bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of a Full-Scale CO2 Fracture Propagation Test
Authors: Gruben Gaute , Dumoulin Stephane , Nordhagen Håkon , Hammer Morten , Munkejord Svend T.
Published: November 2018

In this study, we present results from a numerical model of a full-scale fracture propagation test where the pipe sections are filled with impure, dense liquid-phase carbon dioxide. All the pipe sections had a 24″ outer diameter and a diameter/thickness ratio of ∼32. A near symmetric telescopic set-up with increasing toughness in the West and East directions was applied.

Due to the near symmetric conditions in both set-up and results, only the East direction is modelled in the numerical study. The numerical model is built in the framework of the commercial finite element (FE) software LS-DYNA. The fluid dynamics is solved using an in-house computational fluid dynamics (CFD) solver which is coupled with the FE solver through a user-defined loading subroutine. As part of the coupling scheme, the FE model sends the crack opening profile to the CFD solver which returns the pressure from the fluid. The pipeline is discretized by shell elements, while the backfill is represented by the smoothed-particle hydrodynamics (SPH) method. The steel pipe is described by the J2 constitutive model and an energy-based fracture criterion, while the Mohr-Coulomb material model is applied for the backfill material. The CFD solver applies a one-dimensional homogeneous equilibrium model where the thermodynamic properties of the CO2 are represented by the Peng-Robinson equation-of-state (EOS).

The results from the simulations in terms of crack velocity and pressure agree well with the experimental data for the low and medium toughness pipe sections, while a conservative prediction is given for the high-toughness section. Further work for strengthening the reliability of the model to predict the arrest vs. no-arrest boundary of a running ductile fracture is addressed.
Practical Improvements to Surface Loading Assessment: Building Accuracy, Efficiency and Transparency
Authors: Klementis Jennifer D. , Zhang Shenwei , Law Jonathan , Pino Maria , Yan Jason
Published: November 2018

This paper presents a tool for surface loading stress analysis that was developed in-house by TransCanada (TCPL). This tool utilizes fundamentals of the surface loading assessment method developed by Kiefner & Associates Inc. (KAI) for Canadian Energy Pipeline Association (CEPA), but incorporated many advanced functionalities to improve the accuracy, efficiency and transparency of the analysis. The new functions of the tool include the batch analysis, multiple angle analysis, generic/site-specific loading analysis, graphical display of stress distributions for refined assessment, user-defined impact factor and automated reporting for documentation of surface loading calculations. This tool also incorporated the improved numerical algorithm for longitudinal global bending stress considering the actual live load pressure distribution over a certain length of pipeline.

The accuracy of the developed tool was validated by comparing it to the KAI tool. The improved algorithm for longitudinal global bending stress calculation reduces the conservatism of the longitudinal global bending stress compared to the original simplified method but does not sacrifice safety, which has been demonstrated by comparison with the experimental results. The new functionalities improved the business efficiency and maintains safety and regulatory compliance.
Development of an Industry Test Facility and Qualification Process for ILI Technology Evaluation and Enhancements: Performance Evaluation Phase
Authors: Cazenave Pablo , Gao Ming , Deeb Hans , Black Sean
Published: November 2018

The project “Development of an Industry Test Facility and Qualification Processes for in-line inspection (ILI) technology Evaluation and Enhancements” aims to expand knowledge of ILI technology performance and identify gaps where new technology is needed. Additionally, this project also aims to provide ILI technology developers, researchers and pipeline operators a continuing resource for accessing test samples with a range of pipeline integrity threats and vintages; and inline technology test facilities at the Technology Development Center (TDC) of Pipeline Research Council International, Inc. (PRCI), a PRCI managed facility available for future industry and PHMSA research projects.

An ILI pull test facility was designed and constructed as part of this project based on industry state-of-the-art and opportunities for capability improvement. The major ILI technology providers, together with pipeline operator team members, reviewed the TDC sample inventory and developed a series of ILI performance tests illustrating one of multiple possible research objectives, culminating in 16-inch and 24-inch nominal diameter test strings. The ILI technology providers proposed appropriate inspection tools based on the types of the integrity threats in the test strings, a series of pull tests of the provided ILI tools were performed, and the technology providers delivered reports of integrity anomaly location and dimensions for performance evaluation.

Quantitative measures of detection and sizing performance were confidentially disclosed to the individual ILI technology providers. For instances where ILI predictions were outside of claimed performance, the vendors were given a limited sample of actual defect data to enable re-analysis, thus demonstrating the potential for improved integrity assessment with validation measurements.

