bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study on the Flow Field and the Shielding Effect of a Hemisphere Artificial Reef and Other Alike Sub-Sea Structures
Authors: Zhao Lin , Tan Junwei 
Published: November 2019

Abstract
A hemisphere artificial reef is designed and numerically simulated in this paper. Investigations of this structure subject to various flow fields with different hole ratios and different diameter are carried out. Besides, the effect of the hemisphere structure to the surrounding flow field is discussed. Further studies are carried out for an array of hemisphere structures of this kind. Comparing to the traditional artificial structures like the trapezoidal reefs and square reefs, the hemisphere reef can not only produce a qualified ascending flow field, but his internal shadowing effect is not negligible.This area then can provide a better ocean ecological environment and living environment to attach and promote the marine life.
Cargo Liquefaction and Influence on Ship Stability
Authors: Chua Kie Hian , Zhang Yali , Konovessis Dimitrios 
Published: November 2019

Abstract
Fine grain solid bulk cargo with “sufficient” moisture content may undergo liquefaction during a voyage, posing a danger to the bulk carrier and the crew on-board due to its potential to shift and adversely affect the vessel’s stability. Between the years 2005 to 2017, it is believed that at least 21 bulk carriers have been lost due to cargo liquefaction. Most of these vessels are of 60,000 deadweight tonnes (DWT) and below, i.e. belonging to the “handysize” class. At the present moment, liquefaction is thought to occur through either conventional liquefaction or dynamic separation. In the former, wet granular cargo particles are rearranged through cyclic loads induced by the ship’s motions, resulting in overall compaction of the cargo and a corresponding increase in pore pressure between the particle grains. Shear resistance of the cargo pile decreases and movement of significant portions of the liquefied cargo material may occur, which in turn poses significant risks for the vessel. In dynamic separation, a pile of wet granular cargo particles undergo progressive transformation through intermediate stages, where the moisture separates from the cargo pile, forming fluid slurry comprising water and entrained particles that would be denser than water perched on top of a drier, compacted particle pile. The slurry will slosh with the vessel motion adversely influencing the stability of the vessel. Compared to conventional liquefaction, the compacted particle pile is drier and less susceptible to shift under vessel movement. In this study, a numerical modelling to assess the impact of the two cargo liquefaction mechanisms on a vessel’s stability is undertaken. The numerical models will be described and the results will be discussed.
Evaluation of Entropy Generation Methods in Wells Turbine
Authors: Licheri F. , Ghisu T. , Virdis I. , Puddu P. , Cambuli F. 
Published: November 2019

Abstract
Entropy generation analyses have been applied, in recent years, to a variety of systems, including Wells turbines. This can be a very powerful method, as it can provide important insights into the irreversibilities of the system, as well as a methodology for identifying, and possibly minimizing, the main sources of loss. However, some of the simplifications used in recent studies raise more than a concern on the validity of the approach. This work proposes a method based on RANS equations to evaluate the entropy production in Wells turbines. An estimation of the second-law efficiency of different Wells turbine rotors is also presented, under conditions representative of the air flow inside an OWC device. The main sources of entropy generation are highlighted and compared for the different geometries.
Centrifuge Modelling of a Novel Skirted Spudcan for Penetration in Layered Soil
Authors: O’Loughlin Conleth , Gaudin Christophe , Quah Matthew , Perry Michael 
Published: November 2019

