bluuebunny/crossref_metadata_2025 huggingface dataset:
An Upgraded Direct Forcing Immersed Boundary Method With Integrated Mooring Algorithm for Floating Offshore Wind Turbines
Authors: Soydan Ahmet , Wang Widar Weizhi , Bihs Hans
Published: August 2024

An upgraded direct forcing immersed boundary method is implemented in the open-source hydrodynamic framework REEF3D::CFD for simulating the six-degrees-of-freedom (6DOF) motions of a floating offshore wind turbine (FOWT) based on the OC5 semi-submersible design. The direct forcing method is enhanced with a new density interpolation method across the fluid-structure interface that removes unphysical spurious phenomena and ensures stable and accurate wave load calculations on floating objects. A quasi-static algorithm is used for modeling the mooring system of the OC5 platform and restraining its motions in waves. The Navier-Stokes equations are solved on a staggered structured rectilinear grid for the hydrodynamic simulations. The level-set method is used to capture the free surface of the ocean waves. A ray-casting algorithm is employed to get inside-outside information near the fluid-solid interface while maintaining the underlying Cartesian grid in the hydrodynamic domain. The performance and accuracy of the mooring algorithm are compared to the widely-used mooring model MoorDyn, which is coupled to the hydrodynamic solver in REEF3D::CFD. The study demonstrates that the enhanced direct forcing method with the integrated quasi-static mooring algorithm in REEF3D::CFD provides a robust and accurate tool, suitable for the numerical analysis of the state-of-the-art FOWT in ocean waves.
Risk Monitors Applied to Offshore Installations
Authors: Maturana Marcos C. , M. Schleder Adriana , Frutuoso e Melo Paulo F. F. , O. de Barros Leonardo , Orlowski Thiago C. , R. Martins Marcelo
Published: August 2024

In recent decades, regulation of the offshore sector has migrated from a prescriptive normative base to a risk-based one. This paradigm shift brought to operators the need to adapt the risk management of their current plants and operations, and to deepen their analysis and risk assessments for new ventures (in compliance with regulatory requirements). Experiences in risk analysis, assessment and management and their advantages in other industries can be useful to accelerate and deepen the improvement of this topic in the offshore industry. As an example of what can be used (from the experience of other industries), one can mention the application of Risk Monitors (RMs) in the nuclear industry. A risk monitor can be based on a Top Logic Model (TLM), obtained from the event trees and fault trees that make up probabilistic models of the plant (e.g., focused on systems that are considered important for safety or that may have significant impact on operating costs). In this sense, this paper presents a discussion on how RMs are applied in the nuclear industry, and how they can be adapted and explored to improve risk management in offshore installations, including remotely controlled or automated installations, and provides a simple example of obtaining a model to calculate the point risk curve (a possible variable monitored by means of a RM).
Environmental Load on an Ocean Semisubmersible Structure in the Presence of Rogue Waves With Currents
Authors: Zaman Hasanat , Akinturk Ayhan
Published: August 2024

Renewable and low-carbon energy sources are critical to helping to reduce greenhouse gas emissions in the fight against global warming. One method for generating this renewable, low-carbon energy is offshore wind farms. A consistent wind source is always dependable for carbon-free energy production, equipment performance, and operational safety. In contrast to on land, offshore wind velocities are often steady. All structures in the offshore areas are subjected to a variety of environmental loadings due to the presence of very large waves and strong currents that can have significant impacts on the operation cycles of such structures. The presence of large waves and strong currents, as well as their interactions with the base structures and mooring lines, might produce hazardous operational circumstances. The operation and safety of such structures may be more vulnerable especially when a large wave travels against a strong current and produces abnormally high rogue waves. In this study, the tensions in the mooring lines of a tethered semisubmersible structure due to the presence of large waves, strong currents, various incident angles, and their consequent interactions are considered. The semisubmersible structure often serves as a fundamental framework capable of supporting energy-generating equipment such as wind turbines. Numerical simulations were conducted using an in-house developed 3D tool that incorporates mass, momentum, and energy-balanced equations. Additionally, two commercial codes, OrcaFlex™ and STAR-CCM+™, were employed for result comparisons. OrcaFlex™ is an implicit and explicit commercial code that uses lumped mass elements to streamline equations and the STAR-CCM+™ uses Navier Stokes equations. To explore numerous instances, settings for incident wave and current conditions were systematically changed in the simulations. The semisubmersible structure’s geometry and still water depth were maintained constant. The semisubmersible was anchored to the sea bottom with four mooring lines, one from each column’s bottom, in all simulations.

The model is used for the computation of the hydrodynamic loads on a semisubmersible and its mooring lines in a wave and current co-existence field.
Active Magnetic Ranging in Geothermal Drilling: Identifying Ghost Targets
Authors: Husby Karsten , Ytrehus Jan David , Saasen Arild , Eriksen Tor Jan
Published: August 2024

To achieve proper efficiency, for some geothermal applications it is necessary to drill deep connected closed loop wells. These wells are connected by a series of parallel horizontal well sections pairs for heat transfer from the formations. The separation of these wells, and the distance between them, must be controlled in the drilling operation to ensure efficient heat transfer.

