bluuebunny/crossref_metadata_2025 huggingface dataset:
Avoiding Local Brittle Zones in Offshore Pipeline Girth Welds for Reeling Installation Involving Large Plastic Strain
Authors: Tronskar Jens P. , Andresen Vebjørn
Published: November 2013

Pipelines for reeling are designed to tolerate the large plastic strain associated with the reeling installation process based on widely accepted strain based design principles for subsea pipelines as described in Det Norske Veritas (DNV) Offshore Pipeline Code OS-F101: 2012 [1].

Engineering Critical Assessment (ECA) to develop flaw acceptance criteria for automatic ultrasonic testing (AUT) for girth welds subject to large plastic strain shall according to DNV-OS-F101: 2012 [1] and DNV RP-F108 [2] be carried out in accordance with BS 7910 [3], at assessment Level 3B, with amendments and adjustments described in Appendix A of DNV-OS-F101 for strain-based loading. This is a tearing analysis using the material specific failure assessment diagram (FAD), the material stress-strain curve and the fracture resistance J-R curve (or CTOD-R curve) for the HAZ or WM. It is therefore essential that the pipeline girth welds exhibit maximum load behavior and large tearing capacity to enable development of workable and practical flaw acceptance criteria for the girth welds on the stalks.

Welds in offshore structural steels are known from the early 80s introduction of low carbon-manganese micro-alloyed steels, to occasionally exhibit low fracture toughness associated with so-called local brittle zones (LBZ) in the HAZ. Similarly, in the 90s LBZs were found in pipeline seam welds welded at high arc energies. Presence of such microstructures may have a dramatic effect on the coarse grained HAZ CTOD fracture toughness properties causing unstable fracture in the CTOD tests and CTOD values below 0.1 mm at test temperatures of 0°C and below. Recently low CTOD critical fracture toughness values due to pop-ins and unstable fracture initiation in the HAZ have been experienced for pipeline girth welds for reeling and investigation confirmed these were caused by LBZs. This paper makes a comparison with the situation experienced earlier for welds in structural steels and pipeline seam welds, to understand the factors influencing the LBZ formation, and to show how such problems can be avoided. To avoid LBZs formation in the girth welds is imperative for reeling installation, where the large plastic strain associated with reeling installation affects every girth weld.
Probabilistic Modeling of the Bio-Colonization Effects on Hydrodynamic Forces With Several Combinations of Sea-State Condition: A Study on Jacket-Platforms in the Gulf of Guinea
Authors: Schoefs Franck , Ameryoun Hamed
Published: November 2013

During the stage of designing or re-assessment of a jacket-type offshore structure, one of the most important phases is the re-evaluation of environmental loads, which are exerted by the waves, the wind and the currents, and updating the new data (e.g. meteocean, new regulation, structural damaging etc.). The former is mainly caused by the randomness or uncertainty nature of the marine environment as well as the presence of marine growth that makes the modeling of environmental loading more complicated. The general species of marine growth may be divided into two main categories: vegetable (e.g. algae) and animal (e.g. mussel, anemones, and corals). Indeed, the structures can be covered by many marine organisms quickly (in the first weeks). The influence of bio-colonization on an offshore structure can be measured at several levels: obstruct or prohibits a visual inspection of the subjacent support, cost of procedures of cleaning for oil industries and increasing the hydrodynamic forces on the structure. Considering the latter, loading change due screen effect and added mass are shown to be the most relevant. This study aims to provide a probabilistic modeling of marine growth colonization in the Gulf of Guinea. A physical matrix response surface is used in view to provide a probabilistic modeling of the environmental loading on Jacket type offshore structures for quasi-static behavior in the presence of marine growth. The paper focuses on uncertainty and sensitivity studies respecting to the effects of wave, wind-sea and currents.
CFD Simulation for Vortex Induced Motions of a Multi-Column Floating Platform
Authors: Tan Jaime Hui Choo , Magee Allan , Kim Jang Whan , Teng Yih Jeng , Ahmad Zukni NorBahrain
Published: November 2013

The potential of vortex induced motion (VIM) in multi-column floating platforms such as semi-submersibles and tension leg platforms (TLPs) is well-acknowledged although the industry guidelines for design for VIM are not comprehensive and more research effort is required. Significant VIM in multi-column floating platforms will affect the fatigue life of the steel catenary risers and must be quantified and sometimes reduced. Industry-standard design tools used for drag estimation based on model tests of fixed structures may not accurately reflect the effects of drag augmentation due to VIM. Model tests and Computational Fluid Dynamics (CFD) analysis are feasible methods to investigate VIM, with the latter being more resource-efficient, provided sufficient benchmarking has been carried out to ensure reliable results.

