bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind and Wave Study for Off-Shore Wind Farm Applications
Authors: Armenio Elvira , Laforgia Domenico , Milanese Marco , Mossa Michele
Published: November 2011

The study focuses on wind-waves-bottom characterization as first step in the feasibility evaluation of an offshore windfarm in the offing of Apulian coast - Italy. Planning offshore windfarm, hydrodynamic and aerodynamic fields, and their interaction, must be investigated. Waves studies and their transformation due to diffraction, shoaling, refraction, etc. are fundamental to predict the effects that sea could have on turbine’s foundation, especially for floating turbine, mooring lines, structural stress and moreover to consider the influence that frequently high waves may have on installation, operation and maintenance. In this study, starting from wind data and a nautical map, a good determination of the wave motion has been obtained. Particularly, three-hours measurements of wind intensity and direction, by on-land anemometer, have been used. Wind data of a period of time of 45 years, from 1951 to 1996, have been statistically processed to extract the most relevant winds with velocity and duration bigger than 10 knots and 6 hours respectively. Using the nautical map of the area under investigation, the sea bottom morphology has been reconstructed to obtain a model of bathymetry. After that, the bathymetric curves have been traced on the map, converted in a depth matrix and then transformed into an interpolated grid point. Subsequently, the assessment of waves propagation has been obtained through both Jonswap Spectrum and SPM method and the results have been compared. Finally, the wave heights and peak periods were calculated with reference to return period of fifty years and used as input in two model: Nearshore Spectral Waves (NSW) model and Parabolic Mild Slope Spectra Waves (PMS) model. In conclusion, this study can represent a useful approach to plan an offshore windfarm.
Simulation of Free Surface Benchmark Problems Using Level Set and SPH Methods
Authors: Repalle Nitin , Rafiee Ashkan , Thiagarajan K. P. , Kantharaj Murali
Published: November 2011

Multiphase flows are present in many different industrial and research applications. The accurate tracking of interfaces is therefore an important part of numerical simulation of many physical phenomena. One of the challenges in modeling multiphase flows is to capture a moving interface with a large deformation, especially the breaking and merging of the interface. In the recent past, level set method and Smoothed Particle Hydrodynamics (SPH) have emerged as efficient and robust methods to handle multiphase flows with large topological changes and high density ratios. The capability, efficiency and accuracy of these techniques are compared for a range of benchmark problems, such as gas bubble rising in a viscous liquid and collapse of a column of water. The results are compared with available numerical and experimental data.
Effects of Ammonia on Electrochemical Chlorine Generation for Ballast Water Treatment
Authors: Guney Ceren Bilgin , Yonsel Fatma
Published: November 2011

Chlorine disinfection is one of the most common used techniques to eliminate the ballast water organisms. However safety risks during handling and onboard storage of chlorine gas or HOCl solutions are subjects of concern. Electrochemical generation of active chlorine on board would eliminate such unfavorable features of chlorine disinfection. The characteristics of seawater have a direct effect on the capability of an electrochemical system to function successfully. Seawater contains a wide range of salts at various concentrations and combinations. Additionally, coastal seawater may also contain ammonia beside domestic based organic pollutants. The aim of this study is to determine the effect of ammonia which will go under electrochemical process during disinfectant production. It is figured out that ammonia leads to less total and free available chlorine concentrations in electrochemically generated disinfectant. Consequently, the presence of ammonia increases the volume of disinfectant needed to disinfect the same amount of biomass. This work has been conducted within the project “BaWaPla — Sustainable Ballast Water Management Plant”, funded by the European Union under contract number 031529, which is started at 15/11/2006 and finalized at 15/05/2010.
Evaluation of the Performance of Inconel 718 Fasteners Subjected to Cathodic Protection Systems in Offshore and Subsea Applications
Authors: Pires Fabio , Clements Richard , Santos Fabio , Clevelario Judimar , Sheldrake Terry
Published: November 2011

Fasteners manufactured with Inconel 718 alloy are being widely used in offshore and subsea applications due to the material’s high strength, when compared to other nickel alloys, and its inherent corrosion resistance. However, concerns have been raised over its utilization in applications where cathodic protection or impressed current systems are in place. These concerns relate to the susceptibility to hydrogen embrittlement that Inconel 718 alloy may present depending on its processing, microstructure, hardness and actuating stresses. Over the last few years, much has been discussed on the suitability of the alloy for subsea applications. The development of special thermal cycles for the ageing of the alloy has been necessary to provide a consistent material with a maximum hardness of 35 HRc, and a microstructure free of detrimental phases without jeopardizing the overall mechanical properties of the alloy. Wellstream has developed a test programme focused on the assessment of Inconel 718 behavior when subjected to cathodic protection systems. Through this programme, it was possible to demonstrate the suitability of Inconel 718 alloy in subsea applications when the resulting microstructure and hardness are properly controlled, and bolt loading is within normal working limits.
Modelling and Simulation of a Floating Oscillating Water Column
Authors: Kurniawan Adi , Hals Jo̸rgen , Moan Torgeir
Published: November 2011

