropriate S-N curves. In addition, it is common practice to perform an Engineering Critical Assessment (ECA) based on fracture mechanics fatigue crack growth principles, principally in order to establish acceptance limits for weld flaws that are consistent with the fracture toughness of the welds and the required fatigue life.
However, for the most important case of fatigue failure from the weld toe, the mode of failure principally covered by the S-N curves, a conventional ECA invariably results in tolerable weld toe flaws that are too small for reliable detection by currently available NDE methods. In fact, this situation is not unreasonable since it is known from careful metallurgical examinations that weld toe fatigue cracks initiate at tiny (<0,5 mm deep) sharp imperfections that are an inevitable consequence of welding, whereas the detection limit for even the most sensitive NDE techniques is around 1–2 mm. Hence this paper discusses different models for including crack initiation and early growth of defects in girths weld, in addition some trends found in full-scale data from an on-going girth weld fatigue JIP is shown.
Installing U-OWC Devices Along Italian Coasts
Authors: Arena Felice , Fiamma Vincenzo , Laface Valentina , Malara Giovanni , Romolo Alessandra , Viviano Antonino , Sannino Gianmaria , Carillo Adriana 
Published: November 2013

In the last decades, the research has directed its efforts and resources paper is to investigate towards the possibility to incorporate wave energy converters, into the traditional maritime breakwaters to combine classical use with new opportunities and developments (for example, the Green Ports). Since the nineties, the OWC (Oscillating Water Column) plants were developed at full scale to produce electrical power from ocean waves. For instance, a new plant was built in Mutriku (Spain) recently.
A new kind of OWC caisson, named U-OWC or REWEC3, which has the advantage to obtain an impressive natural resonance without any device for phase control, has been patented by Boccotti [1]. This new U-OWC device gives performances better than those of a conventional OWC either with small wind waves or with high waves [2,3,4]. The properties of the REWEC3 have been verified with two small-scale field experiments carried out in the natural ocean engineering laboratory NOEL of Reggio Calabria off the eastern coast of the Sicily Channel [5–7]. The aim of the present two sites along Italian coasts for possible installations of REWEC3 devices: i) the port of Civitavecchia (Rome, Italy)in the Tyrrhenian sea; ii) the port of Pantelleria, in the Sicily Channel.
Benefit of Measurements and Structural Reliability Analysis for Wellhead Fatigue
Authors: Hørte Torfinn , Russo Massimiliano , Macke Michael , Reinås Lorents 
Published: November 2013

Structural Reliability Analysis (SRA) methods have been applied to marine and offshore structures for decades. SRA has proven useful in life extension exercises and inspection planning of existing offshore structures. It is also a useful tool in code development, where the reliability level provided by the code is calculated by SRA and calibrated to a target failure probability.
The current analysis methods for wellhead fatigue are associated with high sensitivity to variations in some input parameters. Some of these input parameters are difficult to assess, and sensitivity screening is often needed and the worst case is then typically used as a basis for the analysis. The degree of conservatism becomes difficult to quantify, and it is therefore equally difficult to find justification to avoid worst case assumptions.
By applying SRA to the problem of wellhead fatigue, the input parameters are accounted for with their associated uncertainty given by probability distributions. In performing SRA all uncertainties are considered simultaneously, and the probability of fatigue failure is estimated and the conservatism is thereby quantified. In addition SRA also provides so-called uncertainty importance factors. These represent a relative quantification of which input parameter uncertainties contribute the most to the overall failure probability, and may serve well as guidance on where possible effort to reduce the uncertainty preferably should be made. For instance, instrumentation may be used to measure the actual structural response and thus eliminate the uncertainty that is associated with response calculations. Clearly measurements obtained from an instrumented system will have its own uncertainty. Other options could be to perform specific fatigue capacity testing or pay increased attention to logging of critical operational parameters such as the cement level in the annulus between the conductor and surface casing.
This article deals with the use of measurements for fatigue life estimation. Continuous measurements of the BOP motion during the drilling operations have been obtained for a subsea well in the North Sea. These measurements are used both in conventional (deterministic) analysis and in SRA (probabilistic analysis) for fatigue in the wellhead system. From the deterministic analysis improved fatigue life results are obtained if the measured response replaces the response obtained by analysis. Furthermore, SRA is used to evaluate the appropriate magnitude of the design fatigue factor when fatigue analysis is based on measured response. It is believed that the benefit from measurements and SRA serve as an improved input to the decision making process in the event of life extension of existing subsea wells.
Numerical Evaluation of PLEM Structure and Foundation Modes of Failure and Failure Consequences
Authors: Abdalla Basel , Mei Haixia 
Published: November 2013

