Artigos de revistas sobre o tema "Flow phenomena identification"
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Krzysztof, Banasiak, Palacz Michal e Hafner Armin. "1214 STATE OF THE ART IN IDENTIFICATION OF TWO-PHASE TRANSONIC FLOW PHENOMENA IN TRANSCRITICAL CO2 EJECTORS". Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2013.4 (2013): _1214–1_—_1214–6_. http://dx.doi.org/10.1299/jsmeicjwsf.2013.4._1214-1_.
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Olczyk, A. "Identification of dynamic phenomena in pipes supplied with a pulsating flow of gas". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 223, n.º 8 (2 de abril de 2009): 1851–67. http://dx.doi.org/10.1243/09544062jmes1386.
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Pulsating flow is typical of displacement machines such as piston engines, compressors, or other displacement devices. The cyclic movement of the working element (piston, valve, membrane, etc.) generates pulsations, which, from a dynamic point of view, can be considered as excitation in the system composed of a flowing gas and pipes in which the flow takes place. This study shows that under certain conditions, a significant increase of pulse amplitudes occurs and transient values of main flow parameters are up to a few times higher than that for the equivalent steady flow conditions. This unsteadiness can be harmful or even damaging; however, in some cases it can be profitable (e.g. induction ramming of combustion engines). In order to investigate which conditions are favourable to obtain such effects in pipes, four different systems, distinguished by a different level of choking at the pipe outlet section, were tested. The experimental tests performed in the range of excitation frequencies of 0—200 Hz have shown that systems with low choking at the pipe outlet are more prone to strong dynamic effects, characterized by considerable growth of pulse amplitudes and an intensive reverse flow occurring in the proximity of resonance frequencies. In systems with high choking at the pipe outlet section, those effects were very weak. Characteristic frequencies, for which the resonance takes place, depend on the pipe length and can be determined theoretically with a simple acoustic model or a one-dimensional model ‘ x— t’ describing a pulsating flow in the pipe. The experimental verification of those resonance frequencies can be conducted with the use of transient flow parameters recorded by appropriate fast response sensors.
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Manno, V. P., e K. Azar. "Thermal-Fluid Interactions of Neighboring Components on Air-Cooled Circuit Boards". Journal of Electronic Packaging 113, n.º 4 (1 de dezembro de 1991): 374–81. http://dx.doi.org/10.1115/1.2905423.
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The effects of neighboring components on the thermal performance of air-cooled electronic circuit boards are reviewed using a four part framework—identification, anticipation, quantification and optimization. Interactions are categorized as either isothermal fluid flow or thermal-fluid phenomena. Fluid flow phenomena include multi-dimensional, laminar and transitional flow which can have large spatial influences and exhibit unsteady behavior. The importance of all heat transfer mechanisms is demonstrated and the inadequacy of isolated component thermal characterization is illustrated. Effective thermal proximity of a neighboring component is discussed. Current achievements and inadequacies of experimental characterization and predictive models are described. Finally, proactive optimization strategies based upon circuit board layout and exploitation of unsteady flow effects are considered.
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Liesche, Georg, e Kai Sundmacher. "Identification of Key Transport Phenomena in High-Temperature Reactors: Flow and Heat Transfer Characteristics". Industrial & Engineering Chemistry Research 57, n.º 46 (25 de outubro de 2018): 15884–97. http://dx.doi.org/10.1021/acs.iecr.8b03955.
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Roussel, Nicolas, e Christophe Lanos. "Plastic Fluid Flow Parameters Identification Using a Simple Squeezing Test". Applied Rheology 13, n.º 3 (1 de junho de 2003): 132–41. http://dx.doi.org/10.1515/arh-2003-0009.
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Abstract In this paper after a presentation of the compression test and its classical references in the rheological literature a behaviour parameter identification method is introduced using simple compression tests on concentrated geo-suspensions with a plastic fluid behaviour. The obtained theoretical test response is validated for several materials (natural soils, Kaolin clay …). It is also compared with previous solutions obtained by other authors to show that most existing solutions miss one or more terms. Elements are also given on two types of test response perturbations: the induced heterogeneity in the case of slow tests (consolidation phenomena) and the fragmentation of the outer part of sample (granular paste breakings). Finally, compression test results for a nano silica paste are presented as a example and treated as an application of the test exploitation method.
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Muhammad Amirul Hisham Razian, Herdawatie Abdul Kadir, Ahmad Aiman Abd Muttalib, Mohd Adib Mohammad Razi e Babul Salam Ksm Kader Ibrahim. "Design of Vibration and Turbulence Alert System for Headwater Phenomena". Journal of Advanced Research in Applied Mechanics 119, n.º 1 (10 de julho de 2024): 174–92. http://dx.doi.org/10.37934/aram.119.1.174192.
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The deteriorating state of ecosystems poses risks for nature enthusiasts in forests and rivers. The hazardous headwater phenomenon, a frequent and potentially fatal occurrence, threatens human life and the environment. Recognizing the danger is challenging, as existing technologies focus on flow pattern analysis rather than identification. To address this gap, the Headwater Phenomenon Warning and Monitoring System, an IoT and mobile application, was developed. Integrating sensors like accelerometers, vibration, and rain detection, the system enables real-time monitoring and provides early warnings. The prototype contributes to early warning, flood forecast, hydrological research, climate impact assessment, disaster management, and environmental monitoring, aiding our understanding of climate change implications. The prototype underwent multiple DOE to validate sensor and communication system integrity and stability. Turbulence and vibration graphs were successfully recorded, enhancing hazard identification and real-time monitoring capabilities.
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Aafrin Sulthana., S., T. Marieswaran., N. Braghadesh., N. Mithran. e M. Venkatesan. "Slug-bubble regime identification in a square channel using a IR Sensor". MATEC Web of Conferences 172 (2018): 01002. http://dx.doi.org/10.1051/matecconf/201817201002.
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Design of micro thrusters for nano satellites, require a detailed understanding of multiphase flow phenomena in micro/mini-channels. This work focuses on the experimental and numerical investigation of an Infra-red sensor behavior during two phase flow of a slug-bubble train (air-water two-phase flow). The regime flows inside a square channel of sides 2 mm and 0.5 mm thickness made of borosilicate glass. The interference of the slug-bubble train flow pattern on the IR transceiver characteristics is experimentally studied as current signals corresponding to the number of photons received by the photodiode. A numerical model is developed to analyze the IR transceiver characteristics using COMSOL Multiphysics package. The experimental and numerical results are in good agreement and the developed system with proper calibration can be used to design feedback loops for micro thrusters.
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Clifton, Andrew, e Julie K. Lundquist. "Data Clustering Reveals Climate Impacts on Local Wind Phenomena". Journal of Applied Meteorology and Climatology 51, n.º 8 (agosto de 2012): 1547–57. http://dx.doi.org/10.1175/jamc-d-11-0227.1.
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AbstractThe authors demonstrate the utility of k-means clustering for identifying relationships between winds at turbine heights and climate oscillations, thereby developing a method suited for predicting the impacts of climate change on wind resources. Fourteen years of data from an 80-m tower at the National Wind Technology Center (NWTC) in Colorado have been reduced to four dominant flow phenomena using k-means clustering. At this location, this method identifies two clusters of westerly inflow (strong and weak), another cluster of flow from the north, and one of flow from the south. Similar clusters are found for the data at all heights on the tower, and each follow distinct seasonal cycles. Time series of each cluster, as well as the mean wind speed at the NWTC, are retained for comparison with climate oscillations along with the local 500-hPa pressure gradient. The mean wind speed in the surface layer is strongly correlated with the local north–south pressure gradient. The frequency of strong westerly flow is also negatively correlated with the Niño-3.4 index, whereas weaker westerly winds are negatively correlated with the Pacific–North American pattern (PNA) and Arctic Oscillation (AO). Northerly winds at the NWTC did not strongly correlate with any of the investigated climate indices (AO, PNA, and Niño-3.4). These northerly winds occur more frequently in the summer months, suggesting that these winds are more influenced by local conditions than by mesoscale forcing. This method of identifying clusters in wind data allows objective identification of wind phenomena that may benefit the deployment of wind turbines, for example, in choosing combinations of wind speed and direction to investigate for turbine siting.
