bluuebunny/crossref_metadata_2025 huggingface dataset:
Comprehensive definition of genome features in Spirodela polyrhiza by high‐depth physical mapping and short‐read DNA sequencing strategies
Authors: Michael Todd P. , Bryant Douglas , Gutierrez Ryan , Borisjuk Nikolai , Chu Philomena , Zhang Hanzhong , Xia Jing , Zhou Junfei , Peng Hai , El Baidouri Moaine , ten Hallers Boudewijn , Hastie Alex R. , Liang Tiffany , Acosta Kenneth , Gilbert Sarah , McEntee Connor , Jackson Scott A. , Mockler Todd C. , Zhang Weixiong , Lam Eric
Published: October 2016

Spirodela polyrhiza is a fast‐growing aquatic monocot with highly reduced morphology, genome size and number of protein‐coding genes. Considering these biological features of Spirodela and its basal position in the monocot lineage, understanding its genome architecture could shed light on plant adaptation and genome evolution. Like many draft genomes, however, the 158‐Mb Spirodela genome sequence has not been resolved to chromosomes, and important genome characteristics have not been defined. Here we deployed rapid genome‐wide physical maps combined with high‐coverage short‐read sequencing to resolve the 20 chromosomes of Spirodela and to empirically delineate its genome features. Our data revealed a dramatic reduction in the number of the rDNA repeat units in Spirodela to fewer than 100, which is even fewer than that reported for yeast. Consistent with its unique phylogenetic position, small RNA sequencing revealed 29 Spirodela‐specific microRNA, with only two being shared with Elaeis guineensis (oil palm) and Musa balbisiana (banana). Combining DNA methylation data and small RNA sequencing enabled the accurate prediction of 20.5% long terminal repeats (LTRs) that doubled the previous estimate, and revealed a high Solo:Intact LTR ratio of 8.2. Interestingly, we found that Spirodela has the lowest global DNA methylation levels (9%) of any plant species tested. Taken together our results reveal a genome that has undergone reduction, likely through eliminating non‐essential protein coding genes, rDNA and LTRs. In addition to delineating the genome features of this unique plant, the methodologies described and large‐scale genome resources from this work will enable future evolutionary and functional studies of this basal monocot family.
Spurious reticulocyte profiles in a dog with babesiosis
Authors: Piane Laetitia , Théron Marie‐Laure , Aumann Marcel , Trumel Catherine
Published: October 2016

A 9‐year‐old, female Maltese dog was referred to the Veterinary School of Toulouse with a 2‐day history of anorexia and weakness. On clinical examination, the dog had hyperthermia (39.7°C), abdominal discomfort, and polypnea. Significant laboratory findings included pigmenturia, hyperbilirubinemia, hypercreatininemia, hyperfibrinogenemia, abnormal Snap canine pancreas‐specific lipase, and pancytopenia with a nonregenerative anemia. A peripheral blood smear revealed numerous intraerythrocytic large Babesia but no polychromasia. There was a discrepancy between the absolute automated reticulocyte count (Sysmex reticulocyte count: 60 × 109/L; RI 19.4–150.1 × 109/L) and the manual reticulocyte count (3.6 × 109/L) as well as the absence of polychromasia. The optical red blood cell scattergram showed an abnormal isolated reticulocyte cluster at the location of low‐fluorescence ratio cells. These findings were interpreted as erythrocytes parasitized by large Babesia. The discrepancy between the Sysmex reticulocyte count and the manual reticulocyte count has been reported previously in people with falciparum malaria and numerous intra‐erythrocytic Plasmodium falciparum organisms. This spurious reticulocyte profile and reticulocyte count were observed with the Sysmex XT‐2000iV and the ProCyte using the same fluorescent dye polymethine but not with the LaserCyte using new methylene blue which does not stain Babesia organisms on a blood smear performed for manual reticulocyte counting.
COMPUTED TOMOGRAPHIC FINDINGS IN 24 DOGS WITH LIPOSARCOMA
Authors: Fuerst Jason A. , Reichle Jean K. , Szabo David , Cohen Eli B. , Biller David S. , Goggin Justin M. , Griffin John F. , Aarsvold Stacie , Emerson Susan E.
Published: October 2016

Computed tomography (CT) continues to become more widely available for assessment of tumors in dogs, yet there are no studies describing the CT appearance of canine liposarcomas. In this retrospective, multicenter study, CT images of dogs with histologically confirmed liposarcomas were reviewed for size, location, attenuation, contrast enhancement, border definition, internal homogeneity, local infiltration, and mineralization. A total of 24 dogs with 26 liposarcomas were sampled. Mean attenuation was +15.2 (SD = 22.3) Hounsfield units (HU) with a range of –36 to +47.5 HU based on representative regions of interest. Twenty tumors (77%) contained focal areas of fat attenuation. All masses enhanced with contrast medium administration, which is distinct from what has been reported previously in infiltrative lipomas. Other CT features associated with canine liposarcomas included heterogeneous internal attenuation (81%) and lack of a clearly defined capsule (38%) suggesting infiltration of local structures. Six tumors (23%) had foci of mineralization. Findings from the current study indicated that liposarcoma should be considered as a differential diagnosis for mixed‐attenuation, contrast‐enhancing masses in dogs that contain at least one focus of fat attenuation on precontrast images; however, presence of foci of fat attenuation was not a necessary finding for the diagnosis of canine liposarcoma.
Numerical Simulation of Particulates in Multistage Axial Compressors
Authors: Saxena Swati , Jothiprasad Giridhar , Bourassa Corey , Pritchard Byron
Published: October 2016

