bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Validation for Motion of a SPAR-Type Floating Offshore Wind Turbine Using 1/22.5 Scale Model
Authors: Utsunomiya Tomoaki , Sato Tomoki , Matsukuma Hidekazu , Yago Kiyokazu
Published: February 2010

In this paper, motion of a SPAR-type floating offshore wind turbine (FOWT) subjected to wave loadings is examined. The proposed prototype FOWT mounts a 2MW wind turbine of down-wind type, whose rotor diameter is 80m and hub-height 55m. The SPAR-type floating foundation measures 60m in draft, having circular sections whose diameter is 12m at the lower part, 8.4m at the middle (main) part and 4.8m at the upper part. The FOWT is to be moored by a conventional anchor-chain system. In order to design such a FOWT system, it is essential to predict the motion of the FOWT subjected to environmental loadings such as irregular waves, turbulent winds, currents, etc. In this paper, the motion of the FOWT subjected to regular and irregular waves is examined together with the application of steady horizontal force corresponding to steady wind. The wave-tank experiment is made in the deep sea wave-basin at NMRI (National Maritime Research Institute), using a 1/22.5 scale model of the prototype FOWT. The experimental results are compared with the numerical simulation results for validation of the simulation method.
Characterization and Technical Comparison Between Steel Tube Umbilicals and Thermoplastic Hoses Umbilicals
Authors: Athayde Gonc¸alves Andre´ , de Almeida Fernando Buscacio , Dias Marco Antoˆnio , da Silva William Albuquerque , Reboh Yonathan
Published: February 2010

Subsea umbilicals are key part on the development of deep water fields. Generally, they are used to connect Platforms to all type of subsea equipment. Umbilicals’ component failure may result to great production losses. Traditionally, Petrobras uses thermoplastic hoses for chemical injection and control applications in its subsea systems; it has acquired a great deal of technical knowledge. Nevertheless, in recently presented layouts, the steel tubes have gained importance worldwide and this was due the increased water depth, integrity and higher pressure / higher temperature. This present paper makes a technical comparison between Steel Tube Umbilicals and Thermoplastic Hose Umbilicals with focus on Petrobras experience. The first part analyzes material selection criteria considering each structure type. Subjects such as material, welding and construction of both types are commented. This work also points to important subjects that suppliers must consider when designing and manufacturing umbilicals. The second part presents the Petrobras’ qualification tests of control umbilicals. Some of the tests that are used for steel tubes, thermoplastic hoses and high collapse resistant hoses are listed as well. On the third part, the focuses are the fatigue analysis, installation procedures and corrosion aspects. The work concludes listing some advantages and disadvantages when using Steel Tube Umbilicals or Thermoplastic Hoses Umbilicals, considering Petrobras scenarios.
An Evaluation of Wave Impact Indicators
Authors: Tian Zhigang
Published: February 2010

Wave impact on offshore structures has been the focus of several studies, due to its significant effect on offshore operations. We evaluate several parameters (wave impact indicators) which can be adopted to indicate the possibility of wave impact on offshore structures due to extreme waves. The indicators can be estimated quickly with given sea states, and thus may provide useful information to offshore structure designers at early design phases. Definitions of three wave impact indicators are presented and discussed. The first indicator, Ψ, is proposed by Stansberg (2008). The second one considered is a wave breaking parameter, μ, originally presented by Song and Banner (2002) in their construction of a wave breaking criterion. Finally, we propose a more generalized impact indicator, βn. The subscript n indicates its dependence on local wave steepness. Our study demonstrates that the three indicators are analytically related. To evaluate these indicators numerically, 2nd order random surface waves are generated with random phase method and Two-Dimensional Fast Fourier Transform (2D FFT). Hilbert analysis of the wave signal reveals that all indicators are able to identify steep and energetic waves that may potentially cause large wave impact loads. Further numerical study demonstrates that the quantitative correlation of wave impact loads to μ is less promising than that to Ψ and βn; while βn provides the best relationship to both local wave impact load and global wave load with its dependence on local wave steepness adjusted (i.e. adjusting n). The correlation is independent of sea states. Estimations and recommendations for thresholds of the two impact indicators (i.e. Ψ and βn with n = 1) are made based on model test results. With proper estimation of the thresholds, both indicators can be applied to predict wave impact and wave impact probability in given sea states.
Ultra Heavy Wall Linepipe X65: Material Performances for Severe Applications
Authors: Di Vito Luigi , Mannucci Gianluca , Mortali Giuseppe , Armengol Mariano , Novelli Paolo , Izquierdo Alfonso , Richard Gilles , Quintanilla Hector
Published: February 2010

