The study of irradiation hardening and embrittlement is critically important for the development of next-generation structural materials tolerant to neutron irradiation,and could dramatically affect the approach to th...The study of irradiation hardening and embrittlement is critically important for the development of next-generation structural materials tolerant to neutron irradiation,and could dramatically affect the approach to the design of components for advanced nuclear reactors.In addition,a growing interest is observed in the field of research and development of irradiation-resistant materials.This review aims to provide an overview of the theoretical development related to irradiation hardening and embrittlement at moderate irradiation conditions achieved in recent years,which can help extend our fundamental knowledge on nuclear structural materials.After a general introduction to the irradiation effects on metallic materials,recent research progress covering theoretical modelling is summarized for different types of structural materials.The fundamental mechanisms are elucidated within a wide range of temporal and spatial scales.This review closes with the current understanding of irradiation hardening and embrittlement,and puts some perspectives deserving further study.展开更多
In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide （FW） backward wave oscillator （BWO） are described. On the whole, these equations are mainly classified into sm...In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide （FW） backward wave oscillator （BWO） are described. On the whole, these equations are mainly classified into small signal model （SSM）, large signal model （LSM）, and simplified small signal model （SSSM）. Using these linear and nonlinear one-dimensional （1D） models, the oscillation characteristics of the FW BWO of a given configuration of slow wave struc- ture （SWS） can be calculated by numerical iteration algorithm, which is more time efficient than three-dimensional （3D） particle-in-cell （PIC） simulation. The SSSM expressed by analytical formulas is innovatively derived for determining the initial values of the FW SWS conveniently. The dispersion characteristics of the FW are obtained by equivalent circuit analysis. The space charge effect, the end reflection effect, the lossy wall effect, and the relativistic effect are all considered in our models to offer more accurate results. The design process of the FW BWO tube with output power of watt scale in a frequency range between 215 GHz and 225 GHz based on these 1D models is demonstrated. The 3D PIC method is adopted to verify the theoretical design results, which shows that they are in good agreement with each other.展开更多
The title complexes were modeled using the semiempirical MOPAC and the newly developed SPARKLE paramerters of the lanthanides. The calculated bond dis tances and angles agreed well with those found from crystal struct...The title complexes were modeled using the semiempirical MOPAC and the newly developed SPARKLE paramerters of the lanthanides. The calculated bond dis tances and angles agreed well with those found from crystal structure measuremen ts. This technique allows us to screen a large number of molecules and get struc tural information within a very short time.展开更多
Axial piston pumps have been widely used in aircraft hydraulic systems to supply the system with pressurized fluid. The continuous improvement of the aircraft performance has put forward the demand on aviation piston ...Axial piston pumps have been widely used in aircraft hydraulic systems to supply the system with pressurized fluid. The continuous improvement of the aircraft performance has put forward the demand on aviation piston pumps for high power density, safety, and reliability. The lubricating interfaces in axial piston machines are the key design issue that greatly determines the pump performance and service life. The cylinder block/valve plate interface is one of these critical lubricating interfaces and has received considerable attention from many researchers in the last half century. This study aims to review the state-of-the-art literature on the cylinder block/valve plate interface comprehensively and systematically. First, we introduce various theoretical models developed to investigate the lubrication behaviors of the interface and compare them in terms of their assumptions and limitations. Second, the experimental studies on the cylinder block/valve plate interface are presented comprehensively, where the involved test rigs are divided into three types according to their fidelity levels and measurement functionality. Third, we summarize some typical approaches of structure optimization, surface shaping, and surface strengthening, which help improve the load-carrying and anti-wear capacities of the interface under severe operating conditions. Finally, the challenges and future trends of the cylinder block/valve plate interface research are discussed briefly.展开更多
Diverse concepts of space developed in history of natural philosophy,mathematics,physics,and other natural or cultural studies form theoretical models of spatial relations,given in human’s experience.Their diversity ...Diverse concepts of space developed in history of natural philosophy,mathematics,physics,and other natural or cultural studies form theoretical models of spatial relations,given in human’s experience.Their diversity is due not only to the multiplicity of philosophical and methodological approaches to the concept of space,but also to the variety of ways,in which spatial relationships can be organized.This variety gives a possibility to distinct autonomous spaces of different types with diverse sets of properties as well as separate spaces with their own ordinal,metrical,and sequential structures.Particularly,various ways of space semiotization in culture generate different types of autonomous and separate spaces:written texts,maps,pictures,chessboards,etc.In the same time,all particular notions of space are included in a general logical class.Its volume and content are covered by the philosophical category of space.Such general category cannot be reduced to mathematical,physical,or other concepts of space elaborated in particular sciences,however,it serves as a philosophical basis for their comparison.展开更多
