Journal articles on the topic 'Double flux schemes'
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1
Nikitina, I., A. Polyakov, and D. Voronin. "EXPERIMENTAL MEASURES TO IMPROVE THERMAL CHARACTERISTICS IN DOUBLE-SIDED FACE GRINDING MACHINES." Bulletin of Belgorod State Technological University named after. V. G. Shukhov 7, no. 9 (September 16, 2022): 116–26. http://dx.doi.org/10.34031/2071-7318-2022-7-9-116-126.
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The results of full-scale and computational experiments to improve the thermal characteristics of the machine tool are presented. This can lead to a decrease or achieve symmetry of the resulting thermal deformations. The implementation of four schemes for the redistribution of heat fluxes is considered: the heat flux of the main electric motors, directed under the protective casing of the drive pulley, and the heat flux of the belt drive are removed through special windows in the casing to the environment; jointly with the first scheme of redistribution of heat fluxes, cooling of the ends of the grinding headstocks is provided with the help of an impeller fixed on each drive pulley; jointly with the second scheme, heat flux isolation from the left and right electric motors is provided; heating the ends of the machine tool bed. The first three schemes are implemented at idling of the machine tool; the fourth scheme is implemented when the machine is operating under thermal load. The joint implementation of three schemes makes it possible to reduce the displacement of the right circle at idle by 1.5 times, the left circle practically did not move. The test of the first three circuits during the operation of the machine tool under a thermal load does not reveal significant changes in the thermal characteristics. The implementation of the fourth heat flux redistribution scheme help to compensate for thermal deformations from heating in the central part of the bed and reduce changes in the angular position of the grinding wheels.
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Naumann, A. K., A. Seifert, and J. P. Mellado. "A refined statistical cloud closure using double-Gaussian probability density functions." Geoscientific Model Development 6, no. 5 (October 8, 2013): 1641–57. http://dx.doi.org/10.5194/gmd-6-1641-2013.
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Abstract. We introduce a probability density function (PDF)-based scheme to parameterize cloud fraction, average liquid water and liquid water flux in large-scale models, that is developed from and tested against large-eddy simulations and observational data. Because the tails of the PDFs are crucial for an appropriate parameterization of cloud properties, we use a double-Gaussian distribution that is able to represent the observed, skewed PDFs properly. Introducing two closure equations, the resulting parameterization relies on the first three moments of the subgrid variability of temperature and moisture as input parameters. The parameterization is found to be superior to a single-Gaussian approach in diagnosing the cloud fraction and average liquid water profiles. A priori testing also suggests improved accuracy compared to existing double-Gaussian closures. Furthermore, we find that the error of the new parameterization is smallest for a horizontal resolution of about 5–20 km and also depends on the appearance of mesoscale structures that are accompanied by higher rain rates. In combination with simple autoconversion schemes that only depend on the liquid water, the error introduced by the new parameterization is orders of magnitude smaller than the difference between various autoconversion schemes. For the liquid water flux, we introduce a parameterization that is depending on the skewness of the subgrid variability of temperature and moisture and that reproduces the profiles of the liquid water flux well.
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Naumann, A. K., A. Seifert, and J. P. Mellado. "A refined statistical cloud closure using double-Gaussian probability density functions." Geoscientific Model Development Discussions 6, no. 1 (February 18, 2013): 1085–125. http://dx.doi.org/10.5194/gmdd-6-1085-2013.
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Abstract. We introduce a probability density function (PDF) based scheme to parameterize cloud fraction, average liquid water and liquid water flux in large-scale models, that is developed from and tested against large-eddy simulations and observational data. Because the tails of the PDFs are crucial for an appropriate parameterization of cloud properties, we use a double-Gaussian distribution that is able to represent the observed, skewed PDFs properly. Introducing two closure equations, the resulting parameterization relies on the first three moments of the subgrid variability of temperature and moisture as input parameters. The parameterization is shown to be clearly superior to a single-Gaussian approach in diagnosing the cloud fraction and average liquid water profiles and improves existing double-Gaussian closures. We find that the error of the new parameterization is smallest for a horizontal resolution of about 5–20 km and also depends on the appearance of mesoscale structures that are accompanied by higher rain rates. In combination with simple autoconversion schemes that only depend on the liquid water, the error introduced by the new parameterization is orders of magnitude smaller than the difference between various autoconversion schemes. For the liquid water flux, we introduce a parameterization that is depending on the skewness of the subgrid variability of temperature and moisture and that reproduces the profiles of the liquid water flux well.
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Zhu, Huajun, Xiaogang Deng, Meiliang Mao, Huayong Liu, and Guohua Tu. "Osher Flux with Entropy Fix for Two-Dimensional Euler Equations." Advances in Applied Mathematics and Mechanics 8, no. 4 (May 27, 2016): 670–92. http://dx.doi.org/10.4208/aamm.2014.m469.
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AbstractWe compare in this paper the properties of Osher flux with O-variant and P-variant (Osher-O flux and Osher-P flux) in finite volume methods for the two-dimensional Euler equations and propose an entropy fix technique to improve their robustness. We consider both first-order and second-order reconstructions. For inviscid hypersonic flow past a circular cylinder, we observe different problems for different schemes: A first-order Osher-O scheme on quadrangular grids yields a carbuncle shock, while a first-order Osher-P scheme results in a dislocation shock for high Mach number cases. In addition, a second-order Osher scheme can also yield a carbuncle shock or be unstable. To improve the robustness of these schemes we propose an entropy fix technique, and then present numerical results to show the effectiveness of the proposed method. In addition, the influence of grid aspects ratio, relative shock position to the grid and Mach number on shock stability are tested. Viscous heating problem and double Mach reflection problem are simulated to test the influence of the entropy fix on contact resolution and boundary layer resolution.
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Song, Xiaoliang, and Guang Jun Zhang. "Convection Parameterization, Tropical Pacific Double ITCZ, and Upper-Ocean Biases in the NCAR CCSM3. Part I: Climatology and Atmospheric Feedback." Journal of Climate 22, no. 16 (August 15, 2009): 4299–315. http://dx.doi.org/10.1175/2009jcli2642.1.
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Abstract The role of convection parameterization in the formation of double ITCZ and associated upper-ocean biases in the NCAR Community Climate System Model, version 3 (CCSM3) is investigated by comparing the simulations using the original and revised Zhang–McFarlane (ZM) convection schemes. Ten-year model climatologies show that the simulation with the original ZM scheme produces a typical double ITCZ bias, whereas all biases related to the spurious double ITCZ and overly strong cold tongue in precipitation, sea surface temperature (SST), wind stress, ocean thermocline, upper-ocean currents, temperature, and salinity are dramatically reduced when the revised ZM scheme is used. These results demonstrate that convection parameterization plays a critical role in the formation of double ITCZ bias in the CCSM3. To understand the physical mechanisms through which the modifications of the convection scheme in the atmospheric model alleviate the double ITCZ bias in the CCSM3, the authors investigate the impacts of convection schemes on the atmospheric forcing and feedback in the uncoupled Community Atmospheric Model, version 3 (CAM3). It is shown that the CAM3 simulation with the original ZM scheme also produces a signature of double ITCZ bias in precipitation, whereas the simulation with the revised ZM scheme does not. Diagnostic analyses have identified three factors on the atmospheric side (i.e., the sensitivity of convection to SST, the convection–shortwave flux–SST feedback, and the convection–wind–evaporation–SST feedback) that may contribute to the differences in the coupled simulations.
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Parkes, Ben, Alan Gadian, and John Latham. "The Effects of Marine Cloud Brightening on Seasonal Polar Temperatures and the Meridional Heat Flux." ISRN Geophysics 2012 (May 8, 2012): 1–7. http://dx.doi.org/10.5402/2012/142872.
