bluuebunny/crossref_metadata_2025 huggingface dataset:
New Temporal Approach to Evaluate the Lateral Buckling of Armour Wires
Authors: Bouy Ludovic , Frigeri Phellip , Lemonnier Gilles , Estrier Pascal
Published: September 2023

This paper presents a novel approach to manage irregular external loads thro ugh an enhanced design of unbonded flexible pipeline caused by lateral buckling of tensile armour wires. The design challenge is to predict the armour wire kinematics due to random loading conditions.

Over the past decades, efforts have been made to simulate and model lateral buckling phenomenon. Based on more than a hundred full scale tests, including deep immersion performance tests and hyperbaric chamber tests, a design approach was established that reproduces lateral buckling. The analyses performed considered regular sinusoidal loading corresponding to extreme sea states, often leading to overconservative combinations of curvatures and axial compressions. Wire displacements and stress states of steel wires were predicted using in-house software with the aforementioned cyclic loading. This methodology has shown room for improvement to decrease the conservatism and make sure we propose the most optimized armour wire geometry for a flexible pipeline designed to lateral buckling. In this paper, it is demonstrated that loading of compression and bending derived from stochastic extreme sea states allows us to bring the migration calculation to a higher level of accuracy. As a result, armour wires achieve their final migration state with lower stress values with stochastic approach with extreme sea states rather than the regular one.

Some technical challenges appeared when establishing this new approach. For example, bending cycles order as well as the sea states order impacts on wire kinematic and stress state. These observations, shared in this paper, concluded that a temporal approach is required to properly estimate lateral buckling risk when considering irregular loads. A key aspect identified during the development is the need of having two calculation modes when performing lateral buckling calculation with a temporal approach. The first mode allows to manage temporary operation by disregarding sea states order which could be very useful for simulating lateral buckling during installation sequence, whereas the second mode allows to evaluate lateral buckling during service line operation by considering the impact of all the sea states. Calculating armour wire kinematics migration during an entire service life, considering all the sea states, was another challenge requiring significant dedicated software developments. Impact on calculation time has been scrutinized and specific methodology has been implemented to optimize calculation time. Stress comparisons between classical regular approach and this new temporal – two calculation method are presented in this paper to illustrate the improved accuracy.

This temporal – two calculation methods also result in improved installation weather windows, and optimized armour wire selection. Finally, this methodology has been reviewed and certified by an Independent Verification Agent.
Research on Offshore Engineering Equipment Industry in Shandong Based on Sustainable Development
Authors: Deng Yue , Zhao Jingli , Duan Xiaofeng , Song Weiling , Guo Yue
Published: September 2023

Offshore engineering equipment industry is at the core of the marine industry value chain and an important foundation for the development of blue economy. Shandong was selected as the research area in this paper. Comprehensive strength of five industries — offshore oil and gas industry, offshore electric power industry, offshore fishery, offshore mining industry and offshore seawater utilization industry were analyzed from three dimensions of resource endowment, industrial development level and existing production capacity. Based on sustainable development, development suggestions of offshore equipment industry in Shandong were given.
A Method for Optimization of Sensor Locations for Inverse Calculation of Impact Load on Stiffened Panel
Authors: Zhou Xueqian , Shen Xingzhi , Xu Yishi , Ren Huilong
Published: September 2023

There are many scenarios in the area of ships and marine structures where impact on structure members like stiffened panels where the impact loads are difficult to directly measured and one may need to turn to inverse calculation.

The inverse calculation of impact load is very important as impact loads are characterized by short action time and large amplitude, which have adverse effects on structural safety. In practice, one of the difficulties in inverse calculation of impact load is the need of a large number of sensors, which means high cost and huge amount of computation. Therefore, it is necessary to optimize the layout of sensors for inverse calculation of impact load. To investigate the method for optimization of sensor locations for inverse calculation of impact load on stiffened panel, the inverse calculation results of different sensor layout of the stiffened panel are analyzed by applying Particle Swarm Optimization. Based on the optimization principle of Particle Swarm Optimization, a fitness function with the overall relative error and cosine similarity as the judgment criteria is established. The inverse calculation of impact loads on the stiffened panel is carried out with different number of calibration points and sensors. The regularization method is applied to deal with the ill-conditioning of matrix. The effects of the number of calibration points and sensors on the inverse calculation of impact loads are discussed. An optimal sensor layout that meets the requirements of the fitness function is found under a calibration point number and sensor number by Particle Swarm Optimization.
The Adaptation of Condition Monitoring Methodologies From Fixed Wind and Floating Oil and Gas to Floating Offshore Wind
Authors: Jayasinghe Kanishka , Gumley Jonathan , Thomas Clare , Lemmer Frank , Raach Steffen
Published: September 2023

As the Floating Offshore Wind Turbine industry approaches the transition from demonstrators to commercial scale farms, condition monitoring systems will be integral to risk management. Scalable condition monitoring solutions exist for both Fixed Offshore Wind and floating Oil and Gas, however a holistic solution addressing aerodynamic and hydrodynamic challenges on a floating wind unit is lacking.

