Low-electrode capacitive deionization(FCDI)is an emerging desalination technology with great potential for removal and/or recycling ions from a range of waters.However,it still suffers from inefficient charge transfer...Low-electrode capacitive deionization(FCDI)is an emerging desalination technology with great potential for removal and/or recycling ions from a range of waters.However,it still suffers from inefficient charge transfer and ion transport kinetics due to weak turbulence and low electric intensity in flow electrodes,both restricted by the current collectors.Herein,a new tip-array current collector(designated as T-CC)was developed to replace the conventional planar current collectors,which intensifies both the charge transfer and ion transport significantly.The effects of tip arrays on flow and electric fields were studied by both computational simulations and electrochemical impedance spectroscopy,which revealed the reduction of ion transport barrier,charge transport barrier and internal resistance.With the voltage increased from 1.0 to 1.5 and 2.0 V,the T-CC-based FCDI system(T-FCDI)exhibited average salt removal rates(ASRR)of 0.18,0.50,and 0.89μmol cm^(-2) min^(-1),respectively,which are 1.82,2.65,and 2.48 folds higher than that of the conventional serpentine current collectors,and 1.48,1.67,and 1.49 folds higher than that of the planar current collectors.Meanwhile,with the solid content in flow electrodes increased from 1 to 5 wt%,the ASRR for T-FCDI increased from 0.29 to 0.50μmol cm^(-2) min^(-1),which are 1.70 and 1.67 folds higher than that of the planar current collectors.Additionally,a salt removal efficiency of 99.89%was achieved with T-FCDI and the charge efficiency remained above 95%after 24 h of operation,thus showing its superior long-term stability.展开更多
The unique structural features represented by micro-nanoneedle tip structure reflect wonderful physical and chemical properties.The tip effect includes the concentration of energy such as electrons,photons and magneti...The unique structural features represented by micro-nanoneedle tip structure reflect wonderful physical and chemical properties.The tip effect includes the concentration of energy such as electrons,photons and magnetism in the tip region,which has promising applications in the fields of energy conversion,water capture,environmental restoration and so on.In this review,a comprehensive and systematic summary of the latest advances in the application of the tip effect in different fields is provided.Utilizing advanced Finite Difference Time Domain simulation,we further propose our understanding of the fundamental mechanism of the tip effect induced by micro-nanostructure.However,we need to forge the present study to further reveal the essential law of the tip effect from the perspective of theoretical calculations.This review would provide a solid foundation for further development and application of the tip effect.展开更多
Aqueous zinc metal batteries (AZMBs) are hindered by uncontrolled dendrites and side reactions during commercialization,despite their advantages of safety and high capacity density.Herein,we propose the electrical fee...Aqueous zinc metal batteries (AZMBs) are hindered by uncontrolled dendrites and side reactions during commercialization,despite their advantages of safety and high capacity density.Herein,we propose the electrical feedback strategy to restrain the Zn dendrites resulting from the"tip effect"and optimize interfacial Zn^(2+)distribution to accelerate electrodeposition kinetics by using the lithium niobate (LNO) layer.Specifically,at the bumps of the zinc anode,the ferroelectric LNO is polarized by the locally strong electric field,which in turn counteracts the"tip effect".In this way,the dynamic polarization of LNO can repair the uneven tip electric field to achieve uniform and flat zinc deposition.In addition,owing to the interaction between Nb and Zn^(2+),a higher concentration of Zn^(2+)near the zincophilic LNO@Zn surface is obtained for the rapid electrochemical reaction kinetics of plating.Considering the aforementioned advantages,the LNO@Zn anode harvests stable cycling over 1200 h at 10 mA cm^(-2)with a superior cumulative capacity of 5800 mAh cm^(-2).Assembled with the a-MnO_(2) cathode,the full cell using LNO@Zn anode exhibits the slower capacity decay (0.054%per cycle) during 1000 cycles.This strategy provides a perspective for stabilizing zinc metal anodes through dynamic electrical response and interfacial ion redistribution effect.展开更多