In this paper, an evaluation of the ILI data obtained from repeated pull-through testing on the 16 and 24-inch pipeline strings at the TDC is performed. The resulting data was aligned, analyzed, and compared to truth data and the findings of the evaluation are presented.
Using Finite Element Analysis to Prioritize ILI Calls for Combined Features: Dents in Bends
Authors: Kemp David , Gossard Justin , Finneran Shane , Bratton Joseph
Published: November 2018

Pipeline in-line-inspections (ILI) are used to assess and track the integrity of pipelines, aiding in identifying a variety of features such as: metal loss, dents, out-of-roundness, cracks, etc. The presence of these features can negatively affect the operation, integrity, and remaining life of a pipeline. Proper interpretation of the impacts these features may have on a pipeline are crucial to maintaining the integrity of a pipeline. Several codes and publications exist to assess the severity of these features under known operating conditions, either through empirical formulations or more detailed analysis, in order to aid the operator in determining a corrective action plan. These empirical formulations are generally applicable to assess a singular defect but require a more detailed assessment to evaluate combined defects (i.e. dent in a bend). These detailed assessments typically require a higher level numerical simulation, such as Finite Element Analysis (FEA). This detailed FEA can be quite costly and time consuming to evaluate each set of combined features in a given ILI run. Thus, engineering judgement is critical in determining a worst-case scenario of a given feature set in order to prioritize assessment and corrective action.

This study aims to assess dent features (many associated with metal loss) occurring in a pipe bend to determine a worst-case scenario for prioritization of a given feature listing. FEA was used to simulate a field bend of a given radius and angle in order to account for residual stresses in the pipe bend. A rigid indenter was used to form a dent of the approximate length, width, and depth from the ILI data. Separate models were evaluated considering the dent occurring in the intrados, extrados, and neutral axis of the pipe bend to evaluate the worst-case scenario for further assessment. The resulting stresses in the pipe bend-dent geometry, under proper loading were compared to the same dent scenario in a straight pipe segment to develop a stress concentration factor (SCF). This SCF was used in the API 579-1/ASME FFS-1 Fitness for Service (API 579) [1] methodology to determine the impact on the remaining life of the combined features.
Integrating a Pipeline Odorant System Using Open Source Software, Including a Kalman Filter Solution to Virtualize a Flow Rate Indicator
Authors: D. Bezerra Marco Antonio , da Silva Sidney C. , Silva Silvio C.
Published: November 2018

In a Supervisory Control and Data Acquisition (SCADA) system, operators use a human-machine interface (HMI) to interact with the process through industrial protocols, which have specific drivers (software pieces) installed in the SCADA servers. If the process device manufacturer does not develop a driver for its equipment, a gateway, with a protocol translator can be provided with the equipment, to translate its particular protocol to a standard industrial one, like the so popular Modbus.

This work presents the development of a gateway — protocol translator — that connects an odorant unit of a pipeline terminal, which has a proprietary protocol to an industrial protocol Modbus TCP/IP. All development is made with Open Source software.

The subject matter is extended to describe the solution to an issue observed due to the lack of a flowmeter in the odorant unit, where a Kalman filter was used as an estimator, to provide a virtual meter.
Strengthening the Current Class Location Designation System
Authors: Willson Diana , Colquhoun Iain , Carnes Dean
Published: November 2018

CSA Z662, Oil and gas pipeline systems, defines class location as “a geographical area classified according to its approximate population density and other characteristics that are considered when designing and pressure testing piping to be located in the area.” In other words, the purpose of class location designations is to identify areas where specific measures are considered necessary to enhance public safety. Designations range from Class 1 (rural) to Class 4 (urban with high-rise buildings).

The current class location framework relies mainly on a location factor (L) to represent reliability. Higher reliability is achieved by using more resistant pipe — that is thicker and/or stronger — to reduce the probability of failure from operational hazards, such as corrosion and mechanical damage caused by line strikes. Currently, the need for a particular level of reliability is driven principally by the number of people impacted.

This paper discusses possible measures that can be implemented in the next edition of Z662 that, beyond requiring thicker pipe for certain products, will strengthen the class location designation system by considering the potential impact radius of an ignited gas pipeline rupture, as well as the occupancy and nature of buildings within assessment areas. The paper also discusses possible changes to improve environmental protection by introducing the concept of a designated geographical area (DGA) and associated requirements, enhancements to valve spacing requirements, and the handling of changes to class location designations for existing pipelines through interim measures and retroactivity.
Well-Integrated Design of Surge Relief Systems in Oil Storage Facilities
Authors: Perez Emma , Mehta Ashishkumar
Published: November 2018

Oil Storage facilities (terminals) that receive fluids from pipelines or inject fluid into them, are usually designed with a lower pressure rating than the actual pipeline between these facilities. This is mostly due to the fact that the pressure expected in the terminal is much lower than the pressure required to transport the oil. However, these terminals are still subject to pressure surges caused by abnormal transient events during normal operations. In cases where the surge pressures exceed the allowed operating pressure of the equipment, a relief system can be installed to mitigate these surges to acceptable levels.

When constructing a new terminal or altering an existing one, the hydraulic calculations of these terminals are generally based on design values of the project, such as maximum and minimum flow rates. The hydraulic studies and simulations that are normally done by companies are based on steady state conditions, however, to design intrinsically safe facilities, the system’s entire operating envelope should be considered at the design stage of the project. Once transient analysis results show the need to install a pressure relief device, the proper location of this equipment is critical for the effectiveness of the surge relief system to mitigate overpressures properly.

