bluuebunny/crossref_metadata_2025 huggingface dataset:
Centrifuge Model Study of SCR Motion in Touchdown Zone
Authors: Hu Her Jia Eddie , Leung Chun Fai , Chow Yean Khow , Palmer Andrew Clennel
Published: February 2010

Steel catenary risers (SCRs) connect seabed pipelines and flow lines to floating structures used for oil and gas production in deep water. Waves and currents induce motions of the structure and the risers. Repeated horizontal and vertical interactions of SCR at the touchdown zone would induce loads on the seabed soil, and would eventually cause fatigue damage to the risers as the number of load cycle increases. The analysis of SCR fatigue damage is heavily dependent on the soil model. Soil behaviour at touchdown zone such as soil remolding, stiffness degradation and deformation of the seabed at the touchdown zone further complicate the accurate assessment of SCR fatigue damage, which is not appropriately quantified in existing design methods. This paper presents model tests simulating the repeated vertical movement of a length of riser on a geotechnical beam centrifuge at the National University of Singapore. During the tests, the pipe was subject to cyclic motion over fixed vertical displacement amplitude from an invert embedment of 0.5 pipe diameter to 3 pipe diameters into the soil. The results from centrifuge model tests show a significant progressive degradation of soil strength and diminution of excess pore water pressure as the number of load cycle increases. The increased soil strength degradation and diminishing excess negative pore water pressure during cyclic motion of the SCR reduce fatigue damage. In view of different types of environment loadings experienced by the floating platform, test results obtained from parametric studies on the effect of cyclic displacement amplitude on soil stiffness degradation will also be presented in this paper. Lastly, a simple upper bound plasticity solution will be presented and compared with the experimental result.
Physical Model for Small Scale Sandwaves Migration in the North Gulf of South China Sea
Authors: Lin Mian , Li Yong , Jiang Wenbin
Published: February 2010

The aim of this paper is to investigate the mechanism of small scale sand-wave migration. According to the environmental characteristic of the north gulf of South China Sea, a quasi-3D mechanics model has been built for simulating the small scale sand wave migration. The calculation results are shown to be consistent with the observed data in the trough of sand ridge. Considering the effect of environmental actions and sand wave features, we develop an effective formula to predict sand-wave migration. It is indicated that the physical models should be used to predict the migration of the small scale sand-wave, which is rarely dominated by wave activity.
The Effects on Process Performance of Reducing the Pressure From 36 to 1Bar in Hyperbaric MIG Welding
Authors: Fostervoll Hans , Woodward Neil , Akselsen Odd M.
Published: February 2010

Technology for remotely controlled (diverless) repair welding of subsea pipelines from 170 to 1000m water depth is being developed by StatoilHydro. The repair technology is based on a sleeve concept combined with MIG welding and the development is currently nearing completion. Technology for diver-assisted remotely controlled welding down to about 200m has been used in the North Sea for about twenty years. In order to reduce the use of divers, the deep water diverless technology is also being considered for use in shallow waters. The present work has been performed to investigate whether the deepwater welding procedure may also be used in shallow waters, and which modifications for the lower pressure conditions need to be made. Test welding has been performed in the pressure range from 36 to 1bar corresponding to 350 to 0m sea water depth to study the effect of ambient pressure upon the welding process behaviour and weld bead appearance and geometry. For the 12 o’clock welding position tested, welding parameters developed for deep water conditions also worked well for shallow water conditions down to about 2bar. It was also evident that the electrode polarity, which is negative for the deep water procedure, had to be changed to electrode positive for the lowest pressures, which coincides with conventional 1-atm MIG welding. Mechanical property testing and microstructure examinations revealed satisfactory results using the modified welding procedure.
Method for In-Situ Determination of Concentration of Components in Hydrothermal Environments
Authors: Arai Rei , Iwasa Natsumi , Nakatani Naoki , Yamazaki Tetsuo
Published: February 2010

In order to take measures against environmental impacts during the process of mining seafloor massive sulfides (SMS), it is important to measure some of the components of hydrothermal origin with high resolution in time and space on-site as well as to understand the ecosystem in the hydrothermal environments. The adoption of spectrophotometry for measuring concentrations of the components, such as H2S and Fe, is proposed in the study. It is necessary to extract the absorbance spectrum of each component from the one of seawater for the first step. Applying a determination method referred to as principal component regression (PCR), the fundamental solution is obtained.
Fatigue Design of Flowline Systems With Slug Flow
Authors: Cooper Philip , Burnett Christopher , Nash Ian
Published: February 2010

