bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effects of Diffuser Geometry on Rotating Stall Behavior
Authors: Otugen M. V. , So R. M. C. , Hwang B. C. 
Published: March 2015

Experiments were carried out in a model vaneless diffuser rig to investigate the rotating stall phenomenon and its relation to diffuser geometry. The experimental rig consisted of an actual impeller which was used to deliver the flow to the vaneless diffuser. Mass flow rate through the system could be adjusted by varying the rotational speed of the impeller at a fixed inlet opening or by changing the inlet opening at a fixed impeller speed. The flow exited to room condition. As such, the rig was designed to investigate the fluid mechanics of vaneless diffuser rotating stall only. Attention was focused on the effects of diffuser width and radius on rotating stall. Three diffuser widths and three outlet radii were examined. The width-to-inlet radius ratio varied between 0.09 and 0.142 while the outlet-to-inlet radius ratio varied between 1.5 and 2.
Results showed that the critical mass flow rate for the onset of rotating stall decreases with decreasing diffuser width. The critical mass flow rate is affected also by the diffuser radius ratio; larger radius ratios resulted in smaller critical mass flow rates. The ratio of the speed of rotation of the stall cell to impeller speed is found to decrease with increasing number of stall cells. This relative speed also decreases with increasing diffuser radius ratio, but it is largely independent of the diffuser width.
Active Magnetic Bearings for Gas Turbomachinery in Closed-Cycle Power Plant Systems
Authors: McDonald Colin F. 
Published: March 2015

Bearing lubrication systems in closed-loop plants using gas (air or helium) as the working fluid (e.g., gas turbine, gas-cooled nuclear reactor, gas compressor, etc.) are very demanding since liquid lubricant ingress could contaminate the circuit, unlike open-cycle systems where the products would be expelled in the exhaust. Oil-lubricated bearings, the tribology mainstay in the power plant field, are reliable, but in the event of a failure in the seal or buffer system, the impact of oil ingress (e.g., saturation of insulation, coking on high-temperature surfaces, or in the extreme case, conflagration of equipment) can be costly and result in extended plant downtime.
The emergence in the early 1980s of a new tribology technology, namely a system in which the turbomachine rotor is levitated by a magnetic field, and positively sensed and controlled in real-time by an electronic system, now offers the designer an additional option. While an active magnetic system has many advantages, its foremost are (1) potential for very high reliability, (2) obviates the possibility of closed circuit contamination by lubricant ingress, (3) system simplicity, (4) ease of operation, and (5) ease of critical speed problems.
It is projected that utilization of “electronic chips instead of liquid films” will have a significant impact on the design of high-speed rotating machinery across the full spectrum of applications. This paper outlines the emergence of active magnetic bearings in rotating machinery for closed-cycle gas turbines, and in helium circulators for future high-temperature gas-cooled nuclear power plants. The paper highlights the existing industrial technology base that will make possible the deployment of active magnetic bearings in rotating machinery for the next generation of power plants that utilize closed-loop circuits.
Design Possibilities and Performance of Combined Cycle Operation of Converted Steam Power Plants
Authors: Linnemeijer M. J. J. , Van Buijtenen J. P. 
Published: March 2015

An interesting method for “boosting thermal efficiency and/or power output of an existing steam power plant is repowering through the addition of gas turbines.
The forced draught fan is replaced by a gas turbine and the air heater by low-temperature economisers.
This conversion will change the performance of the installation significantly. Therefore the design of the existing installation has to be reviewed based on new unit performance calculations.
Since the conversion has to be economical, it is important to find a good compromise between investment and improvement of performance.
This paper describes the change in performance of the installation created by the conversion in general and a number of design possibilities based on the experience gained with the realisation of a number of conversion projects.
These projects show a possible efficiency increase of over 10% and a power increase of up to 30%.
Investigation Into the Effect of Tip Clearance on Centrifugal Compressor Performance
Authors: Brasz Joost J. 
Published: March 2015

