bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mooring Designs for Floating Offshore Wind Turbines Leveraging Experience From the Oil & Gas Industry
Authors: Ma Kai-tung , Wu Yongyan , Stolen Simen Fodstad , Bello Leopoldo , ver der Horst Menno , Luo Yong 
Published: October 2021

Abstract
As renewable energy developers start venturing into deeper waters, the floating offshore wind turbines (FOWTs) are becoming the preferred solutions over fixed supporting structures. Many similarities can be identified between a FOWT and a floating oil & gas facility, such as floater concepts (spar, semi-submersible, tension leg platform, etc) and their mooring system designs. This paper focuses on the mooring designs for FOWTs by leveraging the extensive experience gained from the offshore oil & gas industry. Similarities and differences are highlighted in design criteria, mooring analysis, long-term integrity management, installation method and project execution. The established practices regarding mooring design and analysis are reviewed. Anchor radius is recommended based on water depth by referencing sample mooring designs from the oil & gas industry. Long-term mooring integrity and failure rates are summarized. Meanwhile, a few well-known issues are discussed, such as line break due to fatigue, corrosion on chain, and known issues with components such as clump weights. Regarding mooring installation, the established method for prelay and hook-up is reviewed. Finally, opportunities for cost reduction of mooring systems of FOWTs are presented related to project execution of large scale wind farms as well as potential areas of innovation, such as installation methods, use of synthetic fiber rope, and digitalization. In summary, the state-of-the-art practices from the oil & gas industry are reviewed and documented to benefit the developments of upcoming FOWT projects.
Experimental and Numerical Study of the Influence of Drag Coefficient on Snap Loads in Mooring Lines of a Floating Offshore Wind Turbine
Authors: Guillouzouic Brendan , Pétrié François , Lafon Vincent , Fremont Fabien 
Published: October 2021

Abstract
Mooring is one of the key components of a floating offshore wind turbine since the mooring rupture may lead to the total loss of one or even several turbines in a farm.
Even if a large experience in moorings of floating bodies was gained in the oil & gas industry, the renewable energies face new challenges such as reducing the cost as much as possible, reducing the footprint to limit environmental impact or avoid any interference between mooring lines and electrical cables in a farm composed of several tens of turbines.
Those constraints may lead to designs suffering snap loads which shall be avoided as far as practicable or addressed with a particular attention, as this quasi-instantaneous stretching of the mooring lines may lead to very high tensions governing the design.
This paper presents the results of physical model tests and numerical simulations performed on a typical floating wind turbine concept of semi-submersible type. Both qualitative and quantitative comparisons are performed. The objective is to provide guidelines for FOWT mooring designers regarding the selection of the drag coefficient to consider.
A very significant influence of the line’s drag coefficient, on both the probability of occurrence and the magnitude of snap loads, was found. This subject is hereby fully documented on a given case study and general discussions on scale effects, marine growth effects and other parameters are also made.
The numerical simulations were performed using the dynamic analysis software ‘OrcaFlex’.
The experiments have been carried out by Océanide, in south of France.
Numerical Estimation of Relative Wave Elevation on a Semi-Submersible Vessel
Authors: Lena Christian , van Basten Batenburg Rinnert 
Published: October 2021

Abstract
Ambition of this research was to numerically reproduce the relative wave elevations measured on and around a semi-submersible vessel during model tests performed at MARIN (Maritime Research Institute of the Netherlands).
Model tests were performed on a semi-submersible model representing, in different setup configurations, a heavy lift vessel and a LPD (Landing Platform Dock). Relative wave elevations were measured at 47 locations on and around the vessel. Tests were made with different regular wave conditions and headings, at anchor, with the model fixed in a soft mooring setup. Data from model tests were used to calibrate and run a time domain potential flow boundary element tool with particular focus on the relative wave elevation at the 47 locations. A comparison between numerical and experimental results is proposed in this paper.
Implementation of a Method for Free-Spanning Pipeline Analysis
Authors: Gullaksen Joannes 
Published: October 2021

