bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Study on the Effect of Splitter Plate Angle on the VIV Behavior of Submarine Pipeline on an Erodible Bed Under Clear Water Condition
Authors: Emamgholizadeh Mohammad Javad , Mostafa Gharabaghi Ahmad Reza , Abedi Karim , Sedaaghi Mohammad Hossein
Published: November 2013

Pipeline is an appropriate method for transmission of oil and gas from seabed hydrocarbon reservoir to the land and platform or any other place where it is needed. Free spans in the line may occur initially by an uneven seabed or be created later due to under-scouring. Vortex Induced Vibration (VIV) may occur in these free spans at high Reynolds’ numbers. Resonance can occur if the frequency of vortex shedding is close to the pipeline’s natural frequency. Otherwise, it can cause pipeline’s fatigue leading to its breakage and consequently economical and environmental losses.

In literature, different methods are presented for decreasing the scouring depth due to the vortex shedding. One of them is the application of splitter plate.

In this paper, the effect of splitter plate’s angle with horizon (α) on the vibrating behavior of pipeline with two degrees of freedom over an erodible bed is studied experimentally. The experiments were performed for reduced velocity in the range of 2.45–5.06 and gap ratio of zero. Image processing technique as a non-contact method is used for measuring the vibrations of cylinder. Experimental results indicate that the splitter plate’s angle is an important factor on the cylinder’s vibration amplitude. According to these results, for the angle in the range of 0 ≤ α ≤ 30, the vibration amplitude is decreased while its frequency is increased, but the results are vice versa for the range of 60 ≤ α ≤ 90.
Oscillation of a Net Panel With Bending Stiffness
Authors: Jensen Østen , Gansel Lars , Føre Martin , Reite Karl-Johan , Jensen Jørgen Haavind , Endresen Per Christian
Published: November 2013

The behaviour of net panels with bending stiffness is dependent on the stiffness and potentially also the density of the material when exposed to oscillatory motions. This needs to be taken into account when net cages are product certified according to NS9415 (Standard Norge 2009). Experiments using two different net panels with bending stiffness were conducted to investigate the behaviour of nets with bending stiffness in oscillatory motion. For low oscillation frequencies the panels moved in a close to rigid body manner. When the oscillation frequencies where increased, however, there was a distinct difference between the copper and the Polyethylene Terephthalate (PET) nets, with a significant increase in the resulting oscillation amplitude for the copper net and a decrease for the PET net.

The proposed numerical model predicts this behaviour well in terms of oscillation amplitudes. It is, however, important to establish good estimates of the net panels bending stiffness in advance, particularly if product certification is the purpose of the numerical analysis.
Hydrodynamic Forces on Subsea Pipelines due to Orbital Wave Effects
Authors: Karreman Annelise , Leggoe Jeremy , Griffiths Terry , King Lisa , Fogliani Nino
Published: November 2013

Ensuring pipeline stability is a fundamental aspect of subsea pipeline design and can contribute a significant proportion of project costs in regions with large diameter trunklines, shallow water and severe geotechnical and metocean conditions [1]. Reducing the conservatism and simplifications of existing pipeline stabilisation design methods therefore offers economic benefits to hydrocarbon producers necessary to ensure the ongoing viability of projects in these regions. To realise this potential and reduce the conservatism of the existing design methods, a more accurate understanding of the hydrodynamic loads exerted by waves and currents is required.

This paper investigates one of the inherent assumptions incorporated into the existing design methods through the arrangement of previous experimental investigations to determine whether rectilinear motion provides a reasonable approximation to simulate the near seabed orbital particle paths in wind-generated waves. This assumption is based on the flattening of particle paths to ellipsoids with depth and ignores the small vertical velocity components near the seabed. Based on the hydrodynamic forces calculated numerically using a validated Computational Fluid Dynamics (CFD) model for rectilinear and orbital wave modelling it is concluded that pipeline stabilisation requirements calculated in accordance with the DNV-RP-F109 absolute lateral static stability design method and rectilinear wave motion assumption are conservative. It is also concluded that the hydrodynamic force asymmetry in favour of the reverse half wave cycle caused by the vertical velocity components in orbital wave conditions requires further consideration to determine the implication for dynamic lateral stability design methods.
Investigation on the Abnormal Crack Front in Fatigue Crack Growth Rate Test for Thick High Tensile Steel Plate
Authors: Dong Yan , Yue Jingxia , Yi Qian , Zhou Heng , Huang Hao
Published: November 2013

