bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid Scaled Testing of a 5MW Floating Wind Turbine Using the SiL Method Compared With Numerical Models
Authors: Vittori Felipe , Bouchotrouch Faisal , Lemmer Frank , Azcona José
Published: September 2018

The design of floating wind turbines requires both, simulation tools and scaled testing methods, accurately integrating the different phenomena involved in the system dynamics, such as the aerodynamic and hydrodynamic forces, the mooring lines dynamics and the control strategies. In particular, one of the technical challenges when testing a scaled floating wind turbine in a wave tank is the proper integration of the rotor aerodynamic thrust. The scaling of the model based on the Froude number produces equivalent hydrodynamic forces, but out of scale aerodynamic forces at the rotor, because the Reynolds number, that governs the aerodynamic forces, is not kept constant. Several approaches have been taken to solve this conflict, like using a tuned drag disk or redesigning the scaled rotor to provide the correct scaled thrust at low Reynolds numbers. This work proposes a hybrid method for the integration of the aerodynamic thrust during the scaled tests. The work also explores the agreement between the experimental measurements and the simulation results through the calibration and improvement of the numerical models. CENER has developed a hybrid testing method that replaces the rotor by a ducted fan at the model tower top. The fan can introduce a variable force which represents the total wind thrust by the rotor. This load is obtained from an aerodynamic simulation that is performed in synchrony with the test and it is fed in real time with the displacements of the platform provided by the acquisition system. Thus, the simulation considers the displacements of the turbine within the wind field and the relative wind speed on the rotor, including the effect of the aerodynamic damping on the tests. The method has been called “Software-in-the-Loop” (SiL). The method has been applied on a test campaign at the Ecole Centrale de Nantes wave tank of the OC4 semisubmersible 5MW wind turbine, with a scale factor of 1/45. The experimental results have been compared with equivalent numerical simulations of the floating wind turbine using the integrated code FAST. Simple cases as only steady wind and free decays with constant wind showed a good agreement with computations, demonstrating that the SiL method is able to successfully introduce the rotor scaled thrust and the effect of the aerodynamic damping on the global dynamics. Cases with turbulent wind and irregular waves showed better agreement with the simulations when mooring line dynamics and second order effects were included in the numerical models.
Effects of Cumulative Buckling Deformation Formed by Cyclic Loading on Ultimate Strength of Stiffened Panel
Authors: Komoriyama Yusuke , Tanaka Yoshiteru , Ando Takahiro , Hashizume Yutaka , Tatsumi Akira , Fujikubo Masahiko
Published: September 2018

In this study, for the stiffened panels subjected to the in-plane cyclic compression loads, the two followings are clarified. One is a generating process of the cumulative buckling deformation at panel parts of stiffened panels. The other is the effect of the cumulative buckling deformation on the ultimate strength of stiffened panels. To clarify them, the cyclic compression loading experiments were carried out with two stiffened panel specimens by using Multi Axis Loading System in National Maritime Research Institute (NMRI) in Japan. For one stiffened panel specimen, the thirty-one sets of compression test cases were conducted with different strokes and for each case. The number of cycles in each set was 100. While, for the other, it was subjected to the cyclic compression loads until it collapsed. In addition, Finite Element Method (FEM) analyses for stiffened panels subjected cyclic compression loads are carried out with the same condition as the experiments by using commercial FEM software, LS-DYNA.
Controller Analysis in Real-Time Hybrid Model Testing of an Offshore Floating System
Authors: Vilsen Stefan A. , Sauder Thomas , Føre Martin , Sørensen Asgeir J.
Published: September 2018

This paper presents an experimental study using Real-Time Hybrid Model (ReaTHM) testing of a moored floating cylindrical buoy, conducted in a wave basin. ReaTHM testing is a method for studying the dynamics of marine structures by partitioning the system into numerical and physical substructures that are then coupled in real-time using a control system. In this study, the floating cylinder buoy is modelled physically, and the mooring system modelled numerically. In this paper, the effect of selected controller parameters on the performance of the control system is studied, for both wave frequency and low-frequency ranges. The architecture/design of the control system is presented in the first part of the paper, while results from experimental tests with wave excitation on the physical substructure are presented in the second part of the paper.
A Methodology to Characterize Internal Solitons in the Ocean
Authors: Coelho Henrique , Peng Zhong , Sproson Dave , Bradon Jill
Published: September 2018

Internal waves in the ocean occur in stably stratified fluids when a water parcel is vertically displaced by some external forcing and is restored by buoyancy forces. A specific case of such internal waves is internal tides and their associated currents. These currents can be significant in areas where internal waves degenerate into nonlinear solitary waves, known as solitons.

