The process of contaminant transport is a problem of multicomponent and multiphase flow in unsaturated zone. Under the presupposition that gas existence affects water transport, a coupled mathematical model of contami...The process of contaminant transport is a problem of multicomponent and multiphase flow in unsaturated zone. Under the presupposition that gas existence affects water transport, a coupled mathematical model of contaminant transport in unsaturated zone has been established based on fluid_solid interaction mechanics theory. The asymptotical solutions to the nonlinear coupling mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of pore pressure, pore water velocity and contaminant concentration in unsaturated zone has been presented under the conditions of with coupling and without coupling gas phase. An example problem was used to provide a quantitative verification and validation of the model. The asymptotical solution was compared with Faust model solution. The comparison results show reasonable agreement between asymptotical solution and Faust solution, and the gas effect and media deformation has a large impact on the contaminant transport. The theoretical basis is provided for forecasting contaminant transport and the determination of the relationship among pressure_saturation_permeability in laboratory.展开更多
Based on the growth mechanism of natural biological branching systems and inspiration from the morphology of plant root tips,a bionic design method called Improved Adaptive Growth Method(IAGM)has been proposed in the ...Based on the growth mechanism of natural biological branching systems and inspiration from the morphology of plant root tips,a bionic design method called Improved Adaptive Growth Method(IAGM)has been proposed in the authors’previous research and successfully applied to the reinforcement optimization of three-dimensional box structures with respect to natural frequencies.However,as a kind of ground structure methods,the final layout patterns of stiffeners obtained by using the IAGM are highly subjected to their ground structures,which restricts the optimization effect and freedom to further improve the dynamic performance of structures.To solve this problem,a novel post-processing geometry and size optimization approach is proposed in this article.This method takes the former layout optimization result as start,and iteratively finds the optimal layout angles,locations,and lengths of stiffeners with a few design variables by optimizing the positions of some specific node lines called active node lines.At the same time,thick-nesses of stiffeners are also optimized to further improve natural frequencies of three-dimensional box structures.Using this method,stiffeners can be successfully separated from their ground structures and further effectively improve natural frequencies of three-dimensional box structures with less material consumption.Typical numerical examples are illustrated to validate the effectiveness and advantages of the suggested method.展开更多
The fatigue crack growth(FCG) mechanism of a cast hybrid metal matrix composite(MMC) reinforced with SiC particles and Al2O3 whiskers was investigated. For comparison, the FCG mechanisms of a cast MMC with Al2O3 whisk...The fatigue crack growth(FCG) mechanism of a cast hybrid metal matrix composite(MMC) reinforced with SiC particles and Al2O3 whiskers was investigated. For comparison, the FCG mechanisms of a cast MMC with Al2O3 whiskers and a cast Al alloy were also investigated. The results show that the FCG mechanism is observed in the near-threshold and stable-crack-growth regions.The hybrid MMC shows a higher threshold stress intensity factor range, ?Kth, than the MMC with Al2O3 and Al alloy, indicating better resistance to crack growth in a lower stress intensity factor range, ?K. In the near-threshold region with decreasing ?K, the two composite materials exhibit similar FCG mechanism that is dominated by debonding of the reinforcement–matrix interface, and followed by void nucleation and coalescence in the Al matrix. At higher ?K in the stable- or mid-crack-growth region, in addition to the debonding of the particle–matrix and whisker–matrix interface caused by cycle-by-cycle crack growth at the interface, the FCG is affected predominantly by striation formation in the Al matrix. Moreover, void nucleation and coalescence in the Al matrix and transgranular fracture of SiC particles and Al2O3 whiskers at high ?K are also observed as the local unstable fracture mechanisms.However, the FCG of the monolithic Al alloy is dominated by void nucleation and coalescence at lower ?K, whereas the FCG at higher ?K is controlled mainly by striation formation in the Al grains, and followed by void nucleation and coalescence in the Si clusters.展开更多
Two types of poppet valves were tested, one is a poppet with a sharp-edged seats, and the other is that with a chamfered seat. During the tests, the effects of backpressure and poppet lift on flow characteristics were...Two types of poppet valves were tested, one is a poppet with a sharp-edged seats, and the other is that with a chamfered seat. During the tests, the effects of backpressure and poppet lift on flow characteristics were considered. Cavitation inception was detected by the appearance and rapid growth of a particular low frequency component of the outlet pressure fluctuation of valve when cavitation occurs. Experimental results show cavitation, back pressure, valve opening and its geometrical shape have significant effects on the flow characteristics of valve. The flow coefficient of throttle with water used as working medium is 0 85～0 95 when there is no cavitation. The pressure drop of flow saturation decreases with the increasing of poppet lift. The sharp-edged throttle has stronger anti-cavitation ability than the chamfered one.展开更多
In order to overcome the trade-offbetween strength and ductility in traditional metallic materials,the gradient lamellar structure was fabricated through an ultrasound-aided deep rolling technique in pure Ni with high...In order to overcome the trade-offbetween strength and ductility in traditional metallic materials,the gradient lamellar structure was fabricated through an ultrasound-aided deep rolling technique in pure Ni with high stacking fault energy after heat treatment.The gradient lamellar Ni was successively di-vided into three regions.In-situ micro-tensile tests were performed in different regions to reveal the corresponding microscopic mechanical behaviors.Microscopic characterization techniques were adopted to explore the effects of microstructural parameters and defects on mechanical properties.This work demonstrates that the micro-tensile sample with small lamellar thickness and large aspect ratio possesses excellent strength and ductility when the loading direction is parallel to the long side of lamellar grain boundaries.The finding is helpful to the design of metallic material microstructure with superior com-prehensive properties.On one hand,the reason for high strength is that the strength increases with the decrease of lamellar thickness according to the Hall-Petch effect.Besides,initial dislocation density also participates in the strengthening mechanism.On the other hand,the deformation mechanisms include dislocation slip,grain rotation,and the effects of grain boundaries on dislocations,jointly contributing to good ductility.展开更多