Tenaris together with Centro Sviluppo Materiali launched a Joint Industrial Project aimed at developing heavy wall linepipes and evaluating their suitability for very severe applications possibly involving high service pressures and temperatures, large strains applied to the line, aggressive sour environment. The full project programme includes development of a the new generation of heavy wall products, laboratory scale evaluation of the material response when subjected to severe mechanical and environmental loading, evaluation of full component, pipe and girth weld, behaviour by means of full scale testing. Another technical publication in this conference (OMAE2009-79153) reports the activities of development of the new generation of heavy wall seamless pipes. In the present paper indeed, main outcomes of laboratory testing activities of the above programme on pipe material (grade X65, outer diameter 10 3/4″, wall thickness 46 mm) are reported as far as pipe body material properties are concerned. A fitted for purpose special testing programme, including mechanical and SSC laboratory scale testing, has been executed. Full thickness longitudinal specimens were extracted from the pipe body to apply severe strain cycling (1% and 2% maximum strain for various numbers of cycles, up to 200 cycles). Material showed a very encouraging behaviour, exhibiting an important reserve of strength even after application of severe strain cycling. Both mechanical, tensile compressive and toughness, properties and stress corrosion properties resulted to be suitable for the envisaged applications. Furthermore the pipe material showed suitable mechanical and stress-corrosion properties even after the severe cycling as well as after severe cycling and subsequent ageing. The influence of different straining conditions was also investigated, showing no significant difference in material properties after strain–ageing, due to different straining histories.
Straight Talk About Riser Tension and More
Authors: Chang Roger
Published: February 2010

One of most confusing issues in riser engineering is the riser tension. The infamous effective tension equation relates it to the so-called material tension with external and internal pressures. Controversy remains after numerous papers published trying to clarify the subject, because different interpretations were presented by different authors. Instead of explaining this ‘abstract’ equation mathematically using the free body diagram and differential equation as done in the literatures, this paper presents a down-to-earth interpretation that follows the riser loading history which starts with the Effective Weight to re-derive the same equation. Four keys to solve the riser tension mystery are identified; they are the hydrostatic head pressure vs. applied pressure, pressure generates the pressure end cap load vs. none generated, the vertical (top-tensioned) riser vs. bent (catenary) riser, and the single string riser vs. multiple strings riser. Based on these four keys, this paper will address the difference between the effective tension and material tension and identify which tension is to be used in the stress calculation. Also presented in the paper is the driver-reactor theory developed to explain the tension load distribution among riser strings due to Poisson’s effect with the applied pressure.
Studying the Impact of Unstructured Mesh Adaptation on Free Surface Flow Simulations
Authors: Allain Olivier , Gue´gan Damien , Alauzet Fre´de´ric
Published: February 2010

Engineering offshore problems require a continuous progress in the simulation of systems coupling structures and fluids with interfaces. The needs concern complex interface motions and fluid-structure interaction with slamming. The proposed methodology combines, in a parallel message passing algorithm, a level set based interface tracking, a standard finite element projection method on unstructured meshes and a dynamic mesh adaptation process for time dependent problems. This numerical method is applied to the study of a wedge impacting a free surface in two dimensions [1, 2] and the three-dimensional simulation of a breaking water column which impacts an obstacle [3] for which experimental results are available.
How Does Sedimentary Layering Affect the Generation of Tsunamis?
Authors: Dutykh Denys , Dias Fre´de´ric
Published: February 2010

This article presents preliminary results on the influence of sediment layers on the process of tsunami generation. The main scope here is to demonstrate and especially quantify the effect of sedimentation on vertical displacements of the seabed due to an underwater earthquake. The effects in the far field are left for future work. The elastodynamics equations are integrated with a finite element method and the fault is modelled as a dislocation in a half-space. A comparison between two cases is performed. The first one corresponds to the classical situation of an elastic homogeneous and isotropic half-space, which is traditionally used for the generation of tsunamis. The second test case takes into account the presence of a sediment layer separating the oceanic column from the hard rock. Some important differences are revealed. We conjecture that deformations in the generation region may be amplified by sedimentary deposits, at least for some parameter values. The mechanism of amplification is studied through careful numerical simulations.
Advanced Dynamic Stability Analysis
Authors: Zeitoun Hammam O. , To̸rnes Knut , Li John , Wong Simon , Brevet Ralph , Willcocks John
Published: February 2010

