Model test studies based on the similarity theory were conducted to investigate vibration effect and damage evolution characteristics of tunnel surrounding rock under push-type cyclic blasting excavation.The model was...Model test studies based on the similarity theory were conducted to investigate vibration effect and damage evolution characteristics of tunnel surrounding rock under push-type cyclic blasting excavation.The model was constructed with a ratio of 1∶15.By simulating the tunnel excavation of push-type cyclic blasting,the influence of the blasting parameter change on vibration effect was explored.The damage degree of tunnel surrounding rock was evaluated by the change of the acoustic wave velocity at the same measuring point after blasting.The relationship between the damage evolution of surrounding rock and blasting times was established.The research results show that：（1）In the same geological environment,the number of delay initiation is larger,the main vibration frequency of blasting seismic wave is higher,and the attenuation of high frequency signal in the rock and soil is faster.The influence of number of delay initiation on blasting vibration effect cannot be ignored;（2）Under push-type cyclic blasting excavation,there were great differences in the decreasing rates of acoustic wave velocity of the measuring points which have the same distance to the blasting region at the same depth,and the blasting damage ranges of surrounding rock were typically anisotropic at both depth and breadth;（3）When blasting parameters were basically kept as the same,the growth trend of the cumulative acoustic wave velocity decreasing rate at the measuring point was nonlinear under different cycle blasting excavations;（4）There were nonlinear evolution characteristics between the blasting cumulative damage（D）of surrounding rock and blasting times（n）under push-type cyclic blasting loading,and different measuring points had corresponding blasting cumulative damage propagation models,respectively.The closer the measuring point was away from the explosion source,the faster the cumulative damage extension.Blasting cumulative damage effect of surrounding rock had typically nonlinear evolution properties and anisotropic characteristics.展开更多
The technology of expansion fracturing with liquid CO_(2)(EFLCO_(2))has attracted increasing attention due to reduced vibration and damage.The disposable fracturing tube has been developed and is gradually replacing t...The technology of expansion fracturing with liquid CO_(2)(EFLCO_(2))has attracted increasing attention due to reduced vibration and damage.The disposable fracturing tube has been developed and is gradually replacing the Cardox tube.However,there is a lack of impact pressure testing of disposable tubes under real working conditions,selection of gas explosion design parameters,and systematic analysis of blasting vibration.This limitation has constrained the widespread application of disposable fracturing tubes in engineering.A joint monitoring of the pressure-time curves in the disposable tubes and boreholes was conducted.The rock-breaking effect of varying hole spacing parameters in the EFLCO_(2)design was analyzed,and a systematic study was carried out on the vibration peak value,frequency,and energy characteristics.The results show that(1)the pressure distribution characteristics,stress peak value,and duration in the disposable tubes are different from those of Cardox tubes,which show multi-peak distribution,low-pressure peak value,and short duration.The correlation between the pressure in the disposable tube,filling pressure,and liquid CO_(2)weight is established,and a theoretical calculation method for the borehole wall pressure is proposed;(2)The hole spacing in rocks of different hardness is suggested;and(3)At the same scale distance,the peak particle velocity(PPV)caused by EFLCO_(2)(PPVCO_(2))is significantly smaller than that caused by blasting(PPVexplosive).The ratio of PPVexplosive to PPVCO_(2)is a power function related to scale distance,and a distance-related zonality exist in this relationship.The frequency composition of the vibration signal caused by EFLCO_(2)is relatively simple with a narrow frequency band.Its PPV and energy are mainly concentrated in the low-frequency band.This research contributes to the optimization of disposable fracturing tubes,gas explosion design,and vibration hazard control.展开更多
This study is focused on the effect of vibration induced by moving trains in tunnels on the surrounding ground and structures.A three-dimensional finite element model is established for a one-track railway tunnel and ...This study is focused on the effect of vibration induced by moving trains in tunnels on the surrounding ground and structures.A three-dimensional finite element model is established for a one-track railway tunnel and an adjacent twelve-storey building frame by using commercial software Midas GTS-NX(2019)and Midas Gen.This study considered the moving load effect of a complete train,which varies with space as well as with time.The effect of factors such as train speed,overburden pressure on the tunnel and variation in soil properties are studied in the time domain.As a result,the variations in horizontal and vertical acceleration for two different sites,i.e.,the free ground surface(without structure)and the area containing the structure,are compared.Also,the displacement pattern of the raft foundation is plotted for different train velocities.At lower speeds,the heaving phenomenon is negligible,but as the speed increases,both the heaving and differential settlement increase in the foundation.This study demonstrates that the effect of moving train vibrations should be considered in the design of new nearby structures and proper ground improvement should be considered for existing structures.展开更多