The effect of flow rate, piping configuration, and initial pressure profiles were simulated and compared to determine their impact on pressure surges and on the critical devices along the flow path. Secondly, simulations were done with the relief system installed in different locations along the terminal pipe and the resulting changes in maximum pressure surges.

The objective of this paper is to show the importance of a detailed transient analysis based not only on design parameters but also on operational scenarios to mitigate surge overpressures in a more cohesive manner. The secondary objective of the paper is to discuss key parameters that need to be considered for selecting the location of the surge relief valve to ensure critical devices are safe during the upset conditions. The analysis presented in this paper is applicable across a broad configuration of oil facilities.
Improving the Accuracy of Traditional Dent Fatigue Analysis: A Method for Quantifying the Initial Damage Caused by Dent Formation
Authors: Turnquist Michael , Parsons Adam
Published: November 2018

The pipeline industry is currently taking several approaches to evaluate the integrity of dents, ovalities, or other geometric anomalies identified from in-line inspection (ILI). A primary threat associated with these features that operators should be concerned with is failure due to fatigue. In order to carry out a more accurate dent fatigue analysis, it is important to be able to quantify the amount of damage accumulated during the initial dent formation process and subsequent shakedown of the dent.

Dents result from permanent deformation of the pipeline which leads to accumulation of plastic strain. Whether this permanent deformation was caused during initial construction (a backhoe striking the pipeline) or in service (changing underground soil conditions), the plastic strains that are observed will result in a decrease in the pipeline’s fatigue life. Pressure cycling has the potential to accumulate additional plastic stain, thus accumulating more fatigue damage. Eventually as the pipeline continues to be cycled, no additional deformation or accumulation of plastic strain will occur; this behavior is referred to as “shakedown.”

Finite element analysis (FEA) can be utilized to quantify how much fatigue damage has been accumulated during the initial dent formation process and subsequent shakedown of the dent. When analyzing pipeline dents using FEA, importance should be placed on accurately simulating the dent forming process so that realistic plasticity effects can be captured. The process of calculating plastic stresses and strains during the dent forming process can be computationally expensive and result in numerical instabilities within the analysis.

As a result, methods for simulating the formation and shakedown of a pipeline dent are continuously being refined. However, since it is difficult to determine exactly how these geometric pipeline anomalies were formed, the applicability and accuracy of such methods contains a great amount of uncertainty and is thus expensive (both from a cost and time standpoint) for an operator to validate.

This paper will identify a new and innovative approach for using FEA to determine the amount of damage accumulated during the initial dent formation process and subsequent shakedown of the dent. This approach uses state-of-the-art FEA modeling techniques coupled with industry knowledge and experience to develop an accurate and efficient method for quantifying this damage. The knowledge gained during this analysis can be used in conjunction with a traditional rapid dent assessment methodology.

A case study will be presented which demonstrates the impact that a direct calculation of this initial damage has on representative pipeline dent assessment analysis. By undertaking this additional analysis, operators will have the potential to eliminate unnecessary digs. Additionally, operators can be more confident that their resources are being applied to the highest priority features.
Predicting Drag Reduction in Turbulent Pipe Flow With Relaxation Time of Polymer Additives
Authors: Zhang Xin , Duan Xili , Muzychka Yuri , Wang Zongming
Published: November 2018

This paper presents an experimental study on drag reduction induced by PEO (Polyethylene oxide) in a fully turbulent pipe flow. The objective of this work is to develop a correlation to predict drag reduction using the relaxation time of the polymer additives under dilute solution conditions, i.e., the polymer concentration is less than the overlap concertation. This paper discusses the meaning of relaxation time of polymers, and why the Weissenberg number, a dimensionless number that is related to the relaxation time and shear rate, is independent on the concentration in the dilute solution. Experimental data of drag reduction in a pipe flow are obtained from measurements using a flow loop. A correlation to predict drag reduction with the Weissenberg number and polymer concentration is established and a good agreement is shown between the predicted values and experimental data. The new correlation using the Weissenberg number and polymer concentration is shown to cost less to develop than one using the Reynolds number, in which larger pipes or higher flow rates are required.
Influence of Mean Load Pressure Fluctuations on Crack Growth Behavior in Steel Pipelines
Authors: Tehinse Olayinka , Chen Weixing , Chevil Karina , Gamboa Erwin , Lamborn Lyndon
Published: November 2018

Internal pressure fluctuations during pipeline operations could contribute to crack growth in steel pipelines. These pressure fluctuations create a variable amplitude loading condition with large amplitude cycles at near-zero stress ratio, R (minimum stress / maximum stress) and small amplitude cycles (minor cycles) at near +1 R ratio which can both affect crack propagation. Mean stresses fluctuate with pressure due to fluid friction losses proportional to the distance from the pump/compressor station. A deeper understanding of mean stress sensitivity on crack growth rate in steel pipelines is sought. The aim of this research is to retard crack growth in pipelines by prescribing pressure fluctuations, thus controlling mean stress effects on imperfection growth in steel pipelines under a near neutral pH environment. This study shows that prescriptive mean load pressure fluctuations can be used to reduce crack growth rates in steel pipelines, thus expanding pipeline integrity management methods.
The Optimum Pipeline Burial Depth Considering Slow Downslope Soil Movement and Seasonal Temperature Variation
Authors: Katebi Mohammad , Liu Hongwei , Maghoul Pooneh , Blatz James
Published: November 2018