Solitons are potentially hazardous for offshore engineering constructions, such as oil/gas pipelines and floating platforms. The most efficient mechanism of soliton generation is the tidal energy conversion from barotropic to baroclinic component over large-scale oceanic bottom obstructions (shelf breaks, seamounts, canyons and ridges).

In this paper, a methodology is provided to compute diagnostics and prognostics for soliton generation and propagation, including the associated currents. The methodology comprises a diagnostic tool which, through the use of a set of theoretical and empirical formulations, selects areas where solitons are likely to occur. These theoretical and empirical formulations include the computation of the integral body force (1), the linear wave theory to compute the phase speed and the empirical model proposed by (2). After the selection procedure, the tool provides initial and boundary conditions for non-hydrostatic numerical models. The numerical models run in 2D-V configuration (vertical slices) with horizontal and vertical resolutions ranging from 50 to 200 m and 5 to 10 m, respectively. Examples are provided for an open ocean location over the Mascarene Plateau in the Indian Ocean. Validation of diagnostics and prognostics are provided against ADCP and satellite data.
A Numerical Investigation on Water Slamming of Stiffened Panels
Authors: Wang Shan , Guedes Soares C.
Published: September 2018

To investigate the slamming pressure on the bottom of a wet-deck structure of a multihull vessel, the water impact problem of a stiffened steel panel is simulated by using a fully coupled ALE/FEM algorithm which is implemented in the commercial software LS-DYNA. The Lagrangian formulation is used to describe plane-strain deformations of the hull panel while the Eulerian formulation is applied to describe the fluid flow. The governing equations of this coupling problem are solved by using finite element method. The explicit finite element method is firstly validated through the comparisons of the slamming pressure and structural deflection between the numerical predictions and the published experimental data, for an elastic horizontal plate. Secondly, the parametric study of the mesh size in the impact domain of the FE model is performed. The total slamming forces obtained from three models are compared. To study the effects of the flexibility of the structure on the slamming load, the predictions of slamming pressure on several locations of the elastic panel are compared with the values obtained by using the rigid body model.

The water entries of the stiffened panel with two different deadrise angles, entry velocities, and thickness of plating are simulated. The results of the total slamming force, slamming pressure are presented and discussed.
An Optimization Framework for PBCF Energy Saving Devices
Authors: Gaggero Stefano , Villa Diego
Published: September 2018

The need of continuously improving propulsive efficiency encourages the development of energy saving devices, the understanding of their underlying principles and the validation of their effectiveness. In this work, a design by optimization of Propeller Boss Cap Fin (PBCF) devices is carried out using Computational Fluid Dynamics analyses. RANS calculations (by the OpenFOAM library) are applied in an automatic optimization design approach involving a parametric description of the main characteristics of PBCFs. The optimization is carried out with multiple purposes: identify a reliable design strategy necessary to customize the PBCF geometry based on the propeller functioning and evaluate the influence of alternative configurations and of main geometrical parameters in achieving higher efficiency. The use of high-fidelity RANS calculations confirm that the decrease of the hub vortex strength, the reduction of the net torque and the influence of the additional fins on blades performance are the major contributors to the increase of efficiency. Results of detailed analyses of optimal PBCF configurations show model scale increases of efficiency of about 1%.
The Syrope Method for Stiffness Testing of Polyester Ropes
Authors: Falkenberg Erik , Yang Limin , Åhjem Vidar
Published: September 2018

The load-elongation properties of polyester ropes are often modelled through a static-dynamic model with parameters based on different proposed test procedures, which may not be sufficient for the mooring analysis since the stretch response to tension of fiber ropes is nonlinear. In the Syrope Joint Industry Project, a new procedure for tension vs. stretch testing of polyester ropes for mooring applications was developed. The test allows for determining parameters in a rope model, which was developed in the JIP, where the length and dynamic stiffness of the rope are given by the actual mean tension and the previous highest mean tension in each mooring line. Test results from this new procedure have been compared with results from the test procedures provided in API, ABS and ISO documents. All tests were performed on samples from the same sub-rope. Differences and similarities between the different test procedures and analysis methods have been investigated.
Surge Height and Current Estimation Along K-G Basin
Authors: Sebastian Maneesha , Behera Manasa Ranjan
Published: September 2018

Numerical investigation on storm surge characteristics would benefit the planners and designers of coastal structures and offshore platforms along the Krishna-Godavari (K-G) basin. The adjoining coastline has a wide range of geomorphological features and varying geometries due to the sediment deposition from the two major rivers, Krishna and Godavari. Two severe cyclonic storms (SCS) Laila (2010) and Helen (2013) that approached the basin from two different directions and made landfalls closer to each other were analyzed for determining the storm surge heights and currents along the K-G river basin. The maximum water elevations and maximum currents during the storm event and evolution of storm surge heights at different locations were studied. It could be concluded from the study that when a SCS event approaches K-G basin, in addition to the tide and wave effect, a maximum storm surge height and current of 1 m and 1.2 m/s can be expected along the coast, respectively. Similarly, the surge and current in the offshore regions were found to be 0.3 m and 0.8 m/s, respectively. These values may be considered while deriving design parameters for the offshore installations. The critical regions in the basin were identified where high surge heights and currents are expected.
Multi-Objective Optimization Design of Flexible Risers Based on Bi-Scale Response Surface Models
Authors: Yang Zhixun , Yan Jun , Sævik Svein , Zhen Luqing , Ye Naiquan , Chen Jinlong , Yue Qianjin
Published: September 2018