This article describes the computation of hydrodynamic parameters, modelling, and simulation of a floating oscillating water column wave energy device. The frequency-domain hydrodynamic parameters are computed using a three-dimensional panel method. Parameters related to wave radiation due to applied air pressure inside the air chamber are evaluated from reciprocity relations, without having to solve explicitly for the radiation potential due to the applied pressure. The dynamics of the whole system, including nonlinear air compressibility and relief valve characteristics, is modelled using bond graph as a tool. Both time- and linear frequency-domain models are described and selected simulation results, especially the converted power, are presented.
Industry Practices for the Management of Ageing Assets Relevant to Offshore Installations
Authors: Sharp John V. , Wintle John B. , Johnston Carol , Stacey Alex
Published: November 2011

This paper describes the results of a survey for the UK regulator of industrial practices for the management of ageing assets and life extension that are relevant to offshore structures. The industry sectors surveyed covered aircraft, process plant, nuclear installations, bridges and ships and tankers, which like the offshore sector, all have mature and/or degrading assets important to safety. The conclusion is drawn that although the offshore sector is aware of the need to give more attention to the management of ageing and life extension, it would benefit from a more integrated and consistent approach that is present in other sectors. Examples of where the offshore sector can benefit from practices in other sectors are described.
Application of Actual In-Service Spectrum to SCR Girth Welds
Authors: Darcis Philippe P. , Marines-Garcia Israel , Aguilar E. , Ruiz Eduardo A. , Quintanilla Hector M.
Published: November 2011

Fatigue is normally the limiting design criterion for Steel Catenary Risers (SCRs) and it represents its major engineering challenge. As a consequence, design of this component generally trusts on a very good fatigue resistance. A common practice, widely adopted in oil recovery industry, is to certify that specific welding procedures have proper fatigue strength equal or better than the one adopted in design; such fatigue strength is commonly evaluated under constant amplitude loading. However, SCRs are subjected to complex loading spectrums which are characterized by a wide range of loading amplitudes induced by different sources that include the overall system response of the barge. Therefore, interest arises in verifying the component response to representative loading spectrums of the actual SCR in-service conditions and determining if actual riser components qualification, under constant amplitude loading, presents discrepancies with their resistance under in-service fatigue conditions. This situation has motivated full scale fatigue performance evaluation of SCR girth welds under constant and variable amplitude loading spectrums. The experimental approach was focused on estimating the damage introduced by loading cycles of various magnitudes. Constant and variable amplitude results were compared and the accuracy of Miner’s linear cumulative damage rule has been evaluated. The experimental approach was focused on estimating the damage introduced by loading cycles of various magnitudes. Constant and variable amplitude results have been compared and the accuracy of Miner’s linear cumulative damage rule [1] has been evaluated.
A Direct Time Domain Simulation of Floating Structures With Mooring Lines
Authors: Chen Jingpu , Zhu Dexiang
Published: November 2011

A direct time domain method is established for analyzing the interactions between the floating structures and mooring lines. The motions of floating structures are solved by a Rankine Panel method in time domain, while the static restoring force characteristics of the mooring system is taken into account. As numerical examples, the motions of two SPARs are solved by this direct time domain method. The numerical results of present method are analyzed and compared with model test results.
Effects of Varying Tension and Stiffness on Dynamic Characteristics and VIV of Slender Riser
Authors: Chen Weimin , Zheng Zhongqin , Li Min
Published: November 2011

A time-domain approach for predicting dynamic characteristics and vortex-induced vibration (VIV) response of deepwater risers is proposed by coupling finite element simulation and a hydrodynamic model. Numerical results indicate that axially varying structural parameters can efficiently change the modal wave length as well as the modal displacement. Further, VIV response indicates that vibration amplitude depends on a complex synthetical effect of tension, stiffness and wave length. Generally speaking, for lower modes the response amplitude is larger at the axial position where tension is smaller, whereas for higher modes the response amplitude is larger at the axial position where bending stiffness is lower. Moreover, vibration wave velocity increases with increasing modal wave length.
A Finite Element Study of Multi-Mode VIV of Slender Riser Experiencing Non-Uniform Flow
Authors: Li Min , Chen Weimin , Zhang Liwu
Published: November 2011