Thermal stress induced in a buried pipeline due to temperature variation is of great concern in Canada due to its extreme cold winter and warm summer. Thermal stress decreases by increasing the pipe’s burial depth while the interaction forces due to ground displacement increase by increasing the burial depth. As a result, the optimum burial depth of a pipeline is of great importance to pipeline companies to minimize interactions between the pipeline and soil in case of temperature variations and ground displacements. Thermal stress is estimated from a heat transfer analysis considering the phase change in the soil using COMSOL. Soil-pipeline interaction based on 1984 ASCE Guidelines [1] is used for considering the effects of ground movements. The combined stress on the pipeline is estimated as a function of burial depth and is presented in a curve for design purposes. Numerical analysis by ABAQUS shows the adequacy of the presented curve.
Criticality Level Assessment From ILI Data
Authors: Jaya Pedro , Köck Rodolfo
Published: November 2018

In the last 10 years, technical and economical efforts have been made to improve pipeline integrity management. Those efforts focus on developing “searching tools”, capable of identifying pipe mechanical damage due to slow landslides.

We identified two main tools: geohazard mapping and inline inspection (OCP is using caliper with inertial navigation system INS). The INS system generates a substantial amount of information about pipe’s geometry and deformation, reported as pitch, yaw and distance cover for each run. Since the caliper has been used for years, the pipeline’s path of evolution over the years is already available.

The INS data was merged with pipeline field inspections to develop an assessment tool based on Machine Learning Technology.

This tool was applied to the complete path of the pipeline, analyzing each girth weld, thus obtaining a so called “criticality level” for each weld. Two models were evaluated, which differ on the size of the vicinity considered for each girth weld: 250m and 500m. The highest precision model was found with 250m, which already has allowed improvements in field inspections.

This paper will describe this technique, capable of improving OCP’s pipeline integrity management.
Threshold Geometrical Dimensions of Stage II Cracks Versus Required Resolution of Crack-Detection Techniques
Authors: Chen Weixing , Zhao Jiaxi , Chevil Karina , Gamboa Erwin , Alvarado Bersi
Published: November 2018

Environmental-assisted cracks in pipeline steels usually undergo the following three sequential stages prior to the failure:

• Stage 1 – crack initiation and early stage crack growth, in which cracks initiate at imperfections but grow slowly depth-wise with time. Crack length may be seen to increase either because of merging with new small cracks in the vicinity of an existing crack or faster crack growth at the crack tip. Some cracks pose little threat to pipeline steel integrity if they remain dormant.

• Stage 2 – Increased crack growth rate where crack growth can be dictated by mechanical driving forces and crack growth rate increases with time.

• Stage 3 – The final stage of crack growth where crack growth rate is very high. Typical crack management programs mitigate cracks prior to entering Stage III.

It is of great importance that pipeline steels with Stage II cracks are detected, monitored, and managed to ensure operational pipeline integrity. Although a range of crack in-line inspection and detection techniques with varied detection limits are available, it is not clear how their detection limits match the threshold geometrical dimensions of Stage 2-cracks. This investigation is aimed to define critical geometrical dimensions of cracks that are considered to be Stage 2 cracks. The determination of critical geometrical dimensions of Stage 2 cracks was made with a consideration of a wide range of situations including pipeline operating conditions, susceptible environments for crack growth, metallurgical, fabrication and construction conditions of pipeline steels. A comparison of the threshold geometrical dimensions of Stage 2 cracks with the crack detection limits of modern crack inspection and detection techniques are made at the end of the paper.
Buried Pipe Span Ovality Assessment
Authors: Phillips Ryan , Martens Michael , McAffee Rodney , Tan Lesley , Barrett John
Published: November 2018

This paper evaluates field ovalization measurements of NPS 24 pipe using 3D continuum finite element analyses. The combination of the soil backfill weight and loose bedding material beneath the pipe near a tie-in concentrates stresses at the location where native undisturbed soil transitions to loose backfill along the trench bottom, which increases the ovality in the pipe cross section. The analysis indicated that at burial depth, transient surface loading temporarily increases the ovality in unpressurized pipe but the ovality is reduced to near normal levels when the transient surface loading is removed. The internal pressure reduces the elastic pipe ovality. This analysis method can be useful for a cost benefit analysis between using thicker pipe, versus the additional costs, such as intervention and/or padding/compacting of soil around the pipe (with inspections).
An Integrated Approach for the Verification of Pipeline Material Using the Latest State-of-the-Art Technologies and Engineering Processes
Authors: Slater Simon , Dwyer Katrina , Ginten Markus , Eiken Thomas , Burkinshaw Ollie
Published: November 2018

Pipeline integrity management systems rely on robust records and data so that the correct decisions are made. The Pipeline industry regulator is intending to ensure operators possess traceable, verifiable and complete (TVC) pipeline records as a basis for sound integrity and risk management. This is being driven by PHMSA in the notice of proposed rulemaking (NPRM) 49 CFR 192. In recent years, ROSEN has introduced RoMat PGS, an inline inspection service that is capable of determining yield strength and other information relevant for the calculation of maximum allowable operating pressure (MAOP).

