bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation of Gap to Diameter Ratio Effects on Flow Pattern and Drag Force Around Offshore Pipeline
Authors: Kazeminezhad Mohammad Hossein , Yeganeh Bakhtiary Abbas , Etemad-Shahidi Amir , Valipour Reza
Published: July 2009

Offshore pipelines are exposed to hydrodynamic forces due to the current actions. The forces (drag and lift) have an unsteady nature and oscillate around their average values because of the occurrence of vortex shedding behind the pipeline. Vortex shedding leads to the Vortex-Induced-Vibration (VIV) which is an important source of fatigue damage of pipeline in free spanning sections. Time-averaged drag force can be calculated using drag equation which has a hydrodynamic coefficient. However it does not take the VIV effects into account. To do so and to consider the unsteady nature of the force, the flow pattern and vortex shedding phenomenon around a pipeline should be simulated accurately. The main objective of this study is to simulate the flow field around an offshore pipeline placed on the plane bed. This study investigates the gap ratio effects on the flow pattern and drag force exerted on the pipeline as well. The flow field was simulated by the two dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with a k-ε turbulence closure model. Results indicate that the k-ε turbulence closure can simulate the vortex shedding behind a pipeline and the oscillation of drag force successfully. By considering different values of gap to diameter ratio, it is found that the drag coefficient is increased gradually as the gap ratio rises up and the increase rate reduces as gap ratio increases.
Analysis of Oil Transfer Lines for Offshore Terminals With Controlled Buoyancy
Authors: dos Santos Costa Ana Paula , Sphaier Sergio , Nishimoto Kazuo , Masetti Isaias Quaresma
Published: July 2009

This paper presents a study on the design and dynamic behavior of hose lines for offshore oil transfer. Moreover, a new configuration of floating hose line that minimizes the dynamic effect in the connections of the line of oil transfer to the Offshore Terminal and to the Shuttle Tanker is analyzed. This conception reduces the damages in the elements of the extremity due to the great accelerations and the small bending radius, which the structure of the hoses is submitted. Although the benefits of the present configuration are applied for abandoning and stowing conditions and a complete set of numerical analysis and model tests were performed, only the results for the offloading operation were presented.
Pipeline Stability: State of the Art
Authors: Zeitoun Hammam O. , To̸rnes Knut , Cumming Gary , Brankovic´ Masˇa
Published: July 2009

Ensuring subsea pipeline stability on the seabed is one of the fundamental aspects of pipeline design. A comprehensive on-bottom stability design will include a detailed assessment of the hydrodynamic loads acting on the pipeline, the pipe-soil interaction, the structural response and a careful consideration of the acceptance criteria. Pipeline stabilisation is a major cost driver in some locations around the world, where the designer is faced with extreme design challenges including severe metocean conditions, shallow waters, large diameter lines, and uncertain or difficult geotechnical conditions. These may all contribute to complex stabilisation solutions resulting in costly construction techniques. The current knowledge and engineering practice applied in pipeline stability design is mostly based on the work performed during the 80s by the Pipeline Stability Design Project (PIPESTAB) and on the research conducted by the American Gas Association (AGA) in another Joint Industry project (JIP). At the time, these studies were aimed at gaining an understanding of the physics governing pipeline stability, in particular hydrodynamic loads on pipelines and soil resistance. These two aspects were investigated independently from each other. Understanding pipeline stability has evolved over the last decade due to the application of this knowledge, findings from further research work, the introduction and requirements of new pipeline codes, and advances in the understanding of pipe-soil interaction. Recently gained understanding has raised the question whether alternatives to the present design approaches and acceptance criteria, as specified in the design codes, could be developed. The areas of debate include the approach used for addressing pipe soil interaction, the hydrodynamic coefficients to be applied, the design kinematics to be considered, the design methodologies, the acceptance criteria, and compliance with design codes limit states. This paper presents an overview of the current available knowledge for addressing pipeline stability. The aim is to briefly summarise the key aspects of the pipeline stability design process and to include some historical perspective. The paper discusses the advantage and shortfalls of the different approaches with a view to consolidate understanding, rather than to provide a ready-made solution to a complex design problem.
Marine Vessel Dynamics Using 6-DOF Simulations
Authors: Pregnalato Craig J. , Lee Kyong-Huhn
Published: July 2009

The response of marine vessels to steady currents and unsteady wave motions is presented using six degrees-of-freedom CFD simulations. The equations governing the fluid flow are coupled with the rigid-body equations of motion to predict the response of surface ships when driven by high-amplitude waves. In addition, the maneuvering performance of a submarine is analysed for a constant heading and depth. Such fully coupled simulations allow the accurate prediction of the hydrodynamic forces acting on the vessel as well as the corresponding vessel motion and are becoming increasingly important from a design standpoint. In these simulations, a high-resolution interface-capturing scheme is used to efficiently capture the dynamics of breaking and overturning waves and to examine their impact on a surface ship. The dynamics of the vessel are investigated in detail with particular emphasis on its angular response (i.e. pitch, roll and yaw).
Research on the Method of Beach Facility Management for Orderly Utilization of Recreation Beach
Authors: Ogawa Shinji , Kondo Takeo , Yamamoto Kazukiyo , Koizumi Yusuke , Kondo Takahiro
Published: July 2009