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Joshi, Jyeshtharaj B., Mandar V. Tabib, Sagar S. Deshpande e Channamallikarjun S. Mathpati. "Dynamics of Flow Structures and Transport Phenomena, 1. Experimental and Numerical Techniques for Identification and Energy Content of Flow Structures". Industrial & Engineering Chemistry Research 48, n.º 17 (2 de setembro de 2009): 8244–84. http://dx.doi.org/10.1021/ie8012506.
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Burian, Ondrej, Vaclav Dostal e Ladislav Vesely. "STUDY OF IDENTIFICATION OF TWO-PHASE FLOW PARAMETERS BY PRESSURE FLUCTUATION ANALYSIS". Acta Polytechnica CTU Proceedings 4 (16 de dezembro de 2016): 1. http://dx.doi.org/10.14311/ap.2016.4.0001.
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This paper deals with identification of parameters of simple pool boiling in a vertical rectangular channel by analysis of pressure fluctuation. In this work is introduced a small experimental facility about 9 kW power, which was used for simulation of pool boiling phenomena and creation of steam-water volume. Several pressure fluctuations measurements and differential pressure fluctuations measurements at warious were carried out. Main changed parameters were power of heaters and hydraulics resistance of channel internals. Measured pressure data was statistically analysed and compared with goal to find dependencies between parameters of two-phase flow and statistical properties of pressure fluctuation. At the end of this paper are summarized final results and applicability of this method for parameters determination of two phase flow for pool boiling conditions at ambient pressure.
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D’Auria, F., N. Aksan e H. Glaeser. "Physical Phenomena in Nuclear Thermal Hydraulics and Current Status". Tecnica Italiana-Italian Journal of Engineering Science 65, n.º 1 (31 de março de 2021): 1–11. http://dx.doi.org/10.18280/ti-ijes.650101.
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116 nuclear Thermal-Hydraulic Phenomena T-HP are identified in the present paper, following documents issued during the last three decades by the Committee on the Safety of Nuclear Installations of Nuclear Energy Agency of the Organization for Economic Cooperation and Development (OECD/NEA/CSNI) and by the International Atomic Energy Agency (IAEA). The derived T-HP list includes consideration of experiments performed in Separate Effect Test (SET) and Integral Effect Test (IET) facilities relevant to reactor coolant system and containment of Water Cooled Nuclear Reactors (WCNR). We consider a dozen WCNR types: Pressurized Water Reactors (PWR), Boiling Water Reactors (BWR), Russian reactors (VVER-440, VVER-1000 and RBMK), pressure tube heavy water reactors by Canada (CANDU) and India (PHWR) and so-called ‘advanced’ reactors (e.g. AP-1000 and APR-1400 designed in US and Korea, respectively). We envisage a variety of applications for the T-HP list. Four of the phenomena are helpful to characterize the current state of art in nuclear thermal-hydraulics: Counter Current Flow Limitation (CCFL), Critical Heat Flux (CHF), reflood and Two-Phase Critical Flow (TPCF). Furthermore, the T-HP identification contributes to addressing the scaling issue, performing uncertainty evaluations, developing constitutive equations and ‘special models’ in codes and prioritizing the research.
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Jakubowski, Marek. "Secondary flows occurring in a whirlpool separator – A study of phenomena – observation, simulation and measurements". Chemical and Process Engineering 36, n.º 3 (1 de setembro de 2015): 277–89. http://dx.doi.org/10.1515/cpe-2015-0019.
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Abstract The whirlpool separator, used for hot trub separation, is prevalent in the brewing industry. It is a kind of a hydrocyclone inside of which a tea leaf effect occurs, which is sediment accumulation into a cone shape at the central part of the tank’s bottom. This manner of sediment accumulation is caused by the secondary flow occurring in the so-called Ekman boundary layer. This article is a summary of the research, which has been conducted for many years and involved observation, simulation and experimental research on the recognition and formation of the secondary flow accumulating the sediment cone. Secondary flows occurring in a whirlpool were identified through CFD simulation and PIV experiments, and are presented in this paper. Based on their location and direction, an attempt to determine their impact on the separation process taking place in the whirlpool has been made. The secondary flow identification methods proposed in this paper can be successfully applied in other solutions, e. g. structural ones, which involve rotational-flow-based separation.
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Lisik, Zbigniew, Ewa Raj e Jacek Podgórski. "Numerical Model of Current Flow and Thermal Phenomena in Lateral GaN/InGaN LEDs". Electronics 10, n.º 24 (16 de dezembro de 2021): 3127. http://dx.doi.org/10.3390/electronics10243127.
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GaN-based light-emitting diodes (LEDs) became one of the most widely used light sources. One of their key factors is power conversion efficiency; hence, a lot of effort is placed on research to improve this parameter, either experimentally or numerically. Standard approaches involve device-oriented or system-oriented methods. Combining them is possible only with the aid of compact, lumped parameter models. In the paper, we present a new electro-thermal model that covers all the complex opto-electro-thermal phenomena occurring within the operating LED. It is a simple and low computational cost solution that can be integrated with package- or system-oriented numerical analysis. It allows a parametric analysis of the diode structure and properties under steady-state operating conditions. Its usefulness has been proved by conducting simulations of a sample lateral GaN/InGaN LED with the aid of ANSYS software. The results presented illustrate the current density and temperature fields. They allow the identification of ‘hot spots’ resulting from the current crowding effect and can be used to optimise the structure.
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Guo, Lei, Shu Sheng Zhang, Ya Qun Chen e Lin Cheng. "Identification of Boiling Two-Phase Flow Regimes Based on Two Kinds of Neural Networks". Applied Mechanics and Materials 29-32 (agosto de 2010): 54–60. http://dx.doi.org/10.4028/www.scientific.net/amm.29-32.54.
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In this paper, the boiling phenomena of steam boiler under atmospheric pressure are simulated by using the UDF program of CFD software. Characteristics including pressure, temperature and vapor fraction respectively for bubble, slug and annular flow regimes are extracted as the input characteristic vectors of the BP neural network and Elman neural network for the purpose of identifying the boiling two-phase (vapor/liquid) flow regimes within wall tubes. It reveals that the rate of recognition accuracy of flow regimes with BP neural network is up to 95.24%, as well as 100% with Elman neural network within the groups taken into consider. By analyzing relations between flow regimes, wall temperature and wall heat transfer coefficient, it is found that changes in flow regimes will cause drastic variation in heat transfer coefficient of the wall surface, and the coefficient reduces rapidly as the wall temperature increases and eventually converge to a minimum. It is a very effective method of using numerical simulation to extract the signal under poor experimental conditions, and is good reference for the further research.
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Fako, Raluca, e M. Soare. "Effect of Flow Disturbed Condition and MEA Inhibitor on Corrosion Behavior of an API 5L Grade A Steel". Advanced Materials Research 38 (março de 2008): 56–62. http://dx.doi.org/10.4028/www.scientific.net/amr.38.56.
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The results of a failure investigation performed on a transportation pipeline for oil products (aromatics – water – DEG) are presented. The damage phenomena of the material were attributed to corrosion – erosion, and secondary to stress corrosion cracking. The analysis aims to identify the mechanisms responsible for service failure of an API 5L grade A pipe after about two years and, also, to mitigate further damage phenomena by a proper identification of the contribution of mechanical, metallurgical and environmental factors (focusing both on technological fluids characteristics and inhibition scheme). Expert report conclusion and other field data give premises for re-designing the maintenance, operating and corrosion-monitoring program in order to avoid future hazards.
