A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the...A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.展开更多
To study the characteristics of the 5-prismatic–spherical–spherical(PSS)/universal–prismatic–universal(UPU)parallel mechanism with elastically active branched chains,the dynamics modeling and solutions of the para...To study the characteristics of the 5-prismatic–spherical–spherical(PSS)/universal–prismatic–universal(UPU)parallel mechanism with elastically active branched chains,the dynamics modeling and solutions of the parallel mechanism were investigated.First,the active branched chains and screw sliders were considered as spatial beam elements and plane beam element models,respectively,and the dynamic equations of each element model were derived using the Lagrange method.Second,the equations of the 5-PSS/UPU parallel mechanism were obtained according to the kinematic coupling relationship between the active branched chains and moving platform.Finally,based on the parallel mechanism dynamic equations,the natural frequency distribution of the 5-PSS/UPU parallel mechanism in the working space and elastic displacement of the moving platform were obtained.The results show that the natural frequency of the 5-PSS/UPU parallel mechanism under a given motion situation is greater than its operating frequency.The maximum position error is -0.096 mm in direction Y,and the maximum orientation error is -0.29°around the X-axis.The study provides important information for analyzing the dynamic performance,dynamic optimization design,and dynamic control of the 5-PSS/UPU parallel mechanism with elastically active branched chains.展开更多
A feasible method to improve the reliability and processing efficiency of large vibrating screen via the application of an elastic screen surface with multiple attached substructures （ESSMAS） was proposed. In the ES...A feasible method to improve the reliability and processing efficiency of large vibrating screen via the application of an elastic screen surface with multiple attached substructures （ESSMAS） was proposed. In the ESSMAS, every screen rod, with ends embedded into elastomer, is coupled to the main screen structure in a relatively flexible manner. The theoretical analysis was conducted, which consists of establishing dynamic model promoted from the fuzzy structure theory as well as calculating for the equivalent stiffness of each attached structure. According to the numerical simulation using the NEWMARK-fl integration method, this assembling pattern significantly leads to the screen surface/rod having larger vibration intensity than that of the corresponding position on screen structure, which specifically, with an averaged acceleration amplitude increasing ratio of 11.37% in theoretical analysis and 20.27% in experimental test. The experimental results, within a tolerant error, also confirm the established model and demonstrate the feasibility of ESSMAS.展开更多
A feasible method was proposed to improve the vibration intensity of screen surface via application of a new type elastic screen surface with multi degree of freedom(NTESSMDF). In the NTESSMDF, the primary robs were c...A feasible method was proposed to improve the vibration intensity of screen surface via application of a new type elastic screen surface with multi degree of freedom(NTESSMDF). In the NTESSMDF, the primary robs were coupled to the main screen structure with ends embedded into the elastomers, and the secondary robs were attached to adjacent two primary robs with elastic bands. The dynamic model of vibrating screen with NTESSMDF was established based on Lagrange's equation and the equivalent stiffnesses of the elastomer and elastic band were calculated. According to numerical simulation using the 4th order Runge-Kutta method, the vibration intensity of screen surface can be enhanced substantially with an averaged acceleration amplitude increasing ratio of 72.36%. The primary robs and secondary robs vibrate inversely in steady state, which would result in the friability of materials and avoid stoppage. The experimental results validate the dynamic characteristics with acceleration amplitude rising by62.93% on average, which demonstrates the feasibility of NTESSMDF.展开更多
The dynamic inhomogeneous finite element method is studied for use in the transient analysis of one dimensional inhomogeneous media. The general formula of the inhomogeneous consistent mass matrix is established based...The dynamic inhomogeneous finite element method is studied for use in the transient analysis of one dimensional inhomogeneous media. The general formula of the inhomogeneous consistent mass matrix is established based on the shape function. In order to research the advantages of this method, it is compared with the general finite element method. A linear bar element is chosen for the discretization tests of material parameters with two fictitious distributions. And, a numerical example is solved to observe the differences in the results between these two methods. Some characteristics of the dynamic inhomogeneous finite element method that demonstrate its advantages are obtained through comparison with the general finite element method. It is found that the method can be used to solve elastic wave motion problems with a large element scale and a large number of iteration steps.展开更多
A motor-driven linkage system with links fabricated from 3-dimensional braided composite materials was studied. A group of coupling dynamic equations of the system, including composite materials parameters, electromag...A motor-driven linkage system with links fabricated from 3-dimensional braided composite materials was studied. A group of coupling dynamic equations of the system, including composite materials parameters, electromagnetism parameters of the motor and structural parameters of the link mechanism, were established by finite element method. Based on the air-gap field of non-uniform airspace of three-phase alternating current motor caused by the vibration eccentricity of rotor, the relation of electromechanical coupling at the actual running state was analyzed. And the motor element, which defines the transverse vibration and torsional vibration of the motor as its nodal displacement, was established. Then, based on the damping element model and the expression of energy dissipation of the 3-dimentional braided composite materials, the damping matrix of the system was established by calculating each order modal damping of the mechanism.展开更多
