Wyniki wyszukiwania - BazTech

1

Analysis of the relevant parameters on small scale of navigable abnormal ship model

Cai C., Lei P., Cai X.

Polish Maritime Research

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2017

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S 2

133--139

EN

At present, ship model tests are based on the normal mode at home and abroad. With the development and application of abnormal hydraulic model, it is necessary to study abnormal ship model. The similarity criterion of abnormal ship model is deduced from the similarity theory of normal hydraulic model in this paper. Some factors that affect the maneuverability of the abnormal ship model are discussed by theoretical analysis of ship maneuvering. The influence of the K and T index of different variable rate on the abnormal ship model maneuvering and the dimensional effect of the abnormal ship model are obtained, which can be used as a reference for the study of the abnormal ship model.

2

Model tests for shallow-water ship maneuverability in Three Gorges Reservoir

Cai C., Cai X., Li Y.

Polish Maritime Research

|

2015

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S 1

136--140

EN

This paper conducts calibration tests on the shallow-water maneuverability of 1:100 ship models for the typical navigation fleets in Three Gorges Reservoir. Major influential factors for the maneuverability similitude between models and prototypes and for scale effect were identified. A correction method for model scale was also established through model tests. Test results indicate that, by correcting the model scales of various fleets based on scale effect, the maneuverability indexes K’ (dimensionless of K) and T’ (dimensionless of T) of ship models are suitable for shallowwater tests, and properly reflect the maneuvering characteristics of prototypes. The findings provide an experimental basis for the navigation safety in Three Gorges Reservoir.

3

Determination of pumped storage capacity combining the entropy weighting method and principal component analysis

Zhang Z., Cai X., Parkun D.

Journal of Power Technologies

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2014

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Vol. 94, nr 3

165--175

EN

The aim of the study is to evaluate methods for determining appropriate pumped storage capacities. This is especially relevant, since pumped storage units are, today, viewed as some of the best means of storing large amounts intermittently-produced power in order to meet peak demands on power supply grids. The determination of appropriate pumped storage capacity is a problem of integrated decision-making. The entropy weighting method and principal component analysis are combined to determine the optimum pumped storage capacity, taking into account several representative indices, whilst using the syntropy method to standardize the data indicators. The entropy weighting method is used to determine the weighting of the indicators, while principal component analysis offers reduction of the dimensions. The optimal solution is then determined by ranking the evaluation values for each design. This method can avoid subjectivity in the weighting assignment and simplifies the calculations to an evaluation problem which contains multiple evaluation indices. Using the principle of energy-saving scheduling, the peak-shaving method is applied to the dispatching over a typical daily load in order to verify the rationality of the calculated pumped storage capacity. The example analysis, here, shows that it is reasonable to determine the optimum pumped storage capacity by using this combination of the entropy weighting method and principal component analysis.

4

Individual pitch control for torque fluctuation reduction in large-scale wind turbine generator systems

Dou Z., Wang H., Ling Z., Cai X.

Przegląd Elektrotechniczny

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2013

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R. 89, nr 3b

29--31

EN

In order to capture maximum wind energy, smooth the wind turbine torque fluctuation and eliminate the unbalanced loads on the wind turbine, the individual pitch control strategy which directly controls the edgewise moment is proposed based on the multi-stage dynamic weight coefficient distribution of the pitch angle according to the blade azimuth. In order to verify the effeteness of the proposed individual pitch control, the simulation experiment is carried out on a 2MW wind turbine generator system. And the results show, compared with collective pitch control, the proposed individual pitch control not only regulates and smoothes the wind turbine torque fluctuation, but also indirectly reduces the fluctuation of the blade flapwise moment, the yaw moment and the tilt moment, and greatly improves the power output as well.

PL

W artykule opisano strategię sterowania kątem natarcia płatami wirnika turbiny wiatrowej w celu lepszej stabilizacji momentu turbiny i eliminacji niezbalansowania obciążenia. Metoda oparta została na wielostopniowej wadze dynamicznej współczynników podziału kąta natarcia, w zależności od azymutu płata. Przedstawiono wyniki badań symulacyjnych sterowania w systemie generatorów wiatrowych o mocy 2MW, potwierdzające jego wysoką skuteczność i zwiększenie generowanej energii elektrycznej.

5

A Novel Arc Suppression Coil

Xu B., Zhang J., Cai X.

