bluuebunny/crossref_metadata_2025_split huggingface dataset:
Controls on methane emissions from Alnus glutinosa saplings
Authors: Pangala Sunitha R. , Gowing David J. , Hornibrook Edward R. C. , Gauci Vincent 
Published: November 2013

Summary

Recent studies have confirmed significant tree‐mediated methane emissions in wetlands; however, conditions and processes controlling such emissions are unclear. Here we identify factors that control the emission of methane from Alnus glutinosa.

Methane fluxes from the soil surface, tree stem surfaces, leaf surfaces and whole mesocosms, pore water methane concentrations and physiological factors (assimilation rate, stomatal conductance and transpiration) were measured from 4‐yr old A. glutinosa trees grown under two artificially controlled water‐table positions.

Up to 64% of methane emitted from the high water‐table mesocosms was transported to the atmosphere through A. glutinosa. Stem emissions from 2 to 22 cm above the soil surface accounted for up to 42% of total tree‐mediated methane emissions. Methane emissions were not detected from leaves and no relationship existed between leaf surface area and rates of tree‐mediated methane emissions. Tree stem methane flux strength was controlled by the amount of methane dissolved in pore water and the density of stem lenticels.

Our data show that stem surfaces dominate methane egress from A. glutinosa, suggesting that leaf area index is not a suitable approach for scaling tree‐mediated methane emissions from all types of forested wetland.
Neonatal pain
Authors: Walker Suellen M. 
Published: November 2013

SummaryEffective management of procedural and postoperative pain in neonates is required to minimize acute physiological and behavioral distress and may also improve acute and long‐term outcomes. Painful stimuli activate nociceptive pathways, from the periphery to the cortex, in neonates and behavioral responses form the basis for validated pain assessment tools. However, there is an increasing awareness of the need to not only reduce acute behavioral responses to pain in neonates, but also to protect the developing nervous system from persistent sensitization of pain pathways and potential damaging effects of altered neural activity on central nervous system development. Analgesic requirements are influenced by age‐related changes in both pharmacokinetic and pharmacodynamic response, and increasing data are available to guide safe and effective dosing with opioids and paracetamol. Regional analgesic techniques provide effective perioperative analgesia, but higher complication rates in neonates emphasize the importance of monitoring and choice of the most appropriate drug and dose. There have been significant improvements in the understanding and management of neonatal pain, but additional research evidence will further reduce the need to extrapolate data from older age groups. Translation into improved clinical care will continue to depend on an integrated approach to implementation that encompasses assessment and titration against individual response, education and training, and audit and feedback.
Optimisation and standardisation of an immunoagglutination assay for the diagnosis of Trypanosoma cruzi infection based on latex‐(recombinant antigen) complexes
Authors: Garcia Valeria S. , Gonzalez Verónica D. G. , Marcipar Ivan S. , Vega Jorge R. , Gugliotta Luis M. 
Published: November 2013

AbstractObjectiveTo determine the conditions under which the immunoagglutination assay to detect Chagas disease, obtained from a novel latex‐(chimeric recombinant antigen) complex, shows greater discrimination between the responses of a positive control serum and a negative control serum. MethodsThe following variables were determined: (i) the sensitisation mechanism, (ii) the emulsifier employed for protein desorption, (iii) the reaction time, (iv) the ionic strength of the reaction medium, (v) the particle concentration, (vi) the presence of blocking agents, (vii) the presence of polyethyleneglycol as potentiator of reaction and (viii) the antigen and antibody concentrations. The search of optimal conditions was investigated by varying one variable at a time. To this effect, monodisperse latex particles sensitised with a recombinant chimeric protein (CP1) were subjected to different conditions. The agglutination reaction was followed by measuring the changes in the optical absorbance by turbidimetry.ResultsThe maximum discrimination between negative and positive sera was obtained at a reaction time of 5 min, when latex complexes with a concentration of covalently coupled protein of 2.90 mg/m2 were put in contact with undiluted sera in buffer borate pH 8–20 mm containing glycine (0.1 m) and polyethyleneglycol 8000 (3% w/v). Finally, the latex–protein complex was tested under the obtained optimal conditions, with a panel of Trypanosoma cruzi‐positive sera, leishmaniasis‐positive sera and ‐negative sera for both parasites.ConclusionThe immunoagglutination test based on the latex‐CP1 complex could be used as a screening method for detecting Chagas disease. This test is rapid, easy to implement and could be used under field conditions; but its results should be confirmed by reference techniques like ELISA, HAI, and IFI.
Unsteady Vibration of a Gas Turbine Compressor Blade at Subsonic Near-Stall Conditions
Authors: Yamaguchi Kazuyuki , Takahashi Yasuo 
Published: November 2013

