Relevant bibliographies by topics / Stall and Surge

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers
  6. Reports

Academic literature on the topic 'Stall and Surge'

Author: Grafiati
Published: 6 September 2023

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Journal articles on the topic "Stall and Surge"

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Akhlaghi, Mohammad, Yahya Azizi, and Nourouz Mohammad Nouri. "Estimations of Compressor Stall and Surge Using Passage Stall Behaviors." Machines 10, no. 8 (August 18, 2022): 706. http://dx.doi.org/10.3390/machines10080706.

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The predictions of the onset of rotating stall and surge are very important in the preliminary design stage of a compressor. Rotating stall and surge are complex instabilities that cause efficiency loss and reduced pressure rise, and, therefore, compressor designers attempt to avoid them in the design stage. There are many criteria for predicting stability limits, including empirical, theoretical, and numerical investigations in the literature. However, these investigations have important limitations. The present study establishes a new method in which the stall and post-stall behavior of a compressor is estimated by an equivalent reconstructed compressor using special combinations of single-passage flow behavior in different mass flow rates. The combinations are generated such that pre-stall, in-stall, and surge flow regimes and between one and eight stall cells are reproduced in the full-annulus compressor. The method requires the least computational requirements and is time efficient. The results indicate that secondary flow total energy and spectral entropy are indeed correlated with compressor operating conditions. The predictions of the onset of stall and surge for the investigated compressor show good agreement with the experimental data.
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Chattopadhyay, N. C., H. E. M. Zahidul Islam Eunus, Md Imtiaz Ikram, and Roohany Mahmud. "Compressor Instability: Stall, Surge and their Control." Applied Mechanics and Materials 390 (August 2013): 408–13. http://dx.doi.org/10.4028/www.scientific.net/amm.390.408.

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Every compressor has a stall line. In the vicinity of the stall line, the flow field is inherently unsteady due to the interactions between adjacent rows of blades, formation of small stall cells, flow separation and the viscous effects including shock-boundary layer interactions. These factors may aggravate to a state of local breakdown of flow or a total breakdown of flow or with a disastrous flow reversal. This paper starts with an overview on the previous researches about compressor stall and surge. Subsequently, it describes the effects of these instabilities in overall engine performance and design with/ without any control. The main objectives of this paper are to review the phenomenon of instability and methodology to suppress the rotating stall and surge by enlarging the stable operating range of compressor with the application of various control systems. This paper surveys research developments in this field and also tries to find an improved solution to increase the engine performance by applying various surge control strategies. Finally, the paper focuses on some recommendations towards a better design of compressor especially for aircraft power plant.
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Wilson, A. G., and C. Freeman. "Stall Inception and Development in an Axial Flow Aeroengine." Journal of Turbomachinery 116, no. 2 (April 1, 1994): 216–25. http://dx.doi.org/10.1115/1.2928356.

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This paper describes the phenomenon of stall and surge in an axial flow aeroengine using fast response static pressure measurements from the compressor of a Rolls-Royce VIPER engine. It details the growth of flow instability at various speeds, from a small zone of stalled fluid involving only a few blades into the violent surge motion of the entire machine. Various observations from earlier theoretical and compressor rig results are confirmed by these new engine measurements. The main findings are as follows: (1) The point of stall inception moves rearward as engine speed increases, and is shown to be simply related to the axial matching of the compressor. (2) The final unstable operation of the machine can be divided into rotating stall at low speed and surge or multiple surge at high speed. (3) The inception process is independent of whether the final unstable operation is rotating stall or multiple surge. (4) Stall/surge always starts as a circumferentially small flow disturbance, rotating around the annulus at some fraction of rotor speed.
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Hickman, Adam R., and Scott C. Morris. "Observations of the Growth and Decay of Stall Cells during Stall and Surge in an Axial Compressor." International Journal of Rotating Machinery 2017 (2017): 1–11. http://dx.doi.org/10.1155/2017/6329382.

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This research investigated unsteady events such as stall inception, stall-cell development, and surge. Stall is characterized by a decrease in overall pressure rise and nonaxisymmetric throughflow. Compressor stall can lead to surge which is characterized by quasi-axisymmetric fluctuations in mass flow and pressure. Unsteady measurements of the flow field around the compressor rotor are examined. During the stall inception process, initial disturbances were found within the rotor passage near the tip region. As the stall cell develops, blade lift and pressure ratio decrease within the stall cell and increase ahead of the stall cell. The stall inception event, stall-cell development, and stall recovery event were found to be nearly identical for stable rotating stall and surge cases. As the stall cell grows, the leading edge of the cell will rotate at a higher rate than the trailing edge in the rotor frame. The opposite occurs during stall recovery. The trailing edge of the stall cell will rotate at the approximate speed as the fully developed stall cell, while the leading edge decreases in rotational speed in the rotor frame.
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Day, I. J. "Active Suppression of Rotating Stall and Surge in Axial Compressors." Journal of Turbomachinery 115, no. 1 (January 1, 1993): 40–47. http://dx.doi.org/10.1115/1.2929216.

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This paper reports on an experimental program in which active control was successfully applied to both rotating stall and surge in a multistage compressor. Two distinctly different methods were used to delay the onset of rotating stall in a four-stage compressor using fast-acting air injection valves. The amount of air injected was small compared to the machine mass flow, the maximum being less than 1.0 percent. In some compressor configurations modal perturbations were observed prior to stall. By using the air injection valves to damp out these perturbations, an improvement of about 4.0 percent in stall margin was achieved. The second method of stall suppression was to remove emerging stall cells by injecting air in their immediate vicinity. Doing this repeatedly delayed the onset of stall, giving a stall margin improvement of about 6.0 percent. Further studies were conducted using a large plenum downstream of the compressor to induce the system to surge rather than stall. The resulting surge cycles were all found to be initiated by rotating stall and therefore the stall suppression systems mentioned above could also be used to suppress surge. In addition, it was possible to arrest the cyclical pulsing of a compressor already in surge.
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Mizuki, S., and Y. Oosawa. "Unsteady Flow Within Centrifugal Compressor Channels Under Rotating Stall and Surge." Journal of Turbomachinery 114, no. 2 (April 1, 1992): 312–20. http://dx.doi.org/10.1115/1.2929145.