Recently, in Japan, some owners of umi no ie (seaside shops) have started illegally occupying the shore for a large part of the year. This has resulted in the problem of the public nature of the beach being violated. In the present research, the following two points were studied. (1) Maintenance of beach facilities, such as restrooms, showers and dressing rooms. (2) Problems concerning the establishment of beach recreation facilities by private businesses, and solutions for these problems. For point (1), a survey was conducted on the maintenance conditions of beach facilities and the needs of beach users all over Japan. We found that users desire facilities such as restrooms and dressing rooms that can be used throughout the year. For point (2), there were problems concerning the procedures required for establishing facilities and conflicts in using such facilities provided by private businesses. As a solution to these problems, we proposed that the local government provide the facilities and private businesses manage the facilities.
Reliability of Lateral Buckling Formation From Planned and Unplanned Buckle Sites
Authors: Rathbone Andrew , Abdel-Hakim Mahmoud , Cumming Gary , To̸rnes Knut
Published: July 2009

Global buckling for exposed HPHT (High Pressure / High Temperature) subsea pipelines is an important feature that needs to be assessed during detailed design. By safely triggering controlled buckles at predetermined locations and considering the potential for rogue buckles to be triggered by seabed or pipelay out-of-straightness features, a robust design solution can be obtained. This paper presents a methodology whereby quantitative risk assessment may be carried out on the reliability of lateral buckling initiation systems, considering the pipeline in its entirety, rather than considering each intended buckle individually. This method accounts for buckle interaction when calculating the post-buckle loads, and allows simple incorporation of potential rogue sites through vertical and/or horizontal out-of-straightness. The results of the risk assessment can be defined in terms of buckle formation reliability, and design stress/strain criteria.
Planning and Designing a Marine Hospital Facility for Use in Times of Disaster
Authors: Kondo Takahiro , Kondo Takeo , Yamamoto Kazukiyo , Sato Chiaki , Kayama Tetsuo
Published: July 2009

Medical support using marine transportation during an earthquake disaster has been attracting attention because the land transportation system is expected to be paralyzed at such times. An earthquake measuring magnitude 7 is predicted to occur in Tokyo Bay in the near future. The aim of this study is to develop an earthquake-proof design for a marine hospital facility, and to calculate the required capacity and number of medical personnel. The scale of the marine hospital facility was determined based on anticipated damage caused by a near-field earthquake in Tokyo Metropolitan Area. The need for preparation of heliports and boat piers was identified.
Full Scale Fatigue Testing of Fatigue Enhanced Girth Welds in Clad Pipe for SCRs Installed by Reeling
Authors: Kristoffersen Steinar , Haagensen Per J. , Ro̸rvik Gisle
Published: July 2009

H2S is reported to degrade the fatigue properties of C-Mn steels with a factor of 10–20 in life, while clad pipes are reported to have a performance close to or as good as in air. Clad pipes could therefore be used in highly fatigue loaded parts of the riser to facilitate design of steel catenary risers (SCRs) that are connected to floaters in deep waters. A literature survey of high quality girth welds intended for SCR is included in this paper and compared with fatigue test data obtained in this project. The first nine full scale 15" clad pipe girth welds out of a program of 24 specimens are fatigue tested in a high frequency resonance test rig and reported. The pipes were tested as welded, hammer-peened and reeled. The 15" OD steel pipes with 316 cladding tested in this work were surplus pipes from the Norne pipeline project. The fatigue test pipes were fabricated using the same welding procedure and welding facilities at Technip’s spool base in Orkanger, Norway, as the Norne pipeline project. The Norne pipeline is the world’s first reeled clad pipeline. The objective of this work was to test premium quality girth welds with best possible fatigue performance in actual pipes under realistic conditions was. The effect of hammer-peening of the OD was therefore investigated. Post failure examination was performed to determine the type and size of defects at the fatigue crack initiation site.
Ship-to-Ship LNG Transfer in Arctic Waters
Authors: Berg Tor E. , Bakke Joachim
Published: July 2009

Ship transport of LNG from shore-based LNG plants on the Yamal Peninsula will pass through waters with seasonal ice. A transport chain using specially designed ice-breaking LNG shuttle tankers is proposed. The shuttles will bring the cargo beyond the ice edge, where it will be transloaded to seagoing winterized LNG carriers. This paper looks at risks related to the operational phases of a side-by-side lightering operation. Climatic changes question the applicability of historic metocean data for locations identified as possible areas for open-sea ship-to-ship transfer of LNG in the eastern Barents Sea.
Hydroelastic Analysis of Floating Performance Stage at Marina Bay, Singapore
Authors: Wang C. M. , Song J. H. , Utsunomiya T. , Koh H. S. , Lim Y. B.
Published: July 2009