Cascade wind tunnel tests were conducted to clarify unsteady blade vibration characteristics near stall conditions. An oscillating strain and pressure on a blade surface were measured. An aerodynamic damping ratio was also measured using the sweep excitation method and the operational modal analysis. Moreover, an unsteady blade vibration response and aerodynamic damping ratios were calculated using a three-dimensional computational fluid dynamics and a three-dimensional structural finite element method.
As a result of the experiments, the natural frequency component oscillated by the broadband frequency component of the fluid force was dominant in the stress, while the discrete low frequency components appeared in the pressure. The amplitudes of the stress and pressure increased when the Mach number or the incidence increased. As a result of the calculations, the discrete low frequency components appeared in the pressure, and those components and the natural frequency components appeared in the stress. The experimental and calculation results of the stress amplitude were generally in agreement.
The measured damping ratios increased when the Mach number increased. The dispersion of the measured damping ratio using the operational modal analysis was small. The calculated damping ratio was 1.3–1.8 times larger than the measured result.
Structural Dynamic Analysis Approach Used in a GE Heavy Duty Gas Turbine Combustor for MTBM Enhancement
Authors: lal Jangid Bihari , Provenzale Michele , Del Puglia Eugenio 
Published: November 2013

Gas turbine combustors are subjected to vibrations due to combustion dynamics pressure and rotor imbalance force which results in forced excitation of hardware. Such structural vibration leads to high cycle fatigue and wear out of contact interfaces of combustor, thus limiting hardware durability with reduced maintenance intervals. To have more realistic hardware life prediction for both failure modes, it is vital to understand structural dynamic behavior of combustor assembly in the presence of vibratory loads.
This paper describes the methodology used in developing MS5002D LHE combustor assembly linearized finite element dynamic models, the strategy to calibrate them with experimental data and the approach used to perform a forced responded analysis with harmonically varying combustion dynamics pressure and rotor imbalance force. Study shows that with adopted approach, an acceptable modal correlation between the model and the experimental test rig can be achieved. The forced dynamic response analysis results, in terms of dynamic stress distribution, interface sliding displacements and contact loads, represent the needed inputs for life prediction and for addressing the design improvements.
Reduced Order Modeling Based on Complex Nonlinear Modal Analysis and its Application to Bladed Disks With Shroud Contact
Authors: Krack Malte , Panning-von Scheidt Lars , Wallaschek Jörg , Siewert Christian , Hartung Andreas 
Published: November 2013

The design of bladed disks with contact interfaces typically requires analyses of the resonant forced response and flutter-induced limit cycle oscillations. The steady-state vibration behavior can efficiently be calculated using the Multi-Harmonic Balance method. The dimension of the arising algebraic systems of equations is essentially proportional to the number of harmonics and the number of degrees of freedom (DOFs) retained in the model. Extensive parametric studies necessary e.g. for robust design optimization are often not possible in practice due to the resulting computational effort.
In this paper, a two-step nonlinear reduced order modeling approach is proposed. First, the autonomous nonlinear system is analyzed using a Complex Nonlinear Modal Analysis technique based on the work of Laxalde and Thouverez [1]. The methodology in [1] was refined by an exact condensation approach as well as analytical calculation of gradients in order to efficiently study localized nonlinearities in large-scale systems. Moreover, a continuation method was employed in order to predict nonlinear modal interactions. Modal properties such as eigenfrequency and modal damping are directly calculated with respect to the kinetic energy in the system. In a second step, a reduced order model is built based on the Single Nonlinear Resonant Mode theory. It is shown that linear damping and harmonic forcing can be superimposed. Moreover, similarity properties can be exploited to vary normal preload or gap values in contact interfaces. Thus, a large parameter space can be covered without the need for re-computation of nonlinear modal properties. The computational effort for evaluating the reduced order model is almost negligible since it contains a single DOF only, independent of the original system.
The methodology is applied to both a simplified and a large-scale model of a bladed disk with shroud contact interfaces. In contrast to [1], the contact constraints account for variable normal load and lift-off in addition to dry friction. Forced response functions, backbone curves for varying normal preload and excitation level as well as flutter-induced limit cycle oscillations are analysed and compared to conventional methods. The limits of the proposed methodology are indicated and discussed.
Probabilistic Structure-Mechanical Assessment of Rotor Discs Considering Geometry Variations
Authors: Reuter Ilko , Weiss Thomas , Voigt Matthias , Vogeler Konrad , Schlums Hartmut , Becker Karl-Helmut , Fischersworring-Bunk Andreas 
Published: November 2013

