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Wyświetlanie 1-8 z 8
Tytuł:
Compressor modeling using Greitzer model validated by pressure oscillations
Autorzy:
Grapow, F.
Liśkiewicz, G.
Powiązania:
https://bibliotekanauki.pl/articles/175456.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
centrifugal compressor
surge
greitzer model
compressor modeling
Opis:
Nowadays compressors are used in almost every industry. Compressor failure can suspend production of the whole system so the importance of preventing from failures is obvious and essential. One of the most dangerous flow instabilities which is capable of destroying machine in few seconds is surge, which occurs in conditions of low mass flow rate. Greitzer model, apart from its long history, is still most common mathematical model describing surge. It is widely used to predict the surge onset and pressure oscillations during it. However, it is based on parameters that are not directly related to real machine and their choice is not always obvious. Therefore, the calculations may be inaccurate which results in wrong surge prediction. The other approach to Greitzer model is presented in this paper, which in some cases can assure that the process of compressor modeling is more accurate. The applicability of Greitzer surge model for real machines has been analyzed. Method of implementation is based on experimental pressure signal gathered during unstable work of compressor. Presented method is based on experimental compressor characteristic and outlet pressure signal from unstable work of compressor. From that data it is possible to determinate the value of Greitzer model’s parameters for selected operational point. Thanks to this method this model could be applied for reliable antisurge protection.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2016, 133; 69-89
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Mathematical surge modeling based on the pressure oscillations in the stable operation range of the compressor
Autorzy:
Jaeschke, A.
Liśkiewicz, G.
Powiązania:
https://bibliotekanauki.pl/articles/175279.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
radial compressors
surge
Greitzer model
Opis:
Prevention of surge phenomenon is a very active field of research in last decades. The Greitzer model is the most widely applied mathematical model describing the surge phenomenon. Two parameters that characterize the given compressing system: the Helmholtz oscillator frequency and the so-called B parameter have to be given as the input to Greitzer model. Although those parameters are easy to determine for simplified compressor models, they are extremely hard to predict in case of real industrial compressors. Moreover, in most cases it is impossible to analyse compressor unstable work, which makes this prediction even more speculative. Therefore the method that determines the parameters basing on the compressor stable operation is indispensable. In paper the regularly perturbed Greitzer model based method of predicting the behaviour of a compressor in the unstable operation basing on signals from its stable operation is proposed and discussed.
Źródło:
Transactions of the Institute of Fluid-Flow Machinery; 2016, 133; 91-108
0079-3205
Pojawia się w:
Transactions of the Institute of Fluid-Flow Machinery
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Local cavitation due to water hammer
Autorzy:
Mitosek, M.
Kodura, A.
Rybak-Wilusz, E.
Powiązania:
https://bibliotekanauki.pl/articles/241414.pdf
Data publikacji:
2003
Wydawca:
Polska Akademia Nauk. Instytut Budownictwa Wodnego PAN
Tematy:
water hammer
cavitation
pressure oscillations
gas desorption
Opis:
The phenomenon of vapour cavitation due to water hammer is investigated ex-perimentally using high frequency pressure transducers (piezoelectric and strain gauges). The water hammer is caused by a sudden closure of a ball valve mounted at the end of the steel pipe. A short-duration pressure pulse, as well as high frequency cavitation pressure oscillations is observed. The high frequency pressure oscillations appear just after the vapour cavity collapse, whereas the pressure pulse does not occur immediately after collapse but is delayed from 0 to the water hammer period $2L/c$, s. The experiments have shown that the maxi-mum high frequency pressure oscillation, directly proportional to the pressure wave velocity, can be many times higher than the maximum water hammer pres-sure amplitude as well as short-duration pressure pulse. The influence of liquid evaporation duration and the steady state losses on the maximum high frequency cavitation pressure oscillation are shown. Growing pressure reduction is accom-panied by gas desorption from the liquid. The liberated air reduces the amplitude of the pressure increase and prolongs the period of oscillations. The experiments have shown that there are three phases of the maximum amplitude of high fre-quency pressure oscillations for each fixed steady state loss. The frequency of va-pour cavitation pressure oscillations depends on the duration of the oscillations. For the test cases, the frequency increases during the cavitation from ca. 400 to 900 Hz for steel pipes.
Źródło:
Archives of Hydro-Engineering and Environmental Mechanics; 2003, 50, 1; 59-72
1231-3726
Pojawia się w:
Archives of Hydro-Engineering and Environmental Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Indicated mean effective pressure oscillations in a natural gas combustion engine by recurrence plots
Analiza wykresów rekurencyjnych dla średniego efektywnego ciśnienia indykowanego w silniku spalinowym zasilanym gazem naturalnym
Autorzy:
Litak, G.
Syta, A.
Yao, B. -F.
