bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverse geroscience: how does exposure to early diseases accelerate the age‐related decline in health?
Authors: Kohanski Ronald A. , Deeks Steven G. , Gravekamp Claudia , Halter Jeffrey B. , High Kevin , Hurria Arti , Fuldner Rebecca , Green Paige , Huebner Robin , Macchiarini Francesca , Sierra Felipe
Published: December 2016

Aging is the major risk factor for both the development of chronic diseases and loss of functional capacity. Geroscience provides links among the biology of aging, the biology of disease, and the physiology of frailty, three fields where enormous progress has been made in the last few decades. While, previously, the focus was on the role of aging in susceptibility to disease and disability, the other side of this relationship, which is the contribution of disease to aging, has been less explored at the molecular/cellular level. Indeed, the role of childhood or early adulthood exposure to chronic disease and/or treatment on accelerating aging phenotypes is well known in epidemiology, but the biological basis is poorly understood. A recent summit co‐organized by the National Institutes of Health GeroScience Interest Group and the New York Academy of Sciences explored these relationships, using three chronic diseases as examples: cancer, HIV/AIDS, and diabetes. The epidemiological literature clearly indicates that early exposure to any of these diseases and/or their treatments results in an acceleration of the appearance of aging phenotypes, including loss of functional capacity and accelerated appearance of clinical symptoms of aging‐related diseases not obviously related to the earlier event. The discussions at the summit focused on the molecular and cellular relationships between each of these diseases and the recently defined molecular and cellular pillars of aging. Two major conclusions from the meeting include the desire to refine an operational definition of aging and to concomitantly develop biomarkers of aging, in order to move from chronological to physiological age. The discussion also opened a dialogue on the possibility of improving late‐life outcomes in patients affected by chronic disease by including age‐delaying modalities along with the standard care for the disease in question.
Simultaneous validation of five activity monitors for use in adult populations
Authors: Powell C. , Carson B. P. , Dowd K. P. , Donnelly A. E.
Published: December 2016

Numerous cut‐points exist to measure physical activity by accelerometry. The ability to compare accelerometer findings from different devices from different locations may be advantageous to researchers. This study aimed to develop and validate cut‐points for 1.5, 3, and 6 METs in five activity monitors simultaneously. Fifty‐six participants (mean age=39.9 [±11.5] years) performed six activities while wearing a CosMED K4b2 and five activity monitors: activPAL3 Micro, activPAL, ActiGraph GT1M, ActiGraph wGT3X‐BT, and GENEActiv. Receiver operating characteristic curves and analysis were used to develop and validate cut‐points for the vertical axis counts (all activity monitors) and sum of the vector magnitude (ActiGraph wGT3X‐BT and GENEActiv) for 15 second (all devices) and 60 second (ActiGraph devices) epochs. A random coefficients statistical model was used to derive MET predictive equations for all activity monitors. Bland‐Altman plots examined the variability in device error. No 1.5 MET cut‐points were developed for the activPAL devices. All developed cut‐points had high levels of sensitivity and specificity. When cross‐validated in an independent group, high levels of sensitivity and specificity remained (≥77.4%, monitor and intensity dependent). The mean bias based on the Bland‐Altman plots ranged from −0.03 METs to 0.35 METs (monitor dependent). This is the first study to develop and validate cut‐points for five activity monitors simultaneously with high levels of sensitivity and specificity (≥77.4%). This is potentially a step toward cross‐comparison/harmonization of data; however, further validation in a free‐living environment is warranted.
Living precariously: property guardianship and the flexible city
Authors: Ferreri Mara , Dawson Gloria , Vasudevan Alexander
Published: December 2016

In this paper we examine the precarious everyday geographies of property guardianship in the United Kingdom. Temporary property guardianship is a relatively new form of insecure urban dwelling existing in the grey area between informal occupation, the security industry and housing. Young individuals, usually in precarious employment, apply to intermediary companies to become temporary ‘guardians’ in metropolitan centres, most notably in London. The scheme allows guardians to pay below market rent to live in unusual locations while ‘performing’ live‐in security arrangements that are not considered as a form of ‘work’. The experiences of becoming and living as a property guardian can be ambivalent and contradictory: guardians express economic and social advantages to being temporary, while also exposing underlying anxieties with ‘flexible living’. In this paper we offer a detailed description of the various practices of property guardianship and how they must be understood, on the one hand, in light of recent geographical scholarship on housing insecurity and, on the other hand, as an example of a precarious subjectivity that has become normalised in recent decades in cities of the global North. Drawing on in‐depth interviews with long‐term property guardians in London, we unpack the narratives and rationales of university‐educated and highly skilled individuals for whom the city is a site of intensified insecurity and flexible negotiation. In the end, we conclude that the form of permanent temporariness experienced by property guardians needs to be understood as a symptom of wider dynamics of work and life precarisation in urban centres and argue that it is imperative to extend recent geographical debates around work and life insecurity to include new housing practices and their role in co‐constituting urban precarity.
Theoretical and Experimental Studies of a New Configuration of Photovoltaic–Thermal Collector
Authors: Ben Cheikh El Hocine Hanene , Touafek Khaled , Kerrour Fouad
Published: December 2016

