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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.
EN
The fatigue behaviour of the load-carrying fillet welded joints was investigated by experimental and numerical approach in this paper. 26 load-carrying cruciform fillet welded joints involving 8 stress levels were tested and the S–N curves of 95% survival probability in terms of toe failure and root failure were established separately. The test results also demonstrate that the design curves of Eurocode3 are not suitable for this batch of specimens. In the following numerical simulations, three types of initial crack assumption were analysed by 3D mix-mode fatigue crack propagation analysis according to experimental observation. All the possible crack growth routes were simulated well. However, the single crack assumptions cannot form satisfactory simulations on fatigue lives with enough safety stock. Therefore, multi-crack analysis was conducted based on the combined data in terms of both toe failure and root failure. It is found that multi-crack analysis with 0.5 mm weld toe initial line crack and 0.1 mm weld root initial line crack can provide appropriate prediction. The findings can be beneficial for the fatigue assessment of load-carrying fillet welded joints fabricated by the normal welding technique in China and offer some references for the fatigue assessment of structural details with different possible failure modes.
3
Content available remote Numerical Study on Thermal Environment in Mine Gob Under Coal Oxidation Condition
EN
The most feared of hazards in underground mines are those of fires and explosions. This study focuses on the temperature-rising process of residual coal under spontaneous combustion condition in coal mine gob. A numerical model has been established considering the chemical reaction, heat transfer and components seepage flow. The temperature distributions and maximum values for different positrons at various times have been calculated by using the coupled model. An experimental model has been also developed for model calibration. The validation indicates the numerical model is accurate and suitable for solving the temperature-rising problem in coalmines. The simulation results show that high temperature zone appears at the air intake roadway side in the gob and enlarging the ventilation flux increases the risk of self-ignition of coal. The research results can be used to predict the temperature-rising of coal spontaneous combustion and coal resources prevention.
PL
Pożary i wybuchy stanowią największe zagrożenia w kopalniach. Opisane w pracy badania dotyczą procesów powodujących wzrost temperatury resztkowego węgla, doprowadzający do jego samozapłonu, w odpadach z kopalni. Model numeryczny sformułowano, biorąc pod uwagę reakcje chemiczne, wymianę ciepła i przepływy składników. Rozkłady temperatury i maksymalne wartości w różnych położeniach i w różnych czasach zostały obliczone z użyciem modelu sprzężonego. Do kalibracji został również opracowany model doświadczalny. Walidacja wykazała, że model numeryczny jest dokładny i odpowiedni do rozwiązania problemu wzrostu temperatury w kopalniach węgla. Wyniki symulacji wskazują, że strefa podwyższonej temperatury pojawia się na szlakach wlotu powietrza do materiału i zwiększenie strumienia wentylującego zwiększa ryzyko samozapłonu węgla. Wyniki badań mogą być wykorzystane do przewidywania wzrostu temperatury grożącego samozapłonem węgla oraz do ochrony jego zasobów.
4
Content available remote Design and Control of Multi-terminal VSC-HVDC for Large Offshore Wind Farms
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.
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