bluuebunny/crossref_metadata_2025 huggingface dataset:
Sustainable Reuse of Decommissioned Jacket Platforms for Offshore Wind Energy Accounting for Accumulated Fatigue Damage
Authors: Heo Taemin , Liu Ding Peng , Manuel Lance , Correia Jose A. F. O. , Mendes Paulo
Published: October 2022

An offshore energy transition, even if only a gradual one, from carbon-emitting fossil fuel extraction to cleaner sources is recommended, if we are to slow the harmful impacts of climate change. The potential for sustainable reuse of decommissioned offshore jacket platforms to support wind turbines is being considered as an attractive proposition in such a transition. To maximize the benefits of such reuse of assets, what is needed is a rational optimization strategy that considers the remaining life of a repurposed platform, associated retrofit and construction costs, and a future period of gross renewable energy generation following installation of the wind turbine. We outline a study that employs a fatigue reliability-based framework to aid in such sustainable reuse planning and optimization. The framework proposed identifies an optimized reuse plan that incorporates metocean data analysis, structural analysis, life-cycle evaluation, and revenue optimization. We employ a case study and sustainable reuse scenario for a site in the vicinity of Porto, Portugal.
Flow Assurance for Gas-Liquid-Solid Three-Phase Flow at High Void Fraction of Gas Phase for Methane Hydrate Transport
Authors: Takano Satoru , Masanobu Sotaro , Kanada Shigeo , Ono Masao
Published: October 2022

Methane hydrate and subsea minerals have been found in the deepwater within Japan’s exclusive economic zone. However, their development has not reached the commercialization stage because many technical issues still need to be solved.

Gas-lift pumping systems are one of the promising methods for methane hydrate transport from the seafloor to the sea surface. Since the internal flow in pipes becomes a three-phase flow for gas-lift pumping systems, flow assurance for the three-phase flow is essential to design the actual systems.

Gas supplied into pipes deep in the sea expands as it returns to the surface. Thus, the void fractions of the gas phase in lines would be larger near sea surface than near seafloor. In addition, there are few studies on flow assurance in the conditions of a high void fraction of the gas phase.

We conducted the experiment of gas-lift pumping systems using clear polyvinyl chloride pipes and resin balls as solid particles. As a result, we obtained mass flux data, void fractions, and frictional pressure drops in those conditions. Furthermore, we investigated whether the methods previously proposed clould calculate the void fractions and the frictional pressure drops in three-phase flow by comparing the calculated results with experimental data obtained from the present experiment.
Shallow Water Equations With Semi-Submerged Structures Solving a Poisson Equation for the Pressure on the Structure Surface
Authors: Schiaveto Neto Luiz André , Rosman Paulo C. C. , Aoun Tannuri Eduardo
Published: October 2022

Interaction between currents and semi-submerged structures in coastal areas is a problem of interest in naval and ocean engineering. CFD commercial codes capable of solving these problems have the drawbacks of the high cost of computational resources and time, making them unsuitable for real-time applications in ship maneuvering simulators.

This work presents a mathematical model that includes semi-submerged structures in the shallow water equations with hydrostatic assumption. The inclusion of a semi-submerged structure implies the addition of a subdomain with no free surface, replaced by the structure surface. The elevation unknown is replaced by the pressure on the structure surface, which is also unknown. Within this subdomain (for the parcel of fluid under the semi-submerged structure), the 2D-integrated continuity equation is replaced by a Poisson-type equation for the pressure on the structure.

This new model is implemented computationally using the finite element method for spatial discretization, and second order schemes for temporal discretization. The results show promising optimization of calculation time per time step, which can lead to the feasibility of real-time applications of hydrodynamic models in ship maneuvering simulators, for example.

The numerical results are compared to simulations performed with a CFD commercial code. It shows fairly good agreement in the current magnitude calculations. The elevation and structure surface results are more discrepant, albeit physically realistic. The analysis of CFD results allows concluding that the inclusion of a 3D module and dynamic pressure estimations may improve the results.
Parametric Modeling Method of Propeller and Reverse Output of 3D Model
Authors: Lu Yu , Wu Chunxiao , Liu Shewen , Gu Zhuhao , Shao Wu , Li Chuang
Published: October 2022

When optimizing the hydrodynamic performance of a propeller, a sufficient sample space for optimization calculations needs to be established and parametric modeling of the initial propeller needs to be implemented. In this paper, the parametric modeling of the propeller is programmed based on the F-spline curve fitting principle, and the radial parameter distributions of the propeller are fitted with one F-spline curve each. The idea of using fewer control variables to fit the curve accurately and minimizing the variance of the fitted points is added to the curve fitting, which greatly reduces the error between the fitted curve and the original curve. Based on the fitted propeller radial parameter curves, the parent propeller shape can be accurately described and the propeller geometry in the generated sample space is guaranteed to be smooth. The fitted curve is then used to write a program that integrates the modeling process and eliminates the need to manually complete the propeller 3D model. The implementation of parametric modeling of the propeller allows for better establishment of the relationship between propeller geometric features and propeller performance. The closed-loop nature of this modeling method ensures efficient propeller hydrodynamic performance forecasting and optimization, and improves the propeller hydrodynamic performance optimization system.
Optimization of a Flexible Flapping-Foil Thruster Based on a Coupled BEM-FEM Model
Authors: Anevlavi Dimitra , Filippas Evangelos , Karperaki Angeliki , Belibassakis Kostas
Published: October 2022

