bluuebunny/crossref_metadata_2025 huggingface dataset:
Risk-Based Multi-Objective Optimisation of a Monopile Offshore Wind Turbine Support Structure
Authors: Yeter Baran , Garbatov Yordan , Guedes Soares Carlos
Published: October 2017

The present work carries out a multi-objective design optimization of a monopile offshore wind turbine support structure. Three objective functions are created related to the minimization of the total construction cost of the monopile support structure, fatigue damage, and permissible stress ratio. The construction cost takes into account the costs associated with welding and labor. The constructional limitations in the offshore industry take into consideration in the selection of the upper boundaries of the design variables. The reliability index is employed to identify the topology of the structure as a part of the Pareto frontier solution in reducing the failure probability for the critical limit states and satisfying the target reliability level. A risk-based assessment of the optimal designs is performed and the output is used to update the life-cycle cost assessment. The ultimate optimization target is deemed to be the minimization of the levelised cost of energy, which is estimated based on the discounted cash-flow method considering the life-cycle costs constituting CAPEX and OPEX.
Vision Based Localization for Subsea Intervention
Authors: Henriksen Eirik Hexeberg , Schjølberg Ingrid , Gjersvik Tor Berge
Published: October 2017

A vision based underwater localization system using fiducial markers is proposed. The system is implemented as a new control mode in a shared control system for ROVs and tested experimentally in a pool. A high accuracy underwater motion capture system in the pool is used as ground truth for performance assessment of the proposed system. The main objective has been to assess the feasibility for using a vision system and fiducial markers for localization of an underwater vehicle performing automated manipulation at subsea facilities. This research show that it is feasible to perform autonomous manipulation using the proposed system. The assessment of the performance in a set of experiments show that all degrees of freedom have a an approximate Gaussian error distribution with zero mean. The largest position errors are experienced in the Y-direction. This is seem to be caused by inherent coupling between yaw and lateral position in the camera projection of the fiducial marker and errors in the yaw direction. The main contribution of this paper is an experimental performance assessment of a localization method commonly used for terrestrial robots in a marine environment.
Effect of the Beam Element Geometric Formulation on the Wind Turbine Performance and Structural Dynamics
Authors: Delhaye Virgile , Karimirad Madjid , Berthelsen Petter Andreas
Published: October 2017

In this paper, the original double symmetric cross section beam formulation in RIFLEX used to model the blades is compared against a newly implemented generalised beam formulation, allowing for eccentric mass, shear and elastic centres. The generalised beam formulation is first evaluated against an equivalent ABAQUS beam model (Using the generalised beam formulation implemented in ABAQUS) which consists of DTU 10MW RWT (reference wind turbine) blade in static conditions. A static displacement is applied to the tip, which is close to an operating load. The results appear very similar and ensure that the implementation is correct.

The extended beam formulation is afterwards used on the Land-based 10MW turbine from DTU with external controller. This case study aims at evaluating the effect of the newly implemented formulation on realistic, flexible structure. During the study, the blades were discretised using both the old and new formulation, and dynamic simulations were performed. The effect of the beam formulation was evaluated using several wind conditions that are thought to be characteristic of operating conditions. Results show slight difference between two formulations but could be more significant for next generation flexible blades.
Sensitivity Study of Calculated Jacket Fatigue Damage due to Long Term Distribution of Wave Heights
Authors: Bang Hege Halseth , Smedsrud Siri Hoel , Hagen Øistein , Nybø Terje
Published: October 2017

Marine structures like jacket structures are often highly utilized structures operating in an environment dominated by dynamic loading. The fatigue limit state is of main concern and is to a large extent governing the structural dimensions and the amount of resources utilized in inspection and maintenance of members and joints.

There is a considerable degree of uncertainty related to the parameters determining the fatigue damage. The models applied, both for describing the fatigue driving mechanisms e.g. the wave-description and load modeling and the deterioration mechanism, are always compromises between the ability to accurately describe the nature and computationally efficiency.

The main focus in this paper is to show how sensitive the calculated fatigue damage of a jacket is to different models for the short term variability of wave heights. To obtain consistent basis for comparison a deterministic fatigue analysis is considered and a potential structural dynamic amplification is not included in the comparison study. Sensitivity to selection of wave spectra will not be addressed.

In a deterministic approach the long term distribution of individual wave heights is used to calculate the stress ranges occurring in the joints and butt welds. Typically, the long term variability of sea state conditions is given by a scatter diagram of significant wave height (Hs) and the peak period (Tp). When converting the scatter diagram of sea states to the long term distribution of wave heights, it is common to assume that the individual waves in the sea states are Rayleigh distributed. Later developments indicate that a Forristall distribution may be a more accurate assumption.