Aircraft engines ingest airborne particulate matter, such as sand, dirt, and volcanic ash, into their core. The ingested particulate is transported by the secondary flow circuits via compressor bleeds to the high pressure turbine and may deposit resulting in turbine fouling and loss of cooling effectiveness. Prior publications focused on particulate deposition and sand erosion patterns in a single stage of a compressor or turbine. This work addresses the migration of ingested particulate through the high pressure compressor (HPC) and bleed systems. This paper describes a 3D CFD methodology for tracking particles along a multistage axial compressor and presents particulate ingestion analysis for a high pressure compressor section. The commercial CFD multiphase solver ANSYS CFX® has been used for flow and particulate simulations. Particle diameters of 20, 40, and 60 μm are analyzed. Particle trajectories and radial particulate profiles are compared for these particle diameters. The analysis demonstrates how the compressor centrifuges the particles radially toward the compressor case as they travel through the compressor; the larger diameter particles being more significantly affected. Nonspherical particles experience more drag as compared to spherical particles, and hence a qualitative comparison between spherical and nonspherical particles is shown.
Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors
Authors: Jenny Philipp , Bidaut Yves
Published: October 2016

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high-cycle fatigue. In addition to the well-established high-frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes (IGVs), the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing the high-cycle fatigue during the design phase. The unsteady fluid–structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns, dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries, a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries; therefore, they are not critical and confirm a robust and reliable design.
Effects of Oil-Based Drilling-Fluid Rheological Properties on Hole-Cleaning Performance
Authors: Werner Benjamin , Myrseth Velaug , Lund Bjørnar , Saasen Arild , Ibragimova Zalpato , Ytrehus Jan David , Gyland Knud Richard
Published: October 2016

Drilling fluids play an important role in safe and efficient drilling operations. Wellbore stability, formation integrity, drill string lubrication, and cuttings transport are among their main requirements. The removal of a cuttings bed is one of the major difficulties while trying to keep up a steady drilling progress. Deviated and long horizontal wellbore sections provide challenges not only to the drilling equipment in use, but also to the fluids. Cuttings accumulate easily on the bottom of a wellbore section due to gravity and can therefore reduce hole cleaning efficiency.

Cuttings transport is highly dependent on the properties of the drilling fluid. Viscosity, density and gel strength are among the key parameters. Drilling fluids have in general a complex composition with either water or oil as a base substance. Demanding operating conditions, for example high temperature difference from topside to the deep downhole sections or varying shear rates throughout the wellbore, also influence the properties of the fluids during operation. Drilling fluids have to be adapted to all these different drilling situations.

The aim of the full project is to compare different water- and oil-based drilling fluids regarding their hole cleaning abilities. As part of the experimental study where drilling fluids are circulated in a 10 m long flow-loop test section with a free-whirling rotating inner drill string, rheological characterization with an Anton Paar MCR rheometer is performed. These measurements include determination of flow properties, yield stress and viscosity-temperature dependence. The results are correlated with the industry standard procedures for the testing of drilling-fluid properties with Fann 35 viscometers (API/ ISO standards). Measurements performed on viscometers at the oil rigs are done to receive fast results in order to control the drilling operation. In contrast, rheometer measurements provide the possibility of a deeper comprehension of the rheological properties of the drilling fluids due to the advanced measurement system.

This work presents rheological properties for a typical oil-based drilling fluid commonly used on the Norwegian Continental Shelf, and includes a comparison with two other oil-based drilling fluids based on previously published work. The rheometer results are analyzed in relation to the flow loop experiments and to the viscosity data measured in accordance with the API/ISO specifications. The results from the rheological comparison together with the results from the flow-loop experiments are expected to make an influencing contribution to the question of why various drilling fluids perform so differently in terms of cuttings transport.
Ultimate Limit State Analysis of FRP Composite Sandwich Plates: Development of a Semi-Analytical Method
Authors: Ringsberg Jonas W. , Blomgren Niklas , Prevc Matej
Published: October 2016

The development of Sandwich PULS, a semi-analytical calculation tool for predicting the ultimate limit state (ULS) of FRP composite sandwich plates is presented. This was done by extending DNV GL’s semi-analytical calculation tool Composite PULS, which is used for quick estimation of the ULS for unstiffened composite plates. ULS was evaluated in terms of the first buckling load and the first ply failure (FPF).