Abstract
The scope of this paper is to provide a method implemented in an application for assessment of dynamic response of free spanning pipelines subjected to combined wave and current loading. The premises for the paper are based on application development within pipeline free span evaluation in a software development project. A brief introduction is provided to the basic hydrodynamic phenomena, principles and parameters for dynamic response of pipeline free spans. The choice of method for static and dynamic span modelling has an influence on calculated modal frequencies and associated stresses. Due to the importance of frequencies and stresses for fatigue and environmental loading calculations, the choice of analysis approach influences the partial safety factor format. The aim of the structural analysis is to provide the necessary input to the calculations of VIV and force model response, and to provide realistic estimations of static loading from functional loads. Environmental flow conditions are implemented in the application, such as steady flow due to current, oscillatory flow due to waves and combined flow due to current and waves. Combined wave and current loading include the long-term current velocity distribution, short-term and long-term description of wave-induced flow velocity amplitude and period of oscillating flow at the pipe level and return period values. Inline and cross-flow vibrations are considered in separate response models. For pipelines and risers, modes are categorized in in-line or cross-flow direction. A force model is also considered for the short-term fatigue damage due to combined current and direct wave actions. Design criteria can be specified for ultimate limit state (ULS) and fatigue limit state (FLS) due to in-line and cross-flow vortex induced vibrations (VIV) and direct wave loading.
Pressure Losses Generated by a Thixotropic Fluid When Subject to an Oscillating Flowrate
Authors: Cayeux Eric , Leulseged Amare 
Published: October 2021

Abstract
Rapid variations in the fluid velocity field influence pressure loss calculations. In this paper, we propose numerical methods for estimating pressure losses in a circular pipe when the flow rate oscillates. The method is described for Newtonian and two non-Newtonian rheological behaviors: the power law and the Quemada models. Also, as drilling fluids are usually thixotropic, i.e., their rheological behavior depends on the shear history, an expansion of the Quemada model is proposed to account for shear history effects.
A laboratory flow-loop has been assembled and measurements conducted with a non-thixotropic aqueous solution of Carbopol and a thixotropic potassium chloride solution of xanthan gum. The measurements were analyzed and compared with estimates made with the proposed models.
It is found that when applying a square wave oscillating flowrate to a non-thixotropic fluid, large surge and swab pressure spikes are generated. The same square wave signal does not produce pressure spikes when circulating a thixotropic fluid; on the contrary the acceleration and deceleration fronts are largely attenuated.
When applying a triangular or sinusoidal wave form to the flowrate while circulating a non-thixotropic fluid, the peak-to-peak pressure gradient gets progressively larger when the oscillation amplitude increases or the signal period reduces, compared to the expected value when estimating the pressure losses with the steady state approximation. However, under the same conditions, when circulating a thixotropic fluid, the peak-to-peak pressure gradients are lower than those estimated with the steady state approximation.
Uplift Capacity of Suction Caissons in Sand for General Conditions Of Drainage
Authors: Gogoi Ragini , Aubeny Charles P. , Watson Phillip , Bransby Fraser 
Published: October 2021