Aqueous zinc-based batteries(ZBBs)have great potential as commercial energy storage devices.However,the poor cycling stability of zinc anode under high areal capacity limits their further application.Herein,a coupled ...Aqueous zinc-based batteries(ZBBs)have great potential as commercial energy storage devices.However,the poor cycling stability of zinc anode under high areal capacity limits their further application.Herein,a coupled non-planar electrode design achieved by the tailored flat-top pyramid carbon felt(TCF)is proposed for ZBBs,which can effectively increase the zinc deposition sites,adjust the deposition morphology,optimize the current and electrolyte flow velocity distribution and provide necessary space for zinc plating.Interestingly,by utilizing "tip effect",the coupled TCFs enable precise control of the zinc dendrite growth position,effectively reducing the risk of short circuit.Based on such coupled TCFs,zinciodine flow batteries can deliver an ultra-high areal capacity of 240 m Ah cm^(-2) and a superb cycling stability over 300 cycles(areal capacity of 160 m Ah cm^(-2))at a high current density of 40 m A cm^(-2).Therefore,we provide an effective strategy for high areal capacity zinc anode design,which may promote the development of high energy density and long cycle life ZBBs.展开更多
The exploration of high-efficiency transition metal-nitrogen-carbon(M-N-C)catalysts is crucial for accelerating the kinetics of oxygen reduction/oxygen evolution reactions(ORR/OER).Fine-tuning the distribution of acce...The exploration of high-efficiency transition metal-nitrogen-carbon(M-N-C)catalysts is crucial for accelerating the kinetics of oxygen reduction/oxygen evolution reactions(ORR/OER).Fine-tuning the distribution of accessible metal sites and the correlated triphase interfaces within the M-N-C catalysts holds significant promise.In this study,we present an integrated electrocatalyst comprised of tip-enriched NiFe nanoalloys encapsulated within N-doped carbon nanotubes(NiFe@CNTs),synthesized using an in-situ wet-electrochemistry mediated approach.The well-defined NiFe@CNTs catalyst possesses a porous heterostructure,synergistic M-N_(x)-C active sites,and intimate micro interfaces,facilitating accelerated redox kinetics.This leads to exceptional OER/ORR activities with a low overallΔE of 630 mV.Experimental results and density functional theory calculations unveil the predominant electronic interplay between the apical bimetallic sites and neighboring N-doped CNTs,thereby enhancing the binding of intermediates on NiFe@CNTs.Molecular dynamics simulations reveal that the local gas-liquid environment surrounding NiFe@CNTs favors the diffusion/adsorption of the OH-/O_(2)reactants.Consequently,NiFe@CNTs contribute to high-performance aqueous Zn-Air batteries(ZABs),exhibiting a high gravimetric energy den-sity(936 Wh kgZn-1)and superb cycling stability(>425 h)at 20 mA cm^(-2).Furthermore,solid-state ZABs based on NiFe@CNTs demonstrate impressive electrochemical performance(e.g.,peak power density of 108 mW cm-2,specific energy of 1003 Wh kgZn-1)and prominent flexibility.This work illuminates a viable strategy for constructing metal site-specific,cobalt-free,and integrated M-N-C electrocatalysts for multifunctional catalysis and advanced/flexible energy storage applications.展开更多
The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force bala...The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.展开更多
The strain gradient effect becomes significant when the size of frac- ture process zone around a crack tip is comparable to the intrinsic material length l, typically of the order of microns. Using the new strain grad...The strain gradient effect becomes significant when the size of frac- ture process zone around a crack tip is comparable to the intrinsic material length l, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that the dom- inant strain field is irrotational. For mode Ⅰ plane stress crack tip asymptotic field, the stress asymptotic field and the couple stress asymptotic field can not exist si- multaneously. In the stress dominated asymptotic field, the angular distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode Ⅱ plane stress and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode Ⅱ plane stress and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode Ⅰ and mode Ⅱ, because the present theory is based only on the rotational gradi- ent of deformation and the crack tip asymptotic fields are irrotational and dominated by the stretching gradient.展开更多
