bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Life Assessment of Offshore Patrol Vessel
Authors: Samanta Asokendu , Kurinjivelan P.
Published: February 2010

Fatigue is a phenomenon, which needs to be considered in the present day’s vessel design. The welded joints are particularly affected by the fatigue damage due to high stress concentrations caused by the metallurgical discontinuities present in the weld. For oil tankers and bulk carriers adequate guidelines for the fatigue strength assessment have been established by the classification societies. But for navy vessel, like offshore patrol vessel, the design guidelines for the fatigue strength analysis are not widely available. In the present paper, an attempt has been made to calculate the fatigue life of offshore patrol vessel (OPV). In general five stages of work is involved in calculating fatigue life of any ship structure. These are, load calculation, nominal and hot spot stress computation, long-term stress distribution, selection of S-N curve and the fatigue damage calculation. In the present study, the wave loads are obtained by the rule based estimation. The finite element analysis with the submodeling approach has been used to get the hot spot stress at critical locations. The two-parameter Weibull curve has been used to get the long-term distribution of stress. And at the end, the fatigue damage and the fatigue life have been computed using the Palmgren-Miner linear cumulative damage theory at the critical locations of the vessel.
Set-Up of Large Diameter Driven Pipe Piles in Deepwater Normally Consolidated High Plasticity Clays
Authors: Dutt Rathindra N. , Ehlers Clarence J.
Published: February 2010

This paper will show on the basis of hindcast wave equation analysis that soil-pile set-up for large diameter driven pipe piles in clay is faster than what the current state-of-practice utilizes for design. Results of hindcast wave equation analyses utilizing observed blowcounts and hammer energy records from two deepwater sites, one in West Africa and the other one in the Gulf of Mexico, are presented to support this conclusion. For offshore structures, this increase in the rate of soil-pile set-up reduces foundation/anchor costs or reduces the waiting time until topsides can be set on the structure or mooring lines can be hooked up to anchors. Hindcast wave equation analyses were performed utilizing the observed blowcount and hammer energy information from two deepwater West Africa and Gulf of Mexico locations where pile driving was stopped and then restarted after a few days. This is a trial and error method of analysis where the soil resistance to driving (SRD) was varied until a good match was obtained between the observed blowcount at the startup of driving and the reported hammer energy using the GRLWEAP wave equation program. The set-up time for the piles ranged from about one to twelve (12) days and the piles ranged from 2134 mm to 2743 mm diameter open-ended pipe piles. The soils generally consisted of normally to slightly overconsolidated highly plastic clays. For the purpose of computing pile set-up, the ultimate pile capacity was computed using the API RP 2A (2000) guidelines. Results show that 60 to 80 percent of the ultimate pile capacity is mobilized in about 7 days, and the extrapolation of the set-up model suggests that the set-up is almost complete in about 60 days.
Design of the Greater Plutonio Riser Tower
Authors: Djia Francis , Zimmermann Charles , de la Cruz Daniel , de Roux Gre´goire , Legras Jean-Luc
Published: February 2010

The Greater Plutonio Riser Tower is installed in Angola in a Water depth of 1310 meters (4300 feet), and gathers 11 risers (two production loops, three water injection, one gas injection and three gas lift lines) and one gas lift umbilical. The total mass of this unique riser system is more than 4000 tons. This paper aims at describing the main challenges associated to the Riser Tower design. After a description of the riser tower main elements (flexible jumpers, buoyancy tank, guiding frames welded to the core pipe, gas lift manifolds...), numerical analyses are presented (in place extreme and fatigue analyses). Assessment of the friction developed by the risers against the guiding frames and associated effects on the global behaviour of the riser tower are detailed. Various sources of conservatism, lessons learned and ways of improvements are also shared for future projects.
Stability of a Trial Quay Wall of Large Diameter Cylinders
Authors: Zhang Jian-Min , Zhang Jianhong , Wang Gang , Chen Yang
Published: February 2010

This paper presents a study of stability of a trial quay wall of large diameter cylinders at the Yangshan Port, China. Stability analysis of the quay wall during construction is carried out using finite element method. The results of the analysis indicate that a turnover failure is potential for the single cylinder subjected to a five year design wave action. The case when the cylinder is empty is the critical situation during construction. Filling the cylinder right after the installation is an effective way to increase the stability. After the quay wall has been formed by joining the single cylinders, the safety against overturning is reevaluated. The factor of safety of the quay wall is assessed to be 1.5 under a fifty year design wave action.
Assessing the Role of Environmental and Regulatory Issues on Offshore Renewable Energy Projects in the United States
Authors: Daughdrill William H.
Published: February 2010

