Wyniki wyszukiwania - Biblioteka Nauki

1

Numerical modeling of unsteady state operation of tube and plate fin heat exchangers

100%

Taler D. , Korzeń A.

Journal of Energy Science

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2012

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tom Vol. 1, nr 2

103--117

EN

Cross-flow tubular heat exchangers are applied as condensers and evaporators in air conditioners and heat pumps or as air heaters in heating systems. They are also applied as water coolers in so called 'dry' water cooling systems of power plants, as well as car radiators. There are analytical and numerical mathematical models of heat exchangers of that type to determine the steady state temperature distribution of fluids and the rate of heat transferred between fluids. In view of the wide range of applications in practice, these heat exchangers were experimentally examined in steady-state conditions, mostly to determine the overall heat transfer coefficient or the correlation for the heat transfer coefficients on the air side and on the internal surface of the tubes. There exist many references on the transient response of heat exchangers. Most of them, however, focus on the non-steady-state heat transfer processes in parallel and counter flow heat exchangers. In this paper, the new equation set describing transient heat transfer process in tube and fin cross-flow tube exchanger will be given and subsequently solved using the finite volume method.

2

Relationships Between Systolic Time Intervals and Heart Rate During Initial Response to Orthostatic Manoeuvre in Men of Different Age

88%

Cybulski G. , Niewiadomski W. , Strasz A. , Laskowska D. , Gąsiorowska A.

Journal of Human Kinetics

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2009

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tom 21

57-64

EN

An analysis of transient changes in physiological parameters in response to the standardized tests could be used to evaluate the efficiency of the regulatory processes. Relationships between systolic time intervals and heart rate following the action of standing up from the supine position were investigated in 41 healthy men, aged 20 to 59 years, classified into three groups: (22 to 26 yrs, n=14), (33 to 49, yrs, n=13) and (51 to 59 yrs, n=14). The protocol consisted of the following sequence: laying down (20 minutes) - standing up (8 minutes). Ejection time, pre-ejection period, electromechanical systole, heart rate and the length of R-R intervals were continuously calculated using automatized impedance cardiography and electrocardiogram. The ratio of ejection time to pre-ejection period in young men was significantly higher in comparison with the other groups. The ratio of ejection time to the length of R-R interval increased with age in supine position and after standing up when R-R interval was maximal. It was suggested that changes of ejection time to pre-ejection period during the orthostatic manoeuvre are rather the result of balance between heart rate and hemodynamic factors, than solely related to heart rate.

3

Influence of lightning current surge shape and peak value on grounding parameters

88%

Łukaszewski A. , Nogal Ł. , Łukaszewski A. , Nogal Ł.

Bulletin of the Polish Academy of Sciences: Technical Sciences

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2021

4

Analysis of Transient Heat Transfer in a Longitudinal Fin with Functionally Graded Material in the Presence of Magnetic Field using Finite Difference Method

88%

Sobamowo M. G. , Oguntala G. A. , Yinusa A. A. , Adedibu A. O.

World Scientific News

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2019

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tom 137

166-187

EN

In this study, finite difference method is used for the numerical analysis of the transient heat transfer analysis of a convective-radiative fin with functionally graded materials under the influence of Lorentz force is presented. Three cases of developed nonlinear thermal models of linear, quadratic, exponential and power-law variations of thermal conductivity are considered. The accuracy of the developed numerical code is verified as the results of the numerical solutions established good agreements with the results of the exact analytical solutions. Through the numerical solutions, parametric studies are carried out. From the results, it is shown that increase in radiative and magnetic field parameters as well as in-homogeneity index improve the thermal performance of the fin. Also, the transient responses reveal that the FGM fin with linear-law and power-law function shows the slowest and fastest thermal responses, respectively. This study will provide a very good platform for further studies on the design of extended surfaces where the surrounding fluid is influenced by a magnetic field.

5

Digital Finite Impulse Response Notch Filter with Non-Zero Initial Conditions, Based on an Infinite Impulse Response Prototype Filter

75%

Kocoń S. , Piskorowski J.

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nr 4

6

Digital finite impulse response notch filter with non-zero initial conditions, based on an infinite impulse response prototype filter

75%

Kocoń S. , Piskorowski J.