Bio-inspired thrusters designed to mimic the propulsive capabilities and mechanisms of fish locomotion pose an alternative to the conventional autonomous underwater vehicle (AUV) propeller propulsion. In this work, we examine a particular configuration of a flapping-foil thruster, employed for AUV propulsion, operating at a constant speed that undergoes prescribed heaving and pitching oscillations about its pivot axis. An optimization study is performed to determine optimal kinematic parameters and flexural rigidity distribution. The performance assessment of the device is carried out using a fluid-structure interaction (FSI) model based on ideal fluid flow assumptions and Kirchhoff-Love plate theory for cylindrical bending. The proposed coupled boundary element and finite element method (BEM-FEM) has been compared against experimental data and has been found to be suitable for the prediction of the hydroelastic response of such systems. The solver predicts the hydrodynamic forces and the flexural response of the system by treating the non-linear FSI problem. A We comparative analysis between the rigid and the passively deforming flapping-foil thruster designs deduced during the proposed optimization process is performed to illustrate that incorporating bio-inspired features leads to considerable performance enhancement.
Transferability of Meta-Model Configurations for Different Wind Turbine Types
Authors: Müller Franziska , Hübler Clemens , Rolfes Raimund
Published: October 2022

The use of meta-models of aero-elastic simulation models is increasing in wind energy. Here, the question arises whether knowledge about meta-modelling, i.e. meta-model configurations, that has been gained for one wind turbine type can also be transferred to other wind turbine types. Here, knowledge of meta-modelling or meta-model configurations means the choice of meta-model settings, e.g. the underlying functions, the choice of the sampling method as well as the required amount of training data. In this work, the transferability of the Kriging meta-model configurations is analysed for two different offshore wind turbine types, an offshore wind turbine with a monopile foundation and an offshore wind turbine with a jacket foundation. First, the Kriging settings are analysed regarding their transferability. After this, a convergence study is conducted to answer the question whether knowledge regarding the required amount of training data and the selected sampling method are transferable. It turns out that it is possible to use the findings regarding the meta-model settings from the monopile for the jacket as well. The results of both offshore wind turbines are also comparable with regard to the chosen sampling method and the convergence behaviour of the meta-models regarding the required amount of training data. Thus, a transferability of meta-model configurations is generally feasible for the investigated offshore wind turbines and the choice for a specific meta-model is quite robust.
Noise Generation and Propagation From Flapping-Foil Thrusters Used for Marine Propulsion
Authors: Malefaki Iro , Karperaki Angeliki , Belibassakis Kostas
Published: October 2022

In the present work, we focus on noise generation by a flapping foil used for small ship and AUV propulsion and its propagation in the inhomogeneous sea environment. The pressure field and the forces produced by flapping thruster motion, obtained by a BEM model, are used to calculate the dipole and monopole terms associated with the initial-boundary value problem governed by the wave equation. Initially, an acoustic model in free space based on the Farassat formulation is derived. Subsequently, the latter is extended to account for a bounded domain and an inhomogeneous medium. For simplicity, the 2D sea acoustic waveguide is considered, and the presented numerical method is based on a Finite Difference scheme (FDM), incorporating free-surface and seabed effects as well as a variable sound speed profile. Moreover, the numerical scheme is supplemented by a perfectly matched layer (PML) for the treatment of the outgoing radiating field behavior in the open boundaries. Numerical results are presented for the verification of the present method in the case of time-harmonic sources. Future extensions are discussed regarding the application of a Finite Element Method (FEM) – PML scheme to treat localized scatterers and curved boundaries as well as 3D effects.
Experimental Study of Newtonian Laminar Annular Horizontal Displacement Flows With Rotating Inner Cylinder
Authors: Jung Heeseok , Frigaard Ian , Zhang Ruizi , Renteria Alondra
Published: October 2022

During the primary cementing of oil and gas wells, it is increasingly becoming common to slowly rotate the inner casing to aid the mud displacement. We present an experimental study of laminar horizontal displacement of Newtonian fluids with rotating inner cylinder with the experimental setup detailed in (Renteria et al., J. Fluid Mech, 905, 2020). Inner cylinder rotation is able to distort the axial flow to helical. When the rotational viscous force dominates buoyancy force, the displacing fluid follows the helical flow path and displaces the in situ fluid azimuthally around the annulus. The dimensionless rotational speed is defined as the ratio of rotational velocity and axial velocity, which determines the degree of azimuthal dispersion. Even in a buoyancy-dominant displacement, inner cylinder rotation acts to increase the dispersion. Displacement efficiency analysis shows that increasing rotational speed results in improved displacement. For high eccentricity cases, bottom side residual fluids are observed, which can easily be removed by rotating the inner cylinder. In practice, where the entire length of casing is rotated, the effect of rotation is expected to be more significant and improve the displacement.
Experimental and Numerical Studies on the Axial Bearing Behaviour of a Pile Due to Relevant Foundation Fill Material on the Coastal Tidal Flat
Authors: Yao Juntian , Shen Kanmin , Wang Kuanjun , Yu Jian , Huang Maosong
Published: October 2022

