bluuebunny/crossref_metadata_2025_split huggingface dataset:
Progress on the Development of a Holistic Coupled Model of Dynamics for Offshore Wind Farms: Phase II — Study on a Data-Driven Based Reduced-Order Model for a Single Wind Turbine
Authors: Lin Z. , Stetco A. , Carmona-Sanchez J. , Cevasco D. , Collu M. , Nenadic G. , Marjanovic O. , Barnes M. 
Published: November 2019

Abstract
At present, over 1500 offshore wind turbines (OWTs) are operating in the UK with a capacity of 5.4GW. Until now, the research has mainly focused 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, mainly due to the assets’ high cost and the harsh environment in which they operate. Focusing on O&M, the HOME Offshore research project (www.homeoffshore.org) aims to derive an advanced interpretation of the fault mechanisms through holistic multiphysics modelling of the wind farm.
With the present work, an advanced model of dynamics for a single wind turbine is developed, able to identify the couplings between aero-hydro-servo-elastic (AHSE) dynamics and drive train dynamics. The wind turbine mechanical components, modelled using an AHSE dynamic model, are coupled with a detailed representation of a variable-speed direct-drive 5MW permanent magnet synchronous generator (PMSG) and its fully rated voltage source converters (VSCs). Using the developed model for the wind turbine, several case studies are carried out for above and below rated operating conditions. Firstly, the response time histories of wind turbine degrees of freedom (DOFs) are modelled using a full-order coupled analysis. Subsequently, regression analysis is applied in order to correlate DOFs and generated rotor torque (target degree of freedom for the failure mode in analysis), quantifying the level of inherent coupling effects. Finally, the reduced-order multiphysics models for a single offshore wind turbine are derived based on the strength of the correlation coefficients. The accuracy of the proposed reduced-order models is discussed, comparing it against the full-order coupled model in terms of statistical data and spectrum. In terms of statistical results, all the reduced-order models have a good agreement with the full-order results. In terms of spectrum, all the reduced-order models have a good agreement with the full-order results if the frequencies of interest are below 0.75Hz.
Potentials of Nano-Designed Plugs: Implications for Short and Long Term Well Integrity
Authors: Kimanzi Raymos , Patel Harshkumar , Khalifeh Mahmoud , Salehi Saeed , Teodoriu Catalin 
Published: November 2019

Abstract
Cement plugs are designed to protect the integrity of oil and gas wells by mitigating movement of formation fluids and leaks. A failure of the cement sheath can result in the loss of zonal isolation, which can lead to sustained casing pressure.
In this study, nanosynthetic graphite with designed expansive properties has been introduced to fresh cement slurry. The expansive properties of nanosynthetic graphite were achieved by controlling the preparation conditions. The material was made from synthetic graphite and has a surface area ranging from 325–375 m2/gram. Several tests including compressive strength, rheology, and thickening time were performed. An addition of 1% nanosynthetic graphite with appropriate reactivity was sufficient to maintain expansion in the cement system, leading to an early compressive strength development. It has excellent thermal and electrical conductivity and can be used to design a cement system with short and long-term integrity. Rheology and thickening time tests confirmed its pumpability. Controlling the concentration of the additive is a promising method that can be used to mitigate gas migration in gas bearing and shallow gas formations.
Effect of Wind Turbulence on Extreme Load Analysis of an Offshore Wind Turbine
Authors: Chen Xiaolu , Jiang Zhiyu , Li Qinyuan , Li Ye 
Published: November 2019

