Ceramics can keep their mechanical characteristics up to 2 000℃ or higher.In this paper,A model to predict ultimate strength of continuous fiber-reinforced brittle matrix composites is developed.A statistical theor...Ceramics can keep their mechanical characteristics up to 2 000℃ or higher.In this paper,A model to predict ultimate strength of continuous fiber-reinforced brittle matrix composites is developed.A statistical theory for the strength of a uni-axially fiber-reinforced brittle matrix composite is presented.Also a semi-empirical frictional heating method for estimating in-situ interfacial shear in fiber-reinforced ceramic matrix composites was improved.Local uneven fiber packing variation as well as uneven micro-damage during fatigue can be expected to have effects on the composites:generation of frictional heating,thermal gradients,and residual stresses around local fiber breaks.This study examined those engineering interests by the finite element method.展开更多
Fall has become the second leading cause of unintentional injury, death, after road traffic injuries, for the elderly in Europe. This proportion will increase in the next decades and become more than ever a real publi...Fall has become the second leading cause of unintentional injury, death, after road traffic injuries, for the elderly in Europe. This proportion will increase in the next decades and become more than ever a real public health issue. France was selected by the World Health Organization to be the first country to implement a program that reduces the coverage of the dependence. Commercial automatic fall detection devices can help seniors get back on their feet faster by reducing the time of emergency procedure. Many seniors do not take advantage of this potentially life-saving technology mainly because of intrusiveness constraints. After having reminded the context and the challenges of fall detection systems, this paper presents an original device which is unobtrusive, comfortable and very effective. The hardware architecture embedded into the sole and a new fall detection algorithm based on acceleration and time thresholds are presented. The algorithm introduces a new concept of differential acceleration to eliminate some drawbacks of current systems. Tests were carried out under real life conditions by 6 young participants for different ADLs. The data were analyzed blindly. We compared the detected falls and found a 100% sensibility and more than 93% sensitivity for all participants and scenarios.展开更多
Impeller hub corner separation flow(IHCS)has a significant influence on energy conversion of the bulb tubular pump,and its unsteady characteristics are investigated with CFD-based method.The generation mechanism and p...Impeller hub corner separation flow(IHCS)has a significant influence on energy conversion of the bulb tubular pump,and its unsteady characteristics are investigated with CFD-based method.The generation mechanism and power loss characteristics of IHCS are investigated by the entropy production method and pressure fluctuation analysis.The main cause can be attributed to the large transverse pressure gradient near the hub at the trailing edge of the impeller,which is aggravated by the circumferential movement trend and the diffuser reverse flow,while the IHCS is significantly weakened with increased flow rate.The undesirable flow behavior is more likely to cause a significant increase in energy loss near the hub region compared to that in the rim region.The relative vortex stretching induced by the velocity gradient is the main cause of the horn-like vortex(HLV),and its intensity and resulting energy loss tend to decrease along the vortex trajectory.The HLV changes the dominant frequency of the pressure fluctuations in the nearby flow field,the value of which increases from 1fr(the blade passing frequency)to 2fr with increased amplitude,mainly due to the lower pressure regions on the impeller suction surface(SS)and HLV vortex core.Due to the effect of rotor-stator interaction(RSI),the HLVs generated between two adjacent impeller blades are cut into several sections by the diffuser vanes and propagate and dissipate along the mainstream direction.展开更多
文摘Ceramics can keep their mechanical characteristics up to 2 000℃ or higher.In this paper,A model to predict ultimate strength of continuous fiber-reinforced brittle matrix composites is developed.A statistical theory for the strength of a uni-axially fiber-reinforced brittle matrix composite is presented.Also a semi-empirical frictional heating method for estimating in-situ interfacial shear in fiber-reinforced ceramic matrix composites was improved.Local uneven fiber packing variation as well as uneven micro-damage during fatigue can be expected to have effects on the composites:generation of frictional heating,thermal gradients,and residual stresses around local fiber breaks.This study examined those engineering interests by the finite element method.
文摘Fall has become the second leading cause of unintentional injury, death, after road traffic injuries, for the elderly in Europe. This proportion will increase in the next decades and become more than ever a real public health issue. France was selected by the World Health Organization to be the first country to implement a program that reduces the coverage of the dependence. Commercial automatic fall detection devices can help seniors get back on their feet faster by reducing the time of emergency procedure. Many seniors do not take advantage of this potentially life-saving technology mainly because of intrusiveness constraints. After having reminded the context and the challenges of fall detection systems, this paper presents an original device which is unobtrusive, comfortable and very effective. The hardware architecture embedded into the sole and a new fall detection algorithm based on acceleration and time thresholds are presented. The algorithm introduces a new concept of differential acceleration to eliminate some drawbacks of current systems. Tests were carried out under real life conditions by 6 young participants for different ADLs. The data were analyzed blindly. We compared the detected falls and found a 100% sensibility and more than 93% sensitivity for all participants and scenarios.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51979125,52209111 and U2016225).
文摘Impeller hub corner separation flow(IHCS)has a significant influence on energy conversion of the bulb tubular pump,and its unsteady characteristics are investigated with CFD-based method.The generation mechanism and power loss characteristics of IHCS are investigated by the entropy production method and pressure fluctuation analysis.The main cause can be attributed to the large transverse pressure gradient near the hub at the trailing edge of the impeller,which is aggravated by the circumferential movement trend and the diffuser reverse flow,while the IHCS is significantly weakened with increased flow rate.The undesirable flow behavior is more likely to cause a significant increase in energy loss near the hub region compared to that in the rim region.The relative vortex stretching induced by the velocity gradient is the main cause of the horn-like vortex(HLV),and its intensity and resulting energy loss tend to decrease along the vortex trajectory.The HLV changes the dominant frequency of the pressure fluctuations in the nearby flow field,the value of which increases from 1fr(the blade passing frequency)to 2fr with increased amplitude,mainly due to the lower pressure regions on the impeller suction surface(SS)and HLV vortex core.Due to the effect of rotor-stator interaction(RSI),the HLVs generated between two adjacent impeller blades are cut into several sections by the diffuser vanes and propagate and dissipate along the mainstream direction.
