bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Investigation of Large Particle Slurry Transport in Vertical Pipes With Pulsating Flow
Authors: Masanobu Sotaro , Takano Satoru , Kanada Shigeo , Ono Masao , Sasagawa Hiroki 
Published: December 2020

Abstract
For subsea mining, it is important to predict the pressure loss in oscillating pipes with pulsating flow for the safe and reliable operation of ore lifting. In the present paper, the authors focused on the pulsating internal flow in static vertical pipe and carried out slurry transport experiment to investigate the effects of flow fluctuation on the pressure loss. The alumina beads and glass beads were used as the solid particles in the experiment, and the fluctuating periods and amplitudes of pulsating water flow were varied. The time-averaged pressure losses calculated by the prediction method for the steady flow proposed in the past by the authors agreed well with the experimental ones. As for the fluctuating component of pressure loss, the calculation results using the quasi-steady expression of a mixture model were compared with the experimental data. The calculated results were different from experimental ones for alumina beads of which densities are almost same as those of the ores of Seafloor Massive Sulfides. It suggests that the expression is insufficient to predict the pressure loss for heavy solid particles. The calculated ones, however, provided those in the safety side. On the other hand, the calculated results for light solid particles such as glass beads agreed well with the experimental ones. It means that the expression would be applicable to the prediction of pressure loss for the mining of manganese nodules which are lighter than the ores of Seafloor Massive Sulfides.
A Preliminary Study on the Site Selection of Offshore Wind Power Generation
Authors: Miki Koki , Tabeta Shigeru , Mizuno Katsunori 
Published: December 2020

Abstract
In Japan, which has a wide EEZ, there are high expectations for the potential of MRE. The spread of MRE may produce various effects such as eliminating dependence on other countries for energy supply and revitalizing local economies through business entry. On the other hand, consensus building with various stakeholders at the time of project development is considered a major obstacle to dissemination. In order to promote commercialization of the MRE development, not only the evaluation of economic feasibility but also various aspects such as environmental conservation and coexistence with other industries should be integrated and evaluated. A rational system should be established to select suitable sites that all stakeholders can be convinced. In this study, especially on offshore wind power generation, existing studies on selecting suitable sites in consideration of economic, environmental, and social aspects were investigated as well as the related efforts of each country to review the current status of marine spatial planning and extract issues for MRE deployment in Japan. A preliminary economic evaluation for offshore wind power generation around Japan was also carried out.
Drilling in Karstified Carbonates: Early Risk Detection Technique
Authors: Maksimov Danil , Pavlov Alexey , Sangesland Sigbjørn 
Published: December 2020

Abstract
Heterogeneous nature and complex rock properties of carbonate reservoirs makes the drilling process challenging. One of these challenges is uncontrolled mud loss. Caves or a system of cavities could be a high-risk zone for drilling as the mud losses cannot always be controlled by conventional methods, such as mud weight (MW) / equivalent mud weight (ECD) optimization, or by increasing concentration of lost circulation material (LCM) in the drilling mud. Seismic-based detection of such karstification objects is inefficient due to relatively small size, various shapes and low contrast environment. In this paper we, based on drilling data from the Barents sea, analyzed possible patterns in real-time drilling data corresponding to drilling through karstification objects. These patterns can serve as real-time indicators of zones with higher risk of karsts and can be used as an online tool for decision support while drilling in karstified carbonates.
On the Validity of CFD for Simulating Extreme Green Water Loads on Ocean-Going Vessels
Authors: Bandringa Henry , Helder Joop A. , van Essen Sanne 
Published: December 2020