Subsequent to the model tests and preliminary Computational Fluid Dynamics (CFD) simulations done for a multi-column floating platform [1, 2], further CFD analyses for the VIM of the floating platform have been carried out using improved simulation techniques with a commercial software. Good agreement between model test results and CFD calculations for VIM of a multi-column floating platform is observed. Sensitivity of CFD results to the modeling assumptions such as mesh size and density, time-step size and different turbulence models is presented.
Wrinkling of Lined Steel Pipes Under Bending
Authors: Vasilikis Daniel , Karamanos Spyros A.
Published: November 2013

Lined pipes are used in energy pipeline applications (oil, gas, etc.); a corrosion-resistant thin-walled liner is fitted inside a carbon-steel outer pipe. The paper focuses on wrinkling of lined pipes (sometimes also referred to as “mechanical clad” pipes), which are candidates for offshore pipeline applications. The lateral confinement of the liner pipe due to the deformable outer pipe and its interaction with the outer pipe has a decisive influence on the wrinkling behaviour of the thin-walled liner. The problem is solved numerically, using nonlinear finite elements to simulate the lined pipe and its interaction with the outer pipe. Nonlinear geometry with large strains is taken into account, and the material of both pipes is elastic-plastic. Stresses and strains are monitored throughout the deformation stage with emphasis on possible detachment of the liner from the outer pipe and the formation of wrinkles. It is shown that the behaviour is characterized by a first bifurcation in a uniform wrinkling pattern, followed by a secondary bifurcation and finally a localization of the buckled pattern. The values of curvature at which liner wrinkling occurs are determined. The numerical results are compared with available experimental results.
Coupling of Two Tools for the Simulation of Floating Wind Turbines
Authors: Gueydon Sébastien , Lindenburg Koert , Savenije Feike
Published: November 2013

For the design of a floating wind turbine it is necessary to take the loading due to the wind, wave and current in equal consideration. The PHATAS computer program from ECN (Energy research Centre of the Netherlands) is a time-domain aero-elastic simulation program, that accounts for the complete mutual interaction of unsteady rotor aerodynamics, structural dynamics of the rotor blades and tower, and interaction with the turbine controller under influence of turbulent wind and wave loading for fixed wind turbines. The aNySIM computer program from MARIN is a multi rigid body time domain model that accounts for wave loadings, current loadings, wind loadings, floating body dynamics, mooring dynamics. The coupled computer program aNySIM / PHATAS accounts for all loadings acting on a floating wind turbine and its response whereas PHATAS can only be used for fixed wind turbines onshore and offshore. This paper reports on the dynamic coupling between PHATAS and aNySIM. As a typical case study, the controller for floating offshore wind turbines is evaluated. This new tool has been used to repeat phase IV of the Offshore Code Comparison Collaboration (OC3) within IEA Wind Task 23, regarding floating wind turbine modelling. The results of these simulations are presented in this paper.
Evaluation of Residual Stresses in Steel-to-Nickel Dissimilar Joints
Authors: Sotoudeh K. , Zhang S. Y. , Eren S. E. , Kabra S. , Milititsky M. , Gittos M. F.
Published: November 2013

Welds between ferritic and austenitic materials, commonly described as dissimilar metal welds (DMW’s), are widely employed in various industrial applications. Failure of such joint can occur by a variety of failure mechanisms including creep, thermal fatigue and hydrogen embrittlement/corrosion While in some cases, the presence of long range stresses, due to design and fit-up, have been linked to failures, triaxial stress distribution across these types of joints have not adequately been investigated.

In the present work, forged low alloy connectors were buttered with a nickel alloy and post-weld heat treated, before making closing welds to a pipeline steel. The DMW received no further post-weld heat treatment (PWHT). The residual strain profiles across dissimilar joints were measured in the axial, radial and hoop directions of a series of these joints containing multi-run girth welds, using the neutron diffraction technique. Residual stresses were calculated from these measurements. Three dissimilar metal interface combinations were investigated: (1) ASTM A182 F22 steel to ERNiCrMo-3 (alloy 625) weld metal (PWHT’d joint), (2) AISI 8630M steel to ERNiCrMo-3 (alloy 625) weld metal (PWHT’d joint) and (3) ASTM A964-F65 low alloy steel to ERNiCrMo-3 (alloy 625) weld metal without PWHT. The current study attempts to create a better insight into the unique stress distributions across these joints.
Experimental Investigation of Fatigue Performance of a 300 mm2 Copper Power Conductor
Authors: Nasution Fachri P. , Sævik Svein , Berge Stig
Published: November 2013