Active Magnetic Ranging (AMR) is an oilfield drilling measurement technique developed for efficient relief well drilling and to drill well sections within a conglomerate of old wells without hitting any existing wells. Different to traditional ranging systems where the ranging is performed using a wireline operation, an AMR system integrate the logging system onto the drill string bottom hole assembly. Such method would save several rig days as the trip-out operations can be skipped.

We have conducted test rig experiments using a full-size drilling rig. Several test wells are drilled on this location for testing different types of drilling equipment. At the depth used in the tests the formation consists of a gneiss. A gneiss would represent typical low porosity and low permeable formations with poor electrical conductivity that is a representative model formation for geothermal heat transfer formations. Possibly because of the low conductivity false measurements can be obtained — so-called Ghost Targets.

In this paper we present an analysis of how ghost targets can look like. Furthermore, it is outlined how to distinguish ghost targets from real targets and how to design systems to reduce the impact of such ghosts.
Sealing Ability of Cement Plugs: Investigation of Critical Testing Parameters
Authors: Opedal Nils , Feneuil Blandine , Wiggen Even , Haug Jakob , N'Gouamba Elie , Skorpa Ragnhild
Published: August 2024

Determination of a sealant material’s ability to provide zonal isolation is important. Any potential well barrier material should ideally be tested and optimized under controlled, reproducible, and relevant conditions. Recent advances in experimental methods for qualification of materials beyond the API-10 standard have been published. For further development, the critical testing parameters relevant for these test methods should be investigated. The objective of this paper was to study the effect of test conditions such as cement curing time and scale dimensions. The curing and test conditions were found to be potentially important factors to ensure reproducible data and for understanding what is actually measured from the setup. For instance, the mechanical strength of cement might not be an adequate proxy to determine the hydraulic bond strength of a material. Also, the experimental determination of sealability of cement to a steel casing is dependent on several factors, such as curing time, presence of water during the cement hydration process, the cement plug dimensions, and the testing protocol itself.
Reinforcement Learning for Fishing Route Planning and Optimization
Authors: Zhu Tiantian , Naseri Masoud , Dhar Sushmit , Ashrafi Behrooz
Published: August 2024

Pelagic fishing is one of the primary economic activities in the Arctic, especially in the Barents Sea region. Optimizing fishing vessel voyage planning is a feasible avenue for enhancing efficiency, profitability, and sustainability while mitigating accidental risks posed by adverse weather conditions and reducing environmental impact through decreased fuel consumption. Currently, fishing voyage planning and route optimization rely heavily on the accumulated experience of skippers. Thus, it is a challenging task for inexperienced skippers. This paper presents an application of the reinforcement learning algorithm for fishing route planning and optimization. Reinforcement learning is a type of machine learning technique to learn an optimal behavior through a trial-and-error search in an environment to discover the sequence of actions under uncertainty that maximizes the defined reward. In this study, several optimization agents for different objectives, including maximizing catch, minimizing distance, maximizing catch while minimizing risk, etc., are trained from a programmed fishing environment to test out the capabilities of reinforcement earning for fishing route optimization. Future research can be developed by building upon the programmed fishing environment by incorporating a more realistic geographical map, uncertain fish stock distribution, a more sophisticated ship model, sound route risk function, fuel consumption function, etc. . Customized agents can be trained and further utilized as a decision support tool by skippers for their fishing trip planning and route optimization.
Hydrodynamic Assessment of the CorPower C4 Point Absorber Wave Energy Converter in Extreme Wave Conditions
Authors: Venugopal Vengatesan , Tan Tian
Published: August 2024

This study focussed on the evaluation of the motion responses exhibited by the CorPower C4 wave energy converter (WEC) when subjected to extreme wave conditions. The hydrodynamic performance of the device is examined through experiments conducted with a 1:25 scale model of the CorPower WEC at the FloWave Ocean Energy Research Facility, University of Edinburgh. The investigation encompasses a range of sea conditions, employing both regular and random waves to comprehensively understand the hydrodynamics of the CorPower WEC, with a particular focus on scenarios representative of the WEC’s survivability. The experimental setup involves the utilization of a Qualisys camera system to measure the six-component motion responses of the WEC at its waterline. Additionally, a 6-component load cell is employed to measure forces and moments acting on the entire model, including its mooring system.

