Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have report...Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have reported surprisingly large measured near-wall velocities of pressure-driven flow in apparent contradiction with the no-slip hy-pothesis and experimental results from other techniques. To better interpret the measured results of the microPIV/PTV, we performed velocity profile measurements near a hy-drophilic wall （z = 0.25-1.5 μm） with two sizes of tracer particles （φ 50 nm and φ200 nm）. The experimental results indicate that, at less than 1 μm from the wall, the deviations between the measured velocities and no-slip theoretical values obviously decrease from 93% of φ200 nm particles to 48% of φ50 nm particles. The Boltzmann-like exponential measured particle concentrations near wall were found. Based on the non linear Boltzmann distribution of particle concentration and the effective focus plane thickness, we illustrated the reason of the apparent velocity increase near wall and proposed a method to correct the measured velocity profile. By this method, the deviations between the corrected measured velocities and the no-slip theoretical velocity decrease from 45.8% to 10%, and the measured slip length on hy-drophilic glass is revised from 75 nm to 16 nm. These results indicated that the particle size and the biased particle concentration distribution can significantly affect near wall velocity measurement via microPIV/PTV, and result in larger measured velocity and slip length close to wall.展开更多
An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account o...An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account of the micro-force between molecules and macro-force from the viscous shearing effect, as they contribute to the achieve- ment of the slip length. The calculated results are compared with those obtained from the molecular dynamics simulation, showing an excellent agreement. Further, the effect of the shear rate on the slip is investigated. The results can well predict the fluid flow behaviors on a solid substrate, but has to be proved by experiment.展开更多
In this letter,the effect of slip boundary on the origin of subcritical transition in two-dimensional chan-nel flows is studied numerically and theoretically.It is shown that both the positive and the negative slip le...In this letter,the effect of slip boundary on the origin of subcritical transition in two-dimensional chan-nel flows is studied numerically and theoretically.It is shown that both the positive and the negative slip lengths will increase the critical Reynolds number of localized wave packet and hence postpone the transition.By applying a variable transformation and expanding the variables about a small slip length,it is illustrated that the slip boundary effect only exists in the second and higher order modulations of the no-slip solution,and hence explains the power law found in simulations,i.e.the relative increment of the critical Reynolds number due to the slip boundary is proportional to the square of the slip length.展开更多
To design a surface with large slip or larger drag reduction is a pop issue in the fields of liquid transporting and body swimming. In this context, it is a crucial problem to measure the slip length for these surface...To design a surface with large slip or larger drag reduction is a pop issue in the fields of liquid transporting and body swimming. In this context, it is a crucial problem to measure the slip length for these surfaces. Here we propose a novel method by using rheometer for this objective. This method is implemented by designing the distribution of the super-hydrophobic area on the sample. Using this method, a slip length of 40 μm for 70 wt% glycerin flow over a super-hydrophobic surface with stripe structure (the period, width and height of ridges are 150 μm, 40 μm and 65 μm, respectively) is measured. The result shows that the slip length measured using this method is in good agreement with former results measured by other methods. This method is fit for measuring the slip length of super-hydrophobic surface whose structure ranges from microto nanoscale.展开更多
The embedded length of anti-slide piles for slope is analyzed by three-dimensional elastoplastic shear strength reduction method. The effect of embedded pile length on the factor of safety and pile behavior is analyze...The embedded length of anti-slide piles for slope is analyzed by three-dimensional elastoplastic shear strength reduction method. The effect of embedded pile length on the factor of safety and pile behavior is analyzed. Furthermore, the effects of pile spacing, pile head conditions, pile bending stiffness and soil properties on length and behavior of pile are also analyzed. The results show that the pile spacing and the pile head conditions have significant influences on the critical embedded length of pile. It is found that the critical embedded length of pile, beyond which the factor of safety does not increase, increases with the decrease in pile spacing. The smaller the pile spacing is, the larger the integrity of the reinforced slope will be. A theoretical analysis of the slip surface is also conducted, and the slip surface determined by the pressure on piles, considering the influences of both soil and piles for slope, is in agreement with the ones in previous studies.展开更多