This paper presents the hydroelastic analysis of the floating performance stage that was constructed at the Marina Bay. The challenge posed in the hydroelastic analysis was the modeling of an equivalent plate that captures the dynamic flexural behaviour of the floating stage. By using a plate model with plate strips along the connecting lines of the floating stage, their Young’s moduli and Poisson’s ratios are adjusted so that the free vibration frequencies and mode shapes of the equivalent plate model match the results of the rigorous finite element model of the floating stage. The analysis shows that the hydroelastic response of the floating structure is relatively mild due to the calm waters in the Marina Bay when compared to the static bending response from imposed loads.
VIV Force Estimation Using Inverse FEM
Authors: Mainc¸on Philippe , Barnardo Celeste , Larsen Carl M.
Published: July 2009

An inverse finite element method (iFEM) is presented for the estimation of load and response of linear dynamic structures, based on measurement data. It produces load and response estimates which exactly verify dynamic equilibrium while the loads are reasonably small and the response in reasonable agreement with the measurements. iFEM is used to process measurement data from VIV experiments on a reduced scale riser model in shear current. The technique allows to visualise the distribution and history of hydrodynamic forces and excitation and damping zones.
Development and Evaluation of Optimal Routing System
Authors: Park Gunil , Choi Jaewoong , Lee Jinho , Kim Munsung , Bang Changseon , Kang Yuntae , Ha Munkeun
Published: July 2009

To improve the safety and efficiency of trans-ocean voyage, authors developed a new onboard weather routing system (so called SORAS). The system utilizes weather forecasting data to evaluate seakeeping performance and to generate optimized route plan with respect to fuel consumption and sailing time. The system can provide decision support for navigator in real time. For this feature, onboard wave measurement system and hull stress monitoring system are integrated to provide real time wave information and actual hull stress and bow acceleration. The optimal route depends on not only weather condition but also ship’s propulsion performance. We performed a simulation study to determine the accuracy limit of mathematical model for propulsion performance. To evaluate the system, we compared calculation results with actual voyage data. The estimation results of speed reduction and fuel consumption showed good coincidence with measurement results. The wave bending moment was estimated on the forecasted wave condition. The results were compared with measured wave bending moment. For optimal route, it was confirmed that the efficiency of optimal route is superior to the efficiency of the actual route which planned by captains or officers, and the improvement of efficiency would be significant.
Prediction of Wave-in-Deck Forces on Fixed Jacket-Type Structures Based on CFD Calculations
Authors: Brodtkorb Benedicte
Published: July 2009

The original design requirement for positive air gap is no longer fulfilled for a number of jacket-type structures still in production. When extreme waves impact the deck, the total loads on the structure are increased significantly, so accurate prediction of wave-in-deck forces is a central element in structural reassessment. Simplified methods for evaluating maximum horizontal and vertical loads are useful in an initial phase. In this study, we compare numerical prediction using CFD with the simplified API method for horizontal wave-in-deck load. The global wave impact loads for 0° head-on and 45° oblique waves are calculated for various deck configurations, all heavily equipped (solid). The effect of current is also addressed. In the case of no current, we found that the CFD simulations generally display a reasonable load level compared with the API load method. However, the CFD calculations indicate that the simplified method should be used with care for situations with large upwelling of water and decks with multiple deck girders. A simplified method for predicting vertical wave-in-deck loads on solid decks is developed. The method, first published in DNV-RP-C205, aims to be useful in an initial phase of reassessment.
Sea Trial Results of ROV “ABISMO” for Deep Sea Inspection and Sampling
Authors: Inoue Tomoya , Osawa Hiroyuki , Yoshida Hiroshi , Tahara Junichiro , Ishibashi Shojiro , Ito Kazuaki , Watanabe Yoshitaka , Sawa Takao , Hyakudome Tadahiro
Published: July 2009

JAMSTEC (Japan Agency for Marine-Earth Science and Technology) has been developing the deep sea ROV ABISMO (Automatic Bottom Inspection and Sampling Mobile) having the capability to dive to the deepest sea. The purposes of ABISMO are to inspect on the seabed in the deep sea and to obtain sediment samples from there. ABISMO consists of a launcher and a vehicle which is launched from the launcher and surveys on the seabed to determine the place for sampling. Core sampling system, which is exchangeable with a gravity piston type or a grab type, is equipped in the launcher. The both of the launcher and the vehicle have cameras to observe. One of the features of ABISMO is that the vehicle has crawlers in addition to thrusters in order to advance mobility. ABISMO is operated with the support ship KAIREI and dived by means of its onboard equipment including a primary cable. We conducted sea trials in January and September 2007 at the areas with the water depths up to 1,300m in Sagami Bay as primary function tests. And we conducted the third sea trial at Izu-Ogasawara trench in December 2007 and made the successful results of diving to the depths up to 9707 m and obtaining a sediment sample from the seabed in 9760 m water depth. This paper describes the features and the outline of ABISMO as well as the sea trial results.
An Analytical Research on the Auditory Disabled Person’s Behavior Limitation and Solution at Sandy Beach
Authors: Koga Takahiro , Kondo Takeo , Yamamoto Kazukiyo , Miyazaki Wataru
Published: July 2009

