bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effects of Solid-Liquid Internal Flow on the Dynamic Behavior of a Reduced-Scale Jumper for Deep-Sea Mining
Authors: Yamamoto Marcio , Fujiwara Tomo , Kanada Shigeo , Ono Masao , Takano Satoru , Yamamoto Joji , Masanobu Sotaro 
Published: December 2020

Abstract
For the exploitation of seafloor massive sulfides, we have investigated the dynamic behavior of the jumper, a piece of flexible pipe that connects the seafloor mining tool to the subsea slurry pump.
In this article, we present the results of the experiment using a 1/5 reduced-scale model of the jumper. This experiment was carried out in Deep-Sea Basin. During the experiment, a slurry fluid was conveyed throughout the jumper’s model. In addition, an oscillator generated harmonic motion on the top end of the model. In terms of instrumentation, we installed load cells on the top and bottom ends of the model and a 3D visual measurement system tracked the motion of measurement stations attached to the model.
We present the experimental results measured by the 3D visual measurement system, loads cells, and differential pressure gauges in the cases where a vertically forced oscillation is imposed on the top of the jumper.
In this experiment, we could observe the effects of slurry on the jumper reduced-scale model. Since the slurry has a larger density than the single liquid phase, the slurry flow changed, as expected, the static shape of the jumper compared to a jumper conveying only water. The vertical top force average and differential pressure average increase with the volume concentration of solid, while their amplitudes increase quadratically with the forced oscillation frequency.
A Novel Hybrid Method of Pre-Tension Adjustment of Mooring Lines in the Model Test
Authors: Du Junfeng , Wang Hongchao , Chang Anteng , Sun Mingyuan , Wang Junrong , Zhang Min 
Published: December 2020

Abstract
Mooring lines are the most commonly used station-keeping systems for floating platforms, and the pre-tension of the mooring lines has significant effect on the dynamics of floater/mooring system. However, during the model test, which is the most important method for the research on the floater/mooring system, the pre-tension of the designed mooring lines in the basin are always significantly different with the target values of the ideal model due to the error of the manufacture of the mooring lines and positon locating of the anchor point and so on. As a result, the adjustment of the pretension of the mooring lines based on the ideal model is an important task during the model test. The pre-tension is always adjusted by increasing or decreasing mooring line length. While all the mooring lines are connected with the floater and coupled with each other, pre-tension adjustment is an unwarranted and cyclic process which often wastes a lot of time.
This paper presents a novel methodology for regulating the mooring line pre-tension based on matrix calculation. The increment matrix of the mooring line tension can be obtained by increasing or decreasing the length of each mooring line in the numerical model. Assuming that the increment the mooring line tension is linear to the change of the mooring line length, the adjustment amount of each mooring line length can be calculated from the difference of the real pre-tension and the target pre-tension. However, the mooring line tension is always nonlinear to the mooring line length. Calculating the increment matrix of the mooring line tension and adjustment of the mooring line length is also a cyclic process until the error of real pre-tension of the model in the basin and target value can meet the accuracy requirement. This method is used in a model of a mooring system with 12 mooring lines which are connected with a semi-submersible platform. The test results show that the pre-tension of mooring lines can be adjusted to the target value quickly based on the method proposed in this paper.
Experimental Study on Cavitation Motion of Underwater Vehicle With Protrusions
Authors: Qu Zhaoyu , Gan Ning , Chen Yingyu , Yang Nana 
Published: December 2020