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Górski, Grzegorz, Grzegorz Litak, Romuald Mosdorf e Andrzej Rysak. "Dynamics of Two-Phase Flow through a Minichannel: Fourier and Multiscale Entropy Analyses". Applied Mechanics and Materials 791 (setembro de 2015): 217–23. http://dx.doi.org/10.4028/www.scientific.net/amm.791.217.
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By changing a air flow rate of the two-phase (air-water) flow through a minichannel weidentified aggregation and partitioning of air bubbles and slugs of different sizes and air bubble arrangement into periodic patterns. The identification of these spatio-temporal behaviour was doneby digital camera. Simultaneously, we provide the detailed studies of these phenomena by using thecorresponding sequences of light transmission time series recorded by a laser-phototransistor sensor.To distinguish the instabilities in air slags and their breakups and aggregations we used the Fourierand multiscale entropy analysis.
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Bloch, Pierre-Yves, Konrad Olejnik, Jean-Francis Bloch, Alexandre Bloch, Jules Hammond e Daniel Brissaud. "Time scales of spontaneous imbibition into porous material: From classic models to papers applications". BioResources 19, n.º 1 (16 de novembro de 2023): 345–65. http://dx.doi.org/10.15376/biores.19.1.345-365.
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Flow and spontaneous imbibition phenomena in porous media are important for various industrial applications, including printing and medical lateral flow assays. Their quantitative characterization is important to better understand and select the appropriate raw materials. However, standard methods often require time-consuming tests, and/or expensive equipment. Different time scales must be considered, limiting the range of possible characterization tools. A novel experimental approach based on image analysis for characterizing spontaneous imbibition processes is presented. Hence, ultra-fast diffusion may be quantitatively characterized. Models are issued from the literature to consider physical phenomena at small (milliseconds) and medium range (seconds) of time scales. The obtained experimental data fit with theoretical results, providing valuable insights into the understanding of fluid flow behavior at different time scales. Furthermore, the identification of some physical properties for either the fluid, or the substrate, based on the theoretical models are possible, as the contact angle, which remains to be otherwise challenging. This study contributes to bridging the gap between spontaneous imbibition and capillary phenomena at different time scales, their modeling, and a characterization of material and/or fluid properties paving the way for enhanced understanding and control of fluid behavior in porous media. Different papers are considered to illustrate the method.
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Cravero, Carlo, e Davide Marsano. "Instability Phenomena in Centrifugal Compressors and Strategies to Extend the Operating Range: A Review". Energies 17, n.º 5 (23 de fevereiro de 2024): 1069. http://dx.doi.org/10.3390/en17051069.
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Centrifugal compressors are widely used in different fields. Their design requires high performance and a wide operating range, where, at lower mass flow rates, unstable flow dynamic phenomena occur, which are extremely harmful and, at the same time, complex to fully understand. This review paper presents the main research from the last 40 years on the subject of instability in centrifugal compressors, aiming to clarify the main (sometimes contradictory) causes, classifying them according to the component in which they are triggered or the interaction between them. Importance is given to works that develop criteria for the identification of the stability limit with simplified models. The main techniques used to extend the stability limit are also presented by distinguishing between passive and active fixed-flow control methods; moreover, the main works on variable geometry techniques are reported, showing the advantages and disadvantages of their use. Finally, an overview of the innovative applications of centrifugal compressors, such as fuel cells, is presented. The aim of this review is to highlight the continued interest in this field of study and provide the tools to understand the different unstable mechanisms and techniques used to extend the operating limit.
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Alcayaga, Leonardo, Gunner Chr Larsen, Mark Kelly e Jakob Mann. "Identification of large-scale atmospheric structures under different stability conditions using Dynamic Mode Decomposition". Journal of Physics: Conference Series 2265, n.º 2 (1 de maio de 2022): 022006. http://dx.doi.org/10.1088/1742-6596/2265/2/022006.
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Abstract We investigate the characteristic of large-scale coherent motions over a large horizontal domain using the Dynamic Mode Decomposition (DMD) spectral analysis algorithm applied on measurements from two long-range pulsed lidars. We show the results and advantages of this methodology on six cases representative of three thermal stratification conditions at two heights relevant for wind energy: near-neutral, unstable and stable stratification at 50m and 200m above ground level. For these cases the DMD algorithm show three types of structures: streaks near the surface for near-neutral for neutral stratification, large-scale convective rolls for the unstable cases and sheet-like rotational patches for stable conditions. The DMD algorithm also shows the stationary effects of the terrain on the flow at 50m above ground level, within the atmospheric surface layer. The possibility of isolating terrain effects from coherent motions makes DMD attractive for studying complex atmospheric flow phenomena as well as to have more realistic input for wind farm flow simulations.
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Szwemin, Paulina, e Wieslaw Fiebig. "The Influence of Radial and Axial Gaps on Volumetric Efficiency of External Gear Pumps". Energies 14, n.º 15 (23 de julho de 2021): 4468. http://dx.doi.org/10.3390/en14154468.
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The design of gear pumps and motors is focused on more efficient units which are possible to achieve using advanced numerical simulation techniques. The flow that appears inside the gear pump is very complex, despite the simple design of the pump itself. The identification of fluid flow phenomena in areas inside the pump, considering the entire range of operating parameters, is a major challenge. This paper presents the results of simulation studies of leakages in axial and radial gaps in an external gear pump carried out for different gap shapes and sizes, as well as various operating parameters. To investigate the processes that affect pump efficiency and visualize the fluid flow phenomena during the pump’s operation, a CFD model was built. It allows for a detailed analysis of the impact of the gears’ eccentricity on leakages and pressure build-up on the circumference. Performed simulations made it possible to indicate the relationship between leakages resulting from the axial and radial gap, which has not been presented so far. To verify the CFD model, experimental investigations on the volumetric efficiency of the external gear pump were carried out. Good convergence of results was obtained; therefore, the presented CFD model is a universal tool in the study of flow inside external gear pumps.
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Pianzola, Federico, Giuseppe Riva, Karin Kukkonen e Fabrizia Mantovani. "Presence, flow, and narrative absorption: an interdisciplinary theoretical exploration with a new spatiotemporal integrated model based on predictive processing". Open Research Europe 1 (26 de março de 2021): 28. http://dx.doi.org/10.12688/openreseurope.13193.1.
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Presence, flow, narrative absorption, immersion, transportation, and similar subjective phenomena are studied in many different disciplines, mostly in relation to mediated experiences (books, film, VR, games). Moreover, since real, virtual, or fictional agents are often involved, concepts like identification and state empathy are often linked to engaging media use. Based on a scoping review which identified similarities in the wording of various questionnaire items conceived to measure different phenomena, we categorize items into the most relevant psychological aspects, and use this categorization to propose an interdisciplinary systematization. Then, based on a framework of embodied predictive processing, we present a new cognitive model of presence-related phenomena for mediated and non-mediated experiences, integrating spatial and temporal aspects and also considering the role of fiction and media design. Key processes described within the model are: selective attention, enactment of intentions, and interoception. We claim that presence is the state of perceived successful agency of an embodied mind able to correctly enact its predictions. The difference between real-life and simulated experiences (“book problem,” “paradox of fiction”) lays in the different precision weighing of exteroceptive and interoceptive signals.
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Pianzola, Federico, Giuseppe Riva, Karin Kukkonen e Fabrizia Mantovani. "Presence, flow, and narrative absorption: an interdisciplinary theoretical exploration with a new spatiotemporal integrated model based on predictive processing". Open Research Europe 1 (23 de julho de 2021): 28. http://dx.doi.org/10.12688/openreseurope.13193.2.