Abstract
Suction caissons have emerged as a viable solution for the foundations of offshore wind turbines, which are gaining momentum worldwide as an alternate energy source. When used in a multi-bucket jacket system, the system capacity is often governed by the uplift capacity of the windward bucket foundation. Seabed conditions at offshore windfarm sites often comprise dense sand where the soil response may be drained, partially drained or undrained depending on the loading regime, the foundation dimensions and the soil conditions. Given the large difference in uplift capacity of caissons for these different drainage conditions, predicting the behavior of a suction caisson under a range of drainage conditions becomes a paramount concern. Consequently, this paper presents the findings of a coupled finite element investigation of the monotonic uplift response of the windward caisson of a multi-bucket jacket system in a typical dense silica sand for a range of drainage conditions. The study adopts a Hypoplastic soil constitutive model capable of simulating the stress-strain-strength behavior of dense sand. This choice is justified by conducting a comparative study with other soil models — namely the Mohr Coulomb and bounding surface sand models — to determine the most efficient soil failure model to capture the complex undrained behavior of dense sand. The numerical predictions made in this study are verified by recreating the test conditions adopted in centrifuge tests previously conducted at the University of Western Australia, and demonstrating that the capacity from numerical analysis is consistent with the test results. The Hypoplastic soil constitutive model also provides an efficient method to produce accurate load capacity transition curves from an undrained to a drained soil state.
Experimental Study on Plugging Inside a Pipe Using Carbonated Ice as a Substitute for Methane Hydrate
Authors: Yamamoto Joji , Yamamoto Marcio , Nakajima Yasuharu , Takano Satoru , Kanada Shigeo , Ono Masao , Otsubo Kazuhisa 
Published: October 2021

Abstract
Methane hydrate has been found below the seafloor in the Exclusive Economic Zone (EEZ) of Japan in a large amount. During the methane hydrate transportation, it is concerned that the riser pipe or the flowline can be plugged by the hydrate reformation and the freezing of seawater. The degradation and reformation kinetics of methane hydrate are mainly controlled by temperature, pressure, and methane concentration in the system; however, it is difficult to predict these factors in the multiphase flow because they are affected by fluid dynamics and heat transfer. To obtain the experimental data of the degradation kinetics, we developed a closed-loop experimental apparatus consisting of jacketed tubings used as heat exchangers, three acrylic units to observe the flow, and a slurry pump. The flow rate, salinity, temperature, and pressure in the apparatus were continuously measured in the circulation experiments. The experiment results showed that the freezing condition of the fluid in the pipe is affected by the temperature of the outside of the pipe or the particle in the fluid. This paper reports some experimental data obtained in several cases, including those conducted under freezing conditions.
Experimental Investigation of Fluid-Structure Interaction in Linked Flexible Net Cages
Authors: Dong Shuchuang , Zhou Jinxin , Li Qiao , Yoshida Takero , Kitazawa Daisuke 
Published: October 2021

Abstract
In the present study, three flexible net cage groups (a single net cage, two net cages arrayed in one column, and three net cages arrayed in one column) were investigated in a flume tank, in order to analyze the hydrodynamic characteristics of the flow and linked flexible net cage, such as the drag force, cage deformation, and flow field inside and around. Based on these results, the fluid-structure interactions of the flexible net cage were discussed. The drag forces and cage deformation of a single flexible net cage were first studied, and their relationships to the current speed were found consistent with existing literature. The averaged current speed inside the single net cage was 0.72 for all incoming current speeds. Furthermore, significant current speed reductions occurred behind the single net cage, at the downstream, for all incoming current speeds. Within the measurement range, the current speed reduction area downstream from the single net cage was almost as wide as the cage diameter, and the length was up to 1.4 times cage diameters along the incoming current direction. The location of this area gradually approached the water surface as the current speed increased. In the case of two flexible net cages arrayed in one column, the differences in drag force occurred when the distance between the two cages was changed. In addition, the current speed incident on the downstream cage tended to decrease, as the distance between the cages increased. The averaged current speeds incident on the downstream cage were 0.54, 0.44, 0.77, and 0.40 when the distances between two cages were 30.0 cm, 60.0 cm, and 90.0 cm, respectively. In the case of three flexible net cages arrayed in one column, the total drag force of three flexible net cages was 2.2 times that of a single net cage. On the other hand, at the maximum current speed of 50 cm/s, the cross-sectional areas of the first net cage, the second net cage, and the third net cage were 177.10 cm2, 274.19 cm2, and 277.37 cm2, respectively. Overall, the findings of this study could not only help to understand and optimize flexible net cage structures but also provide useful information for the configuration of the net cages at the farm sites.
Numerical Towing Model for LNG Carrier Approach in Exposed Environment Calibrated With Full-Scale Measurements and Operability Criterion
Authors: Auburtin Erwan , Delivré Quentin , McConochie Jason , Brown Jim , Drobyshevski Yuriy 
Published: October 2021