It has been experimentally observed that,in the perforation of metal plates by a flat-nosed projectile,there exists a plateau phenomenon where the ballistic limit increases slightly with increasing plate thickness,whi...It has been experimentally observed that,in the perforation of metal plates by a flat-nosed projectile,there exists a plateau phenomenon where the ballistic limit increases slightly with increasing plate thickness,which is related to a change in the mode of failure.No theoretical model has so far explained this phenomenon satisfactorily.This paper presents a combined numerical and theoretical study on the perforation of 2024-T351 aluminum plates struck by flat-nosed projectiles.First,numerical simulations are performed to investigate the failure mechanisms/deformation modes of the aluminum plates.Then,a theoretical model is proposed based on the numerical results and the experimental observations within a unified framework.The model takes into account the main energy absorbing mechanisms and the corresponding energies absorbed are determined analytically.In particular,a dimensionless equation is suggested to describe the relationship between global deformations and impact velocity.It transpires that the model predictions are in good agreement with the test data and the numerical results for the perforation of 2024-T351 aluminum plates struck by rigid flat-nosed projectiles in terms of residual velocity,ballistic limit,relationship between global deformations and impact velocity,and transition of failure modes.It also transpires that the present model can predict the“plateau”phenomenon,which shows a slight increase in ballistic limit as plate thickness increases.Furthermore,the energy absorption mechanisms are discussed on the basis of the theoretical analysis.展开更多
During strike-slip fault dislocation,multiple fault planes are commonly observed.The resulting permanent ground deformation can lead to profound structural damage to tunnels.However,existing analytical models do not c...During strike-slip fault dislocation,multiple fault planes are commonly observed.The resulting permanent ground deformation can lead to profound structural damage to tunnels.However,existing analytical models do not consider multiple fault planes.Instead,they concentrate the entire fault displacement onto a single fault plane for analysis,thereby giving rise to notable errors in the calculated results.To address this issue,a refined nonlinear theoretical model was established to analyze the mechanical responses of the tunnels subjected to multiple strike-slip fault dislocations.The analytical model considers the number of fault planes,nonlinear soil‒tunnel interactions,geometric nonlinearity,and fault zone width,leading to a significant improvement in its range of applicability and calculation accuracy.The results of the analytical model are in agreement,both qualitatively and quantitatively,with the model test and numerical results.Then,based on the proposed theoretical model,a sensitivity analysis of parameters was conducted,focusing on the variables such as the number of fault planes,fault plane distance(d),fault displacement ratio(η),burial depth(C),crossing angle(β),tunnel diameter(D),fault zone width(Wf),and strike-slip fault displacement(Δfs).The results show that the peak shear force(Vmax),bending moment(Mmax),and axial force(Nmax)decrease with increasing d.The Vmax of the tunnel is found at the fault plane with the largest fault displacement.C,D,andΔfs contribute to the increases in Vmax,Mmax,and Nmax.Additionally,increasing the number of fault planes reduces Vmax and Mmax,whereas the variation in Nmax remains minimal.展开更多
Steel tube slab (STS) structure, a novel pipe-roof structure, of which steel tubes are connected with flange plates, bolts and concrete, is an increasingly popular supporting structure for underground space developmen...Steel tube slab (STS) structure, a novel pipe-roof structure, of which steel tubes are connected with flange plates, bolts and concrete, is an increasingly popular supporting structure for underground space development. Whilst the load-bearing of pipe-roof structures has been the subject of much research, uncertainties of deformation mechanism and the derivation of reliable calculation methods remain a challenge. For efficient design and wider deployment, this paper presents a bidirectional bending test to investigate the bending stiffnesses, load capacities and deformation mechanisms. The results show that the STS specimens exhibit good ductility and experience bending failure, and their deformation curves follow a half-sine wave upon loading. On this basis, the development of an STS composite slab deformation prediction model is proposed, along with the estimation for its bending stiffness. Theoretical predictions are shown to be in good agreement with the experimental measurements, with a maximum error of less than 15%. The outcomes of this investigation can provide references for the design and application of STS structures.展开更多
Reconstruction during the oxygen evolution reaction(OER)significantly transforms the geometric structure of transition metal compounds,leading to enhanced catalytic performance.However,the resulting structural disorde...Reconstruction during the oxygen evolution reaction(OER)significantly transforms the geometric structure of transition metal compounds,leading to enhanced catalytic performance.However,the resulting structural disorder complicates the development of accurate theoretical models.In this study,CoS2 is used as a model system to establish a framework for rationally modeling reconstructed OER catalysts based on density functional theory(DFT).In the reconstruction process,sulfur atoms are likely to be substituted by oxygen atoms,leading to the formation of the CoOOH phase.Based on the difference in reconstruction degree,we constructed three types of models:doping,heterostructure,and fully reconstructed,representing the reconstruction degree from minimal to full phase transition,respectively.Fully reconstructed models,which account for strain and vacancy effects,effectively simulate the unique coordination environments of reconstructed catalysts.Model e-CoOOH achieves a theoretical overpotential of 0.38 V,outperforming pristine CoOOH(0.56 V),demonstrating that the unique structural features resulting from reconstruction improve OER performance.The doping model and the heterostructure model are helpful to explain the electronic structure and performance transformation of the reconstruction process.This work provides a rational theoretical modeling approach,which is conducive to improving the reliability of the theoretical OER performance of the reconstructed catalyst.展开更多
Lithium–sulfur(Li–S)batteries have been considered as promising battery systems due to their huge advantages on theoretical energy density and rich resources.However,the shuttle effect and sluggish transformation of...Lithium–sulfur(Li–S)batteries have been considered as promising battery systems due to their huge advantages on theoretical energy density and rich resources.However,the shuttle effect and sluggish transformation of soluble lithium polysulfides(LiPSs)hinder the practical application of Li–S batteries.Tremendous sulfur host materials with unique catalytic activity have been exploited to inhibit the shuttle effect and accelerate LiPSs redox reactions,in which theoretical simulations have been widely adopted.This review aims to summarize the fundamentals and applications of theoretical models in sulfur cathodes.Concretely,the integration of theoretical models provides insights into the adsorption and conversion mechanisms of LiPSs and is further utilized in the smart design of catalysts for the exploitation of practical Li–S batteries.Finally,a perspective on the future combination of calculation technology and theoretical models is provided.展开更多
