bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear Mechanical FE Analysis of Thin-Plate Complex Structures Using the Shell-Solid Mixed Method
Authors: Ikushima Kazuki 
Published: December 2020

Abstract
In the construction of ships and ocean structures, thin steel plates are welded in order to join parts. Due to the welding, deformations and residual stresses may occur. These deformations and residual stresses can cause problems in the assembly process. Therefore, the prediction of welding deformations and residual stresses is necessary in advance of production. Welding deformations and residual stresses can be predicted using thermal elastic plastic (TEP) finite element analysis (FEA). However, solid elements are used in the conventional analysis method of TEP-FEA. The modeling of the thin-plate structures using solid elements is very complicated and difficult. In addition, the number of elements increases when using solid elements compared to shell elements. This leads to an increase in the required computing resources. Therefore, an efficient modeling method is necessary for thin-plate structures.
In the present research, in order to realize an efficient welding mechanics analysis method for thin-plate structures, the authors proposed an efficient FEA method for the welding mechanics problem for thin-plate complex structures using the proposed shell-solid mixed analysis method. For the shell-solid mixed analysis method, the multipoint constraint (MPC) technique was used in the finite element analysis to connect shell elements and solid elements. In order to compare the analysis accuracy with the conventional analysis, which uses solid elements, the proposed shell-solid mixed analysis method was applied to the fundamental welding mechanics problem of thin-plate structures. The results revealed that the proposed method has approximately the same analysis accuracy as the conventional method. These results indicated that the proposed method can effectively analyze the welding deformations and residual stresses in thin-plate complex structures.
Development of a Pile Mooring System for Large Scale FSRUs
Authors: Park Taeyoon , Jeon Junhwan , Kim Jung , Jeon Sangbae , Kim Bongjae , Lee Dongyeon 
Published: December 2020

Abstract
In this paper, a pile mooring system is introduced as an alternative mooring solution for FSRU. Also, the methodologies of mooring analysis and structural analysis to verify a design of pile mooring system are introduced. The mooring performance of pile mooring system can be assessed by coupled mooring analysis considering stiffness of pile, resistance of soil and hull interface mechanism. The structural integrity of pile, foundation and hull interface can be assessed by non-linear contact finite element analysis. Using these methods, the basic design of pile mooring system for 160,000-CBM large scale FSRU is developed considering practical environmental conditions.
Low-Height Lifting System for Offshore Wind Turbine Installation: Modelling and Hydrodynamic Response Analysis Using the Commercial Simulation Tool SIMA
Authors: Vågnes David , Monteiro Thiago Gabriel , Halse Karl Henning , Hildre Hans Petter 
Published: December 2020

Abstract
With the increasing demand for renewable energy sources in the past years, the interest in expanding the use of wind energy has grown. The next frontier in this expansion process is the use of floating wind turbines offshore. One of the main factors dictating the economic feasibility of such wind turbines is the complexity of their installation process. The dimensions of modern offshore wind turbines, the distance from the installation sites to the coast and demanding environmental factors all contribute to the difficult of developing an efficient installation concept for this kind of structures. In this work, we present a new concept for a catamaran vessel capable of handling the deployment of offshore wind turbines on floating spar platforms using a low-height lifting system that connects to the lower end of the wind turbine. The low-height lifting system is controlled by an active heave compensation system and constant tension tugger wires attached to the turbine mid-section are used to ensure the balance of the tower during the installation process. We conducted a series of hydrodynamic analysis using the software suit SIMA to study the dynamic response of the proposed system under different weather conditions and different operational layouts. This preliminary concept was proven feasible from a hydrodynamic point of view and can now be pushed forward for further studies regarding other aspects of the operation, such as impact and structural loads and mechanical design of components.
Floating Hose Behavior During Different Scenarios of an Offloading Operation
Authors: Paruolo Nathalia , Mello Thalita , Brandão Leonardo 
Published: December 2020