Within the solar energy technologies, the hybrid photovoltaic–thermal (PVT) systems offer an attractive option because the absorbed solar radiation is converted into thermal and electrical energies (the conversion can be done separately or simultaneously). In this study, an attempt has been made to evaluate the theoretical and practical performances and evaluation of a hybrid PVT collector based on a new integrated absorber configuration function of climatic and design parameters. Our objective is to obtain a more efficient use of solar energy by cheaper materials and simpler implementation. On the first hand, we considered two different configurations of hybrid collectors which are defined as PVT water with absorber in parallel vertical tubes (model I) and a PVT with absorber in an enclosure (model II). On the second hand, we presented a new integrated absorber configuration for hybrid collector; then we compared it to the two previous models. The last proposed design has the advantage of a simpler implementation and a lower cost compared to other configurations of PVT hybrid collectors. A computer simulation program has been developed in order to calculate the thermal and electrical parameters of the PVT–water collector. The obtained simulation results are found to be in good agreement with the experimental measurements. For a sample climatic, operating, and design parameter, the calculated thermal and electrical energies of the new configuration of PVT are about 125.36 W and 40 W, respectively.
Coupled Concentrating Optics, Heat Transfer, and Thermochemical Modeling of a 100-kWth High-Temperature Solar Reactor for the Thermal Dissociation of ZnO
Authors: Villasmil W. , Cooper T. , Koepf E. , Meier A. , Steinfeld A.
Published: December 2016

This work reports a numerical investigation of the transient operation of a 100-kWth solar reactor for performing the high-temperature step of the Zn/ZnO thermochemical cycle. This two-step redox cycle comprises (1) the endothermal dissociation of ZnO to Zn and O2 above 2000 K using concentrated solar energy, and (2) the subsequent oxidation of Zn with H2O/CO2 to produce H2/CO. The performance of the 100-kWth solar reactor is investigated using a dynamic numerical model consisting of two coupled submodels. The first is a Monte Carlo (MC) ray-tracing model applied to compute the spatial distribution maps of incident solar flux absorbed on the reactor surfaces when subjected to concentrated solar irradiation delivered by the PROMES-CNRS MegaWatt Solar Furnace (MWSF). The second is a heat transfer and thermochemical model that uses the computed maps of absorbed solar flux as radiation boundary condition to simulate the coupled processes of chemical reaction and heat transfer by radiation, convection, and conduction. Experimental validation of the solar reactor model is accomplished by comparing solar radiative power input, temperatures, and ZnO dissociation rates with measured data acquired with the 100-kWth solar reactor at the MWSF. Experimentally obtained solar-to-chemical energy conversion efficiencies are reported and the various energy flows are quantified. The model shows the prominent influence of reaction kinetics on the attainable energy conversion efficiencies, revealing the potential of achieving ηsolar-to-chemical = 16% provided the mass transport limitations on the ZnO reaction interface were overcome.
Formulation of Sasol IPK Surrogate Fuel for Diesel Engine Application Using an Ignition Quality Tester (IQT)
Authors: Zheng Ziliang , Badawy Tamer , Henein Naeim , Schihl Peter , Sattler Eric
Published: December 2016

This paper presents an approach to develop Sasol IPK (Iso-Paraffinic Kerosene) surrogate fuels for diesel engine application using Ignition Quality Tester (IQT). The methodology includes: 1) in-house developed MATLAB code to formulate the appropriate mixture blends, 2) Aspen HYSYS to develop the distillation curve and compares it to the target Sasol IPK fuel, 3) IQT to measure the derived cetane number (DCN) of surrogate fuels and compare it with the target Sasol IPK fuel, 4) analysis of autoignition and combustion characteristics for Sasol IPK surrogate fuels. The ignition delay, combustion gas pressure, and rate of heat release of Sasol IPK and its formulated surrogate fuel are analyzed and compared at five different charge temperatures. Furthermore, the apparent activation energies derived from chemical ignition delay of the surrogate fuel and Sasol IPK are determined and compared.
Potential and Limitations of Dual Fuel Operation of High Speed Large Engines
Authors: Redtenbacher Christoph , Kiesling Constantin , Malin Maximilian , Wimmer Andreas , Pastor Jose V. , Pinotti Mattia
Published: December 2016

Interest is growing in using fully flexible diesel-gas dual fuel engines for power generation and propulsion on land and sea. Benefits such as the flexibility to adapt the type of fuel to the market situation, fail-safe operation and lower NOx emissions than diesel engines are convincing arguments for engine operators. However, diesel-gas engine concepts still suffer from lower efficiency than state-of-the-art monovalent diesel engines and spark ignited gas engines when operated in the corresponding fuel mode. To meet stringent NOx emission legislation, high diesel substitution rates are necessary, which in turn often lead to poor combustion stability. Especially with these small diesel fractions, the challenge remains to ensure stable ignition, fast combustion of the air-fuel mixture and low hydrocarbon emissions.