The purpose of this study is to investigate the suppression effect of a nonlinear energy sink(NES)on the wind-vortex-induced pipe vibration and explore the influence of damping,stiffness,and NES installation position ...The purpose of this study is to investigate the suppression effect of a nonlinear energy sink(NES)on the wind-vortex-induced pipe vibration and explore the influence of damping,stiffness,and NES installation position on the suppression effect.In this work,the wind-vortex-induced vibration of an elastic pipe of a deepwater jacket was studied,and vibrations were suppressed by using an NES.A van der Pol wake oscillator was used to simulate vortex-induced force,and the dynamic equation of the pipe considering the NES was established.The Galerkin method was applied to discretize the motion equation,and the vortex-induced vibration(VIV)of the pipe at reduced wind speeds was numerically analyzed.The novelty of this research is that particle swarm optimization was used to optimize the parameters of the NES to improve vibration suppression.The influence of the installation position,nonlinear stiffness,and damping parameters of the NES on vibration suppression was analyzed.Results showed that the optimized parameter combinations of the NES can effectively reduce wind-vortex-induced pipe vibration.The installation position of the NES had a significant effect on vibration suppression,and the midpoint of the pipe was the optimal NES installation position.An increase in stiffness or a 10% decrease in damping may cause vibration suppression failure.The results of this study provide some guidance for VIV suppression in deepwater jacket pipes.展开更多
Rotary ultrasonic drilling(RUD)has become an effective approach for machining advanced composites which are widely using in the field of aeronautics.The cutting kinematics and the corresponding material removal mechan...Rotary ultrasonic drilling(RUD)has become an effective approach for machining advanced composites which are widely using in the field of aeronautics.The cutting kinematics and the corresponding material removal mechanisms are distinct in different drilling areas during RUD.However,these fundamentals have not been fully considered in the existing studies.In this research,two distinct forms of interaction induced by ultrasonic vibration were considered as impact-separation and vibratory lapping between the abrasives and workpiece.And the conditions to guarantee the effectiveness of these interactions were obtained to eliminate diminishing effects of ultrasonic vibration.Based on indentation fracture theory,the penetration depth of abrasives and the axial drilling force model was derived for RUD.The verification tests of C/SiC composites resulted in a prediction error within 15%.Due to the minimal volume of material removed during each vibration cycle,the drilling force was more stable in vibration assisted mode.The specific drilling energy of RUD was firstly calculated based on the measured drilling load.It was found the drilling parameters should be matched with vibration frequency and amplitude to make better usage of the advantages of ultrasonic vibration,which is critical in the vibration assisted processing of advanced materials.展开更多
It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in ...It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in predict- ing the densities for the α phase crystalline hexahydro-1,3,5-trinitro-l,3,5-triazine （RDX）, and derivation of its high-fidelity Hugoniot locus and Mie-Grfineisen equation of state covering a very wide range of pressures and temperatures. This work can be used to efficiently and accurately predict the thermophysical properties of solid explosives over the pressures and temperatures to which they are subjected, which is a long-standing issue in the field of energetic materials.展开更多
The vibrational motions are usually neglected when calculating(e,2e) triple differential cross sections(TDCSs) of molecules. Here, multi-center distorted-wave method(MCDW) has been modified by including molecular vibr...The vibrational motions are usually neglected when calculating(e,2e) triple differential cross sections(TDCSs) of molecules. Here, multi-center distorted-wave method(MCDW) has been modified by including molecular vibrations. This vibrational MCDW method is employed to calculate the TDCSs of 1b3gorbital of ethylene at low(100 eV) and medium(250 eV) incident electron energies in coplanar asymmetric kinematic condition. The results show that molecular vibrations significantly influence the angular distributions of the TDCSs, especially in the binary region along momentum transfer near the Bethe ridge.展开更多
This paper puts forward the concept of double semi-active vibration isolation systemutilizing the 'on-off' active damper and the 'on-off' active spring. Applying KBM Asympto-tic method, the vibration ...This paper puts forward the concept of double semi-active vibration isolation systemutilizing the 'on-off' active damper and the 'on-off' active spring. Applying KBM Asympto-tic method, the vibration of the system in case of weak semi-active control is studied. ln pcactice, there are two types of vibration isolation. One is to isolate the transmitting of the cyclicunbalanced force generated by the revolving machine to the surroundings. The other is to isolatethe transmitting of the vibration displacement of the surroundings to precise equipment. Deduc-ing the influence of the roadway unflatness on vehicles also belongs to this type. For the firsttype of isolation system, the damper always dissipates energy, and the total work done by the spring in a vibration cycle is zero. For the second type of isolation system, the work done by the damper sometimes is positive, and sometimes negative. The damper dissipates less energy. The work done by the spring in a vibration cycle isn't zero, and it is usually positive. ln thispaper, the vibration isolation is refered to the second type. .展开更多