Abstract
The amount of green water and the associated loads that an ocean-going vessel may encounter during its service life are important aspects to consider in the vessel’s design and classification. As green water is typically a highly non-linear phenomenon, commonly the maritime industry relies on model tests to predict green water loads and their occurrence. In recent years, however, a lot of progress with Computation Fluid Dynamics (CFD) has been made in predicting non-linear flows and associated loads at a high level of accuracy. Especially in the field of wave impacts on (moored) offshore structures at zero speed, significant progress has been made and documented using CFD. A natural extension of this progress is to expand the obtained confidence in the applicability of CFD for simulating extreme wave events to applications involving vessels at forward speed. To that end, this paper presents a validation study towards the prediction of green water loading on a (typical) container vessel at forward speed by CFD.
For validation, two extreme green water events were selected from a model test campaign carried out at MARIN within the context of the CRS (Cooperative Research Ships) working group ‘green water dynamics’. In these tests a KRISO Container Ship (KCS) is sailing in head seas when encountering severe green water. As CFD tool, the Cartesian-grid based Volume-of-Fluid CFD solver ComFLOW was selected. Furthermore, a deterministic approach is taken for the validation, by reconstructing the non-linear incoming wave in a high amount of detail and imposing the 6 degrees of motion of the vessel using the wave basin measurements. Time traces of the green water flow on deck and local- and global impact loads on the breakwater are presented and compared against the experimental data. Detailed visualizations of the CFD results are presented to further illustrate the obtained match with the model test results and emphasize the additional value of complementing model tests with deterministic CFD analysis.
A New Type of Device Used on Submarine Landslides Monitoring
Authors: Ge Yongqiang , Chen Jiawang , Cao Chen , Gao Qiaoling , Zhang Peihao , He Jiamin 
Published: December 2020

Abstract
Submarine landslides in gas hydrate areas are a significant geo-hazard that can cause considerable damage to offshore infrastructures, dramatically change the marine environment and seriously threaten human lives and property. Gas and gas hydrate disassociation was considered to be a main factor inducing submarine landslide. However, the processes and mechanism of submarine landslides caused by gas and gas hydrate dissociation are not clearly understood. Therefore, we design a Micro-Electro-Mechanical Systems (MEMS) accelerometer array to study and monitor the deep displacement of submarine landslides. The MEMS accelerometer array consists of several gravity acceleration-sensing units that are connected to an I2C-communication bus. By sensing the three-axis tilt angles, the direction and magnitude of the displacement for a measurement unit can be calculated. In the end, the laboratory model test was designed to verify the operation of the device in landslide monitoring, which demonstrated the capacities of the monitoring system for collecting real-time and in-situ information during the slope failure.
Hybrid DP Simulations
Authors: Rindarøy Martin , Selvik Ørjan , Ross Andrew 
Published: December 2020

Abstract
Large offshore windfarm development has driven the need for next-generation simulators. These tools are of great utility in both analysis and design. Firstly, they offer the ability to combine advanced dynamic positioning and gangway simulation to evaluate operational safety limits across a large spectrum of weather conditions. Secondly, they can be used as a design tool, in which many variants of design parameters can be altered and simulated, evaluating the design choices with highest efficacy.
This paper presents SINTEF Ocean’s vessel simulator, VeSim, and its results in a numerical DP3 study of a windfarm support vessel operating in DP mode near a platform. These results are presented with a thorough validation against model-scale test results, also performed by SINTEF Ocean in its Ocean Basin Laboratory. In these tests, VeSim used SINTEF Ocean’s in-house DP algorithm to control the model-scale vessel in a realtime hybrid testing environment, which is extensible to arbitrary controller designs. Through this validation task, the simulator’s value is demonstrated as an effective tool for dynamic positioning simulation in its own right. Additionally, the approach taken is shown to emphasise VeSim’s use in both a hardware-in-the-loop and software-in-the-loop testing environment.
The simulation framework is described, including its modelling of environments, propulsion and hydrodynamics, and its implementation of SINTEF Ocean’s in-house DP algorithm. The model test are described in detail, with especial focus on the use of VeSim and how its DP-controller was used as a controller in a hybrid testing environment. The tools and approaches described in the paper offer designers a variety of approaches, both computational and computational-experimental, aiding them in making the best design choices for future offshore vessels.
Residual Stresses and Stress Intensity Factor Calculations for an Orthotropic Steel Deck
Authors: Qiang Bin , Wang Xin 
Published: December 2020