Several design approaches can be used to analyse the stability of subsea pipelines [1]. These design approaches vary in complexity and range between simple force-balance calculations to more comprehensive dynamic finite element simulations. The latter may be used to more accurately simulate the dynamic response of subsea pipelines exposed to waves and steady current kinematics, and can be applied to optimise pipeline stabilisation requirements. This paper describes the use of state-of-the-art transient dynamic finite elements analysis techniques to analyse pipeline dynamic response. The described techniques cover the various aspects of dynamic stability analysis, including: • Generation of hydrodynamic forces on subsea pipelines resulting from surface waves or internal waves. • Modelling of pipe-soil interaction. • Modelling of pipeline structural response. The paper discusses the advantages of using dynamic stability analysis for assessing the pipeline response, presents advanced analysis and modelling capabilities which have been applied and compares this to previously published knowledge. Further potential FE applications are also described which extends the applicability of the described model to analyse the pipeline response to a combined buckling and stability problem or to assess the dynamic response of a pipeline on a rough seabed.
Model Test of Ice-Structure Interaction
Authors: Guo Fengwei , Yue Qianjin , Bi Xiangjun , Liu Yuan
Published: February 2010

Different scales of model tests for investigating ice-structure interaction due to ice crushing have been conducted, and successful experiences and conclusions obtained from previous tests are summarized. On the other hand, the uncertainties within current methodology of ice-structure interaction model tests are discussed. Considering the nature of dynamic ice loads, several main aspects which should be taken into account during design of model tests are analyzed, including layout of the test system, application of scaling laws, and techniques of making model ice sheet, etc. Decision can be made for each of these aspects according to objective of the test, and based on this viewpoint, a small scale model test system was designed and constructed, a series of model tests were conducted and the ice-structure interaction processes which are the same as prototype phenomenon were observed.
Dual Gradient Drilling Will Control Shallow Hazards in Deepwater Environments
Authors: Elieff Brandee A. , Schubert Jerome J.
Published: February 2010

Currently the “Pump and Dump” method employed by Exploration and Production (E&P) companies in deepwater is simply not enough to control increasingly dangerous and unpredictable shallow hazards. “Pump and Dump” requires a heavy dependence on accurate seismic data to avoid shallow gas zones; the kick detection methods are slow and unreliable, which results in a need for visual kick detection; and it does not offer dynamic well control methods of managing shallow hazards such as methane hydrates, shallow gas and shallow water flows. These negative aspects of “Pump and Dump” are in addition to the environmental impact, high drilling fluid (mud) costs and limited mud options. Dual gradient technology offers a closed system, which improves drilling most simply because the mud within the system is recycled. The amount of required mud is reduced, the variety of acceptable mud types is increased and chemical additives to the mud become an option. This closed system also offers more accurate and faster kick detection methods in addition to those that are already used in the “Pump and Dump” method. It has the potential to prevent the formation of hydrates by adding hydrate inhibitors to the drilling mud. And more significantly, this system successfully controls dissociating methane hydrates, over pressured shallow gas zones and shallow water flows. Dual gradient technology improves deepwater drilling operations by removing fluid constraints and offering proactive well control over dissociating hydrates, shallow water flows and over pressured shallow gas zones. There are several clear advantages for dual gradient technology: economic, technical and significantly improved safety, which is achieved through superior well control.
Measurement of the Effect of Power Absorption in the Lee of a Wave Energy Converter
Authors: Ashton Ian G. C. , Johanning Lars , Linfoot Brian
Published: February 2010

Monitoring the effect of floating wave energy converter (WEC) devices on the surrounding wave field will be an important tool for monitoring impacts on the local wave climate and coastlines. Measurement will be hampered by the natural variability of ocean waves and the complex response of WEC devices, causing temporal and spatial variability in the effects. Measurements taken during wave tank tests at MARINTEK are used to analyse the effectiveness of point wave measurements at resolving the influence of an array of WEC on the local wave conditions. The variability of waves is measured in front and in the lee of a device, using spectral analysis to identify changes to the incident wave field due to the operating WEC. The power capture and radiation damping are analysed in order to predict the measured changes. Differences in the wave field across the device are clearly observable in the frequency domain. However, they do not unanimously show a reduction in wave energy in the lee of a device and are not well predicted by measured power capture.
Bends for Critical Line Pipe Projects: Advantages of the Off-Line Full Quenching and Tempering
Authors: Mannucci Aldo , Anelli Ettore , Zana Fabio , Tommasi Claudio , Armengol Mariano , Alleva Laura , Porcu Giorgio
Published: February 2010

