Transmembrane water pores are crucial for substance transport through cell membranes via membrane fusion, such as in neural communication. However, the molecular mechanism of water pore formation is not clear. In this...Transmembrane water pores are crucial for substance transport through cell membranes via membrane fusion, such as in neural communication. However, the molecular mechanism of water pore formation is not clear. In this study, we apply all-atom molecular dynamics and bias-exchange metadynamics simulations to study the process of water pore formation under an electric field. We show that water molecules can enter a membrane under an electric field and form a water pore of a few nanometers in diameter. These water molecules disturb the interactions between lipid head groups and the ordered arrangement of lipids. Following the movement of water molecules, the lipid head groups are rotated and driven into the hydrophobic region of the membrane. The reorientated lipid head groups inside the membrane form a hydrophilic surface of the water pore. This study reveals the atomic details of how an electric field influences the movement of water molecules and lipid head groups, resulting in water pore formation.展开更多
The emergence of smart grids in India is propelled by an intricate interaction of market dynamics,regulatory structures,and stakeholder obligations.This study analyzes the primary factors that are driving the widespre...The emergence of smart grids in India is propelled by an intricate interaction of market dynamics,regulatory structures,and stakeholder obligations.This study analyzes the primary factors that are driving the widespread use of smart grid technologies and outlines the specific roles and obligations of different stakeholders,such as government entities,utility companies,technology suppliers,and consumers.Government activities and regulations are crucial in facilitating the implementation of smart grid technology by offering financial incentives,regulatory assistance,and strategic guidance.Utility firms have the responsibility of implementing and integrating smart grid infrastructure,with an emphasis on improving the dependability of the grid,minimizing losses in transmission and distribution,and integrating renewable energy sources.Technology companies offer the essential hardware and software solutions,which stimulate creativity and enhance efficiency.Consumers actively engage in the energy ecosystem by participating in demand response,implementing energy saving measures,and adopting distributed energy resources like solar panels and electric vehicles.This study examines the difficulties and possibilities in India’s smart grid industry,highlighting the importance of cooperation among stakeholders to build a strong,effective,and environmentally friendly energy future.展开更多
In this paper,the dispersion,attenuation,and bandgap characteristics of in-plane coupled Bloch waves in one-dimensional piezoelectric semiconductor(PSC)phononic crystals are investigated,emphasizing the influence of p...In this paper,the dispersion,attenuation,and bandgap characteristics of in-plane coupled Bloch waves in one-dimensional piezoelectric semiconductor(PSC)phononic crystals are investigated,emphasizing the influence of positive-negative(PN)junctions.Unlike piezoelectric phononic crystals,the coupled Bloch waves in PSC phononic crystals are attenuated due to their semiconductor properties,and thus the solution of Bloch waves becomes more complicated.The transfer matrix of the phononic crystal unit cell is obtained using the state transfer equation.By applying the Bloch theorem for periodic structures,the dispersion relation of the coupled Bloch waves is derived,and the dispersion,attenuation,and bandgap are obtained in the complex wave number domain.It is found that the influence of the PN junction cannot be neglected.Moreover,the effects of the PN junction under different apparent wave numbers and steady-state carrier concentrations are provided.This indicates the feasibility of adjusting the propagation characteristics of Bloch waves through the regulation of the PN heterojunction.展开更多
In this paper,a new temporal-spatial fractional order model is proposed to study the dynamic behavior of thermo-viscoelastic nanoplates.Traditional singular kernel in Caputo fractional order differentiation is replace...In this paper,a new temporal-spatial fractional order model is proposed to study the dynamic behavior of thermo-viscoelastic nanoplates.Traditional singular kernel in Caputo fractional order differentiation is replaced by the non-singular kernel and thus leads to a new generalized fractional order differential model with the integer order differential models as a special case.This improved model can more flexibly describe small-scale mechanical behavior and time-dependent heat conduction behavior and provides a clear physical explanation for the fractional order parameters.Spatial nonlocal effects are described in terms of nonlocal strain gradient elasticity and spatial fractional order derivatives,while the time-dependent effects are described in terms of non-Fourier heat conduction,viscoelasticity,and time fractional order derivatives.In addition,it is the first time that the nonlocal characteristic lengths and the memory characteristic times are introduced as two new small-scale parameters in the fractional order derivatives of non-singular kernels to focus on the short-range nonlocal behaviors and the short-term memory behaviors.Numerical examples of the free vibration and the forced vibration under step loading are given,and the effects of the spatial fractional order parameter and the temporal fractional order parameter are both discussed.展开更多
Both the thickness effect and surface effect should be important in nano-indentation behavior of coatings due to the finite thickness and small indentation size.As a basic solution,the two-dimensional Boussinesq probl...Both the thickness effect and surface effect should be important in nano-indentation behavior of coatings due to the finite thickness and small indentation size.As a basic solution,the two-dimensional Boussinesq problem of a finite elastic layer bonded to a rigid substrate is studied in this paper,employing the surface-energy-density-based elastic theory.The Airy stress function and Fourier integral transform methods are adopted to solve the problem.A nalytical solutions of both the stress and displacement fields are well achieved for a finite elastic layer under a concentrated force and a uniform pressure.Unlike the classical solutions,it is discovered that both the thickness effect and surface effect will show significant influences on the Boussinesq elastic behaviors.The surface effect would harden the finite elastic layer and induce a more uniformly distributing displacements and stresses.Only when the thickness is sufficiently large,the Boussinesq solution of an elastic half space may represent that of a finite elastic layer case.A generalized hardness is further defined to include the coupling effects of thickness and surface for the Boussinesq problem of a finite elastic layer.Such a study would assist in the design and property evaluation of coatings and micro-devices with layer-substrate structures.展开更多