A plane strain mode 1 crack tip field with strain gradient effects is investigated.A new strain gradient theory is used.An elastic-power law hardening strain gradient material is considered and two hardening laws,i.e....A plane strain mode 1 crack tip field with strain gradient effects is investigated.A new strain gradient theory is used.An elastic-power law hardening strain gradient material is considered and two hardening laws,i.e.a separation law and an integration law are used respectively.As for the material with the separation law hardening,the angular distributions of stresses are consistent with the HRR field,which differs from the stress results;the angular distributions of couple stresses are the same as the couple stress results.For the material with the integration law hardening,the stress field and the couple stress field can not exist simultaneously,which is the same as the conclusion,but for the stress dominated field,the an- gular distributions of stresses are consistent with the HRR field;for the couple stress dominated field,the an- gular distributions of couple stresses are consistent with those in Ref.However,the increase in stresses is not observed in strain gradient plasticity because the present theory is based on the rotation gradient of the deformation only,while the crack tip field of mode 1 is dominated by the tension gradient,which will be shown in another paper.展开更多
A new effective propeller performance estimation method is employed to calculate the propeller performance in the preliminary design of unmanned aerial vehicles(UAVs).The propeller three-dimensional aerodynamic charac...A new effective propeller performance estimation method is employed to calculate the propeller performance in the preliminary design of unmanned aerial vehicles(UAVs).The propeller three-dimensional aerodynamic characteristics leading to the blade tip vortices are considered to improve the blade element theory.The rule of the airfoil lift coefficient is summarized to enhance the calculation speed and the universality of this method.Then,wind tunnel test data of the propellers are used to verify the correctness of the approach.The error is less than9%,which is accurate enough in the preliminary design of UAVs.Sensitivity analysis is carried out with the variable empirical parameters,and the values of which only have slight influence on the calculated results.Compared with the strip theory,the proposed method avoids a very high number of iterations and complicated integral.Furthermore,only a few measurable data are needed to get a relatively accurate result.The calculation examples demonstrate excellent effectiveness in obtaining the propeller performance to improve the design of UAVs.展开更多
The crack tip fields are investigated for a cracked functionally graded material （FGM） plate by Reissner＇s linear plate theory with the consideration of the transverse shear deformation generated by bending. The el...The crack tip fields are investigated for a cracked functionally graded material （FGM） plate by Reissner＇s linear plate theory with the consideration of the transverse shear deformation generated by bending. The elastic modulus and Poisson＇s ratio of the functionally graded plates are assumed to vary continuously through the coordinate y, according to a linear law and a constant, respectively. The governing equations, i.e., the 6th-order partial differential equations with variable coefficients, are derived in the polar coordinate system based on Reissner＇s plate theory. Furthermore, the generalized displacements are treated in a separation-of-variable form, and the higher-order crack tip fields of the cracked FGM plate are obtained by the eigen-expansion method. It is found that the analytic solutions degenerate to the corresponding fields of the isotropic homogeneous plate with Reissner＇s effect when the in-homogeneity parameter approaches zero.展开更多
