A high-density tungsten-zirconium-titanium(W-Zr-Ti)reactive alloy was prepared by powder metallurgy.This alloy exhibits high density,high strength,and violent energy release characteristics,resulting in outstanding pe...A high-density tungsten-zirconium-titanium(W-Zr-Ti)reactive alloy was prepared by powder metallurgy.This alloy exhibits high density,high strength,and violent energy release characteristics,resulting in outstanding penetration and ignition abilities.Dynamic impact experiment demonstrated its strain rate hardening effect,and the energetic characteristics were investigated by digital image processing technique and thermal analysis experiment.The results show that W-Zr-Ti reactive alloy performs compressive strength of 2.25 GPa at 5784 s^(-1)strain rate,and its exothermic reaction occurs at about 961 K.Based on the explosion test and shock wave theory,thresholds of enhanced damage effect are less than 35.77 GPa and 5.18×10^(4)kJ/m^(2)for shock pressure and energy,respectively.Furthermore,the transformation of fracture behavior and failure mechanism is revealed,which causes the increase in compressive strength and reaction intensity under dynamic loading.展开更多
The aerial deployment method enables Unmanned Aerial Vehicles(UAVs)to be directly positioned at the required altitude for their mission.This method typically employs folding technology to improve loading efficiency,wi...The aerial deployment method enables Unmanned Aerial Vehicles(UAVs)to be directly positioned at the required altitude for their mission.This method typically employs folding technology to improve loading efficiency,with applications such as the gravity-only aerial deployment of high-aspect-ratio solar-powered UAVs,and aerial takeoff of fixed-wing drones in Mars research.However,the significant morphological changes during deployment are accompanied by strong nonlinear dynamic aerodynamic forces,which result in multiple degrees of freedom and an unstable character.This hinders the description and analysis of unknown dynamic behaviors,further leading to difficulties in the design of deployment strategies and flight control.To address this issue,this paper proposes an analysis method for dynamic behaviors during aerial deployment based on the Variational Autoencoder(VAE).Focusing on the gravity-only deployment problem of highaspect-ratio foldable-wing UAVs,the method encodes the multi-degree-of-freedom unstable motion signals into a low-dimensional feature space through a data-driven approach.By clustering in the feature space,this paper identifies and studies several dynamic behaviors during aerial deployment.The research presented in this paper offers a new method and perspective for feature extraction and analysis of complex and difficult-to-describe extreme flight dynamics,guiding the research on aerial deployment drones design and control strategies.展开更多
The understanding of the impact of high-velocity microparticles on human skin tissue is important for the ad-ministration of drugs during transdermal drug delivery.This paper aims to numerically investigate the dynami...The understanding of the impact of high-velocity microparticles on human skin tissue is important for the ad-ministration of drugs during transdermal drug delivery.This paper aims to numerically investigate the dynamic behavior of human skin tissue under micro-particle impact in transdermal drug delivery.The numerical model was developed based on a coupled smoothed particle hydrodynamics(SPH)and FEM method via commercial FE software RADIOSS.Analytical analysis was conducted applying the Poncelet model and was used as validation data.A hyperelastic one-term Ogden model with one pair of material parameters(μ,α)was implemented for the skin tissue.Sensitivity studies reveal that the effect of parameter α on the penetration process is much more significant than μ.Numerical results correlate well with the analytical curves with various particle diameters and impact velocities,its capability of predicting the penetration process of micro-particle impacts into skin tissues.This work can be further investigated to guide the design of transdermal drug delivery equipment.展开更多
The loss of hydrocarbon production caused by the dynamic behavior of the inner boundary and propped fractures under long-term production conditions has been widely reported in recent studies.However,the quantitative r...The loss of hydrocarbon production caused by the dynamic behavior of the inner boundary and propped fractures under long-term production conditions has been widely reported in recent studies.However,the quantitative relationships for the variations of the inner boundary and propped fractures have not been determined and incorporated in the semi-analytical models for the pressure and rate transient analysis.This work focuses on describing the variations of the inner boundary and propped fractures and capturing the typical characteristics from the pressure transient curves.A generalized semi-analytical model was developed to characterize the dynamic behavior of the inner boundary and propped fractures under long-term production conditions.The pressure-dependent length shrinkage coefficients,which quantify the length changes of the inner zone and propped fractures,are modified and incorporated into this multi-zone semi-analytical model.With simultaneous numerical iterations and numerical inversions in Laplace and real-time space,the transient solutions to pressure and rate behavior are determined in just a few seconds.The dynamic behavior of the inner boundary and propped fractures on transient pressure curves is divided into five periods:fracture bilinear flow(FR1),dynamic PFs flow(FR2),inner-area linear flow(FR3),dynamic inner boundary flow(FR4),and outer-area dominated linear flow(FR5).The early hump during FR2 period and a positive upward shift during FR4period are captured on the log-log pressure transient curves,reflecting the dynamic behavior of the inner boundary and propped fractures during the long-term production period.The transient pressure behavior will exhibit greater positive upward trend and the flow rate will be lower with the shrinkage of the inner boundary.The pressure derivative curve will be upward earlier as the inner boundary shrinks more rapidly.The lower permeability caused by the closure of un-propped fractures in the inner zone results in greater upward in pressure derivative curves.If the permeability loss for the dynamic behavior of the inner boundary caused by the closure of un-propped fractures is neglected,the flow rate will be overestimated in the later production period.展开更多