This work examines the impact of incorporating the physiological conditions of human cancellous bone,by integrating similar porosity of porous Fe with the cancellous bone under dynamic immersion test.All of the porous...This work examines the impact of incorporating the physiological conditions of human cancellous bone,by integrating similar porosity of porous Fe with the cancellous bone under dynamic immersion test.All of the porous Fe specimens with~80%porosity were immersed in Simulated Body Fluid(SBF)with a flow rate of 0.3 ml/min integrated with cancellous bone for 7,14 and 28 days.Porous Fe with the lowest surface area has the highest degradation rate despite having the lowest relative weight loss.The relationship between fluid induced shear stress and weight loss of specimens have been established.展开更多
Understanding strain and fracture evolution in rock masses under climate change is crucial for slope stability.This study presents a fully coupled thermo-hydro-mechanical(THM)simulation of a rock slope at the Požá...Understanding strain and fracture evolution in rock masses under climate change is crucial for slope stability.This study presents a fully coupled thermo-hydro-mechanical(THM)simulation of a rock slope at the Požáry test site in the Czech Republic,integrating field tests and laboratory analyses.The simulations used the exactly measured slope geometry and incorporated a pre-existing upper slope fracture.Key constitutive models for fluid and vapor flow,heat conduction,and porosity-dependent permeability were coupled with a viscoplastic damage model to capture the THM behavior of the rock slope.Laboratory tests on three rock samples(A,B,and C)with varying elastic moduli and porosities informed the material properties for three corresponding models.Simulation results showed greater thermal changes in the upper sections of the slope due to increased exposure to thermal effects.Model A,with the highest elastic modulus,exhibited lower initial strain changes,while Model C showed significant early strain variations.After 30 d,Model A experienced a sudden strain decrease due to thermal contraction-induced damage.The critical fractured zone(CFZ)analysis revealed that rock contraction under cooling led to an increase in pore water pressure,exacerbating the damage.Model B highlighted the impact of geometrical asymmetry on the propagation of the damaged zone.Over time,the thermal effects increased plastic deformation in Model A,while Model C remained elastic and exhibited no damage.These findings have significant implications for assessing rock slope stability,particularly in predicting failure zones due to permeability reduction and pore water pressure generation.展开更多
The field of mechanics of biological and bio-inspired materials underwent an exciting development over the past several years, which made it stand at the cutting edge of both engineering mechanics and biomechanics. As...The field of mechanics of biological and bio-inspired materials underwent an exciting development over the past several years, which made it stand at the cutting edge of both engineering mechanics and biomechanics. As an intriguing interdisciplinary research field, it aims at elucidating the fundamental principles in nature＇s design of strong, multi-functional and smart Materials by focusing on the assembly, deformation, stability and failure of the materials.展开更多
Lower limb injures are frequently observed in passenger car traffic accidents.Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinem...Lower limb injures are frequently observed in passenger car traffic accidents.Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinematics,which lack in-depth study on the fractures in stress analysis.This paper aims to investigate lower limb impact biomechanics in real-world car to pedestrian accidents and to predict fractures of long bones in term of stress parameter for femur,tibia,and fibula.For the above purposes,a 3D finite element(FE) model of human body lower limb(HBM-LL) is developed based on human anatomy.The model consists of the pelvis,femur,tibia,fibula,patella,foot bones,primary tendons,knee joint capsule,meniscus,and ligaments.The FE model is validated by comparing the results from a lateral impact between simulations and tests with cadaver lower limb specimens.Two real-world accidents are selected from an in-depth accident database with detailed information about the accident scene,car impact speed,damage to the car,and pedestrian injuries.Multi-body system(MBS) models are used to reconstruct the kinematics of the pedestrians in the two accidents and the impact conditions are calculated for initial impact velocity and orientations of the car and pedestrian during the collision.The FE model is used to perform injury reconstructions and predict the fractures by using physical parameters,such as von Mises stress of long bones.The calculated failure level of the long bones is correlated with the injury outcomes observed from the two accident cases.The reconstruction result shows that the HBM-LL FE model has acceptable biofidelity and can be applied to predict the risk of long bone fractures.This study provides an efficient methodology to investigate the long bone fracture suffered from vehicle traffic collisions.展开更多
This paper addresses the problem of Hopf-flip bifurcation of high dimensional maps. Using the center manifold theorem, we obtain a three dimensional reduced map through the projection technique. The reduced map is fur...This paper addresses the problem of Hopf-flip bifurcation of high dimensional maps. Using the center manifold theorem, we obtain a three dimensional reduced map through the projection technique. The reduced map is further transformed into its normal form whose coefficients are determined by that of the original system. The dynamics of the map near the Hopf-flip bifurcation point is approximated by a so called “time-2τ^2 map” of a planar autonomous differential equation. It is shown that high dimensional maps may result in cycles of period two, tori T^1 （Hopf invariant circles）, tori 2T^1 and tori 2T^2 depending both on how the critical eigenvalues pass the unit circle and on the signs of resonant terms＇ coefficients. A two-degree-of-freedom vibro-impact system is given as an example to show how the procedure of this paper works. It reveals that through Hopf-flip bifurcations, periodic motions may lead directly to different types of motion, such as subharmonic motions, quasi-periodic motions, motions on high dimensional tori and even to chaotic motions depending both on change in direction of the parameter vector and on the nonlinear terms of the first three orders.展开更多
