The water-lubricated thrust bearings of the marine rim-driven thruster(RDT)are usually composed of polymer composites,which are prone to serious wear under harsh working conditions.Ultrasonic is an excellent non-destr...The water-lubricated thrust bearings of the marine rim-driven thruster(RDT)are usually composed of polymer composites,which are prone to serious wear under harsh working conditions.Ultrasonic is an excellent non-destructive monitoring technology,but polymer materials are characterized by viscoelasticity,heterogeneity,and large acoustic attenuation,making it challenging to extract ultrasonic echo signals.Therefore,this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient.The effects of bearing parameters,objective function,and algorithm parameters on the identification results are simulated and analyzed.Taking the correlation coefficient and root mean square error as the matching parameters,the thickness,sound velocity,density,and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm(DEA),and the wear measurement system is constructed.In order to verify the identification accuracy of this method,an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-etherketone(PEEK)fixed pad and stainless-steel thrust collar as the object.The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system,respectively.Ultimately,the results demonstrate that the thickness identification error of this method is approximately 1%,and in-situ monitoring ability will be realized in the future,which is of great significance to the life prediction of bearings.展开更多
The M_S6. 1 earthquake was a foreshock-mainshock-aftershock type which occurred in the boundary region between Zogang and Markam counties on August 12,2013. Within 9hours before the main shock seven earthquakes of gre...The M_S6. 1 earthquake was a foreshock-mainshock-aftershock type which occurred in the boundary region between Zogang and Markam counties on August 12,2013. Within 9hours before the main shock seven earthquakes of greater than M_L2. 0 occurred,with a maximum of M_L4. 7. In this paper,the earthquake focal mechanism changing process of the Zogang-Markam M_S6. 1 earthquake sequence is studied by calculating the correlation coefficient of body wave spectral amplitudes,and the result shows that the correlation coefficients of spectral amplitude of foreshocks present high value fluctuation with an average value of 0. 86,which shows that the focal mechanism of foreshocks are similar;and the correlation coefficients of spectral amplitude of aftershocks present low value,which shows that the possibility of a large earthquake is not high after a time.展开更多
基金supported by the National Key R&D Program of China(No.2018YFE0197600)European Union’s Horizon 2020 Research and Innovation Programme RISE under Grant Agreement No.823759(REMESH)the National Natural Science Foundation of China(No.52071244).
文摘The water-lubricated thrust bearings of the marine rim-driven thruster(RDT)are usually composed of polymer composites,which are prone to serious wear under harsh working conditions.Ultrasonic is an excellent non-destructive monitoring technology,but polymer materials are characterized by viscoelasticity,heterogeneity,and large acoustic attenuation,making it challenging to extract ultrasonic echo signals.Therefore,this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient.The effects of bearing parameters,objective function,and algorithm parameters on the identification results are simulated and analyzed.Taking the correlation coefficient and root mean square error as the matching parameters,the thickness,sound velocity,density,and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm(DEA),and the wear measurement system is constructed.In order to verify the identification accuracy of this method,an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-etherketone(PEEK)fixed pad and stainless-steel thrust collar as the object.The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system,respectively.Ultimately,the results demonstrate that the thickness identification error of this method is approximately 1%,and in-situ monitoring ability will be realized in the future,which is of great significance to the life prediction of bearings.
基金jointly sponsored by the Special Program of Earthquake Science and Technology of Earthquake Administration of Sichuan Province(LY1302) the National Key Technology R&D Program of China(2012BAK19802)
文摘The M_S6. 1 earthquake was a foreshock-mainshock-aftershock type which occurred in the boundary region between Zogang and Markam counties on August 12,2013. Within 9hours before the main shock seven earthquakes of greater than M_L2. 0 occurred,with a maximum of M_L4. 7. In this paper,the earthquake focal mechanism changing process of the Zogang-Markam M_S6. 1 earthquake sequence is studied by calculating the correlation coefficient of body wave spectral amplitudes,and the result shows that the correlation coefficients of spectral amplitude of foreshocks present high value fluctuation with an average value of 0. 86,which shows that the focal mechanism of foreshocks are similar;and the correlation coefficients of spectral amplitude of aftershocks present low value,which shows that the possibility of a large earthquake is not high after a time.