The axial clearance between the tip of the blades of an unshrouded impeller and its stationary shroud has been varied to study its effect on overall compressor performance. The compressor under investigation consisted of an inlet nozzle, a 3D open impeller with full inducer, a parallel-wall vaneless diffuser and a collector. High-accuracy overall performance data were obtained for this compressor.
The experiments were carried out in a closed-loop centrifugal compressor test rig with the impeller running at a rotational Mach number u2/a0 = 1.39. The impeller tip diameter was 0.516 m, its tip width 0.021 m and the impeller blade exit angle was 30 degrees from radial.
Assuming a linear relationship, the experimental data indicates a pressure ratio decrease of 0.77 percent, an efficiency loss of 0.31 points, an input head reduction of about 0.25 percent and an output head reduction of about 0.65 percent for each percent increase in clearance ratio. However, the data seems to indicate a non-linear effect showing stronger performance sensitivity at smaller clearances.
The test data are compared against a clearance loss model. Improved performance prediction is obtained by including the effect of clearance on impeller work input.
Gas Turbine Application Over Thirty Years in a Middle East Oil Production Facility
Authors: Norris Patrick J. , Cunningham John 
Published: March 2015

Kuwait Oil Company (KOC) has installed and operated gas turbines since 1957. There are currently 79 Gas Turbines ranging in size from 700 to 33,000 H.P. of various types, from industrial to aero-derivative.
Gas turbines provide more than half a million in horsepower, which is more than 80% of the power, for machinery and power generation at KOC.
This paper covers the introduction and the rappid growth of gas turbine power at KOC. Operational sites at KOC are subject to severe heat, dust and humidity. The experience in the operation and maintenance in the early years of the gas turbines at KOC are described.
Gas turbines have played a major role in the success of the Company.
Development of Ceramic Turbine Rotors
Authors: Katayama K. , Sasaki M. , Itoh T. 
Published: March 2015

A ceramic gas turbine engine is one of the most promising candidates for future automotive engines. Among the different ceramic components required to build such an engine, the turbine rotor is thought to be the most difficult to fabricate with ceramics. This is because the rotor has a very complex shape and is subjected to high stress.
This paper describes reliability evaluations of ceramic radial turbine rotors for a gas turbine engine and for a turbocharger. Each rotor was analyzed using a probabilistic approach. This included the use of finite element analysis, Weibull’s distribution function for brittle materials and lifetime predictions based on slow crack growth. The influence of blade thickness on foreign particle damage to a ceramic rotor is also discussed.
The results of these evaluations led to the design and development of a highly reliable turbocharger rotor, which has been used since October 1985 in Nissan passenger cars sold in the domestic market.
Increasing the Capacity Factors of Base Load Generating Facilities by Storage of Electrical Energy in Aquifers as Compressed Air
Authors: Longardner Robert L. , Visnesky Anthony , Strother J. R. 
Published: March 2015

This paper sets out the advantages of using “off-the-shelf” equipment to produce an effective Compressed Air Energy System (CAES) and to develop the storage parameters of those geological entrapments that can be pressurized with air for the generation of electrical energy on demand.
The long lead time and the developmental cost needed to perfect turbo-machinery for aquifer storage has been a deterrant on the utilities in their desire to implement air storage in aquifers. Off-the-shelf hardware and predesigned turbo-machinery specified herein is readily adaptable to aquifer storage parameters and can be manufactured without the expense and uncertainty related to developmental hardware. Hence, normal equipment manufacturer’s assurances and guarantees are available for these applications.
When compared to the alternative storage opportunities such as; pumped hydro, battery storage and superconducting magnetic storage, the cost of compressed air storage in aquifers is a fraction of the first cost of these alternatives and as good or better in operating costs.
How to Achieve Strain Tolerant Thermal Barrier Coatings (TBC’s) by Means of Varying Spray Parameters
Authors: Johner G. , Wilms V. , Schweitzer K. K. 
Published: March 2015

