The breakdown voltage of long air-gaps in high-voltage transmission systems depends on not only the waveform of the applied voltage, but also the atmospheric conditions. Based on the results of the research project on...The breakdown voltage of long air-gaps in high-voltage transmission systems depends on not only the waveform of the applied voltage, but also the atmospheric conditions. Based on the results of the research project on the minimum air clearance for 800-kV HVDC substations at high altitudes, and also on the monthly and yearly statistics of the atmospheric data of last ten years and the altitude correction of the atmospheric data of last ten years, the altitude correction of the air-gaps for the 800-kV DC system under plan, 500-kV AC system to be built, and 1000-kV AC system under plan in the Inner Mongolia Plateau and the Yungui Plateau in China were studied with parameter G method. Correction factors for switching and lightning impulses were calculatod and then compared with those achieved according to IEC 71. It is shown that IEC 71 is appropriate for damp regions, and correction factors differ between plateau regions in China because of different atmospheric conditions.展开更多
There are great differences in the distribution characteristics of shock waves produced by ammunition explosions at different altitudes.At present,there are many studies on plain explosion shock waves,but there are fe...There are great differences in the distribution characteristics of shock waves produced by ammunition explosions at different altitudes.At present,there are many studies on plain explosion shock waves,but there are few studies on the distribution characteristics of plateau explosion shock waves,and there is still a lack of complete analysis and evaluation methods.This paper compares and analyzes shock wave overpressure data at different altitudes,obtains the attenuation effect of different altitudes on the shock wave propagation process and proposes a calculation formula for shock wave overpressure considering the effect of altitude.The data analysis results show that at the same TNT equivalent and the same distance from the measuring point,the shock wave overpressure at high altitude is lower than that at low altitude.With the increase in the explosion center distance of the measuring point,the peak attenuation rate of the shock wave overpressure at high altitudes is smaller than that at low altitudes,and the peak attenuation rate of the shock wave overpressure at high altitudes gradually intensifies with increasing proportional distance.The average error between the shock wave overpressure and measured shock wave overpressure in a high-altitude environment obtained by using the above calculation formula is 11.1389%.Therefore,this method can effectively predict explosion shock wave overpressure in plateau environments and provides an effective calculation method for practical engineering tests.展开更多
Many factors,such as deck motion and air wave,influence the determination of the approach speed which has an important effect on landing safety. Until recently,there are no design criteria about approach speed of carr...Many factors,such as deck motion and air wave,influence the determination of the approach speed which has an important effect on landing safety. Until recently,there are no design criteria about approach speed of carrier aircraft in the current standards and available publications. Therefore,the requirements of stall margin, longitudinal acceleration ability,altitude correction and field-of-view on approach speed were researched. Based on the flight dynamics model,the flight simulations were conducted to study the effect of the response time of engine,wave off requirements,elevator efficiency and deflection rate on the approach speed. The results presented that the approach longitudinal acceleration and altitude correction ability had crucial influence on the approach speed envelope of the aircraft. The limitations of the control requirements,field- of- view requirements and gear were also given through the simulation and analysis. Based on the above results,the approach speed envelope were determined.展开更多
Digital Elevation Models(DEMs)for Antarctica are critical datasets for general circulation models,change analysis of ice sheet dynamics and logistical planning of field expeditions.To date,there are five different DEM...Digital Elevation Models(DEMs)for Antarctica are critical datasets for general circulation models,change analysis of ice sheet dynamics and logistical planning of field expeditions.To date,there are five different DEMs covering all of Antarctica,all of which were derived from satellite radar or laser altimetry data in combination with ground data.Since the margins of ice sheets are highly dynamic in space and time,DEMs of Antarctica should be updated frequently as new data become available.We used Radar Altimeter(RA-2)data from Envisat and laser altimeter(GLAS)data from ICESat to create an up-to-date DEM of Antarctica with high accuracy and precision of elevation measurement.In this paper,these two different sources of satellite altimeter data from 2003 to 2009 were integrated to generate a DEM for the entire continent of Antarctica.We applied five different quality judgment rules to filter unreliable ICESat/GLAS data;as a result,8.36%of the data were filtered out.A relative correction method based on speckle geometry intersection was used to correct Envisat RA-2 elevations to ICESat/GLAS.The data were interpolated to a regu-lar 1000 m polar stereographic grid using ordinary Kriging after semi-variance analysis.The accuracy of the final DEM was assessed through a comparison with two airborne LiDAR datasets,a field GPS strip from China's Zhongshan Station to Dome A and the most recently published DEM.The comparison result shows that the error of the new DEM is from 32.1 m to 27.84 m,and the distribution of errors depends on the surface slope.The new DEM shows an obvious improvement on steep slopes,including the quickly changing ice sheet margin areas.展开更多
文摘The breakdown voltage of long air-gaps in high-voltage transmission systems depends on not only the waveform of the applied voltage, but also the atmospheric conditions. Based on the results of the research project on the minimum air clearance for 800-kV HVDC substations at high altitudes, and also on the monthly and yearly statistics of the atmospheric data of last ten years and the altitude correction of the atmospheric data of last ten years, the altitude correction of the air-gaps for the 800-kV DC system under plan, 500-kV AC system to be built, and 1000-kV AC system under plan in the Inner Mongolia Plateau and the Yungui Plateau in China were studied with parameter G method. Correction factors for switching and lightning impulses were calculatod and then compared with those achieved according to IEC 71. It is shown that IEC 71 is appropriate for damp regions, and correction factors differ between plateau regions in China because of different atmospheric conditions.