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Presence, flow, narrative absorption, immersion, transportation, and similar subjective phenomena are studied in many different disciplines, mostly in relation to mediated experiences (books, film, VR, games). Moreover, since real, virtual, or fictional agents are often involved, concepts like identification and state empathy are often linked to engaging media use. Based on a scoping review that identified similarities in the wording of various questionnaire items conceived to measure different phenomena, we categorize items into the most relevant psychological aspects and use this categorization to propose an interdisciplinary systematization. Then, based on a framework of embodied predictive processing, we present a new cognitive model of presence-related phenomena for mediated and non-mediated experiences, integrating spatial and temporal aspects and also considering the role of fiction and media design. Key processes described within the model are: selective attention, enactment of intentions, and interoception. We claim that presence is the state of perceived successful agency of an embodied mind able to correctly enact its predictions. The difference between real-life and simulated experiences (“book problem,” “paradox of fiction”) lays in the different precision weighting of exteroceptive and interoceptive signals.
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Fořt, Ivan. "Comments on “Dynamics of Flow Structures and Transport Phenomena—Part 1. Experimental and Numerical Techniques for Identification and Energy Control of Flow Structures”". Industrial & Engineering Chemistry Research 49, n.º 9 (5 de maio de 2010): 4468–70. http://dx.doi.org/10.1021/ie9017447.
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Koca, Kemal, Mustafa Serdar Genç, Halil Hakan Açıkel, Mücahit Çağdaş e Tuna Murat Bodur. "Identification of flow phenomena over NACA 4412 wind turbine airfoil at low Reynolds numbers and role of laminar separation bubble on flow evolution". Energy 144 (fevereiro de 2018): 750–64. http://dx.doi.org/10.1016/j.energy.2017.12.045.
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Deshmukh, Rohit, Jack J. McNamara, Zongxian Liang, J. Zico Kolter e Abhijit Gogulapati. "Model order reduction using sparse coding exemplified for the lid-driven cavity". Journal of Fluid Mechanics 808 (27 de outubro de 2016): 189–223. http://dx.doi.org/10.1017/jfm.2016.616.
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Basis identification is a critical step in the construction of accurate reduced-order models using Galerkin projection. This is particularly challenging in unsteady flow fields due to the presence of multi-scale phenomena that cannot be ignored and may not be captured using a small set of modes extracted using the ubiquitous proper orthogonal decomposition. This study focuses on this issue by exploring an approach known as sparse coding for the basis identification problem. Compared with proper orthogonal decomposition, which seeks to truncate the basis spanning an observed data set into a small set of dominant modes, sparse coding is used to identify a compact representation that spans all scales of the observed data. As such, the inherently multi-scale bases may improve reduced-order modelling of unsteady flow fields. The approach is examined for a canonical problem of an incompressible flow inside a two-dimensional lid-driven cavity. The results demonstrate that Galerkin reduction of the governing equations using sparse modes yields a significantly improved predictive model of the fluid dynamics.
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Tiranti, Davide, Paolo Bertolotto, Roberto Cremonini, Armando Riccardo Gaeta e Naima Vela. "The Territorial Debris Flow Early Warning System of Piemonte (North-western Italy)". E3S Web of Conferences 415 (2023): 03030. http://dx.doi.org/10.1051/e3sconf/202341503030.
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Debris flows are one of the most frequent and dangerous phenomena affecting the Alpine environment; they are responsible of 36% of casualties due to gravitational phenomena in the Italian Alps during the last century. In the Western Italian Alps (Piemonte, Italy) a Territorial Debris Flow Early Warning System (Te-DFEWS) aimed to forecast and predict the occurrence of sediment mass-transport has been developed, based on the characterization of small Alpine catchments (< 50 km2) and the processes that take place in these. The Te-DFWES is based on the identification of predisposing and triggering factors that determinate debris flow occurrence. The Te-DFEWS operates from 2010 in present-time and nowcasting using weather radar observations as input data. Recently (2021), the Te-DFEWS has been improved extending the forecasting window (up to 48h from simulation) by the introduction of Quantitative Precipitation Estimate/Forecast (QPE/QPF) input from COSMO-2I and ICON-IT, local high-resolution weather models. The Te-DFEWS, named DEFENSE (DEbris Flows triggEred by storms - Nowcasting SystEm) and the related warning procedures are presented as an operational tool integrated in the Regional Warning System for Geo-hydrological and Hydraulic Risk at the Functional Centre of Piemonte, managed by the Regional Agency for Environmental Protection of Piemonte (Arpa Piemonte).
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Brůha, Tomáš, Pavel Procházka e Václav Uruba. "Investigation of Low-Frequency Phenomena within Flow Pattern in Standard Mixing Vessel Induced by Pitched Blade Impeller". Processes 9, n.º 3 (19 de março de 2021): 545. http://dx.doi.org/10.3390/pr9030545.
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An experimental study on the flow pattern dynamics in a standard mixing vessel with radial baffles filled with water and induced by a pitched blade impeller pumping downward is presented. Investigation is mainly focused on detection and analysis of quasi-periodical or periodical low-frequency phenomenon connected with time- and length-scales considerably exceeding the Blade Passage Frequency (hereinafter BPF) and common turbulent eddies. This phenomenon, which is expressed as large-scale mean-flow variations, is generally known as flow Macro-Instability (hereinafter MI). It could break-down just below the liquid surface, or it crashes to the liquid surface and causes its Macro-Swelling (hereinafter MS). Our investigation was based on classical two-dimensional (2D) Particle Image Velocimetry (hereinafter PIV) measurement within 3 selected vertical planes in the vessel and subsequent analysis of the velocity field. The dominant frequencies evaluated in the selected points and overall analysis of the quasi-periodical macro-flow pattern behavior is to be shown. Identification of the quasi-periodical substructures appeared within the flow pattern was performed using the Oscillation Pattern Decomposition (hereinafter OPD) method. Observation of the macro-flow patterns confirmed presence of the macro-flow structures detected within flow pattern at the identical mixing pilot plant setup by previous investigations of the MIs phenomenon, i.e., the primary circulation loop and strong impeller discharge jet located in the lower vessel segment and the strong ascending wall current at the baffle, which break-down below the surface very often. A further important contribution of the presented work is the investigation of both flow pattern within the baffles vicinity and in the middle of the sector far from the baffle, showing a significant difference. Low-frequency periodical (or quasi-periodical) behavior of the investigated macro-structures was qualitatively confirmed by the presented results and it was quantified using the velocity dominant frequencies evaluation, as noted below. This frequency analysis brings insight into the supposed and detected interconnections between dynamics of the adjacent flow structures. Detected different flow patterns within the main plane near the baffles and in the inclined plane reveal a strong influence of the baffle presence to the local vertical flow, especially within the upper part of the vessel. Quite a different flow pattern appears tangentially in front of and behind the baffle, where a wake is revealed, indicating significant influence of the baffle on the local tangential flow. The new findings represent a contribution to better understanding the physical phenomena behind the standard mixing process.
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Zeng, Qingtian, Sitao Zhu, Zhengrong Li, Aixiang Wu, Meng Wang, Yan Su, Shaoyong Wang, Xiaocheng Qu e Ming Feng. "Research on Real-Time Monitoring and Warning Technology for Multi-Parameter Underground Debris Flow". Sustainability 15, n.º 20 (18 de outubro de 2023): 15006. http://dx.doi.org/10.3390/su152015006.