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Marine cloud brightening (MCB) is one of several proposed solar radiation management (SRM) geoengineering schemes designed to ameliorate some of the undesirable effects of climate change, for example polar ice loss and associated increased sea levels. Satellite measurements over the last 40 years show a general reduction in polar sea ice area and thickness which is attributed to climate change. In our studies, HadGEM1, a fully coupled climate model, is used to predict changes in surface temperatures and ice cover as a result of implementing MCB in a double carbon dioxide concentration atmosphere. The meridional heat flux (MHF) is the mechanism within the earth system for the transport of energy from tropical to polar regions. This poleward transport of heat in a double carbon dioxide atmosphere amplifies the effects in polar regions, where it has a significant impact on both temperatures and ice cover. The results from this work show that MCB is capable of roughly restoring control temperatures and ice cover (where control is defined as 440 ppm carbon dioxide, a predicted 2020 level) in a double carbon dioxide atmosphere scenario. This work presents the first results on the impact of MCB on the MHF and the ability of the MCB scheme to restore the MHF to a control level.
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Bae, Soo Ya, Song-You Hong, and Kyo-Sun Sunny Lim. "Coupling WRF Double-Moment 6-Class Microphysics Schemes to RRTMG Radiation Scheme in Weather Research Forecasting Model." Advances in Meteorology 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/5070154.
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A method to explicitly calculate the effective radius of hydrometeors in the Weather Research Forecasting (WRF) double-moment 6-class (WDM6) microphysics scheme is designed to tackle the physical inconsistency in cloud properties between the microphysics and radiation processes. At each model time step, the calculated effective radii of hydrometeors from the WDM6 scheme are linked to the Rapid Radiative Transfer Model for GCMs (RRTMG) scheme to consider the cloud effects in radiative flux calculation. This coupling effect of cloud properties between the WDM6 and RRTMG algorithms is examined for a heavy rainfall event in Korea during 25–27 July 2011, and it is compared to the results from the control simulation in which the effective radius is prescribed as a constant value. It is found that the derived radii of hydrometeors in the WDM6 scheme are generally larger than the prescribed values in the RRTMG scheme. Consequently, shortwave fluxes reaching the ground (SWDOWN) are increased over less cloudy regions, showing a better agreement with a satellite image. The overall distribution of the 24-hour accumulated rainfall is not affected but its amount is changed. A spurious rainfall peak over the Yellow Sea is alleviated, whereas the local maximum in the central part of the peninsula is increased.
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Vettoliere, Antonio, and Carmine Granata. "Picoammeters Based on Gradiometric Superconducting Quantum Interference Devices." Applied Sciences 12, no. 18 (September 8, 2022): 9030. http://dx.doi.org/10.3390/app12189030.
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High-sensitivity ac current sensors based on a superconducting quantum interference device have been designed, fabricated and characterized. In particular, double-washer schemes in either parallel or series configurations have been considered. The advantages and the drawbacks of both configurations have been examined by measuring the main features and parameters, such as the flux-to-voltage characteristic, the magnetic field spectral noise and flux-to-current transfer factor. The devices are designed to have similar flux-to-current transfer factors and are fabricated on the same chip to avoid differences in parameters due to the fabrication process. Both devices exhibited a current sensitivity as low as 1–2 pA per bandwidth unit, allowing for their use in ultrahigh-sensitivity applications.
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Payeur, Guillaume, Étienne Artigau, Laurence Perreault Levasseur, and René Doyon. "Correlated Read Noise Reduction in Infrared Arrays Using Deep Learning." Astronomical Journal 163, no. 6 (May 25, 2022): 292. http://dx.doi.org/10.3847/1538-3881/ac69d2.
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Abstract We present a new procedure rooted in deep learning to construct science images from data cubes collected by astronomical instruments using HxRG detectors in low-flux regimes. It improves on the drawbacks of the conventional algorithms to construct 2D images from multiple readouts by using the readout scheme of the detectors to reduce the impact of correlated readout noise. We train a convolutional recurrent neural network on simulated astrophysical scenes added to laboratory darks to estimate the flux on each pixel of science images. This method achieves a reduction of the noise on constructed science images when compared to standard flux-measurement schemes (correlated double sampling, up-the-ramp sampling), which results in a reduction of the error on the spectrum extracted from these science images. Over simulated data cubes created in a low signal-to-noise ratio regime where this method could have the largest impact, we find that the error on our constructed science images falls faster than a 1 / N decay, and that the spectrum extracted from the images has, averaged over a test set of three images, a standard error reduced by a factor of 1.85 in comparison to the standard up-the-ramp pixel sampling scheme. The code used in this project is publicly available on GitHub 7 7 https://github.com/GuillaumePayeur/HxRG-denoiser
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Kumar, Sarvesh, Ricardo Oyarzúa, Ricardo Ruiz-Baier, and Ruchi Sandilya. "Conservative discontinuous finite volume and mixed schemes for a new four-field formulation in poroelasticity." ESAIM: Mathematical Modelling and Numerical Analysis 54, no. 1 (January 2020): 273–99. http://dx.doi.org/10.1051/m2an/2019063.
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We introduce a numerical method for the approximation of linear poroelasticity equations, representing the interaction between the non-viscous filtration flow of a fluid and the linear mechanical response of a porous medium. In the proposed formulation, the primary variables in the system are the solid displacement, the fluid pressure, the fluid flux, and the total pressure. A discontinuous finite volume method is designed for the approximation of solid displacement using a dual mesh, whereas a mixed approach is employed to approximate fluid flux and the two pressures. We focus on the stationary case and the resulting discrete problem exhibits a double saddle-point structure. Its solvability and stability are established in terms of bounds (and of norms) that do not depend on the modulus of dilation of the solid. We derive optimal error estimates in suitable norms, for all field variables; and we exemplify the convergence and locking-free properties of this scheme through a series of numerical tests.
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Gerard, Luc. "Bulk Mass-Flux Perturbation Formulation for a Unified Approach of Deep Convection at High Resolution." Monthly Weather Review 143, no. 10 (October 1, 2015): 4038–63. http://dx.doi.org/10.1175/mwr-d-15-0030.1.
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Abstract Parameterizing deep convection at model resolutions of a few kilometers or less requires diverging from several simplifying assumptions valid at coarser resolutions. The separation or complementarity between the deep-convection scheme and the model cloud scheme must be addressed properly to prevent a double counting of some phenomena, account for evolution in time, and keep consistent results while approaching resolutions where deep convection can be treated explicitly (without parameterization). In this paper, the author formulates and tests a perturbation approach of the bulk mass-flux representation of deep convective updrafts and downdrafts. The subgrid deep-convection scheme represents only the effect of the unresolved part of the real updrafts, complementing an explicit part associated with the mean gridbox vertical velocity. Special attention is paid to the ordering and interactions of the moist parameterizations, the formulation of the closure and of the triggering, and the accounting of time evolution aspects. The multiresolution behavior of the scheme is assessed in the operational numerical prediction model ALARO [a version of the Action de Recherche Petite Echelle Grande Echelle-Aire Limitée Adaptation Dynamique Développement International (ARPEGE-ALADIN) operational limited area model with a revised and modular structure of the physical parameterizations]. Unlike most mass-flux schemes, the parameterized part gradually fades out when the model resolution is increased, allowing the results to approach those of an explicit treatment of deep convection.
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Akbarzadeh, M., and M. J. Kermani. "NUMERICAL SIMULATIONS OF INVISCID AIRFLOWS IN RAMJET INLETS." Transactions of the Canadian Society for Mechanical Engineering 33, no. 2 (June 2009): 271–96. http://dx.doi.org/10.1139/tcsme-2009-0021.
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The performances of three different ramjet inlets and an entire ramjet are numerically studied in this paper. The fluid is assumed to be inviscid. Inlet 1 is a SCRAMJET inlet and is chosen from the literature. Inlets 2 and 3 are instead designed based on the Oswatitsch principle. Inlets 2 and 3 produce a series of oblique shocks merging at the engine cowl lip followed by a terminating normal shock just downstream of the inlet throat. In ramjet, the combustion is modeled using a non-uniform volumetric heat source distributed in the combustor area. The position of the terminating normal shock in Inlets 2 and 3 is controlled via the inlet’s back pressure. Instead, in ramjet it is bounded by the amount of heat rate added in combustor and the exhaust nozzle throat area. For the numerical simulations, the Roe (1981) and MacCormack (1969) schemes are used. To prevent the spurious numerical oscillations in high resolution computations by Roe scheme the van Albada flux limiter (1982) is used, while in MacCormack scheme artificial viscosity terms are added to damp the oscillations. To double check the accuracy of the computations, the Fluent software package has also been used. Comparisons show very good agreement.
