bluuebunny/crossref_metadata_2025_split huggingface dataset:
Towards Implementing Condition-Based Maintenance (CBM) Policy for Offshore Blowout Preventer (BOP) System
Authors: Elusakin Tobiloba , Shafiee Mahmood , Adedipe Tosin 
Published: November 2019

Abstract
With the steadily growing demand for energy in the world, oil and gas companies are finding themselves facing increasing capital and operating costs. To ensure the economic viability of investments and improve the safety of operations, oil and gas companies are promoting their asset integrity management (AIM) systems. In the past, the oil and gas industry adopted reactive maintenance regimes, which involved recertification, testing and repair of faulty equipment while trying to achieve minimum downtime. As technology becomes more affordable, operators have been able to carry out improved fault diagnosis, prognosis and maintenance optimisation. As a result of this, condition-based maintenance (CBM) is being adopted more and more as the preeminent maintenance regime for oil and gas equipment. The blowout preventer (BOP) is one of the most expensive and safety critical drilling equipment in the oil and gas industry. However, there have been very few studies and best practices about how to develop a CBM policy and what specific monitoring techniques and devices will be required to implement it for the BOP system. This paper proposes a V-model based architecture for designing a CBM policy in BOP systems. As a result of the model proposed, gaps in implementation are identified and all the hardware, software and training requirements for implementing the CBM solution in BOP systems will be outlined in detail. Our proposed CBM framework will help BOP operators and maintenance personnel make cost savings through less repairs and replacements and minimal downtime.
Non-Linearly Restoring Performance and its Hysteresis Behavior of Dynamic Catenary
Authors: Li Yilun , Guo Shuangxi , Kong Yue , Li Min , Chen Weimin 
Published: November 2019

Abstract
Catenary is increasingly used as mooring-line and riser system as the water depth gets larger due to its lower cost and easier installment. Its dynamic response and restoring performance become more complicated, as the length of the mooring-line become larger, and the structural and fluid dynamics the mooring-line become consequently more obvious. Compared to the quasi-static method where the static restoring force is mainly involved, the dynamic behaviors and its hysteresis of the catenary mooring-line are considered here so as to comprehensively examine the non-linearly restoring performance of mooring-lines. Based on the 3d dynamic vector equations along with the modified FEM simulations, the hysteresis character of the restoring stiffness and the influences of the catenary dynamics on its restoring performance are presented and discussed.
It is found that, principally owing to the damping and inertial effect coming from the fluid and structural dynamics, the restoring force of the mooring-line depends on both the structural displacement and velocity. Moreover, the dynamic stiffness behaves as a hysteresis loop, instead of a curve. Our numerical results show that the energy consumption during one period rises nonlinearly with the increase of the body frequency ωd and amplitude A0. And, the influence of nonlinear restoring stiffness on the structural response along with the slack-taut phenomenon caused by structural /hydrodynamic inertia and damping is discussed.
Fate of Hydrocarbon Leaks From Plugged and Abandoned Wells Compared to Natural Seepages
Authors: Tveit Mari R. , Khalifeh Mahmoud , Nordam Tor , Saasen Arild 
Published: November 2019

Abstract
As the hydrocarbon fields mature and reach the end of their productive lives, their Permanent Plug and Abandonment (PP&A) become inevitable. Even though new technology and verification methods are being researched, it is evident that operational, barrier material and qualification challenges together contribute to a risk of leaks from abandoned wells. Well integrity standard NORSOK D-010 constitutes zero leak acceptance criteria to protect the environment; however, natural hydrocarbon seepages are occurring all over the world on a daily basis. In this study, we introduce the comparison between leaking wells and natural seeps and suggest conducting a fate analysis is appropriate to provide necessary data for evaluating environmental implications of leaking wells. Two case studies were analyzed using SINTEF Ocean’s OSCAR (Oil Spill Contingency And Response) software; one historical gas leak (Field A) and a theoretical oil leak (Field B). It is found that for releases of natural gas at 70 m water depth, 95 to 99 % dissolve in the ocean, and the fraction of gas reaching the atmosphere is dependent on the initial gas bubble size. Fate of oil is more complex than gas, but evaporation, sedimentation and biodegradation are the main contributing mechanisms in the fate analysis.
CFD Analysis on Hydrodynamic Characteristics for Optimizing Torpedo Anchors
Authors: Sun Jing , Liu Haixiao 
Published: November 2019