This article provides a detailed overview of the model setup, experimental procedures, data analysis techniques, and thorough discussions of the results obtained. Drawing insights from the Response Amplitude Operators (RAOs) derived through the experiments, this work asserts that the CorPower WEC exhibits remarkable stability, demonstrating its capability to safely endure extreme wave conditions similar to those simulated in this study. The findings contribute valuable knowledge to the understanding of the CorPower WEC’s performance and resilience in challenging marine environments.
An Equivalent Wind State Method for Efficient Fatigue Screening Assessments
Authors: Jia Junbo
Published: August 2024

A dedicated wind induced fatigue analysis using full scatter diagram is desirable for reducing the design uncertainties in the assessment, even though it is demanding regarding engineering efforts, especially for large structural engineering projects that require the wind buffeting fatigue calculation for many different substructures. To conquer this challenge, the current paper proposes a method by condensing wind scatter diagrams to much fewer wind states for calculating wind induced fatigue damage, which can dramatically reduce the calculation efforts. By adopting a nonlinear time domain dynamic analysis method and applying the proposed method into the fatigue damage calculation of two types of structures, with different dynamic characteristics from each other, the obtained fatigue damage using the proposed method is compared with that using full wind scatter diagram. The comparisons show that the proposed method can reach a satisfied engineering accuracy and efficient for concept and preliminary engineering design. To further reduce the assessment efforts, by adopting the equivalent wind state method, a method to calculate the fatigue damage based on a static analysis is proposed. The method is especially suitable for relevant engineering projects requiring a large amount of screening assessment efforts for wind induced fatigue.
Machine Learning and Deep Learning for Enhanced Spatio-Temporal Wave Parameters Prediction
Authors: Tan Tian , Venugopal Vengatesan
Published: August 2024

Traditional methods of wave prediction, which are mainly reliant on extensive numerical simulations, such as the utilization of spectral wave models SWAN, WaveWatch III, or TOMAWAC, have prompted the question: Can faster wave prediction be achieved? The answer, as demonstrated by this study, lies in the advancements of machine learning and deep neural networks.

In this research, the spatio-temporal relationship between wind and wave conditions is established using the XGBoost machine learning method and Informer deep neural networks. This approach enables effective predictions of wave height and wave period within the waters of the North Atlantic and northern Scotland. Ten years of hourly wind data from ECMWF ERA5 (2012–2021) is used as training data, while field measured wave parameters from CEFAS WaveNet buoys are employed for model training and verification. The final output enable a comparison that ultimately leads to wave predictions for the year 2022. Building upon this foundation, a versatile model for typical weather conditions and a specialized model for extreme weather scenarios are devised, facilitating more precise predictions.

The data-driven model, rooted in wind data, proves adept at predicting wave characteristics across different times and locations. Notably, the trained machine learning and deep learning model delivers significant efficiency gains compared to traditional numerical models. One year’s worth of data can be predicted within a few seconds by machine learning, whereas over 24 hours (on 16 logical CPUs) are required for the same prediction by TOMAWAC spectra wave model. This leap in training efficiency is a crucial development in the realm of wave prediction.
Free Span Assessment: Benchmarking and Parametric Study
Authors: Abdelsalam Mohammed , Karrech Ali , Bransby Fraser , Watson Phil , An Hongwei
Published: August 2024

The assessment of pipeline free-spans may involve non-linearities, including those arising from the mechanical behaviour of the pipeline, soil properties and hydrodynamic loading; as well as the interaction between these factors. Failure to properly quantify and account for these factors may lead to inadequate design outcomes, which can lead to failure (if unconservative) or result in costly remediation when unnecessary (if conservative). This paper is part of an ongoing study into the vibration response of free spanning subsea pipelines, including the development of a numerical model that highlights the value of modal and full fatigue analyses as tools for understanding span behaviour. For quality control and enhancing the reliability of assessment methodologies, the model has been benchmarked against published data in terms of modal analysis, and against industrial fatigue assessment packages in terms of fatigue analysis — and shows excellent agreement with both. Since verification, the model was used to conduct a sensitivity study on a single free span, to explore how pipeline response and fatigue damage is affected by the value of dynamic soil stiffness and damping.
Development of an Experimental System to Investigate Viscous Damping of Oscillatory Flow Between Two Vessels
Authors: Yang Yuhang , Zhao Wenhua , Draper Scott , Wolgamot Hugh
Published: August 2024

An experimental design is proposed for investigating viscous damping in oscillatory flow between two rectangular boxes with sharp corners. It is anticipated that a relationship between Reynolds number and damping coefficient can be established through a series of tests with a wide range of Reynolds numbers, which would be of great significance for extending the database from lab scale to full scale. This experiment considers viscous damping induced by both wall friction and flow separation. The experiment is designed to allow global damping to be determined through measurements of flow rate and differential pressure, while wall friction can be estimated through an analytical solution. Particle image velocimetry technology has been adopted to visualize the flow field. In the paper, detailed design of the experimental approach is presented, together with validation of the instrumentation, demonstrating the reliability of the experimental set-up.
Overview of the Dilemma of Left in Situ: Structures Coated With Weathered Coal Tar
Authors: Candido Cordeiro Marcelle , Couto Thiago , Carneiro Paulo R. F. , Fasca Hanna , Santos Luan , de Souza Marcelo I. L. , Salomon Paulo S.
Published: August 2024

