bluuebunny/crossref_metadata_2025_split huggingface dataset:
Data Assimilation for Phase-Resolved Ocean Wave Forecast
Authors: Wang Guangyao , Pan Yulin 
Published: December 2020

Abstract
The phase-resolved prediction of ocean waves is crucial for the safety of offshore operations. With the development of the remote sensing technology, it is now possible to reconstruct the phase-resolved ocean surface from radar measurements in real time. Using the reconstructed ocean surface as the initial condition, nonlinear wave models such as the high-order spectral (HOS) method can be applied to predict the evolution of the ocean waves. However, due to the error in the initial condition (associated with the radar measurements and reconstruction algorithm) and the chaotic nature of the nonlinear wave equations, the prediction by HOS can deviate quickly from the true surface evolution (in order of one minute). To solve this problem, the capability to regularly incorporate measured data into the HOS simulation through data assimilation is desirable. In this work, we develop the data assimilation capability for nonlinear wave models, through the coupling of an ensemble Kalman filter (EnKF) with HOS. The developed algorithm is validated and tested using a synthetic problem on the simulation of a propagating Stokes wave with random initial errors. We show that the EnKF-HOS method achieves much higher accuracy in the long-term simulation of nonlinear waves compared to the HOS-only method.
A Transient Thermal Flow Model for CO2 Foam and N2 Foam With Phase Transition Effect During Horizontal Well Drilling
Authors: Xu Zhengming , Song Xianzhi , Zhu Zhaopeng 
Published: December 2020

Abstract
Foam is one kind of widely used drilling fluids for underbalanced drilling due to its high cuttings-carrying capacity and low lost circulation rate. However, temperature and pressure change continuously during drilling operations, making the accurate prediction of the bottomhole pressure more difficult. Besides, for fluids near the bottom, CO2 or N2 could change phase state among gas, liquid, and supercritical condition. Thus, density, rheology, and thermal properties of foam fluids could change significantly.
In this study, a transient thermal model is developed to predict pressure and temperature profiles in horizontal wells. The velocity and pressure are calculated based on continuity and momentum equations. Temperature profiles of foam and formation are obtained by simultaneously solving energy equations for different thermal regions in the wellbore-formation system. Foam properties are calculated using the state-of-the-art equation of state with the effect of phase transition.
The effects of four important parameters on the wellbore temperature and pressure distributions are analyzed. As the annulus outlet foam quality and geothermal gradient increase, wellbore pressure decreases accordingly for both CO2 foam flow and N2 foam flow. For both CO2 and N2 foam flow in horizontal wells, the phase state of CO2 and N2 phases are the gas state and supercritical state. And the critical well depths for CO2 and N2 foam flow are different due to their different critical temperature values.
This work provides a transient model to simulate flow and thermal behaviors of CO2 foam and N2 foam during both drilling and making a connection in the horizontal wellbore. Operators may use this model to select the most suitable foam fluids to optimize injection parameters.
Bayesian Multi-Level Modelling for Improved Prediction of Corrosion Growth Rate
Authors: Di Francesco Domenic , Chryssanthopoulos Marios , Havbro Faber Michael , Bharadwaj Ujjwal 
Published: December 2020