Electrical power cables are used in conjunction with floating units for provision of energy to installations on the sea bed, power from land to the floater, or export of power from a wind turbine to land. Power cables that are linked to a floating unit are subjected to fatigue loading from the waves and due to the movement of the vessel in the waves. Fatigue strength needs to be verified for design. Fatigue performance of a 300 mm2 stranded copper conductor was investigated. The experimental work included fatigue tests of individual wires and full cross section conductors including unlubricated and lubricated conductors. Individual wires from different layers were tested in tension-tension mode with stress ratio R = 0.1. Full cross-section conductors were tested in cyclic reversed bending with constant tension at ends, simulating the loading at the top end of a conductor hanging off a floating structure through a bellmouth. The objective of this paper is experimental assessment of the fatigue strength of a 300 mm2 copper conductor and to investigation of the mechanisms of fatigue crack initiation and growth in individual wires. At the time of submission the test program was still in progress, and conclusions are tentative only. An updated paper with complete results will be published at a later stage.
Numerical Simulations for Installation of Offshore Wind Turbine Monopiles Using Floating Vessels
Authors: Li Lin , Gao Zhen , Moan Torgeir
Published: November 2013

Monopiles are the most commonly used support structures for offshore wind turbines with up to 40m water depth due to the simplicity of the structure. The installation of turbine support structures can be carried out by a jack-up vessel which provides a stable working platform. However, the operational weather window using jack-up vessels is very limited due to the low sea states required for jacking up and down.

Compared to jack-up installation vessels, floating vessels have more flexibility due to fast transportations between foundations. However, the vessel motions will affect the motion responses of the lifting objects, which might bring installation difficulties. Therefore, it is necessary to examine the dynamic responses of the coupled system to ensure safe offshore operations.

In this paper, the installation operation of a monopile using a floating installation vessel is studied by a numerical model. Time domain simulations were carried out to study the installation process of a monopile, including lowering phase, landing phase and steady states after landing. Sensitivity studies were performed focusing on the effects by the gripper device stiffness and landing device stiffness. Comparisons of critical responses by using floating vessel and a jack-up vessel were also studied in the paper.
Study of Use of Supercritical CO2 to Enhance Gas Recovery and its Interaction With Carbonate Reservoirs
Authors: El Hajj Hicham , Odi Uchenna , Gupta Anuj
Published: November 2013

It is well known that with continued production from wet gas reservoirs, the reservoir pressure eventually falls below the dew point pressure leading to condensation and loss of gas productivity in the reservoir. The concept of simultaneously injecting CO2 in a gas reservoir for long term storage while at the same time accelerating production of the natural gas is intriguing and promising. CO2 may also interact with carbonate matrix by changing porosity and permeability of the host rock; this is true for reservoirs that are found in the Gulf Region.

To maintain field gas production targets, operators routinely set the bottom hole pressure below the dew point pressure which results in condensate blockage. Injecting CO2 can delay the onset of condensate blockage by reducing the dew point pressure of the condensate blockage zone. The approach illustrated, utilizes CO2 to delay the onset of condensate blockage. Factors such as improved effusion were analyzed to justify the use of CO2 for wellbore condensate removal and enhanced gas recovery (EGR). Experimental verification of a new method of determining dew point pressures for wet gas fluids is presented in this work and compared to simulation results.

Core floods experiments with carbon dioxide were conducted in a core sample analogue to carbonate at reservoir conditions in order to study the interaction between CO2 and carbonate reservoir. CO2 sequestration in carbonate formation was evaluated by XRF and AFM.

Experimental and simulation results show increases in productivity index after CO2 injection. Increases in productivity index were caused by CO2 evaporating the condensate blockage. Condensate vaporization was caused by CO2 reducing the dew point pressure of the condensate. Carbonate aging in presence of CO2 shows two mechanism of CO2 trapping which are dissolution and mineralization.
Experimental Results on Collision Avoidance of Autonomous Ship Manoeuvres
Authors: Perera L. P. , Ferrari V. , Santos F. P. , Hinostroza M. A. , Guedes Soares C.
Published: November 2013

In this paper, experimental results on collision avoidance of autonomous ship manoeuvres are discussed. The collision avoidance experiments are conducted on a navigation & control platform that has been presented in a mathematical formulation as well as in an experimental setup. The mathematical formulation of collision avoidance consists of three systems: vessel traffic monitoring and information system (VTMIS), collision avoidance system (CAS), and vessel control system (VCS). The experimental platform of collision avoidance consists of a physical system that has been used to generate experimental results. The experimental platform is further divided into two sections: vessel model and navigation & control platform. The vessel model consists of a scale ship, where the CAS is implemented. The navigation & control platform consists of hardware structure and software architecture that supported for vessel model navigation. Two ship collision situations are considered in this study, where one ship is implemented under the vessel model and another ship is simulated. Finally, the successful collision avoidance results with respect various collision situations are presented.
A Comparison of Full-Scale Measurements and Numerical Riser Response Simulation
Authors: Stange Ivar , Leira Bernt J.
Published: November 2013