An optimized flexible riser design not only requests that the stress of local cross-section shouldn’t exceed the allowable strength, but also can be compliant with the floater to improve the fatigue life. It should be particularly pointed out that the flexible riser is a typical multi-scale system, which consists of the local cross-sectional scale and the global configuration scale, which differentiates each other a lot from their geometrical scales. A bi-scale response surface model is established to perform the optimized design of flexible risers by considering the parameters of local cross-sections and global configurations simultaneously. The response surface model can be an effective surrogate model to integrate the local and global responses into one loop so that the computational efficiency can be increased significantly. In the bi-scale response model, design variables of a flexible riser are extracted and defined at both the local sectional scale and global configuration scale. Sensitivity analyses of the two objectives, ultimate tension and bending strength on the design variables are then deduced to establish the bi-scale optimization framework through the response surface methodology. Finally, the optimization framework is implemented on a flexible riser with lazy-wave configuration which is considered as a case study. The properties of the optimized flexible risers are compared with those without the optimization. It is found that the ultimate load bearing capacity and fatigue life of the optimized flexible riser are improved significantly. Moreover, the feasibility and effectiveness of the bi-scale optimization strategy are verified through numerical simulations, which indicates that the bi-scale response surface optimization methodology provides a new thought and approach to explore the design potential of flexible risers.
Performance of Pipe-Soil Interaction Models in a Quasi-Dynamic Approach to Pipeline Stability Analysis
Authors: Abdolmaleki Kourosh , Gregory John C.
Published: September 2018

This paper presents performance of pipe-soil interaction models in a quasi-dynamic approach to submarine pipeline stability analysis. The quasi-dynamic method, as implemented in the PRCI-OBS software (Level 2), applies a series of most probable maximum waves to the pipe that are derived from extreme value analysis of the given sea state. The theoretical formulation for selecting the most probable maximum waves are derived for further clarity. The PRCI-OBS software (Level 2) was upgraded to allow for this study. The upgrade included addition of the well known Verley and Sotberg model for sand and Verley and Lund model for clay soils to the existing soil models known as PRCI soil models. The upgrade also included fixing previously reported bugs such as over-prediction of embedment in current-dominated cases. The matrix of performance simulations was sufficiently large to allow for making general conclusions. The results confirmed that the discrepancy between old and new soil models increased as the parameters approached extremities of the input matrix. The newly implemented models are based on larger model test data sets and could produce consistent results across the range of input data and thus are recommended.
Impact of Climate Change on the North Sea Offshore Energy Sector
Authors: Fournier Nicolas , Guentchev Galina , Krijnen Justin , Saulter Andy , Acton Caroline , Hanlon Helen
Published: September 2018

The complex nature of the energy industry across extraction, transportation, processing, delivery and decommissioning creates significant challenges to how the sector responds, adapts and mitigates against risks posed by the changing future climate. Any disruption in this interconnected system will affect both industry and society. For example, in the summer of 2005 Hurricane Katrina and a month later Hurricane Rita had wide reaching impacts on the US offshore Oil and Gas industry which resulted in an increase in global oil prices due to loss of production and refinery shutdowns in the Gulf of Mexico.

Preparing, mitigating and adapting to these climate changes is dependent upon identifying appropriate climate indicators as well as the associated critical operational thresholds and design criteria of the identified vulnerable assets. The characterization and understanding of the likely changes in these climate indicators will form the basis for adaptation plans and mitigating actions.

The Met Office in collaboration with energy industry partners, under the Copernicus Clim4energy European project, has developed a Climate Change Risk Assessment tool, which allows the visualization and extraction of the most recent sea level and wave climate information to evaluate their future changes. This study illustrates the application of this tool for evaluation of the potential vulnerability of an offshore infrastructure in the North Sea.