In Japan, many facilities have been modified for ease of use by socially disadvantaged people because of construction and barrier-free access laws. Currently, however, these modifications are largely limited to public facilities within Tokyo. This research examines the problems for people with hearing disabilities visiting bathing beaches, which attract the maximum number of visitors and which have numerous barriers for people with disabilities, and also proposes measures for resolving some of these problems. People with hearing disabilities do not evoke caution because there is no way to tell them apart based on external appearances. This therefore creates problems such as being unable to recognize warnings regarding dangers and cautions, and being slow to take action to avoid dangers. It has thus become clear that systems for communicating information suitable for people with hearing disabilities have yet to be established. As one of the authors has a hearing disability, methods for resolving these problems are proposed by addressing the problems from the viewpoint of a hearing disabled person.
Defining the Long-Term Wave Resource at Wave Hub: The Role of Measurements and Models
Authors: Phillips Joseph , Cruz Joao , Holbrow Rob , Parkes Jeremy , Rawlinson-Smith Rob
Published: July 2009

Wave measurements made on the site of a potential wave energy project can be of high value to developers. Such data can be used to define both long-term and short-term wave energy resources available to devices as well as the optimal operations and maintenance strategy which should be employed for the project. All three of these applications are addressed in an ongoing study commissioned by the npower Juice Fund for the Wave Hub project which is planned off the South West coast of England. The aim of this work is to extract best value from the historical and future wave measurements from the project site. The programme of this project is outlined here with a technical description of activity in the three parallel strands of the study; wave resource assessment, short-term forecasting and O&M modelling. The focus of this paper is on a key aspect of the ongoing work programme - that relates to the use of measured and modelled wave data to derive a prediction of the long-term wave climate at the Wave Hub site. In particular, various candidate methodologies for correlating short-term measured wave data and long-term modelled data are explored in the context of a Measure-Correlate-Predict (MCP) analysis. This work has also included consideration of the inter-annual variability of wave resource in order to examine the uncertainty associated with assuming that a finite historical reference period is representative of the long-term wave climate.
Integrity Assessment of HP/HT Infield Pipelines: Experiences With a New Methodology Applied in the Norwegian Sea
Authors: Etterdal Birger , Nes Hroar , Kvarme Stig Olav , Svardal Stian
Published: July 2009

The subsea pipeline development for the A˚sgard and Midgard fields in the Norwegian Sea has been challenging due to high operating pressure and temperature (HP/HT pipelines), uneven seabed conditions and the potential for trawl gear interference. A general experience from the first years of operation is that it is not easy to use design information as basis for an integrity assessment of the lines. This is mainly due to the complexity of the global buckling process and the significant load fluctuations applied to the lines. As a consequence of this, analysis models established during design may not represent the actual pipeline behaviour properly, and established design limits do not fit intermediate operational load conditions and configurations observed during surveys. StatoilHydro has developed an integrity assessment methodology where analysis models are calibrated according to the as-surveyed condition, and then exposed to operational cyclic loads in order to predict both intermediate long term conditions and a final design condition. In the assessment of long term fatigue accumulation, process parameters monitored during pipeline operation are used as input. The integrity condition of the HP/HT pipelines is assessed based on a staged approach, depending on the criticality of the considered failure mode. The first level is used for screening and initial ranking. At level two the risk of integrity failure is quantified based on general design criteria, covering relevant operating conditions and the most important input parameters. If the uncertainty related to the assessment of an individual hot-spot location is assumed too high, a detail level three assessment may be specified. The operating condition of the pipeline system is expressed as the risk of failure defined by a limited number of hot-spot locations. The risk matrix concept used for the HP/HT pipelines, provides for a consistent comparison between individual failure modes, between different locations and sections, and between different pipeline systems. StatoilHydro has worked in close cooperation with DNV to develop software tools required to implement this integrity assessment methodology. These tools are now used for integrity assessment and follow-up of all HP/HT pipelines operated by StatoilHydro in the Norwegian Sea. The objective of this paper is to show how the methodology is used in practice, discuss major results and findings, and give general recommendations with respect to operational integrity assessment of HP/HT pipelines.
Probabilistic Fracture Mechanics Assessment of Welded Joints of Offshore Structure Using a Bilinear Crack Growth Law
Authors: Khan Rizwan A. , Ahmad Suhail
Published: July 2009