The dynamic characteristics of deepwater riser usually present serried modes with lower frequencies, because structural flexibility is very large due to high aspect ratio (ratio of length to diameter of riser). Moreover, in practice flow velocity usually distributes non-uniformly along the riser length. A coupling model, for multi-mode VIV (vortex-induced vibration) of slender riser experiencing non-uniform flow, by means of finite element simulation combined with the hydrodynamic model taking account of the interaction between fluid and structure in time-domain, is proposed. VIV responses of slender risers respectively in uniform, stepped and shear flow are explored. Satisfied agreements with experiment results are observed. Additionally, based on the numerical simulations effects of reduced velocity and modal energy on modal weight are explored. We note that for case of multi-mode vibration the participating modes tend to distribute by groups.
Adaptive Vibration Control of Towed Seismic Cable
Authors: Liu Tao , Zhang Weijing , Ma Jie , Zhang Guanglei
Published: November 2011

The vibration of the towed seismic cable (streamer) is the main reason for the efficiency reduction of the seismic survey. In this paper, a vibration suppression scheme of the streamer in the seismic survey is investigated. The system model includes a hyperbolic partial differential equation with variable coefficient describing the seismic cable, and an ordinary differential equation describing the dynamic of the birds. Exact model knowledge and adaptive controllers, based on the Lyapunov method, are designed to suppress the vibration of streamer caused by the course deviations of the towing vessel and variations of streamer density. Under reasonable assumptions, the exact model knowledge and adaptive controllers exponentially and asymptotically drive the controlled span seismic cables displacement to zero, respectively. The proposed control laws not only suit for the depth control, but also the horizontal control.
Fully-Plastic J and CTOD Solutions for Pipes With Circumferential Surface Cracks Subjected to Combined Bending and Tension
Authors: Parise Lui´s F. S. , Ruggieri Claudio
Published: November 2011

This work provides an estimation procedure to determine the J-integral and CTOD for pipes with circumferential surface cracks subjected to combined bending and tensile load for a wide range of crack geometries and material (hardening) based upon fully-plastic solutions. A summary of the methodology upon which J and CTOD are derived sets the necessary framework to determine nondimensional functions h1 and h2 applicable to a wide range of crack geometries and material properties characteristic of structural, pressure vessel and pipeline steels. The extensive nonlinear, 3-D numerical analyses provide a large set of solutions for J and CTOD which enters directly into fitness-for-service (FFS) analyses and defect assessment procedures of cracked pipes and cylinders subjected to bending load.
Collapse of Reinforced Thermoplastic Pipe (RTP) Under External Pressure
Authors: Bai Yong , Wang Nuosi , Cheng Peng , Yu Binbin , Badaruddin Mohd Fauzi , Ashri Mohd
Published: November 2011

Reinforced Thermoplastic Pipe (RTP) is a multi-layered thermoplastic pipe. It is increasingly used for transporting gas, oil and water etc. RTP pipe has many advantages compared with steel pipe, e.g. it is cheaper to produce, easier to install, more corrosion resistant and so on. Collapse under external pressure is often the governing design parameter for offshore pipelines. This paper presents the recent study result of RTP’s capacity under external pressure. Firstly, the calculation is carried out by mathematical analysis. In the mathematical analysis, RTP is assumed to be a 3-layered cylinder. The major factor that affects the collapse pressure is the flexural stiffness in hoop direction, so the reinforced layer (anisotropic) is simplified to be an isotropic layer with the same flexural stiffness as in hoop direction. The stiffness of this isotropic layer is the same with the RTP pipe. Secondly, Finite Element Analysis (FEA) method is employed to predict collapse pressure using ABAQUS. In the model the pipe is established as a 3-layered pipe with continuum shell element. The model is extended to take into account the initial imperfection and the plastic property of materials. Thirdly, to demonstrate the accuracy of the mathematical analysis and the FE model some test is carried out. This paper focuses on the calculation of RTP’s collapse pressure, using three approaches. The results from the three agree very well. The reasons for the deviations and the factors which influence the collapse pressure are discussed. The capacity equations and FEA models can be useful tools for design of RTP pipe.
Use of Capability Maturity Modelling to Ensure Ageing and Life Extension are Adequately Considered in Structural Integrity Management
Authors: Sharp J. V. , Ersdal G. , Galbraith D.
Published: November 2011

An increasing number of offshore installations are in the life extension stage of life, with ageing processes needing to be taken into account. This is particularly important for structural integrity. Capability Maturity Modelling enables the levels of maturity in processes associated with the management of ageing to be identified and improved if required. The paper describes the model and how it has been used for assessing the management of structural integrity for installations on the Norwegian Continental Shelf.
Design Drivers for Offshore Wind Turbine Jacket Support Structures
Authors: Cordle Andrew , McCann Graeme , de Vries Wybren
Published: November 2011