Small gas turbine engines, especially if they are used as automotive propulsion systems, are often compared to diesel engines with regard to their specific fuel consumption. Aside from high gas temperatures and the use of very efficient heat exchangers, there has to be a form of thermal insulation of the turbine casing which can be achieved by means of a thick Thermal Barrier Coating (TBC).
Theoretical considerations about the necessary morphology are made on the calculated stress situation within the coating. It will be described, how the TBC morphology can be influenced as desired, by means of a specific selection of spray parameters. In addition, the correlation between spray parameters and the phase distribution, as obtained from neutron diffraction analyses, will be reported.
The compatibility between theory and practice will be proven by means of a turbine case dummy with an inner TBC with a thickness of 5 mm which was tested very realistically in a specially designed flame rig. Microsections of this coating are used to confirm the theoretical considerations of the necessary morphology.
Total Corrosion Control for Industrial Gas Turbines: Airborne Contaminants and Their Impact on Air/Fuel/Water Management
Authors: Hsu L. L. 
Published: March 2015

Turbine longevity in the field is determined by the extent of its operation within design limits under mechanical and thermal loads as well as the environmental effects that undermine material properties on component surfaces. It is standard practice for the original equipment manufacturer (OEM) to specify maximum concentrations of harmful contaminants in the fuel for corrosion control. Some manufacturers have deployed on-line, in-service monitoring systems designed to incorporate data, such as temperature, speeds and start-stop cycles, into a functional, quasi-empirical equation, with an environmental factor, to continuously assess the condition of the turbine package for maintenance and overhaul purposes. This environmental factor simply categorizes fuel types in some generic correlation of fuel with hot section degradation.
This paper discusses the concept of air, fuel and water management, an approach that has evolved at the author’s Company as a focused and cost-effective means of assessing the total turbomachinery environment. The ultimate objective is to employ the methodology described above for hot section corrosion life prediction and optimized maintenance planning with minimal capitalization and operating costs for maximum economic payback.
The fundamental principle of this approach is represented schematically in Fig. 1 and discussed in more detail in Ref. 1. For total corrosion control, the engine environment is the sum of all contaminants present in the air, fuel and water (or steam). Tradeoffs in fluid quality can be tolerated provided the combined total concentration of a critical contaminant does not exceed the maximum allowable limits. Instead of separate restrictions on air, fuel and water quality, combined limits on total concentrations should be defined which then allows each fluid to vary in quality, thus providing greater flexibility for accommodating customer requirements or site specific conditions.
Development of a 3D Navier Stokes Solver for Application to all Types of Turbomachinery
Authors: Dawes W. N. 
Published: March 2015

This paper describes the current stage of development of a code aimed at solving the 3D Navier-Stokes equations in any type of turbomachinery geometry. The basic algorithm time marches the fully 3D unsteady equations of motion expressed in finite volume form with a two step explicit / one step implicit method. Full multigrid acceleration is used to reduce solution time and maintain code performance on fine meshes. Turbulence modelling is via mixing-length closure and the widely used Baldwin-Lomax model.
The generality and robustness of the code is demonstrated by application to five different test cases, three axial and two radial configurations. Also included is a grid independence study which demonstrates near grid independent solutions for transonic compressor cascade flow (albeit with the actual result subject to transition modelling constraints).
For two of the axial cases (transonic compressor in cascade, secondary flow in a high speed compressor) and one radial case (Eckardt high speed impellor) sufficient mesh is employed for the predictions to be essentially quantitative. The other two cases (radial inflow turbine with clearance and compressor stator with hub clearance) are really simulations rather than predictions, but are included as the flows are novel and provide much physical insight.
Effects of CT‐based attenuation correction of rat microSPECT images on relative myocardial perfusion and quantitative tracer uptake
Authors: Strydhorst Jared H. , Ruddy Terrence D. , Wells R. Glenn 
Published: March 2015