Collective cells are organized to form specific patterns which play important roles in various physiological and pathological processes,such as tissue morphogenesis,wound healing,and cancer invasion.Compared to single...Collective cells are organized to form specific patterns which play important roles in various physiological and pathological processes,such as tissue morphogenesis,wound healing,and cancer invasion.Compared to single cell behaviors,which has been intensively studied from many aspects(cell migration,adhesion,polarization,proliferation,etc.)and at various scales(molecular,subcellular,and cellular),the multiple cell behaviors are relatively less understood,particularly in a quantitative manner.In this paper,we will present our recent studies of collective polarization and orientation of multiple cells through both experimental measurement and theoretical modeling,including those cell behaviors on/in 2D and 3D substrate/tissue.We find that the collective cell behaviors,including polarization,alignment and migration are closely related to local stress states in cell layer or tissue,which demonstrate the crucial roles of mechanical forces in the living organisms.Specifically,the cells prefer to polarize and align along the maximum principal stress in the cell layer,and the aspect ratio of cell increases with the in-plane maximum shear stress,suggesting that the maximum shear stress is the underlying driving force of cell polarization and orientation.This theory of stress-driven cell behaviors of polarization and orientation provides a new perspective for understanding cell behaviors in living organisms and the guideline for tissue engineering in biomedical applications.展开更多
As an intriguing interdisciplinary research field, cell and molecular biomechanics is at the cutting edge of mechanics in general and biomechanics in particular. It has the potential to provide a quantitative understa...As an intriguing interdisciplinary research field, cell and molecular biomechanics is at the cutting edge of mechanics in general and biomechanics in particular. It has the potential to provide a quantitative understanding of how forces and deformation at tissue, cellular and molecular levels affect human health and disease. In this article, we review the recent advances in cell and molecular biomechanics, examine the available computational and experimental tools, and discuss important issues including protein deformation in mechanotransduction, cell deformation and constitutive behavior, cell adhesion and migration, and the associated models and theories. The opportunities and challenges in cell and molecular biomechanics are also discussed. We hope to provide readers a clear picture of the current status of this field, and to stimulate a broader interest in the applied mechanics community.展开更多
Stability for the manifolds of equilibrium states of a generalized Birkhoff system is studied. A theorem for the stability of the manifolds of equilibrium states of the general autonomous system is used to the general...Stability for the manifolds of equilibrium states of a generalized Birkhoff system is studied. A theorem for the stability of the manifolds of equilibrium states of the general autonomous system is used to the generalized BirkhoiYian system and two propositions on the stability of the manifolds of equilibrium states of the system are obtained. An example is given to illustrate the application of the results.展开更多
A hyperbolic Lindstedt-Poincare method is presented to determine the homoclinic solutions of a kind of nonlinear oscillators, in which critical value of the homoclinic bifurcation parameter can be determined. The gene...A hyperbolic Lindstedt-Poincare method is presented to determine the homoclinic solutions of a kind of nonlinear oscillators, in which critical value of the homoclinic bifurcation parameter can be determined. The generalized Lienard oscillator is studied in detail, and the present method＇s predictions are compared with those of Runge-Kutta method to illustrate its accuracy.展开更多
In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into...In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into shakedown after tens （or hundreds） of thousand cycles. After the ratcheting strain is saturated under the condition that stress amplitude is half of peak stress, it will bring about subsequent fatigue failure, and relationship between fatigue life and one of peak stress and saturated ratcheting （SR） strain meets power law. As the alloy is under stress jiggling with stress amplitude that is 1%-2.5% of peak stress, the ratcheting strain still become remarkable and goes into shakedown after several hundreds of thousand cycles but there exists little accessional strain caused by creep effect. It is notable that, when the peak stress is 85%-100% of yield stress, the long-cyclic stressing will lead SR strain to be from 1.4% to 2.5% even if the initial ratio of ratcheting strain is zero. Based on ratcheting threshold property of peak stress and monotonicity of relationship between the peak stress and SR strain, a saturated ratcheting model （SRM） is developed to predict SR strain and to estimate saturated creep strain also. In addition, the classes of ratcheting evolutions of metals are discussed.展开更多
The perturbation of symmetries of the free Birkhoff system under small excitation is discussed. The concept of high-order adiabatic invariant is presented, and the form of adiabatic invariants and the conditions for t...The perturbation of symmetries of the free Birkhoff system under small excitation is discussed. The concept of high-order adiabatic invariant is presented, and the form of adiabatic invariants and the conditions for their existence are given. Then these results are generalized to the constrained Birkhoff system. One example is presented to illustrate these results.展开更多