The analysis shows that for this asset there is a small increase in sea level of 0.20–0.30 m at the location of interest by 2050. However, there is a small decrease or no consistent changes projected in the future wave climate. This wave signal is small compared to the uncertainty of the wave projections and the associated inter-annual variability. Therefore, for the 2050s time horizon, at the location of interest, there is no strong impact of climate change at the annual scale on the significant wave height, the sea level and thus the associated climate change driven extreme water level. However, further analysis are required at the seasonal and monthly scales.
Capturing and Analysing Real-Time Data From Tugs
Authors: Lim Serena , Pazouki Kayvan , Murphy Alan J. , Zhang Ben
Published: September 2018

Holistic energy management in the shipping industry involves reliable data collection, systematic processing and smart analysis. The era of digitisation allows sensor technology to be used on-board vessels, converting different forms of signal into a digital format that can be exported conveniently for further processing. Appropriate sensor selection is important to ensure continuous data collection when vessels sail through harsh conditions. However, without proper processing, this leads to the collection of big data sets but without resulting useful intelligence that benefits the industry. The adoption of digital and computer technology, allows the next phase of fast data processing. This contributes to the growing area of big data analysis, which is now a problem for many technological sectors, including the maritime industry. Enormous databases are often stored without clear goals or suitable uses. Processing of data requires engineering knowledge to ensure suitable filters are applied to raw data. This systematic processing of data leads to transparency in real time data display and contributes to predictive analysis. In addition, the generation of series of raw data when coupled with other external data such as weather information provides a rich database that reflects the true scenario of the vessel. Subsequent processing will then provide improved decision making tools for optimal operations. These advances open the door for different market analyses and the generation of new knowledge. This paper highlights the crucial steps needed and the challenges of sensor installation to obtain accurate data, followed by pre and post processing of data to generate knowledge. With this, big data can now provide information and reveal hidden patterns and trends regarding vessel operations, machinery diagnostics and energy efficient fleet management. A case study was carried out on a tug boat that operates in the North Sea, firstly to demonstrate confidence in the raw data collected and secondly to demonstrate the systematic filtration, aggregation and display of useful information.
Numerical Simulation of Control Strategies at Mutriku Wave Power Plant
Authors: Faÿ François-Xavier , Kelly James , Henriques João , Pujana Ainhoa , Abusara Mohammad , Mueller Markus , Touzon Imanol , Ruiz-Minguela Pablo
Published: September 2018

In order to de-risk wave energy technologies and bring confidence to the sector, it is necessary to gain experience and collect data from sea trials. As part of the OPERA H2020 project, the Mutriku Wave Power Plant (MWPP) is being used as a real condition laboratory for the experiment of innovative technologies. The plant is situated in the North shore of Spain and has been operating since 2011. It uses the Oscillating Water Column (OWC) principle, which consists in compressing and expanding the air trapped in a chamber due to the inner free-surface oscillation resulting from the incident waves. The pressure difference between the air chamber and the atmosphere is used to drive an air turbine. In that case, a self-rectifying air turbine is the best candidate for the energy conversion, as it produces a unidirectional torque in presence of a bi-directional flow. The power take-off system installed is composed of a biradial turbine connected to a 30kW off-the-shelf squirrel cage generator. One of the novelties of the turbine is a high-speed stop-valve installed close to the rotor. The valve may be used to control the flow rate through the turbine or for latching control. This paper focuses on the development, the implementation and the numerical simulation of five control strategies including turbine speed and generator torque controllers. The algorithms were designed thanks to a numerical model describing one of the OWC chambers of the Mutriku power plant. Numerical results are presented for a variety of sea states and a comparison between the proposed control laws in terms of energy production and power quality is performed.
Metocean Conditions in a Norwegian Fjord
Authors: Wang Jungao , Li Lin , Jakobsen Jasna Bogunović , Haver Sverre Kristian
Published: September 2018

The present study investigates the environmental conditions in the Sulafjord in Norway, where a floating bridge is being considered for construction. Fifteen months of wave and wind measurement data in the fjord are compared to the hindcast data at a relevant offshore site and a good overall correlation between the two is found. Furthermore, a quantitative relationship between the wave conditions offshore and in the fjord is established based on the storm event analysis. Accordingly, the identified relationship and the 60-years of offshore hindcast data enable the estimation of the design environmental conditions in the fjord, by adapting the fitted marginal and joint distribution of the wave conditions at the offshore site, which illustrates the possibility of using more data from the hindcast model for the design when the measurement data is limited.
Fatigue Reliability Assessment of Fillet Welded Cruciform Joints Based on the Fatigue Notch Factor and Local Strain Approach
Authors: Dong Yan , Garbatov Yordan , Guedes Soares C.
Published: September 2018