Przegląd Elektrotechniczny

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2013

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R. 89, nr 3a

213--217

EN

The arc suppression coil (ASC) is one of the most important devices in distribution networks to obtain the optimal power supply quality. Though there exits many types of ASC, some problems have been still not solved. In order to develop an ASC with rapid and continuous tuning and limited harmonics, this paper proposes a novel type of ASC, which is based on a single phase matrix converter. Due to pulse width modulation (PWM) control, compensating currents can be adjusted in a wide range and the order of harmonics is so high to be filtered easily. Finally, by using PSCAD/EMTDC, simulations are given to illustrate the feasibility and validity of this novel ASC.

PL

W artykule zaproponowano nowy typ dławika gaszącego ASC, bazujący na jednofazowym przekształtniku matrycowym. Dzięki modulacji PWM, możliwe jest generowanie prądów kompensujących o szerokim zakresie, a co za tym idzie skuteczna eliminacja harmonicznych. Wykonano badania symulacyjne w programie PSCAD/EMTDC, weryfikujące skuteczność działania rozwiązania.

6

Stability analysis of high-order Hopfield-type neural networks based on a new impulsive differential inequality

Liu Y., Yang R., Lu J., Wu B., Cai X.

International Journal of Applied Mathematics and Computer Science

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2013

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Vol. 23, no. 1

201--211

EN

This paper is devoted to studying the globally exponential stability of impulsive high-order Hopfield-type neural networks with time-varying delays. In the process of impulsive effect, nonlinear and delayed factors are simultaneously considered. A new impulsive differential inequality is derived based on the Lyapunov–Razumikhin method and some novel stability criteria are then given. These conditions, ensuring the global exponential stability, are simpler and less conservative than some of the previous results. Finally, two numerical examples are given to illustrate the advantages of the obtained results.

7

Short-term Wind Speed Prediction Based on Grey System Theory Model in the Region of China

Zhang J., Cheng M., Cai X.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 7a

67-71

EN

Short-term wind speed forecasting is useful for power system to regulate power dispatching plan, decrease reserve power needed and increase the reliability of system. The method of the short-term wind speed prediction is proposed in this paper. The data of wind speed in Dafeng, Jiangsu Province of China is predicted by the model combined with the grey system theory (GST). A grey system model consists of accumulating generation operation of original wind speed sequence data, data processing and wind speed forecasting. The hourly mean wind speed data at 85 meters above ground level of one year is generated by meteorological tower operated by the local bureau of meteorology. In this paper, the hourly average wind speed measured every an hour of 24 hours on Jan.1st, 2008 are the initial dataset for predicting. The result of wind speed is predicted by the grey system theory model with 0.14% of minimum relative percentage error (MRPE) and 7.22% of maximum mean absolute percentage error. The wind speed predicted values are given by the graphs and tables, which can be used easily for assessment of short-term wind energy in the different regions within China.

PL

W artykule zaproponowano metodę krótkookresowego prognozowania szybkości wiatru. Do prognozowania zastosowano teorię GST (Grey system theory). System składa się z panelu zbierania i przechowywania danych, przetwarzania danych i prognozowania. Zbierane są dane prędkości wiatru 85 metrów nad powierzchnią ziemi.

8

Design and Control of Multi-terminal VSC-HVDC for Large Offshore Wind Farms

Shi G., Cai X., Chen Z.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 12a

264-268

EN

In this paper, the parameters design of VSC-HVDC terminal is proposed. A four-terminal VSC-HVDC system is configured as the simplified study system. The control schemes of coordinated control and master-slave control for MTDC system power delivery are investigated and their shortages are introduced. The control effect and power system stability is evaluated by three dynamic simulation cases based on PSCAD/EMTDC, which correspond to wind power fluctuation.

PL

W artykule przedstawiono dobór parametrów układu VSC-HVDC. Badania oparto na układzie cztero-stronnym, z wykorzystaniem algorytmu sterowania mocą wyjściową systemu wielostronnego. Wykonano symulacje w PSCAD/EMTDC stanów dynamicznych, odzwierciedlające zmienność wiatru.

9

Control of Voltage Source Inverter with an LCL Filter without Voltage Sensors

Wang H., Yu C., Zhang J., Cai X.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 5b

119-122

EN

The voltage source inverter with LCL filter has to adopt damping method to suppress the resonance of LCL filter, which increases of losses and sensors. With virtual flux estimation idea, grid voltage-sensor-less technology is applied to design observers for the grid voltage, capacitor voltage and current. The observed grid voltage and capacitor voltage is used to realize voltage orientation control and grid current compensation for unit power factor. The observed capacitor current was fed forward to restrain LCL response and keep the control stable. The simulation results verify the correctness of observes design and the control method.

