bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid Parameter Identification for Underwater Snake Robots
Authors: Kelasidi Eleni , Elgenes Gard , Kilvær Henrik
Published: September 2018

Nowadays different types of unmanned underwater vehicles (UUVs), such as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), are widely used for sub-sea inspection, maintenance, and repair (IMR) operations in the oil and gas industry, archaeology, oceanography and marine biology. Also, lately, the development of underwater snake robots (USRs) shows promising results towards extending the capabilities of conventional UUVs. The slender and multi-articulated body of USRs allows for operation in tight spaces where other traditional UUVs are incapable of operating. However, the mathematical model of USRs is more challenging compared to models of ROVs and AUVs, because of its multi-articulated body. It is important to develop accurate models for control design and analysis, to ensure the desired behaviour and to precisely investigate the locomotion efficiency. Modelling the hydrodynamics poses the major challenge since it includes complex and non-linear hydrodynamic effects. The existing analytical models for USRs consider theoretical values for the fluid coefficients and thus they only provide a rough prediction of the effects of hydrodynamics on swimming robots. In order to obtain an accurate prediction of the hydrodynamic forces acting on the links of the USRs, it is necessary to obtain the fluid coefficients experimentally. This paper determines the drag and added mass co-efficients of a general planar model of USRs. In particular, this paper presents methods for identifying fluid parameters based on both computational fluid dynamic (CFD) simulations and several experimental approaches. Additionally, in this paper, we investigate variations of the drag force modelling, providing more accurate representations of the hydrodynamic drag forces. The obtained fluid coefficients are compared to the existing estimates of fluid coefficients for a general model of USRs.
New Flow Assurance System With High Speed Subsea Fiber Optic Monitoring of Pressure and Temperature
Authors: Hedengren John D. , Brower David , Wilson J. Conrad , High Geoff , Witherow Karl
Published: September 2018

Subsea production control systems are instrumented to constantly monitor flowline pressure and temperature at key locations to prevent plugging and introduce mitigating control strategies. New fiber optic sensors with ruggedized construction and non-electrical components are subjected to accelerated aging tests and deployed in several installations with long service life. An overview of current progress with fiber optic technology is provided for fatigue monitoring, temperature, pressure, and strain sensing. Recent developments include improved service life, novel bonding methods, pipeline sensor station improvements, sensor calibration, and long-term fatigue analysis.

The latest advancements are validated on multiple installations on a subsea tieback in the deepwater Mississippi Canyon of the Gulf of Mexico at 6,500 ft depth. A prior third-party sensor design experienced multiple non-recoverable sensor failures. A new sensor station design is employed on two Flowline Terminations to monitor pressure and temperature at a rate of 100 Hz. Subsea tiebacks are susceptible to flow assurance issues caused by plugging events such as hydrate formation. The system was originally designed to track pig location but transitioned to pressure and temperature sensing. An issue with the transition was the lack of calibration relating the fiber Bragg grating (FBG) strain levels to the actual process conditions. A novel method is presented for in situ adjustment of the sensor array calibration.

During the calibration procedure, the sensors produced unanticipated results during pipeline flow shut-in and later startup operations. The sensors helped uncover a configuration of the flowline and sensor locations that is valuable for detecting hydrate forming conditions at a key junction location. The sensors are located before and after the junction of two flowlines in the mixing zone of the pipeline streams. The novel contributions of this study are the high speed data collection, in situ fiber optic calibration, review of advancements in fiber optic sensing technology, and a field case study with multiple sensing arrays.

The developments are part of the Clear Gulf study, a collaboration between the offshore energy industry and NASA that was formed in 2010. The objective of the Clear Gulf study is to employ space technology and testing facilities for use in the up-stream industry to advance subsea sensor technology. The highly sensitive monitoring systems developed as part of this study are used to give early warnings for flow assurance issues, structural failures, or catastrophic events.
Investigating the Influence of Bridge Officer Experience on Ice Management Effectiveness Using a Marine Simulator Experiment
Authors: Veitch Erik , Molyneux David , Smith Jennifer , Veitch Brian
Published: September 2018

The research investigates the influence of human expertise on the effectiveness of ice management operations. Ice management is defined as a systematic operation that enables a marine operation to proceed safely in the presence of sea ice. In this study, a method has been applied for assessing the effectiveness of ice management operations in terms of ability to modify the presence of pack ice around an offshore structure. This was accomplished in a real-time marine simulator environment as the venue for a systematic investigation. In the simulator, volunteer participants from a range of seafaring experience levels were tasked with individually completing ice management tasks. Recorded from 36 individuals’ simulations was the extent to which the ice in a defined area was impacted, measured in terms of tenths ice concentration. These responses were then compared to two independent variables: 1) experience level of the participant, categorized as either cadet or seafarer, and 2) ice severity, measured in ice concentration. The results showed a significant difference in ice management effectiveness between experience categories, where effectiveness was defined as the average drop in ice concentration during simulation. Results also showed that the human factor of experience and the environmental factor of ice concentration both had significant effects on average concentration drop. The research provides insight into the relative importance of vessel operator skills in contributing to effective ice management, as well as how this relative importance changes as ice conditions vary from mild to severe. This may have implications for training in the nautical sciences and could help to inform good practices in ice management.
On the Validity and Sensitivity of CFD Simulations for a Deterministic Breaking Wave Impact on a Semi Submersible
Authors: Bandringa Henry , Helder Joop A.
Published: September 2018