Hydraulic sizing of multiphase flowlines generally leads to significant potential for slug formation. The dynamic loads from the passage of slugs through bends are well understood. Gravity load effects associated with changing contents density are less widely recognised, but potentially more significant. Multiphase flowlines can experience several slugs every minute, which can lead to high cycle fatigue damage. Slug-induced fatigue damage has emerged as a governing design criterion in recent projects. Spans, rather than pipe bends, have become the focus of attention for slug-induced fatigue damage. These may occur at flowline terminations and spool-pieces used to connect flowlines in deepwater developments. Spans introduced by lateral buckling mitigation features can be particularly difficult to protect against slug-induced fatigue. This paper defines the slug-induced fatigue problem, and presents techniques for predicting fatigue damage during design. It describes analysis of pipeline spans, flowline connection spools and spans at buckle mitigation sleepers. Design recommendations are proposed, with suggestions for follow-up investigations to improve understanding of this phenomenon.
On the Influence of Mechanical and Geometrical Property Distribution of the Safe Reeling of Rigid Pipelines
Authors: Denniel Sylvain , Tkaczyk Tomasz , Howard Brett , Levold Erik , Aamlid Olav
Published: February 2010

The reel-lay method is a fast and cost efficient alternative to the S-lay and J-lay installation methods for steel pipelines up to 20″ in diameter. The quality of the pipeline construction is high due to onshore welding under controlled conditions. However, reeled pipelines are subject to plastic straining (up to approx. 2.3%) during installation. It is therefore common practice to specify a minimum required wall thickness to avoid on-reel buckling. For a given pipe outside diameter and bending radius, formulae developed for pipes under pure bending are generally used. In addition, to ensure the integrity of pipelines during reeling, a minimum spooling-on tension is specified and tolerances on pipe properties, such as wall thickness and yield strength, are constrained. Tolerance limits are specified to reduce the likelihood of spooling two consecutive pipe joints, which have a significant difference in plastic moment capacity (mismatch). It has been shown previously that high levels of mismatch can trigger an on-reel buckle [1]. The reliability of the reeling process is indeed related to the uniformity of pipe properties. It can therefore be supposed that more uniform pipe properties may allow reeling of thinner-walled pipes, while achieving the same level of reliability. This issue has been investigated as part of a wider evaluation of reeling mechanics and the development of procedures for optimized assessment of the process, including such aspects as the effect of the geometry of pipelay equipment [2]. This paper explores methods that can be used to evaluate the reliability of reeling a given pipe onto a given vessel. Particular focus is given on the selection of appropriate material variation parameter for the assessment. The concept of an averaging factor is introduced as a means to relate variations in individual wall thickness and yield strength measurements to the variation in pipeline cross-section, which determines the likelihood of buckling. It is suggested that, in the future, this factor could be used as a method for optimizing design for reeling when using higher quality pipe.
A Design Study of Marine Current Turbine-Generator Combinations
Authors: Lundin Staffan , Grabbe Ma˚rten , Yuen Katarina , Leijon Mats
Published: February 2010

Marine currents are an offshore source of renewable energy of increasing importance, with the development of technology for electricity generation from tidal currents or low-head river currents advancing at a quick pace. Two of the major components of a marine current power plant are the generator and the turbine. It is not sufficient to design these components separately, but a system approach, where the power plant is seen as one entity, must be taken to achieve best overall efficiency. In the present paper, the performance of three different combinations of direct-driven permanent magnet generator with cross-stream axis marine current turbine is examined numerically under the variation of water flow speed. The design case chosen is that of a shallow river or tidal channel, where the cross-sectional area limits the physical size of the power plant. The units are designed for a power output of 10 kW at a water current velocity of 1 m/s. Turbines for three different rotational speeds are considered, each in combination with a corresponding generator. The three turbine-generator systems are designed according to similar design criteria to allow for comparisons. The turbines are modelled using an in-house code, based on the double multiple streamtube model. Corrections are made due to the finite aspect ratio and tip losses of the blades. Experimental data for the lift and drag coefficients for different Reynolds numbers are used in the model. The generators are modelled using a FEM tool that has been validated with experimental results. The three generators are designed for the same nominal voltage and with a low load angle to allow for overload operation. The overall performance of each of the three systems is studied under varying flow velocity. The main conclusion is that all three machines exhibit essentially the same performance behaviour, which means that the choice of nominal operational speed for a power plant will not be a major design constraint. Turbines with higher rotational speed allow for a more compact generator design within the limits of the design parameters used in this study. However, this also entails certain mechanical constraints on the turbine. Due to the restricted cross-sectional area in the channel, it is clear that at least one of the three systems would have to be placed with the axis of rotation in a horizontal rather than vertical position.
Flow Around the Free Bottom of Fish Cages in a Uniform Flow With and Without Fouling
Authors: Gansel Lars C. , McClimans Thomas A. , Myrhaug Dag
Published: February 2010