Abstract With the recent products being more reliable, engineers cannot obtain enough failure or degradation information through the design period and even the product lifetime, therefore, accel erated life test （ALT...Abstract With the recent products being more reliable, engineers cannot obtain enough failure or degradation information through the design period and even the product lifetime, therefore, accel erated life test （ALT） ihas become the most popular way to quantify the life characteristics of prod ucts. Test design is the most essential topic, such as testing duration, stress profile, data inference, etc. In this paper, a method and procedure based on theoretical life models is proposed to determine the accelerated stress profile. Firstly, the method for theoretical life calculation is put forward based on the main failure mechanism analysis and the theoretical life models. Secondly, the method is pro vided to determine the accelerated stress profile, including the method to determine the accelerated stress types and the stress range on the basis of the main failure mechanism analysis, the method to determine the acceleration factor and the accelerated stress level based on life quantitative calcula tion models, and the collaborative analysis method of the accelerated test time while taking the mul tiple failure mechanisms into consideration. Lastly, the actuator is taken as an example to describe the procedure of the method and the engineering applicability and the validity are verified.展开更多
Textured surfaces with certain micro/nano structures have been proven to possess some advanced functions,such as reducing friction,improving wear and increasing wettability.Accurate prediction of micro/nano surface te...Textured surfaces with certain micro/nano structures have been proven to possess some advanced functions,such as reducing friction,improving wear and increasing wettability.Accurate prediction of micro/nano surface textures is of great significance for the design,fabrication and application of functional textured surfaces.In this paper,based on the kinematic analysis of cutter teeth,the discretization of ultrasonic machining process,transformation method of coordinate systems and the cubic spline data interpolation,an integrated theoretical model was established to characterize the distribution and geometric features of micro textures on the surfaces machined by different types of ultrasonic vibration-assisted milling(UVAM).Based on the theoretical model,the effect of key process parameters(vibration directions,vibration dimensions,cutting parameters and vibration parameters)on tool trajectories and microtextured surface morphology in UVAM is investigated.Besides,the effect of phase difference on the elliptical shape in 2D/3D ultrasonic elliptical vibration-assisted milling(UEVAM)was analyzed.Compared to conventional numerical models,the method of the cubic spline data interpolation is applied to the simulation of microtextured surface morphology in UVAM,which is more suitable for characterizing the morphological features of microtextured surfaces than traditional methods due to the presence of numerous micro textures.The prediction of surface roughness indicates that the magnitude of ultrasonic amplitude in z-direction should be strictly limited in 1D rotary UVAM,2D and 3D UEVAM due to the unfavorable effect of axial ultrasonic vibration on the surface quality.This study can provide theoretical guidance for the design and fabrication of microtextured surfaces in UVAM.展开更多
The rising motion of single bubble in still liquid is a natural phenomenon,which has high theoretical research significance and engineering application prospect.Experimental observations and numerical simulations for ...The rising motion of single bubble in still liquid is a natural phenomenon,which has high theoretical research significance and engineering application prospect.Experimental observations and numerical simulations for prediction of the rising trajectory of a single bubble in still liquid are being carried out,while the concise but accurate theoretical or mechanism model is still not well developed.In this article,a theoretical model of a single bubble based on experimental observation of flow around bluff body is proposed to predict the rising trajectory of zigzagging bubbles in still water.The prediction correlation of bubble lateral movement frequency and bubble steer angle are established based on three degrees of freedom frame.The model has achieved good trajectory prediction effect in the bubble rising experiment.The average simulation time per unit moving time of bubble is 2.5 s.展开更多
Fathers play an important role in children’s development throughout their lives,and Father-Love Absence(FLA)leads to more behavioral problems,including Non-Suicidal Self-Injury(NSSI).However,there has been no researc...Fathers play an important role in children’s development throughout their lives,and Father-Love Absence(FLA)leads to more behavioral problems,including Non-Suicidal Self-Injury(NSSI).However,there has been no research on the relationship between FLA and NSSI and its influencing mechanism.This study is based on Nock’s integrated theoretical model of NSSI,aiming to explore the influence of FLA on NSSI and further investigate the mechanism of Subjective Vitality(SV)and Forgiveness(FORG).This study recruited 1795 adolescents in central China to complete four scales,including Father-Love Absence Scale(FLAS),The Subjective Vitality Scale(SVS),The Tendency to Forgive Scale(TTF),and Non-Suicidal Self-Injury Scale.FLA can directly affect NSSI,and indirectly affect NSSI through three paths of“FLA→SV→NSSI,FLA→FORG→NSSI,FLA→SV→FORG→NSSI”.These results not only enrich our understanding of the relationship between FLA and NSSI and its internal mechanism but also provide theoretical and practical support for the reduction of NSSI in family education.展开更多
Electrocatalysis has been extensively explored for the storage and conversion of renewable electric power.Understanding the physisorption and chemisorption processes at electrified solid–liquid interfaces(ESLIs)is cr...Electrocatalysis has been extensively explored for the storage and conversion of renewable electric power.Understanding the physisorption and chemisorption processes at electrified solid–liquid interfaces(ESLIs)is crucial for revealing the typical surface restructuring and catalyst dissolution during electrocatalysis.Although advanced in situ tools and theoretical models have been proposed[1,2],identifying the nature of the active sites with atomic-scale spatial resolution remains a challenge,especially at ESLIs.In a recent work published in Nature,Zhang et al.[3]reported a groundbreaking atomic-resolution imaging of the structural dynamics of Cu nanowire catalysts in ESLIs for electrochemical CO_(2)reduction(ECR).展开更多
The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change,respectively.This paper reviews the electrocaloric effect of ferroelectric mat...The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change,respectively.This paper reviews the electrocaloric effect of ferroelectric materials based on different theoretical models.First,it provides four different calculation scales(the first-principle-based effective Hamiltonian,the Landau-Devonshire thermodynamic theory,phase-field simulation,and finite element analysis)to explain the basic theory of calculating the electrocaloric effect.Then,it comprehensively reviews the recent progress of these methods in regulating the electrocaloric effect and the generation mechanism of the electrocaloric effect.Finally,it summarizes and anticipates the exploration of more novel electrocaloric materials based on the framework constructed by the different computational methods.展开更多