Abstract
Evaluation of dynamic responses under extreme environmental conditions is important for the structural design of offshore wind turbines. Previously, a modified environmental contour method has been proposed to estimate extreme responses. In the method, the joint distribution of environmental variables near the cut-out wind speed is used to derive the critical environmental conditions for a specified return period, and the turbulence intensity (TI) of wind is assumed to be a deterministic value. To address more realistic wind conditions, this paper considers the turbulence intensity as a stochastic variable and investigates the impact on the modified environmental contour. Aerodynamic simulations are run over a range of mean wind speeds at the hub height from 9–25 m/s and turbulence levels between 9%–15%. Dynamic responses of a monopile offshore wind turbine under extreme conditions were studied, and the importance of considering the uncertainties associated with wind turbulence is highlighted. A case of evaluating the extreme response for 50-year environmental contour is given as an example of including TI as an extra variant in environmental contour method. The result is compared with traditional method in which TI is set as a constant of 15%. It shows that taking TI into consideration based on probabilistic method produces a lower extreme response prediction.
Research on Fatigue Life Assessment of Fiber Glass Reinforced Flexible Pipe
Authors: Bai Yong , Zhao Jiannan , Sun Xinyu , Zhang Xiaojie , Wang Zhao 
Published: November 2019

Abstract
Fiber glass reinforced flexible pipe (FGRFP) is a kind of submarine pipe widely used in oil and gas transportation and exploration. This paper mainly studies the theoretical and numerical simulation methods for calculating the fatigue life of the FGRFP. Firstly, the tension time-histories and bending moment time-histories of the FGRFP are obtained by using global analysis. The tension and bending moment frequency distribution histograms are obtained by using rain flow method. Then, the finite element software ABAQUS is used to build the model of the FGRFP, and the corresponding tension and bending moment are applied on the finite element model. Then, the stress time histories curve of the FGRFP is obtained. By comparing the results of numerical simulation, the main factors affecting the fatigue life of the FGRFP are studied. Finally, according to rain flow method, S-N curve and numerical simulation results, the fatigue life and single damage rate of FGRFP are obtained.
An Empirical Formula for Predicting Elastic Ultimate Buckling Strength of Flat-Bar Stiffened Panels With Initial Imperfections
Authors: Mei Hongyuan , Wang Deyu 
Published: November 2019

Abstract
Elastic ultimate buckling strength is an important strength design criteria to estimate the safety margin of stiffened panels subjected to axial compressive load. Based on a series of Nonlinear finite elements analysis, an empirical formula is proposed to elastic ultimate buckling strength of stiffened panels with flat-bar stiffener in this study. The elastic ultimate buckling strength is defined as that in the loading process, a certain average compressive stress of stiffened panels when the Vonmises stress of structures firstly reach the yield stress. The range of geometrical sizes for numerical samples is discussed in order to ensure the applicability of presented empirical formula. The extent of models and initial imperfection, namely initial geometrical deformation are also taken into account. Ultimately, it is shown that there are a good agreement between the results of Non-linear finite element method and the proposed empirical formula.
The Experimental Investigation of Completion Fluid Working As a Good Thermal Insulation in the Deepwater Production Well
Authors: Feng Ming , Guo Boyun 
Published: November 2019

Abstract
For wells, risers and pipelines in offshore, the mechanical loads as well as the thermal insulation requirements normally increase with water depth. Hence, the traditional thermal insulation foam technology used in shallow waters and the associated design and test methodology may not be adequate to deep-water projects. This research focuses on investigation of a new material for insulation of deepwater wells and pipelines.
In the research, many samples of insulation fluids are tested to find out attractive alternative to current fluids for deep water production. The paper highlights the development of these new thermal insulation fluid and its application in the lab. Compared to the current existing insulation fluids, these new insulation fluids provide high viscosity.
Numerical Estimation of Multiple Positions of Seepage of Dissolved Matter From Seafloor
Authors: Kanao Shunsuke , Sato Toru 
Published: November 2019

Abstract
To mitigate global warming, it is necessary to emit less CO2 into the atmosphere and the Carbon dioxide Capture and Storage (CCS) attracts attention these days as one of the solutions against the problem. Off Tomakomai coast, Japan, a CCS project has been demonstrated since 2016. However, there may be a risk of CO2 leakage and consequent seepage from the seafloor, even if the probability of such an event is almost nil. In this research, we assumed that CO2 seeps from multiple points on the seafloor and aimed at estimating the seepage locations, time and fluxes, by using CO2 concentration data observed by several sensors set on the seafloor. We adopted the adjoint marginal sensitivity method, which is a probabilistic time-backward method: an adjoint location probability is released by each sensor and spreads in the time-backward direction. The adjoint location probabilities are used to estimate the seepage fluxes. We also combined the least squares method with the adjoint marginal sensitivity method to estimate the seepage fluxes. We considered that CO2 seeps from 2 points in 2-dimensional horizontal domains as test calculations with changing seepage flux ratios, such as 1:1, 1:0.1 or 1:0.01.
Numerical Simulation of Ship-Ship Interactions in Waves
Authors: Xie Xueshen , Wan Yuxiang , Wang Qing , Liu Hao , Feng Dakui 
Published: November 2019