The aim of this paper is to identify and investigate the potential and limitations of diesel-gas combustion concepts for high speed large engines operated in gas mode with very small amounts of pilot fuel (< 5 % diesel fraction1). Experimental tests were carried out on a flexible single cylinder research engine (swept volume approximately 6 1) equipped with a common rail system. Various engine configurations and operating parameters were varied and the effects on the combustion process were analyzed. The results presented in this paper include a comparison of the performance of the investigated dual fuel concept to those of a state-of-the-art monovalent gas engine and a state-of-the-art monovalent diesel engine. Evaluation reveals that certain limiting factors exist that prevent the dual fuel engine from performing as well as the superior gas engine. On the other hand, the potential is already present for the dual fuel concept to compete with the diesel engine.

Since the injection of pilot fuel is of major importance for flame initialization and thus for the main combustion event of the dual fuel engine, optical investigations in a spray box, measurements of injection rates and 3D-CFD simulation were conducted to obtain even more detailed insight into these processes. A study on the influence of the diesel fraction shows that diminishing the diesel fraction from 3 % to lower values has a significant impact on engine performance because of the effects of such a reduction on injection, ignition delay and initial flame formation. An investigation of the influence of the injection timing reveals that with diesel fractions of ≤ 1.5 %, the well-known relationship between the injection timing and combustion phasing of conventional engine concepts is no longer valid.

The presented results illustrate which operating strategy is beneficial for engine performance in terms of low NOx emissions and high efficiency. Moreover, potential measures can be derived which allow for further optimization of the diesel-gas combustion process.
Effects of Ammonia Gas Mixed Into Intake Air on Combustion and Emissions Characteristics in Diesel Engine
Authors: Niki Yoichi , Yoo Dong-Hoon , Hirata Koichi , Sekiguchi Hidenori
Published: December 2016

This paper reports on the experimental results of the combustion and emission characteristics of a conventional diesel engine mixed ammonia (NH3) gas into the intake air, and discusses its usability. In the experiments, NH3 gas was injected into the intake pipe of the diesel engine by a gas injector. The diesel engine has a natural aspiration single cylinder with 7.7 kW rated power at 1500 rpm and a diesel injection system to inject diesel fuel into the cylinder.

As experimental results on the combustion characteristics, it was confirmed that the compression and maximum pressures in the cylinder decreased and the ignition timing delayed with increasing the NH3 gas injection quantity. On the emission characteristics in the exhaust gas, NH3, water (H2O) and nitrous oxide (N2O) increased and carbon dioxide (CO2) decreased proportionally to the NH3 gas injection quantity. In contract, the nitrogen oxide (NO) was nearly the same. Moreover, it was confirmed that NH3 can be reduced by reacting with NO in a selective catalytic reduction (SCR) system.
The Combustion and Emissions Performance of a Syngas-Diesel Dual Fuel Compression Ignition Engine
Authors: Guo Hongsheng , Neill W. Stuart , Liko Brian
Published: December 2016

Remote communities in Canada heavily rely on reciprocating diesel generators for heat and power generation. These engines utilize diesel fuel that is imported at great expense and generate green-house gas (GHG) and pollutant emissions. Replacing diesel fuel in these engines by syngas derived from a thermo-chemical treatment of local renewable biomass can not only lower the fuel cost but also reduce GHG and pollutant emissions for remote communities. Besides, syngas-diesel dual fuel combustion can maintain the ability to revert back to diesel operation and therefore ensure reliable heat and power supply when syngas is not available.

In this study, the combustion and emissions performance of a syngas-diesel dual fuel engine was investigated at low and medium loads. A single cylinder direct injection diesel engine was modified to operate using a dual fuel strategy. The diesel fuel was directly injected to the cylinder, while syngas was injected into the intake port. The effects of syngas fraction and composition on energy efficiency, cylinder pressure, exhaust temperature, and combustion stability were recorded and analyzed. The emissions data, including PM, NOx, CO, and unburned hydrocarbon, were also analyzed and reported in the paper.

The results suggest that the substitution of diesel by a syngas caused a slight decrease in brake thermal efficiency and an increase in CO emissions. The effect of a syngas on soot emissions depended on the composition and/or quality. The inert component content of a syngas significantly affected NOx emissions in a syngas-diesel dual fuel internal combustion engine.
Predicting the Cetane Number of Furanic Biofuel Candidates Using an Improved Artificial Neural Network Based on Molecular Structure
Authors: Kessler Travis , Sacia Eric R. , Bell Alexis T. , Mack J. Hunter
Published: December 2016

