In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the...In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.展开更多
Upon the analysis of the interior and exterior pressures observed on the double-tubbing shaftwalls of the West Ventilation Shaft in Xieqiao Coal Mine of Huainan, deep-going investigations are made into foreign loads o...Upon the analysis of the interior and exterior pressures observed on the double-tubbing shaftwalls of the West Ventilation Shaft in Xieqiao Coal Mine of Huainan, deep-going investigations are made into foreign loads on the shaftwalls of thes kind at each working stage and into the distributiona patterns of interior pressures. As a result, a calculation model is established for forecasting exterior loads on the shaftwalls by using the grey theory.展开更多
The precision of VLBI tracking delays and the positioning reduction results during the real-time tracking phase of the Chang'E-2 satellite are statistically analyzed.The application of the positioning reduction to...The precision of VLBI tracking delays and the positioning reduction results during the real-time tracking phase of the Chang'E-2 satellite are statistically analyzed.The application of the positioning reduction to the real-time monitoring of pivotal arcs of the Chang'E-2 satellite is discussed.The technical specifications of the tests of tracking and control systems in X-band are estimated and evaluated via the positioning reduction method.Useful methodology and software are prepared and practical experience in engineering and technology is accumulated for the follow-up lunar and deep space explorations of China.展开更多
基金Project(50465002) supported by the National Natural Science Foundation of China
文摘In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.
文摘Upon the analysis of the interior and exterior pressures observed on the double-tubbing shaftwalls of the West Ventilation Shaft in Xieqiao Coal Mine of Huainan, deep-going investigations are made into foreign loads on the shaftwalls of thes kind at each working stage and into the distributiona patterns of interior pressures. As a result, a calculation model is established for forecasting exterior loads on the shaftwalls by using the grey theory.
基金supported by the National Natural Science Foundation of China (Grant Nos.10973030 and 11178024)China’s Lunar Exploration Project (Chang’E-2 mission,Chang’E-3 mission)the Committee of Science and Technique of Shanghai (Grant No.06DZ22101)
文摘The precision of VLBI tracking delays and the positioning reduction results during the real-time tracking phase of the Chang'E-2 satellite are statistically analyzed.The application of the positioning reduction to the real-time monitoring of pivotal arcs of the Chang'E-2 satellite is discussed.The technical specifications of the tests of tracking and control systems in X-band are estimated and evaluated via the positioning reduction method.Useful methodology and software are prepared and practical experience in engineering and technology is accumulated for the follow-up lunar and deep space explorations of China.