Metrology and Measurement Systems

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2012

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tom Vol. 19, nr 4

767-776

EN

In this paper a concept of finite impulse response (FIR) narrow band-stop (notch) filter with non-zero initial conditions, based on infinite impulse response (IIR) prototype filter, is proposed. The filter described in this paper is used to suppress power line noise from ECG signals. In order to reduce the transient response of the proposed FIR notch filter, optimal initial conditions for the filter have been determined. The algorithm for finding the length of the initial conditions vector is presented. The proposed values of the length of initial conditions vector, for several ECG signals and interfering frequencies, are calculated. The proposed filters are tested using various ECG signals. Computer simulations demonstrate that the proposed FIR filters outperform traditional FIR filters with initial conditions set to zero.

7

Evolution of Low Drop Out Voltage Regulator in CMOS Technologies

75%

Mustafa N. B. , Amin S. , Reaz M. B. I. , Hashim F. H. , Kamal N.

Przegląd Elektrotechniczny

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2015

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tom R. 91, nr 12

26-33

EN

The demand for low voltage devices has initiated the development of Low Drop Out (LDO) regulator in manifold. This paper presents a review of various LDO frameworks that have been implemented in CMOS technologies and the impact of frameworks related to the parameters of the LDO. The LDO architecture is evaluated through its Power Supply Rejection (PSR) and transient response performance. The transient response performance mostly depends on the added buffer and the PSR performance depends on the pass device capacitance and the LDO loop gain.

PL

W artykule przedstawiono przegląd rozwiązań układów LDO (Low Drop Pout) w technologii CMOS. Przedstawiono także rozwiązania typu PSR – Power Supply Rejection. Analizowano dynamikę tych układów.

8

Transient analysis of transversely functionally graded Timoshenko beam (TFGTB) in conjunction with finite element method

71%

Khafaji S. O. W. , Al-Shujairi M. A. , Aubad M. J. , Khafaji S. O. W. , Al-Shujairi M. A. , Aubad M. J.

Archive of Mechanical Engineering

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2020

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tom 67

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nr 3

9

Modelowanie wymiany ciepła w żebrach o złożonych kształtach

63%

Taler D. , Korzeń A.

Rynek Energii

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2011

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tom Nr 6

61-65

PL

Nieustalony rozkład temperatury w żebrach płytowych osadzonych na rurach owalnych obliczono za pomocą mieszanej metody objętości i elementów skończonych. Najpierw model żebra podzielono na trójkątne elementy, a następnie zostały utworzone objętości skończone wokół węzłów przez połączenie środków ciężkości trójkątów ze środkami boków tych trójkątów. Następnie wyprowadzono równania bilansu ciepła dla wszystkich węzłów wewnętrznych z uwzględnieniem przewodzenia ciepła wewnątrz żebra i konwekcji ciepła na jego powierzchni. Warunki brzegowe pierwszego, drugiego i trzeciego rodzaju wyznaczono dla objętości skończonych przyległych do brzegu żebra. Układ równań różniczkowych zwyczajnych pierwszego rzędu na temperatury chwilowe w węzłach został rozwiązany za pomocą metody Rungego - Kutty - Vernera piątego rzędu. W celu wykazania skuteczności proponowanej metody, przyjęto stan nieustalony na prostokątnej powierzchni żebra. Obliczono chwilowe pola temperatur w żebrach prostokątnych osadzonych na rurach owalnych oraz ilość ciepła przekazywaną od żebra do otoczenia oraz sprawność żebra.

EN

Transient temperature distributions in continuous fins attached to oval tubes were calculated using the finite volume - finite element method. First the fin model was divided into triangular elements and then finite volumes were formed around the nodes by connecting triangle gravity centers with side centers of triangles. Next, heat balance equations were set for all interior nodes taking into account heat conduction inside the fin and convective heat transfer on its surface. The boundary conditions of the first, second, and third kind were accounted for the finite volumes adjacent to the fin boundaries. A system of differential equations of the first order for temperature at the nodes was solved using the Runge-Kutta-Verner method of the fifth order. To show the effectiveness of the proposed method, the transient distribution in rectangular region was determined. Subsequently the transient temperature field in the rectangular fin attached to the oval tube was computed. After calculating the temperature distribution, the heat transferred from the fin to the environment and fin efficiency were computed and compared with the results obtained by using the commercial software Ansys 11.0.

