A shaking table test was performed to investigate the different responses of piles with and without cement-soil reinforcement,considering both inertial and kinematic interactions.A comparison of the dynamic shear stre...A shaking table test was performed to investigate the different responses of piles with and without cement-soil reinforcement,considering both inertial and kinematic interactions.A comparison of the dynamic shear stress−strain hysteresis curves of soil profiles on the pile side with and without cement-soil reinforced piles indicates that cement-soil reinforced piles not only bear more tremendous shear stress but also have smaller strains under the action of cyclic shear stress.Furthermore,the cement-soil on the pile side not only shares part of the shear stress and modifies the bending moment distribution but also significantly enhances the resistance of the pile-side soil,reducing the lateral displacement of the superstructure.Cement-soil reinforcement reduced shear strains,inhibited sand liquefaction,and reduced superstructure displacements by 27%−47%(instantaneous)and 40%−65%(permanent).The proportion of horizontal load sharing between cement-soil reinforcement and saturated sand is considered,along with the change pattern of the subgrade reaction after sand liquefaction.An equivalent subgrade reaction calculation method is proposed,which accounts for the horizontal load-sharing ratios of soils with two different strengths.The test results indicate that the pile stress and displacement,estimated using the equivalent subgrade reaction,are in good agreement with the observed results.展开更多
Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properti...Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properties.The integration of FG materials with auxetic structures enhances their adaptability in advanced engineering applications.However,understanding their dynamic behavior under external excitations is essential for optimal design and structural reliability.Nonlinear interactions in such structures pose significant challenges in vibration analysis,necessitating robust analytical methods.This study presents a closed-form solution for the nonlinear forced vibration analysis of sandwich FG auxetic beams,offering an accurate and efficient method for predicting their dynamic response.The beam consists of two FG face sheets with material properties varying through the thickness and a re-entrant honeycomb auxetic core with an adjustable Poisson's ratio.The governing nonlinear equations of motion are derived using the first-order shear deformation theory(FSDT),the modified Gibson model,and the von Kármán relations,formulated through Hamilton's principle.A closed-form solution is obtained via the Galerkin method and multiple-scale technique.The results demonstrate that FG layers enable control of the overweight and dynamic response amplitude,with positive power law indexes reducing weight.Comparisons with finite element results confirm the accuracy of the proposed formulation.展开更多
Background Obesity is the most common metabolic disease in the world. However, the relationship between obesity and lung function is not fully understood. Although several longitudinal studies have shown that increase...Background Obesity is the most common metabolic disease in the world. However, the relationship between obesity and lung function is not fully understood. Although several longitudinal studies have shown that increases in body weight can lead to reductions in pulmonary function, whether this is the case with the Japanese population and whether high body mass index （BMI） status alone represents an appropriate predictor of obstructive lung dysfunction remains unclear.The purpose of present study was to estimate the effect of BMI on lung function measured by spirometry of Japanese patients in general clinics. We measured BMI and performed spirometry on screening patients who had consulted general clinics.Methods Subjects comprised 1231 patients ≥40 years of age （mean age （65.0±12.0） years, 525 men, 706 women） who had consulted clinics in Nagasaki Prefecture, Japan, for non-respiratory disease. BMI was calculated and lung function was measured by spirometry.Results BMI was found to be positively correlated with forced expiratory volume in 1 second （FEV1）/forced vital capacity （FVC） in men and with maximum mid-expiratory flow （MMF） in all subjects. Following adjustment for relevant factors, a significant positive correlation between BMI and FEV1/FVC was identified for all subjects. Comparison between subjects with normal BMI （18.5-25.0） and higher BMI （25.1-30.0） also demonstrated that FEV1/FVC and percentage of predicted maximum mid-expiratory flow （%MMF） were significantly higher in the latter subjects.Conclusions In a population without marked respiratory disease, higher BMI subjects showed less obstructive pulmonary dysfunction compared to normal BMI subjects. High BMI status alone may be inappropriate as a predictor of obstructive lung dysfunction, particularly in populations with a low prevalence of obesity.展开更多
This article is concerned with the oscillation of the forced second order differ- ential equation with mixed nonlinearities（a（t）（x＇（t））γ）＇＋po（t）xγ（go（t））＋n∑t=1pi（t）｜x（gi（t））｜αi sgn x（gi...This article is concerned with the oscillation of the forced second order differ- ential equation with mixed nonlinearities（a（t）（x＇（t））γ）＇＋po（t）xγ（go（t））＋n∑t=1pi（t）｜x（gi（t））｜αi sgn x（gi（t））=e（t）,where γ is a quotient of odd positive integers αi〉0,i=1,2 ……n,a,e,and pi ∈ C（[0,∞）R）,a（t）〉0,gi：R→R are positive continuous functions on R with lim gi （t）=∞,i=0,1,……,n. Our results generalize and improve the results in a recent article by Sun and Wong[29].展开更多
Using National Centers for Environmental Prediction reanalysis data for the period 28 June to 12 July during 2001 to2013,the secondary circulation(SC)associated with the mei-yu front was quantitatively diagnosed by nu...Using National Centers for Environmental Prediction reanalysis data for the period 28 June to 12 July during 2001 to2013,the secondary circulation(SC)associated with the mei-yu front was quantitatively diagnosed by numerically solving a primitive version of the Sawyer-Eliassen equation.Results demonstrate that a direct SC exists near the mei-yu front zone during mid-summer and the synoptic-scale geostrophic deformations are the main factors determining SC structures.About94%of the sinking strength and 61%of the ascending strength in the SC are induced by the geostrophic deformations.Other terms,such as diabatic heating,ageostrophic dynamical forcing,and frictional forcing,mainly influence the fine flow pattern of the SC.The forced SC produces a frontogenesis area tilting to the north with altitude.Further diagnosis clarifies the positive feedback involving the geostrophic shear forcing and vorticity frontogenesis in the upper-level mei-yu front zone.Furthermore,statistical results indicate that all 34 deep convection cases that occurred in the warm region of the meiyu front over the period 2004-2013 experienced high-level frontogenesis associated with along-jet cold advection.The cyclonic shear forcing"moved"the monsoon SC’s subsidence branch to the warm side of the mei-yu front and caused the subsidence branch to extend downwards to the lower troposphere,conducive to the initiation of deep convection in the warm region of the mei-yu front.展开更多
