bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calibration of Hydrodynamic Coefficients for a Semi-Submersible 10 MW Wind Turbine
Authors: Kvittem Marit I. , Berthelsen Petter Andreas , Eliassen Lene , Thys Maxime 
Published: September 2018

Hydrodynamic model tests and numerical simulations may be combined in a complementary manner during the design and qualification of new offshore structures. In the EU H2020 project LIFES50+ (lifes50plus.eu), a model test campaign of floating offshore wind turbines using Real-Time Hybrid Model (ReaTHM) testing techniques was carried out at SINTEF Ocean in fall 2017. The present paper focuses on the process of calibrating a numerical model to the experimental results. The concepts tested in the experimental campaign was a 1:36 scale model of the public version of the 10MW OO-Star Wind Floater semi-submersible offshore wind turbine.
A time-domain numerical model was developed based on the as-built scale model. The hull was considered as rigid, while bar elements were used to model the mooring system and tower in a coupled finite element approach. First-order frequency-dependent added mass, potential damping, and excitation forces/moments were evaluated across a range of frequencies using a panel method. Distributed viscous forces on the hull and mooring lines were added to the numerical model according to Morison’s equation. Potential difference-frequency excitation forces were also included by applying Newman’s approximation.
The quasi static properties of the mooring system were assessed by comparing the restoring force and maximum line tension with the pull-out test. Drag coefficients for the line segments were estimated by imposing the measured fairlead motion from model tests as forced displacement and comparing the calculated and measured dynamic line tension.
The linear and viscous damping coefficients were first estimated based on the decay tests, and the tuned damping coefficients were compared to initial guesses based on the Reynolds and Keulegan-Carpenter number at model scale. The results were then applied in the numerical model, and simulations in extreme irregular waves were compared to the experiments. It was found that second order drift forces proved to be significant, particularly for the severe irregular seastate. These could not be modelled correctly applying the potential drift forces together with quadratic damping matrix tuned to the free decay test. And the model with viscous drag coefficients tuned to decay tests also underestimated the slow drift motions. Thus, new viscous drag coefficients were determined to match the low frequency platform response.
To inverstigate the performance of the tuned model, comparisons were made for a moderate seastate and for a simulation with both waves and wind on an operating turbine. In the end, possible further improvements to the modelling were suggested.
Field Experiments on Dielectric Elastomer Generators Integrated on a U-OWC Wave Energy Converter
Authors: Arena Felice , Daniele Luca , Fiamma Vincenzo , Fontana Marco , Malara Giovanni , Moretti Giacomo , Romolo Alessandra , Rosati Papini Gastone Pietro , Scialò Andrea , Vertechy Rocco 
Published: September 2018

This paper describes the results of an experimental campaign conducted on a U-Oscillating Water Column (U-OWC) wave energy converter equipped with Dielectric Elastomer Generator (DEG) Power Take-Off (PTO) system. The considered PTO technology has the potential for overcoming some of the limitations associated with the use of traditional self-rectifying turbines. Experiments have been performed in the benign sea test site of the Natural Ocean Engineering Laboratory (NOEL), where the DEG/U-OWC was exposed to sea states with a significant wave height in the range of 0.15 m – 0.45 m and peak spectral periods in the range of 1.8 s – 3.3 s.
The aim of this work is to analyze the dynamic response of the coupled DEG-PTO and U-OWC system. The analysis of the experimental data shows that the presence of the DEG determines a slight decrease in the natural period of the water column oscillations. Through the tests, we also demonstrate that a relief valve can be successfully used to actively tune the dynamic response of the system to ensure the safety of the DEG in severe sea-states.
Numerical Modeling of Sand Production Potential Estimation and Passive Control Optimization: A Case Study
Authors: Lopez-Puiggene Eva , Gonzalez-Molano Nubia Aurora , Alvarellos-Iglesias Jose , Segura Jose M. , Lakshmikantha M. R. 
Published: September 2018