The capturability of the Three-Dimensional(3D)Realistic True Proportional Navigation(RTPN)guidance law is thoroughly analyzed.The true-arbitrarily maneuvering target is considered,which maneuvers along an arbitrary di...The capturability of the Three-Dimensional(3D)Realistic True Proportional Navigation(RTPN)guidance law is thoroughly analyzed.The true-arbitrarily maneuvering target is considered,which maneuvers along an arbitrary direction in 3D space with an arbitrary but upperbounded acceleration.The whole nonlinear relative kinematics between the interceptor and target is taken into account.First,the upper-bound of commanded acceleration of 3D RTPN is deduced,using a novel Lyapunov-like approach.Second,the reasonable selection range of navigation gain of3D RTPN is analyzed,when the maneuver limitation of interceptor is considered.After that,a more realistic definition of capture is adopted,i.e.,the relative range is smaller than an acceptable miss-distance while the approaching speed is larger than a required impact speed.Unlike previous researches which present Two-Dimensional(2D)capture regions,the inequality analysis technique is utilized to obtain the 3D capture region,where the three coordinates are the closing speed,transversal relative speed,and relative range.The obtained capture region could be taken as a sufficient-but-unnecessary condition of capture.The new theoretical findings are all given in explicit expressions and are more general than previous results.展开更多
This paper presents the analysis of dynamic characteristics of horizontal axis wind turbine blade, where the mode coupling among axial extension, flap vibration （out-of-plane bend- ing）, lead/lag vibration （in-plan...This paper presents the analysis of dynamic characteristics of horizontal axis wind turbine blade, where the mode coupling among axial extension, flap vibration （out-of-plane bend- ing）, lead/lag vibration （in-plane bending） and torsion is emphasized. By using the Bernoulli-Euler beam to describe the slender blade which is mounted on rigid hub and subjected to unsteady aero- dynamic force, the governing equation and characteristic equation of the coupled vibration of the blade are obtained. Due to the combined influences of mode coupling, centrifugal effect, and the non-uniform distribution of mass and stiffness, the explicit solution of characteristic equation is impossible to obtain. An equivalent transformation based on Green＇s functions is taken for the characteristic equation, and then a system of integrodifferential equations is derived. The nu- merical difference methods are adopted to solve the integrodifferential equations to get natural frequencies and mode shapes. The influences of mode coupling, centrifugal effect, and rotational speed on natural frequencies and mode shapes are analyzed. Results show that： （1） the influence of bending-torsion coupling on natural frequency is tiny; （2） rotation has dramatic influence on bending frequency but little influence on torsion frequency; （3） the influence of bending-bending coupling on dynamic characteristics is notable at high rotational speed; （4） the effect of rotational speed on bending mode is tiny.展开更多
Soil erosion is a serious problem arising from agricultural intensification, land degradation and other anthropogenic activities. Assessment of soil erosion is useful in planning and conservation works in a watershed ...Soil erosion is a serious problem arising from agricultural intensification, land degradation and other anthropogenic activities. Assessment of soil erosion is useful in planning and conservation works in a watershed or basin. Modelling can provide a quantitative and consistent approach to estimate soil erosion and sediment yield under a wide range of conditions. In the present study, the soil loss model, Revised Universal Soil Loss Equation （RUSLE） integrated with GIS has been used to estimate soil loss in the Nethravathi Basin located in the southwestern part of India. The Nethravathi Basin is a tropical coastal humid area having a drainage area of 3128 km2 up to the gauging station. The parameters of RUSLE model were estimated using remote sensing data and the erosion probability zones were determined using GIS. The estimated rainfall erosivity, soil erodibility, topographic and crop management factors range from 2948.16 to 4711.4 MJ/mm.ha-1hr-1/year, 0.10 to 0.44 t ha-1 -MJ-1.mm 1, 0 to 92,774 and 0 to 0.63 respectively. The results indicate that the estimated total annual potential soil loss of about 473,339 t/yr is comparable with the measured sediment of 441,870 t/yr during the water year 2002 2003. The predicted soil erosion rate due to increase in agricultural area is about 14,673.5 t/yr. The probability zone map has been derived by the weighted overlay index method indicate that the major portion of the study area comes under low probability zone and only a small portion comes under high and very high probability zone. The results can certainly aid in implementation of soil management and conservation practices to reduce the soil erosion in the Nethravathi Basin.展开更多
Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contai...Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contains both structural and aerodynamic nonlinearities. Hopf bifurcation theory is used to analyze the flutter speed of the system. The effects of system parameters on the flutter speed are studied. The 4th order Runge-Kutta method is used to calculate the stable limit cycle responses and chaotic motions of the aeroelastic system. Results show that the number and the stability of equilibrium points of the system vary with the increase of flow speed. Besides the simple limit cycle response of period 1, there are also period-doubling responses and chaotic motions in the flutter system. The route leading to chaos in the aeroelastic model used here is the period-doubling bifurcation. The chaotic motions in the system occur only when the flow speed is higher than the linear divergent speed and the initial condition is very small. Moreover, the flow speed regions in which the system behaves chaos axe very narrow.展开更多
基金supported by the National Natural Science Foundation of China (Grants 11372042, 11221202, 11532009, and 11202026)
文摘Transmembrane water pores are crucial for substance transport through cell membranes via membrane fusion, such as in neural communication. However, the molecular mechanism of water pore formation is not clear. In this study, we apply all-atom molecular dynamics and bias-exchange metadynamics simulations to study the process of water pore formation under an electric field. We show that water molecules can enter a membrane under an electric field and form a water pore of a few nanometers in diameter. These water molecules disturb the interactions between lipid head groups and the ordered arrangement of lipids. Following the movement of water molecules, the lipid head groups are rotated and driven into the hydrophobic region of the membrane. The reorientated lipid head groups inside the membrane form a hydrophilic surface of the water pore. This study reveals the atomic details of how an electric field influences the movement of water molecules and lipid head groups, resulting in water pore formation.