Complex environmental loads unavoidably lead to fatigue damage in marine structures, and it becomes worse in high tensile steel thick-welded structure which has typical tri-axial stress state and the feature of brittleness. In this paper, a standard fatigue crack growth rate test for high-tensile steel Q370QE with thickness of 36 mm was carried out, and some material parameters and the threshold of stress intensity factor were obtained. Then, the abnormal behavior of a crack front during crack growth was analyzed by finite element method. Accordingly, the varying tendency of crack front shape could be qualitatively defined, and the plastic zoon at both flat and slope crack fronts for different crack depth was demonstrated based on plasticity analysis. Finally, local constraint factor was introduced to quantitatively describe the stress state along the crack front with the growth of fatigue crack, which provided proper explanation to why the crack front changes from slope to straight with the crack growing.
Application of Wave Devouring Propulsion System for Ocean Engineering
Authors: Terao Yutaka , Sakagami Norimitsu
Published: November 2013

A Wave Devouring Propulsion System (WDPS) generates thrust directly from wave power while simultaneously generating a strong damping force. A simple WDPS design consists of hydrofoils mounted below the bow of a vessel. If a WDPS is integrated with the hull of a vessel, then it can power the vessel forward, even against the wave direction itself. One example of a successful WDPS was installed on the vessel named Mermaid II, which completed a trans-Pacific voyage in 2008, traveling approximately 7,800 km from Hawaii to Japan using wave power alone. This success indicates that the WDPS has potential for use in the field of ocean engineering. As described in this paper, we intend to apply the WDPS to the small autonomous boat and to conduct sea trials. We designed and built an autonomous WDPS boat, developed a data acquisition system, and experimentally investigated its performance in Orida Bay. The experimentally obtained results indicate that the autonomous navigation of the WDPS boat is possible when the wave height is greater than 5–10 cm.
Design of Leg Mating Unit for Float-Over Installation of Decks
Authors: Chaitanya Krishna , Nair Sajith B.
Published: November 2013

The Leg Mating Unit (LMU) is a critical component in ensuring safe method of installing topsides of offshore oil and gas platforms by the float-over method. Traditionally, topsides are lifted onto the substructure (e.g. jacket) using heavy lift crane vessels. However, the ‘lift’ method of installation is constrained by the availability of a limited number of heavy lift vessels in the region, with high day rates. As an alternative to modular installation with light crane vessels, float-over installation enables installation of a single pre-commissioned integrated deck, minimizing offshore hook-up time and cost. Further, float-over method is particularly suited to shallow water depth locations, remote locations (with no access to crane vessels). In a float-over installation, the deck is transported on a cargo barge to the pre-installed substructure location. The barge is guided into the jacket slot and positioned so that the stabbing cone on each leg is aligned with the corresponding jacket leg. The barge is then ballasted down (aided by the falling tide) so that the topside load is transferred from the barge to the jacket. Once the load is transferred and sufficient clearance is achieved between the deck structure and barge support structure, the barge is withdrawn from the slot. The transfer of load is the crucial step of a float-over installation and should occur in a controlled manner under the dynamic influence of environmental forces. This smooth load transfer is achieved using LMU’s. LMU’s are customized leg and deck mating units, used to dampen the impact loads generated during the mating process. They consist of steel structures with elastomer elements and are designed to perform three primary functions, absorb shocks, limit hammering onto the structures and provide defined stiffness between deck and sub-structure. The objective of this paper is to outline the design philosophy of a LMU and address the behavior of the LMU under the combination of vertical and horizontal loads during the mating process. The paper also recommends guidelines on the selection of elastomer stiffness based on load-displacement relationship. The LMU is analysed in ABAQUS, a commercially available finite element (FE) analysis package considering a non-linear time-domain analysis. The results from the FE analysis are compared with the qualification tests for the elastomer and LMU assembly performed on-site to establish correlation.
Performance Modelling of an Offshore Floating Wind Turbine-Driven Deep Sea Water Extraction System for Combined Power and Thermal Energy Production: A Case Study in a Central Mediterranean Context
Authors: Sant Tonio , Farrugia Robert N.
Published: November 2013

Current research is exploring a new design concept for offshore wind turbines whereby the electrical generator in a conventional wind turbine is replaced by a large positive displacement pump that supplies pressurized sea water to a centralized hydro-electric plant. This paper investigates the potential of applying this concept to concurrently exploit thermocline thermal energy through deep sea water extraction in conjunction with offshore wind energy. A performance analysis is presented for a single wind turbine-driven pump supplying combined power and thermal energy by delivering pressurised deep sea water to a land-based plant consisting of a hydro-electric generator coupled to a heat exchanger. The steady-state power-wind speed characteristics are derived from a numerical thermo-fluid model. The latter integrates the hydraulic characteristics of the wind turbine-pump combination and a numerical code to simulate the heat gained/lost by deep sea water as it flows through a pipeline to shore. The model was applied to a hypothetical megawatt-scale wind turbine installed in a deep offshore site in the vicinity of the Central Mediterranean island of Malta. One year of wind speed and ambient measurements were used in conjunction with marine thermocline data to estimate the time series electricity and thermal energy yields. The total energy yield from the system was found to be significantly higher than that from a conventional offshore wind turbine generator that only produces electricity. It could also be shown that in regions where the offshore wind resource is not as rich, but where the ambient temperature is high as a result of a hotter climate, the cooling energy component that can be delivered is relatively high even at periods of low wind speeds.
Ice-Resistant Turret-Based Mobile Drilling Unit With the Wedge-Shaped Hull Approximating Ship Form (Wedge-Shaped Ship)
Authors: Blagovidov Lev B. , Kovalyov Maksym V. , Blagovidova Iryna L. , Kolchenko Leonid V. , Lenskyy Victor F.
Published: November 2013

Nowadays, the development of Arctic oil/gas fields is still more challenging. Designing of various-type drilling unit solutions operable in rigorous ice conditions is underway to meet that challenge.