For deep water pipeline end manifold (PLEM) subject to complex loading conditions, a combined 3D finite element (FE) model has been developed by the authors to determine the foundation bearing capacity by studying the interaction between individual parts, including the PLEM structure, flowline, mudmat and soil. The advanced numerical techniques have proven that the resulting factor of safety against bearing failure is higher when compared to the classical approach given in API-RP-2A/2GEO. However, the minimum required safety factor of 2.0 is not reached. Therefore, risk assessment using reliability analysis becomes mandatory to assess the probability of failure of the mudmat. As an input to the risk assessment, this paper presents an investigation of the system’s modes of failure and failure consequences on the environment and project cost.
Using the developed 3D FE model, plausible excessive loads beyond design considerations are applied until a failure in soil foundation occurs. Then, loads are increased until the capacity of structural and mechanical components in the system is reached putting the containment of carried hydrocarbons at risk. A direct relationship between the hydrocarbon temperature and the capacity of structural/mechanical components is developed to evaluate the system flexibility and resistance to induced excessive deformations.
The paper demonstrates the advantages of numerical techniques in evaluating the ultimate capacity of a PLEM structure and foundation soil system. The methodology can be used in the design of a new system or to assess the stability of an existing system under future loadings.
On the Design of the In-Plane Bending Fatigue Test
Authors: Agustsson Geir , Bendiksen Erik , Nielsen Christian B. 
Published: November 2013

The fatigue design of the steel armour layers is an important factor in flexible riser design. Typically, the riser must be able to endure the loads of a field condition for a period of 20 years. In flexible pipe design, this is analyzed in global and local flexible pipe fatigue modeling, which needs to be supported by proper testing. One of the widespread test methods is the so-called in-plane bending fatigue test, which is one of the important qualification tests for flexible pipes.
API 17B references two purposes for performing in-plane bending fatigue tests. One is to demonstrate that the pipe can endure the loads which it is exposed to during its lifetime (service simulation). The other is to validate the design methodologies (service-life model validation).
The first purpose calls for test conditions being as close to reality as possible. However, testing in conditions close to reality does not necessarily call for field environment conditions being present during the in-plane testing itself. This is because field conditions are covered with a combination of small-, mid- and full-scale tests according to the recommendations given in API 17B.
The second purpose can be, or is even best fulfilled with simplifications compared to field conditions.
This study will go through the options and discuss the pros and cons of simplifications versus a more complicated test. The discussions in the paper are based on the author’s experience and can be supported with examples from actual testing.
Non-Destructive Measurement of Residual Stresses by an Ultrasonic Method
Authors: Kleiman Jacob , Kudryavtsev Yuri , Smilenko Volodimir 
Published: November 2013

An ultrasonic computerized complex for measurement of residual and applied stresses UltraMARS® was recently introduced. Average through thickness stresses can be measured based on the acoustic-elasticity effect, according to which the velocity of elastic wave propagation in solids is dependent on the mechanical stress. The system was used successfully in numerous applications proving to be a reliable, fast and economical way to evaluate residual and applied stresses in materials and structures. The newly developed complex was used in a number of applications that called for non-destructive evaluation of stresses. Examples of such applications will be discussed in the paper.
The system was further developed to allow for measurement of subsurface and surface stresses in structural materials and made of them structures.
Communication in the High North: Supporting Safe Maritime Operations
Authors: Kvamstad Beate 
Published: November 2013

The special Arctic conditions with the presence of ice and harsh weather require complex offshore maritime operations compared to more central parts of the world. In order to maintain the safety level of the operations one need to share information amongst numerous actors across large distances. This is especially important in critical situations, when correct decisions need to be made very fast. Having a shared situational awareness becomes crucial. This again requires reliable and robust communication infrastructure such that undisrupted information is received by the end user in time. This represents a major challenge in the Arctic, since communication infrastructure above 75°N is relatively poor.
Ships operating in open seas use maritime communication systems based on geostationary (GEO) satellites which orbit the earth above the equatorial line, such as for example Inmarsat and VSAT. However, they have little or no coverage at all in the Arctic and the low elevation angles makes them vulnerable to external influences. The theoretical coverage limit for GEO systems is 81.3°N, but field tests performed in the Norwegian MarSafe North1 project showed that instability and signal dropouts can be experienced already at 70° N during certain conditions. The only satellite system that provides full coverage in the Arctic area is Iridium, and it offers digital capacity through the Iridium OpenPort services. However, users have reported unstable performance, and the field tests showed that Iridium has unstable digital throughput in Arctic areas. The paper will present results from field tests performed in the MarSafe North project.
The projects MarCom2, MarSafe North and ArctiCOM3 have investigated the state-of-the-art of Arctic communications; they have investigated future needs for satellite communications and proposed potential solutions. This paper will present the main results from these projects, as well as describing the main activities and tentative results achieved in the on-going project MARENOR, which analyses the factors that influence the quality of service of navigation and communication systems in the Arctic.
DRX Wet-Cell and Static Displacement Tests to Understand Salt Deposition and Shale Inhibition Mechanisms
Authors: Khodja Mohamed , Belkadi Mustapha , Kaouane Ahcene , Saber-Khodja Malika , Guellil Khadidja , Khadraoui Sofiane 
Published: November 2013

