We deal with the development of a solidification benchmark experiment in order to investigate the structure formation as well as solute macro-mesosegregation,by means of a well-controlled solidification experiment.The...We deal with the development of a solidification benchmark experiment in order to investigate the structure formation as well as solute macro-mesosegregation,by means of a well-controlled solidification experiment.The experiment consists in solidifying a rectangular ingot of Sn-3wt.%Pb alloy,by using two lateral heat exchangers which allow extraction of the heat flux from one or two vertical sides of the sample.The domain is a quasi two dimensional parallepipedic ingot(100×60×10)mm.The temperature difference AT between the two lateral sides is 40 K and the cooling rate CR=0.03 K/s.The instrumentation consists in recording the instantaneous temperature maps by means of an array of 50 thermocouples in order to provide the time evolution of the isotherms.After each experiment the patterns of the segregations have been obtained by X-ray radiograph and confirmed by eutectic fraction measurements.The local solute distribution determined by means of induction coupled plasma analysis is provided.The originality of the present study is to examine the effect of the forced convection driven by a travelling magnetic field(TMF)induced by a linear inductor located on the bottom part of the sample.A periodically reversed stirring with a modulation frequency equal to 0.5 Hz stirring have been investigated.This study allows us to evaluate the evolution due to the forced convection induced by a TMF field,as well as its influence on the initial conditions,the solidification macrostructure and the segregation behavior.Measurements of the velocity field by ultrasonic Doppler velocimetry(UDV)method in a Ga-In-Sn pool were performed and transposed to the tin-lead alloy case before solidification.Post-mortem patterns of the macromesosegregations have been obtained by X-ray radiography.The results show the transport effects of the flow on both the maerosegregations and the channel formation.The reversal of the TMF produces a decrease of the level of mesosegregations,namely channel formation.展开更多
The conventional Al2O3-13 wt. % TiO2 composite ceramic coatings are fabricated by plasma spraying on the surface of extrusion wheel. The microstrueture, morphology and phase compositions of the substrate and coat- ing...The conventional Al2O3-13 wt. % TiO2 composite ceramic coatings are fabricated by plasma spraying on the surface of extrusion wheel. The microstrueture, morphology and phase compositions of the substrate and coat- ing are investigated by using X-ray diffractometry （XRD） , scanning electron microsopy （SEM） and energy dis- persive spectroscopy （EDS）. Moreover, the microhardness of the substrate and the coating are investigated using Vickers mierohardness tester, the friction and wear behaviors of the substrate and the coating are investigated by using a block-on-ring tribometer under dry sliding conditions with the load of 245 N. The results show that both γ-Al2O3 and α-Al2O3 phases are observed in the as-sprayed coatings, the mian phase is γ-Al2O3. There are white particulates Al2O3 on its surface. The Al2O3-13 wt. % TiO2 coating possesses higher mierohardness which is about 1018HV and 1.6 times that of the substrate. The wear performance of coating is better than that of the substrate. In a practical application, the life of the extrusion wheel which is plasma sprayed Al2O3-13 wt. % TiO2 coating on the surface is 1.2 times that of the conventional extrusion wheel, and the life is about 330 h.展开更多
The addition of Ni element into steel to prolong the service life of coated steel was investigated in marine atmospheric environment by laboratory simulated accelerated experiment.The scanning electron microscope and ...The addition of Ni element into steel to prolong the service life of coated steel was investigated in marine atmospheric environment by laboratory simulated accelerated experiment.The scanning electron microscope and electron probe microanalysis combined with electrochemical impedance spectroscopy were used to characterize coated steel properties and examined the anti-corrosion performance.The results showed that 3 wt.%Ni-advanced steel(3Ni steel)substrate obviously delayed the failure time of coating compared to carbon steel,therefore prolonging the service life of coating on the steel.X-ray diffraction patterns for the corrosion products under the scratched coating on 3Ni steel exhibited that FeNi_(2)O_(4) and Fe_(2)O_(3) occurred in the corrosion product of 3Ni steel.It was also found that Ni element enriched in the product layer through analyzing the appearance and composition of corrosion products by electron probe micro-analysis.Chloride ions were blocked out of product by the enrichment of Ni element in rust layer.展开更多