To assess the integrity and safety of structures offshore, prediction of run-up, green water, and impact loads needs to be made during the structure’s design. For predicting these highly non-linear phenomena, most of the offshore industry relies on detailed model testing. In the last couple of years however, CFD simulations have shown more and more promising results in predicting these events, see for instance [1]–[4]. To obtain confidence in the accuracy of CFD simulations in the challenging field of extreme wave impacts, a proper validation of such CFD tools is essential.

In this paper two CFD tools are considered for the simulation of a deterministic breaking wave impact on a fixed semi submersible, resulting in flow phenomena like wave run-up, horizontal wave impact and deck impacts. Hereby, one of the CFD tools applies an unstructured gridding approach and implicit free-surface reconstruction, and uses an implicit time integration with a fixed time step. The other CFD tool explicitly reconstructs the free surface on a structured grid and integrates the free surface explicitly in time, using a variable time step. The presented simulations use a compact computational domain with wave absorbing boundary conditions and local grid refinement to reduce CPU time. Besides a typical verification and validation of the results, for one of the CFD tools a sensitivity study is performed in which the influence of small variations in the incoming breaking wave on the overall results is assessed. Such an analysis should provide the industry more insight in the to-be-expected sensitivity (and hence uncertainty) of CFD simulations for these type of applications. Experiments carried out by MARIN are used to validate all the presented simulation results.
Finite Element Analysis of Umbilical Cables Anchoring Systems Including Frictional Contact
Authors: Toni Fernando Geremias , Malta Eduardo Ribeiro , Martins Clóvis de Arruda , Morini Rafael Giovane , Freitas André Barbosa
Published: September 2018

The armor pots on an umbilical system are critical accessories that are subjected to high tensile loads. To ensure tensile resistance to an umbilical cable connection, its structural elements must be properly anchored to the armor pot. One way to provide that connection is the use of the adhesive properties of an epoxy resin. When designing this type of ancillary, it is important to determine the stress and strain distributions along the structural anchored components and thus ensure that they can withstand the loads. In this context, three-dimensional fully parameterized finite element models with bonded contact have already been developed, consisting of a good alternative to evaluate the critical delamination load. However, for a more complete understanding of the anchoring phenomenon, it is also important to analyze the effects caused by the sliding of the tendons and tubes inside the resin: friction gives additional axial resistance and bending-torsion effects can occur while these elements are being pulled out. Therefore, in this article three-dimensional anchoring models are presented with standard contact, which enables normal and unilateral tangential gap formations and considers the effects of friction, allowing the reproduction of the desired phenomenon.
Numerical Model Development and Validation for the WECCCOMP Control Competition
Authors: Tom Nathan , Ruehl Kelley , Ferri Francesco
Published: September 2018

This paper details the development and validation of a numerical model of the Wavestar wave energy converter (WEC) developed in WEC-Sim. This numerical model was developed in support of the WEC Control Competition (WECCCOMP), a competition with the objective of maximizing WEC performance over costs through innovative control strategies. WECCCOMP has two stages: numerical implementation of control strategies, and experimental implementation. The work presented in this paper is for support of the numerical implementation, where contestants are provided a WEC-Sim model of the 1:20 scale Wavestar device to develop their control algorithms. This paper details the development of the numerical model in WEC-Sim and of its validation through comparison to experimental data.
CFD Numerical Simulation for Downhole Thruster Performance Evaluation
Authors: Mohamed Bashir , Abugharara Abdelsalam N. , Rahman M. A. , Butt Stephen D.
Published: September 2018

This study focuses on numerical simulation and evaluation of a hydraulically powered downhole Thruster. This device is numerically simulated and evaluated using ANSYS Fluent 17.2 to show its generation of pressure pulses that can induce downhole forces that magnify the downhole dynamic weight on bit (DWOB) using drilling mud. Such magnification of the DWOB can produce axial motion of the Thruster. Such axial motions, as proved by many publications can improve the drilling rate of penetration (ROP), release stuck pipes, and reduce frictions in non-vertical wells. The special inner design of the Thruster creates pressure pulses that can provide load impact on the drill bit leading to the increase of WOB that can enhance the drilling performance. The current stage of the study of the Thruster involves a mechanical design of the Thruster by the SolidWorks and an evaluation of the tool function and performance through pressure effect simulation by ANSYS Fluent 17.2. Initially, water is used as the fluid and the main parameters involved in the analysis are pressure and velocity. However, power-law as a non-Newtonian fluid is also used for comparison study in the section of pressure drop analysis.