Abstract
For underwater vehicles with protrusions (external structure), the geometric shape of the protrusions is bound to affect the local flow field of the vehicles during the moving process of the vehicles, thus affecting the generation, development and collapse of cavitation around the vehicles. The cavitation may break, fall off and collapse randomly, and other local movements may affect the motion attitude of the underwater vehicle. It is an effective method to study fluid dynamics to simulate prototype cases with small scale models. In this paper, we mainly use the small scale model test method to explore the cavitation motion characteristics of the vehicle in water with protrusions. Through the establishment of a set of vehicle motion test equipment under reduced pressure, a series of experiments were conducted on this basis to explore the motion characteristics of vehicle cavitation under different bump shapes. In this study, two high-speed cameras were used to simultaneously record cavitation generation, development, collapse and other characteristics, to analyze the bubble generation mechanism and scale characteristics caused by the bulge, and then to study the influence of cavitation induced by the bulge on the motion attitude of the vehicle.
Development of a 10-MW Semisubmersible Type Floating Offshore Wind Turbine for the East Sea, Korea
Authors: Ahn Hyeonjeong , Shin Hyunkyoung 
Published: December 2020

Abstract
The area of renewable energy is expanding rapidly worldwide, with wind turbines being an example. In Korea, many researchers are conducting studies on floating offshore wind turbines (FOWTs) on areas with suitable wind resources. In particular, Ulsan, which is the site selected in this study, started research on the development of a 200-MW floating offshore wind farm. In this study, the references for upscaling are the 5-MW reference wind turbine of the National Renewable Energy Laboratory (NREL), and the OC4-DeepCwind semisubmersible type floating wind turbine. We upscaled the 5-MW wind turbine to a 10-MW FOWT by applying the appropriate scale ratio for each component of the turbine. We upscaled the specifications related to items such as the blades, hub, and nacelle using the power ratio. The mass of the blades was reduced by using carbon fiber-reinforced plastic (CFRP). We upscaled the specifications related to the tower using its deflection ratio, and the tower clearance criterion and the tower campbell diagram were used to confirm that the design is appropriate. We upscaled the specifications related to the platform using the upper structure mass ratio. The GZ curve of the platform was used to confirm the stability, and we used the air gap for safety. Three catenary type mooring lines were also designed. To understand the static response of the initial model of the 10-MW FOWT, a steady-state analysis was performed according to each wind speed. We followed the IEC and DNV standards, and we used NREL FAST in all simulations.
Assessing RANS Numerical and Modeling Properties in the Simulation of the Flow Around Captive and Moving Cylinders
Authors: Costa Rita M. , Eça Luís , Koop Arjen 
Published: December 2020

Abstract
In many Engineering applications, the Reynolds-Averaged Navier-Stokes (RANS) equations are still used to simulate high Reynolds numbers (turbulent) flows around complex geometries. In flows that exhibit significant regions of flow separation leading to vortex shedding, it does not make sense to define the mean flow using time-averaging. Therefore, the use of RANS (even if locally) in statistically unsteady flows requires the application of ensemble-averaging to the flow variables and to the mass and momentum equations, which generates the appearance of the Reynolds stresses. Turbulence models available in the open literature have been developed for the simulation of statistically steady flows (mean flow defined by time-averaging). Nonetheless, the same models are used for the simulation of statistically unsteady flows. Therefore, it is not guaranteed that such models provide sufficient diffusion (damping) to capture only the mean flow.
In this paper, we have investigated the modeling and numerical properties of RANS supplemented by the k–ω SST eddy-viscosity model when applied to the classical problem of the flow around captive and moving (imposed motion) cylinders with Reynolds numbers ranging from 102 to 106. Two and three-dimensional simulations are performed and numerical (statistical, iterative and discretization) convergence properties are assessed for moving and deforming grids techniques. The quantities of interest are the drag and lift coefficients, for which we determine the frequency content of the time signal to assess if the numerical results correspond (as intended) to the mean flow. Results obtained at a Reynolds number of 104 are compared with experimental data available in the open literature.
CFD-Based Operation Optimization of Hybrid Ships
Authors: Guo Bingjie , Vartdal Bjørn-Johan , Alnes Øystein Åsheim 
Published: December 2020