W-2 wt.%Y2O3 composite material with uniform distribution of yttrium element was fabricated through processes of mechanical alloying （MA） and spark plasma sintering （SPS）. The relevant productions were characteriz...W-2 wt.%Y2O3 composite material with uniform distribution of yttrium element was fabricated through processes of mechanical alloying （MA） and spark plasma sintering （SPS）. The relevant productions were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. The XRD showed that the W-2 wt.%Y2O3 composite powder, including tungsten matrix and Y2O3 particles, was refined to nanometer sizes during the MA process. The SEM and TEM micrographs showed that the MA produced composite powder presented a lamellar morphology and contained many dislocations and microcracks. The EDS showed that the Y and O elements were uniformly distributed in the W matrix after mechanically alloying for 15 h. The W-2 wt.%Y2O3 composite material with uniform distribution of yttrium was obtained by sintering of the MA produced composite powder.展开更多
Disconnections due to voltage drops in the grid cannot be permitted if wind turbines(WTs)contribute significantly to electricity pro-duction,as this increases the risk of production loss and destabilizes the grid.To m...Disconnections due to voltage drops in the grid cannot be permitted if wind turbines(WTs)contribute significantly to electricity pro-duction,as this increases the risk of production loss and destabilizes the grid.To mitigate the negative effects of these occurrences,WTs must be able to ride through the low-voltage conditions and inject reactive current to provide dynamic voltage support.This paper investigates the low-voltage ride-through(LVRT)capability enhancement of a Type-3 WT utilizing a dynamic voltage restorer(DVR).During the grid voltage drop,the DVR quickly injects a compensating voltage to keep the stator voltage constant.This paper proposes an active disturbance rejection control(ADRC)scheme to control the rotor-side,grid-side and DVR-side converters in a wind–DVR integrated network.The performance of the Type-3 WT with DVR topology is evaluated under various test conditions using MATLAB®/Simulink®.These simulation results are also compared with the experimental results for the LVRT capability performed on a WT emulator equipped with a crowbar and direct current(DC)chopper.The simulation results demonstrate a favourable transient and steady-state response of the Type-3 wind turbine quantities defined by the LVRT codes,as well as improved reactive power support under balanced fault conditions.Under the most severe voltage drop of 95%,the stator currents,rotor currents and DC bus voltage are 1.25 pu,1.40 pu and 1.09 UDC,respectively,conforming to the values of the LVRT codes.DVR controlled by the ADRC technique significantly increases the LVRT capabilities of a Type-3 doubly-fed induction generator-based WT under symmetrical voltage dip events.Although setting up ADRC controllers might be challenging,the proposed method has been shown to be extremely effective in reducing all kinds of internal and external disturbances.展开更多
基金Item Sponsored by European Space Agency through the CETSOL project (ESA-MAP AO-99-117) as well as the SMACS ANR project
文摘We deal with the development of a solidification benchmark experiment in order to investigate the structure formation as well as solute macro-mesosegregation,by means of a well-controlled solidification experiment.The experiment consists in solidifying a rectangular ingot of Sn-3wt.%Pb alloy,by using two lateral heat exchangers which allow extraction of the heat flux from one or two vertical sides of the sample.The domain is a quasi two dimensional parallepipedic ingot(100×60×10)mm.The temperature difference AT between the two lateral sides is 40 K and the cooling rate CR=0.03 K/s.The instrumentation consists in recording the instantaneous temperature maps by means of an array of 50 thermocouples in order to provide the time evolution of the isotherms.After each experiment the patterns of the segregations have been obtained by X-ray radiograph and confirmed by eutectic fraction measurements.The local solute distribution determined by means of induction coupled plasma analysis is provided.The originality of the present study is to examine the effect of the forced convection driven by a travelling magnetic field(TMF)induced by a linear inductor located on the bottom part of the sample.A periodically reversed stirring with a modulation frequency equal to 0.5 Hz stirring have been investigated.This study allows us to evaluate the evolution due to the forced convection induced by a TMF field,as well as its influence on the initial conditions,the solidification macrostructure and the segregation behavior.Measurements of the velocity field by ultrasonic Doppler velocimetry(UDV)method in a Ga-In-Sn pool were performed and transposed to the tin-lead alloy case before solidification.Post-mortem patterns of the macromesosegregations have been obtained by X-ray radiography.The results show the transport effects of the flow on both the maerosegregations and the channel formation.The reversal of the TMF produces a decrease of the level of mesosegregations,namely channel formation.