Forced imbibition,the invasion of a wetting fluid into porous rocks,plays an important role in the effective exploitation of hydrocarbon resources and the geological sequestration of carbon dioxide.However,the interfa...Forced imbibition,the invasion of a wetting fluid into porous rocks,plays an important role in the effective exploitation of hydrocarbon resources and the geological sequestration of carbon dioxide.However,the interface dynamics influenced by complex topology commonly leads to non-wetting fluid trapping.Particularly,the underlying mechanisms under viscously unfavorable conditions remain unclear.This study employs a direct numerical simulation method to simulate forced imbibition through the reconstructed digital rocks of sandstone.The interface dynamics and fluid–fluid interactions are investigated through transient simulations,while the pore topology metrics are introduced to analyze the impact on steady-state residual fluid distribution obtained by a pseudo-transient scheme.The results show that the cooperative pore-filling process promoted by corner flow is dominant at low capillary numbers.This leads to unstable inlet pressure,mass flow,and interface curvature,which correspond to complicated interface dynamics and higher residual fluid saturation.During forced imbibition,the interface curvature gradually increases,with the pore-filling mechanisms involving the cooperation of main terminal meniscus movement and arc menisci filling.Complex topology with small diameter pores may result in the destabilization of interface curvature.The residual fluid saturation is negatively correlated with porosity and pore throat size,and positively correlated with tortuosity and aspect ratio.A large mean coordination number characterizing global connectivity promotes imbibition.However,high connectivity characterized by the standardized Euler number corresponding to small pores is associated with a high probability of non-wetting fluid trapping.展开更多
The phase-field method is used to study the free dendritic crystal growth under forced convection with hypergravity,the hypergravity term is introduced into the liquid-phase momentum equation to examine the dendritic ...The phase-field method is used to study the free dendritic crystal growth under forced convection with hypergravity,the hypergravity term is introduced into the liquid-phase momentum equation to examine the dendritic growth.The paper focuses on the morphology of dendrite growth as well as the tip radius of the upstream dendritic arm and the average growth velocity of dendrite tips under different hypergravity levels.The results show that the morphology of dendrite changes significantly under represent simulation conditions when the hypergravity reaches 35_(g0),the upstream dendritic arm will bifurcate and the horizontal dendrite arms gradually tilt upwards.This change is mainly caused by the hypergravity and flow changing the temperature field near the dendrite interface.In addition,before the morphology of the dendrite is significantly altered,the radius of the tip of the dendrite upstream arm becomes larger with the increase in hypergravity,and the average growth velocity will increase linearly with it.The morphology of dendritic growth under different hypergravity and the changes in the tip radius along with the average growth velocity of the upstream dendritic tip with hypergravity are given in this paper.Finally,the reasons for these phenomena are analyzed.展开更多
The unsteady magnetohydrodynamical(MHD)free convection flow of an incompressible,electrically conducting hybrid nanofluid within a vertical cylindrical geometry is investigated,incorporating the effects of thermal rad...The unsteady magnetohydrodynamical(MHD)free convection flow of an incompressible,electrically conducting hybrid nanofluid within a vertical cylindrical geometry is investigated,incorporating the effects of thermal radiation,viscous dissipation,and internal heat generation.The system is subjected to a time-periodic boundary temperature condition.The Laplace and finite Hankel transforms are used to derive the exact solutions for the velocity and temperature distributions.The effects of various key physical parameters,including the Richardson number,the Eckert number,the radiation parameter,the heat source parameter,and the nanoparticle volume fraction,are considered.The numerical results reveal that increasing the volume fraction significantly enhances the thermal conductivity and temperature,while the magnetic field intensity and viscous dissipation strongly influence the fluid motion and heat transport.Additionally,the pulsating boundary conditions produce distinct oscillatory behaviors in both the velocity and temperature fields.These findings provide important insights into optimizing the heat transfer performance in cylindrical systems such as electronic cooling modules and energy storage devices operating under dynamic thermal conditions.展开更多
Flutter and forced response, as two main branches of aeroelasticity, can lead to high-cycle fatigue failure of turbomachinery blades. Efficiently and accurately assessing aeroelastic performance of turbomachinery blad...Flutter and forced response, as two main branches of aeroelasticity, can lead to high-cycle fatigue failure of turbomachinery blades. Efficiently and accurately assessing aeroelastic performance of turbomachinery blades is essential in the routine design. In this work, the Time Collocation Method (TCM) which uses the cubic B-spline to approximate flow variables is first thoroughly studied and then combined with the moving grid technique to analyze aeroelastic flow fields. To showcase its advantage over the Harmonic Balance (HB) method which uses a truncated Fourier series to approximately represent flow variables, a matrix analysis of the one-dimensional advection equation is first performed. The results of stability analysis are verified by two test cases: the Durham linear oscillating turbine cascade and a two-blade-row transonic compressor. The vibration of the blade of the first case is driven by a motor while the excitation force of the second case comes from blade row interaction. The results show that the time collocation method has a faster convergence rate and is more stable than the harmonic balance method, especially for cases with a large maximum grid reduced frequency. More importantly, the time collocation method is capable of accurately predicting aeroelastic performance of turbomachinery blades.展开更多
Solidification structure of casting strands significantly impacts the subsequent processing and service properties of the steel products,which correlates closely with the melt flow during the solidification process.Se...Solidification structure of casting strands significantly impacts the subsequent processing and service properties of the steel products,which correlates closely with the melt flow during the solidification process.Several abnormal solidification phenomena and segregation characteristics observed in slab casting are elucidated by referencing to their related flow patterns of molten steel calculated by a multi-field coupling model for actual casting conditions.Eventually,the effect of forced convection on the solidification structure was discussed.The results show that the forced convection generated by electromagnetic stirring and/or nozzle jet will remove the solute-enriched molten steel between the dendrite in front of the solidifying shell,and change solute distribution at the interface of dendrite tips,leading to the white bands and dendrite deflection.In the white band region,a dense dendrite structure without dendrite segregation appears.Moreover,forced convection results in a higher growth rate on the upstream side than the backflow side of the dendrite tip,promoting the columnar crystal deflection.In addition,dendrite fragmentation upon the forced convection during solidification will increase the equiaxed crystal ratio of the as-cast slab and the number of the spot-like semi-macrosegregation.The carbon extreme range decreased with the change in electromagnetic stirring process,indicating a significant improvement in the composition uniformity of the slab casting.It is suggested that the final quality of rolled products could be improved from the very beginning of casting and solidification through regulating the as-cast solidification structure.展开更多