Abstract
Considering the deep water oil exploitation in remote fields far away from the coast, the use of shuttle tankers connected to FPSOs (Floating, Production, Storage and Offloading) for offloading and oil transporting shows to be a preferred alternative compared to constructing oil pipelines considering technic and economic matters, even if offshore offloading operation is still considered one of the riskiest operations in the offshore environment.
From the concerns about hazards of an offloading operation, one is related to hose failure during oil transferring and the consequences on the environment. Different aspects of FPSO and shuttle tanker influence floating hose behavior during offloading operation as environmental condition, ships loading conditions, ships distance, heading, FPSO offloading station position and number of hose sections. The different aspects may be combined in several scenarios, in which integrity of floating hoses in terms of tension and bending strength shall be guaranteed.
In the present paper, global numerical analyses of offloading operation considering a spread moored FPSO and a typical dynamic positioning shuttle tanker (DPST) moored in tandem are carried out. The analyses are based on a coupled numerical model of FPSO, DPST and floating hose [2]. Covering a wide combination of the scenarios considering the aspects listed above, full time domain simulation is used to estimate hose sections force and moments during the operation. Numerical model results are validated for a couple of scenarios against field data.
With focus on floating hose integrity, the main objective is to define minimum requirements for a safe offloading operation, as environmental criteria, maximum and minimum distances between FPSO and DPST, limit operating sectors and minimum number of hose sections. The results can be used as reference to offloading procedures and manuals of owners and operators in combination with recommendations of international organizations.
Design, Analysis, and Development of a Wave-Current Laboratory
Authors: Nguyen Nhu , Davis Jacob , Alshuwaykh Ahmed , Sharman Krish Thiagarajan 
Published: December 2020

Abstract
In real ocean environments, offshore structures are exposed to a combination of wave and current loading conditions. This scenario presents the need to study fluid-structure interactions in the presence of both conditions, achievable through experimentation in a recirculating flume coupled with a wavemaker. The Ocean Resources and Renewable Energy (ORRE) group set out to design a recirculating wave-current flume at the University of Massachusetts Amherst to enable the study of technologies such as scale floating platforms and marine energy converters. In this paper, we present the methods used to arrive at an optimal flume design under strict spatial constraints posed by the available lab space. Limitations on the length, width, and height of flume are overcome via innovative flow designs and compact structures. The final design is approximately 11.5 m (37.7 ft) in length and 1.2 m (3.9 ft) wide with a nominal water depth of 1 m (3.3 ft). The 2 m long test section begins 6 m beyond the inlet of the flume to maximize flow uniformity. A 24” thruster driven by 75 hp electric motor maintains a current velocity of 0.5 m/s throughout the section while a wedge-shape plunger is implemented at the inlet to generate 0.6–2.8 s period waves with a maximum height of 0.2 m. During the design process, 2D computational fluid dynamics (CFD) simulations are employed to maximize flow uniformity over a range of inlet angles and guide vane configurations. In the optimal scenario, a flow nonuniformity of 8.7 % was obtained across a 0.7 m water column measured from the free surface. Results from the 3D simulation around the tight corner section showed significant increase in flow nonuniformity. The implementation of the screens along the flow path might be necessary in the future.
Nonlinear and Machine-Learning-Based Station-Keeping Control of an Unmanned Surface Vehicle
Authors: Sinisterra Armando J. , Barker Alexandrea , Verma Siddhartha , Dhanak Manhar R. 
Published: December 2020

Abstract
This study is part of ongoing work on situational awareness and autonomy of a 16’ WAM-V USV. The objective of this work is to determine the potential and merits of application of two different station-keeping controllers for a fixed-pose motion control of the USV. The assessment includes performance and power consumption metrics tested under harsh environmental disturbances to evaluate the robustness of the control methods. The first is a nonlinear trajectory-tracking control method based on the sliding-mode control technique, while the second method uses a machine-learning approach based on Deep Reinforcement Learning. Results from both the approaches are compared for various case studies.
Improved Empirical Formulation for Seabed Trench Profile at Touchdown Zone and its Effects on Fatigue of Steel Catenary Risers
Authors: Zhuang S. , Shi C. , Lou M. , Liu Y. , Bao X. , Li H. 
Published: December 2020