A series of centrifuge model tests of sandy slopes were conducted to study the dynamic behavior of pile-reinforced slopes subjected to various motions.Time histories of accelerations,bending moments and pile earth pre...A series of centrifuge model tests of sandy slopes were conducted to study the dynamic behavior of pile-reinforced slopes subjected to various motions.Time histories of accelerations,bending moments and pile earth pressures were obtained during excitation of the adjusted El Centro earthquake and a cyclic motion.Under a realistic earthquake,the overall response of the pile-reinforced slope is lower than that of the non-reinforced slope.The histories of bending moments and dynamic earth pressures reach their maximums soon after shaking started and then remain roughly stable until the end of shaking.Maximum moments occur at the height of 3.5 m,which is the deeper section of the pile,indicating the interface between the active loading and passive resistance regions.The dynamic earth pressures above the slope base steadily increase with the increase of height of pile.For the model under cyclic input motion,response amplitudes at different locations in the slope are almost the same,indicating no significant response amplification.Both the bending moment and earth pressure increase gradually over a long period.展开更多
In this paper,we propose a combined form of the bilinear Kadomtsev-Petviashvili equation and the bilinear extended(2+1)-dimensional shallow water wave equation,which is linked with a novel(2+1)-dimensional nonlinear m...In this paper,we propose a combined form of the bilinear Kadomtsev-Petviashvili equation and the bilinear extended(2+1)-dimensional shallow water wave equation,which is linked with a novel(2+1)-dimensional nonlinear model.This model might be applied to describe the evolution of nonlinear waves in the ocean.Under the effect of a novel combination of nonlinearity and dispersion terms,two cases of lump solutions to the(2+1)-dimensional nonlinear model are derived by searching for the quadratic function solutions to the bilinear form.Moreover,the one-lump-multi-stripe solutions are constructed by the test function combining quadratic functions and multiple exponential functions.The one-lump-multi-soliton solutions are derived by the test function combining quadratic functions and multiple hyperbolic cosine functions.Dynamic behaviors of the lump solutions and mixed solutions are analyzed via numerical simulation.The result is of importance to provide efficient expressions to model nonlinear waves and explain some interaction mechanism of nonlinear waves in physics.展开更多
In order to reduce economic and life losses due to terrorism or accidental explosion threats, reinforced concrete （RC） slabs of buildings need to he designed or retrofitted to resist blast loading. In this paper the...In order to reduce economic and life losses due to terrorism or accidental explosion threats, reinforced concrete （RC） slabs of buildings need to he designed or retrofitted to resist blast loading. In this paper the dynamic behavior of RC slabs under blast loading and its influencing factors are studied. The numerical model of an RC slab subjected to blast loading is established using the explicit dynamic analysis software. Both the strain rate effect and the damage accumulation are taken into account in the material model. The dynamic responses of the RC slab subjected to blast loading are analyzed, and the influence of concrete strength, thickness and reinforcement ratio on the behavior of the RC slab under blast loading is numerically investigated. Based on the numerical results, some principles for blast-resistant design and retrofitting are proposed to improve the behavior of the RC slab subjected to blast loading.展开更多
The dynamic behavior of a bridge-erecting machine, carrying a moving mass suspended by a wire rope, is investigated. The bridge-erecting machine is modelled by a simply supported uniform beam, and a massless equivale...The dynamic behavior of a bridge-erecting machine, carrying a moving mass suspended by a wire rope, is investigated. The bridge-erecting machine is modelled by a simply supported uniform beam, and a massless equivalent ＂spring-damper＂ system with an effective spring constant and an effective damping coefficient is used to model the moving mass suspended by the wire rope. The suddenly applied load is represented by a unitary Dirac Delta function. With the expansion method, a simple closed-form solution for the equation of motion with the replaced spring-damper-mass system is formulated. The characters of the rope are included in the derivation of the differential equation of motion for the system. The numerical examples show that the effects of the damping coefficient and the spring constant of the rope on the deflection have significant variations with the loading frequency. The effects of the damping coefficient and the spring constant under different beam lengths are also examined. The obtained results validate the presented approach, and provide significant references in the design process of bridgeerecting machines.展开更多
The marine risers are often subjected to parametric excitations from the fluctuation top tension. The top tension on the riser may fluctuate with multiple frequencies caused by irregular waves. In this paper, the infl...The marine risers are often subjected to parametric excitations from the fluctuation top tension. The top tension on the riser may fluctuate with multiple frequencies caused by irregular waves. In this paper, the influence between different frequency components in the top tension on the riser system is theoretically simulated and analyzed. With the Euler-Bernoulli beam theory, a dynamic model for the vibrations of the riser is established. The top tension is set as fluctuating with time and it has two different frequencies. The influences from the fluctuation amplitudes, circular frequencies and phase angles of these frequency components on the riser system are analyzed in detail. When these two frequencies are fluctuating in the stable regions, the riser system may become unstable because ω1+ω2≈2Ωn. The fluctuation amplitudes of these frequencies have little effect on the components of the vibration frequencies of the riser. For different phase angles, the stability and dynamic behaviors of the riser would be different.展开更多