Data from full scale measurements have been collected for a marine drilling riser connected to a moored semi-submersible rig which is operating at a site with a water depth of 325 m. The flex joint angles at the bottom of the riser just above the lower marine riser package are recorded and applied for the purpose of estimating the accumulated fatigue damage by means of rainflow cycle counting and Miner-Palmgren summation. A numerical simulation model is also established. Both unidirectional wave excitations as well as directional spreading are considered, where the latter generally implies a reduced response level. Different main heading directions of the waves are analyzed. These are 0, 30, 60 and 90 degrees relative to the rig. The effect of applying a linear versus a non-linear stiffness model for the lower flex joint is also investigated. The frequency content of the measured full scale motion versus the simulated motion is studied in some detail. Observed differences are discussed.
Competition of Class I and II Instabilities in Evolution of Crescent Waves
Authors: Yan Kai , Zou Zhili , Zhou Yalong
Published: November 2013

A laboratory experiment on the instability of Stokes wave trains with large steepness in finite water depths in a wave basin is performed. Two class instabilities of Stokes wave, quartet interaction and quintet interaction, were observed, and it is found that the evolution of crescent wave pattern is affected by the development of quintet interaction. The dependence of this effect on relative water depth was analyzed. The wave steepness for the occurrence of the competition is examined by applying linear instability analysis of Stokes wave.
Deep Water Carcass Development: Effects of Carcass Profile on Collapse Resistance
Authors: Zhao Jian , Tan Zhimin , Sheldrake Terry
Published: November 2013

The increasing application of flexible pipes in deep water requires extension of the product’s capability through higher design pressures with large diameters, while one of the most important structural capacities is collapse resistance. In addition to the introduction of new materials and manufacturing capability, the carcass structure is also expected to be optimized for maximum purpose. The carcass is an interlocked metallic construction that is used as the innermost layer to prevent for example, either totally or partially, the collapse of the internal pressure sheath due to decompression, or the pipe, due to external hydrostatic pressure, tensile armour pressure, and mechanical crushing loads. During manufacture of the carcass, its profile may differ from the nominal designed profiles and this may affect the collapse resistance. In this paper the effects of the carcass profile on the wet collapse strength of flexible pipes via numerical simulation are investigated. The wet collapse strength is referred to as the hydrostatic collapse strength of the pipe when the annulus is assumed to be flooded with seawater. In this condition, the external hydrostatic pressure acts directly on the barrier layer above the carcass. Using ANSYS, a 3D finite element model with the consideration of helical effects and cyclic boundary condition, which was developed to check the effect of each part of the carcass profile on the collapse strength by varying the design parameters, e.g. inclination angles, etc, and manufacturing ovality. As both verification and comparison, the principle of the effects is explored and explained analytically. The results can be used as an acceptance criterion on the as-built profiles in the manufacturing process, and as a guideline for the innovation and optimization of the carcass for maximum performance.
Revisiting the Mechanics of Onset of Scour Below Subsea Pipelines in Steady Currents
Authors: Zhang Qin , Draper Scott , Cheng Liang , An Hongwei , Shi Hongda
Published: November 2013

This paper summarizes the results of a series of experiments performed in a recirculating flume (namely the mini O-tube) to investigate the onset of scour below pipelines in steady currents. The experiments were performed on model seabed with two different lengths, to assess the effects of sediment supply on the potential for onset of scour.

In each experiment the flow velocity and pipeline embedment were recorded continuously. These measurements have been compared with an empirical formula proposed by Sumer et al. (2001) which predicts the onset velocity of a pipeline partially buried in a flat seabed. In general, present experimental results show that when the upstream sediment supply is limited, onset of scour may happen due to piping at a velocity well below that predicted by the empirical formula, but following significant local scouring around the pipe. This result, although only preliminary, suggests the potential for tunnel erosion beneath deeply embedded pipelines in the field where the sediment supply upstream of the pipe may be interrupted by rock outcrops or seabed slopes.

A series of numerical simulations have also been conducted to investigate the dynamic pressure difference between upstream and downstream of the pipeline prior to onset of scour. The numerical results show that despite local scour significantly alters the surrounding seabed for a deeply embedded pipe, the pressure gradient across the pipe is similar in magnitude to that measured for a flat seabed and is of sufficient size to cause piping.
Structural Response Analysis of LNG CCS Experiencing the Sloshing Impact Determined by Both Convolution and Fluid Structure Interaction Method
Authors: Hwang Se Yun , Lee Jang Hyun , Kim Sung Chan , Nho In Sik , Jang Beom Seon , Kim Yooil
Published: November 2013

Sloshing assessment of LNG cargo tanks is expected to satisfy the required structural strength of insulation components. It is difficult to estimate the sloshing pressure and structural response of cargo containment in real size because of the uncertainty of intensive computation time as well as the complexity of sloshing motion. In this study, several procedural components are suggested to meet the endurable strength of LNG CCS during the design of LNG cargo containment. The measured sloshing impacts from small scale model test are treated by individual impacts. Thereafter, static and transient structural response of LNG CCS is sequentially performed in order to evaluate the structural strength. The structural response is also calculated in time series through convolution method considering the history of pressure. It is used to investigate the structural response induced by the history of impacts. Finally, an idealized fluid structure interaction on the localized insulation panel is investigated in order to evaluate the structural strength in actual scale.
Installation Methodologies for a Tension Leg Platform Under Ocean Swell Conditions
Authors: Rijken Oriol
Published: November 2013

