On the basis of the traditional mechanical model of a grinding wheel rotor and the mechanical-electric coupling model with ideal sinusoidal supply, taking high-frequency converting current of inverter power switches i...On the basis of the traditional mechanical model of a grinding wheel rotor and the mechanical-electric coupling model with ideal sinusoidal supply, taking high-frequency converting current of inverter power switches into further consideration, a modified mechanical-electric coupling model is created. The created model consists of an inverter, a motorized spindle, a grinding wheel and grinding loads. Some typical non-stationary processes of the grinding system with two different supplies, including the starting, the speed rising and the break in grinding loads, are compared by making use of the created model. One supply is an ideal sinusoidal voltage source, the other is an inverter. The theoretical analysis of the high-order harmonic is also compared with the experimental result. The material strategy of suppressing high-order harmonic mechanical-electric coupling vibration by optimizing inverter operating parameters is proposed.展开更多
Microdroplets and their dispersion,with a large specific surface area and a short diffusion distance,have been applied in various unit operations and reaction processes.However,it is still a challenge to control the s...Microdroplets and their dispersion,with a large specific surface area and a short diffusion distance,have been applied in various unit operations and reaction processes.However,it is still a challenge to control the size and size distribution of microdroplets,especially for high-throughput generation.In this work,a novel ultra-high speed rotating packed bed(UHS-RPB)was invented,in which rotating foam packing with a speed of 4000-12000 r·min^(-1) provides microfluidic channels to disperse liquid into microdroplets with high throughput.Then generated microdroplets can be directly dispersed into a continuous falling film for obtaining a mixture of microdroplet dispersion.In this UHS-RPB,the effects of rotational speed,liquid initial velocity,liquid viscosity,liquid surface tension and packing pore size on the average size(d_(32))and size distribution of microdroplets were systematically investigated.Results showed that the UHS-RPB could produce microdroplets with a d_(32) of 25-63μm at a liquid flow rate of 1025 L·h^(-1),and the size distribution of the microdroplets accords well with Rosin-Rammler distribution model.In addi-tion,a correlation was established for the prediction of d_(32),and the predicted d_(32) was in good agreement with the experimental data with a deviation within±15%.These results demonstrated that UHS-RPB could be a promising candidate for controllable preparation of uniform microdroplets.展开更多
Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed l...Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.展开更多
Controlling the flow behavior in the mold in an appropriate way is the basis for realizing the billet ultra-high speed continuous casting.Based on the new proposed physical water modeling experiment considering the ef...Controlling the flow behavior in the mold in an appropriate way is the basis for realizing the billet ultra-high speed continuous casting.Based on the new proposed physical water modeling experiment considering the effects of solidified shell and hydrostatic pressure,the flow behavior in the mold with cross section of 160 mm 9160 mm during continuous casting of billet is regulated by optimizing the inner diameters and immersion depths of submerged entry nozzle at the ultra-high casting speeds of 5.0–6.5 m/min.The results show that under the premise of no slag entrainment,as well as uniform coverage and keeping good fluidity of liquid slag layer on the top free surface of the fluid in the mold,the appropriate parameters of submerged entry nozzle under the ultra-high casting speed of billet are 50 mm in inner diameter,95 mm in outer diameter and 180 mm in immersion depth.And on the basis of the obtained parameters of submerged entry nozzle,it can be known that the reasonable ranges of level fluctuation and impacting depth of the stream in the mold are about 0.82-1.11 and 593-617 mm,respectively.展开更多
For a 120 kW hydrogen fuel cell system,a centrifugal air compressor with fixed power of 22 kW fuel cell is designed.Firstly,the theoretical calculation is carried out for the aerodynamic characteristics of a ultra-hig...For a 120 kW hydrogen fuel cell system,a centrifugal air compressor with fixed power of 22 kW fuel cell is designed.Firstly,the theoretical calculation is carried out for the aerodynamic characteristics of a ultra-high-speed permanent magnet synchronous motor,an air compressor,and an aerodynamic foil bearing.Then,a prototype is trial-produced and a related test bench is built for test verification.Finally,both the simulation and test results indicate that the designed centrifugal air compressor meets the overall requirements of the hydrogen fuel cell system,and the relevant conclusions provide both theoretical and experimental references for the subsequent series development and design of the centrifugal air compressor.展开更多