The results are analyzed based on velocity pressure profiles, pressure drops, pressure effects with applications of various back pressures at several planes using water and power-law fluids.
Qualification Testing of Titanium Stress Joints Designed for Galvanic Hydrogen Mitigation Conveying Hot, Sour Well Fluids
Authors: Schutz Ronald W. , Rombado Gabriel , Baker David A. , Walker Heath W. , Caldwell Christopher S.
Published: September 2018

A three-phase laboratory test qualification program for Titanium Stress Joint (TSJ) use in an offshore steel catenary riser (SCR) system handling hot, marginally sour well brine fluid offers guidance for expanded, safe TSJ use in hot sour well service. Phase 1 results indicated a reasonable concern and risk for long-term excessive hydrogen uptake and damage to the TSJ when directly coupled with the steel riser and steel topside piping. An alternative TSJ design, incorporating an Alloy 625 cathode buffer transition between adjoining steel tubulars, was proposed for mitigation of galvanic hydrogen charging uptake and damage prevention for hot sour fluid service. This “Tri-Metal couple” design was modeled in Phase 2 using polarization curves as input, and simulations projected insignificant hydrogen charging on TSJ bore surfaces exposed to “Worst-Case Sour” brine fluid at 250°F (121°C). Phase 3 aimed at qualifying the TSJ welds for even more severe and acidic sour well fluid service conditions up to 275°F (135°C), via fatigue crack growth rate (FCGR) and J-R fracture toughness testing of weld metal, and S-N fatigue and slow strain rate (SSR) tensile testing of cross-welds. These tests confirmed the high degree of hot sour environmental resistance for Grade 29 Titanium welded joints, and reasonable compatibility with TSJ design requirements.
Numerical Analysis of Debris Containment Grid Fluid-Body Interaction
Authors: Katsuno Eduardo Tadashi , Gomes Gustavo de Goes , de Castro Felipe Santos , Dozzi Dantas Joao Lucas
Published: September 2018

Debris containment grid is an important part of hydroelectric power plant, since it retains objects, preventing damage to the turbine. In the case of the Santo Antonio hydropower plant, located in the Amazon rainforest, in the north of Brazil, the most significant debris are logs. This paper aims to analyze the interaction between several log boom modules (type of debris containment grids developed specifically for containing logs) present in a debris containment line present in Santo Antonio hydropower plant, as well as its interactions with the fluid, varying the advance velocity and side-slip angle. The analysis of the fluid-body interaction is performed using CFD software with Finite Volume Method approach. The problem is divided into steps. Firstly, one log boom module is simulated with several velocities and side-slip flow angle, obtaining a relation between forces, moments and movements. Next, in order to save the expected computational cost, the module is analyzed and compared through the porosity approach. Finally, the analysis of a line with several log boom modules, including the interaction between each module, is carried out. The results of the simulations will allow to perform an analysis of the line stability, obtaining the forces, moments and movements of each log boom module, observing its influence in the log boom line. With a fluid-body hydrodynamic analysis of several modules in a line, data are provided for a structural analysis. Since the porosity approach is used to reduce the computational cost, this paper also contributes to similar cases, with a main interest in larger scales of forces and movements.
Integrity Management of Marine Structures; With Emphasis on Design for Structural Robustness
Authors: Moan Torgeir
Published: September 2018

Based on relevant accident experiences with oil and gas platforms, a brief overview of structural integrity management of offshore structures is given; including an account of adequate design criteria, inspection, repair and maintenance as well as quality assurance and control of the engineering processes. The focus is on developing research based design standards for Accidental Collapse Limit States to ensure robustness or damage tolerance in view damage caused by accidental loads due to operational errors and to some extent abnormal structural damage due to fabrication errors. Moreover, it is suggested to provide robustness in cases where the structural performance is sensitive to uncertain parameters. The use of risk assessment to aid decisions in lieu of uncertainties affecting the performance of novel and existing offshore structures, is briefly addressed.
The TripleSpar Campaign: Validation of a Reduced-Order Simulation Model for Floating Wind Turbines
Authors: Lemmer (né Sandner) Frank , Yu Wei , Cheng Po Wen , Pegalajar-Jurado Antonio , Borg Michael , Mikkelsen Robert F. , Bredmose Henrik
Published: September 2018

