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Wyświetlanie 1-15 z 114
Tytuł:
Turbine stage expansion model including internal air film cooling and novel method of calculating theoretical power of a cooled stage
Autorzy:
Trawiński, Paweł
Powiązania:
https://bibliotekanauki.pl/articles/2134930.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
gas turbine
expansion line
air film cooling
theoretical stage power
Opis:
Systematic attempts to maximise the efficiency of gas turbine units are achieved, among other possibilities, by increasing the temperature at the inlet to the expansion section. This requires additional technological solutions in advanced systems for cooling the blade rows with air extracted from the compressor section. This paper introduces a new mathematical model describing the expansion process of the working medium in the turbine stage with air film cooling. The model includes temperature and pressure losses caused by the mixing of cooling air in the path of hot exhaust gases. The improvement of the accuracy of the expansion process mathematical description, compared with the currently used models, is achieved by introducing an additional empirical coefficient estimating the distribution of the cooling air along the profile of the turbine blade. The new approach to determine the theoretical power of a cooled turbine stage is also presented. The model is based on the application of three conservation laws: mass, energy and momentum. The advantage of the proposed approach is the inclusion of variable thermodynamic parameters of the cooling medium. The results were compared with the simplified models used in the literature: separate Hartsel expansion, mainstream pressure, weighted-average pressure and fully reversible. The proposed model for expansion and the determination of theoretical power allows for accurate modelling of the performance of a cooled turbine stage under varying conditions.
Źródło:
Archives of Thermodynamics; 2022, 43, 3; 3--27
1231-0956
2083-6023
Pojawia się w:
Archives of Thermodynamics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical Implications of Maritime Sociology
Autorzy:
Cocco, Emilio
Powiązania:
https://bibliotekanauki.pl/articles/520217.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
sea
land
sociology
maritime
social space
Opis:
The sea is certainly not one of the favourite research topics of sociology and despite a recent and new popularity among historians and geographers, the sea remains generally a stranger to contemporary sociologists. Conversely, I think that to frame and shed light on the wider theoretical implications of maritime sociology would be beneficial to all possible approaches within sociological research. In this article I intend to give my contribution to the fulfillment of the expectation of above by discussing the ways sociology can understand the sea as a truly social space, beyond any abstract dichotomies separating “grounded” societies and offshore voids. Also, I try to suggest some concrete moves to relocate maritime sociology within the wider sociological debate and to develop the heuristic potential of the sea.
Źródło:
Roczniki Socjologii Morskiej; 2013, 22; 5-18
0860-6552
Pojawia się w:
Roczniki Socjologii Morskiej
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A theoretical analysis of vibrational stress relief in AISI 1008 as a mechanical treatment
Autorzy:
Vardanjani, Mehdi Jafari
Senkara, Jacek
Powiązania:
https://bibliotekanauki.pl/articles/1845027.pdf
Data publikacji:
2021
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
vibrational stress relief (VSR)
equation
theoretical analysis
residual stress
odprężanie wibracyjne
równanie
analiza teoretyczna
naprężenie szczątkowe
Opis:
Vibrational stress relief (VSR) treatment as a method of stress relief is currently performed on different alloys and sizes as an appropriate alternative for thermal stress relief (TSR) method. Although many studies have been performed to extend the knowledge about this process, analytical studies in the field of VSR process seems to require wider efforts to introduce the concept more clearly and extensively. In this study, a theoretical model is proposed based on an analytical equation. The proposed equation was modified in terms of required variables including frequency, amplitude, and vibration duration to encompass more practical parameters compared to the previous models. Thus, essential VSR parameters including the number of cycles as a representative of treatment duration, strain rate as a representative of frequency, and the amplitude were embedded in the model to make it comprehensively practical. Experimental tests were also performed and residual stress distribution was measured by X-ray diffractometry (XRD) method for certain points to compare the experimental results with the theoretical output. An acceptable range of conformation was observed between theoretical and experimental results.