A common procedure of installing a Tension Leg Platform is to float it over the tendons and lower it over the tendons. A key phase of this procedure is lock-off, i.e. the instant when the tendons become firmly attached to the TLP hull. The lock-off position of the tendons on the hull should be within specified tolerances. Lock-off on the tendons higher than targeted results in a reduced draft which implies reduced displacement and therefore typically reduced payload capacity or reduced payload reserve. Lock-off on the tendons lower than targeted results in increase in draft and brings the deck closer to mean water which adversely affects the airgap requirements. Hence lock-off at the correct draft is a key aspect of a successful installation procedure. The general geometric properties of several TLPs are such that there is a significantly more heave motion under swell conditions than under sea states with much smaller peak periods (for the same significant wave height). These larger motions under swell conditions can make it harder to achieve the desired lock-off elevation. Such swell conditions are known to occur of the West Coast of Africa. Waiting for the swell to subside may not be an attractive alternative for TLP installation as these swells may be present for extended periods of time. Two engineering solutions are provided which reduce the heave motion of a free floating TLP. Both of these solutions are temporary changes to the TLP itself and should be implemented as a part of the TLP design spiral. One of the solutions implies an increase of TLP mass; the second solution reduces the vertical stiffness of the free floating TLP. The heave natural period is significantly increased in both methods, and heave motions are reduced. Both methods increase the heave response amplitude operator (RAO) for periods below 8 to 12 seconds and reduce the heave RAO magnitudes above 12 seconds. Implementing one of these methods in the installation procedure may be most applicable to situations where the installation window may contain prolonged periods of persistent swell.
A Methodology for Calculating Wave Crest Enhancement in Extreme Seas
Authors: Martin Bruce , Rijken Oriol
Published: November 2013

The deck height of a tension leg platform or semi-submersible depends in large part on the expected crest height. This expected crest height is the result of the sea state, i.e. the incoming wave train, and local enhancement due to the vessels diffraction of the wave train. These local enhancements are usually determined by a combination of numerical computations and model tests. Quite often a crest enhancement factor is defined which takes into consideration these local amplification effects. Extrapolating the enhancement factor from extreme conditions to survival conditions may lead to significantly large crests and result in a very high deck elevation.

Many studies, including the CresT JIP address the characteristics of the crests within a given sea state and in the absence of a vessel. This paper addresses the effect of the presence of a vessel on the crest heights, and in particular the high crests which will ultimately determine deck height. The paper is based on experimental measurements of wave elevations underneath and around various tension leg platforms and semi submersibles. The investigated sea states comprise of a series of long crested irregular waves, generated in a model basin, which describe extreme and survival conditions in the Gulf of Mexico. The crest heights underneath the vessel are measured and compared with crests which occur without the presence of the vessel. Numerical predictions of the local amplification are also made, based on 1st order diffraction analysis and the as-measured incident wave train. A narrative is provided on the differences in crest height and observed phenomena.
On Wind-Wave Misalignment, Directional Spreading and Wave Loads
Authors: Van Vledder Gerbrant Ph.
Published: November 2013

Causes of wind-wave misalignment, the difference between wind and mean wave direction, are investigated for stationary and non-stationary situations using numerical modeling. This includes the effects of upwind fetch restrictions, refraction, choice of source terms and integration time step on wind-wave misalignment are illustrated. A statistical analysis is performed to quantify wind-wave misalignment as a function of wind speed and significant wave height. In addition, the effect of spectral partitioning in separate wind sea and swell systems on the statistics of wind-wave misalignment is illustrated. Apart from the differences in mean direction, attention is given to the associated directional spreading. Implications for the design of offshore structures and the movements of moored ships are discussed.
Loop Formation in Catenary Risers on Installation Conditions: A Comparison of Statics and Dynamics
Authors: Gay Neto Alfredo , Pimenta Paulo de Mattos , Martins Clóvis de Arruda
Published: November 2013

Loop formation may occur in cables, ropes, and also risers — flexible pipes or umbilical cables — used for offshore exploitation. The phenomenon occurs when there is enough torsion moment in the line and also a low tension condition or, even in the cases of cable slack (almost zero tension) with some torsion moment. Many references discuss about the loop formation prediction in different conditions, but mostly for the cases of an initial straight cable (rope or riser) which is usually represented by a beam. The problem of the loop formation in a catenary riser including the nonlinear contact with the seabed is very important, once during the riser installation in some conditions a low tension combined with torsion moment can lead to the loop formation, which is undesirable. There is a necessity of a better understanding of this theme. The present work explores the loop formation in catenary risers comparing the results of the static and the dynamic predictions, showing an asymptotic tendency from the dynamics to the statics. For that study, geometrically-exact nonlinear beam models were employed in the statics and in dynamics, leading to very realistic loop formation predictions.
Issues With the Density and Rheology of Drilling Fluids Exposed to Extreme Temperatures and Pressures
Authors: Zamora Mario , Roy Sanjit , Slater Kenneth
Published: November 2013

The 1980’s introduction of costly non-aqueous drilling fluids finally sent the industry a wake-up call to seriously acknowledge the significant impacts of temperature and pressure on the downhole density and rheological properties of drilling fluids. Despite notable progress since then, key issues remain, mostly related to inherent complexities and uncertainties associated with quantifying these effects.