Recent trends for linepipe projects reflect a sustained increasing complexity: Sour Service (SS), High Temperature & High Pressure (HT/HP) field conditions, deep and ultra-deep water oil and gas transportation, Artic and Artic “alike” areas. This reflects into stringent requirements for manufacturing and testing of the concerned products, which are not only the straight pipes but also a number of accessories, among which bends are the ones presenting the most complex combination of critical issues. As long as a whole chain reliability standpoint is assumed as the main concern, the design, production and supply of the bends have become a key stage within a linepipe project. Bends for linepipe projects are produced in general by hot induction bending (HIB). Two different fabrication routes can be clearly identified: HIB followed by Stress Relieving (SR) and HIB followed by off-line full quenching and tempering (Q&T). The first method is known as “Traditional route (TR)”, while the second one as “Quenching-Tank (QT)”. A large investigation program was carried out involving the most recognised benders in Europe. The matrix of industrial trials comprised a dimensional size range from 168 to 406 mm OD, 8 to 34 mm WT; X60 to X70 steel grades, different bending and post-bending heat treatments conditions and mother pipe chemistries. For each analysed item, the final bend, the corresponding mother pipe and samples taken in as-bent / as-quenched (TR / QT) conditions were fully characterised in terms of mechanical properties, hardness profiles and microstructure features. As a result, a much better performance was found for the bends produced by the off-line full Q&T method, principally due to the better quenching efficiency with respect to the in-line system. Production of bends through out the traditional method can be seen as a reliable option for bends which are not going to face hard conditions in the field, and therefore the corresponding specification requirements are no stringent as well (i.e. X52 grade or lower, Charpy tests required at 0°C or higher temperature, no corrosion tests required, etc.). If either stringent conditions are required or X60-X80 steel grades are involved, the off-line quenching tank route becomes the reliable option.
Wave Measurements at Eastern Green Canyon During Hurricane Ike
Authors: Rijken Oriol , Bangs Adam
Published: February 2010

Wave measurements were obtained at an Eastern Green Canyon location during hurricane Ike in September 2009. The eye of the hurricane passed approximately 68 nautical miles to the South West of the measurement location. The significant wave height was above 30 ft for about 20 hours and above 40 ft for about 5.5 hours. The wave time series provide an insight into the wave field as the storm approaches and leaves the location. One of the interesting features observed was that there were repetitive sequences, where each sequence consisted of a period of increased wave energy followed by periods of reduced wave energy. Each sequence lasted approximately one hour. Measured wave crest, wave trough and wave height distributions are discussed. One unique wave event was observed. This event was characterized by a predictably-sized crest followed by a very deep trough.
Video Observations of Dynamic Embedment During Pipelaying in Soft Clay
Authors: Westgate Z. J. , White D. J. , Randolph M. F.
Published: February 2010

The as-laid embedment of a pipeline is an important parameter that affects many aspects of pipeline design. Offshore pipelaying is a dynamic process that causes pipelines to embed deeper than predicted based on static penetration models. This additional embedment is due to cyclic pipeline motions at the seabed that soften and displace the soil. This study presents observations from an ROV-based video survey of dynamic pipeline motion and as-laid embedment. The pipeline had a diameter of 12 inches and was installed from a J-lay vessel in 140 m water depth onto soft clay. The observations illustrate typical trends of embedment and seabed disturbance. Different lay conditions were encountered including downtime events and laydown of the final section of pipeline using a chain. From these observations, the effect of the dynamic behavior is quantified. The results show that in this case dynamic lay effects resulted in an as-laid embedment that was an order of magnitude greater than that from the submerged pipeline self weight alone, and was up to five times greater than the static embedment accounting for the vertical stress concentration from the pipeline catenary.
New Positioning of the Ocean Space as a Marine Resource: Emotional Values Inherent in the Ocean Space
Authors: Oikawa Tomoe , Kondo Takeo , Yamamoto Kazukiyo , Ogawa Shinji
Published: February 2010

The sea is abundant in various resources. In fact, energy resources, mineral resources, and food resources have come to be regarded as marine resources. On the other hand, the positioning of the ocean space as a marine resources is tenuous. It has been evaluated just from a geopolitical viewpoint, such as the physical extent and depth or political/economical relationships. The ocean space, however, emotional values as humanity, including relaxing, comforting, and encouraging effects. These emotional values of the ocean space have undoubtedly contributed to urban waterfront redevelopment and ocean resort development. The aim of our research is to position the ocean space as a new form of marine resource by clarifying emotional values inherent in the ocean space through psychological analysis while focusing on its value from the viewpoint of human sensibility.
Psychological Effects Resulting From Sailing Access Dinghies
Authors: Kondo Takahiro , Kondo Takeo , Yamamoto Kazukiyo , Matsushita Rumi , Kobayashi Takako
Published: February 2010

Access dinghies were designed in Australia to improve the quality of life and extend the scope of people’s activity. Unlike other dinghy yachts, access dinghies are universal-design pleasure boats that allow a wide range of people to enjoy sailing, regardless of age, the degree of disability, and experience. In this research, a questionnaire survey was conducted on people enjoying access dinghies using the semantic differential method to investigate broadening of the range of spatial activities and the mental rehabilitation effect resulting from sailing access dinghies. The results demonstrated that sailing access dinghies has a positive mental effect upon people.
Assessment of Designated Managers of Public Marinas From the Viewpoint of User’s Convenience
Authors: Katayama Yoshiyuki , Kondo Takeo , Yamamoto Kazukiyo , Watanabe Shuta , Okuzawa Bungo , Tamura Kouta , Egami Kazuya
Published: February 2010