Źródło:
Archive of Mechanical Engineering; 2021, LXVIII, 4; 353-374
0004-0738
Pojawia się w:
Archive of Mechanical Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
City Marketing: the Theoretical and Practical Aspects (the Example of Latvia)
Autorzy:
Ignatyev, Sergey
Ratanova, Inese
Powiązania:
https://bibliotekanauki.pl/articles/2029658.pdf
Data publikacji:
2011
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Źródło:
Studia komitetu przestrzennego zagospodarowania kraju PAN; 2011, 141; 259-271
0079-3507
Pojawia się w:
Studia komitetu przestrzennego zagospodarowania kraju PAN
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical geodesy
Autorzy:
Borkowski, A.
Kosek, W.
Powiązania:
https://bibliotekanauki.pl/articles/145440.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
M-estimation
robust estimation
reliability
time series
polar motion
niezawodność
szeregi czasowe
estymacja
Opis:
The paper presents a summary of research activities concerning theoretical geodesy performed in Poland in the period of 2011-2014. It contains the results of research on new methods of the parameter estimation, a study on robustness properties of the M-estimation, control network and deformation analysis, and geodetic time series analysis. The main achievements in the geodetic parameter estimation involve a new model of the M-estimation with probabilistic models of geodetic observations, a new Shift-Msplit estimation, which allows to estimate a vector of parameter differences and the Shift-Msplit(+) that is a generalisation of Shift-Msplit estimation if the design matrix A of a functional model has not a full column rank. The new algorithms of the coordinates conversion between the Cartesian and geodetic coordinates, both on the rotational and triaxial ellipsoid can be mentioned as a highlights of the research of the last four years. New parameter estimation models developed have been adopted and successfully applied to the control network and deformation analysis. New algorithms based on the wavelet, Fourier and Hilbert transforms were applied to find time-frequency characteristics of geodetic and geophysical time series as well as time-frequency relations between them. Statistical properties of these time series are also presented using different statistical tests as well as 2nd, 3rd and 4th moments about the mean. The new forecasts methods are presented which enable prediction of the considered time series in different frequency bands.
Źródło:
Geodesy and Cartography; 2015, 64, 2; 261-279
2080-6736
2300-2581
Pojawia się w:
Geodesy and Cartography
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Determination and analysis of the theoretical production of a bucket wheel excavator
Określanie i analiza teoretycznej wydajności pracy koparki wielonaczyniowej kołowej
Autorzy:
Zhao-Xue, C.
Yan-Long, C.
Powiązania:
https://bibliotekanauki.pl/articles/219168.pdf
Data publikacji:
2014
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
koparka kołowa wielonaczyniowa
teoretycznie obliczone wydobycie
prędkość obrotowa
korpus koparki
bucket wheel excavator
theoretical production
rotary speed
excavator body
Opis:
The theoretical capacity of a bucket wheel excavator is the basis of mining theory. The paper concludes that the use of “1/cosφ” to adjust the speed of a bucket wheel excavator will result in rapid speeds, which may cause nonuniform flow from the distribution of material flow, and decreased capacity utilization. Consequently, this scenario may produce unreasonable structure parameters and performance parameters that are based on theoretical analysis and mathematical derivation. If the rotary speed of an excavator body is too fast, it will require excessive mechanical strength and will generate increased rotary drive power, power consumption and extractive costs. Thus, the rotary speed of an excavator body should be appropriately reduced.
Teoretyczna wydajność koparki wielonaczyniowej kołowej jest podstawą w teoretycznych obliczeniach wydajności wydobycia. Autorzy pracy wyciągnęli wniosek, że wykorzystanie zależności 1/cosφ przy sterowaniu prędkością pracy koparki prowadzi do zbyt dużych prędkości, co powodować może nierównomierność strumienia urobku i ograniczone wykorzystanie mocy przerobowych koparki. W konsekwencji, mamy do czynienia z nieuzasadnionymi parametrami konstrukcyjnymi i eksploatacyjnymi opartymi na analizach teoretycznych i matematycznych wyprowadzeniach. Jeśli prędkość obrotowa w ruchu korpusu koparki jest zbyt duża, wymagane będzie dostarczenie nadmiernej siły by wygenerować odpowiednio dużą prędkość obrotową, prowadząc do wzrostu zużycia energii i kosztów wydobycia. Dlatego też konieczna jest odpowiednia kontrola prędkości obrotowej w ruchu koparki.