A theoretical analysis on the perforation of Weldox 460E steel plates struck by flat-nosed projectiles is presented using a previously developed model within a unified framework.This model contains a dimensionless emp...A theoretical analysis on the perforation of Weldox 460E steel plates struck by flat-nosed projectiles is presented using a previously developed model within a unified framework.This model contains a dimensionless empirical equation to describe the variation of energy absorbed through global deformation as a function of impact velocity.The study further investigates the energy absorption mechanisms of Weldox 460E steel plates,with particular focus on the“plateau”phenomenon,i.e.,limited increase in ballistic limit with increasing plate thickness.This phenomenon is explained and compared with results from previously studied 2024-T351 aluminium plates.The model predictions agree well with experimental data for Weldox 460E steel plates impacted by flat-nosed projectiles,including:relationship between global deformation and impact velocity,ballistic limit,residual velocity,and critical conditions for the transition of failure modes.Moreover,the model effectively predicts the“plateau”phenomenon observed in intermediate plate thickness range.It is also found that the indentation absorption energy contributes a significantly larger fraction of the total absorption energy in Weldox 460E steel plates perforated by flat-nosed projectiles than in 2024-T351 aluminium plates,due to the differences in material properties.展开更多
This study presents the design of an erbium-doped fiber laser(EDFL) featuring switchable wavelength intervals achieved through the implementation of cascaded and parallel Lyot filters. The proposed laser system utiliz...This study presents the design of an erbium-doped fiber laser(EDFL) featuring switchable wavelength intervals achieved through the implementation of cascaded and parallel Lyot filters. The proposed laser system utilizes a cascaded and parallel configuration of three Lyot filters, facilitated by a polarization beam splitter(PBS) for branch switching. The transmission properties of the filter are analyzed through theoretical modeling and experimental validation using the transmission matrix method. The experimental results are found to be consistent with the theoretical predictions, demonstrating the effectiveness of the proposed design. By adjusting the polarization controllers(PCs), the proposed laser can switch between wavelength spacings of 0.46 nm, 0.27 nm, and 0.76 nm, with a maximum optical signal-to-noise ratio(OSNR) of 38 d B. However, the stability of the laser with a 0.27 nm spacing is not high due to wavelength competition. Power fluctuation for 0.46 nm and 0.76 nm intervals is less than 0.93 d B and 0.78 d B in 1 h, with wavelength fluctuation less than 0.068 nm and 0.19 nm, respectively. This EDFL has the advantages of simple structure, great flexibility, and switchability, which can be applied to fiber optic sensing, wavelength division multiplexing(WDM) networks, and other fields that require a very flexible light source.展开更多
We present a minimal theoretical model for self-sustained oscillations of a thin elastic sheet on a hot plate,induced by thermomechanical coupling.As the plate temperature increases,the sheet’s static deflection beco...We present a minimal theoretical model for self-sustained oscillations of a thin elastic sheet on a hot plate,induced by thermomechanical coupling.As the plate temperature increases,the sheet’s static deflection becomes unstable via a Hopf bifurcation at a critical temperature TC,giving rise to spontaneous periodic motion.Linear stability analysis yields analytical expressions for the critical oscillation temperature TC and the oscillation period at onset.Numerical simulations of the nonlinear equations confirm the bifurcation and reveal how key parameters(stiffness,thermal softening,thermal coupling,etc.)govern the oscillation amplitude and waveform.Finally,we demonstrate that the self-oscillating sheet can perform mechanical work as a heat engine,and we compare its performance to the Carnot efficiency limit.This work provides design principles for thermally driven selfoscillators with potential applications in soft robotics,adaptive structures,and thermal energy harvesting.展开更多
It is generally believed that cuttings have a significant impact on the forces of tubular string in extended-reach drilling.However,there are few studies attempted to investigate and quantify it.In this paper,a three-...It is generally believed that cuttings have a significant impact on the forces of tubular string in extended-reach drilling.However,there are few studies attempted to investigate and quantify it.In this paper,a three-layer transient model for cuttings transport is established to simulate the characteristics of dynamic cuttings transport over time under various conditions.The simulation results indicate that the change in drilling parameters like ROP(rate of penetration)and flow rate of drilling fluid will lead to the non-uniform distribution of cuttings bed.And the alternation of drilling and circulation will lead to a clear wavy distribution of cuttings bed in the wellbore.Then,the effect of cuttings on tubular string is obtained through a large number of numerical simulations and the nonlinear regression method,and this influence is introduced into the conventional stiff rod model of tubular string.Finally,the transient model for cuttings transport is coupled with the modified tubular mechanic model and applies to a case study of extended-reach drilling.The results show that there is a delay effect for the effect of the changes in drilling parameters on the ground torques because the changes in drilling parameters occur instantaneously,while the changes in cuttings bed distribution are slow due to its low transport velocity.Based on the coupling analysis of transient cuttings transport and tubular mechanical behaviors,the drilling parameters are optimized,including the recommended adjustment period and adjustment range for the ROP,the proper drilling time for the increased flow rate.Furthermore,the circulation and back reaming are optimized.For circulation,the keys are choosing appropriate time interval between the two adjacent circulations and the time for each circulation.To avoid pipe stuck,at least 20 min of circulation is required to remove the cuttings bed near the large-sized BHA((Bottom Hole Assembly))before back reaming,and the maximum back reaming velocity should be smaller than the minimum transport velocity of the uniform bed.展开更多
基金the National Natural Science foundation of China(NSFC)(Grants 11632001,11521202,11802344)Natural Science Foundation of Hunan Province,China(Grant 2019JJ50809).