For the purposes of offshore wind turbine support structure design it is important to understand the relative importance of the various external conditions applied to the structure in the design process. This paper presents results from integrated load calculations performed for an offshore wind turbine on a jacket support structure subject to combined wind and wave loading. A sensitivity analysis is performed on a number of design load case parameters for both fatigue and extreme conditions. Damage equivalent loads and ULS loads are derived using the GH Bladed software tool at a number of key locations on the jacket. Conclusions are drawn regarding the influence of these parameters from comparisons with the baseline load set.
A Study on Construction of Evaluation Method for Defect Sizing Utilizing Numerical Simulation
Authors: Yoshikawa Takao , Maeda Masahiro , Hirasawa Hideyuki
Published: November 2011

To prevent the brittle fracture of the extremely thick plate which is used in the deck plate and the hatch side coaming of the large container ships, it is important to detect surely and repair the inner defects, which are possible to lead the brittle fracture at an early stage. Now Ultrasonic Testing is used in order to inspect the inner defect in a thick plate, and it is necessary to select adequately the probe size and oscillating frequency to evaluate the defect size accurately. The estimation of the defect size in vertical direction to plate surface is important from the viewpoint of fatigue strength. But the vertical flaw length and also the inclined flaw length are hardly to be estimated accurately. In this study, to clarify the characteristics of reflected ultrasonic wave from the defect, the wave propagation behavior is simulated with the numerical simulation program by FEM which is developed by the authors. In this program, the governing equation of elastic wave propagation is calculated in time domain with explicit method utilizing the central-difference scheme. First, the effect of the probe size and oscillating frequency on the accuracy of defect sizing are investigated utilizing the developed program. The numerical simulation is performed for imaging to examine the length of flaw which is parallel to plate surface by normal beam technique. And, the applicability of 6dB method, which is one of the methods for estimating flaw length, is examined. Moreover, a new method for estimating flaw length which cannot be estimated by 6dB method is proposed. Secondly, in order to examine the inclined flaw length, the angel beam test is performed. The accuracy of numerical simulation for angle beam technique is confirmed by comparing experimental result. And, it is examined how the inclined angle of flaw affects the echo height, and it is shown that 6dB method and L level method are useful for the defect which is perpendicular to wave beam and the tip echo method is useful for the defect which is inclined to wave beam. The actual structure usually has a paint film. Therefore, the echo height level will be affected by paint thickness, and the paint film effects on the accuracy of defect sizing. Thirdly, the effects on echo height by film thickness are clarified by experiments and numerical simulations.
New Approach of Deep Sea Dredging
Authors: van Duursen Ewout , Winkelman Mark
Published: November 2011

A new approach of trailing suction dredging is presented. This approach is especially useful for dredging at depths over 100m. Normally a Jumbo Trailing Suction Hopper Dredger is used for dredging at depths of over 100m. This requires a large investment. The expensive dredging equipment is only used while dredging. This equipment is mainly “dead cargo” when sailing to the place of delivering the sand. Our new approach requires a significant lower investment. As the dredging equipment is used continuously, idle time is decreased and time for return of investment is shortened. The dredging depth is independent of the length of the trailing suction pipe and thus the length of the ship, unlike a normal Trailing Suction Hopper Dredger. Our approach consists of modular dredging equipment placed on e.g. a standard Platform Supply Vessel. By using the dredging equipment on this vessel, standard barges are continuously filled with sand. The dredging equipment consists of a submersible dredging unit connected to a hose. This dredging unit is suspended by wires from the Platform Supply Vessel. It is lowered to the required dredging depth by winches. The application of the dredging unit is like a normal Trailing Suction Hopper Dredger. The barges are loaded while sailing along the Platform Supply Vessel. The position of the dredging unit is constantly monitored. An extensive research project is initiated to develop this concept. Several scale model tests are performed at MARIN. Also a numerical model was designed. Extensive tests were performed on the hose. Another test was performed at TU Delft to investigate the transport of sand/water mixture through a hose stored on a reel. All this research has resulted in a reliable, inexpensive system to dredge at sea at great depths over 100m.
Analysis of Towing-Gear Concepts Using Iceberg Towing Simulations
Authors: Vetter Christin , Ulrich Christian , Rung Thomas
Published: November 2011

The paper reports on the development and application of an iceberg towing simulation procedure, whose efficiency allows an on-board use. Different solution techniques for the integration of the governing equations are compared with respect to performance and accuracy. Supplementary, the predictive accuracy of the employed rope models is outlined. Moreover, the merits of two different concepts for the towing gear set-up, i.e. utilizing a floating polypropylene part together with a submerged steel hawser or a single floating line, are discussed. Investigated application examples focus on towing medium sized icebergs with changes in ship speed. Based on a given towing speed profile, the acting forces and accelerations on the iceberg and the rope tension are simulated. Furthermore, the influence of modelling parameters, e.g. added hydrodynamic masses, is reported.
Power Absorption Measures and Comparisons of Selected Wave Energy Converters
Authors: Babarit Aure´lien , Hals Jorgen , Kurniawan Adi , Moan Torgeir , Krokstad Jorgen
Published: November 2011