The Sandwich PULS code was developed by implementing formulations for sandwich plate theory. First-order shear deformation theory (FSDT) was implemented to include the transverse shear deformations that are highly important for sandwich plates with poor shear stiffness of the core. The Sandwich PULS code was evaluated against nonlinear finite element analyses (FEA).

It was concluded that Sandwich PULS shows good agreement with FEA-predicted critical buckling loads. For all inspected plates, Sandwich PULS shows improved results compared to Composite PULS. Differences between Sandwich PULS and FEA are caused by the difference in evaluating shear stiffness. It has been shown that neglecting shear stiffness of faces results in good agreement between Sandwich PULS and FEA, while use of conventional shear correction factors proved to be unfavourable for sandwich plates. It was found that Sandwich PULS is limited in terms of slenderness. Sandwich plates with soft core should not have slenderness below 20 to assure an accurate solution.
Benjamin-Feir Wave Instability on the Opposite Current
Authors: Shugan Igor V. , Hwung Hwung-Hweng , Yang Ray-Yeng
Published: October 2016

An analytical weakly nonlinear model of Benjamin–Feir instability of a Stokes wave on nonuniform unidirectional current is presented. The model describes evolution of a Stokes wave and its two main sidebands propagating on a slowly-varying steady current. In contrast to the models based on versions of the cubic Schrodinger equation the current variations could be strong, which allows us to examine the blockage and consider substantial variations of the wave numbers and frequencies of interacting waves. Interaction with countercurrent accelerates the growth of sideband modes on a short spatial scale. An increase in initial wave steepness intensifies the wave energy exchange accompanied by wave breaking dissipation, results in asymmetry of sideband modes and a frequency downshift with an energy transfer jump to the lower sideband mode, and depresses the higher sideband and carrier wave. Nonlinear waves may even overpass the blocking barrier produced by strong adverse current. The frequency downshift of the energy peak is permanent and the system does not revert to its initial state. We find reasonable correspondence between the results of model simulations and available experimental results for wave interaction with blocking opposing current.
Numerical Study of Pipeline-Riser Slugging in an Open Source Way
Authors: Meng Xiangyin , Tao Longbin
Published: October 2016

This paper describes an open source numerical investigation into slugging flow in a typical two-dimensional pipeline-riser for the first time. CFD tools Gmsh, OpenFOAM and ParaView are employed for mesh generation, numerical simulation and post process respectively. Original OpenFOAM solver ‘twoPhaseEulerFoam’ is used to simulate the gas-liquid flow in the system consisting of inclined pipeline and vertical riser. By comparing the numerical results of slugging phenomena and pressure fluctuation periods to previous experimental observations, it can be confirmed that it is possible to carry out such simulations in a complete open source way. Based on case studies, pressure fluctuation features in a typical single slugging cycle is also discussed in details. Furthermore, temperature variation of the internal flow due to air compressibility is found to have similar fluctuation period as that of pressure. In the end, the impacts of fluid properties on system pressure variations are discussed too. To future numerical investigations of subsea pipeline-riser induced slugging, present work is a basis for further open source solvers development.
The Estimation of Carbonic Gas Emission by Ice-Class Large-Size Ships Moving in Ice Using Different Escorting Methods
Authors: Dobrodeev Aleksei , Sazonov Kirill
Published: October 2016

Today, there is a strong emphasis on navigation safety in polar waters. IMO Subcommittee on Ship Design and Equipment has issued the Polar Code encompassing the matters of design, structure, equipment and operation of ships intended for polar waters. One of the main objectives of this Code is to work out the rules for man-made pollution management in the Arctic. Modern marine logistics systems developed to transport hydrocarbons and natural gas produced at the Arctic offshore include the ships with high ice class capable of operating both autonomously and with ice-breaker pilotage. This work explains how to assess, as per IMO formulas, the CO2 emissions from large ice-going ships in different scenarios of their ice-breaker pilotage. Obtained results served to assess power efficiency of large ships allowing evaluation of the pilotage techiques, both existing and those suggested by the authors of this paper, in terms of environmental safety.
Study on Numerical Methodologies for Assessing Ultimate Bending Moment of Ship Hull Girder
Authors: Xu Ming Cai , Song Zhao Jun
Published: October 2016

Nonlinear finite element analysis is usually used to assess the ultimate strength of hull girder, which includes implicit analysis and explicit dynamic analysis. So far, most of researchers use the implicit analysis to assess the ultimate strength of various vessels or stiffened plates. Comparing with the implicit analysis, the explicit dynamic analysis may be more stable since this method doesn’t need to consider the convergence of solution, and can consider the transient influence of time. However, the accuracy of solution results and time in the explicit dynamic method is very important. This depends on modelling configurations, such as the loading time, geometric ranges of finite element models, element types and applying methods of loading. The purpose of the present paper is to investigate the influences of these factors, and then to figure out a reliable numerical method which meets permitted accuracy and consumes acceptable computer resource in explicit dynamic analysis.
Comparison of Offshore Wind Farm Layout Optimization Using a Genetic Algorithm and a Particle Swarm Optimizer
Authors: Pillai Ajit C. , Chick John , Johanning Lars , Khorasanchi Mahdi , Barbouchi Sami
Published: October 2016