文摘The conventional Al2O3-13 wt. % TiO2 composite ceramic coatings are fabricated by plasma spraying on the surface of extrusion wheel. The microstrueture, morphology and phase compositions of the substrate and coat- ing are investigated by using X-ray diffractometry （XRD） , scanning electron microsopy （SEM） and energy dis- persive spectroscopy （EDS）. Moreover, the microhardness of the substrate and the coating are investigated using Vickers mierohardness tester, the friction and wear behaviors of the substrate and the coating are investigated by using a block-on-ring tribometer under dry sliding conditions with the load of 245 N. The results show that both γ-Al2O3 and α-Al2O3 phases are observed in the as-sprayed coatings, the mian phase is γ-Al2O3. There are white particulates Al2O3 on its surface. The Al2O3-13 wt. % TiO2 coating possesses higher mierohardness which is about 1018HV and 1.6 times that of the substrate. The wear performance of coating is better than that of the substrate. In a practical application, the life of the extrusion wheel which is plasma sprayed Al2O3-13 wt. % TiO2 coating on the surface is 1.2 times that of the conventional extrusion wheel, and the life is about 330 h.
基金National Key Research and Development Program of China(2016YFC0401205).
文摘The addition of Ni element into steel to prolong the service life of coated steel was investigated in marine atmospheric environment by laboratory simulated accelerated experiment.The scanning electron microscope and electron probe microanalysis combined with electrochemical impedance spectroscopy were used to characterize coated steel properties and examined the anti-corrosion performance.The results showed that 3 wt.%Ni-advanced steel(3Ni steel)substrate obviously delayed the failure time of coating compared to carbon steel,therefore prolonging the service life of coating on the steel.X-ray diffraction patterns for the corrosion products under the scratched coating on 3Ni steel exhibited that FeNi_(2)O_(4) and Fe_(2)O_(3) occurred in the corrosion product of 3Ni steel.It was also found that Ni element enriched in the product layer through analyzing the appearance and composition of corrosion products by electron probe micro-analysis.Chloride ions were blocked out of product by the enrichment of Ni element in rust layer.
文摘W-2 wt.%Y2O3 composite material with uniform distribution of yttrium element was fabricated through processes of mechanical alloying （MA） and spark plasma sintering （SPS）. The relevant productions were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. The XRD showed that the W-2 wt.%Y2O3 composite powder, including tungsten matrix and Y2O3 particles, was refined to nanometer sizes during the MA process. The SEM and TEM micrographs showed that the MA produced composite powder presented a lamellar morphology and contained many dislocations and microcracks. The EDS showed that the Y and O elements were uniformly distributed in the W matrix after mechanically alloying for 15 h. The W-2 wt.%Y2O3 composite material with uniform distribution of yttrium was obtained by sintering of the MA produced composite powder.
文摘Disconnections due to voltage drops in the grid cannot be permitted if wind turbines(WTs)contribute significantly to electricity pro-duction,as this increases the risk of production loss and destabilizes the grid.To mitigate the negative effects of these occurrences,WTs must be able to ride through the low-voltage conditions and inject reactive current to provide dynamic voltage support.This paper investigates the low-voltage ride-through(LVRT)capability enhancement of a Type-3 WT utilizing a dynamic voltage restorer(DVR).During the grid voltage drop,the DVR quickly injects a compensating voltage to keep the stator voltage constant.This paper proposes an active disturbance rejection control(ADRC)scheme to control the rotor-side,grid-side and DVR-side converters in a wind–DVR integrated network.The performance of the Type-3 WT with DVR topology is evaluated under various test conditions using MATLAB®/Simulink®.These simulation results are also compared with the experimental results for the LVRT capability performed on a WT emulator equipped with a crowbar and direct current(DC)chopper.The simulation results demonstrate a favourable transient and steady-state response of the Type-3 wind turbine quantities defined by the LVRT codes,as well as improved reactive power support under balanced fault conditions.Under the most severe voltage drop of 95%,the stator currents,rotor currents and DC bus voltage are 1.25 pu,1.40 pu and 1.09 UDC,respectively,conforming to the values of the LVRT codes.DVR controlled by the ADRC technique significantly increases the LVRT capabilities of a Type-3 doubly-fed induction generator-based WT under symmetrical voltage dip events.Although setting up ADRC controllers might be challenging,the proposed method has been shown to be extremely effective in reducing all kinds of internal and external disturbances.