Solids/sand production is an unintended byproduct of the hydrocarbon production that, from an operational point of view, might potentially lead to undesirable consequences. This paper focuses on a study centered in the geomechanical perspective for solids production. An integrated workflow is presented to analyze the combined effect of reservoir pore-pressure, drawdown, in-situ stress, rock properties and well/perforations orientation on the onset of solid production. This workflow incorporates analyses at multiple scales: rock constitutive modeling at lab scale, 1D geomechanical models at wellbore scale along well trajectories, a 3D geomechanical model at the reservoir scale and 3D/4D high resolution reservoir - geomechanical coupled models at the well and perforation scale.
1D geomechanical models were built using log and field data, drilling experience and laboratory tests in order to characterize in situ stresses, pore pressure and rock mechanics properties (stiffness and strength) profiles for several wells. Rock shear failure mechanism was also analyzed in order to build a pre-drill model and evaluate the wellbore stability from a geomechanical point of view.
Pre-production stress modeling was simulated to obtain a representative initial stress state integrating 1D geomechanics well results, 3D dynamic model and seismic interpretations. Mechanical properties were distributed considering properties calculated in the 1D geomechanical models as input. 3D stress field was validated with in-situ stress profiles from 1D modeling results. This simulated pre-production stress state was then used as an initial condition for the reservoir - geomechanical coupled simulations. Effective stress changes and deformations associated to pore pressure changes were calculated including the coupling between reservoir and geomechanical modeling.
Finally, a 3D/4D high resolution well scale reservoir - geomechanical coupled numerical model was built in order to determine the threshold of sand production. A limit of plastic strain was obtained based on numerical simulations of available production data, DST and ATWC tests. This critical plastic strain limit was used as a criterion (strain-based) for rock failure to define the onset of sand production as a function of pore pressure, perforation orientation and rock strength. Conclusions regarding the perforation orientations related to the possibility of producing solids can support operational decisions in order to avoid undesirable solid production and therefore optimize the production facilities capacity and design to handle large amounts of solids and/or the clogging of the well.
Analysis of Rogue Waves in North-Sea In-Situ Surface Wave Data
Authors: Gramstad Odin , Bitner-Gregersen Elzbieta , Breivik Øyvind , Magnusson Anne Karin , Reistad Magnar , Aarnes Ole Johan 
Published: September 2018

The statistical properties of individual wave heights and wave crests from time series of recorded surface elevation are analyzed with a particular focus on the occurrence of extreme and rogue waves in the datasets. The datasets include surface elevation measurements from three different sensors: a wave buoy, a wave laser and a Saab wave radar — all situated at the Ekofisk field in the North-Sea and providing sea surface elevation measurements at 2Hz temporal resolution.
The resulting statistical properties of wave heights and wave crests are compared with common reference statistical distributions such as Rayleigh, Tayfun (1980) and Forristall (1978, 2000) distributions for wave heights and crest heights. In particular, the occurrence of rogue waves (H > 2.2Hs or C > 1.25Hs) in the datasets is investigated. Possible relations between the occurrence of rogue waves and spectral characteristics of the corresponding sea states are briefly discussed.
The Quantification of Soliton Current Profiles for Offshore Engineering
Authors: Jeans Gus , Osborne Alfred R. , Jackson Christopher R. 
Published: September 2018

In widely used metocean terminology, solitons are large amplitude, often highly nonlinear, internal waves. They are responsible for complex vertical profiles of rapidly varying ocean currents. These current profiles need to be reliably quantified for a wide range of offshore engineering applications, often with very limited suitable data.
Some recent advances in this field of applied research were described at OMAE2017 by Jeans et al (2017) [1]. Vertical displacements, derived from temperature measurements, were the primary input for soliton quantification. Associated current speeds were estimated from relevant theory and validated using available measured current data. This represents a notable development, because soliton current profiles are traditionally quantified via direct measurements of velocity. However, reliable current measurements can be a challenge, so the new approach is considered more reliable in some circumstances.
Jeans et al (2017) [1] applied one simple and elegant theory for relating vertical displacement to velocity. This theory performed well, considering its limitations. This paper further evaluates different theoretical options, using a new dataset with much larger amplitude solitons. Theories with higher order nonlinearity are required for estimation of soliton current profiles in such challenging conditions.
Machine Learning Approaches to Anomaly Detection of Top Drive Torque Causing Drill Pipe Failure
Authors: Inoue Tomoya , Sugiyama Daisuke , Shimotomai Takayuki 
Published: September 2018