Fracture and ground vibration of rock subjected to different decoupling decked charges are investigated based on the numerical simulation. The dynamic pressure value is studied, which demonstrates that simulation of f...Fracture and ground vibration of rock subjected to different decoupling decked charges are investigated based on the numerical simulation. The dynamic pressure value is studied, which demonstrates that simulation of fracture zone is feasible. Attenuation index of dynamic pressure is 2.06, 2.05 and 1.93 for air, water and sand intervals respectively. The small attenuation of sand in- terval results in the large ground vibration. The predicted vertical vibration waveform and peak parti- cle velocities （PPV） in far-field are in agreement with the monitoring results. The results show that the air and water decked charges can improve the effect of rock fracture in near-field and reduce ground vibration in far-field.展开更多
Ground vibration accelerations caused by the collapse of blasting demolition of urban viaducts was recorded in ordered to analyze the engineering characteristics and effects on the surrounding buildings. Through the a...Ground vibration accelerations caused by the collapse of blasting demolition of urban viaducts was recorded in ordered to analyze the engineering characteristics and effects on the surrounding buildings. Through the analysis of peak ground acceleration,peak frequency,duration and response spectra of the recorded vibrations in different acceleration arrays,some conclusions are drawn: the peak ground acceleration decreases with increasing distance, and the amplitude of vertical component is higher than that of the horizontal components,especially in near source region. The peak frequency of ground acceleration decreases with distance,and in near source region,it is larger than the natural frequency of the surrounding buildings,and thus it will not have much effect on the buildings. The duration of ground acceleration caused by collapse is longer than that caused by blasting itself. The vertical response spectrum is the largest of the three components,and it decreases rapidly in the near source region of about 30 m,but beyond that the distance decreases slowly.The horizontal components are smaller than the local seismic design spectrum,while the vertical component for natural period under 0.15 s exceeds the seismic design spectrum,but the natural periods of general buildings are usually beyond that domain,so this will not have much effect on the nearby buildings.展开更多
The nonlinear dynamic model of the marine diesel crankshaft system with a propeller and 6 cranks is established, in which the variable moment of inertia of the linkage and the piston, coupling effect between torsional...The nonlinear dynamic model of the marine diesel crankshaft system with a propeller and 6 cranks is established, in which the variable moment of inertia of the linkage and the piston, coupling effect between torsional and axial vibration, the actuating force applied on the piston, the actuating torque and force applied on the propeller is included. The governing equations of the model denote a strong nonlinear and non autonomous system. By numeric simulation, the dynamic response of the system to initial displacement and initial speed, variable moment of inertia, the pressure applied on the piston by combustion gas, the torque and the axial force applied on the propeller by fluid is researched respectively. According to the research results, the variable moment of inertia and coupling effect between torsional and axial vibration are the fundamental reason for nonlinear vibration. Different actuating factors can not only result in different frequency components of the response, but make the same frequency component have different vibration amplitude. The dynamic behavior of the system is not influenced obviously by the actuating torque and force applied on the propeller. There is obvious difference in sensitivity of the dynamic response in the different direction to the same actuating factor.展开更多
A novel linear ultrasonic motor based on d15 effect of piezoelectric materials was presented. The design idea aimed at the direct utilization of the shear-induced vibration modes of piezoelectric material. Firstly, th...A novel linear ultrasonic motor based on d15 effect of piezoelectric materials was presented. The design idea aimed at the direct utilization of the shear-induced vibration modes of piezoelectric material. Firstly, the inherent electromechanical coupling mechanism of piezoelectric material was investigated, and shear vibration modes of a piezoelectric shear block was specially designed. A driving point’s elliptical trajectory induced by shear vibration modes was discussed. Then a dynamic model for the piezoelectric shear stator was established with finite element（FE） method to conduct the parametric optimal design. Finally, a prototype based on d15 converse piezoelectric effect is manufactured, and the modal experiment of piezoelectric stator was conducted with laser doppler vibrometer. The experimental results show that the calculated shear-induced vibration modes can be excited completely, and the new linear ultrasonic motor reaches a speed 118 mm/s at noload, and maximal thrust 12.8 N.展开更多