Where sensors should be minimized, or for unmeasurable parameters, digital twins offer an alternative for predicting major component condition, relying instead on numerical models based on floater global response and metocean conditions.

This paper demonstrates the potential of reconstructed load signals, state-of-the-art sensors and first principles physics-based digital twins using approaches from the Wind and Oil and Gas sectors. Existing motion-based integrity monitoring methods are adapted to a real-time reduced-order model of a floating wind unit. Specifically, a state-observer model is used to reproduce position and mooring tension, enabling mooring failure identification and fatigue tracking.

The methods are demonstrated through a 15 MW synthetic case study, including examination of the impact of noise and sensor loss on reliability. The results show that the integration of digital twins into sensor-based monitoring systems can reconstruct missing data with sufficient certainty to facilitate early detection of failures.
On the Relationship Between Spectral Models of Ice Drift and Wind Turbulence
Authors: Sinsabvarodom Chana , Leira Bernt J. , Høyland Knut V. , Chai Wei , Naess Arvid , Radhakrishnan Gowtham
Published: September 2023

At present, there is quite limited research activity related to mathematical models of the ice drift spectrum. The intention of this work is to propose a novel mathematical model of a generalized ice drift speed spectrum to describe the ice drift behavior in the frequency domain. The drift of sea ice is naturally influenced by external forces such as wind stress at the air-ice interface, water stress at the water-ice interface, the Coriolis force, pressure gradients due to sea surface tilting, and internal stress within the sea ice itself. Typically, wind dominates the ice drift at higher frequencies, while current is likely to play an important role in the lower frequency range. This is due to the slow rate of change for the ocean current. Typically, sea ice will drift at approximately 2–3% of the wind speed as referred to a height of 10-meter above the ocean surface in the Arctic region. The magnitude of the ice drift speed can approximately be predicted by the Nansen number corresponding to the drift speed magnitude as a percentage of the wind speed. The physical connection between the wind speed and the ice drift speed is presently utilized in order to generate a generalized ice drift spectrum. The ice drift data is collected from local subsurface measurements by means of acoustic Doppler current profilers (ADCP) in the Beaufort Sea. The frequency spectra of the wind speed and ice drift speed are calculated by application of the Fourier transform (as implemented in the WAFO software) based on the measured time series. It is found that the sea ice drifts at around 2.5% of the wind speed in the winter season (which corresponds to non-free drift conditions). However, during the summer season the sea ice tends to drift faster than 2.5% of the wind speed (which corresponds to free drift conditions). According to the scaling relationship between the ice drift speed and the wind speed, the Kaimal turbulence spectra are adopted to describe the ice drift behavior. This provides a good match for the winter season. However, the empirical ice drift spectrum contains higher energy levels than the Kaimal turbulence spectra in the high frequency range during the summer season. Accordingly, a generalized ice drift spectrum is proposed in the present paper, which is developed based on expressions for the general turbulence spectrum. The corresponding expression is more flexible in order to capture the ice drift behavior in the high frequency range for both the winter and the summer seasons. The generalized ice drift spectrum is found to provide a better match to the empirical spectra from ADCP measurements than the Kaimal turbulence spectrum.
A Data Driven Decision Support System for Structural Safety of Ships Moving in Waves
Authors: Zhou Xueqian , Yang Yu , Liu Yujie , Feng Guoqing , Ren Huilong
Published: September 2023

The safety of ship hull structure is the most important and fundamental premise of ship operational safety at sea. For ships moving in large waves, the wave loads vary with the loading condition, ship speed and heading, incorrect operation decisions may result in large wave loads on the ship and cause severe accidents. In recent years, the technological advances made in the durability and stability of sensors, data acquisition, data processing units have made it possible to close monitor the stresses in the hull structures of ships. Such technologies are not only an approach for the crew to identify the structural state of the ship hull, but also provide the possibility of sophisticated decision support of safe operations. Although it is possible to reduce vertical bending moment by changing the heading from head seas to quartering seas, but the increasing horizontal bending moment and torsional moment might become a new threat to the structural safety of ships with large deck openings. In this paper, a data driven decision support system for structural safety of ships moving in waves is proposed. The stresses in the deck and in the bottom structure of a ship are used to calculate vertical bending moment, horizontal bending moment and torsional moment in real time, the assessment of overall strength of the ship hull under the wave loads is conducted. To construct a model for the proposal of safe operation of ships driven by monitor data, a method is devised for accurate identification of current navigation parameters based on the sensor data, which are then used for the calculation of parameters for safe operation of ship moving in waves. The method is applied to the case of a container ship moving in waves, and some conclusions are drawn based on the analysis of the results.
Investigation of the Formation and Detection of Casing-Cement Debonding in Small Scale Samples
Authors: Feneuil Blandine , N'gouamba Elie , Larsen Idar , Skorpa Ragnhild
Published: September 2023

In oil and gas wells, cement is generally placed in the annulus between the steel casing and the rock formation to avoid migration of fluids from the formation to the well. Though, during the operation of the well, casing dilatation and contraction may lead to the loss of the sealing ability of the cement annulus: casing dilatation tends to induce cracks in the cement, while casing retractation may create casing-cement debonding (microannulus). At the end of the well’s life, when the well is to be abandoned, it is essential to be able to evaluate the integrity of the cement, to decide whether the cement annulus must be repaired or replaced during the plugging operation.