This paper explores the flow around fish cages in a uniform flow with the focus on the flow patterns close to the bottom of the models. Towing tests were conducted with six straight cylinders with the prosities 0%, 30%, 75%, 82% and 90%, two cylinders with an inclination of 12.5 degrees and the porosities 0% and 75% and two cylinders with an inclination of 25 degrees and the porosities 0% and 75%. The models all had a height-to-diameter ratio of 3 and were made from metal mesh. The Reynolds number was 5000 based on the diameter of the models and from 15 to 300 based on the diameter of individual strings of the mesh for all tests. Particle Image Velocimetry (PIV), a non-intrusive optical technique, was used to analyze the flow around the models in the plane of symmetry through the center of the cylinders. The porosities of 82%, 75% and 60% correspond to those of a clean fish cage netting in Norwegian Salmon farming with no fouling, light fouling and heavy fouling, respectively. The inclinations of 12.5 degrees and 25 degrees reflect the inclination of the net of a commercial fish cage in a slow and a fast current, respectively. The Reynolds number of the strings was within the range of Reynolds numbers occurring on fish cages along the Norwegian coast. The results from this study are discussed with respect to the flow around and through the same models at identical Reynolds numbers. It is shown that the inclination of the net cage and fouling of the netting have major effects on the flow pattern around fish cage. The flow around and through net cages defines the water exchange within fish cages and the distribution patterns of particles and nutrients released from a net-pen. The information provided in this study can be valuable for the fish farming industry, as the decrease of the porosity due to fouling, as well as the deformation of the netting of fish cages, can be controlled by fish farmers.
Fault Detection for Shipboard Monitoring and Decision Support Systems
Authors: Lajic Zoran , Nielsen Ulrik Dam
Published: February 2010

In this paper a basic idea of a fault-tolerant monitoring and decision support system will be explained. Fault detection is an important part of the fault-tolerant design for in-service monitoring and decision support systems for ships. In the paper, a virtual example of fault detection will be presented for a containership with a real decision support system onboard. All possible faults can be simulated and detected using residuals and the generalized likelihood ratio (GLR) algorithm.
Offshore Pipelay Operations From a Control Perspective
Authors: Jensen Gullik A. , Breivik Morten , Fossen Thor I.
Published: February 2010

This paper considers the problem of installing offshore pipelines by means of pipelay vessels from a control perspective. Specifically, the paper is divided into two main parts, where the first part gives a thorough introduction to the fundamentals of pipelay operations and the challenges and possibilities associated with such operations. The second part then suggests how pipelay operations can be further automated by augmenting the manually-operated dynamic positioning (DP) systems of today with sophisticated guidance functionality that may improve operational precision and safety by relying on advance mathematical models.
AGaPaS: Autonomous Galileo-Supported Rescue Vessel for Persons Overboard
Authors: Clauss Gu¨nther F. , Kauffeldt Andre´ , Otten Nils
Published: February 2010

For any seagoing mission such as rescue missions, coast guard or pilot duties, crew safety is a key parameter. However, in extreme situations there is always a residual risk for crew members to go overboard. In this case the probability of survival is relatively low until today. This paper presents the joint research project “AGaPaS”, which is aimed to significantly raise the chances of survival for a drifting person. The main objective is to develop a self activating, partially autonomously operating rescue system being able to search, find and rescue people gone overboard. The project accounts for all aspects of the rescue process including: • the life jacket equipped with various sensors and a radio transmitter; • the construction of the rescue vessel; • a real time positioning system for the rescue vessel based on Galileo; • a recovery unit for the person overboard; • a recovery system for the rescue vessel; and • the integration into a conventional bridge system. A crucial part of the rescue process is the recovery of the remotely operating vessel including the retrieved person by a mother ship. Similar problems have already been investigated by the Technical University Berlin before [1], [2]. Whereas launching operations are less critical, the recovery of a boat, especially in severe weather, is a challenging task. Therefore, strength analyses, as well as relative motions are to be systematically investigated using model tests and numerical simulations considering a coupled system consisting of the mother ship with an articulated recovery system and the rescue vessel. Furthermore, the manoeuvrability of the rescue system is evaluated at high sea states. As a result of the research project a fully operational testing model at full scale is designed and built.
Effects of Girth Weld on the Local Buckling Response of Conventional Grade Pipelines
Authors: Barrett John , Kenny Shawn , Phillips Ryan
Published: February 2010