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Unsteady flow patterns throughout a centrifugal compressor system during the rotating stall and the surge were measured experimentally. Various kinds of unsteady behavior of the flow appeared both continuously and suddenly as the flow rate decreased. The part-span stall, the full-span stall, the mild and deep stalls, and the deep surge appeared clearly. The fluctuations caused by the full-span stall were seen even during surge and affected the flow within the scroll through the vaneless diffuser. The experimental results were compared with those computed by the lumped parameter theory. Good agreements between them were obtained when appropriate values were selected for the lumped parameters.
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Coller, B. D. "Hopf-Hopf Interactions of Surge and Rotating Stall." Journal of Computational and Nonlinear Dynamics 1, no. 4 (June 6, 2006): 320–27. http://dx.doi.org/10.1115/1.2338324.

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In this paper, we examine the interaction of two instabilities that occur in axial compressors using the Hopf-Hopf normal form. As a result, we illuminate some gaps in understanding the dynamics of standard compressor models. We find a possible dynamic mechanism, which explains certain “curious” behavior observed in experiments, and are able to predict and explain failure mechanisms in previously proposed control strategies.
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Hönen, H. "Axial Compressor Stall and Surge Prediction by Measurements." International Journal of Rotating Machinery 5, no. 2 (1999): 77–87. http://dx.doi.org/10.1155/s1023621x9900007x.

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The paper deals with experimental investigations and analyses of unsteady pressure distributions in different axial compressors. Based on measurements in a single stage research compressor the influence of increasing aerodynamic load onto the pressure and velocity fluctuations is demonstrated. Detailed measurements in a 14-stage and a 17-stage gas turbine compressor are reported. For both compressors parameters could be found which are clearly influenced by the aerodynamic load.For the 14-stage compressor the principles for the monitoring of aerodynamic load and stall are reported. Results derived from a monitoring system for multi stage compressors based on these principles are demonstrated. For the 17-stage compressor the data enhancement of the measuring signals is shown. The parameters derived from these results provide a good base for the development of another prediction method for the compressor stability limit. In order design an on-line system the classification of the operating and load conditions is provided by a neural net. The training results of the net show a good agreement with different experiments.
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Eveker, K. M., D. L. Gysling, C. N. Nett, and O. P. Sharma. "Integrated Control of Rotating Stall and Surge in High-Speed Multistage Compression Systems." Journal of Turbomachinery 120, no. 3 (July 1, 1998): 440–45. http://dx.doi.org/10.1115/1.2841735.

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Aeroengines operate in regimes for which both rotating stall and surge impose low-flow operability limits. Thus, active control strategies designed to enhance operability of aeroengines must address both rotating stall and surge as well as their interaction. In this paper, a previously developed nonlinear control strategy that achieves simultaneous active control of rotating stall and surge is applied to a high-speed three-stage axial flow compression system with operating parameters representative of modern aeroengines. The controller is experimentally validated for two compressor builds and its robustness to radial distortion assessed. For actuation, the control strategy utilizes an annulus-averaged bleed valve with bandwidth on the order of the rotor frequency. For sensing, measurements of the circumferential asymmetry and annulus-averaged unsteadiness of the flow through the compressor are used. Experimental validation of simultaneous control of rotating stall and surge in a high-speed environment with minimal sensing and actuation requirements is viewed as another important step toward applying active control to enhance operability of compression systems in modern aeroengines.
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Langston, Lee S. "Out Through the Intake." Mechanical Engineering 139, no. 04 (April 1, 2017): 36–41. http://dx.doi.org/10.1115/1.2017-apr-2.

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This article elaborates various challenges presented by stall and surge to the gas turbine research community and jet engine designers. The article also presents several examples of stall and surge faced by the pilots. Stall and surge emerge from basic physics: the behavior of the boundary layer on the compressor blades and stators; however, current technology has no means to completely eliminate it. Engine control systems, such as the Full Authority Digital Electric Control (FADEC), are programmed to keep the operating point of the compressor well away from the surge line. Researchers have been studying stall and surge for decades, looking for ways to predict and combat the phenomena. Meanwhile, there has been some success in using FADEC to either prevent a stall and surge or to limit the number of repetitions. FADEC can also step in during flights in heavy rain or hailstorms. In those conditions, extra fuel is needed to process and evaporate the water being swallowed by the engine. The electronic control system can sense the mismatch between the power setting and the fuel flow and take action to prevent possible engine instability.
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Dissertations / Theses on the topic "Stall and Surge"

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Dahl, Ståle. "Stall og surge i tørr- og våtgasskompressorer." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13581.

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I denne oppgaven beskrives de aerodynamiske ustabilitetene kalt stall og surge. Oppgaven består hovedsakelig av tre deler. I første del gjennomgås noe fundamental teori på aerodynamikken i sentrifugalkompressorer, før funn gjort i tidligere eksperiment på ustabilitetene presenteres. I litteraturen er det bevist at stall og surge forekommer i flere former og med flere karakteristikker. Med tørrgass som arbeidsmedium kan disse karakteristikkene identifiseres ved hjelp av trykksensorer. Karakteristikkene har vist seg å være svært avhengig av kompressorens geometri.Visualiseringsmetoder som tidligere har vist seg å fungere godt på turbomaskineri gjennomgåes og det diskuteres rundt applikasjonen med våtgass. Laser Doppler Velocimetry ble prøvet ut, men det viste seg at denne måleteknikken er for ømfintelig til at den kan brukes med våtgasstrømning. En spesialløsning med pitot-prober er en mulig metode for fremtidige visualiseringsforsøk. Til slutt presenteres et eget eksperiment hvor en industriell kompressor utsettes for tørr- og våtgass. Formålet med eksperimentet var å dokumentere ustabiliteter, med hovedfokus på frekvens og størrelse. Karakteristikken til tørrgassustabilitetene ble kartlagt ved hjelp av dynamiske trykksensorer plassert i diffusoren. Resultatene ble sammenligning med resultat fra tidliger eksperiment funnet i litteraturen. Funnene stemte godt med tidligere forsøk gjort med tørrgass. Karakteristikken til våtgass lot seg ikke identifisere like lett. De dynamiske sensorene plukket ikke opp noen stallfrekvenser eller størrelser, selv om ustabiliteter var observert visuelt ved testkjøring. Det ble heller ikke funnet noe bevis på at maskinen gikk i surge.
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Zoppellari, Serena. "Analytical modeling of rotating stall and surge." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9385.