10

Time-efficient removal of power-line noise from EMG signals using IIR notch filters with non-zero initial conditions

63%

Piskorowski J.

Biocybernetics and Biomedical Engineering

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2013

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tom Vol. 33, no. 3

171--178

EN

Power-line interference is always a problem when biopotential signals are recorded. This paper presents a technique for time-efficient power-line interference suppression from EMG signals using digital IIR (Infinite Impulse Response) notch filters with reduced transient response. The reduction of the transient response is obtained by finding optimal non-zero initial conditions for the considered notch filters. Simulations verifying the effectiveness of the proposed technique are presented and compared with the performance of the traditional notch filters with zero initial conditions using EMG signal with unwanted sinusoidal interferences as a study case.

11

Amelioration of ship control with improved dynamic response of motor controller

63%

Hasan S. , Sarowar G.

Przegląd Elektrotechniczny

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2021

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tom R. 97, nr 4

32--40

EN

During a sea voyage, it is significantly important to fix the speed and angle of movement of the ship precisely depending on the distance of the destination and also in icebreaking purpose. So, enhancement of transient response of commutator motor used in the ship is essential. Due to their better reliabilities as well as low costing, nowadays, Direct Current (commutator) motors are utilized in icebreaking ships, in industrial near and far applications, robotic manipulators, and also for home appliances. Thus, it is vital to introduce a suitable controller for managing the speed and transient behavior of a Direct Current. In this study, for the enhancement of dynamic response, various DC commutator motor controllers have been simulated. At first, the DC commutator motor parameters are selected and four optimized controllers: Ziegler-Nichols (ZN)-based conventional Proportional Integral Derivative (PID) controller, Genetic Algorithm (GA)-based PID controller (GA-PID), as well as Flower Pollination Algorithm (FPA)-based PID (FPA-PID) are designed and simulated to manage the angular speed together with dynamic response of shaft of a Direct Current commutator motor actuator. The electric actuator response for every controller is ascertained as well as compared after applying step input that is necessary for the simulation of transient response of the motor. The performance analysis shows that the FPA-PID controller is adequate for the steering task in the ship, which requires precision and associated with transient response properties.

PL

W artykule analizowano różne metody sterowania silnikiem komutacyjnym DC. Szczególną uwagę poświęcono sterownikom PID , PID wspomaganym algorytmami genetycznymi oraz Flower Pollination FPA-PID. . Analizowano możliwości sterowania prędkością przy odpowiednich parametrach dynamicznych. (odpowiedź na wymuszenie skokowe). Stwierdzono, że najlepsze właściwości do sterowani silnikiem statku ma algorytm FPA-PID.

12

Analytical and numerical model of transient heat transfer in a single tube row heat exchanger

63%

Taler D.

Archives of Thermodynamics

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2007

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tom Vol. 28, no. 1

51-64

EN

Cross-flow tubular heat exchangers are widely applied as condensers and evaporators in air conditioners and heat pumps or as air heaters in heating systems. There are analytical and numerical mathematical models of heat exchangers of that type to determine the steady state temperature distribution of fluids. In this paper the transient response of a single-row tubular cross-flow tube - and - fin heat exchanger is analyzed. Partial differential equations for both hot and cold fluid are solved by the Laplace transform method with numerical inversion and by the finite-difference (finite-volume) method. The transient response of one-row tube - and - fin heat exchanger due to step change of air temperature is calculated using both developed approaches. Good agreement between the analytical predictions (the Laplace transform method and analytical exact steady state solution) and the finite difference solution has been found. After eliminating the time, using the Laplace transform, a simpler system of partial equations is formed, which can be solved analytically. In view of the complex form of the achieved solutions, the inverse Laplace transform is obtained numerically by the method due to Crump improved by de Hoog. The solutions presented in the paper can be used to analyze the operation of heat exchangers in transient conditions and can find application in systems of automatic control or in the operation of heat exchangers.