In this paper, the following conclusions are reached: The influence of damage on the stress and strain feilds can be neglected in an asymptotic sense for the solutions of damage field in a plastic solid containing sma...In this paper, the following conclusions are reached: The influence of damage on the stress and strain feilds can be neglected in an asymptotic sense for the solutions of damage field in a plastic solid containing small damage. The formulation of the problem is simplified with an uncoupled approach. Based on experimental results of plastic damage, most of the damage in the material are con- sidered as small damage with the critacal damage variable ω_c<<1. Using this approach, closed form ex- pressions of the near tip damage fields for mode Ⅲ, mode I and the temperature distribution induced by plastic dissipation in a hardening material containing damage are deduced. We point out that the temperature distribution in the process zone is strongly dependent on the damage of materials even for the small damage case. The results of the predicted value of the temperature rise near the tip region ignoring the damage effect is appreciably higher than the observed data. The main reason of this discrepancy is the presence of damage dissipation and the fact that its influence on the calculation of plas- tic dissipation have not been appropriately taken account of. The calculation is improved by taking in- to account the damage effect on the temperature rise, then the T_(max) value is in better accord with the experimental value.展开更多
Purpose: To evaluate the performance of a phacoemulsification system in terms of effective (EPT) and total phaco time (TPT) using 20G and 21G phaco tips. Methods: Retrospective comparative study including 143 consecut...Purpose: To evaluate the performance of a phacoemulsification system in terms of effective (EPT) and total phaco time (TPT) using 20G and 21G phaco tips. Methods: Retrospective comparative study including 143 consecutive cataractous eyes undergoing phacoemulsification cataract surgery with the Visalis 500 device. The 20G and 21G phaco tips were used in 46 and 97 eyes, respectively. The EPT and TPT values were evaluated. Results: Median TPT was 11.25 s and 17.50 s in the 20G and 21G groups, respectively (p = 0.0011). Median EPT values were 3.15 s and 5.00 s in the 20G and 21G groups, respectively (p = 0.0032). TPT and EPT were significantly lower in 3/3+ cataract eyes compared to 4/4+ using both tips (p < 0.001). Conclusions: The Visalis 500 allows cataract surgery with reduced TPT and EPT, even in hard cataracts. The use of the 20G phaco tip provides an additional benefit in terms of reduction of phaco time.展开更多
基金supported by the Shenzhen Science and Technology Program(JCYJ20230808105111022,JCYJ20220818095806013)Natural Science Foundation of Guangdong(2023A1515012267)+1 种基金the National Natural Science Foundation of China(22178223)the Royal Society/NSFC cost share program(IEC\NSFC\223372).
文摘Low-electrode capacitive deionization(FCDI)is an emerging desalination technology with great potential for removal and/or recycling ions from a range of waters.However,it still suffers from inefficient charge transfer and ion transport kinetics due to weak turbulence and low electric intensity in flow electrodes,both restricted by the current collectors.Herein,a new tip-array current collector(designated as T-CC)was developed to replace the conventional planar current collectors,which intensifies both the charge transfer and ion transport significantly.The effects of tip arrays on flow and electric fields were studied by both computational simulations and electrochemical impedance spectroscopy,which revealed the reduction of ion transport barrier,charge transport barrier and internal resistance.With the voltage increased from 1.0 to 1.5 and 2.0 V,the T-CC-based FCDI system(T-FCDI)exhibited average salt removal rates(ASRR)of 0.18,0.50,and 0.89μmol cm^(-2) min^(-1),respectively,which are 1.82,2.65,and 2.48 folds higher than that of the conventional serpentine current collectors,and 1.48,1.67,and 1.49 folds higher than that of the planar current collectors.Meanwhile,with the solid content in flow electrodes increased from 1 to 5 wt%,the ASRR for T-FCDI increased from 0.29 to 0.50μmol cm^(-2) min^(-1),which are 1.70 and 1.67 folds higher than that of the planar current collectors.Additionally,a salt removal efficiency of 99.89%was achieved with T-FCDI and the charge efficiency remained above 95%after 24 h of operation,thus showing its superior long-term stability.
基金financially supported by the Natural Science Foundation of China(No.51902101)Natural Science Foundation of Jiangsu Province(No.BK20201381)+1 种基金Science Foundation of Nanjing University of Posts and Telecommunications(No.NY219144)the National College Student Innovation and Entrepreneurship Training Program(No.202210293017Z).