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Sudden debris flows in underground mines are characterized by strong burstiness, great destructiveness, and difficult monitoring. Traditional single monitoring methods can only roughly judge the probability of underground debris flow occurrences through one-sided potential phenomena, making it difficult to accurately predict sudden underground debris flows. Therefore, effective monitoring methods can prevent or reduce waste and damage to mineral resources caused by mine debris flow disasters. This study is based on the theoretical foundations of rainfall automatic identification program, unsteady flow theory, and wavelet threshold denoising theory. It preprocesses key data such as rainfall, groundwater, and surface displacement with the aim of reducing criterion errors and improving the accuracy of determination. By utilizing the underground debris flow warning determination program, warning determination algorithm, and information management system hosted on the monitoring and warning platform, a comprehensive underground debris flow warning system is integrated. This system incorporates determining parameters such as rainfall, water inflow, groundwater level, surface subsidence, pore water pressure, surrounding rock stress, microseismic phenomena, and underground video recognition, with the innovative approach of “weather-surface-underground” multi-directional monitoring. The system was successfully installed and applied in the Pulang Copper Mine in Yunnan Province, demonstrating good application effectiveness. The results indicate that compared to traditional single monitoring methods, the multi-directional monitoring and warning system for underground debris flows has advantages such as low fault tolerance and high accuracy, making it more suitable for ensuring safe mining in mining areas.
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Roth, Christopher, Jan Hartmann, Constanze Schiewe e Stephan Staudacher. "Asymmetric Flow Phenomena Affecting the Characterization of the Control Plant of an Altitude Test Facility for Aircraft Engines". Symmetry 15, n.º 10 (14 de outubro de 2023): 1918. http://dx.doi.org/10.3390/sym15101918.
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As an indispensable part of the engine manufacturer supply chain, the eco-efficiency of altitude test facility (ATF) operations must improve. Automation is a key enabler in this context since it not only increases precision and reproducibility but also allows for reducing the test time and energy consumption. A suitable controller and reliable validation are crucial to ensure the stability and appropriate response of the control system. Both aspects necessitate a thorough understanding of the control plant, expressed in a numerical model. These models have to be suitable for control system design and validation while covering asymmetric flow phenomena that occur in the pipe system and detailing the nonlinear system dynamics to a high degree of accuracy. One-dimensional network models, state-space models, highly resolving numerical models, and data-driven models are relevant applications for this task. We compare the results of state-of-the-art one-dimensional network models which mainly imply symmetric flow conditions with those of three-dimensional Reynolds-averaged-Navier–Stokes (RANS) simulations which cover asymmetric flow phenomena. The findings show that the assumptions of idealized, axis-symmetric flow in the one-dimensional flow elements do not hold true for the complex flows in an altitude test facility. In a second step, we have compared the results of one-dimensional simulations with in-service measurements taken during ATF test campaigns. Deviations were observed, which become explainable based on the insights gained from the comparison with the RANS simulation. The findings reveal that the one-dimensional simulation-based approach is insufficient to adequately reflect the plant and subsequently for validation due to the observed asymmetric flow phenomena. To overcome this limitation, the application of an empirical first-order transfer function using system identification methods is proposed. Its applicability is successfully demonstrated for the exhaust gas section of the ATF. Subsequently, essential criteria for the design of a suitable control concept for the outlet condition are derived.
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Rezaei, Mohsen, Ahmad Ali Akbari Motlaq, Ali Rezvani Mahmouei e Seyed Hojjatollah Mousavi. "River Flow Forecasting using artificial neural network (Shoor Ghaen)". Ciência e Natura 37 (21 de dezembro de 2015): 207. http://dx.doi.org/10.5902/2179460x20849.
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In our country, most of the rivers located in dry and warm climate areas are seasonal, and many of them have experienced floods. That, along with concerns about scarcity of water resources and the need to control surface water, makes identification, modeling, and simulation of rivers’ behavior, necessary for to long-term planning and proper and rational use of river flows potential. Rainfall phenomenon and the resulting runoff in watersheds, as well as predicting them are of nonlinear system types. Artificial neural networks are able to analyze and simulate phenomena in nonlinear and uncertain system where the relationship between the components and system parameters are not well known or describable. Shoor Ghayen River, with 100 km length is the biggest seasonal river of Qaenat city and the main source of water in Farrokhi storage dam. Therefore, in this study according to the rainfall and runoff statistic of Khonik Olya hydrometric and Ghayen synoptic stations between 1976-1977 and 2010-2011 water years, precipitation phenomena and river runoff was predicted. MATLAB software is used to perform calculations. For modeling artificial neural network, 85 percent of data were used for training the proposed method, the remaining 15% were used for validating the method using 10 neurons, and a network with an error of less than 5% was developed for each month. The maximum correlation in evaluation phase was for April with the value of 0.99, and the minimum was for June and August with a value of 0.92. Overall results indicate optimum performance of artificial neural networks in predicting runoff caused by rainfall. It is also found that better results can be achieved by standardizing the data.
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Pieprzyca, J., P. Warzecha, T. Merder e M. Warzecha. "Experimental Methods of Validation for Numerical Simulation Results on Steel Flow through Tundish". Archives of Metallurgy and Materials 61, n.º 4 (1 de dezembro de 2016): 2057–60. http://dx.doi.org/10.1515/amm-2016-0331.
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Abstract The article presents experimental results on the impact of tundish flow regulator influencing the liquid steel flow course. The research was conducted based on the hybrid modelling methods understood as a complementary use of Computational Fluid Dynamics (CFD) methods and physical modelling. Dynamic development of numerical simulation techniques and accessibility to highly advanced and specialized software causes the fact that these techniques are commonly used for solving problems related to liquid flows by using analytical methods. Whereas, physical modelling is an important cognitive tool in the field of empirical identification of these phenomena. This allows for peer review and specification of the researched problems. By exploiting these relationships, a comparison of the obtained results was performed in the form of residence time distribution (RTD) curves and visualization of particular types of liquid steel flow distribution zones in the investigated tundish.
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Yin, Peng-Yeng, Ray-I. Chang, Rong-Fuh Day, Yen-Cheng Lin e Ching-Yuan Hu. "Improving PM2.5 Concentration Forecast with the Identification of Temperature Inversion". Applied Sciences 12, n.º 1 (22 de dezembro de 2021): 71. http://dx.doi.org/10.3390/app12010071.
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The rapid development of industrialization and urbanization has had a substantial impact on the increasing air pollution in many populated cities around the globe. Intensive research has shown that ambient aerosols, especially the fine particulate matter PM2.5, are highly correlated with human respiratory diseases. It is critical to analyze, forecast, and mitigate PM2.5 concentrations. One of the typical meteorological phenomena seducing PM2.5 concentrations to accumulate is temperature inversion which forms a warm-air cap to blockade the surface pollutants from dissipating. This paper analyzes the meteorological patterns which coincide with temperature inversion and proposes two machine learning classifiers for temperature inversion classification. A separate multivariate regression model is trained for the class with or without manifesting temperature inversion phenomena, in order to improve PM2.5 forecasting performance. We chose Puli township as the studied site, which is a basin city easily trapping PM2.5 concentrations. The experimental results with the dataset spanning from 1 January 2016 to 31 December 2019 show that the proposed temperature inversion classifiers exhibit satisfactory performance in F1-Score, and the regression models trained from the classified datasets can significantly improve the PM2.5 concentration forecast as compared to the model using a single dataset without considering the temperature inversion factor.
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Mathpati, Channamallikarjun S., Mayur J. Sathe e Jyeshtharaj B. Joshi. "Reply to “Comments on ‘Dynamics of Flow Structures and Transport Phenomena—Part I: Experimental and Numerical Techniques for Identification and Energy Content of Flow Structures’”". Industrial & Engineering Chemistry Research 49, n.º 9 (5 de maio de 2010): 4471–73. http://dx.doi.org/10.1021/ie100129t.