Different research groups have recently tested scaled floating offshore wind turbines including blade pitch control. A test conducted by the University of Stuttgart (Germany), DTU (Denmark) and CENER (Spain) at the Danish Hydraulic Institute (DHI) in 2016 successfully demonstrated a real-time blade pitch controller on the public 10MW TripleSpar semi-submersible concept at a scale of 1/60. In the presented work a reduced-order simulation model including control is compared against the model tests. The model has only five degrees of freedom and is formulated either in the time-domain or in the frequency-domain. In a first step the Morison drag coefficients are identified from decay tests as well as irregular wave cases. The identified drag coefficients depend clearly on the sea state, with the highest ones for the decay tests and small sea states. This is an important finding, for example for the design of a robust controller, which depends on the system damping. It is shown that the simplified model can well represent the dominant physical effects of the coupled system with a substantially reduced simulation time, compared to state-of-the-art models.
Behavior Evaluation of Subsea Jumpers Exposed to Current by Experiment and FEM
Authors: Mobasheramini Mohammad , Alves Luciene , Fernandes Antonio Carlos , Ellwanger Gilberto Bruno
Published: September 2018

The oil and gas industry is headed toward deep water in recent years. Oil companies are seeking new technologies to meet the challenges of deep-water oil exploration and in the near future, this will bring new discoveries. The most difficulty of exploring oil in this region is the depth where the equipment is installed and the production lines must be safe for such activities. Full understanding of the dynamics of the behavior of this equipment is vital to the success of offshore production and operation due to environmental problems that can occur in an accident and a large amount of economic and human resources involved. The phenomenon of the vortex induced vibration (VIV) is complex and involves an interaction between hydrodynamic forces and the response of the structure. The force and displacement can be determined through experimental tests or the complete numerical simulation of the interaction between the structure and fluid. DNV-GL has recently published a guideline about the design of a subsea jumper [1], but it is still needed many studies and experiments to improve the evaluation of VIV in rigid subsea jumpers in the oil industry. The main objective of the present work is to investigate VIV phenomenon in a jumper exposed to uniform flow and verify its oscillation in the flow direction, which called inline VIV (VIVx). Throughout this study, the finite element method was used to perform the structural and modal analysis of the structure, in order to obtain the modes, frequencies and then validate the experimental result. Experimental analysis of jumpers was also performed in a current tank to evaluate the behavior of the jumper with the current flow.
Modal Identification of an Electrical Submersible Pump Installed in a Test Well Using Drop Tests
Authors: Monteiro U. A. , Minette R. S. , Gutiérrez R. H. R. , Vaz L. A.
Published: September 2018

Electrical submersible pumps (ESPs) are used in the petroleum industry to pump large amount of fluids from subsea deep wells. Currently, ESPs are responsible for approximately 10% of the world’s crude oil production. When high flow rates are required, gas lift and the ESP are the only available technologies that can be applied. ESP systems are much more complex and less reliable than the gas lift method, but they are more efficient and able to yield higher flow rates and pressure. ESPs are installed inside or near production wells, with the entire auxiliary infrastructure for power supply and control system. This means that maintenance is prohibitive because of production losses and the need for expensive and unavailable drill ships. Assembly errors and manufacturing defects must be avoided to make the method feasible and to prevent premature failure and, this goal, can only be achieved through rigorous quality control, operations procedure, qualification and dynamic tests. In this paper, modal parameters of an ESP installed in a test well were experimentally identified using the Enhanced Frequency Domain Decomposition (EFDD) technique. Drop tests were used to excite the ESP and vibration signals were acquired along the equipment’s structure. Results were compared with modal parameters obtained using impact tests and showed that the drop test is an useful method for modal testing of ESP’s in test well.
Direct Time Domain Life Cycle Loading Analysis on a Floating Platform
Authors: Lim Ho-Joon , Jegannathan Manoj , Koo Bonjun , Kyoung Johyun , Beyko Eleni
Published: September 2018

Time domain numerical simulations with TechnipFMC’s in-house program were performed to estimate life cycle loading on a floating platform using High Performance Computing (HPC). Direct Simulation Analysis (DSA) were conducted to estimate fatigue life of mooring lines of two Spar platforms and the results were compared with fatigue life estimated from the condensed bin approach.

In the Direct Simulation Analysis, 35-year hindcast wave and wind data with 3-hour interval for Gulf of Mexico was used. The wind and wave data covers from January 1979 to December 2013 for every 3-hours. The current data was not available so associated current information was approximately estimated.

The time domain direct simulation results include nonlinear loads, nonlinear responses and seasonal effects such as hurricane events. The life cycle loading analysis tool developed will reduce uncertainties and increase the accuracy and reliability of the estimation of the mooring fatigue life during the service life of platform.