Abstract
The Prelude Floating Liquefied Natural Gas (FLNG) platform is designed to offload liquefied natural and petroleum gas products to carrier vessels moored in a Side-by-Side (SBS) configuration. Prior to the mooring operation, the carrier vessel is escorted and held alongside the FLNG with the assistance of tugs connected to her bow and stern to ensure sufficient control over the vessel in this critical phase.
In order to better understand the impact of environmental conditions, to determine the optimum length, strength, material and configuration of the towline stretcher, and to estimate the maximum operable environments, coupled multi-body simulations have been performed in time domain. The numerical model, which considered both the LNG carrier and the forward tug, was calibrated using full-scale measurements of tug motions and tow line tension recorded during a real approach and berthing manoeuvre at Prelude FLNG.
The measured environment effects were generated numerically and the model parameters were adjusted to reproduce the recorded behavior as accurately as possible. Since actions of the tug master are difficult to model numerically and only the statistical environment parameters are known, a simplified approach has been adopted for modelling the tug propulsion and steering using a combination of static forces, stiffness and linear and quadratic damping for relevant horizontal degrees of freedom.
The calibrated numerical model was first subjected to several sensitivity assessments of the modelling level (single- or multi-body, inclusion of second-order wave loads, inclusion of forward speed). Then sensitivity studies were performed to help address operational requirements related to the wave height and direction, and the stretcher length and strength. The conclusions have been taken into consideration for the selection of the tow line configurations for future operations.
Finally, the calibrated coupled LNG carrier and tug model was used to derive Prelude-specific tug operability criteria that may be used for decision-making based on weather forecasts, prior to the SBS offloading operations. A large matrix of swell and wind driven waves was simulated over a range of wave heights, periods, directions and static towing forces to allow a criterion to be developed based on a stochastic extreme tow line tension. Such criterion considers relevant wave parameters while remaining simplified enough for easy use in operations.
This paper describes the assumptions and process to numerically model the towing configuration and calibrate the different coefficients, discusses the results obtained for the various sensitivities, and explains the operability criteria. Important conclusions and lessons learnt are also shared.
First Iteration Design of the Flotant Concept
Authors: Serret Jordi , Kahn Bernardo , Cavanagh Bruce , Lorente Patricia , Pascal Remy , Girandier Clementine , Cortes Carlos , Duran Ruben , McEvoy Paul , Castro Ayoze 
Published: October 2021

Abstract
This paper presents the first iteration design of the Flotant concept developed within the framework of a Cooperation Research Project funded by the European Union’s Horizon 2020 research and innovation programme. The Flotant concept is a hybrid concrete-plastic barge-type floating offshore substructure holding a 12MW wind turbine with the singularity of getting floatability by using plastic foam material fitted within the floater substructure.
The INS12MW generic wind turbine, an upscaling exercise based on the DTU10MW reference wind turbine, is presented and simulated using open-source certified aeroelastic code.
The floating platform and the mooring system are designed for two different sites, West of Barra and South East of Gran Canaria island. The principal dimensions are presented along with the hydrostatic and hydrodynamic properties of the floating system.
A relevant subset of design load cases derived from International Electrotechnical Commission and Det Norske Veritas standards was simulated using an open-source aeroelastic code (NREL FAST) to check the coupled aero-hydro-elastic behaviour of the floating system and to generate the required load-matrix for the structural assessment of the different components.
The evaluation of the design includes the seakeeping performance, the stability of the floating platform and the global performance analysis for the abovementioned sites. It demonstrates the technology developed within the Flotant project is feasible even in rough conditions like the ones in the West of Barra site.
On Uncertainty Assessment of Fatigue Damage of Propulsion Shaft Under Ice Impact
Authors: Purcell Etienne , Nejad Amir R. , Valavi Mostafa , Bekker Anriëtte 
Published: October 2021