Źródło:
Archives of Mining Sciences; 2014, 59, 1; 283-291
0860-7001
Pojawia się w:
Archives of Mining Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical Studies of Nonlinear Generation Efficiency in a Bubble Layer
Autorzy:
Baranowska, A.
Powiązania:
https://bibliotekanauki.pl/articles/176687.pdf
Data publikacji:
2012
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
nonlinear acoustics
bubble layer
transmitted and reflected waves
Opis:
The aim of the paper is a theoretical analysis of propagation of high-intensity acoustic waves throughout a bubble layer. A simple model in the form of a layer with uniformly distributed mono-size spherical bubbles is considered. The mathematical model of the pressure wave’s propagation in a bubbly liquid layer is constructed using the linear non-dissipative wave equation and assuming that oscillations of a single bubble satisfy the Rayleigh-Plesset equation. The models of the phase sound speed, changes of resonant frequency of bubbles and damping coefficients in a bubbly liquid are compared and discussed. The relations between transmitted and reflected waves and their second harmonic amplitudes are analyzed. A numerical analysis is carried out for different environmental parameters such as layer thicknesses and values of the volume fraction as well as for different parameters of generated signals. Examples of results of the numerical modeling are presented.
Źródło:
Archives of Acoustics; 2012, 37, 3; 287-294
0137-5075
Pojawia się w:
Archives of Acoustics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Problems related to theoretical modeling of production and behavior of thermal barrier coatings
Autorzy:
Kaczmarek, J.
Powiązania:
https://bibliotekanauki.pl/articles/175391.pdf
Data publikacji:
2010
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
thermal barrier coating
deposition
multiscalemodeling
Opis:
In this paper one discusses the problem of modeling of thermal barrier coatings in an unified way. This approach takes into account both mechanics of materials responsible for behavior of the thermal barrier coatings and its production relying on preparation of material for deposition and the deposition itself. Two pillars of the unified description are considered. The first one is the notion of index of structure. The second one is created by criteria of design of properties of the thermal barrier coatings. It is suggested to apply the multiscale method of modeling for the behavior of material in deposited layer called collection of dynamical systems with dimensional reduction. This multiscale approach is viewed as appropriate theoretical environment for expression of design criteria of the layer. We mean by this the criteria related to mechanical resistance against damage and criteria for thermal properties. It is accentuated that the two-scale segment of multicale modeling composed of molecular dynamics and nanoscale modeling is of primary importance for the design tasks. Possibility of consideration of both mentioned methods of modeling follows from properties of the collection of dynamical system approach which allow us to treat molecular dynamics and continuum mechanics models within one theoretical scheme. Premises for design of production of thermal barrier coatings process are placed in the design of layer properties which could be next transformed into design of indexes of structure corresponding to various stages of the deposition.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2010, 122; 3-43
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical modelling of MWIR thermoelectrically cooled nBn HgCdTe detector
Autorzy:
Martyniuk, P.
Rogalski, A.
Powiązania:
https://bibliotekanauki.pl/articles/201922.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
barrier detectors
unipolar barrier
nBn
HgCdTe
photodetectors
Opis:
The paper reports on the medium wavelength infrared (MWIR) unipolar barrier infrared detector (UBIRD) nBn/B-n type (n-type barrier) HgCdTe detector’s photoelectrical performance. The UBIRD nBn/B-n type HgCdTe detector was modelled using commercially available software APSYS. Detailed analysis of the detector’s performance (such as dark current, photocurrent, responsivity, and detectivity) versus bias voltage, operating temperatures, and structural parameters (cap, barrier, and absorber’s doping as well as cap and barrier compositions) were performed pointing out optimal working conditions. Both conduction and valence band alignments of the HgCdTe nBn/B-n type detector structure was simulated stressing their importance on detectors performance. It was shown that higher operation temperature (HOT) conditions achieved by commonly used thermoelectric (TE) coolers allow to obtain detectivities of D* = (3-10)×109 cmHz1/2/W at T = 200 K for detectors with cut-off wavelength of 5.2 ?m The differential resistance area product of RA = 0.15-0.4 cm2 at T = 230 K for bias voltage V = 50 mV was estimated. Finally, the state of the art of UBIRD HgCdTe nBn/B-n type detector performance was compared to InAs/GaSb/B-Al0.2Ga0.8Sb T2SLs nBn detector, InAs/GaSb T2SLs PIN and the HOT HgCdTe bulk photodiodes’ operated at near-room temperature (T = 230 K). It was shown that the RA product of the MWIR UBIRD nBn/B-n type HgCdTe detector can reach a comparable level to the state of the art of the HgCdTe HOT bulk photodiodes and two types of type-II superlattice detectors: PIN photodiodes and nBn detectors.