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Boby Rachmat, Kristi Agust, Nur Indri Rahayu, M Muktiarni e Tomoliyus. "Concept of Computational Fluid Dynamics and Its Application in Sport Science: Bibliometric Analysis of Modelling Thermal Comfort in Sport Hall". CFD Letters 16, n.º 1 (29 de novembro de 2023): 1–21. http://dx.doi.org/10.37934/cfdl.16.1.121.
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Computational Fluid Dynamics (CFD) has become a very effective tool in modeling and analyzing various complex phenomena, including being an integral part of analyzing thermal comfort phenomena. Therefore, this research was carried out to identify developments in the scientific literature related to research on sports science to carry out initial identification of sports hall thermal comfort modeling using dynamic computing concepts, analyzing trends and research focus in this field through bibliometrics. In addition, this research provides a comprehensive insight into the latest scientific contributions and developments in the field of sports science as an initial identification of sports hall thermal comfort modeling using a dynamic computing approach. Bibliometric analysis and theoretical analysis were chosen as research methods. This research also consists of five steps, namely (i) determining the theme and sources of research data; (ii) article data collection; (iii) data processing, (iv) bibliometric analysis, and (v) report preparation. "Computational Fluid Dynamics Design (CFD) in Sport Science" was used as a keyword in this research. Based on the search results, 823 documents were obtained from 1996 to 2023. Research on CFD in sports science will increase in 2022. Many countries, affiliates, and authors have contributed to increasing the number of publications on CFD in sports science, such as the United States with a total of 103 publications. With this research, it is hoped that it will provide insight to researchers, practitioners, and policymakers regarding research directions that may not have been fully explored in the application of CFD in the field of sports in particular, as well as other fields.
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Mao, Beibei, Hua Yang, Fei Sun, Ying Zhang e Xinrui Zhang. "A Spatial Correlation Identification Model for Coherent Structure Extraction and Three-Dimensional Visualization". Journal of Marine Science and Engineering 12, n.º 3 (14 de março de 2024): 483. http://dx.doi.org/10.3390/jmse12030483.
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Multi-scale coherent structures have been observed in ocean currents, which are induced by the interaction of shear flows with different velocities. Understanding the spatial configuration and scale characteristics of coherent structures will promote the explanation of physical ocean phenomena. Considering the self-similarity, we propose a spatial correlation identification model for coherent structure extraction and three-dimensional visualization based on the wavelet transform and time-dependent intrinsic correlation method. The spatial and scale distributions of coherent structures are related to the dissipation rate variation. Most large-scale coherent structures, with the largest length scale of 13 m, are found to exist in stable fluid, such as the water column below 50 m. However, small-scale structures are found in chaotic fluids, such as the upper layer. Furthermore, we found that coherent structures of different scales coexist simultaneously in the same depth range, indicating a simultaneous multi-scale structure pattern for turbulent flow investigations.
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Schuster, Cristiano Henrique, Jean Jonathan Schuster, Eduardo Stüker, Daniel Michelon dos Santos, Luiz Eduardo Medeiros, Felipe Denardin Costa, Luis Gustavo Nogueira Martins, Giuliano Demarco e Otávio Costa Acevedo. "IDENTIFICATION AND ESTIMATION OF THE PERIOD OF NON TURBULENT OSCILLATORY PROCESSES IN THE STABLE BOUNDARY LAYER THROUGH AUTOCORRELATION FUNCTIONS". Ciência e Natura 38 (20 de julho de 2016): 312. http://dx.doi.org/10.5902/2179460x20240.
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The autocorrelation function of the flow speed components, measures the relationship that the speed in a certain instant, has with the speed at an earlier instant. In some conditions, in the atmospheric flow, this autocorrelation presents a low frequency oscillatory shape, presenting negative lobes. This behavior is known as meandering phenomenon and becomes prevalent in low wind conditions. The objective of this study is to compare the adjustments of autocorrelation functions, present in the literature, with trial of the experimental data of FLOOSS II experiment, for determining the meandering oscillation period. Initially, three selection criteria were used to select the windows of analysis. Among the criteria the magnitude of the wind showed the most satisfactory. The fitting curves showed that both autocorrelation functions performed well, even with a large variability of oscillation periods that were found. The great variability in the oscillation period of the meandering phenomena can be associated with the nature of the physical phenomenon that is responsible for its origin. However, this hypothesis needs confirmation.
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Pátý, Marek, Michael Valášek, Emanuele Resta, Roberto Marsilio e Michele Ferlauto. "Passive Control of Vortices in the Wake of a Bluff Body". Fluids 9, n.º 6 (31 de maio de 2024): 131. http://dx.doi.org/10.3390/fluids9060131.
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Vortices belong to the most important phenomena in fluid dynamics and play an essential role in many engineering applications. They can act detrimentally by harnessing the flow energy and reducing the efficiency of an aerodynamic device, whereas in other cases, their presence can be exploited to achieve targeted flow conditions. The control of the vortex parameters is desirable in both cases. In this paper, we introduce an optimization strategy for the control of vortices in the wake of a bluff body. Flow modelling is based on RANS and DES computations, validated by experimental data. The algorithm for vortex identification and characterization is based on the triple decomposition of motion. It produces a quantitative measure of vortex strength which is used to define the objective function in the optimization procedure. It is shown how the shape of an aerodynamic device can be altered to achieve the desired characteristics of vortices in its wake. The studied case is closely related to flame holders for combustion applications, but the conceptual approach has a general applicability to vortex control.
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Bou-Said, B., e J. P. Chaomleffel. "Hybrid Journal Bearings: Theoretical and Experimental Results". Journal of Tribology 111, n.º 2 (1 de abril de 1989): 265–69. http://dx.doi.org/10.1115/1.3261903.
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The analysis of actual lubrication problems needs to take into account particularities in the flow coming from kinematic conditions and contact geometry. For hybrid journal bearings lubricated by low dynamic viscosity fluid, turbulence and pressure drops due to inertia forces in the recess outlets are phenomena which must be taken into account to compute their working characteristics. A global method of study of lubricated contacts in isothermal laminar or not laminar flow by finite element method is presented. It can solve a great number of lubrication problems. A new type of approximation element for lubrication (Hermitian type) is used because it offers the following advantages: The nonlinearities in lubrication which come from turbulence phenomena, geometrical discontinuities (pressure drops) or boundary conditions (recess pressure) require the derivation of unknown functions. Added interpolations are not necessary to determine these values because the nodal unknowns are the values of the function and its derivatives in the two directions. As the modified Reynolds equation is in Cartesian coordinates, in the case of closed geometries such as journal bearings, joining is done just by nodal identification which guarantees continuity of the pressure and of its derivatives. The validity of this numerical model is realized with an experimental study done with a three recess hybrid journal bearing for different kinematic and geometric configurations. In a general way, experimental and theoretical results are in good agreement.
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Rood, E. P. "Review—Mechanisms of Cavitation Inception". Journal of Fluids Engineering 113, n.º 2 (1 de junho de 1991): 163–75. http://dx.doi.org/10.1115/1.2909476.
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A review is made of progress in research during the period 1979–1989 on the fundamental physical mechanisms of hydrodynamic cavitation inception. During that decade identification of the physical phenomena has been made, and techniques have been developed to reproduce on laboratory scale selected forms of full scale cavitation inception. Understanding of the mechanisms remains shallow, and analytical/numerical prediction methods are nonexistent except for the restricted case of travelling bubble cavitation inception in a passive pressure field. The control of inception is seen to be related in part to control of the underlying viscous flow features. A growing body of experimental evidence points to microscale vortex cavitation as a primal inception event.
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Gibiino, Gian Piero, Alberto Santarelli e Fabio Filicori. "Charge-conservative GaN HEMT nonlinear modeling from non-isodynamic multi-bias S-parameter measurements". International Journal of Microwave and Wireless Technologies 11, n.º 5-6 (8 de fevereiro de 2019): 431–40. http://dx.doi.org/10.1017/s1759078719000059.