Design of welded structures for fatigue limit state is normally carried out by means of either linear or bilinear S-N curves approaches. To properly assess the effects of design, fabrication, inspection and repair strategy for structures degradation due to crack growth, Fracture mechanics (FM) models need to be applied. This paper deals with the application of a probabilistic fracture mechanics approach to predict the fatigue life of welded steel structure in the presence of cracks under random spectral loading. It is based on a BS7910 [1] proposed bi-linear relationship to model fatigue crack growth and incorporates a failure criterion to describe the interaction between fracture and plastic collapse. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using the Monte Carlo Simulation technique, and emphasis is placed on a comparison between linear and bi-linear crack growth models. The bi-linear crack growth model is found to lead to higher fatigue life estimates and shows sensitivity to many other parameters in addition to the state of stress of the component. This leads to implications on inspection schemes for components of the marine structures and to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment. Variations in the system configuration, service life and coefficients of crack growth laws have been studied on the parametric basis.
Including Ergonomics in the Design Process to Address the Risks of Slips, Trips and Falls: Methodology and Application
Authors: Mery Nicolas , Lassagne Marc , McGregor Jonathan
Published: July 2009

Much effort has been spent by the offshore and maritime industries in order to improve the safety of the vessels and installations. However, accidents such as Slips, Trips & Falls (STFs) still need to be particularly addressed since their likelihood and severity are often underestimated. According to a study by Jensen et al. [1], they cause more than 40% of non-fatal injuries onboard and a study by the American Club P&I [2] asserts they are responsible for 23% of the cost of claims for illness and injury. The best way to prevent personnel from slipping, tripping and falling is to integrate safety early in the design of the ships or offshore installations. This paper describes the way a classification society has developed guidelines based on ergonomic design principles in order to improve the design of the means of access onboard ships. The outcome of this exercise is to increase the safety of surveyors, seafarers and sea-going personnel who inspect, operate or work aboard the vessels. The methodology we used featured a two step approach: a risk analysis based on feedback from surveyors and other sources was performed; an anthropometric analysis was then used to establish the guidelines. Both exercises are detailed in the paper along with the resulting guidance. We show how this work is a first step towards a more general methodology for the inclusion of ergonomic consideration in the design process.
Influence of Rain Protection Louver on the Noise Generated by Ship Engine Room Air Intake
Authors: Kumar Manoj , Nikam S. L.
Published: July 2009

The air supply system, of a ship engine room, is a tremendous source of noise. Apart from the noise from air-intake fan, the rain protection louver, which guides the airflow and protects the fan and the duct from rain, is also a significant source of noise. The influence of the air-intake louver, on the noise generated by the engine room air-intake, has been studied by numerically simulating the flow field as well as on the basis of on-board measurements and simple experiments. In order to analyze the noise generated by the louver, a parametric study has been carried out based on two variables, the angular orientation of the slats of the louver and the spacing between the slats. The study shows that the noise level reduces significantly by changing the angular orientation of the slats, making them inline with the flow. It is also observed that, by increasing the spacing between the slats, the noise level can be reduced. The current work is a part of a study to develop guidelines to limit noise level, due to engine room air intake, on-board a ship.
Suppression of Ocean Waves by Uniform Forced Currents
Authors: Zaman M. Hasanat
Published: July 2009

Ocean current might be a useful tool to suppress ocean waves that approach a particular region of interest. A reliable short term sheltering approach might be enough in some areas where a heavy and/or permanent protection system is impractical, considering its usage, duration of deployment and money involved. This study is carried out using a 3D finite difference numerical model. The model is presently developed for long crested waves and uniform current by the vertical integration of the continuity equation and the equations of motion. A semi-implicit finite difference technique is employed for the discretization of the governing equations in time and space. Results are shown in terms of wave height distributions, reflection and transmission coefficients for varying currents, incident wave and current angles.
On the Use of Online Monitored Key Parameters From Pipe Lay Operations
Authors: O̸kland Ole David , Giertsen Egil , Sævik Svein , Taby Joakim
Published: July 2009

For pipe lay operations parameters like heading and position of the lay vessel, lay-back and information about feeding of joints are usually collected and stored by the contractor. Many lay vessels are also equipped with a MRU unit for measurements of dynamic vessel motions, and in some cases the current profile is also monitored. This is especially the case for pipes with low bending stiffness and low ratio between weight and drag diameter (i.e. small pipe diameter) where current is important for the configuration of the pipe catenary. Together with the seabed these parameters constitutes the boundary conditions for a nonlinear time domain analysis of the lay operation. Such an analysis approach will have a wide range of application areas, from online monitoring to realistic back-calculation of a lay operation. During recent year’s work with the Ormen Lange field (see Figure 1) Marintek has developed a new generation of 3D pipeline analysis tools. Ormen Lange is the largest natural gas field on the Norwegian continental shelf. The field is situated 120 km northwest of Kristiansund. The seabed depths in the reservoir area vary between 800–1100m, and the terrain is very rough due to remnants from the Storegga slide. In the period 2006–2007 two 30" import lines, two MEG lines, and two umbilicals were installed at the Ormen Lange field. In the present paper monitored data collected during the installation of the 30" pipelines are used to back-calculate the lay operation. The agreement between observed and calculated lay parameters are reported and discussed.
Efficient Finite Element for Evaluation of Strain Concentrations in Concrete Coated Pipelines
Authors: Sævik Svein , Storheim Martin , Levold Erik
Published: July 2009