Abstract
The welding residual stress in an orthotopic steel deck is investigated through experimental measurements and finite-element simulations. The simulated residual stress fields are in reasonable agreement with the measured results. The weight function method are used to investigate the stress intensity factors (SIFs) at the surface and deepest points of the semi-elliptical surface cracks, subjected to a combination of external load and through-thickness welding residual stress. Different crack aspect ratios and relative depths are analyzed. The results reveal that the transverse residual stress is always tensile through the plate thickness at the middle section, which makes the SIFs of the surface and deepest points larger than those without considering the residual stress. However, the non-linear reduction for transverse residual stress through the thickness causes the SIFs to decrease for aspect ratios of 0.4, 0.6 and 1.0.
Operational Challenges for Drilling Shallow Water Wells With Dynamically Positioned Rigs
Authors: Vaidya Rohit , Sonawane Mahesh 
Published: December 2020

Abstract
Traditionally, shallow water wells have been drilled from fixed platforms, jack-ups or moored drilling rigs. Recently there has been increased interest in performing operations on these wells using new generation of Dynamically Positioned (DP) rigs, driven by available capacity of these rigs and environmental regulations that restrict laying anchors on the seabed. Shallow water offshore drilling operations present a set of unique challenges and these challenges are further amplified when operations are performed on older wells with legacy conductor hardware with newer DP vessels and larger BOPs.
The objective of the paper is to present challenges that occur during drilling in shallow water and discuss mitigation options to make these operations feasible through a series of case studies.
Key challenges to optimizing riser operability and rig uptime are discussed. Potential modifications to the upper riser stack-up and rig deck structure for maximizing operational uptime are discussed. Riser system weak point assessment is presented along with solutions for mitigating risks in case the wellhead or conductor structural pipe is identified as the weak link. Selection of the drilling rig can have significant impact on wellhead fatigue response. Some criteria for rig selection based on drilling riser and wellhead system performance is presented with the objective of optimizing the fatigue performance of the wellhead and conductor system. Wellhead fatigue monitoring solutions in combination with physical fatigue mitigation options are presented to enable operations for fatigue critical wells.
Second-Order Correlation of Klinkenberg-Corrected Permeability and its Experimental Verification on Heterogeneously-Stressed Gas Shale
Authors: Chen Yufei , Jiang Changbao , Leung Juliana Y. , Wojtanowicz Andrew K. , Zhang Dongming , Zhong Chuanyao 
Published: December 2020

Abstract
Shale is an extremely tight and fine-grained sedimentary rock with nanometer-scale pore sizes. The nanopore structure within a shale system contributes not only to the low to ultra-low permeability coefficients (10−18 to 10−22 m2), but also to the significant gas slippage effect. The Klinkenberg equation, a first-order correlation, offers a satisfying solution to describe this particular phenomenon for decades. However, in recent years, several scholars and engineers have found that the linear relation from the Klinkenberg equation is invalid for most gas shale reservoirs, and a need for a second-order model is, therefore, proceeding apace. In this regard, the purpose of this study was to develop a second-order approach with experimental verifications.
The study involved a derivation of a second-order correlation of the Klinkenberg-corrected permeability, followed by experimental verifications on a cubic shale sample sourced from the Sichuan Basin in southwestern China. We utilized a newly developed multi-functional true triaxial geophysical (TTG) apparatus to carry out permeability measurements with the steady-state method in the presence of heterogeneous stresses. Also discussed were the effects of two gas slippage factors, Klinkenberg-corrected permeability, and heterogeneous stress. Finally, based on the second-order slip theory, we analyzed the deviation of permeability from Darcy flux.
The results showed that the apparent permeability increased more rapidly as the pore pressure declined when the pore pressures are relatively low, which is a strong evidence of the gas slippage effect. The second-order model could reasonably match the experimental data, resulting in a lower Klinkenberg-corrected permeability compared with that from the linear Klinkenberg equation. That is, the second-order approach improves the intrinsic permeability estimation of gas shales with the result being closer to the liquid permeability compared with the Klinkenberg approach.
Analysis of the experimental data reported that both the first-order slippage factor A and the second-order slippage factor B increased with increasing stress heterogeneity, and that A was likely to be more sensitive to stress heterogeneity compared with B. Interestingly, both A and B first slightly increased and then significantly as the permeability declined. It is recommended that when the shale permeability is below 10−18 m2, the second-order approach should be taken into account. Darcy’s law starts to deviate when Kn &gt; 0.01 and is invalid at high Knudsen numbers. The second-order approach seems to alleviate the problem of overestimation compared with the Klinkenberg approach and is more accurate in permeability evolution.
Numerical and Experimental Study on Ultimate Strength of Stiffened Column Under Axial Compression
Authors: Mei Hongyuan , Wang Deyu , Wan Qi 
Published: December 2020