Purpose:Our goal in this work was to investigate the impact of CT‐based attenuation correction on measurements of rat myocardial perfusion with 99mTc and 201Tl single photon emission computed tomography (SPECT).Methods:Eight male Sprague‐Dawley rats were injected with 99mTc‐tetrofosmin and scanned in a small animal pinhole SPECT/CT scanner. Scans were repeated weekly over a period of 5 weeks. Eight additional rats were injected with 201Tl and also scanned following a similar protocol. The images were reconstructed with and without attenuation correction, and the relative perfusion was analyzed with the commercial cardiac analysis software. The absolute uptake of 99mTc in the heart was also quantified with and without attenuation correction.Results:For 99mTc imaging, relative segmental perfusion changed by up to +2.1%/−1.8% as a result of attenuation correction. Relative changes of +3.6%/−1.0% were observed for the 201Tl images. Interscan and inter‐rat reproducibilities of relative segmental perfusion were 2.7% and 3.9%, respectively, for the uncorrected 99mTc scans, and 3.6% and 4.3%, respectively, for the 201Tl scans, and were not significantly affected by attenuation correction for either tracer. Attenuation correction also significantly increased the measured absolute uptake of tetrofosmin and significantly altered the relationship between the rat weight and tracer uptake.Conclusions:Our results show that attenuation correction has a small but statistically significant impact on the relative perfusion measurements in some segments of the heart and does not adversely affect reproducibility. Attenuation correction had a small but statistically significant impact on measured absolute tracer uptake.
Over/Undervoltage and Undervoltage Shift of Hybrid Islanding Detection Method of Distributed Generation
Authors: Yingram Manop , Premrudeepreechacharn Suttichai 
Published: March 2015

The mainly used local islanding detection methods may be classified as active and passive methods. Passive methods do not perturb the system but they have larger nondetection zones, whereas active methods have smaller nondetection zones but they perturb the system. In this paper, a new hybrid method is proposed to solve this problem. An over/undervoltage (passive method) has been used to initiate an undervoltage shift (active method), which changes the undervoltage shift of inverter, when the passive method cannot have a clear discrimination between islanding and other events in the system. Simulation results on MATLAB/SIMULINK show that over/undervoltage and undervoltage shifts of hybrid islanding detection method are very effective because they can determine anti‐islanding condition very fast. ΔP/P > 38.41% could determine anti‐islanding condition within 0.04 s; ΔP/P < −24.39% could determine anti‐islanding condition within 0.04 s; −24.39% ≤ ΔP/P ≤ 38.41% could determine anti‐islanding condition within 0.08 s. This method perturbed the system, only in the case of −24.39% ≤ ΔP/P ≤ 38.41% at which the control system of inverter injected a signal of undervoltage shift as necessary to check if the occurrence condition was an islanding condition or not.
Monotone and Concave Positive Solutions to Three-Point Boundary Value Problems of Higher-Order Fractional Differential Equations
Authors: Zhong Wenyong , Wang Lanfang 
Published: March 2015

We study the three-point boundary value problem of higher-order fractional differential equations of the formDc0+ρut+ft, ut=0,0<t<1,2⩽n-1<ρ<n,u′(0)=u′′(0)=⋯=un-1(0)=0,u(1)+pu′(1)=qu′(ξ), where cD0+ρis the Caputo fractional derivative of orderρ, and the functionf:[0,1]×[0,∞)↦[0,+∞)is continuously differentiable. Here,0⩽q⩽p,0<ξ<1,2⩽n-1<ρ<n. By virtue of some fixed point theorems, some sufficient criteria for the existence and multiplicity results of positive solutions are established and the obtained results also guarantee that the positive solutions discussed are monotone and concave.
PS-Modules over Ore Extensions and Skew Generalized Power Series Rings
Authors: Salem Refaat M. , Farahat Mohamed A. , Abd-Elmalk Hanan 
Published: March 2015

A rightR-moduleMRis called a PS-module if its socle,SocMR, is projective. We investigate PS-modules over Ore extension and skew generalized power series extension. LetRbe an associative ring with identity,MRa unitary rightR-module,O=Rx;α,δOre extension,MxOa rightO-module,S,≤a strictly ordered additive monoid,ω:S→EndRa monoid homomorphism,A=RS,≤,ωthe skew generalized power series ring, andBA=MS,≤RS,≤, ωthe skew generalized power series module. Then, under some certain conditions, we prove the following: (1) IfMRis a right PS-module, thenMxOis a right PS-module. (2) IfMRis a right PS-module, thenBAis a right PS-module.
Individual performance in socio-cognitive tasks predicts social behaviour in carrion crows
Authors: Wascher Claudia A.F. 
Published: March 2015