文摘The emergence of smart grids in India is propelled by an intricate interaction of market dynamics,regulatory structures,and stakeholder obligations.This study analyzes the primary factors that are driving the widespread use of smart grid technologies and outlines the specific roles and obligations of different stakeholders,such as government entities,utility companies,technology suppliers,and consumers.Government activities and regulations are crucial in facilitating the implementation of smart grid technology by offering financial incentives,regulatory assistance,and strategic guidance.Utility firms have the responsibility of implementing and integrating smart grid infrastructure,with an emphasis on improving the dependability of the grid,minimizing losses in transmission and distribution,and integrating renewable energy sources.Technology companies offer the essential hardware and software solutions,which stimulate creativity and enhance efficiency.Consumers actively engage in the energy ecosystem by participating in demand response,implementing energy saving measures,and adopting distributed energy resources like solar panels and electric vehicles.This study examines the difficulties and possibilities in India’s smart grid industry,highlighting the importance of cooperation among stakeholders to build a strong,effective,and environmentally friendly energy future.
基金Project supported by the National Natural Science Foundation of China(Nos.11872105,12072022,11911530176,and 12202039)。
文摘In this paper,the dispersion,attenuation,and bandgap characteristics of in-plane coupled Bloch waves in one-dimensional piezoelectric semiconductor(PSC)phononic crystals are investigated,emphasizing the influence of positive-negative(PN)junctions.Unlike piezoelectric phononic crystals,the coupled Bloch waves in PSC phononic crystals are attenuated due to their semiconductor properties,and thus the solution of Bloch waves becomes more complicated.The transfer matrix of the phononic crystal unit cell is obtained using the state transfer equation.By applying the Bloch theorem for periodic structures,the dispersion relation of the coupled Bloch waves is derived,and the dispersion,attenuation,and bandgap are obtained in the complex wave number domain.It is found that the influence of the PN junction cannot be neglected.Moreover,the effects of the PN junction under different apparent wave numbers and steady-state carrier concentrations are provided.This indicates the feasibility of adjusting the propagation characteristics of Bloch waves through the regulation of the PN heterojunction.
基金supported by the National Natural Science Foundation of China(Grant Nos.12072022 and 11872105)Fundamental Research Funds for the Central Universities(Grant Nos.FRF-TW-2018-005 and FRF-BR-18-008B).
文摘In this paper,a new temporal-spatial fractional order model is proposed to study the dynamic behavior of thermo-viscoelastic nanoplates.Traditional singular kernel in Caputo fractional order differentiation is replaced by the non-singular kernel and thus leads to a new generalized fractional order differential model with the integer order differential models as a special case.This improved model can more flexibly describe small-scale mechanical behavior and time-dependent heat conduction behavior and provides a clear physical explanation for the fractional order parameters.Spatial nonlocal effects are described in terms of nonlocal strain gradient elasticity and spatial fractional order derivatives,while the time-dependent effects are described in terms of non-Fourier heat conduction,viscoelasticity,and time fractional order derivatives.In addition,it is the first time that the nonlocal characteristic lengths and the memory characteristic times are introduced as two new small-scale parameters in the fractional order derivatives of non-singular kernels to focus on the short-range nonlocal behaviors and the short-term memory behaviors.Numerical examples of the free vibration and the forced vibration under step loading are given,and the effects of the spatial fractional order parameter and the temporal fractional order parameter are both discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.12032004,12293000,12293002,and 12272043).
文摘Both the thickness effect and surface effect should be important in nano-indentation behavior of coatings due to the finite thickness and small indentation size.As a basic solution,the two-dimensional Boussinesq problem of a finite elastic layer bonded to a rigid substrate is studied in this paper,employing the surface-energy-density-based elastic theory.The Airy stress function and Fourier integral transform methods are adopted to solve the problem.A nalytical solutions of both the stress and displacement fields are well achieved for a finite elastic layer under a concentrated force and a uniform pressure.Unlike the classical solutions,it is discovered that both the thickness effect and surface effect will show significant influences on the Boussinesq elastic behaviors.The surface effect would harden the finite elastic layer and induce a more uniformly distributing displacements and stresses.Only when the thickness is sufficiently large,the Boussinesq solution of an elastic half space may represent that of a finite elastic layer case.A generalized hardness is further defined to include the coupling effects of thickness and surface for the Boussinesq problem of a finite elastic layer.Such a study would assist in the design and property evaluation of coatings and micro-devices with layer-substrate structures.