Abstract
In pipelines, pressure vessels and various other steel structures, the remaining thickness of a corroding ligament can be measured directly and repeatedly over time. Statistical analysis of these measurements is a common approach for estimating the rate of corrosion growth, where the uncertainties associated with the inspection activity are taken into account.
An additional source of variability in such calculations is the epistemic uncertainty associated with the limited number of measurements that are available to engineers at any point in time. Traditional methods face challenges in fitting models to limited or missing datasets. In such cases, deterministic upper bound values, as recommended in industrial guidance, are sometimes assumed for the purpose of integrity management planning. In this paper, Bayesian inference is proposed as a means for representing available information in consistency with evidence. This, in turn, facilitates decision support in the context of risk-informed integrity management.
Aggregating inspection data from multiple locations does not account for the possible variability between the locations, and creating fully independent models can result in excessive levels of uncertainty at locations with limited data. Engineers intuitively acknowledge that the areas with more sites of corrosion should, to some extent, inform estimates of growth rates in other locations. Bayesian multi-level (hierarchical) models provide a mathematical basis for achieving this by means of the appropriate pooling of information, based on the homogeneity of the data.
Included in this paper is an outline of the process of fitting a Bayesian multi-level model and a discussion of the benefits and challenges of pooling inspection data between distinct locations, using example calculations and simulated data.
Tuning of Nacelle Feedback Gains for Floating Wind Turbine Controllers Using a Two-DOF Model
Authors: Lenfest Eben , Goupee Andrew J. , Wright Alan , Abbas Nikhar 
Published: December 2020

Abstract
Designing a collective blade pitch controller for floating offshore wind turbines (FOWTs) poses unique challenges due to the interaction of the controller with the dynamics of the platform. The controller must also handle the competing objectives of power production performance and fatigue load management. Existing solutions either detune the controller with the result of slowed response, make use of complicated tuning methods, or incorporate a nacelle velocity feedback gain. With the goal of developing a simple control tuning method for the general FOWT researcher that is easily extensible to a wide array of turbine and hull configurations, this last idea is built upon by proposing a simple tuning strategy for the feedback gain. This strategy uses a two degree-of-freedom (DoF) turbine model that considers tower-top fore-aft and rotor angular displacements. For evaluation, the nacelle velocity term is added to an existing gain scheduled proportional-integral controller as a proportional gain. The modified controller is then compared to baseline land-based and detuned controllers on an example system for several load cases. First-pass results are favorable, demonstrating how researchers can use the proposed tuning method to efficiently schedule gains for adequate controller performance as they investigate new FOWT configurations.
New Approach for Offshore Pile Decommissioning With Hydraulic Presses and Floating Panels
Authors: Lehn Patrick , Hinzmann Nils , Gattermann Jörg 
Published: December 2020

Abstract
Renewable Energies become more and more important in industries and society all over the world. In Germany, offshore wind farms generated 49 % of the renewable energies in 2018. Monopiles are the preferred system for the foundation of offshore wind turbines in water depths up to 40 m. They are authorized by the competent authority for 25 years. When reaching the end of lifetime, the structure inclusive the foundation must be decommissioned. The decommissioning of monopiles will be challenging in the future and can lead to unexpected costs and risks for the owners. Removing the monopiles in it’s entirely ensures the opportunity to reuse the space for new offshore wind farms.
The Institute of Geomechanics and Geotechnics of the Technische Universität Braunschweig (IGG-TUBS) obtained the funding for the research program on technical solutions with large-scale tests for decommissioning of offshore monopiles named DeCoMP.
Several decommissioning methods such as vibratory extraction, internal dredging, external jet drilling, decommissioning with overpressure and the use of buoyancy force are investigated. The proposed paper will present technical opportunities and issues for extracting the pile with hydraulic presses in combination with a steel framework. Hydraulic presses brace the steel framework with the monopile. Further hydraulic presses, positioned at a certain distance to the pile on the framework, use the seabed as abutments to push out the monopile. In addition, results of a feasibility study to remove monopiles with floatation panels are presented in this paper. This method is based on floating panels, which are attached to the monopile above the mud line. These panels are inflated with air pressure to reach the required amount of buoyancy to overcome the pullout resistance. The decommissioning solutions are compared to point out possible combinations.
Numerical Wave Tank Including a Fixed Vertical Cylinder Subjected to Waves, Towards the Investigation of Floating Offshore Wind Turbine Hydrodynamics
Authors: Clément Constance , Bozonnet Pauline , Vinay Guillaume , Borras Nadal Adria , Pagnier Philippe , Réveillon Julien 
Published: December 2020