Abstract
Steel catenary risers (SCRs) offer a cost-effective solution to deep water deployments. Hanging from a floater, an SCR is commonly subjected to large tension at hangoff location and large bending moments at touchdown zone (TDZ) which lead to fatigue damage. Field observations showed that the depth of a seabed trench might reach to a depth of four to five times of the diameter of a riser, however, a flat seabed was often assumed for the modeling of SCRs which surely affects simulations of fatigue behavior of the SCR at the touchdown zone. Studies on the effects of seabed trench on TDZ fatigue conducted by different researchers led to contradictory conclusions, i.e., some studies suggested that considering seabed trench reduced fatigue damage at TDZ of SCRs, while, others drew opposing conclusions. The contradiction may be explained by factors including inappropriate trench profiles and different sea states assumed in the analysis model. An iterative procedure initially developed by Wang and Low and further improved in the present work was used to estimate the position and the length of a seabed trench beneath an SCR and, then, an improved empirical formulation was generated to approximate the profile of the seabed trench. Additionally, dynamic simulations were conducted to study the effects of seabed trench on fatigue behaviors of SCRs encountering variant directional waves.
A Principal Strain Data-Driven Method for Damage Identification of an Offshore Pile Structure
Authors: Bao Xingxian , Yang Guanlan , Li Hongwei , Shi Chen 
Published: December 2020

Abstract
Vibration-based damage identification technique, categorized as parametric and nonparametric methods, plays an important role in guaranteeing the success of offshore operations and the integrity management of marine structures. In the parametric approaches, modal parameters and their derivative are usually applied to obtain the damage-sensitive features. Nevertheless, there are still some challenging problems for the parametric method in application. Nonparametric (data-driven) approaches are aim to extract damage sensitive features directly from the measured data. For the data-driven approaches, it is vital to find which indicator derived from the response signal is sensitive to structural damage. Considering the derivatives of strain are more sensitive to small structural damage than that of displacement, the strain-related damage detection methods have currently gotten more attention. In this study, a principal strain data-driven method is proposed, which is derived from strain energy dispersion theory and directly employs the time history data of three principal strains of an intact and damaged structure to construct the damage identification indicator. The efficiency of the method is validated by a numerical offshore pile structure with several damage cases considering noise scenarios. Due to the difficulty of determine the correct three principal strains in the real experimental measurements, the approximation damage indicators are constructed based on one, two or three kinds of strain response among the axial, radial and hoop strains response, instead of the three principal strains response. The results show that satisfying damage identification results can still be gotten for both the single- and multiple-damage scenarios using only axial or hoop strain response even under noise conditions. The proposed principal strain data-driven damage identification method can be used as a viable and effective technique for damage localization and severity estimation of marine structures.
Study on Acid Fracturing Technology for Carbonate Reservoirs in Ordos Basin
Authors: Li Mu , Zhang Lufeng , Li Minghui 
Published: December 2020

Abstract
Acid fracturing, a key stimulation technology, has been widely applied in carbonate formations, which have the complex reservoir space and natural fracture. However, the conventional acid fracturing technology has limitations in target reservoir due to serious acid leakage and rapid acid-rock reaction speed. Therefore, a deep-penetration acid fracturing technology was proposed to enhance the stimulation effect. The reservoir basic physical properties, such as permeability and porosity, microstructure characteristic of pore throats, mineral composition, and rock mechanics characteristics, were systemically investigated by a series of laboratory experiments. The acid system was also optimized by evaluating rheological properties and residual acid damage. Furthermore, the most important two parameters of acid fracturing, conductivity and effective acid-etched fracture length, were obtained by numerical simulation with commercial software Fracpro PT. Based on the laboratory studies, the acid fracturing technology was applied in the field, and the production of well increased by 1.7 times after stimulation.
Nonlinear Optimal Control of a Deep Borehole Trajectory Design
Authors: Gulyayev Valery , Glazunov Sergii , Andrusenko Olena 
Published: December 2020