In this study, we investigate the use of a pulse-echo and a pitch-catch ultrasonic tools to assess the severity of cement-casing debonding.

In the first stage, we measure the evolution of acoustic logs just after the sample preparation. We compare the evolution of the logging curves with measurements of the cement strength with Ultrasonic Cement Analyzer. We observe that for the samples cured at room temperature and pressure, the quality of the bonding first increases before the setting time, then tends to decrease due to debonding.

In the second stage, we simulate defects at the casing-cement interface by placing tape stripes of different thickness. We observe how these defects affect the acoustic logs and observe the morphology of the defects on Computed Tomography pictures, to analyze the relation between the logs and the geometry of the microannuli.
Laboratory-Scale Experiments to Predict Barite Sedimentation in Drilling Fluids in Wells
Authors: Feneuil Blandine , Lund Bjørnar , Skorpa Ragnhild
Published: September 2023

Barite sedimentation in drilling fluids at rest is a challenge for plugging and abandonment operations (P&A) of oil wells. On the one hand, the barite sediments can complicate the operations by preventing casing removal. On the other hand, they could be used as a barrier material. Therefore, it is essential to be able to understand the sedimentation process in order to predict the sealing properties of the sedimented material. As in-situ measurements can be difficult and time-consuming, it would be helpful to be able to predict the sedimentation properties of a drilling fluid from laboratory experiments. In this paper, we perform small-scale experiments on barite sedimentation and focus on how these results can be used to predict barite sedimentation at field scale.

We perform several experiments using two oil-based drilling fluids, with various barite content. First, we investigate the effect of scale by observing the drilling fluid left at rest for two months in static cylinders of different heights and diameters. We observe a phase separation in the drilling fluid columns: a layer of dark liquid appears at the top. We track the growth of the liquid layer with time and observe how it is affected by the barite content and the sample dimensions. Secondly, rheological measurements are performed on the liquid layer to investigate its composition. We also measure the yield stress of the drilling fluid, i.e., the stress required to make the fluid flow and investigate how it is related to the barite content. We observe that the drilling fluids are strongly thixotropic, as the yield stress increases from a few Pascals to several 10 Pa when left at rest for several days. Finally, we centrifuge small samples and compare phase separation caused by centrifugation with phase separation caused by static sedimentation. We note that in centrifugation tests, the liquid layer appears only if the centrifugation velocity is large enough. We discuss whether and how centrifugation can help to predict barite sedimentation at field-scale.
Probabilistic Approach for Fatigue Life Extension of Subsea Wells Using Pressure Testing
Authors: Fjeldstad Arne , Hørte Torfinn , Sigurdsson Gudfinnur , Sætre Stian
Published: September 2023

This article presents a fatigue life extension procedure for subsea wells based on probabilistic fracture mechanics analysis. The dominating fatigue loading of subsea wells occurs when a drilling rig with a marine riser and blow out preventer is connected to the subsea wellhead, imposing bending loads due rig motions and wave loads acting on the riser. The challenge of life extension of these type of components is that the fatigue governing hot spots are not easily available for inspection. This makes it difficult to document safe operation in cases when the calculated fatigue damage has exceeded the acceptance criterion specified in the design code. However, during the last decade significant effort has been directed towards reducing the external loads on subsea wells. This has made it possible to document sufficient fatigue strength for continued operation by assuming the presence of relatively large cracks. This has in turn reduced the need for using inspection methods that can detect small crack and allow the use of less efficient, but practicable methods of estimating the size of potential cracks, such as pressure testing. This article presents an approach where probabilistic fracture mechanics analysis is used to estimate the size of a potential fatigue crack based on a successful pressure test and document the time required for continued operation or plug and abandonment within the required safety level.
Response Analysis of Composite Blades of Offshore VAWT Using CFD and FSI for the Indian Ocean
Authors: Arora Prince , Parmeshwar Atkale Prashant , Prasad Patel Badri , Ahmad Suhail
Published: September 2023

Conventional HAWTs dominate the wind industry commercially, whereas VAWTs are receiving researchers’ interest now across the globe due to their inherent advantages over HAWTs. VAWTs are more suitable for the offshore environment due to their omnidirectionality and lower center of gravity. The centrifugal forces play a dominant role in the bending of the vertical axis wind turbine blades in addition to aerodynamic forces. Thus, there is a scope for the optimization of VAWT blades’ wall thickness and material such that the contributions of aerodynamic and centrifugal forces in the bending of blades are equalized. Further, the probabilistic nature of the wind causes more complexities in the system. So far, many studies have been performed employing computational fluid dynamics and FSI approaches to analyze VAWTs. However, only a few publications give insight into its structural behaviour as a result of interaction with the random nature of the wind velocity.