The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to...The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to complex mechanical vibrations with magnitudes as small as tens of picometers.Measurements of the shape and acoustically induced motions of different components of the ear are essential if we are to expand our understanding of hearing mechanisms,and also provide quantitative information for the development of numerical ear models that can be used to improve hearing protection,clinical diagnosis,and repair of damaged or diseased ears.We are developing digital holographic methods and instrumentation using an ultra-high speed camera to measure shape and acoustically-induced motions in the middle ear.Specifically we study the eardrum,the first structure of the middle ear which initializes the acoustic-mechanical transduction of sound for hearing.Our measurement system is capable of performing holographic measurement at rates up to 2.1 M frames per second.Two shape measurement modalities had previously been implemented into our holographic systems:(1)a multi-wavelength method with a wavelength tunable laser;and(2)a multi-angle illumination method with a single wavelength laser.In this paper,we present a third method using a miniaturized fringe projection system with a microelectromechanical system(MEMS)mirror.Further,we optimize the processing of large data sets of holographic displacement measurements using a vectorized Pearson's correlation algorithm.We validate and compare the shape and displacement measurements of our methodologies using a National Institute of Standards and Technology(NIST)traceable gauge and sound-activated latex membranes and human eardrums.展开更多
High speed imaging technology has opened applications in many fields,such as collision,detonating, high voltage discharge,disintegration and transfer of phonon and exciton in solid,photosynthesis primitive reaction,an...High speed imaging technology has opened applications in many fields,such as collision,detonating, high voltage discharge,disintegration and transfer of phonon and exciton in solid,photosynthesis primitive reaction,and electron dynamics inside atom shell.In principle,all of the transient processes need to be explained theoretically and,at the same time,the time amplifying technique is required for observations of these processes.The present review concerns the atomic time amplifying mechanism of optical information and the extremely-high speed imaging methods,which are expressed in terms of the short time amplifying techniques.It is well-known that for extremely-high speed imaging with the converter tube,the temporal resolution is in the order of sub-picosecond of the streak imaging,and the imaging frequency is 6×10 8 ―5×10 9 fps(frame per second)of the frame imaging.On the other hand,for the tubeless extremely-high speed imaging,the imaging frequency is 10 7 ―10 14 fps,and its mechanism of forming high speed and framing could involve a lot of factors of the light under investigation,for instance,light speed,light parallelism,the parameters of light wave such as amplitude,phase,polari- zation and wavelength,and even quantum properties of photon.In the cascaded system of electro- magnetic wave and particle wave,it is possible to simultaneously realize extremely-high resolution in time and space,which is higher than a kite resolution.Then it would be possible to break the limit of the Heisenberg uncertainty relation of the optical frequency band.展开更多
Large amounts of crop stalks left in the field as a result of conservation agriculture cause blockage during no-till planting.To solve this issue,pure waterjet was used to cut off the maize stalks so that the rear fur...Large amounts of crop stalks left in the field as a result of conservation agriculture cause blockage during no-till planting.To solve this issue,pure waterjet was used to cut off the maize stalks so that the rear furrow opener could pass through without blockage.In this investigation,an experimental study on depth of cut,which was the main performance indicator of pure waterjet on cutting maize stalks,was presented.A full factorial design with 200 tests was implemented with respect to three operation parameters,that is traverse speed,waterjet pressure,and standoff distance were considered as variables.An analysis of variance(ANOVA)was carried out in order to determine the statistical significance of individual operation parameters.Using multilinear stepwise regression analysis,a model to predict the cut of depth from the predicted pure waterjet operation to cut maize stalks was then developed.All three operation parameters significantly influenced the cutting performance.Moreover,the results indicated that depth of cut increased with the increase of waterjet pressure,the decrease of traverse speed,and decrease in standoff distance.Waterjet pressure provided major contribution to depth of cut,followed by traverse speed,then standoff distance,which was demonstrated by both ANOVA and regression analysis.The experimental results showed that when the standoff distance was closer than 10 mm and waterjet pressure was 280 MPa,all maize stalks specimen could be cutoff thoroughly.With the consideration of field operating conditions,waterjet pressure of 280 MPa or higher and 10 mm to 15 mm standoff distance were recommended for maize stalks cutting.This analysis provided a realistic approach for the optimization of the ultra-high pressure pure waterjet parameters in maize stalks cutting,which could be used to relieve the occurrence of straw blockage in no-till planting.展开更多
基金National Hi-tech Research and Development Program of China(863 Program,No.2008AA04Z116)and Natural Science Foundation of Hunan Province,China.