Abstract
In modern oil/gas producing industry, vertical, 2D and 3D directed, and multilateral (branched) boreholes are drilled. Their trajectories are designed depending on the petroleum deposit depth and structure, properties of mining rocks, their hardness, heterogeneity, fracturing anisotropy, permeability, and so on. Therefore, the borehole cost and its productivity are determined by the length, smoothness, and configuration of its trajectory. To enhance efficiency of a borehole and to reduce cost of its drivage, to enlarge rate and volume of the reservoir depletion, it is proposed to use methods of optimal control for the best tracking of its trajectory. Through application of the differential geometry correlations, the mathematic model of the borehole outline in the form of nonlinear ordinary differential equations system is elaborated. Different objective functions, representing total integral curvature of the borehole axis line, its length, and cost of its drivage, are selected; additional constraints, separating allowed and forbidden zones of passing, are chosen. The functions of the trajectory curvature and torsion are used as controlling variables.
The continuous correlations of the model are discretized and, further, the techniques of nonlinear programming and optimal control are employed.
On the basis of the method of objective function gradient (antigradient) projection on the linearized constraint planes, the step-by-step algorithm of approaching to the optimal trajectory is elaborated. To correct the spoilt constraints, at every step of calculations, the Newton method is used. The elaborated approach is applied to optimization of deep curvilinear borehole outlines. The results of numerical analysis are discussed. It is shown that smoothing the hole trajectory permits also to diminish the contact and frictional interaction between the drill string and bore-hole wall and, by this, to decrease the resistance forces acting on the string during tripping in/out operations performing and to diminish energy expenditures for these operations fulfillment; to decrease the rate of the drill string tube wear; and to reduce the drill string sticking occurrence probability.
Steel Lazy Wave Riser Optimization Using Artificial Intelligence Tool
Authors: Lal Mayank , Sebastian Abhilash , Wang Feng , Lu Xiaohua 
Published: December 2020

Abstract
Use of steel lazy wave risers has increased as oil and gas developments are happening in deeper waters or in parts of the world with no pipeline infrastructure. These developments utilize FPSO’s with offloading capabilities necessary for these developments. However, due to more severe motions compared to other floating platforms, traditional catenary form of risers are unsuitable for such developments and this is the reason Steel lazy wave risers (SLWR) are required. SLWRs have shown to have better strength and fatigue performance and lower tensions at the hang-off compared to steel catenary risers. A suitable Lazy-Wave form of the catenary riser is achieved by targeted placement of a custom configured buoyancy section. The strength and fatigue performance of steel lazy wave risers are governed by parameters such as length to start of this buoyancy section, length of the buoyancy section, hang-off angle and the buoyancy factor. Achieving these key performance drivers for a SLWR takes several iterations throughout the design process.
In this paper, genetic algorithm which is an artificial intelligence optimization tool has been used to automate the generation of an optimized configuration of a steel lazy wave riser. This will enable the riser designer to speed up the riser design process to achieve the best location, coverage and size of the buoyancy section. The results that the genetic algorithm routine produces is compared to a parametric study of steel lazy wave risers varying the key performance drivers. The parametric analysis uses a regular wave time domain analysis and captures trends of change in strength and fatigue performance with change in steel lazy wave parameters.
Numerical Analyses of the Effects of Bend Orientation on Sand Erosion in Elbows for Annular Flow
Authors: Kang Rong , Liu Haixiao 
Published: December 2020