PL

W artykule analizuje się przekształtnik o źródle napięciowym VSI z filtrem LCL w zastosowaniu do sieci elektrowni wiatrowych. Analizę przeprowadza się na podstawie monitorowania napięcia sieci, prądu sieci i napięcia na kondensatorze.

10

Comparison of wind turbine efficiency in maximum power extraction of wind turbines with doubly fed induction generator

Ling Y., Wu G., Cai X.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 5b

157-163

EN

So far, much attention has been not received by the influence of the control modes on the wind turbine efficiency in maximum wind energy extraction, which is investigated based on variable speed wind turbines with doubly fed induction generator (DFIG) under vector control in stator flux orientation (SFO) in the paper. Prior art has tended to have an importance on investigating the principle and behaviors of control strategies in itself. As a result, two control modes, optimal rotor speed control mode and peak power control mode is investigated in detail. At first, Stator flux-orientated vector control for the rotor side converter of DFIG is reviewed, and in turn a comparison on two control modes is presented. Finally, a complete simulation model is developed to investigate how the operation of maximum wind energy extraction of the turbine below rated wind velocity, especially the wind turbine efficiency is affected by the two control methods. Simulation results are presented and compared under the two different control modes. Simulation results show that maximum wind energy extraction of the turbine and its efficiency is affected by different control modes.

PL

W artykule porównano różne strategie zarządzania systemem elektrowni wiatrowych z podwójnie zasilanym generatorem indukcyjnym. Jedna ze strategii polega na kontroli optymalnej prędkości wirnika, druga na kontroli mocy szczytowej.

11

Investigation of Transient Torque during a Power System Fault in Wind Power Turbines Having a DFIG and Crowbar Circuit

Cheng M., Cai X., Wu G.

Przegląd Elektrotechniczny

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2011

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R. 87, nr 11

245-250

EN

To study the influence of power system voltage drop on the doubly-fed induction generator (DIFG) shaft, this paper analyzes the electromagnetic torque change of the DFIG through approximated analytical expression of the stator fault current and rotor fault current obtained by the superposition between transient current based on vector method and steady-state current based on equivalent circuit method, and then the DFIG torque change situations under the following circumstances: the three-phase symmetrical voltage dip of stator terminal, the converter of the rotor side is cut off, and the crowbar circuit is put into the operation, will be analyzed through the method. Furthermore, on the basis of theoretical analysis, a 2MW DFIG model is established by PSCAD, and the simulation results validate that the torque changes of the DFIG shaft could be analyzed by the expression of the DFIG torque during the grid voltage drops through the superposition of the transient current and steadystate current. At last, the optimizing value of the crowbar resistance is given.

PL

W artykule analizuje się zmiany momentu elektromagnetycznego podwójnie zasilanego generator indukcyjnego DFIG poprzez ocenę prądów wirnika i stojana otrzymaną przez superpozycję prądów przejściowych (metoda wektorowa) i prądu stanu ustalonego (metoda obwodów zastępczych). Badania symulacyjne potwierdziły słuszność metody.

12

Can Potentilla fruticosa Linn. shrubs facilitate the herb layer of heavily grazed pasture on the eastern Tibetan Plateau

Li P., Krusi B., Li S., Cai X., Yu F.

Polish Journal of Ecology

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2011

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Vol. 59, nr 1

129-140

EN

The facilitative and competitive effects of shrubs on herbaceous species have been extensively studied, but little is known about the roles of the shrub distribution patterns in such effects. On a heavily grazed pasture on the Tibetan Plateau, we investigated the effects of Potentilla fruticosa Linn. shrubs of different distribution patterns on the small-scale vegetation pattern of the herb layer. We made same-sized releves at five micro-site types, i.e., beneath and outside the canopies of solitary Potentilla individuals, beneath and outside the canopies of edge-of-patch individuals and at the central openings of torusshaped large Potentilla patches. Shrubs protected certain species by increasing their frequencies of occurrence or flowering. However, only few species benefited from shrubs and more occurred or flowered more frequently outside. The data at community level indicated that species richness and diversity index were higher outside. The patch openings did not benefit species richness, pooled cover, diversity index or evenness of central vegetations. No special species was found growing beneath shrubs exclusively and few species were found with higher occurrences beneath shrubs. Furthermore, no significant difference was found between the two different distribution patterns at either community or species level. Vegetation ordinations confirmed this and vegetations beneath and outside the shrubs were distinguished merely. In conclusion, Potentilla facilitated some species in the herb layer and the patch openings did not show large protective effects. Also, distribution patterns of Potentilla did not affect the difference between vegetations beneath and outside shrub canopies.

13

Integral Particle Swarm Optimization with Dispersed Accelerator Information

Cui Z., Cai X.