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The life and performance of axial compressors are limited by the occurrence of instabilities such as rotating stall and surge. Indeed, in the course of the design phase a great effort is usually devoted to guarantee an adequate safety margin from the region of instabilities’ onset. On the other hand, during its operating life, an axial compressor can be subjected to several conditions that can lead to the inception of stall and its dynamics. A few examples of possible stall causes, for the specific case of an axial compressor embedded in an aircraft engine, are inlet flow distortion, engine wear or shaft failure. The shaft failure case can be seen as an exception, as a matter of fact, after this event surge is a desirable outcome since it can potentially decelerate the over-speeding turbine by reducing the mass flow passing through the engine. The possible occurrence of surge and stall should be predicted and controlled in order to avoid severe damage to the compressor and its surroundings. A lot of research has been carried out in the past years to understand the inception and development of stall to achieve the capability for predicting and controlling this severe phenomenon. Nonetheless, this problem is still not well understood and unpredictable outcomes are still a great concern for many axial compressor’s applications. The lack of knowledge in what concerns inception and development of stall and surge reflects in a lack of tools to investigate, predict and control these unstable phenomena. The tools available to study stall and surge events are still not highly reliable or they are very time consuming as 3D CFD simulations. The doctoral research described herein, aimed at the investigation of the rotating stall phenomenon and the derivation of the compressor characteristic during this unstable condition. Following a detailed analysis of the tools and techniques available in the public domain and the identification of their limitations, the development of a FORTRAN through-flow tool was the methodology chosen. A distinctive feature of the developed tool is the independency from steady state characteristics which is a limitation for the majority of the available tools and its computational efficiency. Particular attention was paid to capture various viscous flow features occuring during rotating stall through the selection and implementation of appropriate semiempirical models and correlations. Different models for pressure loss, stall inceptions and stall cell growth/ speed were implemented and verified along with different triggering techniques to achieve a very close to reality simulation of the overall phenomenon, from stall inception to full development. lel compressors’ technique that allows the correct modeling of asymmetric phenomena. The methodology implemented has proved promising since several simulations were run to test the tool adopting different compressor geometries. Verifications were performed in terms of overall compressor performance, with simulations in all the three possible operating regions (forward, stall and reverse flow), in order to verify the tool’s capability in predicting the compressor characteristics. In terms of flow field, the ability to capture the right circumferential trends of the flow properties was checked through a comparison against 3D CFD simulations. The results obtained have demonstrated the ability of the tool to capture the real behavior of the flow across a compressor subjected to several different unstable conditions that can lead to the onset of phenomena such as rotating stall, classic and deep surge. Indeed, the tool has shown ability to tackle steady and transient phenomena characterized by asymmetric and axis-symmetric flow fields. This document provides several examples of investigations emphasizing the flexibility of the developed methodology. As a matter of fact, within this dissertation, many examples can be found on the effect of the plenum size, on the different transient phenomena experienced by the compressor when subjected to multiple regions of inlet distortion instead of a localized region of low or high flow, on the differences between temporary and stationary inlet disturbances and so on. This document describes in detail the methodology, the implementation of the tool, its verification and possible applications and the recommended future work. The work was funded by Rolls-Royce plc and was carried out within the Rolls-Royce UTC in Performance Engineering at Cranfield as three-year Ph.D. program that started in October 2010.
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Wilson, Alexander George. "Stall and surge in axial flow compressors." Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/10432.

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The objective of the work described in this thesis is twofold; to elucidate the nature of stall and surge in an axial flow aeroengine compressor, and to improve on current computational stall modelling techniques. Particular attention is paid to the initial stages of the stall/surge transient, and to the possibility of using active control techniques to prevent or delay the onset of stall/surge. A detailed analysis is presented of measurements of the stalling behaviour of a Rolls- Royce VIPER jet engine, showing a wide variety of stall inception and post-stall behaviour. Stall transients are traced from disturbances through to stable rotating stall or axisymmetic surge. The stall inception pattern at nearly all speeds is shown to conform to the short circumferential length scale pattern described by Day [1993a]. A multiple compressors in parallel stall model is developed using conventional stall modelling techniques, but extended to include the effects of the jet engine environment The model is shown to give a good representation of the overall stalling behaviour of the engine, although the details of the stall inception period are not accurately predicted. A system identification technique is applied to the results of the model in order to develop a method of active control of stall/surge. A new stall model is introduced and developed, based on a time-accurate three dimensional (but pitchwise averaged) solution of the viscous flow equations, with bladerow performance represented by body forces. The flow in the annulus boundary layers is calculated directly, and hence this new method is sufficiently complex to model the initial localised disturbances that lead to stall/surge. At the same time the computational power required is compatible with application to long multistage compressors.
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Protz, Jonathan M. (Jonathan Michael). "Nonlinear active control of rotating stall and surge." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10515.

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Niazi, Saeid. "Numerical simulation of rotating stall and surge alleviation in axial compressors." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/12011.

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Cousins, William T. "The Dynamics of Stall and Surge Behavior in Axial-Centrifugal Compressors." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29794.

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The phenomena of stall and surge in axial-centrifugal compressors is investigated through high-response measurements of both the pressure field and the flowfield throughout the surge cycle. A unique high-response forward-facing and aft-facing probe provides flow information. Several axial-centrifugal compressors are examined, both in compressor rigs and engines. Extensive discussion is presented on the differences in axial and centrifugal rotors and their effect on the system response characteristics. The loading parameters of both are examined and data is presented that shows the increased tolerance of the centrifugal stage to instability. The dynamics of the compressor blade response are shown to be related to the transport time of a fluid particle moving through a blade passage. The data presented provides new insight into the dynamic interactions that occur prior to and during stall and surge. In addition, the inception of rotating stall and the inception of surge are shown to be the same phenomena . An analytical dynamic model (DYNTECC) is applied to one of the compression systems and the results are compared to data. The results show that the model can capture the global effects of rotating stall and surge. The data presented, along with the analytical results, provide useful information for the design of active and passive stall control systems.
Ph. D.
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Fahim, Ahmed 1974. "Experimental evaluation of asymmetric bleed actuation for rotating stall and surge control." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50004.

