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Wyświetlanie 1-15 z 194
Tytuł:
Co dalej z polskim węglem?
Polish coal: what next?
Autorzy:
Steffek, Żaneta
Powiązania:
https://bibliotekanauki.pl/articles/470322.pdf
Data publikacji:
2014
Wydawca:
Polski Uniwersytet na Obczyźnie w Londynie
Tematy:
two-phase heating
ecology, air pollution
„Universitas” quarterly
two-phase heating stove
Opis:
This paper concerns ecology, one of the many fields covered in the T.P. PUNO Polish quarterly „Universitas” in Switzerland, which was researched by the author. The author explains two-phase heating and the benefits of the use of this type of stove with regards to air pollution. This article also touches upon the subject of ecological aid measures undertaken in Poland by Swiss institutions, at a time when Polish interest in ecological problems was just beginning.
Źródło:
Zeszyty Naukowe PUNO; 2014, 2; 255-264
2052-319X
Pojawia się w:
Zeszyty Naukowe PUNO
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical study of a polydisperse two-phase jet
Badania numeryczne polidyspersyjnej strugi dwufazowej
Autorzy:
Barata, J.
Perestrelo, N.
Powiązania:
https://bibliotekanauki.pl/articles/263159.pdf
Data publikacji:
2000
Wydawca:
Sieć Badawcza Łukasiewicz. Przemysłowy Instytut Motoryzacji
Tematy:
turbulent dispersion
two-phase flow
Opis:
Low emissions gas turbine combustors will demand fuel injection systems that are efficient in the accomplishment of the mixing of fuel and air in the shortest possible residence time. This paper describes a computational study of a polydisperse two-phase turbulent jet, which is the basic configuration to analyze how the various parameters influence the size distribution and the dispersion of the droplets in the injection process. An Eulerian frame for the for the gas phase was used in conjunction with a Lagrangian approach to describe both interphase slip and turbulence on particle motion. Good agreement of the computations with the experimental data is obtained for both the gas and the particles turbulence modulation and anisotropy effects were introduced and were found to be very important to the successful performance of the computational method. The exchange of monumentum and turbulence energy between the two phases was shown to play a decisive role on the flow development. The predictions confirmed the measurements and showed that the particles do not follow the turbulent gas flow, but they affect it significantly. Considerably high values of the radial velocity were detected around the centerline far from the jet exit where the velocity of the particles lags that of the fluid, that seems to be associated with the effect of shear induced lift forces.
Przedstawiono studium komputerowe polidyspersyjnej dwufazowej strugi turbulentnej, które jest bazą wyjściową do oceny wpływu różnych parametrów na rozkład średnicy kropel podczas wtrysku do ośrodka gazowego. Wykorzystano Eulerowską analizę do fazy gazowej oraz analizę Lagrange'a do obliczania drogi cząstek. Uzyskane wyniki obliczeniowe są zgodne z eksperymentalnymi. Turbulencja i niejednorodność średnic kropel mają istotny wpływ na rozwój strumienia. Stwierdzono także, że składowe promieniowe prędkości z daleka od otworu rozpylacza uzyskują wysokie wartości.
Źródło:
Archiwum Motoryzacji; 2000, 2; 113-125
1234-754X
2084-476X
Pojawia się w:
Archiwum Motoryzacji
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Maintenance policy of degradation components based on the two-phase Wiener process
Autorzy:
Song, Minqiao
Zhang, Yingzhi
Yang, Fang
Wang, Xiaofeng
Guo, Guiming
Powiązania:
https://bibliotekanauki.pl/articles/28328273.pdf
Data publikacji:
2023
Wydawca:
Polska Akademia Nauk. Polskie Naukowo-Techniczne Towarzystwo Eksploatacyjne PAN
Tematy:
condition-based maintenance
two-phase inspection
two-phase Wiener process
Particle Swarm Optimization
sensitivity analysis
Opis:
This paper proposes a condition-based maintenance policy for the two-phase Wiener degradation process components. The main contribution of this article is to provide the time distribution of degradation failures for the two-phase Wiener process degradationcomponent, as well as the modeling and solving methods for two-phase maintenance. The two-phase maintenance policy includes two-phase inspection and preventive replacement maintenance operations. The established optimization maintenance policy model aims to minimize long-term operation costs. The specific cost calculation equation and the solution method of the maintenance model are given. The feasibility of the maintenance policy model is verified using the two-phase degradation data of the Liquid Coupling Devices. The Particle swarm optimization algorithm can stably solve the described problem, and the results show that the two-phase maintenance policy can be more economical and improve components availability. After that, we also analyzed the impact of the cost parameters on the maintenance policy through sensitivity analysis.