Abstract
Compared with other types of anchors, gravity-installed anchors (GIAs) have several main advantages such as simple structure, convenient installation way and cost reduction. The torpedo anchor is one type of GIAs. The geometric configurations have a direct influence on the hydrodynamic characteristics of the anchor, and thus affect its installation performance in water. The present work aimed to put forward some new aspects for optimizing the existing geometries of torpedo anchors by comprehensively improving the hydrodynamic characteristics of the anchor during installation in water. A computational fluid dynamics (CFD) model was established and numerical simulations were carried out using the software of ANSYS FLUENT. The hydrodynamic characteristics concerned involved the drag coefficient, the terminal velocity and the directional stability. The present study paid more attention to the fin’s design. By changing the fin parameters, including the aspect ratio and the area of the fin, the optimum design method of the fin was proposed, which would make sure of a higher terminal velocity as well as good directional stability. Besides, effects of the mass distribution on the hydrodynamic characteristics were investigated. The present work provides a design reference for torpedo anchors and is also beneficial to the research and development of new types of GIAs.
Nonlinear Analysis of a Heaving Point Absorber in Frequency Domain via Statistical Linearization
Authors: S. P. da Silva Leandro , Morishita Helio M. , Pesce Celso P. , Gonçalves Rodolfo T. 
Published: November 2019

Abstract
The majority of wave energy devices operate close to resonant conditions to enhance energy conversion resulting in large displacements. As a result, nonlinearities significantly contribute to the dynamics of the system. A typical approach to predict the behavior of the system and power output relies on the derivation of a mathematical model in the time domain to simulate the dynamics through some numerical codes. However, a relatively high computational demand is required for those simulations. In this regard, the present work deals with the nonlinearities in the frequency domain via Statistical Linearization. Two different power-take-off systems are investigated, a linear and a hydraulic one, and their mean power calculations are derived based on the Statistical Linearization. The reliability of the method is verified against the Power Spectrum Density (PSD) of nonlinear time domain simulations. Only the heave motion is analyzed, and several nonlinearities commonly reported for Point Absorbers (PA) were considered, such as cubic stiffness, geometric nonlinearities, drag forces, and Coulomb forces. The approach employed in this work offers a reliable estimation of body dynamics for all nonlinearities considered. In addition, the present method produced a fast estimation, which can be valuable for the assessment of several designs and sea load conditions.
Evaluation of Uncertainty of Damage Results in Experimental Modelling of Monopile Foundation Scour Protection
Authors: Wu Minghao , Arnout Jonas , Molina Ruiz Josep , Arboleda Chavez Carlos , Stratigaki Vasiliki , Troch Peter 
Published: November 2019

Abstract
The waves and currents acting near a monopile foundation will potentially lead to scour, which may affect the stability of the wind turbine. The design of scour protection against the seabed lowering around a wind turbine monopile foundation is an important issue for wind energy industries. Many laboratory tests have been carried out to investigate the relationship between the hydrodynamic conditions and the monopile foundation scour protection layer damage, and various design criteria have been proposed. However, the experimental uncertainty of the underlying test results has not been discussed in detail.
In the present research, small scale wave flume experiments of a 5m diameter monopile foundation scour protection under waves combined with currents in shallow water are described. Two groups of repetitive experiments are completed under the same wave and current conditions. The erosion development of the scour protection armor layer is measured by using a laser profiler and is evaluated based on three dimensional damage numbers. Together with visualization of the damage pattern, the damage analysis discusses the erosion in different subareas and the variances of the subarea damage number.
The analysis of the uncertainty of the erosion results based on two sets of repetitive tests has been carried out. Using the uncertainty analysis methodology stated in ISO GUM standard: JCGM 100-2008, the Type A uncertainty, calibration uncertainty and combined uncertainty of the experiment are evaluated separately. The Type A uncertainty gives an overall uncertainty level and it shows that higher uncertainty occurs in the regions where stronger vortices exist. The combined uncertainty is analyzed based on scour protection dynamic stability design formula. Analysis result shows that the uncertainty due to modelling is a major source of the total uncertainty. The study gives a preliminary result of uncertainty level in wave flume test of monopile scour protection and provides a reference for future experimental research.
Multi-Phase Simulation of Droplet Trajectories of Wave-Impact Sea Spray Over a Vessel
Authors: Mintu Shafiul A. , Molyneux David , Colbourne Bruce 
Published: November 2019