Pipeline structural integrity is a critical component of pipeline design in extreme environmental conditions. Severe loads may be an issue in pipeline design if differential ground movement is prevalent in the design region, e.g. ground faulting and permafrost heave and settlement. Iceberg or ice keel interaction and large seabed deformations interacting may also be a critical design integrity issue for offshore pipelines in ice environments. Numerical finite element modelling procedures have been developed to assess the bending moment and strain capacity of several pipelines over various typical pipeline parameters. This study looks at the effects of girth-weld imperfection on the bending response of welded pipelines. Limited guidance is provided by pipeline design standards, for example DNV OS-F101 and CSA Z662, as to how to account for girth weld effects on the local buckling response. This paper investigates girth weld effects across a range of practical design parameters. Calibration of the numerical analysis was performed using available data, from full-scale tests and finite element analysis, for girth welded pipes in order to obtain confidence in the numerical procedure. The significance of girth weld effects was to reduce the peak bending moment capacity by 10% whereas strain capacity was reduced by as much as 35% based on the degree of girth weld imperfection. Girth weld effects have been acknowledged in industry, however, further research and physical testing is required to fully understand the problem, as shown in this paper.
Waves Run-Up and Overtopping Simulations Using Lagrangian Blocks
Authors: Tan Lai Wai , Chu Vincent H.
Published: February 2010

Wave run-up and overtopping of coastal structures are simulated using Lagrangian Blocks on Eulerian Mesh (LBEM). In the LBEM simulations, the blocks carry the mass and momentum. The movement of the blocks is calculated in a Lagrangian reference frame. The water depth defined by the volume blocks is non-negative. The wave fronts across the wet-and-dry interface are simulated by the block method without interruption by the oscillation problem that has limited the applicability of many existing computational methods. To evaluate the accuracy of the LBEM method in this paper, simulations are carried out for (i) the dam-break waves, (ii) the wave run-up on plane beach, and (iii) the overtopping of solitary waves over levee. The simulations of the dam-break wave have produced excellent agreement with the exact solutions by Ritter [1] and Stoker [2], and the semi-analytical solution by Sakkas and Strelkoff [3,4]. The simulations of the wave run-up on plane beach agree with the experimental data and the nonlinear theory of Synolakis [5]. The simulations of wave overtopping trapezoidal dike agree with the finite-volume simulations of Stansby [6]. The results have demonstrated the accuracy of the LBEM method and the versatility of the method for general wave simulations over variable terrain.
Evaluation of Shear Area of DWTT Fracture Surface With Instrumented System
Authors: Ahn Seong Soo , Ham You Sun
Published: February 2010

The test method to evaluate fracture toughness can be divided by the loading type to specimen. A static load is given to specimen for testing KIC, JIC, CTOD, etc. while a dynamic load is given to those for testing Charpy impact test, DWTT, etc. In case of fracture toughness tests with static loading, the data of load and displacement should be gathered during test because they were driven from fracture mechanics. In case of fracture toughness tests with dynamic loading, however, we don’t gather any data during specimen broken. We measure an absorbed energy for fracture and shear area from fracture surface after Charpy impact test and a shear area from fracture surface after DWTT. To analyze the results from these toughness tests of dynamic loading type with using fracture mechanics, recently, an instrumented system is installed to these dynamic loading test machines. An instrumented system can measure load and displacement during specimen broken. On the displacement-load curve made with data from an instrumented system, in general, the area in the region before peak-force is the energy for crack initiation while area in the region after peak-force is that for crack propagation. Meanwhile, it takes a long time and effort to evaluate the shear area from both fracture surfaces after Charpy impact test and DWTT test. For Charpy impact test, the method how to calculate the shear area with the information from a load-displacement curve has been studied for a long time. So the method for it is well established and known. For DWTT, however, the method how to calculate the shear area from a load-displacement curve was not known well. In this paper, a shear area could be calculated from an instrumented data without any more time or effort in addition to test. A shear area could be expressed as a function of total absorbed energy, fractured area, maximum force, time at 50kN and time at maximum force. Especially, the material with shear area more than 85% could be distinguished from that with shear area less than 85% because the transition curve of DWTT changes dramatically around 85% shear area.
SCR-Seafloor Interaction Modeling With Winkler, Pasternak and Kerr Beam-on-Elastic-Foundation Theories
Authors: de Almeida Barros Persio Leister , Pavanello Renato , Mesquita Euclides , Morooka Celso Kazuyuki
Published: February 2010

This paper discusses the use of three analytical models for the SCR-soil interaction analysis. Analytical derivations for Winkler, Pasternak and Kerr models are presented. The effects of the adopted model on displacements and stresses near the riser touchdown point are addressed. Comparisons with the results from a continuous soil model calculated with finite elements are also presented. In the regions with large displacement gradients, the Kerr model, which considers the influence of the elasticity from neighboring area, presents the best agreement with the 3D Finite Element model.
Improved Prediction of External Pressure Collapse of Seamless Pipe
Authors: Navarro Josef , Cooper Philip
Published: February 2010