Abstract
Specific engineering tools are used to design Floating Offshore Wind Turbines (FOWT). These so-called aero-hydro-servo-elastic solvers simulate the coupled behaviour of the turbine subjected to wind with the floater motion due to waves, including elasticity of the whole structure. The implemented hydrodynamic forces rely on a strong Oil&Gas background and include potential flow theory and empirical laws, such as Morison forces. The undergoing study aims at re-evaluating the validity range of such theories, when applied to FOWT. To do so, CFD simulations will be run to model wave propagation and interaction with a FOWT floater. Hydrodynamic forces will be extracted from the CFD simulations and compared to current hydrodynamic theories.
A fixed cylinder in regular second order deep water waves (steepness of 0.9) is simulated and results are validated against experiments [1]. This basic first case implemented with Open-FOAM using waves2Foam library allows to master regular wave generation and interaction with a rather simple structure, running multiple simulations. Convergence (mesh refinement, time step) and parameterization (numerical schemes, turbulence models) studies are carried out to ensure controlled wave generation. An accurate Numerical Wave Tank (NWT) is finally obtained. However, the resolution of air/water interface with Volume Of Fluid (VOF) MULES method seems to be responsible for extreme air velocities on crests resulting in wave damping. This phenomena is solved by decreasing time step. Hydrodynamic forces on the cylinder match experiments with an error below 3%. As the flow is turbulent (Re = 105), a turbulence model is included in the simulation giving results rather close to the ones obtained without turbulence model.
Model Tests and Numerical Prediction of the Low Frequency Motions of a Moored Ship in Shallow Water With a Wave Splitting Method
Authors: Fonseca Nuno , Tahchiev Galin , Fouques Sébastien , Stansberg Carl Trygve , Rodrigues José Miguel 
Published: December 2020

Abstract
Prediction of shallow water low frequency (LF) motions of vessels in the context of mooring analysis is challenging. Model tests are often performed to calibrate and validate numerical models and, in this way, reduce the uncertainty. Model tests are part of the positioning system qualifying process. However, model tests also present challenges and uncertainties related to parasitic low frequency wave systems which are unavoidable in shallow water ocean basin conditions.
The paper presents model tests with a ship moored in shallow water (20 m), the analysis and discussion of the test data and comparisons with numerical predictions. The focus is on the low frequency motions and related wave drift forces. The tests have been performed in harmonic waves, bi-harmonic waves and irregular seastates, including conditions with and without current. The first part of the study consists of analysing the wave field measured by a long array of wave sensors distributed along the ocean basin. The analysis provides split wave systems, namely the low frequency components including the bound wave, the incoming free parasitic wave, the reflected component and additional very long waves. The second part proposes a method to calibrate and validate mooring analysis numerical models, based on comparisons with model test data which includes the unavoidable effects from parasitic waves. Simulations of LF motions with the calibrated model show a good agreement with the measurements.
Evaluation of the Ice Load Acting on an Arctic Offshore Structure With Different Ice Drifting Angle
Authors: Kim Young-Shik , Kim Yun-Ho , Song Hyung-Do , Jang Jin-Ho , Han Solyoung , Kim Joosung , Kim Hyunjoe , Cahay Marc 
Published: December 2020

Abstract
In this study, an evaluation method and results for ice load acting on an Arctic offshore structure with various ice drifting angles are discussed. Korea Research Institute of Ships and Ocean Engineering (KRISO) has conducted a research project to develop a hull form design for year-round floating type offshore structures in the Arctic condition with dynamic positioning and mooring system. Six cooperating organizations participated in the project: Samsung Heavy Industry, Korean Register, Pusan National University, Korea Maritime & Ocean University, Dong-Eui University, and Inha Technical College. In the design stage of an Arctic offshore structure, ice load consideration is the key component for the safety and reliability analysis. However, there is no generally used tool for evaluation of ice load acting on an Arctic offshore structures. In this study, ice loads acting on an Arctic FPSO in managed ice conditions with various ice drifting angles are examined by experimental methodology. Dramatic mean value changes in ice load with different ice drifting angles are observed in the model test. This experimental ice load evaluation method can be applied to the other types of offshore structure which might operate in sea ice condition.
Sequential Annular Fluid Expansion Analysis for Wellbore Completion Design
Authors: Liu Zhengchun , Samuel Robello , Gonzales Adolfo , Kang Yongfeng 
Published: December 2020