In this study, a selection of Wave Energy Converters (WECs) with different working principle is considered. It comprises a heaving device reacting against the seabed, a heaving self-reacting two-bodies device, a pitching device, and a floating OWC device. They are inspired by concepts which are currently under development. For each of these concepts, a numerical Wave To Wire (W2W) model is derived. Numerical estimates of the energy delivery which one can expect are derived using these numerical models on a selection of wave site along the European coast. This selection of wave site is thought to be representative with levels of mean annual wave power from 15 to 88 kW/m. Using these results, the performance of each WEC is assessed not only in terms of yearly energy output, but also in terms of yearly absorbed energy/displacement, yearly absorbed energy/wetted surface, and yearly absorbed energy per unit significant Power Take Off force. By comparing these criteria, one gets a better idea of the advantages and drawbacks of each of the studied concepts.
Fatigue and Environmental Loading of Small-Bore Manifold Piping
Authors: Vedeld Knut , Sollund Ha˚var , Fyrileiv Olav
Published: November 2011

Small-bore pipes inside manifold structures are designed to be flexible. The piping must absorb thermal and pressure loading, as well as installation tolerances, well growth and in some cases stroking and/or other temporarily imposed displacement controlled conditions. Depending on well conditions and functional requirements the piping is often highly utilised statically. Vortex-induced vibrations (VIV) are on the other hand directly related to the frequency of the piping, and the more flexible a system is, the more prone it is to respond to cyclic loading induced by waves and current. Generally small-bore piping responds easily to VIV since the VIV onset flow velocity is directly proportional to the diameter. Small-bore piping have by default very small diameters, therefore the onset value for VIV is lowered compared to systems with larger diameters. In order to mitigate this environmental loading effect, it is favourable to increase the frequency of the system. Increasing the frequency is however normally done by making the system stiffer, more rigid, which generally is not desirable since this in turn increases the level of static utilisation. The current industry practice for VIV design of small-bore piping systems is to apply onset criteria. Onset criteria are in themselves applicable for small-bore systems, but they are very conservative, and DNV has in projects encountered several systems where a balance between onset of VIV and static utilisation was not obtainable. As temperatures, well growth and operational pressures increase with more complicated well conditions, the challenges with flexibility versus rigidity in small-bore piping will only increase, and previous design methodologies using typical onset criteria will be more difficult to apply successfully. There are many possible solutions to this problem; such as shielding, clever layout design, and/or direct VIV mitigation measures mounted on the pipes. This paper proposes a general methodology for advanced fatigue calculations to decrease the level of conservatism, and introduces some mitigation techniques which have been successfully applied in projects for systems where both onset criteria and fatigue utilisation criteria fail, and where fulfilling them is not possible within the confines of acceptable static utilisation.
Fatigue and Environmental Loading of Large-Bore Manifold Piping
Authors: Vedeld Knut , Sollund Ha˚var , Fyrileiv Olav
Published: November 2011

Large-bore piping inside manifold structures are designed to be flexible. The piping must absorb thermal and pressure loading, as well as installation tolerances, well growth and in some cases stroking and/or other temporarily imposed displacement-controlled conditions. In order for branch pipes, flex-loops or other jumper type configurations to cope with the functional, fabrication and installation loads they are designed to be highly flexible. Depending on well conditions and functional requirements the piping is commonly highly utilised statically. Vortex-induced vibrations (VIV) and wave-induced loading on the other hand are directly related to the Eigen-frequencies of the piping systems, and the more flexible a system is, the more prone it is to respond to cyclic loading induced by waves and current. In order to mitigate environmental loading effects, it is favourable to heighten the harmonic frequency of a system. Increasing the harmonic frequency is however done by making the system more rigid, which generally is undesirable for flexible large-bore piping systems in manifolds, since this in turn increases the level of static utilisation. There is to DNV’s knowledge currently no standard industry practice on VIV and environmental loading for large-bore manifold piping, since these normally are sufficiently rigid to prevent VIV. Recently, however, DNV has encountered systems where VIV and environmental loading have presented significant challenges for flexible large-bore systems, and this paper proposes a series of methodologies to estimate fatigue and extreme environmental loading of such systems. Advanced applications of DNV-RP-F105 and DNV-RP-C205 are detailed from recent project experience.
Reliability Based Assessment of Minimum Wall Thickness for Reeling: A Focus on Cold Worked Pipe
Authors: Smith Daniel , Tkaczyk Tomasz , Denniel Sylvain
Published: November 2011