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Shankar, Usha, Neminath B. Naduvinamani, and Hussain Basha. "A generalized perspective of Fourier and Fick’s laws: Magnetized effects of Cattaneo-Christov models on transient nanofluid flow between two parallel plates with Brownian motion and thermophoresis." Nonlinear Engineering 9, no. 1 (April 23, 2020): 201–22. http://dx.doi.org/10.1515/nleng-2020-0009.
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AbstractPresent research article reports the magnetized impacts of Cattaneo-Christov double diffusion models on heat and mass transfer behaviour of viscous incompressible, time-dependent, two-dimensional Casson nanofluid flow through the channel with Joule heating and viscous dissipation effects numerically. The classical transport models such as Fourier and Fick’s laws of heat and mass diffusions are generalized in terms of Cattaneo-Christov double diffusion models by accounting the thermal and concentration relaxation times. The present physical problem is examined in the presence of Lorentz forces to investigate the effects of magnetic field on double diffusion process along with Joule heating. The non-Newtonian Casson nanofluid flow between two parallel plates gives the system of time-dependent, highly nonlinear, coupled partial differential equations and is solved by utilizing RK-SM and bvp4c schemes. Present results show that, the temperature and concentration distributions are fewer in case of Cattaneo-Christov heat and mass flux models when compared to the Fourier’s and Fick’s laws of heat and mass diffusions. The concentration field is a diminishing function of thermophoresis parameter and it is an increasing function of Brownian motion parameter. Finally, an excellent comparison between the present solutions and previously published results show the accuracy of the results and methods used to achieve the objective of the present work.
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Grabowski, Wojciech W., and Hugh Morrison. "Indirect Impact of Atmospheric Aerosols in Idealized Simulations of Convective–Radiative Quasi Equilibrium. Part II: Double-Moment Microphysics." Journal of Climate 24, no. 7 (April 1, 2011): 1897–912. http://dx.doi.org/10.1175/2010jcli3647.1.
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Abstract This paper extends the previous cloud-resolving modeling study concerning the impact of cloud microphysics on convective–radiative quasi equilibrium (CRQE) over a surface with fixed characteristics and prescribed solar input, both mimicking the mean conditions on earth. The current study applies sophisticated double-moment warm-rain and ice microphysics schemes, which allow for a significantly more realistic representation of the impact of aerosols on precipitation processes and on the coupling between clouds and radiative transfer. Two contrasting cloud condensation nuclei (CCN) characteristics are assumed, representing pristine and polluted conditions, as well as contrasting representations of the effects of entrainment and mixing on the mean cloud droplet size. In addition, four sets of sensitivity simulations are also performed with changes that provide a reference for the main simulation set. As in the previous study, the CRQE mimics the estimates of globally and annually averaged water and energy fluxes across the earth’s atmosphere. There are some differences from the previous study, however, consistent with the slightly lower water vapor content in the troposphere and significantly reduced lower-tropospheric cloud fraction in current simulations. There is also a significant reduction of the difference between the pristine and polluted cases, from ∼20 to ∼4 W m−2 at the surface from ∼20 to ∼9 W m−2 at the top of the atmosphere (TOA). The difference between the homogeneous and extremely inhomogeneous mixing scenarios, ∼20 W m−2 in the previous study, is reduced to a mere 2 (1) W m−2 at the surface (TOA). An unexpected difference between the previous and current simulations is the lower Bowen ratio of the surface heat flux, the partitioning of the total flux into sensible and latent components. It is shown that most of the change comes from the difference in the representation of rain evaporation in the subcloud layer in the single- and double-moment microphysics schemes. The difference affects the mean air temperature and humidity near the surface, and thus the Bowen ratio. The differences between the various simulations are discussed, contrasting the process-level approach with the impact of cloud microphysics on the quasi-equilibrium state with a more appropriate system dynamics approach. The key distinction is that the latter includes the interactions among all the processes in the modeled system.
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Vieira, V. M. N. C. S., F. Martins, J. Silva, and R. Santos. "Numerical tools to estimate the flux of a gas across the air–water interface and assess the heterogeneity of its forcing functions." Ocean Science 9, no. 2 (March 21, 2013): 355–75. http://dx.doi.org/10.5194/os-9-355-2013.
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Abstract. A numerical tool was developed for the estimation of gas fluxes across the air–water interface. The primary objective is to use it to estimate CO2 fluxes. Nevertheless application to other gases is easily accomplished by changing the values of the parameters related to the physical properties of the gases. A user-friendly software was developed allowing to build upon a standard kernel a custom-made gas flux model with the preferred parameterizations. These include single or double layer models; several numerical schemes for the effects of wind in the air-side and water-side transfer velocities; the effects of atmospheric stability, surface roughness and turbulence from current drag with the bottom; and the effects on solubility of water temperature, salinity, air temperature and pressure. An analysis was also developed which decomposes the difference between the fluxes in a reference situation and in alternative situations into its several forcing functions. This analysis relies on the Taylor expansion of the gas flux model, requiring the numerical estimation of partial derivatives by a multivariate version of the collocation polynomial. Both the flux model and the difference decomposition analysis were tested with data taken from surveys done in the lagoon system of Ria Formosa, south Portugal, in which the CO2 fluxes were estimated using the infrared gas analyzer (IRGA) and floating chamber method, whereas the CO2 concentrations were estimated using the IRGA and degasification chamber. Observations and estimations show a remarkable fit.
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Ghorbani, Hamidreza, Mohammadreza Moradian, and Mohamed Benbouzid. "On the Optimal Selection of Flux Barrier Reconfiguration for a Five-Phase Permanent Magnet Assisted Synchronous Reluctance Machine for Low-Torque Ripple Application." Electronics 11, no. 1 (December 23, 2021): 41. http://dx.doi.org/10.3390/electronics11010041.
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This paper aims to investigate the reconfigurations of rotor flux barriers for a five-phase Permanent Magnet Assisted Synchronous Reluctance Machine (PMASynRM). To precisely study the performance of the proposed configurations, a conventional PMASynRM with double-layer flux barriers is included in the study. Since the novel rotor schemes consume the same amount of rare-earth magnets, steel sheet materials, and copper wire, resulting in no extra manufacturing costs, the optimal reconfiguration should be determined, providing developed electromagnetic characteristics. Thus, all the proposed models are designed and analyzed under the same condition. The Lumped Parameter Model (LPM) is exported to the Finite Element Method (FEM) for precise analysis to reach developed torque and lower values of torque ripple. Based on the FEM results the model presenting the lowest torque fluctuations is selected as the optimal model and dynamically investigated. According to the results, in comparison with the conventional model, the introduced rotor designs provide a much lower value of torque fluctuations with a desirable amount of electromagnetic torque and power. In addition, the optimal model presents high values of power factor and efficiency, making it a vital alternative for low-torque ripple high-speed operations with no extra cost to the implementation process.
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Wong, May, Mikhail Ovchinnikov, and Minghuai Wang. "Evaluation of Subgrid-Scale Hydrometeor Transport Schemes Using a High-Resolution Cloud-Resolving Model." Journal of the Atmospheric Sciences 72, no. 9 (September 1, 2015): 3715–31. http://dx.doi.org/10.1175/jas-d-15-0060.1.
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Abstract Potential ways of parameterizing vertical turbulent fluxes of hydrometeors are examined using a high-resolution simulation of continental deep convection. The cloud-resolving model uses a double-moment microphysics scheme that contains prognostic variables for four hydrometeor types: rain, graupel, cloud ice, and snow. The benchmark simulation with a horizontal grid spacing of 250 m is analyzed to evaluate three different ways of parameterizing the turbulent vertical fluxes of hydrometeors: an eddy-diffusion approximation, a quadrant-based decomposition, and a scaling method that accounts for within-quadrant (subplume) correlations. Results show that the downgradient nature of the eddy-diffusion approximation enforces transport of mass away from concentrated regions, whereas the benchmark simulation indicates that the vertical transport often moves mass from below the level of maximum concentration to aloft. Unlike the eddy-diffusion approach, the quadrimodal decomposition is able to capture the signs of the flux gradient but underestimates the magnitudes. The scaling approach, which accounts empirically for within-quadrant correlations, improves the representation of the vertical fluxes for all hydrometeors except snow. A sensitivity study is performed to illustrate how vertical transport effects on the vertical distribution of hydrometeors are compounded by accompanying changes in microphysical process rates. Results from the sensitivity tests show that suppressing rain or graupel transport drastically alters vertical profiles of cloud ice and snow through changes in the distribution of cloud water, which in turn governs the production of cloud ice and snow aloft. Last, a viable subgrid-scale hydrometeor transport scheme in an assumed probability density function parameterization is discussed.