文摘The unique structural features represented by micro-nanoneedle tip structure reflect wonderful physical and chemical properties.The tip effect includes the concentration of energy such as electrons,photons and magnetism in the tip region,which has promising applications in the fields of energy conversion,water capture,environmental restoration and so on.In this review,a comprehensive and systematic summary of the latest advances in the application of the tip effect in different fields is provided.Utilizing advanced Finite Difference Time Domain simulation,we further propose our understanding of the fundamental mechanism of the tip effect induced by micro-nanostructure.However,we need to forge the present study to further reveal the essential law of the tip effect from the perspective of theoretical calculations.This review would provide a solid foundation for further development and application of the tip effect.
基金supported by the National Natural Science Foundation of China (52172159)the Postdoctoral Fellowship Program of CPSF (GZB20230631)。
文摘Aqueous zinc metal batteries (AZMBs) are hindered by uncontrolled dendrites and side reactions during commercialization,despite their advantages of safety and high capacity density.Herein,we propose the electrical feedback strategy to restrain the Zn dendrites resulting from the"tip effect"and optimize interfacial Zn^(2+)distribution to accelerate electrodeposition kinetics by using the lithium niobate (LNO) layer.Specifically,at the bumps of the zinc anode,the ferroelectric LNO is polarized by the locally strong electric field,which in turn counteracts the"tip effect".In this way,the dynamic polarization of LNO can repair the uneven tip electric field to achieve uniform and flat zinc deposition.In addition,owing to the interaction between Nb and Zn^(2+),a higher concentration of Zn^(2+)near the zincophilic LNO@Zn surface is obtained for the rapid electrochemical reaction kinetics of plating.Considering the aforementioned advantages,the LNO@Zn anode harvests stable cycling over 1200 h at 10 mA cm^(-2)with a superior cumulative capacity of 5800 mAh cm^(-2).Assembled with the a-MnO_(2) cathode,the full cell using LNO@Zn anode exhibits the slower capacity decay (0.054%per cycle) during 1000 cycles.This strategy provides a perspective for stabilizing zinc metal anodes through dynamic electrical response and interfacial ion redistribution effect.
基金financially supported by the National Natural Science Foundation of China(21935003,21908217 and 21908214)Liaoning Revitalization Talents Program(XLYC1802050)+1 种基金CAS STS ProgramCAS Engineering Laboratory for Electrochemical Energy Storage。
文摘Aqueous zinc-based batteries(ZBBs)have great potential as commercial energy storage devices.However,the poor cycling stability of zinc anode under high areal capacity limits their further application.Herein,a coupled non-planar electrode design achieved by the tailored flat-top pyramid carbon felt(TCF)is proposed for ZBBs,which can effectively increase the zinc deposition sites,adjust the deposition morphology,optimize the current and electrolyte flow velocity distribution and provide necessary space for zinc plating.Interestingly,by utilizing "tip effect",the coupled TCFs enable precise control of the zinc dendrite growth position,effectively reducing the risk of short circuit.Based on such coupled TCFs,zinciodine flow batteries can deliver an ultra-high areal capacity of 240 m Ah cm^(-2) and a superb cycling stability over 300 cycles(areal capacity of 160 m Ah cm^(-2))at a high current density of 40 m A cm^(-2).Therefore,we provide an effective strategy for high areal capacity zinc anode design,which may promote the development of high energy density and long cycle life ZBBs.
基金supported by the Natural Science Foundation of Guangdong Province(No.2023A1515030131,2022A1515010476)the National Natural Science Foundation of China(22078118).