Vibrations or dither's are features of the PWM servo control system in their steady outputs. On the grounds of analyses and experiments of a PWM pneumatic servo control system, the paper puts forward four varietie...Vibrations or dither's are features of the PWM servo control system in their steady outputs. On the grounds of analyses and experiments of a PWM pneumatic servo control system, the paper puts forward four varieties of PWM modulation methods, and concludes on the relationship between dithers and the different methods, and then discusses the influence of friction to the dithers. Results from experiments regarding the dynamic and static responses on the given system support the theories presented.展开更多
Ultrasonic vibration-assisted grinding(UVAG)is an effective and promising method for machining of hard-to-cut materials.This article proposed an ultrasonic vibration plate device enabling the longitudinal full-wave an...Ultrasonic vibration-assisted grinding(UVAG)is an effective and promising method for machining of hard-to-cut materials.This article proposed an ultrasonic vibration plate device enabling the longitudinal full-wave and transverse half-wave(L2T1)vibration mode for UVAG.The characteristics of two-dimensional coupled vibration in different directions were analyzed on the basis of apparent elastic method and finite element method.Furthermore,a correction factor was applied to correct the frequency error caused by the apparent elastic method.Finally,the comparative experiments between the conventional creep-feed grinding and UVAG of Inconel 718 nickel-based superalloy were carried out.The results indicate that the apparent elastic method with the correction factor is accurate for the design of plate device under the L2T1 vibration mode.Compared with the conventional creep-feed grinding,the UVAG causes the reduction of grinding force and the improvement of machined surface quality of Inconel 718 nickel-based superalloy.Furthermore,under the current experimental conditions,the optimal ultrasonic vibration amplitude is determined as 6μm,with which the minimum surface roughness is achieved.展开更多
This paper deals with the study of the temperature effect on the nonlinear vibration behavior of nanoplate-based nano electromechanical systems（NEMS） subjected to hydrostatic and electrostatic actuations. Using Erin...This paper deals with the study of the temperature effect on the nonlinear vibration behavior of nanoplate-based nano electromechanical systems（NEMS） subjected to hydrostatic and electrostatic actuations. Using Eringen＇s nonlocal elasticity and Gurtin–Murdoch theory, the nonlocal plate model is derived through Hamilton＇s principle. The governing equation which is extremely nonlinear due to the geometrical nonlinearity and electrostatic attraction forces is solved numerically using the differential quadrature method（DQM）. The accuracy of the present method is veriied by comparing the obtained results with the experimental data and those in the literature and very good agreement is obtained. Finally a comprehensive study is carried out to determine the inluence of temperature on the nonlinear vibration characteristics of NEMS made of two different materials including aluminum（Al）and silicon（Si） and some conclusions are drawn.展开更多
The low frequency vibration response of a specimen in acoustic fatigue tests depends not only on the dynamic characteristics and the boundary conditions of the specimen itself, but also on the test unit which couples ...The low frequency vibration response of a specimen in acoustic fatigue tests depends not only on the dynamic characteristics and the boundary conditions of the specimen itself, but also on the test unit which couples the specimen to a given sound field. Further, the latter can even be dominant instead the former in some circumstances. This fact is shown in the paper by using the experimental results and the theoretical analysis of the acoustic-induced vibration of a boundary clamped rectangular thin plate. In analysing the systems of acoustic fatigue test, an approach of electro-mechano-acoustical analogous circuit is used. The application of the approach can give an estimation of the effects on the low frequency vibration modes of various parameters in a system quantitatively. This supplies a theoretical basis and a means for the rational layout of acoustic fatigue tests.展开更多
The voltage was recorded to investigate the influence of the static magnetic field on droplet evolution during the mag-netically controlled electroslag remelting （MC-ESR） process. MC-ESR experiments were carried out...The voltage was recorded to investigate the influence of the static magnetic field on droplet evolution during the mag-netically controlled electroslag remelting （MC-ESR） process. MC-ESR experiments were carried out under differentremelting current, and transverse static magnetic fields （TSMF） of 85 mT, 130 mT and 160 mT were superimposed.Statistical work was performed to obtain the quantitative data of the droplets. The ASPEX Explorer was utilized toinvestigate the inclusions evolution of GCr15 ingots. The number of the droplets was 31 in 20 s during the traditional ESRprocess and reached 50 and 51 under the MC-ESR process with the TSMF of 85 mT and 130 mT, respectively. Whencompared the traditional ESR process with the MC-ESR process, the inclusions amount reduced 67%.展开更多
