Three types of natural soils are studied in this paper: 1) a postglacial silt, 2) a glacial till, and 3) a postglacial sand. The former two are soils from embankment dam sites in Sweden, and the latter is a soil from ...Three types of natural soils are studied in this paper: 1) a postglacial silt, 2) a glacial till, and 3) a postglacial sand. The former two are soils from embankment dam sites in Sweden, and the latter is a soil from a natural deposit situated in the Swedish east coastal region. In situ Double-ring infiltrometer (DRI) tests are compared with laboratory constant-head permeability determinations. This study shows that the DRI tests conducted on sandy-silty soils are within sufficient range to the laboratory results, to suggest that in situ near-saturated infiltration capacity may be used as a field estimate of hydraulic conductivity (permeability) for this range of soils. In situ infiltrometer testing may be the better alternative when there is difficulty in achieving representative field conditions in a laboratory setting, e.g., for widely graded soils such as glacial tills.展开更多
Insulation failure significantly contributes to the unpredictable shutdown of power equipment.Compared to the partial discharge and high-frequency(HF)injection methods,the HF common-mode(CM)leakage current method offe...Insulation failure significantly contributes to the unpredictable shutdown of power equipment.Compared to the partial discharge and high-frequency(HF)injection methods,the HF common-mode(CM)leakage current method offers a non-intrusive and highly sensitive alternative.However,the detection of HF CM currents is susceptible to interference from differential-mode(DM)currents,which exhibit high-amplitude and multifrequency components during normal operation.To address this challenge,this paper proposes a double-ring current sensor based on the principle of magnetic shielding for inverter-fed machine winding insulation monitoring.The inner ring harnesses the magnetic aggregation effect to isolate the DM current magnetic field,whereas the outer ring serves as the magnetic core of the Rogowski current sensor,enabling HF CM current monitoring.First,the magnetic field distributions of the CM and DM currents were analyzed.Then,a correlation between the sensor parameters and signal-to-noise ratio of the target HF CM current was established.Finally,an experimental study was conducted on a 3-kW PMSM for verification.The results indicate that the proposed double-ring HF CM sensor can effectively mitigate DM current interference.Compared to a single-ring sensor,a reduction of approximately 40%in the DM component was achieved,which significantly enhanced the precision of online insulation monitoring.展开更多
Compared with the traditional radial flow reactors(RFRs), the double-ring RFRs possess advantages including lower pressure drop, shorter flow path and greater flow area. According to the Ergun's equation and the c...Compared with the traditional radial flow reactors(RFRs), the double-ring RFRs possess advantages including lower pressure drop, shorter flow path and greater flow area. According to the Ergun's equation and the continuity equation, a two-dimensional hydrodynamic model was established to describe the hydrodynamic behavior in the double-ring RFRs. The successive over-relaxation(SOR) method was applied to solve the two-dimensional hydrodynamic model. The flow assignment parameters(T_i) of mass flow in the inner channel to the outer catalyst bed and the inner catalyst bed were optimized by the Powell method. Simulations showed the trend of change in gas distribution uniformity along the axial direction and the weight hourly space velocity(WHSV) with the variation of reactor size. The model can be used to analyze the reasonability of dehydrogenation reactor design, and it can also provide quantitative reference for the design of new double-ring RFRs.展开更多
文摘Three types of natural soils are studied in this paper: 1) a postglacial silt, 2) a glacial till, and 3) a postglacial sand. The former two are soils from embankment dam sites in Sweden, and the latter is a soil from a natural deposit situated in the Swedish east coastal region. In situ Double-ring infiltrometer (DRI) tests are compared with laboratory constant-head permeability determinations. This study shows that the DRI tests conducted on sandy-silty soils are within sufficient range to the laboratory results, to suggest that in situ near-saturated infiltration capacity may be used as a field estimate of hydraulic conductivity (permeability) for this range of soils. In situ infiltrometer testing may be the better alternative when there is difficulty in achieving representative field conditions in a laboratory setting, e.g., for widely graded soils such as glacial tills.
基金supported in part by the National Natural Science Foundation of China under Grant 51907116in part sponsored by Natural Science Foundation of Shanghai 22ZR1425400sponsored by Shanghai Rising-Star Program 23QA1404000。
文摘Insulation failure significantly contributes to the unpredictable shutdown of power equipment.Compared to the partial discharge and high-frequency(HF)injection methods,the HF common-mode(CM)leakage current method offers a non-intrusive and highly sensitive alternative.However,the detection of HF CM currents is susceptible to interference from differential-mode(DM)currents,which exhibit high-amplitude and multifrequency components during normal operation.To address this challenge,this paper proposes a double-ring current sensor based on the principle of magnetic shielding for inverter-fed machine winding insulation monitoring.The inner ring harnesses the magnetic aggregation effect to isolate the DM current magnetic field,whereas the outer ring serves as the magnetic core of the Rogowski current sensor,enabling HF CM current monitoring.First,the magnetic field distributions of the CM and DM currents were analyzed.Then,a correlation between the sensor parameters and signal-to-noise ratio of the target HF CM current was established.Finally,an experimental study was conducted on a 3-kW PMSM for verification.The results indicate that the proposed double-ring HF CM sensor can effectively mitigate DM current interference.Compared to a single-ring sensor,a reduction of approximately 40%in the DM component was achieved,which significantly enhanced the precision of online insulation monitoring.
文摘Compared with the traditional radial flow reactors(RFRs), the double-ring RFRs possess advantages including lower pressure drop, shorter flow path and greater flow area. According to the Ergun's equation and the continuity equation, a two-dimensional hydrodynamic model was established to describe the hydrodynamic behavior in the double-ring RFRs. The successive over-relaxation(SOR) method was applied to solve the two-dimensional hydrodynamic model. The flow assignment parameters(T_i) of mass flow in the inner channel to the outer catalyst bed and the inner catalyst bed were optimized by the Powell method. Simulations showed the trend of change in gas distribution uniformity along the axial direction and the weight hourly space velocity(WHSV) with the variation of reactor size. The model can be used to analyze the reasonability of dehydrogenation reactor design, and it can also provide quantitative reference for the design of new double-ring RFRs.