Atomic-scale polar topologies such as skyrmions offer important potential as technological paradigms for future electronic devices.Despite recent advances in the exploration of topological domains in complicated perov...Atomic-scale polar topologies such as skyrmions offer important potential as technological paradigms for future electronic devices.Despite recent advances in the exploration of topological domains in complicated perovskite oxide superlattices,these exotic ferroic orders are unavoidably disrupted at the atomic scale due to intrinsic size effects.Here,based on first-principles calculations,we propose a new strategy to design robust ferroelectricity in atomically thin films by properly twisting 2 monolayers of centrosymmetric SrTiO_(3).Surprisingly,the emerged polarization vectors curl in the plane,forming a polar skyrmion lattice with each skyrmion as small as 1 nm,representing the highest polar skyrmion density to date.The emergent ferroelectricity originates from strong interlayer coupling effects and the resulting unique strain fields with obvious ion displacements,contributing to electric polarization comparable to that of PbTiO_(3).Moreover,we observe ultraflat bands(band width of less than 5 meV)at the valence band edge across a wide range of twist angles,which show widths that are smaller than those of common twisted bilayers of 2-dimensional materials.The present study not only overcomes the critical size limitation for ferroelectricity but also reveals a novel approach for achieving atomic-scale polar topologies,with important potential for applications in skyrmion-based ultrahigh-density memory technologies.展开更多
Straight and Bent nano-cantilever specimens are respectively proposed to investigate the single-mode and mixed-mode crack initiation at the Cu/Si interface edge in nanoscale components. With a minute loading apparatus...Straight and Bent nano-cantilever specimens are respectively proposed to investigate the single-mode and mixed-mode crack initiation at the Cu/Si interface edge in nanoscale components. With a minute loading apparatus, all nanoscale samples are in situ loaded and observed. Numerical analysis is employed to acquire the critical interfacial stress distributions during crack initiation. The stress concentration regions near the edge of Cu/Si interface in all specimens are within the scale of 100 nm, and the critical normal and shear stresses have a circular relation in nanoscale components, which represents the fracture criterion of the interface in nanoscale components.展开更多
Contents of fly ash are important factors for the operation of coal-fired plants. Real-time monitoring of coal and fly ash such as unburned carbon in fly ash can be an indicator of the combustion conditions. Because o...Contents of fly ash are important factors for the operation of coal-fired plants. Real-time monitoring of coal and fly ash such as unburned carbon in fly ash can be an indicator of the combustion conditions. Because of the strong signal intensity and the relative simplicity of the LIBS (Laser- Induced Breakdown Spectroscopy) technique, LIBS can be applicable for real-time composition measurement of coal and fly ash. This research presented here focused on the clarification of the effects of plasma temperature and coexisting materials on quantitative measurement of fly ash contents. Quantitative capability of LIBS was improved using the proposed plasma temperature correction method. The CO2 effect was also discussed to accurately evaluate unburned carbon in fly ash in exhausts. Using the results shown in this study, quantitative measurement of fly ash contents has been improved for wider applications of LIBS to practical fields.展开更多
Self-shaping materials such as shape memory polymers have recently drawn considerable attention owing to their high shape-changing ability in response to changes in ambient conditions, and thereby have promising appli...Self-shaping materials such as shape memory polymers have recently drawn considerable attention owing to their high shape-changing ability in response to changes in ambient conditions, and thereby have promising applications in the biomedical, biosensing, soft robotics and aerospace fields. Their design is a crucial issue of both theoretical and technological interest. Motivated by the shape-changing ability of Towel Gourd tendril helices during swelling/deswelling, we present a strategy for realizing self-shaping function through the deformation of micro/nanohelices. To guide the design and fabrication of selfshaping materials, the shape equations of bent configurations, twisted belts, and helices of slender chiral composite are developed using the variation method. Furthermore, it is numerically shown that the shape changes of a chiral composite can be tuned by the deformation of micro/nanohelices and the fabricated fiber directions. This work paves a new way to create self-shaping composites.展开更多
Gas exchange in human lungs is established by several flow mechanisms. In the present study, the features of gas displacement in the distal bronchioles of a human lung are investigated by both numerical calculation an...Gas exchange in human lungs is established by several flow mechanisms. In the present study, the features of gas displacement in the distal bronchioles of a human lung are investigated by both numerical calculation and experimental observation with particle image velocimetry. The effect of respiration frequency is considered, such as high frequency oscillatory ventilation. By comparing the obtained results, it has been found that the redistribution of gas is attributed to irreversible flow, which is remarkable in higher frequencies oscillation with even lower tidal volumes. Owing to the continuous driving, a time-averaged net flow was induced and intensified by the oscillation. Thus, the gas in the centre region penetrated the deeper region and the outer gas was evacuated to the upper region. Consequently, this streaming contributes to prompt gas replacement. Furthermore, we analysed the effect of the respiration wave form to consider the flow acceleration. From this inspection, it was found that the enhanced inertial force tends to encourage the irreversible flow.展开更多