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Liao, Shengfang 1968. "Robust control of a surge and rotating stall in an axial compressor." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8823.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.
Includes bibliographical references (p. 123-127).
This thesis presents an investigation of the stability of axial compression systems when external disturbances are introduced. Aerodynamic stability is considered from a nonlinear perspective. From this perspective, the goal is to enhance the ability of compressor systems to remain stable in the face of external disturbances. Experiments were conducted on a low-speed three-stage axial compressor. Instead of achieving extension of linearly stable operating range, this research is focused on the followings: (1). The operability of the compressor, the ability of maintaining the stable operations of the compressor near the operating points in the presence of the external disturbances, was considered. The concept of domain of attraction was adopted to characterize the operability or the disturbance rejection of the compressor. An experimental method was developed to generate disturbances and measure the approximate domain of attraction in terms of the zeroth and first mode flow perturbations. (2). Improvement of the approximate domain of attraction was demonstrated by active control. Both the constant gain control which has been used in many range extension tests and the sliding mode control which is model based, doubles the maximum allowable amplitudes of the zeroth and first mode flow perturbations. (3). The downstream bleed was chosen as the actuation, which is easy to implement and more practical. The number of the bleed valves was chosen to be four to compromise the goal of reducing the number of actuators and the requirement of achieving a satisfactory control effectiveness. (4). The domain of attraction was also examined under inlet distortions. The nonlinear simulation showed that the disturbance rejection of the compressor with background distorted flow was improved by active control.
by Shengfang Liao.
Ph.D.
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Osborne, Denver Jackson Jr. "Time-resolved measurements of a transonic compressor during surge and rotating stall." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07102009-040321/.

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Badmus, Olanrewju O. "Nonlinear dynamic analysis and control of surge and rotating stall in axial compression systems." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/11296.

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Books on the topic "Stall and Surge"

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Compressor surge and stall. Norwich, Vt: Concepts ETI, 1993.

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Gravdahl, Jan Tommy, and Olav Egeland. Compressor Surge and Rotating Stall. London: Springer London, 1999. http://dx.doi.org/10.1007/978-1-4471-0827-6.

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1931-, Egeland Olav, ed. Compressor surge and rotating stall: Modelling and control. London: Springer, 1999.

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Gravdahl, Jan Tommy. Compressor Surge and Rotating Stall: Modeling and Control. London: Springer London, 1999.

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L, Mattern Duane, Le Dzu K, and United States. National Aeronautics and Space Administration., eds. Comparisons of rig and engine dynamic events in the compressor of an axi-centrifugal turboshaft engine. [Washington, D.C: National Aeronautics and Space Administration, 1996.

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L, Mattern Duane, Le Dzu K, and United States. National Aeronautics and Space Administration., eds. Comparisons of rig and engine dynamic events in the compressor of an axi-centrifugal turboshaft engine. [Washington, D.C: National Aeronautics and Space Administration, 1996.

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Hompson, Davi Det. "S ure, sure. Davi Det Hompson, I know about you. You used to Fluxus stuff and artist's books. I've read some of your pamphlets. Are you still making throw-away art?". [Richmond, Virginia]: Davi Det Hompson, 1991.

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Rajaeesani, Ali. Robust output feedback stabilization, compressors surge and stall example. 2003, 2003.

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Far Side Older, Sure--But You Still Have Great Legs: Happy Birthday Card. Andrews McMeel Publishing, 2001.

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Brogaard, Berit. Synesthetic Binding and the Reactivation Model of Memory. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780199688289.003.0007.

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Despite the recent surge in research on, and interest in, synesthesia, the mechanism underlying this condition is still unknown. Feedforward mechanisms involving overlapping receptive fields of sensory neurons as well as feedback mechanisms involving a lack of signal disinhibition have been proposed. Here I show that a broad range of studies of developmental synesthesia indicate that the mechanism underlying the phenomenon may in some cases involve the reinstatement of brain activity in sensory or cognitive streams in a way that is similar to what happens during memory retrieval of semantically associated items. In the chapter’s final sections I look at the relevance of synesthesia research, given the memory model, to our understanding of multisensory perception and common mapping patterns.
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Book chapters on the topic "Stall and Surge"

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Gravdahl, Jan Tommy, and Olav Egeland. "Passivity Based Surge Control." In Compressor Surge and Rotating Stall, 109–19. London: Springer London, 1999. http://dx.doi.org/10.1007/978-1-4471-0827-6_3.

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Gravdahl, Jan Tommy, and Olav Egeland. "Compressor Surge and Stall: An Introduction." In Compressor Surge and Rotating Stall, 1–62. London: Springer London, 1999. http://dx.doi.org/10.1007/978-1-4471-0827-6_1.

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Gravdahl, Jan Tommy, and Olav Egeland. "Close Coupled Valve Control of Surge and Rotating Stall for the Moore-Greitzer Model." In Compressor Surge and Rotating Stall, 63–107. London: Springer London, 1999. http://dx.doi.org/10.1007/978-1-4471-0827-6_2.

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Gravdahl, Jan Tommy, and Olav Egeland. "A Moore-Greitzer Type Model for Axial Compressors with Non-Constant Speed." In Compressor Surge and Rotating Stall, 121–42. London: Springer London, 1999. http://dx.doi.org/10.1007/978-1-4471-0827-6_4.

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Gravdahl, Jan Tommy, and Olav Egeland. "Modelling and Control of Surge for a Centrifugal Compressor with Non-Constant Speed." In Compressor Surge and Rotating Stall, 143–76. London: Springer London, 1999. http://dx.doi.org/10.1007/978-1-4471-0827-6_5.

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Gravdahl, Jan Tommy, and Olav Egeland. "Concluding Remarks and Further Research." In Compressor Surge and Rotating Stall, 177–79. London: Springer London, 1999. http://dx.doi.org/10.1007/978-1-4471-0827-6_6.

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Soodani, Sara, SeyedVahid Hosseini, Mohammad Hakimi, and Mohammad Akhlaghi. "The Effect of Vane Number in Casing Treatment of an Axial-Flow Compressor." In Springer Proceedings in Energy, 341–50. Cham: Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-30960-1_32.