Coal Tar coatings were extensively utilized from the 1960s to around 1990 to waterproof offshore oil facilities, such as pipelines, and shield them from corrosion. However, in the 2000s, Coal Tar was found to be linked with a significant release of polycyclic aromatic hydrocarbons (PAHs) into the environment, prompting a decline in its usage. Nevertheless, numerous aging oil structures coated with Coal Tar persist on the seabed. As these facilities near the end of their service life, a pivotal question emerges: does this mass of weathered Coal Tar coating still pose a risk to marine life? In response to these concerns, this overview explores the scientific understanding of Coal Tar and its toxic components degradation in seawater. Our objective is to foster discussions regarding decommissioning options that mitigate environmental harm, underscoring the crucial necessity of evaluating the effects of prolonged exposure to Coal Tar in marine ecosystems, particularly within the context of the left in situ (LIS) approach. We seek to heighten awareness among the academic community and project operators responsible for decommissioning initiatives about the gravity and complexity of this issue.
Exploring the Technical Boundaries in Upscaling Floating Offshore Wind Turbines
Authors: Janocha Marek Jan , Lee Chern Fong , Wen Xueliang , Ong Muk Chen , Raunholt Lars , Helgaland Larsen Ørjan , Søyland Svein
Published: August 2024

Recent advancements in offshore wind turbine technology have led to a rapid increase in the size of turbines. In the early 1980s, wind turbines had a relatively small power rating of 50 kW with rotor diameters of around 15 meters. This size grew significantly, reaching 18 MW with 260-meter rotor diameters currently under construction. The market is transitioning to even larger turbines, with a power rating expected to achieve 22 MW by 2025. This trend of increasing turbine sizes shows no signs of reaching its limit. However, it is anticipated that the cost curve will break at some point due to material limitations necessary to withstand increasing forces and moments from the environmental loads and exponentially increasing mass of the components. For floating offshore wind turbines specifically, the design complexity increases as these systems comprise of both a turbine and a floating foundation. Innovations in this area include using advanced composite materials for larger components such as blades and towers, high-fidelity numerical models for structural optimization to mitigate excessive dynamic response and employing unconventional solutions such as combined wind and wave energy conversion systems or multirotor wind turbines. Recent developments in wind turbine systems have also seen improvements in control systems and generator design, including direct-drive and multi-generator solutions. To further increase electrical energy production from wind turbines in the future, it is necessary to develop strategies that reduce costs through technological innovation, enhance performance and efficiency, and decrease maintenance, operation, and manufacturing costs. The evolution of wind turbine technology plays a pivotal role in the global wind power generation landscape, and the trend toward larger turbines is a significant aspect of this evolution. The present paper focuses on the theoretical technical limits of floating wind turbine upscaling and determining the optimal turbine size for minimizing energy costs.
A Simplified Formulation of the Linear Design VWBM Based on IACS Rec. No. 34 Rev.2
Authors: Mikulić Antonio , Ćorak Maro , Parunov Joško
Published: August 2024

A simplified formulation for the linear part of the design vertical wave bending moment (VWBM) at midship is proposed. The formulation is based on the computation of the long-term VWBM for 25 ships of diverse types, using assumptions embedded in the new IACS Rec. No. 34 Rev.2. Transfer functions of VWBM at midship are calculated using semi-analytical Closed-Form Expressions. Long-term probability distributions of VWBM are fitted by the two-parameter Weibull probability function. Weibull scale and shape parameters are then approximated by linear multiple regression analysis, where the main ship particulars are taken as the regression parameters. As the most probable extreme value according to the IACS Rec. No. 34 Rev.2 is determined for the return period of 25 years, the average zero crossing response period in the ship design lifetime is also subjected to the linear regression analysis. Design VWBM is then calculated as the most probable extreme value by the proposed formulation and compared to the results of the long-term distribution. The results indicate that the regression equations can accurately approximate the results of the long-term distribution. Although numerical comparison with the existing Rule formulation is not the aim of the study, results are nevertheless compared with the VWBM from IACS UR S11 and UR S11A. It was found that the design VWBM from this study is lower compared with the existing IACS rule formulations. The proposed approach can be considered as the rule formulation of design VWBM and as a surrogate model of extreme VWBM for ship structural reliability analysis.
Variational Autoencoders for Exteroceptive Perception in Reinforcement Learning-Based Collision Avoidance
Authors: Larsen Thomas Nakken , Barlaug Eirik Runde , Rasheed Adil
Published: August 2024