13

Transients in Transformers with Non-Uniform Inductance and Capacitance Distributions

63%

Saied M. M.

Electrical Power Quality and Utilisation. Journal

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2017

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tom Vol. 20, no. 1

7--14

EN

The electromagnetic transients in transformer windings exhibiting location–dependent inductances and capacitances are investigated in the time domain. Analytical functions describing this dependence are assumed and incorporated in the two integro–differential equations governing the transient voltage and current distributions. The boundary conditions are available from the source initiating the transients and the winding’s end termination. A numerical procedure is applied in order to get frequency domain solutions for the voltage and current in the form of Interpolating and Parametric Functions. The numerical Laplace inversion is then applied to these s–domain expressions. Results pertinent to transients initiated by step- and double-exponential impulse sources are presented and discussed. All possible transformers’ neutral connections are considered. The possible error introduced by neglecting either or both of the inductance and capacitance non-uniformities is addressed. Results indicate that the main error is attributed to neglecting the inductance non-uniformity, whereas the impact of the capacitance non-uniformity is relatively small. In most cases, the winding’s copper and insulation losses have a small effect on the transient response.

14

Influence of lightning current surge shape and peak value on grounding parameters

63%

Łukaszewski A. , Nogal Ł.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2021

|

tom Vol. 69, nr 2

art. no. e136730

EN

Groundings are necessary parts included in lightning and shock protection. In the case of a surge current, high current phenomena are observed inside the grounding. They are result of the electrical discharges around the electrode when the critical field is exceeded in a soil. An available mathematical model of grounding was used to conduct computer simulations and to evaluate the influence of current peak value on horizontal grounding parameters in two cases. In the first simulations, electrode placed in two different soils were considered. The second case was a test of the influence of current peak value on grounding electrodes of various lengths. Simulation results show that as soil resistivity increases in value, the surge impedance to static resistance ratio decreases. In the case of grounding electrodes lengths, it was confirmed that there is a need to use an operating parameter named effective grounding electrode length, because when it is exceeded, the characteristics of grounding is not significantly improved during conductance of lightning surges. The mathematical model used in the paper was verified in a comparison with laboratory tests conducted by K.S. Stiefanow and with mathematical model described by L. Grcev.

15

Performance analysis of SRF PLL type-3 with dynamic feed forward frequency estimator for abnormal grid conditions

51%

Agrawal S. , Kumar M. , Palwalia D. K.

Journal of Power Technologies

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2021

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tom Vol. 101, nr 2

87--95

EN

A phase-locked loop (PLL) is a closed-loop feedback control device that synchronizes its output signal with an input signal in both frequency and time. This paper presents a robust method for tracking against adverse conditions of the fundamental sequence component of utility voltage. The proposed phase-locked loop (PLL) is a hybrid configuration of the phase- locked loop type-3 (SRF type-3) synchronous reference frame coupled with a feed-forward frequency estimator using a selective harmonic filtering technique. A SRF type -2 based PLL has a secondary closed path. Under the ramp frequency transition, it has a steady-state step and a frequency error. In the proposed PLL, the constant gain loop filter is used to eliminate the phase and frequency error. Feed-forward operation with selective harmonic pre-filtering enables fast-tracking with a low tracking error of the reference signal. From the results it is evident that the proposed PLL achieves a high bandwidth and quick dynamic response without endangering the stability and filtering capability. The proposed system has been tested through MATLAB Simulink platform under abnormal conditions.

16

Transient analysis of transversely functionally graded Timoshenko beam (TFGTB) in conjunction with finite element method

51%

Khafaji S. O. W. , Al-Shujairi M. A. , Aubad M. J.

Archive of Mechanical Engineering

|

2020

|

tom LXVII, nr 3

299--321

EN

In this work, transient and free vibration analyses are illustrated for a functionally graded Timoshenko beam (FGM) using finite element method. The governing equilibrium equations and boundary conditions (B-Cs) are derived according to the principle of Hamilton. The materials constituents of the FG beam that vary smoothly along the thickness of the beam (along beam thickness) are evaluated using the rule of mixture method. Power law index, slenderness ratio, modulus of elasticity ratio, and boundary conditions effect of the cantilever and simply supported beams on the dynamic response of the beam are studied. Moreover, the influence of mass distribution and continuous stiffness of the FGM beam are deeply investigated. Comparisons between the current free vibration results (fundamental frequency) and other available studies are performed to check the formulation of the current mathematical model. Good results have been obtained. A significant effect is noticed in the transient response of both simply supported and cantilever beams at the smaller values of the power index and the modulus elasticity ratio.

