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1
Content available Performance metrics in OFDM wireless networks supporting quasi-random traffic
Panagoulias P., Moscholios I., Sarigiannidis P., Piechowiak M., Logothetis M.
Bulletin of the Polish Academy of Sciences. Technical Sciences
|
2020
|
Vol. 68, nr 2
215--223
EN
We consider the downlink of an orthogonal frequency division multiplexing (OFDM) based cell that accommodates calls from different service-classes with different resource requirements. We assume that calls arrive in the cell according to a quasi-random process, i.e., calls are generated by a finite number of sources. To calculate the most important performance metrics in this OFDM-based cell, i.e., congestion probabilities and resource utilization, we model it as a multirate loss model, show that the steady-state probabilities have a product form solution (PFS) and propose recursive formulas which reduce the complexity of the calculations. In addition, we study the bandwidth reservation (BR) policy which can be used in order to reserve subcarriers in favor of calls with high subcarrier requirements. The existence of the BR policy destroys the PFS of the steady-state probabilities. However, it is shown that there are recursive formulas for the determination of the various performance measures. The accuracy of the proposed formulas is verified via simulation and found to be satisfactory.
2
Content available Call-level Analysis of a Two-Link Multirate Loss Model based on a Convolution Algorithm
Sagkriotis S. G., Pantelis S. K., Moscholios I. D., Vassilakis V. G.
Journal of Telecommunications and Information Technology
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2018
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nr 1
3--10
EN
We consider a two-link system that accommodates Poisson arriving calls from different service-classes and propose a multirate teletraffic loss model for its analysis. Each link has two thresholds, which refer to the number of in-service calls in the link. The lowest threshold, named support threshold, defines up to which point the link can support calls offloaded from the other link. The highest threshold, named offloading threshold, defines the point where the link starts offloading calls to the other link. The adopted bandwidth sharing policy is the complete sharing policy, in which a call can be accepted in a link if there exist enough available bandwidth units. The model does not have a product form solution for the steady state probabilities. However, we propose approximate formulas, based on a convolution algorithm, for the calculation of call blocking probabilities. The accuracy of the formulas is verified through simulation and found to be quite satisfactory.
3
Content available Review of loss models for high pressure turbines
Back da Trindade D., Bugała P., Simone D.
Journal of KONES
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2018
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Vol. 25, No. 2
38--44
EN
This article presents a literature review about the physical analysis of the loss models, which are used in offdesign procedure for high-pressure turbines. A high-pressure turbine is designed to have maximum performance at design point. However, engines are operating in different conditions, and the comprehension of off-design conditions is very important. The loss mechanisms are very complex and predictions considering empirical methods are a good approach to have preliminary results. Based on these results, different researches have proposed theories about the loss mechanisms, and over the time, these models have been modified to describe better the phenomena involved between blades and flow. Once the physical mechanisms behind the loss models are known, it is possible to compare them and understand the reason why the results given for some methods present a higher agreement to experimental or numerical data. In this framework, 2D numerical simulations of the flow around the blades of an axial high pressure turbine with different off design conditions have been realized, by using ANSYS FLUENT® code, to show the losses described by some of these models. Using these simulations a loss model has been selected and implemented in Matlab® to compare its results with the experimental data found in literature.
4
Content available remote Uogólniona metoda wyznaczania parametrów zasilania dla minimalizacji strat mocy w indukcyjnym silniku klatkowym
Banach H.
Przegląd Elektrotechniczny
|
2013
|
R. 89, nr 6
139--142
PL
Przedstawiona metoda pozwala na wyznaczenie optymalnych parametrów zasilania dla dowolnej częstotliwości napięcia zasilającego i dowolnej wartości obciążenia. Jej budowa oparta jest na modelu strat. Model ten został sporządzony z uwzględnieniem nieliniowości obwodu magnetycznego silnika i z uwzględnieniem dokładnego opisu strat w żelazie w funkcji częstotliwości i prądu magnesującego. Wyprowadzona zależność na minimum strat całkowitych po jej numerycznym rozwiązaniu pozwala na wyznaczenie optymalnych wartości składowych prądu i napięcia fazowego stojana oraz składowych wektora przestrzennego prądu i napięcia stojana w układzie osi wirujących d-q.