Abstract
A numerical simulation of the hydrodynamic interaction and attitude of a ship and two ships of different sizes navigating in parallel in waves were carried out in this paper. The study of the two ships navigating in parallel is of great significance in marine replenishment. This paper used in house computational fluid dynamics (CFD) code to solve unsteady RANS equation coupled with six degrees of freedom (6DOF) solid body motion equations. URANS equations are solved by finite difference method and PISO algorithm. Structured grid with overset technology have been used to make computations. Turbulence models used the Shear Stress Transport (SST) k-ω model. The method used for free surface simulation is single phase level set. In this paper, two DTMB 5415 with different scales are selected for simulation analysis. This paper analyzed the impact of the big ship on the small ship when the two ships were navigating in parallel. This paper also analyzed the relationship between interaction and velocity between hulls, which has certain guiding significance for the ship’s encounter on the sea.
Evaluation of the Performance of an Integrated WEC Type of Breakwater System
Authors: Ding Haoyu , Zang Jun , Ning Dezhi , Zhao Xuanlie , Chen Qiang , Blenkinsopp Chris , Gao Junliang 
Published: November 2019

Abstract
A new type of coastal structure is proposed to reduce construction-cost and construction-space by integrating wave energy converters (WECs) into breakwater system. To develop this type of system to be more stable and effective, this paper focuses on investigating and improving an existing concept of integrated WEC type of breakwater system using a numerical method based on OpenFOAM®. Validation of the numerical setup is conducted by comparing the numerical predictions with relevant experimental data collected in a wave tank at Dalian University of Technology. The integrated WEC type of breakwater system considered in this paper is a pile-restrained WEC-type dual-floating breakwater system. The two floating breakwaters in this system are constrained to heave motion independently and work as a heaving-oscillating buoy type of WECs driven by a linear power take-off damping system (PTO system). Two parameters including wave transmission factor and capture width ratio (which is defined as the ratio of absorbed wave power to the incident wave power in the device width) are studied and discussed in the paper. The range of effective frequencies (range with wave transmission factor KT &lt; 0.5 and capture width ratio CWR &gt; 0.2) is obtained to evaluate the performance of this system with regard to both breakwater and WEC. These results indicate that damping coefficient of PTO system and gap width between two floating bodies influence wave transmission factor and capture width ratio, and the range of effective frequencies can be improved by the appropriate damping coefficient and gap width.
An Arrow-Shaped Honeycomb Pedestal With Negative Poisson Ratio and its Impact Resistance
Authors: Wu Haoran , Lin Xiaobin , Zhang Jie 
Published: November 2019

Abstract
The ship’s pedestal is the connection structure between the ship’s equipment and the hull, and is also the basis for the installation of the equipment. The pedestal bears both the static load generated by the weight of the equipment and the dynamic load generated during the operation of the equipment, and at the same time transmits the external load received by the hull to the equipment, and the load it bears is very complicated. If there is a problem with the pedestal in an impact environment, the accuracy of the system equipment will be affected, the system equipment will not work properly. Negative Poisson’s ration structures have a unique set of properties because of their tensile expansion, such as increased shear modulus, enhanced fracture toughness, better energy absorption and co-curvature. In recent years, the negative Poisson’s ration honeycomb structure has been applied to the pedestal of marine equipment, which demonstrates good vibration damping effect. However, the pedestal has two functions: vibration damping and impact resistance, there is not much research on the impact resistance of the pedestal. In this paper, an “arrow-shaped” honeycomb pedestal is taken as the research object. Firstly, the analytical expression of the Poisson’s ration of the honeycomb pedestal is derived theoretically and the influence of each parameter on the Poisson’s ration is analyzed. Secondly, the effect of Poisson’s ration on the impact resistance of the pedestal was analyzed by ensuring that the pedestal height was constant. It was found that with the reduction of Poisson’s ration, the impact resistance of the pedestal and the output impact environment of the pedestal panel were effectively optimized. Finally, by ensuring that the height of the pedestal is constant and the Poisson’s ration is the same, the influence of the number of honeycomb layers on the impact resistance of the pedestal is analyzed.
Impact of Rotor Misalignment due to Platform Motions on Floating Offshore Wind Turbine Blade Loads
Authors: Smith Rachael E. , Pillai Ajit C. , Tabor Gavin , Thies Philipp R. , Johanning Lars 
Published: November 2019