The scientific drillship Chikyu, operated by JAMSTEC has faced the problems with drill pipe damage and failure. After a failure, we examined the surface-measured drilling data, including Fourier transform analysis and spectrogram, and conducted an outlier investigation with an autoregressive model. We found some possible indications of top drive torque anomalies among the surface-measured drilling data. The purpose of this study is to attempt anomaly detection of top drive torque by applying machine learning approaches to such pre-examinations.
Data acquired during the drilling operations of the Chikyu are first analyzed to observe the operations and determine the characteristics of the drilling data. Several hundred sets of surface drilling data are extracted and prepared as labeled learning data. Machine learning is then performed using several algorithms to build predictive models for anomaly detection of top drive torque. Simulations using these predictive models are then conducted for other sets of drilling data, including the anomaly conditions acquired during the operations of the Chikyu. The results demonstrate the validity of the predictive models.
This study applies machine learning technique to the anomaly detection of the top drive torque with aim of preventing the drill pipe damage and failure. This paper describes our approaches in detail and discuss the results.
Progress on the Development of a Holistic Coupled Model of Dynamics for Offshore Wind Farms: Phase I — Aero-Hydro-Servo-Elastic Model, With Drive Train Model, for a Single Wind Turbine
Authors: Lin Z. , Cevasco D. , Collu M. 
Published: September 2018

Currently, around 1500 offshore wind turbines are operating in the UK, for a total of 5.4GW, with further 3GW under construction, and 13GW consented. Until now, the focus of the research on offshore wind turbines has been mainly on how to minimise the CAPEX, but Operation and maintenance (O&M) can represent up to 39% of the lifetime costs of an offshore wind farm, due mainly to the high cost of the assets and the harsh environment, limiting the access to these assets in a safe mode.
The present work is a part of a larger project, called HOME Offshore (www.homeoffshore.org), and it has as aim an advanced interpretation of the fault mechanisms through a holistic multiphysics modelling of the wind farm.
The first step (presented here) toward achieving this aim consists of two main tasks: first of all, to identify and rank the most relevant failure modes within a wind farm, identifying the component, its mode of failure, and the relative environmental conditions. Then, to assess (for each failure mode) how the full-order, nonlinear model of dynamics used to represent the dynamics of the wind turbine can be reduced in order, such that is less computationally expensive (and therefore more suitable to be scaled up to represent multiple wind turbines), but still able to capture and represent the relevant dynamics linked with the inception of the chosen failure mode.
A methodology to rank the failure modes is presented, followed by an approach to reduce the order of the Aero-Hydro-Servo-Elastic (AHSE) model of dynamics adopted. The results of the proposed reduced-order models are discussed, comparing it against the full-order coupled model, and taking as case study a fixed offshore wind turbine (monopile) in gearbox failure condition.
Remnant Life Assessment of Bonga FPSO and SPM Mooring Chains
Authors: Ibekwe Achinike , Sorensen Kjeld , Fernández Jonathan , Arredondo Alberto , Mena Alex 
Published: September 2018