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Chikira, Minoru, and Masahiro Sugiyama. "A Cumulus Parameterization with State-Dependent Entrainment Rate. Part I: Description and Sensitivity to Temperature and Humidity Profiles." Journal of the Atmospheric Sciences 67, no. 7 (July 1, 2010): 2171–93. http://dx.doi.org/10.1175/2010jas3316.1.
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Abstract A new cumulus parameterization is developed for which an entraining plume model is adopted. The lateral entrainment rate varies vertically depending on the surrounding environment. Two different formulations are examined for the rate. The cumulus ensemble is spectrally represented according to the updraft velocity at cloud base. Cloud-base mass flux is determined with prognostic convective kinetic energy closure. The entrainment rate tends to be large near cloud base because of the small updraft velocity near that level. Deep convection tends to be suppressed when convective available potential energy is small because of upward reduction of in-cloud moist static energy. Dry environmental air significantly reduces in-cloud humidity mainly because of the large entrainment rate in the lower troposphere, which leads to suppression of deep convection, consistent with observations and previous results of cloud-resolving models. The change in entrainment rate has the potential to influence cumulus convection through many feedbacks. The results of an atmospheric general circulation model are improved in both climatology and variability. A representation of the South Pacific convergence zone and the double intertropical convergence zone is improved. The moist Kelvin waves are represented without empirical triggering schemes with a reasonable equivalent depth. A spectral analysis shows a strong signal of the Madden–Julian oscillation. The scheme provides new insights and better understanding of the interaction between cumuli and the surrounding environment.
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Merschiev, A., P. Golovinskiy, M. Svirin, and A. Seminenko. "SIMULATION OF A NON-STATIONARY THERMAL MODE OF PREMISE WITH THE WOOD ENCLOSING STRUCTURES." Bulletin of Belgorod State Technological University named after. V. G. Shukhov 7, no. 8 (August 16, 2022): 35–49. http://dx.doi.org/10.34031/2071-7318-2022-7-8-35-49.
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A non-stationary approach to the calculation of periodic thermal regimes of low-rise buildings with enclosing structures made of wooden beams equipped with double-glazed windows is considered. The application of the proposed method allows to determine the non-stationary thermal load of the air conditioning system for this type of house, as well as the required compensating capacities during the day. The conditions of applicability of plane-layered thermophysical calculation schemes in the presence of spatially inhomogeneous heating are analyzed. A refinement of the procedure for averaging convective heat transfer coefficients for vertical walls by periodic temperature fluctuations is carried out. An algorithm for calculating the periodic thermal regime based on the representation of time dependencies in the form of a Fourier series is proposed. The role of solar radiation flow through double-glazed windows in the heat exchange and energy efficiency of a wooden house is shown. The proposed mathematical model of room heat exchange takes into account the effects of the delay in the propagation of the temperature field in the walls when the ambient temperature changes and the dynamic change in heat flux from light flows outside and inside the room. It is determined that protection from direct sunlight entering the room through the window opening allows reducing peak air conditioning costs in the summer by a third for peak air conditioning modes.
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Thuburn, John, Hilary Weller, Geoffrey K. Vallis, Robert J. Beare, and Michael Whitall. "A Framework for Convection and Boundary Layer Parameterization Derived from Conditional Filtering." Journal of the Atmospheric Sciences 75, no. 3 (March 1, 2018): 965–81. http://dx.doi.org/10.1175/jas-d-17-0130.1.
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Abstract A new theoretical framework is derived for parameterization of subgrid physical processes in atmospheric models; the application to parameterization of convection and boundary layer fluxes is a particular focus. The derivation is based on conditional filtering, which uses a set of quasi-Lagrangian labels to pick out different regions of the fluid, such as convective updrafts and environment, before applying a spatial filter. This results in a set of coupled prognostic equations for the different fluid components, including subfilter-scale flux terms and entrainment/detrainment terms. The framework can accommodate different types of approaches to parameterization, such as local turbulence approaches and mass flux approaches. It provides a natural way to distinguish between local and nonlocal transport processes and makes a clearer conceptual link to schemes based on coherent structures such as convective plumes or thermals than the straightforward application of a filter without the quasi-Lagrangian labels. The framework should facilitate the unification of different approaches to parameterization by highlighting the different approximations made and by helping to ensure that budgets of energy, entropy, and momentum are handled consistently and without double counting. The framework also points to various ways in which traditional parameterizations might be extended, for example, by including additional prognostic variables. One possibility is to allow the large-scale dynamics of all the fluid components to be handled by the dynamical core. This has the potential to improve several aspects of convection–dynamics coupling, such as dynamical memory, the location of compensating subsidence, and the propagation of convection to neighboring grid columns.
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Almakki, Ali Nadhim Jbarah, and Andrey Mazalov. "Improved dfig dftc by using a fractional-order super twisting algorithms in wind power application." Modern Transportation Systems and Technologies 7, no. 3 (September 30, 2021): 131–49. http://dx.doi.org/10.17816/transsyst202173131-149.
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Background: The direct flux and torque control are a robust, simple, and alternative approach control formulation that does not require decomposition into symmetrical components; the direct flux and torque control schemes have been proved to be preponderant for doubly-fed induction generators due to the simple implementation.
Aim: This work presents the minimization of electromagnetic torque and rotor flux undulations of doubly-fed induction generators using fractional-order super twisting algorithms and modified space vector modulation techniques.
Methods: The main role of direct flux and torque control is to regulate and control the electromagnetic torque and rotor flux of doubly-fed induction generators for wind turbine systems. The direct flux and torque control is a traditional control algorithm and robust technique. Fractional-order super twisting algorithms are a new and proposed nonlinear controller; characterized by a robust controller and a simpler algorithm, which gives a good harmonic distortion of current compared to other methods.
Novelty: The A fractional-order super twisting algorithm is proposed. Proposed nonlinear controller construction is based on the traditional super twisting algorithm and fractional calculus to obtain a robust controller and reduces the electromagnetic torque and rotor flux undulations of doubly-fed induction generators. We use in our study a 1.5 MW doubly-fed induction generator integrated into a single-rotor wind turbine system to minimizes the electromagnetic torque, stator current, rotor flux undulations. As shown in the results figures using fractional-order super twisting algorithms ameliorate effectiveness especially minimizes the electromagnetic torque and rotor flux, and minimizes harmonic distortion of stator current (0.16 %) compared to the traditional control scheme.
Results: As shown in the results figures using fractional-order super twisting algorithms ameliorate effectiveness especially minimizes the electromagnetic torque and rotor flux, and minimizes harmonic distortion of stator current (0.16 %) compared to the traditional control scheme.
Conclusion: The direct flux and torque control are a robust, simple, and alternative approach control formulation that does not require decomposition into symmetrical components; the direct flux and torque control schemes have been proved to be preponderant for doubly-fed induction generators due to the simple implementation.
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Nie, Peng Fei. "Study of the Capacity Extension Scheme for 600 MW Unit Wet Flue Gas Desulfurization in a Power Plant." Advanced Materials Research 1092-1093 (March 2015): 917–22. http://dx.doi.org/10.4028/www.scientific.net/amr.1092-1093.917.
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A power plant of Datang Corporation in Hebei province is to reconstruct its wet flue gas desulfurization system. The power plant proposes three viable capacity extension schemes based on actual conditions: adding spray layers and increasing the height of the existing absorber, desulphurizing with series double-absorber and desulphurizing with dual-cycle double-absorber. This paper describes the technical characteristics of the schmes and compares their advantages and disadvantages based on performance, project investment and construction period. The result shows that the double-absorber scheme is more suitable for the power plant than the single-absorber scheme.