文摘On the basis of the traditional mechanical model of a grinding wheel rotor and the mechanical-electric coupling model with ideal sinusoidal supply, taking high-frequency converting current of inverter power switches into further consideration, a modified mechanical-electric coupling model is created. The created model consists of an inverter, a motorized spindle, a grinding wheel and grinding loads. Some typical non-stationary processes of the grinding system with two different supplies, including the starting, the speed rising and the break in grinding loads, are compared by making use of the created model. One supply is an ideal sinusoidal voltage source, the other is an inverter. The theoretical analysis of the high-order harmonic is also compared with the experimental result. The material strategy of suppressing high-order harmonic mechanical-electric coupling vibration by optimizing inverter operating parameters is proposed.
基金supported by National Natural Science Foundation of China(21725601)。
文摘Microdroplets and their dispersion,with a large specific surface area and a short diffusion distance,have been applied in various unit operations and reaction processes.However,it is still a challenge to control the size and size distribution of microdroplets,especially for high-throughput generation.In this work,a novel ultra-high speed rotating packed bed(UHS-RPB)was invented,in which rotating foam packing with a speed of 4000-12000 r·min^(-1) provides microfluidic channels to disperse liquid into microdroplets with high throughput.Then generated microdroplets can be directly dispersed into a continuous falling film for obtaining a mixture of microdroplet dispersion.In this UHS-RPB,the effects of rotational speed,liquid initial velocity,liquid viscosity,liquid surface tension and packing pore size on the average size(d_(32))and size distribution of microdroplets were systematically investigated.Results showed that the UHS-RPB could produce microdroplets with a d_(32) of 25-63μm at a liquid flow rate of 1025 L·h^(-1),and the size distribution of the microdroplets accords well with Rosin-Rammler distribution model.In addi-tion,a correlation was established for the prediction of d_(32),and the predicted d_(32) was in good agreement with the experimental data with a deviation within±15%.These results demonstrated that UHS-RPB could be a promising candidate for controllable preparation of uniform microdroplets.
基金supported by the National Natural Science Foundation of China(Nos.52105233 and 52275366)the Tianjin Science and Technology Plan Project(No.22JCYBJC01590).
文摘Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.
基金financially supported by the National Science Foundation of China(NSFC)(Grant Nos.51874060 and 52074053).
文摘Controlling the flow behavior in the mold in an appropriate way is the basis for realizing the billet ultra-high speed continuous casting.Based on the new proposed physical water modeling experiment considering the effects of solidified shell and hydrostatic pressure,the flow behavior in the mold with cross section of 160 mm 9160 mm during continuous casting of billet is regulated by optimizing the inner diameters and immersion depths of submerged entry nozzle at the ultra-high casting speeds of 5.0–6.5 m/min.The results show that under the premise of no slag entrainment,as well as uniform coverage and keeping good fluidity of liquid slag layer on the top free surface of the fluid in the mold,the appropriate parameters of submerged entry nozzle under the ultra-high casting speed of billet are 50 mm in inner diameter,95 mm in outer diameter and 180 mm in immersion depth.And on the basis of the obtained parameters of submerged entry nozzle,it can be known that the reasonable ranges of level fluctuation and impacting depth of the stream in the mold are about 0.82-1.11 and 593-617 mm,respectively.
基金supported in part by the Key R&D projects in Hebei Province under Grant 20312202D。
文摘For a 120 kW hydrogen fuel cell system,a centrifugal air compressor with fixed power of 22 kW fuel cell is designed.Firstly,the theoretical calculation is carried out for the aerodynamic characteristics of a ultra-high-speed permanent magnet synchronous motor,an air compressor,and an aerodynamic foil bearing.Then,a prototype is trial-produced and a related test bench is built for test verification.Finally,both the simulation and test results indicate that the designed centrifugal air compressor meets the overall requirements of the hydrogen fuel cell system,and the relevant conclusions provide both theoretical and experimental references for the subsequent series development and design of the centrifugal air compressor.
基金support from the US National Institute on Deafness and Other Communication Disorders(NIDCD R01 DC016079)is gratefully acknowledgedsupport by the Center for Holographic Studies and Laser micro-mechaTronics(CHSLT)at WPI.