In order to find out the dynamic characteristics of a steel frame structure project in the 8 degree (0.3g) area, the artificial wave, Taft wave and El Centro wave were input by using the finite element analysis softwa...In order to find out the dynamic characteristics of a steel frame structure project in the 8 degree (0.3g) area, the artificial wave, Taft wave and El Centro wave were input by using the finite element analysis software ANSYS. The dynamic time-history analysis of the structure shows the dynamic performance of the structure under the frequent earthquakes and rare earthquakes.展开更多
In this paper, an explicit finite element method to analyze the dynamic responses of three-medium coupled systems with any terrain is developed on the basis of the numerical simulation of the continuous conditions on ...In this paper, an explicit finite element method to analyze the dynamic responses of three-medium coupled systems with any terrain is developed on the basis of the numerical simulation of the continuous conditions on the bounda-ries among fluid saturated porous medium, elastic single-phase medium and ideal fluid medium. This method is a very effective one with the characteristic of high calculating speed and small memory needed because the formulae for this explicit finite element method have the characteristic of decoupling, and which does not need to solve sys-tem of linear equations. The method is applied to analyze the dynamic response of a reservoir with considering the dynamic interactions among water, dam, sediment and basement rock. The vertical displacement at the top point of the dam is calculated and some conclusions are given.展开更多
A flight dynamics model based on elastic blades for helicopters is developed.Modal shape analysis is used to describe the rotating elastic blades for the purpose of reducing the elastic degrees of freedom for blades.T...A flight dynamics model based on elastic blades for helicopters is developed.Modal shape analysis is used to describe the rotating elastic blades for the purpose of reducing the elastic degrees of freedom for blades.The analytical result is employed to predict the rotor forces and moments.The equilibrium equation of the flight dynamics model is then constructed for the elastic motion for blades and the rigid motion for other parts.The nonlinear equation is further simplified,and the gradient descent algorithm is adopted to implement the trim simulation.The trim analysis shows that the effect of blade elasticity on the accuracy of rotor forces and moments is apparent at high speed,and the proposed method presents good accuracy for trim performance.The timedomain response is realized by a combination of the Newmark method and the adaptive RungeKutta method.The helicopter control responses of collective pitch show that the response accuracy of the model at a yaw-and-pitch attitude is improved.Finally,the influence of blade elasticity on the helicopter dynamic response in low-altitude wind shear is investigated.An increase in blade elasticity reduces the oscillation amplitude of the yaw angle and the vertical speed by more than 70%.Compared with a rigid blade,an elastic blade reduces the vibration frequency of the angular velocity and results in a fast return of the helicopter to its stable flight.展开更多
A diagonal or lumped mass matrix is of great value for time-domain analysis of structural dynamic and wave propagation problems,as the computational efforts can be greatly reduced in the process of mass matrix inversi...A diagonal or lumped mass matrix is of great value for time-domain analysis of structural dynamic and wave propagation problems,as the computational efforts can be greatly reduced in the process of mass matrix inversion.In this study,the nodal quadrature method is employed to construct a lumped mass matrix for the Chebyshev spectral element method(CSEM).A Gauss-Lobatto type quadrature,based on Gauss-Lobatto-Chebyshev points with a weighting function of unity,is thus derived.With the aid of this quadrature,the CSEM can take advantage of explicit time-marching schemes and provide an efficient new tool for solving structural dynamic problems.Several types of lumped mass Chebyshev spectral elements are designed,including rod,beam and plate elements.The performance of the developed method is examined via some numerical examples of natural vibration and elastic wave propagation,accompanied by their comparison to that of traditional consistent-mass CSEM or the classical finite element method(FEM).Numerical results indicate that the proposed method displays comparable accuracy as its consistent-mass counterpart,and is more accurate than classical FEM.For the simulation of elastic wave propagation in structures induced by high-frequency loading,this method achieves satisfactory performance in accuracy and efficiency.展开更多
The dynamic response of polycrystalline alumina was investigated in the pressure range of 0 - 13 GPa by planar impact experiments. Velocity interferometer system for any reflector（VISAR） was used to obtain free surf...The dynamic response of polycrystalline alumina was investigated in the pressure range of 0 - 13 GPa by planar impact experiments. Velocity interferometer system for any reflector（VISAR） was used to obtain free surface velocity profile and determine the Hugoniot elastic limit, and manganin gauges were employed to obtain the stress-time histories and determine Hugoniot curve. Both the free surface particle velocity profiles and Hugoniot curves indicate the dispersion of the ＂plastic＂ wave for alumina. With the measured stress histories, the complete histories of strain, particle velocity, specific volume and specific internal energy are gained by using path line principle of Lagrange analysis. The dynamic mechanical behaviors for alumina under impact loading are analyzed, such as nonlinear characteristic, strain rate dependence, dispersion and declination of shock wavein the material.展开更多
Under certain conditions, starting from the three-dimensional dynamic equations of elastic shells the author gives the justification of dynamic equations of flexural shells by means of the method of asymptotic analysis.