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AbstractImprovement of the operating range of compressors will help the power and energy plant to work more flexibly to integrate with other energy generation systems. The stall, rotating stall, and resulting surge are the most dominant limiting phenomenon in axial compressor operating envelop. Several active and passive methods have been employed to eliminate occurring of these phenomena and to extend compressors’ stable range. Among these, casing treatment is one of the most useful methods. This study aims to investigate the effect of the number of stationary blades on the performance and stall margin of an axial compressor through numerical simulation. Casing treatments in two different configurations of 33.3 and 53.5% of rotor blade tip exposure and with six different numbers of vanes, 30, 40, 60, 80, 90, and 120, are simulated with computational fluid dynamics in ANSYS software. The numerical simulation is validated with available experimental data. The results reveal that in a high rotor exposure configuration, the highest number of vanes provides the best performance for the compressor. However, in a low exposure configuration, the optimum number of the vanes, 90 for the 33.3% exposure, can be found with the proposed numerical procedure based on stall margin improvement.
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Azizia, M., and J. Brouwer. "Mitigation of Compressor Stall/Surge in a Hybrid Solid Oxide Fuel Cell-Gas Turbine System." In Proceedings of the 41st International Conference on Advanced Ceramics and Composites, 1–6. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2018. http://dx.doi.org/10.1002/9781119474746.ch1.

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Sari, Gholam-Reza, Ouassima Akhrif, and Lahcen Saydy. "Bifurcation Analysis and Active Control of Surge and Rotating Stall in Axial Flow Compressors via Passivity." In Informatics in Control, Automation and Robotics, 91–116. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-55011-4_5.

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Sundén, Jenny. "10. “I’m still not sure she’s a she”." In Talking Gender and Sexuality, 289–312. Amsterdam: John Benjamins Publishing Company, 2002. http://dx.doi.org/10.1075/pbns.94.12sun.

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Conference papers on the topic "Stall and Surge"

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Longley, John P. "Calculating Stall and Surge Transients." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27378.

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Many aspects of the aerodynamic operation and the mechanical integrity of an aeroengine are determined by the stall and surge transients of the compression system. A, physically based, blockage-mixing method and a novel blockage-transport equation are presented that can be used to estimate blade row operation at severe off-design conditions. The blockage-mixing method is proposed based on an analysis of the large separations that are present within a blade passage during reverse-flow (negative axial velocity) conditions. A time accurate computational simulation has been developed, based on the blockage-mixing method, which solves for the moderate to long lengthscale compressible unsteady flowfield within a compression system. The flow through each blade row is resolved in the axial, circumferential and radial directions. Calculated stall and surge events are compared with experimental data and the ability to calculate an aeroengine transient is demonstrated. The simulation is presented as a computational tool for estimating the aerodynamic loads during compression system instability events.
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ISHII, H., and Y. KASHIWABARA. "Surge and rotating stall in axial compressors." In 25th Joint Propulsion Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1989. http://dx.doi.org/10.2514/6.1989-2683.

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Day, I. J. "Stall, Surge and 75 Years of Research." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-44109.

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Work on rotating stall and its related disturbances has been in progress since the Second World War. During this period, certain ‘hot topics’ have come to the fore — mostly in response to pressing problems associated with new engine designs. This paper will take a semi-historical look at some of these fields of study (stall, surge, active control, rotating instabilities etc.) and will examine the ideas which underpin each topic. Good progress can be reported, but the paper will not be an unrestricted celebration of our successes because, after 75 years of research, we are still unable to predict the stalling behaviour of a new compressor or to contribute much to the design a more stall resistant machine. Looking forward from where we are today, it is clear that future developments will come from CFD in the form of better performance predictions, better flow modelling and improved interpretation of experimental results. It is also clear that future experimental work will be most effective when focussed on real compressors with real problems — such as stage matching, large tip clearances, eccentricity and service life degradation. Today’s topics of interest are mostly associated with compressible effects and so further research will require more high speed testing.
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Dhingra, Manuj, Yedidia Neumeier, J. V. R. Prasad, and Hyoun-Woo Shin. "Stall and Surge Precursors in Axial Compressors." In 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2003. http://dx.doi.org/10.2514/6.2003-4425.

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Halawa, Taher, Mohamed Alqaradawi, Osama Badr, and Mohamed S. Gadala. "Numerical Simulation of Stall Development Into Surge and Stall Control Using Air Injection in Centrifugal Compressors." In ASME 2014 Power Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/power2014-32053.

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This study presents a numerical simulation of the formation of rotating stall and the initiation of surge in order to study the connection between stall and surge in centrifugal compressors. Also, the current paper introduces an optimization of the air injection method as a way to increase the surge margin. Results showed that during stall, the compressor is exposed to velocity and pressure fluctuations varying with time, and these fluctuations are increased suddenly and causing surge initiation. The major part which is responsible for the sudden increase in fluctuations is the vaneless region because it was found that the problem starts at the impeller exit near the shroud surface and then transfers to the impeller inlet. Results also showed that during surge, forces on the impeller blades increase to nearly double of its initial value and then decrease again. By using air injection at the vaneless region with different injection angles, it was found that injection with angle of 30° has a good effect on preventing surge and minimizing the pressure fluctuations comparing to other injection angles results. Results showed finally that the surge margin can be increased by using the injection with angle of 30° and with injection mass flow rate of 1% of the design inlet mass flow rate and this causes the surge limit to shift from 4 kg/s to 3.9 kg/s.
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Sankar, L., J. Prasad, Y. Naumeier, W. Haddad, N. Markopoulos, A. Stein, S. Niazi, and A. Leonessa. "Recent progress in compressor stall and surge control." In 17th Applied Aerodynamics Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1999. http://dx.doi.org/10.2514/6.1999-3124.

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Harris, L. P., and H. A. Spang. "Compressor Modeling and Active Control of Stall/Surge." In 1991 American Control Conference. IEEE, 1991. http://dx.doi.org/10.23919/acc.1991.4791831.

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Sakata, Yuu, Shuji Ando, Nobumichi Fujisawa, and Yutaka Ohta. "Development of Rotating Stall Cell Under Coexisting Phenomena of Surge and Rotating Stall in an Axial-Flow Compressor." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5310.