The objective of this work is to analyze the fatigue reliability of fillet welded cruciform joints considering the uncertainty of the load and capacity. The weld shape is defined by multivariate normally distributed variables, which represent the position variations of the shape control points on the fillet welds. Finite element analyses are performed to calculate the fatigue notch factors of the weld root and toe, where the fatigue crack is usually initiated. Various weld shapes associated with various correlation conditions and weld quality levels are generated and the corresponding probability distributions of the fatigue notch factors are obtained by using the Monte Carlo simulation method. Sensitivity analyses are carried out to identify which location is more important for the fatigue notch factors. Within the context of the local strain approach, a critical fatigue notch factor that can exactly trigger fatigue failure is proposed. Its statistical descriptors are determined by using the Monte Carlo simulation method, in which the nominal stress range, material properties and fatigue damage at failure are treated as random variables. The limit state functions of the weld root and toe are formulated based on the actual and critical fatigue notch factors. The first order reliability method is applied to evaluate the fatigue reliability. The cruciform joint, composed by two fatigue-prone locations, is evaluated as a series system of components. Two different loading conditions, which make the cruciform joints load-carrying and non-load-carrying respectively, are considered.
Novel Erosion Control Technology for Production Debottlenecking
Authors: Kane Prasad Laxman , Pliszka Dominic
Published: September 2018

Erosion of piping systems is a significant issue for many operators of Hydrocarbon infrastructure. Until now mitigation measures have been limited to detection / measurement and reducing production. For many operators this can be a significant loss in revenue and an increase in IMR costs. A novel Erosion Control Technology (ECT) is being developed that can significantly reduce the impact of erosion on piping infrastructure. This technology has the potential of adding immense value when it is used to debottleneck and optimize flow rates. The patented ECT has been designed to control sand erosion in real-time by deflecting and redistributing sand in the product flow stream.

Preliminary laboratory testing of the ECT has been very successful. The ECT inserts designed for the ambient test conditions have shown substantial reduction in erosion (both global and local). Computational Fluid Dynamics (CFD) has been the key enabling factor allowing the critical breakthrough in this technology. Experimental results have shown very good correlation with the CFD sand erosion model results. A roadmap in line with industry practices and standards has been developed for project implementation of the ECT solution in the near future.
Methodology for Calculating Floating Offshore Wind Foundation Internal Loads Using Bladed and a Finite Element Analysis Software
Authors: Alexandre Armando , Urbano Ricard Buils , Roadnight John , Harries Robert
Published: September 2018

In the recent years, the floating offshore wind industry has developed quickly and most authors are now converging towards the need of a coupled loads analysis using aero-hydro-servo-elastic software on time domain simulations for floating foundations design. Different hydrodynamic theories still exist and their application depends on the floating platform characteristics. The Morison equation and the boundary element method (BEM, not to be confused with the Blade Element Momentum theory) theory approaches are often used in combination on the same platform model, sometimes applied to different elements of the same structure depending on their shape.

When using the potential flow theory approach calculating internal distributed loads and later on transferring them to stress for hull design purposes is still a challenge due to the large ammount of load cases needed and the complexity of the structure. Furthermore, accounting for platform flexibility is also difficult in most codes using BEM theory due to the same reasons. Different approaches have been proposed by different authors, and currently there is not a single best industry practice for this.

This paper presents a method for accounting for platform flexibility when using BEM theory. A range of methods for the load to stress transfer are also presented and the advantages and disadvantages between them are discussed. The choice of one or another method will depend heavily on the platform structure, and different methods might be used and combined for the same platform depending on the shape of the different elements within it.

The different methods presented here involve performing coupled loads analysis using the aero-elastic software Bladed and multiple bodies to represent the floating platform in order to obtain internal loads at different points in the structure, as well as allowing for platform flexiblity modelling. Bladed can model multiple hydrodynamic bodies including the hydrodynamic effects between (e.g. coupled terms in the radiation force). The approach used in the current study is based on a platform modelled with the hydrodynamic loading distributed over independent sections, but originally computed from a single body BEM calculation. This simplification offers significant gains in computational efficiency and is expected to be valid for many types of floating structure, whist still allowing for some platform flexiblity to be modelled.

The simulation resultant time series can later on be postprocessed to obtain distributed pressure forces on the platform wetted surface and transfer those onto a Finite Element code. Different options are presented here on how to perform this last step for both extreme and fatigue analysis of the hull structure. A couple of examples are shown using the OC3 spar and OC4 semisubmersible, focusing on a subsection of the structures to demonstrate the methodology.
Dynamic Constitutive Model Application and Validation for Offshore Structures Under Dropped Object Impact Loads
Authors: Mortazavi Maryam , Heo YeongAe
Published: September 2018

It is critical to incorporate an appropriate constitutive model into a finite element analysis model to evaluate the nonlinear and dynamic effects on offshore structures subjected to dropped object impact loads. This paper demonstrates the high sensitivity of a dynamic constitutive model to mechanical properties of a specific offshore structural steel and its effect on nonlinear transient finite element analysis results for a steel plate system subjected to dropped object impact loads. Available stress-strain data obtained from dynamic tensile tests are used to validate the numerical results. The dynamic constitutive model recommended by Det Norske Veritas (DNV) was examined at both constitutive level and structural level. This paper proposes constitutive model parameters to improve the DNV’s recommendation.
Fatigue Strength of Heavy Wall Line Pipe Girth Weld for J-Lay Installation
Authors: Marines-Garcia Israel , Pelcastre Mauricio , Garcia Enrique , Darcis Philippe P. , Yang Guangqiang , Bourgeois Desmond , Visco Tyler
Published: September 2018