Under certain conditions, the dynamic equations of membrane shells and the dynamic equations of flexural shells are obtained from dynamic equations of Koiter shells by the method of asymptotic analysis.
In this paper. :LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling thedynamic process of the M,=7.8 Tang shan earthquake on July 28, 1976 and obtain directly the dynamic and quasi static d...In this paper. :LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling thedynamic process of the M,=7.8 Tang shan earthquake on July 28, 1976 and obtain directly the dynamic and quasi static dislocations. shear stress drops, fracture velocities of the Tang shan earthquake fault. The simulation showsthai the slip history at each point of the fault is different. The displacement vectors at the concave side of the faultis greater than that of the convex side of the fault. The 'over shoot' of the fault slip is greatest at the middle part ofthe fault and attenuates to its ends. The rupture velocities of the fault from the epicenter towards south-west andtowards north-east are 3.08 m/s and 1. 18 m/s, respectively, the average one is 2.13 In/s. The maximum dynamic.m quasi-static dislocations are 7. 1 m and 6.2 m respectively. the average quasi-static one on the fault is 4.5 m.initial stress dynamic and quasi-static shear stress drops are 8.1 M Pa and 5.4 MP4 respectively, the averagequasi-static shear stress drop is 3.9 M Pa. We found that the rupture velocities and shear stress are related to theinitial stress states of the fault.展开更多
This article discusses the problems of the dynamic computation for thin-walled structures such as thin plates and thin shells under impact load to find the dynamic factor mainly. In calculation we take into account th...This article discusses the problems of the dynamic computation for thin-walled structures such as thin plates and thin shells under impact load to find the dynamic factor mainly. In calculation we take into account the effect of the mass of the striking object and the system of thin-walled structures to be struck and transform the distributed mass of thin-walled structures into only one concentrated 'equivalent mass' by the method of reduced mass. Accordingly we derive the dynamic factor for the system of thin-walled structures under impact load.展开更多
The seismic analysis of a rigid-framed prestressed concrete bridge in Tianjin Light Railway is performed. A 3-D dynamic finite element model of the bridge is established considering the weakening effect caused by the ...The seismic analysis of a rigid-framed prestressed concrete bridge in Tianjin Light Railway is performed. A 3-D dynamic finite element model of the bridge is established considering the weakening effect caused by the soft soil foundation. After the dynamic characteristics are calculated in terms of natural frequencies and modes, the seismic analysis is carried out using the modal response spectrum method and the time-history method, respectively. Based on the calculated results, the reasonable design values are finally suggested as the basis of the seismic design of the bridge, and meanwhile the problems encountered were also analyzed. Finally, some conclusions are drawn as: 1) Despite the superiority of rigid-framed prestressed concrete bridge, the upper and lower ends of the piers of the bridge are proved to be the crucial parts of the bridge, which are easily destroyed under designed earthquake excitations and should be carefully analyzed and designed; 2) The soft soil foundation can possibly result in rather weakening of the lateral rigidity of the rigid-framed bridge, and should be paid considerable attention; 3) The modal response spectrum method, combined with time-history method, is suggested for the seismic analysis in engineering design of the rigid-framed prestressed concrete bridge.展开更多
