This study presents a nitrogen-doped microporous carbon nanospheres(N@MCNs)prepared by a facile polymerization–carbonization process using low-cost styrene.The N element in situ introduces polystyrene(PS)nanospheres ...This study presents a nitrogen-doped microporous carbon nanospheres(N@MCNs)prepared by a facile polymerization–carbonization process using low-cost styrene.The N element in situ introduces polystyrene(PS)nanospheres via emulsion polymerization of styrene with cyanuric chloride as crosslinking agent,and then carbonization obtains N@MCNs.The as-prepared carbon nanospheres possess the complete spherical structure and adjustable nitrogen amount by controlling the relative proportion of tetrachloromethane and cyanuric chloride.The friction performance of N@MCNs as lubricating oil additives was surveyed utilizing the friction experiment of ball-disc structure.The results showed that N@MCNs exhibit superb reduction performance of friction and wear.When the addition of N@MCNs was 0.06 wt%,the friction coefficient of PAO-10 decreased from 0.188 to 0.105,and the wear volume reduced by 94.4%.The width and depth of wear marks of N@MCNs decreased by 49.2% and 94.5%,respectively.The carrying capacity of load was rocketed from 100 to 400 N concurrently.Through the analysis of the lubrication mechanism,the result manifested that the prepared N@MCNs enter clearance of the friction pair,transform the sliding friction into the mixed friction of sliding and rolling,and repair the contact surface through the repair effect.Furthermore,the tribochemical reaction between nanoparticles and friction pairs forms a protective film containing nitride and metal oxides,which can avert direct contact with the matrix and improve the tribological properties.This experiment showed that nitrogen-doped polystyrene-based carbon nanospheres prepared by in-situ doping are the promising materials for wear resistance and reducing friction.This preparing method can be ulteriorly expanded to multi-element co-permeable materials.Nitrogen and boron co-doped carbon nanospheres(B,N@MCNs)were prepared by mixed carbonization of N-enriched PS and boric acid,and exhibited high load carrying capacity and good tribological properties.展开更多
Fluidic oscillators(FOs)can be used as an efficient fluidic vibration tool to solve high friction problems in extended-reach wells.However,the complex mechanism of FOs makes the design challenging,and the dynamic eros...Fluidic oscillators(FOs)can be used as an efficient fluidic vibration tool to solve high friction problems in extended-reach wells.However,the complex mechanism of FOs makes the design challenging,and the dynamic erosion behavior inside FOs is still unclear.In this paper,new FOs are proposed and the working characteristics under the influence of periodic particle-laden jets are investigated.Firstly,the results reveal the working mechanism of new FOs,showing that the generation of pressure pulses is closely connected with periodic jet switching and the development of vortices.Secondly,the important performance parameters,i.e.,pressure pulse and oscillation frequency,are extensively studied through numerical simulation and experimental verification.It is found that the performance can be optimized by adjusting the tool structure according to different engineering requirements.Finally,the oscillating solid-liquid two-phase flow inside FO is studied.It is demonstrated that the accumulation of particles leads to a significant reduction in performance.The results also reveal five locations that are susceptible to erosion and the erosion behavior of these locations are studied.It has been shown that the periodic jet causes fluctuations in the amount of erosion at the outlet and splitter.This research can provide valuable references for the design and optimization of vibration friction-reduction tools.展开更多
The use of bionic non-smooth surfaces is a popular approach for saving energy because of their drag reduction property. Conventional non-smooth structures include riblets and dimples. Inspired by sand dunes, a novel v...The use of bionic non-smooth surfaces is a popular approach for saving energy because of their drag reduction property. Conventional non-smooth structures include riblets and dimples. Inspired by sand dunes, a novel variable ovoid non-smooth structure is proposed in this study. The body of the variable ovoid dimple was designed based on three size parameters, the radius, semimajor, and depth, and a 3D model was created based on UG software. The constructed variable dimples were placed in a rectangular array on the bottom of a square tube model. Following ANSYS meshing, the grid model was imported into FLUENT, where the flow characteristics were calculated. Results of skin friction reduction were achieved and the effect of the design parameters on different variable ovoid dimples was obtained by orthogonal testing. Various aspects of the skin friction reduction mechanism were discussed including the distribution of velocity vectors, variation in boundary layer thickness, and pressure distribution.展开更多
The two-dimensional flow on the flat plate with injected microbubbles issimulated using the software, PHOENICS (V3. 2), usually used in the CFD (Computational FluidDynamics). A set of formulas for K-ε turbulence mode...The two-dimensional flow on the flat plate with injected microbubbles issimulated using the software, PHOENICS (V3. 2), usually used in the CFD (Computational FluidDynamics). A set of formulas for K-ε turbulence model modified with the presence of microbubbles,is employed. With considering the effect of gravity, interfacial lift, inter-phase friction, virtualmass force and interfacial pressure on the flow with microbubbles, numerical calculations for theinfluence of variable air volume fracton as well as distribution, injecting speed, microbubblediameter and position of introducing microbubbles on the friction reduction are presented. Resultsshow that the friction reduction increases with increasing volume fraction and microbubble diameterwithin the range of 100μm, and that the velocity in the boundary layer with microbubbles is greaterthan that without microbubbles. The order of magnitude and trends of the experimental skin-frictionare reproduced well. The uniform free-stream speed in all cases is 4m/s, giving Reynolds number ofup to 20 million.展开更多
Nanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure,suitable mechanical property,and tunable surface functionalities.However,the poor c...Nanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure,suitable mechanical property,and tunable surface functionalities.However,the poor compatibility between nanomaterials and base oil limits their further applications.In this work,we demonstrated oil-soluble poly(lauryl methacrylate)(PLMA)brushes-grafted metal-organic frameworks nanoparticles(nanoMOFs)as lubricating oil additives that can achieve efficient friction reduction and anti-wear performance.Macroinitiators were synthesized by free-radical polymerization,which was coordinatively grafted onto the surface of the UiO-67 nanoparticles.Then,PLMA brushes were grown on the macroinitiator-modified UiO-67 by surface-initiated atom transfer radical polymerization,which greatly improved the lipophilic property of the UiO-67 nanoparticles and significantly enhanced the colloidal stability and long-term dispersity in both non-polar solvent and base oil.By adding UiO-67@PLMA nanoparticles into the 500 SN base oil,coefficient of friction and wear volume reductions of 45.3%and 75.5%were achieved due to their excellent mechanical properties and oil dispersibility.Moreover,the load-carrying capacity of 500 SN was greatly increased from 100 to 500 N by the UiO-67@PLMA additives,and their excellent tribological performance was demonstrated even at a high friction frequency of 65 Hz and high temperature of 120℃.Our work highlights oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient lubricating additives.展开更多
The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A ser...The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A series of laboratory tests,numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance.Firstly,the experiments on trapezoidal key block under various clamping loads and disturbance were conducted,followed by numerical simulations using the fast Lagrangian analysis of continua(FLAC3D).Then,based on the conventional wave propagation model and the classical shear-slip constitutive model,a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block.The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide(without instability).Meanwhile,when the key block was disturbed to fall,two types of instability process may appear as immediate type or delayed type.In addition,the propagation of stress waves in the block system exhibited obvious low-velocity and lowfrequency characteristics,resulting in the friction reduction effect appearing at the contact interface,which is the essential reason for the sliding of rock blocks.The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rockfalling disasters.展开更多
Our extensive nonequilibrium and equilibrium molecular dynamics simulations reveal the ion-induced interfacial friction reduction of NaCl-containing water nanoflow over graphene.Even under a normal pressure,with the i...Our extensive nonequilibrium and equilibrium molecular dynamics simulations reveal the ion-induced interfacial friction reduction of NaCl-containing water nanoflow over graphene.Even under a normal pressure,with the increase in ion concentration,the friction coefficients of water nanoflow at the water/graphene interfaces decrease,and the slip lengths and shear viscosities of water nanoflow increase.The interfacial friction reduction with the increase in ion concentration is mainly attributed to the decrease in interfacial hydrated ions and the weaker binding of water molecules with graphene at a higher ion concentration.The presence of ions changes the hydrogen bond networks and structural configuration of water molecules close to the underlying graphene sheets and plays a key role in reducing the interfacial friction between water nanoflow and graphene.展开更多
Bent-housing motor is the most widely used directional drilling tool,but it often encounters the problem of high friction when sliding drilling in horizontal wells.In this paper,a mathematical model is proposed to sim...Bent-housing motor is the most widely used directional drilling tool,but it often encounters the problem of high friction when sliding drilling in horizontal wells.In this paper,a mathematical model is proposed to simulate slide drilling with a friction reduction tool of axial vibration.A term called dynamic effective tractoring force(DETF)is defined and used to evaluate friction reduction effectiveness.The factors influencing the DETF are studied,and the tool placement optimization problem is investigated.The studyfinds that the drilling rate of penetration(ROP)can lower the DETF but does not change the trend of the DETF curve.To effectively work,the shock tool stiffness must be greater than some critical value.For the case study,the best oscillating frequency is within 15∼20 Hz.The reflection of the vibration at the bit boundary can intensify or weaken the friction reduction effec-tiveness,depending on the distance between the hydraulic oscillator and the bit.The optimal placement position corresponds to the plateau stage of the DETF curve.The reliability of the method is verified by thefield tests.The proposed method can provide a design and use guide to hydraulic oscillators and improve friction reduction effectiveness in horizontal wells.展开更多
Two novel ashless additives - benzothiazole derivatives containing boron and chlorine, OBC and BBC, were synthesized. The tribological performances of OBC and BBC at different mass ratios as additives in rapeseed oil ...Two novel ashless additives - benzothiazole derivatives containing boron and chlorine, OBC and BBC, were synthesized. The tribological performances of OBC and BBC at different mass ratios as additives in rapeseed oil (RO) were examined on a four-ball machine. The worn surfaces of the lower steel balls lubricated by oil samples were analyzed by means of scanning electron microscopy (SEM). The test results showed that OBC and BBC had good solubility in the base oil, and could effectively increase the load-carrying capacity of the base oil. The maximum non-seizure load of oil sample containing 1.5 m% BBC was 1117 N, which was 2.3 times as much as that of the base oil. Both OBC and BBC could improve the anti-wear and corrosion inhibiting performance and thermal stability of the base oil, whose initial decomposition temperatures was above 350 ~C. However, OBC and BBC at different concentrations could increase the friction coefficient of the base oil. The SEM morphology of steel balls lubricated by oil samples containing 1.5 m% additives seemed to be more uniform and smoother than that of the base oil, and the scars formed were very shallow.展开更多