The following cases have been considered:

1. Assuming that the individual waves in each sea state are Rayleigh distributed.

2. Assuming that the individual waves in each sea state follows a Forristall distribution.

3. Calculating the long term wave height distribution from time domain simulations.

In the third method, second order wave theory was used to simulate all sea states in the Hs/Tp scatter diagram. I.e. extensive time domain simulations were carried out to cover the complete scatter diagram of possible sea states.

The study is performed for an 8-legged jacket. The analyses are performed for a typical North Sea wave environment for water depth about 110 m.

The objective of this study is to investigate the robustness in the current design practice for jacket structures where the individual waves in the sea states are Rayleigh distributed. The paper documents the calculated fatigue lives for main joints along the height of the jacket for the three wave height distributions. Further, the paper gives advice on application of wave distribution models for design of new structures and reassessment of existing structures.
Automated Identification of Critical Tubular Joints of Offshore Jacket Structure by Deterministic Fatigue Analysis
Authors: Dhandapani Shrikarpagam
Published: October 2017

Fatigue occurs in structures due to the stresses from cyclic environmental loads. Offshore environmental loads being highly cyclic and recurring in nature, fatigue analysis with high degree of accuracy is required for reliable and optimized design of offshore structures. The main aim of this paper is to automate the process of identification of fatigue critical tubular joints of an offshore jacket structure using deterministic fatigue analysis with emphasis on the Hot Spot Stress Range (HSSR), an important measure in estimating fatigue damage, calculated using three different approaches for each tubular joint. The first approach determines HSSR at the time of maximum base shear of the jacket, the second, by calculating the difference between maximum and minimum Hot Spot Stress (HSS) and the third, at all time-instants of the wave cycle. Thus fatigue damage and fatigue life of the tubular joints are estimated using the highest HSSR value and the joints with lower fatigue life are identified as fatigue sensitive joints. This ensures effective identification of critical tubular joints of the offshore jacket structure which needs detailed investigation or redesign for fatigue. The deterministic approach discussed in this paper is applicable to large jackets which contains more number of tubular joints where sophisticated fatigue assessment at the preliminary stage is computationally intensive and manual identification of fatigue critical joints is laborious.
Interaction Between Advanced Spar and Regular Waves
Authors: Yamanaka Shingo , Hirai Takayuki , Nihei Yasunori , Sou Akira
Published: October 2017

Advanced spar type of the floating wind turbine with a short spar and a cylindrical column floater has been developed and tested recently. However, numerical methods to accurately simulate the interaction between the advanced spar and waves have not been established yet. In this study we simulated the free surface flow around an advanced spar in regular waves using open source computational fluid dynamics (CFD) software OpenFOAM to examine its applicability. We used olaFOAM which equipped with the functions to set the boundary conditions of wave generation at the inlet and wave absorption at the exit. An experiment of the advanced spar model fixed in space in the regular waves with various wave periods was also conducted to obtain an experimental database on the horizontal and vertical forces acting on the structure and pressure distribution on the floater surface. The results of the forces obtained by the numerical simulation, experiment, Morison’s equation were compared to examine the validity of the numerical model. Numerical and experimental results of the horizontal and vertical forces as well as pressure distribution on the floater surface were in good agreement, which confirmed the validity of the present numerical method. Then, we evaluated numerically the effects of the edge of the column by simulating a sharp-edged and a chamfered column floater. The result clarified that a chamfered edge decreased the wake which reduced the forces acting on the floater structure.
Development of a New Advanced Fender Design With High Shock-Absorbing and Damping Properties
Authors: Lebedev Dmitrii , Kryzhevich Gennadiy
Published: October 2017

A fender with both shock-absorbing and damping properties was developed. This fender permits to decrease impact loads from berthing vessels on both berth structures and vessel hulls themselves. A developed procedure for calculation of berthing vessel – fender interaction dynamics, as well as numerical calculation of effectiveness of the developed fender use are presented in the paper.
Fatigue Analyses of a Flexible Riser Considering End Fitting Effects
Authors: de Sousa José Renato M. , Campello George C. , de Sousa Fernando Jorge M. , Vaillant Alyson G. , Ellwanger Gilberto B.
Published: October 2017

During the end fitting (EF) mounting process, the tensile armor wires of flexible pipes are folded and then unfolded. This process usually leaves plastic deformations and generates sharp curvatures on these wires just at the EF entrance. Dissections performed in several flexible risers, which were in operation or subjected to qualification tests, revealed that this region is especially prone to fatigue failure thus affecting the overall performance of these structures. In this work, an analytical approach devoted to predict the stresses induced in the tensile armor wires at the EF entrance is combined with a previously presented methodology to compute the fatigue life of flexible risers in order to account for the EF mounting process. A parametric study is also conducted aiming at evaluating the effect of the folding radius, the stress level induced during pre-operational tests and the contact conditions between the epoxy resin and the tensile armor wires on the fatigue resistance of a free hanging flexible riser. These analyses indicate that the choice of the mean stress correction model, the folding radius and the stress level induced during the pre-operational tests significantly modify the fatigue resistance of the tensile armor wires. The contact conditions also influence the fatigue resistance, but their effect is less significant.
Subsea Structural Monitoring With Machine Vision
Authors: Authén Kristian
Published: October 2017

Structural monitoring of subsea structures is widely used subsea in the oil and gas industry. Monitoring may be performed to keep track on position, movements, loads and fatigue accumulation. BOPs may have motions sensors installed to monitor the lower flex joint angle and the movements of the BOP itself. Installing subsea equipment like templates or conductors may also require monitoring to ensure the installation is within the set requirements.