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2013, 61, 1; 211-220
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical analysis of LNG regasifier supplementing gas turbine cycle
Autorzy:
Szczygieł, Ireneusz
Rutczyk, Bartłomiej
Powiązania:
https://bibliotekanauki.pl/articles/1955037.pdf
Data publikacji:
2021
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
LNG
gas turbine
cryogenic exergy
energy recovery
Opis:
Liquefied natural gas (LNG) is transported by the sea-ships with relatively low pressure (0.13–0.14 MPa) and very low temperature (about 100 K) in cryo-containers. Liquid phase, and the low temperature of the medium is connected with its high exergy. LNG receives this exergy during the liquefaction and is related with energy consumption in this process. When the LNG is evaporated in atmospheric regasifiers (what takes place in many on-shore terminals as well as in local regasifier stations) the cryogenic exergy is totally lost. fortunately, there are a lot of installations dedicated for exergy recovery during LNG regasification. These are mainly used for the production of electricity, but there are also rare examples of utilization of the LNG cryogenic exergy for other tasks, for example it is utilized in the fruit lyophilization process. In the paper installations based on the Brayton cycle gas turbine are investigated, in the form of systems with inlet air cooling, liquid phase injection, exhaust gas based LNG evaporation and mirror gas turbine systems. The mirror gas turbine system are found most exegetically effective, while the exhaust gas heated systems the most practical in terms of own LNG consumption.
Źródło:
Archives of Thermodynamics; 2021, 42, 4; 47-67
1231-0956
2083-6023
Pojawia się w:
Archives of Thermodynamics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Experimental and theoretical study of surface cooling using a single microjet
Autorzy:
Mikielewicz, D.
Muszyński, T.
Powiązania:
https://bibliotekanauki.pl/articles/175373.pdf
Data publikacji:
2010
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
surface cooling
microjets
heat transfer intensification
Opis:
The experimental research of heat transfer due to impingement of a single microjet of water and air has been studied on a specially designed rig. Systematic data on radial wall temperature distribution were collected, which enabled development of empirical correlation for heat transfer coefficient applicable both for air and water flows. Two microjet nozzle diameters were studied, i.e. 180 and 260 ěm. The correlation describing the heat transfer coefficient was later used in validation of a model of a single microjet impinging on a flat plate, developed earlier by the authors. Such analytical model of microjet is of a great value in future analysis as it enables to carry out for example sensitivity tests or to appropriately select operational parameters. The presented model is quite general and its further modifications are possible when some of the imposed assumptions are relaxed. More experiments on the structure of a single microjet are needed which will confirm the correlation presented in the paper.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2010, 122; 95-110
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical Elements in Fourier Analysis of q-Gaussian Functions
Autorzy:
Rodrigues, P S. S.
Giraldi, G. A.
Powiązania:
https://bibliotekanauki.pl/articles/375832.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
q-Gaussian kernel
signal processing
Opis:
There is a consensus in signal processing that the Gaussian kernel and its partial derivatives enable the development of robust algorithms for feature detection. Fourier analysis and convolution theory have a central role in such development. In this paper, we collect theoretical elements to follow this avenue but using the q-Gaussian kernel that is a nonextensive generalization of the Gaussian one. Firstly, we review the one-dimensional q-Gaussian and its Fourier transform. Then, we consider the two-dimensional q-Gaussian and we highlight the issues behind its analytical Fourier transform computation. In the computational experiments, we analyze the q-Gaussian kernel in the space and Fourier domains using the concepts of space window, cut-o frequency, and the Heisenberg inequality.
Źródło:
Theoretical and Applied Informatics; 2015, 27, 2; 16-44
1896-5334
Pojawia się w:
Theoretical and Applied Informatics
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 114

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