High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load,high temperature,high shock conditions due to in-sufficient sup...High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load,high temperature,high shock conditions due to in-sufficient supply of lubricating oil and grease.Traditional self-lubricating coatings prepared by inorganic,organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function,so that it is difficult to meet the engineering requirements of high-temperature lubrication.We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy.Polytetrafluoroethylene(PTFE,T_(m)=329℃)and polyphenylene sulfide(PPS,T_(g)=84℃,T_(m)=283℃)are used to prepare a PTFE/PPS polymer alloy coating.As the temperature increases from 25 to 300℃,the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state,which is owing to the thermodynamic transformation characteristic of the PPS component.Additionally the friction coefficient(μ)decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300℃.The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature(T),temperature–centrifugal force(T–F_(ω)),temperature–centrifugal force–shearing force(T–F_(ω)–F_(τ))were investigated.The physical model of“thermoviscoelasticity driven solid–liquid interface reducing friction”is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers.The high-temperature adjusts the viscosity(η)of the coating,increases interface slipping and intensifies shear deformation(τ),reducing the friction coefficient.The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.展开更多
A novel air bubble lubrication method using the winged air induction pipe (WAIP) device is used to reduce the frictional drag of the hull of the ship and hence increase the efficiency of the propulsion system. This bu...A novel air bubble lubrication method using the winged air induction pipe (WAIP) device is used to reduce the frictional drag of the hull of the ship and hence increase the efficiency of the propulsion system. This bubble lubrication technique utilizes the negative pressure region above the upper surface of the hydrofoil as the ship moves forward to drive air to the skin of the hull. In the present study, the reduction rate of the drag by applying the WAIP device is numerically investigated with the open source toolbox OpenFOAM. The generated air layer and the bubbles are observed. The numerical results indicate that the reduction rate of the drag closely depends on the depth of the submergence of the hydrofoil, the angle of attack of the hydrofoil, and the pressure in the air inlet. It is also proportional to the air flow rate. The underlying physics of the fluid dynamics is explored.展开更多
Osteoarthritis(OA)has been regarded as a lubrication deficiency related joint disease.Combination of both joint lubrication and drug intervention may provide a promising nonsurgical strategy for treatment of OA.Develo...Osteoarthritis(OA)has been regarded as a lubrication deficiency related joint disease.Combination of both joint lubrication and drug intervention may provide a promising nonsurgical strategy for treatment of OA.Developing novel and simple approaches to fabricate superlubricating nanoparticles with drug release property is highly required.Herein,dopamine triggered one-step polymerization method was employed to fabricate polydopamine/poly(3-sulfopropyl methacrylate potassium salt)(PDA-PSPMA)conjugate coating on hollow silica(h-SiO_(2))nanosphere surfaces to engineer functional nanoparticles(h-SiO_(2)/PDA-PSPMA).The as-prepared h-SiO_(2)/PDA-PSPMA exhibits excellent aqueous lubrication performance on biomaterial substrates as well as natural bovine articular cartilage based on hydration effect of negatively charged PDA-PSPMA coating and"rolling"effect of h-SiO_(2)nanospheres.In vitro drug loading-release experiments demonstrate that PDA-PSPMA coating functionalized h-SiO_(2)nanospheres show high drug-loading and sustained-release capability of an anti-inflammatory drug,diclofenac sodium(DS).Such h-SiO_(2)/PDA-PSPMA nanospheres can be potentially used as a synergistic therapy agent for OA treatment combining by simultaneous joint lubrication anddrugrelease.展开更多
Numerous tribological applications,wherein the use of liquid lubricants is infeasible,require adequate dry lubrication.Despite the use of polymers as an effective solution for dry sliding tribological applications,the...Numerous tribological applications,wherein the use of liquid lubricants is infeasible,require adequate dry lubrication.Despite the use of polymers as an effective solution for dry sliding tribological applications,their poor wear resistance prevents the utilization in harsh industrial environment.Different methods are typically implemented to tackle the poor wear performance of polymers,however sacrificing some of their mechanical/tribological properties.Herein,we discussed the introduction of a novel additive,namely microencapsulated phase change material(MPCM)into an advanced polymeric coating.Specifically,paraffin was encapsulated into melamine-based resin,and the capsules were dispersed in an aromatic thermosetting co-polyester(ATSP)coating.We found that the MPCM-filled composite exhibited a unique tribological behavior,manifested as“zero wear”,and a super-low coefficient of friction(COF)of 0.05.The developed composite outperformed the state-of-the-art polytetrafluoroethylene(PTFE)-filled coatings,under the experimental conditions examined herein.展开更多
Surface texturing has been considered as an effective approach to improve the tribological performances.Based on the consideration of enhancing the tribological performance,the experiments are carried out to investiga...Surface texturing has been considered as an effective approach to improve the tribological performances.Based on the consideration of enhancing the tribological performance,the experiments are carried out to investigate tribological performance of triangular textures in water lubrication.The textures are generated by the Nd:YAG laser marking system,with an area density of 20%and a depth of 7 m and are distributed uniformly on the surface of the SiC rings.Compared with the circular textures,the triangular textures have obvious tribological anisotropy.The triangular textures in clockwise direction show the best friction reduction effect among the three textures.The friction reduction mechanisms of the triangular textures in clockwise direction are also analyzed and discussed.展开更多