文摘There are great differences in the distribution characteristics of shock waves produced by ammunition explosions at different altitudes.At present,there are many studies on plain explosion shock waves,but there are few studies on the distribution characteristics of plateau explosion shock waves,and there is still a lack of complete analysis and evaluation methods.This paper compares and analyzes shock wave overpressure data at different altitudes,obtains the attenuation effect of different altitudes on the shock wave propagation process and proposes a calculation formula for shock wave overpressure considering the effect of altitude.The data analysis results show that at the same TNT equivalent and the same distance from the measuring point,the shock wave overpressure at high altitude is lower than that at low altitude.With the increase in the explosion center distance of the measuring point,the peak attenuation rate of the shock wave overpressure at high altitudes is smaller than that at low altitudes,and the peak attenuation rate of the shock wave overpressure at high altitudes gradually intensifies with increasing proportional distance.The average error between the shock wave overpressure and measured shock wave overpressure in a high-altitude environment obtained by using the above calculation formula is 11.1389%.Therefore,this method can effectively predict explosion shock wave overpressure in plateau environments and provides an effective calculation method for practical engineering tests.
文摘Many factors,such as deck motion and air wave,influence the determination of the approach speed which has an important effect on landing safety. Until recently,there are no design criteria about approach speed of carrier aircraft in the current standards and available publications. Therefore,the requirements of stall margin, longitudinal acceleration ability,altitude correction and field-of-view on approach speed were researched. Based on the flight dynamics model,the flight simulations were conducted to study the effect of the response time of engine,wave off requirements,elevator efficiency and deflection rate on the approach speed. The results presented that the approach longitudinal acceleration and altitude correction ability had crucial influence on the approach speed envelope of the aircraft. The limitations of the control requirements,field- of- view requirements and gear were also given through the simulation and analysis. Based on the above results,the approach speed envelope were determined.
文摘Digital Elevation Models(DEMs)for Antarctica are critical datasets for general circulation models,change analysis of ice sheet dynamics and logistical planning of field expeditions.To date,there are five different DEMs covering all of Antarctica,all of which were derived from satellite radar or laser altimetry data in combination with ground data.Since the margins of ice sheets are highly dynamic in space and time,DEMs of Antarctica should be updated frequently as new data become available.We used Radar Altimeter(RA-2)data from Envisat and laser altimeter(GLAS)data from ICESat to create an up-to-date DEM of Antarctica with high accuracy and precision of elevation measurement.In this paper,these two different sources of satellite altimeter data from 2003 to 2009 were integrated to generate a DEM for the entire continent of Antarctica.We applied five different quality judgment rules to filter unreliable ICESat/GLAS data;as a result,8.36%of the data were filtered out.A relative correction method based on speckle geometry intersection was used to correct Envisat RA-2 elevations to ICESat/GLAS.The data were interpolated to a regu-lar 1000 m polar stereographic grid using ordinary Kriging after semi-variance analysis.The accuracy of the final DEM was assessed through a comparison with two airborne LiDAR datasets,a field GPS strip from China's Zhongshan Station to Dome A and the most recently published DEM.The comparison result shows that the error of the new DEM is from 32.1 m to 27.84 m,and the distribution of errors depends on the surface slope.The new DEM shows an obvious improvement on steep slopes,including the quickly changing ice sheet margin areas.