Coastal spaces (including land areas and sea areas) in Japan are managed by the state or local governments, and their private use by individuals was not allowed unless contribution to public interest was ensured. Since the Designated Manager System for public facilities was established in 2003, management of an increasing number of public facilities based on the Local Autonomy Laws has been consigned to private sectors (called “designated managers”) nominated through the decisions of the local councils, rather than to public bodies based on the conventional “Management Commission System.” Regarding marinas including land areas and sea areas, we conducted a comparative analysis of their convenience, comfort, serviceability, and so forth before and after introduction of the Designated Manager System from the viewpoint of marina users to discuss how the private sector should manage coastal regions.
Main Factors of Ice Sheet-Conical Structure Interaction Process Based on Field Monitoring
Authors: Xu Ning , Qu Yan , Yue Qianjin , Bi Xiangjun , Palmer Andrew Clennel
Published: February 2010

Ice-structure interaction plays a central part in determining ice loads and ice-induced vibrations. This is a controversial research issue, and many factors make the problem more complicated. The authors have been monitoring several ice resistant structures in the Bohai Sea for twenty years, and have measured ice forces and simultaneously observed ice-structure interaction processes. This paper describes typical physical ice sheet-conical structure interaction processes, field data and theoretical explanations, for different ice conditions and structure dimensions. The conclusions are more widely applicable, and we relate them to field work on ice-resistant conical structures in other ice-covered regions. Further work will quantify ice loads on conical structures once the interaction process is understood.
Measurement of Green Water on a 3D Structure
Authors: Ariyarathne Kusalika , Chang Kuang-An , Mercier Richard
Published: February 2010

The present study investigates the velocity fields of plunging breaking waves impinging on a three-dimensional simplified ship-shape structure in a laboratory wave tank. Green water was generated as the waves break and overtop the structure. Bubble image velocimetry (BIV) was used to measure the velocity field of green water along the centerline of the deck. Two plunging wave conditions were tested and compared: one with waves impinging on the vertical wall of the structure at the initial still water level; the other with waves impacting on the horizontal deck surface. The velocity fields are quite different for the two cases even though the incoming wave heights and the wave periods are nearly identical. It was observed that the maximum horizontal velocity is higher for the case with waves compacting on the deck. The waves also passed the deck quicker than the other case. For both cases the profiles of the green water velocity shows a non-linear distribution with the maximum velocity occurring near the front of the water.
A Stability Design Rationale: A Review of Present Design Approaches
Authors: To̸rnes Knut , Zeitoun Hammam , Cumming Gary , Willcocks John
Published: February 2010

Pipeline hydrodynamic stability is one of the most fundamental design topics which are addressed by pipeline engineers. In its simplest form, a simple force balance approach may be considered to ensure that the pipeline is not displacing laterally when exposed to the maximum instantaneous hydrodynamic loads associated with extreme metocean conditions. If stability can be ensured in a cost efficient way by applying a minimal amount of concrete weight coating only, this method when applied correctly, can be regarded as a robust and straightforward approach. However in many cases pipeline stabilisation can be a major cost driver, leading to complex and costly stabilisation solutions. In these circumstances, the designer is likely to consider more refined methods in which the pipeline is allowed to displace under extreme conditions. This paper discusses various design approaches and acceptance criteria that are typically adopted in pipeline stability design. Both force balance methods and calibrated empirical methods which are typically defined in modern design codes, are discussed in terms of their applicability as well as their limitations. Both these approaches are based on the assumption, directly or indirectly, that lateral displacement is a Limit State in its own right. It will be argued that this assumption may lead to unnecessary conservative design in many circumstances. It will be demonstrated that even if relatively large displacements are permitted, this may not necessarily affect the structural integrity of the pipeline. An alternative stability design rationale is presented which is based on a detailed discussion of the Limit States pertaining to pipeline stability. This approach is based on the application of advanced dynamic stability analysis for assessing the pipeline response. Pipeline responses obtained through advanced transient finite element analyses is used to illustrate how a robust design can be achieved without resorting to strict limits on the permissible lateral displacement.
Three-Dimensional Numerical Model of Wind-Driven Current in a Lake Based on POM Model
Authors: Hao Jialing , Jiang Xiaoxin , Yang Juan
Published: February 2010