文摘The study of irradiation hardening and embrittlement is critically important for the development of next-generation structural materials tolerant to neutron irradiation,and could dramatically affect the approach to the design of components for advanced nuclear reactors.In addition,a growing interest is observed in the field of research and development of irradiation-resistant materials.This review aims to provide an overview of the theoretical development related to irradiation hardening and embrittlement at moderate irradiation conditions achieved in recent years,which can help extend our fundamental knowledge on nuclear structural materials.After a general introduction to the irradiation effects on metallic materials,recent research progress covering theoretical modelling is summarized for different types of structural materials.The fundamental mechanisms are elucidated within a wide range of temporal and spatial scales.This review closes with the current understanding of irradiation hardening and embrittlement,and puts some perspectives deserving further study.
基金Project supported by the Innovative Research Foundation of China Academy of Engineering Physics(Grant No.426050502-2)
文摘In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide （FW） backward wave oscillator （BWO） are described. On the whole, these equations are mainly classified into small signal model （SSM）, large signal model （LSM）, and simplified small signal model （SSSM）. Using these linear and nonlinear one-dimensional （1D） models, the oscillation characteristics of the FW BWO of a given configuration of slow wave struc- ture （SWS） can be calculated by numerical iteration algorithm, which is more time efficient than three-dimensional （3D） particle-in-cell （PIC） simulation. The SSSM expressed by analytical formulas is innovatively derived for determining the initial values of the FW SWS conveniently. The dispersion characteristics of the FW are obtained by equivalent circuit analysis. The space charge effect, the end reflection effect, the lossy wall effect, and the relativistic effect are all considered in our models to offer more accurate results. The design process of the FW BWO tube with output power of watt scale in a frequency range between 215 GHz and 225 GHz based on these 1D models is demonstrated. The 3D PIC method is adopted to verify the theoretical design results, which shows that they are in good agreement with each other.
文摘The title complexes were modeled using the semiempirical MOPAC and the newly developed SPARKLE paramerters of the lanthanides. The calculated bond dis tances and angles agreed well with those found from crystal structure measuremen ts. This technique allows us to screen a large number of molecules and get struc tural information within a very short time.
基金supported by Chinese Civil Aircraft Project [No. MJ-2017-S49]China National Postdoctoral Program for Innovative Talents [No. BX20200210]China Postdoctoral Science Foundation [No. 2019M660086]。
文摘Axial piston pumps have been widely used in aircraft hydraulic systems to supply the system with pressurized fluid. The continuous improvement of the aircraft performance has put forward the demand on aviation piston pumps for high power density, safety, and reliability. The lubricating interfaces in axial piston machines are the key design issue that greatly determines the pump performance and service life. The cylinder block/valve plate interface is one of these critical lubricating interfaces and has received considerable attention from many researchers in the last half century. This study aims to review the state-of-the-art literature on the cylinder block/valve plate interface comprehensively and systematically. First, we introduce various theoretical models developed to investigate the lubrication behaviors of the interface and compare them in terms of their assumptions and limitations. Second, the experimental studies on the cylinder block/valve plate interface are presented comprehensively, where the involved test rigs are divided into three types according to their fidelity levels and measurement functionality. Third, we summarize some typical approaches of structure optimization, surface shaping, and surface strengthening, which help improve the load-carrying and anti-wear capacities of the interface under severe operating conditions. Finally, the challenges and future trends of the cylinder block/valve plate interface research are discussed briefly.
文摘Diverse concepts of space developed in history of natural philosophy,mathematics,physics,and other natural or cultural studies form theoretical models of spatial relations,given in human’s experience.Their diversity is due not only to the multiplicity of philosophical and methodological approaches to the concept of space,but also to the variety of ways,in which spatial relationships can be organized.This variety gives a possibility to distinct autonomous spaces of different types with diverse sets of properties as well as separate spaces with their own ordinal,metrical,and sequential structures.Particularly,various ways of space semiotization in culture generate different types of autonomous and separate spaces:written texts,maps,pictures,chessboards,etc.In the same time,all particular notions of space are included in a general logical class.Its volume and content are covered by the philosophical category of space.Such general category cannot be reduced to mathematical,physical,or other concepts of space elaborated in particular sciences,however,it serves as a philosophical basis for their comparison.
文摘It has been experimentally observed that,in the perforation of metal plates by a flat-nosed projectile,there exists a plateau phenomenon where the ballistic limit increases slightly with increasing plate thickness,which is related to a change in the mode of failure.No theoretical model has so far explained this phenomenon satisfactorily.This paper presents a combined numerical and theoretical study on the perforation of 2024-T351 aluminum plates struck by flat-nosed projectiles.First,numerical simulations are performed to investigate the failure mechanisms/deformation modes of the aluminum plates.Then,a theoretical model is proposed based on the numerical results and the experimental observations within a unified framework.The model takes into account the main energy absorbing mechanisms and the corresponding energies absorbed are determined analytically.In particular,a dimensionless equation is suggested to describe the relationship between global deformations and impact velocity.It transpires that the model predictions are in good agreement with the test data and the numerical results for the perforation of 2024-T351 aluminum plates struck by rigid flat-nosed projectiles in terms of residual velocity,ballistic limit,relationship between global deformations and impact velocity,and transition of failure modes.It also transpires that the present model can predict the“plateau”phenomenon,which shows a slight increase in ballistic limit as plate thickness increases.Furthermore,the energy absorption mechanisms are discussed on the basis of the theoretical analysis.