Abstract
This paper reports on a series of centrifuge tests to investigate the feasibility and performance of a novel spudcan foundation design featuring a peripheral skirt with side openings. The ‘skirted spudcan’, designed and patented by Keppel, is particularly beneficial in layered seabeds with a clay layer overlaying sand. The purpose of the side openings is to enable the clay trapped within the spudcan skirt to flow outside the skirt, so the skirt can penetrate into the sand and develop the required fixities against combined vertical, horizontal and moment loading. The centrifuge tests considered different skirted spudcan designs, each 10 m in diameter, but with a skirt length of either 1.38 m or 2.76 m, two spudcan invert shapes and various configurations of side and top openings. The model skirted spudcans were penetrated into a soil sample featuring a clay layer 6 m thick (in prototype scale) with an average undrained shear strength of about 15 kPa, overlaying a silica sand layer with a relative density of about 40%. The skirted spudcan embedded the sand layer by more than the skirt height at the maximum penetration resistance of about 4 MPa. However, examination of the model after retrieval demonstrated that a clay layer remained inside the skirt, despite the openings on the side of the skirt. The comparison between the eight tests demonstrated that the thickness of the clay plug reduces with the strength of the soil and with the size of the openings. Large horizontal openings located at the top of the skirt were shown to generate the lowest plug thickness and the largest skirt embedment into the sand. Somehow surprisingly, the addition of top openings (in addition of side openings) does not have beneficial effects. In general, the results demonstrated the efficiency of the skirted spudcan with side openings concept. Although the clay plug inside the skirt compartment was only partially expelled, significant skirt embedment into the sand layer (and hence high fixities) could be achieved. The high compressive stresses within the residual clay plug should limit concerns about potential rocking of the spudcan when clay remains trapped within the skirt compartment.
Realistic Adaptive DP Controller for Flotel Operating in Side-by-Side Configuration With FPSO
Authors: Yenduri A. , Magee A. R. , Liu J. , Xu W. , Choudhary A. , Hussain A. A. 
Published: November 2019

Abstract
Side-by-side operation of multiple floaters in the ocean environment is very challenging and the operators always prefer a maximum operable weather window, in order to minimise the cost incurred from the downtime. The safety of the gangway connecting the floaters is very crucial and its dynamic response in the ocean environment raises concerns during operations. Therefore, an efficient dynamic positioning system is essential to maintain the floater and ultimately, the gangway response within the desired limits. In this work, a novel dynamic positioning system for floater operating aside another vessel is presented. The system includes an adaptive controller combined an optimised thruster allocation law and with a sea state detector. The adaptive control is achieved by using the barrier Lyapunov function and a predictor-based method in combination with the neural network scheme. The limitations include the saturation of inputs and the forbidden zones due to thruster-thruster or thruster-hull interaction. An optimised allocation for lower fuel consumption, wear and tear of the thruster equipment and to ensure the resultant command in the respective direction of the azimuth thrusters is designed. The optimisation here is a non-convex problem and a locally convex reformulation of second order is implemented. The presence of unknown shielding effect due to nearby vessel in a side-by-side configuration and input time delay is also considered in the development of this thruster allocation law. In order to overcome these effects, a novel sea state detector is designed. The sea state detector can effectively monitor the variation of drift wave-induced force on the vessel and activate the neural network compensator in the controller when a large wave drift force is identified. Simulation studies are conducted to verify the efficiency of this dynamic position system and a demonstration of flotel in side-by-side configuration with a turret moored FPSO is presented for the non-collinear ocean environment.
Research on the Probability Distribution of the Underwater Moving of the Wrecked Targets
Authors: Duan Wenyang , Shi Zhang , Chen Yunsai , Huang Limin , Cao Guanzhou , Zhang Hongsen 
Published: November 2019

Abstract
There has a great challenge for deep-sea exploration and search because the underwater motion trajectories and sinking location of wrecked targets are uncertain under the influence of random factors such as currents. The traditional underwater motion model can’t know exactly the probability distribution of wrecked targets. This thesis introduces Monte-Carlo random function into the underwater non-dynamic motion equations and the targets sinking location probability model based on Monte-Carlo method is established as well. The purpose is to get the targets’ sinking probability distribution and to improve the successful probability of searching the wrecked targets. In this thesis, the motion reference frame is introduced firstly, and the motion model of underwater non-dynamic subsidence based on the motion reference frame is established then. The Monte-Carlo method of stochastic simulation is discussed at the same time. After that the drop point of the sandbag is taken as an example to verify the reliability of the model. Finally, the probability of targets dispersion underwater is simulated and analyzed, and the conclusion is drawn that the whole points are normally distributed.
Fundamental Engineering Characteristics of Cohesive Sediments in the Northern Region of South China Sea
Authors: Li Shuzhao , Jia Xu , Li Zhigang , Li Jiagang 
Published: November 2019

