Leakage currents accelerate surface degradation of metal contacts via small scale arcing across lubricating films,but recent observations suggest that metallic nanoparticle additives in lubricants may be useful to imp...Leakage currents accelerate surface degradation of metal contacts via small scale arcing across lubricating films,but recent observations suggest that metallic nanoparticle additives in lubricants may be useful to improve contact performance.These findings prompted a study that examined electrically induced surface pitting of steel contacts in the presence of several lubricating greases including some containing nanometer-sized colloidal silver(Ag)particles.Reciprocating rolling sphere-on-disk experiments were conducted under electro-tribological loads employing polyurea greases derived from mineral and synthetic base oils with and without additives.Friction forces and electrical resistance were monitored continuously during the tests;surface changes were characterized by means of optical spectroscopy,stylus profilometry,and scanning electron microscopy(SEM)including compositional analysis using energy dispersive spectroscopy(EDS).The observations demonstrate that surface pitting induced by arcing occurs mainly at the points were the rolling motion changes direction and that eroded metal is deposited along the wear grove.Micron-sized pits are formed which contain carbon and oxygen indicating that arcing causes decomposition of the hydrocarbon lubricants.Numerous findings indicate a significant inhibition of pitting is induced by the Ag nanoparticles;some greases containing other additives exhibit a similar,although less pronounced,effect.展开更多
The need for the mitigation of brown bears has become so severe that many nomads have given up repairing their houses in Maryo Township’s Mendang Village(also named the First Administrative Village),a remote place lo...The need for the mitigation of brown bears has become so severe that many nomads have given up repairing their houses in Maryo Township’s Mendang Village(also named the First Administrative Village),a remote place located in the southwestern section of the Changtang National Nature Reserve(CNNR).Only part of the village belongs to Serling Tso Nature Reserve.展开更多
This article presents methodologies for improving wind turbine condition monitoring using physics-based data analysis techniques.The unique operating conditions of the wind turbine drivetrain are described,and the com...This article presents methodologies for improving wind turbine condition monitoring using physics-based data analysis techniques.The unique operating conditions of the wind turbine drivetrain are described,and the complex kinematics of the gearbox is analyzed in detail.The pros and cons of the current wind turbine condition monitoring system(CMS)are evaluated.To improve the wind turbine CMS capability,it is suggested to use linear models with unsteady excitations,instead of using nonlinear and nonstationary process models,when dealing the wind turbine dynamics response model.An analysis is undertaken of the damage excitation mechanisms cause for various components in a gearbox,especially for those associated with lower-speed shafts.Physics(mechanics)-based data analysis methods are presented for different component damage excitation mechanisms.Validation results,using the wind farm and manufacturing floor data,are reported.展开更多
文摘Leakage currents accelerate surface degradation of metal contacts via small scale arcing across lubricating films,but recent observations suggest that metallic nanoparticle additives in lubricants may be useful to improve contact performance.These findings prompted a study that examined electrically induced surface pitting of steel contacts in the presence of several lubricating greases including some containing nanometer-sized colloidal silver(Ag)particles.Reciprocating rolling sphere-on-disk experiments were conducted under electro-tribological loads employing polyurea greases derived from mineral and synthetic base oils with and without additives.Friction forces and electrical resistance were monitored continuously during the tests;surface changes were characterized by means of optical spectroscopy,stylus profilometry,and scanning electron microscopy(SEM)including compositional analysis using energy dispersive spectroscopy(EDS).The observations demonstrate that surface pitting induced by arcing occurs mainly at the points were the rolling motion changes direction and that eroded metal is deposited along the wear grove.Micron-sized pits are formed which contain carbon and oxygen indicating that arcing causes decomposition of the hydrocarbon lubricants.Numerous findings indicate a significant inhibition of pitting is induced by the Ag nanoparticles;some greases containing other additives exhibit a similar,although less pronounced,effect.
文摘The need for the mitigation of brown bears has become so severe that many nomads have given up repairing their houses in Maryo Township’s Mendang Village(also named the First Administrative Village),a remote place located in the southwestern section of the Changtang National Nature Reserve(CNNR).Only part of the village belongs to Serling Tso Nature Reserve.
文摘This article presents methodologies for improving wind turbine condition monitoring using physics-based data analysis techniques.The unique operating conditions of the wind turbine drivetrain are described,and the complex kinematics of the gearbox is analyzed in detail.The pros and cons of the current wind turbine condition monitoring system(CMS)are evaluated.To improve the wind turbine CMS capability,it is suggested to use linear models with unsteady excitations,instead of using nonlinear and nonstationary process models,when dealing the wind turbine dynamics response model.An analysis is undertaken of the damage excitation mechanisms cause for various components in a gearbox,especially for those associated with lower-speed shafts.Physics(mechanics)-based data analysis methods are presented for different component damage excitation mechanisms.Validation results,using the wind farm and manufacturing floor data,are reported.