An assembly robot needs to be capable of executing an assembly task robustly under various uncertainties.To attain this goal,we use a task sequence tree model originally proposed for manual assembly.This model regards...An assembly robot needs to be capable of executing an assembly task robustly under various uncertainties.To attain this goal,we use a task sequence tree model originally proposed for manual assembly.This model regards an assembly task under uncertainties as a transformation of the contact state concept.The concept may contain several contact states with probabilities but these are transformed through a series of task elements into the contact state concept having only the goal state at the end.The transformed contact state concept can be classified according to the terminal condition of each task element.Thus,the whole assembly task can be designed as a tree-shaped contingent strategy called a task sequence tree.This paper proposes a systematic approach for reconfiguring a task sequence tree model for application to a robotic assembly task.In addition,by taking a 2D peg-in-hole insertion task to be performed by a robot equipped with a force sensor as an example,we confirm that the proposed approach can provide a robust motion strategy for the task and that the robot can actually execute the task robustly under bounded uncertainty according to the strategy.展开更多
The aim of the experiment is to analyze and view the distribution of gangue withdifferent particle sizes in mine spoil pile cross section.According to the Dimensionalmethod,'Pi'theorem was employed first to ab...The aim of the experiment is to analyze and view the distribution of gangue withdifferent particle sizes in mine spoil pile cross section.According to the Dimensionalmethod,'Pi'theorem was employed first to abbreviate ten physical and mechanical parametersto three dimensionless groups, and then the similarity criterion and coefficient ofthe experiment were determined and calculated based on particle size distribution curve.The similarity model was designed and constructed to represent the process of the minespoil pile.The profile of the final model shows that the small sized particles mainly composethe upper zone of the mine spoil pile, while the bottom of the pile is dominated bybigger sized particles, and the intermediate section presents a zigzag stripe cross-beddingstructure which is composed by small-medium scale particles and medium-large scaleparticles.Each stripe has two critical angles: one is the angle in which gangue particlescan maintain their stability condition, with approximate range from 24° to 26°; and theother is the angle in which particles can stop gliding downwards, approximately varyingfrom 34° to 36°.展开更多
This paper discusses a force control problem for a flexible Timoshenko arm. The effect of shear deformation and the effect of rotary inertia are considered in Timoshenko beam theory. Most of the research about force c...This paper discusses a force control problem for a flexible Timoshenko arm. The effect of shear deformation and the effect of rotary inertia are considered in Timoshenko beam theory. Most of the research about force control of the flexible arm is based on Euler Bernoulli beam theory. There are a few researches about force control of the flexible arm using Timoshenko beam theory. The aim of the force control is to control the contact force at the contact point. To solve this problem, we propose a simple controller using Timoshenko beam theory. Finally, we describe simulation results using a numerical inversion of Laplace transform carried out to investigate the validity of the proposed controller for the force control problem. The results of the time response show the transverse displacement, the angle of deflection, the slider position, the rotational angle and the contact force toward the desired their values.展开更多
The optimal design of shape memory alloys(SMAs)with specific properties is crucial for the innovative application in advanced technologies.Herein,inspired by the recently proposed design concept of concentration modul...The optimal design of shape memory alloys(SMAs)with specific properties is crucial for the innovative application in advanced technologies.Herein,inspired by the recently proposed design concept of concentration modulation,we explore martensitic transformation(MT)in and design the mechanical properties of Ti-Nb nanocomposites by combining high-throughput phase-field simulations and machine learning(ML)approaches.Systematic phase-field simulations generate data of the mechanical properties for various nanocomposites constructed by four macroscopic degrees of freedom.An ML-assisted strategy is adopted to perform multiobjective optimization of the mechanical properties,through which promising nanocomposite configurations are prescreened for the next set of phase-field simulations.The ML-guided simulations discover an optimized nanocomposite,composed of Nb-rich matrix and Nb-lean nanofillers,that exhibits a combination of mechanical properties,including ultralow modulus,linear superelasticity,and near-hysteresis-free in a loading-unloading cycle.The exceptional mechanical properties in the nanocomposite originate from optimized continuous MT rather than a sharp first-order transition,which is common in typical SMAs.This work demonstrates the great potential of ML-guided phase-field simulations in the design of advanced materials with extraordinary properties.展开更多
We present numerical simulations of a new system of micro-pump based on the thermal creep effect described by the kinetic theory of gases.This device is made of a simple smooth and curved channel with a periodic tempe...We present numerical simulations of a new system of micro-pump based on the thermal creep effect described by the kinetic theory of gases.This device is made of a simple smooth and curved channel with a periodic temperature distribution.Using the Boltzmann-BGK model as the governing equation for the gas flow,we develop a numerical method based on a deterministic finite volume scheme,implicit in time,with an implicit treatment of the boundary conditions.This method is comparatively less sensitive to the slow flow velocity than the usual Direct Simulation Monte Carlo method in case of long devices,and turns out to be accurate enough to compute macroscopic quantities like the pressure field in the channel.Our simulations show the ability of the device to produce a one-way flow that has a pumping effect.展开更多