Lake current is the cause for the transport of many matters such as suspended sediment, algae, contaminant, therefore, it must be estimated fairly accurately. Generally speaking, the flow in many lakes is weak and the flow direction is follows dominated mainly by the wind direction on lake surface. Correct simulation of the wind-driven current in a lake requires using a three-dimensional hydrodynamic numerical model. The main factor affecting the lake hydrodynamic processes is wind. Because wind-driven current have important influence for the matter exchange and energy transform in a lake, and field observations are comparatively difficult, numerical modeling is the main method to estimate the wind-driven current nowadays. The numerical modeling of 3D tidal flow and mass transportation in this study was performed using the Princeton Ocean Model (POM). The model is validated by calculating wind-driven current in a rectangular flume [1][2]. The contaminant transport modeling in the Yangchenghu Lake is performed with POM using an orthogonal curvilinear grid in horizontal direction and sigma coordinate variation in vertical direction. An analysis of model results is presented.
Development of an Acoustic-Based Riser Monitoring System
Authors: Wei Dai , Bai Yong
Published: February 2010

Recent incidents with drilling risers in the Gulf of Mexico have led the industry’s application of more stringent integrity assurance requirements to its deepwater risers. Riser monitoring provides information that enables the operator to measure riser configurations and fatigue damage, confirm the integrity of the riser, assist with operational decisions, optimize inspection, maintenance and repair schedules /procedures and calibrate design tools. Monitoring can also improve the understanding of complex behavior of risers for the improvement to future design and analysis tools. This paper presents the characters of three different monitoring systems that suit specific objectives and requirements. An example project of acoustic approach is introduced with its working mode and design scheme.
Polynomial Models Applied to the Analysis of Slender Marine Structures
Authors: de Sousa Fernando Jorge Mendes , Sagrilo Lui´s Volnei Sudati , de Lima Edison Castro Prates
Published: February 2010

Until recently, risers were designed considering only few regular sea analyses and high safety factors. The increase of the computers processing capability and the simultaneous reduction of their costs, however, allowed riser designers to change their project procedures. Nowadays, risers can be designed considering not only much more analyses, but also more complex ones. Following this new tendency, methodologies that aim to reduce the computational costs of random analyses represent an important research line. The main purpose of this work is to develop a methodology based on polynomial models to predict time series of a riser response parameter. This methodology considers as inputs the movements of the platform caused by wind, wave and current. The desired response parameter investigated in this paper is the top tension, although the procedure to evaluate stresses is very similar. This methodology can be applied in the initial phases of the riser project, accelerating the selection of a structure that satisfies project criteria, and in the representation of the riser dynamic response in coupled analyses, reducing their computational costs.
A Moored Arctic Floater in First-Year Sea Ice Ridges
Authors: Dalane Oddgeir , Aksnes Vegard , Lo̸set Sveinung , Aarsnes Jan Vidar
Published: February 2010

First-year sea ice ridges are a major concern for structures operating in the Arctic and will in many cases give the design mooring load. In this paper, a moored conical floater, somewhat similar to the well-known Kulluk, is studied in first-year ridges. The study is based on model tests performed at HSVA in several ridges with different properties. Mooring forces and floater response resulting from interaction with different ridges were compared with respect to ridge properties, ridge behaviour and simulated ice management. Clearance of accumulated rubble upstream the structure was the dominating physical process in the ridge-structure interaction. Accumulation of rubble caused large mooring forces. The amount of accumulated rubble depended on the ridge cross-sectional area, thus the mooring forces increased with ridge cross-sectional area. Large mooring forces were also experienced after the initial position of the ridge was passed due to difficulties with clearing of accumulated rubble.
Time Domain Simulation of the Maneuvering of a Vessel in a Seaway
Authors: Hermundstad Elin Marita , Hoff Jan R.
Published: February 2010

This paper presents a new unified seakeeping-maneuvering simulation model valid for surface ships and underwater vessels. If the total ship motions are derived from the traditional formulations for the hydrodynamic and maneuvering models, considering them as two separate problems, the results will be inconsistent. It has therefore been necessary to develop a unified formulation which calculates the total ship motions including both the maneuvering aspects and the wave induced motions. Focus in this study has been on submarines. Examples of application of the developed time domain simulation code are given. These are simulations of the response and corresponding control plane forces of a submarine in straight line motions in regular waves at given headings. The developed code can also be used to e.g. simulate turning circles. This has been conducted for the same submarine, and the results are compared to experimental results. Additionally, simulations of the response of a surface vessel (Wigley hull) with forward speed in regular waves at given headings are presented. In this case only the potential forces are considered. The results from the simulations are used to establish motion transfer functions, which are compared to other numerical and experimental results. There are some limitations in the developed method which affects the application area of the numerical code. This refers particularly to underwater vessels. This will be addressed, and further possible development of the method will be discussed.
Construction Techniques and Theoretical Researches of Modern Pneumatic Caisson
Authors: Qing Bao-Hua , Li Yao-Liang , Zhou Xiang-Lian , Wang Jian-Hua
Published: February 2010