Finger seal is a new technology developed for gas path sealing in gas turbine engine.It has been paid attention to its good sealing performance and lower manufacture cost.The vibration behavior of finger seal is not b...Finger seal is a new technology developed for gas path sealing in gas turbine engine.It has been paid attention to its good sealing performance and lower manufacture cost.The vibration behavior of finger seal is not be considered in performance analysis for the contact finger seal with compliant geometric configuration,then this will influence the reliability of the performance analysis and the parametric design of a finger seal.According to the dynamic character of finger seal,the harmonic vibration and free vibration models of a repetitive section of a two-layer finger seal that contains one high and one low finger seal are established separately.The dynamic behavior of finger seal in different working conditions is obtained based on the dynamic response analysis of finger＇s vibrations.The dynamic low hysteresis and low wear terms based on the equivalent dynamic model of finger seal are put forward,which can be used to predict the dynamic behavior of finger seal.As an example,the dynamic behaviors of an 8-layer finger seal and a 10-layer finger seal were predicted,and the validity of the prediction was demonstrated by the leakage test results of these two finger seals.The work presented here not only could make the dynamic analysis of finger seal with complicated structure simple and easy especially for multi-layer finger seal system,but also suggest a useful method for designing the finger seal with good dynamic behavior by means of different seal layers assembly.展开更多
The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of singl...The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.展开更多
This paper presents a numerical analysis of the dynamic transient behaviors of undersea cables.In this numerical study,the governing equations based on Euler-Bernoulli beam theory are adopted,and they can satisfy many...This paper presents a numerical analysis of the dynamic transient behaviors of undersea cables.In this numerical study,the governing equations based on Euler-Bernoulli beam theory are adopted,and they can satisfy many applications no matter what the magnitude of the cable tension is.The nonlinear coupled equations are solved by a popular central finite difference method,and the numerical results of transient behaviors are presented when several kinds of surrounding conditions,such as different towing speeds of surface vessel,different currents and waves with various frequencies and amplitudes,are exerted.Then a detailed comparison of the results,including the upper end tension and cable shape in time-domain,is made under the above external excitations,and finally the possible reasons for these are further explained.展开更多
An improved numerical method is used to simulate the dynamic behavior of a two part towing cable systems during turnings. In U turns and full turns, periodical heave motions are found both for the towed vehicle and fo...An improved numerical method is used to simulate the dynamic behavior of a two part towing cable systems during turnings. In U turns and full turns, periodical heave motions are found both for the towed vehicle and for the depressor. Periodic motions of the subsea units and of the cable surface tension are closely related to the turning parameters, such as turning velocity and turning radius. System parameters, such as length of the second cable and the vehicle bydrodynamics, also damp turning instability.展开更多
To investigate the dynamic behavior and energy dissipation of the rock−concrete interface,dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar.The test results reveal t...To investigate the dynamic behavior and energy dissipation of the rock−concrete interface,dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar.The test results reveal that with the change of the interface inclination angles(θ),the influence of interface groove width on the bearing capacity of specimens also varies.Whenθincreases from 0°to 30°,the bearing capacity of the specimen increases first and then decreases with the rise of the interface groove width;the optimal groove width on the rock surface in this range of interface inclination angles is 5 mm.Whenθincreases from 45°to 90°,the bearing capacity of the specimen has no obvious change.Moreover,whenθincreases from 0°to 45°,the dissipated energy of the specimens rises obviously at first and then tends to be stable as the width of the interface groove increases.展开更多
In this paper three types of dual- chamber shock- struts are considered in dynamic analyses of landing-gear behavior during impact and taxi. Their dynamic characteristics are compared with each other according to calc...In this paper three types of dual- chamber shock- struts are considered in dynamic analyses of landing-gear behavior during impact and taxi. Their dynamic characteristics are compared with each other according to calculation results, and some conclusions are presented.It is very helpful for selecting a suitable type of dual-chamber shock-strut in landing-gear design.展开更多
Based on the Magneto-Hydro-Dynamic（MHD） theory, a united three-dimensional（3D） transient numerical model is developed to investigate the dynamic behaviors of arc plasma for a magnesium alloy AZ61A gas tungsten arc...Based on the Magneto-Hydro-Dynamic（MHD） theory, a united three-dimensional（3D） transient numerical model is developed to investigate the dynamic behaviors of arc plasma for a magnesium alloy AZ61A gas tungsten arc welding（GTAW） arc. The arc, electrode and workpiece are integrated into one calculation domain to avoid both presumed distribution of the current density at the electrode tip and the assumption of constant conditions of interface between welding arc and workpiece. The distributions of electric potential, current density, magnetic flux density, electromagnetic force, velocity, temperature, and pressure of the arc plasma in the 3D space are analyzed by using the numerical model. Results indicate that the maximum gradient of the electric potential in the whole arc space exists around the electrode tip, where the electric current density, electromagnetic force, and temperature are also the maximum. However, maximum pressure is found at the velocity stagnation, which is above the workpiece.Comparison between predicted temperature and measured one in arc region shows a good agreement.展开更多