Despite excellent tribological behaviors of ionic liquids (ILs) as lubricating oils, their friction-reducing and anti-wear properties must be improved when they are used under severe conditions. There are only a few r...Despite excellent tribological behaviors of ionic liquids (ILs) as lubricating oils, their friction-reducing and anti-wear properties must be improved when they are used under severe conditions. There are only a few reports exploring additives for ILs. Here, MoS2 and WS2 quantum dots (QDs, with particle size less than 10 nm) are prepared via a facile green technique, and they are dispersed in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm]PF6), forming homogeneous dispersions exhibiting long-term stabilities. Tribological test results indicate that the addition of MoS2 and WS2 QDs in the IL can significantly enhance the friction-reducing and anti-wear abilities of the neat IL under a constant load of 500 N and a temperature of 150 °C. The exceptional tribological properties of these additives in the IL are ascribed to the formation of protective films, which are produced not only by the physical absorption of MoS2 and WS2 QDs at the steel/steel contact surfaces, but also by the tribochemical reaction between MoS2 or WS2 and the iron atoms/iron oxide species.展开更多
Water snails developed a distinct appendage, the operculum, to better protect the body against predators. When the animal is active and crawling, part of the underside of the shell rests on the outer surface of the op...Water snails developed a distinct appendage, the operculum, to better protect the body against predators. When the animal is active and crawling, part of the underside of the shell rests on the outer surface of the operculum. We observed the water snails (Pomacea canaliculata) spend -3 hours per day foraging, and the relative angular velocity between the shell and operculum can reach up to 10°·s^-1, which might inevitably lead to abrasion on the shell and operculum interface. However, by electron microscopy images, we found that the underside of the shell and outer surface of the operculum is not severely worn, which indicates that this animal might have a strategy to reduce wear. We discovered the superimposed rings distributed concentrically on the surface, which can generate micro-grooves for a hydrodynamic lubrication. We theoretically and experimentally revealed the mechanism of drag reduction combing the groove geometry and hydrodynamics. This textured operculum surface might provide a friction coefficient up to 0.012 as a stability-resilience, which protects the structure of the snail's shell and operculum. This mechanism might open up new paths for studies of micro-anti-wear structures used in liquid media.展开更多
An array of distributed round synthetic jets was used to control a fully developed turbulent boundary layer.The study focused on the related skin friction drag reduction and mechanisms involved.The control effects wer...An array of distributed round synthetic jets was used to control a fully developed turbulent boundary layer.The study focused on the related skin friction drag reduction and mechanisms involved.The control effects were analyzed by measuring the streamwise velocities using a hot-wire anemometer downstream of the array.A reduction in the skin friction was observed both in the regions downstream of the orifices and in the regions between two adjacent orifices.A statistical analysis with the variable-interval time-averaging(VITA)technique demonstrated a weakened bursting intensity with synthetic jet in the near-wall region.The streamwise vortices were lifted by the upwash effect caused by synthetic jet and induced less low-speed streaks.The control mechanism acted in a way to suppress the dynamic interaction between the streamwise vortices and low-speed streaks and to attenuate the turbulence production in the near-wall region.The forcing frequency was found to be a more relevant parameter when synthetic jet was applied in turbulent boundary layer flow control.A higher forcing frequency induced a higher reduction in the skin friction.The power spectral density and autocorrelation of the fluctuating velocities showed that the synthetic jets gradually decayed in the streamwise direction,having an effect as far as 34.5 times the displacement thickness that was on the trailing edge of the distributed synthetic jets array.展开更多
Rectangular pipe jacking or box jacking has become more popular in municipal applications because of its better adaptability to shallow overburdens and its higher structural section utilization than the conventional c...Rectangular pipe jacking or box jacking has become more popular in municipal applications because of its better adaptability to shallow overburdens and its higher structural section utilization than the conventional circular pipe jacking.This case study presents a utility tunnel constructed by using rectangular box jacking in Suzhou,China.The utility tunnel,which has a cross section of 9.1 m in width and 5.5 m in height,was jacked 233.6 m,which is the longest known single jacking length of a rectangular box jacking project in China.The box jacking mainly passed through a silty sand layer with high groundwater levels with a minimum depth of cover of only 3.5 m underneath the Yuanhetang River.In this zone,the structures on the surface are sensitive to external disturbance,thus increasing the challenges of construction.A series of measures were taken during the jacking process,and the project was successfully completed.This paper provides an overview of this project and introduces key techniques in the construction of working shafts as well as in the installation and retrieval of the box jacking machine.In addition,the use of lubrication to reduce friction resistance,navigation and application of an anti-buoyancy slab under the Yuanhetang River,and analyses of soil deformation caused by box jacking are described.展开更多
The movement pattern of ellipsoidal nanoparticles confined between copper surfaces was examined using a theoretical model and molecular dynamics simulation.Initially,we developed a theoretical model of movement patter...The movement pattern of ellipsoidal nanoparticles confined between copper surfaces was examined using a theoretical model and molecular dynamics simulation.Initially,we developed a theoretical model of movement patterns for hard ellipsoidal nanoparticles.Subsequently,the simulation indicated that there are critical values for increasing the axial ratio,driving velocity of the contact surface,and lowering normal loads(i.e.,0.83,15 m/s,and 100 nN under the respective conditions),which in turn change the movement pattern of nanoparticles from sliding to rolling.Based on the comparison between the ratio of arm of force(e/h)and coefficient of friction(μ),the theoretical model was in good agreement with the simulations and accurately predicted the movement pattern of ellipsoidal nanoparticles.The sliding of the ellipsoidal nanoparticles led to severe surface damage.However,rolling separated the contact surfaces and thereby reduced friction and wear.展开更多
基金supported by the National Natural Science Foundation of China(Nos.U21A2046 and 51972272)the Western Light Project of CAS(No.xbzg-zdsys-202118).