Seamless pipe typically features well controlled average wall thickness around its cross-section, but is prone to significant local thickness variation arising from the manufacturing process. Pipeline design codes, such as DNV OS-F101, provide little guidance on how to treat thickness variation whilst designing for collapse resistance. Standard practice is to consider minimum wall thickness across the whole cross-section, an assumption that two dimensional finite element simulations have proven conservative. This justifies the need for an improved design method. A program of simulations has been carried out to investigate the effect of wall thickness variation on collapse pressure. A modification to the DNV OS-F101 collapse design equation using average wall thickness over the whole crossection together with a fabrication factor is presented based on the results of this study. The fabrication factor de-rates the collapse pressure according to the amount of thickness variation present. The correction has been calibrated for thickness variations up to the maximum permitted by typical line pipe specifications. A number of FE trials demonstrate that the proposed formula predicts simulated collapse pressures with 98% accuracy. Adopting this method could provide significant wall thickness savings for deep water flowlines which in turn could lead to a reduction in steel costs and transportation and lay vessel requirements.
Investigation of the Horizontal Drifting Effects on Ships With Forward Speed
Authors: Zhang Sheguang , Weems Kenneth M. , Lin Woei-Min
Published: February 2010

This paper is concerned with the horizontal drifting effects on ships moving with forward speed in waves. The ship configurations can be a single or multiple ships operating alongside one another. In close-in position (CIP) ship operations, the position of the ships often needs to be maintained relatively steady by means of Dynamic Positioning (DP) systems that incorporate thrusters or control surfaces. In developing such systems, especially those using wave feed-forward (WFF) control algorithms, the mean or low frequency drift force and moment in the horizontal plane are required to set up the control loop. The present study uses the Large Amplitude Motions Program (LAMP), a time domain, 3-D panel code for the prediction of motions and wave loads for a ship or ships in waves, to calculate the drifting forces in the horizontal plane for ships moving with or without forward speed. Since the drifting effects are second order in association with the incident wave amplitude, the formulation in LAMP has been expanded to account for the additional second order terms. This paper presents the mathematical formulation — including the second order drifting effects, its numerical implementation in LAMP, and the results from several validation cases — for a single body with or without forward speed. The analysis of the horizontal drifting effects on two-ship configurations with or without a DP system will be conducted in a future study.
Critical Situations of Vessel Operations in Short Crested Seas: Forecast and Decision Support System
Authors: Clauss Gu¨nther F. , Kosleck Sascha , Testa Daniel
Published: February 2010

The encounter of extreme waves, extreme wave groups or of unfavourable wave sequences is a dangerous thread for ships and floating/fixed marine structures. The impact of extreme waves causes enormous forces whereas the encounter of an unfavourable wave sequence — not necessarily extreme waves — can arouse critical motions or even resonance, often leading to loss of cargo, ship and crew. Thus, besides a well thought-out maritime design, a system detecting critical incoming wave sequences in advance can help avoiding those dangerous situations, increasing the safety of sea transport or offshore operations. During the last two years (see [1] and [2]) a new system for decision support on board a ship or floating/fixed marine structure named CASH — Computer Aided Ship Handling — has been introduced. The preceding papers showed the step wise development of the main components of the program code — 3D–WAVE FORECAST and 3D–SHIP MOTION FORECAST. These procedures provide a deterministic approach to predict the short-crested seas state within radar range of the ship, as well as resulting ship motions in 6 degrees of freedom. Both methods have been enhanced with special focus on the speed of calculation to ensure a just-in-time forecast. A newly developed component is the ADAPTIVE 3D-PRESSURE DISTRIBUTION. This method calculates the pressure distribution along the wetted surface of the ship hull using a newly developed stretching approach [3]. With the end of the joint project LaSSe — Loads on Ships in Seaway (funded by the German Government) the paper presents the CASH-system, giving the possibility to detect critical situations in advance. Thus not only decision support on board a cruising ship can be provided, but also time windows for offshore operations are identified well in advance.
CFD as a Design Tool for Hydrodynamic Loading on Offshore Structures
Authors: Atluri Sampath , Magee Allan , Lambrakos Kostas
Published: February 2010

Time-domain numerical integration of the rigid body equations of motion is a popular choice for analyzing the global motions of a single or multi-module floating platform. Potential flow theory cannot accurately account for all the hydrodynamic forces on certain components of the platform. However, for practical analysis, these members can be modeled as Morison members in the time-domain simulations. Computational Fluid Dynamics (CFD) can be used to calculate Morison coefficients for the given flow conditions on the exact geometry of the member. This paper presents the results from CFD simulations performed on several individual components of a floating platform (like heave plates, truss members etc.,) in realistic environment conditions. The procedure used for extracting the linear and non-linear coefficients from the total calculated hydrodynamic force is also explained. Results from CFD are compared to existing published experimental results. Differences between full-scale and model-scale results will be emphasized where important. Some of the advantages of using CFD as opposed to model tests are highlighted.
Development of Fatigue Resistant Heavy Wall Riser Connectors for Deepwater HPHT Dry Tree Riser Systems
Authors: Sches Ce´line , Shilling Roy , Shademan Steve , Massaglia Jacky , Payne Mike , Gateaud Arnaud
Published: February 2010