Delivering full service life performance for mooring systems of Floating Production Storage & Offloading assets (FPSO) has been a frustrating challenge to operators across the industry.
Remaining strength and fatigue assessment on degraded top mooring chains of the Bonga FPSO and Single Point Mooring (SPM) loading Buoy has been investigated as part of an in-house Bonga Asset Preservation Program. Both facilities are located approximately 120 km off the coast of Nigeria in the Gulf of Guinea operating in tropical waters just North of the Equator, where top chain links have been subjected to accelerated deterioration from Sun Corals and other forms of Microbiologically Induced Corrosion (MIC). These phenomena have led to overall corrosion rates being slightly above general design requirements, but more importantly to formations of large pitting on several sections of the top chain links.
Remotely Operated Vehicles (ROV) assisted inspections, chain link cleaning and underwater 3D photogrammetry have allowed capturing the surface geometry of representative degraded chain links of the mooring lines to provide detailed input data for further analyses.
Reverse engineering has been performed via Finite Element Analysis and fracture mechanics methodologies using the scanned geometry of selected highly exposed critical links to estimate the residual strength and fatigue life performance of the degraded links relative to their original design criteria.
To evaluate the potential impact of cracks on the capacity of degraded chains relative to a reference link, crack tip Stress Intensity Factors have been computed at worst case stress-raising pits and parametric analyses using varying initial crack sizes have been performed to calculate the number of years for the cracks to propagate to critical sizes.
A baseline for benchmarking the strength, fatigue and crack growth behaviour of the degraded links investigated has been provided by analysing non-degraded and uniformly corroded links after 12 years of service with projection to end of service life capacity.
The paper provides a comprehensive application of numerical methods for assessing the fitness-for-service of the chains and recommendations on in-situ performance integrity management by circumventing the need to retrieve chain samples for testing.
Effect of Tensile Force for Wear Performance of Mooring Chain
Authors: Gotoh Koji , Nakagawa Masataka , Murakami Koji , Utsunomiya Tomoaki 
Published: September 2018

Floating wind turbine facilities, which are installed in the deep sea area, plays an essential role to promote the green energy application. One of the problems associated with the commercialization of facilities installed in the deep sea is the reduction of the maintenance cost of mooring chain, because breaking of the mooring chain caused by the wear between links leads to enormous economic losses. Therefore, it is necessary to establish a quantitative wear evaluation method for mooring chains.
Experimental facility to reproduce the wear caused by sliding between links in actual scale applied for floating wind turbine, which had been proposed by the authors, was updated and the wear tests was conducted by setting some tensile force conditions between the links. Besides, procedure of the nonlinear finite element analysis was improved to estimate the behaviour of wearing between links.
From experiments and numerical analysis, it has been confirmed that the tensile force between links is an important factor of the wear amount between links.
Seakeeping Behavior of an Innovative, Twin-Hull LNG-FPSO Design During Side by Side Offloading Operations: A Numerical and Experimental Investigation
Authors: Gkikas Georgios 
Published: September 2018

A numerical and experimental investigation is performed with respect to the seakeeping behavior of a prototype, twin-hull, LNG-FPSO and its hydromechanic interactions with the offtake (LNG) shuttle carrier during Side-by-Side offloading. The numerical model describing the SbS mooring system as well as the assumptions and calibration steps made towards the development of a robust numerical realization are presented herewith.
Following calibration, the numerical model was tested against dedicated seakeeping experiments in order to assess the effectiveness of the proposed approach as well as the hydrodynamic performance of the overall offloading system. For a more realistic offloading-scenario case, three-component, i.e., wave, wind and current, offloading environments were used for validation purposes.
For the time domain simulation, as far as the hydrodynamic (diffraction) database is concerned, the multibody response amplitude operators are implemented directly, instead of employing retardation functions, in order to observe whether such an approach can still yield robust results for such complicated hydromechanic system.
Statistics of the relative motions between the LNG-FPSO and LNGC manifolds, fender loads and lines’ tensions are obtained and presented, illustrating the good agreement between numerical and experimental results.
Lessons learned and further recommendations are subsequently summarized and stated.
Numerical Simulation of Shear Ram Performance
Authors: Zhu Lei , Estefen Segen F. , Jorge Nilo de Moura , Chujutalli John H. , Souza Marcelo Igor Lourenço 
Published: September 2018