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Abstract The relationship between the growth of the stall cell and variation in the surge behavior was experimentally investigated. The aim of this study was to reveal the effect of the stall cell on the surge behavior from the viewpoint of the inner flow structure. In the experiment, the unsteady compressor characteristics during the surge and rotating stall were obtained by using a precision pressure transducer and a one-dimensional single hotwire anemometer. Under the coexisting states of surge and rotating stall, various surge behaviors were observed by throttling the mass flow rate. When the flow rate was set such that the surge behavior switched, an irregular surge was observed. During the irregular cycle, two different cycles were selected randomly corresponding to the stall behavior. When the amplitude of the plenum pressure is relatively large among the measurement results, the absolute value of the time-change rate in the flow coefficient and the static pressure-rise coefficient tend to be high. This shows that the flow field during stable operation near the peak point of the unsteady characteristics changes rapidly. In this case, an auto-correlation function of the wall-pressure fluctuation data showed that the stall inception of the compressor was induced earlier in the large cycle compared with the case of the top cycle. When studying the growth of the stall cell during the stalling process of the large cycle, the wall-pressure fluctuation data showed that the stall cell rapidly grew by gathering more than one spike-type disturbance into one stall cell. In this case, the stall cell fully expanded along the circumferential direction and developed into a deep stall. Therefore, the key factors that determine the surge behavior are the sudden change in the flow field near the peak point of the unsteady characteristics and the rapid growth in the stall cell during the stalling process.
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Huang, Paul Xiubao, and JianAn Yin. "From Rotating Stall to Surge: A Shock Tube Mechanism." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94128.

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Compressor surge is a complete breakdown in compression resulting in an abrupt momentary reversal of gas flow and the violent pressure fluctuation with relatively low frequency and high amplitude. It commonly exists in dynamic type turbo compressors, particularly axial compressor and jet engine, or turbo charger for reciprocating engines. It is generally accepted that surge is preceded by a rotating stall, a situation of a few stalled blades rotating around compressor annulus (cascade) with much higher frequency. In jet engine, violent surge event typically produces a frightening loud bang, lots of vibrations and could cause catastrophic structural failures if not timely managed. Naturally, as important matters as rotating stall and surge, there have been tremendous R/D efforts from academia, government and industry devoted to this area, especially since jet engines became the prime powerhouses for modern airplanes. Despite of all the efforts, there still seems to be a more urgent need to understand the physical characteristics of the transition from a rotating stall to surge that has mystified researchers due to its transient nature. Fundamental questions remain unanswered even today, such as: What exactly triggers the surge to take place from a rotating stall? What is the physical nature of a compressor system or a local incipient surge: is it a movement of wave or fluid particles or both? How to estimate the quantitative destructive forces of a severe surge, that is, the maximum possible surge strength? This paper attempts to answer these questions by applying the classical Shock Tube Theory to the transient process from rotating stall to surge. The Shock Tube analogy is established with the hypothesis (implied from experimental observations) that an instant zero through flow condition exists inside a stalled cascade cell or dynamic compressor that triggers surge. It is revealed that surge event consists of a pair of non-linear compression and expansion waves (CW & EW) that instantly reverse gas flow (IRFF) by the pushing force of upstream propagating CW and the pulling force from downstream travelling EW. The surge strength is shown to be proportional to the square root of the pressure ratio of the involved cascade or compressor. Surge Rules are deduced to predict the location of surge initiation, the minimum and maximum surge strengths, travelling directions and speed. Moreover, a pro-active control strategy called SEWI (Surge Early Warning Initiative) is proposed using the unique characteristics of CW-IRFF-EW formation of a cascade cell induced surge as precursors for subsequent warning and controls before the destructive compressor surge takes place.
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Eveker, Kevin M., D. L. Gysling, Carl N. Nett, and O. P. Sharma. "Integrated control of rotating stall and surge in aeroengines." In SPIE's 1995 Symposium on OE/Aerospace Sensing and Dual Use Photonics, edited by James D. Paduano. SPIE, 1995. http://dx.doi.org/10.1117/12.210515.

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Reports on the topic "Stall and Surge"

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Boussios, C., A. H. Epstein, E. M. Greitzer, G. Hendricks, J. Paduano, and L. Valavani. Active Control of Compressor Surge and Stall. Fort Belvoir, VA: Defense Technical Information Center, January 1992. http://dx.doi.org/10.21236/ada252771.

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Torres, Marissa, and Norberto Nadal-Caraballo. Rapid tidal reconstruction with UTide and the ADCIRC tidal database. Engineer Research and Development Center (U.S.), August 2021. http://dx.doi.org/10.21079/11681/41503.

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The quantification of storm surge is vital for flood hazard assessment in communities affected by coastal storms. The astronomical tide is an integral component of the total still water level needed for accurate storm surge estimates. Coastal hazard analysis methods, such as the Coastal Hazards System and the StormSim Coastal Hazards Rapid Prediction System, require thousands of hydrodynamic and wave simulations that are computationally expensive. In some regions, the inclusion of astronomical tides is neglected in the hydrodynamics and tides are instead incorporated within the probabilistic framework. There is a need for a rapid, reliable, and accurate tide prediction methodology to provide spatially dense reconstructed or predicted tidal time series for historical, synthetic, and forecasted hurricane scenarios. A methodology is proposed to combine the tidal harmonic information from the spatially dense Advanced Circulation hydrodynamic model tidal database with a rapid tidal reconstruction and prediction program. In this study, the Unified Tidal Analysis program was paired with results from the tidal database. This methodology will produce reconstructed (i.e., historical) and predicted tidal heights for coastal locations along the United States eastern seaboard and beyond and will contribute to the determination of accurate still water levels in coastal hazard analysis methods.
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Matar, Walid, and Doaa Filali. Alternative Fuels for Saudi Cement Manufacturing with Time-varying Carbon Pricing. King Abdullah Petroleum Studies and Research Center, January 2023. http://dx.doi.org/10.30573/ks--2022-dp12.

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After cement production in Saudi Arabia surged in the first half of the 2010s due to the country’s rapid economic development, it has slowed measurably in recent years as economic growth has declined. This is shown in Figure 1, along with the evolution of the Kingdom’s real gross domestic income (RGDI). Still, it ranks among the top 10 countries for existing cement kiln capacity. The Saudi cement industry has relied on Arab Heavy crude oil, heavy fuel oil (HFO), and natural gas to produce clinker, a key cement ingredient.
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Reyes-Tagle, Gerardo, and Jorge E. Muñoz-Ayala. Debt and Economic Growth: Does Size Matter? Evidence from Dynamic Parametric and Static Non-parametric Approaches. Inter-American Development Bank, April 2023. http://dx.doi.org/10.18235/0004818.