The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel.In this paper,a novel three-dimensional mesoscopic model of steel fiber reinforced concr...The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel.In this paper,a novel three-dimensional mesoscopic model of steel fiber reinforced concrete(SFRC)is constructed by discrete element method.The model encompasses the concrete matrix,aggregate,interfacial transition zone and steel fibers,taking into account the random shape of the coarse aggregate and the stochastic distribution of steel fibers.It captures microscopic-level interactions among the coarse aggregate,steel fibers,and matrix.Subsequently,a comprehensive procedure is formulated to calibrate the microscopic parameters required by the model,and the reliability of the model is verified by comparing with the experimental results.Furthermore,a coupled finite difference method-discrete element method approach is used to construct the model of the split Hopkinson pressure bar.Compression tests are simulated on SFRC specimens with varying steel fiber contents under static and dynamic loading conditions.Finally,based on the advantages of DEM analysis at the mesoscopic level,this study analyzed mechanisms of enhancement and crack arrest in SFRC.It shed a light on the perspectives of interface failure process,microcrack propagation,contact force field evolution and energy analysis,offering valuable insights for related mining engineering applications.展开更多
Disk-drum structures jointed by bolted flanges(DDSJBFs)are core parts in aircraft engines,whose dynamic responses affect structural overall safety and service performance.However,studies on the dynamic response of DDS...Disk-drum structures jointed by bolted flanges(DDSJBFs)are core parts in aircraft engines,whose dynamic responses affect structural overall safety and service performance.However,studies on the dynamic response of DDSJBFs under base excitation are not found in available literature.In the present work,the dynamic responses for DDSJBFs subjected to base excitation are investigated both theoretically and experimentally.The kinetic energy and potential energy of disk,drum,and flange are derived according to the Kirchhoff plate,the Sanders’shell,and the Euler-Bernoulli beam theories,respectively,where the influences of flange and the mass of bolt are taken into account.The artificial spring method is applied to model the bolted joint.The Chebyshev orthogonal polynomials are adopted as the admissible functions of disk and drum,and the Lagrange equations are used to obtain the motion equation.The motion equation is solved by using the Newmark-beta approach and the dynamic responses under base excitation are acquired.A series of experiment studies are conducted on a DDSJBF to demonstrate the correctness of established theoretical model.Finally,study results show that because the relative motion between bolted flange joint interfaces generates friction damping,increasing the excitation amplitude causes the increase of damping ratio of DDSJBFs on the whole,and the increase of resonant peak value exhibits a slowing trend.The above phenomenon becomes more evident when the number of bolt is less.With the increase of bolt mass and flange size,the resonant frequency significantly decreases,while the resonant peak value remains unchanged.展开更多
Revealing the combined influence of interfacial damage and nonlinear factors on the forced vibration is significant for the stability design of fluid-conveying pipes, which are usually assembled in aircraft. The nonli...Revealing the combined influence of interfacial damage and nonlinear factors on the forced vibration is significant for the stability design of fluid-conveying pipes, which are usually assembled in aircraft. The nonlinear forced resonance of fluid-conveying layered pipes with a weak interface and a movable boundary under the external excitation is studied. The pipe is simply supported at both ends, with one end subject to a viscoelastic boundary constraint described by KelvinVoigt model. The weak interface in the pipe is considered in the refined displacement field of the layered pipe employing the interfacial cohesive law. The governing equations are derived by Hamilton's variational principle. Geometric nonlinearities including nonlinear curvature, longitudinal inertia nonlinearity and nonlinear constraint force are comprehensively considered during the theoretical derivation. Amplitude-frequency bifurcation diagrams are obtained utilizing a perturbation-Incremental Harmonic Balance Method(IHBM). Results show that interfacial damage and viscoelastic constraints from boundary and foundation have an important influence on the linear and nonlinear dynamic behavior of the system.展开更多
This research focuses on developing innovative hybrid solar dryers that combine solar Photovoltaic(PV)and solar thermal systems for sustainable food preservation in Pakistan,addressing the country’s pressing issues o...This research focuses on developing innovative hybrid solar dryers that combine solar Photovoltaic(PV)and solar thermal systems for sustainable food preservation in Pakistan,addressing the country’s pressing issues of high post-harvest losses and unreliable energy sources.The proposed active hybrid solar dryer features a drying cabinet,two Direct Current(DC)fans for forced convection,and a resistive heating element powered by a 180 W solar PV panel.An energy-storing battery ensures continuous supply to the auxiliaries during periods of low solar irradiance,poor weather conditions,or nighttime.Tomatoes,a delicate and in-demand crop,were selected for experimentation due to their high perishability.Three experiments were conducted on the same prototype:natural convection direct solar dryer(NCDSD),forced convection direct solar dryer(FCDSD),and forced convection hybrid solar dryer(FCHSD).Each experiment began with 0.2 kg of tomatoes at 94%moisture content,achieving significant reductions:28.57%with NCDSD,16.667%with FCDSD,and 16.667%with FCHSD.The observed drying rates varied:1.161 kg/h for NCDSD,2.062 kg/h for FCDSD,and 2.8642 kg/h for FCHSD.This study presents a comparative analysis of efficiency,drying rate,and cost-effectiveness,alongside the system’s economic and environmental feasibility.展开更多
The present work details a numerical simulation of forced convective laminar flow in a channel with a heated obstacle attached to one wall. The second law analysis is employed to investigate the distribution of entrop...The present work details a numerical simulation of forced convective laminar flow in a channel with a heated obstacle attached to one wall. The second law analysis is employed to investigate the distribution of entropy generation in the flow domain to demonstrate the rate of irreversibilities in thermal system. The conjugate problem including the convection heat transfer in the fluid flow and conduction one inside the obstacle is solved numerically to obtain the velocity and temperature fields in both gas and solid phases. To reach this goal, the set of governing equations including momentum and energy equations for the gas phase and conduction equation for the obstacle are solved by CFD technique to determine the hydrodynamic and thermal behaviors of the fluid flow around the obstacle and the temperature distribution in the solid element. An attempt is made to detail the local Nusselt number distribution and mean Nusselt number and also the local entropy generation distribution for the individual exposed obstacle faces. A good consistency is found between the present numerical results with experiment.展开更多