The data obtained from multiple ILI services forms the fundamental basis for an engineering assessment that integrates ILI data and other pertinent information to assign pipe grade for each individual pipe, within identified populations, with minimized field verification efforts.

For pipeline sections with incomplete records, the addition of strength data to other available information allows reliable identification of different populations along a pipeline. This permits the operator to better optimize integrity and material verification strategies.

In early 2017, Xcel Energy and ROSEN partnered to conduct a materials characterization assessment of a 20″ gas distribution pipeline. This was the second time that Xcel had implemented the service. This pipeline was originally installed in two sections, in 1928 and 1947, and has since been largely replaced over time through a series of reroutes and replacements. With more than 25 different assumed construction dates, the RoMat PGS service was used to identify the different pipe populations and confirm that these align with available records.

This paper presents the results and subsequent analysis. It represents a significant marker in the industry, demonstrating how a cooperative and integrated approach using state-of-the-art technology, engineering processes, and material verification techniques can be used to improve the integrity of operators’ records. The paper discusses the various stages of the process, the significant findings, such as the types of pipes identified and their properties, and — most importantly — how the results were implemented into a pipeline integrity and risk management system.
What Lies Beneath: Geophysical Approaches for Assessing Trenchless Water Crossings
Authors: McClymont Alastair , Bauman Paul , Ernst Erin , Parker Dan
Published: November 2018

When tied to drilling results, geophysical surveys of trenchless water crossings provide important information on subsurface geotechnical conditions, including bedrock elevation and the locations of zones of granular material within overburden. Because the terrain can change quite dramatically at water crossings, it is difficult to acquire geophysical data that is continuous between the geotechnical boreholes. The resulting data gaps can decrease confidence in understanding the site geotechnical conditions, which increases uncertainties in the detailed engineering design of the trenchless water crossing (e.g., HDD, or MTBM method). We demonstrate here how some of the technical challenges associated with acquiring continuous geophysical data at water crossings can be overcome. These include the use of suspended ERT cables, and complementary waterborne ERT and seismic refraction surveys. To illustrate the efficacy of these techniques, we present case-studies from proposed HDD crossings of three different types of water bodies at sites in British Columbia and Alberta.
Development of Strain Demand and Capacity Distributions to Use in Limit States Design for Geotechnical Loads
Authors: Koduru Smitha D. , Nessim Maher A.
Published: November 2018

A limit states design approach for onshore pipelines has been developed as part of a multi-year joint industry project (JIP). As part of this project, reliability-based design rules were developed for geotechnical loads, including landslides, slope creep, seismic loads, frost heave and thaw settlement. In consideration of the modelling complexity of the soil movement mechanisms and pipe-soil interaction, and to allow for flexibility to incorporate future model developments, the design rule formulation is directly based on the distribution parameters of the strain demand and capacity of the pipeline.

This paper describes the approach used to develop the strain demand and capacity distributions that are required to apply the design rules, as well as the applicable range of distribution parameters. Slope creep was selected as a basis for demonstrating the proposed process, as this loading mechanism occurs more frequently and the data to characterize the necessary uncertainties is available. General guidance related to the development of the strain demand distribution parameters for other geotechnical loads is also provided.
Assessment of Dents Under High Longitudinal Strain
Authors: Wang Bo , Wang Yong-Yi , Ayton Brent , Stephens Mark , Nanney Steve
Published: November 2018

Pipeline construction activities and in-service interference events can frequently result in dents on the pipe. The pipelines can also experience high longitudinal strain in areas of ground movement and seismic activity. Current assessment procedures for dents were developed and validated under the assumption that the predominant loading is internal pressure and that the level of longitudinal strain is low. The behavior of dents under high longitudinal strain is not known. This paper discusses work funded by US DOT PHMSA on the assessment of dents under high longitudinal strain.