This article explores the application of a binary genetic algorithm and a binary particle swarm optimizer to the optimization of an offshore wind farm layout. The framework developed as part of this work makes use of a modular design to include a detailed assessment of a wind farm’s layout including validated analytic wake modeling, cost assessment, and the design of the necessary electrical infrastructure considering constraints. This study has found that both algorithms are capable of optimizing wind farm layouts with respect to levelized cost of energy when using a detailed, complex evaluation function. Both are also capable of identifying layouts with lower levelized costs of energy than similar studies that have been published in the past and are therefore both applicable to this problem. The performance of both algorithms has highlighted that both should be further tuned and benchmarked in order to better characterize their performance.
Numerical Simulation of Dynamics of a Spar Type Floating Wind Turbine and Comparison With Laboratory Measurements
Authors: Min Hyunseong , Peng Cheng , Duan Fei , Hu Zhiqiang , Zhang Jun
Published: October 2016

Wind turbines are popular for harnessing wind energy. Floating offshore wind turbines (FOWT) installed in relatively deep water may have advantages over their on-land or shallow-water cousins because winds over deep water are usually steadier and stronger. As the size of wind turbines becomes larger and larger for reducing the cost per kilowatt, it could bring installation and operation risks in the deep water due to the lack of track records. Thus, together with laboratory tests, numerical simulations of dynamics of FOWT are desirable to reduce the probability of failure.

In this study, COUPLE-FAST was initially employed for the numerical simulations of the OC3-HYWIND, a spar type platform equipped with the 5-MW baseline wind turbine proposed by National Renewable Energy Laboratory (NREL). The model tests were conducted at the Deepwater Offshore Basin in Shanghai Jiao Tong University (SJTU) with a 1:50 Froude scaling [1]. In comparison of the simulation using COUPLE-FAST with the corresponding measurements, it was found that the predicted motions were in general significantly smaller than the related measurements. The main reason is that the wind loads predicted by FAST were well below the related measurements. Large discrepancies are expected because the prototype and laboratory wind loads do not follow Froude number similarity although the wind speed was increased (or decreased) in the tests such that the mean surge wind force matched that predicted by FAST at the nominal wind speed (Froude similarity) in the cases of a land wind turbine [1]. Therefore, an alternative numerical simulation was made by directly inputting the measured wind loads to COUPLE instead of the ones predicted by FAST. The related simulated results are much improved and in satisfactory agreement with the measurements.
Experimental and Numerical Studies of the Plastic Behavior of Large Structural Grillages Subjected to Ice Loads
Authors: Kim Hyunmin , Dolny John , Daley Claude
Published: October 2016

Significant research efforts have been carried out to investigate the plastic behavior of grillage structures. However, most experimental work has used steel or other rigid indenters rather than real ice. The tests therefore showed certain structural response behavior that may occur differently if subjected to ice loads. In this study, ice samples were used to load the structure rather than rigid indenters. This allowed for investigation into structural deformation considering the failure of ice. Two large grillages were prepared and tested. The first grillage tests were intended to study the ultimate load-carrying capacity when subjected to central and symmetric loading. The second grillage was tested to study the influence of variable ice loading positions along a single frame. A finite element (FE) model was developed to analyze the experiments numerically. The load-deflection curves and deformation shapes measured by the MicroScribe® were used to validate the numerical results.
A Study of Multi-Method Based Subsea Pipeline Leak Detection System
Authors: Li Yanyao , Zhang Tianyu , Ruan Weidong , Bai Yong , Zhao Chuntian
Published: October 2016

Pipelines are of most importance to subsea systems. The leakage of pipelines which may be caused by aging or corrosion will lead to serious environmental damage and significant economic losses. In this paper, a submarine pipeline leak detection system is developed to protect environment and also improve the safety of subsea system via quick detection and relatively correct location. The leak detection system includes data acquisition devices, wireless communication devices, the calculation part is also involved, like data processing module, leak detection module, pattern recognition module and positioning module. The corrected flow balance principle and a statistical analysis method, namely Wald’s Sequential Probability Ratio Test (SPRT), are used to decide whether it is leak-free or leak-present. Besides, a pattern recognition system is developed to minimize false alarms. The method of Hydraulic Grade Line was employed to locate the leakage. Our study provides a quick response to leak detection as well as leak location. A quick and convenient method to leak detection and location is provided by this paper.
Data Analytics for Capturing Marine Engine Operating Regions for Ship Performance Monitoring
Authors: Perera Lokukaluge P. , Mo Brage
Published: October 2016