Second-order axially moving systems are common models in the field of dynamics, such as axially moving strings, cables, and belts. In the traditional research work, it is difficult to obtain closed-form solutions for ...Second-order axially moving systems are common models in the field of dynamics, such as axially moving strings, cables, and belts. In the traditional research work, it is difficult to obtain closed-form solutions for the forced vibration when the damping effect and the coupling effect of multiple second-order models are considered.In this paper, Green's function method based on the Laplace transform is used to obtain closed-form solutions for the forced vibration of second-order axially moving systems. By taking the axially moving damping string system and multi-string system connected by springs as examples, the detailed solution methods and the analytical Green's functions of these second-order systems are given. The mode functions and frequency equations are also obtained by the obtained Green's functions. The reliability and convenience of the results are verified by several examples. This paper provides a systematic analytical method for the dynamic analysis of second-order axially moving systems, and the obtained Green's functions are applicable to different second-order systems rather than just string systems. In addition, the work of this paper also has positive significance for the study on the forced vibration of high-order systems.展开更多
The damped Helmholtz-Duffing oscillator is a topic of great interest in many different fields of study due to its complex dynamics.By transitioning from conventional continuous differential equations to their fractal ...The damped Helmholtz-Duffing oscillator is a topic of great interest in many different fields of study due to its complex dynamics.By transitioning from conventional continuous differential equations to their fractal counterparts,one gains insights into the system's response under new mathematical frameworks.This paper presents a novel method for converting standard continuous differential equations into their fractal equivalents.This conversion occurs after the nonlinear system is transformed into its linear equivalent.Numerical analyses show that there are several resonance sites in the fractal system,which differ from the one resonance point found in the continuous system.One important finding is that the fractal system loses some of its stabilizing power when decaying behavior is transformed into a diffuse pattern.Interestingly,a decrease in the fractal order in resonance settings shows a stabilizing impact,highlighting the dynamics'complexity inside fractal systems.This endeavor to convert to fractals is a revolutionary technique that is being employed for the first time.展开更多
The high-quality assembly of Large Aircraft Components(LACs)is essential in modern aviation manufacturing.Numerical control locators are employed for the posture adjustment of LAC,yet the system's multi-input mult...The high-quality assembly of Large Aircraft Components(LACs)is essential in modern aviation manufacturing.Numerical control locators are employed for the posture adjustment of LAC,yet the system's multi-input multi-output,nonlinearity,and strong coupling presents significant challenges.The substantial internal force generated during the adjustment process can potentially damage the LAC and degrade the assembly quality.Hence,a workspace-based hybrid force position control scheme was developed to achieve high quality assembly with high-precision and lower internal force.Firstly,an offline workspace analysis with inherent geometric characteristics to form time-varying posture error constraint.Then,the posture error is integrated into the online position axis control to ensure tracking the ideal posture,while the force control axis compensates for posture deviation by minimizing internal force,thereby achieving high precision and low internal force.Finally,the effectiveness was demonstrated through experiments.The root mean square errors of orientation and position are 104 rad and 0.1 mm,respectively.A reduction in internal force can range from 10.96%to 57.4%compared to the traditional method.Key points'max position error is decreased from 0.32 mm to 0.18 mm,satisfying the 0.5 mm tolerance.Therefore,the proposed method will help promote the development of high-performance manufacturing.展开更多
The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payl...The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.展开更多
This interview examines the theoretical foundations,pedagogical applications,developmental trajectory,and future directions of the xu-argument.Professor Wang Chuming offers a comprehensive account of the xu-argument,c...This interview examines the theoretical foundations,pedagogical applications,developmental trajectory,and future directions of the xu-argument.Professor Wang Chuming offers a comprehensive account of the xu-argument,clarifying its theoretical framework,the learning mechanisms underlying xu,and its interface with international theories of second language acquisition(SLA).From the perspective of the xu-argument,he proposes novel interpretations of core issues in SLA.Drawing on the development of the xu-argument,Wang further discusses the essence,directions,and methodology of innovation in SLA theory.He emphasizes that theoretical advances must capture and illuminate underlying natural laws,arguing that innovative approaches are typically rooted in deep reflection on common sense.He also calls for theoretical innovation in SLA in the Chinese context,advocating a robust research paradigm that shifts from local observation to global theoretical generalization,thereby promoting bottom-up theoretical development.In closing,he highlights the promising prospects for SLA theory in the era of artificial intelligence.展开更多
基金Project(52078129)supported by the National Natural Science Foundation of ChinaProject(MTF2023009)supported by the Open Project of Key Laboratory of Transport Industry of Comprehensive Transportation Theory(Nanjing Modern Multimodal Transportation Laboratory),ChinaProject(2242024K40037)supported by the Fundamental Research Funds for the Central Universities,China。
文摘A shaking table test was performed to investigate the different responses of piles with and without cement-soil reinforcement,considering both inertial and kinematic interactions.A comparison of the dynamic shear stress−strain hysteresis curves of soil profiles on the pile side with and without cement-soil reinforced piles indicates that cement-soil reinforced piles not only bear more tremendous shear stress but also have smaller strains under the action of cyclic shear stress.Furthermore,the cement-soil on the pile side not only shares part of the shear stress and modifies the bending moment distribution but also significantly enhances the resistance of the pile-side soil,reducing the lateral displacement of the superstructure.Cement-soil reinforcement reduced shear strains,inhibited sand liquefaction,and reduced superstructure displacements by 27%−47%(instantaneous)and 40%−65%(permanent).The proportion of horizontal load sharing between cement-soil reinforcement and saturated sand is considered,along with the change pattern of the subgrade reaction after sand liquefaction.An equivalent subgrade reaction calculation method is proposed,which accounts for the horizontal load-sharing ratios of soils with two different strengths.The test results indicate that the pile stress and displacement,estimated using the equivalent subgrade reaction,are in good agreement with the observed results.