The dynamic cumulative damage of rigid-flexible coupling model of high-speed train with flexible bogie frame is performed by using the coupled scheme of elastic and multibody dynamics theories.The motion equations of ...The dynamic cumulative damage of rigid-flexible coupling model of high-speed train with flexible bogie frame is performed by using the coupled scheme of elastic and multibody dynamics theories.The motion equations of the present problem are firstly established by integrating the finite element method and floating frame of reference approach based on the virtual power principle and D'Alembert principle.The process of condensing the elastic DOFs of the obtained finite element model involving the incorporation of the substructure technique and sparse approximate inverse method is tentatively carried out.Then,the motion equations are further solved by virtue of the generalized α method and the Jacobian-free Newton-Krylov technologies.And the superiority of coupled scheme is proven by comparing with the traditional approach.Finally,besides the dynamic behaviors of the considered vehicle model,the time-variations of stresses on the elastic bogie frame's dangerous nodes and the distributions of stresses of bogie frame at some specified moments are synchronously calculated and analyzed.More importantly,the real-time and time-varying cumulative damages of some typical nodes on bogie frame are investigated.展开更多
板结构与其他构件的装配关系可用不同的边界条件进行模拟,然而针对不同边界条件的板结构进行动力学特性分析,目前缺乏统一的数学建模方法。以混合弹性边界条件下加筋、开孔的板类结构的横向振动为例,利用Rayleigh-Ritz法和模态叠加法求...板结构与其他构件的装配关系可用不同的边界条件进行模拟,然而针对不同边界条件的板结构进行动力学特性分析,目前缺乏统一的数学建模方法。以混合弹性边界条件下加筋、开孔的板类结构的横向振动为例,利用Rayleigh-Ritz法和模态叠加法求解矩形加筋多孔板在简谐激励下的动力学响应问题。采用将开孔板与加强筋沿交界面进行分离,结合改进的傅里叶级数设定开孔板的横向振动位移函数,利用不同刚度弹簧模拟混合弹性边界,推导加筋矩形开多孔板和边界弹簧系统的动能与势能,求解其在简谐激励下的动力学响应。经对比,理论计算结果与有限元(Finite Element Method,FEM)结果吻合良好。此外,用同样的方法分析不同孔尺寸对结构固有频率和响应的影响。研究发现,可通过改变加筋板的开孔形状、尺寸对结构的振动特性进行调整。研究成果可为混合弹性边界板结构动力分析提供一种新的技术途径,可以简化加筋开孔板结构动力分析的步骤。展开更多
基金support from the Exploring Youth Project of Zhejiang Natural Science Foundation (Grant No.LQ24E080009)the Key Project of Natural Science Foundation of Zhejiang Province (Grant No.LXZ22E080001)the National Natural Science Foundation of China (Grant No.52108347).
文摘A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.
基金Supported by Zhejiang Provincial Natural Science Foundation of China (Grant No. LR18E050003)National Natural Science Foundation of China (Grant Nos. 51975523,51905481)+1 种基金Postdoctoral Preferred Funding Project of Zhejiang Province (Grant No. zj2019019)Open Foundation of the Key Laboratory of E&M,Ministry of Education&Zhejiang Province (Grant No. EM2019120102)
文摘To study the characteristics of the 5-prismatic–spherical–spherical(PSS)/universal–prismatic–universal(UPU)parallel mechanism with elastically active branched chains,the dynamics modeling and solutions of the parallel mechanism were investigated.First,the active branched chains and screw sliders were considered as spatial beam elements and plane beam element models,respectively,and the dynamic equations of each element model were derived using the Lagrange method.Second,the equations of the 5-PSS/UPU parallel mechanism were obtained according to the kinematic coupling relationship between the active branched chains and moving platform.Finally,based on the parallel mechanism dynamic equations,the natural frequency distribution of the 5-PSS/UPU parallel mechanism in the working space and elastic displacement of the moving platform were obtained.The results show that the natural frequency of the 5-PSS/UPU parallel mechanism under a given motion situation is greater than its operating frequency.The maximum position error is -0.096 mm in direction Y,and the maximum orientation error is -0.29°around the X-axis.The study provides important information for analyzing the dynamic performance,dynamic optimization design,and dynamic control of the 5-PSS/UPU parallel mechanism with elastically active branched chains.