This study proposes marine engine centered data analytics as a part of the ship energy efficiency management plan (SEEMP) to overcome the current shipping industrial challenges. The SEEMP enforces various emission control measures, where ship energy efficiency should be evaluated by collecting vessel performance and navigation data. That information is used to develop the proposed data analytics that are implemented on the engine-propeller combinator diagram (i.e. one propeller shaft with its own direct drive main engine). Three marine engine operating regions from the initial data analysis are noted under the combinator diagram and the proposed data analytics (i.e. data clustering methodology) to capture the shape of these regions are implemented. That consists of implementing the Gaussian Mixture Models (GMMs) to classify the most frequent operating regions of the marine engine. Furthermore, the Expectation Maximization (EM) algorithm is used to calculate the respective parameters of the GMMs. This approach can also be seen as a data clustering algorithm that facilitated by an iterative process for capturing each operating region of the marine engine (i.e. the combinatory diagram) with the respective mean and covariance values. Hence, these data analytics can be used in the SEEMP to monitor the performance of a vessel with respect to the marine operating regions. Furthermore, it is expected to develop advanced mathematical models of ship performance monitoring under these operational regions of the marine engine as the future work.
Numerical Investigation on Spectrum Evolution of Narrow-Banded Random Waves in Shallow Water Based on KdV and Fully Nonlinear Model
Authors: Wang Jinghua , Ma Q. W. , Yan Shiqiang
Published: October 2016

The wave energy density spectrum provides useful information for both coastal engineering practice and applied sciences. However, it is not always available at desired location which can be far away from the observation stations, and should be achieved using approximated approaches. Nevertheless, the spectrum at the desired location may differ significantly from the approximated one due to nonlinear effects. In this paper, long-duration and large-scale evolutions of the wave spectrum in shallow water is investigated numerically. Direct simulations of random seas are carried out by using the weakly nonlinear KdV equation and the fully nonlinear Enhanced Spectral Boundary Integral (ESBI) model respectively. Due to nonlinear effects, the spectral shape is modified and the energy is redistributed after a long-duration (∼1000 peak periods) and large-scale (∼128 peak wave lengths) evolution. The results obtained by using fully nonlinear ESBI model here demonstrate that the flatness occurs only when both the conditions, i.e., large Ursell number and large wave steepness, are satisfied; It will not happen if the Ursell number is large but the steepness is small. This is different from the existing understanding in literature, i.e. spectra tended to become flat (or nearly uniformly distributed) in low frequency part as long as Ursell number is sufficiently large.
Performance of Vibroacoustic Technology for Pipeline Leak Detection
Authors: Giunta Giuseppe , Morrea Silvia , Gabbassov Renat , Bernasconi Giancarlo , Del Giudice Silvio
Published: October 2016

Integrity and operational reliability of pipelines requires a continuous monitoring, able to detect, in real time, failure, sabotage and leak of fluids (e.g. natural gas, crude oil, water, products), and to protect the safety of personnel and local communities.

In the framework of a research project, eni has developed a proprietary pipeline monitoring technology based on vibroacoustic (negative pressure wave) sensing. This paper presents some experimental and theoretical activities for the evaluation of the system performance versus fluid leaks, in terms of maximum detection distance and sensitivity. The field scenario is a 12 km, 3 inch inner diameter sealine in south of Italy, conveying a fluxing agent from an onshore terminal to an offshore platform.

Leak-like events have been produced by opening discharge valves at the terminals. The associated travelling pressure transient, recorded by several monitoring stations, has been compared with the environmental noise (generated by the flow regulation equipment) and with the theoretical models. The predicted propagation parameters and maximum detection distance are in very good agreement with the measured ones: this allows us to use the theoretical simulator for design and performance evaluation of new installations.
Vortex-Induced Motion of a Square Cylinder at Moderate Reynolds Numbers
Authors: Wu Chih-Hua , Ma Shengwei , Kang Chang-Wei , Lim Teck-Bin Arthur , Jaiman Rajeev Kumar , Weymouth Gabriel , Tutty Owen
Published: October 2016