The fabrication of superhydrophobic surfaces and the studies on water flow characteristics therein are of great significance to many industrial areas as well as to science and technology development. Experiments were ...The fabrication of superhydrophobic surfaces and the studies on water flow characteristics therein are of great significance to many industrial areas as well as to science and technology development. Experiments were carried out to investigate slip characteristics of water flowing in circular superhydrophobic microtubes within laminar flow region. The superhydrophobic microtubes of stainless steel were fabricated with chemical etching–fluorination treatment. An experimental setup was designed to measure the pressure drop as function of water flow rate. For comparison, superhydrophilic tubes were also tested. Poiseuille number Po was found to be smaller for the superhydrophobic microtubes than that for superhydrophilic ones. The pressure drop reduction ranges from 8% to 31%. It decreases with increasing Reynolds number when Re b 900, owing to the transition from Cassie state to Wenzel state. However, it is almost unchanged with further increasing Re after Re N 900. The slip length in superhydrophobic microtubes also exhibits a Reynolds number dependence similarly to the pressure drop reduction. The relation between slip length and Darcy friction factor is theoretically analyzed with consideration of surface roughness effect, which was testified with the experimental results.展开更多
The boundary slip condition is pivotal for nanoscale fluid motion.Recent research has primarily focused on simulating the interaction mechanism between the electronic structure of two-dimensional materials and slip of...The boundary slip condition is pivotal for nanoscale fluid motion.Recent research has primarily focused on simulating the interaction mechanism between the electronic structure of two-dimensional materials and slip of water at the nanoscale,raising the possibility for ultralow friction flow of water at the nanoscale.However,experimentally elucidating electronic interactions at the dynamic solid–liquid interface to control boundary slip poses a significant challenge.In this study,the crucial role of electron structures at the dynamic solid–liquid interface in regulating slip length was revealed.Notably,the slip length of water on the molybdenum disulfide/graphene(MoS_(2)/G)heterostructure(100.9±3.6 nm)significantly exceeded that of either graphene(27.7±2.2 nm)or MoS_(2)(5.7±3.1 nm)alone.It was also analyzed how electron transfer significantly affected interface interactions.Excess electrons played a crucial role in determining the type and proportion of excitons at both MoS_(2)–water and MoS_(2)/G–water interfaces.Additionally,by applying voltage,distinct photoluminescence(PL)responses at static and dynamic interfaces were discovered,achieving a 5-fold modulation in PL intensity and a 2-fold modulation in the trion to exciton intensity ratio.More electrons transfer from the top graphene to the bottom MoS_(2)at the MoS_(2)/G–water interface,reducing surface charge density.Thus,the reduction of electrostatic interactions between the solid and water leads to an increased slip length of water on the MoS_(2)/G heterostructure.The process aids in comprehending the origin of frictional resistance at the subatomic scale.This work establishes a foundation for actively controlling and designing of fluid transport at the nanoscale.展开更多
针对桥梁墩柱和承台内的粘结滑移现象,基于fib混凝土规范(fib Model Code)推荐的混凝土粘结滑移模型,推导了纵筋滑移量的计算公式,并通过对墩柱塑性区域受拉纵筋的应力-应变本构进行修正,以引入墩柱塑性区域和承台内的纵筋滑移量,作为...针对桥梁墩柱和承台内的粘结滑移现象,基于fib混凝土规范(fib Model Code)推荐的混凝土粘结滑移模型,推导了纵筋滑移量的计算公式,并通过对墩柱塑性区域受拉纵筋的应力-应变本构进行修正,以引入墩柱塑性区域和承台内的纵筋滑移量,作为一种等效方法,以考虑粘结滑移对墩柱地震响应的影响,并用试验结果验证了该方法的合理性。此外,还对所提等效方法和零长度截面单元法的计算结果进行了对比。结果表明:未考虑粘结滑移会高估墩柱的侧向刚度、累计滞回耗能和残余位移,且无法客观反映滑移导致的墩柱强度退化问题;零长度截面单元法和所提等效方法均能考虑强度退化问题,但前者对粘结滑移的模拟效果受纵筋直径影响显著,后者则能合理捕捉滑移影响下的墩柱往复加载过程。展开更多
基金supported by the National Natural Science Foundation of China (10872203)the National Basic Research Program(2007AC744701)the CAS Research and Development Program of China (KSCX2-YW-H18)