This paper will describe some of the key environmental and regulatory issues affecting development of offshore renewable energy projects in the United States. Offshore wind, wave, tidal current, and ocean thermal energy conversion (OTEC) projects all have unique environmental and social issues that must be addressed to the satisfaction of federal, state, and local authorities. This paper examines the existing federal regulatory schemes applicable to offshore renewable energy development in the United States including a discussion of an on-going jurisdictional debate between agencies at the U.S. federal government level. The various permitting processes for offshore renewable energy projects all involve an examination of the potential environmental and social/human effects of each proposed project. Typically, the agency with primary permitting authority must prepare an environmental impact statement (EIS) or equivalent document that includes a transparent process that encourages the participation of the interested public and other affected stakeholders. While acknowledging the importance of social/human impact issues, this paper will focus primarily on the potential physical and biological effects from offshore renewable energy projects including a discussion of the uncertainty that surrounds predicting the impact of new or innovative technologies. The U.S. Department of Interior, Minerals Management Service (MMS) recently published a programmatic environmental impact statement (EIS) that includes 52 “best management practices” for reducing environmental and social impacts from offshore alternative energy projects. Finally the paper will examine the important role of environmental monitoring and adaptive management in informing regulators and developers of potential adverse impacts and adapting project design and operations to avoid or minimize these effects.
On the Resonance-Motion-Free SWATH (RMFS) as an Oceangoing Large Fast Platform
Authors: Yoshida Motoki , Kihara Hajime , Iwashita Hidetsugu , Itakura Hiroshi , Bao Weiguang , Kinoshita Takeshi
Published: February 2010

The speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely for oceangoing large fast ship, because of the strict time-punctuality and high value of the cargo. In the present work, comparison of seaworthiness properties, such as no speed reduction and absolutely no slamming, is made among four types of ship hulls, i.e. mono-hull, ordinary SWATH, trimaran and Resonance-Motion-Free SWATH (RMFS). The last one can be regarded as a special type of catamaran. As a result of extremely small water plane, the restoring moments are negative for the RMFS hull, which leads to free of resonance in the motion responses. Experiments in towing tank and calculations are carried out to examine hydrodynamic forces and motion responses in waves. Calculations are generally based on potential theory modified by adding the viscous effects and including fin lifts. The results of RMFS are compared with those of mono-hull ship, ordinary SWATH ship as well as trimaran ship. The heave motion responses of RMFS are very small in comparison with those of other ship hulls. On the other hand, the pitch motion responses of RMFS are considerably small in comparison with those of mono-hull or trimaran, but are not as small as expected in comparison with those of ordinary SWATH. The reason is that a soft spring system is applied in experiments, to replace the proportional control action supplied by the fin lift. The spring system can not make use of the advantage of the negative restoring moment, which is a characteristic of RMFS. Accordingly, a new control system of ship motion by means of the lift force from fins should be developed.
Study on Separation Performance of the Compound Hydrocyclone Under Self-Vibration Condition
Authors: Li Sen , Wang Zunce , Lv Fengxia , Xu Yan , Zhang Jinlong
Published: February 2010

The compound hydrocyclone, combining merit of both dynamic hydrocyclone and hydrocyclone, is an efficient separator. Flow field and separation performance are affected by unavoidable vibration, when it operates. This paper discusses vibration of the compound hydrocyclone using modal analysis. Characteristics of modal parameters such as natural frequency, damping and mode of vibration are obtained. The main objective of this work is to investigate the effect on flow field and separation performance caused by the behavior of vibration. The finding showed the flow rate and running of the electric motor not only cause the vibration but also affect principal factor of the separation performance. This work provided a foundation for stable operation of compound hydrocyclone.
Extreme Load Predictions for Floating Offshore Wind Turbines
Authors: Jensen Jo̸rgen Juncher
Published: February 2010

An effective stochastic procedure for extreme value predictions related to wave and wind induced stochastic loads is applied to a tension-leg concept for floating offshore wind turbines. The method is based on the First Order Reliability Method (FORM) and as the procedure makes use of only short time-domain simulations all kinds of non-linearities can be included. The procedure has been used previously for wave induced loads and is in this note extended to combined wave and wind loads.
Vortex-Induced Vibration of Catenary Riser: Reduced-Order Modeling and Lock-In Analysis Using Wake Oscillator
Authors: Srinil Narakorn , Wiercigroch Marian , O’Brien Patrick , Younger Rae
Published: February 2010

A novel reduced-order fluid-structure interaction model for the vortex-induced vibration of catenary riser subject to the ocean current is developed and systematically investigated. The semi analytical-numerical approach accommodates multi-mode nonlinear dynamic responses and accounts for the effect of varying initial curvature of the inclined flexible cylinder. The geometrically nonlinear equations of riser motion are based on a pinned-pinned beam-cable model with bending and extensibility stiffness. The empirical hydrodynamic model is based on a distributed van der Pol wake oscillator which approximates the space-time varying fluid forces. In this initial study, the incoming current flow is assumed to be steady, uniform, unidirectional and perpendicular to the riser initial plane of curvatures. Thus, emphasis is placed on evaluating the riser cross-flow responses due to fluctuating lift forces. A preliminary validation of model and analysis results has been performed. Several insights into the vortex-induced vibration of catenary risers are highlighted through a series of parametric studies. These include the characterization of single-mode vs. multi-mode lock-in, the limitations of a single-mode solution through a convergence analysis which accounts for a varying number of considered riser modes, the prediction of riser maximum response amplitudes, the quantitative/qualitative behaviors of tension- or beam-dominant catenary risers and the overall influence of fluid-riser parameters. Moreover, recent industrial concepts of modes switching/sharing are discussed along with the meaningful effect of Reynolds number.
Assessment of Design S-N Curve for Umbilical Tubes
Authors: Lotsberg Inge , Fredheim Stein
Published: February 2010