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HADŽIABDIĆ, M., and K. HANJALIĆ. "Vortical structures and heat transfer in a round impinging jet." Journal of Fluid Mechanics 596 (January 17, 2008): 221–60. http://dx.doi.org/10.1017/s002211200700955x.
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In order to gain a better insight into flow, vortical and turbulence structure and their correlation with the local heat transfer in impinging flows, we performed large-eddy simulations (LES) of a round normally impinging jet issuing from a long pipe at Reynolds number Re = 20000 at the orifice-to-plate distance H = 2D, where D is the jet-nozzle diameter. This configuration was chosen to match previous experiments in which several phenomena have been detected, but the underlying physics remained obscure because of limitations in the measuring techniques applied. The instantaneous velocity and temperature fields, generated by the LES, revealed interesting time and spatial dynamics of the vorticity and eddy structures and their imprints on the target wall, characterized by tilting and breaking of the edge ring vortices before impingement, flapping, precessing, splitting and pairing of the stagnation point/line, local unsteady separation and flow reversal at the onset of radial jet spreading, streaks pairing and branching in the near-wall region of the radial jets, and others. The LES data provided also a basis for plausible explanations of some of the experimentally detected statistically-averaged flow features such as double peaks in the Nusselt number and the negative production of turbulence energy in the stagnation region. The simulations, performed with an in-house unstructured finite-volume code T-FlowS, using second-order-accuracy discretization schemes for space and time and the dynamic subgrid-scale stress/flux model for unresolved motion, showed large sensitivity of the results to the grid resolution especially in the wall vicinity, suggesting care must be taken in interpreting LES results in impinging flows.
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Chen, Xian Biao. "The Rotor Current Orientation Decoupling Control of Doubly-Fed Motor." Advanced Materials Research 816-817 (September 2013): 375–78. http://dx.doi.org/10.4028/www.scientific.net/amr.816-817.375.
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This paper presents a vector control scheme of doubly-fed motor based on stator flux orientation. The scheme achieves decoupled flux and torque component of stator current through directional control of the rotor current vector. It is suitable for both motor sub synchronous operating condition and super synchronous operating condition. Simulation experiment based on the scheme is carried out by Matlab/Simulink and simulating waveforms are given to prove the correctness of the scheme.
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Arshakian, Tigran G. "Kiloparsec Jet Speeds in Classical Double Radio Sources." Symposium - International Astronomical Union 205 (2001): 152–53. http://dx.doi.org/10.1017/s0074180900220810.
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On the basis of an intrinsically symmetric relativistic jet model, analytical equations between the mean jet speed and the mean jet flux asymmetry, and between their variances are derived in the context of an orientation-based unification scheme. The mean jet speeds of classical double radio sources are estimated on kiloparsec scales by using the asymmetry of jet-counterjet flux densities taken from the 3CRR and B2 samples. For FRI radio sources the mean jet speed is ∼ (0.54 ± 0.03)c, while for FRII low-redshift radio galaxies and intermediate-redshift quasars the values found are ∼ (0.4 ± 0.06)c and ≳ 0.6c respectively.
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Bobrov, Maxim, Vladislav Artamonov, and Nikita Dubov. "Flux linkage estimation strategies for sensorless field-oriented control of doubly-fed induction motor drive." E3S Web of Conferences 244 (2021): 09014. http://dx.doi.org/10.1051/e3sconf/202124409014.
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In this paper authours propose two different strategies of flux linkage estimation for sensorless FOC system of doubly-fed induction motor drive implementation. Possibility to measure currents and voltages of rotor and stator circuits in doubly-fed motor gives place to a simplier flux linkage observers model. Functional scheme of electric drive and two models of flux linkage observers are proposed - a model using the voltage and a model using the rotor current. The stability of the present field-oriented control system when implementing these flux-linkage estimations strategies are investigated using LabView software. The results of theoretical research are confirmed by simulation results in Matlab software.
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Zhang, Guang J., and Xiaoliang Song. "Convection Parameterization, Tropical Pacific Double ITCZ, and Upper-Ocean Biases in the NCAR CCSM3. Part II: Coupled Feedback and the Role of Ocean Heat Transport." Journal of Climate 23, no. 3 (February 1, 2010): 800–812. http://dx.doi.org/10.1175/2009jcli3109.1.
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Abstract This study investigates the coupled atmosphere–ocean feedback and the role of ocean dynamic heat transport in the formation of double ITCZ over the tropical Pacific in the NCAR Community Climate System Model, version 3 (CCSM3) and its alleviation when a revised Zhang–McFarlane (ZM) convection scheme is used. A hierarchy of coupling strategy is employed for this purpose. A slab ocean model is coupled with the atmospheric component of the Community Atmosphere Model, version 3 (CAM3) to investigate the local feedback between the atmosphere and the ocean. It is shown that the net surface energy flux differences in the southern ITCZ region between the revised and original ZM scheme seen in the stand-alone CAM3 simulations can cool the SST by up to 1.5°C. However, the simulated SST distribution is very sensitive to the prescribed ocean heat transport required in the slab ocean model. To understand the role of ocean heat transport, the fully coupled CCSM3 model is used. The analysis of CCSM3 simulations shows that the altered ocean dynamic heat transport when the revised ZM scheme is used is largely responsible for the reduction of SST bias in the southern ITCZ region, although surface energy flux also helps to cool the SST in the first few months of the year in seasonal variation. The results, together with those from Part I, suggest that the unrealistic simulation of convection over the southern ITCZ region in the standard CCSM3 leads to the double-ITCZ bias through complex coupled interactions between atmospheric convection, surface winds, latent heat flux, cloud radiative forcing, SST, and upper-ocean circulations. The mitigation of the double-ITCZ bias using the revised ZM scheme is achieved by altering this chain of interactions.
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Benyoussef, Elakhdar, Abdelkader Meroufel, and Said Barkat. "Three-Level DTC Based on Fuzzy Logic and Neural Network of Sensorless DSSM Using Extended Kalman Filter." International Journal of Power Electronics and Drive Systems (IJPEDS) 5, no. 4 (April 1, 2015): 453. http://dx.doi.org/10.11591/ijpeds.v5.i4.pp453-463.
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This paper presents a direct torque control is applied for salient-pole double star synchronous machine without mechanical speed and stator flux linkage sensors. The estimation is performed using the extended Kalman filter known by it is ability to process noisy discrete measurements. Two control approaches using fuzzy logic DTC, and neural network DTC are proposed and compared. The validity of the proposed controls scheme is verified by simulation tests of a double star synchronous machine. The stator flux, torque, and speed are determined and compared in the above techniques. Simulation results presented in this paper highlight the improvements produced by the proposed control method based on the extended Kalman filter under various operation conditions.
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Klaes, Norbert, Florian Pöschke, and Horst Schulte. "Grid Forming Stator Flux Control of Doubly-Fed Induction Generator." Energies 14, no. 20 (October 17, 2021): 6766. http://dx.doi.org/10.3390/en14206766.
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The doubly fed induction generator is widely used in wind power applications. For stand-alone operation of this machine, the control of the stator flux with fixed voltage and frequency has been proposed. This paper extends the stator flux control of the doubly fed induction machine by droop mechanisms, which vary the setpoint of flux magnitude and frequency depending on active and reactive power. This gives the doubly fed induction generator system unknown grid supporting and grid forming performance. The validation of the proposed control scheme has been conducted on a 10kVA testbed system. The closed-loop behavior of the system has been proven to enable grid-tied and islanded operation with the same control structure. The system response to load changes and islanding events show no disruptive transients in both conditions.
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Sun, Yu, Chang Shu, Liming Yang, and C. J. Teo. "A Switch Function-Based Gas-Kinetic Scheme for Simulation of Inviscid and Viscous Compressible Flows." Advances in Applied Mathematics and Mechanics 8, no. 5 (July 8, 2016): 703–21. http://dx.doi.org/10.4208/aamm.2015.m1071.