Bluff body structures exposed to ocean current can undergo vortex-induced motion (VIM) for certain geometric and physical conditions. Recently, the study of VIM has been gaining attention for many engineering applications, in particular offshore structures such as buoys, FPSOs, semi-submersibles, Spars and TLPs. The present work is a part of a systematic effort to investigate the VIM response of multi-columns floating platform. In real sea condition, floating platforms are in high Reynolds numbers region and flow patterns around structures are turbulent in nature. For the purpose of investigating and simulating accurately the nonlinear dynamic processes of vortex shedding, transport and wake interactions with the bluff body, the fundamental study of VIM around a square column at moderate Reynolds numbers (1500 ≤ Re ≤ 14000) is firstly investigated. In the present work, the transient flow pattern around a free vibrating square cylinder at moderate Reynolds numbers is numerically investigated by an open source CFD toolbox, OpenFOAM. Good consistency and agreement are found between the present numerical findings and that of experiments. The cylinder, with a blockage area of 4.2%, is mounted on an elastic support for free vibration in the transverse direction. Hybrid RANS-LES turbulence models are considered here for accurate prediction of massively separated turbulent wake flow while maintaining the reasonable computational cost. Three hybrid turbulence models, the DDES (Delayed Detached Eddy Simulation, the k-ω SST-DES (Detached Eddy Simulation), and the k–ω SST-SAS (Scale Adaptive Simulation), are studied and their results are compared with the reported experimental measurements. It is shown that the result of simulation with the k–ω SST-SAS model is closer to the reported literature than the other two and therefore, subsequently adopted for all the simulations of our study in this paper. The scaling effect of cylinder length in the spanwise direction is also studied with the objective to reduce the computational cost. From the comparison with the recent experimental measurements, the discrepancy between the present simulations of reducing cylinder length and the experiment increases only when Re ≥ 4000. This might stem from the increase in wavelength of some vortex shedding modes and turbulence intensity variation in the spanwise direction near the cylinder as Re ≥ 4000. The detailed flow patterns, 3D vortex structures (based on Q-criterion) and vortex-shedding modes are presented in this work as well.
Damping Effect on the Wave Propagation in Carbon Steel Pipelines Under Fluid Hammer Conditions
Authors: Pavlou Dimitrios G. , Ong Muk Chen
Published: October 2016

A sudden reduction of the fluid flow yields a pressure shock, which travels along the pipeline with a high speed. Due to this transient loading, dynamic hoop stresses are developed, that may cause catastrophic damages in pipeline integrity. The vibration of the pipe wall is affected by the flow parameters as well as by the elastic and damping characteristics of the material. Most of the studies on dynamic response of pipelines (a) neglect the effect of the material damping, and (b) are usually limited to harmonic pressure oscillations. The present work is an attempt to fill the above research gap. To achieve this target, an analytic solution of the governing motion equation of pipelines under moving pressure shock is derived. The proposed methodology takes into account both elastic and damping characteristics of the steel. With the aid of Laplace and Fourier integral transforms and generalized functions properties, the solution is based on the transformation of the dynamic partial differential equation into an algebraic form. Analytical inversion of the transformed dynamic radial deflection variable is achieved, yielding the final solution. The proposed methodology is implemented in an engineering example; and the results are shown and discussed.
Chain Out of Plane Bending (OPB) Fatigue Joint Industry Project (JIP) Static Test Program and OPB Interlink Stiffness
Authors: Rampi Lucile , Dewi Fata , Francois Michel , Gerthoffert Arnaud , Vargas Pedro
Published: October 2016

In 2002, several mooring chains of a deepwater offloading buoy failed prematurely within a very small time frame. These chains were designed according to conventional offshore fatigue assessment using API recommendations. With this first deepwater buoy application, a new mooring chain fatigue mechanism was discovered. High pretension levels combined with significant mooring chain motions caused interlink rotations that generated significant Out of Plane Bending (OPB) fatigue loading. Traditionally, interlink rotations are relatively harmless and generate low bending stresses in the chain links. The intimate mating contact that occurs due to the plastic deformation during the proof loading and the high pretension of the more contemporary mooring designs have been identified as aggravating factors for this phenomenon.

A Joint Industry Project (JIP), gathering 26 different companies, was started in 2007 to better understand the Out of Plane Bending (OPB) mooring chain fatigue mechanism and to propose mooring chain fatigue design recommendations.

This paper summarizes the quasi static OPB stiffness measurement campaign and the post processing work to derive the OPB interlink stiffness.
A New User Defined Element for Nonlinear Riser-Soil Interaction Analysis of Steel Catenary Riser Systems
Authors: Liu Jiayue , Kimiaei Mehrdad , Randolph Mark
Published: October 2016

Steel Catenary Risers (SCRs) provide a technically feasible and commercially efficient solution for the offshore field developments in deep waters. Fatigue design of SCRs in the touchdown zone (TDZ) is among the most complicated engineering challenges in riser design.

The cyclic interaction of the riser with seabed leads to a number of complex nonlinear behaviors including soil suction, separation of the riser from the soil, trench formation and degradation of soil resistance during cyclic loading. Accurate simulation of the riser-soil interaction has significant effects on the fatigue performance in the TDZ. Few hysteretic nonlinear riser-soil interaction models have recently been introduced and some of them have been implemented in commercial software packages for analysis and design of riser systems. Due to complexity of the models and also limited access to special software packages with in-built nonlinear soil models, traditional simple linear soil models are still being used widely for riser analysis, in particular for fatigue design.

In this paper, one of the existing nonlinear hysteretic seabed model, already been used in a commercial analysis program OrcaFlex [1], has been implemented into general finite element software Abaqus [2], through the coding of a user defined element (UEL) subroutine. The paper documents the implementation of UEL into Abaqus and the establishment of global riser model for both static and dynamic analysis on which the pipe is modelled efficiently as series of unidirectional beam elements from floater to seabed, resting on a bed of nonlinear springs. Longitudinal friction between pipe and seabed has also been considered.