Modern control systems are increasingly turning to machine learning algorithms to augment their performance and adaptability. Within this context, Deep Reinforcement Learning (DRL) has emerged as a promising control framework, particularly in the domain of marine transportation. Its potential for autonomous marine applications lies in its ability to seamlessly combine path-following and collision avoidance with an arbitrary number of obstacles. However, current DRL algorithms require disproportionally large computational resources to find near-optimal policies compared to the posed control problem when the searchable parameter space becomes large. To combat this, our work delves into the application of Variational AutoEncoders (VAEs) to acquire a generalized, low-dimensional latent encoding of a high-fidelity range-finding sensor, which serves as the exteroceptive input to a DRL agent. The agent’s performance, encompassing path-following and collision avoidance, is systematically tested and evaluated within a stochastic simulation environment, presenting a comprehensive exploration of our proposed approach in maritime control systems.
Digital Twin for Wind Energy: Latest Updates From the NorthWind Project
Authors: Rasheed Adil , Stadtmann Florian , Fonn Eivind , Tabib Mandar , Tsiolakis Vasileios , Panjwani Balram , Johannessen Kjetil Andre , Kvamsdal Trond , San Omer , Tande John Olav , Barstad Idar , Christiansen Tore , Rishoff Elling , Frøyd Lars , Rasmussen Tore
Published: August 2024

NorthWind, a collaborative research initiative supported by the Research Council of Norway, industry stakeholders, and research partners, aims to advance cutting-edge research and innovation in wind energy. The core mission is to reduce wind power costs and foster sustainable growth, with a key focus on the development of digital twins. A digital twin is a virtual representation of physical assets or processes that uses data and simulators to enable real-time forecasting, optimization, monitoring, control and informed decision-making. Recently, a hierarchical scale ranging from 0 to 5 (0 - Standalone, 1 - Descriptive, 2 - Diagnostic, 3 - Predictive, 4 - Prescriptive, 5 - Autonomous has been introduced within the NorthWind project to assess the capabilities of digital twins. This paper elaborates on our progress in constructing digital twins for wind farms and their components across various capability levels.
Optimizing Aluminum Alloys for Dynamic Cables in Floating Wind Energy Transmission
Authors: Johanson Audun , Viespoli Luigi
Published: August 2024

Floating wind energy presents a promising opportunity to harness vast wind resources that remain inaccessible using today’s bottom-fixed offshore wind technology. Transmitting the electricity generated by floating wind turbines to shore lies in dynamic cables. However, the implementation of these cables is beset by technological and knowledge gaps, leading to increased costs compared to conventional static subsea cables. One significant challenge is the use of aluminum as a conductor material. Aluminum offers a more cost-effective alternative to copper, which can potentially reduce the overall cost of dynamic cables. High-conductivity aluminum grades like AA1350/70 exhibit excellent electrical properties but are hindered by low mechanical characteristics, especially in terms of creep and fatigue strength. Alloys that combine high strength and conductivity, such as AA6101 with appropriate aging treatment, offer a reasonable yield strength, but also 10–15 % reduced conductivity. and conductivity. In this study, we explore a subset of the AA1120 series aluminum alloy with tailored chemistry to improve fatigue strength while maintaining excellent conductivity. Our results reveal a significant enhancement in fatigue properties compared to AA1370, with the optimized alloy exhibiting fatigue characteristics akin to copper. These findings emphasize the importance of meticulous alloy and processing design for the safe and cost-effective integration of aluminum conductors into dynamic cable systems.
Numerical Investigation of Manoeuvring Performance of an Icebreaking Tanker in Ice-Prone Baltic Sea Environments
Authors: Panahi Saeid , von Bock und Polach Rüdiger Ulrich Franz , Abdel-Maksoud Moustafa , Oberhagemann Jan
Published: August 2024

The maritime trade and activities in regions with ice-covered waters such as the Arctic, Antarctica, the Baltic Sea, the Caspian Sea and the Great Lakes are expected to experience growth in the near future, mainly influenced by factors like: increased dry bulk and cargo freight in Arctic regions, rising tourism in Arctic and Antarctic waters, and increased exploitation and transport of oil and gas in Arctic areas.

Most importantly, global warming — particularly in the North Pole — is opening new navigation routes through ice melting, affecting susceptible ecosystems and making previously inaccessible areas more navigable [1]. This highlights the need for a deeper understanding of Ship-Ice Interaction (SII) and manoeuvring performance in ice-infested waters. For a vessel advancing in ice, the primary focus pertains to the prediction of the ice resistance; however, the transverse force and turning moment are also of significance contemplating the manoeuvrability aspect whilst in turning circumstance.

This paper focuses on developing a numerical model to simulate SII and ship manoeuvres in level ice. The model integrates existing semi-empirical formulas for calculating ice-pertinent forces and moments, and a coefficient-based model (by the Taylor series expansion) for hydrodynamic forces. Key findings indicate the Lindqvist method’s effectiveness in predicting ice resistance, and confirm the reliability of the turning circle manoeuvre (in open water) with the experimental data of Wolff [2]. Nonetheless, to improve the accuracy of the turning circle manoeuvre in ice, it is imperative to have access to all the characteristics of the model tests and ice distribution in the ice tank.
Design of Cement Sheaths in Offshore Oil Wells Based on Structural Reliability
Authors: Estrela Gabriela Alves , de Sousa Fernando Jorge Mendes , Lopes Guilherme Kronemberger , Sagrilo Luís Volnei Sudati , e Silva Ana Beatriz de Carvalho Gonzaga , Fairbairn Eduardo de Moraes Rego , de Andrade Henrique Conde Carvalho , Telles José Cláudio de Faria , de Siqueira Andréia Arenari , Reales Oscar Aurelio Mendoza , Carvalho Carlos Pessanha , da Silva Ingrid Ezechiello , Rocha José Marcelo Silva , Moreira Rafael Peralta Muniz
Published: August 2024

The design of cement sheaths in offshore oil wells is usually performed following a deterministic approach, which doesn’t consider explicitly the variability and uncertainties in material properties and loads. Cement properties can vary, for instance, due to the intrinsic nature of the cementation process. Load uncertainties are attributed to the random character of the loading environment or to inadequate knowledge of the physical phenomena associated with them.