A reliable design methodology for fatigue design of umbilical tubes is required by the industry. A documented design S-N curve is part of such a fatigue analysis procedure. During the last years a number of new fatigue test data have been derived for umbilical tubes. A design S-N curve for as welded and strained tubes during reeling has been debated. The present paper presents an overview of data presented in the literature. In addition it presents a significant number of fatigue test data of umbilical tubes performed at DNV test laboratories in Oslo. In addition it includes an assessment of recommended design S-N curve based on relevant available fatigue test data for umbilical tubes.
A Cohesive Element Framework for Dynamic Ice-Structure Interaction Problems—Part I: Review and Formulation
Authors: Konuk Ibrahim , Gu¨rtner Arne , Yu Shenkai
Published: February 2010

A framework incorporating dynamic crack propagation and continuum mechanics for modeling ice-structure interaction processes is developed. The framework is build upon a comprehensive review of recent developments in the analysis of dynamic fragmentation problems for materials such as ceramics, concrete, and metals. A review of alternative crack propagation modeling methods is also included in order to illustrate how the developed framework may overcome the shortcomings of existing techniques. This is the first paper (Part I) in a series of three papers. The formulation of the framework is presented in this paper. In the second paper (Part II), implementation of the framework will be described. The application of the framework to various ice-structure interaction problems will be presented in Part III along with the demonstration and investigation of important aspects of these scenarios.
Numerical Analysis of Pneumatic Damping Effect on a Motion-Constraint Floating Breakwater
Authors: Koo Weoncheol
Published: February 2010

A pneumatic-type floating breakwater is simulated by the fully nonlinear Numerical Wave Tank (NWT) to evaluate the effect of pneumatic damping and retrained body motion on wave blocking. In particular, One DOF (degree of freedom) motion such as a heave-only-allowable body coupled with pneumatic damping in the chamber is investigated. For the accurate nonlinear time-domain simulation, the NWT technique includes the mode-decomposition method in the acceleration potential field. The effect of pneumatic damping on the motion amplitude (RAO) and wave transmission is analyzed. The overall performance of wave blocking for various motion allowable types of pneumatic floating breakwater is compared with a box-shape breakwater.
Fracture Toughness Testing Using SENT Specimens in a Sour Environment
Authors: Yang Zhengmao , Xu Da Qin , Tronskar Jens P.
Published: February 2010

Offshore pipelines and risers constructed from carbon steel have reduced levels of performance when operating in a sour environment. Fatigue crack growth rates can be significantly higher and material fracture toughness may be significantly lower. In this paper a fracture toughness test procedure for the pipeline girth weld in a sour environment is introduced. The single edge notched tensile (SENT) specimen, which has been widely accepted for the pipeline girth weld fracture toughness tests, was used in this proposed procedure. As expected it was found that the fracture toughness of the girth weld was reduced significantly after exposure to simulated sour service (NACE solution A), and this result is used for the assessment of the weld root defects that may work in the sour environment.
Numerical Studies of the Effect of Sloshing on Ship Motions
Authors: Cho Seok Kyu , Choi Hang Shoon , Sung Hong Gun , Hong Sa Young , Park Il Ryong
Published: February 2010

The effects of sloshing on ship motions are simulated in view of FSRU design and operation. The Navier-Stokes equation is solved for sloshing motion. For the analysis of free surface, Volume of Fluid (VOF) techniques is adopted. The ship motion is solved in time domain by taking account of memory effects, which are obtained from the linear potential theory. The ship motion and sloshing are linked by explicitly coupling the ship motion and sloshing force. The coupling method is used to simulate the interaction of side-by-side moored LNG FSRU and LNGC for beam sea condition. Also the effect of sloshing on the two body interaction is studied for the case including sloshing in LNGC.
Laboratory Investigation of Clay Mineral Fines as Dispersant for Combating Oil Spill
Authors: Samuel Devadoss R. , Sannasiraj S. A. , Murali K.
Published: February 2010

