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1
Content available Damping low-frequency oscillations in a multi-machine power system using a fuzzy-multi-band power system stabilizer
Essallah Sirine, Khedher Adel
Journal of Power Technologies
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2022
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Vol. 102, nr 4
140--148
EN
Synchronous generators are usually eguipped with power system stabilizers (PSS) to damp low-freguency oscillations. Among the various types of PSS, it has recently been demonstrated that the Multi-Band PSS (MB-PSS) has a better performance to handle all global, inter-area and local modes. However, the performance of this PSS may degrade since the power supply system is intrinsically non-linear and its operating conditions freguently change. This paper introduces a new design of MB-PSS based on Mamdani Fuzzy inference (Fuzzy-MB-PSS). Compared to the IEEE standard MB-PSS, the proposed stabilizer is more efficient owing to its ability to deal with oscillations at different operating points. The controller is tested on a power system benchmark under various disturbance conditions to prove its robustness and to demonstrate its superiority over conventional PSS and MB-PSS.
2
Content available remote An experimental study on the complex resistivity of fractured rock under different saturation conditions
Pan Baozhi, Ruhan A., Guo Yuhang, Zhang Lihua, Wei Boyang, Zhou Weiyi
Acta Geophysica
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2022
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Vol. 70, no 3
1061--1081
EN
The fracture can be a good channel for oil and gas migration, which has a great influence on the permeability of the reservoir. Therefore, it is of major significance to identify fractures and determine the characterization parameters and physical proper ties of fractured reservoirs. In this study, homogeneous sandstone was used to simulate different artificially fractured rocks. The fractured rock samples had different fracture widths, fracture numbers, and fracture dip angles. In addition, the complex impedance and weights of the rock samples were measured during the process of natural evaporation, and the relationships between the water saturation and the complex resistivity values at different frequencies were examined. The frequency range is 100 Hz–10 kHz. It was found that the influence effects of frequency on the resistivity, dielectric constant, and loss factor had differed among the homogeneous samples and the fractured rock sample. The fracturing had led to the resistivity index and the water saturation curves separating under the different frequencies, and the degree of the dielectric constant index and water saturation curve separation became larger. Furthermore, the influencing effects of the fracture widths, fracture numbers, and fracture dip angles mainly occurred in terms of three aspects. The first was the slope of the resistivity index and water saturation curves (IR–Sw). The second was the slope of the dielectric constant index and water saturation curves (Iε–Sw), and the third was the loss tangent D and water saturation Sw curves.
3
Content available Fretting Corrosion Effect on Fatigue Resistance of Gas Turbine Engine Part Material
Bezyazychny Vyacheslav F., Szczerek Marian, Timofeev Mikhail V., Lyubimov Roman V.
Tribologia
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2020
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nr 2
7--14
EN
The paper presents the results of a study on the fretting corrosion effect on strength as per the diagrams of material fatigue of low-cycle and high-cycle loading. An experimental study of the effect of fretting corrosion on fatigue of a titanium alloy VT3-1 showed that, when choosing a particular technological method to increase fatigue resistance of gas turbine engine parts operating under fretting corrosion conditions, it is necessary to take into account the fact that fretting itself is intensive strengthening and at the same time a softening factor affecting the surface layers of the material. Technological methods of surface plastic deformation treatment result in a significant change in the parameters of metal surface layer state, which depends on both the type and duration of treatment. If the power and time parameters of processing are too high, the surface may be re-cold worked and the surface layer of the material almost completely exhausts the reserve of plasticity, as a result dangerous microcracks occur, and the formation of particles of flaking metal emerge. Possible ways using technological methods have been suggested by the authors to improve fretting strength of part surfaces operating under fretting corrosion conditions.
PL
W artykule przedstawiono wyniki badań wpływu korozji ciernej na wytrzymałość zmęczeniową przy niskiej i wysokiej częstotliwości obciążania. Eksperymentalne badania wpływu korozji ciernej na zmęczenie stopu tytanu VT3-1 wykazały, że wybierając metodę technologicznego zwiększania odporności zmęczeniowej części silników turbogazowych pracujących w warunkach korozji ciernej, należy wziąć pod uwagę fakt, że sam fretting jest czynnikiem wzmacniającym i jednocześnie osłabiającym warstwy wierzchnie materiału. Technologiczne metody powierzchniowej obróbki plastycznej powodują istotną zmianę parametrów stanu warstwy metalu w zależności zarówno od rodzaju, jak i czasu trwania obróbki. Gdy parametry obróbki (moc i czas) są zbyt duże, powierzchnia zostaje poddana obróbce na zimno, warstwa wierzchnia materiału nie jest podatna na odkształcenie plastyczne, wobec czego powstają niebezpieczne mikropęknięcia oraz tworzą się odpryski. Wskazano potencjalne zabiegi technologiczne rekomendowane do zwiększenia odporności elementów maszyn pracujących w warunkach występowania korozji ciernej.