文摘Sandwich functionally graded(FG)auxetic beams are extensively utilized in aerospace,automotive,and biomedical industries due to their excellent strength-toweight ratio,impact resistance,and tunable mechanical properties.The integration of FG materials with auxetic structures enhances their adaptability in advanced engineering applications.However,understanding their dynamic behavior under external excitations is essential for optimal design and structural reliability.Nonlinear interactions in such structures pose significant challenges in vibration analysis,necessitating robust analytical methods.This study presents a closed-form solution for the nonlinear forced vibration analysis of sandwich FG auxetic beams,offering an accurate and efficient method for predicting their dynamic response.The beam consists of two FG face sheets with material properties varying through the thickness and a re-entrant honeycomb auxetic core with an adjustable Poisson's ratio.The governing nonlinear equations of motion are derived using the first-order shear deformation theory(FSDT),the modified Gibson model,and the von Kármán relations,formulated through Hamilton's principle.A closed-form solution is obtained via the Galerkin method and multiple-scale technique.The results demonstrate that FG layers enable control of the overweight and dynamic response amplitude,with positive power law indexes reducing weight.Comparisons with finite element results confirm the accuracy of the proposed formulation.
文摘Background Obesity is the most common metabolic disease in the world. However, the relationship between obesity and lung function is not fully understood. Although several longitudinal studies have shown that increases in body weight can lead to reductions in pulmonary function, whether this is the case with the Japanese population and whether high body mass index （BMI） status alone represents an appropriate predictor of obstructive lung dysfunction remains unclear.The purpose of present study was to estimate the effect of BMI on lung function measured by spirometry of Japanese patients in general clinics. We measured BMI and performed spirometry on screening patients who had consulted general clinics.Methods Subjects comprised 1231 patients ≥40 years of age （mean age （65.0±12.0） years, 525 men, 706 women） who had consulted clinics in Nagasaki Prefecture, Japan, for non-respiratory disease. BMI was calculated and lung function was measured by spirometry.Results BMI was found to be positively correlated with forced expiratory volume in 1 second （FEV1）/forced vital capacity （FVC） in men and with maximum mid-expiratory flow （MMF） in all subjects. Following adjustment for relevant factors, a significant positive correlation between BMI and FEV1/FVC was identified for all subjects. Comparison between subjects with normal BMI （18.5-25.0） and higher BMI （25.1-30.0） also demonstrated that FEV1/FVC and percentage of predicted maximum mid-expiratory flow （%MMF） were significantly higher in the latter subjects.Conclusions In a population without marked respiratory disease, higher BMI subjects showed less obstructive pulmonary dysfunction compared to normal BMI subjects. High BMI status alone may be inappropriate as a predictor of obstructive lung dysfunction, particularly in populations with a low prevalence of obesity.
文摘This article is concerned with the oscillation of the forced second order differ- ential equation with mixed nonlinearities（a（t）（x＇（t））γ）＇＋po（t）xγ（go（t））＋n∑t=1pi（t）｜x（gi（t））｜αi sgn x（gi（t））=e（t）,where γ is a quotient of odd positive integers αi〉0,i=1,2 ……n,a,e,and pi ∈ C（[0,∞）R）,a（t）〉0,gi：R→R are positive continuous functions on R with lim gi （t）=∞,i=0,1,……,n. Our results generalize and improve the results in a recent article by Sun and Wong[29].
基金jointly supported by the National Key R&D Programs of China(Grant No.2018YFC1507300)the National Natural Science Foundation of China(Grant No.41505086)。
文摘Using National Centers for Environmental Prediction reanalysis data for the period 28 June to 12 July during 2001 to2013,the secondary circulation(SC)associated with the mei-yu front was quantitatively diagnosed by numerically solving a primitive version of the Sawyer-Eliassen equation.Results demonstrate that a direct SC exists near the mei-yu front zone during mid-summer and the synoptic-scale geostrophic deformations are the main factors determining SC structures.About94%of the sinking strength and 61%of the ascending strength in the SC are induced by the geostrophic deformations.Other terms,such as diabatic heating,ageostrophic dynamical forcing,and frictional forcing,mainly influence the fine flow pattern of the SC.The forced SC produces a frontogenesis area tilting to the north with altitude.Further diagnosis clarifies the positive feedback involving the geostrophic shear forcing and vorticity frontogenesis in the upper-level mei-yu front zone.Furthermore,statistical results indicate that all 34 deep convection cases that occurred in the warm region of the meiyu front over the period 2004-2013 experienced high-level frontogenesis associated with along-jet cold advection.The cyclonic shear forcing"moved"the monsoon SC’s subsidence branch to the warm side of the mei-yu front and caused the subsidence branch to extend downwards to the lower troposphere,conducive to the initiation of deep convection in the warm region of the mei-yu front.