The oil-mineral aggregate formation tests are commonly conducted in batch-scale testing apparatus in order to find the effectiveness in reducing the oil concentration in water column. However, for the assessment of effectiveness of mineral as dispersant under real sea state conditions, test protocols are required to have hydrodynamic conditions closer to the natural sea state environment, including transport and dilution effects. To achieve this goal, experimental program designed and constructed in a wave flume system to study the oil-mineral aggregation and it’s effectiveness in reducing the oil toxicity, in a controlled mixing energy conditions (non-breaking and breaking waves). Quantification of oil mineral aggregation effectiveness was based on observed changes in dispersed oil concentrations and distribution of oil in the beach sediments. The study results quantitatively demonstrated that total dispersed oil concentration in the water column were strongly dependent on the presence of mineral aggregates and the influence of breaking waves. The effectiveness of application of minerals, as a function of sea state was studied and would be useful in drafting of future operational guidelines for mineral dispersant use at sea.
Numerical Simulations of Wrinkle Sleeve Repair on Norman Wells: Zama Pipeline
Authors: Song Peter , Cheng J. J. Roger , Murray David W. , Ironside Scott , McNeill Dave , Skibinsky Darren
Published: February 2010

The Norman Wells–Zama pipeline, the first ever buried pipeline built in Canadian north, which is owned and operated by Enbridge Pipelines Inc., traverses challenging terrains along the route. Certain segments of the line have been inspected annually using the GEOPIG ILI tool since 1989. This has provided Enbridge with a database with a large amount of curvature, pipe ID geometry etc. information available. Over the years, through the GEOPIG data it was identified that the pipeline developed a wrinkle along an unstable, monitored slope. Because of the high cost of the cutout and replacement work, it was determined to repair the wrinkle by encasing it using a pressure containing steel sleeve. An additional wrinkle subsequently developed adjacent to the repair, thus multiple sleeves were installed. This paper describes the numerical simulations of the double sleeve repair system (DSRS) carried out in the University of Alberta using finite element (FE) package ABAQUS 6.4. The numerical simulations utilize the data from the yearly GEOPIG measurements and the operational pressure history to try to trace back the loading history that the critical pipe segment might have experienced and to predict the possible behavior of the pipe segment under DSRS. A technique in the FE package ABAQUS, which was initially developed to simulate the assembly process, was successfully used to simulate the wrinkle sleeve repair sequential activities. A summary moment vs. curvature curve was obtained based on the numerical simulations.
Bending Capacity Analyses of Corroded Pipelines
Authors: Yu Weiwei , Vargas Pedro M. , Karr Dale G.
Published: February 2010

Appendix G of the ASME B31 pipeline and piping codes addresses the pressure containment capacity of pipelines and vessels with locally corroded sections. However, the ability of corroded sections to carry moment, for example in thermal loops, is not addressed in fitness-for-service codes today. This paper presents nonlinear FEA and full-scale 4-point-bend testing of pipes with locally-thinned-areas (LTAs) to simulate corrosion. The LTAs are loaded in compression, and the buckle moment is used as the carrying capacity of the corroded section. The nonlinear FEA is found to match the experimental results, validating this methodology for computing moment capacity in corroded sections. Significant secondary effects were found to affect the testing results. This paper identifies and quantifies these effects. Also, somewhat contrary to intuition, internal pressure is demonstrated to adversely affect the bending capacity for the intermediate-low D/t ratio (17.25) pipe tested.
From Installation to Operation: A Full-Scale Finite Element Modeling of Deep-Water Pipe-in-Pipe System
Authors: Sun Jason , Jukes Paul
Published: February 2010

Developments of deep water oil reservoirs are presently being considered in the Gulf of Mexico (GoM). Pipe-in-Pipe (PIP) systems are widely used and planned as the tie-back flowline for high pressure and high temperature production (HPHT) due to their exceptional thermal insulation capabilities. The installation of PIP flowline in deep water, disregarding the laying method, can present real challenges because of the PIP string weight. The effect of the lowering displacement as well as the lock-in compressive load acting on the inner pipe for the commonly used un-bonded PIP is also a major concern. Such effects will enhance the total flowline compression when the high temperature and high pressure are applied after start-up; they greatly increase the severity of the global buckling and result in local plastic collapse at a larger bending curvature section or strain localization area. An even greater concern is that industry fails to realize the seriousness of such failure potential, and the PIP is generally treated as a composite single pipe which does not evaluate the PIP load response correctly, especially the inner pipe lock-in compression omitted. It could result in an unsafe design for HPHT production. This paper endeavors to provide a trustworthy solution for the HPHT PIP systems from installation to operation by using the advanced analysis tool — “Simulator”, an ABAQUS based in-house Finite Element Analysis (FEA) engine. “Simulator” allows the PIP pipes being modeled individually with realistic interaction between the pipes. A systematic process was introduced by using a generic deep-water PIP flowline as a working example of J-Lay installation and HPHT production. The load and stress responses of the PIP at all installation stages were calculated with a high level of accuracy, they were then included in the global buckling analysis for the HPHT operation. The study demonstrated the effectiveness of Loadshare, an industry-leading solution; which reduces or eliminates the inner pipe lock-in compression and improves the PIP compressive load capacity for the high temperature operation.
Applicability Evaluation of the Weight Function Based Strip Yield Model for an Embedded Crack Problems
Authors: Gotoh Koji , Nagata Yukinobu
Published: February 2010