Abstract
Annular fluid expansion analysis (AFEA) is a vital step when designing an oil/gas well or geothermal well. Traditionally, an AFEA is performed between a drilling operation (initial condition) and a production operation (final condition). However, well design engineers desire to perform an AFEA between any two operations. The objective of this work is to address that challenge.
Sequential AFEA refers to the procedure in which output data (e.g., fluid volume change) of one AFEA are used as input data for another AFEA; the underlying operations are “sequential”. As a result, an AFEA can be configured between any two operations, provided that the “initial condition” operation is before the “final condition” operation.
This two-pass AFEA model has been implemented in computer programs and has been integrated with a commercial software tool, including a wellbore thermal flow simulator and tubular stress analyzer. Offshore well examples were used to validate the model. Case study results indicate that a sequential AFEA is in good agreement with a traditional one-pass AFEA in terms of both forward and backward operation sequences.
Instantaneous Center of Rotation of a Vessel Submitted to Oblique Waves
Authors: de Oliveira Costa Daniel , Sena Sales Junior Joel , Fernandes Antonio Carlos 
Published: December 2020

Abstract
When under influence of an incident wave system, any freely floating body presents a general motion with all six degrees of freedom. The Instantaneous Center of Rotation, as defined in classical mechanics, is a concept that allows the description of a general motion in 6 degrees of freedom as a pure rotation around such point. This approach, although not widely used in ocean engineering, might be an alternative tool that allows fast and precise analysis in many cases. Recent studies have shown that under specific conditions, such as a heading wave condition, the ICR varies in time but it is always located along a line for one wave frequency. Similar results were presented regarding beam waves as well.
The present work continues with the investigation regarding the behavior of ICR under more generic conditions, assuming oblique waves exciting a vessel with typical geometry of a FPSO platform. The study extends the knowledge derived based on 2D approaches from previous works, comparing the results obtained from the different methods. An analytical model is presented, assuming only harmonic motion to all 6 degrees of freedom and showing that, similar to what was observed in the simplified 2D cases, the ICR tends to present dependence on the frequency of motion. Numerical data acquired from commercial codes based on potential theory is also presented.
The Use of Dominance, Influence, Steadiness and Compliance (DISC) Personality Test in the Assessment of Accidents Likelihood on Offshore Drilling Operations
Authors: Morais Carlos Henrique Bittencourt , Barini Filho Ulrico , Martins Marcelo Ramos 
Published: December 2020

Abstract
Brazilian offshore drilling operations are carried out in a highly demanding and complex working environment. The geological characteristics of the most productive Brazilian reservoirs, located on the so-called Pre-Salt basin, actually implies for their exploration the overcoming of water depths greater than 1,500 meters and the construction of wells that can reach up to 7,000 meters of length. In such environment, human reliability plays a primordial role regarding safety issues. On the same token, in the field of risk analysis, the consideration of human behavior holds a unique position and its relevance for the consubstantiation of accidents is widely recognized throughout the literature. Nonetheless, a comprehensive way to model it is still an ongoing effort. In this challenge, human error, understood both as a success or a failure probability, provided the first base for the development of techniques capable to infer the outcome towards man machine interaction (MMI). Such stand point gave birth to a series of tools and methodologies, usually called as human reliability analysis (HRA) first generation tools. In an attempt to address the perceived deficiencies of the first-generation tools, the decade of the 1990’s saw the introduction of HRA models based on cognitive assumptions, naturally called HRA second-generation tools. On its turn, the cognitive modeling perspective has demanded the adoption of more sophisticated architectures that, ultimately, have been leading to the dynamically account of the cognitive process. In this context, the present work aims to contribute for this debate analyzing the use of the Dominance, Influence, Steadiness and Compliance (DISC) personality test in the assessment of accidents likelihood on offshore drilling operations in Brazil. By means of actual data collected during the years 2016 and 2017, the paper develops a qualitative discussion of the foreseen outcomes regarding accident proneness considering the working and the under-pressure profiles advocated on DISC.
Data-Based Approach to Optimizing the Ocean Wave Energy Carpet Using Deep Neural Network
Authors: Do Ninh Hai , Alam Mohammad-Reza 
Published: December 2020