For rotating critical parts, like compressor or turbine discs of aero engines, it is essential to perform reliable life predictions. Probabilistic methods are ideal to investigate these life predictions with regard to their sensitivities and robustness. Beside other system properties, the variation of geometrical disc parameters has a strong influence on the physical system behavior.
Within this paper, the system behavior of a turbine disc is assessed with regard to its sensitivities, to enable the continuous optimization of the disc and to verify a new post-processing method. To suit this purpose, a process chain was developed from CAD-model to lifing analysis and embedded into a Monte Carlo Simulation (MCS). As input parameters geometrical parameters and their optimization ranges are used. The statistical evaluation of an MCS with regard to sensitivities is based on comparison of topologically similar locations. Similarity is achieved by the standard operation of “mesh morphing”, in which the original mesh of the initial geometry is deformed onto the new geometry. This method is limited to small variations. Another method is remeshing of the new geometry. This makes direct comparison at identical FE-nodes impossible and post-processing is done based on significant local features. The post-processing method described in this paper is a combination of aforementioned approaches. Based on this new method, the result variables von-Mises stress and life cycles are investigated for their sensitivities to geometrical parameters within the disc bore.
Impact of Measurement Uncertainty in the Characteristic Maps of a Turbocharger on Engine Performance
Authors: Mai Holger , Vogt Mathias , Baar Roland , Kinski Andreas 
Published: November 2013

The main goal of current engine development is to increase power density and efficiency and to minimize engine emissions. The idea is to obtain the desired power output with a highly charged combustion engine in combination with exhaust gas turbocharging and a very small engine displacement, so-called downsizing.
The selection of a turbocharger is based on the maps of the turbine and compressor, which are usually measured on a test bench. They also provide important boundary conditions on the engine process simulation of a supercharged engine with this turbocharger. In general, a very accurate measurement of the characteristic maps is desired to ensure the best possible matching.
However, random and systematic errors have an impact on the measurement results. In order to assess the quality of the measured and calculated values, it is necessary to determine the uncertainties of the measurement variables as accurately as possible, particularly the error propagation in calculating the efficiencies.
The uncertainties are based on a systematic uncertainty component of the sensor and the confidence interval. In this way the measurement uncertainty is estimated by linear and geometric combination of the calculated random and systematic uncertainties. After that, the respective uncertainty contributions and the identification of the relevant parameters that influence the resulting measurement uncertainty are evaluated. Knowing the measurement uncertainties of the characteristic maps of a turbocharger, the influence on engine operation will be determined with a one-dimensional engine process simulation model. Consequently, the determined measurement uncertainty will be applied as a deviation on the efficiencies and will be investigated in a GT POWER simulation. The impact of the measurement uncertainty on the engine performance is shown on the basis of load steps.
A Modified Theta Projection Creep Model for a Nickel-Based Super-Alloy
Authors: Day W. David , Gordon Ali P. 
Published: November 2013

Accurate prediction of creep deformation is critical to assuring the mechanical integrity of heavy-duty, industrial gas turbine (IGT) hardware. The classical description of the creep deformation curve consists of a brief primary, followed by a longer secondary, and then a brief tertiary creep phase. An examination of creep tests at four temperatures for a proprietary, nickel-based, equiaxed, super-alloy revealed many occasions where there is no clear transition from secondary to tertiary creep. This paper presents a new creep model for a Nickel-based super-alloy, with some similarities to the Theta Projection (TP) creep model by Evans and all [1].
The alternative creep equation presented here was developed using meaningful parameters, or θ’s, such as: the primary creep strain, time at primary creep strain, minimum (or secondary) creep rate, and time that tertiary creep begins. By plotting the first and second derivative of creep, the authors were able to develop a creep equation that accurately matches tests. This creep equation is identical to the primary creep portion of the theta projection model, but has a modified second term. An additional term is included to simulate tertiary creep. An overall scaling factor is used to satisfy physical constraints and ensure solution stability. The new model allows a constant creep rate phase to be maintained, captures tertiary creep, and satisfies physical constraints.
The coefficients of the creep equations were developed using results from 27 creep tests performed at 4 temperatures. An automated routine was developed to directly fit the θ coefficients for each phase, resulting in a close overall fit for the material. The resultant constitutive creep model can be applied to components which are subjected to a wide range of temperatures and stresses. Useful information is provided to designers in the form of time to secondary and tertiary creep for a given stress and temperature. More accurate creep predictions allow PSM to improve the structural integrity of its turbine blades and vanes.
Theoretical Study on the Origin of Radial Cracks in Labyrinth Seal Fins due to Rubbing
Authors: Pychynski Tim , Dullenkopf Klaus , Bauer Hans-Jörg 
Published: November 2013