Applicability evaluation of the developed weight function based strip yield model for an embedded crack by applying the slice synthesis methodology in elastic-perfect plastic bodies under monotonic uniform loading is performed. Although the weight function based strip yield model for a part-through semi-elliptical surface crack in an elastic-perfect plastic bodies under monotonic uniform loading was proposed by Daniewicz and Aveline (2000), applicable geometries of cracked bodies is limited. Their proposed strip yield model treats only a semi-elliptical surface crack in semi-infinite bodies. Besides, quantitative investigations of the applicability seem to be insufficient. The authors proposed the improved strip yield model with slice synthesis methodology for an embedded crack, which enables to treat the finite boundary problems. By applying proposed model, the back surface effect of the crack opening behaviour and the plastic zone growth can be considered. The validity of improved strip yield model for embedded cracks is confirmed by comparing crack opening profiles under some crack geometries with elastic-plastic finite element analyses.
Dense Ocean Floor Network for Earthquakes and Tsunamis (DONET) Around the Nankai Trough Mega Thrust Earthquake Seismogenic Zone in Southwestern Japan—Part 2: Real Time Monitoring of the Seismogenic Zone
Authors: Kaneda Yoshiyuki , Kawaguchi Katsuyoshi , Araki Eiichiro , Matsumoto Hiroyuki , Nakamura Takeshi , Kamiya Shinichiro , Ariyoshi Keisuke , Hori Takane
Published: February 2010

The Nankai Trough is well known as the mega thrust earthquake generating tsunamis, with the interval of 100–200 years. The 1944 Tonankai and the 1946 Nankai earthquakes around the Nankai trough, each hypocenter was located off the Kii peninsula. However, according to Prof. Okamura of KOCHI University, super mega thrust earthquakes such as Hoei earthquake (1707) and Hakuho earthquakes (684) are occurring with an interval of 300–400 years or 700 years. Based on structural research, observational research and simulation researches, we proposed and have been starting to deploy the dense ocean floor observatory network system around the Tonankai seismogenic zone, to monitor crustal activities using broadband seismometer, accelerometer and precise pressure gauges. The probability of next Tonankai earthquake recurrence is estimate as 60–70% (The Headquarters for Earthquake Research Promotion; http://www.jishin.go.jp/main/index-e.html). Therefore, the ocean floor network is significant ant important to monitor the crustal activities around mega-thrust earthquakes. In this paper, we explain the recent and detailed developing of this oceanfloor network system (DONET). Especially, the installation of sensors and improvement of ROV for the deploying system in the deep seafloor will be developed. Furthermore, the new project including observation simulation and mitigation researches of mega thrust earthquakes around the Nankai trough is starting as 5 years project (2008–20012). Especially, the Ocean floor network data is very important and powerful to progress the new project.
Asymmetry in Directional Spreading Function of Sea Waves Due to Refraction
Authors: Lee Changhoon , Jung Jae-Sang , Haller Merrick C.
Published: February 2010

In this study, a more general directional spreading function is developed that allows for asymmetric directional distributions. For multi-directional random waves that approach the shore obliquely over a planar slope, we demonstrate that directional asymmetry is generated due to wave refraction. The asymmetry created by refraction increases with the offshore peak wave direction. The present spreading function is compared to a pre-existing symmetric spreading function and is shown to better capture changes in the directional distribution that occur in a refracting, random wave field. Finally, the new asymmetric spreading function is compared to a long time series of wave directional spectra measured at a nearshore field site. The results demonstrate that refraction-induced asymmetry is common in the nearshore and the asymmetric spreading function gives an improved analytic representation of the overall directional distribution as compared to the symmetric function.
Modeling of Heave Induced Lateral Motion
Authors: Le Cunff Ce´dric , Bonnissel Me´lanie , Szydlowski Julien , Damy Gilbert
Published: February 2010

A simplified model is proposed to predict Heave Induced Lateral Motion (HILM) for Steel Catenary Risers (SCR), based on experimental measurements carried out at IFREMER Brest. Two campaigns were conducted to obtain data on the displacement of a SCR in the Touch-Down Zone (TDZ) induced by top motion. The first campaign was used to understand the response of the structure and develop the model. A second campaign was launched to obtain a wider range of data in terms of heave amplitude and frequency. This data were used to define the model parameters. The influence of heave lateral motion on riser damage was then assessed.
Numerical Modeling and Evaluation of Wave Energy Converters
Authors: Peng Heather , Qiu Wei , Spencer Don
Published: February 2010