Tenaris and ExxonMobil conducted a qualification program focused on Heavy Wall Seamless Line Pipe (HW SMLS LP) and its girth welds, to experimentally demonstrate and validate the material potential to be used as riser or fatigue sensitive flowline for the development of challenging deep and ultra-deep offshore fields. The qualification program was divided in three phases.

Phase I [1] included: 1) HW SMLS LP, X65QS, 273 mm OD, 46 mm WT plain pipe qualification; and 2) development and qualification of a WPS (STT® process for root pass and GMAW process for hot, fill & cap passes, narrow groove J-bevel type, 1G welding torch position) and full scale fatigue testing qualification.

Phase II [2] was focused on evaluating the root girth weld fatigue endurance, taking into account the fatigue behavior observed in Phase I (fatigue crack initiation mainly occurred from the outer surface). The fatigue strength of the weld root surface is needed as the weld root surface is in direct contact with corrosive fluids and is the most sensitive area for sour service applications. Thus, to obtain the root girth weld fatigue endurance, full scale fatigue specimens were manufactured with their caps fully removed (by grinding and flapping) to generate weld cap toe free of stress raisers/imperfections. In addition, pipe outer surface was grinded to mitigate the fatigue crack nucleation from outer pipe surface. With this special preparation, the fatigue strength of weld root surface was able to be assessed.

This paper presents Phase III qualification outcomes. The objective was to develop and qualify a WPS representative of J-Lay installation, meaning 2G welding torch position (CMT® for the root pass and pGMAW process for hot, fill and cap passes, Narrow groove J3°-bevel type). The qualification included full scale fatigue assessment as well. The LP material was from the same batch used in Phase I & II (HW SMLS, X65QS, 273 mm OD, 46 mm WT).

The WPS was successfully developed and qualified. The full scale resonant fatigue testing included three specimens with cap smoothed similarly to Phase I, and three specimens with full cap removal plus outer pipe surface grinding similar to Phase II. The fatigue results surpassed the expectations (Class D, S-N curve). Most of the specimen’s fatigue lifetime is above the class B, S-N curve classification (reference for plain material). Obtaining a smooth root weld overfill was key to delaying the fatigue crack nucleation from the weld root toe.
Recent Development and Validation of the Latest FlawPRO™ ECA Methodology
Authors: Bezensek Bostjan , Chell Graham , Popelar Carl , Luo Meng
Published: September 2018

The graphical user interface driven engineering software tool FlawPRO™ has been extensively used for subsea pipeline design and installation under high strain or fatigue intense applications. The methodology included in the program has evolved since its inception in 2002 through a series of JIPs involving major oil and gas operators and installation contractors. This paper summarises the fracture mechanics concepts incorporated in the methodology of the latest version of FlawPRO™ and the results of an extensive full scale flawed pipe testing programme that included over 45 reeling simulations and other fracture tests performed to validate the methodology.

It is shown that the program’s crack growth predictions under large strain reeling are consistent with test data obtained from reeled pipes containing centreline flaws in over-matched welds, with the majority of the predicted results obtained using average material property data scattering around the mean 1:1 line consistent with uncertainties in the mechanical property values used in the validation. The results of an assessment of some of the reeling test data using the DNV ECA methodology (DNV-RP-F108) are also presented.

It is concluded that the FlawPRO™ methodology is consistently more accurate in assessing the test data compared with the DNV methodology which may yield some non-conservative results.

Both methodologies require suitable factors of safety or adjustments to either material and / or load inputs to maintain conservatism in applications to the pipeline projects.
Effect of Wave-Current Interaction on Strong Tidal Current
Authors: Jakovljević Aleksandar , Dumont Martin , Dias Frédéric
Published: September 2018

We consider the influence of wave-current interactions (WCI) on the tidal energy resource through changes in the velocity field of tidal currents. In order to investigate this, we have run three models: SWAN (stand-alone), ROMS (stand-alone) and COAWST (two-way coupled ROMS and SWAN model). The research area of our studies is Alderney Race, France, an area with strong currents, which has a strong potential for tidal turbine deployment. The time period used for the simulations was March 2008, when a strong storm hit the Alderney Race area and produced significant wave heights (Hs) of up to 7 m and a Stokes drift near the surface close to 0.3 m/s. Furthermore, in order to see the extent of the influence of large waves on current parameters, two virtual storms with larger waves have been generated by magnifying the wave energy spectrum and changing the frequency of the spectrum of the real storm in March 2008. The 3D and the barotropic velocity field were analysed in order to see if the WCI in the waters of Alderney Race during storm conditions can cause a significant increase or decrease of the current speed and through which mechanisms. This study also investigates the Turbulent Kinetic Energy (TKE) in order to portray the turbulent conditions in the area of interest which are important for resource characterisation and device design.
Simulating the Response of Untrenched Flowlines due to Iceberg-Flowline-Soil Interaction
Authors: Pike Kenton , Blundon Andrew
Published: September 2018