A subsea Blowout Preventer system plays an extremely important role in providing safe working conditions for drilling activities in deepwater oil exploration. However, estimating the performance of Shear Ram Blowout Preventeris still a challenge for the industry.
This paper considers different scenarios that may influence the shear capability of a typical subsea Blind Shearing Ram: the pipe size, ram shape, preload of pipe, off-center distance and tool joint of pipe. Element method analysis is conduct on the Abaqus software to calculate the maximum required shearing force for each scenario. Results of those simulations are collected and analyzed according to mechanic theories and oil field experience.
Furthermore, some recommendations are offered both in theoretical and practical aspects to build the criterion for the shear ability of a specific type of Blind Shearing Ram. Factors influencing shearing capabilities have been listed according to the result of the numerical simulation.
Influence of Viscosity and Non-Linearities in Predicting Motions of a Wind Energy Offshore Platform in Regular Waves
Authors: del Águila Ferrandis José , Rodríguez Ricardo Zamora , Chryssostomidis Chryssostomos , Bonfiglio Luca 
Published: September 2018

Motion prediction of floating bodies in waves represents one of the most challenging problems in naval hydrodynamics. The solution of the seakeeping problem involves the study of complex non-linear wave-body interactions that require large computational costs. For this reason, over the years many seakeeping models have been formulated in order to predict ship motions using simplified flow theories, usually based on potential flow theories solved within the linear assumption.
Neglecting viscous effects in the computation of radiation forces might largely underestimate the energy dissipated by the system while moving at the free surface. This problem is particularly relevant for unconventional floating bodies at resonance. In these operating conditions the linear assumption is no longer valid and conventional Boundary Element Methods, solved in the frequency domain, might predict unrealistic large responses if not corrected with empirical damping coefficients.
The application considered in this study is an offshore platform to be operated in a wind farm requiring operability even in extreme meteorological conditions. In this paper, we compare heave and pitch Response Amplitude Operators, predicted for an offshore platform using three different seakeeping models of increasing complexity; namely a frequency-domain BEM, a high-order BEM solved in time-domain and a non-linear fully viscous model based on the solution of the Unsteady Reynolds Averaged Navier-Stokes equations (URANS). Results are critically compared in terms of accuracy, applicability and computational costs.
Comparing Fracture Toughness Transition Curves for Girth Welds in X70 Pipe
Authors: Mohr William , McGaughy Tom 
Published: September 2018

Most materials for offshore applications are tested for brittle fracture resistance at a single temperature related to the minimum design temperature and by a single fracture test method. It is much rarer to perform tests at multiple temperatures to compare the fracture performance across a range of temperatures and testing methods. EWI recently compared the fracture toughness transition behaviors for an X70 steel pipe across Charpy V-notch (CVN), single-edge notched bending (SENB) crack-tip open displacement (CTOD), and single-edge notched tension (SENT) CTOD test geometries. This showed variability of the material behavior better described by the inhomogeneous behavior models considered for welded joints. It also suggested the possibility that near the ductile-to-brittle transition temperature, the toughness under SENT CTOD may be higher than for SENB CTOD testing where the failure mode is brittle fracture.
The testing methods used full-size CVN and nearly full-thickness CTOD specimens in bending, as limited by the pipe curvature of the 219-mm diameter pipe with 35.4-mm wall thickness. The SENT CTOD specimens were pre-cracked in bending with the same dimensions as the SENB specimens, but are then cut down to place the pre-cracked crack tip at approximately one quarter of the thickness through the resulting specimen. This modification places the tip in the higher constraint region for the tension test.
Girth welds in the same X70 pipe were prepared using a pulsed GMAW process with ER80S-D2 welding wire. Similar testing was performed with weld centerline notches for the CVN and CTOD specimens. The transition behavior was related between the three testing methods for the weld centerline at the mid-wall of the pipe thickness.
Using representative values equivalent to the minimum of three tests, the SENT values were 4.8 to 4.9 times the values for the SENB tests.