4
Content available remote Frequency extension and robust full waveform inversion based on nth power operation
Zhang Pan, Han Liguo, Gao Rui, Zhang Fengjiao, Xing Zhenzhen
Acta Geophysica
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2020
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Vol. 68, no. 5
1317--1333
EN
The conventional full-waveform inversion (FWI) often minimizes the objective function using some local optimization algorithms. As a result, when the initial model is not good enough, the inversion process will drop into a local minimum. The low-frequency components contained in seismic data are of vital importance for reducing the initial model dependence and mitigating the cycle-skipping phenomenon of FWI. In this research, a frequency extension method using the nth power operation is proposed, which compresses the seismic data in time domain and extends their frequency band. Based on this, we construct a new objective function using the nth power wavefeld and derive the corresponding gradient formula. The new objective function shows better property to overcome local minimum than the conventional one. When conduct inversion, we can invert from high-order to low-order successively, which is a new multiscale strategy. Since seismic data is more sensitive to source wavelet errors after high-order operation, we make the method more robust by proposing a source-independent method to mitigate the efects of source wavelet inaccuracy. After that, we extend the proposed method to encoded multisource waveform inversion. The numerical examples on the Marmousi model demonstrate that the proposed method can efectively mitigate the cycle-skipping of FWI, and it also has good anti-noise property.
5
Content available remote Denoising of desert seismic signal based on synchrosqueezing transform and Adaboost algorithm
Sun Xiaofu, Li Yue
Acta Geophysica
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2020
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Vol. 68, no. 2
403--412
EN
Seismic data in desert area generally have low signal-to-noise ratio (SNR) due to special surface conditions. Desert noise is characterized as low-frequency, non-Gaussian and non-stationary noise, which makes the noise suppression in desert area more challenging by conventional methods. Conventional methods are efective for the signal with high SNR, but in desert seismic signal, the SNR is low and the signal can easily be obliterated in desert noise. In this paper, we propose an approach that operates in synchrosqueezing transform (SST) domain and use classifcation techniques obtained from supervised machine learning to identify the coefcients associated with signal and noise. First of all, we transform the real desert seismic data into time–frequency domain by SST. Secondly, we select features by calculating the SST coefcients of signal and noise. And then, we train them in the Adaboost classifer. Finally, when the training is completed, we can obtain the fnal classifer that can efectively separate the signal from noise. We perform tests on synthetic and feld records, and the results show great advantages in suppressing random noise as well as retaining efective signal amplitude.
6
Content available Conjugate heat and mass transfer on fluctuating mixed convection flow along a vertical wedge with thermal radiation
Firoza M. N., Roy N. C., Hossain A.
International Journal of Applied Mechanics and Engineering
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2017
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Vol. 22, no. 3
539--565
EN
We study the boundary layer characteristics of heat and mass transfer flow past a vertical wedge in the presence of thermal radiation. The surface temperature and the species concentration are assumed to be oscillating in the magnitude but not in the direction of oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the straightforward finite difference method for the entire frequency range, and the series solution for the low frequency range and the asymptotic series expansion method for the high frequency range. Numerical solutions have been presented in terms of the amplitudes and phase angles of the skin friction, the rate of heat transfer and the mass transfer with the variations of Richardson’s number, the Prandtl number, the conduction–radiation parameter, the surface temperature parameter and the Schmidt number. Furthermore, the effects of these parameters are examined in terms of the transient skin friction, heat transfer and mass transfer.
7
Content available remote Analyzing effects of ELF electromagnetic fields on removing bacterial biofilm
Karaguler T., Kahraman H., Tuter M.
Biocybernetics and Biomedical Engineering
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2017
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Vol. 37, no. 2
336--340
EN
Use of extremely low frequency electromagnetic field (ELF-EMF) to prevent and/or remove bacterial biofilm formation is rather a new research area. However the technique is becoming popular as the conventional methods such as antimicrobial surfaces, quorum-sensing and usage of phage are mostly insufficient. In this work, 1 mT–50 Hz and 100 Hz magnetic fields are applied on bacterial biofilm produced locally in our MOBGAM laboratory and found reasonable level of success of its removal.
8
Content available remote Field models in low-frequency bioelectromagnetics
Mognaschi M. E.
Przegląd Elektrotechniczny
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2016
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R. 92, nr 12
1--4
EN
In the paper, a review of the state of the art on numerical models of the electromagnetic field in biological entities is proposed. In particular, the field produced by cells and the one in which cells and biological tissues are exposed to, is considered; low frequency problems are investigated. Issues and drawbacks of field models in bioelectromagnetics with respect to field models for industrial applications are discussed.
PL
W artykule dokonano przeglądu stanu wiedzy na temat numerycznych modeli pola elektromagnetycznego w biologicznych komórkach. W szczególności, rozważane jest pole wytwarzane przez komórki i to, na które narażone są komórki i tkanki biologiczne; badane są problemy niskiej częstotliwości.. W artykule omówiono problemy i wady spotykane w adaptacji modeli polowych w bioelektromagnetyzmie w odniesieniu do modeli polowych w zastosowaniach przemysłowych.
9
Content available remote Magnetoterapia - zastosowanie lecznicze pola magnetycznego
Rutowski R., Szpilczyńska-Maciejewska M., Krynicka I.
Acta Bio-Optica et Informatica Medica. Inżynieria Biomedyczna
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1998
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Vol. 4, nr 1
3-6
PL
Przedstawiono podstawowe mechanizmy oddziaływania i lecznicze zastosowanie pola magnetycznego. W pracy wykorzystano kilkuletnie obserwacje polskich i zagranicznych ośrodków.
EN
The basic biophysical mechanisms and therapeutic use of the magnetic fields are presented. The observations from Polish and abroad centres are discussed.
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