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This paper provides new evidence on the effect of debt on economic growth through two alternative methodological approaches. On the one hand, by using a panel error correction model with a sample of 130 countries between 1980 and 2020, we found evidence of the existence of a range of debt-to-GDP ratios for which economic growth remains positive after debt surges. This threshold may lie between 32 percent and 136 percent, with optimal economic growth achieved at an 84 percent debt-to-GDP ratio for the whole sample of countries. The error correction form for the economic growth was dynamically consistent and non-linear with respect to the debt-to-GDP ratio. On the other hand, recent evidence has shown that commodity price volatility increases external debt accumulation for commodity-exporting countries. Still, there is no evidence of the effects of debt surges on these countries' economic growth. This paper provides original insights into the relationship between economic growth and the debt-to-GDP ratio for commodity and non-commodity-driven economies by employing a regression discontinuity design (RDD) approach. This method allows us to estimate differences in economic growth around an estimated threshold without assuming any specific function for the underlying relationship between the two variables. Our findings suggest that non-commodity-driven economies benefit from a higher threshold (85 percent) than commodity-exporting economies (50 percent).
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Wilkinson, Annie, Hayley MacGregor, Ian Scoones, Megan Schmidt-Sane, Melissa Leach, Peter Taylor, Santiago Ripoll, Shandana Khan Mohmand, Syed Abbas, and Tabitha Hrynick. Pandemic Preparedness for the Real World: Why We Must Invest in Equitable, Ethical and Effective Approaches to Help Prepare for the Next Pandemic. Institute of Development Studies, March 2023. http://dx.doi.org/10.19088/cc.2023.002.

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The cost of the Covid-19 pandemic remains unknown. Lives directly lost to the disease continue to mount, while related health, livelihood and wellbeing impacts are still being felt, and the wider ramifications across society, politics and the economy are yet to fully materialise. What is known about these costs though, is that they have been unequally distributed both within and between countries. Preparedness plans proved inadequate in many settings – especially when it came to protecting those most vulnerable, including those marginalised by geography, poverty, or exclusion along the lines of religion, ethnicity or gender. The top-down, surge-style, biomedically dominated and technologically driven preparedness approach that has dominated global health thinking and which was propelled into action with Covid-19 was found wanting not only on the grounds of effectiveness, but also of social justice. This presents both a challenge and an opportunity for a convergence of the preparedness and development agendas. Drawing on a growing body of social science evidence, this report contends that securing health in the face of today’s uncertain disease threats in often unpredictable settings means making social, economic and political priorities as core to the preparedness agenda as biological and technological ones. We present here a framework for a vision of pandemic preparedness for the real world – one that accepts that context is paramount, embraces inclusivity and justice, shifts power centres and rejects simplistic, one-size-fits-all solutions.
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Babenko, Oksana. Ідеї екуменізму в публіцистиці митрополита Андрея Шептицького: сучасне прочитання. Ivan Franko National University of Lviv, March 2023. http://dx.doi.org/10.30970/vjo.2023.52-53.11717.

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Subject of the article’s study – ecumenism of Metropolitan Andrei Sheptytskyi and reflection of this phenomenon in the works of scientists and modern Ukrainian media. Main objective of the study: analyze what Ukrainian scientists, journalists and different media are writing about Sheptytkyi’s ecumenism. Methodology: We used a bibliographic method to accumulate factual material, a qualitative content analysis to isolate the ideas of ecumenism from the journalism of Metropolitan Andrey Sheptytskyi, a cultural-historical method that made it possible to consider the ideas of ecumenism in the context of the era, the connection with the historical context, as well as methods of synthesis and generalization, induction and deduction. The study process description: In our scientific article, we analyzed the doctoral dissertation of His Beatitude Lubomyr Huzar entitled «Andrei Sheptytskyi, Metropolitan of Halytskyi (1901-1944). Herald of ecumenism». His Beatitude Lubomyr defended this fundamental work at the Pontifical Urbaniana University in Rome back in 1972. Therefore, we observed how this work reflects the historical prerequisites, features and development of Sheptytskyi’s ecumenism, who, according to His Beatitude Lubomir, was a kind of innovator in this field, a person who was ahead of his time. We also analyzed the reflections on the ecumenism of Sheptytskyi´s father, doctor Ivan Datsk, which are reflected in his book «In Search of Faithfulness and Truth». In addition, we turned to the scientific text «Ecumenism of Sheptytskyi» by professors Mykola Vegesh and Mykola Palinchak. Subsequently, it was analyzed how the scientific work became a useful basis for the coverage of Sheptytskyi’s ecumenism in the press. In particular, in the columns of the cultural and social site «Zbruch» in Diana Motruk’s article «In Search of Church Unity». We also turned to the «Spiritual Greatness of Lviv» website, where in 2020 an interview with Mykhailo Perun, who shot the film «Sheptytskyi: Relevant information», was published, illustrating the ecumenical initiatives of this figure. In addition, we analyzed the publication on Radio Svoboda for 2022, dedicated to the anniversary of Sheptytsky’s stepping into eternity. It is also mentioned there about of Sheptytskyi’s ecumenism as his landmark activity. Subsequently, we found an article on the website «Christian and the World», where in a conversation with the scientist Dr. Andrii Sorokovskyi entitled «Andrei Sheptytskyi believed that the union is a synthesis, communion and dialogue between the East and the West, – Andrii Sorokovskyi» also analyzed the phenomenon of Sheptytskyi’s ecumenism. Results: we discovered that Sheptytskyi’s ecumenism was studied not only by numerous scientists, but this meaningful legacy of his is a valuable phenomenon for media coverage. Therefore, Sheptytskyi’s ecumenism becomes the subject of interest of journalists not only of publications that write mainly on church topics, but also socio-political and artistic ones. We are sure that Sheptytskyi’s ecumenism will continue to be studied by professional scientists and representatives of the wider media community. Significance: journalism of a religious orientation, high-quality and substantiated coverage of religious processes and phenomena in the press is still something quite new for modern Ukraine. In Soviet times, journalists were afraid to write about religion in order not to incur the wrath of the authorities, so such materials could not be included in the press. That is why it is very important to study how today’s journalists cover important issues of religion, which, in addition, have a strong scientific basis. In addition, the development of ecumenism and religious unity are extremely important for building national unity, which is necessary for our state to effectively confront the enemy in full-scale war. Key words: ecumenism; Metropolitan Andrey Sheptytskyi; media; interreleigion cooperation; dialogue.
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Hertel, Thomas, David Hummels, Maros Ivanic, and Roman Keeney. How Confident Can We Be in CGE-Based Assessments of Free Trade Agreements? GTAP Working Paper, June 2003. http://dx.doi.org/10.21642/gtap.wp26.