基金support from the National Natural Science Foundation of China(Grant Nos.52378411,52208404)China National Railway Group Limited Science and Technology Research and Development Program(Grant No.K2023G041).
文摘During strike-slip fault dislocation,multiple fault planes are commonly observed.The resulting permanent ground deformation can lead to profound structural damage to tunnels.However,existing analytical models do not consider multiple fault planes.Instead,they concentrate the entire fault displacement onto a single fault plane for analysis,thereby giving rise to notable errors in the calculated results.To address this issue,a refined nonlinear theoretical model was established to analyze the mechanical responses of the tunnels subjected to multiple strike-slip fault dislocations.The analytical model considers the number of fault planes,nonlinear soil‒tunnel interactions,geometric nonlinearity,and fault zone width,leading to a significant improvement in its range of applicability and calculation accuracy.The results of the analytical model are in agreement,both qualitatively and quantitatively,with the model test and numerical results.Then,based on the proposed theoretical model,a sensitivity analysis of parameters was conducted,focusing on the variables such as the number of fault planes,fault plane distance(d),fault displacement ratio(η),burial depth(C),crossing angle(β),tunnel diameter(D),fault zone width(Wf),and strike-slip fault displacement(Δfs).The results show that the peak shear force(Vmax),bending moment(Mmax),and axial force(Nmax)decrease with increasing d.The Vmax of the tunnel is found at the fault plane with the largest fault displacement.C,D,andΔfs contribute to the increases in Vmax,Mmax,and Nmax.Additionally,increasing the number of fault planes reduces Vmax and Mmax,whereas the variation in Nmax remains minimal.
基金Project(BK20210721) supported by the Natural Science Foundation of Jiangsu Province,ChinaProjects(52108380,52078506) supported by the National Natural Science Foundation of ChinaProject(2023A1515012159) supported by the Guangdong Basic and Applied Basic Research Foundation,China。
文摘Steel tube slab (STS) structure, a novel pipe-roof structure, of which steel tubes are connected with flange plates, bolts and concrete, is an increasingly popular supporting structure for underground space development. Whilst the load-bearing of pipe-roof structures has been the subject of much research, uncertainties of deformation mechanism and the derivation of reliable calculation methods remain a challenge. For efficient design and wider deployment, this paper presents a bidirectional bending test to investigate the bending stiffnesses, load capacities and deformation mechanisms. The results show that the STS specimens exhibit good ductility and experience bending failure, and their deformation curves follow a half-sine wave upon loading. On this basis, the development of an STS composite slab deformation prediction model is proposed, along with the estimation for its bending stiffness. Theoretical predictions are shown to be in good agreement with the experimental measurements, with a maximum error of less than 15%. The outcomes of this investigation can provide references for the design and application of STS structures.
基金supported by the National Key Research and Development program(2022YFA1504000)the National Natural Science Foundation of China(22302101)+4 种基金the Fundamental Research Funds for the Central Universities(63185015)Shenzhen Science and Technology Program(JCYJ20210324121002007,JCYJ20230807151503007)Yunnan Provincial Science and Technology Project at Southwest United Graduate School(202402AO370001)China Postdoctoral Science Foundation(2022M721699)Guangdong Basic and Applied Basic Research Foundation(2024A1515010347).
文摘Reconstruction during the oxygen evolution reaction(OER)significantly transforms the geometric structure of transition metal compounds,leading to enhanced catalytic performance.However,the resulting structural disorder complicates the development of accurate theoretical models.In this study,CoS2 is used as a model system to establish a framework for rationally modeling reconstructed OER catalysts based on density functional theory(DFT).In the reconstruction process,sulfur atoms are likely to be substituted by oxygen atoms,leading to the formation of the CoOOH phase.Based on the difference in reconstruction degree,we constructed three types of models:doping,heterostructure,and fully reconstructed,representing the reconstruction degree from minimal to full phase transition,respectively.Fully reconstructed models,which account for strain and vacancy effects,effectively simulate the unique coordination environments of reconstructed catalysts.Model e-CoOOH achieves a theoretical overpotential of 0.38 V,outperforming pristine CoOOH(0.56 V),demonstrating that the unique structural features resulting from reconstruction improve OER performance.The doping model and the heterostructure model are helpful to explain the electronic structure and performance transformation of the reconstruction process.This work provides a rational theoretical modeling approach,which is conducive to improving the reliability of the theoretical OER performance of the reconstructed catalyst.
基金Beijing Municipal Natural Science Foundation,Grant/Award Number:Z200011National Natural Science Foundation of China,Grant/Award Numbers:22109086,21825501Taian Municipal Technology Foundation,Grant/Award Number:2019GX049。
文摘Lithium–sulfur(Li–S)batteries have been considered as promising battery systems due to their huge advantages on theoretical energy density and rich resources.However,the shuttle effect and sluggish transformation of soluble lithium polysulfides(LiPSs)hinder the practical application of Li–S batteries.Tremendous sulfur host materials with unique catalytic activity have been exploited to inhibit the shuttle effect and accelerate LiPSs redox reactions,in which theoretical simulations have been widely adopted.This review aims to summarize the fundamentals and applications of theoretical models in sulfur cathodes.Concretely,the integration of theoretical models provides insights into the adsorption and conversion mechanisms of LiPSs and is further utilized in the smart design of catalysts for the exploitation of practical Li–S batteries.Finally,a perspective on the future combination of calculation technology and theoretical models is provided.