Fundamenta Informaticae

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2009

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Vol. 95, nr 4

427-447

EN

Integral-controlled particle swarm optimization (ICPSO) is an effective variant of particle swarm optimization (PSO) aiming to increase the population diversity. Due to the additional accelerator items, the behavior of ICPSO is more complex, and provides more chances to escaping from a local optimum than the standard version of PSO. However, many experimental results show the performance of ICPSO is not always well because of the particles’ un-controlled movements. Therefore, a new variant, integral particle swarm optimization with dispersed accelerator information (IPSO-DAI) is designed to improve the computational efficiency. In IPSO-DAI, a predefined predicted velocity index is introduced to guide the moving direction. If the average velocity of one particle is superior to the index value, it will choice a convergent manner, otherwise, a divergent manner is employed. Furthermore, the choice of convergent manner or divergent manner for each particle is associated with its performance to fit different living experiences. Simulation results show the proposed variant is more effective than other three variants of particle swarm optimization especially for multi-modal numerical problems. The IPSO-DAI algorithm is also applied to directing the orbits of discrete chaotic dynamical systems by adding small bounded perturbations, and achieves the best performance among four different variants of PSO.

14

Measurement of wet steam in a 300 mw direct air cooling steam turbine

Cai X, Niu F, Ning T, Ning T, Wu G, Song Y

Zeszyty Naukowe. Cieplne Maszyny Przepływowe - Turbomachinery / Politechnika Łódzka

|

2008

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nr 133

77--86

EN

For study the wet steam flow in the direct air-cooling steam turbine, measurements were carried out in a 300MW turbine with a newly developed combined probe. The wetness in the direct air-cooling steam turbine is lower and varies not much along the blade height. Droplets size distribution and mean diameter are smaller too comparing to water-cooling steam turbine. The measured relative inner efficiencies of LP obtained by the probe agree well with the results obtained by thermal performance test.

15

Effect of hadronic rescattering on the elliptic flow after the hydrodynamics model

Ma G., Ma Y., Sa B., Cai X., He Z., Huang H., Long J., Shen W., Zhong Ch., Chen J., Zuo J., Zhang S., Shi X.

Nukleonika

|

2006

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Vol. 51,suppl.3

21-27

EN

Abstract A hydrodynamics + hadronic rescattering model is used to simulate Au+Au collisions at 200 GeV and a Cooper-Frye method is adopted for hadronization. The effect of hadronic rescattering on elliptic flow V2 in 20 40% Au+Au collisions at 200 GeV has been investigated. It is found that the hadronic rescattering can suppress elliptic flow V2 and makes an asymmetric system in momentum space tend to be less anisotropic. The suppression effect becomes weak with increasing transverse momentum. In addition, the effect of hadronic rescattering on transverse momentum spectra and anisotropy of hadronic coordinate space is presented.

16

New Methods to Study Thin Organic Films at Electrode Surfaces

Zawisza I., Cai X., Zamlynny V., Burgess I., Majewski J., Szymański G., Lipkowski J.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 9

1165-1181

EN

Chronocoulometry, scanning tunneling microscopy (STM), neutron reflectometry (NR) and in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) have been employed to study the properties of a monolayer of n-octadecanol at a Au(111) electrode surface. Chronocoulometry has been used to determine the charge density at the electrode surface covered by the film of n-octadecanol. The surface pressure of this film was calculated from the charge density data. The film pressure data were used to describe the film properties at the gold solution interface. It has been found that at film pressures larger than 12 mNm-1 the monolayer is in a compressed state and at lower film pressures in a decompressed state. STM imaging, NR and PM-IRRAS have been employed to determine the nature of the two states.We have demonstrated that the properties of a monolayer of n-octadecanol at the metal-solution interface display many similarities to the properties of an equivalent film at the air-solution interface.

17

Investigation of wet steam flow in LP steam turbine using a novel integrated probe: experimental results

Wang L., Cai X., Ouyang X.

Archives of Thermodynamics

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2002

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Vol. 23, no 4

49-57

EN

In low-pressure (LP) steam turbine, the wetness fraction of steam causes dangerous erosion of turbine blades and decrease of turbine efficiency. In the study of wet steam flow, wetness, droplet size and velocity are of the main concern. These parameters are closely correlated to the vapour phase of the flow field and have to be measured simultaneously. Following this line, a novel integrated probe system has been successfully developed, based on light scattering technique, correlation theory and common methods for flow field measurement. By using this system, experiment has been performed in a 200 MW and a 350 MW condensing steam turbine. Part of the results are presented and some newly detected phenomena are put forward and discussed.