Abstract
Six specimens with one Tee-bar stiffener and its attached plating were tested under axial compression to investigate the ultimate strength. The specimens have one longitudinal span and the simply supported boundary conditions at the end edge of loading were produced based on a horizontal test fixture. The initial geometrical imperfections were measured and tensile tests of high tensile steel used in the specimens with different thickness were conducted. The results calculated by FE analysis with true stress-strain curves, average measured thickness and measured initial geometrical deformation could reach a good agreement with experimental results. The ultimate strength calculated with elastic/perfectly plastic curve is approximately 10% larger than that with true stress-strain curve. The reason is that the proportional limit stress of material is significantly lower than 0.2% proof stress for the high strength steel used in specimens. And the occurrence of buckling is earlier than the time that the material enters into plastic stage. As a result, the ultimate strength assessed with elastic/perfectly plastic curve doesn’t always the lowest result and it should be adopted carefully.
Application of Machine Learning Algorithm in Optimization of PSV for 110000Dwt Oil Tanker
Authors: Xiyang Liu , Jingpu Chen , Wenyu Sun , Wei Xu 
Published: December 2020

Abstract
The pre-shrouded vane (PSV) in front of propeller is a kind of energy-saving device which can change the inflow to improve the received power of the propeller. The device needs to be optimized according to the flow field of the stern. Most of the existing design methods rely on the experience of the designer. In order to improve the design efficiency of PSV and obtain a design scheme with higher energy-saving effect, this paper presents an optimization and analysis method for PSV in front of propeller based on agent model.
Aiming at an 110000dwt oil tanker, 11 design parameters such as stator angle and duct radius are determined by means of parameterization. The design parameters are sampled by Latin hypercube sampling method (LH), and the sample space with 300 samples is generated. The energy-saving effect of each sample is analyzed by CFD method. The data set is formed and next divided into training set and test set. Then, machine learning methods are used to build the agent model of sample space. The error of each model in the test set is analyzed. To obtain the best model, the performance of several models in the test set and training set is considered. The applicability of different models is also highly considered. On this basis, the sensitivity analysis method is used to analyze the sensitivity of each design parameter. Then, the main influencing parameters are found. Finally, particle swarm optimization and genetic algorithm are compared to optimize the design parameters of PSV for 110000dwt oil tanker. The optimization results are verified by CFD method.
The results show that the artificial neural network model is better on this dataset, and the model error on test set is less than 1% compared with the CFD result. The optimal solution by genetic algorithm method is better than all the sample points, and a better design scheme of PSV is obtained.
Swept Blade for Performance Improvement on a Vertical Axis Wind Turbine
Authors: Su Jie , Chen Yaoran , Zhou Dai , Han Zhaolong , Bao Yan 
Published: December 2020