The control centers of wind power plants are usually located in coastal tidal flat areas. To ensure the design elevation of the control centres is maintained above the water table, a thick fill will be placed on the original ground level. However, the filling would cause a long-term ground settlement and further lead to the development of the NSF (short for negative skin friction) of the pile foundations for the control centers. In this study, a series of full-scale axial compressive tests were conducted to investigate the effect of fills on the pile bearing behaviour. The numerical analysis method is also established to study the influence of additional ground pressures on the pile axial bearing behavior over time and the influence of NSF caused by consolidation on pile bearing capacity. The rationality is verified by comparisons with the full-scale tests. Finally, a simple procedure is further employed to study the evolution of the long-term pile bearing behavior.
Full-Scale Unsteady RANS Simulations of a 5500DWT Self-Propulsion Tanker
Authors: Ye Bin , Yu Jiawei , Zhang Zhiguo , Long Xin , Feng Dakui
Published: October 2022

Accurately predicting the ship’s speed power performance is a key step in calculating the ship’s energy efficiency design index (EEDI). Recently, numerical simulation using CFD has become a reliable method for predicting the performance of full-scale ships. However, the accuracy of full-scale simulation is still difficult to validate, for the high cost of full-scale sea trials. In this study, the in-house URANS solver based on finite difference method and structured overset grid technology is used for simulation. The PISO algorithm is employed to solve the pressure field, and the six-degree-of-freedom motion (6DOF) equation of rigid body is introduced to predict the ship’s 6DOF motion. The level-set method is adopted to capture the change of free surface. Hydrodynamic performance of a 5500DWT tanker is studied. Firstly, the resistance of the tanker model in calm water is caculated and compared with the towing tank results, and the numerical uncertainty is studied, and then, full-scale self-propulsion performance of the tanker has been simulated. Besides, the sea-trial results of the tanker have been analyzed and corrected to the ideal conditions based on the ITTC sea-trial guidelines and the ISO 15016: 2015 standard. The numerical simulation results were directly compared with the corrected results and showed quite good agreement, which verified the reliability of the CFD solver on the simulation of full-scale ship performance.
Experimental Investigation on Hydrodynamic Forces of Semi-Submerged Cylinder in Combined Steady and Oscillatory Flow
Authors: Hu Tengyan , Ren Haojie , Shen Jiawei , Niu Zhibo , Zhang Mengmeng , Xu Yuwang
Published: October 2022

The hydrodynamic forces on the semi-submerged cylinder under the combination of steady and oscillatory flow are experimentally investigated. The semi-submerged cylinder is forced to move with different periods and amplitudes as towing in the still water to simulate the equivalent combined flow. Compared with the steady flow and oscillatory flow, the feasibility of Morison equation, the hydrodynamic coefficients including drag and added mass coefficients are respectively studied. The results show that the hydrodynamic forces on semi-submerged cylinder in these three types of flows under non-overtopping and overtopping have very different features. The Morison equation is further verified that it can well describe the hydrodynamic force on the semi-submerged cylinder in steady flow and oscillatory flow, while its limitation under combined steady and oscillatory flow when the overtopping occurs is clearly witnessed. The modified Morison equation by changing the of flow velocity squared term to the higher order index term is then proposed. The flow velocity indexes in the modified equation under the non-overtopping and overtopping conditions are respectively determined. The magnification of flow velocity indexes can be clearly found when the overtopping starts to happen. The maximum index can reach 4.4. Moreover, the distributions of drag and added mass coefficients with Froude number and KC number are also observed. This work can provide a useful reference for the design of related marine structures and more valuable guidance for future research.
Numerical Modelling of Liquefaction Around Marine Structures - Progress and Recent Developments
Authors: Windt C. , Goseberg N. , Schimmels S. , Kudella M. , Shanmugasundaram R. , Rusche H. , Sumer B. M. , Kirca V. S. O. , Vanjakula V. , Adam F. , Majewski D. , Kazimierowicz-Frankowska K. , Hrycyna Grzegorz
Published: October 2022