The present study is carried out in two steps. The first step involves the probabilistic analysis of the actual wind speed of 13 months (1 November 2017 to 30 November 2018) recorded using LIDAR in the Gulf of Khambhat, in the Indian Ocean. The probabilistic wind data is then used to estimate the wind-induced pressure on blades using the standard commercial CFD tool, ANSYS Fluent considering a three-bladed vertical axis wind turbine with a symmetrical NACA airfoil. The aerodynamic pressure is estimated based on the Reynolds-Averaged Navier Stokes (RANS) equations.

The latter part of the study involves structural analysis of the hollow composite blades of VAWT due to the aerodynamic pressure estimated from the first part and centrifugal forces due to rotation. The risk of failure arises due to the exceedance of stresses/strains beyond a threshold. Each hollow blade is modeled with different layers of material and thickness to minimize the blade mass such that the stresses/deflections are within the allowable limits and blades do not exhibit dynamic instabilities such as flutter. The study will be useful for an improved and efficient design of the VAWT in an Indian offshore environment.
Development of Phase-Resolved Real-Time Wave Forecasting With Unidirectional and Multidirectional Seas
Authors: Kim In-Chul , Ducrozet Guillaume , Perignon Yves
Published: September 2023

The development of phase-resolved real-time wave forecasting is outlined. This framework is an enhancement over previous work in that the algorithm of real-time wave prediction is extended into multidirectional seas by including the wave measurements and components in direction. However, the computations with multidirectional seas become much more numerically expensive, and hence it is often not possible to accomplish a real-time system of nonlinear ocean wave prediction. Accordingly, we suggest an improved assimilation procedure in the process of wave reconstruction, which is proven to alleviate the computational costs and establish the numerical stability of the Lagrangian approach. In addition, given an observation zone recorded by an optical sensor mounted on a fixed offshore structure, we provide a spatio-temporal prediction zone where it is suitable to obtain the prediction of the wave field by evolving the reconstructed wave information in time and space. In order to validate the phase-resolved wave forecasting, we conducted a tank-scale experimental campaign with unidirectional seas (long-crested waves) and multidirectional seas (short-crested waves). Through the comparison of model performance against the laboratory data between unidirectional and multidirectional seas, it is confirmed that the directional wave components are necessarily considered to increase model accuracy in the multidirectional case as in the unidirectional case.
Influence of Tower Design on Floating Offshore Wind Turbine Dynamics
Authors: Papi Francesco , Bianchini Alessandro , Ferri Giulio , Bruschi Niccolò , Marino Enzo
Published: September 2023

As research and industrial interests around FOWTs has grown, an aspect that has recently emerged is the fact that, because a floating foundation is inherently more compliant than a fixed one, in many instances tower resonance frequencies are effectively shifted upwards. While onshore wind turbine towers are typically designed with a soft-stiff approach, increasing tower natural frequencies often pushes them into or near the 3P excitation range; this aspect is exacerbated by the fact that blade-pitch controllers are often de-tuned to avoid controller-induced floater-pitch instabilities. A prudent solution to this issue is to stiffen the tower, placing the first side-side and foreaft natural frequencies above the 3P excitation, with a stiff-stiff approach. This may turn however into heavier towers, negatively influencing system stability but more importantly increasing tower base loads significantly. In this context, the current study aims at exploring the potential influence of careful tower design on FOWT dynamics and loads. The IEA 15MW RWT is used as testcase, since in its floating configuration it features a stiff-stiff tower. Four different lightweight towers are proposed. Base and top outer diameters are kept equal to 10 m and 6.5 m, whereas wall thickness and distributed structural properties vary with the height following similar patterns with respect to the fixed-bottom 15MW reference tower. The impact of these different design solutions is discussed in terms of performance, extreme and fatigue loading on the turbine and the floater. Results prove that improved and lighter tower designs may represent a key aspect to further improve FOWT design and operation.
A Report From the Drilling Riser VIV and Wellhead Fatigue JIP: Full-Scale Drilling Riser VIV Measurements and Comparisons With Predictions
Authors: Resvanis Themistocles L. , Vandiver J. Kim , McNeill Scot
Published: September 2023

This paper discusses some of the results and observations that were made in the Drilling Riser VIV and Wellhead Fatigue Joint Industry Project that was formed by a consortium of industry partners with the goal of studying wellhead fatigue that is caused by Vortex Induced Vibrations (VIV) of the drilling riser.