Abstract
The rotor of a horizontal-axis floating offshore wind turbine is more frequently misaligned with the oncoming wind than that of a fixed offshore or onshore wind turbine due to the pitch and yaw motions of the floating support structure. This can lead to increased unsteady loading and fatigue on the components beyond those considered in the standard load cases. In this work, the Simulator fOr Wind Farm Applications (SOWFA) tool within the CFD toolbox OpenFOAM is used to perform simulations of a wind turbine at different stationary angles to the oncoming wind flow that a floating wind turbine may experience, so that the impact of misaligned flow on power production and blade loading can be studied. The turbine is modelled using an actuator line method which is coupled with NREL’s aeroelastic code FAST to compute the structural response. The results of this study will be used in future work to optimise the rotor geometry of a floating offshore wind turbine.
Study on Gust Parameters and Wind Spectrum of South China Sea
Authors: Xie Botao , Ren Xuhe , Li Jiagang , Duan Wenyang , Wang Junrong , Zhao Binbin 
Published: November 2019

Abstract
Wind loads are one of the main loads on offshore structures during typhoons in the South China Sea (SCS). The accuracy of wind turbulence characteristic parameters were very important for the calculation of wind load of these large structures and floating platforms. The parameters of the gust factor and wind spectra are studied in this paper. Characteristics of the gust factor and the turbulence during typhoon and monsoon period were analyzed by using the observational data of long-term wind on a platform in South China Sea. The relationships among the gust factor, mean wind speed and turbulence intensity were described. The most suitable wind spectrum for SCS had been compared for the different wind speed conditions. The results can provide reference and technical guarantee for the offshore constructions of SCS.
An Experimental Investigation of the Trim Effect on the Behaviour of a Containership in Shallow Water
Authors: Elsherbiny Khaled , Tezdogan Tahsin , Kotb Mohamed , Incecik Atilla , Day Sandy 
Published: November 2019

Abstract
A new division of the Suez Canal in Egypt, termed the New Suez Canal, was opened for international navigation in August 2015. It is therefore important to ensure the safety of ships navigating this new section of the canal. Measures to avoid grounding and/or drifting to the canal banks are necessary. Additionally, accurate prediction data for ship squat and under keel clearance is crucial.
This paper presents the results of experimental work carried out at the Kelvin Hydrodynamic Laboratory at the University of Strathclyde, Glasgow, to study the effect of trim on containership sailing characteristics in shallow waters using Kriso Container Ship (KCS) model.
A series of model tests were conducted to measure the resistance, sinkage variations with speed, water depth and loading conditions under different trimming angles at 1:75 scale. The objective of this work is to examine the range of ship trim for safe and efficient sailing in restricted water in both depth and width. The study also aimed to provide data to be used in validating numerical computations to be carried on the same type of vessel to detect the best trim angle for ships during sailing in restricted waters to reduce resistance and therefore fuel consumption.
For depth Froude numbers higher than 0.4, the results show that the ship model sinkage is less for aft trim than for level trim or forward trim. Concurrently, it can be observed that there is less water resistance for aft trim than for forward trim, albeit level trim shows the least resistance. The test was conducted for one value of model draft which was 0.144 m. Side bank effect were also examined.
Characterizing Impacts of Atmospheric Turbulence on Wind Farms Through Large Eddy Simulation (LES)
Authors: Alam Jahrul M. , Afanassiev Anton , Singh Jagdeep 
Published: November 2019