BP is currently looking at the next generation of dry tree development projects in the US Gulf of Mexico (GOM) deepwater operating region. Some HPHT wells call for the design of 15 ksi or greater riser systems with sour service requirements. Over the last 10 years, NACE compliant high strength steels (HSS) together with fatigue resistant threaded and coupled connectors have proved to be reliable technical solutions top tensioned riser (TTR). Today their light weight and increased performance capabilities enable cost effective dry tree systems for water depths up to 10,000 feet. In the frame of BP xHPHT development projects, the design and qualification of Heavy Wall Threaded and Coupled (T&C) riser connectors for TTR applications was launched. Comprehensive development programs were built, involving numerous design variations, Finite Element Analysis evaluation and optimization — including parametric studies —, followed by intensive full scale static and fatigue testing campaigns. Those developments benefited from the design and field running experience accumulated with previous TTR projects, where innovative fatigue enhancement techniques and premium fatigue compliant sealing devices were engineered. In addition, combined static, dynamic and corrosion testing of base material is being conducted to assess and qualify the fatigue resistance of HSS up to 140 ksi under those conditions. This paper will present results and conclusions from these developments and will report the performance levels reached by Heavy Wall High Pressure T&C riser connectors and the associated high strength base material. Forward work plans on riser connectors for xHPHT, SCR and flowlines will also be discussed.
FEA of a Laminate Internal Buckle Arrestor for Deep Water Pipe-in-Pipe Flowlines
Authors: Wang Haoyu , Sun Jason , Jukes Paul
Published: February 2010

Development of deepwater oil reservoirs has been undertaken in the Gulf of Mexico (GoM) where flowlines are installed in water depths in the vicinity of 2,740m (9,000ft). Preventing the propagation of local collapse/buckle failures is one of the key engineering design limit states that is defined in the industry codes to ensure the pipeline integrity. Deep-water buckle propagation is almost unavoidable as the wall thickness selection cannot be directly driven by the buckle propagation limit state. Field data indicates that once a buckle happens, the flowline could collapse for many kilometers instantly. Buckle propagation could cause substantial economic impact if left uncontrolled. For Pipe-in-Pipe (PIP) flowline, due to lack of pressure differential, the jacket pipe is a fragile component in terms of buckle propagation. It is crucial to prevent any possible local buckling during the flowline installation and during the entire operational lifetime. One way to stop buckle propagation is to utilize buckle arrestors of various types. Successfully designed buckle arrestors can contain such disasters to a limited pipeline section. Internal buckle arrestors are a relatively new solution for PIP systems being investigated by the industry. As it is installed in the annulus of PIP, it becomes a preferred choice since it fits all types of installation methods. The objective of this paper is to present the design and finite element analysis (FEA) of a laminate type internal buckle arrestor, and to investigate the effectiveness of this innovative buckle arrestor design for deepwater flowline. Sensitivities of key design parameters are explored with the purpose of guiding detailed mechanical design.
Research on Stability of Crawler System for Deep Sea ROV
Authors: Inoue Tomoya , Katsui Tokihiro , Murakami Hisataka , Tahara Junichiro
Published: February 2010

A deep sea ROV is desired to be light from the viewpoints of reducing a tension on an underwater cable and possessing the adequate movability by thrusters in water. On the other hand, when moving by a crawler system on the seabed, such a lightweight will influence on its movability characteristics. As an initial investigation experiments using an actual ROV were conducted in a water tank. And it was observed that the ROV ran in wheelie in some cases and almost fell down in extreme case in spite of the fact that it could run stably on land. In order to clarify the results fundamental theory of stability of the ROV in steady running is presented. The theory gives the discriminant chart of stable running for the combination of the center of gravity and the center of buoyancy. Experiments using a model were conducted to verify the theory. In order to increase the stable area and also to change meaningly the center of gravity, this paper proposes a method to virtually increase the weight and to change the center of gravity by using thrusters. And preliminary experiments were conducted to confirm its advantageous effect.
Simulation of Flow and Motion of Lifeboats
Authors: Mo̸rch Hans Jo̸rgen , Peric´ Milovan , Schreck Eberhard , el Moctar Ould , Zorn Tobias
Published: February 2010