Abstract
Sea spray, generated by ship-wave collisions, is the main source of marine icing. In certain, but not all, circumstances a cloud of spray forms after a wave impacts a ship. The spray cloud comprises numerous water droplets of various sizes. These droplets are dispersed and transported over the vessel deck by the surrounding wind and fall onto the deck or into the ocean under the effect of gravity. The motion of these droplets is important since they determine the extent of the spray cloud and its duration over the deck, which consequently affects the distribution of icing accumulation on a ship in freezing weather. In this paper, a multi-phase air-water simulation of droplet trajectory is used to predict the cloud motion of various size droplets. A smooth particle hydrodynamics (SPH) computational fluid dynamics (CFD) model is implemented and the simulation is accelerated using GPU computing.
The field observation data is used to simulate the trajectory. The results of the simulations are compared with an available theoretical model and reasonable agreement is found. The inverse dependence of size and velocity for droplets after the breakup process is examined. The simulation results are consistent with the theoretical model in that neither the largest nor the smallest droplets reach the maximum height of the spray cloud, but the mid-size droplets do. The spray cloud spreads faster and crosses the front of the vessel quicker than predicted by the theoretical model. It is also found that the trajectory of a single droplet is significantly affected by surrounding droplets in a multi-droplet trajectory model. A mono-droplet theoretical trajectory model, therefore, is not as accurate as the multi-droplet CFD model.
Introducing a Novel MEG/EtOH Mixture to Improve Gas Hydrate Blockages Removal During Offshore Oil and Gas Production
Authors: Paz Paulo , Netto Theodoro Antoun 
Published: November 2019

Abstract
Offshore oil and gas production may present gas hydrate formation problems. Using thermodynamic hydrate inhibitors as methanol, mono ethylene glycol, (MEG), and ethanol among others to deal with these issues is frequent. The inhibition process initially consists of pumping thousands of barrels from topside to seabed in order to be injected into the reservoir or into the flowlines where the hydrates may form. Research has shown the difference between injecting MEG or Methanol. Methanol has a better performance dissolving hydrates and MEG can be cleaned and used again. A disadvantage for methanol is that part of it goes to the gas phase where is not useful for hydrate inhibition. Recently there has been proposed the possibility to mix them in order to increase their individual performance, which has been proved as satisfactory to both hydrate dissolving, and injection operation. In this study, the characteristics of current inhibition treatments and a new mixture of Ethanol and MEG were used to simulate the efficiency of the process to pump them from topside to seabed. To compare the mixture performance as a new hydrate inhibitor with the other THI treatments, data from real scenarios were used. The results can be used on the selection process for the THI pumping system, in order to optimize the needs of the gas hydrate inhibition system, in terms of power and storage on the platform.
A Hybrid Data-Driven Deep Learning Technique for Fluid-Structure Interaction
Authors: Miyanawala T. P. , Jaiman Rajeev K. 
Published: November 2019

Abstract
This paper is concerned with the development of a hybrid data-driven technique for unsteady fluid-structure interaction systems. The proposed data-driven technique combines the deep learning framework with a projection-based low-order modeling. While the deep learning provides low-dimensional approximations from datasets arising from black-box solvers, the projection-based model constructs the low-dimensional approximations by projecting the original high-dimensional model onto a low-dimensional subspace. Of particular interest of this paper is to predict the long time series of unsteady flow fields of a freely vibrating bluff-body subjected to wake-body synchronization. We consider convolutional neural networks (CNN) for the learning dynamics of wake-body interaction, which assemble layers of linear convolutions with nonlinear activations to automatically extract the low-dimensional flow features. Using the high-fidelity time series data from the stabilized finite element Navier-Stokes solver, we first project the dataset to a low-dimensional subspace by proper orthogonal decomposition (POD) technique. The time-dependent coefficients of the POD subspace are mapped to the flow field via a CNN with nonlinear rectification, and the CNN is iteratively trained using the stochastic gradient descent method to predict the POD time coefficient when a new flow field is fed to it. The time-averaged flow field, the POD basis vectors, and the trained CNN are used to predict the long time series of the flow fields and the flow predictions are quantitatively assessed with the full-order (high-dimensional) simulation data. The proposed POD-CNN model based on the data-driven approximation has a remarkable accuracy in the entire fluid domain including the highly nonlinear near wake region behind a freely vibrating bluff body.
Numerical Simulation of Submarine Self-Propulsion Based on Different Turbulent Simulation Models
Authors: Bai Tiechao , Wu Yongfeng , Wei Peng , Wang Shuang , Liu Liwei 
Published: November 2019

Abstract
Design requirements for submarines regarding resistance, maneuverability, stability and stealth tighten with each new generation. Fully understanding the hydrodynamics of the vessels is key if performance requirements need to be met. In this paper, the numerical simulation with three different turbulent models, Reynolds averaged Navier-Stokes (RANS) Realizable k-ε model, RANS SST (Menter’s Shear Stress Transport) k-ω model and the large eddy simulation (LES) are used to simulate the self-propulsion of DARPA SUBOFF submarine under V = 2.755m/s, and the simulation results are compared and analyzed. The comparisons show that the RANS method can be used to simulate the drag and pressure of submarine self-propulsion accurately. The surface pressure of LES is more accurate for fine flow field, the simulation of self-propelled parameters is less as accurate might because the mesh is not refine enough.
REEF3D Wave Generation Interface for Commercial CFD Codes
Authors: Pakozdi Csaba , Bihs Hans , Kamath Arun , Hermundstad Elin Marita 
Published: November 2019