Although the research history of triboelectrification has been more than 2000 years, there are still many problems to be solved so far.The use of scanning probe microscopy provides an important way to quantitatively s...Although the research history of triboelectrification has been more than 2000 years, there are still many problems to be solved so far.The use of scanning probe microscopy provides an important way to quantitatively study the transfer, accumulation, and dissipation of triboelectric charges in the process of triboelectrification. Two-dimensional materials are considered to be key materials for new electronic devices in the post-Moore era due to their atomic-scale size advantages. If the electrostatic field generated by triboelectrification can be used to replace the traditional gate electrostatic field, it is expected to simplify the structure of two-dimensional electronic devices and reconfigure them at any time according to actual needs. Here, we investigate the triboelectrification process of various two-dimensional materials such as MoS_(2), WSe_(2),and ZnO. Different from traditional bulk materials, after two-dimensional materials are rubbed, the triboelectric charges generated may tunnel through the two-dimensional materials to the underlying substrate surface. Because the tunneling triboelectric charge is protected by the twodimensional material, its stable residence time on the substrate surface can reach more than 7 days, which is more than tens of minutes for the traditional triboelectric charge. In addition, the electrostatic field generated by the tunneling triboelectric charge can effectively regulate the carrier transport performance of two-dimensional materials, and the source–drain current of the field effect device regulated by the triboelectric floating gate is increased by nearly 60 times. The triboelectric charge tunneling phenomenon in two-dimensional materials is expected to be applied in the fields of new two-dimensional electronic devices and reconfigurable functional circuits.展开更多
Beam structures are extensively used in many engineering branches.For marine engineering,the ship shafting system is generally simplified as a vibration model with single or multiple beam structures connected by the c...Beam structures are extensively used in many engineering branches.For marine engineering,the ship shafting system is generally simplified as a vibration model with single or multiple beam structures connected by the coupling stiffness.In engineering,multiple nonlinear energy sinks(NESs)can be arranged on the premise of sufficient installation space to ensure their vibration suppression effect.Considering engineering practice,this study investigates the dynamic behavior and vibration suppression of a generally restrained pre-pressure beam structure with multiple uniformly distributed NESs,where the prepressure is typically caused by thrust bearings,installation ways,and others.System governing equations are derived through the generalized Hamiltonian principle and the variational procedure.Dynamic responses of the pre-pressure beam structure are predicted by the Galerkin truncation method.The effect of NESs on dynamic responses and vibration suppression of the pre-pressure beam structure is studied and discussed.Suitable parameters of NESs have a beneficial effect on the vibration suppression at both ends of the pre-pressure beam structure.NESs can modify the vibration frequency and energy transmission characteristics of the vibration system.For different boundary conditions,the optimized parameters of NESs significantly suppress the vibration energy of the pre-pressure beam structure.展开更多
Nonlinear forces and moments caused by ball bearing were calculated based on relationship of displacement and deflection and quasi-dynamic model of bearing.Five-DOF dynamic equations of rotor supported by ball bearing...Nonlinear forces and moments caused by ball bearing were calculated based on relationship of displacement and deflection and quasi-dynamic model of bearing.Five-DOF dynamic equations of rotor supported by ball bearings were estimated.The Newmark-β method and Newton-Laphson method were used to solve the equations.The dynamic characteristics of rotor system were studied through the time response,the phase portrait,the Poincar?maps and the bifurcation diagrams.The results show that the system goes through the quasi-periodic bifurcation route to chaos as rotate speed increases and there are several quasi-periodic regions and chaos regions.The amplitude decreases and the dynamic behaviors change as the axial load of ball bearing increases;the initial contact angle of ball bearing affects dynamic behaviors of the system obviously.The system can avoid non-periodic vibration by choosing structural parameters and operating parameters reasonably.展开更多
Frozen ground is significantly stiffer than unfrozen ground. For bridges supported on deep foundations, bridge stiffness is also measurably higher in winter months. Significant changes due to seasonal freezing in brid...Frozen ground is significantly stiffer than unfrozen ground. For bridges supported on deep foundations, bridge stiffness is also measurably higher in winter months. Significant changes due to seasonal freezing in bridge pier boundary conditions require addi- tional detailing in order to ensure a ductile performance of the bridge during a design earthquake event. This paper reports the lat- est results obtained from a project that systematically investigated the effects of seasonally frozen soil on the seismic behavior of highway bridges in cold regions. A bridge was chosen and was monitored to study its seismic performance and assess the impact of seasonally frozen soil on its dynamic properties. A Finite Element （FE） model was created for this bridge to analyze the impact of seasonal frost. It was found that when frost depth reaches 1.2 m, the first transverse modal frequency increases about 200% when compared with the no-frost case. The results show that seasonal frost has a significant impact on the overall dynamic be- havior of bridges supported by pile foundations in cold regions, and that these effects should be accounted for in seismic design.展开更多
基金National Natural Science Foundation of China(12002045)Supported by State Key Laboratory of Explosion Science and Safety Protection,Beijing Institute of Technology(QNKT22-09)。
文摘A high-density tungsten-zirconium-titanium(W-Zr-Ti)reactive alloy was prepared by powder metallurgy.This alloy exhibits high density,high strength,and violent energy release characteristics,resulting in outstanding penetration and ignition abilities.Dynamic impact experiment demonstrated its strain rate hardening effect,and the energetic characteristics were investigated by digital image processing technique and thermal analysis experiment.The results show that W-Zr-Ti reactive alloy performs compressive strength of 2.25 GPa at 5784 s^(-1)strain rate,and its exothermic reaction occurs at about 961 K.Based on the explosion test and shock wave theory,thresholds of enhanced damage effect are less than 35.77 GPa and 5.18×10^(4)kJ/m^(2)for shock pressure and energy,respectively.Furthermore,the transformation of fracture behavior and failure mechanism is revealed,which causes the increase in compressive strength and reaction intensity under dynamic loading.