Abstract
Hybrid propulsion technology is interesting for shipping, both due to possible reduction in fuel cost and strict emission regulations. The efficiency of a hybrid propulsion system will however depend on the power system configuration and the choice of power and energy management strategies. In this study, a simulation model is developed based on CFD, to investigate power management strategies of hybrid propulsion during transit operation. Two engineering operation approaches using fixed RPM mode and fixed power mode are simulated, in order to investigate power management strategy of the hybrid propulsion system. The transition operation of offshore supply vessel Viking Lady is used as an investigated object in the present study. The numerical simulations are performed in both regular sea and irregular sea. CFD results show that the models with the fixed RPM mode and the fixed Power mode give similar results in the power consumption, provided that the ship resistance in waves is predicted accurately as well as the output power and propeller revolution rate are properly designed. The model with the fixed RPM was expected to be able to reduce the power consumption by minimizing ship speed fluctuations when running in heavy sea conditions. The present numerical results show that the fixed RPM mode tried to reduce ship speed change by changing output power. However, it is not able to reduce the change of ship speed efficiently when the first-order wave forces are significantly large, and the power consumption is consequently not reduced.
An Optimization Method for Economical Ship-Routing and Ship Operation Considering the Effect of Wind-Assisted Rotors
Authors: Sun Wenyu , Liu Xiyang , Yang Li 
Published: December 2020

Abstract
With the increasingly strict regulations for energy saving and emission reduction technology of ships, minimizing fuel cost is one of the most critical issues in the design and operation of merchant ships. A method to reduce the fuel cost for merchant ship is to select an economical route based on the real-time meteorological environment and weather forecasting data. So far, numerous ship routing strategies have been proposed with the development of weather routing system. More recently, many wind-assisted devices like rotors, wind sails, etc. have been investigated and designed to utilize the renewable wind energy. With the equipment of wind-assisted rotors, the optimization of ship route becomes more important because the effect of this wind-assisted device highly depends on the local wind field along the ship route. In this paper, an improved optimization strategy with the combination of the A* algorithm and a realtime optimizer has been proposed to determinate the optimal ship route and ship operations including ship heading, propeller’s rpm and rotor’s rpm. The real-time information for the weather conditions, ocean climate and sea states are obtained from European Center for Medium-range Weather Forecasts and the ship performance is evaluated by data-driven models. Finally, the proposed method was applied to test cases of ships operating in Pacific route and Indian Ocean route and the results show that the total fuel consumption could be reduced compared to the minimum distance route.
Numerical Trials for the Soil-Spudcan Interface of Self-Elevating Units
Authors: Alegre F. , Logarzo J. , Alibakhshi S. , Achard A. 
Published: December 2020

Abstract
This paper describes the development of a numerical model of a jack-up leg supported on the seabed and the study performed in order to analyze the interaction at the interface between the soil and its spudcan.
Self-elevating units or jack-ups are widely used for offshore operations and the strength of their whole structure is to be ensured for the environmental conditions encountered during the operations. This is why the determination of the soil-spudcan interface is a major challenge since it depends on a wide range of factors, such as sea conditions, properties of the soil, geometry and material of the structure, etc.
In light of the unpredictable and non-linear behavior of the marine environment and the soil, it is necessary to develop further studies on this subject to reduce uncertainties and to ensure the safety of offshore structures, as most of the failures in the offshore oil platforms are related to foundations.
To do so, different approaches have been used:
• Abaqus/ Standard and Abaqus/Explicit solvers;
• Rigid bodies and deformable bodies afterwards;
• Three kind of meshes:
○ Lagrangian mesh;
○ Arbitrary Lagrangian - Eulerian mesh;
○ Coupled Eulerian - Lagrangian mesh.
To validate the model and the results obtained numerically in the end of the project, a comparison with an analytical calculation of the spudcan penetration has to be performed, based on the geometry of the structure and the properties of the soil.
Numerical Investigation of Scour Beneath a Subsea Piggyback Pipeline
Authors: Huang Jun , Yin Guang , Ong Muk Chen , Jia Xu 
Published: December 2020