基金Supported by the National Natural Science Foundation of China(51064009,51464015)the Natural Science Foundation of Guangdong Province of China(2016A030313121)+1 种基金the Higher School Talent Introduction Project of Guangdong Province(A413.0210)the Science and Technology Project of Huizhou City of Guangdong Province of China(2014B020004018)
文摘Model test studies based on the similarity theory were conducted to investigate vibration effect and damage evolution characteristics of tunnel surrounding rock under push-type cyclic blasting excavation.The model was constructed with a ratio of 1∶15.By simulating the tunnel excavation of push-type cyclic blasting,the influence of the blasting parameter change on vibration effect was explored.The damage degree of tunnel surrounding rock was evaluated by the change of the acoustic wave velocity at the same measuring point after blasting.The relationship between the damage evolution of surrounding rock and blasting times was established.The research results show that：（1）In the same geological environment,the number of delay initiation is larger,the main vibration frequency of blasting seismic wave is higher,and the attenuation of high frequency signal in the rock and soil is faster.The influence of number of delay initiation on blasting vibration effect cannot be ignored;（2）Under push-type cyclic blasting excavation,there were great differences in the decreasing rates of acoustic wave velocity of the measuring points which have the same distance to the blasting region at the same depth,and the blasting damage ranges of surrounding rock were typically anisotropic at both depth and breadth;（3）When blasting parameters were basically kept as the same,the growth trend of the cumulative acoustic wave velocity decreasing rate at the measuring point was nonlinear under different cycle blasting excavations;（4）There were nonlinear evolution characteristics between the blasting cumulative damage（D）of surrounding rock and blasting times（n）under push-type cyclic blasting loading,and different measuring points had corresponding blasting cumulative damage propagation models,respectively.The closer the measuring point was away from the explosion source,the faster the cumulative damage extension.Blasting cumulative damage effect of surrounding rock had typically nonlinear evolution properties and anisotropic characteristics.
基金financially supported by the National Key R&D Program of China(Grant No.2020YFA0711802)the Wuhan Science and Technology Bureau of China(Grant No.2023020201010081)the National Nature Science Foundation of China(Grant No.U22A20239).
文摘The technology of expansion fracturing with liquid CO_(2)(EFLCO_(2))has attracted increasing attention due to reduced vibration and damage.The disposable fracturing tube has been developed and is gradually replacing the Cardox tube.However,there is a lack of impact pressure testing of disposable tubes under real working conditions,selection of gas explosion design parameters,and systematic analysis of blasting vibration.This limitation has constrained the widespread application of disposable fracturing tubes in engineering.A joint monitoring of the pressure-time curves in the disposable tubes and boreholes was conducted.The rock-breaking effect of varying hole spacing parameters in the EFLCO_(2)design was analyzed,and a systematic study was carried out on the vibration peak value,frequency,and energy characteristics.The results show that(1)the pressure distribution characteristics,stress peak value,and duration in the disposable tubes are different from those of Cardox tubes,which show multi-peak distribution,low-pressure peak value,and short duration.The correlation between the pressure in the disposable tube,filling pressure,and liquid CO_(2)weight is established,and a theoretical calculation method for the borehole wall pressure is proposed;(2)The hole spacing in rocks of different hardness is suggested;and(3)At the same scale distance,the peak particle velocity(PPV)caused by EFLCO_(2)(PPVCO_(2))is significantly smaller than that caused by blasting(PPVexplosive).The ratio of PPVexplosive to PPVCO_(2)is a power function related to scale distance,and a distance-related zonality exist in this relationship.The frequency composition of the vibration signal caused by EFLCO_(2)is relatively simple with a narrow frequency band.Its PPV and energy are mainly concentrated in the low-frequency band.This research contributes to the optimization of disposable fracturing tubes,gas explosion design,and vibration hazard control.
文摘This study is focused on the effect of vibration induced by moving trains in tunnels on the surrounding ground and structures.A three-dimensional finite element model is established for a one-track railway tunnel and an adjacent twelve-storey building frame by using commercial software Midas GTS-NX(2019)and Midas Gen.This study considered the moving load effect of a complete train,which varies with space as well as with time.The effect of factors such as train speed,overburden pressure on the tunnel and variation in soil properties are studied in the time domain.As a result,the variations in horizontal and vertical acceleration for two different sites,i.e.,the free ground surface(without structure)and the area containing the structure,are compared.Also,the displacement pattern of the raft foundation is plotted for different train velocities.At lower speeds,the heaving phenomenon is negligible,but as the speed increases,both the heaving and differential settlement increase in the foundation.This study demonstrates that the effect of moving train vibrations should be considered in the design of new nearby structures and proper ground improvement should be considered for existing structures.