Lifeboats are important for safety of passengers and crew on floating vessels and offshore platforms. They need to be designed so that evacuation can be performed quickly and safely in case of emergency. This requires that the lifeboat is not damaged during water entry, that it moves afterwards away from the dangerous area, and that accelerations experienced by occupants do not exceed allowable limits. In this paper, the use of numerical simulation is proposed as a tool for design and optimization of lifeboats. While experimental studies will still be needed to validate the final design, the use of simulation can greatly increase the number of parameters relevant for structural integrity and wellbeing of occupants that can be studied in the design process. In a simulation, full size and realistic operating conditions can be realized, and the computational effort is affordable even for a small design group. The comparisons with experimental data performed so far indicate that the accuracy of simulation is comparable to that of an experiment.
The Impact of Flexbarrier Ingress on Flexlok Stress
Authors: Lu Jing , Ma Frank , Tan Zhimin , Sheldrake Terry
Published: February 2010

An unbonded flexible pipe typically consists of multiple metallic and thermoplastic layers, where each layer is designed to provide a specific structural function. The burst resistance against the internal pressure in an unbonded flexible pipe is provided mainly by its Flexlok layer. The Flexlok is made by helically-wound steel wires, with neighbouring wires interlocking each other. Beneath the Flexlok is the Flexbarrier, a polymer layer, acting as the boundary for conveyed fluids. The internal pressure is passed onto the Flexlok through the Flexbarrier layer. Under internal pressure, the Flexbarrier can creep into the gaps between Flexlok wires. Theoretically, the polymer material ingress could reduce the flexibility of the Flexlok due to premature lock-up between Flexlok wires and subsequently increase the stress levels. This study presents a 3D finite element analysis model developed to quantify the stress elevation in the Flexlok wire, caused by the Flexbarrier layer ingress. In terms of Flexlok gap size distribution, both nominal and worst case scenarios are studied. In the nominal scenario, the Flexlok gap sizes are evenly distributed. In the worst case scenario, the Flexlok gap is assumed to be completely closed at one position while the gaps at the neighbouring positions are twice the nominal size. Flexbarrier ingress with different temperatures is also studied. Conclusions are obtained by analyzing the simulation results. The work presented is part of an ongoing research and development project.
A Good Practice of Coastal and Ocean Space Utilization for Redevelopment of Fishing Village in Case of South Korea and Japan
Authors: Jung Wonjo , Kondo Takeo , Yamamoto Kazukiyo , Lee Hanseok
Published: February 2010

The aim of our research was to investigate the characteristics of fishing-village development work in Japan and South Korea. After analyzing individual success cases, we identified success factors and propose considers for more successful fishing-village development work in the future. The success cases were selected according to criteria such as the degree of contribution to an increase in income of the fishing village, the degree of contribution to an increase in consumption of marine products using local natural resources, the number of tourists to the village, and so forth. For this purpose, we conducted interviews with persons concerned and utilizing administrative materials.
Progressive Drifting of Floating Wind Turbines in a Wind Farm
Authors: Suzuki Hideyuki , Kurimoto Masaru , Kitahara Yu , Fukumoto Yukinari
Published: February 2010

A wide range of platform types have been investigated for a floating wind turbine. Most of the research projects on a floating wind turbine assume that a land based wind turbine is to be installed on a platform with minimum modification to reduce the overall cost. For this reason, allowable limit of a motion of wind turbine is limited to lower value, for example, five degrees for static inclination and one to two degrees for pitching motion. So far analysis and design of motion characteristics of the platform have been main research concern. One key research area less focused is floating platform related risk. If the wind energy would be one of the major sources of power supply, wind farms which are comprised of large number of floating wind turbines must be deployed in the ocean. Wind turbines will be closely spaced in a wind farm so that installation cost should be minimized. In such an arrangement, a wind turbine accidentally started drifting has some possibility to collide or contact with the moorings of neighboring wind turbines and might cause progressive drifting of wind turbines. This paper present investigation of scenario of progressive drifting of floating wind turbines and evaluate risk of the scenario. Quantitative risk of several arrangements of wind farms is estimated. Effect of arrangement of wind turbines in a wind farm and safety factor used in design moorings is discussed.
Fatigue Life Prediction Due to Slug Flow in Extra Long Submarine Gas Pipelines Using Fourier Expansion Series
Authors: Casanova Euro , Pelliccioni Orlando , Blanco Armando
Published: February 2010