A ventilation shaft of internal metro tunnel in complicated geological conditions was constructed by unmanned remote controllable pneumatic caisson. Axisymmetric finite element model and large deformation analysis were employed to simulate its construction. The optimum excavation scheme was obtained by comparing caisson stable state and soil plastic zone distribution in various construction stages. In-situ monitoring was also adopted to analyze the influence of its construction on ground lateral displacement and surface settlement. Results show that all changes of surrounding environment were controlled in the allowable range. The key construction techniques in this successful project would be beneficial reference for similar projects in the future.
Prediction of Hydrogen Embrittlement in 25% Cr Duplex Stainless Steel Based on Cohesive Zone Simulation
Authors: Olden Vigdis , Thaulow Christian , Berstad Torodd , O̸stby Erling
Published: February 2010

Laboratory experiments and cohesive zone simulation of Hydrogen Induced Stress Cracking in SENT tests specimens of 25% Cr duplex stainless steel have been performed. A polynomial formulation of the traction separation law and hydrogen dependent critical stress was applied. Best agreement with the experiments was found for an initial critical stress of 2200 MPa and a critical separation of 0.005 mm. Proposed threshold stress intensity factor and lower bound net section stress is 20 MPa√m and 480 MPa. High crack growth rates and typical hydrogen influenced fracture topography suggest large influence of the stress and strain in the fracture process zone on the hydrogen diffusion rate.
Use of a Stem Device for VIV Mitigation on a Dry Tree Semi-Submersible
Authors: Gupta Apurva , Murray John , Li Bin , Mukundan Harish , Hussain Anis
Published: February 2010

The offshore industry is devoting considerable effort to develop a dry tree production Semi-submersible with motion characteristics similar to a Spar but with the functionality of a Tension Leg Platform (TLP) or a Semi-submersible in terms of fabrication, installation and commissioning. Installation of these Semi-submersibles in the Gulf of Mexico environment exposes the risers to high surface current which result in high fatigue damage due to Vortex Induced Vibration (VIV). In the existing dry tree production systems, the Spar shields the riser from the high velocity surface currents in depths to approximately 600 ft. In the dry tree Semi-submersible the upper sections of the risers are exposed to surface currents. In addition, most dry tree Semi-submersibles designs have to support Keel Joints similar to a Spar. Thus, installing and replacing conventional VIV mitigation devices like the fairings and strakes could become difficult. In comparison, the TLP has no keel guides making it easier to install risers with strakes or fairings to improve the riser’s response to currents in terms of VIV. There are two basic proven techniques to reduce VIV damage on a riser. These involve application of standard fairings or strakes and direct protection of an exposed riser to currents. This paper discusses a methodology for VIV suppression using a riser stem. This mechanism does not reduce the VIV directly on the riser, but it in fact shields the riser from the surface currents, and thus reduces the fatigue damage on risers. This riser is shielded inside a conduit section called a stem which extends from the deck of the Semi-submersible to the keel. The paper quantifies and discusses the reduction in fatigue damage when the stem is used. The analysis is based on typical deep water current conditions for the Gulf of Mexico.
CFD Modeling of Fully Nonlinear Water Wave Tank
Authors: Wu Guangyu , Oakley Owen H.
Published: February 2010

In this study, we use CFD simulations to model a fully nonlinear water wave tank. Firstly, for validation purpose, regular waves with different wave steepness are simulated and the results are compared with the second-order potential flow solution for the free surface displacement time history at fixed locations, the instantaneous free surface spatial profiles, and the velocity and pressure fields under the free surface. It is shown that for small wave steepness, the CFD solutions agree very well with the second-order potential flow solutions while for large wave steepness, apparent differences between these two solutions are observed. The validation and fully nonlinear feature of the CFD solutions are therefore demonstrated. Secondly, plunging breaking waves are simulated using the CFD wave tank by focusing a large number of linear wave components at a prescribed time and location. The time histories and normalized variance of free surface displacement at various locations along the tank are obtained from the CFD simulation and compared to the lab experiments. In particular, the CFD results predict reasonably well the wave breaking location and the loss of energy flux due to wave breaking. Finally, a vertical circular cylinder is placed in the CFD wave tank to simulate the breaking wave impact on a fixed structure. The pressure time histories at various points on the cylinder surface are obtained for several cylinder locations with respect to the prescribed wave breaking point. The CFD results are compared with previous experiments and discussed.
Numerical Analysis of a Flexible Pipe With Damaged Tensile Armor Wires
Authors: de Sousa Jose´ Renato M. , Pinho Aline Nacif , Ellwanger Gilberto Bruno , Lima Edison C. P.
Published: February 2010