基金supported by the Tianjin Municipal Transportation Commission Project(No.2018-b2).
文摘The purpose of this study is to investigate the suppression effect of a nonlinear energy sink(NES)on the wind-vortex-induced pipe vibration and explore the influence of damping,stiffness,and NES installation position on the suppression effect.In this work,the wind-vortex-induced vibration of an elastic pipe of a deepwater jacket was studied,and vibrations were suppressed by using an NES.A van der Pol wake oscillator was used to simulate vortex-induced force,and the dynamic equation of the pipe considering the NES was established.The Galerkin method was applied to discretize the motion equation,and the vortex-induced vibration(VIV)of the pipe at reduced wind speeds was numerically analyzed.The novelty of this research is that particle swarm optimization was used to optimize the parameters of the NES to improve vibration suppression.The influence of the installation position,nonlinear stiffness,and damping parameters of the NES on vibration suppression was analyzed.Results showed that the optimized parameter combinations of the NES can effectively reduce wind-vortex-induced pipe vibration.The installation position of the NES had a significant effect on vibration suppression,and the midpoint of the pipe was the optimal NES installation position.An increase in stiffness or a 10% decrease in damping may cause vibration suppression failure.The results of this study provide some guidance for VIV suppression in deepwater jacket pipes.
基金supported by the National Natural Science Foundation of China(No.U1737201)the National Science and Technology Major Project(No.2017-VII-0015-0111)+1 种基金the Key Basic and Applied Research Program of Guangdong Province,China(No.2019B030302010)the Science and Technology Innovation Commission Shenzhen(No.JCYJ20170412111216258).
文摘Rotary ultrasonic drilling(RUD)has become an effective approach for machining advanced composites which are widely using in the field of aeronautics.The cutting kinematics and the corresponding material removal mechanisms are distinct in different drilling areas during RUD.However,these fundamentals have not been fully considered in the existing studies.In this research,two distinct forms of interaction induced by ultrasonic vibration were considered as impact-separation and vibratory lapping between the abrasives and workpiece.And the conditions to guarantee the effectiveness of these interactions were obtained to eliminate diminishing effects of ultrasonic vibration.Based on indentation fracture theory,the penetration depth of abrasives and the axial drilling force model was derived for RUD.The verification tests of C/SiC composites resulted in a prediction error within 15%.Due to the minimal volume of material removed during each vibration cycle,the drilling force was more stable in vibration assisted mode.The specific drilling energy of RUD was firstly calculated based on the measured drilling load.It was found the drilling parameters should be matched with vibration frequency and amplitude to make better usage of the advantages of ultrasonic vibration,which is critical in the vibration assisted processing of advanced materials.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11372053,11402031,11221202 and 11172044the Opening Project of the State Key Laboratory of Explosion Science and Technology under Grant No KFJJ14-06M
文摘It is shown that the introduction of thermal effect, zero-point vibration, and phonon anharmonicity to a high quality and first-principle-Sased force field （atomic potential） results in a significant improvement in predict- ing the densities for the α phase crystalline hexahydro-1,3,5-trinitro-l,3,5-triazine （RDX）, and derivation of its high-fidelity Hugoniot locus and Mie-Grfineisen equation of state covering a very wide range of pressures and temperatures. This work can be used to efficiently and accurately predict the thermophysical properties of solid explosives over the pressures and temperatures to which they are subjected, which is a long-standing issue in the field of energetic materials.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12004370 and 12127804)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB34020000)。
文摘The vibrational motions are usually neglected when calculating(e,2e) triple differential cross sections(TDCSs) of molecules. Here, multi-center distorted-wave method(MCDW) has been modified by including molecular vibrations. This vibrational MCDW method is employed to calculate the TDCSs of 1b3gorbital of ethylene at low(100 eV) and medium(250 eV) incident electron energies in coplanar asymmetric kinematic condition. The results show that molecular vibrations significantly influence the angular distributions of the TDCSs, especially in the binary region along momentum transfer near the Bethe ridge.