This paper presents a theoretical approach to analyse the macroscopic thermo-mechanical behaviour of labyrinth seal fins (knife edges) during and after a rubbing event. The study helps to understand the mechanism behind radial cracking in labyrinth fins and identifies its driving parameters. To begin with, a generic analytical model is developed in order to determine the elastic thermo-mechanical stresses in a thin rotating disk representing the seal fin for a given radial temperature distribution and contact pressure. Secondly, the analytical model is used to explain the high tensile stresses which may result from a rubbing process in labyrinth seals and which are a prerequisite for radial cracks to occur. The driving parameters and simple criteria to compare different materials with respect to cracking are discussed in detail. Crack initiation criteria and fracture mechanics are not considered in this paper.
Finally, the analytical model is validated for various seal fin geometries and rub conditions using a three-dimensional Finite-Element model. The interaction of the seal fin with the stator is not taken into account in this numerical simulation. Instead, the rubbing process is modeled by assuming a time-constant surface friction heat flux and contact pressure on the seal fin tip. Both friction heat flux and contact pressure were varied in a sensitivity study in order to account for different rubbing conditions.
Nozzle Guide Vane Assembly for Air-Cooled Retrofit Turbine Case Kit
Authors: Dabiru Venkata Rambabu , Gorte Devidasa Pai , Colantoni Simone 
Published: November 2013

Variable Guide Vanes are common to many of the Gas Turbines. Nozzle Guide Vane (NGV) is a variable nozzle present in the hot gas path of a twin-shaft gas turbine. In addition to guiding the hot gases onto the buckets, the NGV also controls the energy split between the high-pressure turbine and power turbine. The NGV is rotated to the desired position for different machine operability requirements through an actuation system. A twin shaft gas turbine equipped with NGV allows higher operational flexibility and higher efficiency at partial load/speed.
MS3002F is a heavy duty gas turbine developed by GE in 1960’s with water cooling system for the turbine casing and the NGV. Over the period of time, technology has evolved and water cooling system in Gas Turbines has become obsolete, as it leads to uneven cooling of the casing and scaling that cause performance losses, unplanned outages and down-time. To cater the existing fleet with improved reliability and availability, a new product introduction program was launched to design air-cooled system to replace the water-cooled system, within the boundaries of retrofit ability. The air cooling is achieved by extracted secondary flow air; the reduction on performance due to this is compensated by increasing the firing temperature. Owing to the removal of water cooling and increased firing temperature, the turbine casing and hot gas path components including NGV have to be redesigned.
The present paper discusses the redesign of the NGV assembly for new air-cooled configuration. This redesign includes geometry modification, assembly interface definition (contact geometry and coating), and material selection. The key challenge is to redesign the NGV with no cooling (neither water nor extracted secondary flow) while maintaining the steady state clearances of the NGV assembly as those of water-cooled kit. These redesigned components are validated for structural integrity under loads affecting fatigue, creep and oxidation. The verification of the functional integrity of NGV actuation system (that was originally designed for water-cooled system) for all operating conditions relevant to the new air-cooled turbine case kit is also discussed.
Validation of FE Simulated Structural Dynamic Behaviour of Heavy Duty Gas Turbines: A Case Study
Authors: Ugel Diego , Clark Alastair , Knopf Eric 
Published: November 2013

The increasing market demand for operational flexibility has highlighted the importance of gas turbines optimized for fast transient load variations. Dynamics is a key element in achieving these requirements.
The advanced FE modeling techniques used by ALSTOM for dynamic simulations of the GT (including rotor, bearings and structural parts) have been taken further by the detailed validation of the models used.
The validation exercise involved cold testing with impact hammer and shaker of individual parts and sub-assemblies at the ALSTOM Power Plant in Switzerland.
The influence of operational conditions has been investigated by warm testing, operating the engine with imbalance weights. Important eigenmodes / displaced shapes have been identified during the validation phases and compared with predicted mode shapes. For defined modes, the understanding is increased with particular reference to their excitability.
On the analytical side, key parameters, which affect the dynamic behavior, have been identified by using a detailed systematic approach. Factors affecting individual parts, sub-assemblies and final GT assembly are examined, physically understood and adjusted accordingly. Thus the accuracy of the prediction has been improved in both structural dynamic and rotordynamic assessments.
Furthermore, the guidelines defined for these parameters have been applied to the dynamic calculation for design modifications, successfully introduced on medium sized heavy duty gas turbines for service retrofit. Finally the validation exercise has enabled ALSTOM to improve the understanding of vibration data from engines in the field.