Pipelines installed by the reel lay method are plastically deformed during installation. The nominal level of plastic deformation is determined by the vessel equipment geometry and pipe dimensions. The natural variation of wall thickness and yield strength determines the potential differences in bending stiffness (also called mismatch) that can occur between adjacent pipe joints. These mismatches cause a localized peak in strain and can drive gross deformation of the pipe, which may result in a buckle if not addressed at the engineering stage. The slenderness of a pipe and the strain hardening capacity determines the capacity of a pipe to handle the effects of mismatches during reeling A minimum wall thickness for reeling design equation has been defined for seamless pipe and has a proven track record and demonstrable reliability. There is a recent increase in the level of interest in cold worked pipe such as HFI/HFW, which appears to be an attractive cost effective alternative to seamless pipes. HFI/HFW potentially has inferior strain hardening properties due to cold forming, but have superior tolerance control of yield strength and wall thickness. This paper presents the results of a reliability based study, demonstrating the applicability of existing minimum wall thickness for reeling criteria, when applied to HFI/HFW linepipe.
Cyclic Response of Granular Subsoil Under a Gravity Base Foundation for Offshore Wind Turbines
Authors: Safinus Stefanus , Sedlacek Germa´n , Hartwig Udo
Published: November 2011

It is essential in the design of gravity foundations under cyclic loading that inadmissibly large reductions of the subsoil bearing capacity due to the accumulated pore water pressure (loss of stability) and tilting of the foundation caused by the accumulation of settlements (loss of serviceability) are ruled out. This paper describes a procedure to predict these phenomena in non-cohesive subsoils. Real irregular loads during the service life of the structure can be idealized into parcels of uniform cyclic loads. Using the “High Cyclic Accumulation Model” proposed by Niemunis [1] the strain accumulation and thus the settlement of the subsoil due to the cyclic loads occurring within the service life of the wind turbine can be estimated. The pore pressure development is analyzed by dividing the mechanism in a pore pressure build-up phase in undrained condition (analytical calculation) and a dissipation phase (3D-FEM-Calculation).
Influence of Bore Pressure on the Creep Behaviour of Polymer Barrier Layer Inside an Unbonded Flexible Pipe
Authors: Shen Yijun , Zhao Jian , Tan Zhimin , Sheldrake Terry
Published: November 2011

This paper investigates the influence of bore pressure, combined with the nonlinear behaviour of the polymer material, on the creep behaviour of the polymer barrier layer inside an unbonded flexible pipe. Creep behaviour in the barrier layer may result in its reduction in thickness and is therefore an important design consideration in ensuring the structural integrity of this layer. It is meaningful to study the variation in creep behaviour in an unbonded flexible pipe under different bore pressures and temperatures, especially in high pressure pipelines for deep or ultra-deep sea applications. Creep behaviour in polymer material is complex, as it is governed by a number of variables such as the stress/strain state, temperature, and pressure for example. It is generally time-dependent and often associated with larger strains or states of deformation. Owing to the complexity of polymer material creep, an implicit time hardening creep model, based on the Maxwell viscoelastic model, has been selected to represent the creep behaviour in polymer materials and implemented into the Gap Span model, which is an in-house ANSYS based finite element model. The coefficients of this creep model were initially calibrated according to standard creep tests performed on polymer materials. The study presented in this paper focuses on the influence of bore pressure and high temperature on the creep behaviour of the polymer barrier layer. Comparisons between the simulation results of the calibrated Gap Span creep model and the corresponding small-scale creep tests demonstrate that these model predictions are overly conservative for the polymer material of the barrier layer inside an unbonded flexible pipe. Comparisons between the experimental test results and the finite element modelling results show good correlation.
The Challenge to Develop a Software Manual Facing Complex Activities in the Oil and Gas Sector
Authors: de Menezes Paula Cabral
Published: November 2011

This paper presents the stages of preparation of the C4D software user manual. This software has been developed by PhDsoft and is intended to be used in connection with complex tasks such as the management of the integrity of the structures of offshore platforms, FPSOs and vessels, by providing repair and maintenance services such as sizing and placing of anodes, assessment of paint deterioration, among others. Oil companies tend to be huge in size and number of employees with different skills, psychological and behavior profiles. Considering that the software also serves as an interface with service providers, many other professionals were added, thereby greatly increasing this diversity. Therefore, meeting the needs of such heterogeneous expectations is the challenge faced by the author of the user manual. The purpose of the software manual is to facilitate the transfer of information and knowledge so as to develop the user’s skills and competencies. Since the software is an engineering tool, it is not enough to present the directions and the steps of the software’s specific tasks and procedures. It is necessary to provide the users with the technical principles used in the software functions. The manual must also be integrated to the company’s strategy by adding value to the product so as to be perceived by the stakeholders as a strong aspect as regards the competitors, being also an effective instrument for establishing closer ties. This paper presents the experience of using a journalist to draft an essentially technical text, in an attempt to unite the attractiveness of the text to the accuracy necessary for its effective use, by following the best practices recommended for documentation and establishing metrics to check the efficacy of same, especially in accordance with norm IEE 1063 — Standard for Software User Documentation.
CFD Based Hydrodynamic Databases for Wake Interference Assessment
Authors: Corson David , Cosgrove Steve , Hays Paul R. , Constantinides Yiannis , Oakley Owen H. , Mukundan Harish , Leung Ming
Published: November 2011