文摘The exploration of high-efficiency transition metal-nitrogen-carbon(M-N-C)catalysts is crucial for accelerating the kinetics of oxygen reduction/oxygen evolution reactions(ORR/OER).Fine-tuning the distribution of accessible metal sites and the correlated triphase interfaces within the M-N-C catalysts holds significant promise.In this study,we present an integrated electrocatalyst comprised of tip-enriched NiFe nanoalloys encapsulated within N-doped carbon nanotubes(NiFe@CNTs),synthesized using an in-situ wet-electrochemistry mediated approach.The well-defined NiFe@CNTs catalyst possesses a porous heterostructure,synergistic M-N_(x)-C active sites,and intimate micro interfaces,facilitating accelerated redox kinetics.This leads to exceptional OER/ORR activities with a low overallΔE of 630 mV.Experimental results and density functional theory calculations unveil the predominant electronic interplay between the apical bimetallic sites and neighboring N-doped CNTs,thereby enhancing the binding of intermediates on NiFe@CNTs.Molecular dynamics simulations reveal that the local gas-liquid environment surrounding NiFe@CNTs favors the diffusion/adsorption of the OH-/O_(2)reactants.Consequently,NiFe@CNTs contribute to high-performance aqueous Zn-Air batteries(ZABs),exhibiting a high gravimetric energy den-sity(936 Wh kgZn-1)and superb cycling stability(>425 h)at 20 mA cm^(-2).Furthermore,solid-state ZABs based on NiFe@CNTs demonstrate impressive electrochemical performance(e.g.,peak power density of 108 mW cm-2,specific energy of 1003 Wh kgZn-1)and prominent flexibility.This work illuminates a viable strategy for constructing metal site-specific,cobalt-free,and integrated M-N-C electrocatalysts for multifunctional catalysis and advanced/flexible energy storage applications.
基金supported by the National Natural Science Foundation of China(11072142)Shanghai Program for Innovative Research Team in Universities
文摘The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.
文摘The strain gradient effect becomes significant when the size of frac- ture process zone around a crack tip is comparable to the intrinsic material length l, typically of the order of microns. Using the new strain gradient deformation theory given by Chen and Wang, the asymptotic fields near a crack tip in an elastic-plastic material with strain gradient effects are investigated. It is established that the dom- inant strain field is irrotational. For mode Ⅰ plane stress crack tip asymptotic field, the stress asymptotic field and the couple stress asymptotic field can not exist si- multaneously. In the stress dominated asymptotic field, the angular distributions of stresses are consistent with the classical plane stress HRR field; In the couple stress dominated asymptotic field, the angular distributions of couple stresses are consistent with that obtained by Huang et al. For mode Ⅱ plane stress and plane strain crack tip asymptotic fields, only the stress-dominated asymptotic fields exist. The couple stress asymptotic field is less singular than the stress asymptotic fields. The stress asymptotic fields are the same as mode Ⅱ plane stress and plane strain HRR fields, respectively. The increase in stresses is not observed in strain gradient plasticity for mode Ⅰ and mode Ⅱ, because the present theory is based only on the rotational gradi- ent of deformation and the crack tip asymptotic fields are irrotational and dominated by the stretching gradient.
基金the National Natural Science Foundation of China (No.19704100)Science Foundation of Chinese Academy of Sciences (Project KJ951-1-20)CASK.C.Wong Post-doctoral Research Award Fund and the Post Doctoral Science Fund of China.
文摘A plane strain mode 1 crack tip field with strain gradient effects is investigated.A new strain gradient theory is used.An elastic-power law hardening strain gradient material is considered and two hardening laws,i.e.a separation law and an integration law are used respectively.As for the material with the separation law hardening,the angular distributions of stresses are consistent with the HRR field,which differs from the stress results;the angular distributions of couple stresses are the same as the couple stress results.For the material with the integration law hardening,the stress field and the couple stress field can not exist simultaneously,which is the same as the conclusion,but for the stress dominated field,the an- gular distributions of stresses are consistent with the HRR field;for the couple stress dominated field,the an- gular distributions of couple stresses are consistent with those in Ref.However,the increase in stresses is not observed in strain gradient plasticity because the present theory is based on the rotation gradient of the deformation only,while the crack tip field of mode 1 is dominated by the tension gradient,which will be shown in another paper.