MARINTEK has developed software for detailed analysis of pipelines during installation and operation. As part of the software development a new coating finite element was developed in cooperation with StatoilHydro enabling efficient analysis of field joint strain concentrations of long concrete coated pipeline sections. The element was formulated based on sandwich beam theory and application of the Principle of Potential Energy. Large deformations and non-linear geometry effects were handled by a Co-rotated “ghost” reference description where elimination of rigid body motion was taken care of by referring to relative displacements in the strain energy term. The non-linearity related to shear interaction and concrete material behaviour was handled by applying non-linear springs and a purpose made concrete material model. The paper describes the theoretical formulation and numerical studies carried out to verify the model. The numerical study included comparison between model and full-scale tests as well as between model and other commercial software. At last a 3000 m long pipeline was analysed to demonstrate the strain concentration behaviour of a concrete coated pipeline exposed to high temperature snaking on the seabed.
Constraint Effects and Crack Driving Forces in Surface Cracked Pipes Subjected to Reeling
Authors: Donato Gustavo H. B. , Hippert Eduardo , Donato Guilherme V. P. , Ruggieri Claudio
Published: July 2009

This study reports an extensive set of non-linear analyses of circumferentially cracked pipe subjected to reeling. To describe the evolving levels of stress triaxiality ahead of crack front with increased loading, the present work employs the J-Q methodology to characterize fracture response for different crack configurations. The numerical simulations demonstrate that large values of crack-tip driving forces arise in cracked pipes under reeling which, at the same time, are accompanied by strong constraint loss at the crack-tip. Moreover, plane-strain analyses of clamped SE(T) fracture specimens reveal crack-tip conditions which are more similar to cracked pipes subjected to reeling with identical (relative) crack depths, which contrasts sharply to conditions displayed by standard fracture specimens such as the C(T) specimen. Overall, the results reported here encourage further investigations in the development and utilization of constraint-designed SE(T) specimens under clamp conditions in fracture assessments of cracked pipes subjected to reeling.
Life Extension Issues for Ageing Offshore Installations
Authors: Stacey A. , Birkinshaw M. , Sharp J. V.
Published: July 2009

With many offshore installations in the UK sector of the North Sea now reaching or being in excess of their original anticipated design life, there is a particular need to evaluate approaches to structural integrity management by offshore operators. Ageing processes can affect the structural integrity of the installation and demonstration of adequate performance beyond its original design life is thus a necessary requirement. This paper addresses the issues relevant to the life extension of ageing installations.
Design of Suction Piles for Deepwater HPHT Subsea Pipelines
Authors: Eltaher Ayman , Sun Jason , Jukes Paul
Published: July 2009

Thermal expansion management of high pressure and high temperature (HPHT) pipelines using buckle initiators and anchors has proven to be a viable approach for projects in the deepwater Gulf of Mexico. In this study, using suction piles as pipeline anchors is discussed, as suction piles represent the most commonly used anchoring technology in deepwater. Considerations and issues particular to the pipeline anchoring application are discussed and possible solutions are presented. In this study, the traditional suction pile analysis and design procedures (based on simple calculations and/or the finite element method) are discussed, and modifications and simplifications are proposed to suit the new application. In particular, applying the anchor loads at the mudline level, long-term loading and the absence of significant axial loading are examples of issues and particulars that are common to pipeline anchoring that would either simplify analysis or put restrictions on the validity of current suction pile design procedures. Different types of connections to pipelines and subsea structures are also proposed and addressed. This study extends the applicability of suction piles from mooring applications to thermal buckle and walking management for HPHT pipeline applications. It presents solutions to connection and design issues particular to suction piles as anchoring means for HPHT pipeline thermal management.
Evaluating Riser Interference From Experimental and Numerical Analysis
Authors: Ribeiro Elton J. B. , Ellwanger Gilberto Bruno , de Siqueira Queija Marcos , Uto Shotaro
Published: July 2009

When the oil exploration and exploitation moved away from the shore to deeper ocean, the riser interference became an important issue to be addressed during platform design. It became so important, particularly, when a great numbers of rigid risers are installed on the platform. Those kinds of risers are particularly used at Spar buoy and TLP platform. A conservative approach for riser interference design can result on the oversize platform or to reduce the number of wells hanging on it. On the other hand, a non conservative approach can bring serious problems, like collision of risers, which can cause a dent on the riser wall and it may reduce its fatigue life. In order to identify the hydrodynamic behavior of one riser placed in the vicinity of other one, Petrobras R&D Center carried out some experimental and numerical studies for getting their hydrodynamic behavior when they are aligned and spaced by 2, 3, and 5 times diameter.
On the Estimation of Directional Wave Spectrum Based on Stationary Vessels 1st Order Motions: A New Set of Experimental Results
Authors: Sparano Joa˜o V. , Tannuri Eduardo A. , Simos Alexandre N. , Matos Vini´cius L. F.
Published: July 2009