基金supported by the Ministry Level Project of China
文摘Abstract With the recent products being more reliable, engineers cannot obtain enough failure or degradation information through the design period and even the product lifetime, therefore, accel erated life test （ALT） ihas become the most popular way to quantify the life characteristics of prod ucts. Test design is the most essential topic, such as testing duration, stress profile, data inference, etc. In this paper, a method and procedure based on theoretical life models is proposed to determine the accelerated stress profile. Firstly, the method for theoretical life calculation is put forward based on the main failure mechanism analysis and the theoretical life models. Secondly, the method is pro vided to determine the accelerated stress profile, including the method to determine the accelerated stress types and the stress range on the basis of the main failure mechanism analysis, the method to determine the acceleration factor and the accelerated stress level based on life quantitative calcula tion models, and the collaborative analysis method of the accelerated test time while taking the mul tiple failure mechanisms into consideration. Lastly, the actuator is taken as an example to describe the procedure of the method and the engineering applicability and the validity are verified.
基金Supported by Shandong Provincial Natural Science Foundation of China(Grant No.ZR2023QE041)China Postdoctoral Science Foundation(Grant No.2023M731862)National Natural Science Foundation of China(Grant No.51975112).
文摘Textured surfaces with certain micro/nano structures have been proven to possess some advanced functions,such as reducing friction,improving wear and increasing wettability.Accurate prediction of micro/nano surface textures is of great significance for the design,fabrication and application of functional textured surfaces.In this paper,based on the kinematic analysis of cutter teeth,the discretization of ultrasonic machining process,transformation method of coordinate systems and the cubic spline data interpolation,an integrated theoretical model was established to characterize the distribution and geometric features of micro textures on the surfaces machined by different types of ultrasonic vibration-assisted milling(UVAM).Based on the theoretical model,the effect of key process parameters(vibration directions,vibration dimensions,cutting parameters and vibration parameters)on tool trajectories and microtextured surface morphology in UVAM is investigated.Besides,the effect of phase difference on the elliptical shape in 2D/3D ultrasonic elliptical vibration-assisted milling(UEVAM)was analyzed.Compared to conventional numerical models,the method of the cubic spline data interpolation is applied to the simulation of microtextured surface morphology in UVAM,which is more suitable for characterizing the morphological features of microtextured surfaces than traditional methods due to the presence of numerous micro textures.The prediction of surface roughness indicates that the magnitude of ultrasonic amplitude in z-direction should be strictly limited in 1D rotary UVAM,2D and 3D UEVAM due to the unfavorable effect of axial ultrasonic vibration on the surface quality.This study can provide theoretical guidance for the design and fabrication of microtextured surfaces in UVAM.
基金supported by the National Natural Science Foundation of China(22008169,91834303)the Open Research Fund of State Key Laboratory of Multiphase Complex Systems(MPCS-2021-D-06).
文摘The rising motion of single bubble in still liquid is a natural phenomenon,which has high theoretical research significance and engineering application prospect.Experimental observations and numerical simulations for prediction of the rising trajectory of a single bubble in still liquid are being carried out,while the concise but accurate theoretical or mechanism model is still not well developed.In this article,a theoretical model of a single bubble based on experimental observation of flow around bluff body is proposed to predict the rising trajectory of zigzagging bubbles in still water.The prediction correlation of bubble lateral movement frequency and bubble steer angle are established based on three degrees of freedom frame.The model has achieved good trajectory prediction effect in the bubble rising experiment.The average simulation time per unit moving time of bubble is 2.5 s.
基金supported by the National Social Science Fund of China(23BSH144).
文摘Fathers play an important role in children’s development throughout their lives,and Father-Love Absence(FLA)leads to more behavioral problems,including Non-Suicidal Self-Injury(NSSI).However,there has been no research on the relationship between FLA and NSSI and its influencing mechanism.This study is based on Nock’s integrated theoretical model of NSSI,aiming to explore the influence of FLA on NSSI and further investigate the mechanism of Subjective Vitality(SV)and Forgiveness(FORG).This study recruited 1795 adolescents in central China to complete four scales,including Father-Love Absence Scale(FLAS),The Subjective Vitality Scale(SVS),The Tendency to Forgive Scale(TTF),and Non-Suicidal Self-Injury Scale.FLA can directly affect NSSI,and indirectly affect NSSI through three paths of“FLA→SV→NSSI,FLA→FORG→NSSI,FLA→SV→FORG→NSSI”.These results not only enrich our understanding of the relationship between FLA and NSSI and its internal mechanism but also provide theoretical and practical support for the reduction of NSSI in family education.
基金financially supported by the Natural Science Foundation of Shandong(ZR2023ME014)。
文摘Electrocatalysis has been extensively explored for the storage and conversion of renewable electric power.Understanding the physisorption and chemisorption processes at electrified solid–liquid interfaces(ESLIs)is crucial for revealing the typical surface restructuring and catalyst dissolution during electrocatalysis.Although advanced in situ tools and theoretical models have been proposed[1,2],identifying the nature of the active sites with atomic-scale spatial resolution remains a challenge,especially at ESLIs.In a recent work published in Nature,Zhang et al.[3]reported a groundbreaking atomic-resolution imaging of the structural dynamics of Cu nanowire catalysts in ESLIs for electrochemical CO_(2)reduction(ECR).
基金supported by the National Natural Science Foundation of China(Grant No.51972028)the State Key Development Program for Basic Research of China(Grant No.2019YFA0307900).