The present report includes results of the development of a promising design of an ice-resistant turret-based floating drilling unit with the hull of wedge shape similar to ice-going ship’s fore in terms of angle of bow rake, entrance angle of water line, flare of frames. This architectonic type was selected based on the survey of world experience and comparison with similar Arctic solutions.

Testing in the seaworthiness basin and ice test basin proved high seaworthiness performances of this ship. Particularly demonstrative are good controllability in ice conditions achieved by the specific hull shape and use of turret arrangement, as well as relatively lower ice loads compared with other solutions.
VIV Analysis of Deep Water Steel Catenary Riser Within Pull Tube
Authors: Qiu Lun , Lee Li
Published: November 2013

The method of pulling a steel catenary riser (SCR) through a steel tube (termed as a pull tube) is common practice for deepwater riser tie back applications. Vortex-induced vibration (VIV) of such a system is complex. VIV analysis programs, such as Shear7 [1], are suitable only for a single, chain-like structure. The application of such a software tool in VIV design of the SCR-pull tube system requires careful consideration of a number of structural and hydrodynamic factors.

This paper presents a methodology for VIV analysis of the combined structural system of the SCR with the pull tube. Firstly, the entire SCR-pull tube system is modeled with the finite element program Flexcom [2]. The modes are then calculated for the entire structure with program Modes [3]. Afterwards, the structural nodes are rearranged for VIV analysis with Shear7. The pull tube is secured on the platform through a number of guides on the truss structure of the hull. The diameter of the pull tube is much larger than that of the SCR, and the pull tube is much stiffer in bending than the SCR is. If the entire structure is analyzed with Shear7, the mode for the pull tube (a mode involving a large motion of the pull tube section), which is very high in order, would be embedded in the analysis. It makes sense to single out the pull tube mode for study as if it is the first mode. A computer program, named as V-Span [4] for subsea span VIV analysis, is used to analyze both in-line and cross-flow VIV of the pull tube.

A numerical example is presented to demonstrate this methodology. This is a deepwater SCR, which has a diameter of 9 inches. The water depth is 6,300 ft. The pull tube is 640 feet long and 20 inch in diameter. Both the loop-eddy and background currents are analyzed. The fatigue damage resulted from both in-line and cross-flow VIV is estimated.
Validation of Solid Modeling and Analysis Techniques for Response Prediction of Deepwater Flexible Pipe
Authors: Connaire Adrian , Smyth John , Nestor Ruairi , Tanaka Rafael , Albuquerque Elson
Published: November 2013

Accurate prediction of the load capacity of the constituent components of flexible risers and flowline structures is critical in demonstrating fitness for purpose, particularly as the envelope of application of flexible pipe is being extended to incorporate higher flow rates, greater water depths, more aggressive fluid contents and challenging installation conditions. Analytical techniques and numerical solid modelling methods have evolved significantly in recent years as a means of improving the ability to accurately predict flexible pipe load capacity.

Due to the complexity of the flexible pipe structure and the load sources and load paths to which it can be subjected, different analysis methods are required, depending on the type of response being evaluated. Specific effects can be difficult to simulate using analytical approaches and require local stress analysis using numerical techniques. This paper presents numerical approaches to two such effects, the extreme loading of tensile armour wires within a flexible pipe end fitting and the stability of tensile armour wires in axial compression.
The Development of an Experimental Force Feedback Dynamometer to Investigate the Real Time Control of an Oscillating Wave Surge Converter
Authors: Banks Daniel , van ’t Hoff Jos , Doherty Kenneth
Published: November 2013

An Oscillating Wave Surge Converter (OWSC) is a Wave Energy Converter (WEC) that consists of a bottom-hinged flap which oscillates due to wave action. Extensive research has been performed on this type of WEC through small scale experimental wave tank tests. One of the key challenges of experimental testing is replicating the characteristics of the Power Take-Off (PTO) system of the equivalent full scale WEC. Many scale models rely on simplified mechanical designs to simulate a PTO system. This can often restrict the experimental research into the influence of PTO design and control strategies of WECs. In order to model PTO systems and control strategies more accurately other tools are needed. This paper describes the design and build of a PLC controlled Force Feedback Dynamometer (FFD) system that enables the testing of more sophisticated control strategies applicable to an OWSC through fast application of a variable PTO damping torque. A PLC system is shown to be a viable control for PTO strategy investigations through velocity triggered damping levels. Examples of both PTO and position control strategies are presented.
Instrumenting Giant Piston Corers: A Decisive Step in Understanding the Coring Process and Interpreting Data
Authors: Po Stanislas , Woerther Patrice
Published: November 2013

Giant piston corers were introduced to the marine geotechnical site investigations market towards the end of the nineties. Such corers are also used for scientific studies by research institutes as Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER). Cores were observed to show distortion or mismatches between core length and the position of the sample in the soil.