The next generation of alternative fuels is being investigated through advanced chemical and biological production techniques for the purpose of finding suitable replacements to diesel and gasoline while lowering production costs and increasing process yields. Chemical conversion of biomass to fuels provides a plethora of pathways with a variety of fuel molecules, both novel and traditional, which may be targeted. In the search for new fuels, an initial, intuition-driven evaluation of fuel compounds with desired properties is required. Due to the high cost and significant production time needed to synthesize these materials at a scale sufficient for exhaustive testing, a predictive model would allow chemists to preemptively screen fuel properties of potentially desirable fuel candidates. Recent work has shown that predictive models, in this case artificial neural networks (ANN’s) analyzing quantitative structure property relationships (QSPR’s), can predict the cetane number (CN) of a proposed fuel molecule with relatively small error. A fuel’s CN is a measure of its ignition quality, typically defined using prescribed ASTM standards and a cetane testing engine. Alternatively, the analogous derived cetane number (DCN), obtained using an Ignition Quality Tester (IQT), is a direct measurement alternative to the CN that uses an empirical inverse relationship to the ignition delay found in the constant volume combustion chamber apparatus. DCN data points acquired using an IQT were utilized for model validation and expansion of the experimental database used in this study. The present work improves on an existing model by optimizing the model architecture along with the key learning variables of the ANN and by making the model more generalizable to a wider variety of fuel candidate types, specifically the class of furans and furan derivatives, by including specific molecules for the model to incorporate. The new molecules considered include tetrahydrofuran, 2-methylfuran, 2-methyltetrahydrofuran, 5,5′-(furan-2-ylmethylene)bis(2-methylfuran), 5,5′-((tetrahydrofuran-2-yl)methylene)bis(2-methyltetrahydrofuran), tris(5-methylfuran-2-yl)methane, and tris(5-methyltetrahydrofuran-2-yl)methane. Model architecture adjustments improved the overall root-mean-squared error (RMSE) of the base database predictions by 5.54%. Additionally, through the targeted database expansion, it is shown that the predicted cetane number of the furan-based molecules improves on average by 49.21% (3.74 CN units) and significantly for a few of the individual molecules. This indicates that a selected subset of representative molecules can be used to extend the model’s predictive accuracy to new molecular classes. The approach, bolstered by the improvements presented in this paper, enables chemists to focus on promising molecules by eliminating less favorable candidates in relation to their ignition quality.
Physical Model for Real-Time Simultaneous Estimation of Intake Mass and Cylinder Pressure in an SI Engine
Authors: Xu Shuonan , Wang Zhe , Prucka Robert , Filipi Zoran , Prucka Michael , Dourra Hussein
Published: December 2016

Stringent emission regulations require spark ignited (SI) engines to operate at stoichiometry to enable the use of a three way catalyst (TWC). Thus, accurate prediction of the intake charge mass flow rate is paramount. Current speed-density air mass-flow prediction techniques require extensive calibration for predicting volumetric efficiency, while mass air flow (MAF) meter based approaches suffer from a loss of accuracy during transients. This work aims to provide an alternative, i.e. a model based air charge estimation algorithm that can reduce calibration effort and provide a universal solution across engine platforms. An additional objective is to minimize the number of required sensors and associated cost. The foundation is established with a 0-D physics-based air charge model, where air flow through intake and exhaust valves is modeled on a crank-angle basis, without the need to measure in-cylinder pressure. The proposed algorithm solves differential equations for cylinder pressure and mass flow rate in/out of the cylinder to simultaneously obtain instantaneous pressure and mass-flow estimations, hence eliminating the need to install cylinder pressure transducers. An additional benefit is the robustness of the new model, due to its ability to self-compensate for an error in the intake runner pressure or initial estimation of the cylinder pressure. The model has been validated with GT-Power simulations and steady-state engine tests with multiple actuator sweeps. Transient tests and real-time implementations were performed as well.
High-Speed Rainbow Schlieren Deflectometry of N-Heptane Sprays Using a Common Rail Diesel Injector
Authors: Mirynowski Eileen M. , Agrawal Ajay K. , Bittle Joshua A.
Published: December 2016

More precise measurements of the fuel injection process can enable better combustion control and more accurate predictions resulting in a reduction of fuel consumption and toxic emissions. Many of the current methods researchers are using to investigate the transient liquid fuel sprays are limited by cross sensitivity when studying regions with both liquid and vapor phases present (i.e. upstream of the liquid length). The quantitative rainbow schlieren technique has been demonstrated in the past for gaseous fuel jets and is being developed here to enable study of the spray near the injector. In this work an optically accessible constant pressure flow rig and a modern common rail diesel injector are used to obtain high speed images of vaporizing fuel sprays at elevated ambient temperatures and pressures.

Quantitative results of full-field equivalence ratio measurements are presented as well as more traditional measurements such as vapor penetration and angle for a single condition (13 bar, 180°C normal air) using nheptane injected through a single hole (0.1mm diameter) common rail fuel injector at 1000 bar fuel injection pressure. This work serves as a proof of concept for the rainbow schlieren technique being applied to vaporizing fuel sprays and full details of the image processing routine are provided. The ability of the imaging technique combined with the constant pressure flow rig make this approach ideal for generating large data sets in short periods of time for a wide range of operating conditions.
Evaluation of Spark Plug and Timing Configurations on the Fuel Consumption, Combustion Stability, and Emissions of a Large-Bore, Two-Stroke, Natural Gas Engine
Authors: Johnson Derek , Besch Marc , Fowler Nathaniel , Heltzel Robert , Covington April
Published: December 2016