Abstract
Sand erosion is a severe problem during the transportation of oil and gas in pipelines. The technology of multiphase transportation is widely applied in production, due to its high efficiency and low cost. Among various multiphase flow patterns, annular flow is a common flow pattern in the transportation process. During the transportation of oil and gas from the hydrocarbon reservoir to the final destination, the flow direction of the mixture in pipelines is mainly changed by the bend orientation. The bend orientation obviously changes the distributions of the liquid film and sand particles in annular flow, and this would further affect the sand erosion in elbows. Computational Fluid Dynamics (CFD) is an efficient tool to investigate the issues of sand erosion in multiphase flow. In the present work, a CFD-based numerical model is adopted to analyze the effects of bend orientation on sand erosion in elbows for annular flow. Volume of Fluid (VOF) method is adopted to simulate the flow field of annular flow, and sand particles in the flow field are tracked by employing Discrete Particle Model (DPM) simultaneously. Then, the particle impingement information is combined with the erosion model to obtain the maximum erosion ratio. The present numerical model is validated by experiments conducted in vertical-horizontal upward elbows. Finally, the effects of various bend orientations on the erosion magnitude are investigated according to the numerical simulations.
Reproduction probabilities and size distributions of the smooth snake Coronella austriaca in the Netherlands and Norway
Authors: Dalessi Domin , Bolle Harm , Jongejans Eelke , Sørensen Pål , Siepel Henk 
Published: December 2020

Abstract
Whether females participate in reproduction every year or rather skip years is pivotal information for understanding the dynamics of animal populations. In ectotherms this reproduction frequency might depend on factors like temperature, individual size, and prey availability. Here we studied the reproduction rate of the smooth snake Coronella austriaca at two latitudes: in Norway and The Netherlands. Reproductive and morphological data were collected in Norway (34 years) and The Netherlands (5 years). To account for differential resighting probabilities of pregnant and non-pregnant females, we performed multi-state mark-recapture analyses. Reproductive rate, quantified as the probability of participating in reproduction in consecutive years, was calculated for both pregnant and non-pregnant females. The results showed a clear difference in reproductive rate between the two latitudes, with only 15% of pregnant females reproducing again in the following year in Norway versus 93% in The Netherlands. Furthermore, in Norway females grew larger and started reproduction at a higher age. Litter size and juvenile total length and body mass were also significantly higher in Norwegian smooth snakes.
Assimilating In Situ and Remote Sensing Observations in a Highly Variable Estuary–Shelf Model
Authors: Lai Wenfeng , Gan Jianping , Liu Ye , Liu Zhiqiang , Xie Jiping , Zhu Jiang 
Published: December 2020

AbstractTo improve the forecasting performance in dynamically active coastal waters forced by winds, tides, and river discharges in a coupled estuary–shelf model off Hong Kong, a multivariable data assimilation (DA) system using the ensemble optimal interpolation method has been developed and implemented. The system assimilates the conductivity–temperature–depth (CTD) profilers, time series buoy measurement, and remote sensing sea surface temperature (SST) data into a high-resolution estuary–shelf ocean model around Hong Kong. We found that the time window selection associated with the local dynamics and the number of observation samples are two key factors in improving assimilation in the unique estuary–shelf system. DA with a varied assimilation time window that is based on the intratidal variation in the local dynamics can reduce the errors in the estimation of the innovation vector caused by the model–observation mismatch at the analysis time and improve simulation greatly in both the estuary and coastal regions. Statistically, the overall root-mean-square error (RMSE) between the DA forecasts and not-yet-assimilated observations for temperature and salinity has been reduced by 33.0% and 31.9% in the experiment period, respectively. By assimilating higher-resolution remote sensing SST data instead of lower-resolution satellite SST, the RMSE of SST is improved by ~18%. Besides, by assimilating real-time buoy mooring data, the model bias can be continuously corrected both around the buoy location and beyond. The assimilation of the combined buoy, CTD, and SST data can provide an overall improvement of the simulated three-dimensional solution. A dynamics-oriented assimilation scheme is essential for the improvement of model forecasting in the estuary–shelf system under multiple forcings.