基金supported by the National Aerospace Science Foundation of China(2011ZA72003)
文摘A new effective propeller performance estimation method is employed to calculate the propeller performance in the preliminary design of unmanned aerial vehicles(UAVs).The propeller three-dimensional aerodynamic characteristics leading to the blade tip vortices are considered to improve the blade element theory.The rule of the airfoil lift coefficient is summarized to enhance the calculation speed and the universality of this method.Then,wind tunnel test data of the propellers are used to verify the correctness of the approach.The error is less than9%,which is accurate enough in the preliminary design of UAVs.Sensitivity analysis is carried out with the variable empirical parameters,and the values of which only have slight influence on the calculated results.Compared with the strip theory,the proposed method avoids a very high number of iterations and complicated integral.Furthermore,only a few measurable data are needed to get a relatively accurate result.The calculation examples demonstrate excellent effectiveness in obtaining the propeller performance to improve the design of UAVs.
基金supported by the National Natural Science Foundation of China(Nos.90305023 and 11172332)
文摘The crack tip fields are investigated for a cracked functionally graded material （FGM） plate by Reissner＇s linear plate theory with the consideration of the transverse shear deformation generated by bending. The elastic modulus and Poisson＇s ratio of the functionally graded plates are assumed to vary continuously through the coordinate y, according to a linear law and a constant, respectively. The governing equations, i.e., the 6th-order partial differential equations with variable coefficients, are derived in the polar coordinate system based on Reissner＇s plate theory. Furthermore, the generalized displacements are treated in a separation-of-variable form, and the higher-order crack tip fields of the cracked FGM plate are obtained by the eigen-expansion method. It is found that the analytic solutions degenerate to the corresponding fields of the isotropic homogeneous plate with Reissner＇s effect when the in-homogeneity parameter approaches zero.
基金The project supported by the National Natural Science Foundation of China.
文摘In this paper, the following conclusions are reached: The influence of damage on the stress and strain feilds can be neglected in an asymptotic sense for the solutions of damage field in a plastic solid containing small damage. The formulation of the problem is simplified with an uncoupled approach. Based on experimental results of plastic damage, most of the damage in the material are con- sidered as small damage with the critacal damage variable ω_c<<1. Using this approach, closed form ex- pressions of the near tip damage fields for mode Ⅲ, mode I and the temperature distribution induced by plastic dissipation in a hardening material containing damage are deduced. We point out that the temperature distribution in the process zone is strongly dependent on the damage of materials even for the small damage case. The results of the predicted value of the temperature rise near the tip region ignoring the damage effect is appreciably higher than the observed data. The main reason of this discrepancy is the presence of damage dissipation and the fact that its influence on the calculation of plas- tic dissipation have not been appropriately taken account of. The calculation is improved by taking in- to account the damage effect on the temperature rise, then the T_(max) value is in better accord with the experimental value.
文摘Purpose: To evaluate the performance of a phacoemulsification system in terms of effective (EPT) and total phaco time (TPT) using 20G and 21G phaco tips. Methods: Retrospective comparative study including 143 consecutive cataractous eyes undergoing phacoemulsification cataract surgery with the Visalis 500 device. The 20G and 21G phaco tips were used in 46 and 97 eyes, respectively. The EPT and TPT values were evaluated. Results: Median TPT was 11.25 s and 17.50 s in the 20G and 21G groups, respectively (p = 0.0011). Median EPT values were 3.15 s and 5.00 s in the 20G and 21G groups, respectively (p = 0.0032). TPT and EPT were significantly lower in 3/3+ cataract eyes compared to 4/4+ using both tips (p < 0.001). Conclusions: The Visalis 500 allows cataract surgery with reduced TPT and EPT, even in hard cataracts. The use of the 20G phaco tip provides an additional benefit in terms of reduction of phaco time.