Abstract
Wind farms extract energy from the lowest part of the atmospheric boundary layer (ABL). Thus, characterizing the impacts of atmospheric turbulence — precisely, which aspect of it enhances or hinders the capacity factor of wind farms — is currently the least understood and the most demanding topic of wind energy research. This article demonstrates a Large Eddy Simulation (LES) of atmospheric turbulence around an array of 41 full-scale wind turbines with a rotor diameter of 126 m. A wall-adaptive subgrid-scale (SGS) model for atmospheric turbulence around wind farms has been examined. For a moist-free atmosphere in the afternoon, the spectra of kinetic energy are compared with Kolmogorov’s energy spectrum. The power production is discussed with respect to staggered arrangements of turbines. Results show that the LES model has the potential to account for atmospheric turbulence for optimizing tower placements in wind farms.
Active Control of Flexible Riser Vibration by Boundary Control Based on LQR Controller
Authors: Yu Jinxin , Chen Weimin 
Published: November 2019

Abstract
The lateral displacement and the rotational angle of marine riser are likely to get larger as it is in stronger ocean current and, particularly, undergoes the consequences such as vortex-induced vibration or collisions between individual risers. The riser vibration with large amplitude value will lead to fatigue or coating damage of the structural body. In this study, the active vibration control, in terms of its angle and the displacement reductions, of a flexible riser under time-varying distributed load are considered using boundary control. The governing equations of the structural dynamics involving the control system of a flexible riser are built. The riser is modeled as an Euler-Bernoulli beam under the actions of ocean loads and the feedback controller. A torque actuator is introduced at the upper riser boundary, and the control law is employed to generate the required signal for riser angle control and displacement reduction. The feed-back control law is designed in state space, and the optimization of the control law is implemented based on the LQR approach. The linear quadratic regulator is used to determine the gain matrix, which can calculate the boundary control law by solving the Recatti equation. Based on the numerical simulations, the responses of the open-loop system and closed-loop system are presented and compared. The effectiveness of the vibration suppression of the flexible riser is examined.
Investigation of the 2D Behavior of a Rotating Cylinder in Flow Using the Discrete Vortex Method
Authors: Rheem Chang-Kyu 
Published: November 2019

Abstract
The influence of rotation on the behavior of a two-dimensional rotating cylinder in flow was investigated by using the discrete vortex method combined with the 4th order Runge-Kutta method. There are three stages for rotational speed dependence of hydrodynamic force on a fixed rotating cylinder, the stage where lift force increases and drag force decreases, the stage where lift and drag forces increase in proportion to the square of rotation ratio, and the stage where lift and drag forces increase in proportion to rotation ratio. As a fixed rotating cylinder begins to rotate and the rotational speed increases, the vortex train that causes VIV weakens and disappears. When the cylinder is mounted on a spring, the vibration frequency of the spring mounted rotating cylinder becomes lower. This indicates that the added mass of the rotating cylinder is increasing as the rotation ratio increases.
CFD Investigations of 2D Greenwater Overtopping of a Floating Offshore Vessel
Authors: Zhang Xiantao , Draper Scott , Wolgamot Hugh , Zhao Wenhua , Chen Lifen , Cheng Liang 
Published: November 2019

Abstract
In this paper, 2D greenwater overtopping of a floating box is numerically investigated using CFD. The incident waves used are compact wave groups which correspond to the maximum relative wave elevation at the edge of the box according to linear theory. The motion of the box for which only heave and pitch modes are considered is calculated using linear potential flow theory and then prescribed in the CFD simulation. It is found that the normalized maximum horizontal momentum flux of greenwater overtopped onto the moving box is consistent with that for a fixed box when the incident wave length is much smaller than the box length. For longer incident wave lengths there is arguably more scatter in the momentum flux compared with that of a fixed box, although the result is still bounded by a value of 1.5 times that predicted by a classical dam break solution. This additional scatter is shown to be due to the effect of box motion.