Źródło:
Eksploatacja i Niezawodność; 2023, 25, 4; art. no. 172537
1507-2711
Pojawia się w:
Eksploatacja i Niezawodność
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A Two-phase Sampling Strategy for Estimating Multiple Mean Values in the Presence of Nonresponse
Strategia losowania dwufazowego dla estymacji wartości przeciętnej wielu cech w obecności braków odpowiedzi
Autorzy:
Gamrot, Wojciech
Powiązania:
https://bibliotekanauki.pl/articles/904925.pdf
Data publikacji:
2004
Wydawca:
Uniwersytet Łódzki. Wydawnictwo Uniwersytetu Łódzkiego
Tematy:
nonresponse
callbacks
subsampling
two-phase sampling
Opis:
The phenomenon of nonresponse in sample surveys usually results in biased estimates of population characteristics. One of the means to deal with nonresponse is the subsampling technique. It relies on re-contacting some subset of nonrespondents by using more expensive and more efficient tools (e.g. direct interview) than those used in the first attempt to collect data. This allows to increase response rate and to obtain unbiased estimates of population characteristics. In this paper, the problem of establishing the sample and subsample sizes minimizing the expected cost of the survey, while achieving desired precision of multiple mean value estimates, is considered. An algorithm is proposed that allows to establish the optimum initial sample and subsample sizes for two-phase sampling strategy.
Źródło:
Acta Universitatis Lodziensis. Folia Oeconomica; 2004, 175
0208-6018
2353-7663
Pojawia się w:
Acta Universitatis Lodziensis. Folia Oeconomica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
CFD simulation as a tool for the identification of the manifold element reaction to pressure pulsations excitation (one- and two-phase flow)
Autorzy:
Cyklis, P.
Kantor, R.
Powiązania:
https://bibliotekanauki.pl/articles/1955745.pdf
Data publikacji:
2003
Wydawca:
Politechnika Gdańska
Tematy:
pressure pulsations
two-phase flow
CFD
Opis:
The periodicity of compressor operation is a source of pressure pulsations in volumetric compressor manifolds. An analysis of pressure pulsations is important for several reasons. The Helmholtz model, applied in all commercial programs offered by the companies professionally dealing with damping pressure pulsations, contains numerous simplifying assumptions; a straight pipe segment, with an ideal gas isentropic flow assumption, substitutes each element of the piping system. In many cases this model is insufficient. The existing experimental methods could not be used in the design of a muffler. The aim of this paper is to show a new method to identify an arbitrary fragment of a manifold, i.e. a method of identification of the appropriate complex transmittance matrix elements using CFD simulation. This method allows the liquid phase dispersed in the compressed gas and non ideal gas as a working medium to also be considered. The most important conclusion of this work is that identification of acoustic element parameters in the manifold, based on multi-dimensional simulation model, is feasible. The author obtained much better results from the developed method than those yielded by the classic Helmholtz model. A comparison between pure gas and gas with oil contamination is also shown in the paper.
Źródło:
TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2003, 7, 3; 363-374
1428-6394
Pojawia się w:
TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Modelling of two phase filtration in fractures of hydraulic fracturing
Modelowanie filtracji dwufazowej podczas zabiegu szczelinowania
Autorzy:
Beisembetov, I. K.
Assilbekov, B. K.
Zhapbasbayev, U. K.
Kenzhaliev, B. K.
Powiązania:
https://bibliotekanauki.pl/articles/300107.pdf
Data publikacji:
2010
Wydawca:
Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie. Wydawnictwo AGH
Tematy:
symulacje
filtracja dwufazowa
two-phase filtration
simulations
Opis:
Aim of this work is to demonstrate a simulation of two-phase filtration in ruptures of breakdown which stated by mechanical conception of interpenetrating continuums. The worked out computing method forecasts degree of drowning, an amount of stocked up oil extraction and oil extraction ratio. Design data is in satisfactory fit with hydraulic fracturing coefficients got in industrial acceptance of oil fields.