The paper focuses on presenting the field measurements of the VIV of full-scale drilling risers. The emphasis is placed on revealing the most important characteristics that need to be modelled by VIV prediction software and how modelling choices can affect the predicted VIV response. Comparisons of VIV predictions with the field measured VIV are shown and a revised set of recommended parameters is issued for use with the SHEAR7 VIV prediction program. This revised set of prediction parameters leads to less conservative response predictions on the drilling riser and lowers the wellhead fatigue. Finally, some of the challenges and limitations that exist when trying to carry out such comparisons are discussed so that future instrumentation programs can be even more fruitful.
Torque Evaluation of Cable Under Transport
Authors: Yin Decao , Mainçon Philippe , Longva Vegard , Warringa Sjoerd , Smith Carl
Published: September 2023

Flexible products such as power cables, flexible pipes and umbilicals may display torsion-related motion under handling, including production, load-out and installation. The torque encountered are a function of the shape of the route they follow, so routes must be designed to minimize the torques generated during handling. SINTEF Ocean evaluated the torque generated when handling cables with DEME’s cable installation & multipurpose vessel - Living Stone.

The objective of the study was to evaluate the relative magnitude of the “flip” torque induced by internal friction when the flexible product follows various routes: a proposed new concept (ConnecTT) is thus compared to the existing route on board Living Stone, and in particular, to the torques developed in a loading catenary (quayside chute to CLV chute), and the torque generated in the free span into the carousel. Both of these catenaries are inherent to any cable lay vessel, and therefore provide a good benchmark to compare results.
Scale Effect Study on the Resistance of a Double-Bow Ferryboat
Authors: Cascelli Luis Antonio Matile , Ordóñez Juan C. , Souza Jeferson Avila , Marques Crístofer Hood
Published: September 2023

Energy management in inland waterway transportation has become an urgent topic to address as green shipping has been receiving ever more importance from society and regulatory bodies. Since energy consumption depends on the ship’s resistance, the present work aims to simulate the sailing of a double-bow ferryboat in still water to predict accurately its resistance in model and full scale and compare the results. The numerical solution is performed with the interFoam solver, which is a standard utility to simulate multi-phase flows of incompressible, isothermal, and immiscible fluids using the Volume Of Fluid (VOF) method in OpenFOAM. Simplifying assumptions suitable to this specific problem are made, such that the incompressible Reynolds Averaged Navier-Stokes (RANS) is used herein. To close the system of equations, the SST k-ω turbulence model is employed. The numerical model is validated through experimental measurements available in the literature and then the ferryboat is simulated in both model and full scale. The resistance results for the model scale are then extrapolated to full scale and compared to the results of the full-scale simulation. Results showed that the extrapolated resistance results deviated by 8.68% on average from the full-scale simulation results.
Application of Technique for Early Consideration of Human Reliability in the Specification of the Maximum Acceptable Probability of Failure on Demand and the Maximum Spurious Operation Frequency of a Floating Nuclear Power Plant Safety Control System
Authors: Maturana Marcos Coelho , Abreu Danilo Taverna M. Pereira , Martins Marcelo Ramos
Published: September 2023

It is currently possible to say that there is consensus among experts that safety considerations are most effective when accounted for throughout the critical systems life cycle, starting from their conceptual design stage. However, this was not always the case and the available tools and techniques for safety evaluations were traditionally developed with the purpose of analyzing already installed systems, making it possible to identify expected failure phenomena and mechanisms just in more advanced stages of the system’s life cycle. With the evolution of the accidents studies, techniques applicable to the pre-operational phases were developed in order to reduce the risks posed by the system operation. Complementarily, as a fundamental part of risk analysis, Human Reliability Analysis (HRA) have a potential contribution for designing new systems. For this, it is essential to develop models able to feed analyzes at the conceptual design stage and to bring results that can support the decision-making. The Technique for Early Consideration of Human Reliability (TECHR) was developed for this purpose. This technique is based on the use of different sources of information to obtain probability estimates of various human error types that may occur during a specific action, and to estimate human error probabilities of generic actions. This paper presents a real application of a human performance model obtained by TECHR in specifying the maximum acceptable probability of failure on demand (PFD) and the maximum spurious operation frequency (SOF) of the Safety Control System (SCS) and of the SCS-D (a redundant system for the SCS) of a Floating Nuclear Power Plant (FNPP), incorporating the data presented in its Probabilistic Safety Assessment (PSA). This application showed the TECHR potential contribution to an SCS specification.
Probabilistic Economic Assessment of an Offshore Energy Hub Supplying Electrical Power to a Floating Production Storage and Offloading Unit
Authors: Abritta Aguiar Santos Ramon , Pavlov Alexey , Varagnolo Damiano , Børresen Børre T.
Published: September 2023