A series of simulations are performed to illustrate the capabilities of the model. All these results have good agreement with those from OrcaFlex. Results indicate that the proposed UEL is capable of modelling nonlinear riser-soil interaction phenomena and has been verified to be a cost-effective alternative to OrcaFlex in terms of global analysis of SCRs. In addition, as an open source code, UEL provides the required tool for future development on nonlinear soil models. A new type of nonlinear soil with bilinear soil shear strength is modeled and its effect on structural performances of SCRs is investigated.
Geomechanical Responses During Gas Hydrate Production Induced by Depressurization
Authors: Kim Ah-Ram , Cho Gye-Chun , Lee Joo-Yong , Kim Se-Joon
Published: October 2016

Methane hydrate has been received large attention as a new energy source instead of oil and fossil fuel. However, there is high potential for geomechanical stability problems such as marine landslides, seafloor subsidence, and large volume contraction in the hydrate-bearing sediment during gas production induced by depressurization. In this study, a thermal-hydraulic-mechanical coupled numerical analysis is conducted to simulate methane gas production from the hydrate deposits in the Ulleung basin, East Sea, Korea. The field-scale axisymmetric model incorporates the physical processes of hydrate dissociation, pore fluid flow, thermal changes (i.e., latent heat, conduction and advection), and geomechanical behaviors of the hydrate-bearing sediment. During depressurization, deformation of sediments around the production well is generated by the effective stress transformed from the pore pressure difference in the depressurized region. This tendency becomes more pronounced due to the stiffness decrease of hydrate-bearing sediments which is caused by hydrate dissociation.
Performance Analysis for Grid Plate Wave Absorbing Device
Authors: Geng Baolei , Wang Rongquan
Published: October 2016

With the fluid assumed incompressible and inviscid, and the flow irrotational, the fluid motion can be described by a potential ϕ which satisfies the Laplace equation within the whole domain Ω. The seabed and wall are impermeable and grid plate is transversely permeable only. Then the relationship between horizontal velocity and pressure difference could be deduced without considering the vertical component of the fluid in the grid plate. Reflection coefficient, transmission coefficient and energy-loss coefficient could be calculated when regular waves travel across one grid plate or multi-grid plates, by matching velocity potential and boundary conditions at each grid plate. For the given case, if 0.8 < Gr < 4.6 and Gi < 1.6, the wave absorptivity is more than 90% for four grid plates wave absorbing device.
Underground Gas Storage With CO2 Sequestration in a Depleted Gas Field
Authors: Kim Juhyeon , Han Sunlee , Sung Gilyong , Lee Youngsoo
Published: October 2016

In this study, simulation research was performed in order to switch producing gas field over to UGS (Underground Gas Storage). Generally, a large amount of cushion gas that is mainly composed of CH4 is required to maintain the enough pressure in the UGS reservoir and it cannot be produced during the UGS operation. If there is an alternative way to mitigate the volume of cushion gas, more cost-effective operation is possible. In this reason, we injected CO2 as a cushion gas and determined optimal number of wells and injection/withdrawal rate without CO2 production. The reservoir opportunity index was used to select the target drilling points. The proper volume of working and cushion gas were obtained respectively in various gas rate case. As a result, injected CO2 can supply additional pressure to the reservoir that more effective UGS operation is possible. And injection rate is a critical factor for the stable working gas injection and production from the economic point of view. Also, a design for a complete CCS system was developed based on the existing off-shore pipeline in combination with new on-shore CO2 transport infrastructure.
Analytical Solution of Stress Intensity Factor for Clamped SENT Specimens
Authors: Zhu Xian-Kui
Published: October 2016

Single edge-notched tension (SENT) specimen in clamped end conditions was identified as a low-constraint fracture test specimen, and is preferred for use in the oil and gas industry in direct determination of fracture toughness or resistance curves for low-constraint conditions. Over the years, different SENT test methods have been developed, including DNV-RP-F108 (2006) test practice, CanMet (2008) J-integral resistance curve test procedure, ExxonMobil (2010) CTOD test procedure, and others. On this basis, a SENT test standard BS 8571 was developed and published in December of 2014. However, the stress intensity factor K used in BS 8571 was expressed in a very complicated function. Recently, the present author found that this K solution is incorrect for deep cracks of a/W>0.6, and corrected the K solution in the original format of polynomial functions. To verify the corrected result, this paper obtained a wide-range, simpler analytical K solution for clamped SENT specimens using the crack compliance method. Results show that the proposed K solution and its curve-fit are more accurate over the full range of crack sizes, and agree well with available finite element results.
Numerical Study of Transient Harbor Oscillations Induced by N-Waves
Authors: Gao Junliang , Ji Chunyan , Liu Yingyi
Published: October 2016