Abstract
The northern region of South China Sea is the important strategic region for the offshore oil and gas resources development in China. The main shallow sediment of the region is the cohesive soil with diverse engineering characteristics difficult to be determined. The paper collects the comprehensive geotechnical data obtained from the laboratory test and the in-situ Cone Penetration Test (CPT) for the offshore oil and gas projects in the northern region of South China Sea, and presents the fundamental engineering characteristics of the cohesive soil. Results indicate that the cohesive soil with the low plasticity index and the low clay particle content in shallow water is obviously different from that in deep water in the northern region of South China Sea. The physical properties of the clay soil with the high plasticity index and high clay particle content in the northern deep water region of South China Sea are similar to those found in the Gulf of Mexico and West Africa. Moreover, there are two different deposit modes for the sediment in the northern region of South China Sea, which are the fine-grained and coarse-grained govern deposit modes in deep and shallow water respectively. It is found that the sleeve friction ratio of the cohesive sediment is very low in shallow water. The normalized values of the clay soil in deep water are consistent with those from the Gulf of Mexico and West Africa.
Qualification of TMCP Pipe for Severe Sour Service: Mitigation of Local Hard Zones
Authors: Newbury B. D. , Fairchild D. P. , Prescott C. A. , Anderson T. D. , Wasson A. J. 
Published: November 2019

Abstract
C-Mn steels are extensively used as line pipe material for sour service oil and gas applications, i.e. in the presence of hydrogen sulfide (H2S), because of their ease of fabrication, weldability and significantly lower cost compared to Corrosion Resistant Alloys (CRAs). However, use of C-Mn steel in sour conditions can be limited by its susceptibility to various hydrogen damage mechanisms such as sulfide stress cracking (SSC) and hydrogen induced cracking (HIC). Presently, there are several industry standards which provide guidelines for materials selection and qualification testing to ensure the integrity of carbon steel pipelines in sour service. In recent years, examples of line pipe susceptibility to SSC have occurred due to undetected Local Hard Zones (LHZs) produced during steel plate manufacture. A companion paper (Fairchild, et al, [1]) describes historical and one newly recognized root causes for LHZs. Due to this newly recognized root cause, the adequacy of the current industry practice for specifying and qualifying C-Mn line pipe for severe sour service should be evaluated. In this work, a new approach to monitoring steel plate manufacture during Thermo Mechanical Controlled Processing (TMCP) in order to manage LHZs is explained. Results from implementing this qualification approach will be discussed. In addition, several gaps were identified in the current test methods and various potential modifications to address these gaps were identified. Based on the results of these studies, recommendations to the test methods are made to improve the robustness in the materials qualification process used for sour pipeline projects.
Hole Cleaning Related Stuck Pipe Analysis During Extended Reach Drilling by Using a Transient Cuttings Transport Model: A Case Study
Authors: Zeng Hao , Zeng Yijin , Zhang Feifei , Yang Guang , Wang Yuezhi , Wang Xi 
Published: November 2019