Motion sensors containing accelerometers and gyroscopes are commonly used for these applications. These sensors are well suited for accurately determining inclination, but the sensors estimate displacements poorly.

An alternative approach for such measurements is to use machine vision. The machine vision tracks selected features from a video feed and calculates position, displacement and inclination directly. A benefit of this monitoring technique is that it does not require any hardware on the actual structure, only a camera and a tracking software.

Two video tracking algorithms are proposed for tracking. One marker based algorithm that require a pre-installed visual marker, and a markerless algorithm that uses natural features on the structure. The article presents the accuracy and project examples of in-field use of these algorithms.
Numerical Prediction of Ship-Ice Interaction: A Project Presentation
Authors: Hahn Malte , Dankowski Hendrik , Ehlers Sören , Erceg Sandro , Rung Thomas , Huisman Michael , Sjöblom Henrik , Leira Bernt J. , Chai Wei
Published: October 2017

It is inevitable that commercial shipping and oil and gas resource exploitation activities in the Arctic will increase due to decreasing sea ice extent caused by global climate changes. Significantly more demanding and at the same time less well known environmental conditions create a need for reliable methods to assess icebreaking performance guaranteeing safe performance of the ships operating in this area subjected to various ice conditions. The classic approach of assessing ice-going performance, which combines class rules, experience and model tests, may not be applicable for the Arctic region in full. Furthermore, ship yards experience difficulties due to decreasing time frames and financial restrictions. Therefore this paper seeks to introduce a new development for a realistic and validated direct simulation approach for prediction of the hull load and icebreaking resistance that covers all aspects of the industrial design process and allows a more comprehensive analysis. The breaking model will provide a variable breaking pattern and is able to mimic the influence of the vessel speed and the environment on the ice loading and the predicted breaking length. In order to predict the extreme representative conditions to be simulated, a reverse extreme load prediction methodology is incorporated. An efficient, time dependent dynamic coupling between broken ice fragments, ice features, the 3D flow field and the ship’s hull provides resistance values for performance calculations. The computational model will be validated against full-scale data and class rules using deterministic and probabilistic measures. This simulation approach is developed within international research collaboration between Pella Sietas, Rolls Royce Marine, TUHH and NTNU. An overview of the project together with the current status of the ongoing work including first results is presented.
Simulation-Based Evaluation of Upstream Logistics System Concepts for Offshore Operations in Remote Areas
Authors: Norstad Inge , Gribkovskaia Victoria , Johnsen Trond , Lindstad Haakon-Elizabeth , Uthaug Eirik
Published: October 2017

Increased competition and low oil prices coupled with promising prospects for new oil and gas (O&G) reserves in the Arctic region has led to expansion of activities into the offshore Arctic. This brings along new challenges for the offshore logistics that need to be addressed. These challenges impose more stringent requirements for the logistics system setup, especially on the design and operation of vessels. Copying the logistics system and vessels designed for the North Sea operations is not a sustainable way forward. The few existing studies related to Arctic logistics mainly focus on ship technology solutions for cold and ice infested areas or solutions to the area-specific operational challenges for shipping companies. However, there is a need to understand how these solutions are connected and impact each other in a larger offshore supply logistics system, and thus address the challenges of Arctic logistics as a whole. A methodology for quick evaluation of the feasibility and costs of the logistics system in the early stages of offshore supply planning was developed and presented in previous research [1]. It allows for testing the effects of using alternative ship designs and the overall supply fleet composition on system’s cost and performance while satisfying prospective campaign requirements. Safety standards and requirements for emergency preparedness and environmental performance are taken into account while cost effectiveness of the logistics system as a whole is the main quantifiable measure. Building on the new methodology a simulation tool for remote offshore operations has been developed and is presented in current work. Simulation models allow us to consider the dynamic and uncertain nature of variables, such as variation in weekly transport demand, weather impact on sailing times and fuel consumption, and schedule deviations. The evaluation of the performance of a logistic system is done by simulating the logistic operation over a large number of scenarios. Input parameters are weather data generated from historical observations and probability distributions for transport demand. Output from the tool are key performance indicators for: system costs, logistic robustness and emergency preparedness. The tool consists of three main components: simulation of a regular supply logistics operation, simulation of emergency situations, and visualization of the simulated operations. The proposed methodology and tool are tested on real-life cases for offshore supply planning of drilling campaigns in remote areas for one of the major international O&G operators.
Dynamic Behavior of Flexible vs Rigid Spools During Seismic Loading Events
Authors: Kaurin Christian , Panjaitan Hans , Dybwad Jacob , Damsleth Per
Published: October 2017