Celem pracy jest pokazanie symulacji filtracji dwufazowej w szczelinach w trakcie zabiegu mechanicznego przerywania ciągłości wzajemnie penetrujących się continuów. Opracowana metoda obliczeniowa stosowana jest do szacowania stopnia zatopienia, stosunku ilości produktywnej ropy do produktywnego gazu. Dane projektowe w pełni zgadzają się ze współczynnikami uzyskanymi ze złóż naftowych.
Źródło:
Wiertnictwo, Nafta, Gaz; 2010, 27, 1--2; 81-89
1507-0042
Pojawia się w:
Wiertnictwo, Nafta, Gaz
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spatial distribution and settling velocity of heavy particles in synthetic turbulent fields
Autorzy:
Łuniewski, M.
Pozorski, J.
Powiązania:
https://bibliotekanauki.pl/articles/175528.pdf
Data publikacji:
2017
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
two-phase flow
heavy particles
turbulent dispersion
Opis:
We analyse numerically the motion of small inertial particles, subject to gravity, in two simple velocity fields: two-dimensional cellular flow, and a three-dimensional flow being the superposition of random Fourier velocity modes. The latter, also known as the kinematic simulation or synthetic turbulence, has often been applied in various studies, including those aiming to predict particle dispersion. The interplay of the particle inertia and the acceleration of gravity has non-trivial consequences for trajectories of particles and their spatial distribution, known as a preferential concentration. Also, we compute the average settling velocity of particles in function of their inertia and the number of fluid velocity modes used in simulations. The present paper aims to study these efects, as the synthetic turbulence represents an interesting option for subfilter modeling in particle-laden large-eddy simulation.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2017, 135; 87-100
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical Simulation of One-Dimensional Two-Phase Flow in Porous Media
Autorzy:
Szymkiewicz, A.
Powiązania:
https://bibliotekanauki.pl/articles/241426.pdf
Data publikacji:
2007
Wydawca:
Polska Akademia Nauk. Instytut Budownictwa Wodnego PAN
Tematy:
two-phase flow
porous media
numerical methods
Opis:
The flow of two immiscible fluids in porous media is described by two coupled non-linear partial differential equations of the parabolic type. In this paper a numerical algorithm to simulate one-dimensional two-phase flow is presented. Cell-centered finite volume method and a generalized two-level scheme with weighting parameter are applied for the discretization in space and time, respectively. The performance of the algorithm is tested for different values of the weighting parameter in the time-discretization scheme and for various methods of approximation of the average conductivities between two adjacent gridblocks. The results are compared with an analytical solution for the horizontal flow and with a reference numerical solution performed on a dense grid for the vertical flow.
Źródło:
Archives of Hydro-Engineering and Environmental Mechanics; 2007, 54, 2; 117-136
1231-3726
Pojawia się w:
Archives of Hydro-Engineering and Environmental Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Two-Phase Flow Measuring with Ultrasonic Tomography
Autorzy:
Qorbani, Omid
Aghdam, Esmaeil Najafi
Powiązania:
https://bibliotekanauki.pl/articles/176579.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Czasopisma i Monografie PAN
Tematy:
two-phase flowmeter
ultrasonic flowmeter
ultrasonic tomography
Opis:
The exact measurement of multiphase flow is an important and essential task in the oil and petrochemical related industries. Several methods have already been proposed in this field. In the existing methods, flow rate measurement depends on the fluid flow pattern. Flow pattern recognition requiring calibration has created instability in such systems. In this paper, a imple and reliable method is proposed which is based on ultrasonic tomography. It is free from calibration and instability problems that existing methods have. The obtained data from a 32-digit array of ultrasonic sensors have been used and the two-phase flow rate including liquid and gas phases have been calculated through a simple algebraic algorithm. Simulation results show that while applying this method the measurement technique is independent from the fluid flow pattern and the system error is decreased. For the proposed algorithm, the average amount of the spatial imaging error (SIE) for a bubble at different positions inside the pipe is about 5%.
Źródło:
Archives of Acoustics; 2020, 45, 3; 459-465
0137-5075
Pojawia się w:
Archives of Acoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Turbulent mixing of a cloud wit h the enviranment: two-phase evaporating flow. Numerical simulations, laboratory experiments and field measurements
Turbulencyjne mieszanie chmury z otoczeniem jako przepływ dwufazowy z parowaniem. Symulacje numeryczne, eksperymenty laboratyjne i pomiary in situ
Autorzy:
Malinowski, S. P.