Fatigue life of a mooring line from condensed bin analysis is highly variable with more than 20% depending on the selected wave seed number. In addition, the fatigue life from condensed bin analysis is about 20% less than the fatigue life from the Direct Simulation Analysis. This paper presents the systematic comparisons between the conventional approach and the direct time domain simulation results and also provides some major findings. In addition to the mooring line fatigue analysis, the structural fatigue analysis is also being performed and the results will be presented in the near future.
Eco-Friendly Drilling Fluid Deflocculant for Drilling High Temperature Well: A Review
Authors: Ghazali Nurul Aimi , Naganawa Shigemi , Masuda Yoshihiro , Ibrahim Wan Asma , Bakar Noor Fitrah Abu
Published: September 2018

Conventional clay-based drilling fluids often experienced difficulties in controlling the rheological properties, gelation, and filtration due to flocculation of clay at the temperature higher than 121°C. Deflocculant or thinner, one of the drilling fluid additives, serves a significant role in preventing the association of clay particles particularly in high temperature environments such as high-pressure and high-temperature (HPHT) deep-water drilling. Lignosulfonate has been commonly used in the industry as deflocculant for clay-based drilling fluids since the late 1950s as a replacement for Quebracho tannin. Degradation at the elevated temperature limits the usage of anionic polymer and lignosulfonate. In improving the stability of deflocculant at high temperature, lignosulfonate is admixed or reacted with chromium and iron compound to obtain ferro-chrome lignosulfonate whose temperature limit is approximately 190°C. While recent ferro-chrome lignosulfonate contains less chrome than in the past, development of more environmentally friendly and higher thermally stable deflocculant is still needed. In HPHT environment which requires high-density drilling fluid, a higher thermally-stable deflocculant is also valuable for barite sagging that becomes problematic at a temperature higher than 200°C.

Several findings in the past development of adhesives show that addition of tannin improves the thermal stability of lignosulfonate. Tannin is a polyphenolic compound that is natural, non-toxic and biodegradable and can be found in various part of a vascular plant other than Quebracho. Lignosulfonate, on the other hand, is a byproduct of the paper pulping process. Tannin and lignosulfonate are cross-linked to obtain tannin–lignosulfonate for use as a high-temperature drilling fluid deflocculant. Tannin and lignin are the most abundant compounds extracted from biomass. The wide availability of tannin and lignosulfonate is an advantage from a manufacturing cost viewpoint.

In this paper, an overview of drilling fluids, classification of drilling fluid, high temperature reservoir environment, and mechanisms of dispersion and deflocculation are presented. Further discussion on the potential development of eco-friendly tannin–lignosulfonate based drilling fluid system for the high temperature well development also presented.
An Integrated Numerical and Mineralogical Study of a High Pressure High Temperature Well
Authors: Segura Jose M. , Caja Miguel A. , García Laura , Jiménez Juan M. , Díez Jorge , Polo Teresa , Alvarellos Iglesias Jose , Lakshmikantha M. R.
Published: September 2018

Predicting drilling risks in advance is a major challenge in areas that lack drilling experience, and even when information from offset wells is available. Large overpressure was found at TD of an offshore exploratory well drilled mainly through shale. None of the other two previously drilled offset wells in the area had shown any sign of such a high overpressure. This study presents two complementary approaches to gain insight on the overpressure generation mechanisms. The effect of chemical compaction is first evaluated in terms of well cuttings analysis, including sample washing, high-resolution photo catalog, automated mineralogy and X-ray diffraction clay mineralogy analysis. The obtained mineralogical results confirm the presence of the dehydration diagenetic process involving the transformation of smectite to illite. Consequently, a numerical model is presented which combines the effect of mechanical and chemical compaction to predict pore pressure values very close to the overpressure observed during drilling. The model reproduces the depositional history of the lithological column by coupling mechanical and chemical compaction with fluid flow over geological time, and it allows predicting stress, porosity and pore pressure evolution at different geological ages. Calibration and verification of the results of the pore pressure model is done by comparison to drilling experience and logs (post-drill pore pressure profile, geology tops and density/porosity logs).
Efficient Wave Modeling Using Non-Hydrostatic Pressure Distribution and Free Surface Tracking on Fixed Grids
Authors: Bihs Hans , Kamath Arun , Aggarwal Ankit , Pakozdi Csaba
Published: September 2018

For the estimation of wave loads on offshore structures, relevant extreme wave events need to be identified. In order to achieve this, long term wave simulations of relatively large scales need to be performed. Computational Fluid Dynamics (CFD) based Numerical Wave Tanks (NWT) with an interface capturing two-phase flow approach typically require too large computational resources to achieve this efficiently. They are more suitable for the near-field hydrodynamics of steep and breaking wave impacts on the structures. In the current paper, a three-dimensional non-hydrostatic wave model is presented. While it also solves the Navier-Stokes equations, it employs an interface tracking method for the calculation of the free surface location. The algorithm for the simulation of the free surface is based on the continuity of the horizontal velocities along the vertical water column. With this approach, relatively fewer cells are needed in the vicinity of the air-water interface compared to CFD based NWTs. With coarser grids and larger time steps, the wave propagation can be accurately predicted. The numerical model solves the governing equations on an rectilinear grid, which allows for the employment of high-order finite differences. For time stepping, a fractional step method with implicit treatment of the diffusion terms is employed. The projection method is used for the calculation of the non-hydrostatic pressure. The resulting Poisson equation is solved with Hypres geometric multigrid preconditioned conjugated gradient algorithm. The numerical model is parallelized following the domain decomposition strategy and MPI communication between the individual processors.