The liquefaction around marine structures can lead to severe structural failure and the susceptibility of seabed soil to liquefaction at a specific installation site of, e.g., floating offshore wind turbines should be included within the design process and site evaluation. To that end, advanced prediction tools based on numerical modelling can provide valuable insight into the hydro-geotechnical processes. However, due to the complex interaction of the underlying physics, developing a holistic modelling framework for seabed liquefaction is a challenging task. The NuLIMAS research project (Numerical modelling of seabed liquefaction around marine structures) aims at the development of such a numerical model of seabed liquefaction implemented in the OpenFOAM® framework. This paper provides an overview of the NuLIMAS project, laying out the current state of the art of experimental and numerical modelling approaches for seabed liquefaction and presenting some initial results.
Effect of Temperature on Resistance to Hydrogen Embrittlement of Dissimilar Metal Welds Subjected to SENB and SENT Testing
Authors: Dodge Michael , Haldorsen Lars Magne , Gittos Mike , Sotoudeh Kasra
Published: October 2022

Dissimilar metal welds (DMWs), as manifested by low alloy steels welded with nickel alloys, are commonly used in subsea production systems. In such applications, there is a risk of hydrogen embrittlement, due to the use of cathodic protection. Historically, one of the most reliable means of establishing the resistance of DMWs to hydrogen embrittlement has been to conduct fracture mechanics-based tests, under representative service conditions. These tests have proved valuable in ranking the performance of various DMWs and, also, emulating the fracture morphologies observed in many subsea failures.

Much of the established data from these tests has been generated using single edge notched bend (SENB) specimens, tested at the seabed temperature, to produce ‘tearing resistance’ J R-curves. However, whilst it is recognized that most failures have occurred after equipment has been shut down, there has been little exploration of how parameters, such as temperature and loading mode, influence the resistance to hydrogen-assisted cracking. This paper uses the results of SENB and single edge notched tension (SENT) tests on DMWs, consisting of 2.25Cr-1Mo Grade F22 welded with ERNiCrMo-3 (Alloy 625), to understand how temperature and level of constraint affect fracture resistance, at a range of temperatures (4 to 80°C). The merits and drawbacks of both techniques are summarized, alongside the practical implications for subsea components currently in operation.
Pipeline Reel-Lay FE Simulation: An Advanced Material Model Calibrated From Testing
Authors: Giry Eric , Shen Chen , Stableford Richard
Published: October 2022

For small to medium size rigid pipelines, reel-laying is an efficient installation method. Higher lay rates are achieved thanks to unreeling rigid pipeline down to seabed. However, the process is mechanically onerous. Pipelines go through successive large bending strains up to 2% or 3%. This is the primary degradation mechanism and affects the mechanical in-service performance of the subsea line. Assessment of material response to the installation sequence is a key point for pipeline engineering. Conventional monotonic material stress-strain relation or cyclic Ramberg-Osgood models are not suitable for repeated large bending sequences or reel-lay installation FE simulations. A parameter-based material model has been tailored for carbon steel seamless pipe under reeling. The evolution of the material behaviour from the first load to stabilised cycle is addressed, by introducing an Abaqus User Subroutine written in FORTRAN. The material properties are programmed in each straining cycle, then active in their corresponding loading cycle. Specimens from DNV450 grades pipe have been tested in an extensive small-scale test and bending trial campaign in order to calibrate finite element model. DIC is used during tensile test and LCF (Low Cycle Fatigue) test to allow accurate measurement on large straining ranges. The parameter-based model can provide response to the first load, including Lüders plateau, up to stabilized hysteresis loop; it is fully parametric by Python. Comparison is made with the more conventional material model or full-scale bending trials demonstrating improved accuracy and agreement with testing. The proposed material model is part of an in-house material model library integrated in a numerical tool package dedicated to rigid pipeline design.
Methodology for Installation of Under-Straight Pipe for Lateral Buckling Mitigation
Authors: Roy Alan , Sriskandarajah Thurairajah , Gunawan Suwarno , Ragupathy Pasupathy , Roberts Graeme , Kassim Yasin , Cederfeldt Markus
Published: October 2022

The residual curvature (RC) method has been implemented by Subsea 7 for lateral buckling mitigation on various projects in recent years. The method involves deploying short sections of under-straight pipe in the catenary from a reel-lay vessel. The objective of this paper is to present RC results on bending moment and curvature and to show how these results can be combined with those from dynamic Orcaflex runs to predict the allowable sea-state for installation.

ABAQUS models to simulate the reeling/unreeling/straightening procedure on one of Subsea 7’s reel-lay vessels are presented, together with a description of the settings adjustment to achieve under-straight pipe with a prescribed level of residual plastic strain. These models describe the pipe profile on the reel, free-span, aligner, passage through the straightener and finally within the catenary to the seabed. The model is used to simulate the deployment of an RC section and to quantify its tendency to rotate in the sag-bend. The dynamic loads are captured by running an equivalent RC section model in Orcaflex.

Results for installation of a typical 14″ × 18″ pipe-in-pipe (PIP) are presented in 115m water depth (WD). Plots showing the spatial distribution of the bending moment and curvature of the RC section at various time increments within the catenary are provided. Attention is focused on the sag-bend. Stress-strain hysteresis loops are presented showing the multiple bending cycles experienced by the RC section from initial spooling-on until eventual deployment on the seabed.