Abstract
Insufficient hole cleaning is one of the major challenges in drilling, particularly in extended-reach drilling (ERD). This paper presents a case study of a stuck pipe incident caused by cuttings pack off during drilling an extended-reach well. A generalized, transient, solid-transport model that can handle different flow patterns is used to replay the hole-cleaning process. Results show that, although cuttings beds in the deviated part of the wellbore are not significant while drilling ahead, cuttings can still cause problems during tripping. This study reinforces the facts that hole cleaning in wells with long deviated sections is complicated and a transient approach is required to fully understand the hole-cleaning condition. Effective hole cleaning does not only mean that the cuttings concentration is low or the cuttings transport ratio is high. In addition, the absence of additional cuttings being produced from the shale shaker during circulation does not necessarily indicate that the hole is clean. The cuttings accumulated behind the BHA can lead to tight spots and over-pull incidents during tripping. By conducting drill string reciprocations without circulation, the tight spots can be “worked through” but packed cuttings cannot be removed from the wellbore. This paper presents lessons learned from this incident, as well as recommendations for future operations.
Time-Varying Vector Field Guidance Law for Path Following and Obstacle Avoidance for Underactuated Autonomous Vehicles
Authors: Xu Haitong , Hinostroza M. A. , Guedes Soares C. 
Published: November 2019

Abstract
This paper presents a time-varying vector field guidance law for path-following control of underactuated autonomous vehicles. The proposed guidance law employs a time-varying equation to calculate the desired heading angle. A sliding mode controller is designed to track the desired heading angle, and it is proved to be globally exponentially stable (GES). With this controller, the stability proof for guidance system is presented and the equilibrium point of the guidance system is Uniform Global Asymptotic Stable (UGAS). In order to avoid the obstacle when ship approaching the predefined path, a combined Path-following and repelling field based obstacle avoidance system is proposed in this paper. Simulations are carried out to validate the performance of the combined path-following and collision avoidance system.
Extreme Wind and Wave Predictability From Operational Forecasts at the Drake Passage
Authors: Campos Ricardo Martins , D’Agostini Andressa , Machado Cruz Leandro , Reis Leite França Bruna , Guedes Soares C. 
Published: November 2019

Abstract
The Drake Passage is an ocean area between the South America and Antarctic with very extreme wind and wave climates. The forecast accuracy of surface winds and significant wave heights is analyzed in the present paper, in order to study the behavior and distribution of model uncertainties as a function of: forecast range, severity, location, and numerical model. The operational forecast considered is run twice a day by the Brazilian Navy, and a period of one year (2017) is selected for the assessment. Observations consist of four satellite missions: JASON2, JASON3, CRYOSAT, and SARAL. The numerical atmospheric models with 10-m winds are GFS (Global Forecast System) and ICON (Icosahedral Nonhydrostatic Model). They force wave simulations using the model WAVEWATCH III with a mosaic of two grids. The forecast horizon analyzed is five days, which is made publicly available by the Brazilian Navy. Results show that under calm to moderate conditions, within the first two days of forecast, the wind and wave model skill is very high. However, above the 90th percentile and beyond the third forecast day, the predictability drops significantly. It highlights specific contours of forecast range versus percentiles where the wind and wave modelers should focus, in order to anticipate and to improve the predictability of extreme events at the Drake Passage.
Buoyancy Induced Convection of Riser Gas in Deepwater Drilling Operations
Authors: Nahri Syed Y. , Chen Yuanhang , Williams Wesley , Santos Otto , Sun Ting 
Published: November 2019

Abstract
Riser gas migration has been an area of interest since the last three decades due to its importance in gas handling in deepwater drilling operations. A previously conducted full-scale test at LSU Petroleum Engineering Research & Technology Transfer (PERTT) well facility indicates, as contrary to traditional belief, significant migration of dissolved gas taking place even when circulation had ceased. In order to understand whether a reduction in density of the underlying contaminated mud resulting from gas absorption is the contributing factor to the above-mentioned phenomenon, a computational fluid dynamics (CFD) analysis was conducted to study the transport of the gas influx while in solution due to buoyancy induced convective mass transfer and simultaneous diffusion.
Simulations performed in this study include the hydrodynamics of the upward moving gas cut mud and simultaneous mass transfer of natural gas into the under-saturated drilling fluid. The parameters studied here are the distance traveled of the gas cut mud and saturation levels in the drilling fluid along the length of the riser. The dense phase behavior was shown to have considerable effects on gas loading capacities which in turn affected the density of the gas cut mud, and at pressures upwards of 5,000 psi, the solubility of a natural gas influx can be seen to be infinite in certain synthetic and oil-based drilling fluids. The rate and extent of mass transfer are dependent on drilling fluid density gradients, which in turn are based on gas influx saturation level. Results obtained from this study can help better comprehend migration phenomena of a dissolved influx in oil-based muds in a riser with the BOP shut in and when circulation has ceased.
Anti-Icing and De-Icing of Pipe Structures on Marine Vessels Using Waste Heat Recovery
Authors: Æsøy Lene , Piehl Henry , Bjørnøy Palmar 
Published: November 2019