文摘This study presents a nitrogen-doped microporous carbon nanospheres(N@MCNs)prepared by a facile polymerization–carbonization process using low-cost styrene.The N element in situ introduces polystyrene(PS)nanospheres via emulsion polymerization of styrene with cyanuric chloride as crosslinking agent,and then carbonization obtains N@MCNs.The as-prepared carbon nanospheres possess the complete spherical structure and adjustable nitrogen amount by controlling the relative proportion of tetrachloromethane and cyanuric chloride.The friction performance of N@MCNs as lubricating oil additives was surveyed utilizing the friction experiment of ball-disc structure.The results showed that N@MCNs exhibit superb reduction performance of friction and wear.When the addition of N@MCNs was 0.06 wt%,the friction coefficient of PAO-10 decreased from 0.188 to 0.105,and the wear volume reduced by 94.4%.The width and depth of wear marks of N@MCNs decreased by 49.2% and 94.5%,respectively.The carrying capacity of load was rocketed from 100 to 400 N concurrently.Through the analysis of the lubrication mechanism,the result manifested that the prepared N@MCNs enter clearance of the friction pair,transform the sliding friction into the mixed friction of sliding and rolling,and repair the contact surface through the repair effect.Furthermore,the tribochemical reaction between nanoparticles and friction pairs forms a protective film containing nitride and metal oxides,which can avert direct contact with the matrix and improve the tribological properties.This experiment showed that nitrogen-doped polystyrene-based carbon nanospheres prepared by in-situ doping are the promising materials for wear resistance and reducing friction.This preparing method can be ulteriorly expanded to multi-element co-permeable materials.Nitrogen and boron co-doped carbon nanospheres(B,N@MCNs)were prepared by mixed carbonization of N-enriched PS and boric acid,and exhibited high load carrying capacity and good tribological properties.
基金funded by the National Key Research and Development Program of China under grant number 2020YFC1807200the National Natural Science Foundation of China under grant number 41872186the National Natural Science Foundation of China(Grant number 51978674)。
文摘Fluidic oscillators(FOs)can be used as an efficient fluidic vibration tool to solve high friction problems in extended-reach wells.However,the complex mechanism of FOs makes the design challenging,and the dynamic erosion behavior inside FOs is still unclear.In this paper,new FOs are proposed and the working characteristics under the influence of periodic particle-laden jets are investigated.Firstly,the results reveal the working mechanism of new FOs,showing that the generation of pressure pulses is closely connected with periodic jet switching and the development of vortices.Secondly,the important performance parameters,i.e.,pressure pulse and oscillation frequency,are extensively studied through numerical simulation and experimental verification.It is found that the performance can be optimized by adjusting the tool structure according to different engineering requirements.Finally,the oscillating solid-liquid two-phase flow inside FO is studied.It is demonstrated that the accumulation of particles leads to a significant reduction in performance.The results also reveal five locations that are susceptible to erosion and the erosion behavior of these locations are studied.It has been shown that the periodic jet causes fluctuations in the amount of erosion at the outlet and splitter.This research can provide valuable references for the design and optimization of vibration friction-reduction tools.
基金Project supported by the National Natural Science Foundation of China (No. 51375439)
文摘The use of bionic non-smooth surfaces is a popular approach for saving energy because of their drag reduction property. Conventional non-smooth structures include riblets and dimples. Inspired by sand dunes, a novel variable ovoid non-smooth structure is proposed in this study. The body of the variable ovoid dimple was designed based on three size parameters, the radius, semimajor, and depth, and a 3D model was created based on UG software. The constructed variable dimples were placed in a rectangular array on the bottom of a square tube model. Following ANSYS meshing, the grid model was imported into FLUENT, where the flow characteristics were calculated. Results of skin friction reduction were achieved and the effect of the design parameters on different variable ovoid dimples was obtained by orthogonal testing. Various aspects of the skin friction reduction mechanism were discussed including the distribution of velocity vectors, variation in boundary layer thickness, and pressure distribution.
文摘The two-dimensional flow on the flat plate with injected microbubbles issimulated using the software, PHOENICS (V3. 2), usually used in the CFD (Computational FluidDynamics). A set of formulas for K-ε turbulence model modified with the presence of microbubbles,is employed. With considering the effect of gravity, interfacial lift, inter-phase friction, virtualmass force and interfacial pressure on the flow with microbubbles, numerical calculations for theinfluence of variable air volume fracton as well as distribution, injecting speed, microbubblediameter and position of introducing microbubbles on the friction reduction are presented. Resultsshow that the friction reduction increases with increasing volume fraction and microbubble diameterwithin the range of 100μm, and that the velocity in the boundary layer with microbubbles is greaterthan that without microbubbles. The order of magnitude and trends of the experimental skin-frictionare reproduced well. The uniform free-stream speed in all cases is 4m/s, giving Reynolds number ofup to 20 million.
基金the Research Fund of State Key Laboratory of Solidification Processing(NPU)(2022-QZ-04)the National Natural Science Foundations of China(52071270).