Li, G.-X
Powiązania:
https://bibliotekanauki.pl/articles/280206.pdf
Data publikacji:
2009
Wydawca:
Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Tematy:
engine
combustion
recurrence plot
nonlinear oscillations
Opis:
We investigate the nonlinear time series of Indicated Mean Effective Pressure (IMEP) of the spark ignition engine cyclic combustion process of a natural gas. By applying the embedding theorem and the recurrence plots technique, we show changes in the engine dynamics for different equivalence ratios. Especially, we provide arguments for intermittency behaviour.
Zbadano nieliniowe przebiegi czasowe Średniego Ciśnienia Indykowanego cyklicznego procesu spalania w silniku spalinowym zasilanym gazem naturalnym. Stosując twierdzenie o zanurzeniu oraz technikę wykresów rekurencyjnych, pokazano istotne różnice w dynamice silnika przy zmianie składu mieszanki paliwa wyrażonej wartością współczynnika równowagowego. W szczególności podano argumenty przemawiające za występowaniem zjawiska intermitencji.
Źródło:
Journal of Theoretical and Applied Mechanics; 2009, 47, 1; 55-67
1429-2955
Pojawia się w:
Journal of Theoretical and Applied Mechanics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analiza i modelowanie wahań podciśnienia w aparacie udojowym w relacji do zmian pojemności komory mlecznej kolektora
Analysis and modelling of (under pressure oscillations) vacuum fluctuations in the milking apparatus in relation to the volume changes of the milk chamber of a (collector) claw
Autorzy:
Wiercioch, M.
Luberański, A.
Krzyś, A.
Skalska, D.
Powiązania:
https://bibliotekanauki.pl/articles/289542.pdf
Data publikacji:
2013
Wydawca:
Polskie Towarzystwo Inżynierii Rolniczej
Tematy:
aparat udojowy
kolektor
pojemność
wahania podciśnienia
modelowanie
milking apparatus
claw
volume
vacuum fluctuation
modelling
Opis:
Celem pracy była analiza wahań podciśnienia w cyklu w aparacie udojowym wyposażonym w kolektory o zmiennej pojemności komory mlecznej przy doju przemiennym do rurociągu mlecznego górnego i do bańki w warunkach symulowanego doju mechanicznego oraz opracowanie formuły matematycznej do ich wyznaczania. Pomiary przeprowadzono w warunkach laboratoryjnych przy zmiennych masowych natężeniach przepływu cieczy (w zakresie 0–8 kg·min-1), dla czterech pojemności kolektorów (500, 300, 150 i 45 cm3) i trzech wartości podciśnień systemowych (44, 46 i 48 kPa). Wykazano stosując analizę statystyczną istotny wpływ zmiennych niezależnych doświadczenia (z wyjątkiem podciśnienia) na wahania podciśnienia w cyklu dp. Najniższe wartości wahań podciśnienia w cyklu zaobserwowano przy stosowaniu kolektora o pojemności 500 cm3. Wykorzystując metodę regresji wielorakiej z krokową eliminacją zmiennych niezależnych zbudowano na podstawie wyników badań model matematyczno-statystyczny do wyznaczania wahania podciśnienia w cyklu, który przyjmuje charakter 3-parametrowego równania empirycznego o postaci dp = 4,11 + 0,93Qm + 1,02H – 0,01Vk ze współczynnikiem determinacji R2= 0,77.
The objective of the paper was to analyse (under pressure oscillations) vacuum fluctuations within the cycle in the milking apparatus equipped with (collectors) claws with a variable volume of the milk chamber at the alternative milking to the upper (milk pipeline) milkline and to the (bulb) bucket in the conditions of simulated mechanical milking and to develop a mathematical formula for their determination. Measurements were carried out in the laboratory conditions at variable mass intensities of liquid flow (within 0-8 kg·min-1), for four volumes of (collectors) claws (500, 300, 150 and 45 cm3) and three values of system (under pressures) vacumms (44, 46 and 48 kPa). With the use of statistical analysis a significant (impact) effect of independent variables of experience (except for (under pressure) ) on the (under pressure oscillations) vacuum fluctuations within the dp cycle was proved. The lowest values of (under pressure oscillations) vacuum fluctuations within the cycle were reported at the use of the (collector) claw with 500cm3 volume. Using the multiple regression method with step elimination of independent variables based on the research results a mathematical and statistical model was constructed for determination of the (under pressure oscillation) vacuum fluctuation within the cycle, which takes a character of 3-parameters empirical equation in the form of dp = 4.11 + 0.93Qm + 1.02H – 0.01Vk with coefficient of determination R2= 0.77.
Źródło:
Inżynieria Rolnicza; 2013, R. 17, nr 4, t. 1, 4, t. 1; 383-392
1429-7264
Pojawia się w:
Inżynieria Rolnicza
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Modelling of Pressure-Drop Instability in Single and Multi Microchannels System
Autorzy:
Grzybowski, H.
Mosdorf, R.