The impact that the RC length, residual plastic strain and ramp angle has on the bending moment/curvature is discussed. Orcaflex results are presented which show dynamic change in curvature at the sag-bend over a typical three-hour interval due to vessel motion. The most characteristic dynamic load (Ref. /15/) on the RC section is calculated to establish the loading envelope seen in the sag-bend region. Checks are also undertaken at other locations to ensure that the dynamic loads are not introducing any additional residual plastic strain in the RC section.

The maximum bending moment seen by the RC section in the sagbend has an important bearing on the allowable sea-state for installation. The presented methodology for calculating the allowable sea-state (combining results of static and dynamic simulations) is a novel feature in the present work.
Roll Stability Evaluation of the Floating Multi-Body System at TML (Twin Marine Lifter) Operation
Authors: Meng Xun , Deng Xingqi , Zhao Shujie , Li Dejiang , Fu Qiang
Published: October 2022

Twin Marine Lifter (TML) is a specially designed heavy-lifting system consisting of two vessels for offshore installation & decommissioning. The system is developed multi-functionally in the heavy lifting sector to be cost-effective. Conceptually, they can be used in tandem for the platform installation and decommissioning of both topsides and jackets or carrying out by single lift configuration for other offshore construction tasks such as wind farm equipment installation. These flexible and versatile solutions to a wider range of potential clients also constrain the shape and the main particulars of the vessels, which results in extra challenges coming from the stability properties of the specific multi-body system compared to traditional single vessel operations, and there are few literatures could be referred to.

In view of the highly complicated motions in the multi-body system at lifting phases, the topological model reflecting the flexible connections among bodies in system during the operation is constructed to obtain theoretical estimation of the roll stability of the targeted decommission topside. The virtual prototype technology based on ADAMS (Automatic Dynamic Analysis of Mechanical Systems) considering the coupling boundary of control factors including capability of the DP power and the compensation system are introduced by experimental data to correctly estimate the influence of multi-body motions on the roll stability of the topside in a synchronized way. A fast analysis and prediction methodology on the roll stability limiting criteria of the multi-body system is proposed. It would provide a safety guarantee and technical support for the design of the specific apparatus and the successful decision making on schemes of a new type of offshore operation mode.
Generation of Controlled Irregular Wave Crest Statistics in a Numerical Wavetank Using HOS-NWT Solver
Authors: Canard Maxime , Ducrozet Guillaume , Bouscasse Benjamin
Published: October 2022

In order to assess the reliability of offshore structures facing extreme environmental conditions, sea keeping tests are performed at model scale in experimental or numerical wave tanks. The scope of the present paper is limited to the generation of wave condition for such tests. The vast majority of industrial practices follow a stochastic approach. For each design sea state, several realizations of long irregular wave sequences are generated. The qualification of the waves mainly relies on the analysis of the mean spectrum and the ensemble crest height distribution at the structure (target) location (Xt). However, the wave propagation from the wavemaker to Xt is affected by nonlinear mechanisms and dissipation phenomena which lead to uncontrolled variations of the quantities of interest. To face those issues, the most advanced wave generation procedures usually focus on the quality of the wave spectrum at Xt, iterating on the wave maker motions. Nevertheless, depending on Xt, the crest height statistics can significantly differ. For instance with steep and narrow-banded unidirectional sea states, the distributions obtained at target locations far from the wave maker (Xt > 20λp, λp being the peak wavelength) enlighten a significant number of extreme events that are likely to strongly affect the response of the tested structure. On those grounds, the present study proposes a procedure that offers the possibility to reproduce those extreme statistics at locations closer to the wavemaker. The framework is limited to non breaking unidirectional waves. The procedure is numerically tested with the open-source nonlinear potential wave solver HOS-NWT. The study opens the way to an accurate control of the wave statistics at any location in a wave tank environment.
Estimating Joint Extremes of Significant Wave Height and Wind Speed for Tropical Cyclones
Authors: Sando Kosuke , Wada Ryota , Rohmer Jeremy , Lecacheux Sophie , Jonathan Philip
Published: October 2022

We provide a computationally-efficient scheme for the estimation of joint extremes of significant wave height (Hs) and wind speed (U) for tropical cyclones. The method incorporates the simple spatial extremes method (STM-E) of Wada et al., 2019 (for spatial extremes of each of Hs and U) and the conditional extremes model of Heffernan and Tawn, 2004 (for conditional modeling of Hs given extreme U and U given extreme Hs). We demonstrate the methodology in application to data generated from hindcast simulations and track shifting of past tropical cyclones in the neighborhood of Réunion island in the Indian Ocean. Following the STM-E approach, spatio-temporal maxima (STM) and exposures (E) of both Hs and U are extracted for each tropical cyclone event. Marginal extreme value distributions are then estimated independently for the STM samples of Hs and U, providing a means for marginal extrapolation to long return periods. Exposure data are used to estimate densities for the spatial distribution of Hs and U. The conditional extremes model is then used to characterize the joint structure of STM for Hs and U, conditional on one of those variables being extreme. The estimated joint return values for Hs and U are validated by comparison with the original data.
Prelude FLNG Free Weathervaning Heading Prediction and Uncertainties, Based on Machine Learning Model
Authors: Delivré Quentin , Rajaobelina Jery , Kang Mengchen , McConochie Jason , Drobyshevski Yuriy
Published: October 2022

Prelude Floating Liquefied Natural Gas (FLNG) facility is moored with an internal turret allowing it to free weathervane (FW), i.e. by leaving the unit to rotate according to environmental loads. During the engineering phase, the FLNG FW heading is estimated by the heading analysis (i.e. physics-based approach), and results are then used as input for other studies.

