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1

Static instability of an inverted plate in channel flow: state-space representation and solution approximation

Li P., Zhang D., Cui J., Yin H., Yang Y.

Archives of Mechanics

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2023

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Vol. 75, nr 6

695--727

EN

Plate-like structures in channel flow are commonly found in engineering. This paper reports a theoretical study on the static aeroelastic instability of an inverted cantilevered plate in an inviscid channel flow through the state space. This study begins with the kernel function of the flow potential determined in the Fourier domain with the help of the mirror image method. Then, the instability equation is derived from the operator theory and transformed in the state space. Finally, with Glauert’s expansion, model functions, and error functions, the instability problem of such a plate has been modeled as a mathematical function approximation problem and solved by the least squares method. The derived instability equation is considered at the continuum level of description, and no approximation appears at the first equation level. The convergence and reliability of the proposed modeling and its solutions approximation are entirely tested, and it can successfully predict the instability boundary, behavior, and the channel effect. Numerical results show that the decreased channel height and asymmetric plate placement in the channel significantly decrease the critical flow velocity. The plate instability modes are close to the plate’s first natural ones and not sensitive to the channel parameters. This conclusion allows further theoretical exploration of a semi-analytical approximation of the instability boundary from the obtained instability equation. The current modeling strategy in a continuum sense may provide a new idea and essential reference for other instability problems.

2

A Fast Classification Method of Faults in Power Electronic Circuits Based on Support Vector Machines

Cui J., Shi G., Gong C.

Metrology and Measurement Systems

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2017

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Vol. 24, nr 4

701--720

EN

Fault detection and location are important and front-end tasks in assuring the reliability of power electronic circuits. In essence, both tasks can be considered as the classification problem. This paper presents a fast fault classification method for power electronic circuits by using the support vector machine (SVM) as a classifier and the wavelet transform as a feature extraction technique. Using one-against-rest SVM and one-against-one SVM are two general approaches to fault classification in power electronic circuits. However, these methods have a high computational complexity, therefore in this design we employ a directed acyclic graph (DAG) SVM to implement the fault classification. The DAG SVM is close to the one-against-one SVM regarding its classification performance, but it is much faster. Moreover, in the presented approach, the DAG SVM is improved by introducing the method of Knearest neighbours to reduce some computations, so that the classification time can be further reduced. A rectifier and an inverter are demonstrated to prove effectiveness of the presented design.

3

Investigating the Effect of the Opening Unit on the Airflow Field in Rotor Spinning

Jin Y., Zhu S., Cui J., Li J., Zhu Z.

Fibres & Textiles in Eastern Europe

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2017

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Vol. 25, no. 5 (125)

18--24

EN

The opening unit is an important device in a rotor spinning unit to comb fibres and remove trash. In this paper, numerical simulation is carried out to study the flow structure in the rotor spinning channel and the trash removal process in the trash removal unit. Firstly the effect of the opening unit on the airflow field in the rotor channel is investigated by singlephase simulation. The result shows that the effective area for fibre conveyance enlarges as the absolute value of negative pressure at the outlet increases, while it decreases as the opening roller speed increases. However, the effect of the negative pressure and the opening roller speed on the length of the vortex in the axial direction is quite small. Secondly the trash separation process in the trash removal unit is simulated using the Discrete Phase Model (DPM). Suitable rotational speeds of particles of different diameters are acquired. These results could provide a valuable reference for parameter selection in the trash-removal process.

PL

Jednostka otwierająca jest ważnym urządzeniem w przędzarce rotorowej służącym do rozczesywania włókien i usuwania odpadów. W artykule przeprowadzono symulację numeryczną mającą na celu zbadanie struktury przepływu w kanale przędzalniczym wirnika oraz procesu usuwania odpadów. Wpływ jednostki otwierającej na pole przepływu powietrza w kanale wirnika badano symulacją jednofazową. Wyniki wykazały, że efektywny obszar transportu włókien powiększa się, gdy wartość bezwzględnej wartości ujemnego ciśnienia na wylocie wzrasta, a zmniejsza się wraz ze wzrostem prędkości wału otwierającego. Jednakże wpływ podciśnienia i prędkość wału otwierającego na długość wiru w kierunku osiowym jest stosunkowo niewielka. Stwierdzono także, że proces separacji odpadów w jednostce usuwania odpadów jest symulowany przy użyciu modelu dyskretnego fazy (DPM). Otrzymuje się odpowiednie prędkości obrotowe cząstek o różnych średnicach. Wyniki te mogą stanowić cenny punkt odniesienia dla wyboru parametrów w procesie usuwania odpadów.

4

Faults Classification Of Power Electronic Circuits Based On A Support Vector Data Description Method

Cui J.