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AbstractGuaranteeing charge conservation of empirically extracted Gallium Nitride (GaN) High-Electron-Mobility Transistor (HEMT) models is necessary to avoid simulation issues and artifacts in the prediction. However, dispersive effects, such as thermal and charge-trapping phenomena, may compromise the model extraction flow resulting in poor model accuracy. Although GaN HEMT models should be extracted, in principle, from an isodynamic dataset, this work deals with the systematic identification of an approximate, yet most suitable, charge-conservative empirical model from standard multi-bias S-parameters, i.e., from non-isodynamic data. Results show that the obtained model maintains a reasonable accuracy in predicting both small- and large-signal behavior, while providing the benefits of charge conservation.
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Poets, Christian F., Martin P. Samuels e David P. Southall. "Potential Role of Intrapulmonary Shunting in the Genesis of Hypoxemic Episodes in Infants and Young Children". Pediatrics 90, n.º 3 (1 de setembro de 1992): 385–91. http://dx.doi.org/10.1542/peds.90.3.385.
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A number of physiologic phenomena during some apneic/cyanotic episodes in infants and young children cannot be explained sufficiently on the basis of a cessation or reduction in aveolar ventilation alone. These include (1) the extremely rapid development of hypoxemia during some episodes, (2) the occurrence of hypoxemic episodes despite continuous ventilation, (3) differences in the speed of desaturation between different forms of apneic episodes, (4) the presence of continued breathing efforts and yet absent airflow despite bypass of the upper airway, and (5) evidence that apnea and hypoxemia may begin simultaneously. Potential mechanisms to explain these phenomena include the sudden development of an unevenness in the matching between ventilation and lung perfusion, the flow of blood through unventilated areas of lung, and a sudden impairment in gas diffusion. Evidence from physiological and morphological studies suggests that all of these mechanisms, although to a different extent, may be involved in apneic/cyanotic episodes. The recognition that nonapneic mechanisms can cause sudden profound hypoxemia may alter our approach to the identification, treatment, and prevention of these episodes.
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Zhang, Xinshuai, Tingwei Ji, Fangfang Xie, Changdong Zheng e Yao Zheng. "Data-driven nonlinear reduced-order modeling of unsteady fluid–structure interactions". Physics of Fluids 34, n.º 5 (maio de 2022): 053608. http://dx.doi.org/10.1063/5.0090394.
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A novel data-driven nonlinear reduced-order modeling framework is proposed for unsteady fluid–structure interactions (FSIs). In the proposed framework, a convolutional variational autoencoder model is developed to determine the coordinate transformation from a high-dimensional physical field into a reduced space. This enables the efficient extraction of nonlinear low-dimensional manifolds from the high-dimensional unsteady flow field of the FSIs. The sparse identification of a nonlinear dynamics (SINDy) algorithm is then used to identify the dynamical governing equations of the reduced space and the vibration responses. To investigate and validate the effectiveness of the proposed framework for modeling and predicting unsteady flow fields in FSI problems, the two-dimensional laminar vortex shedding of a fixed cylinder is considered. Furthermore, the proposed data-driven nonlinear reduced-order modeling framework is applied to the three-dimensional vortex-induced vibration of a flexible cylinder. Using the SINDy model to analyze the vibration responses, the dynamics of the flexible cylinder are found to be correlated with the flow wake patterns, revealing the underlying FSI mechanism. The present work is a significant step toward the establishment of machine learning-based nonlinear reduced-order models for complex flow phenomena, the discovery of underlying unsteady FSI physics, and real-time flow control.
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Xu, Guixing, Ping Yu, Ping Xu e Donghua Zheng. "Identification of separation phenomenon during brain death determination of potential organ donor and analysis of relative factors". International Surgery Journal 7, n.º 5 (23 de abril de 2020): 1347. http://dx.doi.org/10.18203/2349-2902.isj20201845.
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Background: With analyzing the incongruent phenomenon of electrical active and cerebral blood flow in brain death determination and screening the related factors, offer correct explanations and countermeasure to ensure the successful implementation of donation after brain death.Methods: Relevant clinical data of potential brain death organ donors were prospectively collected between June 2018 and May 2019. The related parameters of neurological examination, laboratory examination and neuroimaging examination during the period of brain death determination were dynamically recorded. Separation phenomenon was used as grouping factors to screen the factors related to separation phenomena through univariate and multivariate analysis.Results: According to the inclusion criteria, 127 patients were included in the study. Among 22 patients (17.3%) with incongruent phenomenon, 17 (77.3%) had electrical silence earlier than cerebral blood flow arrest, and 9 (22.7%) had cerebral blood flow arrest earlier than electrical silence. Univariate and multivariate analysis showed that age <14 years (OR=6.25, 95%CI 1.21-32.22, p=0.028), SBP≥140 mmHg (OR=7.43, 95%CI 1.62-33.99, p=0.010), primary brainstem injury (OR=15.89, 95%CI 3.04-82.93, p=0.006), spontaneous respiratory arrest time ≤72 hours (OR=11.96, 95%CI 1.59-89.78, p=0.009) and decompression craniotomy(unilateral or bilateral) (OR=16.28, 95%CI 2.25-117.73, p=0.001) were associated with separation phenomenon..Conclusions: Separation phenomenon is a common during the confirmation test of brain death determination in China, and should be correctly recognized. To adopt corresponding measures according to risk factors is useful for successful implementation of donation after brain death.
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Rizzo, Fabio, Chiara Bedon, Sulyman Mansour, Aleksander Pistol, Maria Francesca Sabbà, Łukasz Flaga, Renata Klaput e Dora Foti. "Dynamics of a Flexible Roof Test Model under Ambient Vibrations Measurements". Applied Sciences 13, n.º 7 (24 de março de 2023): 4135. http://dx.doi.org/10.3390/app13074135.
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Flexible roofs are sensitive to wind actions because they are light, and their deformability can induce local or global instability. In most cases, their design requires experimental wind tunnel testing to investigate the aeroelastic phenomena and the structural response under the wind. However, the reduced scale necessary in wind tunnels makes the dynamic identification of the test model difficult. Several approaches of multi-modal dynamic identification can be used, even if a specific approach is not defined for geometric nonlinear flexible roofs. Many times, the choice of the position of the sensors is affected by the unknown roof dynamics. This paper investigates the ambient vibration time-dependent accelerations for a flexible roof scaled model through Singular Value Decomposition (SVD) and their spatial correlations with the purpose of analyzing the signal structure and its acquisition to perform the dynamic identification of the test model.
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Kim, Hyoung Tae, e Jongtae Kim. "MELCOR Analysis of a SPARC Experiment for Spray-PAR Interaction during a Hydrogen Release". Energies 13, n.º 21 (30 de outubro de 2020): 5696. http://dx.doi.org/10.3390/en13215696.
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A series of experiments were performed in the SPARC (spray-aerosol-recombiner-combustion) test facility to simulate a hydrogen mitigation system with the actuation of a PAR (passive auto-catalytic re-combiner) and spray system. In this study, the SPARC-SPRAY-PAR (SSP1) experiment is chosen to benchmark the MELCOR (a lumped-parameter code for severe accident analysis) predictions against test data. For this purpose, firstly we prepared the base input model of the SPARC test vessel, and tested it by a simple verification problem with well-defined boundary conditions. The implementation of a currently used PAR correlation in MELCOR is shown to be appropriate for the simulation of a PAR actuation experiment. In an SSP1 experiment, the PAR is reacting with hydrogen, and the spray actuation starts as soon as hydrogen injection is complete. The MELCOR simulation well predicts the pressure behavior and the gas flow affected by operating both a PAR and spray system. However, the local hydrogen concentration measurement near the inlet nozzle is much higher than the volume average-value by MELCOR, since high jet flow from the nozzle is dispersed in the corresponding cell volume. The experimental reproduction of the phenomena we expect, or, conversely, the identification of phenomena we do not understand, will continue to support the verification of analytical models using experimental data and to analyze the impact of spray on PAR operations in severe accident conditions.