The objective of this work is to present a reliability-based methodology for designing cement sheaths, which uses probability distribution functions to describe material properties and loads, obtained from several laboratory tests and from literature review, respectively. Reliability calculations were performed combining the FORM (First Order Reliability Method) and a dedicated structural analysis computer program developed at COPPE/UFRJ named as TENCIM-1D. The proposed methodology allows an easy determination of failure probabilities with low computational costs. The importance factors derived from FORM help to identify variables that deserve a better statistical description. These results will help the development of future research, setting priorities in new lab tests and field surveys. Additionally, this methodology can contribute to change the way cement sheaths are designed, considering explicitly the uncertainties in materials properties and loads.
Data Driven Identification and Model Predictive Control for a Catamaran Surface Vessel
Authors: Deogaonkar Vallabh , Ibrahim M. Mohammed , Vijayakumar Akash , Somayajula Abhilash
Published: August 2024

Autonomous Surface Vehicles (ASVs) have received increasing attention in various maritime applications over the years. Their ability to operate autonomously in complex and confined environments, such as narrow inland waterways, presents a unique set of opportunities and challenges. This paper presents a comprehensive study on the dynamics identification and subsequent development of a Model Predictive Controller (MPC) for a catamaran surface vessel. The catamaran surface vessel under investigation was fabricated in-house with a holonomic thruster configuration and a comprehensive sensor suite. This study focuses on experimental identification of a 3 degree of freedom maneuvering model of the fully actuated surface vessel. With a well-defined dynamic model in place MPC is designed for efficiently tracking a path while maintaing surge velocity. The MPC framework is chosen due to its ability to optimize control inputs over a finite prediction horizon, ensuring the catamaran follows desired trajectories while adhering to operational constraints and actuator constraints. This paper outlines a holistic study on the dynamics identification and MPC development of an ASV to impact a wide range of applications, from oceanographic research to coastal security, by providing a robust control framework that can navigate the challenges of dynamic marine environments.
Study on Fatigue Assessment Considering Mooring Chain Wear for Floating Offshore Wind Turbines
Authors: Takeuchi Takaaki , Kurokawa Kazuki , Nozoe Eisuke
Published: August 2024

For the achievement of a carbon-neutral society by 2050, floating offshore wind turbines (FOWTs) have high expectations, especially in regions deeper than a water depth of 60 m because of the vast potential in Japan. For station keeping of FOWTs, the application in such a region generally requires mooring chains. Since the reliability assessment of mooring chains is one of the key issues to ensure the integrity of FOWTs during the design life, the mooring design limit state shall be properly evaluated.

For investigation on the effect of wear and corrosion on fatigue damage, some researchers consider the only uniform decrease in chain diameter, which is insufficient to represent a change in the stress distribution due to local deformation. The local diameter loss could increase local stress and lead to the unexpected early failure of the mooring chain. In order to estimate the fatigue life accurately, it is necessary to estimate the local diameter loss due to the interlink wear considering the motion of floating structures. In this study, such fatigue assessment method is investigated by assuming the installation of UMaine VolturnUS-S reference platform developed for the IEA wind 15MW wind turbine at Ishikari Bay, Hokkaido, Japan. This is based on a method to estimate interlink wear quantitatively by finite element analysis considering the plastic deformation caused by the proof load test, and coupled dynamic analysis of a floating structure and mooring system using OpenFAST. As a result, the estimated wear amount at the fairlead has been much larger than the specified allowance. Additionally, from the estimated fatigue damage it has been found that mooring chains cannot withstand design life without replacement, and deterioration due to interlink wear and corrosion could lead to unexpected early failure of mooring chains.
High- and Mid-Fidelity Modeling Comparison for a Floating Marine Turbine System
Authors: Tran Thanh Toan , Ross Hannah , Wiley Will , Wang Lu , Sirnivas Senu
Published: August 2024