In regions of high seismic activity, the most severe loading experienced by subsea production systems during earthquake events can be significantly greater than normal static design loads. The major components of such systems comprising pipelines, manifolds and wells linked by tie-in spools and jumpers all respond differently when excited by seabed accelerations. Individual components may resonate or move out of phase with each other. It is of vital importance that the design of the system accounts for the dynamic loading at interfaces such as flanges, connectors and pipe supports. High dynamic loads due to a severe earthquake may damage the connection and cause leakage of hydrocarbons to the marine environment.

Tie-in spools and well jumpers provide flexibility in the system but layouts and physical properties that satisfy static loads may not be as suitable in a dynamic environment. Where earthquake loads are severe, the dynamic response of the entire system needs to be considered, including the structure and connected spool response together as they interact individually with the soil movement.

A comparative study of the seismic responses of flexible and rigid spools has been performed using 3D non-linear finite element simulation in the time domain. The system analyzed consists of a flexible or a rigid spool tied-in to a subsea manifold via a mechanical connector. The FE analysis model of the spool configurations includes the free-span at the structure and seabed contact with both static and dynamic pipe-soil interaction. The effects of spool metrology and fabrication tolerances are included as well as complete static load histories due to displacements from installation to operation phases as the starting point for the seismic simulations.

The flexible spool was found to provide significantly lower of dynamic interface stresses compared to a rigid spool with similar geometry. The load stress variance was also found to be reduced, indicating that flexibles may also offer more predictable behavior when subject to the highly variable spectral energy of extreme earthquakes.
Strain Capacity of Girth Welded Joints in HSAW Pipes
Authors: Van Minnebruggen Koen , Hertelé Stijn , De Waele Wim
Published: October 2017

The general aim of a recently finalized European project, i.e. EU RFCS SBD-Spipe, is to generate specific know-how concerning the development and possible use of spirally welded pipes for demanding applications. The demanding applications relate especially to structural integrity issues, both onshore and offshore, requiring good performance under application of large strains resulting in buckling, collapse and/or tensile loading. The outcome of this project can also be used as technical basis for improving standards and guidelines, that address design and safety of spirally welded pipelines.

The contribution of Ghent University to this project focusses on the aspects of tearing resistance, defect tolerance and strain capacity of girth welded joints subjected to remote axial tensile load. A numerical and experimental approach is used for the assessment of flaw tolerability and strain development upon tensile loading. Spiral pipes of steel grade API-5L X70 with 36” and 48” diameters have been girth welded using both a manual and semi-automatic welding processes. Curved wide plate specimens have been extracted from the pipes and artificial weld defects have been introduced. The specimens have been loaded in tension up to failure at a temperature of −10°C. This paper reports on the experimental result of a series of curved wide plate tests.
Risk Management in Aquaculture: Integrating Sustainability Perspectives
Authors: Utne Ingrid Bouwer , Schjølberg Ingrid , Holmen Ingunn Marie , Bar Eirin Marie Skjøndal
Published: October 2017

The aquaculture industry in Norway produced 1.3 million metric tons of fish in 2014, and further expansion is expected if the main sustainability challenges related to production and operation are mitigated. Major biological, operational and environmental challenges are parasite infection, fish escape, fish health, human injuries and fatalities. The larger farms, exposed locations, and sustainability challenges related to more production of salmon increases the need for efficient decision support methods and risk management. The combined effect of the technological development, with increased remote operation, autonomy and automation, and the production and operational challenges related to sustainability means that an interdisciplinary and systemic approach integrating risks to the environment, as well as to fish welfare and human safety, is needed. Therefore, the main contents of such a risk management approach are outlined in this paper. Potential users are fish farming companies, but the paper also addresses the need for an industry standard for sustainability and risk performance monitoring, which should be of interest to authorities and the whole industry. The paper concludes that risk management and sustainable development are complementary concepts that benefit each other because efficient risk management is decisive for achieving sustainability in aquaculture.
Improved Dynamic Structural Modelling for Subsea Power Cables With Bitumen Coated Armour Wires
Authors: Martindale Hugh , Rossiter Steven , Sheldrake Terence , Langdon Richard
Published: October 2017

This paper presents improved dynamic modelling of subsea power cables using new models for the determination of non-linear cable mechanical properties. The modelling has been developed for cables typically used in offshore wind and for interconnectors, as well as dynamic power umbilicals. The results provide a better simulation of the dynamic response and allow better integration of local and global modelling for determination of stress and fatigue in offshore power cables.