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AbstractIn this paper, a switch function-based gas-kinetic scheme (SF-GKS) is presented for the simulation of inviscid and viscous compressible flows. With the finite volume discretization, Euler and Navier-Stokes equations are solved and the SF-GKS is applied to evaluate the inviscid flux at cell interface. The viscous flux is obtained by the conventional smooth function approximation. Unlike the traditional gas-kinetic scheme in the calculation of inviscid flux such as Kinetic Flux Vector Splitting (KFVS), the numerical dissipation is controlled with a switch function in the present scheme. That is, the numerical dissipation is only introduced in the region around strong shock waves. As a consequence, the present SF-GKS can well capture strong shock waves and thin boundary layers simultaneously. The present SF-GKS is firstly validated by its application to the inviscid flow problems, including 1-D Euler shock tube, regular shock reflection and double Mach reflection. Then, SF-GKS is extended to solve viscous transonic and hypersonic flow problems. Good agreement between the present results and those in the literature verifies the accuracy and robustness of SF-GKS.
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Abedinzadeh, Taher, and Sajjad Tohidi. "A comprehensive sensorless control of DFIG-based wind turbines." COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 35, no. 1 (January 4, 2016): 27–43. http://dx.doi.org/10.1108/compel-09-2014-0236.
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Purpose – The purpose of this paper is to present an improved approach for estimation of the rotor position and speed of doubly fed induction generator, which can be used in vector control and direct torque control (DTC) schemes. Design/methodology/approach – Some novel equations are developed for calculation of the rotor position and rotor speed. Such equations do not need to the value of stator flux linkage and just, measured values of the stator voltage and currents as well as rotor current are required to be known. Findings – The simulation results verify the satisfactory steady-state and dynamic performance of proposed approach with both the vector control and DTC schemes. The results show that the proposed estimation approach benefits from the starting on the fly, robustness against the variations of the most of the stator and rotor parameters and immunity against the noise. Originality/value – The proposed estimation approach is novel and the outcome of the research of authors. It is simple and effective and, no approximation is made in the calculations. The simulation results demonstrate that the proposed scheme can be successfully implemented in various control strategies, e.g. DTC and vector control.
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Fu, S. C., R. M. C. So, and W. W. F. Leung. "A Discrete Flux Scheme for Aerodynamic and Hydrodynamic Flows." Communications in Computational Physics 9, no. 5 (May 2011): 1257–83. http://dx.doi.org/10.4208/cicp.311009.241110s.
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AbstractThe objective of this paper is to seek an alternative to the numerical simulation of the Navier-Stokes equations by a method similar to solving the BGK-type modeled lattice Boltzmann equation. The proposed method is valid for both gas and liquid flows. A discrete flux scheme (DFS) is used to derive the governing equations for two distribution functions; one for mass and another for thermal energy. These equations are derived by considering an infinitesimally small control volume with a velocity lattice representation for the distribution functions. The zero-order moment equation of the mass distribution function is used to recover the continuity equation, while the first-order moment equation recovers the linear momentum equation. The recovered equations are correct to the first order of the Knudsen number(Kn);thus, satisfying the continuum assumption. Similarly, the zero-order moment equation of the thermal energy distribution function is used to recover the thermal energy equation. For aerodynamic flows, it is shown that the finite difference solution of the DFS is equivalent to solving the lattice Boltzmann equation (LBE) with a BGK-type model and a specified equation of state. Thus formulated, the DFS can be used to simulate a variety of aerodynamic and hydrodynamic flows. Examples of classical aeroacoustics, compressible flow with shocks, incompressible isothermal and non-isothermal Couette flows, stratified flow in a cavity, and double diffusive flow inside a rectangle are used to demonstrate the validity and extent of the DFS. Very good to excellent agreement with known analytical and/or numerical solutions is obtained; thus lending evidence to the DFS approach as an alternative to solving the Navier-Stokes equations for fluid flow simulations.
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Park, Sun-Young, Hyung-Jin Ahn, and Dong-Myung Lee. "A New Flux Tracking LVRT Control Scheme for Doubly Fed Induction Generators." Journal of international Conference on Electrical Machines and Systems 2, no. 3 (September 1, 2013): 306–12. http://dx.doi.org/10.11142/jicems.2013.2.3.306.
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Chaabane, H., D. E. Khodja, S. Chakroune, and D. Hadji. "Model reference adaptive backstepping control of double star induction machine with extended Kalman sensorless control." Electrical Engineering & Electromechanics, no. 4 (July 8, 2022): 3–11. http://dx.doi.org/10.20998/2074-272x.2022.4.01.
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Introduction. Newly, the design of a controller for speed control of double star induction motor as a research focus. Consequently, backstepping technique is used to recursively construct a stable control law for speed and flux. Nevertheless, this control law coming from backstepping requires the knowledge of speed and flux values; in practice the measurement sensors are expensive and fragile. The novelty of this work consists to propose a control strategy which based on accurate Kalman filter observer that estimates speed, flux and torque. This extended Kalman filter is an optimal state estimator and is usually applied to a dynamic system that involves a random noise environment. Purpose. Apply a backstepping control of double star induction motor based on principle of rotor flux orientation. This approach consists in finding a Lyapunov function that allows deducing a control law and a modified adaptation rule is referred and sufficient conditions for the stability of the command-observer, in contrast to other techniques who use nonlinear principle. Results. The simulation results are shown to illustrate the performance of the proposed scheme under parametric uncertainties by simulation on MATLAB. The obtained results showed the robustness of the sensorless control in front of load and parameters variation of double stator induction motor. The research directions of the model were determined for the subsequent implementation of results with simulation samples.
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Hore, Debirupa, and Runumi Sarma. "Neural network–based improved active and reactive power control of wind-driven double fed induction generator under varying operating conditions." Wind Engineering 42, no. 5 (June 6, 2018): 381–96. http://dx.doi.org/10.1177/0309524x18780402.
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Artificial neural network–based power controllers are trained using back propagation algorithm for controlling the active and reactive power of a wind-driven double fed induction generator under varying wind speed conditions and fault conditions. Vector control scheme is used for control of the double fed induction generator. Here stator flux–oriented vector control scheme is implemented for the rotor side converter and grid voltage vector scheme is used for control of grid side converter using tuned proportional–integral active and reactive power controllers, which is later replaced by artificial neural network–based controllers. The artificial neural network controllers are trained using the data obtained from simulation of conventional proportional–integral controllers under varying operating conditions. The intelligent controller makes the generated stator active power to track the reference active power more precisely at specified power factor in both sub-synchronous and super-synchronous modes of operations. Simulation results reveal that the neural network–based controller significantly improves the performance of variable speed wind power generating double fed induction generator under various conditions.
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Zarghami, Ahad, Stefano Ubertini, and Sauro Succi. "Finite volume formulation of thermal lattice Boltzmann method." International Journal of Numerical Methods for Heat & Fluid Flow 24, no. 2 (February 25, 2014): 270–89. http://dx.doi.org/10.1108/hff-11-2011-0234.
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Purpose – The main purpose of this paper is to develop a novel thermal lattice Boltzmann method (LBM) based on finite volume (FV) formulation. Validation of the suggested formulation is performed by simulating plane Poiseuille, backward-facing step and flow over circular cylinder. Design/methodology/approach – For this purpose, a cell-centered scheme is used to discretize the convection operator and the double distribution function model is applied to describe the temperature field. To enhance stability, weighting factors are defined as flux correctors on a D2Q9 lattice. Findings – The introduction of pressure-temperature-dependent flux-control coefficients in the streaming operator, in conjunction with suitable boundary conditions, is shown to result in enhanced numerical stability of the scheme. In all cases, excellent agreement with the existing literature is found and shows that the presented method is a promising scheme in simulating thermo-hydrodynamic phenomena. Originality/value – A stable and accurate FV formulation of the thermal DDF-LBM is presented.
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A. Mossa, Mahmoud, Houari Khouidmi, and Alfian Ma’arif. "Robust Flux and Speed State Observer Design for Sensorless Control of a Double Star Induction Motor." Journal of Robotics and Control (JRC) 3, no. 4 (July 1, 2022): 464–75. http://dx.doi.org/10.18196/jrc.v3i4.15667.