Emissions compliance is a driving factor for internal combustion engine research pertaining to both new and old technologies. New standards and compliance requirements for off-road spark ignited engines are currently under review and include greenhouse gases. To continue operation of legacy natural gas engines, research is required to increase or maintain engine efficiency, while reducing emissions of carbon monoxide, oxides of nitrogen, and volatile organic compounds such as formaldehyde. A variety of technologies can be found on legacy, large-bore natural gas engines that allow them to meet current emissions standards — these include exhaust after-treatment, advanced ignition technologies, and fuel delivery methods. The natural gas industry uses a variety of spark plugs and tuning methods to improve engine performance or decrease emissions of existing engines. The focus of this study was to examine the effects of various spark plug configurations along with spark timing to examine any potential benefits. Spark plugs with varied electrode diameter, number of ground electrodes, and heat ranges were evaluated against efficiency and exhaust emissions. Combustion analyses were also conducted to examine peak firing pressure, location of peak firing pressure, and indicated mean effective pressure. The test platform was an AJAX-E42 engine. The engine has a bore and stroke of 0.216 × 0.254 meters (m), respectively. The engine displacement was 9.29 liters (L) with a compression ratio of 6:1. The engine was modified to include electronic spark plug timing capabilities along with a mass flow controller to ensure accurate fuel delivery. Each spark plug configuration was examined at ignition timings of 17, 14, 11, 8, and 5 crank angle degrees before top dead center. The various configurations were examined to identify optimal conditions for each plug comparing trade-offs among brake specific fuel consumption, oxides of nitrogen, methane, formaldehyde, and combustion stability.
“Lost Available IMEP”: A Second-Law-Based Performance Parameter for IC Engines
Authors: Mahabadipour H. , Srinivasan K. K. , Krishnan S. R.
Published: December 2016

The second law of thermodynamics is a powerful tool for investigating thermodynamic irreversibilities and to identify pathways for improving efficiencies of energy systems, including IC engines. In the present work, second law analysis is applied to quantify irreversibilities in diesel-ignited natural gas dual fuel low temperature combustion (LTC), which utilizes diesel to ignite natural gas to simultaneously reduce emissions of oxides of nitrogen and particulate matter. A previously validated multi zone thermodynamic model of dual fuel LTC was used as the basic framework to perform the second law analysis. The multi-zone model, which simulates closed cycle processes between intake valve closure (IVC) and exhaust valve opening (EVO), divides the cylinder contents into four main zones: (i) an unburned zone containing a premixed natural gas-air mixture, (ii) a pilot fuel zone (or “packets”) containing diesel vapor and entrained natural gas-air mixture, (iii) a flame zone, and (iv) a burned zone. By applying the second law systematically to each zone, the total entropy generated over the closed cycle (Sgen) and the lost available work (Wlost = T0*Sgen) were quantified. Subsequently, the lost available work was divided by the displaced volume to calculate a new engine performance parameter labeled “lost available indicated mean effective pressure” (LAIMEP). Proceeding analogously from the definition of indicated mean effective pressure (IMEP) as an engine-size-normalized measure of indicated work, the LAIMEP may be interpreted as an engine-size-normalized measure of available work that is lost due to thermodynamic irreversibilities. Since LAIMEP is independent of engine size, it can be used to compare thermodynamic irreversibilities between engines of various displaced volumes as well as between different engine combustion strategies. Two additional second-law-based parameters: fuel conversion irreversibility (FCI) as the ratio of Wlost to total fuel chemical energy input and normalized LAIMEP as the ratio of LAIMEP to IMEP, were also defined. Parametric studies were performed at different diesel injection timings (SOI ∼ 300–340 CAD), intake temperatures (Tin ∼ 50°–150°C), and intake boost pressures (Pin ∼ 1–2.4 bar) to characterize their impact on LAIMEP and FCI. It was determined that both LAIMEP and FCI increased with SOI advancement (from 340 to 300 CAD) and decreased with increasing Tin and Pin. These trends were explained using predicted combustion parameters, especially burned mass fraction and average in-cylinder temperature at EVO. While the present work focused on diesel-natural gas dual fuel LTC (as an example), the overall methodology adopted for the second law analysis as well as the conceptual definitions of LAIMEP, FCI, etc., are generally applicable to any IC engine operating on any combustion strategy (e.g., SI, CI, LTC, etc.).
Investigation of Multi-Pole Spark Ignition on Flame Kernel Development and in Engine Operation
Authors: Xie Kelvin , Yu Shui , Gao Tongyang , Yu Xiao , Zheng Ming , Li Liguang
Published: December 2016