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GIONA, MASSIMILIANO, ALESSANDRO PAGLIANTI e ALFREDO SOLDATI. "THE APPLICATION OF DIFFUSIONAL TECHNIQUES IN TIME-SERIES ANALYSIS TO IDENTIFY COMPLEX FLUID DYNAMIC REGIMES". Fractals 02, n.º 04 (dezembro de 1994): 503–20. http://dx.doi.org/10.1142/s0218348x94000727.
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The diffusional analysis of time series is introduced and compared with corresponding results derived from rescaled-range (R/S) techniques. It is shown by means of simple examples that diffusional analysis is able to capture some details of the statistics of the time series which can become lost when other techniques (e.g. R/S) are applied. Examples of the application of this method to chaotic time series are briefly discussed. The problem of the identification of fluid dynamic regimes is investigated in detail by considering experimental time series derived from two-phase flow measurement in tubes. The results obtained confirm the validity of this method in dealing with time series derived from periodic or quasiperiodic phenomena with superimposed stochastic perturbations.
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Niccolini Marmont Du Haut Champ, Carlo Alberto, Paolo Silvestri, Federico Reggio, Mario Luigi Ferrari e Aristide Fausto Massardo. "Early surge detection on a turbocharger used to pressurize a SOFC plant emulator". E3S Web of Conferences 414 (2023): 02008. http://dx.doi.org/10.1051/e3sconf/202341402008.
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High-speed centrifugal compressors are commonly exploited to pressurize fuel cell-based hybrid energy systems. In such complex plants, because of significant interposed volumes due to fuel cells, dynamic compressor response can induce severe vibrations caused by low mass flow rates instability. In particular, surge strongly limits centrifugal compressors stable working region when moving towards low mass flow rate due to a change in system operating point. Consequently, a complete system identification is performed in order to adequately characterize compressor dynamic response for early surge detection. To this goal, a tailored experimental activity has been carried out at the Thermochemical Power Group of the University of Genoa on a vaneless diffuser compressor turbocharger used for the pressurization of an innovative solid oxide fuel cell (SOFC) emulator plant. Several post-processing methods have been performed on system vibro-acoustic responses to better predict and classify compressor status as stable or unstable. The obtained results provide original diagnostic insights for monitoring systems capable of preventing surge and other low mass flow unstable phenomena, such as rotating stall cells inception. Low mass flow rate fluid-dynamic instabilities prevention can extend compressor operating range, performance, and reliability to allow better integration with other plant components.
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Maslennikov, V. V., e A. V. Larionov. "Conceptual Approaches to the Development of a Cash Flow Classifier". Vestnik of the Plekhanov Russian University of Economics, n.º 3 (21 de junho de 2023): 90–101. http://dx.doi.org/10.21686/2413-2829-2023-3-90-101.
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Cash flows are a convenient source of operational information for analyzing the state of the economy. Obtaining this information will ensure the use of operational regulatory tools to achieve the goals of economic security. The purpose of the study is to conceptualize the problem of creating a domestic classifier of cash flows, which acts as an early identification tool for crisis phenomena in the economy. The authors systematize foreign and domestic approaches to the creation of a classifier of cash flows, the organization of monitoring of the volatility of cash flows. The article reveals the differences between the classifier of payments and cash flows, identifies the key limitations associated with the creation of the classifier. There are three levels of cash flows: individual, group and territorial. These levels can form the basis of the created cash flow classifier. The authority to monitor cash flows should be assigned to the Bank of Russia. Considering the prospects of expanding the capabilities of the Bank of Russia's payment system and the introduction of the digital ruble, the Bank of Russia can collect and promptly analyze information about cash flows. The object of monitoring is the level of volatility of cash flows. Subsequently, the information received can be automatically transmitted to the relevant authority for the use of state regulation tools.
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Gkirmpas, Panagiotis, George Tsegas, Giannis Ioannidis, Christos Vlachokostas e Nicolas Moussiopoulos. "Identification of an Unknown Stationary Emission Source in Urban Geometry Using Bayesian Inference". Atmosphere 15, n.º 8 (23 de julho de 2024): 871. http://dx.doi.org/10.3390/atmos15080871.
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Estimating the parameters of an unidentified toxic pollutant source is crucial for public safety, especially in densely populated urban areas. Implementing source term estimation methods in real-world urban environments is challenging due to complex phenomena and the absence of concentration observational data. This work combines a computational fluid dynamics numerical simulation with the Metropolis–Hastings MCMC algorithm to identify the location and quantify the release rate of an unknown source within the geometry of Augsburg city center. To address the lack of concentration measurements, synthetic observations are generated by a forward dispersion model. The methodology is tested using these datasets, both as directly calculated by the forward model and with added Gaussian noise under different source release and wind flow scenarios. The results indicate that in most cases, both the source location and the release rate are estimated accurately. Although a higher performance is achieved using synthetic datasets without additional noise, high accuracy predictions are also obtained in many applications of noisy measurement datasets. In general, the outcomes demonstrate that the presented methodology can be a useful tool for estimating unknown source parameters in real-world urban applications.
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Shandrivska, O., e N. Shynkarenko. "APPLIED RISK ASSESSMENT IN THE SYSTEM OF SOCIO-ECONOMIC PROCESSES IN CYBERSPACE". Journal of Lviv Polytechnic National University. Series of Economics and Management Issues 4, n.º 2 (10 de novembro de 2020): 94–105. http://dx.doi.org/10.23939/semi2020.02.094.
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In the paper investigated safety of socio-economic processes in the virtual space. Studied the main trends influence on formation of preventive and adaptive mechanisms for ensuring information and cyber security enterprises. Key trends of the modern business and social environment include: globalization, informatization and individualization of consumer needs; mediatization, territorialization and universalization of social phenomena. Presented an original ensuring security model for the virtual information sphere. In this model was invented a conceptual scheme for identifying the information security system: given the identification sequence and risks assessment in cyberspace by stages; risk identification; a description of the threats it poses; identification of vulnerable market segments; analysis and assessment of the risk occurrence probability level; analysis and assessment of the risk manifestation consequences level; score determination of the general rick level; proposal to eliminate the development environment risks of the study object; net risk identification; risks in cyberspace have been identified and assessed in terms of security and financial flows. Among the dominant risks of the external and internal security environment in the information virtual Ukrainian space the following are highlighted: insufficient system security, processes and technologies, disinformation and information asymmetry; high sensitivity of financial flows to the processes of the implementation of shock macroeconomic phenomena (including almost unsignificant currencies devaluation against the pandemic background) in terms of the safety of financial flows; technical, technological and personal vulnerability growth in the information sphere, due to the increasing cybercrime in terms of the information flow security. Among the mitigation measures and neutralization of the general risk level, was proposed the creation of a single protection system. The single data protection system should be based on: data protection progressive principles, tasks to ensure security from information influences, information infrastructure security, information rights, open access to information, publicity of open information, etc.; organizational and right mechanism of data protection. This mechanism is based on the need to streamline the responsibilities of information marked actors; state control over data manipulation; data manipulation standards development; information systems certification for their processing. Construction of database registers, as well as registration of owners and/or data administrators, third parties to whom the data was transferred for further manipulation; an independent coordination center formation for the state policy implementation in terms of monitoring compliance with data protection requirements, etc.; increasing the financial flow transparency, namely risk-oriented monitoring in digital currency exchanges and licensing of transactions in virtual currencies requires support from the Financial Action Task Force on Money Laundering and the Financial Intelligence Unit.