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In this paper, a robust flux and speed observer for sensorless control of a double star induction motor is presented. Proper operation of vector control of the double star induction motor requires reliable information from the process to be controlled. This information can come from mechanical sensors (rotational speed, angular position). Furthermore, mechanical flux and speed sensors are generally expensive and fragile and affect the reliability of the system. However, the control without sensors must-have performance that does not deviate too much from that which we would have had with a mechanical sensor. In this framework, this work mainly deals with the estimation of the flux and speed using a robust state observer in view of sensorless vector control of the double star induction motor. The evaluation criteria are the static and dynamic performances of the system as well as the errors between the reference values and those estimated. Extensive simulation results and robustness tests are presented to evaluate the performance of the proposed sensorless control scheme. Furthermore, under the same test conditions, a detailed comparison between the proposed state observer and the sliding mode-MRAS technique is carried out where the results of its evaluation are investigated in terms of their speed and flux tracking capability during load and speed transients and also with parameter variation. It is worth mentioning that the proposed state observer can obtain both high current quality and low torque ripples, which show better performance than that in the MRAS system.
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Park, Sun-Young, Yeong-Han Chun, and Dong-Myung Lee. "LVRT Scheme for Doubly Fed Induction Generator Systems Based on Flux Tracking Method." Transactions of The Korean Institute of Electrical Engineers 62, no. 8 (August 1, 2013): 1059–65. http://dx.doi.org/10.5370/kiee.2013.62.8.1059.
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Chu, Wenchao, Yanluan Lin, and Ming Zhao. "Implementation and Evaluation of a Double-Plume Convective Parameterization in NCAR CAM5." Journal of Climate 35, no. 2 (January 15, 2022): 617–37. http://dx.doi.org/10.1175/jcli-d-21-0267.1.
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Abstract Performance of global climate models (GCMs) is strongly affected by the cumulus parameterization (CP) used. Similar to the approach in GFDL AM4, a double-plume CP, which unifies the deep and shallow convection in one framework, is implemented and tested in the NCAR Community Atmospheric Model version 5 (CAM5). Based on the University of Washington (UW) shallow convection scheme, an additional plume was added to represent the deep convection. The shallow and deep plumes share the same cloud model, but use different triggers, fractional mixing rates, and closures. The scheme was tested in single-column, short-term hindcast, and AMIP simulations. Compared with the default combination of the Zhang–McFarlane scheme and UW scheme in CAM5, the new scheme tends to produce a top-heavy mass flux profile during the active monsoon period in the single-column simulations. The scheme increases the intensity of tropical precipitation, closer to TRMM observations. The new scheme increased subtropical marine boundary layer clouds and high clouds over the deep tropics, both in better agreement with observations. Sensitivity tests indicate that regime-dependent fractional entrainment rates of the deep plume are desired to improve tropical precipitation distribution and upper troposphere temperature. This study suggests that a double-plume approach is a promising way to combine shallow and deep convections in a unified framework.
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Zhang, Yue, Zhi Cai Ma, and Hui Min Yu. "Asynchronous Operation Analysis of Brushless Doubly-Fed Machine with Magnetic Barrier Rotor." Applied Mechanics and Materials 668-669 (October 2014): 607–10. http://dx.doi.org/10.4028/www.scientific.net/amm.668-669.607.
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To restrain the influence of armature reaction, flux barriers is added to rotor structure and enhance the output power ability of brushless doubly-fed machine. Design scheme of brushless doubly-fed machine with barrier rotor is provided. Based on field-circuit coupled finite element method, The asynchronous operation performance of brushless doubly-fed machine with barrier rotor is studied under the condition of no-load, including adjusting voltage adjusting speed and series resistance adjusting voltage. The prototype is carried out on the condition of no-load asynchronous operation; comparison analysis of simulation speed values and tested speed values is realized. The designed machine is reasonable and reliable.
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Feng, Su Mei, Zhi Ping Yan, and Xue Mei Wu. "Based on Multi-Estimator Technology to Control Speed of Induction Motor." Applied Mechanics and Materials 577 (July 2014): 329–33. http://dx.doi.org/10.4028/www.scientific.net/amm.577.329.
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In order to improve the reliability of the control system, and to reduce the uncertainty of control process, this paper presents an excellent algorithm to control the induction motor speed using series estimator technology. The physical speed sensor is not used to detect speed of the motor, while applying the vector analysis method, through the stator current and the rotor flux are calculated to estimate motor speed. Corresponding to sensorless control drawbacks, the self-tuning control scheme is proposed through control scheme reformed. The double estimator technology is applied to reform scheme, the first order estimator is used to identify the system parameters, the second order estimator is used to calculate the parameters of the controller on-line, and control function is given real-time to control the speed of the motor, the simulation results show that the given control technology is advanced.
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Park, Sungsu. "A Unified Convection Scheme (UNICON). Part I: Formulation." Journal of the Atmospheric Sciences 71, no. 11 (October 29, 2014): 3902–30. http://dx.doi.org/10.1175/jas-d-13-0233.1.
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Abstract The author develops a unified convection scheme (UNICON) that parameterizes relative (i.e., with respect to the grid-mean vertical flow) subgrid vertical transport by nonlocal asymmetric turbulent eddies. UNICON is a process-based model of subgrid convective plumes and mesoscale organized flow without relying on any quasi-equilibrium assumptions such as convective available potential energy (CAPE) or convective inhibition (CIN) closures. In combination with a relative subgrid vertical transport scheme by local symmetric turbulent eddies and a grid-scale advection scheme, UNICON simulates vertical transport of water species and conservative scalars without double counting at any horizontal resolution. UNICON simulates all dry–moist, forced–free, and shallow–deep convection within a single framework in a seamless, consistent, and unified way. It diagnoses the vertical profiles of the macrophysics (fractional area, plume radius, and number density) as well as the microphysics (production and evaporation rates of convective precipitation) and the dynamics (mass flux and vertical velocity) of multiple convective updraft and downdraft plumes. UNICON also prognoses subgrid cold pool and mesoscale organized flow within the planetary boundary layer (PBL) that is forced by evaporation of convective precipitation and accompanying convective downdrafts but damped by surface flux and entrainment at the PBL top. The combined subgrid parameterization of diagnostic convective updraft and downdraft plumes, prognostic subgrid mesoscale organized flow, and the feedback among them remedies the weakness of conventional quasi-steady diagnostic plume models—the lack of plume memory across the time step—allowing UNICON to successfully simulate various transitional phenomena associated with convection (e.g., the diurnal cycle of precipitation and the Madden–Julian oscillation).
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Zhang, Bao Luo. "Simulation Study on Decoupling Control of Active and Reactive Power in Doubly Fed Induction Generator." Applied Mechanics and Materials 716-717 (December 2014): 1376–81. http://dx.doi.org/10.4028/www.scientific.net/amm.716-717.1376.
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The decoupled control of active and reactive power in doubly fed induction generator (DFIG) is a key technology of wind power generation system. First, this paper introduces the principle of DFIG, then proposes an useful method for decoupling control of active and reactive power by analyzing the mathematical model of DFIG and the stator-flux-oriented vector control scheme. Finally, use the Matlab/Simulink tools for simulation studies, the results indicated that the decoupling control of active and reactive power in DFIG can be efficiently implemented, which can be considered as a reference control scheme for variable-speed constant-frequency (VSCF) wind power generation system.
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Hu, Bei, Pan Duan, Shi Cheng Feng, Qi Chang Duan, and Ming Xuan Mao. "Speed Sensor-Less Vector Control Used in DFIG Wind Power Generation Based on EKF Algorithm." Applied Mechanics and Materials 654 (October 2014): 196–202. http://dx.doi.org/10.4028/www.scientific.net/amm.654.196.
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Wind power generation system is a typical nonlinear system. As wind speed is changing constantly, induction motor with conventional speed sensor-less control method has great estimated error. Wind power generation system with the control method cannot be good at tracking maximum power point. The paper put forward a novel control method that estimates the angular velocity and the rotor flux of the wind turbine based on EKF, As a result, induction motor with double-loop sensor-less Vector Control is realized. Simulation results show that the control scheme is effective.