Therefore, a good estimation of the various environmental effects (waves, current and wind) and their contributions in terms of loads on the FLNG is critical to ensure a correct prediction of the FW heading. For the predominant contributions (wind and current), the force coefficients have been initially derived from wind tunnel tests during the engineering phase. However, Prelude FLNG being now installed on-site, measurements over recent years have shown slight discrepancies with the numerical predictions by the heading analysis.

Preliminary investigations were carried out and were aimed to improve some parameters of the numerical model. Nevertheless, it appeared that even with these improvements, discrepancies between numerical predictions and measurements were not always resolved. These discrepancies may have several origins, such as inadequacy of the numerical model, variability of the metocean data, uncertainties in measurements, etc.

In order to overcome the aforementioned uncertainties and unknowns, it has been decided to set-up a machine learning model (i.e. data-based approach). This machine learning model (RBF ANN - Radial Basis Function Artificial Neural Network) was trained with the recorded metocean data (input) and measured FLNG FW heading (output). Considering the amount of the measured data available (two years with a time step of 10 minutes), the necessity to optimize the model’s hyperparameters and the computer capability, a stepwise approach has been applied to ensure an accurate model can be built in a reasonable timeframe.

Finally, the machine learning model calculation shows a significant improvement in the prediction capability when compared to the measured FLNG FW heading. The resulting surrogate model is hence used to predict the FW heading and to derive the associated prediction intervals, which define the range of error with certain probability (for instance 95%). This paper describes the machine learning model used, the methodology and challenges of the approach, and discusses the results. The main conclusions and lessons learnt are also shared.
Simulation of a Ship Advancing in Pre-Sawn Ice
Authors: Huang Luofeng , Li Fang , Li Minghao
Published: October 2022

Pre-sawn ice test is the standard testing method to negate ice-breaking resistance from the whole resistance of a ship breaking level ice, which is of great importance for understanding ship-ice interactions and predicting various sea-ice loads on ships. This work has developed a computational model that can realistically simulate a ship advancing in a pre-sawn ice channel. The model applies Computational Fluid Dynamics to solve ship hydrodynamics, which is coupled with a novel particle-bonded Discrete Element Method to model pre-sawn ice pieces. Experiments were also conducted to validate the simulations. Upon validation, analyses were performed to investigate the ship-ice interaction. It was demonstrated that the pre-sawn ice resistance’s speed dependence has three regimes: for low ship speeds, the ice resistance slightly increases with decreased speed due to ice piling up; for middle ship speeds, the ship-ice interaction could remain similar and there is no distinctive change in the ice resistance; for high ship speeds, ice resistance evidently increases with increasing ship speed, which results from strong ship-ice collisions that cause ice pieces to move dramatically.
Importance of Numerical Analyses to Inform Laboratory Testing for Offshore Slope Stability Assessment
Authors: Carlton Brian , Suroor Hadi , Choi Young Jae , Hansen Ragnhild , Nadim Farrokh , Saqab Mudasar , Kaynia Amir M
Published: October 2022

An offshore pipeline will cross a series of steep rocky escarpments. Borehole samples show that there are thin layers of uncemented sand deposits at the head and middle of the largest escarpment. Bathymetry data also show evidence of past landslide activity, and the escarpments lie in a moderately seismic area. As a result, advanced, site-specific slope stability analyses were carried out to assess the failure potential of the slope in the event of project-specific design earthquakes. Analyses included deterministic and probabilistic static and pseudo-static slope stability analyses as well as dynamic time domain analyses. The initial results showed unacceptably low factors of safety against slope instability in the event of an earthquake based on empirically derived soil parameters. Consequently, additional advanced laboratory testing was performed to characterize better the dynamic properties and strength of the critical soil layer, and the pseudo-static and time domain analyses were repeated. Using the updated soil properties, the factor of safety and expected displacements during seismic shaking were reduced to satisfactory levels. The case history presented in this paper provides a clear example of the benefit of performing additional advanced laboratory testing to reduce uncertainty after numerical analyses have identified critical soil layers.
Procedure for Torsional-Vibration Calculations in Ice
Authors: Kistner Gunnar , Lal Kevin , Klüss Jörn , Kaeding Patrick
Published: October 2022

The safety of navigation at sea is closely connected to the reasonable operation of the marine power transmission system of a vessel. The propulsion unit inside a ship is considered as one of the most significant on-board systems that is mostly subjected to dynamic loading. The dynamic behaviour can cause various vibrations along the propulsion line that will substantially affect the propulsion shaft’s reliability and efficiency. One vital factor that can influence the shafting design is the shafting vibration behaviour, particularly the torsional vibration behaviour.