文摘Nanomaterials as lubricating oil additives have attracted significant attention because of their designable composition and structure,suitable mechanical property,and tunable surface functionalities.However,the poor compatibility between nanomaterials and base oil limits their further applications.In this work,we demonstrated oil-soluble poly(lauryl methacrylate)(PLMA)brushes-grafted metal-organic frameworks nanoparticles(nanoMOFs)as lubricating oil additives that can achieve efficient friction reduction and anti-wear performance.Macroinitiators were synthesized by free-radical polymerization,which was coordinatively grafted onto the surface of the UiO-67 nanoparticles.Then,PLMA brushes were grown on the macroinitiator-modified UiO-67 by surface-initiated atom transfer radical polymerization,which greatly improved the lipophilic property of the UiO-67 nanoparticles and significantly enhanced the colloidal stability and long-term dispersity in both non-polar solvent and base oil.By adding UiO-67@PLMA nanoparticles into the 500 SN base oil,coefficient of friction and wear volume reductions of 45.3%and 75.5%were achieved due to their excellent mechanical properties and oil dispersibility.Moreover,the load-carrying capacity of 500 SN was greatly increased from 100 to 500 N by the UiO-67@PLMA additives,and their excellent tribological performance was demonstrated even at a high friction frequency of 65 Hz and high temperature of 120℃.Our work highlights oil-soluble polymer brushes-functionalized nanoMOFs for highly efficient lubricating additives.
基金This work was financially supported by National Key Research and Development Program of China(Grant No.2022YFC2903903)National Natural Science Foundation of China(Grant No.52304132)Yunnan Major Scientific and Technological Projects(Grant No.202202AG050014).These support is gratefully acknowledged.
文摘The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A series of laboratory tests,numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance.Firstly,the experiments on trapezoidal key block under various clamping loads and disturbance were conducted,followed by numerical simulations using the fast Lagrangian analysis of continua(FLAC3D).Then,based on the conventional wave propagation model and the classical shear-slip constitutive model,a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block.The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide(without instability).Meanwhile,when the key block was disturbed to fall,two types of instability process may appear as immediate type or delayed type.In addition,the propagation of stress waves in the block system exhibited obvious low-velocity and lowfrequency characteristics,resulting in the friction reduction effect appearing at the contact interface,which is the essential reason for the sliding of rock blocks.The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rockfalling disasters.
基金supported by the National Natural Science Foundation of China(11972186,11890674,51921003),the Western Light Project of CAS(xbzg-zdsys-202118)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Our extensive nonequilibrium and equilibrium molecular dynamics simulations reveal the ion-induced interfacial friction reduction of NaCl-containing water nanoflow over graphene.Even under a normal pressure,with the increase in ion concentration,the friction coefficients of water nanoflow at the water/graphene interfaces decrease,and the slip lengths and shear viscosities of water nanoflow increase.The interfacial friction reduction with the increase in ion concentration is mainly attributed to the decrease in interfacial hydrated ions and the weaker binding of water molecules with graphene at a higher ion concentration.The presence of ions changes the hydrogen bond networks and structural configuration of water molecules close to the underlying graphene sheets and plays a key role in reducing the interfacial friction between water nanoflow and graphene.
文摘Bent-housing motor is the most widely used directional drilling tool,but it often encounters the problem of high friction when sliding drilling in horizontal wells.In this paper,a mathematical model is proposed to simulate slide drilling with a friction reduction tool of axial vibration.A term called dynamic effective tractoring force(DETF)is defined and used to evaluate friction reduction effectiveness.The factors influencing the DETF are studied,and the tool placement optimization problem is investigated.The studyfinds that the drilling rate of penetration(ROP)can lower the DETF but does not change the trend of the DETF curve.To effectively work,the shock tool stiffness must be greater than some critical value.For the case study,the best oscillating frequency is within 15∼20 Hz.The reflection of the vibration at the bit boundary can intensify or weaken the friction reduction effec-tiveness,depending on the distance between the hydraulic oscillator and the bit.The optimal placement position corresponds to the plateau stage of the DETF curve.The reliability of the method is verified by thefield tests.The proposed method can provide a design and use guide to hydraulic oscillators and improve friction reduction effectiveness in horizontal wells.
文摘Two novel ashless additives - benzothiazole derivatives containing boron and chlorine, OBC and BBC, were synthesized. The tribological performances of OBC and BBC at different mass ratios as additives in rapeseed oil (RO) were examined on a four-ball machine. The worn surfaces of the lower steel balls lubricated by oil samples were analyzed by means of scanning electron microscopy (SEM). The test results showed that OBC and BBC had good solubility in the base oil, and could effectively increase the load-carrying capacity of the base oil. The maximum non-seizure load of oil sample containing 1.5 m% BBC was 1117 N, which was 2.3 times as much as that of the base oil. Both OBC and BBC could improve the anti-wear and corrosion inhibiting performance and thermal stability of the base oil, whose initial decomposition temperatures was above 350 ~C. However, OBC and BBC at different concentrations could increase the friction coefficient of the base oil. The SEM morphology of steel balls lubricated by oil samples containing 1.5 m% additives seemed to be more uniform and smoother than that of the base oil, and the scars formed were very shallow.
基金The authors are grateful for the financial support from National Natural Science Foundation of China(No.52075560).
