This paper presents the principle and critical factors of adaptive cancellation of structural vibration in time domain(ACSV-TD).Digital-analog simulations and model tests are conducted on cancelling forced vibration o...This paper presents the principle and critical factors of adaptive cancellation of structural vibration in time domain(ACSV-TD).Digital-analog simulations and model tests are conducted on cancelling forced vibration of a cantilever beam.Filtered-X RLS algorithm is used to get faster convergence speed and stronger adaptability (in comparison with LMS algorithm). The results demonstrate the efficiency and adaptability of the ACSV-TD.展开更多
In this paper, the vibration arid sound radiation of the underwater complexshell-structure which is the cylindrical shell with hemi-spherical shell on the ends are studied bystatistical energy analysis (SEA). The whol...In this paper, the vibration arid sound radiation of the underwater complexshell-structure which is the cylindrical shell with hemi-spherical shell on the ends are studied bystatistical energy analysis (SEA). The whole shell-structure is divided into the four subsystems,and the SEA physical model and power flow balance equations among these subsystems are established.The similitude relations of input power, coupling loss factor and modal density of the subsystemsbetween the complex shell-structure and its scaled-down model are analyzed. According to thesimilitude theory and power flow balance equations, when the immerged shell-structures are excited,the similar relations of spatially averaged vibration response and underwater radiating sound powerare established for the complex shell-structure and its scaled-down model.展开更多
With the liquid propellant making up 60%—70% of the takeoff weight of the hypersonic vehicle,the dynamic load caused by great propellant sloshing interacts with the flexible structure of the aircraft.Therefore,the dy...With the liquid propellant making up 60%—70% of the takeoff weight of the hypersonic vehicle,the dynamic load caused by great propellant sloshing interacts with the flexible structure of the aircraft.Therefore,the dynamic model displays characteristics of strong coupling with structure/control and nonlinearity.Based on the sloshing mass dynamic simplified as a spring-mass-damping model,a rigid-flexible-sloshing model is constructed.Moreover,the effect on the dynamic performance of the coupled model is analyzed with changing frequency and damping.The results show that propellant sloshing dynamics significantly affects the rigid body motion modes,especially flexible mode and short mode.The right half plane pole(RHP)moves far from the imaginary axis with the consumption of the propellant.The flexible mode attenuates with the increase of the sloshing damping,and the coupling becomes stronger when sloshing frequency is close to the short mode frequency or the flexible frequency of the beam.展开更多
The aerodynamic characteristics are vital for short cylindrical Terminal Sensitive Bullets(TSB)with lowaspect ratio,especially in terminal trajectory.Currently,there is little research in terms of the TSB andshort cyl...The aerodynamic characteristics are vital for short cylindrical Terminal Sensitive Bullets(TSB)with lowaspect ratio,especially in terminal trajectory.Currently,there is little research in terms of the TSB andshort cylinder with two free ends,and particularly in this trajectory,where the scanning angleβand rollangle a vary over a broad range between 0°and 180.In this work wind tunnel experiments are firstconducted to learn the effects of Reynolds number and scanning angle on aerodynamic parameters forshort cylinder with aspect ratio L/D=1.Similar to infinite cylinder,for the short cylinder with two freeends,the drag crisis phenomenon still exists in the critical regime 1.7×10^(5)≤Re≤6.8×10^(5).Then 3Dsimulations are performed to demonstrate the aerodynamic characteristics of short cylinder and TSBover a broad range of Re,L/D,a and 6.The sensitivity analysis of time step and grid are presented as well.whenβ3=0,for short cylinder,the drag crisis phenomenon was also observed in the simulation,but notas obvious as in the wind tunnel test.In some attitudes,there is an obvious Karman vortexin the wake ofshort cylinder and TSB.The correlation between time-averaged aerodynamic coefficients and L/D,Re,a&l is discussed.The vortex shedding frequency and shear layer behavior are obtained for quasi-steadyand unsteady flow.Finally,the effect of end's shape on drag reduction and vortex shedding frequency isanalyzed.展开更多
With the purpose of efficiently predicting structural radiated noise of internal combustion engine（I.C.E.）,a new simulation technique is introduced,which is an approach based on boundary element method （BEM）,acous...With the purpose of efficiently predicting structural radiated noise of internal combustion engine（I.C.E.）,a new simulation technique is introduced,which is an approach based on boundary element method （BEM）,acoustic transfer vector（ATV） technique and coupled boundary element model and finite element model （BEM-FEM） approach.Analyses of vibration exciting loads,computing structural dynamic characteristics and dynamic responses have led to theoretical results,which are tested on an L6 diesel engine to validate this proposed technique in engineering practice.展开更多
Stiffness is one of the basic performance parameters for railway track. The efficient and accurate stiffness measurement has been considered as the foundation for further development of railway engineering, and theref...Stiffness is one of the basic performance parameters for railway track. The efficient and accurate stiffness measurement has been considered as the foundation for further development of railway engineering, and therefore has great theoretical and practical significance. Based on a summary of the connotation and measurement of track stiffness, the state of the art of measurement methods for track stiffness was analyzed systematically. The standstill measurement of track stiffness can be performed with the traditional jack-loading method, impact hammer method, FWD （falling weight deflectometer） method, and track loading vehicle method. Although these methods can be adopted in stiffness measurement for a section of railway track, they are not desirable owning to small range and low efficiency. In the recent 20 years, researchers have proposed many methods like unbalancedloading laser displacement method, deflection basin deformation rate method, and eccentricity excitation method to continuously measure track stiffness; however, these methods have drawbacks like poor accuracy, low speed, and insufficient data analysis. In this work, the merits and demerits of these methods were summarized, and optimization suggestions were presented. Based on the wave transmission mechanism and principle of vibration energy harvesting, an overall conception on continuous measurement of stiffness and long-term stiffness monitoring for special sections was proposed.展开更多