The practicability of estimating directional wave spectra based on a vessel 1st order response has been recently addressed by several researchers. The interest is justified since on-board estimations would only require only a simple set of accelerometers and rate-gyros connected to an ordinary PC. The on-board wave inference based on 1st order motions is therefore an uncomplicated and inexpensive choice for wave estimation if compared to wave buoys and radar systems. The latest works in the field indicate that it is indeed possible to obtain accurate estimations and a Bayesian inference model seems to be the preferable method adopted for performing this task. Nevertheless, most of the previous analysis has been based exclusively on numerical simulations. At Polytechnic School, an extensive research program supported by Petrobras has been conducted since 2000, aiming to evaluate the possibility of estimating wave spectrum on-board offshore systems, like FPSO platforms. In this context, a series of small-scale tests has been performed at the LabOceano wave basin, comprising long and short crested seas. A possible candidate for on-board wave estimation has been recently studied: a crane barge (BGL) used for launching ducts offshore Brazil. The 1:48 model has been subjected to bow and quartering seas with different wave heights and periods and also different levels of directional spreading. A Bayesian inference method was adopted for evaluating the wave spectra based on the time-series of motions and the results were directly compared to the wave spectra measured in the basin by means of an array of wave probes. Very good estimations of the statistical parameters (significant wave height, peak period and mean wave direction) were obtained and, in most cases, even the directional spreading could be properly predicted. Inversion of the mean direction (180° shift), mentioned by some authors as a possible drawback of the Bayesian inference method, was not observed in any case. Sensitivity analysis on errors in the input parameters, such as the vessel inertial characteristics, has also been performed and attested that the method is robust enough to cope well with practical uncertainties. Overall results once again indicate a good performance of the inference method, providing an important additional validation supported by a large set of model tests.
Using CFD to Study the Effects of Staggered Buoyancy on Dilling Riser VIV
Authors: Holmes Samuel , Oakley Owen H. , Raghavan Kamaldev , Constantinides Yiannis
Published: July 2009

This paper examines the potential benefit of the spaced arrangement of buoyancy modules to reduce the vortex induced vibration of deepwater drilling risers. Buoyancy modules are most often continuously applied to a riser to manage the top tension in the riser but they can also be spaced apart so that segments of bare riser are exposed. Field experience suggests this “staggering” of the buoyancy modules tends to suppress vortex induced vibration (VIV). However, the effects of staggered buoyancy are not well understood. In this paper we use CFD simulations to find the flow characteristics of various combinations of buoyancy modules and bare sections which include choke and kill lines. The effect of varying the percentage of buoyancy coverage is estimated based on the forced and free vibration characteristics of individual sections and combinations of the sections. Some direct reduction in VIV was observed but the benefits seem small.
A Numerical and Physical Comparison of a Geometrically Simple Fixed and Floating Oscillating Water Column
Authors: Sykes Rebecca K. , Lewis Anthony W. , Thomas Gareth
Published: July 2009

A truncated hollow vertical circular cylinder provides a useful conduit for analysing the behaviour and performance of an offshore Oscillating Water Column wave energy device. This paper presents the preliminary results from a numerical and physical modelling study of a fixed thin-walled and a floating thick-walled cylinder, together with the numerical modelling of a thick-walled fixed cylinder of the same internal diameter. Comparisons of the measured pressures internal to the column, and external to the body in the case of the floating model, are made with the predictions obtained using the numerical boundary-element model WAMIT. Body motions are also given for the floating model. The numerical modelling enables a comparison to be made between the diffraction pressure on a thin and thick walled cylinder of the same internal diameter.
Modal Dynamics of Large Wind Turbines With Different Support Structures
Authors: Bir Gunjit , Jonkman Jason
Published: July 2009

This paper presents modal dynamics of floating-platform-supported and monopile-supported offshore turbines, which are gaining attention for their ability to capture the immense wind resources available over coastal waters. Minimal dynamic loads and the absence of instability are imperative to the success of these turbines. Modal dynamics determine both loads and instabilities to a large extent, and therefore must always be analyzed. Also, to model the turbine, several aeroelastic computer codes require modes of the major components, e.g., the rotor blades and the rotor-nacelle support structure. To compute such modes, we used a recently developed finite-element code called BModes. The code provides coupled modes either for the rotating blades or for the support structure. A coupled mode implies presence of coupled flexural, axial, and torsion motions in a natural mode of vibration. In this paper, we use BModes to provide modes only for flexible towers, which carry head mass (rotor-nacelle subassembly modeled as a rigid body) and are mounted atop either a floating platform or a soil-supported monopile. The code accounts for the effects of hydrodynamic inertia, hydrostatic restoring, and mooring lines stiffness on the floating platform. It also accounts for the distributed hydrodynamic mass on the submerged part of the tower and for the elastic foundation surrounding the monopile. Results are obtained for three turbine configurations: land-based turbine, floating-platform-supported turbine, and monopile-supported turbine. Three foundation models are used for the monopile configuration. Results show that the hydrodynamic and elastic-foundation effects strongly influence the turbine modal dynamics.
Steady Drift of Floating Objects in Waves: Experimental and Numerical Investigation
Authors: Le Boulluec Marc , Forest Bertrand , Mansuy Emmanuel
Published: July 2009