Abstract
One of the major challenges for a ship sailing in Arctic waters is ice aggregation. Atmospheric water or sea spray that comes into contact with the cold railing, equipment and superstructure deposits ice on the exposed surfaces. This ice can build up over time to such an extend, that the weight of the ice can severely impair the ships stability, even lead to capsizing. To prevent such accidents, the IMO Polar Code for ships operating in Arctic areas requires countermeasures against icing. Ulmatec Pyro has developed a “double pipe system” that makes use of waste heat, recovered from the ships propulsion and energy system.
The main objective of this research project has been to investigate the behavior of anti-icing and de-icing for pipe structures to provide design rules and operational guidelines for such systems.
Pipe systems have been studied using both numerical and experimental methods. First a simple 1D pipe system, simulating the steady heat transfer with a finite difference method, was implemented. The purpose of this model is was to be able to quickly study design variations. Next, a more advanced 3D axis-symmetric heat flow model was simulated, using a commercial transient finite element solver. The results of the advanced model was used to evaluate the simple model. Subsequently these simulation tools were used to support the design decisions for the experimental setup. To get the IMO approval for the double pipe system, the experiments were conducted at the site of the classification society. The experimental setup was used to validate the simulation model, and furthermore as a design verification lab for Ulmatec Pyro.
A comparison of the results between both numerical simulation models and experiments show a good correlation. In addition, the experiments provide a valuable insight into the icing- and anti-icing processes. Specifically, a better understanding of the complex ice melting process.
Non-Repeatability, Scale- and Model Effects in Laboratory Measurement of Impact Loads Induced by an Overtopped Bore on a Dike Mounted Wall
Authors: Streicher Maximilian , Kortenhaus Andreas , Altomare Corrado , Hughes Steven , Marinov Krasimir , Hofland Bas , Chen Xuexue , Suzuki Tomohiro , Cappietti Lorenzo 
Published: November 2019

Abstract
Overtopping bore impact forces on a dike mounted vertical wall were measured in similar large-scale (Froude length scale factor 1-to-4.3) and small-scale (Froude length scale factor 1-to-25) models. The differences due to scale effects were studied, by comparing the up-scaled force measurements from both models in prototype. It was noted that if a minimum layer thickness, velocity of the overtopping flow and water depth at the dike toe were maintained in the small-scale model, the resulting differences in impact force due to scale effects are within the range of differences due to non-repeatability and model effects.
Study on Desulfurization and Decarbonization Technology of Natural Gas on Bohai Offshore Platform
Authors: Lu Ping , Qu Zhaoguang , Gao Guoqiang , Huang Yan , Qian Xin , Cheng Lin 
Published: November 2019

Abstract
Based on the latest developments of desulfurization and decarbonization technologies of acidic natural gas, the process characteristics, product purity, consumptions, occupied area, advantages and disadvantages of various desulfurization and decarbonization methods are analyzed and compared, and the adaptability of the methods on offshore platform is fully considered. According to the actual situation of a Bohai offshore gas field, the low temperature separation method is adopted and the desulfurization and decarbonization process is simulated by using HYSYS software, and then the technical scheme is put forward to meet the requirements of the gas turbines on surrounding platforms and the transportation quality index of the southwest Bohai gas supply pipeline network. This research has a certain reference value for technical programs of natural gas desulfurization and decarbonization on similar offshore projects.