This paper analyzes the viability of an offshore energy hub consisting of wind turbines, batteries, fuel cells and electrolyzers connected to, and powering, an oil producing floating production storage and offloading unit. We assess these components considering an oil production setup that strives for reduced CO2 emissions. The problem is addressed from a probabilistic perspective. First, we utilize a quasirandom Monte Carlo approach to generate multiple scenarios regarding the uncertainties of the problem. Then, we evaluate the estimated net present value and total CO2 emissions of the system. As a highlight, our method is capable of exploiting a larger variety of data and capturing more sources of uncertainties compared to the literature. Open-source wind data is used to simulate wind power generation. Wind speed is modeled via a kernel density estimator to benefit the most from the data. The obtained results indicate that the renewable energy technologies enable outcomes with significant reduction to CO2 emissions. However, at the current prices of these technologies, operating a low emitting field links to the loss of a significant share of the expected profits.
Design of a Two-Body Wave Energy Converter Featuring Controllable Geometry
Authors: Tom Nathan , Ogden David , Byrne Michaela
Published: September 2023

While the field of wave energy has been the subject of numerical simulation, scale model testing, and precommercial project testing for decades, wave energy technologies remain in the early stages of development and must continue to prove themselves as a promising modern renewable energy field. A wave energy converter (WEC) concept currently being explored is the variable-geometry WEC (VGWEC), which aims to add an extra control option to WEC design. VGWECs attempt to incorporate controllable geometric features to adjust the floating body hydrodynamics to favor either power absorption, load shedding, or other operational goals. These variable geometry components have been proposed to be controlled on a sea-state-to-sea-state or wave-to-wave time scale depending on the force (or torque) and bandwidth limitations of the actuators required to manipulate just the controllable geometric hull features. Having control over both the WEC geometry components and the power takeoff (PTO) offers the potential to improve overall system performance and reliability if a cost-effective solution can be found for a given WEC architecture. This paper will present the recent developments and results of a VGWEC concept that incorporates variable-geometry modules into a two-body WEC. In the proposed VGWEC concept, the variable-geometry modules consist of air-inflatable bags in the surface float and a water inflatable ring in the subsurface body. The surface float is tethered directly to the subsurface body through tether lines, each connected to a separate PTO. Adjusting the geometry of both the surface and subsurface bodies along with the PTO coefficients can maximize power in design sea states while reducing motion response and PTO forces when transitioning to sea states where rated power is reached and load shedding is prioritized. The ability to transition between operating condition is expected to increase the sea state operational map and power capacity.
Offshore Oil Wells Integrity: Safety Analysis of an Offshore Oil Well at the Production Phase Using STPA (System-Theoretic Process Analysis)
Authors: Almeida Lucas Ribeiro de , Santos Joaquim Rocha dos , Pestana Marco Aurélio , Martins Marcelo Ramos
Published: September 2023

Despite the growing share of renewable sources, the world energy matrix still depends heavily on fossil fuels, especially oil. The exploration of this product brings severe challenges and risks which must be managed during all phases of an oil well’s lifetime. Analysis methodologies have already been developed and established to contribute to safety; however, with the growing complexity of the system, these methodologies may need a more structured way to identify some arising loss scenarios. The System-Theoretic Accident Model and Process (STAMP) deals with this problem. STAMP is a causality model that, attacking the problem from different paradigms, treats safety as a control problem, shifting emphasis from preventing failures to enforcing safety constraints. Based on a system model that spells out the control levels of a system and the control and feedback interactions between them, named SCS (Safety Control Structure), it focuses on preventing those interactions that lead the system to a hazardous condition, making it vulnerable to losses. This paper presents an analysis technique built on STAMP named System Theoretic Process Analysis (STPA), applied in the case of a submarine oil well at the production phase to highlight the benefits of using STAMP as a complement to more traditional analysis methodologies. The results conclude that STPA analysis can identify safety breaches from different sources. The first relevant source relates to the component failure events — also covered by more conventional methods such as PRA (Probabilistic Risk Assessment). The most significant contribution relates to safety breaches related to components interaction, managerial decisions, organizational factors, and others. The latter are manageable by structuring the loss scenario generation, which is the primary goal of STAMP.
CFD Investigation of the IEA Offshore 15 MW Reference Wind Turbine Performance in Full Scale: A Temporal Discretization Analysis
Authors: de Oliveira Marielle , Silva Leandro , Puraca Rodolfo , Carmo Bruno
Published: September 2023