The instrumentation of corer provides valuable information on the behaviour of the corer. The instrumentation also allows the correction of sample length to its true penetration.

This paper:

• Describes the instrumentation now permanently mounted on the STACOR® giant piston corer

• Presents the installation of sensors,

• Describes the data interpretation,

• Provides some recommendations for extending this monitoring to other large gravity corers.
Vertical Axis Current Turbine (VACT) and its Efficiency
Authors: Fernandes Antonio Carlos , Rostami Ali Bakhshandeh , Canzian Lucas Gomes , Sefat Sina Mirzaei
Published: November 2013

This study examines the efficiency of a vertical axis current turbine (VACT) according to various non-dimensional mass moments of inertia. The vertical axis current turbine of drag force type with flat plate-shaped blade is tested. From experiments in a circulating water channel the angular velocity, the power coefficient and tip speed ratio of the vertical axis current turbine are obtained. The property changes for various conditions give the relationships between efficiency-related parameters. The maximum power coefficients of experiments occur at the tip speed ratio of approximately 0.35∼0.40. From the experiments, turbine is found to give a 7% power coefficient which related to I* = 0.52.
Monte Carlo Prediction of the Extreme Values of the Combined Load Effect and Semi-Probabilistic Design of Ocean-Going Ships
Authors: Huang Wenbo , Xiao Ying
Published: November 2013

Based on Poisson models, the Monte Carlo simulation of the combined still-water and wave load effects is carried out to estimate extreme values of the combined load effects of oceangoing ships. The extreme values predicted are compared with those based on the theoretical methods. The numerical analyses show that the results based on the two methods agree with very well. Moreover, the empirical distribution of the combine extreme values simulated and numerical theoretical distribution based on a load combination analysis can both be well fitted to an analytical extreme value distribution model of Type II. Besides, a strength model of a ship hull beam is developed based on the fatigue analyses. Finally, with the models developed for load effect and strength, the simplified reliability analyses are carried out for an ocean going ship.
Smoothed Particle Hydrodynamics: Benchmarking on Selected Test Cases Within the NextMuSE Initiative
Authors: le Touzé David , Barcarolo Daniel A. , Kerhuel Matthieu , Oger Guillaume , Grenier Nicolas , Quinlan Nathan , Lobovsky Libor , Basa Mihai , Leboeuf Francis , Caro Joelle , Colagrossi Andrea , Marrone Salvatore , de Leffe Matthieu , Guilcher Pierre-Michel , Marongiu Jean-Christophe
Published: November 2013

In this paper are presented comparisons of SPH variants on academic test cases classically used to validate numerical fluid dynamics software. These comparisons are extracted from NextMuSE FP7 project activities which will be published more extensively in the near future. One of the goals of this project was to better understand the SPH method and to leave the path to its establishment within CFD methods. An important work load was thus dedicated to benchmark SPH variants on selected test cases.

A number of results and conclusions of this comparative study are presented in this paper. The studied variants are: standard weekly-compressible SPH, δ-SPH, Riemann-SPH, incompressible SPH, and FVPM. The majority of the test cases also present a reference solution, either experimental or computed using a mesh-based solver. Test cases include: wave propagation, flow past a cylinder, jet impact, floating body, bubble rise, dam break on obstacle, floating body dynamics, etc. Conclusions may help SPH practitioners to choose one variant or another and shall give detailed understanding necessary to derive further improvements of the method.
Physical Component Testing to Simulate Dynamic Marine Load Conditions
Authors: Thies Philipp R. , Johanning Lars , Gordelier Tessa , Vickers Andrew , Weller Sam
Published: November 2013

The reliability and integrity of components used in the marine offshore environment is paramount for the safety and viability of offshore installations. The engineering challenge is to design components that are robust enough to meet reliability targets whilst lean enough to minimise cost. This is particularly the case for offshore marine renewable installations which operate in the same, possibly harsher, environment as offshore oil and gas installations, and are subjected to highly cyclic and dynamic wave, wind and operational load conditions. The cost of electricity produced has to compete with other means of electricity generation and does thus not offer the same profit margins available as oil and gas commodities. As a result, components for marine renewable installations have to meet the target reliability, without the application of costly safety factors to account for load and environmental uncertainties. Industries with similar design tasks such as the aviation or automotive industry have successfully used a service simulation test approach to develop robust yet lean designs.