Parametric numerical analyses were conducted to identify and examine key parameters and mechanisms controlling the compressive strain capacity (CSC) of pipes with dents. Selected full-scale tests were also conducted to experimentally examine the impact of dents on CSC. The focus of this work was on CSC because tensile strain capacity is known not to be significantly affected by the presence of dents. Through the parametric analyses and full-scale validation tests, guidelines on the CSC assessment of dented pipes under high longitudinal strain were developed.
A Simplified Simulation Model for Buried Hot Oil Pipeline Temperature Field During Shutdown
Authors: Chen Lei , Gao Junjie , Liu Gang , Chen Cheng
Published: November 2018

The temperature drop of waxy crude oil after a shutdown is the basic premise for restarting relative mechanical calculation. However, computational accuracy has been paid much more attention excessively in the relevant techniques proposed in the previous researches for this calculation but ignoring the practicability of the calculation results. In this paper a new mathematical model is established for a buried hot crude oil pipeline during shutdown with the simplified complex physical process of oil cooling process reasonably, in which the heat transfer mode of crude oil is divided into pure convection heat transfer and pure heat conduction with stagnation point temperature neglecting the difference of radial temperature. The quasi periodic property theory of soil temperature field is referenced to be as the boundary condition for the thermal influence region. A numerical solution with a structured grid and an analytical solution under polar coordinate are respectively applied for the soil region and other regions including pipe wall, wax layer and insulation layer. The finite volume method is adopted to discretize the heat transfer control equation at the same time the boundary conditions are treated by the additional source term method. The simulation results of the new model are verified by a temperature field tested experiment, especially analyzing the temperature deviation between the simulation and the equivalent mean value of actual oil temperature. At last the effect of buried depth of pipeline on the temperature profiles during normal operation and the temperature drop process of crude oil were investigated based on the simplified model.
Effect of Straining and Ageing on Longitudinal Tensile Properties of Linepipe Suitable for Deepwater Applications
Authors: Marsay Melissa , Connelly Martin , Alderton Graham
Published: November 2018

The offshore oil and gas industry has seen a continual trend of conservatism in design for applications where a high level of strain is expected during the installation phase, leading to a tightening of the acceptable mechanical property performance of the linepipe. This is especially true with regards to longitudinal tensile properties in the strained and aged condition. Due to the expected change in data seen throughout previous projects, are the tightening expectations realistic for the manufacturers and cost effective for the client?

The current condition that is widely accepted for the release of pipes suitable for high strain events is straining and ageing. However is this appropriate given that pipes are coated (aged), installed (strained) then left over time (aged)? These questions will be investigated through a series of tests and data analysis. For this project a conventional ageing as per the standard and a coating simulation were used, with all test pieces having either 0% or 1% applied strain. The test pieces for this project were tested in one of seven conditions;

• As manufactured

• Aged (at 200°C/5min or 250°C/1hr)

• Strained and aged (1% strain applied then aged at 200°C/5min or 250°C/1hr)

• Aged and strained (aged at 200°C/5min or 250°C/1hr then 1% strain applied)

To ensure a direct comparison in the data the comparable test pieces were taken from the same circumferential position on the pipe. All testing for this project was carried out on material of a similar composition and future development of this work will comprise of documenting the effect on different microstructures, t/D ratios and levels of strain. It was clear from the project that changing the conditions used had an impact on the results. This could have implications for the industry in the future and has set up a scheme of development following on from this project to gain a greater understanding.
Simultaneous electromagnetic articulography and electroglottography data acquisition of natural speech
Authors: Harper Sarah , Lee Sungbok , Goldstein Louis , Byrd Dani
Published: November 2018

This paper reports on the concurrent use of electroglottography (EGG) and electromagnetic articulography (EMA) in the acquisition of EMA trajectory data for running speech. Static and dynamic intersensor distances, standard deviations, and coefficients of variation associated with inter-sample distances were compared in two conditions: with and without EGG present. Results indicate that measurement discrepancies between the two conditions are within the EMA system's measurement uncertainty. Therefore, potential electromagnetic interference from EGG does not seem to cause differences of practical importance on EMA trajectory behaviors, suggesting that simultaneous EMA and EGG data acquisition is a viable laboratory procedure for speech research.
Hypoxia Promotes Immune Evasion by Triggering β-Glucan Masking on the Candida albicans Cell Surface via Mitochondrial and cAMP-Protein Kinase A Signaling
Authors: Pradhan Arnab , Avelar Gabriela M. , Bain Judith M. , Childers Delma S. , Larcombe Daniel E. , Netea Mihai G. , Shekhova Elena , Munro Carol A. , Brown Gordon D. , Erwig Lars P. , Gow Neil A. R. , Brown Alistair J. P.
Published: November 2018

Animal, plant, and fungal cells occupy environments that impose changes in oxygen tension. Consequently, many species have evolved mechanisms that permit robust adaptation to these changes. The fungal pathogen
Candida albicans
can colonize hypoxic (low oxygen) niches in its human host, such as the lower gastrointestinal tract and inflamed tissues, but to colonize its host, the fungus must also evade local immune defenses. We reveal, for the first time, a defined link between hypoxic adaptation and immune evasion in
C. albicans
. As this pathogen adapts to hypoxia, it undergoes changes in cell wall structure that include masking of β-glucan at its cell surface, and it becomes better able to evade phagocytosis by innate immune cells. We also define the signaling mechanisms that mediate hypoxia-induced β-glucan masking, showing that they are dependent on mitochondrial signaling and the cAMP-protein kinase pathway. Therefore, hypoxia appears to trigger immune evasion in this fungal pathogen.
Chlamydia trachomatis
Inhibits Homologous Recombination Repair of DNA Breaks by Interfering with PP2A Signaling
Authors: Mi Yang , Gurumurthy Rajendra Kumar , Zadora Piotr K. , Meyer Thomas F. , Chumduri Cindrilla
Published: November 2018