Owing to the increasing worldwide demand for natural gas,the development of a large submerged combustion vaporizer is required.Its burner is equipped with a water spray nozzle to reduce nitrogen oxides,and a practi-ca...Owing to the increasing worldwide demand for natural gas,the development of a large submerged combustion vaporizer is required.Its burner is equipped with a water spray nozzle to reduce nitrogen oxides,and a practi-cal simulation method is required for the optimal design.The non-adiabatic flamelet approach can predict the combustion emissions and is useful for reducing simulation costs.However,as the number of control variables increases,the database requires larger memory and cannot be dealt with by general computers.In this study,an artificial neural network(ANN)model based on a five-dimensional flamelet database,which includes the effects of heat loss and vapor concentration by sprayed water evaporation,is developed.Furthermore,large eddy sim-ulations(LESs)for turbulent combustion fields with and without water spray are conducted employing flamelet generated manifold(FGM)approach with this ANN model,and the validity is investigated.For comparison,a lab-scale burner equipped with a water spray nozzle is manufactured,and combustion experiments with and without water spray are conducted.The results show that CO,NO,temperature,and reaction rate of progress variable predicted by the present ANN model are in good agreement with those of a five-dimensional flamelet database.In the condition without water spray,the flame behavior predicted by the LES employing the FGM/ANN ap-proach is in good agreement with that employing the conventional FGM approach,while indicating much lower memory,although there appeared some quantitative discrepancies in the temperature against the experiment probably partially because of the insufficiency of the FGM approach for the present complex flame structure.In the condition with water spray,the LES employing the FGM/ANN approach is able to capture the effect of the water spray on the flame behavior in the experiment,such that the water spray decreases the temperature,which causes the decrease in NO but increase in CO.展开更多
Low-dimensional multiferroic metals characterized by the simultaneous coexistence of ferroelectricity,conductivity,and magnetism hold tremendous potential for scientific and technological endeavors.However,the mutuall...Low-dimensional multiferroic metals characterized by the simultaneous coexistence of ferroelectricity,conductivity,and magnetism hold tremendous potential for scientific and technological endeavors.However,the mutually exclusive mechanisms among these properties impede the discovery of multifunctional conducting multiferroics,especially at the atomic-scale.Here,based on first-principles calculations,we design and demonstrate intrinsic one-dimensional(1D)ferroelectrics and carrier dopinginduced metallic multiferroics in an atomicWOF4 wire.TheWOF4 atomic wire that can be derived from a 1D van derWaals crystal exhibits pronounced ferroelectricity manifested in the form of large cooperative atomic displacements.By performing Monte Carlo simulations with an effective Hamiltonian method,we obtain the nanowire that can sustain a high Curie temperature,indicating its potential for roomtemperature applications.Moreover,doping with electrons is found to induce magnetism and metallic conductivity that coexists with the ferroelectric distortion in the nanowire.These appealing properties in conjunction with the experimental feasibility enable the doped WOF4 nanowire to act as a promising atomic-scale multifunctional material.展开更多
The coexistence of ferroelectricity,conductivity,and magnetism in a single-phase material has attracted considerable attention due to fundamental interest and tremendous technological potential.However,their mutually ...The coexistence of ferroelectricity,conductivity,and magnetism in a single-phase material has attracted considerable attention due to fundamental interest and tremendous technological potential.However,their mutually exclusive mechanisms hinder the discovery of multifunctional conducting multiferroics.Here,we propose a new material design approach for electron engineering to enable these conflicting properties to coexist.We use first principles calculations to demonstrate that appropriate mechanical strain can turn the excess electrons in doped BaTiO_(3) from a free-carrier configuration to a localized polaronic state by modulating the electron–phonon coupling.The resulting localized spin-polarized electron survives the host ferroelectricity and consequently manifests as a multiferroic polaron.The multiferroic properties coexist with the electronic conductivity arising from the highhopping mobility of the polaron,which enables the doped epitaxial BaTiO_(3) to act as a multiferroic conducting material.This mechanical control over the electron configuration is a potential path toward unusual coexisting properties.展开更多
Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal o...Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal orientation,and especially why the two-wave structure depends on the crystal orientation.In this work,molecular dynamics simulations of shock compressions in copper single crystals are performed to investigate the orientation dependence of shock responses and the corresponding deformation mechanisms.Four copper single crystals with[001],[011],[012],and[123]crystal orientations along the depth direction are investigated.The[011],[012],and[123]crystal orientations of copper single crystals show distinct two-wave structures in their shock responses,while such a two-wave structure in the shock response is not seen for those orientations having a[001]crystal orientation.The potential causes are analyzed by considering the propagation velocities of both elastic and plastic waves.We develop a technique for identifying twin structures in face-centered cubic crystals and this technique can effectively identify the twin structure.The morphology of shock-induced defects(e.g.,dislocations and twins)shows the significant dependence of crystal orientation and the mechanisms behind these are discussed in detail.Finally,the Johnson-Cook constitutive model describing dynamic deformations at high temperatures and high strain rates is used to analyze the relationships between the shock responses and microscopic defects.The predictions of the Johnson-Cook constitutive model are consistent with the results of the molecular dynamics simulations.展开更多
文摘The process of contaminant transport is a problem of multicomponent and multiphase flow in unsaturated zone. Under the presupposition that gas existence affects water transport, a coupled mathematical model of contaminant transport in unsaturated zone has been established based on fluid_solid interaction mechanics theory. The asymptotical solutions to the nonlinear coupling mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of pore pressure, pore water velocity and contaminant concentration in unsaturated zone has been presented under the conditions of with coupling and without coupling gas phase. An example problem was used to provide a quantitative verification and validation of the model. The asymptotical solution was compared with Faust model solution. The comparison results show reasonable agreement between asymptotical solution and Faust solution, and the gas effect and media deformation has a large impact on the contaminant transport. The theoretical basis is provided for forecasting contaminant transport and the determination of the relationship among pressure_saturation_permeability in laboratory.