This paper builds on an approach to establish and validate the reliability of floating renewable energy devices in which dedicated component testing using the purpose built Dynamic Marine Component test rig (DMaC) plays a pivotal role to assess, validate and predict the reliability of components in the marine environment. This paper presents a test rig for both static and fatigue tests of marine components such as mooring lines and mooring shackles under simulated or measured load conditions and provides two case studies from recently conducted mooring component tests. This includes an investigation into the load behaviour of synthetic mooring ropes and the ageing of mooring shackles.
Nonlinear Wave Group Impact on a Cylindrical Monopile
Authors: Peng Zhong , Raaijmakers Tim , Wellens Peter
Published: November 2013

The ComFLOW wave model has been employed to study the impact of nonlinear wave groups on cylindrical monopiles. Four nonlinear wave groups are selected from fully nonlinear waves generated by a 2D ComFLOW model, representing wave groups with the largest or the second largest crest heights, the largest wave height and a wave group consisting of consecutive large waves. These four wave groups are used to investigate the wave loads on the foundation and the platform in a 3D ComFLOW model. Model results show that the maximum wave loads on the foundation and the platform by nonlinear wave groups are determined by their individual wave crest height. This study presents a relationship between platform level and wave impact on the platform, as the vertical force on the platform is the combination of buoyancy force (if inundated) and wave impact force due to wave run-up. Results also show that wave loads on the foundation and wave impact on the platform decrease as the wave period increases from 13s to 16s (typical wave period at German Bight). A wave group can cause a larger wave load on the foundation and the platform than regular waves, considering a regular wave height equal to the maximum wave height, regardless of the associated wave period (period of individual wave or peak period).
Considerations for Seabed Rare Earth Mining in the Pacific
Authors: Wolgamot Hugh A. , Zhang Wei , Kiosidou Evangelia , Kim Sung-hee , Bashir Musa
Published: November 2013

A number of deep-sea mineral resources are well known and have been the subject of mining proposals. However, a recent paper has identified a new resource on the deep seabed in the form of rare-earth-rich seabed sediment. This paper considers issues associated with harvesting this resource from some of the identified locations, including demand for rare earths, methods of exploration, environmental concerns and some technological aspects.
Human Factor Risk Assessment During Emergency Condition in Harsh Environment
Authors: Musharraf Mashrura , Khan Faisal , Veitch Brian , MacKinnon Scott , Imtiaz Syed
Published: November 2013

This paper presents a quantitative approach to human factors risk analysis during emergency conditions on an offshore petroleum facility located in a harsh environment. Due to the lack of human factors data for emergency conditions, most of the available human factors risk assessment methodologies are based on expert judgment techniques. Expert judgment is a valuable technique, however, it suffers from vagueness, subjectivity and incompleteness due to a lack of supporting empirical evidence. These weaknesses are often not accounted for in conventional human factors risk assessment. The available approaches also suffer from the unrealistic assumption of independence of the human performance shaping (HPS) factors and actions. The focus of this paper is to address the issue of handling uncertainty associated with expert judgments and to account for the dependency among the HPS factors and actions. These outcomes are achieved by integrating Bayesian Networks with Fuzzy and Evidence theories to estimate human error probabilities during different phases of an emergency. To test the applicability of the approach, results are compared with an analytical approach. The study demonstrates that the proposed approach is effective in assessing human error probability, which in turn improves reliability and auditability of human factors risk assessment.
Effect of Material Plasticity and Metallic Layer Profiles on the Crushing Resistance of Flexible Pipes
Authors: Sato Marcel , Tanaka Rafael L. , Albuquerque Elson L. , Morini Rafael G. , Godinho Carlos A. F.
Published: November 2013

This paper presents a numerical 3D finite element model to simulate a flexible pipe under crushing-traction condition, which is a typical situation found during its laying operation. This model considers the geometry of some layers from the flexible pipe, responsible of providing the most contribution to its radial strength (e.g., interlocked carcass, internal polymeric layer, pressure armor, and external polymeric layer) and geometry of laying system shoes. It also considers the flexible pipe initial ovalization and the squeezing effect due to the tensile armor layers under traction. A numerical-experimental comparison is presented, in order to show the model validity.
Advanced Deepwater Monitoring System
Authors: Brower David , Hedengren John D. , Shishivan Reza Asgharzadeh , Brower Alexis
Published: November 2013