文摘High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load,high temperature,high shock conditions due to in-sufficient supply of lubricating oil and grease.Traditional self-lubricating coatings prepared by inorganic,organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function,so that it is difficult to meet the engineering requirements of high-temperature lubrication.We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy.Polytetrafluoroethylene(PTFE,T_(m)=329℃)and polyphenylene sulfide(PPS,T_(g)=84℃,T_(m)=283℃)are used to prepare a PTFE/PPS polymer alloy coating.As the temperature increases from 25 to 300℃,the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state,which is owing to the thermodynamic transformation characteristic of the PPS component.Additionally the friction coefficient(μ)decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300℃.The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature(T),temperature–centrifugal force(T–F_(ω)),temperature–centrifugal force–shearing force(T–F_(ω)–F_(τ))were investigated.The physical model of“thermoviscoelasticity driven solid–liquid interface reducing friction”is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers.The high-temperature adjusts the viscosity(η)of the coating,increases interface slipping and intensifies shear deformation(τ),reducing the friction coefficient.The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions.
基金Project supported by the National Natural Science Youth Foundation of China(Grant No.11902125).
文摘A novel air bubble lubrication method using the winged air induction pipe (WAIP) device is used to reduce the frictional drag of the hull of the ship and hence increase the efficiency of the propulsion system. This bubble lubrication technique utilizes the negative pressure region above the upper surface of the hydrofoil as the ship moves forward to drive air to the skin of the hull. In the present study, the reduction rate of the drag by applying the WAIP device is numerically investigated with the open source toolbox OpenFOAM. The generated air layer and the bubbles are observed. The numerical results indicate that the reduction rate of the drag closely depends on the depth of the submergence of the hydrofoil, the angle of attack of the hydrofoil, and the pressure in the air inlet. It is also proportional to the air flow rate. The underlying physics of the fluid dynamics is explored.
基金This work was financially supported by National Natural Science Foundation of China(52065061,22032006)Outstanding Youth Fund of Gansu Province(21JR7RA158,21JR7RA095)+1 种基金Innovation Fund for Universities of Gansu Province(2021A-015)Youth Innovation Promotion Association CAS(2019411).
文摘Osteoarthritis(OA)has been regarded as a lubrication deficiency related joint disease.Combination of both joint lubrication and drug intervention may provide a promising nonsurgical strategy for treatment of OA.Developing novel and simple approaches to fabricate superlubricating nanoparticles with drug release property is highly required.Herein,dopamine triggered one-step polymerization method was employed to fabricate polydopamine/poly(3-sulfopropyl methacrylate potassium salt)(PDA-PSPMA)conjugate coating on hollow silica(h-SiO_(2))nanosphere surfaces to engineer functional nanoparticles(h-SiO_(2)/PDA-PSPMA).The as-prepared h-SiO_(2)/PDA-PSPMA exhibits excellent aqueous lubrication performance on biomaterial substrates as well as natural bovine articular cartilage based on hydration effect of negatively charged PDA-PSPMA coating and"rolling"effect of h-SiO_(2)nanospheres.In vitro drug loading-release experiments demonstrate that PDA-PSPMA coating functionalized h-SiO_(2)nanospheres show high drug-loading and sustained-release capability of an anti-inflammatory drug,diclofenac sodium(DS).Such h-SiO_(2)/PDA-PSPMA nanospheres can be potentially used as a synergistic therapy agent for OA treatment combining by simultaneous joint lubrication anddrugrelease.
基金The authors also acknowledge the use of the Texas A&M Materials Characterization Core Facility(RRID:SCR_022202)We gratefully acknowledge the financial support from the Robert A.WELCH Foundation through the W.T.Doherty-WELCH Chair in Chemistry(A-0001)Mariela VAZQUEZ appreciates the support by the National Science Foundation Graduate Research Fellowship Program(Grant No.M1703014).
文摘Numerous tribological applications,wherein the use of liquid lubricants is infeasible,require adequate dry lubrication.Despite the use of polymers as an effective solution for dry sliding tribological applications,their poor wear resistance prevents the utilization in harsh industrial environment.Different methods are typically implemented to tackle the poor wear performance of polymers,however sacrificing some of their mechanical/tribological properties.Herein,we discussed the introduction of a novel additive,namely microencapsulated phase change material(MPCM)into an advanced polymeric coating.Specifically,paraffin was encapsulated into melamine-based resin,and the capsules were dispersed in an aromatic thermosetting co-polyester(ATSP)coating.We found that the MPCM-filled composite exhibited a unique tribological behavior,manifested as“zero wear”,and a super-low coefficient of friction(COF)of 0.05.The developed composite outperformed the state-of-the-art polytetrafluoroethylene(PTFE)-filled coatings,under the experimental conditions examined herein.
基金supported by the National Basic Research Program of China(Grant No.2009CB724304)the National Key Technology R&D Program(Grant No.2011BAF09B05)the National Natural Science Foundation of China(Grant No.50975157)
文摘Surface texturing has been considered as an effective approach to improve the tribological performances.Based on the consideration of enhancing the tribological performance,the experiments are carried out to investigate tribological performance of triangular textures in water lubrication.The textures are generated by the Nd:YAG laser marking system,with an area density of 20%and a depth of 7 m and are distributed uniformly on the surface of the SiC rings.Compared with the circular textures,the triangular textures have obvious tribological anisotropy.The triangular textures in clockwise direction show the best friction reduction effect among the three textures.The friction reduction mechanisms of the triangular textures in clockwise direction are also analyzed and discussed.
基金The authors are thankful for financial support of this work by National Key Research and Development Program of China(No.2018YFBO703802)National NaturalScienceFoundationofChina(Nos.NSFC51875553 and 51775536).