Powiązania:
https://bibliotekanauki.pl/articles/279222.pdf
Data publikacji:
2007
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
two-phase flow
turbulent mixing
cloud interface
Opis:
A brief overview of numerical simulations, laboratory experiments and in-situ measurements aimed at investigation of the cloud-clear air interfacial-mixing, conducted in recent years at the Institute of Geophysics, University of Warsaw is presented. The most interesting finding from these studies is that the evaporative cooling at the interface separating cloudy and clear filaments results in density differences in scale of centimeters. This effect influences smallest scales of turbulent motions through production of TKE by buoyancy forces and makes the small-scale turbulence anisotropic.
W artykule zawarto zwarty przegląd symulacji numerycznych, eksperymentów prowadzonych w laboratorium oraz pomiarów in situ, których celem było badanie mieszania turbulencyjnego na granicy chmury z nienasyconym otoczeniem. Badania te prowadzono w Instytucie Geofizyki Uniwersytetu Warszawskiego. Najciekawszym wynikiem tych prac jest pokazanie wpływu, jaki ma parowanie wody chmurowej na granicy chmury na dynamikę turbulencji w małych skalach. Parowanie powoduje powstanie lokalnych różnic gęstości o skali przestrzennej rzędu centymetrów. Działanie sił wyporu prowadzi do produkcji drobnoskalowej turbulencji. Ponieważ wyróżniony jest kierunek pionowy, turbulencja ta jest anizotropowa.
Źródło:
Journal of Theoretical and Applied Mechanics; 2007, 45, 3; 587-601
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Impact of a discretization scheme on an autoignition time in LES of a reacting droplet-laden mixing layer
Autorzy:
Stempka, J.
Kuban, L.
Tyliszczak, A.
Powiązania:
https://bibliotekanauki.pl/articles/38621390.pdf
Data publikacji:
2021
Wydawca:
Instytut Podstawowych Problemów Techniki PAN
Tematy:
autoignition process
two-phase flow
mixing layer
Opis:
We analyse an autoignition process in a two-phase flow in a temporally evolving mixing layer formed between streams of a cold liquid fuel (heptane at 300 K) and a hot oxidizer (air at 1000 K) flowing in opposite directions. We focus on the influence of a discretization method on the prediction of the autoignition time and evolution of the flame in its early development phase. We use a high-order code based on the 6th order compact difference method for the Navier–Stokes and continuity equations combined with the 2nd order Total Variation Diminishing (TVD) and 5th order Weighted Essentially Non-Oscillatory (WENO) schemes applied for the discretization of the advection terms in the scalar transport equations. The obtained results show that the autoignition time is more dependent on the discretization method than on the flow initial conditions, i.e., the Reynolds number and the initial turbulence intensity. In terms of mean values, the autoignition occurs approximately 15% earlier when the TVD scheme is used. In this case, the ignition phase characterizes a sharp peak in the temporal evolution of the maximum temperature. The observed differences are attributed to a more dissipative character of the TVD scheme. Its usage leads to a higher mean level of the fuel in the gaseous form and a smoother distribution of species resulting in a lower level of the scalar dissipation rate, which facilitates the autoignition process.
Źródło:
Archives of Mechanics; 2021, 73, 2; 153-174
0373-2029
Pojawia się w:
Archives of Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Modeling of selected phenomena governing surface icing
Autorzy:
Sznajder, J.
Powiązania:
https://bibliotekanauki.pl/articles/248155.pdf
Data publikacji:
2013
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
icing
transport
air transport
simulation
two-phase flow
Opis:
Atmospheric icing poses a threat for safety in many areas of transport, especially in air transport and exerts harmful impact on operation of external sensors and mechanisms of aircraft, ships and land vehicles. In order to investigate phenomena leading to ice accretion on sensitive parts of objects exposed to icing conditions numerical simulation models are in use. These models are typically composed of submodels dealing with a fragment of the complex phenomenon of ice accretion and its interaction with external flow. A practical approach to simulation of icing process is to divide it into three problems being solved interactively: 1) simulation of two-phase flow of air and dispersed supercooled water and determination of distribution of mass of water hitting the object’s surface, 2) determination of conditions on the surface collecting supercooled water from the external flow and simulation of freezing and water film flow, and 3) modification of computational grid as a consequence of change of shape of the surface with deposits of ice. A simulation system directed at investigation of atmospheric icing on moving object is being developed as an extension of capabilities of a commercial CFD code ANSYS FLUENT. Solutions of two-phase flow of air and dispersed water with specific boundary conditions enabling the determination of distribution of water hitting the surface, as well as results of modelling of water film flow on the surface will be presented. The system of equations describing the transport of the dispersed water consists of the continuity and momentum equations. It is assumed, that interactions between the phases are onedirectional, i.e. the air flow influences the water droplet flow and not vice-versa. It is also assumed that the water film velocity distribution is linear in direction normal to surface. This way, both phenomena are being described with first order partial differential equations with respect to space and time and the solution approaches may be similar.