The interaction of the wake between pairs of long flexible cylindrical structures is of major consequence in the design of offshore oil and gas production facilities. Modern designs of these facilities often utilize arrays of flexible pipes (risers) extending from the mean water line to the mud-line and then to the subsea reservoir. As ocean currents interact with these structures, wakes are formed at the upstream structure and propagate to the downstream structure (a perturbed flow-field) resulting in a modified force on the downstream structure. This effect, known as the shielding effect, needs to be properly accounted for during the design of offshore facilities. Conservative yet realistic estimates of the effect of separation between the structures under a variety of ocean currents are sought. It is common industry practice to evaluate the clearance between a pair of long flexible cylindrical structures using a finite element based tool. Hydrodynamic loads are based on experiments on a pair of short rigid cylinders. Recent advances in Computational Fluid Dynamics (CFD) technology have made it cheaper and quicker to perform simulations of these conditions without compromising the underlying physics. This alternative is preferred to more expensive and time consuming physical prototype experiments. This paper presents the results of high resolution, time accurate CFD simulations used to understand and quantify the wake interaction between a straked cylinder and a cylinder mounted with the AIMS Dual Fin Splitter (ADFS). No prior experimental data were available for the riser configurations and conditions that were investigated. The simulations were performed using prototypic current velocities and geometries. This paper will describe the CFD technology used in detail. The paper will cover the model setup, the extent of and discretization of the model, the choice of time-step, the boundary conditions, and a discussion on the results from the simulation.
Interval Estimation of Return Wave Height for Marine Structural Design
Authors: Tao Shanshan , Dong Sheng , Lei Shuhe , Guedes Soares C.
Published: November 2011

The general procedure is discussed for determining the interval estimation of N-year return period extreme wave height with maximum likelihood method (MLM). The specific interval estimation expressions of the N-year return extreme wave height with MLM are given when the extreme wave height series fits a sort of maximum value distribution, such as Weibull distribution, generalized extreme value distribution and log-normal distribution. This paper also proposes a sign test method (STM) to estimate the interval of return extreme wave height. It is a non-parametric method that does not depend on the type of maximum value distributions. By adopting both MLM and STM, a stochastic simulation of the interval estimation is conducted to estimate the quantiles of the above maximum value distributions. The results indicate that SMT behaves well only when the sample size is sufficiently large (generally above 100), and the advantage of simulation with MLM is apparent if the sample size is smaller. Finally, a case study has been carried out with the extreme wave height measured at Weizhoudao hydrological station in the northern area of South China Sea.
Positioning of the Offshore Platform
Authors: Korkmaz Mahmut Olcay , Gu¨ney Caner , C¸elik Rahmi Nurhan
Published: November 2011

In the scope of this study, it is targeted to develop a tool, equipment and a web-based software system that provides integration of positioning systems and prevents production of erroneous or inadequate real-time/DGNSS positioning data in order to navigate a petroleum platform while it transports between two locations and to track it dynamically where they are precisely positioned. Moreover with the support of web-based implementation of the system designed will provide online remotely monitoring availability for the moving platform activities in offshore. Eventually, it is intended to achieve utilizing spatial informatics technologies like geoimagery, geospatial information system, etc. in the exploration and production of hydrocarbon reserves. This work has been conducted within the project “Integration of Positioning Systems for Positioning and Tracking Offshore Platforms”, funded by the Turkish Republic Ministry of Industry and Trade under contract number 00369.STZ.2009-1, which is started at 01/07/2009 and finalized at 31/01/2011.
An Experimental Investigation Assessing the Validity of Quasi-Static Calculations for an Oscillating Hydrofoil
Authors: Fernandez Rajan , Alexander Keith
Published: November 2011