Abstract
In this paper, we present the Neural Network-based Optimization Method, applied to optimizing the wave energy converter “wave carpet”. The proposed method can be applied to optimizing the computationally expensive objective function that other sequential optimization approaches fail to do. The results show that, in the simple case of single-frequency unidirectional incoming waves, this optimization method achieves the optimal carpet shape that can absorb 2.18 times more energy than the baseline circular shape, and in its best performance the neural network can optimize the carpet shape that absorbs 7 times more energy than the baseline, after being trained on a medium data set. Thus, the proposed method can be considered an effective approach to solving the optimization problems involving computationally expensive objective functions.
On the Use of Artificial Neural Networks for Estimating the Long-Term Mooring Lines Response Considering Wind Sea and Swell
Authors: Gonzalez Gabriel Mattos , de Siqueira Marcos Queija , Simão Marina Leivas , Videiro Paulo Maurício , Sagrilo Luis Volnei Sudati 
Published: December 2020

Abstract
Nowadays, artificial intelligence algorithms are regaining visibility mainly due to the increase in computational capability. Among those, artificial neural networks (ANN) are very useful for the regression of highly nonlinear phenomena, such as the dynamic response of offshore structures. Due to the escalating demand in the oil and gas industry, offshore fields have been explored in deeper waters, which leads to more severe environmental conditions. A reliable and efficient evaluation of the long-term response of mooring systems, a crucial element of floating offshore structures, is then imperative. The estimation of the mooring long-term response is usually obtained numerically through the convolution of the short-term responses, based on short-term stationary environmental conditions (typically 3-h). Each of these short-term responses is obtained through a time-domain dynamic structural analysis from which statistical parameters of interest are calculated, such as the mean of the tension maxima sample or the maxima frequency. Such analyses tend to be quite time-consuming and a reliable estimator of these short-term statistical parameters may be of great help. In this paper, an ANN is trained to predict the short-term extreme peak response statistical parameters. The used training datasets include the wave significant height and spectral peak period for both wind sea and swell waves, generated by Importance Sampling Monte Carlo Simulation (ISMCS) method. Fixed directions of wind sea and swell are considered. It is shown that the ANN successfully predicts the short-term response statistical parameters for both cases, which are later used for the evaluation of the long-term N-year mooring response.
Dynamic Response Comparison of Mono and Dual Submerged Floating Tunnels
Authors: Chung Woo Chul , Jin Chungkuk , Kim MooHyun 
Published: December 2020

Abstract
Submerged floating tunnel (SFT) concept has been studied by many researchers as an alternative of conventional or floating bridges, especially in the fjord or as a connection between island and land. One of the major challenges is large dynamic responses under extreme wave and earthquake excitations. In this regard, two different types of SFT, which are mono and dual SFTs, are suggested in this study, and the global performance of them is compared through tunnel-mooring fully-coupled time-domain numerical simulations. The tunnel and mooring lines are modeled by the lumped-mass-based line model. The Morison equation is utilized for hydrodynamic load estimations of the tunnel and mooring lines at their instantaneous positions. To check dynamic response of SFT under operating condition, 10-yr waves with the current are considered as an environmental condition. Dynamic responses, mooring tensions, and inertial and drag forces are systematically compared.