As offshore oil and gas fields mature on the Grand Banks, offshore Newfoundland and Labrador, marginal field subsea tie-backs are necessary to maintain production levels. Existing untrenched flowline lengths have been limited by the assumption that iceberg contact equates to flowline failure. However, extended tie-backs will be necessary to develop stranded resources. To potentially reduce the number of failure cases, we can consider a better definition of failure that accounts for the pipeline response due to iceberg-soil-pipeline interaction events. Reducing the failure rate from free-floating iceberg contacts alone can significantly increase safe tie-back lengths.

This paper examines the flowline response from impacts with free-floating icebergs using large deformation finite element analysis. The plane strain pipe-soil interaction response is first simulated for pure vertical loading and compared against analytical bearing capacity theory. The influence of non-associativity in the soil constitutive model is demonstrated with respect to predicting the pipe drained penetration resistance in dense sands. Oblique vertical-horizontal plane strain pipe-soil interaction is also investigated, and it is shown that the vertical penetration resistance is reduced when the pipe trajectory deviates from pure vertical, consistent with published interaction diagrams. Lastly, the fully coupled interaction scenario of free-floating iceberg-pipe-soil interaction is simulated, showing the effects of the pipe wall thickness and soil strength. The numerical modelling procedures are described and the soil constitutive model that incorporates dense sand behavior is detailed.
Nonlinear Truss-Based Quasi-Static Structural Model for Force Distribution Predictions on Debris Containment Grids
Authors: Chreim Jose Rodolfo , Dozzi Dantas Joao Lucas , de Lima Alessandro Alberto
Published: September 2018

At the Madeira River, north of Brazil, a natural phenomenon threatens the integrity and normal operation of an on-site hydroelectric power plant; thus, assemblies of containment structures, called logbooms, are installed across the river in order to protect the power plant installations. A truss-based nonlinear finite element method numerical tool is developed with the objective of designing and analyzing these assemblies. Initially, only the influence of the upstream velocity field is considered, and future modifications to account for the debris are expected. Code and solution verifications show that the tool converges reasonably well; the numerical error is about 0.2% of the theoretical value, and the uncertainty is about the same order: the results agree with analytical solutions from the simple catenary model. Finally, the method is validated by comparing numerical and experimental data; a satisfactory agreement is obtained, ascertaining the accuracy of the method: differences between experimental and numerical results are no higher than 6% and the trend of the tension force as a function of the free stream is followed by the numerical method.
A Study on the Added Resistance Performance of Catamarans in Waves
Authors: Ageno Emanuela , Bonfiglio Luca , Bruzzone Dario , Vernengo Giuliano , Villa Diego
Published: September 2018

The added resistance of a catamaran advancing in waves is investigated in the framework of a non-viscous potential theory. A linear Boundary Element Method (BEM) is used for the first order seakeeping prediction and the mean longitudinal component of the second-order steady-state force is computed by using a near-field method.

Both methods are briefly presented and preliminary validations on both a mono-hull and a catamaran are shown. A systematic analysis of the added resistance of the so-called DUT catamaran is presented highlighting the effects of the advancing speed and those of the ship-wave heading angle.
Equivalent Layer Approaches to Predict the Bisymmetric Hydrostatic Collapse Strength of Flexible Pipes
Authors: de Sousa José Renato M. , Protasio Marcelo K. , Sagrilo Luis V. S.
Published: September 2018

The hydrostatic collapse strength of a flexible pipe is largely dependent on the ability of its carcass and pressure armor to resist radial loading and, therefore, its prediction involves an adequate modeling of these layers. Hence, initially, this work proposes a set of equations to estimate equivalent thicknesses and physical properties for these layers, which allows their modeling as equivalent orthotropic cylinders. These equations are obtained by simulating several two-point static ring tests with a three-dimensional finite element (FE) model based on beam elements and using these results to form datasets that are analyzed with a symbolic regression (SR) tool. The results of these analyses are the closed-form equations that best fit the provided datasets. After that, these equations are used in conjunction with a three-dimensional shell FE model and a previously presented analytical model to study the dry and wet hydrostatic collapse mechanisms of a flexible pipe. The predictions of these models agreed quite well with the collapse pressures obtained in experimental tests thus indicating that the use of the equivalent approach is promising.
Control of a DC-DC Boost Converter for Fuel-Cell-Powered Marine Applications
Authors: Xiros Nikolaos I. , Tsakyridis Georgios , Scharringhausen Marco , Witte Lars
Published: September 2018