Salts scale is one of the most important problems found in the oil and gas industry. Precipitation of salts can occur near wellbore as well as in the wellbore. The resulting reduces drastically well performance and causes a significant decrease in production rate. In order to remove salt deposits as well as prevent the precipitation of salt, fresh water treatments are performed at regular intervals during production operations. In drilling activity, shale is the most common rock types encountered while drilling wells. The combination of KCl/Polymer in water base mud (WBM) reduced frequency and severity of shale instability problems. In the order, all polymers are not able to resolve problems and inhibition mechanism comprehension still complex. Chemical treatment is an alternative approach to inhibit salts formation and shale instability. Bad inhibitor selections or/and high concentration provide limited performance and will cause damage which mechanism still unclear. In addition, it is extremely difficult to test salts formation and shale inhibition in the laboratory under reel conditions. Research shows that variation on temperature and pressures affect seriously inhibition mechanisms. In this way, our work tends to follow salts crystallization and shale swelling by using two methods: X-ray diffraction wet-cells for the in situ monitoring of fine powder reactions and displacement tests to follow permeability reduction under reservoir conditions. The possible mechanisms of halite and shale inhibition are discussed. Some experiences combining with using fines minerals particles to simulate compacted rock are realized. The following conclusions have been drawn:
- At ambient conditions, the contact between the water mixture and fines reservoir rock shows that crystallization was increased with time and affected by fines particles compaction and surface rugosity,
- Technique of chemical inhibition restrain salt deposit (60% of crystallization reduction) and enhances shale stability,
- A minimum polymer inhibitor concentration effectively was confirmed by X Ray Wet-Cell and Dynamic test under reservoir conditions.
Roll Decay Model Test of a Post Panamax Container Ship: Experimental and Numerical Analysis
Authors: Piehl Henry , el Moctar Ould 
Published: November 2013

The slender shape of a modern ship hull, exhibits a roll motion that is — in contrast to heave and pitch motion — submitted to large amplitudes and weak damping. This effect explains the importance of determining the roll damping of a hull and denotes the difficulty to measure such a small dynamic property.
For the joint research project Best-Roll a series of roll decay tests were conducted with the model of a post panamax container ship. To capture the influence of the draft and the ship velocity, the roll motion was measured for a systematic variation of these parameter. In addition the tests were performed with an initial roll angle of 20 degrees, in order to investigate the nonlinear damping behavior at large roll angles.
The objective of the subsequent study was to test the capability of OpenFOAM to compute the overall roll damping of a ship hull and appendages. For the numerical comparison, the roll decay test was simulated with OpenFOAM, using a transient multiphase solver with a RANS turbulence model, dynamic mesh motion and a rigid body motion model of the ship. The results were compared by calculating the roll damping coefficient for both experiment and numerical simulation by means of time series analysis of the roll angle.
Riser VIV Suppression Device Tests for Application to a Southeast Asia TLP
Authors: Yen Kien Min , Magee Allan , Aramanadka Shankar Bhat , Abdul Malik Adi Maimun , Abdul Ghani Mohamad Pauzi , Ismail Nasrudin Haji , Ahmad Zukni NorBahrain , Teng Yih Jeng 
Published: November 2013

The Southeast Asia metocean environment is characterized by moderate wind and waves with relatively strong and persistent currents. The design of a Tension Leg Platform (TLP) for Southeast Asia is strongly affected by the current and resulting drag loads, particularly if many risers are required. To reduce vortex-induced vibrations (VIV) of offshore tubular members i.e. top tension risers (TTRs), vortex suppression devices such as helical strakes and fairings are used.
This paper gives an insight into a set of riser VIV model tests which is carried out to study the effectiveness of an open-back “U”-shaped fairing in suppressing riser VIV. The splitting loads and the drag loads of the fairings are also investigated during these tests. The tests are being done at the Marine Technology Center (MTC), Universiti Teknologi Malaysia (UTM) in support of this application, and also in part to increase local technological capabilities. Two sizes of risers are being tested in three configurations: (a) bare riser without any fairings; (b) riser with weathervaning fairings (normal condition) and (c) riser with fairings fixed at different headings (abnormal condition). The test results show that in the normal condition, the fairing is effective at suppressing VIV.