Abstract
In present study, two-dimensional numerical simulations have been carried out to investigate scour beneath a piggyback pipeline subjected to a subsea boundary layer flow using SedFoam (an open-source multi-dimensional Eulerian two-phase solver for sediment transport based on OpenFOAM). In the piggyback configuration, a small pipeline is attached on the upstream and downstream sides of a large pipeline. This form of piggyback can reduce the scour depth beneath the pipeline (Yang et al., 2019). In the solver, the turbulence Reynolds stress is resolved using a two-phase modified k-ε model. The particle stresses caused by the binary collisions and contacts are modeled by the kinetic theory for granular flow and a phenomenological frictional model, respectively. The effects of the locations of the small pipelines attached on the large pipeline on the scour and the surrounding flow field are discussed.
Study on the Structural Safety Evaluation of the Self-Elevating Offshore Wind Turbine Installation Platform
Authors: Jiayi Hou , Yu Li , Haihua Zhang , Tiantian Kan 
Published: December 2020

Abstract
In order to accurately evaluate the influencing factors of the structural safety of the self-elevating offshore wind turbine installation platform, the load in the standing operating state and towing state is studied in this paper, which includes self-gravity load, wind load, current load, wave load, wave-induced inertia force, dynamic amplification load and operating load. This paper focuses on two working states of the platform. In the standing state, the effect of environmental load, as well as the dynamic amplification load is considered under both normal operating condition and storm condition. In the towing state, mainly the wave environmental load is taking into consideration. According to the data calculated above, the strength calculation is carried out. The results show that the design strength of the platform meets the requirements. This calculation method can provide a basis for the design of the self-elevating platform.
Experimental Investigation on a Point Absorber Moored by Taut Mooring System and Mooring Fatigue Analysis
Authors: Xu Sheng , Guedes Soares C. 
Published: December 2020

Abstract
In this paper, a taut wire mooring system has been designed consisting of three wire ropes symmetrically arranged. The power take-off system is modelled by a linear spring and a heave plate to simulate the linear damping of the power take-off. A series of regular wave tests in head seas are performed to study the dynamics of the system. Irregular wave tests were then conducted to simulate the system performance in the operational sea states, where the irregular waves are modelled by the Jonswap spectrum. The WEC motion responses and mooring tensions are studied. The short term mooring fatigue damage estimated by different spectral methods are compared to the rainflow counting method. The spectral method for estimating fatigue damage include the Dirlik formula, Jiao-Moan method and Tovo-Benasciutti approach. The accuracy of spectral methods for predicting mooring fatigue damage are discussed.
Space-Time Statistics via Trapezoidal Storm Model for Offshore Installations
Authors: Laface Valentina , Romolo Alessandra , Bitner-Gregersen Elzbieta M. 
Published: December 2020

Abstract
The paper proposes an approach for estimating the long-term statistics of random wave crests occurring over a certain space–time domain. Such a problem is relevant for a number of marine engineering applications, as classical analyses based, exclusively, on time domain approaches underestimates wave crest amplitudes associated with a given return period. The return period of a certain wave crest is derived by combining the Trapezoidal Storm (TS) Model, based on DNV GL storm profile, with the Euleric Characteristic (EC) of an excursion set concept, recently applied to the study of sea wave statistics. By computing the average EC, an explicit solution for the probability distribution of the wave crests during a sea storm can be derived by an approximation of the EC. Return period of linear wave crests is derived in the paper. The proposed solution is applied for the calculation of extreme waves during an ocean storm over a certain area. The results presented can be used as good approximation in design work of offshore installations. An extension of the proposed approach to account for nonlinearities of sea surface will be a subject of future research.
Torque Control of a Laboratory Scale Variable Speed Hydrokinetic Tidal Turbine: CFD Simulation and Validation
Authors: Ortega Arturo , Nambiar Anup , Ingram David , Sale Danny 
Published: December 2020