文摘The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change,respectively.This paper reviews the electrocaloric effect of ferroelectric materials based on different theoretical models.First,it provides four different calculation scales(the first-principle-based effective Hamiltonian,the Landau-Devonshire thermodynamic theory,phase-field simulation,and finite element analysis)to explain the basic theory of calculating the electrocaloric effect.Then,it comprehensively reviews the recent progress of these methods in regulating the electrocaloric effect and the generation mechanism of the electrocaloric effect.Finally,it summarizes and anticipates the exploration of more novel electrocaloric materials based on the framework constructed by the different computational methods.
文摘A theoretical analysis on the perforation of Weldox 460E steel plates struck by flat-nosed projectiles is presented using a previously developed model within a unified framework.This model contains a dimensionless empirical equation to describe the variation of energy absorbed through global deformation as a function of impact velocity.The study further investigates the energy absorption mechanisms of Weldox 460E steel plates,with particular focus on the“plateau”phenomenon,i.e.,limited increase in ballistic limit with increasing plate thickness.This phenomenon is explained and compared with results from previously studied 2024-T351 aluminium plates.The model predictions agree well with experimental data for Weldox 460E steel plates impacted by flat-nosed projectiles,including:relationship between global deformation and impact velocity,ballistic limit,residual velocity,and critical conditions for the transition of failure modes.Moreover,the model effectively predicts the“plateau”phenomenon observed in intermediate plate thickness range.It is also found that the indentation absorption energy contributes a significantly larger fraction of the total absorption energy in Weldox 460E steel plates perforated by flat-nosed projectiles than in 2024-T351 aluminium plates,due to the differences in material properties.
基金supported by the Primary Research and Development Plan of Zhejiang Province (No.2023C03014)the Key Research and Development Program of Zhejiang Province (No.2022C03037)。
文摘This study presents the design of an erbium-doped fiber laser(EDFL) featuring switchable wavelength intervals achieved through the implementation of cascaded and parallel Lyot filters. The proposed laser system utilizes a cascaded and parallel configuration of three Lyot filters, facilitated by a polarization beam splitter(PBS) for branch switching. The transmission properties of the filter are analyzed through theoretical modeling and experimental validation using the transmission matrix method. The experimental results are found to be consistent with the theoretical predictions, demonstrating the effectiveness of the proposed design. By adjusting the polarization controllers(PCs), the proposed laser can switch between wavelength spacings of 0.46 nm, 0.27 nm, and 0.76 nm, with a maximum optical signal-to-noise ratio(OSNR) of 38 d B. However, the stability of the laser with a 0.27 nm spacing is not high due to wavelength competition. Power fluctuation for 0.46 nm and 0.76 nm intervals is less than 0.93 d B and 0.78 d B in 1 h, with wavelength fluctuation less than 0.068 nm and 0.19 nm, respectively. This EDFL has the advantages of simple structure, great flexibility, and switchability, which can be applied to fiber optic sensing, wavelength division multiplexing(WDM) networks, and other fields that require a very flexible light source.
基金supported by the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2025B1515020077 and 2024A15150301-39)the National Natural Science Foundation of China(Grant No.12205138)the Shenzhen Science and Technology Innovation Committee(Grant No.JCYJ2022-0530113206015).
文摘We present a minimal theoretical model for self-sustained oscillations of a thin elastic sheet on a hot plate,induced by thermomechanical coupling.As the plate temperature increases,the sheet’s static deflection becomes unstable via a Hopf bifurcation at a critical temperature TC,giving rise to spontaneous periodic motion.Linear stability analysis yields analytical expressions for the critical oscillation temperature TC and the oscillation period at onset.Numerical simulations of the nonlinear equations confirm the bifurcation and reveal how key parameters(stiffness,thermal softening,thermal coupling,etc.)govern the oscillation amplitude and waveform.Finally,we demonstrate that the self-oscillating sheet can perform mechanical work as a heat engine,and we compare its performance to the Carnot efficiency limit.This work provides design principles for thermally driven selfoscillators with potential applications in soft robotics,adaptive structures,and thermal energy harvesting.
基金support from the Natural Science Foundation of China(Grant Nos.52222401,52234002,52394255)National Key Research and Development Program of China(Grant No.2023YFC2810901)Science Foundation of China University of Petroleum,Beijing(Grant No.ZXZX20230083).
文摘It is generally believed that cuttings have a significant impact on the forces of tubular string in extended-reach drilling.However,there are few studies attempted to investigate and quantify it.In this paper,a three-layer transient model for cuttings transport is established to simulate the characteristics of dynamic cuttings transport over time under various conditions.The simulation results indicate that the change in drilling parameters like ROP(rate of penetration)and flow rate of drilling fluid will lead to the non-uniform distribution of cuttings bed.And the alternation of drilling and circulation will lead to a clear wavy distribution of cuttings bed in the wellbore.Then,the effect of cuttings on tubular string is obtained through a large number of numerical simulations and the nonlinear regression method,and this influence is introduced into the conventional stiff rod model of tubular string.Finally,the transient model for cuttings transport is coupled with the modified tubular mechanic model and applies to a case study of extended-reach drilling.The results show that there is a delay effect for the effect of the changes in drilling parameters on the ground torques because the changes in drilling parameters occur instantaneously,while the changes in cuttings bed distribution are slow due to its low transport velocity.Based on the coupling analysis of transient cuttings transport and tubular mechanical behaviors,the drilling parameters are optimized,including the recommended adjustment period and adjustment range for the ROP,the proper drilling time for the increased flow rate.Furthermore,the circulation and back reaming are optimized.For circulation,the keys are choosing appropriate time interval between the two adjacent circulations and the time for each circulation.To avoid pipe stuck,at least 20 min of circulation is required to remove the cuttings bed near the large-sized BHA((Bottom Hole Assembly))before back reaming,and the maximum back reaming velocity should be smaller than the minimum transport velocity of the uniform bed.