Some issues are technical; others are procedural. Concerns are particularly critical on wells drilled under extreme HTHP (high-temperature/high pressure) conditions, in deepwater, and in Arctic and other ultra-cold locations.

The primary objective of this paper is to discuss existing issues from well-integrity and wellbore-integrity perspectives, with focus on determining hydrostatic pressures and rheological properties under downhole conditions. Also included are new representative volumetric-behavior and viscometric data measured in the laboratory under extreme HTHP conditions.
Sparse Spectrum Seas and Waves Statistics
Authors: Charnotskii Mikhail
Published: November 2013

A novel Sparse Spectrum (SS) model of the sea surface (M. Charnotskii, Proc. OMAE, 2011) is based on the conjecture that each surface realization contains a finite, possibly random, number of sinusoidal components with random frequency, phase and amplitude. Unlike the conventional FFT-based model, the number of spectral components forming the surface is determined by the sea state, but not the desired spatial resolution and domain size. A single constrain on the probability distribution of the wavenumbers, and the amplitude variances of the components and the number of spectral components allows the SS surface to conform to any prescribed spectral density.

Spectra and single-point probability distribution of the surface elevations are not sensitive to the number of sparse spectral components. In order to gain information about the spectral sparsity of the surface elevation we use our SS-based Monte-Carlo model for the surface elevations to examine the sensitivity of the statistics of the individual waves to the number of the sparse spectral components. We analyze the probability distributions of the wave heights; mean zero crossing period, and exceedance probability of the crest height at a fixed point and over a given region of area for the wave records generated by the SS model and compare it to the statistics based on the traditional FFT-based Monte-Carlo models corresponding to the dense spectrum model.

We use the Elfouhaily et.al. spectral model [3] that is common for the ocean remote sensing applications and discuss the sensitivity of the wave statistics to the spectral model choice.
Performance Based Seismic Design of Suction Pile Foundations
Authors: Parker Eric J. , Ardoino Fabrizio , Bughi Sabrina
Published: November 2013

Deepwater subsea developments require installation of relatively large, heavy structures in poor soil conditions. In many cases, the foundations of choice are large diameter suction piles. The industry has excellent experience in design of these foundations for operational conditions, but offshore codes provide little guidance regarding performance during earthquakes. This paper presents an example of a recent project where suction piles were used to support large manifold structures in a seismically active region. Preliminary verifications using a conventional pseudostatic approach showed that the planned foundations would have been unsatisfactory for seismic loadings. More detailed performance based design was employed to avoid over-dimensioning the piles. Dynamic finite element analysis was used to evaluate structure displacements during and after the design earthquake. Advanced soil models were required to capture the nonlinear behavior of the soft soils at the site. The manifold displacements were compared to operational requirements to assess foundation acceptability. The approach provided considerable savings. This paper outlines the main aspects of the two approaches, and shows the advantages of performance based design for these structures. Our conclusion is that careful analysis is required for the soil conditions typically found at deepwater sites; standard simplified approaches may not suffice.
Peakedness of Wave Systems Observed on the French Wave Energy Test Site (SEM-REV) Using a Spectral Partitioning Algorithm
Authors: Saulnier Jean-Baptiste , Le Crom Izan
Published: November 2013

Located off the Guérande peninsula, SEM-REV is the French maritime facility dedicated to the testing of wave energy converters and related components. Lead by Ecole Centrale de Nantes through the LHEEA laboratory, its aim is to promote research alongside the development of new offshore technologies. To this end, the 1km2, grid-connected zone is equipped with a comprehensive instruments network sensing met-ocean processes and especially waves, with two identical directional Waverider buoys deployed on the site since 2009.

For the design of moored floating structures and, a fortiori, floating marine energy converters, the knowledge of the main wave resource — for regular operation — but also extreme conditions — for moorings and device survivability — has to be as precise as possible. Also, the consideration of the multiple wave systems (swell, wind sea) making up the sea state is a key asset for the support of developers before and during the testing phase.