文摘Despite excellent tribological behaviors of ionic liquids (ILs) as lubricating oils, their friction-reducing and anti-wear properties must be improved when they are used under severe conditions. There are only a few reports exploring additives for ILs. Here, MoS2 and WS2 quantum dots (QDs, with particle size less than 10 nm) are prepared via a facile green technique, and they are dispersed in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm]PF6), forming homogeneous dispersions exhibiting long-term stabilities. Tribological test results indicate that the addition of MoS2 and WS2 QDs in the IL can significantly enhance the friction-reducing and anti-wear abilities of the neat IL under a constant load of 500 N and a temperature of 150 °C. The exceptional tribological properties of these additives in the IL are ascribed to the formation of protective films, which are produced not only by the physical absorption of MoS2 and WS2 QDs at the steel/steel contact surfaces, but also by the tribochemical reaction between MoS2 or WS2 and the iron atoms/iron oxide species.
文摘Water snails developed a distinct appendage, the operculum, to better protect the body against predators. When the animal is active and crawling, part of the underside of the shell rests on the outer surface of the operculum. We observed the water snails (Pomacea canaliculata) spend -3 hours per day foraging, and the relative angular velocity between the shell and operculum can reach up to 10°·s^-1, which might inevitably lead to abrasion on the shell and operculum interface. However, by electron microscopy images, we found that the underside of the shell and outer surface of the operculum is not severely worn, which indicates that this animal might have a strategy to reduce wear. We discovered the superimposed rings distributed concentrically on the surface, which can generate micro-grooves for a hydrodynamic lubrication. We theoretically and experimentally revealed the mechanism of drag reduction combing the groove geometry and hydrodynamics. This textured operculum surface might provide a friction coefficient up to 0.012 as a stability-resilience, which protects the structure of the snail's shell and operculum. This mechanism might open up new paths for studies of micro-anti-wear structures used in liquid media.
基金The authors would like to acknowledge the financial support received from the project“Drag Reduction via Turbulent Boundary Layer Flow Control(DRAGY)”.The DRAGY project(April 2016-March 2019)is a China-EU Aeronautical Cooperation project,which is co-funded by Ministry of Industry and Information Technology(MIIT),China,and Directorate-General for Research and Innovation(DG RTD),European Commission.
文摘An array of distributed round synthetic jets was used to control a fully developed turbulent boundary layer.The study focused on the related skin friction drag reduction and mechanisms involved.The control effects were analyzed by measuring the streamwise velocities using a hot-wire anemometer downstream of the array.A reduction in the skin friction was observed both in the regions downstream of the orifices and in the regions between two adjacent orifices.A statistical analysis with the variable-interval time-averaging(VITA)technique demonstrated a weakened bursting intensity with synthetic jet in the near-wall region.The streamwise vortices were lifted by the upwash effect caused by synthetic jet and induced less low-speed streaks.The control mechanism acted in a way to suppress the dynamic interaction between the streamwise vortices and low-speed streaks and to attenuate the turbulence production in the near-wall region.The forcing frequency was found to be a more relevant parameter when synthetic jet was applied in turbulent boundary layer flow control.A higher forcing frequency induced a higher reduction in the skin friction.The power spectral density and autocorrelation of the fluctuating velocities showed that the synthetic jets gradually decayed in the streamwise direction,having an effect as far as 34.5 times the displacement thickness that was on the trailing edge of the distributed synthetic jets array.
文摘Rectangular pipe jacking or box jacking has become more popular in municipal applications because of its better adaptability to shallow overburdens and its higher structural section utilization than the conventional circular pipe jacking.This case study presents a utility tunnel constructed by using rectangular box jacking in Suzhou,China.The utility tunnel,which has a cross section of 9.1 m in width and 5.5 m in height,was jacked 233.6 m,which is the longest known single jacking length of a rectangular box jacking project in China.The box jacking mainly passed through a silty sand layer with high groundwater levels with a minimum depth of cover of only 3.5 m underneath the Yuanhetang River.In this zone,the structures on the surface are sensitive to external disturbance,thus increasing the challenges of construction.A series of measures were taken during the jacking process,and the project was successfully completed.This paper provides an overview of this project and introduces key techniques in the construction of working shafts as well as in the installation and retrieval of the box jacking machine.In addition,the use of lubrication to reduce friction resistance,navigation and application of an anti-buoyancy slab under the Yuanhetang River,and analyses of soil deformation caused by box jacking are described.
基金The authors acknowledge the financial support from the National Natural Science Fundation of China(NSFC)(51905433)the National Key R&D Program of China(No.2018YFB0703800)the Fundamental Research Funds for the Central Universities(No.3102019TS0405).
文摘The movement pattern of ellipsoidal nanoparticles confined between copper surfaces was examined using a theoretical model and molecular dynamics simulation.Initially,we developed a theoretical model of movement patterns for hard ellipsoidal nanoparticles.Subsequently,the simulation indicated that there are critical values for increasing the axial ratio,driving velocity of the contact surface,and lowering normal loads(i.e.,0.83,15 m/s,and 100 nN under the respective conditions),which in turn change the movement pattern of nanoparticles from sliding to rolling.Based on the comparison between the ratio of arm of force(e/h)and coefficient of friction(μ),the theoretical model was in good agreement with the simulations and accurately predicted the movement pattern of ellipsoidal nanoparticles.The sliding of the ellipsoidal nanoparticles led to severe surface damage.However,rolling separated the contact surfaces and thereby reduced friction and wear.