Inspired by animals, flapping wing propulsion has been of interest since the early 1900s. Flapping hydrofoil propulsion has been attempted by designers of human powered watercraft because of the novelty and the apparent high theoretical efficiency, but with limited success. The earliest human powered hydrofoil, the Wasserlaufer, was invented by Julius Schuck in 1953. The first really successful human powered hydrofoil, the Trampofoil, was invented by Alexander Sahlin in 1998. While these craft function adequately the design data for flapping hydrofoils is inadequate or not available. This paper describes an experimental program and initial results for the required data. To design a vehicle with a lifting and thrusting oscillating hydrofoil the force that the hydrofoil will exert on the vehicle through its entire oscillating cycle must ideally be known. The force profiles could be estimated via quasi-static calculations based on steady flow lift and drag coefficients, but these often do not cover the full 360 degree range that can be required and there is doubt that the steady flow coefficients properly represent the dynamic situation of an oscillating hydrofoil. Hence a valuable process would be one that could determine dynamic drag and lift coefficient loops as function of the Strouhal number, heaving and pitching profiles. To work toward the collection of this information, experimental data is being recorded in a towing tank with an oscillating NACA4415 hydrofoil over a range of Strouhal numbers and types of oscillating profiles. While there are still some limitations to the experimental equipment preliminary experimental results show the limitations of using quasi-static calculations and go some way to providing the design data for the hydrofoil section tested. We conclude that quasi-static calculations based on the gliding coefficient curve for for an oscillating hydrofoil are only valid for very small Strouhal numbers (St≪0.05). We have shown that as the Strouhal number increases, the error in such calculations increases very rapidly. We also note that the lift coefficient of the hydrofoil has a strong dependence on the angle of attack and is not affected by the gliding stall.
Approaches for Environmental Impact Assessment of Seafloor Massive Sulfide Mining
Authors: Yamazaki Tetsuo
Published: November 2011

Seafloor Massive Sulfides (SMS) including Au, Ag, Cu, Zn, and Pb exist in exclusive economic zones (EEZ) of the Pacific island countries. Some of SMS are interested in as immediate targets for commercial mining ventures. Little information, however, is available for the mining impacts on marine ecosystem, because no actual deep-sea mining operation is there in the world. In case of SMS, in addition, some of them accompany active hydrothermal vents beside the possible mining sites. High primary biomass production and dense ecosystem population on seafloor are found around the vent system. On the basis of physical, chemical, and biological baseline survey data, Nautilus Minerals submitted an environmental impact statement for the Solwara 1 Project to Papua New Guinea (PNG) Government. The other approach is the environmental impact assessment program for SMS mining driven by Japan. In contrast with PNG, the feature of Japan’s program is the step-by-step process for the assessment. The importance of the step-by-step process is introduced in detail.
Float-Over Analysis for World’s Largest Float-Over Barge
Authors: Bokhorst Job , Willemse Olaf , Zoontjes Richard
Published: November 2011

Heerema Marine Contractors has recently converted its launch barge H-851 into a float-over barge able to install ultra heavy topsides with weights up to 38,000 mT. With a length of 260 m, width of 63 m and height of 15 m, the H-851 is the world’s largest float-over barge. By narrowing the bow section to 42 m, the required sub-structure slot to fit the barge is reduced significantly decreasing the size of sub-structure and topsides hence optimizing platform weight and cost. Initially the sheer size of the H-851 was thought to result in high forces on topsides, sub-structure and interface systems during installation. However, engineering analyses show that by choosing the appropriate float-over equipment, loads can be kept below limits which are considered conceivable for the platform design. Special measures are taken to minimize the exposure during load transfer by equipping the barge with a high capacity ballast system. As with all vessels with large displacement, maneuvering before and after float-over requires thorough planning and risk identification during the engineering stage. This paper discusses the critical phases during the float-over operations and demonstrates that the platform design can be optimized by considering float-over equipment and operational limits in an early stage of the project. The approach for extensive hydrodynamic analyses is discussed which have matured over recent times thanks to available software tools and extensive research with respect to comparison with model tests and full scale experience.
Dynamics of the Vertical Hydraulic Transport System for Deep Sea Mining
Authors: Verichev Stanislav , Metrikine Andrei , Plat Robert , Hendrikse Hayo
Published: November 2011

Extractable deposits of silver, gold, copper, zinc, lead, gas hydrates and other valuable materials can be found at the ocean floor. The most valuable minerals are found at large depths, starting from 1000 m and deeper. Therefore, the leading offshore companies are currently designing systems and tools for deep sea mining. The mining at the desired depth of a few kilometers is a great challenge though as it has never been attempted before at the commercial scale. One of the fundamental design challenges lays in the understanding of and preventing from the problems associated with the dynamics of a subsea Vertical Transport System (VTS). The function of the VTS is to transport slurry (a thin mixture of water and finely divided minerals) from the seafloor to the mining support vessel. The VTS consists of a vertically hanging submerged pipe through which the slurry is transported upwards and a number of booster stations which maintain the pressure in the pipe that enables the desired slurry flow. The VTS system is subject to a number of the dynamic excitations such as the vessel motion, the slurry flow in the pipe, the sea current and a propulsion device that is envisaged to control the position of the lower end of the pipe at the desired location. To design a reliable VTS system the effect of all the above-mentioned excitation mechanisms has to be accounted for.