Abstract
The vertical axis wind turbine (VAWT) is considered an important device to utilize the renewable and sustainable wind energy. However, the relatively lower power coefficient has hampered its development. Therefore, this paper attempts to investigate the effect of swept blade employed in a VAWT on the enhancement in aerodynamic performance. A series of swept blades were studied in a small VAWT rotor, and the RANS SST k-ω turbulence model was utilized to simulate the flow field. The numerical model was validated against experimental data, and the aerodynamic performance was investigated with respect to force coefficients, vorticity distribution, static pressure distribution, and wind turbine wake, respectively. The results indicated that the swept blade could effectively increase power outputs by about 20% for the wind turbine. By reducing the drag coefficient, a high lift-drag ratio was achieved. And this configuration prevented the blade from suffering severe dynamic stall. Besides, the swept blade changed the distribution of low wind speed area in the wind turbine wake, which should be considered in the wind farm. It was concluded that this work provided a new way for the practical design and optimization of wind turbine.
Hydrodynamic Response of Tethered Underwater Robot by Feed-Forward and Incremental PID Control Techniques
Authors: Wu Jiaming , Chen Dongjun , Lin Jinhua , Chen Yan , Dou Yizhe 
Published: December 2020

Abstract
The trajectory of tethered underwater robot is usually controlled by actuating the rotating speeds of control propellers attached to the robot and/or adjusting the length of umbilical cable. When the trajectory control problem of a tethered underwater robot is studied, it is necessary to couple the main body of underwater robot, umbilical cable and control propellers together forming an integrated hydrodynamic model so that the robot is in a comprehensive dynamic equilibrium condition, suitable control algorithms are then jointed into the hydrodynamic model constructing a hydrodynamic and control model for the tethered underwater robot system. Only in this way the hydrodynamic and control nature of a tethered underwater robot during different kinds of control manipulations can be numerically revealed objectively.
In this paper, a hydrodynamic and control model to simulate the trajectory following control of a tethered underwater robot system is proposed, and the hydrodynamic performances of the robot and the umbilical cable are observed. To achieve this goal, three-dimensional hydrodynamic model of tethered underwater robot system is first introduced, feed-forward control technique for adjusting the length of umbilical cable and incremental PID algorithm for regulating the rotating speeds of propellers are then incorporated into the hydrodynamic model forming the hydrodynamic and control model. Based on the established hydrodynamic and control mode, relationships between the thrusts from the propellers and the rotating speeds of the propellers, and those among the trajectory following of the underwater robot and the control actions of adjusting the length of umbilical cable and governing the rotating speeds of the propellers are analyzed, and also the hydrodynamic performances of the tethered underwater robot system under the control manipulation are observed. In the research, the amplitude limit filtering method is applied in solving the governing equations of the umbilical cable, this technique is applied to avoid the chattering effect in the cable tension computation, so that a successive and stable computation process is maintained. The main factors affecting the singular nature of coefficient matrices during the numerical solutions of the proposed model are also investigated in the paper.
Topology Optimization Design of the Cantilever Pedestal on a Stiffened Cylindrical Hull
Authors: Yuan Siming , Wang Yue , Cheng Yuansheng , Zhang Pan , Liu Jun 
Published: December 2020

Abstract
The impedance value of the pedestal on a stiffened cylindrical hull directly reflects its resistance to the transmission of vibration waves. In this study, the topology optimization is used to obtain the pedestal with improved impedance and reduced weight. Taking a cuboid with the given dimensions as the research object, the mathematical model of topology optimization is established, in which the element densities is taken as the design variables. According to the optimization results, a new type of cantilever pedestal is obtained. On this basis, the position, size and shape of the main components of the new pedestal are further optimized. Then, the strength and vibration characteristics are calculated and compared. The final optimization results show that the optimized cantilever pedestal with three brackets and a closure plate can effectively improve the minimum impedance of the base. And the thickness of the middle bracket should be much larger than that of the two sides and the closure plate. Compared with the original scheme, the minimum impedance of the optimized pedestal increases by 8.67% while the weight of the structure decreases by 25.69%. The research work provides a good reference for the design of the pedestal.