To this end, a spectral partitioning algorithm has been implemented which enables the individual characterisation of wave systems, in particular that of their spectral peakedness which is especially addressed in this work. Peakedness has been shown to be strongly related to the groupiness of large waves and is defined here as the standard JONSWAP’s peak enhancement factor γ. Statistics related to this quantity are derived from the measurement network, with a particular focus on the extreme conditions reported on SEM-REV (Joachim storm).
The Use of Centrifuge Model Testing to Provide Geotechnical Input Parameters for Pipeline Engineering
Authors: Bransby M. Fraser , White David J. , Low Han Eng , Rodriguez Antonio Borges
Published: November 2013

Pipe-soil interaction testing in geotechnical centrifuges is used as a means of providing project-specific information to support the assessment of ‘friction factors’ and other geotechnical inputs to pipeline engineering. The centrifuge testing method allows moderate-sized soil samples (−0.01–1 m3) taken from the field to be used directly to determine site-specific behavior. The tests might involve simple uplift resistance testing for buried, backfilled pipelines or complicated installation and loading sequences designed to mimic the complex laying and loading histories relevant to laterally-buckling or storm loading of unburied pipelines. The paper explains briefly the principles behind centrifuge modeling and describes more fully how such testing should be used to gain benefit for a project.
Particle Based Numerical Analysis of Green Water on FPSO Deck
Authors: Bellezi Cezar Augusto , Cheng Liang-Yee , Nishimoto Kazuo
Published: November 2013

The green water phenomenon is boarding of sea water onto the deck due to high amplitude waves, which can cause several damages to the equipment on deck. In the present paper the green water phenomenon on three-dimensional models is analyzed using the Moving Particles Semi-Implicit Method (MPS), a fully lagrangian method for incompressible flow. This work is focused on the validation of the method comparing the numerical results with experimental results for green water on reduced scale models. The pressure on sensors over the deck of the models shows good agreement with experimental data.
Modern Rheological Analysis of Drilling Fluids
Authors: Schulz Anne , Strauß Heike , Reich Matthias
Published: November 2013

Rheological analysis provides a good comprehension of the deformation and flow of substances under different stress conditions. The complex composition of the drilling fluid and the versatile functions makes rheological studies here indispensable as well as in other scientific fields like the food industry and material science. In spite of adding many high-quality additives to the drilling fluids, problems still occur, such as barite-sag, lost circulation, change of mud properties (particularly at high and very low temperature), solids transport. Others are often mentioned as reasons for increasing the cost of wells. The areas in which rheology plays an important role in drilling technology will be highlighted in this article. The reason, why the characterization with the Fann-viscometer alone is not enough for a detailed view on rheology will be focused on. In addition, measuring methods which are able to provide detailed information about gel strength, consistency, gel destruction, gel build up process and yield point have been investigated. A short overview of the basics of rheology is given. In this article, novel procedures will be shown on the basis of flow curve, hysteresis loops, amplitude sweep and 3-interval-thixotropy-test (3ITT). With these procedures, deeper knowledge about the drilling fluid system can be obtained. Implementing these procedures and considering their results in hydraulic calculation programs or taking them into account by the design of drilling fluids, can reduce costs and lead to safer drilling process in general.
Influence of Sloshing on the Transfer of Water Between Neighbouring Compartments Considering Three Different Opening Configurations
Authors: Manderbacka Teemu L. , Vitola Marcelo , Celis C. Miguel A. , Matusiak Jerzy E. , Neves Marcelo A. S. , Esperança Paulo T. T.
Published: November 2013

Model tests to generate validation data for the codes predicting the sloshing and progression of water through an opening in case of a damaged ship were planned and performed. Behaviour of the flooding water after the damage is greatly dependent on the internal compartment geometries and vessel motions. Vessels angular position and motions in turn are affected by the flooding water. Thus accurate prediction of this strongly coupled flooding phenomenon requires simultaneous solving of the ship motions and behaviour of the internal water. In order to produce validation data for calculation methods for internal flood water behaviour, tests for water motion between two connected neighbouring compartments were designed. Model tests concentrated purely on the internal sloshing motion under forced compartment motions, thus uncoupling the vessel response.
Evaluation Method of Large Inclusions in High-Grade Pipeline Steel
Authors: Li Yan-hua , Wang Hai-tao , Ji Ling-kang , Chi Qiang , Chen Hong-yuan
Published: November 2013

Good internal quality of steel pipes is a basic guarantee for the safe and efficient operation of pipeline system. While presence of large inclusions has adverse effect on the mechanical properties, weldability and corrosion resistance of the steel pipes, and then it would bring huge risk to the safe operation of oil and gas transmission pipeline. In order to reduce the risk to a minimum extent, it is quite necessary to analysis and study the characteristics of large inclusions in high grade pipeline steel, and then it would provide evidence for the formulation of level-determination standard of large inclusions during steel pipe acceptance. Optimized production technology such as electromagnetic stirring is put forward accordingly to prevent the occurrence of large inclusions in pipeline steel.
Development of a New Cartesian Explicit Solver for Hydrodynamics Flows
Authors: Bigay P. , Leroy C. , Oger G. , Le Touzé D. , Guilcher P.-M.
Published: November 2013