In order to meet the future carbon dioxide legislation, advanced clean combustion engines are tending to employ low temperature diluted combustion strategies along with intensified cylinder charge motion. The diluted mixtures are made by means of excess air admission or exhaust gas recirculation. A slower combustion speed during the early flame kernel development because of the suppressed mixture reactivity will reduce the reliability of the ignition process and the overall combustion stability. In an effort to address this issue, an ignition strategy using a multi-pole spark igniter is tested in this work. The igniter uses three electrically independent spark gaps to allow three spatially distributed spark discharge. The multi-pole spark strategy, when observed in an optical combustion vessel with lean methane-air mixtures, visually showed increased early flame kernel growth rate. The strategy was tested on an engine using gasoline fuel and low load, lean operation at 1.35 excess air ratio. The results indicated that the combustion phasing parameters were consistently advanced under the multi-pole spark strategy. In conditions where a conventional single spark exhibited stable operation, relatively little additional benefits were seen with the multi-pole strategy. At later spark timings when cycle-to-cycle variations had a greater impact on the engine stability, the multi-pole spark reduced the combustion variability.
An Improved Method of Evaluating the Stress Intensity Factor for a Penetrating Circumferential Defect in a Self-Balancing Residual Stress Field in a Weld
Authors: Wei Liwu , Shi Jinhua , Buckland John
Published: December 2016

It is required to determine the stress intensity factor (SIF) contributed from a through-wall residual stress distribution when assessing the structural integrity of a welded joint containing flaws. By decomposing the through-wall residual stress distribution into a membrane stress component (σm), bending stress component (σb) and self-balancing stress component (σsb), the total SIF from the through-wall residual stress distribution (Ktotal) comprises Km (due to σm), Kb (due to σb) and Ksb (due to σsb). Km and Kb can be relatively easy to determine as there are standard solutions available for common geometries and flaw types. However, it is not straightforward to calculate Ksb owing to the arbitrary distribution of the self-balancing stress component. In particular, no SIF solutions are available for a through-wall penetrating defect in a plate or a cylinder subjected to an arbitrary through-wall self-balancing stress distribution other than for three special distributions (cosine, triangular and square distributions). Neglecting the contribution of σsb to the Ktotal could significantly underestimate the crack driving force, thus leading to a non-conservative assessment of limiting defect size.

Therefore, the calculation of Ksb for a though-wall penetrating defect in a plate or a cylinder under an arbitrary stress distribution is of the primary concern in this work. Understandably, finite element analysis (FEA) can be used to calculate the Ksb in these situations, but it is costly to perform such analysis. In this work, a simple method is proposed for estimating Ksb due to the self-balancing component which has a different distribution from the cosine, triangular and square distributions. This method is an extension of the approach adopted by Annex Q, BS 7910:2013 in dealing with the calculations of Ksb resulted from the σsb profiles which are decomposed from the proposed upper bound through-wall welding residual stress profiles. Some typical through-wall welding residual stress distributions are investigated with the proposed method in estimation of the Ksb for a through-wall penetrating defect in a plate or a cylinder. Discussion and highlights are given in the aspects of the effects of welding residual stress profiles on SIFs, the implications for limiting defect sizes, and the likelihood of underestimating the Ksb when using the equation established in R6 Revision 4 with a cosine distribution for any other distributions.
Development of Design Curve for Sweepolet Subjected to Acoustic Induced Vibration
Authors: Liu Yuqing , Diwakar Philip , Lin Dan , Eljaouhari Ismat , Prakash Ajay
Published: December 2016

High acoustic energy has the potential to cause severe Acoustic Induced Vibration (AIV) that leads to fatigue failure at high stress concentration regions such as fittings in a piping system. Sweepolet fittings have been extensively used as mitigation to counteract the risk of fatigue failure caused by AIV. The advantages of a sweepolet are its integrally reinforced contoured body and low stress concentration. However, there are inconsistencies in published standards and regarding the design limits for sweepolet subjected to AIV. In this paper, Finite Element Analysis is conducted to simulate high frequency pipe shell wall vibration caused by acoustic energy inside the pipe. Peak stress and the associated minimum fatigue life are calculated for sweepolet and sockolet under the same acoustic excitation. By comparing the stress level to that of a sockolet whose design limit to AIV had been published, the design curve and fatigue life equation for sweepolet are developed.
Quantitative Characterization of Hydride Spacing for Cohesive-Zone Modelling of Fracture Toughness in Zr-2.5Nb Pressure Tubes
Authors: Liu Cheng , Gutkin Leonid , Scarth Douglas
Published: December 2016

Zr-2.5Nb pressure tubes in CANDU 1 reactors are susceptible to hydride formation when the solubility of hydrogen in the pressure tube material is exceeded. As temperature decreases, the propensity to hydride formation increases due to the decreasing solubility of hydrogen in the Zr-2.5Nb matrix. Experiments have shown that the presence of hydrides is associated with reduction in the fracture toughness of Zr-2.5Nb pressure tubes below normal operating temperatures. Cohesive-zone approach has recently been used to address this effect. Using this approach, the reduction in fracture toughness due to hydrides was modeled by a decrease in the cohesive-zone restraining stress caused by the hydride fracture and subsequent failure of matrix ligaments between the fractured hydrides. As part of the cohesive-zone model development, the ligament thickness, as represented by the radial spacing between adjacent fractured circumferential hydrides, was characterized quantitatively. Optical micrographs were prepared from post-tested fracture toughness specimens, and quantitative metallography was performed to characterize the hydride morphology in the radial-circumferential plane of the pressure tube. In the material with a relatively low fraction of radial hydrides, further analysis was performed to characterize the radial spacing between adjacent fractured circumferential hydrides. The discrete empirical distributions were established and parameterized using continuous probability density functions. The resultant parametric distributions of radial hydride spacing were then used to infer the proportion of matrix ligaments, whose thickness would not exceed the threshold value for low-energy failure. This paper describes the methodology used in this assessment and discusses its results.
Guidelines for MACA: The Optimization of Corrosion Allowance
Authors: Taagepera Jaan , Boyak Craig
Published: December 2016