In the current paper, the capabilities of the new wave model are presented by comparing the wave propagation in the tank with the CFD approach in a 2D simulation. Further, a 3D simulation is carried out to determine the wave forces on a vertical cylinder. The calculated wave forces using the new approach is compared to that obtained using the CFD approach and experimental data. It is seen that the new approach provides a similar accuracy to that from the CFD approach while providing a large reduction in the time taken for the simulation. The gain is calculated to be about 4.5 for the 2D simulation and about 7.1 for the 3D simulation.
Dynamic Modeling of Flow Induced Vibration Power-Plants
Authors: Xiros Nikolaos I. , Bernitsas Michael M. , Sun Hai , Saxton Ralph , Ioup Juliette W.
Published: September 2018

Based on experimental data from the Marine Renewable Energy Laboratory (MRELab) at the University of Michigan, a data model is developed in order to permit dynamical analysis and controller synthesis for power-plants based on Vortex Induced Vibrations (VIV) for power generation and energy production. For the particular experimental settings used at the MRELab, data series of various kinematic, dynamic and energetic variables were recorded through the use of one to two cylinders as bluff bodies in a cross-flow. In the present research, these data series are analyzed in order to produce a dynamical model in an appropriate phase space. The process of model derivation is entirely data-driven in the sense that the number of degrees of freedom, or state variables, reflects the dimension of the phase space for the process. The outcome is a model which allows the identification of regime-dependent features such as attractors, basins of attraction, separatrices, etc., which can occur in the basic system dynamics.
Reeled CRA Clad/Lined Pipeline Installation: Seastate Optimisation From Fatigue and Fracture Perspective
Authors: Zhou Daowu , Sriskandarajah T. , Bowlby Heidi , Skorpen Ove
Published: September 2018

The deformation mechanism in reel-lay of corrosive resistance alloy (CRA) clad/lined pipes can facilitate defect tearing and low cycle fatigue crack growth in the girth welds. Pipe-lay after straightening will subject the CRA welds to high cycle fatigue. The permissible seastate for installation will be governed by failure limit states such as local collapse, wrinkling of the liner, fatigue and fracture.

By means of a recently completed offshore project in North Sea, this paper discusses seastate optimisation when installing pipelines with CRA girth welds, from a fatigue and fracture perspective. The additional limiting requirement in CRA welds to maintain CRA liner integrity can lead to significant assessment work since all critical welds shall be examined. AUT scanned defect data were utilised to maximise permissible seastates based on fatigue allowance from a fatigue crack growth calculation.

An alternative simplified approach to derive the crack growth based on a superposition method is studied. It enables a straightforward real-time prediction of crack growth and has the potential to be used during the offshore campaign to improve the installation flexibility.

Post-installation fracture assessment under more critical seastates is examined for CRA partial over-matching welds. A comparison of CDF between conventional ECA procedure and 3D FE is provided.
Design Load Analysis for Wave Energy Converters
Authors: van Rij Jennifer , Yu Yi-Hsiang , Coe Ryan G.
Published: September 2018

This study demonstrates a systematic methodology for establishing the design loads of a wave energy converter. The proposed design load methodology incorporates existing design guidelines, where they exist, and follows a typical design progression; namely, advancing from many, quick, order-of-magnitude accurate, conceptual stage design computations to a few, computationally intensive, high-fidelity, design validation simulations. The goal of the study is to streamline and document this process based on quantitative evaluations of the design loads’ accuracy at each design step and consideration for the computational efficiency of the entire design process. For the wave energy converter, loads, and site conditions considered, this study demonstrates an efficient and accurate methodology of evaluating the design loads.
Studies on Meta-Modeling for Lazy-Wave Steel Catenary Risers
Authors: Monteiro Bruno da Fonseca , Baioco Juliana Souza , Delgado Edivaldo Ramos , Albrecht Carl Horst , de Lima Beatriz Souza Leite Pires , Jacob Breno Pinheiro
Published: September 2018

Steel Catenary Riser (SCR) design is a complex issue for the petroleum industry. The fact that it is strongly influenced by safety and cost saving factors has motivated the use of optimization techniques mostly based on metaheuristic algorithms such as Genetic Algorithms, Artificial Immune Systems and Particle Swarm Optimization. However, this particular offshore engineering problem requires high computational costs, associated to the time-domain nonlinear dynamic analyses with Finite Element (FE) models that are needed for a large number of loading cases for each candidate solution of the optimization process. This fact motivates studies the use of meta-models (or surrogate models) to replace the expensive FE analyses, leading to results with adequate accuracy and remarkably lower computational costs. In this context, this work applies as meta-models Artificial Neural Networks (ANN) and Multivariate Adaptive Regression Splines (MARS) to estimate the response of SCR risers in a lazy-wave configuration. Case studies are presented to assess the results comparing to a FE analysis.
Study on Influence of Bow Configuration on Dynamic Response of Ship Collision With Ice
Authors: Li Hui , Feng Yan , Yang Zheng , Sheng Weijia , Qian Yuan
Published: September 2018