In order to solve complex problems in hydrodynamics, a new method is developed. This method aims at finding a good compromise between computational efficiency, accuracy, and easy handling of complex geometries. The chosen method is an Explicit Cartesian Finite Volume method for Hydrodynamics (ECFVH) based on a compressible (hyperbolic) solver, with an embedded method for interfaces and geometry handling. The explicit nature of the solver is obtained through a weakly-compressible approach chosen to simulate nearly-incompressible flows. The explicit cell-centered resolution allows for an efficient solving of very large simulations together with a straightforward handling of multi-physics. The use of an embedded Cartesian grid ensures accuracy and efficiency, but also implies the need for a specific treatment of complex solid geometries, such as the cut-cell method in the fixed or moving body frame. Robustness of the cut-cell method is ensured by specific procedures to circumvent small cell volume numerical errors. A characteristic flux method for solving the hyperbolic part of the Navier-Stokes equations is used for which upwinding is necessary, also introducing numerical viscosity. This numerical viscosity is evaluated before trying to model viscous and turbulent effects. In a first approach viscous effects are computed via a finite difference Laplacian operator introduced as a source term. This solver is validated on 2-D test cases and future improvements are discussed.
Model Test Correlation Study for a Floating Wind Turbine on a Tension Leg Platform
Authors: Koo Bonjun , Goupee Andrew J. , Lambrakos Kostas , Lim Ho-Joon
Published: November 2013

The challenges related to floating wind turbine analysis simulations relate to the modeling of the flexible turbine tower dynamics, the rotor dynamics, and the floating platform dynamics. In order to simulate the interactions between the wind turbine and the floating platform, two existing numerical codes, FAST [1], developed by the National Renewable Energy Laboratory (NREL), and MLTSIM, a Technip proprietary software, were integrated into one code, MLTSIM-FAST. In this integrated program, the turbine tower and rotor dynamics are simulated by the subroutines of FAST, and the hydrodynamic loads and mooring system dynamics are simulated by the subroutines of MLTSIM.

This paper presents validation of the MLTSIM-FAST code on the basis of data from the DeepCwind floating wind turbine model tests [2] and [3]. For the present MLTSIM-FAST validation study, the TLP floating wind turbine, which showed the strongest interactions between the wind turbine and the floating platform among the three platforms TLP, SEMI, and SPAR tested, is selected. The validation results are given on the basis of full scale measured and simulated motions and loads.
Development of a Computer Program for Three Dimensional Analysis of Zero Speed First Order Wave Body Interaction in Frequency Domain
Authors: Guha Amitava , Falzarano Jeffrey
Published: November 2013

Evaluation of motion characteristics of ships and offshore structures at the early stage of design as well as during operation at the site is very important. Strip theory based programs and 3D panel method based programs are the most popular tools used in industry for vessel motion analysis. These programs use different variations of the Green’s function or Rankine sources to formulate the boundary element problem which solves the water wave radiation and diffraction problem in the frequency domain or the time domain.

This study presents the development of a 3D frequency domain Green’s function method in infinite water depth for predicting hydrodynamic coefficients, wave induced forces and motions. The complete theory and its numerical implementation are discussed in detail. An in house application has been developed to verify the numerical implementation and facilitate further development of the program towards higher order methods, inclusion of forward speed effects, finite depth Green function, hydro elasticity, etc. The results were successfully compared and validated with analytical results where available and the industry standard computer program for simple structures such as floating hemisphere, cylinder and box barge as well as complex structures such as ship, spar and a tension leg platform.
Introduction to Offshore Platform Global Weight Management Database Program
Authors: Xu Lixin , Tu Qin , Zhou Joe
Published: November 2013

An Offshore Platform Global Weight Management Database Program (OPGWMDP) has been developed and used to manage and monitor the platform system weights in design, fabrication, installation and operation. It is the first weight management database specialized to support the Spar system engineering design, construction, installation and offshore operation. This database program, which was developed in the Microsoft Access environment, is portable, cost friendly and integrated with graphic user interfaces (GUI). This program not only has the data storage and operational functions like a common database program, but also provides calculation functions specifically developed for offshore platform design and operation, such as horizontal force and moment calculation for mooring or other positioning systems, riser systems, fixed ballast and variable ballast automatic balance calculation, adjustment of displacement and topsides payloads eccentricity and variation. The program can also provide fast data for the platform stability verification under various operational conditions. These functions usually are not included in other similar weight control database programs. This system includes 4 main modules to provide the data input, edit and output functions and several sub-modules to manage different group data. This architecture gives the system a flexible structure which can be easily supplemented with new functions in the future. The specifically designed GUI provides a friendly interface for the user to interact with this system. This weight control database program has been verified with as-built platform data, and is applicable for a variety of offshore platforms, including Spar, semisubmersible, TLP and FPSO.