Źródło:
Journal of KONES; 2013, 20, 2; 377-384
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of stereology for assessment of two-phase flow structures
Autorzy:
Masiukiewicz, M.
Ulbrich, R.
Zając, D.
Powiązania:
https://bibliotekanauki.pl/articles/175510.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
stereological analysis
two-phase flow pattern
pattern recognition
Opis:
This paper describes a method for two-phase flow structures evaluation of gas-liquid mixture based on theoretical assumptions for the stereology in materials science. This assessment is based on the analysis of digital images, obtained with a high-speed camera. The bright field technique was used for process visualization. The images obtained during the visualisation were, in fact, projections of the structures. For the given recording conditions, the stereological analysis applied was based on the linear method and on the method of random and directed secants. The new methods of determining important parameters of two-phase flow were proposed on the basis of collected data. The parameters are as follows: the volume fraction, the interfacial area, the number of objects in one of the phases of the mixture and two other structural parameters of the selected two-phase fluid obtained from the analysis of the two-dimensional image (average length of chords for projected objects, average free distance for convex shapes from the projection).
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2013, 125; 39-54
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Numerical calculations of RVE dimensions for two-phase material
Autorzy:
Miedzińska, D.
Niezgoda, T.
Powiązania:
https://bibliotekanauki.pl/articles/242298.pdf
Data publikacji:
2011
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
microstructure
two-phase material
metal-ceramic composite
RVE
Opis:
A representative volume element (RVE) is a statistical representation of typical material properties. It should contain enough information on the microstructure thereby be sufficiently smaller than the macroscopic structural dimensions. The paper deals with the numerical calculations of the dimensions of the RVE for a two-phase material microstructure. Two and three dimensional models are taken into consideration. The structure of the samples are developed on the base of randomization of elements belonging to one of the phases. The phases volume share is 50/50%. The following series of the models are analyzed: from 10 x 10 to 100 x 100 elements for 2D samples and from 10 x 10 x 10 to 100 x 100 x 100 elements for 3D samples. The element characteristic dimension is 10 jm. The elastic behavior of the base materials (magnesium and alumina) is taken into account. The quasi-static compression tests of the developed structures are carried out with the use of LS-DYNA computer code. The results are presented as the equivalent Young modulus values and compared to the calculations based on the rule of mixtures. The stabilization of the achieved results allows to assess the dimensions of the RVE for two-phase material with random distribution.
Źródło:
Journal of KONES; 2011, 18, 2; 303-310
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Simplified Volume of Fluid Method (SVOF) for two-phase flows
Autorzy:
Marek, M.
Aniszewski, W.
Bogusławski, A.
Powiązania:
https://bibliotekanauki.pl/articles/1943237.pdf
Data publikacji:
2008
Wydawca:
Politechnika Gdańska
Tematy:
two-phase flow modeling
volume of fluid
eulerian simulation
Opis:
The PLIC approach has been usually used in recent implementations of the VOF method i.e. the interphasal surface is approximated by a plane with an arbitrary orientation with respect to the computational cell. Although this method is accurate, it is rather difficult to implement, as a large number of orientations need to be taken into account and the calculation of volume fraction fluxes is not straightforward. A simpler approach to VOF – SLIC – requires much less effort from the programmer but the interface approximation by a plane parallel to the cell surfaces is too crude and the results are not satisfactory. The method presented in the article may be considered as an intermediate approach between PLIC and SLIC – fluxes are computed directly only for the interface’s special orientations and linear interpolation is used for calculation of the fluxes for the remaining cases. Some classical tests of the proposed method are performed and an example of a broken dam problem simulation is presented.
Źródło:
TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2008, 12, 3-4; 255-265
1428-6394
Pojawia się w:
TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
Dostawca treści:
Biblioteka Nauki
Artykuł
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