文摘Direct measurement of slip length is based on the measured fluid velocity near solid boundary. However, previous micro particle image velocimetry/particle tracking velocimetry （microPIV/PTV） measurements have reported surprisingly large measured near-wall velocities of pressure-driven flow in apparent contradiction with the no-slip hy-pothesis and experimental results from other techniques. To better interpret the measured results of the microPIV/PTV, we performed velocity profile measurements near a hy-drophilic wall （z = 0.25-1.5 μm） with two sizes of tracer particles （φ 50 nm and φ200 nm）. The experimental results indicate that, at less than 1 μm from the wall, the deviations between the measured velocities and no-slip theoretical values obviously decrease from 93% of φ200 nm particles to 48% of φ50 nm particles. The Boltzmann-like exponential measured particle concentrations near wall were found. Based on the non linear Boltzmann distribution of particle concentration and the effective focus plane thickness, we illustrated the reason of the apparent velocity increase near wall and proposed a method to correct the measured velocity profile. By this method, the deviations between the corrected measured velocities and the no-slip theoretical velocity decrease from 45.8% to 10%, and the measured slip length on hy-drophilic glass is revised from 75 nm to 16 nm. These results indicated that the particle size and the biased particle concentration distribution can significantly affect near wall velocity measurement via microPIV/PTV, and result in larger measured velocity and slip length close to wall.
基金Supported by the National Natural Science Foundation of China under Grant No 51305033the Ministry of National Defense of China under Grant No 9140C340506
文摘An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account of the micro-force between molecules and macro-force from the viscous shearing effect, as they contribute to the achieve- ment of the slip length. The calculated results are compared with those obtained from the molecular dynamics simulation, showing an excellent agreement. Further, the effect of the shear rate on the slip is investigated. The results can well predict the fluid flow behaviors on a solid substrate, but has to be proved by experiment.
基金The present research is financially supported by the National Natural Science Foundation of China(Grants No.91752203).
文摘In this letter,the effect of slip boundary on the origin of subcritical transition in two-dimensional chan-nel flows is studied numerically and theoretically.It is shown that both the positive and the negative slip lengths will increase the critical Reynolds number of localized wave packet and hence postpone the transition.By applying a variable transformation and expanding the variables about a small slip length,it is illustrated that the slip boundary effect only exists in the second and higher order modulations of the no-slip solution,and hence explains the power law found in simulations,i.e.the relative increment of the critical Reynolds number due to the slip boundary is proportional to the square of the slip length.
基金Supported by the Foundation for the Author of National Excellent Doctoral Disserta-tion of China (Grant No.2006039)Key Research Foundation of the National Natural Science Foundation of China (Grant No. 50435030)
文摘To design a surface with large slip or larger drag reduction is a pop issue in the fields of liquid transporting and body swimming. In this context, it is a crucial problem to measure the slip length for these surfaces. Here we propose a novel method by using rheometer for this objective. This method is implemented by designing the distribution of the super-hydrophobic area on the sample. Using this method, a slip length of 40 μm for 70 wt% glycerin flow over a super-hydrophobic surface with stripe structure (the period, width and height of ridges are 150 μm, 40 μm and 65 μm, respectively) is measured. The result shows that the slip length measured using this method is in good agreement with former results measured by other methods. This method is fit for measuring the slip length of super-hydrophobic surface whose structure ranges from microto nanoscale.
文摘The embedded length of anti-slide piles for slope is analyzed by three-dimensional elastoplastic shear strength reduction method. The effect of embedded pile length on the factor of safety and pile behavior is analyzed. Furthermore, the effects of pile spacing, pile head conditions, pile bending stiffness and soil properties on length and behavior of pile are also analyzed. The results show that the pile spacing and the pile head conditions have significant influences on the critical embedded length of pile. It is found that the critical embedded length of pile, beyond which the factor of safety does not increase, increases with the decrease in pile spacing. The smaller the pile spacing is, the larger the integrity of the reinforced slope will be. A theoretical analysis of the slip surface is also conducted, and the slip surface determined by the pressure on piles, considering the influences of both soil and piles for slope, is in agreement with the ones in previous studies.