Cable response due to bending is modelled by including non-linear adhesion induced stresses due to a yielding bond between armour wire and neighbouring layers, which captures the effects of temperature and strain rate and provides better representation than purely friction-based modelling especially at low tension. Local armour bending stiffness is included by using average wire strain energy after slip along the strained helical path to determine the armour layer bending stiffness contribution. Mathematical modelling for mechanical properties is verified by sample testing and FEA, to provide a robust method for predicting cable response.

Although dynamic subsea power cables are essentially non-bonded structures there is a certain amount of adhesion within the structure. Previous work has focused on friction-tension based modelling of armour wire-core interaction, that is not appropriate as critical slip curvatures at low tension are understated and full-slip stress distributions do not account for work done against friction during further bending. The principal result of this new approach is the improved determination of lifetime stresses for critical components within the cable structure. Non-linear bend stiffness modelling produces characteristic moment-curvature relations including hysteresis on reversal of bending. These curves provide an improved representation of the onset of slip in the armour wires and allow for the influence of temperature and strain rate on the cable bending stiffness to be included. The bend-stiffness model has been validated against test data both of complete bundles and individual components.

The overall result is a methodology that typically results in increased fatigue life and can reduce the requirement for ancillary products such as ballast/buoyancy and bend stiffeners/restrictors. Additionally, the non-linear, hysteretic response of a cable significantly reduces certain phenomena that are often associated with numerical modelling of cables using a linear bend stiffness. Specifically, a cable catenary attached to a vessel and modelled with a linear bend stiffness will often experience ‘compression waves’ when the vessel is moving in response to wave loading. Use of a non-linear, hysteretic bend stiffness minimises the compression wave phenomenon, giving a much more realistic response and often greatly improving operability windows for offshore operations.
Experimental and Numerical Study on Point Absorber Type Wave Energy Converter With Linear Generator
Authors: Taniguchi Tomoki , Umeda Jun , Fujiwara Toshifumi , Goto Hiroki , Inoue Shunji
Published: October 2017

This paper addresses experimental and numerical validation of power output efficiency about an approximate complex-conjugate control with considering the copper loss (ACL) method. A bottom-fixed point absorber type wave energy convertor (WEC) model was used for the experiments carried out at National Maritime Research Institute, Japan (NMRI). In order to model a power take-off (PTO) system constructed by a permanent magnet linear generator (PMLG), a liner shaft motor (LSM) was used for the model test. To investigate characteristics of the ACL method, the resistive load control (RLC) method and approximate complex-conjugate control (ACC) method were also tested by the WEC model. A simulation code based on WEC-Sim (Wave Energy Converter SIMulator) v2.0 written by MATLAB/Simulink, which is developed by collaboration works between the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (Sandia), was used for the validation. The simulated results in regular waves have good agreement with measured ones in terms of the float heave motion, the vertical force and the control input force. Through the experiments and numerical simulations in regular waves, the ACL method has advantages in high power production compared with the RLC and the ACC methods for the WEC model. In addition, the power output characteristics of the ACL method in irregular waves were checked experimentally and numerically.
Wind and Wave Climate in Open Sea and Coastal Waters
Authors: Bitner-Gregersen Elzbieta M.
Published: October 2017

Wind and wave climate is much region and location dependent, affected by local properties of ocean environment. For safety of world-wide sailing ships knowledge about wind and wave climate is important, not only for open sea, but also in coastal areas. Wind and waves impact ship design, marine operations and they challenge ability of ships to maintain manoeuvrability in sea states. Their description differs in open sea and coastal waters, and recently it has got an attention due to the issue of the 2013 Interim Guidelines by IMO where adverse weather conditions to be used in assessment of ship manoeuvrability have been proposed. The present study shows differences between open sea and coastal water wind and wave climate using hindcast data in the analysis. The description of open sea metocean conditions is limited to the North Atlantic while European waters are used as representative for coastal regions. Correlations between wind speed and significant wave height as well as significant wave height and spectral peak period are established and compare with the ones suggested by the 2013 Interim Guidelines. Challenges in providing metocean description for assessment of ship manoeuvrability and uncertainties related to it are discussed.
Evaluation of Nonlinear Material Behavior for Offshore Structures Subjected to Accidental Actions
Authors: Storheim Martin , Alsos Hagbart S. , Amdahl Jørgen
Published: October 2017

Evaluation of the nonlinear structural response of any structure is a challenging task; a range of input parameters are needed, most of which has significant statistical variability and the evaluations require a high degree of craftsmanship. Hence, high demands are set forth both to the analyst and the body in charge of verification of the results. Recent efforts by DNVGL attempts to mitigate this with the second edition of the DNVGL-RP-C208 for determination of nonlinear structural response, in which guidance or requirements are given on many of the challenging aspects.