基金co-supported by the Natural Science Basic Research Program of Shaanxi,China(No.2023-JC-QN-0043)the ND Basic Research Funds,China(No.G2022WD).
文摘The aerial deployment method enables Unmanned Aerial Vehicles(UAVs)to be directly positioned at the required altitude for their mission.This method typically employs folding technology to improve loading efficiency,with applications such as the gravity-only aerial deployment of high-aspect-ratio solar-powered UAVs,and aerial takeoff of fixed-wing drones in Mars research.However,the significant morphological changes during deployment are accompanied by strong nonlinear dynamic aerodynamic forces,which result in multiple degrees of freedom and an unstable character.This hinders the description and analysis of unknown dynamic behaviors,further leading to difficulties in the design of deployment strategies and flight control.To address this issue,this paper proposes an analysis method for dynamic behaviors during aerial deployment based on the Variational Autoencoder(VAE).Focusing on the gravity-only deployment problem of highaspect-ratio foldable-wing UAVs,the method encodes the multi-degree-of-freedom unstable motion signals into a low-dimensional feature space through a data-driven approach.By clustering in the feature space,this paper identifies and studies several dynamic behaviors during aerial deployment.The research presented in this paper offers a new method and perspective for feature extraction and analysis of complex and difficult-to-describe extreme flight dynamics,guiding the research on aerial deployment drones design and control strategies.
基金supported by the Nanjing Institute of Technology(Grant No.YKJ202301).
文摘The understanding of the impact of high-velocity microparticles on human skin tissue is important for the ad-ministration of drugs during transdermal drug delivery.This paper aims to numerically investigate the dynamic behavior of human skin tissue under micro-particle impact in transdermal drug delivery.The numerical model was developed based on a coupled smoothed particle hydrodynamics(SPH)and FEM method via commercial FE software RADIOSS.Analytical analysis was conducted applying the Poncelet model and was used as validation data.A hyperelastic one-term Ogden model with one pair of material parameters(μ,α)was implemented for the skin tissue.Sensitivity studies reveal that the effect of parameter α on the penetration process is much more significant than μ.Numerical results correlate well with the analytical curves with various particle diameters and impact velocities,its capability of predicting the penetration process of micro-particle impacts into skin tissues.This work can be further investigated to guide the design of transdermal drug delivery equipment.
基金financial funding of National Natural Science Foundation of China (No.52004307)China National Petroleum Corporation (No.ZLZX2020-02-04)the Science Foundation of China University of Petroleum,Beijing (No.2462018YJRC015)。
文摘The loss of hydrocarbon production caused by the dynamic behavior of the inner boundary and propped fractures under long-term production conditions has been widely reported in recent studies.However,the quantitative relationships for the variations of the inner boundary and propped fractures have not been determined and incorporated in the semi-analytical models for the pressure and rate transient analysis.This work focuses on describing the variations of the inner boundary and propped fractures and capturing the typical characteristics from the pressure transient curves.A generalized semi-analytical model was developed to characterize the dynamic behavior of the inner boundary and propped fractures under long-term production conditions.The pressure-dependent length shrinkage coefficients,which quantify the length changes of the inner zone and propped fractures,are modified and incorporated into this multi-zone semi-analytical model.With simultaneous numerical iterations and numerical inversions in Laplace and real-time space,the transient solutions to pressure and rate behavior are determined in just a few seconds.The dynamic behavior of the inner boundary and propped fractures on transient pressure curves is divided into five periods:fracture bilinear flow(FR1),dynamic PFs flow(FR2),inner-area linear flow(FR3),dynamic inner boundary flow(FR4),and outer-area dominated linear flow(FR5).The early hump during FR2 period and a positive upward shift during FR4period are captured on the log-log pressure transient curves,reflecting the dynamic behavior of the inner boundary and propped fractures during the long-term production period.The transient pressure behavior will exhibit greater positive upward trend and the flow rate will be lower with the shrinkage of the inner boundary.The pressure derivative curve will be upward earlier as the inner boundary shrinks more rapidly.The lower permeability caused by the closure of un-propped fractures in the inner zone results in greater upward in pressure derivative curves.If the permeability loss for the dynamic behavior of the inner boundary caused by the closure of un-propped fractures is neglected,the flow rate will be overestimated in the later production period.