基金funded by the Ministry of Higher Education,Malaysia under the Fundamental Research Grant Scheme(FRGS/1/2018/TK03/UTM/02/8).
文摘This work examines the impact of incorporating the physiological conditions of human cancellous bone,by integrating similar porosity of porous Fe with the cancellous bone under dynamic immersion test.All of the porous Fe specimens with~80%porosity were immersed in Simulated Body Fluid(SBF)with a flow rate of 0.3 ml/min integrated with cancellous bone for 7,14 and 28 days.Porous Fe with the lowest surface area has the highest degradation rate despite having the lowest relative weight loss.The relationship between fluid induced shear stress and weight loss of specimens have been established.
基金support from the European Commission via a Marie Curie Fellowship(Grant No.101033084)awarded to Dr.Saeed Tourchi(corresponding author)the Research Grant Office at Sharif University of Technology for grants G4010902 and QB020105funding from the TACR project SS02030023,Rock Environment and Resources,under the“Environment for Life”program and the Institutional Research Plan RVO67985891 of the Institute of Rock Structure and Mechanics of the Czech Academy of Sciences.
文摘Understanding strain and fracture evolution in rock masses under climate change is crucial for slope stability.This study presents a fully coupled thermo-hydro-mechanical(THM)simulation of a rock slope at the Požáry test site in the Czech Republic,integrating field tests and laboratory analyses.The simulations used the exactly measured slope geometry and incorporated a pre-existing upper slope fracture.Key constitutive models for fluid and vapor flow,heat conduction,and porosity-dependent permeability were coupled with a viscoplastic damage model to capture the THM behavior of the rock slope.Laboratory tests on three rock samples(A,B,and C)with varying elastic moduli and porosities informed the material properties for three corresponding models.Simulation results showed greater thermal changes in the upper sections of the slope due to increased exposure to thermal effects.Model A,with the highest elastic modulus,exhibited lower initial strain changes,while Model C showed significant early strain variations.After 30 d,Model A experienced a sudden strain decrease due to thermal contraction-induced damage.The critical fractured zone(CFZ)analysis revealed that rock contraction under cooling led to an increase in pore water pressure,exacerbating the damage.Model B highlighted the impact of geometrical asymmetry on the propagation of the damaged zone.Over time,the thermal effects increased plastic deformation in Model A,while Model C remained elastic and exhibited no damage.These findings have significant implications for assessing rock slope stability,particularly in predicting failure zones due to permeability reduction and pore water pressure generation.
文摘The field of mechanics of biological and bio-inspired materials underwent an exciting development over the past several years, which made it stand at the cutting edge of both engineering mechanics and biomechanics. As an intriguing interdisciplinary research field, it aims at elucidating the fundamental principles in nature＇s design of strong, multi-functional and smart Materials by focusing on the assembly, deformation, stability and failure of the materials.
基金supported by National Hi-tech Research and Development Program of China (863 Program,Grant No. 2006AA110101)"111 Program" of Ministry of Education and State Administration of Foreign Experts Affairs of China (Grant No. 111-2-11)+1 种基金General Motors Research and Development Center (Grant No. RD-209)Project of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body,Hunan University,China (Grant No. 60870004)
文摘Lower limb injures are frequently observed in passenger car traffic accidents.Previous studies of the injuries focus on long bone fractures by using either cadaver component tests or simulations of the long bone kinematics,which lack in-depth study on the fractures in stress analysis.This paper aims to investigate lower limb impact biomechanics in real-world car to pedestrian accidents and to predict fractures of long bones in term of stress parameter for femur,tibia,and fibula.For the above purposes,a 3D finite element(FE) model of human body lower limb(HBM-LL) is developed based on human anatomy.The model consists of the pelvis,femur,tibia,fibula,patella,foot bones,primary tendons,knee joint capsule,meniscus,and ligaments.The FE model is validated by comparing the results from a lateral impact between simulations and tests with cadaver lower limb specimens.Two real-world accidents are selected from an in-depth accident database with detailed information about the accident scene,car impact speed,damage to the car,and pedestrian injuries.Multi-body system(MBS) models are used to reconstruct the kinematics of the pedestrians in the two accidents and the impact conditions are calculated for initial impact velocity and orientations of the car and pedestrian during the collision.The FE model is used to perform injury reconstructions and predict the fractures by using physical parameters,such as von Mises stress of long bones.The calculated failure level of the long bones is correlated with the injury outcomes observed from the two accident cases.The reconstruction result shows that the HBM-LL FE model has acceptable biofidelity and can be applied to predict the risk of long bone fractures.This study provides an efficient methodology to investigate the long bone fracture suffered from vehicle traffic collisions.