This study investigates new methods to improve deepwater monitoring and addresses installation of advanced sensors on “already deployed” risers, flowlines, trees, and other deepwater devices. A major shortcoming of post installed monitoring systems in subsea is poor coupling between the sensor and structure. This study provided methods to overcome this problem. Both field testing in subsea environments and laboratory testing were performed. Test articles included actual flowline pipe and steel catenary risers up to twenty-four inches in diameter. A monitoring device resulting from this study can be installed in-situ on underwater structures and could enhance productivity and improve safety of offshore operations. This paper details the test results to determine coupling methods for attaching fiber optic sensor systems to deepwater structures that have already been deployed. Subsea attachment methods were evaluated in a forty foot deep pool by divers. Afterword, structural testing was conducted on the systems at the NASA Johnson Space Center. Additionally a 7,000 foot deep sensor station was attached to a flowline with the aid of a remote operated vehicle. Various sensor to pipe coupling methods were tested to measure tensile load, shear strength and coupling capability. Several adhesive bonding methods in a subsea environment were investigated and subsea testing yielded exceptionally good results. Tensile and shear properties of subsea application were approximately 80 percent of those values obtained in dry conditions. Additionally, a carbide alloy coating was found to increase the shear strength of metal to metal clamping interface by up to 46 percent. This study provides valuable data for assessing the feasibility of developing the next generation fiber optic sensor system that could be retrofitted onto existing subsea pipeline structures.
U-Oscillating Water Column in Random Waves: Modelling and Performances
Authors: Malara Giovanni , Arena Felice
Published: November 2013

This paper deals with the analytical modelling of an U-Oscillating Water Column (U-OWC). It is shown that this device can be adequately described by a nonlinear equation of motion including hydrodynamic memory effects. The excitation of the system, the added mass and the retardation function are derived by approximating the solution of a pertinent initial boundary value problem via eigen-function expansions of the (linear) velocity potential.

Next, the performance of the system is investigated in random waves by relying on Monte Carlo simulations. The excitation of the system is synthesized from a given power spectral density. Then, the nonlinear equation of motion is numerically integrated. Pertinent statistical measures are estimated for assessing the efficiency of the U-OWC in exploiting sea wave energy. In this regard, the parameters show that the device can absorb most part of the incident wave energy. Further, the device can work in safe conditions even in quite rough sea states.
Structural Integrity Control of Ageing Offshore Structures: Repairing and Strengthening With Grouted Connections
Authors: Samarakoon S. M. S. M. K. , Ratnayake R. M. Chandima , Siriwardane S. A. S. C.
Published: November 2013

Structural integrity control (SIC) is an increasingly important element of offshore structures. Not only is it used in newly built and existing offshore structures (e.g. oil and gas (O&G) production & process facilities (P&PFs), wind turbine installations, etc.), but SIC is also essential for ageing offshore platforms which are subjected to an extension of their design service life. In these cases, SIC programs must be performed to assess the platforms. If any significant changes in structural integrity (SI) are discovered, then it is essential to implement an appropriate strengthening, modification and/or repair (SMR) plan. Currently, welded and grouted repairs are mostly used for SMR. Although a welded repair may typically restore a structure to its initial condition, if the damage is due to fatigue loading and welded repairs have been carried out, then historical evidence reveals that there is a high potential for the damage to reappear over time. On the other hand, mechanical connections are significantly heavier than grouted connections. Consequently, grouted repairs are widely used to provide additional strength, for instance, to handle situations such as preventing propagation of a dent or buckle, sleeved repairs, leg strengthening, clamped repair for load transfer, leak sealing and plugging, etc. This manuscript examines current developments in grouted connections and their comparative pros and cons in relation to welded or mechanical connections. It also provides recommendations for future research requirements to further develop SMR with grouted connections.
Assessment of Specimen Geometry for All-Weld Metal Tensile Test in Narrow Groove Welding
Authors: Mota-Solis Noé , Ruiz Eduardo , Pelcastre Mauricio , Quintanilla Hector
Published: November 2013

The development of adequate welding procedures for the offshore pipeline industry has required improvement of weld designs due to stringent field operations, e.g., deep and ultra-deep water application, strain-based design, weld overmatching, low temperature toughness, fatigue resistance, etc. Gas-metal arc welding (GMAW) procedures have required the optimization of the groove design, from conventional (wide opening) to narrow-groove (NG) solutions. The assessment of the weld metal tensile properties, based on international codes and specifications, is necessary to deliver full compliance and reliability of requirements for the girth weld performance. However; complexities arise in order to establish weld metal testing procedures, when narrow-groove design is used for welding a heavy-wall (HW) seamless pipe material. The latter requires the assessment of specimen geometry in HW line pipe in order to produce reliable measurements of all-weld metal tensile properties, which can be representative of the weld metal performance.