Excess capacity in the design of a pressure vessel can be recognized in a maximum allowable working pressure (MAWP). This pressure value is the result of the calculations for minimum thickness, in the new condition, being rounded up to the next nominal plate thickness and then working the formulae to establish limiting pressure based on the actual thickness used.

Another variable which may be optimized is the design temperature. Raising the design temperature tends to result in a reduced allowable stress. Once a plate thickness has been determined, the necessary allowable stress can be back calculated. From this allowable stress, an optimized design temperature can be determined.

Excess capacity can also be recognized in the form of increased corrosion allowance or MACA, the Maximum Allowable Corrosion Allowance. This is particularly helpful in the maintenance and inspection realms where life extension or unexpected thinning can force an unplanned shutdown of the unit, a fitness for service evaluation, or repair once the specified corrosion allowance is exhausted.

This paper presents a set of guidelines or rules for establishing a MACA based optimization for the design of new pressure vessels.
Sensitivity Analyses for a PWR SCC Case Using the Probabilistic Loss-of-Coolant-Accident (Pro-LOCA) Software
Authors: Young Bruce A. , Lee Sang-Min , Scott Paul M.
Published: December 2016

As a means of demonstrating compliance with the United States Code of Federal Regulations 10CFR50 Appendix A, General Design Criterion 4 (GDC-4) requirement that primary piping systems for nuclear power plants exhibit an extremely low probability of rupture, probabilistic fracture mechanics (PFM) software has become increasingly popular. One of these PFM codes for nuclear piping is Pro-LOCA which has been under development over the last decade. Currently, Pro-LOCA is being enhanced under an international cooperative program entitled PARTRIDGE-II (Probabilistic Analysis as a Regulatory Tool for Risk-Informed Decision GuidancE - Phase II).

This paper focuses on the use of a pre-defined set of base-case inputs along with prescribed variation in some of those inputs to determine a comparative set of sensitivity analyses results. The benchmarking case was a circumferential Primary Water Stress Corrosion Crack (PWSCC) in a typical PWR primary piping system. The effects of normal operating loads, temperature, leak detection, inspection frequency and quality, and mitigation strategies on the rupture probability were studied. The results of this study will be compared to the results of other PFM codes using the same base-case and variations in inputs. This study was conducted using Pro-LOCA version 4.1.9.
Analysis of Class Evaluation in Ultrasonic Test on Pressure Vessel and Pipe Weld Seams
Authors: Zhang Youwei , Yang Yuqing , Chen Le
Published: December 2016

In the ultrasonic test of girth or longitudinal butt joints in boiler, pressure vessel and pipe, there are multiple defects perpendicular to the length of the weld in a straight line. It is inappropriate of considering only the two adjacent defects in a line in quality classification without considering the defects located in different depth while in same lateral position. Hereby, we make tensile strength test of the rectangle samples with different numbers of side drilled holes, then do collection and analysis about the test result, so that we can get the relationship between elongation and tensile strength of the specimen under external force.
Fragility Analysis Methods for Steel Storage Tanks in Seismic Prone Areas
Authors: Phan Hoang Nam , Paolacci Fabrizio , Alessandri Silvia
Published: December 2016

Catastrophic failure of above ground storage tanks was observed due to past earthquakes causing serious economic and environmental consequences. Therefore, the evaluation of the seismic vulnerability of existing liquid storage tanks located in seismic prone areas is an important task. Seismic fragility functions are useful tools in order to quantify the seismic vulnerability of structures. These functions give a probability that a seismic demand on a structural component meets or exceeds its capacity, and are generally derived by a variety of approaches, e.g., field observations of damage, static structural analyses, judgment, or analytical fragility functions. Unlike the other methods, the analytical fragility functions are developed from a coupling of the structural response analysis and a probabilistic seismic demand model. The objective of this study is to investigate the seismic vulnerability of above ground steel storage tanks using different analytical methods of the fragility function. A comparison of the well-known cloud method and the incremental dynamic analysis is performed at different limit states for two existing cylindrical steel storage tanks. The first tank represents a slender geometry with a fixed-roof and the second one is a broad tank, unanchored, and provided with a floating roof.
Inclusion of Warm Pre-Stress Concept in French RPV Structural Integrity Assessment
Authors: Moinereau Dominique , Ait-Bachir Malik , Chapuliot Stéphane , Marie Stéphane , Jacquemoud Clémentine , Tanguy Benoit
Published: December 2016

Evaluation of the fracture resistance of nuclear reactor pressure vessel (RPV) regarding the risk of brittle fracture is a key point in the structural integrity assessment of the component (RPV). Such approach is codified in French RSE-M code, based on a very conservative methodology. With respect to long term operation, an improvement of the present methodology is necessary and in progress to reduce this conservatism.