This paper discuss the various challenges and the direction to which the RP-C208 points compared to published research. Parameters affecting the plastic hardening, strain-rate effects and ductile fracture are discussed separately. Then, the combined effect of the range of assumptions is evaluated to assess the resulting level of safety.
Analysis on Wellhead Stability During Drilling Operation in Arctic Permafrost Region
Authors: Wang Zhiyuan , Wang Xuerui , Sun Baojiang , Deng Xuejing , Zhao Yang , Gao Yonghai , Li Hao
Published: October 2017

The arctic region hold abundant oil & gas resources according to the assessment by United States Geological Survey (USGS) in 2009. While, the thaw of permafrost during drilling operation can lead to the instability of wellhead. A coupled thermal model between wellbore and formation is given considering the latent heat of fusing and migration of water during the thaw of permafrost, and the thawed permafrost zone can be estimated. A wellhead stability analysis method considering heat transferred from wellbore is also proposed in this paper. FLAC3D software is applied to analyze the wellhead stability. Some conclusions are made through a case study: Flow in the wellbore delivers heat from deep part of formation to the shallow part of the formation, which leads to the permafrost thaws. Thawed permafrost losses most of the shear strength compared to that of the frozen permafrost which leads to the settlement of wellhead. The calculated results using FLAC3D software shows that the wellhead settles as deep as 0.66 m resulting from the permafrost thaw. In addition, the installation of anti-sinking pad is suggested to reduce the wellhead settlement. According to our simulation, the anti-sinking pad with radius of 8 times the wellhead radius is suggested, which can reduce the wellhead settlement to 0.1 m.
Design Challenges of the Next Generation of All Electric Umbilical Systems
Authors: Deighton Alan , Dobson Alan
Published: October 2017

Since the first umbilicals were developed and installed to control and preserve subsea equipment they have continued to evolve to ensure effective operation in an increasingly challenging subsea environment. New material technologies, complex analysis tools and umbilical architectures have been developed to ensure umbilical systems operate through-out their service life irrespective of the ambient temperature, fatigue loading, hyperbaric pressure and tensile loads applied.

In more recent years, as the subsea industry adapts to the challenge of reducing CAPEX costs driven by reduced oil prices, the potential cost savings through adapting the subsea processing system to treat processed fluids on the seabed and / or utilising longer step out systems from existing facilities is driving a new step in umbilical evolution.

To support the potential evolution in subsea processing systems, the conventional control umbilical must evolve to incorporate the supply of electrical power and potentially electrical control to replace hydraulic control over long step out distances. This has a significant influence on the design of the umbilical system, introducing several new challenges which need to be addressed through material selection and advanced analysis techniques.

This paper will provide an overview of the potential evolution of the Next Generation All Electric umbilical and outline the design challenges and methods developed to maximise the reliability of the umbilical system.
Marine Autonomous Exploration Using a Lidar and SLAM
Authors: Ueland Einar S. , Skjetne Roger , Dahl Andreas R.
Published: October 2017

This paper presents the implementation of a 2D-lidar to a model-scale surface vessel, and the design of a control system that makes the vessel able to perform autonomous exploration of a small-scale marine environment by the use of the lidar and SLAM. This includes a presentation and discussion of experimental results. The completion of this system has involved the development of a suitable control system that merges exploration strategies, path planners, a motion controller, and a strategy for generating controller setpoints. The system was implemented on the Robot Operating System platform, which made it possible to utilize open-source algorithms for state of the art SLAM.
ECAs: Lifting the Lid of the Black Box
Authors: Cosham Andrew , Macdonald Kenneth A. , Hadley Isabel , Moore Philippa
Published: October 2017

An engineering critical assessment (ECA) is commonly conducted during the design of a pipeline in order to determine the tolerable sizes for flaws in the girth welds. An ECA is a method for assessing the acceptability of a flaw in a structure, i.e. to demonstrate fitness-for-service. API 579-1/ASME FFS-1 2016 and BS 7910:2013+A1:2015 Incorporating Corrigenda Nos. 1 and 2 give guidance for conducting fitness-for-service assessments of cracks and crack-like flaws. Appendix A of DNV-OS-F101, 2013 provides detailed procedures for evaluation of the fracture limit state of girth welds, based on BS 7910:2005, but prescribes a number of amendments and modifications. API 579-1/ASME FFS-1 and BS 7910:2013 will give similar, but slightly different, results.

An ECA can be something of a black box because of the use of software to conduct the calculations. Software can have the unfortunate side-effect of obscuring the understanding of the calculations. ECAs are also seen as a thing that is very complicated.