Wave energy converters use the motion of floating or submerged bodies to extract energy from the waves. Power absorption can be simulated using a simple linear damper with a resistance to motion which is proportional to velocity. Because of the interaction between energy production and motion, there will be an optimum rate of energy production for each wave frequency. Too much damping or too little damping can cause little energy produced. The wave absorption range also depends on the tuned frequency. In this paper, the maximum rates of energy absorption for submerged and floating wave energy converters are evaluated by employing the panel-free method for the motions of the converters in the frequency domain. A general expression for the wave power absorption is described. Numerical studies show that the optimal energy efficiencies of wave energy converters can be well predicted by employing the panel-free method for motion computations.
Study on the Two Patters of Vertical Velocity Profile of Tidal Current and Their Law in Estuary and Coastal Waters
Authors: Ni Zhihui , Song Zhiyao
Published: February 2010

Many scholars at home and abroad have studied tidal velocity profile in estuarine and coastal waters. The results show that velocity profile of tidal current often deviated obviously from the traditional logarithmic profile, due to the flow including wind-driven current, wave-driven current, salinity and so on. In estuarine waters, runoff should be included as a component. In this paper, two patters of vertical velocity profile of tidal current are firstly divided, that are monotone increasing I-velocity profile (during flood tide and ebb tide stage) and non-monotone increasing II -velocity profile (during slack tide stage). Then, by use of variable fractal dimension to obtain the law of II-velocity profile, the results show that: (1)The II -velocity vertical profile does express a first-order accumulated variable-dimensional fractal phenomenon. (2) Through of the fractal dimension, the various formula fitting II-velocity profile were compared, and the results showed that, in practical applications of engineering, cubic function formula is the best fit as the measured data have been verified. Finally, the cubic function formula is applied to flow separation of II -velocity measured in Yangtze River. By the easily separation of the measured flow, we can not only get a reasonable surface flow velocity, such as wind-driven current, runoff, salinity, as well as their driving force weight in the hydrodynamic of estuarine and coastal waters, but also gain the data of bed roughness length and sea surface wind speed, providing reasonable border conditions of the seabed and sea surface for the hydrodynamic numerical simulation in estuarine and coastal waters.
Pipe-in-Pipe for Gas Production in Deep Water Offshore Brazil
Authors: de Azevedo Fabio Braga , Solano Rafael Familiar , Lacerda Vitor Tiago
Published: February 2010

Based on flow assurance studies a Pipe-in-Pipe solution was selected to assure the flow for a gas pipeline connecting the well 4-ESS-138 to FPSO Cidade de Vito´ria located in Canapu field. The flow assurance studies also define the value of 0.8W/m2K for the overall heat transfer coefficient (OHTC) in order to prevent hydrate formation. The temperature of 87°C on the wellhead should be preserved to permit the proper gas flow in 20km PIP length between wellhead and FPSO. Canapu field is located in the offshore area of Brazil (Espirito Santo state) in water depths of 1608m. This paper presents the main aspects related to the detailed design, thermo-mechanical requirements, materials specifications, functional qualification tests performed on materials and on pipe-in-pipe systems to satisfy installation constraints defined by the reel-lay method and operational issues.
Non-Darcy Binomial Deliverability Equations for Partially Penetrating Vertical Gas Wells and Horizontal Gas Wells
Authors: Zhu Tao , Lu Jing
Published: February 2010

Many gas reservoirs are with bottom water drive. In order to prevent or delay unwanted water into the wellbore, the producing wells are often completed as partially penetrating vertical wells, and more and more horizontal wells have been drilled in recent years in bottom water drive gas reservoirs to reduce water coning and increase productivity. For a well, non-Darcy flow is inherently a near wellbore phenomenon. In spite of the considerable study that non-Darcy behavior of fully penetrating vertical wells, there has been no study of a partially penetrating vertical well or a horizontal well in a gas reservoir with bottom water drive. This paper presents new binomial deliverability equations for partially penetrating vertical gas wells and horizontal gas wells, assuming that only radial flow occurs in the near wellbore non-Darcy’s flow domain. The inflow performance of a vertical gas well is compared with that of a horizontal gas well. The proposed equations can account for the advantages of horizontal gas wells.
Experimental Visualization of 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. An experimental facility has been designed and constructed to enable flow pattern visualization inside the second stage of a real ESP. Special high speed instrumentation was selected to acquire visual flow dynamics and bubble size measurements inside the impeller channel. Experimental data was acquired utilizing two types of tests (surging test and bubble diameter measurement test) to completely evaluate the pump behavior at different operational conditions. A similarity analysis performed for single-phase flow inside the pump concluded that viscosity effects are negligible compared to the centrifugal field effects for rotational speeds higher than 600 rpm. Therefore, the two-phase flow tests were performed for rotational speeds of 600, 900, 1200, and 1500 rpm. Results showed formation of a large gas pocket at the pump intake during surging conditions.
A Modified Linear Lagrangian Model for Irregular Long-Crested Waves
Authors: Fouques Se´bastien , Stansberg Carl Trygve
Published: February 2010