基金supported by the National Natural Science Foundation of China(Grant Nos.42172159 and 42302143)the Postdoctora Fellowship Program of the China Postdoctoral Science Foundation(CPSF)(Grant No.GZB20230864).
文摘Forced imbibition,the invasion of a wetting fluid into porous rocks,plays an important role in the effective exploitation of hydrocarbon resources and the geological sequestration of carbon dioxide.However,the interface dynamics influenced by complex topology commonly leads to non-wetting fluid trapping.Particularly,the underlying mechanisms under viscously unfavorable conditions remain unclear.This study employs a direct numerical simulation method to simulate forced imbibition through the reconstructed digital rocks of sandstone.The interface dynamics and fluid–fluid interactions are investigated through transient simulations,while the pore topology metrics are introduced to analyze the impact on steady-state residual fluid distribution obtained by a pseudo-transient scheme.The results show that the cooperative pore-filling process promoted by corner flow is dominant at low capillary numbers.This leads to unstable inlet pressure,mass flow,and interface curvature,which correspond to complicated interface dynamics and higher residual fluid saturation.During forced imbibition,the interface curvature gradually increases,with the pore-filling mechanisms involving the cooperation of main terminal meniscus movement and arc menisci filling.Complex topology with small diameter pores may result in the destabilization of interface curvature.The residual fluid saturation is negatively correlated with porosity and pore throat size,and positively correlated with tortuosity and aspect ratio.A large mean coordination number characterizing global connectivity promotes imbibition.However,high connectivity characterized by the standardized Euler number corresponding to small pores is associated with a high probability of non-wetting fluid trapping.
基金supported by the National Natural Science Foundation of China(Grant No.52588202)。
文摘The phase-field method is used to study the free dendritic crystal growth under forced convection with hypergravity,the hypergravity term is introduced into the liquid-phase momentum equation to examine the dendritic growth.The paper focuses on the morphology of dendrite growth as well as the tip radius of the upstream dendritic arm and the average growth velocity of dendrite tips under different hypergravity levels.The results show that the morphology of dendrite changes significantly under represent simulation conditions when the hypergravity reaches 35_(g0),the upstream dendritic arm will bifurcate and the horizontal dendrite arms gradually tilt upwards.This change is mainly caused by the hypergravity and flow changing the temperature field near the dendrite interface.In addition,before the morphology of the dendrite is significantly altered,the radius of the tip of the dendrite upstream arm becomes larger with the increase in hypergravity,and the average growth velocity will increase linearly with it.The morphology of dendritic growth under different hypergravity and the changes in the tip radius along with the average growth velocity of the upstream dendritic tip with hypergravity are given in this paper.Finally,the reasons for these phenomena are analyzed.
基金Project supported by the National Natural Science Foundation of China(No.12250410244)the Jiangsu Funding Program for Excellent Postdoctoral Talent of China(No.2023ZB884)+2 种基金the Foreign Expert Project funding of China(No.WGXZ2023017L)the Shuang-Chuang(SC)Doctor Program of Jiangsu Provincethe Longshan Scholar Program of Nanjing University of Information Science&Technology。
文摘The unsteady magnetohydrodynamical(MHD)free convection flow of an incompressible,electrically conducting hybrid nanofluid within a vertical cylindrical geometry is investigated,incorporating the effects of thermal radiation,viscous dissipation,and internal heat generation.The system is subjected to a time-periodic boundary temperature condition.The Laplace and finite Hankel transforms are used to derive the exact solutions for the velocity and temperature distributions.The effects of various key physical parameters,including the Richardson number,the Eckert number,the radiation parameter,the heat source parameter,and the nanoparticle volume fraction,are considered.The numerical results reveal that increasing the volume fraction significantly enhances the thermal conductivity and temperature,while the magnetic field intensity and viscous dissipation strongly influence the fluid motion and heat transport.Additionally,the pulsating boundary conditions produce distinct oscillatory behaviors in both the velocity and temperature fields.These findings provide important insights into optimizing the heat transfer performance in cylindrical systems such as electronic cooling modules and energy storage devices operating under dynamic thermal conditions.
基金supported by the Science Center for Gas Turbine Project,China(No.P2022-C-II-001-001)the National Science and Technology Major Project,Chinathe Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX2022045).
文摘Flutter and forced response, as two main branches of aeroelasticity, can lead to high-cycle fatigue failure of turbomachinery blades. Efficiently and accurately assessing aeroelastic performance of turbomachinery blades is essential in the routine design. In this work, the Time Collocation Method (TCM) which uses the cubic B-spline to approximate flow variables is first thoroughly studied and then combined with the moving grid technique to analyze aeroelastic flow fields. To showcase its advantage over the Harmonic Balance (HB) method which uses a truncated Fourier series to approximately represent flow variables, a matrix analysis of the one-dimensional advection equation is first performed. The results of stability analysis are verified by two test cases: the Durham linear oscillating turbine cascade and a two-blade-row transonic compressor. The vibration of the blade of the first case is driven by a motor while the excitation force of the second case comes from blade row interaction. The results show that the time collocation method has a faster convergence rate and is more stable than the harmonic balance method, especially for cases with a large maximum grid reduced frequency. More importantly, the time collocation method is capable of accurately predicting aeroelastic performance of turbomachinery blades.