EN
The presented method allows the determination of optimal supply parameters for any frequency and for any load. Its construction is based on the loss model. This model has been made taking into account the nonlinear magnetic circuit, and a detailed description of the iron loss as a function of the frequency and the magnetizing current. Deduced dependence of the minimum total losses after its numerical solution is possible to determine the optimum value of components of the current and voltage stator phasors and components of space vector of stator current and stator voltage in the d-q rotating coordinate system.
5
Content available remote Metoda wyznaczania optymalnych parametrów zasilania dla minimalizacji strat mocy w indukcyjnym silniku pierścieniowym
Banach H.
Przegląd Elektrotechniczny
|
2013
|
R. 89, nr 1a
34--37
PL
Opisana metoda wyznaczania optymalnych parametrów zasilania pierścieniowego silnika indukcyjnego oparta jest na modelu strat. Model ten został zbudowany z uwzględnieniem nieliniowości obwodu magnetycznego silnika i z uwzględnieniem dokładnego opisu strat w żelazie. Wyprowadzona zależność na minimum strat całkowitych po jej numerycznym rozwiązaniu pozwala na wyznaczenie optymalnej wartości prądu magnesującego, a następnie kolejno optymalnej wartości prądu wirnika, prądu strat w żelazie oraz optymalnej wartości napięcia zasilającego.
EN
The described method of optimal supply parameters determining of an induction slip-ring motor based on the loss model. This model has been made taking into account the nonlinear magnetic circuit, and a detailed description of the iron loss. Deduced dependence of the minimum total losses after its numerical solution is possible to determine the optimum value of the magnetizing current, and then the optimum value of rotor current, iron losses current and the optimum value of supply voltage.
6
Content available The off-design performance prediction of axial compressor based on a 2D approach
Zhu X. C., Hu J. F., Ou-Yang H., Tian J., Qiang X. Q., Du Z. H.
Journal of Theoretical and Applied Mechanics
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2013
|
Vol. 51 nr 3
523--531
EN
The two-dimensional compressor flow simulation approach has always been a very valuable tool in compressor preliminary design studies, as well as performance predictions. In this context, a general development of the streamline curvature (SLC) method is elucidated firstly. Then a numerical method based on SLC is developed to simulate the internal flow of the compressor according to the development analysis and conclusion. Two certain transonic axial compressors are calculated by this 2D method. The speed lines and span-wise aerodynamic parameters are compared with the experiment data in order to demonstrate the method presented in this paper.
7
Content available remote Derivatives of Blocking Probabilities in Multirate Access Tree Networks
Moscholios I. D., Vardakas J. S., Logothetis M. D., Boucouvalas A. C.
Advances in Electronics and Telecommunications
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2013
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Vol. 3, no. 5
38--48
EN
We consider a multirate access tree network accommodating service-classes of Poisson traffic, and focus on the determination of derivatives of Call Blocking Probabilities (CBP) with respect to offered traffic-load of any service-class. Based on the derivatives, we further show how we can successfully approximate CBP for small variations of offered traffic-load.
8
Content available remote Metoda wyznaczania optymalnych parametrów zasilania dla minimalizacji strat mocy w indukcyjnym silniku klatkowym
Banach H.
Przegląd Elektrotechniczny
|
2012
|
R. 88, nr 9a
196-199
PL
Przedstawiona metoda wyznaczania optymalnych parametrów zasilania silnika indukcyjnego oparta jest na modelu strat. Model ten został sporządzony z uwzględnieniem nieliniowości obwodu magnetycznego silnika i z uwzględnieniem dokładnego opisu strat w żelazie. Wyprowadzona zależność na minimum strat całkowitych po jej numerycznym rozwiązaniu pozwala na wyznaczenie optymalnej wartości prądu magnesującego, a następnie kolejno optymalnej wartości prądu wirnika, prądu strat w żelazie oraz optymalnej wartości napięcia zasilającego.
EN
The presented method of optimal supply parameters determining of an induction cage motor based on the loss model. This model has been made taking into account the nonlinear magnetic circuit, and a detailed description of the iron loss. Deduced dependence of the minimum total losses after its numerical solution is possible to determine the optimum value of the magnetizing current, and then the optimum value of rotor current, iron losses current and the optimum value of supply voltage.
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