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Mei, Bai Shan, Han Kun Jiang, and Jiang Yu. "Research on Squirrel-Cage Induction Generator Full Power Converter Control Strategies of Wind Power Generation System with Dynamic Systems." Advanced Materials Research 496 (March 2012): 104–8. http://dx.doi.org/10.4028/www.scientific.net/amr.496.104.
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In this paper, a new control scheme of a variable speed grid connected wind energy generation system was presented. The scheme used a squirrel-cage induction generator (SCIG) as generator and it connected to the grid through a back-to-back double PWM converter. According to the characteristics of induction motor, the generator side adopted rotor flux linkage oriented slip frequency vector control technology, and the grid side used the network voltage oriented control and voltage and current dual close-loop control strategy. The simulation results show that the system can work in the state of variable speed constant frequency (VSCF)power generation and the active and reactive power can be controlled with no mutual interference and with good static-dynamic performance.
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Sun, Guodong, Guijie Yang, Jianyong Su, and Guangxu Lu. "A Flux−Linkage Torque Ripple Suppression Method of Dual−Series FPMSMs Decoupling Control Based on Dual−Frequency Vector Modulation." Energies 15, no. 13 (June 27, 2022): 4700. http://dx.doi.org/10.3390/en15134700.
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A novel cross−series connection of two five−phase permanent magnet synchronous motors (FPMSM) supplied by single inverter can halve the number of required power units and current sensors. This, along with a decoupling control strategy for FPMSMs in series based on an improved dual−frequency vector modulation (DFV−SVPWM) and a flux−linkage torque ripple suppression method with current compensation are proposed in this paper, each of which have great significance for multi−unit industrial equipment. The third harmonic flux−linkage will produce torque ripple in the FPMSM in series, which has an adverse effect on accuracy. In this paper, a synchronous decoupling mathematical model of dual−series FPMSM with harmonic flux−linkage is established to analyze the decoupling relationship between torque and current. In addition, an enhanced DFV−SVPWM with higher modulation ratio is proposed for the decoupling control of double motors in series. Furthermore, based on the torque influence of two series−connected motors by harmonic flux−linkage and the decoupling control with improved DFV−SVPWM, a torque ripple compensation method with current compensation is proposed, which can effectively suppress the torque ripple of FPMSM with harmonic flux−linkage and not affect the other. The correctness and superiority of the scheme are verified by simulation and experiment in this paper.
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Neggers, Roel A. J. "A Dual Mass Flux Framework for Boundary Layer Convection. Part II: Clouds." Journal of the Atmospheric Sciences 66, no. 6 (June 1, 2009): 1489–506. http://dx.doi.org/10.1175/2008jas2636.1.
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Abstract This paper presents the extension of the eddy diffusivity mass flux (EDMF) framework for turbulent transport into the statistical modeling of boundary layer clouds. The advection–diffusion decomposition that defines EDMF is projected onto the turbulent distribution as used in the statistical cloud model. Each EDMF component is thus assigned its own independent probability density function (PDF), resulting in an updraft PDF and a diffusive PDF. This double PDF system is configured and integrated in conserved variable space, with the position and orientation of each PDF determined by its unique nature. The parameterization of the associated updraft/diffusion decomposition of variance introduces close ties to the transport scheme; whereas the grid box mean variance is reconstructed using a prognostic variance budget, the variance of the updraft component is parameterized as a function of the spread among various resolved model updrafts. Individual model components and the scheme as a whole are evaluated in detail against large-eddy simulations of a number of prototype subtropical trade wind cases. The results show that various structures in cloud fraction, condensate, and variance are reproduced. The diffusive PDF acts to represent stratiform clouds; the advective PDF represents cumuliform clouds in conditionally unstable layers. This allows representation of complex scenarios in which both cloud forms occur, such as the transitional trade wind regime featuring cumulus rising into stratocumulus.
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Hong, Qingguo, Johannes Kraus, Maria Lymbery, and Fadi Philo. "Parameter-robust Uzawa-type iterative methods for double saddle point problems arising in Biot’s consolidation and multiple-network poroelasticity models." Mathematical Models and Methods in Applied Sciences 30, no. 13 (December 10, 2020): 2523–55. http://dx.doi.org/10.1142/s0218202520500499.
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This work is concerned with the iterative solution of systems of quasi-static multiple-network poroelasticity equations describing flow in elastic porous media that is permeated by single or multiple fluid networks. Here, the focus is on a three-field formulation of the problem in which the displacement field of the elastic matrix and, additionally, one velocity field and one pressure field for each of the [Formula: see text] fluid networks are the unknown physical quantities. Generalizing Biot’s model of consolidation, which is obtained for [Formula: see text], the MPET equations for [Formula: see text] exhibit a double saddle point structure. The proposed approach is based on a framework of augmenting and splitting this three-by-three block system in such a way that the resulting block Gauss–Seidel preconditioner defines a fully decoupled iterative scheme for the flux-, pressure-, and displacement fields. In this manner, one obtains an augmented Lagrangian Uzawa-type method, the analysis of which is the main contribution of this work. The parameter-robust uniform linear convergence of this fixed-point iteration is proved by showing that its rate of contraction is strictly less than one independent of all physical and discretization parameters. The theoretical results are confirmed by a series of numerical tests that compare the new fully decoupled scheme to the very popular partially decoupled fixed-stress split iterative method, which decouples only flow — the flux and pressure fields remain coupled in this case — from the mechanics problem. We further test the performance of the block-triangular preconditioner defining the new scheme when used to accelerate the generalized minimal residual method (GMRES) algorithm.
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Annan, Kodwo. "Finite Volume Scheme for Double Convection-Diffusion Exchange of Solutes in Bicarbonate High-Flux Hollow-Fiber Dialyzer Therapy." Computational and Mathematical Methods in Medicine 2012 (2012): 1–16. http://dx.doi.org/10.1155/2012/973424.
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Maher, Penelope, and Paul Earnshaw. "The Flexible Modelling Framework for the Met Office Unified Model (Flex-UM, using UM 12.0 release)." Geoscientific Model Development 15, no. 3 (February 9, 2022): 1177–94. http://dx.doi.org/10.5194/gmd-15-1177-2022.
Full textAbstract:
Abstract. The Met Office Unified Model (UM) is a world-leading atmospheric weather and climate model. In addition to comprehensive simulations of the atmosphere, the UM is capable of running idealised simulations, such as the dry physics Held–Suarez test case, radiative convective equilibrium and simulating planetary atmospheres other than Earth. However, there is a disconnect between the simplicity of the idealised UM model configurations and the full complexity of the UM. This gap inhibits the broad use of climate model hierarchy approaches within the UM. To fill this gap, we have developed the Flexible Modelling Framework for the UM – Flex-UM – which broadens the climate model hierarchy capabilities within the UM. Flex-UM was designed to replicate the atmospheric physics of the Geophysical Fluid Dynamics Laboratory (GFDL) idealised moist physics aqua-planet model. New parameterisations have been implemented in Flex-UM, including simplified schemes for convection, large-scale precipitation, radiation, boundary layer and sea surface temperature (SST) boundary conditions. These idealised parameterisations have been implemented in a modular way, so that each scheme is available for use in any model configuration. This has the advantage that we can incrementally add or remove complexity within the model hierarchy. We compare Flex-UM to ERA5 and aqua-planet simulations using the Isca climate modelling framework (based on the GFDL moist physics aqua-planet model) and comprehensive simulations of the UM (using the GA7.0 configuration). We also use two SST boundary conditions to compare the models (fixed SST and a slab ocean). We find the Flex-UM climatologies are similar to both Isca and GA7.0 (though Flex-UM is generally a little cooler, with higher relative humidity and a less pronounced storm track). Flex-UM has a single Intertropical Convergence Zone (ITCZ) in the slab-ocean simulation but a double-ITCZ in the fixed-SST simulation. Further work is needed to ensure that the atmospheric energy budget closes to within 1–2 W m−2, as the current configuration of Flex-UM gains 9–11 W m−2 (the range covers the two SST boundary conditions). Flex-UM greatly extends the modelling hierarchy capabilities of the UM and offers a simplified framework for developing, testing and evaluating parameterisations within the UM.