基金Project(50639060) supported by the National Natural Science Foundation of ChinaProject(610103002) supported by the State Key Laboratory of Hydroscience and Engineering,Tsinghua University,China
文摘A series of centrifuge model tests of sandy slopes were conducted to study the dynamic behavior of pile-reinforced slopes subjected to various motions.Time histories of accelerations,bending moments and pile earth pressures were obtained during excitation of the adjusted El Centro earthquake and a cyclic motion.Under a realistic earthquake,the overall response of the pile-reinforced slope is lower than that of the non-reinforced slope.The histories of bending moments and dynamic earth pressures reach their maximums soon after shaking started and then remain roughly stable until the end of shaking.Maximum moments occur at the height of 3.5 m,which is the deeper section of the pile,indicating the interface between the active loading and passive resistance regions.The dynamic earth pressures above the slope base steadily increase with the increase of height of pile.For the model under cyclic input motion,response amplitudes at different locations in the slope are almost the same,indicating no significant response amplification.Both the bending moment and earth pressure increase gradually over a long period.
基金supported by the Project of the Fundamental Research Funds for the Central Universities of China(2022JBMC034)the National Natural Science Foundation of China under Grant No.12275017Beijing Laboratory of National Economic Security Early-warning Engineering,Beijing Jiaotong University
文摘In this paper,we propose a combined form of the bilinear Kadomtsev-Petviashvili equation and the bilinear extended(2+1)-dimensional shallow water wave equation,which is linked with a novel(2+1)-dimensional nonlinear model.This model might be applied to describe the evolution of nonlinear waves in the ocean.Under the effect of a novel combination of nonlinearity and dispersion terms,two cases of lump solutions to the(2+1)-dimensional nonlinear model are derived by searching for the quadratic function solutions to the bilinear form.Moreover,the one-lump-multi-stripe solutions are constructed by the test function combining quadratic functions and multiple exponential functions.The one-lump-multi-soliton solutions are derived by the test function combining quadratic functions and multiple hyperbolic cosine functions.Dynamic behaviors of the lump solutions and mixed solutions are analyzed via numerical simulation.The result is of importance to provide efficient expressions to model nonlinear waves and explain some interaction mechanism of nonlinear waves in physics.
基金Supported by National Natural Science Foundation of China (No. 50638030)National Key Technologies R&D Program of China (No. 2006BAJ13B02).
文摘In order to reduce economic and life losses due to terrorism or accidental explosion threats, reinforced concrete （RC） slabs of buildings need to he designed or retrofitted to resist blast loading. In this paper the dynamic behavior of RC slabs under blast loading and its influencing factors are studied. The numerical model of an RC slab subjected to blast loading is established using the explicit dynamic analysis software. Both the strain rate effect and the damage accumulation are taken into account in the material model. The dynamic responses of the RC slab subjected to blast loading are analyzed, and the influence of concrete strength, thickness and reinforcement ratio on the behavior of the RC slab under blast loading is numerically investigated. Based on the numerical results, some principles for blast-resistant design and retrofitting are proposed to improve the behavior of the RC slab subjected to blast loading.
基金supported by the National Natural Science Foundation of China(No.11472179)
文摘The dynamic behavior of a bridge-erecting machine, carrying a moving mass suspended by a wire rope, is investigated. The bridge-erecting machine is modelled by a simply supported uniform beam, and a massless equivalent ＂spring-damper＂ system with an effective spring constant and an effective damping coefficient is used to model the moving mass suspended by the wire rope. The suddenly applied load is represented by a unitary Dirac Delta function. With the expansion method, a simple closed-form solution for the equation of motion with the replaced spring-damper-mass system is formulated. The characters of the rope are included in the derivation of the differential equation of motion for the system. The numerical examples show that the effects of the damping coefficient and the spring constant of the rope on the deflection have significant variations with the loading frequency. The effects of the damping coefficient and the spring constant under different beam lengths are also examined. The obtained results validate the presented approach, and provide significant references in the design process of bridgeerecting machines.
基金financially supported by the National Natural Science Foundation of China(Grant No.51679167 and 51979193)
文摘The marine risers are often subjected to parametric excitations from the fluctuation top tension. The top tension on the riser may fluctuate with multiple frequencies caused by irregular waves. In this paper, the influence between different frequency components in the top tension on the riser system is theoretically simulated and analyzed. With the Euler-Bernoulli beam theory, a dynamic model for the vibrations of the riser is established. The top tension is set as fluctuating with time and it has two different frequencies. The influences from the fluctuation amplitudes, circular frequencies and phase angles of these frequency components on the riser system are analyzed in detail. When these two frequencies are fluctuating in the stable regions, the riser system may become unstable because ω1+ω2≈2Ωn. The fluctuation amplitudes of these frequencies have little effect on the components of the vibration frequencies of the riser. For different phase angles, the stability and dynamic behaviors of the riser would be different.