This paper focus on the structural analysis of a 2.5″ flexible pipe with one up to five broken wires in its outer tensile armor. The pipe is supposed to be under pure tension and the effect of the number of ruptured wires on its response is discussed. A three-dimensional nonlinear finite element model devoted to analyze the local mechanical response of flexible pipes is proposed and employed in all performed analyses. This model is capable of representing each wire of the tensile armors and, therefore, localized defects, including total rupture, may be adequately represented. The obtained results pointed to high stress concentration in the wires near the damaged ones as well as a significant increase in the axial rotation of the pipe. Moreover, the stresses in the inner carcass and the pressure armor are also affected by the rupture of wires in the outer tensile armor.
Numerical Experiments of Acoustic Path Travel Time Variations Due to Combined Surface Wave Effects
Authors: Lewis James K.
Published: February 2010

A study was conducted to investigate the impacts of various ocean surface wave effects on ray path arrival times between an acoustic source and receiver. Observations collected during 2003 showed arrival time variations up to 6 ms over ∼30 s intervals. Numerical experiments were performed to see if these variations could be accounted for by wave-induced background currents, the Doppler effect resulting from surface motion due to waves, and changes in path lengths due to sea level variations due to waves. The simulations gave maximum impacts on travel times of < 1 ms. The Doppler effect was quite small, with the effect of the wave-induced currents at times being ∼3 times larger than the Doppler effect. The greatest effect on travel times was the change in path length due to wave-induced sea level changes. The work suggests that the larger observed arrival time variations are a result of some phenomenon that occasionally masks ray paths between a source and receiver. Based on the numerical experiments and observations, a paradigm is put forward to best determine arrival times.
Clay-Concrete Pile Interface in Various Marine Environments
Authors: Baykal Go¨khan , Edinc¸liler Ays¸e
Published: February 2010

The interface shear strength between soil and concrete is an important design parameter for the calculation of the capacity of a pile. Due to small displacements required for the mobilization of the friction capacity of piles, the interface shear strength is a reliable parameter for the determination of axial pile capacity. For bored piles the end bearing capacity development requires large displacements for full mobilization. In the coastal regions piles are frequently used as deep foundation systems for several near shore and marine structures. The effect of different salt contents of various marine environments on the interface shear strength of pile soil interface is investigated. The objective of this study is to evaluate the interface properties between kaolinite clay sedimented at different salt contents and concrete to model the piles constructed in various marine environments ranging from Black Sea with the lowest salt content to Red Sea with the highest salt content. Kaolinite clay is mixed with marine salt and water at salt percentages of 0, 0.1, 0.2, 0.3, and 0.4 per cent by weight and the samples are placed in a consolidation cell. The mixtures are prepared at a water content of two times the liquid limit of kaolinite. The samples are consolidated at over consolidation ratios of 1, 2 and 4 to study the effect of stress history. Split samples are prepared having one half concrete and the other half clay. The direct shear test results revealed that the interface friction angle increased by increasing salt contents upto 20 per cent when compared to that of fresh water sedimented samples. The overconsolidation ratio did not cause a significant change in the interface properties for the case studied. The results of this preliminary study may help to understand better any change in salt content on the capacity of piles constructed at saline environments. Fresh water leaching of sediments formed at saline environments may be a concern when the capacity of piles is considered under such conditions.
Friction Pressure Correlations for Oilfield Polymeric Solutions in Eccentric Annulus
Authors: Ogugbue Chinenye C. , Shah Subhash N.
Published: February 2010

Polymer fluids are utilized extensively in the petroleum industry for viscosity enhancement and friction pressure reduction during turbulent flow. Selection of the appropriate correlation for the desired fluid and flow regime is very important for the accurate determination of frictional pressure losses. A range of correlations has been published for predicting frictional losses under annular flow conditions. All these correlations are based on certain assumptions, which limit their application under different operating conditions. This paper presents the results of an experimental study carried out to develop a reliable frictional pressure loss correlation for polymeric solutions in a fully eccentric annulus. Fluids investigated include Water, Guar, Xanthan, and Welan gum under conditions typically encountered in drilling and completion operations. The frictional pressure losses of these polymeric fluids exhibiting drag-reducing characteristics are investigated and analyzed as a function of generalized Reynolds number for each fluid. The experimental set-up includes 200 ft of 1 1/2-in. straight tubing, and 200 ft of (3 1/2-in. × 1 3/4-in.) fully eccentric annuli. Data analysis enabled the development of an improved correlation for polymer solutions in a fully eccentric annulus. Fluids apparent viscosity at 511 sec−1, generalized Reynolds number, and diameter ratio, all of which can be easily determined in the field, were selected as independent variables for the new correlation. Experimental data show that the new correlation estimates friction pressure losses in fully eccentric annuli much better than previously published equations.