The ice breaking capacity of the icebreaker depends on the geometric characteristics of the bow. Selecting reasonable bow configuration and characteristic parameters is helpful to improve the ice breaking capacity. In the ship parameters, the bow rake angle directly influences the ice breaking ability and the dipping efficiency. The ship collision with ice is simulated by using nonlinear dynamic analysis software LS-DYNA. By changing the bow rake angle, the collision force curves are obtained, and the ice breaking ability and efficiency of the polar ship with three bow configurations are calculated and compared with the ice resistance calculated by Riska formula. Through the analysis of the average longitudinal collision force and the ice breaking distance, the optimum bow configuration is selected. Combined with the calculation of the open water resistance, the scheme with the bow rake angle of 13 degrees is the best in the resistance performance.
Study on the Flow Characteristics of Rope and Cylinder With Large-Eddy Simulation
Authors: Cheng Hui , Huang Liuyi , Ni Yi , Zhao Fenfang , Wang Xinxin , Tang Yanli , Liang Zhenlin
Published: September 2018

Three-strand rope is the dominant material in fishing net and fish cage. Smooth cylinder is a common numerical model of net twines in the drag force calculation. This paper studied the hydrodynamic characteristics of ropes and smooth cylinders. Large Eddy Simulation was applied to the numerical simulation. Numerical results indicated that the drag coefficient of rope was much smaller than that of smooth cylinder when Re = 3900. The detailed analysis and comparison of their flow characteristics explained the reason. The specific of eddy shedding and wake pattern were presented in the numerical results.
Fatigue Analysis of a 12-MW Wind Turbine Blade
Authors: Ahn Hyeonjeong , Shin Hyunkyoung
Published: September 2018

In 2017, the MHI Vestas released a 9.5-MW offshore wind turbine. It is also actively researching and developing a 10-MW offshore wind turbine. As the capacity of a wind turbine increases, the sizes of all its system components, including length and weight, correspondingly increase. Consequently, as a wind turbine becomes larger, it becomes necessary to analyze the fatigue load applied to its entire system. The first reason for such an analysis is to achieve a safe but not overly designed large wind turbine. Second, most wind turbine accidents involve aging turbines and are related to fatigue analysis.

Accordingly, the purpose of fatigue analysis is to safely design a wind turbine that sustains repeated loads within its design life. In this study, the blades and loads for the fatigue analysis of a 12-MW floating offshore wind turbine are calculated based on the National Renewable Energy Laboratory (NREL) 5-MW wind turbine blades. The calculated loads are applied to the Markov matrix through a preprocessing, such as the cycle counting method. Finally, the equivalent fatigue load is estimated based on both mean and range.

In this study, only the equivalent fatigue load on the turbine blade is calculated. However, if fatigue analysis is to be performed for all parts using equivalent loads, it is possible to design the wind turbine to fully withstand such loads throughout its design life, and prevent the overdesign of each part as well.
Experimental Tests of a 1:16th-Scale Model of the Spar-Buoy OWC in a Large Scale Wave Flume in Regular Waves
Authors: Gomes R. P. F. , Henriques J. C. C. , Gato L. M. C. , Falcão A. F. O.
Published: September 2018

This paper presents the experimental tests of a 16th-scale model of the Spar-buoy oscillating water column (OWC) carried out at a large scale wave flume. The model is slack-moored to the flume floor by two mooring lines. The turbine effect is replicated using calibrated orifice plates. The device six degree-of-freedom motion, inner free surface displacement and air chamber pressure are measured. The influence of wave height, turbine damping and mass distribution on the system dynamics is analysed for regular waves. An in-house developed numerical time-domain model is used to simulate the motion and power absorption under the same wave conditions as the physical model tests. The formulation considers linear hydrodynamic forces, viscous drag effects and drift forces. The floater is assumed to oscillate in six degrees of freedom and the OWC can move vertically in the tube. The mooring system is simulated using a quasi-static model. The comparison between experiments and numerical simulations shows a good agreement for wave periods outside the zone where parametric resonance in roll and pitch occurs.
Hybrid Tool to Prevent Ship Propeller Erosion
Authors: Llull T. , Mujal-Colilles A. , Castells M. , Gironella X. , Martínez de Osés X. , Martín A. , Sánchez Arcilla A.
Published: September 2018

The present contribution aims to implement a new methodology to prevent Roll on-Roll off vessels (RO-RO) from causing severe scouring actions. The methodology combines field, experimental, theoretical and numerical tools exchanging information to establish the manoeuvre potential scouring damage. The main contribution is the introduction of a manoeuvre ship simulator to obtain variables that otherwise cannot be obtained in field studies. These variables, all related to ship’s propeller behaviour, are the rotational speed, the pitch ratio and the engine power during the whole manoeuvre.