There is a lack of suitable numerical tools, particularly open-source tools, that can be used for designing and optimizing marine turbine systems. The National Renewable Energy Laboratory has added features to their widely used mid-fidelity wind turbine modeling code, OpenFAST, to enable modeling of axial-flow marine turbines. This necessitated the addition of several physical effects relevant to marine turbines that are neglected for wind turbines. These include buoyancy, added mass and inertial loads, wave-current superposition, and changes to the coordinate systems. This updated version of OpenFAST allows for the modeling of both fixed and floating marine turbines at a speed comparable to real time. While efficient for large sets of load cases and design studies, mid-fidelity codes make simplifying assumptions that may impact their accuracy. High-fidelity computational fluid dynamics (CFD) simulations can capture more flow effects with fewer assumptions and provide detailed body pressure mapping and flow-field information. It is important to compare predictions between mid-fidelity and high-fidelity codes, both to verify the models and to understand the limitations. A floating marine turbine system was modeled both with OpenFAST and with the commercial CFD code STAR-CCM+. The CFD model used a three-dimensional unsteady Reynolds-averaged Navier-Stokes solver for a volume-of-fluid numerical wave and current tank. The blade-resolved simulations used the sliding-interface technique for the spinning rotor and an overset grid to accommodate the rigid-body motion of the floating system. The mooring system was modeled with a custom coupling of the CFD solver with the open-source code MoorDyn. This improves upon the existing quasi-static catenary solver in STAR-CCM+, which lacks seabed contact or line-to-line connections. Simulation results for a floating marine turbine are compared between OpenFAST and CFD, highlighting the capabilities of the mid-fidelity code and identifying the areas where a high-fidelity approach is needed.
Vessel Motion During Side-By-Side Offloading: Comparison of Field Data and Numerical Model
Authors: Wang Yutao , Wolgamot Hugh , Zhao Wenhua , Draper Scott , Watson Phillip
Published: August 2024

The side-by-side (SBS) offloading operation is a conventional industry practice when an FLNG facility offloads liquid cargo onto carriers. There are several criteria for this operation to ensure safety and operability. Carrier motion during the SBS offloading has been studied extensively by either computational models or laboratory scaled models. Comparison between these results and full-scale measurements of vessel motions that are recorded during actual offloads has also been studied by JIPs and companies, but almost none of this is presently available in the public literature. This paper presents, for the first time, a vessel motion comparison between numerical model and field measurements. In particular, aspects which are challenging to model numerically, and therefore interesting to investigate in the comparison include roll motion, motions coupled to gap resonance, and motions coupled to sloshing.
Decision Support System for the Selection of Offshore Oil Wells Configuration
Authors: dos Santos Joaquim Rocha , León Chinchay Carlos Alberto , Martins Pereira de Abreu Danilo Taverna , Arguello Rodrigues Eric Tierre , Colombo Danilo , Ramos Martins Marcelo
Published: August 2024

Much of the hydrocarbon production in Brazil originates from offshore operations in pre-salt fields. The pre-salt fields are located more than 300 km from the coast, in water depths of around 2,000 meters, with reservoirs 7,000 meters from the sea surface. Operating in such conditions presents challenges regarding operational safety and keeping low downtime, guaranteeing a high financial return. A critical decision in developing these fields is choosing the best configuration for their wells, as in addition to the points already highlighted, maintenance in the pre-salt is also expensive. During oil well design, engineers suggest several configurations, leaving the field manager to choose the best options. An oil and gas operator is developing a decision support system to assist managers in this decision. This article deals with a software module — ReliaWell — that aims to calculate indicators of integrity (operations safety) and production equipment reliability (ensuring operation continuity). The article briefly presents the software requirements and the process of surveying the indicators to be considered, discusses the methodology adopted for the simulation models, and shows the system architecture and some screens, especially those for data entry and results output.
Development of Time Series Drilling Datasets for Stuck Pipe Prediction Using Volve Field Data
Authors: Bo Cao , Yu Song , Feng Xu , Fukang Peng
Published: August 2024

Numerous machine learning algorithms are applied in the oil and gas industry. However, the data used in these studies are difficult to obtain due to various limitations. Due to the lack of benchmark datasets, it is challenging to make performance comparisons across different algorithms. Volve field dataset was made public by Equinor, which provides raw data availability for the development of drilling and completion datasets.

In this paper, we utilize the time-based drilling data from the Volve drilling platform and transform it into time series datasets for stuck pipe prediction. Specifically, we introduce our concepts and principles for data development, the rules for selecting time intervals and attributes, the challenges encountered during the data development process and the methods for overcoming them. We discuss the applicability of these methods, the issues they bring, and their impact on data quality. Furthermore, we provide a well development case that includes complex data. The results indicated that our research shows promise in providing time series reference datasets for the application of machine learning algorithms in stuck pipe prediction.