In an attempt to lift the lid on the black box that is, or is perceived to be, the ECA, the assessment of circumferentially orientated, surface-breaking crack-like flaw (a planar flaw) in a girth weld is illustrated through a comparison of the relevant stress intensity factor and reference stress solutions in API 579-1/ASME FFS-1 and BS 7910:2013; and through illustrating the effect of the choice of the Level or Option of the assessment, and assumptions made in the assessment with respect to constraint, misalignment, residual stresses, etc. Also illustrated are the implications of defining the fracture toughness in terms of the crack tip opening displacement or J-integral, and of using a single value of fracture toughness, based on the initiation of stable tearing or the first attainment of a maximum force plateau (maximum load), or of using tearing resistance data.

A comparison is also made with the notionally simplified fitness-for-service procedures given in Annex A of API Standard 1104, Annex K of CSA Z662-15, and the EPRG guidelines on the assessment of defects in transmission pipeline girth welds–Revision 2014.

The result is an outline of what might be considered to be good practice for when conducting an ECA during the design of a pipeline.
A Numerical-Experimental Approach of Indentation Problem: Part I — Force-Dent Response of Steel Pipes
Authors: Polanco-Loria Mario A. , Ilstad Håvar , Levold Erik
Published: October 2017

Accidents by trawling impact have the potential of environmental consequences, in terms of safety, monetary values and reputation. Aware of this situation a technology development plan on “Pipeline subject to high interference loads” has been established at STATOIL in close collaboration with GASSCO. The overall achievement is to adapt and introduce more reliable assessment methods in the load and response of pipelines under a trawling impact scenario. This work includes a review of some known force-indentation models appeared in the literature. Some comments on the recently updated version of the DNV-RP-F111 document. Next, the description of the numerical results of 12 analyses of steel pipes studied is described and based on these results a new force-dent proposal is presented. The proposed equations are validated against experimental tests and the findings indicated fairly good predictions as indicated in the conclusions.
A Numerical-Experimental Approach of Indentation Problem: Part II — Force-Dent Response of Polymeric Coated Steel Pipes
Authors: Polanco-Loria Mario A. , Ilstad Håvar , Levold Erik
Published: October 2017

Accidents by trawling impact have the potential of environmental consequences, in terms of safety, monetary values and reputation. Aware of this situation a technology development plan on “Pipeline subject to high interference loads” has been established at STATOIL in close collaboration with GASSCO. The overall achievement is to adapt and introduce more reliable assessment methods in the load and response of pipelines under a trawling impact scenario. Polymeric coating systems have been manly designed and used as thermal isolating material for flow assurance; and little attention has been addressed to mechanical benefits to dissipate energy by large deformation. This property is of special interest to handle impact events typically found during the trawl board impact scenario. The experimental results show the beneficial effect of polymeric coating to protect the steel pipe against indentation when compared to an uncoated system. The results presented in this work focus on new developed analytical expressions to predict the force-dent response of polymeric coated steel pipes using a numerical-experimental research methodology. The proposed equations are validated against experimental tests and the findings indicate fairly good predictions.
WEC Geometry Optimization With Advanced Control
Authors: Abdelkhalik Ossama , Coe Ryan G. , Bacelli Giorgio , Wilson David G.
Published: October 2017

A study was performed to optimize the geometry of a point absorber style wave energy converter (WEC). An axisymmetric single-body device, moving in heave only, was considered. Design geometries, generated using a parametric definition, were optimized using genetic algorithms. Each geometry was analyzed using a boundary element model (BEM) tool to obtain corresponding frequency domain models. Based on these models, a pseudo-spectral method was applied to develop a control methodology for each geometry. The performance of each design was assessed using a Bretschneider sea state. The objective of optimization is to maximize harvested energy. In this preliminary investigation, a constraint is imposed on the the geometry to guarantee a linear dynamic model would be valid for all geometries generated by the optimization tool. Numerical results are presented for axisymmetric buoy shapes.
A Methodology for DP Capability Studies on Remotely Operated Vehicles
Authors: Ramírez-Macías Juan A. , Vásquez Rafael E. , Sørensen Asgeir J. , Sævik Svein
Published: October 2017

Dynamic Positioning (DP) capability studies are used to assess if a vessel has sufficient thrust capacity to withstand environmental loads while keeping its position and orientation at a specified set-point or path. These studies are usually performed on ships and other DP-controlled surface vessels; consequently, standards and procedures for these are widely known. In this work, a methodology for conducting a DP capability study for Remotely Operated Vehicles (ROV) is presented. Due to the nature of ROV operations, a DP capability study should include different features that are not common to surface vessels. In this case, an ROV connected to a surface vessel through a tether is considered. During operation, the tether is subject to varying current loads that are accumulated along the water column and transferred to the vehicle. Therefore, the ROVs thrusters must be able to withstand, in addition to its own drag, three-dimensional loads due to three-dimensional currents and umbilical-related loads. To illustrate the methodology, two case studies are considered: the DP capability of an ROV that has to operate in the Colombian Caribbean and an existing ROV operating in the North Sea.
Climatic Forecasting of Wind and Waves Using Fuzzy Inference Systems
Authors: Stefanakos Christos N. , Vanem Erik
Published: October 2017