This paper focuses on developing a FEM based Torsional Vibration Calculation (TVC) method to identify and examine the vibratory stresses arising in the propulsion shaft line of a container vessel with a new design approach of TVC analysis in ice conditions. The aim is to model the ice-based response of the propulsion system for different loading conditions and obtain the results in time-domain. Therefore, it has to be a completely numerical based approach. The developed method gives the dynamic response of the shafting system subjected to torsional vibrations for different engine operation conditions that are based on the Finnish-Swedish Ice Class Rules (FSICR).
Numerical Investigations on Ultimate Strength of a Double Hull VLCC Under Combined Loads and Initial Imperfections
Authors: Lindemann Thomas , Okpeke Bright Ebikemefa , La Ferlita Alessandro , Mühmer Markus , Kaeding Patrick
Published: October 2022

Nonlinear finite element analyses are performed to determine the ultimate strength of a double hull VLCC under pure vertical, horizontal and biaxial bending. A parametric finite element model is developed and the influence of nonlinear material behavior, mesh size and model length on the hull girder ultimate strength is demonstrated exemplarily for hogging and sagging conditions. An appropriate parameter configuration with respect to numerical efforts and accuracy is used to perform static implicit analyses for horizontal bending and biaxial load cases. Convergence is reached by using the full Newton-Raphson scheme — an incremental iterative solution approach. The results are validated against the well-established Smith method. Due to welding, initial deflections and residual stresses are produced. For the proposed finite element model initial deflections of plating and stiffeners have been considered. Furthermore, the influence of welding residual stresses on the ultimate hull girder strength is demonstrated for the different load cases. Nonlinear finite element analyses are also performed to determine the residual strength of the damaged double hull VLCC under combined loads. Different symmetric grounding damages are implemented by removing structural components of the model. Expectedly, the results show that the ultimate strength of the structure decreases as the damage extent increases.
Design of a Prototype Renewably-Powered Offshore AUV Servicing Platform
Authors: Haji Maha N. , Tran Jimmy , Woodcock Luke , de Weck Olivier L.
Published: October 2022

This paper describes the design, fabrication, and field testing plans of a 1:2 Froude-scale prototype of a Platform for Expanding AUV exploRation to Longer ranges (PEARL). PEARL is an autonomous floating platform that utilizes renewable energy to recharge docked AUVs, while simultaneously uploading their mission data to a high-bandwidth low-Earth orbit satellite constellation for remote access and monitoring. The prototype has a diameter of 2.28 m, a draft of 1.04 m, and a mass of 147.42 kg. It is equipped with two 110 W solar panels, a 100 Ah battery, and two 205 N (46 lbf) electric trolling motors. A suite of environmental sensors are integrated on the platform constantly measuring air and water quantities to mimic the data transfer needs of an AUV. The prototype was field tested for six months in Deep Pond in Orleans, MA to test solar power generation, autonomous data logging, autonomous data transmission via the Iridium satellite network, and autonomous manuevering via MOOS-IvP.
A Strategy for the Reduction of Structural Weight of Composite Vessels
Authors: Gaiotti Marco , Vergassola Gianmarco , Pais Tatiana
Published: October 2022

Hull weight is a main structural concern in pleasure craft design, being in such project the maximum speed one of the most important contractual limits imposed by owner to shipyards. This is particularly true for composite structures, where the structural layouts and the beams’ dimensions may vary significantly among very similar projects, resulting in very different structural weights. Moreover, for this type of vessels, the structural weight is a significant percentage of the total displacement, and, consequently, reducing the structural components leads to important total weight reduction.

The present work aims to orient the preliminary design stage of composite pleasure yacht structural design towards an optimal configuration of the structural layout in terms of hull weight, within the current framework of rules provided by classification societies.
Metocean Database of the North Sea
Authors: Chu Kai , Breugem W. Alexander , Decrop Boudewijn
Published: October 2022

To fulfil the needs of using reliable metocean data, IMDC North Sea Metocean Database has been constructed based on a long-term hindcast simulation of in-house ICSM model for 26 years from 1995 to 2020. The North Sea Metocean Database provides 26-year time series of water level and velocity data with 10-minute interval at +15,000 specific sites including all the conventional measurement stations and all the present wind farm sites inside of the North Sea. Online statistics were performed during the 26-year hindcast simulation, providing various statistics on water level and velocities, serving as a reliable data source for offshore engineering projects in the North Sea.
Ice Pressure Measurements With TekScan Sensors - Behaviour, Calibration and Application Limits
Authors: Kubiczek Jan M. , Herrnring Hauke , Kellner Leon , Ruckert Phil , Ehlers Sören
Published: October 2022