One possible significant improvement is the inclusion of the warm pre-stress (WPS) concept in the assessment. After a short description of the WPS concept, the process engaged in France to allow inclusion of WPS in the integrity assessment is presented.

In a first step, experimental and numerical studies have been conducted in France by EDF, CEA and AREVA (also including international collaborations and projects) to demonstrate and validate the beneficial effect of WPS on the brittle fracture resistance of RPV steels. A large panel of experimental results and data is now available obtained on small, medium and large scale specimens on representative RPV steels (including highly irradiated RPV materials). These data have been included in a specific WPS experimental database.

Main experiments have been interpreted by refined computations, based on elastic plastic analyses and local approach to cleavage fracture.

In a second step, a new criterion (ACE criterion) has been proposed by French organizations (AREVA, CEA and EDF) for an easy simplified evaluation of warm pre-stress effect on the brittle fracture resistance of RPV steels. Accuracy and conservatism of the criterion is verified by comparison to experimental data results and numerical analyses.

Finally, implementation of the WPS effect in the French RSE-M code (for in service assessment) is in progress, based on the ACE criterion.

The present paper summarizes all these steps leading to codification of WPS in RSE-M code.
Evolution of Fatigue Post-Processing Methods in the EDF Open-Access FEA Code ASTER
Authors: Métais Thomas , Plessis Sarah , Chau The-Hiep , Le Roux Jean-Christophe
Published: December 2016

Fatigue is identified as a significant degradation mode that affects nuclear power plants world-wide. The various international codes and standards (ASME, RCC-M, JSME, etc...) offer rules to predict its damaging effect on the locations of the various components of an NPP. These rules, which ensure conservatism and safe operation, have grown in complexity over the years because they have integrated R&D results showing aggravating effects that were not included in the original analyses (such as Environmental Assisted Fatigue [1]) but also because an economically viable design of components has required optimization and refinement of mechanical assessment methods.

EDF has been developing since 1989 its own open-source FEA code baptised code ASTER that is included in the Salome Meca mechanical package. Salome Meca is open-access and can be used freely by international users. It is continuously improved with a release at a rate of one new software version per year and it integrates the most recent results obtained by the EDF R&D, in fields as broad as fracture mechanics, XFEM and fatigue.

The fatigue post-processing in code ASTER offers a span of criteria (Dang Van, Stress Intensity, etc...) to pick and choose from and even offers the possibility to make up one owns fatigue criteria. It also offers the possibility to post-process fatigue according to the RCC-M rules (POST_RCCM operator).

Recent developments have enabled to update the POST_RCCM operator to make it bridge the gap with modern fatigue industrial codes as well as to integrate the EAF calculations per the methodology proposed in [2]. The work is currently ongoing within EDF R&D and will give birth to a stabilized and validated version of the code by end of 2016.

This paper presents the updates and the new possibilities of the POST_RCCM operator and gives an update of the work as of early 2016.
Modifications of the 2016 Edition of the RCC-M Code to Account for Environmentally Assisted Fatigue
Authors: Courtin Stéphan , Métais Thomas , Triay Manuela , Meister Eric , Marie Stéphane
Published: December 2016

The French nuclear industry has to face nowadays a series of challenges it did not have to face a decade ago. The most significant one is to ensure a reliable and safe operation of Nuclear Power Plants (NPP) in a context of both an ageing reactor fleet and new builds. The new constructions need rules that integrate a strong operation feedback while the older NPPs need rules that will guarantee the life extension beyond 40 years of operation.

In this context, a new edition of the French RCC-M Code is planned for 2016. This new edition integrates the modifications made to the Code as a result of Requests for Modification (RM), which can be submitted by anyone and which help to continuously improve the quality and robustness of the Code.

Concerning fatigue analyses, the RCC-M Code steering committee has acknowledged end of 2014 the reception of two RM to modify the fatigue design curve for austenitic stainless steels and Nickel base alloys, as well as to integrate environmental effects in the fatigue evaluation for austenitic stainless steel components. The contents of these two RM were based on the proposals presented in Reference [1].

AFCEN required a technical review of these two RM and this task was performed by a working group composed by French and international experts. This process concluded to the approval of these two RM to be integrated to the 2016 edition of the RCC-M Code. This paper offers a presentation of these two new Rules in Probation Phase (RPP), this format being quite similar to Code Cases proposed by ASME Code.
An Analytical Solution Based on Shell Theory for Calculating Stresses on Full Encirclement Sleeves Used on Pipes and Pressure Vessels
Authors: Nadarajah Chithranjan
Published: December 2016

Welded full encirclement sleeve repairs are used frequently in petrochemical industries as repairs for piping and pressure vessels. This publication describes a proposed methodology for calculating the stresses on a welded full encirclement sleeve using a closed from solution derived from shell theory. The analytical results are compared with finite element results and are found to be in reasonable agreement.