Wave crest height and steepness are crucial parameters for the design of ships and offshore structures. For irregular sea states, they are commonly predicted by using linear wave theory and a Eulerian description of the fluid motion. This theory only applies when the wave steepness is small and it fails to capture extreme wave events. Such linear solutions can also be extended by including second-order terms in order to provide more realistic wave properties. The paper describes a model for irregular long-crested waves that is based on a modified linear solution derived from a Lagrangian description of the fluid, i.e. by considering the motion of individual fluid particles. Lagrangian solutions have the advantage of showing realistic wave profiles with sharp crests and broad troughs already at the first order, whereas these features only appear at the second order when using the Eulerian approach. Still, a severe drawback with the former is that the mass conservation is not fulfilled exactly. The aim of the modification in the present Lagrangian model is to ensure that the mass conservation is always fulfilled in the solution. This is done by using the second-order residual in the continuity equation to lift up the fluid particles vertically. Comparative investigations of wave properties such as the crest height and the wave steepness are further carried out by making use of both numerical case studies and wave tank recordings. The wave models used in the comparisons include linear and second-order Eulerian solutions as well as the modified linear Lagrangian one.
Modelling Downhole Separation Efficiency Using a Stream Function Approach
Authors: Marquez Richard , Prado Mauricio Gargaglione
Published: February 2010

A new technique for solving simultaneously the mass and momentum balance equations for a gas-liquid mixture is proposed in this paper. The technique is based on the vorticity-stream function approach, under a cylindrical coordinate system. Important variables such as slip velocity in the radial and vertical direction, characteristic of the bottomhole, gas and liquid flow rates, pressures, flow pattern, among others, are considered simultaneously in the solution of the problem. The two-phase model proposed in this work allows obtaining the liquid and gas velocities fields as well as the two-phase flow pressure and gas fraction fields. Experimental data is used to close the model. The model was used to simulate downhole separation efficiency and to determine the influence of liquid flowrate, GLR, casing size and liquid viscosity on the natural separation efficiency. The model agrees very well with experimental data obtained by The University of Tulsa.
Offshore Hydrokinetic Energy Conversion for Onshore Power Generation
Authors: Jones Jack A. , Chao Yi
Published: February 2010

Design comparisons have been performed for a number of different tidal energy systems, including a fully submerged, horizontal-axis electro-turbine system, similar to Verdant Tidal Turbines in New York’s East River, a platform-based Marine Current Turbine, now operating in Northern Ireland’s Strangford Narrows, and the Rotech Lunar Energy system, to be installed off the South Korean Coast. A fourth type of tidal energy system studied is a novel JPL/Caltech hydraulic energy transfer system that uses submerged turbine blades which are mechanically attached to adjacent high-pressure pumps, instead of to adjacent electrical turbines. The generated high-pressure water streams are combined and transferred to an onshore hydroelectric plant by means of a closed-cycle pipeline. The hydraulic energy transfer system was found to be cost competitive, and it allows all electronics to be placed onshore, thus greatly reducing maintenance costs and corrosion problems. It also eliminates the expenses of conditioning and transferring multiple offshore power lines and of building offshore platforms embedded in the sea floor. For time-dependent tidal energy, the pressurized hydraulic energy can be stored in an elevated onshore reservoir that can be used as per consumer energy demand, rather than as per tidal energy supply. This technology is a spinoff of a miniature ocean hydraulic energy transfer system that JPL is developing for the Office of Naval Research (ONR). The ONR device uses ocean temperature differences to provide pressurized hydraulic energy which supplies all electrical power for small submersibles. This type of hydraulic energy device is expected to allow submersibles to stay submerged for years. A three-month ocean endurance test is scheduled for late 2009. Similar types of hydraulic energy transfer systems are potentially applicable to all types of hydrokinetic energy, including free-flowing rivers, ocean wave energy, and energy from ocean currents, such as the Gulf Stream. In each case, the corrosion-prone, submerged electrical turbines are replaced by all-mechanical water pumps without any electrical components, and the energy is hydraulically transferred to remote onshore hydroelectric plants by inexpensive pipes. The submerged mechanical turbine blade/pump assemblies can be attached by long, small-diameter, flexible pressurized lines to the larger submerged, stationary pipe lines, thus allowing the submerged blade/pump assemblies to be lifted to the surface and serviced by boat. Check valves in the flexible lines allow damaged turbine blade/pump assemblies to be automatically taken off-line and later repaired or replaced as required.
Global Analysis of Ultra-Deepwater Drilling Risers
Authors: Wei Dai , Feng Gao , Bai Yong
Published: February 2010