The objective of the present work is to present the assessment in the differences on specimen geometry for all-weld metal tensile test (AWMTT). The work includes the welding of a HW seamless pipe material; 273.1 mm OD × 46 mm WT, X65 steel grade using STT®+GMAW, single-torch, as welding process, with narrow J-bevel, in 2° angle opening. Experiments considered the use of an ER80S-G solid wire as filler material for behavior analysis. The assessment methodology consisted in the machining of three different specimen geometries; strip, round and cross weld specimens were prepared for tensile tests. Efforts were dedicated to extracted tensile specimens avoiding heat affected zone areas in the specimen. Assessment of obtained results is based on tensile tests as well as the analysis of stress-strain data for the yielding behavior regarding the specimen geometry.
Qualification of UOE SAWL Linepipes With Enhanced Collapse Resistance for Ultra Deepwater Applications
Authors: Arroyo Fábio , Solano Rafael F. , Mantovano Luciano , de Azevedo Fábio B. , Alves Hélio , Swanek Doug , Silva Ronaldo , Ernst Hugo
Published: November 2013

Large diameter UOE pipes are being increasingly used for the construction of offshore pipelines. Since oil discoveries are moving towards ultra-deepwater areas, such as Pre-Salt in Brazil, collapse resistance is a key factor in the design of the pipelines.

It is known that the cold forming, and the final expansion in the UOE linepipe manufacturing process, reduces the elastic limit of the steel in subsequent compression. Due to this, the DNV collapse formula includes a fabrication factor that derates by a 15% the yield strength of UOE Pipes. However, DNV also recognizes the effect of thermal treatments and the code allows for improvement of the fabrication factor when heat treatment or external cold sizing (compression) is applied, if documented.

This paper presents the qualification of UOE pipes with enhanced collapse capacity focusing the use of a fabrication factor (αfab) equal to 1. TenarisConfab has performed a technology qualification process according to DNV-RP-A203 standard “Qualification Procedures for New Technology”. The main aspects of the qualification process are presented in this paper which included significant material and full scale testing, including combine load testing, and final analysis.

The qualification process achieved successful results and this will allow use of a fabrication factor equal to 1 directly in deepwater and ultra-deepwater offshore pipeline projects with a possible reduction in material and offshore installation costs and also potentially enhancing the feasibility of many challenging offshore projects.
Qualification and Assessment of Subsea Insulation Systems
Authors: Tello Alejandro D.
Published: November 2013

As offshore oil and gas production continues to push into deeper waters, subsea production systems are challenged to manage the inherently higher operating temperatures and pressures. As a consequence of their direct exposure to seawater, subsea “wet” insulation systems on subsea trees, manifolds, and jumpers are amongst the most affected by this progression. Due to the significant thermal gradient between the production stream and subsea environment, subsea insulation systems are constantly trying to inhibit the natural heat transfer. In an effort preserve the operational integrity of the production system, the subsea insulation system maintains the production stream temperature above the hydrate formation and wax deposition temperatures. Thus, any failures such as cracks, disbondment, or hydrolysis, substantially influence the subsea system’s operational philosophy. As a result of ExxonMobil’s observed performance challenges with wet insulation systems, a thorough qualification program was initiated in 2007 to validate the performance of a wet insulation system under simulated service conditions. The qualification consisted of 3 test phases, including basic material property tests, simulated service tests, and an extended service test, for multiple insulation systems. This paper presents an overview of select subsea insulation failures, the qualification program, and subsequent assessment of key material properties, such as tensile strength/elongation, density, and hardness.
Thrusters Dimensioning for Vessel’s Stationkeeping Close to Other Floating Structures: Two Case Studies
Authors: Tannuri Eduardo A. , Madureira Rafael M. L. , Igreja Haroldo
Published: November 2013

Brazilian offshore scenario requires innovative solutions in order to increase the efficiency of operations, while still keeping the safety and the economical constraints. The global market and naval industry cannot meet the demand of the growing exploration activities, related to the recent discovery of new oil fields. Furthermore, they are located at a large distance from the shore (approximately 300km) and the environmental conditions are severe. These facts impose more logistics problems for materials and persons transportations.

The retrofitting of vessels is an alternative for increasing their operability and this option has been studied by Transpetro, subsidiary of Petrobras responsible for the Ducts, Terminals, Maritime Transport and Natural Gas segments. This paper presents two real cases of retrofitting related to the application of new technologies for positioning, including Dynamic Positioning (DP) Systems or manually operated thrusters.

In the first case, a conventional tanker will be converted to a DP2 tanker, in order to operate close to drill ships and to transfer fluids during the drilling operation. The second case is related to an offshore delivering vessel used for bunkering operation. This vessel is moored at a monobuoy, and up to 2 receiving vessels may be connected to it. An aft-azimuth thruster will be installed in the vessel, increasing its capacity to change heading in harsh environmental conditions and to keep a safe distance from the monobuoy during fast variations of environmental conditions.