基金The authors are grateful to Weifang Science and Technology Development Plan Project(2023ZJ1166)for supporting this work.
文摘Solidification structure of casting strands significantly impacts the subsequent processing and service properties of the steel products,which correlates closely with the melt flow during the solidification process.Several abnormal solidification phenomena and segregation characteristics observed in slab casting are elucidated by referencing to their related flow patterns of molten steel calculated by a multi-field coupling model for actual casting conditions.Eventually,the effect of forced convection on the solidification structure was discussed.The results show that the forced convection generated by electromagnetic stirring and/or nozzle jet will remove the solute-enriched molten steel between the dendrite in front of the solidifying shell,and change solute distribution at the interface of dendrite tips,leading to the white bands and dendrite deflection.In the white band region,a dense dendrite structure without dendrite segregation appears.Moreover,forced convection results in a higher growth rate on the upstream side than the backflow side of the dendrite tip,promoting the columnar crystal deflection.In addition,dendrite fragmentation upon the forced convection during solidification will increase the equiaxed crystal ratio of the as-cast slab and the number of the spot-like semi-macrosegregation.The carbon extreme range decreased with the change in electromagnetic stirring process,indicating a significant improvement in the composition uniformity of the slab casting.It is suggested that the final quality of rolled products could be improved from the very beginning of casting and solidification through regulating the as-cast solidification structure.
基金financial support by the National Natural Science Foundation of China(52174101&52408310)Guangdong Basic and Applied Basic Research Foundation(2023A1515011634&2024A1515012528)Guangdong Provincial Department of Science and Technology(2021ZT09G087)for the research.
文摘The frequent or occasional impact loads pose serious threats to the service safety of conventional concrete structures in tunnel.In this paper,a novel three-dimensional mesoscopic model of steel fiber reinforced concrete(SFRC)is constructed by discrete element method.The model encompasses the concrete matrix,aggregate,interfacial transition zone and steel fibers,taking into account the random shape of the coarse aggregate and the stochastic distribution of steel fibers.It captures microscopic-level interactions among the coarse aggregate,steel fibers,and matrix.Subsequently,a comprehensive procedure is formulated to calibrate the microscopic parameters required by the model,and the reliability of the model is verified by comparing with the experimental results.Furthermore,a coupled finite difference method-discrete element method approach is used to construct the model of the split Hopkinson pressure bar.Compression tests are simulated on SFRC specimens with varying steel fiber contents under static and dynamic loading conditions.Finally,based on the advantages of DEM analysis at the mesoscopic level,this study analyzed mechanisms of enhancement and crack arrest in SFRC.It shed a light on the perspectives of interface failure process,microcrack propagation,contact force field evolution and energy analysis,offering valuable insights for related mining engineering applications.
基金supported by the National Natural Science Foundation of China(Grant No.12272088)the Outstanding Youth Science Foundation of Liaoning Province(Grant No.2024JH3/50100013).
文摘Disk-drum structures jointed by bolted flanges(DDSJBFs)are core parts in aircraft engines,whose dynamic responses affect structural overall safety and service performance.However,studies on the dynamic response of DDSJBFs under base excitation are not found in available literature.In the present work,the dynamic responses for DDSJBFs subjected to base excitation are investigated both theoretically and experimentally.The kinetic energy and potential energy of disk,drum,and flange are derived according to the Kirchhoff plate,the Sanders’shell,and the Euler-Bernoulli beam theories,respectively,where the influences of flange and the mass of bolt are taken into account.The artificial spring method is applied to model the bolted joint.The Chebyshev orthogonal polynomials are adopted as the admissible functions of disk and drum,and the Lagrange equations are used to obtain the motion equation.The motion equation is solved by using the Newmark-beta approach and the dynamic responses under base excitation are acquired.A series of experiment studies are conducted on a DDSJBF to demonstrate the correctness of established theoretical model.Finally,study results show that because the relative motion between bolted flange joint interfaces generates friction damping,increasing the excitation amplitude causes the increase of damping ratio of DDSJBFs on the whole,and the increase of resonant peak value exhibits a slowing trend.The above phenomenon becomes more evident when the number of bolt is less.With the increase of bolt mass and flange size,the resonant frequency significantly decreases,while the resonant peak value remains unchanged.
文摘Revealing the combined influence of interfacial damage and nonlinear factors on the forced vibration is significant for the stability design of fluid-conveying pipes, which are usually assembled in aircraft. The nonlinear forced resonance of fluid-conveying layered pipes with a weak interface and a movable boundary under the external excitation is studied. The pipe is simply supported at both ends, with one end subject to a viscoelastic boundary constraint described by KelvinVoigt model. The weak interface in the pipe is considered in the refined displacement field of the layered pipe employing the interfacial cohesive law. The governing equations are derived by Hamilton's variational principle. Geometric nonlinearities including nonlinear curvature, longitudinal inertia nonlinearity and nonlinear constraint force are comprehensively considered during the theoretical derivation. Amplitude-frequency bifurcation diagrams are obtained utilizing a perturbation-Incremental Harmonic Balance Method(IHBM). Results show that interfacial damage and viscoelastic constraints from boundary and foundation have an important influence on the linear and nonlinear dynamic behavior of the system.
基金supported by the Ignite National Technology fund,under National Grassroots Initiatives Program of ICT R&D(NIGRI),Project ID.NGIRI-2024-23901 of 2024.