A significant increase in wind turbine size was noticed in the past decade due to the expansion of the wind energy market to offshore sites, where steadier and stronger wind resources are available. This continuous rising in the wind turbines size leads to several design and manufacturing challenges. From the design perspective, the prediction of the flow behavior and wind turbine performance is a difficult task, since the use of reduced-scale experimental testing may not lead to a proper representation of the physics in the full scale. In this context, numerical simulations in full scale became a valuable tool to assist the design process and performance analysis of the wind turbine. This paper presents a Computational Fluid Dynamics (CFD) methodology to perform blade-resolved simulations of the IEA 15 MW Offshore Reference Wind Turbine to predict its performance. In this regard, a temporal discretization investigation is performed by testing three different values of Courant-Friedrichs-Lewy (CFL) number. The rotor performance is assessed when the turbine operates in optimal wind-power conversion efficiency, for a wind speed of 10 m/s at hub height. The results are compared against those obtained using the blade element momentum theory implemented in OpenFAST, in terms of power production, generated thrust, and distribution of forces along the blade span. The adequacy of each CFL number is assessed considering the computational cost and accuracy of the results in capturing the physics of the flow. Amongst the CFL numbers investigated, the results obtained with CFL = 1 and 2 presented similar behavior and satisfactory accuracy, while those obtained with CFL = 4 presented unsatisfactory results. Detailed information of the flow field in the wake internal gradient region and the flow structures that detach along the blade span were noticed using CFL = 1, while a significant reduction in the computational demand was achieved with CFL = 2. Based on the results presented, we concluded that for the cases being investigated in this paper, a good balance between accuracy and computational demand can be achieved using a CFL number equal to 2.
Study of the Influence of Microwave Irradiation on Hard Formation Property Alteration Through Nondestructive/Destructive Tests and Drilling/Coring Operations
Authors: Abugharara Abdelsalam , Mafazy Salum , Butt Stephen
Published: September 2023

Enhancing the Drilling Rate of Penetration (D-ROP) is a target for lowering the ultimate cost in reaching hydrocarbon reservoirs, evaluating reservoir formation, and extracting minerals and reducing rock crushing consumed energy through mining operations. It has been reported that ROP can be positively influenced depending on optimization of several factors such as drilling parameters alteration and rock fragmentation process. In this research, D-ROP is evaluated by altering the status of the formations being drilled by the use of Microwave Irradiation (MI) while all other applied parameters are kept constant. Unlike published works, this research collectively investigates the influence of MI on D-ROP of hard formation providing confirmation on rock property alteration through non-destructive tests including ultrasonic wave velocities measurement and destructive tests including Indirect Tensile Strength (ITS). Results show gradual alteration in rock properties as per MI exposure time including a reduction in P-wave and S-wave velocity, a decrease in Young’s Modulus of elasticity (E) as well as Poisson’s ratio (v). Results also show formation fractures occur when exposed to MI, which lead to a decrease in the rock strength and ultimately lead to the increase of D-ROP.
The Challenges and Opportunities for the Use of Robotic Autonomous Robotic Systems in Support of the Blue Economy
Authors: Guihen Damien
Published: September 2023

Economic activity in the marine environment requires the timely delivery of high-quality data that has both spatial and temporal relevance. Operation within this environment is complicated by the often-harsh working conditions that may pose a danger to staff and infrastructure. Robotic and Autonomous Systems (RAS) in the maritime domain, are increasingly seen as central to supporting the scaling-up of the blue economy.

In 2020, a scoping study on the use of RAS was conducted for the Blue Economy Cooperative Research Centre. The study involved engagement with representatives of the offshore energy and aquaculture industries, government regulators, and academics. The identified operating conditions and system roles are such that no one platform is sufficient. What is clear, however, is the need to couple more directly the efforts of platform designers, builders, and integrators with the anticipated needs of a growing stakeholder base.

The further development of technologies such as underwater communication and navigation, environmental sensing for situational awareness, power systems, and efficient and flexible autonomous logic will set the pace of RAS development. A framework for communicating operational context is proposed. This is based on the segmentation of industrial environmental conditions, assessment of the technology underpinning RAS, and the readiness of components.
Quality Assurance of Digital Twins
Authors: Eriksson Kjell , Markussen Christian
Published: September 2023

Digital twins, replicating the physical assets it represents, can significantly improve efficiency in the execution and operational phase. However, building robust and trustworthy digital twins that can be used for critical operational decisions, is a key industrial challenge. As a response to this challenge DNV has developed a recommended practice [1] (DNV-RP-A204) for development and assurance of digital twins. The methodology was developed in close collaboration with TechnipFMC and Aker BP and is currently being used by several leading operators and suppliers. While there are standards and commonly agreed best practices for how to assure components and systems of physical assets there is until now no common agreed standard that a digital twin can be developed, delivered, and operated according to. In the recommended practice DNV propose the following definition of a digital twin:

A digital twin is a virtual representation of a system or asset that calculates system states and makes system information available, through integrated models and data, with the purpose of providing decision support over its life cycle.

The concept of digital twins was first described by David Gelernter’s 1991 book Mirror Worlds and the term ‘digital twin’ was first coined by John Vickers of NASA in a 2010 roadmap report. The digital twin concept consists of three distinct parts: the asset, the virtual representation, and the connection between the two.

The original definitions have been included in the recommended practice, and we further propose to define the level of capability of the digital twin from descriptive, via diagnostic and predictive to fully automated solutions to increase granularity and to be able to clearly define quality assurance requirements.