文摘This paper puts forward the concept of double semi-active vibration isolation systemutilizing the 'on-off' active damper and the 'on-off' active spring. Applying KBM Asympto-tic method, the vibration of the system in case of weak semi-active control is studied. ln pcactice, there are two types of vibration isolation. One is to isolate the transmitting of the cyclicunbalanced force generated by the revolving machine to the surroundings. The other is to isolatethe transmitting of the vibration displacement of the surroundings to precise equipment. Deduc-ing the influence of the roadway unflatness on vehicles also belongs to this type. For the firsttype of isolation system, the damper always dissipates energy, and the total work done by the spring in a vibration cycle is zero. For the second type of isolation system, the work done by the damper sometimes is positive, and sometimes negative. The damper dissipates less energy. The work done by the spring in a vibration cycle isn't zero, and it is usually positive. ln thispaper, the vibration isolation is refered to the second type. .
文摘Fracture and ground vibration of rock subjected to different decoupling decked charges are investigated based on the numerical simulation. The dynamic pressure value is studied, which demonstrates that simulation of fracture zone is feasible. Attenuation index of dynamic pressure is 2.06, 2.05 and 1.93 for air, water and sand intervals respectively. The small attenuation of sand in- terval results in the large ground vibration. The predicted vertical vibration waveform and peak parti- cle velocities （PPV） in far-field are in agreement with the monitoring results. The results show that the air and water decked charges can improve the effect of rock fracture in near-field and reduce ground vibration in far-field.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51578516 and 51238012)the Basic Research Foundation of Institute of Engineering Mechanics,CEA(Grant No.2011B02)+1 种基金973 Program(Grant No.2011CB013601)the Wuhan Blasting Company
文摘Ground vibration accelerations caused by the collapse of blasting demolition of urban viaducts was recorded in ordered to analyze the engineering characteristics and effects on the surrounding buildings. Through the analysis of peak ground acceleration,peak frequency,duration and response spectra of the recorded vibrations in different acceleration arrays,some conclusions are drawn: the peak ground acceleration decreases with increasing distance, and the amplitude of vertical component is higher than that of the horizontal components,especially in near source region. The peak frequency of ground acceleration decreases with distance,and in near source region,it is larger than the natural frequency of the surrounding buildings,and thus it will not have much effect on the buildings. The duration of ground acceleration caused by collapse is longer than that caused by blasting itself. The vertical response spectrum is the largest of the three components,and it decreases rapidly in the near source region of about 30 m,but beyond that the distance decreases slowly.The horizontal components are smaller than the local seismic design spectrum,while the vertical component for natural period under 0.15 s exceeds the seismic design spectrum,but the natural periods of general buildings are usually beyond that domain,so this will not have much effect on the nearby buildings.
文摘The nonlinear dynamic model of the marine diesel crankshaft system with a propeller and 6 cranks is established, in which the variable moment of inertia of the linkage and the piston, coupling effect between torsional and axial vibration, the actuating force applied on the piston, the actuating torque and force applied on the propeller is included. The governing equations of the model denote a strong nonlinear and non autonomous system. By numeric simulation, the dynamic response of the system to initial displacement and initial speed, variable moment of inertia, the pressure applied on the piston by combustion gas, the torque and the axial force applied on the propeller by fluid is researched respectively. According to the research results, the variable moment of inertia and coupling effect between torsional and axial vibration are the fundamental reason for nonlinear vibration. Different actuating factors can not only result in different frequency components of the response, but make the same frequency component have different vibration amplitude. The dynamic behavior of the system is not influenced obviously by the actuating torque and force applied on the propeller. There is obvious difference in sensitivity of the dynamic response in the different direction to the same actuating factor.
基金Funded by the National Basic Research Program of China(973 Program,No.2015CB057501)the National Natural Science Foundation of China(Nos.50975135,51275235)+1 种基金the Fundamental Research Funds for the Central Universities(No.NJ20140024)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘A novel linear ultrasonic motor based on d15 effect of piezoelectric materials was presented. The design idea aimed at the direct utilization of the shear-induced vibration modes of piezoelectric material. Firstly, the inherent electromechanical coupling mechanism of piezoelectric material was investigated, and shear vibration modes of a piezoelectric shear block was specially designed. A driving point’s elliptical trajectory induced by shear vibration modes was discussed. Then a dynamic model for the piezoelectric shear stator was established with finite element（FE） method to conduct the parametric optimal design. Finally, a prototype based on d15 converse piezoelectric effect is manufactured, and the modal experiment of piezoelectric stator was conducted with laser doppler vibrometer. The experimental results show that the calculated shear-induced vibration modes can be excited completely, and the new linear ultrasonic motor reaches a speed 118 mm/s at noload, and maximal thrust 12.8 N.