The response amplitudes of different resonant modes in an elongated harbor with constant depth induced by N-waves with different amplitudes and different types are calculated using the Normal Mode Decomposition (NMD) method. Wave conditions inside the harbor are simulated with a fully nonlinear Boussinesq model FUNWAVE-TVD. It is found that, for the small amplitude of the incident N-wave, wave energy inside the harbor is dominated by the lowest few modes, while only a small proportion of the wave energy is distributed over the higher modes. However, with the increase of the incident wave amplitude, most of the wave energy inside the harbor tends to concentrate on the higher resonant modes, hence the relative wave energy distributed over the lowest few modes decreases. On the other hand, the wave energy distribution inside the harbor is also significantly affected by the type of the N-wave. The wave energy inside the harbor excited by the MS-type incident N-wave is more concentrated than that excited by the TS-type N-wave. The MS- and TS-type N-waves correspond to the N-wave expressions proposed by Madsen and Schäffer (Madsen, Schäffer, 2010. Analytical solutions for tsunami runup on a plane beach single waves, N-waves and transient waves. Journal of Fluid Mechanics 645, 27–57) and Tadepalli and Synolakis (Tadepalli, Synolakis, 1994. The run-up of N-waves on sloping beaches. Proceedings of the Royal Society London A: Mathematical, Physical & Engineering Sciences 445, 99–112), respectively.
Influence of Impact Location on the Plastic Response and Failure of Rectangular Cross-Section Tubes Struck Transversely by a Hemispherical Indenter
Authors: Liu Bin , Guedes Soares C.
Published: October 2016

Drop weight impact tests are performed to examine the plastic response and failure of clamped rectangular cross-section tubes struck transversely by a hemispherical indenter. The laboratory results are compared with numerical simulations. The span lengths of the tube specimens are 125 and 250 mm, and they are impacted at the mid-span and the quarter-span. Moreover, the impact point along the width direction is located at the central position and displaced 10 mm from the centre, respectively. The results show that the impact location strongly influences the impact response of the tubes. The experimental results are presented in terms of the force-displacement responses and the failure modes, showing a good agreement with the simulations performed by the LS-DYNA finite element solver. The numerical results manage to describe the process of initiation and propagation of the material fracture and provide detailed information to analyse the large inelastic deformation and failure of tubular components subjected to impact loading. The deformation and failure characteristics of the rectangular tubes are well described on the basis of the relevant failure modes observed in beams, plates and circular tubes. Moreover, the influence of the impact location on the strength of tube specimens is elaborated.
A Temperature-Gradient-Dependent Elastic-Plastic Material Model of Iceberg and its Application on the Simulation of FPSO-Iceberg Collision
Authors: Shi Chu , Luo Yu , Hu Zhiqiang
Published: October 2016

An accurate constitutive material model of iceberg ice is important for the finite element simulation of ship-iceberg collision process. A temperature-gradient-dependent elastic-plastic material model of iceberg ice, proposed by the authors in reference [5], is adopted in this paper. The model behaves linear elastic before reaching the ‘Tsai-Wu’-type yield surface, which are a series of concentric elliptical curves with different sizes. Increasing temperature leads to small curves which means the strength of iceberg is weak. Upon reaching yield surface, the iceberg model response is perfectly plastic. A failure criteria based on accumulated plastic strain and hydrostatic pressure is adopted. In order to reflect the change of temperature with depth of iceberg, three typical types of iceberg temperature profiles are assumed in the model. According to these profiles, iceberg ice element located at different depth has different temperature. Therefore, mechanical property of iceberg differs along depth. The iceberg model is implemented as a user-defined subroutine in the commercial explicit finite element code LS-DYNA. Collisions between FPSO side and iceberg are simulated. Four typical shapes of iceberg (sphere, prism, cone and cube) with three temperature profiles are applied. Also, different temperature ranges are assumed in each simulation case. The influence of temperature profile, temperature range and iceberg shape on relative strength between iceberg and side structure are analyzed. The energy dissipation ratio of side structure and iceberg in collision process is examined. Moreover, energy dissipation of the component structures of FPSO side is analyzed. The simulation results show that the iceberg model can be used to demonstrate the influence of temperature on collision process between FPSO-iceberg.
The Analysis on the Sorption Effects About Inflow Performance Relationship in the Coalbed
Authors: Kim K. H. , Kang I. H. , Han J. M. , Lee S. M.
Published: October 2016

This study performed the simulation to identify the effects of sorption behavior about inflow performance relationship in the coalbed. In the conventional gas reservoir without sorption, the turbulence flow is gradually generated as the pressure drop between the reservoir and bottom-hole is higher. Thus, it is ineffective production method for maximizing the pressure difference due to turbulence flow. In the CBM reservoir within sorption, the deliverability exponent becomes higher with increasing desorption gas. As the Langmuir volume ranges from 200 to 250 SCF/ton, it has been observed that the deliverability exponent exceeds the standard range from 0.5 to 1.0. When the deliverability exponent increases, the effects on pressure drop about production rate are preferred. Consequently, it was identified that it is effective production method for maximizing the pressure drop due to deliverability exponent in CBM field.