文摘The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to complex mechanical vibrations with magnitudes as small as tens of picometers.Measurements of the shape and acoustically induced motions of different components of the ear are essential if we are to expand our understanding of hearing mechanisms,and also provide quantitative information for the development of numerical ear models that can be used to improve hearing protection,clinical diagnosis,and repair of damaged or diseased ears.We are developing digital holographic methods and instrumentation using an ultra-high speed camera to measure shape and acoustically-induced motions in the middle ear.Specifically we study the eardrum,the first structure of the middle ear which initializes the acoustic-mechanical transduction of sound for hearing.Our measurement system is capable of performing holographic measurement at rates up to 2.1 M frames per second.Two shape measurement modalities had previously been implemented into our holographic systems:(1)a multi-wavelength method with a wavelength tunable laser;and(2)a multi-angle illumination method with a single wavelength laser.In this paper,we present a third method using a miniaturized fringe projection system with a microelectromechanical system(MEMS)mirror.Further,we optimize the processing of large data sets of holographic displacement measurements using a vectorized Pearson's correlation algorithm.We validate and compare the shape and displacement measurements of our methodologies using a National Institute of Standards and Technology(NIST)traceable gauge and sound-activated latex membranes and human eardrums.
基金Supported by the National Natural Science Foundation of China(Grant Nos.60477042 and 60127501)
文摘High speed imaging technology has opened applications in many fields,such as collision,detonating, high voltage discharge,disintegration and transfer of phonon and exciton in solid,photosynthesis primitive reaction,and electron dynamics inside atom shell.In principle,all of the transient processes need to be explained theoretically and,at the same time,the time amplifying technique is required for observations of these processes.The present review concerns the atomic time amplifying mechanism of optical information and the extremely-high speed imaging methods,which are expressed in terms of the short time amplifying techniques.It is well-known that for extremely-high speed imaging with the converter tube,the temporal resolution is in the order of sub-picosecond of the streak imaging,and the imaging frequency is 6×10 8 ―5×10 9 fps(frame per second)of the frame imaging.On the other hand,for the tubeless extremely-high speed imaging,the imaging frequency is 10 7 ―10 14 fps,and its mechanism of forming high speed and framing could involve a lot of factors of the light under investigation,for instance,light speed,light parallelism,the parameters of light wave such as amplitude,phase,polari- zation and wavelength,and even quantum properties of photon.In the cascaded system of electro- magnetic wave and particle wave,it is possible to simultaneously realize extremely-high resolution in time and space,which is higher than a kite resolution.Then it would be possible to break the limit of the Heisenberg uncertainty relation of the optical frequency band.
基金supported by the Special Fund for Agro-scientific Research in the Public Interest from the Ministry of Agriculture,China(Grant No.201503136).
文摘Large amounts of crop stalks left in the field as a result of conservation agriculture cause blockage during no-till planting.To solve this issue,pure waterjet was used to cut off the maize stalks so that the rear furrow opener could pass through without blockage.In this investigation,an experimental study on depth of cut,which was the main performance indicator of pure waterjet on cutting maize stalks,was presented.A full factorial design with 200 tests was implemented with respect to three operation parameters,that is traverse speed,waterjet pressure,and standoff distance were considered as variables.An analysis of variance(ANOVA)was carried out in order to determine the statistical significance of individual operation parameters.Using multilinear stepwise regression analysis,a model to predict the cut of depth from the predicted pure waterjet operation to cut maize stalks was then developed.All three operation parameters significantly influenced the cutting performance.Moreover,the results indicated that depth of cut increased with the increase of waterjet pressure,the decrease of traverse speed,and decrease in standoff distance.Waterjet pressure provided major contribution to depth of cut,followed by traverse speed,then standoff distance,which was demonstrated by both ANOVA and regression analysis.The experimental results showed that when the standoff distance was closer than 10 mm and waterjet pressure was 280 MPa,all maize stalks specimen could be cutoff thoroughly.With the consideration of field operating conditions,waterjet pressure of 280 MPa or higher and 10 mm to 15 mm standoff distance were recommended for maize stalks cutting.This analysis provided a realistic approach for the optimization of the ultra-high pressure pure waterjet parameters in maize stalks cutting,which could be used to relieve the occurrence of straw blockage in no-till planting.