文摘Vibrations or dither's are features of the PWM servo control system in their steady outputs. On the grounds of analyses and experiments of a PWM pneumatic servo control system, the paper puts forward four varieties of PWM modulation methods, and concludes on the relationship between dithers and the different methods, and then discusses the influence of friction to the dithers. Results from experiments regarding the dynamic and static responses on the given system support the theories presented.
基金financially supported by the National Natural Science Foundation of China(Nos.51921003 and 51775275)National Key Laboratory of Science and Technology on Helicopter Transmission(Nanjing University of Aeronautics and Astronautics)(No.HTL-A-20G01)Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX20_0179)。
文摘Ultrasonic vibration-assisted grinding(UVAG)is an effective and promising method for machining of hard-to-cut materials.This article proposed an ultrasonic vibration plate device enabling the longitudinal full-wave and transverse half-wave(L2T1)vibration mode for UVAG.The characteristics of two-dimensional coupled vibration in different directions were analyzed on the basis of apparent elastic method and finite element method.Furthermore,a correction factor was applied to correct the frequency error caused by the apparent elastic method.Finally,the comparative experiments between the conventional creep-feed grinding and UVAG of Inconel 718 nickel-based superalloy were carried out.The results indicate that the apparent elastic method with the correction factor is accurate for the design of plate device under the L2T1 vibration mode.Compared with the conventional creep-feed grinding,the UVAG causes the reduction of grinding force and the improvement of machined surface quality of Inconel 718 nickel-based superalloy.Furthermore,under the current experimental conditions,the optimal ultrasonic vibration amplitude is determined as 6μm,with which the minimum surface roughness is achieved.
文摘This paper deals with the study of the temperature effect on the nonlinear vibration behavior of nanoplate-based nano electromechanical systems（NEMS） subjected to hydrostatic and electrostatic actuations. Using Eringen＇s nonlocal elasticity and Gurtin–Murdoch theory, the nonlocal plate model is derived through Hamilton＇s principle. The governing equation which is extremely nonlinear due to the geometrical nonlinearity and electrostatic attraction forces is solved numerically using the differential quadrature method（DQM）. The accuracy of the present method is veriied by comparing the obtained results with the experimental data and those in the literature and very good agreement is obtained. Finally a comprehensive study is carried out to determine the inluence of temperature on the nonlinear vibration characteristics of NEMS made of two different materials including aluminum（Al）and silicon（Si） and some conclusions are drawn.
文摘The low frequency vibration response of a specimen in acoustic fatigue tests depends not only on the dynamic characteristics and the boundary conditions of the specimen itself, but also on the test unit which couples the specimen to a given sound field. Further, the latter can even be dominant instead the former in some circumstances. This fact is shown in the paper by using the experimental results and the theoretical analysis of the acoustic-induced vibration of a boundary clamped rectangular thin plate. In analysing the systems of acoustic fatigue test, an approach of electro-mechano-acoustical analogous circuit is used. The application of the approach can give an estimation of the effects on the low frequency vibration modes of various parameters in a system quantitatively. This supplies a theoretical basis and a means for the rational layout of acoustic fatigue tests.
基金financial support of the National Key Research and Development Program of China(No.2016YFB0300401)the National Natural Science Foundation of China(Nos.U1732276 and 51704193)+2 种基金the General Financial Grant from the China Postdoctoral Science Foundation(No.2017M621431)the Science and Technology Commission of Shanghai Municipality(No.15520711000)Independent Research and Development Project of State Key of Advanced Special Steel,Shanghai University(SKLASS2015-Z021,SELF-2014-02)
文摘The voltage was recorded to investigate the influence of the static magnetic field on droplet evolution during the mag-netically controlled electroslag remelting （MC-ESR） process. MC-ESR experiments were carried out under differentremelting current, and transverse static magnetic fields （TSMF） of 85 mT, 130 mT and 160 mT were superimposed.Statistical work was performed to obtain the quantitative data of the droplets. The ASPEX Explorer was utilized toinvestigate the inclusions evolution of GCr15 ingots. The number of the droplets was 31 in 20 s during the traditional ESRprocess and reached 50 and 51 under the MC-ESR process with the TSMF of 85 mT and 130 mT, respectively. Whencompared the traditional ESR process with the MC-ESR process, the inclusions amount reduced 67%.