Metrology and Measurement Systems

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2015

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Vol. 22, nr 2

205--220

EN

Power electronic circuits (PECs) are prone to various failures, whose classification is of paramount importance. This paper presents a data-driven based fault diagnosis technique, which employs a support vector data description (SVDD) method to perform fault classification of PECs. In the presented method, fault signals (e.g. currents, voltages, etc.) are collected from accessible nodes of circuits, and then signal processing techniques (e.g. Fourier analysis, wavelet transform, etc.) are adopted to extract feature samples, which are subsequently used to perform offline machine learning. Finally, the SVDD classifier is used to implement fault classification task. However, in some cases, the conventional SVDD cannot achieve good classification performance, because this classifier may generate some so-called refusal areas (RAs), and in our design these RAs are resolved with the one-against-one support vector machine (SVM) classifier. The obtained experiment results from simulated and actual circuits demonstrate that the improved SVDD has a classification performance close to the conventional one-against-one SVM, and can be applied to fault classification of PECs in practice.

5

Variations in foliar nutrient resorption efficiency of different plant growth forms in a temperate sandy grassland

Mao W., Li Y., Cui J., Zuo X., Zhao X.

Polish Journal of Ecology

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2011

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Vol. 59, nr 2

355-365

EN

Foliar nutrient resorption is an important strategy which allows leaf nutrients to be reused rather than lost with leaf fall, particularly in nutrient-poor ecosystems where even small nutrient losses can have significantly negative impacts on plant survival, competitive ability, and fitness. However, plants vary greatly in nitrogen (N) and phosphorus (P) resorption among plant growth forms during leaf senescence, which may be vital to understand the role of plant growth forms in ecosystem functioning. Green and senesced leaf N and P concentrations of 39 plant species in sandy grassland (Horqin Sand Land) of northern China were analyzed to detect variations of nutrient resorption efficiency among plant growth forms. The results showed that nitrogen resorption efficiency (NRE) ranged from 29% to 74%, with an average ([plus or minus] SD) of 50.3 [plus or minus] 11.2%, and phosphorus resorption efficiency (PRE) varied among species between 46% and 82%, with a mean ([plus or minus] SD) of 68.4 [plus or minus] 6.9%, suggesting that nutrient resorption is a vital nutrient conservation strategy in this ecosystem. In addition, NRE and PRE differed significantly among the dominant plant growth forms in this sandy grassland. NRE for N-fixing species and graminoids were significantly lower relative to NRE for shrubs and forbs, but mean PRE of graminoids was significantly higher than those of N fixers, shrubs and forbs. These data give indirect evidence that the differentiation of N and P conservation serve as an important mechanism permitting the co-existence of growth forms in arid systems.

6

Analog Circuit Fault Classification Using Improved One-Against-One Support Vector Machines

Cui J., Wang Y.

Metrology and Measurement Systems

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2011

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Vol. 18, nr 4

569-582

EN

This paper presents a novel strategy of fault classification for the analog circuit under test (CUT). The proposed classification strategy is implemented with the one-against-one Support Vector Machines Classifier (SVC), which is improved by employing a fault dictionary to accelerate the testing procedure. In our investigations, the support vectors and other relevant parameters are obtained by training the standard binary support vector machines. In addition, a technique of radial-basis-function (RBF) kernel parameter evaluation and selection is invented. This technique can find a good and proper kernel parameter for the SVC prior to the machine learning. Two typical analog circuits are demonstrated to validate the effectiveness of the proposed method.

7

A novel approach of analog fault classification using a support vector machines classifier

Cui J., Wang Y.

Metrology and Measurement Systems

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2010

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Vol. 17, nr 4

561-581

EN

In order to make the analog fault classification more accurate, we present a method based on the Support Vector Machines Classifier (SVC) with wavelet packet decomposition (WPD) as a preprocessor. In this paper, the conventional one-against-rest SVC is resorted to perform a multi-class classification task because this classifier is simple in terms of training and testing. However, this SVC needs all decision functions to classify the query sample. In our study, this classifier is improved to make the fault classification task more fast and efficient. Also, in order to reduce the size of the feature samples, the wavelet packet analysis is employed. In our investigations, the wavelet analysis can be used as a tool of feature extractor or noise filter and this preprocessor can improve the fault classification resolution of the analog circuits. Moreover, our investigation illustrates that the SVC can be applicable to the domain of analog fault classification and this novel classifier can be viewed as an alternative for the back-propagation (BP) neural network classifier.

8

Direct Transformation of Ethanol to Ethyl Acetate over MoSx/C Catalyst

Wang L. X., Zheng D. F., Ma C. X., Zhu W. C., Liu S. Y., Cui J., Wang Z. L., Zhang W. X.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 11

1993-2000

EN

Activated carbon-supported sulfided molybdenum catalysts were tested in transformation of ethanol to ethyl acetate. The catalytic activity of MoSx/C catalysts was found to depend strongly on preparation procedure. Surface atomic ratio of S/Mo on these catalysts was different and the catalyst with the ratio of S/Mo = 2.2 had better catalytic properties. For the purpose of enhancement of catalytic activity, the treatment of activated carbon support by HNO3 had been applied. Physicochemical characterization showed that the pretreatment was effective in obtaining a highly dispersed molybdenum species on the surface of the catalyst, which led to an in crease in conversion of ethanol.