基金Projects(50574091,50774084) supported by the National Natural Science Foundation of China
文摘A feasible method to improve the reliability and processing efficiency of large vibrating screen via the application of an elastic screen surface with multiple attached substructures （ESSMAS） was proposed. In the ESSMAS, every screen rod, with ends embedded into elastomer, is coupled to the main screen structure in a relatively flexible manner. The theoretical analysis was conducted, which consists of establishing dynamic model promoted from the fuzzy structure theory as well as calculating for the equivalent stiffness of each attached structure. According to the numerical simulation using the NEWMARK-fl integration method, this assembling pattern significantly leads to the screen surface/rod having larger vibration intensity than that of the corresponding position on screen structure, which specifically, with an averaged acceleration amplitude increasing ratio of 11.37% in theoretical analysis and 20.27% in experimental test. The experimental results, within a tolerant error, also confirm the established model and demonstrate the feasibility of ESSMAS.
基金Project(51221462)supported by the National Natural Science Foundation of China for Innovative Research GroupProject(20120095110001)supported by the Doctoral Fund of Ministry of Education of China+1 种基金Project supported by the Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutions,ChinaProject(CXJJ201303)supported by the Innovation Foundation of Xuyi Research and Development Center of Mining Equipment and Materials,China University of Mining and Technology,China
文摘A feasible method was proposed to improve the vibration intensity of screen surface via application of a new type elastic screen surface with multi degree of freedom(NTESSMDF). In the NTESSMDF, the primary robs were coupled to the main screen structure with ends embedded into the elastomers, and the secondary robs were attached to adjacent two primary robs with elastic bands. The dynamic model of vibrating screen with NTESSMDF was established based on Lagrange's equation and the equivalent stiffnesses of the elastomer and elastic band were calculated. According to numerical simulation using the 4th order Runge-Kutta method, the vibration intensity of screen surface can be enhanced substantially with an averaged acceleration amplitude increasing ratio of 72.36%. The primary robs and secondary robs vibrate inversely in steady state, which would result in the friability of materials and avoid stoppage. The experimental results validate the dynamic characteristics with acceleration amplitude rising by62.93% on average, which demonstrates the feasibility of NTESSMDF.
基金the Fundamental Research Funds for the Central Universities under Grant No.HEUCFZ1125National Natural Science Foundation of China under Grant No.10972064
文摘The dynamic inhomogeneous finite element method is studied for use in the transient analysis of one dimensional inhomogeneous media. The general formula of the inhomogeneous consistent mass matrix is established based on the shape function. In order to research the advantages of this method, it is compared with the general finite element method. A linear bar element is chosen for the discretization tests of material parameters with two fictitious distributions. And, a numerical example is solved to observe the differences in the results between these two methods. Some characteristics of the dynamic inhomogeneous finite element method that demonstrate its advantages are obtained through comparison with the general finite element method. It is found that the method can be used to solve elastic wave motion problems with a large element scale and a large number of iteration steps.
基金Project(50175031) supported by the National Natural Science Foundation of China
文摘A motor-driven linkage system with links fabricated from 3-dimensional braided composite materials was studied. A group of coupling dynamic equations of the system, including composite materials parameters, electromagnetism parameters of the motor and structural parameters of the link mechanism, were established by finite element method. Based on the air-gap field of non-uniform airspace of three-phase alternating current motor caused by the vibration eccentricity of rotor, the relation of electromechanical coupling at the actual running state was analyzed. And the motor element, which defines the transverse vibration and torsional vibration of the motor as its nodal displacement, was established. Then, based on the damping element model and the expression of energy dissipation of the 3-dimentional braided composite materials, the damping matrix of the system was established by calculating each order modal damping of the mechanism.
文摘In order to find out the dynamic characteristics of a steel frame structure project in the 8 degree (0.3g) area, the artificial wave, Taft wave and El Centro wave were input by using the finite element analysis software ANSYS. The dynamic time-history analysis of the structure shows the dynamic performance of the structure under the frequent earthquakes and rare earthquakes.
基金National Natural Scienccs Foundation of China (50178005).
文摘In this paper, an explicit finite element method to analyze the dynamic responses of three-medium coupled systems with any terrain is developed on the basis of the numerical simulation of the continuous conditions on the bounda-ries among fluid saturated porous medium, elastic single-phase medium and ideal fluid medium. This method is a very effective one with the characteristic of high calculating speed and small memory needed because the formulae for this explicit finite element method have the characteristic of decoupling, and which does not need to solve sys-tem of linear equations. The method is applied to analyze the dynamic response of a reservoir with considering the dynamic interactions among water, dam, sediment and basement rock. The vertical displacement at the top point of the dam is calculated and some conclusions are given.