Results show an over-prediction of the theoretical and experimental axial velocity and maximum erosion depth, indicating their clear limitations and the necessity of accurate data to apply the method. The methodology used with the key incorporation of the manoeuvre simulator is revealed to be a very useful tool to study new manoeuvres (including the possibility to work with a single or a couple of tugboats during the docking and undocking manoeuvres) to prevent propeller scouring actions.
Yield Point Determination Using Cyclic Loading in Polymer
Authors: Ychisawa Lucas K. , Costa Celio A.
Published: September 2018

Defining the yielding point of semicrystalline polymers is a matter to be established in the literature. ASTM D638-14 and ISO 527-1 standards define the yielding point as the point where there is an increase in strain without an increase in stress, which coincides with the beginning of necking of the test samples. The literature has been reevaluating this matter, taking into account the methods used and their respective damage generation in the material. Polymer materials are used in the oil and gas industry, for example, in risers. The understanding of the transition between the elastic and plastic regions is necessary, as well as the understanding of the damage done in both regions. This study is about the effects of cyclic loadings with triangular and sinusoidal loading, with different strain levels and their effect on the mechanical behavior of a fluorinated polymer(Halar ECTFE). The cyclic loading tests were strain-controlled and done with frequencies around 0.1Hz, equivalent to a strain rate of 0.2 and 0.4%/s, and strains up to 2%, with the effects on the transition from the elastic and on the stress relaxation being observed. The results show that up to strains of 0.5% the material has elastic behavior, irrespective of the loading. When the strains are greater than 0.75%, the material shows relaxation on all loadings cycles. Between 0.5% and 0.75%, the triangular loading led to cyclic hardening, while the sinusoidal lead to stress relaxation. The stress relaxation is then related to the damage accumulation on the structure of the material, while the hardening to the chain orientation.
Comparison of Taut and Catenary Mooring Systems for Finfish Aquaculture
Authors: Turner Adam A. , Steinke Dean M. , Nicoll Ryan S. , Stenmark Patrik
Published: September 2018

Finfish aquaculture has been expanding in areas like Norway and Canada over the last 20 years, and is projected to expand further in the next decades as the planet’s population and demand for seafood increases. Finding appropriate salmon farm sites is becoming increasingly difficult, as there are fewer protected nearshore locations available for development. As a result, there is interest in increased utilization of existing leases (i.e. permitted sites). These leases have a boundary in which the anchors and mooring lines must be contained. Reducing the footprint of the mooring arrangement will allow for an increased utilization of existing leases. A possible method to reduce the footprint of a spread moored salmon farm is to use a taut mooring rather than a chain catenary mooring. This requires the use of mooring materials and components that allows for handling of tidal elevation changes and wave action. This paper investigates the performance of a taut moored configuration with integrated Seaflex elastomeric mooring components in comparison with a conventional chain catenary configuration using dynamic analysis.

The results show that a reduced footprint taut mooring configuration with integrated elastomeric mooring components can be substituted for a typical chain catenary mooring with no significant increase in peak mooring line loads at extreme sea states and significant reduction in peak loading at moderate and calm seastates.
Probabilistic Wall Thickness Verification for the TurkStream Pipeline
Authors: Liu Ping , Meijer Arjen , DeGeer Duane , Jurdik Erich , Chaudhuri Jay , Zhou Shirley
Published: September 2018

The TurkStream pipeline system is currently being constructed across the Black Sea for supply of natural gas from the Russian coast near Anapa to landfall on the Turkish coastline. The pipeline design is extremely challenging from a technical perspective with water depths along most of the route exceeding 2200m, difficult seabed conditions with steep slopes and geohazard risks, a potentially aggressive and corrosive subsea environment, and high gas deliveries requiring a large pipeline diameter.

The combination of diameter, wall thickness, and quality requirements for the TurkStream linepipe is at the limit of leading mills around the world, and outside their normal production envelope. In order to demonstrate that the manufactured linepipe will meet target reliability levels, a material development program was completed, which included a major testing program involving testing prototype TurkStream pipes manufactured by both the UOE and JCOE methods of linepipe fabrication. The results from this test program formed the basis for a probabilistic verification of the pipeline wall thickness.

This paper presents the reliability-based verification of the wall thickness for the TurkStream subsea pipelines. The collapse limit state was identified as the governing mode of failure, and was defined by a collapse prediction formula developed specifically for the TurkStream pipelines. The model was verified by full-scale tests from the test program, and then used to define the failure surface of the collapse envelope due to external pressure and bending.

The probabilistic analyses resulted in reliability levels that exceed design code requirements. In addition, these analyses highlighted the need for certain criteria to be met during coated linepipe production. These requirements are summarized in this paper.