基金supported by National Natural Science Foundation of China(Nos.51975380,52005377)China Postdoctoral Science Foundation(No.2020M681346)Japan Society for the Promotion of Science(No.JP21J13418)。
文摘Based on the growth mechanism of natural biological branching systems and inspiration from the morphology of plant root tips,a bionic design method called Improved Adaptive Growth Method(IAGM)has been proposed in the authors’previous research and successfully applied to the reinforcement optimization of three-dimensional box structures with respect to natural frequencies.However,as a kind of ground structure methods,the final layout patterns of stiffeners obtained by using the IAGM are highly subjected to their ground structures,which restricts the optimization effect and freedom to further improve the dynamic performance of structures.To solve this problem,a novel post-processing geometry and size optimization approach is proposed in this article.This method takes the former layout optimization result as start,and iteratively finds the optimal layout angles,locations,and lengths of stiffeners with a few design variables by optimizing the positions of some specific node lines called active node lines.At the same time,thick-nesses of stiffeners are also optimized to further improve natural frequencies of three-dimensional box structures.Using this method,stiffeners can be successfully separated from their ground structures and further effectively improve natural frequencies of three-dimensional box structures with less material consumption.Typical numerical examples are illustrated to validate the effectiveness and advantages of the suggested method.
基金the Ministry of Education, Science, Sports and Culture of the Government of Japan for providing financial support during this research work
文摘The fatigue crack growth(FCG) mechanism of a cast hybrid metal matrix composite(MMC) reinforced with SiC particles and Al2O3 whiskers was investigated. For comparison, the FCG mechanisms of a cast MMC with Al2O3 whiskers and a cast Al alloy were also investigated. The results show that the FCG mechanism is observed in the near-threshold and stable-crack-growth regions.The hybrid MMC shows a higher threshold stress intensity factor range, ?Kth, than the MMC with Al2O3 and Al alloy, indicating better resistance to crack growth in a lower stress intensity factor range, ?K. In the near-threshold region with decreasing ?K, the two composite materials exhibit similar FCG mechanism that is dominated by debonding of the reinforcement–matrix interface, and followed by void nucleation and coalescence in the Al matrix. At higher ?K in the stable- or mid-crack-growth region, in addition to the debonding of the particle–matrix and whisker–matrix interface caused by cycle-by-cycle crack growth at the interface, the FCG is affected predominantly by striation formation in the Al matrix. Moreover, void nucleation and coalescence in the Al matrix and transgranular fracture of SiC particles and Al2O3 whiskers at high ?K are also observed as the local unstable fracture mechanisms.However, the FCG of the monolithic Al alloy is dominated by void nucleation and coalescence at lower ?K, whereas the FCG at higher ?K is controlled mainly by striation formation in the Al grains, and followed by void nucleation and coalescence in the Si clusters.
文摘Two types of poppet valves were tested, one is a poppet with a sharp-edged seats, and the other is that with a chamfered seat. During the tests, the effects of backpressure and poppet lift on flow characteristics were considered. Cavitation inception was detected by the appearance and rapid growth of a particular low frequency component of the outlet pressure fluctuation of valve when cavitation occurs. Experimental results show cavitation, back pressure, valve opening and its geometrical shape have significant effects on the flow characteristics of valve. The flow coefficient of throttle with water used as working medium is 0 85～0 95 when there is no cavitation. The pressure drop of flow saturation decreases with the increasing of poppet lift. The sharp-edged throttle has stronger anti-cavitation ability than the chamfered one.
基金supported by the National Natural Science Foun-dation of China(grant Nos.52222505,51975211,and 51725503)Shanghai Rising-Star Program(grant No.20QA1402500)Foun-dation Strengthening Plan Technology Field Fund Project(grant No.2019-JCJQ-JJ-454).
文摘In order to overcome the trade-offbetween strength and ductility in traditional metallic materials,the gradient lamellar structure was fabricated through an ultrasound-aided deep rolling technique in pure Ni with high stacking fault energy after heat treatment.The gradient lamellar Ni was successively di-vided into three regions.In-situ micro-tensile tests were performed in different regions to reveal the corresponding microscopic mechanical behaviors.Microscopic characterization techniques were adopted to explore the effects of microstructural parameters and defects on mechanical properties.This work demonstrates that the micro-tensile sample with small lamellar thickness and large aspect ratio possesses excellent strength and ductility when the loading direction is parallel to the long side of lamellar grain boundaries.The finding is helpful to the design of metallic material microstructure with superior com-prehensive properties.On one hand,the reason for high strength is that the strength increases with the decrease of lamellar thickness according to the Hall-Petch effect.Besides,initial dislocation density also participates in the strengthening mechanism.On the other hand,the deformation mechanisms include dislocation slip,grain rotation,and the effects of grain boundaries on dislocations,jointly contributing to good ductility.