Abstract
In recent years CFD developments have shown a trend to combine RANS CFD simulation with other methods such as wave theories or velocity potential based numerical wave tanks, in order to reduce to computation costs. This is however not a new approach, and there exists a large amount of literature about domain decomposition techniques describing a two way coupling between the RANS CFD models and other methods. One can also observe an increasing popularity in the use of a less sophisticated technique where different fluid solvers are combined with one-way coupling. In these methods a predefined solution is provided in the far-field (ignoring the structure), while a three-dimensional (3D) CFD simulation is applied in a limited zone near the structure. The predefined solution is used to specify the background far-field solution. The governing equations are extended by the addition of a source term. The published solutions use wave theory or a numerical wave tank where the predefined solution is calculated parallel to the RANS solver. In this way it is possible to reduce the interpolation inaccuracy and the amount of transferred data to the CFD simulation. The disadvantage of this technique is that the far field solver has to be prepared in order to run in parallel with the CFD solver. Due to the one way coupling it is possible to predefine this information in tables before the CFD simulation. This technique makes it possible to define a general interface between difference solvers without modifying existing codes. This paper presents such a technique where the predefined solution is stored into files. An interpolation function delivers all data to the far-field solution for the CFD simulation. The paper analyses the necessary accuracy of the interpolation and the costs of the input/output operation of the CFD simulation through several verification cases.
Effect of Tensile Pre-Strain on Collapse Pressure of Coated Linepipe
Authors: Sakimoto Takahiro , Handa Tsunehisa , Tajika Hisakazu , Murakami Yoshiaki , Kondo Joe 
Published: November 2019

Abstract
As offshore pipeline projects have expanded to deeper water regions with depths of more than 2,000 m, linepipes are required to have higher resistance against collapse by external pressure. Collapse resistance is mainly controlled by the pipe geometry and compressive yield strength. In UOE pipe, the compressive yield strength along the circumferential direction changes dramatically due to tensile pre-strain that occurs in pipe forming processes such as the expansion process. In order to improve the compressive yield strength of pipes, it is important to consider the Bauschinger effect caused by pipe expansion. As the mechanism of this effect, it is understood that internal stress is generated by the accumulation of dislocations, and this reduces reverse flow stress. Compressive yield strength is also changed by the thermal cycle associated with application of fusion-bond epoxy in pipe anti-corrosion coating by the induction heating process. In the typical thermal heat cycle of this coating process, the maximum heat temperature is from 200 °C to 250 °C. In this case, compressive yield strength increases as an effect of the thermal cycle, resulting in increased collapse resistance. Thus, for deep water application of UEO linepipe, it is important to clarify the conflicting effects of the Bauschinger effect and the thermal heat cycle on compressive yield strength. Based on this background, in this study, the combined effect of the Bauschinger effect and the thermal heat cycle on compressive stress is investigated by conducting tensile pre-strain tests and simulation of the thermal cycle associated with coating. Compressive yield strength was obtained for several pre-strain and thermal cycle conditions, and the collapse pressure was calculated by an FE analysis based on the obtained compressive yield strength. This study discusses the effect of tensile pre-strain on the collapse pressure of linepipes with these simulated thermal heat cycles.
Design Methodology for a Floating Offshore Wind Turbine Large-Scale Outdoor Prototype
Authors: Fontanella Alessandro , Taruffi Federico , Muggiasca Sara , Belloli Marco 
Published: November 2019

Abstract
This paper discusses the methodology introduced by the authors to design a large-scale wind turbine model starting from the DTU 10MW RWT. The wind turbine will be coupled with the model of a multi-purpose floating structure, designed within the EU H2020 Blue Growth Farm project, and it will be deployed at the Natural Ocean Engineering Laboratory (NOEL). In this paper the different strategies used to design the wind turbine model rotor, tower and nacelle are discussed, focusing on how it has been possible to reproduce the full-scale system aero-elastic response while ensuring the same functionalities of a real wind turbine.
The Vortex and Wall Fluctuating Pressure Around Submarine Sail Based on DDES Method
Authors: Luo Rui , Sun Yue , Zhang Hang , Zhan Jin , Cai Xiao 
Published: November 2019

Abstract
Vortex around ships is easy to cause noise, vibration and fatigue of propellers. In addition, the complexity and variability of vortex will also have a greater impact on sensors and detection equipment installed on the surface of the vehicle. It is necessary to carry out corresponding research. In this paper, the fluctuating pressure was numerically analyzed using improved DDES model. And applying overset grids to better capture vortices around submarine sail. The numerical study of a three-dimensional unsteady vortex structure was performed for calculation. There were two vortex tubes and some broken small vortices behind the sail. The simulation results showed that trailing vortices behind sail slightly swept up and the distance between two vortex tubes became larger.