Some offshore gas production fields require transporting of production fluids through very long submarines pipelines, without a previous separation process. In these cases, a slug flow pattern may develop for some production conditions. Condensate slugs traveling in the pipeline, act as moving loads for the piping structure, especially for the unsupported pipe spans which can be of even hundreds of meters long, due to irregular sea bottom, therefore producing a dynamic response of the pipeline that in some cases may significantly reduce its fatigue life. In this work a previously presented model [1], which combines fluid equations for predicting slug characteristics and a structural finite element model of horizontal pipelines transporting slugs, is modified for reducing computational cost and to adapt fatigue life calculations to the case of submarine piping. In order to calculate maximum amplitudes of the dynamic response without a time integration scheme, it is considered that traveling slugs produce periodical loads in time for every spatial point of the pipeline, and consequently these loads may be expressed by means of Fourier expansion series. With these assumptions, a more realistic fatigue calculation for a diversity of pipelines conditions is obtained. Results show that for this improved model computational time is dramatically reduced, without a lost in precision, when compared to the previous model requiring a time integration process.
Hydrogen Induced Stress Cracking (HISC) in Duplex Stainless Steels: DNV-RP-F112, Design of Duplex Stainless Steel Subsea Equipment Exposed to Cathodic Protection
Authors: Wa¨stberg Stig , Solno̸rdal Morten , Heiberg Gustav , To¨rnqvist Rikard , Vargas Pedro M.
Published: February 2010

Both 22Cr and 25Cr duplex (ferritic-austenitic) stainless steels have been extensively used for subsea equipment. In general the experience is good but some significant failures have occurred where Hydrogen Induced Stress Cracking (HISC) have been identified as a contributing factor. Because of these failures there was identified a need within the offshore industry for a design guideline treating HISC as a failure mode and reflecting best practice based on today’s knowledge, experience from in-service failures and recent research. The paper starts with a brief review of some of the failures and the main results from the comprehensive test program in the HISC JIP conducted in cooperation between Sintef and DNV. The JIP is supported by several major oil companies, subsea contractors and material suppliers and constitute the main scientific background for the recently issued Recommended Practice, DNV-RP-F112, Design of Duplex Stainless Steel Subsea Equipment Exposed to Cathodic Protection (October 2008).
Predictions of Ecological Effects of Artificial Upwelling in Semi-Enclosed Bay and Enclosed Lake
Authors: Sato Toru , Mizumukai Kentaro , Lin Chun-ju , Tabeta Shigeru , Kitazawa Daisuke
Published: February 2010

An apparatus, which mixes waters in upper and lower layers in density stratification and discharges the mixture at the middle depth, has made a remarkable success in enhancing water quality for ecosystems in a small semi-enclosed bay and an enclose lake in Japan. In this study, we conducted numerical simulations by using a three-dimensional tidal current model and an ecosystem model to predict the effects of the apparatus in two different waters: a larger semi-enclosed bay and an enclosed lake. Isahaya Bay in Ariake Sea was chosen as the former case to see how effectively the apparatus can reduce oxygen-deficient water, and Feng-Shan dam-lake located in South Taiwan represents the latter case, where we are interested in the effect of the apparatus on reduction of Microcystis aeruginosa, which is harmful blue-green alga and causes environmental problems in the neighbouring area. As a result, it is suggested that the apparatus averages temperature of water vertically in its vicinity and this increases phytoplankton in the lower layers resulting in reducing oxygen-deficient water in Isahaya Bay. However, it is not very effective in reducing the blue-green alga in the Taiwanese lake because the temperature in the lower layer is still preferable for the alga even after the mixing.
A Numerical Investigation of the Hysteresis Effect on Vortex Induced Vibration on an Elastically Mounted Rigid Cylinder
Authors: Wanderley Juan B. V. , Sphaier Sergio H. , Levi Carlos
Published: February 2010

The hysteresis effect on the vortex induced vibration (VIV) on a circular cylinder is investigated by the numerical solution of the Reynolds average Navier-Stokes equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates and the k-ε turbulence model is used to simulate the turbulent flow in the wake of the body. The cylinder is supported by a spring and a damper and free to vibrate in the transverse direction. In previous work, numerical results for the amplitude of oscillation and vortex shedding frequency were compared to experimental data obtained from the literature to validate the code for VIV simulations. In the present work, results of practical interest are presented for the power absorbed by the system, phase angle, amplitude, frequency, and lift coefficient. The numerical results indicate that the hysteresis effect is observed only when the frequency of vortex shedding gets closer to the natural frequency of the structure in air.
Modeling Two Phase Flow Inside an Electrical Submersible Pump Stage
Authors: Barrios Lissett , Prado Mauricio Gargaglione
Published: February 2010

Dynamic multiphase flow behavior inside a mixed flow Electrical Submersible Pump (ESP) has been studied experimentally and theoretically for the first time. The overall objectives of this study are to determine the flow patterns and bubble behavior inside the ESP and to predict the operational conditions that cause surging. The theoretical study includes a mechanistic model for the prediction of the flow behavior inside the pump. The model comprises a one-dimensional force balance to predict occurrence of the stagnant bubbles at the channel intake. This model depends on two important variables, namely the stagnant bubble size and the bubble drag coefficient. The bubble size has been measured and a physically based correlation is presented. A new correlation for the drag coefficient is proposed as a function of rotational speed and Reynolds number. The model enables the prediction of the operational envelope of the ESP, namely the transition to surging.