Economic factors together with protection laws and policies pertaining to marine pollution drive research for improved power generation. Fuel cells, being fuel efficient and environmentally friendly, could provide a desirable option and suitable alternative to conventional propulsion systems based on fossil fuels or even nuclear fission. Fuel cells are becoming fast a mature technology and employed in many various other areas. Flexibility of special purpose watercraft, power autonomy and modularity can all benefit from the use of fuel cells. Specifically, proton exchange membrane fuel cells are considered among the most promising options for marine propulsion applications. Switching converters are the common interface intermitted between fuel cells and the load in order to provide a stable regulated voltage. DC-DC converters have been widely used since the advent of semiconductors. These devices are typically adopted to accomplish voltage regulation tasks for a multitude of applications: from renewable energy power-plants to military, medical and transportation systems. Nonetheless voltage regulators exhibit the need for consistent closed- and open-loop control. Most common approaches are PID controllers, sliding mode controllers and artificial neural networks that are considered in this work. An artificial neural network (ANN) is an adaptive, often nonlinear system that learns to perform a functional mapping from data. In our approach, a typical example of a fuel cell, a power converter outfitted with an ANN controller, and a resistive load configuration is investigated. Simulation studies are crucial in power electronics to essentially predict the behavior of the device before any hardware implementation. General requirements, design specification together with control strategies can be iteratively tested using computer simulations. This paper shows the simulation results of the full system behavior, as described above, under dynamic conditions. Initially, an open-loop simulation of the system is performed. Next, an appropriately trained ANN is incorporated to the switching model of the DC-DC converter to perform simulations for validation. Conversely, during design and calibration of the ANN controller, instead of the switching model of the DC-DC converter, a trained ANN equivalent is employed.
State of the Art in 3D Seismic Survey Design for Petroleum Exploration in the Arctic Regions
Authors: Munoz P. A. , Sanabria Nestor , Ocampo German , Uribe Juan , Rodríguez Luis , Parrado Roberto
Published: September 2018

3D seismic acquisition for Petroleum Exploration in the Artic Region is typically restricted to four operational months during the winter season. The area of the survey and the acquisition parameters need to be optimized and constrained to match the narrow time frame. Seismic operations must follow environmental regulations to avoid adverse impacts to the wildlife and sensitive terrains, including lakes, rivers, abandoned meanders, and the flora able to grow in the region. No vehicles or seismic equipment is allowed to operate above them in winter regardless of their protection by the snow cover. Furthermore, only vehicles and machinery are allowed to work on the frozen tundra or over frozen lakes and rivers with grounded ice. However, the ice thickness in the frozen lakes and rivers is not capable of supporting the heavy seismic vibrator. Therefore, many source points must be relocated which finally results in irregular source point distribution over the survey acquisition area.

The conventional method to recover source points around obstructions causes a concentrated redistribution of source points in the vicinity around the obstructions. An alternative operational method to recover source positions is presented in this paper. We used different types of geophysical analysis to evaluate the proposed optimized method for source recovery including traditional geophysical attribute analysis, illumination studies and attribute analysis of seismic data acquired in the Horse Shoe 3D project.

The proposed method can be implemented in areas with significant surface obstructions, either due to environmental restrictions, population, industrial or oilfield areas, or natural obstructions, etc.

An important conclusion is that the improvement in S/N and attributes obtained by the implementation of the proposed method for source recovery did require only a marginal increase in the work volume or resources for the project and so the cost and time of execution were not affected.
A Pragmatic Approach to Sizing and Selection of Pipeline Systems in Concept Design of Deepwater Gas Development
Authors: Kanu Akachidike , Briceño Corina Ruiz
Published: September 2018

Deepwater gas pipeline development projects present unique technical challenges. These technical constraints must be considered during concept engineering to minimize total development cost and deliverability risk and effectively support early stage investment decisions. Export gas pipeline system is an important part of a deepwater gas development project and makes up a significant part of total cost of field development, given the necessity to effectively export produced gas from remote offshore location to shore. Large volume flow, long distance transport, and water depth constitute extreme operating conditions that tend to push the limits on equipment design specification and project cost. Optimal design of the pipeline system requires identifying a set of line pipe sizing and selection parameters that gives the minimum cost of both the subsea and topsides components of the fluid transport system. This paper presents an analytical study of concept design of a deep offshore gas development project involving large volume long distance product pipeline to shore. Sensitivity analysis of variation of sets of sizing parameters with development cost estimate, given the specified operating system constraints, are conducted and presented.