Abstract
Hydrokinetic tidal turbines are a promising alternative for the generation of clean electrical energy. They are still far behind, with respect to their technological development, in comparison to offshore wind turbines, which are currently in the stage of commercial energy production. Thus, more studies and analyses of the behaviour of tidal devices and their interaction with the surrounding ocean space are required. How this interaction is interrelated to the power production system is also necessary to be further examined. In this paper, the development of a whole system, fully-coupled model of a laboratory-scale hydrokinetic tidal turbine, along with its interactions with the ocean environment and its electrical control system is described. The model was developed in fastFlume (SOWFA, NREL) coupled with an external torque control system. The control system is developed from the optimal torque speed curve based Maximum Power Point Tracking (MPPT) algorithm. The optimal torque speed curve of the turbine used in the model was obtained from experimental work in a test tank. The hydrokinetic tidal turbine and the control system models were implemented independently. They were coupled in order to reach an energy balance between the surrounding flow, the tidal turbine, and the control system. Three flow stream velocities were imposed in the inlet of the model domain, starting the rotor from zero rotational speed. After the optimal rotational speed is attained, the electrical power generated and the loads experienced by the turbine rotor were studied. In the simulations, the tidal device is controlled to keep the optimal power production for any flow stream velocity. The results of the modelling work were compared with experimental measurements taken from 1:15th scaled testing of a fully-instrumented and controllable tidal device at the Flowave Ocean Energy Research Facility, The University of Edinburgh, a combined wave and current test facility. The results show time series of turbine and generator variables like mechanical and electrical torque and power, as well as thrust and the optimal rotational speed for each of the tested cases. The validation shows good agreement between the numerical and experimental results which encourages futures studies using the coupled model, including the turbine working in more complex flow conditions and controlled by more complex control schemes.
Study of the Efficiency and Reliability of Pressure Vessel Composite Repair
Authors: Drumond Geovana , Ribeiro Rodrigo , Pasqualino Ilson , de Souza Marcelo Igor , Perrut Valber , Lana Luiz Daniel 
Published: December 2020

Abstract
The degradation of equipment used in production platforms operating in a maritime environment occurs, in most cases, by corrosion defects. High to low pressure separators remain operational but suffer from a progressive reduction of wall thickness by external corrosion. Repair techniques for tubes and pressure vessels using laminate composite material are widely known and already defined by technical standards. However, there are doubts regarding the effectiveness of these repairs when performed near openings, nozzles or other stress concentrators. The objective of the present work is to verify the efficiency of the composite repair and the influence of the defect thickness. To meet these objectives, four vessels were tested until burst. The results showed that composite repair was efficient since the burst pressure of the repaired vessel was considerably higher than its limit pressure without repair.
Widening Drilling Operation: Performance Analysis on the Application of Fixed Cutter Drill Bits in Hard Rock Formation
Authors: De Moura Jeronimo , Xiao Yingjian , Ahmed Daiyah , Yang James , Butt Stephen D. 
Published: December 2020

Abstract
This study is an evaluation of drilling mechanisms for widening drilling operations, which are also called hole opening or enlarge drilling operations, in hard rock formations during drilling operation with fixed cutter bits. This paper focuses on correlating drilling performance, or Rate of Penetration (ROP), with drilling parameters such as Weight on Bit (WOB), rotary speed, Torque on Bit (TOB) and bit type. Laboratory Drill-Off Tests (DOT) were conducted using a drilling simulator. Natural granite specimens were penetrated using different types of fixed cutter bits with different diameters. Various magnitudes of WOB were applied during these drilling experiments in order to study drilling performance in this type of formation. A well-organized drilling experimental plan was proposed to cover both procedures of pilot holes and widening drilling operations. Comparison were made between performance conditions obtained during the drilling operations of pilot holes and similar conditions during widening drilling operations. Furthermore, bit-rock interaction was studied by comparing experimental data with that obtained from empirical models. The focus of this paper was to analyze the ROP during each stage of the widening drilling operations of a pilot hole and its correlation with other parameters. The applicability of current empirical models and their limitations in widening drilling operations in hard rock formation was analyzed. In this way, this drilling model is applied in widening drilling operations of hard rock formation with fixed cutter bits.