We used satellite altimetry data to investigate the Kuroshio Current because of the higher resolution and wider range of observations. In previous studies, satellite absolute geostrophic velocities were used to study ...We used satellite altimetry data to investigate the Kuroshio Current because of the higher resolution and wider range of observations. In previous studies, satellite absolute geostrophic velocities were used to study the spatiotemporal variability of the sea surface velocity field along the current, and extraction methods were employed to detect the Kuroshio axes and paths. However, sea surface absolute geostrophic velocity estimated from absolute dynamic topography should be regarded as the geostrophic component of the actual surface velocity, which cannot represent a sea surface current accurately. In this study, mathematical verification between the climatic absolute geostrophic and bin-averaged drifting buoy velocity was established and then adopted to correct the satellite absolute geostrophic velocities. There were some differences in the characteristics between satellite geostrophic and drifting buoy velocities. As a result, the corrected satellite absolute geostrophic velocities were used to detect the Kuroshio axis and path based on a principal-component detection scheme. The results showed that the detection of the Kuroshio axes and paths from corrected absolute geostrophic velocities performed better than those from satellite absolute geostrophic velocities and surface current estimations. The corrected satellite absolute geostrophic velocity may therefore contribute to more precise day-to-day detection of the Kuroshio Current axis and path.展开更多
Inevitable geometric variations significantly affect the performance of turbines or even that of entire engines;thus,it is necessary to determine their actual characteristics and accurately estimate their impact on pe...Inevitable geometric variations significantly affect the performance of turbines or even that of entire engines;thus,it is necessary to determine their actual characteristics and accurately estimate their impact on performance.In this study,based on 1781 measured profiles of a typical turbine blade,the statistical characteristics of the geometric variations and the uncertainty impact are analyzed,and some commonly used uncertainty modelling methods based on Principal-Component Analysis(PCA)are verified.The geometric variations are found to be evident,asymmetric,and non-uniform,and the non-normality of the random distributions is non-negligible.The performance is notably affected,which is manifested as an overall offset,a notable scattering,and significant deterioration in several extreme cases.Additionally,it is demonstrated that the PCA reconstruction model is effective in characterizing major uncertainty characteristics of the geometric variations and their impact on the performance with almost the first 10 PCA modes.Based on a reasonable profile error and mean geometric deviation,the Gaussian assumption and stochasticprocess-based model are also found to be effective in predicting the mean values and standard deviations of the performance variations.However,they fail to predict the probability of some extreme cases with high loss.Finally,a Chi-square-based correction model is proposed to compensate for this deficiency.The present work can provide a useful reference for uncertainty analysis of the impact of geometric variations,and the corresponding uncertainty design of turbine blades.展开更多
基金The National Science and Technology Major Project of the Ministry of Science and Technology of China under contract No.2018YFF01014100the National Programme on Global Change and Air-Sea Interaction under contract No.GASI-IPOVAI-01-05the NSFC-Shandong Joint Fund for Marine Science Research Centers under contract No.U1606405
文摘We used satellite altimetry data to investigate the Kuroshio Current because of the higher resolution and wider range of observations. In previous studies, satellite absolute geostrophic velocities were used to study the spatiotemporal variability of the sea surface velocity field along the current, and extraction methods were employed to detect the Kuroshio axes and paths. However, sea surface absolute geostrophic velocity estimated from absolute dynamic topography should be regarded as the geostrophic component of the actual surface velocity, which cannot represent a sea surface current accurately. In this study, mathematical verification between the climatic absolute geostrophic and bin-averaged drifting buoy velocity was established and then adopted to correct the satellite absolute geostrophic velocities. There were some differences in the characteristics between satellite geostrophic and drifting buoy velocities. As a result, the corrected satellite absolute geostrophic velocities were used to detect the Kuroshio axis and path based on a principal-component detection scheme. The results showed that the detection of the Kuroshio axes and paths from corrected absolute geostrophic velocities performed better than those from satellite absolute geostrophic velocities and surface current estimations. The corrected satellite absolute geostrophic velocity may therefore contribute to more precise day-to-day detection of the Kuroshio Current axis and path.
基金supported by the National Science and Technology Major Project, China (No. J2019-II-0012-0032)
文摘Inevitable geometric variations significantly affect the performance of turbines or even that of entire engines;thus,it is necessary to determine their actual characteristics and accurately estimate their impact on performance.In this study,based on 1781 measured profiles of a typical turbine blade,the statistical characteristics of the geometric variations and the uncertainty impact are analyzed,and some commonly used uncertainty modelling methods based on Principal-Component Analysis(PCA)are verified.The geometric variations are found to be evident,asymmetric,and non-uniform,and the non-normality of the random distributions is non-negligible.The performance is notably affected,which is manifested as an overall offset,a notable scattering,and significant deterioration in several extreme cases.Additionally,it is demonstrated that the PCA reconstruction model is effective in characterizing major uncertainty characteristics of the geometric variations and their impact on the performance with almost the first 10 PCA modes.Based on a reasonable profile error and mean geometric deviation,the Gaussian assumption and stochasticprocess-based model are also found to be effective in predicting the mean values and standard deviations of the performance variations.However,they fail to predict the probability of some extreme cases with high loss.Finally,a Chi-square-based correction model is proposed to compensate for this deficiency.The present work can provide a useful reference for uncertainty analysis of the impact of geometric variations,and the corresponding uncertainty design of turbine blades.