基金supported by National Natural Science Foundation of China (Grant No. 50575182)Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20060699021)Shaanxi Provincial Natural Science Foundation of China (Grant No. 2009JM7002)
文摘Finger seal is a new technology developed for gas path sealing in gas turbine engine.It has been paid attention to its good sealing performance and lower manufacture cost.The vibration behavior of finger seal is not be considered in performance analysis for the contact finger seal with compliant geometric configuration,then this will influence the reliability of the performance analysis and the parametric design of a finger seal.According to the dynamic character of finger seal,the harmonic vibration and free vibration models of a repetitive section of a two-layer finger seal that contains one high and one low finger seal are established separately.The dynamic behavior of finger seal in different working conditions is obtained based on the dynamic response analysis of finger＇s vibrations.The dynamic low hysteresis and low wear terms based on the equivalent dynamic model of finger seal are put forward,which can be used to predict the dynamic behavior of finger seal.As an example,the dynamic behaviors of an 8-layer finger seal and a 10-layer finger seal were predicted,and the validity of the prediction was demonstrated by the leakage test results of these two finger seals.The work presented here not only could make the dynamic analysis of finger seal with complicated structure simple and easy especially for multi-layer finger seal system,but also suggest a useful method for designing the finger seal with good dynamic behavior by means of different seal layers assembly.
基金National Natural Science Foundation of China,Grant No.59895410
文摘The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.
基金the National High Technology Research and Development Program (863) of China(No. 2008AA092301-1)the National Natural Science Foundation of China(No. 50909061)the Ph.D. Programs Foundation of Ministry of Education of China(No. 20070248103)
文摘This paper presents a numerical analysis of the dynamic transient behaviors of undersea cables.In this numerical study,the governing equations based on Euler-Bernoulli beam theory are adopted,and they can satisfy many applications no matter what the magnitude of the cable tension is.The nonlinear coupled equations are solved by a popular central finite difference method,and the numerical results of transient behaviors are presented when several kinds of surrounding conditions,such as different towing speeds of surface vessel,different currents and waves with various frequencies and amplitudes,are exerted.Then a detailed comparison of the results,including the upper end tension and cable shape in time-domain,is made under the above external excitations,and finally the possible reasons for these are further explained.
文摘An improved numerical method is used to simulate the dynamic behavior of a two part towing cable systems during turnings. In U turns and full turns, periodical heave motions are found both for the towed vehicle and for the depressor. Periodic motions of the subsea units and of the cable surface tension are closely related to the turning parameters, such as turning velocity and turning radius. System parameters, such as length of the second cable and the vehicle bydrodynamics, also damp turning instability.
基金supported by the National Natural Science Foundation of China (No.41772313)the National Natural Science Foundation for Young Scientists of China (No.52104111)+3 种基金the Hunan Science and Technology Planning Project,China (No.2019RS3001)the Natural Science Foundation of Hunan Province,China (No.2021JJ30819)Key Science and Technology Project of Guangxi Transportation Industry (Research on fine blasting and disaster control technology of mountain expressway tunnel),Chinathe financial contribution and convey their appreciation for supporting this basic research。
文摘To investigate the dynamic behavior and energy dissipation of the rock−concrete interface,dynamic splitting tests on bi-material discs were conducted by using the split Hopkinson pressure bar.The test results reveal that with the change of the interface inclination angles(θ),the influence of interface groove width on the bearing capacity of specimens also varies.Whenθincreases from 0°to 30°,the bearing capacity of the specimen increases first and then decreases with the rise of the interface groove width;the optimal groove width on the rock surface in this range of interface inclination angles is 5 mm.Whenθincreases from 45°to 90°,the bearing capacity of the specimen has no obvious change.Moreover,whenθincreases from 0°to 45°,the dissipated energy of the specimens rises obviously at first and then tends to be stable as the width of the interface groove increases.
文摘In this paper three types of dual- chamber shock- struts are considered in dynamic analyses of landing-gear behavior during impact and taxi. Their dynamic characteristics are compared with each other according to calculation results, and some conclusions are presented.It is very helpful for selecting a suitable type of dual-chamber shock-strut in landing-gear design.
基金supported by the Fundamental Research Funds for the Central Universities (No. 2012ZZ0059)the National Natural Science Foundation of China (No. E51375173)+1 种基金the Open Fund of State Key Laboratory of Materials Processing and Die & Mould Technology (No. 2011-P02)a project of Shandong Province Higher Educational Science and Technology Program (No. J12LA16)
文摘Based on the Magneto-Hydro-Dynamic（MHD） theory, a united three-dimensional（3D） transient numerical model is developed to investigate the dynamic behaviors of arc plasma for a magnesium alloy AZ61A gas tungsten arc welding（GTAW） arc. The arc, electrode and workpiece are integrated into one calculation domain to avoid both presumed distribution of the current density at the electrode tip and the assumption of constant conditions of interface between welding arc and workpiece. The distributions of electric potential, current density, magnetic flux density, electromagnetic force, velocity, temperature, and pressure of the arc plasma in the 3D space are analyzed by using the numerical model. Results indicate that the maximum gradient of the electric potential in the whole arc space exists around the electrode tip, where the electric current density, electromagnetic force, and temperature are also the maximum. However, maximum pressure is found at the velocity stagnation, which is above the workpiece.Comparison between predicted temperature and measured one in arc region shows a good agreement.