Ships and offshore structures operating in ice-covered sea areas have to withstand ice loads. In particular, the distribution of ice pressure in the contact area is critical. The pressure distribution changes temporally and spatially and depends on the ice failure behaviour. Experimental measurements of ice pressures are possible with pressure mapping systems. A commonly used system in academia uses sensors manufactured by TekScan. The resulting measurements can be used to gain insight into ice failure behaviour, to establish design pressure patches, and to develop numerical models. However, various issues emerge when using these pressure measurement systems, e.g., equilibration and calibration, which result in measurement uncertainties. Hence, this paper summarize and discuss possible issues and gives recommendations to address them.
Generating a Digital Twin of the Glen Lyon FPSO
Authors: Bailey Jonathan , Bamford Richard J. , Das Suvabrata , Maroju Soma S. , Barker Robert J.
Published: October 2022

A Digital Twin has been developed for the Glen Lyon FPSO to maintain vessel integrity and ensure operation within the allowable design limits. At the core of this Digital Twin are two components: the Integrated Marine Monitoring System (IMMS) installed on the FPSO, and BMT DEEP, a cloud-based platform that stores, manages, integrates, post-processes and displays the vast data sets collected by the IMMS as well as other data sources. This paper focuses on harnessing the benefits of Digital Twin Technology, by bringing in data from all sources and enabling to synthesize and monitor the FPSO in near real-time from any remote location. This Digital Twin is designed to allow rapid query of the data by filtering with any time window in terms of hour, day, month, quarter, and year of data collection for the life of the asset.

Several sensors feed data to the Glen Lyon IMMS. The sensors include FPSO motion, stress response monitoring, and metocean monitoring. In addition to the FPSO based measurements, metocean data is also available from Met Office weather buoy K7, and wind measurements from the nearby Clair platform. A composite of the measured metocean parameters is generated from the quality control of the data. This quality-controlled data is visualized on DEEP as a time series, as well as comparisons with the basis of design data for the facility in terms of several statistical charts that form the metocean and structural dashboards. Some key insights and findings from these comparisons are presented.
Picking the Optimum Directional Drilling Technology (RSS vs PDM): A Machine Learning-Based Model
Authors: Nour Muhammad , Farahat Mohamed S. , Mahmoud Omar
Published: October 2022

Introducing rotary steerable systems (RSS) to the drilling industry has extended the directional drilling envelope to new horizons. Its role in better hole cleaning, faster rate of penetration (ROP), and less stuck pipe incidents is unquestionable. However, it comes with more economical challenges in terms of operating rates and Lost-in-Hole (LIH) charges. Many factors control the operator decision to run RSS rather than positive displacement mud motors (PDMs) — which have been the industry standards for decades — and vice versa. The intent of this paper is to introduce an advisor system based on machine learning that makes the selection process easier and more straightforward.

The system predicts total section time (including casing running) and cost for both RSS and PDM, the user may use either section time or cost criterion to assess which technology is preferred based on drilling campaign needs. The system input features include offset data of interval measured length, formations encountered, ROP, dogleg severities, operating cost of both technologies, rig operating cost, and many other variables. Input data to the system are divided into training and testing data for more reliable modeling. Many algorithms are tested to avoid over-fitting or under-fitting of training data.

The past performance of both RSS and PDM technologies in different formation plays a major role in determining the result. The result comes in both visual and tabulated forms to give the drilling engineer both quick impression and detailed insights about the selection process. As the result depends on formation-specific performance, it would change between wells depending on the formations thickness at these wells. This means that the result is not fixed per field and may vary considerably based on small changes of input.

The use of this advisor system should help in speeding up operator companies’ decisions and improving drilling performance and cost-effectiveness. This occurs through automating the whole process and making best use of offset drilling data thought implementation of machine learning algorithms.
On Rogue Waves Generated by Abrupt Depth Transitions
Authors: Li Zhenhao , Tang Tianning , Draycott Samuel , Li Yan , van den Bremer Ton , Adcock Thomas
Published: October 2022

Wave propagation over variable bathymetry is known as one of the possible mechanisms that can provoke rogue waves. In this paper, we use a fully nonlinear potential-flow solver, Ocean-Wave3D, to simulate the process of waves propagating over variable bathymetry and analyse the kinematics under the free surface near the top of the slope. To achieve this, we first evaluate the accuracy of the numerical results generated by Ocean-Wave3D. We carry out convergence tests to examine the influence of different parameters in OceanWave3D on the numerical results. Based on verification and validation tests, we evaluate the accuracy of OceanWave3D for problems with variable bathymetry comparing numerical and experimental results. We find that OceanWave3D is accurate enough to solve equations for problems with abrupt depth transitions and the agreement between experimental results and numerical results is good. Finally, we investigate the kinematics and we find that a slope can not only amplify crest amplitudes but also increase the wave kinematics near the top of the slope, which has obvious implications for loads on offshore structures.