Various objects, such as containers and barrels lost from cargo and container ships, can drift at sea. When remaining afloat they can be dangerous obstacles to navigation and in any case a danger for environment. The description of their probable trajectories is a key point for their location and recovery (Daniel et al, 2002). A simplified theoretical model based on the equilibrium between steady drift forces and viscous drag forces is proposed to calculate the steady drift velocity in waves only, without effect of wind nor current. Several comparisons with experimental results obtained from trials in a wave tank are given for cylindrical and box shaped objects.
Assessment of Offshore Structures for Life Extension
Authors: Ersdal Gerhard , Ho¨rnlund Erik
Published: July 2009

A considerable part of the structures on the Norwegian continental shelf have passed or are close to the design service life. Several of these structures are planned to be used further in an extended life. In most cases, traditional analyses in accordance with design methods are used for evaluating the structures for life extension. The present regulation and standards have so far had emphasis on design of new facilities, and a need for updated regulations and standards also taking into account ageing facilities and life extension is well overdue. This paper will discuss aspects of ageing that may reduce safety of offshore facilities, maintenance needs for ageing facilities, and propose general principles of assessment of ageing facilities for life extension. The paper is a summary of the research performed by and for the Petroleum Safety Authority - Norway.
Modeling and Simulation of an Underwater Remotely Operated Vehicle (ROV) for Surveillance and Inspection of Port Facilities Using CFD Tools
Authors: Valencia Rau´l A. , Rami´rez Juan A. , Gutie´rrez Luis B. , Garci´a Manuel J.
Published: July 2009

This article presents theoretical and computational studies with Computational Fluids Dynamics (CFD) tools of an Underwater Remotely Operated Vehicle (ROV), required to obtain reliable visual information, used for surveillance and maintenance of ship shells and underwater structures of Colombian port facilities. The thrust force is analyzed at the operational conditions by using CFD tools (FLUENT™, CFX™, COSMOSFLOW™) and the information about forces, torques and power of the vehicle’s thrusters is obtained. The commercial propellers were modeled by using a reverse engineering process with a 3D scanner and Computer Aided Design (CAD) software (RAPIDFORM™). The results obtained with the CFD package allowed to evaluate several operating scenarios of the vehicle that are used for feedback purposes in the design process of the ROV before it be manufactured.
Experimental Study on New Wave Measurement Using Passive Underwater Acoustics
Authors: Li Jing , Yu Dingyong , Liu Huaxing
Published: July 2009

The passive acoustic-based wave measurement via hydrophones is presented in this paper. It has the potential to measure non-intrusively, implement with low cost and with higher resolution. Details of experiments, real-time data recording and processing are described respectively. Particularly, the portable data acquisition system based on virtual instrument technique is designed to make the in situ measurement convenient and user-friendly. Special emphasis is put on FFT filtering technique to band pass the signal fast and efficiently. The key wave parameters, i.e. the mean wave period and the significant wave height, can be obtained from the comparatively safe and stable underwater by means of submerged hydrophones. Considering the pressure sensor has been widely used in the ocean wave measurement, it is deployed simultaneously to test the feasibility of the new system. The result shows that the present measuring system can give satisfactory measurement of significant wave heights and average wave periods in shallow water despite of the little deviation.
Prediction of Heave, Pitch and Roll Ship Motions in Waves Using RANSE Method
Authors: Kumar Manoj , Ananthasubramanian V. , Singh S. P.
Published: July 2009

The work aims to validate the usage of a general Computational Fluid Dynamics code to compute flow induced ship motions in waves. The motions of the ship and the wave dynamics have been implemented in the RANSE solver through user codes. Rigid body Motion equations are solved every iteration and the mesh is updated subsequently. The model chosen is a Wigley hull, for which experimental data are available in published literature. The 3D viscous free surface flow has been solved using finite-volume method, on a structured grid composed of hexahedral cells. The waves, which are produced in the numerical tank, are compared with experiments. The motion results, obtained in the current work, have also been compared with the results obtained using potential flow solver, SWAN. The ship motions predicted by the numerical simulation agree well with the experiments and promises to be a robust method for solving more practical and complex problems like prediction of slamming loads and ship behavior in an irregular seaway.