基金the National Natural Science Foundation of China(20476014,51376030)
文摘The fabrication of superhydrophobic surfaces and the studies on water flow characteristics therein are of great significance to many industrial areas as well as to science and technology development. Experiments were carried out to investigate slip characteristics of water flowing in circular superhydrophobic microtubes within laminar flow region. The superhydrophobic microtubes of stainless steel were fabricated with chemical etching–fluorination treatment. An experimental setup was designed to measure the pressure drop as function of water flow rate. For comparison, superhydrophilic tubes were also tested. Poiseuille number Po was found to be smaller for the superhydrophobic microtubes than that for superhydrophilic ones. The pressure drop reduction ranges from 8% to 31%. It decreases with increasing Reynolds number when Re b 900, owing to the transition from Cassie state to Wenzel state. However, it is almost unchanged with further increasing Re after Re N 900. The slip length in superhydrophobic microtubes also exhibits a Reynolds number dependence similarly to the pressure drop reduction. The relation between slip length and Darcy friction factor is theoretically analyzed with consideration of surface roughness effect, which was testified with the experimental results.
基金supported by the National Natural Science Foundation of China(Nos.52075284,52105195,and 11890672)the Postdoctoral Research Foundation of China(Nos.2020M680528,BX2021151,and 2022M711805).
文摘The boundary slip condition is pivotal for nanoscale fluid motion.Recent research has primarily focused on simulating the interaction mechanism between the electronic structure of two-dimensional materials and slip of water at the nanoscale,raising the possibility for ultralow friction flow of water at the nanoscale.However,experimentally elucidating electronic interactions at the dynamic solid–liquid interface to control boundary slip poses a significant challenge.In this study,the crucial role of electron structures at the dynamic solid–liquid interface in regulating slip length was revealed.Notably,the slip length of water on the molybdenum disulfide/graphene(MoS_(2)/G)heterostructure(100.9±3.6 nm)significantly exceeded that of either graphene(27.7±2.2 nm)or MoS_(2)(5.7±3.1 nm)alone.It was also analyzed how electron transfer significantly affected interface interactions.Excess electrons played a crucial role in determining the type and proportion of excitons at both MoS_(2)–water and MoS_(2)/G–water interfaces.Additionally,by applying voltage,distinct photoluminescence(PL)responses at static and dynamic interfaces were discovered,achieving a 5-fold modulation in PL intensity and a 2-fold modulation in the trion to exciton intensity ratio.More electrons transfer from the top graphene to the bottom MoS_(2)at the MoS_(2)/G–water interface,reducing surface charge density.Thus,the reduction of electrostatic interactions between the solid and water leads to an increased slip length of water on the MoS_(2)/G heterostructure.The process aids in comprehending the origin of frictional resistance at the subatomic scale.This work establishes a foundation for actively controlling and designing of fluid transport at the nanoscale.
文摘针对桥梁墩柱和承台内的粘结滑移现象,基于fib混凝土规范(fib Model Code)推荐的混凝土粘结滑移模型,推导了纵筋滑移量的计算公式,并通过对墩柱塑性区域受拉纵筋的应力-应变本构进行修正,以引入墩柱塑性区域和承台内的纵筋滑移量,作为一种等效方法,以考虑粘结滑移对墩柱地震响应的影响,并用试验结果验证了该方法的合理性。此外,还对所提等效方法和零长度截面单元法的计算结果进行了对比。结果表明:未考虑粘结滑移会高估墩柱的侧向刚度、累计滞回耗能和残余位移,且无法客观反映滑移导致的墩柱强度退化问题;零长度截面单元法和所提等效方法均能考虑强度退化问题,但前者对粘结滑移的模拟效果受纵筋直径影响显著,后者则能合理捕捉滑移影响下的墩柱往复加载过程。