Both cases require the application of a comprehensive design methodology for thruster dimensioning. The retrofitting imposes tight constraints to the layout and positioning of the thrusters. Also, the proximity to others vessels and the harsh environmental conditions in the offshore fields requires a combination of static and dynamic calculation in order to evaluate power consumption and drift motions of the vessels.
Buckling and Tensile Strain Capacity of Girth Welded 48″ X80 Pipeline
Authors: Igi Satoshi , Ohata Mitsuru , Sakimoto Takahiro , Shimamura Junji , Oi Kenji
Published: November 2013

This paper presents the experimental and analytical results focused on the compressive and tensile strain capacity of X80 linepipe. A full-scale bending test of girth welded 48″ OD X80 linepipes was conducted to investigate the compressive strain limit regarding to the local buckling and tensile strain limit regarding to the girth weld fracture. As for the compressive buckling behavior, one large developing wrinkle and some small wrinkles on the pipe surface were captured relatively well from observation and strain distribution measurement after pipe reaches its endurable maximum bending moment. The tensile strain limit is discussed from the viewpoint of competition of two fracture phenomena: ductile crack initiation / propagation from an artificial notch at the HAZ of the girth weld, and strain concentration and necking / rupture in the base material.

The ductile crack growth behavior from the girth weld notch is simulated by FE-analysis based on the proposed damage model, and compared with the experimental results. In this report, it is also demonstrated that the simulation model can be applicable to predicting ductile crack growth behaviors from a circumferentially notched girth welded pipe with internal high pressure subjected to post-buckling loading.
Detailed Modeling of Drilling Fluid Flow in a Wellbore Annulus While Drilling
Authors: Podryabinkin Evgeny , Rudyak Valery , Gavrilov Andrey , May Roland
Published: November 2013

To produce a well safely, the wellbore pressure during drilling must be in a range that prevents collapse yet avoids fracturing. This range is often called “the operating window”. Exceeding the limits of this range can trigger wellbore instability or initiate well control incidents. Pressure prediction requires an understanding of the hydrodynamics processes that occur in a borehole while drilling.

Describing these processes is complicated by many factors: the mud rheology is usually non-Newtonian, the flow mode can be laminar or turbulent, and the drillstring can rotate and be positioned eccentrically. Known semi-analytical approaches cannot account for the full range of fluid flows that can arise during drilling. These techniques don’t take into account all factors. Accurate numerical simulation of the flow of drilling fluids is a means to describe the fluid behavior in detail.

For numerical solutions of hydrodynamics equations a unique algorithm based on a finite-volume method and a new model of turbulence for non-Newtonian fluids was developed. The model considers string rotation and eccentricity of the drillstring. Newtonian and non-Newtonian fluids as described by the Herschel–Bulkley rheological model have been implemented. Data obtained via systematic parameter studies of the flow in a borehole are available for fast determination of parameters like pressure drop, velocity field, and stresses corresponding to any drilling condition.

Applying the new model for the annulus flow and comparing the results to the parallel plate flow approximation enabled us to quantify the error made due to the approximated solution for non-Newtonian fluid rheology.

The difference between the solutions grows as the annular gap increases. This situation is a function of the rheological parameters. Secondary flow effects can only be seen when applying the new solution method.
Ocean Engineering Mooring Rope Residual Strength and Broken Wires Probability Calculation
Authors: Ren Huilong , Zou Jiaxing , Li Chenfeng , Wang Hao
Published: November 2013

During the service period, the mooring rope will get broken wires inner or outer because of corrosion, attrition, distortion and bending fatigue. This paper provides a calculation formula of steel wire strength and a calculation method for residual strength. Simplify the inner structure, which is convenient for calculation. Consider the friction influence among the wires and the probability distribution of broken wires. Provide the wire distribution probability model. Basis on the calculation result to get the confidence interval, then get the extent of mooring rope residual strength.
Shakedown Study of Pipes With External Corrosion Under Cyclic Bending and Internal Pressure
Authors: Lourenço Marcelo Igor , Netto Theodoro A.
Published: November 2013

Pipelines and rigid risers are susceptible to corrosion. This is also a concern for pipes onshore and on process plants of floating platforms. Once detected the corrosion defect on pipes under cyclic loads, the analysis carried out to decide on keeping the pipe in operation or repair/replace should consider that the defect may experience cyclic plasticity caused by stress concentrations and thickness reductions. In this condition, ratcheting can cause rapid failure. This paper presents a study combining experiments and different analysis techniques to evaluate the occurrence of ratcheting in pipes subjected to cyclic bending and internal pressure. Experiments with different defect geometries were carried out. Numerical analysis using incremental plasticity and shakedown procedures are presented and compared with the experiments.
Robust Control for Ship Course-Keeping Based on Support Vector Machines: Particle Swarm Optimization and L2-Gain
Authors: Luo Weilin , Fu Bin , Guedes Soares Carlos , Zou Zaojian
Published: November 2013

To achieve a robust autopilot for ship course-keeping, a controller based on support vector machines (SVM) and L2-gain is proposed. A cascaded plant consists of a nonlinear ship response model and the rudder actuator dynamics. Uncertainties including modeling errors and external disturbances are taken into account in the response model. SVM is applied to identify the complicated nonlinear dynamics including the modeling errors, while L2-gain design is used to suppress the uncertain disturbances. To obtain the optimized structural parameters in SVM, particle swarm optimization (PSO) method is incorporated. Stability analysis and simulation results demonstrate the validity of the proposed control scheme.