Powiązania:
https://bibliotekanauki.pl/articles/386991.pdf
Data publikacji:
2012
Wydawca:
Politechnika Białostocka. Oficyna Wydawnicza Politechniki Białostockiej
Tematy:
przepływ dwufazowy
niestabilność
mikrokanał
spadek ciśnienia
oscylacja przepływu
two-phase flow
instabilities
microchannels
pressure drop
flow oscillations
Opis:
In the paper the model of pressure-drop oscillations has been proposed. The model was based on the iterative solution to equations. The dynamics of pressure-drop oscillations in a single channel and in two neighbouring channels have been analyzed. There has been assumed that the pressure-drop oscillations in the system are caused by interactions between the heat supply system and liquid supply system. These interactions influence the heat and mass transfer inside the microchannel. Obtained results indicate that the shape of pressure drop curve has a significant influence on the system stability. When the slope of curve ? = () in the region between function extremes increases then the pressure oscillations become chaotic. In case of multichannel system the thermal interactions (occurring through the channel walls) and hydrodynamic interactions (occurring inside the common channels outlet) have been considered. Four types of two-phase flow behaviours in parallel channels have been observed depending on the intensity of interactions: alternate oscillations, consistent oscillations, periodic oscillations and completely synchronized oscillations. Obtained qualitative results have been compared with conclusions of experimental results reported by other researches. The good qualitative agreement with experimental results has been obtained.
Źródło:
Acta Mechanica et Automatica; 2012, 6, 3; 45-51
1898-4088
2300-5319
Pojawia się w:
Acta Mechanica et Automatica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Development of generalized dynamic model of oscillations of cylinder case of diesel engine of locomotive
Разработка обобщенной динамической модели колебаний гильзы цилиндра дизеля тепловоза
Autorzy:
Yutkina, I.
Powiązania:
https://bibliotekanauki.pl/articles/374350.pdf
Data publikacji:
2014
Wydawca:
Politechnika Śląska. Wydawnictwo Politechniki Śląskiej
Tematy:
dynamic model
cylinder case
pulsed pressure
model dynamiczny
ciśnienie impulsowe
Opis:
An engineering method of design, worked out by the authors, is considered in the paper. It allows to carry out design of amplitude-frequency specter and vibration loading of cylinder cases of the diesel engine of locomotive with account of cavitationerosion damage. Offered method of design of parameters of cavitation-erosion damage may be used in design of new structures of diesel engines of locomotives and systems of cooling.
В статье приведен полученный авторами инженерный метод расчета, позволяющий проводить расчет амплитудно-частотного спектра и вибрационного нагружения цилиндровых гильз дизеля тепловоза с учетом кавитационно-эрозионного разрушения. Предложенный метод расчета параметров кавитационно-эрозионного разрушения можно использовать при проектировании новых конструкций дизелей тепловозов и систем охлаждения.
Źródło:
Transport Problems; 2014, 9, 1; 95-102
1896-0596
2300-861X
Pojawia się w:
Transport Problems
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effects of global climate oscillations on intermonthly to interannual variability of sea levels along the English Channel Coasts (NW France)
Autorzy:
Turki, I.
Massei, N.
Laignel, B.
Shafiei, H.
Powiązania:
https://bibliotekanauki.pl/articles/2079277.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Instytut Oceanologii PAN
Tematy:
sea level
interannual variability
storm
atmospheric circulation
climatic oscillation
sea surface temperature
sea level pressure
North Atlantic oscillation
English Channel
Opis:
This work examines the multiscale variability in sea level along the English Channel coasts (NW France) using a wavelet multiresolution decomposition of water level values and climate oscillations in order to gain insights in the connection between the global atmospheric circulation and the local-scale variability of the monthly extreme surges. Changes in surges have exhibited different oscillatory components from the intermonthly (~3–6-months) to the interannual scales (~1.5-years, ~2–4-years, ~5–8-years) with mean explained variances of ~40% and ~25% of the total variability respectively. The correlation between the multiresolution components of surges and 28 exceptional stormy events with different intensities has revealed that energetic events are manifested at all timescales while moderate events are limited to short scales. By considering the two hypotheses of (1) the physical mechanisms of the atmospheric circulation change according to the timescales and (2) their connection with the local variability improves the prediction of the extremes, the multiscale components of the monthly extreme surges have been investigated using four different climate oscillations (Sea Surface Temperature (SST), Sea-Level Pressure (SLP), Zonal Wind (ZW), and North Atlantic Oscillation (NAO)); results show statistically significant correlations with ~3–6-months, ~1.5-years, ~2–4-years, and ~5–8-years, respectively. Such physical links, from global to local scales, have been considered to model the multiscale monthly extreme surges using a time-dependent Generalized Extreme Value (GEV) distribution. The incorporation of the climate information in the GEV parameters has considerably improved the fitting of the different timescales of surges with an explained variance higher than 30%. This improvement exhibits their nonlinear relationship with the large-scale atmospheric circulation.
Źródło:
Oceanologia; 2020, 62, 2; 226-242
0078-3234
Pojawia się w:
Oceanologia
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-8 z 8

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