基金The project supported by the Nutional Natural Science Foundation of China(10472096)
文摘This paper addresses the problem of Hopf-flip bifurcation of high dimensional maps. Using the center manifold theorem, we obtain a three dimensional reduced map through the projection technique. The reduced map is further transformed into its normal form whose coefficients are determined by that of the original system. The dynamics of the map near the Hopf-flip bifurcation point is approximated by a so called “time-2τ^2 map” of a planar autonomous differential equation. It is shown that high dimensional maps may result in cycles of period two, tori T^1 （Hopf invariant circles）, tori 2T^1 and tori 2T^2 depending both on how the critical eigenvalues pass the unit circle and on the signs of resonant terms＇ coefficients. A two-degree-of-freedom vibro-impact system is given as an example to show how the procedure of this paper works. It reveals that through Hopf-flip bifurcations, periodic motions may lead directly to different types of motion, such as subharmonic motions, quasi-periodic motions, motions on high dimensional tori and even to chaotic motions depending both on change in direction of the parameter vector and on the nonlinear terms of the first three orders.
基金the National Natural Science Foundation of China(Grants 11772055,11532009,11521062,11372042).
文摘Collective cells are organized to form specific patterns which play important roles in various physiological and pathological processes,such as tissue morphogenesis,wound healing,and cancer invasion.Compared to single cell behaviors,which has been intensively studied from many aspects(cell migration,adhesion,polarization,proliferation,etc.)and at various scales(molecular,subcellular,and cellular),the multiple cell behaviors are relatively less understood,particularly in a quantitative manner.In this paper,we will present our recent studies of collective polarization and orientation of multiple cells through both experimental measurement and theoretical modeling,including those cell behaviors on/in 2D and 3D substrate/tissue.We find that the collective cell behaviors,including polarization,alignment and migration are closely related to local stress states in cell layer or tissue,which demonstrate the crucial roles of mechanical forces in the living organisms.Specifically,the cells prefer to polarize and align along the maximum principal stress in the cell layer,and the aspect ratio of cell increases with the in-plane maximum shear stress,suggesting that the maximum shear stress is the underlying driving force of cell polarization and orientation.This theory of stress-driven cell behaviors of polarization and orientation provides a new perspective for understanding cell behaviors in living organisms and the guideline for tissue engineering in biomedical applications.
基金supported by the National Heart,Lung,and Blood Institute,National Institutes of Health,as a Program of Excellence in Nanotechnology Award,N01 HV-08234,to Gang Baothe support from the National Natural Science Foundation of China through Grant Nos.10872115,11025208 and 10732050
文摘As an intriguing interdisciplinary research field, cell and molecular biomechanics is at the cutting edge of mechanics in general and biomechanics in particular. It has the potential to provide a quantitative understanding of how forces and deformation at tissue, cellular and molecular levels affect human health and disease. In this article, we review the recent advances in cell and molecular biomechanics, examine the available computational and experimental tools, and discuss important issues including protein deformation in mechanotransduction, cell deformation and constitutive behavior, cell adhesion and migration, and the associated models and theories. The opportunities and challenges in cell and molecular biomechanics are also discussed. We hope to provide readers a clear picture of the current status of this field, and to stimulate a broader interest in the applied mechanics community.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10772025,10932002 and 10972127)the Natural Science Foundation of Henan Province,China(Grant No.102300410144)the Beijing Municipal Key Disciplines Fund for General Mechanics and Foundation of Mechanics,China
文摘Stability for the manifolds of equilibrium states of a generalized Birkhoff system is studied. A theorem for the stability of the manifolds of equilibrium states of the general autonomous system is used to the generalized BirkhoiYian system and two propositions on the stability of the manifolds of equilibrium states of the system are obtained. An example is given to illustrate the application of the results.
基金supported by the National Natural Science Foundation of China (10672193)Sun Yat-sen University (Fu Lan Scholarship)the University of Hong Kong (CRGC grant).
文摘A hyperbolic Lindstedt-Poincare method is presented to determine the homoclinic solutions of a kind of nonlinear oscillators, in which critical value of the homoclinic bifurcation parameter can be determined. The generalized Lienard oscillator is studied in detail, and the present method＇s predictions are compared with those of Runge-Kutta method to illustrate its accuracy.
文摘In order to investigate the ratcheting behavior of T225NG alloy, a series of ratcheting tests under uniaxial long-cyclic stressing were performed. The results show that the ratcheting strain of this alloy can get into shakedown after tens （or hundreds） of thousand cycles. After the ratcheting strain is saturated under the condition that stress amplitude is half of peak stress, it will bring about subsequent fatigue failure, and relationship between fatigue life and one of peak stress and saturated ratcheting （SR） strain meets power law. As the alloy is under stress jiggling with stress amplitude that is 1%-2.5% of peak stress, the ratcheting strain still become remarkable and goes into shakedown after several hundreds of thousand cycles but there exists little accessional strain caused by creep effect. It is notable that, when the peak stress is 85%-100% of yield stress, the long-cyclic stressing will lead SR strain to be from 1.4% to 2.5% even if the initial ratio of ratcheting strain is zero. Based on ratcheting threshold property of peak stress and monotonicity of relationship between the peak stress and SR strain, a saturated ratcheting model （SRM） is developed to predict SR strain and to estimate saturated creep strain also. In addition, the classes of ratcheting evolutions of metals are discussed.
基金The project supported by the National Natural Science Foundation(19972010)the Doctoral Program Foundation of Institution of Higher Education of Chinathe Natural Science Foundation of Henan Province
文摘The perturbation of symmetries of the free Birkhoff system under small excitation is discussed. The concept of high-order adiabatic invariant is presented, and the form of adiabatic invariants and the conditions for their existence are given. Then these results are generalized to the constrained Birkhoff system. One example is presented to illustrate these results.