基金supported by the National Natural Science Foundation of China(grant nos.12172370,12432007,12272338,12192214,and 12204496)the Natural Science Foundation of Ningbo City(grant nos.2022J295 and 2023J360)+2 种基金JSPS KAKENHI(grant nos.JP23H00159,JP23K17720,and JP20H05653)JST FOREST Program(grant no.JPMJFR222H)JSPS International Research Fellow(grant no.P22065).
文摘Atomic-scale polar topologies such as skyrmions offer important potential as technological paradigms for future electronic devices.Despite recent advances in the exploration of topological domains in complicated perovskite oxide superlattices,these exotic ferroic orders are unavoidably disrupted at the atomic scale due to intrinsic size effects.Here,based on first-principles calculations,we propose a new strategy to design robust ferroelectricity in atomically thin films by properly twisting 2 monolayers of centrosymmetric SrTiO_(3).Surprisingly,the emerged polarization vectors curl in the plane,forming a polar skyrmion lattice with each skyrmion as small as 1 nm,representing the highest polar skyrmion density to date.The emergent ferroelectricity originates from strong interlayer coupling effects and the resulting unique strain fields with obvious ion displacements,contributing to electric polarization comparable to that of PbTiO_(3).Moreover,we observe ultraflat bands(band width of less than 5 meV)at the valence band edge across a wide range of twist angles,which show widths that are smaller than those of common twisted bilayers of 2-dimensional materials.The present study not only overcomes the critical size limitation for ferroelectricity but also reveals a novel approach for achieving atomic-scale polar topologies,with important potential for applications in skyrmion-based ultrahigh-density memory technologies.
基金Project supported by the Foundation of President of China Academy of Engineering Physics(CAEP)(No.2014-1-097)the Special Fund from Institute of Systems Engineering of CAEP(No.2013KJZ02)+2 种基金the National Natural Science Foundation of China(No.11302205)the Key Project of Science and Technology Development Foundation of CAEP(No.2014A0203006)the key subject ‘Computational Solid Mechanics’ of CAEP
文摘Straight and Bent nano-cantilever specimens are respectively proposed to investigate the single-mode and mixed-mode crack initiation at the Cu/Si interface edge in nanoscale components. With a minute loading apparatus, all nanoscale samples are in situ loaded and observed. Numerical analysis is employed to acquire the critical interfacial stress distributions during crack initiation. The stress concentration regions near the edge of Cu/Si interface in all specimens are within the scale of 100 nm, and the critical normal and shear stresses have a circular relation in nanoscale components, which represents the fracture criterion of the interface in nanoscale components.
文摘Contents of fly ash are important factors for the operation of coal-fired plants. Real-time monitoring of coal and fly ash such as unburned carbon in fly ash can be an indicator of the combustion conditions. Because of the strong signal intensity and the relative simplicity of the LIBS (Laser- Induced Breakdown Spectroscopy) technique, LIBS can be applicable for real-time composition measurement of coal and fly ash. This research presented here focused on the clarification of the effects of plasma temperature and coexisting materials on quantitative measurement of fly ash contents. Quantitative capability of LIBS was improved using the proposed plasma temperature correction method. The CO2 effect was also discussed to accurately evaluate unburned carbon in fly ash in exhausts. Using the results shown in this study, quantitative measurement of fly ash contents has been improved for wider applications of LIBS to practical fields.
基金supported by the National Basic Research Program of China(2012CB937500)Grants-in-Aid for Scientific Research(21226005)from the Japan Society for the Promotion of Science(JSPS)+1 种基金the National Natural Science Foundation of China(11272230 and 11172207)the Basic Application and Advanced Technology Research Project in Tianjin(11JCYBJC09700)
文摘Self-shaping materials such as shape memory polymers have recently drawn considerable attention owing to their high shape-changing ability in response to changes in ambient conditions, and thereby have promising applications in the biomedical, biosensing, soft robotics and aerospace fields. Their design is a crucial issue of both theoretical and technological interest. Motivated by the shape-changing ability of Towel Gourd tendril helices during swelling/deswelling, we present a strategy for realizing self-shaping function through the deformation of micro/nanohelices. To guide the design and fabrication of selfshaping materials, the shape equations of bent configurations, twisted belts, and helices of slender chiral composite are developed using the variation method. Furthermore, it is numerically shown that the shape changes of a chiral composite can be tuned by the deformation of micro/nanohelices and the fabricated fiber directions. This work paves a new way to create self-shaping composites.
文摘Gas exchange in human lungs is established by several flow mechanisms. In the present study, the features of gas displacement in the distal bronchioles of a human lung are investigated by both numerical calculation and experimental observation with particle image velocimetry. The effect of respiration frequency is considered, such as high frequency oscillatory ventilation. By comparing the obtained results, it has been found that the redistribution of gas is attributed to irreversible flow, which is remarkable in higher frequencies oscillation with even lower tidal volumes. Owing to the continuous driving, a time-averaged net flow was induced and intensified by the oscillation. Thus, the gas in the centre region penetrated the deeper region and the outer gas was evacuated to the upper region. Consequently, this streaming contributes to prompt gas replacement. Furthermore, we analysed the effect of the respiration wave form to consider the flow acceleration. From this inspection, it was found that the enhanced inertial force tends to encourage the irreversible flow.