Chlamydia trachomatis
induces DNA double-strand breaks in host cells but simultaneously inhibits proper DNA damage response and repair mechanisms. This may render host cells prone to loss of genetic integrity and transformation. Here we show that
C. trachomatis
prevents activation of the key DNA damage response mediator ATM by preventing the release from PP2A, leading to a complete absence of homologous recombination repair in host cells.
Inside-protonated 1-azaadamantane: computational studies on the structure, stability, and generation
Authors: Beshara Cory , Shustov Gennady
Published: November 2018

Post Hartree–Fock and density functional theory methods have been employed to study inside-protonated 1-azaadamantane 7 and its complexes with the fluoride counterion (contact ion pairs) 10 and 11. The study also involved 1-azaadamantane 4, its outside-protonated form 8, and 1-azaadamantane radical cation 17. Inside-protonated 1-azaadamantane 7 is more than 82 kcal mol−1less stable than out-isomer 8. The repulsive interaction between the internal N+–H group and the azaadamantane cage and a substantial deformation of this cage greatly weaken the C–N and C–C bonds and, consequently, lead to a low kinetic stability of in-ion 7 in the studied unimolecular and bimolecular reactions involving the removal of the encapsulated proton from the cage. Among these reactions, a 7 → 8 rearrangement through a reversible cage opening at the C–N bond was found to be the main transformation channel ([Formula: see text] < 16 kcal mol−1) for in-ion 7. This rearrangement can be catalyzed by an external base, e.g., the fluoride anion. A 1,4-hydrogen migration in 1-azaadamantane radical cation 17 as a possible pathway to the inside-protonated 1-azaadamantane 7 was explored. It was found that this process has a prohibitively high activation barrier, [Formula: see text] > 104 kcal mol−1, and is not able to compete with the α-C–C cleavage of the azaadamantane cage ([Formula: see text] < 26 kcal mol−1).
The underwater vocal complexity of seals (Phocidae) is not related to their phylogeny
Authors: Terhune J.M.
Published: November 2018

Closely related mammalian species often make similar vocalizations, but this is not so with the underwater calls of the true seals. Some seal species have diverse underwater vocal repertoires, whereas others only make pulsed calls. Vocal complexity scores of underwater calls of 13 seal species were compared with their phylogeny and life-history traits. Waveform types, repertoire sizes, repetition and rhythm patterns, and frequency and duration measures (15 attributes, scaled 0 to 1) were summed to give a vocal complexity score. The lowest complexity group use low frequency, burst pulse or irregular waveforms and have small repertoires. The intermediate group have both sinusoidal and noisy waveforms, songs, and a single rhythm pattern in repeated element calls. The most complex group have large repertoires, sinusoidal and noisy waveforms, songs, and two or more rhythm patterns in repeated element calls. There is no evidence of a relationship between phylogeny and vocal complexity. The low vocal complexity species are serially monogamous, do not form breeding groups, breed on beaches or pack ice, and are subject to higher predation risk. Species with higher vocal complexity are promiscuous or polygamous, form breeding groups on pack or landfast ice, and have a lower predation risk.
A High Gain, 808MHz GBW Four-Stage OTA in 65nm CMOS
Authors: Li Zhe , Ma Rui , Liu Maliang , Ding Ruixue , Zhu Zhangming
Published: November 2018

A four-stage operational transconductance amplifier (OTA) with a novel compensation structure combining multipath [Formula: see text]-[Formula: see text] compensation and no capacitor feed-forward compensation is proposed in this paper. Based on the small-signal model, stability analysis and design consideration are carried out to demonstrate the stability of the compensation technique. To verify the effectiveness of the compensation scheme, the proposed OTA which drives a 2 pF capacitance, is simulated in TSMC 65[Formula: see text]nm 1.2[Formula: see text]V CMOS process, achieving 808[Formula: see text]MHz gain-bandwidth, 119[Formula: see text]dB DC gain, 585[Formula: see text]V/[Formula: see text]s slew rate (SR) and 6 ns 1% settling time. The circuit is operated at the single supply voltage of 1.2[Formula: see text]V with power consumption of 2.17[Formula: see text]mW and the layout area is 0.011[Formula: see text]mm2.
Theoretical study on the oscillation mechanism of p53-Mdm2 network
Authors: Wang Conghua , Yan Fang , Liu Haihong , Zhang Yuan
Published: November 2018