We aim to provide a reference methodology for the development of raw data, reducing barriers to data utilization. We hope to provide data availability, possibly even serving as a reference benchmark dataset for the further applications of machine learning algorithms in the oil and gas sector. Our datasets are made publicly available on GitHub : https://github.com/promiseeee/Time-series-stuck-pipe-prediction.
Prediction of Scour Around Subsea Shallow Foundations Under Time-Varying Currents
Authors: Qu Lili , Draper Scott , An Hongwei , Watson Phil , Cheng Liang , Harris John M. , Whitehouse Richard J. S.
Published: August 2024

This paper describes the development of a framework to predict scour and undermining around squat, shallowly embedded structures under time-varying currents. Squat structures, with height equal to or smaller than their horizontal dimensions, are frequently employed offshore for a range of purposes, including pipeline and cable infrastructure, offshore substations, and innovative applications like offshore data centers and artificial reefs. These structures typically feature a rectangular base with a seabed-embedded skirt to increase the geotechnical capacity of the foundation and guard against the risk of local scour compromising the foundation. To investigate scour development at these structures, and to develop a framework to predict scour and undermining, experiments have been conducted using a generic squat structure with a shallow skirt foundation placed on a sandy bed within uniform grain size. Initially four experiments with different unidirectional currents were performed. For each of these experiments scour was initiated by the flow at the corners of the structure and scour holes developed, eventually leading to the undermining of the structure. The flow conditions were run until an equilibrium profile was observed, and the equilibrium scour depth, the equilibrium extent of undermining, and the associated timescales of these processes were obtained. These values were then used in a STEP model (Scour Time Evolution Predictor) scheme to predict how scour would evolve in time-varying currents. Comparisons of the STEP model with an additional experiment simulating a time-varying unidirectional current show that the time-history of scour depth, extent and the undermining area can be predicted reasonably well, indicating that the STEP model can be applied to scour assessment in time-varying currents.
Integrity of Drilling Fluid As Primary Barrier for CCS Wells
Authors: N'Gouamba Elie , Feneuil Blandine , Skogestad Jan Ole , Linga Harald , Skår Gjertrud , Roggeband Serge M. , Nedrum Jack , Ødegård Sven Inge
Published: August 2024

The primary barrier in the well during drilling is the drilling fluid, both in terms of hydrostatic pressure from the fluid column, its frictional pressure drop resistance and the influence from the drilling fluid for mitigating reservoir fluid influx. Accordingly, it is of crucial importance that threats to this barrier are understood. When drilling infill wells for carbon capture and storage (CCS), a potential threat to this barrier is the risk of influx of already stored CO2 from the formation. This is a situation that must be understood as the geological storage of CO2 is scaled up in order to contribute to achieving climate goals.

While there is substantial experience and knowledge in the industry on interactions between natural gas and drilling fluids, far less is known about the effects of CO2 of the drilling fluids and how this affects the barrier properties of the fluid. In order to increase the understanding of the risk of primary barrier collapse, laboratory studies of drilling fluids exposed to CO2 are performed. Challenges to the primary barrier integrity and possible mitigations are discussed in light of the results.
Technology Development for Offshore Emission Reductions in Order to Reach Emission Reduction Targets
Authors: Skorpa Ragnhild , Ytrehus Jan David , Gardarsdottir Stefania
Published: August 2024

Norway has committed to ambitious greenhouse gas reduction targets over the coming decades. Reducing emissions linked to oil and gas exploitation on the Norwegian continental shelf (NCS) is crucial to reaching those goals. Oil and gas exploitation accounts for 27 percent of Norwegian greenhouse gas emissions and are the second largest source of such emissions in the country, after the transportation sector. In particular, Norway has set targets for 55% emission reductions on the Norwegian Continental Shelf by 2030 and to move towards zero emission activities on the Norwegian Continental Shelf by 2050.

In this paper we present and discusses how a solution-portfolio approach is required to reach emission reduction targets on the Norwegian Continental Shelf.
Assessment of Nonlinear Loads and Motions Through Response Conditioned Design Waves: Practical Application and Limits
Authors: Bouscasse Benjamin , Dermatis Athanasios , Kim Shinwoong , Ducrozet Guillaume , de Hauteclocque Guillaume , Lasbleis Marine
Published: August 2024

Assessment of the extreme responses that offshore structures will experience within their life-cycle, involves numerous long-duration calculations for various weather and service conditions. The response distribution of any quantity driven by wave-structure interaction can be obtained efficiently with linear theory. However, the accuracy of that method is known to quickly deteriorate in severe sea states and for highly nonlinear quantities. In those cases, simulations with a high-fidelity solver or experiments are necessary which, although accurate, imply a significant cost (computational or experimental time) and in several cases become unfeasible. For this reason, the concept of response-conditioned waves (RCW) has been developed, as a way of investigating solely wave patterns of short duration, which can be considered tantamount to brute-force simulations. This approach consists of computing short-time wave episodes, that induce a given target response of the studied quantity. At a later stage, these waves can be generated and propagated in a computational domain, so that the fully nonlinear responses are obtained, by using only brief high-fidelity numerical simulations. The present paper demonstrates the relevance of such an approach, designed as a two-step method. First, the RCW is computed with a low-fidelity surrogate model, based on a nonlinear High Order Spectral (HOS) potential flow solver for wave modeling and a linear wave-structure interaction model. The method has been validated for two distinct response cases, namely the prediction of the vertical bending moment (VBM) of a zero-speed containership and the nacelle acceleration of a floating wind turbine. An overview of those applications is provided and the principal strengths, as well as the potential limitations of the method, are identified and discussed.