The framework developed by DNV address requirements to the functionality, operations, the digital twin platform including data quality and cyber security aspects, and requirements to the organisation developing and operating a digital twin. For each of these areas clearly defined working and quality assurance processes and requirements has been defined and described.

The presentation will share the philosophy and key features of the methodology in DNV-RP-A204 as well as learnings from ongoing projects.
Relating Stress-Overshoot Measurements of Drilling Fluids to Rheological Properties by Utilizing Inertia Calculations, Oscillatory Tests and Modelling
Authors: Gjerstad Kristian
Published: September 2023

Stress-overshoot tests on drilling fluids are used to acquire information about the fluids during drilling operations in realtime. It is, however, not straightforward, for the thixotropic elasto-viscoplastic (TEVP) fluids used in many operations today, to determine exactly which properties of the mud the reported peak values reveal. In this paper we investigate this relationship by performing stress-overshoot tests on a scientific rheometer where the target rotational rate and the acceleration of the bob at start-up can be accurately controlled. This allow us to relate the responses to inertia forces. We also perform oscillatory tests and try to link results from frequency sweeps and amplitude sweeps to mud properties that can be used to describe the stress-overshoot responses. Based on this improved insight into the properties of the mud, we propose a new model that qualitatively matches the stress transients for different combinations of input parameters. The model parameters are representing physical quantities, and can therefore give useful insight into the mud properties. Such a model can also be used as a basis for predicting the behavior of the fluid in the well, for example the pressure surges at pump start-up.
On the Performance of a Data-Driven Backward Compatible Physics Informed Neural Network (BC-PINN) for Prediction of Flow Past a Cylinder
Authors: Malineni Vamsi Sai Krishna , Rajendran Suresh
Published: September 2023

This paper discusses a sparse data driven approach for training Physics Informed Neural Networks (PINNs) to solve the Navier-Stokes equation. A benchmark problem of 2D unsteady laminar flow past a cylinder is chosen for comparing the accuracy of existing PINN training approaches to the proposed methodology. The proposed training scheme is an improvement on the existing Backward Compatible PINN (BC-PINN) methodology. We have demonstrated that the performance of BC-PINN methodology in solving Navier Stokes equation is at a similar level to that of Standard PINN methodology using mini-batches. The proposed methodology resulted in a significant increase in accuracy in comparison with vanilla BC-PINN. Furthermore, transfer learning of parameters of a pre-trained model for different Reynolds numbers has resulted in a reduction of training time.
Numerical Investigation of Sloshing Inside a Column of the OC4 Floating Offshore Wind Turbine
Authors: Zhang Renjie , Liu Yuanchuan , Li Liang
Published: September 2023

Floating offshore wind turbines (FOWT) with multiple-column designs are usually ballasted with water in cylindrical columns for stability purposes. Excited by environmental loads from wind and waves, sloshing can occur inside the columns of an FOWT, which can induce significant sloshing loads and affect its dynamic responses. In the present work, sloshing in one of the three columns of the widely known OC4 DeepCwind semi-submersible FOWT is investigated numerically. A sinusoidal translational motion with a wide range of predefined excitation amplitudes and frequencies is imposed to the tank to simulate the surge response of the FOWT in waves. Effects of excitation parameters on the sloshing force and surface elevation of the tank are analyzed. The sloshing force amplitude increases linearly with the excitation amplitude but decreases as the excitation period increases. Close to the natural frequency of the sloshing tank, strongly nonlinear responses are observed in sloshing force and surface elevation. Compared to cases without the base column, the sloshing force and surface elevation are smaller when the base column is present, especially close to the natural frequency. This work will serve as a foundation for possible response control of FOWTs by taking advantage of ballast water flow.
Numerical Prediction of Dynamic Pressure Loads in a Dam Break Case With the Direct Surface Description Method
Authors: Roland Kjærgaard Qwist Jesper , Damgaard Christensen Erik
Published: September 2023

Accurate prediction of wave loads from extreme waves on individual beams in offshore jacket structures are important to ensure the structural integrity. As the load distribution along a beam is strongly tied to the wave kinematics it is crucial to have an accurate prediction of the surface elevation and the velocity field.

We have recently developed a new method called the Direct Surface Description (DSD) method in OpenFOAM (Qwist & Christensen, 2023)[1]. Here it was shown that the DSD method is superior compared to the existing official release OpenFOAM solver with respect to prediction of wave kinematics and surface elevation.

In this paper our recently developed Direct Surface Description (DSD) solution algorithm in OpenFOAM simulates a dam-break and its interactions with a solid wall.

This is a step towards improved predictions of the slamming forces when large waves impact offshore structures. In addition to the comparison of dynamics pressure loads, the paper aims to address several aspects of the DSD method including mass conservation, current handling of violent flows and effect of adaptive time stepping.