In this paper, a delayed mathematical model was developed based on experimental data to understand how the time delays required for transcription and translation in Mdm2 gene expression affect the kinetic behavior of the p53-Mdm2 network. Taking the time delays as the main research parameters, the stability of the system at the positive equilibrium was studied by using the theoretical method of delay differential equation. We found that such delays can induce oscillations by undergoing a supercritical Hopf bifurcation. Then, we used the normal form theory and the center manifold reduction to study the direction and stability of the bifurcation in detail. Furthermore, we also studied the effects of the length of time delays and the model parameters by numerical simulations. We found that time delays in Mdm2 synthesis are required for p53 oscillations and the length of such delays can determine the amplitude and period of the oscillations. In addition, the model parameters can also change the stability of the system. These results illustrate that the repair process after DNA damage can be regulated by varying time delays and the model parameters.
A numerical framework for the approximate solution of fractional tumor-obesity model
Authors: Arshad Sadia , Baleanu Dumitru , Defterli Ozlem , Shumaila
Published: November 2018

In this paper, we have proposed the efficient numerical methods to solve a tumor-obesity model which involves two types of the fractional operators namely Caputo and Caputo-Fabrizio (CF). Stability and convergence of the proposed schemes using Caputo and CF fractional operators are analyzed. Numerical simulations are carried out to investigate the effect of low and high caloric diet on tumor dynamics of the generalized models. We perform the numerical simulations of the tumor-obesity model for different fractional order by varying immune response rate to compare the dynamics of the Caputo and CF fractional operators.
Learning From Sleeping Experts
Authors: Truong Anh , Etesami S. Rasoul , Kiyavash Negar
Published: November 2018

We consider a generalized model of learning from expert advice in which experts could abstain from participating at some rounds. Our proposed online algorithm falls into the class of weighted average predictors and uses a time-varying multiplicative weight update rule. This update rule changes the weight of an expert based on his or her relative performance compared to the average performance of available experts at the current round. This makes the algorithm suitable for recommendation systems in the presence of an adversary with many potential applications in the new emerging area of the Internet of Things. We prove the convergence of our algorithm to the best expert, defined in terms of both availability and accuracy, in the stochastic setting. In particular, we show the applicability of our definition of best expert through convergence analysis of another well-known algorithm in this setting. Finally, through simulation results on synthetic and real datasets, we justify the out-performance of our proposed algorithms compared to the existing ones in the literature.
Novel Delay-Dependent Stability Criteria for Discrete-Time Neural Networks with Time-Varying Delay
Authors: Stojanovic Sreten , Stojanovic Milan , Stevanovic Milos
Published: November 2018

The delay-dependent stability problem is investigated for discrete-time neural networks with time-varying delays. A new augmented Lyapunov-Krasovskii functional (LKF) with single and double summation terms and several augmented vectors is proposed by decomposing the time-delay interval into two nonequidistant subintervals to derive less conservative stability conditions. Then, by using Wirtinger-based inequality, reciprocally, and extended reciprocally convex combination lemmas, tight estimations for sum terms in the forward difference of the LKF are given. Several zero equalities are introduced to further relax the existing results. Less conservative stability criteria are proposed in terms of linear matrix inequalities (LMIs). Finally, numerical examples are proposed to show the effectiveness and less conservativeness of the proposed method.
The Existence and Uniqueness of Solutions and Lyapunov-Type Inequality for CFR Fractional Differential Equations
Authors: Wang Xia , Xu Run
Published: November 2018

In this paper, we research CFR fractional differential equations with the derivative of order 3<α<4. We prove existence and uniqueness theorems for CFR-type initial value problem. By Green’s function and its corresponding maximum value, we obtain the Lyapunov-type inequality of corresponding equations. As for application, we study the eigenvalue problem in the sense of CFR.
Silicon Powder-Based Wafers for Low-Cost Photovoltaics: Laser Treatments and Nanowire Etching
Authors: Jia G. , Plentz J. , Gawlik A. , Azar A. S. , Stokkan G. , Syvertsen M. , Carvalho P. A. , Dellith J. , Dellith A. , Andrä G. , Ulyashin A.
Published: November 2018

In this study, laser-treated polycrystalline Si (pc-Si) wafers, fabricated by wire sawing of hot-pressed ingots sintered from Si powder, have been investigated. As-cut wafers and those with high-quality thin Si layers deposited on top of them by e-beam have been subjected to laser irradiation to clarify typical trends of structural modifications caused by laser treatments. Moreover, possibility to use laser-treated Si powder-based substrates for fabrication of advanced Si structures has been analysed. It is established that (i) Si powder-based wafers with thicknesses ~180 μm can be fully (from the front to back side) or partly (subsurface region) remelted by a diode laser and grain sizes in laser-treated regions can be increased; (ii) a high-quality top layer can be fabricated by crystallization of an additional a-Si layer deposited by e-beam evaporation on top of the pc-Si; and (iii) silicon nanowires can be formed by metal-assisted wet chemical etching (MAWCE) of polished Si powder-based wafers and as-cut wafers irradiated with medium laser power, while a surface texturing on the as-cut pc-Si wafers occur, and no nanowires can form in the region subject to a liquid phase crystallization (LPC) caused by high-power laser treatments.