基金co-supported by the National Natural Science Foundation of China-China(No.11302011)the Specialized Research Fund for the Doctoral Program of Higher Education-China(No.20131102120051)
文摘A flight dynamics model based on elastic blades for helicopters is developed.Modal shape analysis is used to describe the rotating elastic blades for the purpose of reducing the elastic degrees of freedom for blades.The analytical result is employed to predict the rotor forces and moments.The equilibrium equation of the flight dynamics model is then constructed for the elastic motion for blades and the rigid motion for other parts.The nonlinear equation is further simplified,and the gradient descent algorithm is adopted to implement the trim simulation.The trim analysis shows that the effect of blade elasticity on the accuracy of rotor forces and moments is apparent at high speed,and the proposed method presents good accuracy for trim performance.The timedomain response is realized by a combination of the Newmark method and the adaptive RungeKutta method.The helicopter control responses of collective pitch show that the response accuracy of the model at a yaw-and-pitch attitude is improved.Finally,the influence of blade elasticity on the helicopter dynamic response in low-altitude wind shear is investigated.An increase in blade elasticity reduces the oscillation amplitude of the yaw angle and the vertical speed by more than 70%.Compared with a rigid blade,an elastic blade reduces the vibration frequency of the angular velocity and results in a fast return of the helicopter to its stable flight.
基金Supported by:Joint Research Fund for Earthquake Science,launched by the National Natural Science Foundation of China and the China Earthquake Administration under Grant No.U2039208。
文摘A diagonal or lumped mass matrix is of great value for time-domain analysis of structural dynamic and wave propagation problems,as the computational efforts can be greatly reduced in the process of mass matrix inversion.In this study,the nodal quadrature method is employed to construct a lumped mass matrix for the Chebyshev spectral element method(CSEM).A Gauss-Lobatto type quadrature,based on Gauss-Lobatto-Chebyshev points with a weighting function of unity,is thus derived.With the aid of this quadrature,the CSEM can take advantage of explicit time-marching schemes and provide an efficient new tool for solving structural dynamic problems.Several types of lumped mass Chebyshev spectral elements are designed,including rod,beam and plate elements.The performance of the developed method is examined via some numerical examples of natural vibration and elastic wave propagation,accompanied by their comparison to that of traditional consistent-mass CSEM or the classical finite element method(FEM).Numerical results indicate that the proposed method displays comparable accuracy as its consistent-mass counterpart,and is more accurate than classical FEM.For the simulation of elastic wave propagation in structures induced by high-frequency loading,this method achieves satisfactory performance in accuracy and efficiency.
基金the National Natural Science Foundation of China (10625208)
文摘The dynamic response of polycrystalline alumina was investigated in the pressure range of 0 - 13 GPa by planar impact experiments. Velocity interferometer system for any reflector（VISAR） was used to obtain free surface velocity profile and determine the Hugoniot elastic limit, and manganin gauges were employed to obtain the stress-time histories and determine Hugoniot curve. Both the free surface particle velocity profiles and Hugoniot curves indicate the dispersion of the ＂plastic＂ wave for alumina. With the measured stress histories, the complete histories of strain, particle velocity, specific volume and specific internal energy are gained by using path line principle of Lagrange analysis. The dynamic mechanical behaviors for alumina under impact loading are analyzed, such as nonlinear characteristic, strain rate dependence, dispersion and declination of shock wavein the material.
基金Project supported by the National Natural Science Foundation of China (No.10071024).
文摘Under certain conditions, starting from the three-dimensional dynamic equations of elastic shells the author gives the justification of dynamic equations of flexural shells by means of the method of asymptotic analysis.
基金the National Natural Science Foundation of China (No.10071024).
文摘Under certain conditions, the dynamic equations of membrane shells and the dynamic equations of flexural shells are obtained from dynamic equations of Koiter shells by the method of asymptotic analysis.