基金supported in part by the National Natural Science Foundation of China(No.12002370)in part by the Hunan Provincial Natural Science Foundation of China(No.2019JJ50736)。
文摘The capturability of the Three-Dimensional(3D)Realistic True Proportional Navigation(RTPN)guidance law is thoroughly analyzed.The true-arbitrarily maneuvering target is considered,which maneuvers along an arbitrary direction in 3D space with an arbitrary but upperbounded acceleration.The whole nonlinear relative kinematics between the interceptor and target is taken into account.First,the upper-bound of commanded acceleration of 3D RTPN is deduced,using a novel Lyapunov-like approach.Second,the reasonable selection range of navigation gain of3D RTPN is analyzed,when the maneuver limitation of interceptor is considered.After that,a more realistic definition of capture is adopted,i.e.,the relative range is smaller than an acceptable miss-distance while the approaching speed is larger than a required impact speed.Unlike previous researches which present Two-Dimensional(2D)capture regions,the inequality analysis technique is utilized to obtain the 3D capture region,where the three coordinates are the closing speed,transversal relative speed,and relative range.The obtained capture region could be taken as a sufficient-but-unnecessary condition of capture.The new theoretical findings are all given in explicit expressions and are more general than previous results.
基金supported by the National Natural Science Foundation of China(Nos.11372257 and 11601007)Sichuan Provincial Project for Young Research Group of Scientific and Technological Innovations(2013)+1 种基金the Anhui Provincial Natural Science Foundation(No.1708085QA17)Pre-research Project Funds of Anhui University of Science and Technology(No.2016yz007)
文摘This paper presents the analysis of dynamic characteristics of horizontal axis wind turbine blade, where the mode coupling among axial extension, flap vibration （out-of-plane bend- ing）, lead/lag vibration （in-plane bending） and torsion is emphasized. By using the Bernoulli-Euler beam to describe the slender blade which is mounted on rigid hub and subjected to unsteady aero- dynamic force, the governing equation and characteristic equation of the coupled vibration of the blade are obtained. Due to the combined influences of mode coupling, centrifugal effect, and the non-uniform distribution of mass and stiffness, the explicit solution of characteristic equation is impossible to obtain. An equivalent transformation based on Green＇s functions is taken for the characteristic equation, and then a system of integrodifferential equations is derived. The nu- merical difference methods are adopted to solve the integrodifferential equations to get natural frequencies and mode shapes. The influences of mode coupling, centrifugal effect, and rotational speed on natural frequencies and mode shapes are analyzed. Results show that： （1） the influence of bending-torsion coupling on natural frequency is tiny; （2） rotation has dramatic influence on bending frequency but little influence on torsion frequency; （3） the influence of bending-bending coupling on dynamic characteristics is notable at high rotational speed; （4） the effect of rotational speed on bending mode is tiny.
文摘Soil erosion is a serious problem arising from agricultural intensification, land degradation and other anthropogenic activities. Assessment of soil erosion is useful in planning and conservation works in a watershed or basin. Modelling can provide a quantitative and consistent approach to estimate soil erosion and sediment yield under a wide range of conditions. In the present study, the soil loss model, Revised Universal Soil Loss Equation （RUSLE） integrated with GIS has been used to estimate soil loss in the Nethravathi Basin located in the southwestern part of India. The Nethravathi Basin is a tropical coastal humid area having a drainage area of 3128 km2 up to the gauging station. The parameters of RUSLE model were estimated using remote sensing data and the erosion probability zones were determined using GIS. The estimated rainfall erosivity, soil erodibility, topographic and crop management factors range from 2948.16 to 4711.4 MJ/mm.ha-1hr-1/year, 0.10 to 0.44 t ha-1 -MJ-1.mm 1, 0 to 92,774 and 0 to 0.63 respectively. The results indicate that the estimated total annual potential soil loss of about 473,339 t/yr is comparable with the measured sediment of 441,870 t/yr during the water year 2002 2003. The predicted soil erosion rate due to increase in agricultural area is about 14,673.5 t/yr. The probability zone map has been derived by the weighted overlay index method indicate that the major portion of the study area comes under low probability zone and only a small portion comes under high and very high probability zone. The results can certainly aid in implementation of soil management and conservation practices to reduce the soil erosion in the Nethravathi Basin.
基金supported by the National Natural Science Foundation of China and China Academy of Engineering Physics(No. 10576024).
文摘Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contains both structural and aerodynamic nonlinearities. Hopf bifurcation theory is used to analyze the flutter speed of the system. The effects of system parameters on the flutter speed are studied. The 4th order Runge-Kutta method is used to calculate the stable limit cycle responses and chaotic motions of the aeroelastic system. Results show that the number and the stability of equilibrium points of the system vary with the increase of flow speed. Besides the simple limit cycle response of period 1, there are also period-doubling responses and chaotic motions in the flutter system. The route leading to chaos in the aeroelastic model used here is the period-doubling bifurcation. The chaotic motions in the system occur only when the flow speed is higher than the linear divergent speed and the initial condition is very small. Moreover, the flow speed regions in which the system behaves chaos axe very narrow.