The social intelligence hypothesis links the evolution of exceptional cognitive skills to the requirements of complex social systems. Empirical evidence of a connection between cognitive skills and social behaviour on an individual level is lacking. I investigated how cognitive performance in carrion crows correlates with social behaviour. Social behaviour was observed and crows were tested in four tasks previously published elsewhere: qualitative exchange, quantity preference, inequity aversion, heterospecific recognition. I describe correlations between an individuals’ involvement in affiliative and aggressive encounters and performance during these different cognitive tasks. For example, individuals performing better in the qualitative exchange task received more approaches and affiliative interactions. There was a correlation between birds choosing higher quantities during testing and their propensity to initiate aggressive and affiliative interactions with others. Overall these results show a link between social behaviour and individual performance in cognitive tasks.
Quadrature Methods for the Calculation of Subgrid Microphysics Moments
Authors: Chowdhary K. , Salloum M. , Debusschere B. , Larson V. E. 
Published: March 2015

AbstractMany cloud microphysical processes occur on a much smaller scale than a typical numerical grid box can resolve. In such cases, a probability density function (PDF) can act as a proxy for subgrid variability in these microphysical processes. This method is known as the assumed PDF method. By placing a density on the microphysical fields, one can use samples from this density to estimate microphysics averages. In the assumed PDF method, the calculation of such microphysical averages has primarily been done using classical Monte Carlo methods and Latin hypercube sampling. Although these techniques are fairly easy to implement and ubiquitous in the literature, they suffer from slow convergence rates as a function of the number of samples. This paper proposes using deterministic quadrature methods instead of traditional random sampling approaches to compute the microphysics statistical moments for the assumed PDF method. For smooth functions, the quadrature-based methods can achieve much greater accuracy with fewer samples by choosing tailored quadrature points and weights instead of random samples. Moreover, these techniques are fairly easy to implement and conceptually similar to Monte Carlo–type methods. As a prototypical microphysical formula, Khairoutdinov and Kogan’s autoconversion and accretion formulas are used to illustrate the benefit of using quadrature instead of Monte Carlo or Latin hypercube sampling.
A randomized double-blind placebo-controlled study adding high dose vitamin D to analgesic regimens in patients with musculoskeletal pain
Authors: Gendelman O , Itzhaki D , Makarov S , Bennun M , Amital H 
Published: March 2015

Background The current mode of therapy for many patients with musculoskeletal pain is unsatisfactory. Purpose We aimed to assess the impact of adding 4000 IU of vitamin D on pain and serological parameters in patients with musculoskeletal pain. Materials and methods This was a randomized, double-blinded and placebo-controlled study assessing the effect of 4000 IU of orally given vitamin D3 (cholecalciferol) (four gel capsules of 1000 IU, (SupHerb, Israel) vs. placebo on different parameters of pain. Eighty patients were enrolled and therapy was given for 3 months. Parameters were scored at three time points: prior to intervention, at week 6 and week 12. Visual analogue scale (VAS) scores of pain perception were recorded following 6 and 12 weeks. We also measured serum levels of leukotriene B4 (LTB4), interleukin 6 (IL-6), tumor necrosis factor alpha (TNFα) and prostaglandin E2 (PGE2) by ELISA. Results The group receiving vitamin D achieved a statistically significant larger decline of their VAS measurement throughout the study compared with the placebo group. The need for analgesic ‘rescue therapy’ was significantly lower among the vitamin D-treated group. TNFα levels decreased by 54.3% in the group treated with vitamin D and increased by 16.1% in the placebo group. PGE2 decreased by39.2% in the group treated with vitamin D and increased by 16% in the placebo group. LTB4 levels decreased in both groups by 24% ( p < 0.05). Conclusion Adding 4000 IU of vitamin D for patients with musculoskeletal pain may lead to a faster decline of consecutive VAS scores and to a decrease in the levels of inflammatory and pain-related cytokines.