基金Project (No.19GS0208) supported by the Grant-in-Aid for Creative Scientific Research 2007–2011 funded by the Ministry of Education,Culture,Sports,Science and Technology,Japan
文摘An assembly robot needs to be capable of executing an assembly task robustly under various uncertainties.To attain this goal,we use a task sequence tree model originally proposed for manual assembly.This model regards an assembly task under uncertainties as a transformation of the contact state concept.The concept may contain several contact states with probabilities but these are transformed through a series of task elements into the contact state concept having only the goal state at the end.The transformed contact state concept can be classified according to the terminal condition of each task element.Thus,the whole assembly task can be designed as a tree-shaped contingent strategy called a task sequence tree.This paper proposes a systematic approach for reconfiguring a task sequence tree model for application to a robotic assembly task.In addition,by taking a 2D peg-in-hole insertion task to be performed by a robot equipped with a force sensor as an example,we confirm that the proposed approach can provide a robust motion strategy for the task and that the robot can actually execute the task robustly under bounded uncertainty according to the strategy.
基金Supported by the National Natural Science Foundation of China(50874102,50974070)
文摘The aim of the experiment is to analyze and view the distribution of gangue withdifferent particle sizes in mine spoil pile cross section.According to the Dimensionalmethod,'Pi'theorem was employed first to abbreviate ten physical and mechanical parametersto three dimensionless groups, and then the similarity criterion and coefficient ofthe experiment were determined and calculated based on particle size distribution curve.The similarity model was designed and constructed to represent the process of the minespoil pile.The profile of the final model shows that the small sized particles mainly composethe upper zone of the mine spoil pile, while the bottom of the pile is dominated bybigger sized particles, and the intermediate section presents a zigzag stripe cross-beddingstructure which is composed by small-medium scale particles and medium-large scaleparticles.Each stripe has two critical angles: one is the angle in which gangue particlescan maintain their stability condition, with approximate range from 24° to 26°; and theother is the angle in which particles can stop gliding downwards, approximately varyingfrom 34° to 36°.
文摘This paper discusses a force control problem for a flexible Timoshenko arm. The effect of shear deformation and the effect of rotary inertia are considered in Timoshenko beam theory. Most of the research about force control of the flexible arm is based on Euler Bernoulli beam theory. There are a few researches about force control of the flexible arm using Timoshenko beam theory. The aim of the force control is to control the contact force at the contact point. To solve this problem, we propose a simple controller using Timoshenko beam theory. Finally, we describe simulation results using a numerical inversion of Laplace transform carried out to investigate the validity of the proposed controller for the force control problem. The results of the time response show the transverse displacement, the angle of deflection, the slider position, the rotational angle and the contact force toward the desired their values.
基金The work is supported by the National Key R&D Program of China(No.2018YFB0704404)the National Natural Science Foundation of China(Grant Nos.11802169 and 12172370).
文摘The optimal design of shape memory alloys(SMAs)with specific properties is crucial for the innovative application in advanced technologies.Herein,inspired by the recently proposed design concept of concentration modulation,we explore martensitic transformation(MT)in and design the mechanical properties of Ti-Nb nanocomposites by combining high-throughput phase-field simulations and machine learning(ML)approaches.Systematic phase-field simulations generate data of the mechanical properties for various nanocomposites constructed by four macroscopic degrees of freedom.An ML-assisted strategy is adopted to perform multiobjective optimization of the mechanical properties,through which promising nanocomposite configurations are prescreened for the next set of phase-field simulations.The ML-guided simulations discover an optimized nanocomposite,composed of Nb-rich matrix and Nb-lean nanofillers,that exhibits a combination of mechanical properties,including ultralow modulus,linear superelasticity,and near-hysteresis-free in a loading-unloading cycle.The exceptional mechanical properties in the nanocomposite originate from optimized continuous MT rather than a sharp first-order transition,which is common in typical SMAs.This work demonstrates the great potential of ML-guided phase-field simulations in the design of advanced materials with extraordinary properties.
基金This research was supported partially by“Projet International de Cooperation Scientifique(PICS)”of CNRS(Grant No.3195)by grants-in-aid for scientific research from JSPS(Nos.17656033 and 20360046).
文摘We present numerical simulations of a new system of micro-pump based on the thermal creep effect described by the kinetic theory of gases.This device is made of a simple smooth and curved channel with a periodic temperature distribution.Using the Boltzmann-BGK model as the governing equation for the gas flow,we develop a numerical method based on a deterministic finite volume scheme,implicit in time,with an implicit treatment of the boundary conditions.This method is comparatively less sensitive to the slow flow velocity than the usual Direct Simulation Monte Carlo method in case of long devices,and turns out to be accurate enough to compute macroscopic quantities like the pressure field in the channel.Our simulations show the ability of the device to produce a one-way flow that has a pumping effect.
基金The temperature measurements and PIA were supported by Prof.M.Nishioka of University of Tsukuba and Prof.K.Nishino of Yokohama National University,respectively.This work was partially supported by MEXT as"Program for Promoting Researches on the Supercomputer Fu-gaku"(Digital Twins of Real World’s Clean Energy Systems with Inte-grated Utilization of Super-simulation and AI).