文摘This research focuses on developing innovative hybrid solar dryers that combine solar Photovoltaic(PV)and solar thermal systems for sustainable food preservation in Pakistan,addressing the country’s pressing issues of high post-harvest losses and unreliable energy sources.The proposed active hybrid solar dryer features a drying cabinet,two Direct Current(DC)fans for forced convection,and a resistive heating element powered by a 180 W solar PV panel.An energy-storing battery ensures continuous supply to the auxiliaries during periods of low solar irradiance,poor weather conditions,or nighttime.Tomatoes,a delicate and in-demand crop,were selected for experimentation due to their high perishability.Three experiments were conducted on the same prototype:natural convection direct solar dryer(NCDSD),forced convection direct solar dryer(FCDSD),and forced convection hybrid solar dryer(FCHSD).Each experiment began with 0.2 kg of tomatoes at 94%moisture content,achieving significant reductions:28.57%with NCDSD,16.667%with FCDSD,and 16.667%with FCHSD.The observed drying rates varied:1.161 kg/h for NCDSD,2.062 kg/h for FCDSD,and 2.8642 kg/h for FCHSD.This study presents a comparative analysis of efficiency,drying rate,and cost-effectiveness,alongside the system’s economic and environmental feasibility.
文摘The present work details a numerical simulation of forced convective laminar flow in a channel with a heated obstacle attached to one wall. The second law analysis is employed to investigate the distribution of entropy generation in the flow domain to demonstrate the rate of irreversibilities in thermal system. The conjugate problem including the convection heat transfer in the fluid flow and conduction one inside the obstacle is solved numerically to obtain the velocity and temperature fields in both gas and solid phases. To reach this goal, the set of governing equations including momentum and energy equations for the gas phase and conduction equation for the obstacle are solved by CFD technique to determine the hydrodynamic and thermal behaviors of the fluid flow around the obstacle and the temperature distribution in the solid element. An attempt is made to detail the local Nusselt number distribution and mean Nusselt number and also the local entropy generation distribution for the individual exposed obstacle faces. A good consistency is found between the present numerical results with experiment.
基金Project supported by the National Natural Science Foundation of China (No. 12272323)。
文摘Second-order axially moving systems are common models in the field of dynamics, such as axially moving strings, cables, and belts. In the traditional research work, it is difficult to obtain closed-form solutions for the forced vibration when the damping effect and the coupling effect of multiple second-order models are considered.In this paper, Green's function method based on the Laplace transform is used to obtain closed-form solutions for the forced vibration of second-order axially moving systems. By taking the axially moving damping string system and multi-string system connected by springs as examples, the detailed solution methods and the analytical Green's functions of these second-order systems are given. The mode functions and frequency equations are also obtained by the obtained Green's functions. The reliability and convenience of the results are verified by several examples. This paper provides a systematic analytical method for the dynamic analysis of second-order axially moving systems, and the obtained Green's functions are applicable to different second-order systems rather than just string systems. In addition, the work of this paper also has positive significance for the study on the forced vibration of high-order systems.
文摘The damped Helmholtz-Duffing oscillator is a topic of great interest in many different fields of study due to its complex dynamics.By transitioning from conventional continuous differential equations to their fractal counterparts,one gains insights into the system's response under new mathematical frameworks.This paper presents a novel method for converting standard continuous differential equations into their fractal equivalents.This conversion occurs after the nonlinear system is transformed into its linear equivalent.Numerical analyses show that there are several resonance sites in the fractal system,which differ from the one resonance point found in the continuous system.One important finding is that the fractal system loses some of its stabilizing power when decaying behavior is transformed into a diffuse pattern.Interestingly,a decrease in the fractal order in resonance settings shows a stabilizing impact,highlighting the dynamics'complexity inside fractal systems.This endeavor to convert to fractals is a revolutionary technique that is being employed for the first time.
基金co-supported by the National Natural Science Foundation of China(No.52125504)the Liaoning Revitalization Talents Program(No.XLYC2202017)Dalian Support Policy Project for Innovation of Technological Talents(No.2023RG001)。
文摘The high-quality assembly of Large Aircraft Components(LACs)is essential in modern aviation manufacturing.Numerical control locators are employed for the posture adjustment of LAC,yet the system's multi-input multi-output,nonlinearity,and strong coupling presents significant challenges.The substantial internal force generated during the adjustment process can potentially damage the LAC and degrade the assembly quality.Hence,a workspace-based hybrid force position control scheme was developed to achieve high quality assembly with high-precision and lower internal force.Firstly,an offline workspace analysis with inherent geometric characteristics to form time-varying posture error constraint.Then,the posture error is integrated into the online position axis control to ensure tracking the ideal posture,while the force control axis compensates for posture deviation by minimizing internal force,thereby achieving high precision and low internal force.Finally,the effectiveness was demonstrated through experiments.The root mean square errors of orientation and position are 104 rad and 0.1 mm,respectively.A reduction in internal force can range from 10.96%to 57.4%compared to the traditional method.Key points'max position error is decreased from 0.32 mm to 0.18 mm,satisfying the 0.5 mm tolerance.Therefore,the proposed method will help promote the development of high-performance manufacturing.
基金the National Key Research&Development Program of China(Grant No.2022YFC2203901)the State Key Laboratory of Spatial Datum(Grant No.SKLSD2025-KF-03)+1 种基金Fundamental Research Funds for the Central UniversitiesSun Yat-sen University for the support。
文摘The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.
文摘This interview examines the theoretical foundations,pedagogical applications,developmental trajectory,and future directions of the xu-argument.Professor Wang Chuming offers a comprehensive account of the xu-argument,clarifying its theoretical framework,the learning mechanisms underlying xu,and its interface with international theories of second language acquisition(SLA).From the perspective of the xu-argument,he proposes novel interpretations of core issues in SLA.Drawing on the development of the xu-argument,Wang further discusses the essence,directions,and methodology of innovation in SLA theory.He emphasizes that theoretical advances must capture and illuminate underlying natural laws,arguing that innovative approaches are typically rooted in deep reflection on common sense.He also calls for theoretical innovation in SLA in the Chinese context,advocating a robust research paradigm that shifts from local observation to global theoretical generalization,thereby promoting bottom-up theoretical development.In closing,he highlights the promising prospects for SLA theory in the era of artificial intelligence.