17

Mathematical modelling of the unsteady operation of a plate and fin heat exchanger for the time-varying mass flow rate of liquid and air velocity

51%

Korzeń A. , Taler D.

Technical Transactions

|

2017

|

tom Vol. 3(114)

183--196

EN

The mathematical simulation of a plate fin and tube heat exchanger is presented in this paper. The simulation of the transient operation of the heat exchanger was carried out using a general numerical model that was previously developed by the authors. The Reynolds number of the water flowing inside the tubes varied in the range from 4000 to 12000. A detailed analysis of the transient response of a heat exchanger to sudden increase in water mass flow rate and the simultaneous reduction in air flow velocity was modelled. Heat transfer correlations for air and water were determined based on the experimental data. Unknown parameters appearing in the relationships for the Nusselt numbers on the airand water-sides were estimated using the least squares method. A set of partial differential equations for the temperature of water, air, tube wall, and fins was solved using the finite volume method. The results of the numerical simulations of a heat exchanger using experimentally determined air and water-side heat transfer formulas for the calculation of heat transfer coefficients were compared with the experimental data. Excellent agreement between computation results (air and water temperatures at the outlet of the heat exchanger) and experimental results was obtained.

PL

Przedstawiona została symulacja matematyczna wymiennika ciepła z rur ożebrowanych. Symulacja nieustalonej pracy wymiennika przeprowadzona została za pomocą modelu matematycznego opracowanego wcześniej przez autorów. Liczba Reynoldsa po stronie wody zmieniała się w zakresie od 4000 do 12 000. Szczegółowa analiza zmian temperatury została przeprowadzona dla przypadku nagłego wzrostu strumienia masowego płynu z jednoczesnym obniżeniem prędkości powietrza. Korelacje na współczynniki wnikania ciepła dla powietrza i wody określono na podstawie danych doświadczalnych. Nieznane parametry, które pojawiają się w równaniach na liczbę Nusselta dla powietrza i wody wyznaczono za pomocą metody najmniejszych kwadratów. Układ równań różniczkowych cząstkowych umożliwiający wyznaczenie temperatury wody, powietrza, ścianki rury i żeber zostały rozwiązane z użyciem metody objętości skończonej. Wyniki numerycznej symulacji pracy wymiennika z użyciem współczynników wnikania ciepła wyznaczonych z korelacji na liczby Nusselta od strony powietrza i wody porównano z danymi eksperymentalnymi. Uzyskano bardzo dobrą zgodność wyników obliczeń i pomiarów.

18

Digital filters to separate the first and second harmonics of signals in microprocessor-bases protection of electrical installations equipped with transformers

51%

Romanyuk F. , Kachenya V. , Kierczyński K.

Przegląd Elektrotechniczny

|

2018

|

tom R. 94, nr 7

46--49

EN

The shortcomings of the sine and cosine digital filters used in microprocessor-based protection of electrical installations are discussed in the article; a technique to overcome the shortcomings is proposed. The mathematical description of non-recursive filters is presented. One of the models of the proposed method of formation of the orthogonal components is presented as well. The study of frequency and transient responses of digital filters at different types of input impact was performed. The reaction of various filters to inrush of magnetization currents of power transformers is investigated.

PL

W artykule omówiono wady cyfrowych filtrów sinusoidalnych i cosinusoidalnych stosowanych w mikroprocesorowej ochronie instalacji elektrycznych, zaproponowano technikę poprawy tych wad. Przedstawiono matematyczny opis filtrów nierekurencyjnych. Omówiono również jeden z modeli proponowanej metody tworzenia składowych ortogonalnych. Przeprowadzono badania częstotliwości i odpowiedzi filtrów cyfrowych przy różnych typach sygnału wejściowego. Zbadano reakcję różnych filtrów na oddziaływanie prądów magnesujących transformatorów mocy.