Wind and wave climatic simulations are of great interest in a number of different applications, including the design and operation of ships and offshore structures, marine energy generation, aquaculture and coastal installations. In a climate change perspective, projections of such simulations to a future climate are of great importance for risk management and adaptation purposes. This work investigates the applicability of FIS/ANFIS models for climatic simulations of wind and wave data. The models are coupled with a nonstationary time series modelling, which decomposes the initial time series into a seasonal mean value and a residual part multiplied by a seasonal standard deviation. In this way, the nonstationary character is first removed before starting the fuzzy forecasting procedure. Then, the FIS/ANFIS models are applied to the stationary residual part providing us with more unbiased climatic estimates. Two long-term datasets for an area in the North Atlantic Ocean are used in the present study, namely NORA10 (57 years) and ExWaCli (30 years in the present and 30 years in the future). Two distinct experiments have been performed to simulate future values of the time series in a climatic scale. The assessment of the simulations by means of the actual values kept for comparison purposes gives very good results.
Calculation of Time-to-Freeze for Liquids in Pipes
Authors: Kvamme Bjarte O. , Peechanatt Jino , Gudmestad Ove T.
Published: October 2017

In recent years, there has been unprecedented interest shown in the Arctic region by the industry, as it has become increasingly accessible for oil and gas exploration, shipping, and tourism. The decrease in ice extent in the Arctic has renewed the interest in the Northern Sea route, necessitating further research to evaluate the adequacy of the equipment and appliances used on vessels traversing in polar waters. In the oil and gas industry, exploration and production vessels and platforms are highly dependent on the piping facilities for rendering their intended function, and therefore, flow assurance is extremely crucial. If the winterization of pipes is not done properly, this could lead to massive cost overruns due to unplanned production shutdowns or even worse, accidents. A temperature drop between the different areas of the production facilities will change the thermodynamic properties of the fluids, and could cause the processing of the crude oil to become inefficient.

The introduction of the Polar Code by the International Maritime Organization (IMO) attempts to mitigate some of the risks endangering the vessels in polar waters. The Polar Code is scheduled to take effect on 01.01.2017, and applies to all vessels traversing in polar waters. The Polar Code requires that all machinery installations and associated equipment required for the safe operation of ships shall be protected against the effect of freezing and increased viscosity of liquids, and that working liquids shall be maintained in a viscosity range that ensures the operation of the machinery. To account for this, the heat loss of pipes carrying liquid (water for fire extinguishing and hydraulic fluid amongst others) needs to be estimated and mitigating measures must be taken.

In this study, methodology from the refrigeration industry is applied to calculate the estimated time to freeze for liquids in pipes. The methodology is adapted for use in the maritime industry, and results are presented in this study. The methodology used was found to be quite flexible, allowing for the calculation of complex scenarios and shapes, including the effect of varying degrees of insulation on pipes, and can easily be applied for approximating the best suitable method of insulating pipes to ensure flow assurance and maintain fluid properties at desired levels. Tables estimating the time-to-freeze for insulated pipes of different diameters and insulation thicknesses exposed to cross-winds of varying speeds are provided. The methodology is found to have great potential, and should be investigated further with experiments. The objective of the paper is thus to introduce the methodology for cold-climate engineering and use it for practical analysis of realistic estimates of insulated and non-insulated piping.
Reelability and Wall Thickness Optimization of HFI Pipeline Against the Sensitivity of Variation in Mismatch Parameters
Authors: Achani Dasharatha , Andreev Vladimir
Published: October 2017

High frequency Induction welded (HFW/HFI) linepipe is produced by cold forming from steel strip, bent into pipe and longitudinal seam welded. HFW/HFI linepipe has been attractive due to less expensive, improved lead time and tighter wall thickness tolerances and better control of mechanical properties compared to the seamless.

Typical design drivers for wall thickness optimization of reeled pipeline are geometric and strength mismatch. HFI pipes gained the attention of reeling contactors because of tighter mismatch tolerances of geometry and strength. However, the limitation of wall thickness in producing the larger diameter pipes needs optimized wall thickness considering the sensitivity of the variation in mismatch properties and stress ratio.

The present work is intended to check the capacity of the pipeline against the sensitivity of variation in mismatch parameters. A case study has performed for the reelability of 16” HFW pipe for a selected limiting wall thickness. The different cases of variation in mismatch parameters are considered for the sensitivity check. Finite element (FE) analyses using ABAQUS tool were performed to reel the sections of the pipe joint over the reel hub of the selected installation vessel. The model predictions for axial compressive strain are compared and discussed against the DNV local buckling criterion for displacement control.