In recent years, the exploration activity of oil and gas industry in ultra deepwater is numerous. Global offshore industry is building systems today for drilling in even deeper water, progressively using new technologies, and significantly extending existing technologies. This is the general trend in the offshore oil and gas industry. So the technology of Ultra-Deepwater Risers, which is the main tool in drilling of oil, is more and more standard. This paper manly focuses on the global analysis of the drilling risers. And it is divided into two parts, operability analysis and hang-off analysis that are used to check the design of the Riser. In the paper, the following is discussed: 1. Calculation of the rotation angle and stress of the Riser in the drilling mode, as well as the stroke of the telescopic joint; 2. Determination of the operability envelop; 3. Calculation of the rotation angle and stress of the Riser on the hang-off condition, and the telescopic joint’s stroke; 4. Determination of the number of the buoyancy module; 5. Check all the worked out values according to the API standard. From all the above, it is obtained that the operability envelop is relatively small on the harsh condition and the number of the buoyancy modules is a little large. And above all, the design of this Riser is successful.
Hydrodynamic Characteristics of the Surface-Piercing Propeller for the Planing Craft
Authors: Ghassemi Hassan , Shademani Roya , Ardeshir Abdollah
Published: February 2010

Market demands for high-speed marine vehicles (HSMVs) are high in both commercial and naval branches. It is the naval architects’ task to design the hull and propulsion system to diminish drag, improve the propulsive efficiency, higher safety and better maneuverability. Surface Piercing Propellers (SPPs) may provide those possessions for the vehicles. Unlike immersed propellers, behavior of the SPPs is susceptible to immersed depth, Weber number and shaft inclination angle. This paper uses a specially practical and numerical method to predict the hydrodynamic characteristics of the SPPs. Critical advance ratio is obtained by practical formula, using Weber number and pitch ratio in the transition mode. Numerical method employs the potential based boundary element method (BEM) on the engaged surfaces. Two models of three and six bladed of the SPPs (SPP-1 and SPP-2) are selected and some results are shown.
Flow Field Analysis Around the Ship Fin Stabilizer Including Free Surface
Authors: Dadmarzi Fatemah Hoseini , Ghassemi Hassan , Ghadimi Parviz , Ommani Babak
Published: February 2010

Fin stabilizers are very important device for controlling the ship roll motion against the external moments due to wave. This paper presents numerical results for flow field simulation and the hydrodynamic performance of fin stabilizer attached to a ship hull with free surface effects. Combination of CFD and RANS method has been used for this study. The fin is non-rectangular NACA0015 profile section with a finite aspect ratio. The numerical results include pressure distributions and flow field around the fin which are used to calculate lift coefficients and free surface elevation as the main interest. Some results are compared with available experimental and numerical data in literature and they show good agreement.
The Mulberry Harbours: A Review of an Early Example of Offshore Engineering
Authors: Adcock Thomas A. A. , Taylor Paul H.
Published: February 2010

The Mulberry Harbours were used to support Operation Overlord, the invasion of occupied Europe, in 1944. This paper reviews the design of the breakwaters used, given the major advances made in ocean engineering and wave dynamics made over the last half century. The expected sea state is estimated and compared to the original design parameters. The failure mechanisms associated with the Phoenix caissons are discussed. The engineering decisions on the floating Bombardon breakwaters are considered; the authors conclude that some of the units were positioned in an area where unusually high waves could be expected, which may have contributed to their failure.
Roll Response of Ship-Shaped Hulls in Waves
Authors: Yu Yi-Hsiang , Kinnas Spyros A.
Published: February 2010

This paper addresses the hydrodynamic interaction and the response of typical FPSO and LNG hull-forms with an emphasis on roll. In particular, the study focuses on the prediction of the roll response of hulls in free-decay motions and also in regular waves for various wave frequencies and for hulls with or without bilge keels. A 2-D finite volume method-based Navier-Sokes solver (NS2D) is applied to analyze the flow around the hull-sections. The effectiveness of using bilge keels on roll reduction is presented, and the bilge keel loads on the up-wave and down-wave sides of the hull are examined.
Mooring Analysis of a Weathervaning FPSO in Bi-Directional Sea-States
Authors: Chillamcharla G. K. , Thiagarajan K. P. , Winsor F.
Published: February 2010

Experimental studies were carried out at the Institute for Ocean Technology, Canada, in collaboration with the University of Western Australia (UWA) to assess the response of a moored 1:60 scaled Floating Production Storage and Offloading (FPSO) model in bi-directional seastates. The seastates comprise of a regular swell approaching in the head sea condition, and a JONSWAP wind sea approaching at various angles. The FPSO was moored in position by four spring-loaded mooring lines attached to an internal turret about which the model could weathervane. Previous papers by the authors have described the unpredictable yaw instability of the FPSO driven by long period swells, which was evidenced in the experiments. This creates difficulties in comparing motions from unidirectional and bi-directional seas, because the headings alter the response. However, the mooring tensions are relatively immune to yaw instabilities and this paper discusses effects of bi-directional seas on the mooring tensions. Numerical simulations are conducted using a time domain analysis software which simulates the motions of floating and moored structures in response to irregular seas. Simulations based on the software when compared with model tests at 45, 60 and 90 deg separation between the sea and swell shows reasonable agreement in terms of mooring tensions. Simulations are then conducted for a range of separation angles, and the effects of bi-directionality are further evaluated. It is found that a linear addition of the individual seastates can produce non-conservative results, which reinforces the fact that bi-directional seastates are important considerations for offshore operations of an FPSO.