基金supported by the National Key Research and Development Program of China (No.2018YFA0703500)the National Natural Science Foundation of China(Nos.52232006,52188101,52102153,52072029,51991340,and 51991342)+2 种基金the Overseas Expertise Introduction Projects for Discipline Innovation (No.B14003)the China Postdoctoral Science Foundation (No.2021M700379)the Fundamental Research Funds for Central Universities(No.FRF-TP-18-001C1)。
文摘Although the research history of triboelectrification has been more than 2000 years, there are still many problems to be solved so far.The use of scanning probe microscopy provides an important way to quantitatively study the transfer, accumulation, and dissipation of triboelectric charges in the process of triboelectrification. Two-dimensional materials are considered to be key materials for new electronic devices in the post-Moore era due to their atomic-scale size advantages. If the electrostatic field generated by triboelectrification can be used to replace the traditional gate electrostatic field, it is expected to simplify the structure of two-dimensional electronic devices and reconfigure them at any time according to actual needs. Here, we investigate the triboelectrification process of various two-dimensional materials such as MoS_(2), WSe_(2),and ZnO. Different from traditional bulk materials, after two-dimensional materials are rubbed, the triboelectric charges generated may tunnel through the two-dimensional materials to the underlying substrate surface. Because the tunneling triboelectric charge is protected by the twodimensional material, its stable residence time on the substrate surface can reach more than 7 days, which is more than tens of minutes for the traditional triboelectric charge. In addition, the electrostatic field generated by the tunneling triboelectric charge can effectively regulate the carrier transport performance of two-dimensional materials, and the source–drain current of the field effect device regulated by the triboelectric floating gate is increased by nearly 60 times. The triboelectric charge tunneling phenomenon in two-dimensional materials is expected to be applied in the fields of new two-dimensional electronic devices and reconfigurable functional circuits.
基金supported by the National Natural Science Foundation of China(Grant No.11972125)the Fok Ying Tung Education Foundation(Grant No.161049).
文摘Beam structures are extensively used in many engineering branches.For marine engineering,the ship shafting system is generally simplified as a vibration model with single or multiple beam structures connected by the coupling stiffness.In engineering,multiple nonlinear energy sinks(NESs)can be arranged on the premise of sufficient installation space to ensure their vibration suppression effect.Considering engineering practice,this study investigates the dynamic behavior and vibration suppression of a generally restrained pre-pressure beam structure with multiple uniformly distributed NESs,where the prepressure is typically caused by thrust bearings,installation ways,and others.System governing equations are derived through the generalized Hamiltonian principle and the variational procedure.Dynamic responses of the pre-pressure beam structure are predicted by the Galerkin truncation method.The effect of NESs on dynamic responses and vibration suppression of the pre-pressure beam structure is studied and discussed.Suitable parameters of NESs have a beneficial effect on the vibration suppression at both ends of the pre-pressure beam structure.NESs can modify the vibration frequency and energy transmission characteristics of the vibration system.For different boundary conditions,the optimized parameters of NESs significantly suppress the vibration energy of the pre-pressure beam structure.
基金Sponsored by the National Natural Science Foundation of China(Grant No. 50575054)
文摘Nonlinear forces and moments caused by ball bearing were calculated based on relationship of displacement and deflection and quasi-dynamic model of bearing.Five-DOF dynamic equations of rotor supported by ball bearings were estimated.The Newmark-β method and Newton-Laphson method were used to solve the equations.The dynamic characteristics of rotor system were studied through the time response,the phase portrait,the Poincar?maps and the bifurcation diagrams.The results show that the system goes through the quasi-periodic bifurcation route to chaos as rotate speed increases and there are several quasi-periodic regions and chaos regions.The amplitude decreases and the dynamic behaviors change as the axial load of ball bearing increases;the initial contact angle of ball bearing affects dynamic behaviors of the system obviously.The system can avoid non-periodic vibration by choosing structural parameters and operating parameters reasonably.
基金funded by the Alaska University Transportation Center (AUTC) and the State of Alaska Department of Transportation and Public Facilities (AKDOT&PF),under AUTC Project No. 107014
文摘Frozen ground is significantly stiffer than unfrozen ground. For bridges supported on deep foundations, bridge stiffness is also measurably higher in winter months. Significant changes due to seasonal freezing in bridge pier boundary conditions require addi- tional detailing in order to ensure a ductile performance of the bridge during a design earthquake event. This paper reports the lat- est results obtained from a project that systematically investigated the effects of seasonally frozen soil on the seismic behavior of highway bridges in cold regions. A bridge was chosen and was monitored to study its seismic performance and assess the impact of seasonally frozen soil on its dynamic properties. A Finite Element （FE） model was created for this bridge to analyze the impact of seasonal frost. It was found that when frost depth reaches 1.2 m, the first transverse modal frequency increases about 200% when compared with the no-frost case. The results show that seasonal frost has a significant impact on the overall dynamic be- havior of bridges supported by pile foundations in cold regions, and that these effects should be accounted for in seismic design.