Abstract
In this paper, the importance of maintenance of marine propulsion is discussed with specific focus on the use of condition monitoring to inform maintenance schedules. The design requirements of DNV GL for shafts expected to operate in ice infested waters is adapted and a method is proposed to calculate the short-term fatigue damage during ice impacts. This method uses the Palmgren-Miner rule to calculate fatigue damage based on a transient, lumped-mass model simulation of the shaft with ice loads calculated from shaft measurements using inverse methods. Relevant sources of uncertainty in this assessment method are identified and quantified in order to express the short-term fatigue damage in a stochastic form. Sources of uncertainty include uncertainty in the calculation of ice loads, uncertainty of the transient analysis and uncertainty regarding the actual failure of the shaft as predicted by the S-N material curve and the Palmgren-Miner method. Uncertainties that influence the stress history are found to be the greatest contributor to fatigue damage uncertainty. A method is discussed that calculates the remaining useful life of the shaft as a function of short-term fatigue damage and the identified sources of uncertainty. The S.A. Agulhas is used as a case study to quantify the fatigue damage.
The Influence of Leading-Edge Tubercles on the Sheet Cavitation Development of a Benchmark Marine Propeller
Authors: Stark Callum , Shi Weichao 
Published: October 2021

Abstract
Cavitation is an undesirable phenomenon in the maritime industry as it causes damage to the propeller, degrading hydrodynamic performance and increasing the subsequent underwater radiated noise (URN). Therefore, mitigating cavitation on marine propellers is an important area of research in order to reduce carbon emissions emitted from the shipping industry and reduce the rate at which ocean ambient noise levels are increasing. The Humpback whale has provided inspiration to research in the fluid-structure interaction field due to the presence of leading-edge (LE) tubercles on the pectoral fins that allow it to perform acrobatic maneuvers to catch prey. This paper assesses the cavitation containment capability of the LE tubercles on a benchmark marine propeller in both heavy and light cavitating conditions using commercial code STAR-CCM+, unsteady incompressible Reynolds-averaged Navier Stokes (RANS) solver and the Schnerr-Sauer cavitation model to quantify the sheet cavitation present over a range of operating conditions. In summary, in heavy-cavitating conditions, a reduction in sheet cavitation with the inclusion of LE tubercles was observed to a maximum value of 2.75% in all operating conditions considered. A maximum improvement of 3.51% and 1.07% was predicted in propulsive thrust and hydrodynamic efficiency, respectively. In light cavitating conditions, although in some conditions a reduction in cavity volume was observed, this did not result in an improvement in hydrodynamic performance.
A Reactive Flex Joint System for Reducing Wellhead Fatigue: Analysis and Measurement
Authors: Gustad Halvor S. , Moe Per Thomas , Fjeldstad Dag André , Sønåsen Knut Olav , Bjørset Arve 
Published: October 2021

Abstract
The Reactive Flex-Joint (RFJ) is a nitrogen gas torsion springfully integrated in the LMRP-BOP stack. Its purpose is to reduce the dynamic loads and the fatigue damage applied to wellheads during drilling operations. The system achieves the reduction by applying a bending moment opposing and inverting the bending moment at the Lower Flex-Joint (LFJ). The RFJ is continuously monitored by the WAMS measurement system.
The second generation RFJ has been extensively tested in a full scale workshop test rig before being shipped offshore for a year of operations on two semi-submersible rigs operating in the North Sea/Barents Sea. This paper demonstrates by calculation and measurement that the RFJ is capable of reducing wellhead loads by more than 50% and the wellhead fatigue by more than 95%. The accuracy of the measurement system is discussed.