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With the proliferation of Free Trade Agreements (FTAs) over the past decade, demand for quantitative analysis of their likely impacts has surged. The main quantitative tool for performing such analysis is Computable General Equilibrium (CGE) modeling. Yet these models have been widely criticized for performing poorly (Kehoe, 2002) and having weak econometric foundations (McKitrick, 1998; Jorgenson, 1984). FTA results have been shown to be particularly sensitive to the trade elasticities, with small trade elasticities generating large terms of trade effects and relatively modest efficiency gains, whereas large trade elasticities lead to the opposite result. Critics are understandably wary of results being determined largely by the authors’ choice of trade elasticities. Where do these trade elasticities come from? CGE modelers typically draw these elasticities from econometric work that uses time series price variation to identify an elasticity of substitution between domestic goods and composite imports (Alaouze, 1977; Alaouze, et al., 1977; Stern et al., 1976; Gallaway, McDaniel and Rivera, 2003). This approach has three problems: the use of point estimates as “truth”, the magnitude of the point estimates, and estimating the relevant elasticity. First, modelers take point estimates drawn from the econometric literature, while ignoring the precision of these estimates. As we will make clear below, the confidence one has in various CGE conclusions depends critically on the size of the confidence interval around parameter estimates. Standard “robustness checks” such as systematically raising or lowering the substitution parameters does not properly address this problem because it ignores information about which parameters we know with some precision and which we do not. A second problem with most existing studies derives from the use of import price series to identify home vs. foreign substitution, for example, tends to systematically understate the true elasticity. This is because these estimates take price variation as exogenous when estimating the import demand functions, and ignore quality variation. When quality is high, import demand and prices will be jointly high. This biases estimated elasticities toward zero. A related point is that the fixed-weight import price series used by most authors are theoretically inappropriate for estimating the elasticities of interest. CGE modelers generally examine a nested utility structure, with domestic production substitution for a CES composite import bundle. The appropriate price series is then the corresponding CES price index among foreign varieties. Constructing such an index requires knowledge of the elasticity of substitution among foreign varieties (see below). By using a fixed-weight import price series, previous estimates place too much weight on high foreign prices, and too small a weight on low foreign prices. In other words, they overstate the degree of price variation that exists, relative to a CES price index. Reconciling small trade volume movements with large import price series movements requires a small elasticity of substitution. This problem, and that of unmeasured quality variation, helps explain why typical estimated elasticities are very small. The third problem with the existing literature is that estimates taken from other researchers’ studies typically employ different levels of aggregation, and exploit different sources of price variation, from what policy modelers have in mind. Employment of elasticities in experiments ill-matched to their original estimation can be problematic. For example, estimates may be calculated at a higher or lower level of aggregation than the level of analysis than the modeler wants to examine. Estimating substitutability across sources for paddy rice gives one a quite different answer than estimates that look at agriculture as a whole. When analyzing Free Trade Agreements, the principle policy experiment is a change in relative prices among foreign suppliers caused by lowering tariffs within the FTA. Understanding the substitution this will induce across those suppliers is critical to gauging the FTA’s real effects. Using home v. foreign elasticities rather than elasticities of substitution among imports supplied from different countries may be quite misleading. Moreover, these “sourcing” elasticities are critical for constructing composite import price series to appropriate estimate home v. foreign substitutability. In summary, the history of estimating the substitution elasticities governing trade flows in CGE models has been checkered at best. Clearly there is a need for improved econometric estimation of these trade elasticities that is well-integrated into the CGE modeling framework. This paper provides such estimation and integration, and has several significant merits. First, we choose our experiment carefully. Our CGE analysis focuses on the prospective Free Trade Agreement of the Americas (FTAA) currently under negotiation. This is one of the most important FTAs currently “in play” in international negotiations. It also fits nicely with the source data used to estimate the trade elasticities, which is largely based on imports into North and South America. Our assessment is done in a perfectly competitive, comparative static setting in order to emphasize the role of the trade elasticities in determining the conventional gains/losses from such an FTA. This type of model is still widely used by government agencies for the evaluation of such agreements. Extensions to incorporate imperfect competition are straightforward, but involve the introduction of additional parameters (markups, extent of unexploited scale economies) as well as structural assumptions (entry/no-entry, nature of inter-firm rivalry) that introduce further uncertainty. Since our focus is on the effects of a PTA we estimate elasticities of substitution across multiple foreign supply sources. We do not use cross-exporter variation in prices or tariffs alone. Exporter price series exhibit a high degree of multicolinearity, and in any case, would be subject to unmeasured quality variation as described previously. Similarly, tariff variation by itself is typically unhelpful because by their very nature, Most Favored Nation (MFN) tariffs are non-discriminatory in nature, affecting all suppliers in the same way. Tariff preferences, where they exist, are often difficult to measure – sometimes being confounded by quantitative barriers, restrictive rules of origin, and other restrictions. Instead we employ a unique methodology and data set drawing on not only tariffs, but also bilateral transportation costs for goods traded internationally (Hummels, 1999). Transportation costs vary much more widely than do tariffs, allowing much more precise estimation of the trade elasticities that are central to CGE analysis of FTAs. We have highly disaggregated commodity trade flow data, and are therefore able to provide estimates that precisely match the commodity aggregation scheme employed in the subsequent CGE model. We follow the GTAP Version 5.0 aggregation scheme which includes 42 merchandise trade commodities covering food products, natural resources and manufactured goods. With the exception of two primary commodities that are not traded, we are able to estimate trade elasticities for all merchandise commodities that are significantly different form zero at the 95% confidence level. Rather than producing point estimates of the resulting welfare, export and employment effects, we report confidence intervals instead. These are based on repeated solution of the model, drawing from a distribution of trade elasticity estimates constructed based on the econometrically estimated standard errors. There is now a long history of CGE studies based on SSA: Systematic Sensitivity Analysis (Harrison and Vinod, 1992; Wigle, 1991; Pagon and Shannon, 1987) Ho
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