文摘Owing to the increasing worldwide demand for natural gas,the development of a large submerged combustion vaporizer is required.Its burner is equipped with a water spray nozzle to reduce nitrogen oxides,and a practi-cal simulation method is required for the optimal design.The non-adiabatic flamelet approach can predict the combustion emissions and is useful for reducing simulation costs.However,as the number of control variables increases,the database requires larger memory and cannot be dealt with by general computers.In this study,an artificial neural network(ANN)model based on a five-dimensional flamelet database,which includes the effects of heat loss and vapor concentration by sprayed water evaporation,is developed.Furthermore,large eddy sim-ulations(LESs)for turbulent combustion fields with and without water spray are conducted employing flamelet generated manifold(FGM)approach with this ANN model,and the validity is investigated.For comparison,a lab-scale burner equipped with a water spray nozzle is manufactured,and combustion experiments with and without water spray are conducted.The results show that CO,NO,temperature,and reaction rate of progress variable predicted by the present ANN model are in good agreement with those of a five-dimensional flamelet database.In the condition without water spray,the flame behavior predicted by the LES employing the FGM/ANN ap-proach is in good agreement with that employing the conventional FGM approach,while indicating much lower memory,although there appeared some quantitative discrepancies in the temperature against the experiment probably partially because of the insufficiency of the FGM approach for the present complex flame structure.In the condition with water spray,the LES employing the FGM/ANN approach is able to capture the effect of the water spray on the flame behavior in the experiment,such that the water spray decreases the temperature,which causes the decrease in NO but increase in CO.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172370,11874059 and 12174405)Natural Science Foundation of Zhejiang Provincial(Grant Nos.LY22E020012 and LR19A040002)+1 种基金National Key R&D Program of China(Grant No.2022YFB3807601),the Key Research Project of Zhejiang Laboratory(Grant No.2021PE0AC02)Zhejiang Laboratory Open Research Project(Grant No.K2022PE0AB06)and JSPS International Research Fellow(No.P22065).
文摘Low-dimensional multiferroic metals characterized by the simultaneous coexistence of ferroelectricity,conductivity,and magnetism hold tremendous potential for scientific and technological endeavors.However,the mutually exclusive mechanisms among these properties impede the discovery of multifunctional conducting multiferroics,especially at the atomic-scale.Here,based on first-principles calculations,we design and demonstrate intrinsic one-dimensional(1D)ferroelectrics and carrier dopinginduced metallic multiferroics in an atomicWOF4 wire.TheWOF4 atomic wire that can be derived from a 1D van derWaals crystal exhibits pronounced ferroelectricity manifested in the form of large cooperative atomic displacements.By performing Monte Carlo simulations with an effective Hamiltonian method,we obtain the nanowire that can sustain a high Curie temperature,indicating its potential for roomtemperature applications.Moreover,doping with electrons is found to induce magnetism and metallic conductivity that coexists with the ferroelectric distortion in the nanowire.These appealing properties in conjunction with the experimental feasibility enable the doped WOF4 nanowire to act as a promising atomic-scale multifunctional material.
基金The authors acknowledge the financial support for T.X.by the National Natural Science Foundation of China(Grant no.11802169)for T.S.and T.K.by JSPS KAKENHI(25000012,26289006,15K13831,and 17H03145)for J.W.by the Fundamental Research Funds for the Central Universities 2018XZZX001-05,and for T.Y.Z.by the 111 project(No.D16002)from the State Administration of Foreign Experts Affairs and the Ministry of Education,PRC.
文摘The coexistence of ferroelectricity,conductivity,and magnetism in a single-phase material has attracted considerable attention due to fundamental interest and tremendous technological potential.However,their mutually exclusive mechanisms hinder the discovery of multifunctional conducting multiferroics.Here,we propose a new material design approach for electron engineering to enable these conflicting properties to coexist.We use first principles calculations to demonstrate that appropriate mechanical strain can turn the excess electrons in doped BaTiO_(3) from a free-carrier configuration to a localized polaronic state by modulating the electron–phonon coupling.The resulting localized spin-polarized electron survives the host ferroelectricity and consequently manifests as a multiferroic polaron.The multiferroic properties coexist with the electronic conductivity arising from the highhopping mobility of the polaron,which enables the doped epitaxial BaTiO_(3) to act as a multiferroic conducting material.This mechanical control over the electron configuration is a potential path toward unusual coexisting properties.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972165,and 11502085)the Japan Society for the Promotion of Science(Grant No.P18067)the Fundamental Research Funds for the Central Universities of China(Grant No.2016YXMS097)。
文摘Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal orientation,and especially why the two-wave structure depends on the crystal orientation.In this work,molecular dynamics simulations of shock compressions in copper single crystals are performed to investigate the orientation dependence of shock responses and the corresponding deformation mechanisms.Four copper single crystals with[001],[011],[012],and[123]crystal orientations along the depth direction are investigated.The[011],[012],and[123]crystal orientations of copper single crystals show distinct two-wave structures in their shock responses,while such a two-wave structure in the shock response is not seen for those orientations having a[001]crystal orientation.The potential causes are analyzed by considering the propagation velocities of both elastic and plastic waves.We develop a technique for identifying twin structures in face-centered cubic crystals and this technique can effectively identify the twin structure.The morphology of shock-induced defects(e.g.,dislocations and twins)shows the significant dependence of crystal orientation and the mechanisms behind these are discussed in detail.Finally,the Johnson-Cook constitutive model describing dynamic deformations at high temperatures and high strain rates is used to analyze the relationships between the shock responses and microscopic defects.The predictions of the Johnson-Cook constitutive model are consistent with the results of the molecular dynamics simulations.