文摘In this paper. :LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling thedynamic process of the M,=7.8 Tang shan earthquake on July 28, 1976 and obtain directly the dynamic and quasi static dislocations. shear stress drops, fracture velocities of the Tang shan earthquake fault. The simulation showsthai the slip history at each point of the fault is different. The displacement vectors at the concave side of the faultis greater than that of the convex side of the fault. The 'over shoot' of the fault slip is greatest at the middle part ofthe fault and attenuates to its ends. The rupture velocities of the fault from the epicenter towards south-west andtowards north-east are 3.08 m/s and 1. 18 m/s, respectively, the average one is 2.13 In/s. The maximum dynamic.m quasi-static dislocations are 7. 1 m and 6.2 m respectively. the average quasi-static one on the fault is 4.5 m.initial stress dynamic and quasi-static shear stress drops are 8.1 M Pa and 5.4 MP4 respectively, the averagequasi-static shear stress drop is 3.9 M Pa. We found that the rupture velocities and shear stress are related to theinitial stress states of the fault.
文摘This article discusses the problems of the dynamic computation for thin-walled structures such as thin plates and thin shells under impact load to find the dynamic factor mainly. In calculation we take into account the effect of the mass of the striking object and the system of thin-walled structures to be struck and transform the distributed mass of thin-walled structures into only one concentrated 'equivalent mass' by the method of reduced mass. Accordingly we derive the dynamic factor for the system of thin-walled structures under impact load.
文摘The seismic analysis of a rigid-framed prestressed concrete bridge in Tianjin Light Railway is performed. A 3-D dynamic finite element model of the bridge is established considering the weakening effect caused by the soft soil foundation. After the dynamic characteristics are calculated in terms of natural frequencies and modes, the seismic analysis is carried out using the modal response spectrum method and the time-history method, respectively. Based on the calculated results, the reasonable design values are finally suggested as the basis of the seismic design of the bridge, and meanwhile the problems encountered were also analyzed. Finally, some conclusions are drawn as: 1) Despite the superiority of rigid-framed prestressed concrete bridge, the upper and lower ends of the piers of the bridge are proved to be the crucial parts of the bridge, which are easily destroyed under designed earthquake excitations and should be carefully analyzed and designed; 2) The soft soil foundation can possibly result in rather weakening of the lateral rigidity of the rigid-framed bridge, and should be paid considerable attention; 3) The modal response spectrum method, combined with time-history method, is suggested for the seismic analysis in engineering design of the rigid-framed prestressed concrete bridge.
基金support for the research:National Natural Science Foundation of China(Grant No.11872257 and 11572358)Key Project of Natural Science Foundation of Hebei Province(Grant No.A2020210008)Hebei Provincial Department of Education Youth Top Talents Project(Grant No.BJK2023018).
文摘The dynamic cumulative damage of rigid-flexible coupling model of high-speed train with flexible bogie frame is performed by using the coupled scheme of elastic and multibody dynamics theories.The motion equations of the present problem are firstly established by integrating the finite element method and floating frame of reference approach based on the virtual power principle and D'Alembert principle.The process of condensing the elastic DOFs of the obtained finite element model involving the incorporation of the substructure technique and sparse approximate inverse method is tentatively carried out.Then,the motion equations are further solved by virtue of the generalized α method and the Jacobian-free Newton-Krylov technologies.And the superiority of coupled scheme is proven by comparing with the traditional approach.Finally,besides the dynamic behaviors of the considered vehicle model,the time-variations of stresses on the elastic bogie frame's dangerous nodes and the distributions of stresses of bogie frame at some specified moments are synchronously calculated and analyzed.More importantly,the real-time and time-varying cumulative damages of some typical nodes on bogie frame are investigated.
文摘板结构与其他构件的装配关系可用不同的边界条件进行模拟,然而针对不同边界条件的板结构进行动力学特性分析,目前缺乏统一的数学建模方法。以混合弹性边界条件下加筋、开孔的板类结构的横向振动为例,利用Rayleigh-Ritz法和模态叠加法求解矩形加筋多孔板在简谐激励下的动力学响应问题。采用将开孔板与加强筋沿交界面进行分离,结合改进的傅里叶级数设定开孔板的横向振动位移函数,利用不同刚度弹簧模拟混合弹性边界,推导加筋矩形开多孔板和边界弹簧系统的动能与势能,求解其在简谐激励下的动力学响应。经对比,理论计算结果与有限元(Finite Element Method,FEM)结果吻合良好。此外,用同样的方法分析不同孔尺寸对结构固有频率和响应的影响。研究发现,可通过改变加筋板的开孔形状、尺寸对结构的振动特性进行调整。研究成果可为混合弹性边界板结构动力分析提供一种新的技术途径,可以简化加筋开孔板结构动力分析的步骤。