We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polarontransformed Redfield equation combined with full counting statistics.The steady state heat currents are...We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polarontransformed Redfield equation combined with full counting statistics.The steady state heat currents are obtained via this unified approach over a wide region of system–bath coupling,and can be analytically reduced to the Redfield and nonequilibrium noninteracting blip approximation results in the weak and strong coupling limits,respectively.A giant heat amplification phenomenon emerges in the strong system–bath coupling limit,where transitions mediated by the middle thermal bath are found to be crucial to unravel the underlying mechanism.Moreover,the heat amplification is also exhibited with moderate coupling strength,which can be properly explained within the polaron framework.展开更多
Counter-rotating-wave terms(CRWTs)are traditionally viewed to be crucial in open small quantum systems with strong system–bath dissipation.Here by exemplifying in a nonequilibrium qubit–phonon hybrid model,we show t...Counter-rotating-wave terms(CRWTs)are traditionally viewed to be crucial in open small quantum systems with strong system–bath dissipation.Here by exemplifying in a nonequilibrium qubit–phonon hybrid model,we show that CRWTs can play the significant role in quantum heat transfer even with weak system–bath dissipation.By using extended coherent phonon states,we obtain the quantum master equation with heat exchange rates contributed by rotating-waveterms(RWTs)and CRWTs,respectively.We find that including only RWTs,the steady state heat current and current fluctuations will be significantly suppressed at large temperature bias,whereas they are strongly enhanced by considering CRWTs in addition.Furthermore,for the phonon statistics,the average phonon number and two-phonon correlation are nearly insensitive to strong qubit–phonon hybridization with only RWTs,whereas they will be dramatically cooled down via the cooperative transitions based on CRWTs in addition.Therefore,CRWTs in quantum heat transfer system should be treated carefully.展开更多
文摘This paper presents the principle and critical factors of adaptive cancellation of structural vibration in time domain(ACSV-TD).Digital-analog simulations and model tests are conducted on cancelling forced vibration of a cantilever beam.Filtered-X RLS algorithm is used to get faster convergence speed and stronger adaptability (in comparison with LMS algorithm). The results demonstrate the efficiency and adaptability of the ACSV-TD.
文摘In this paper, the vibration arid sound radiation of the underwater complexshell-structure which is the cylindrical shell with hemi-spherical shell on the ends are studied bystatistical energy analysis (SEA). The whole shell-structure is divided into the four subsystems,and the SEA physical model and power flow balance equations among these subsystems are established.The similitude relations of input power, coupling loss factor and modal density of the subsystemsbetween the complex shell-structure and its scaled-down model are analyzed. According to thesimilitude theory and power flow balance equations, when the immerged shell-structures are excited,the similar relations of spatially averaged vibration response and underwater radiating sound powerare established for the complex shell-structure and its scaled-down model.
基金supported by the Fundamental Research Funds for the Central Universities(No.NS2015097)
文摘With the liquid propellant making up 60%—70% of the takeoff weight of the hypersonic vehicle,the dynamic load caused by great propellant sloshing interacts with the flexible structure of the aircraft.Therefore,the dynamic model displays characteristics of strong coupling with structure/control and nonlinearity.Based on the sloshing mass dynamic simplified as a spring-mass-damping model,a rigid-flexible-sloshing model is constructed.Moreover,the effect on the dynamic performance of the coupled model is analyzed with changing frequency and damping.The results show that propellant sloshing dynamics significantly affects the rigid body motion modes,especially flexible mode and short mode.The right half plane pole(RHP)moves far from the imaginary axis with the consumption of the propellant.The flexible mode attenuates with the increase of the sloshing damping,and the coupling becomes stronger when sloshing frequency is close to the short mode frequency or the flexible frequency of the beam.
基金The authors would like to acknowledge the financial supports from the National Natural Science Foundation of China(Grant No.11372136)the Special fund for basic scientific research of Central University(Grant No.30916011306)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX17_0386).
文摘The aerodynamic characteristics are vital for short cylindrical Terminal Sensitive Bullets(TSB)with lowaspect ratio,especially in terminal trajectory.Currently,there is little research in terms of the TSB andshort cylinder with two free ends,and particularly in this trajectory,where the scanning angleβand rollangle a vary over a broad range between 0°and 180.In this work wind tunnel experiments are firstconducted to learn the effects of Reynolds number and scanning angle on aerodynamic parameters forshort cylinder with aspect ratio L/D=1.Similar to infinite cylinder,for the short cylinder with two freeends,the drag crisis phenomenon still exists in the critical regime 1.7×10^(5)≤Re≤6.8×10^(5).Then 3Dsimulations are performed to demonstrate the aerodynamic characteristics of short cylinder and TSBover a broad range of Re,L/D,a and 6.The sensitivity analysis of time step and grid are presented as well.whenβ3=0,for short cylinder,the drag crisis phenomenon was also observed in the simulation,but notas obvious as in the wind tunnel test.In some attitudes,there is an obvious Karman vortexin the wake ofshort cylinder and TSB.The correlation between time-averaged aerodynamic coefficients and L/D,Re,a&l is discussed.The vortex shedding frequency and shear layer behavior are obtained for quasi-steadyand unsteady flow.Finally,the effect of end's shape on drag reduction and vortex shedding frequency isanalyzed.
基金Sponsored by the National Natural Science Foundation of China (50505047)Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi
文摘With the purpose of efficiently predicting structural radiated noise of internal combustion engine（I.C.E.）,a new simulation technique is introduced,which is an approach based on boundary element method （BEM）,acoustic transfer vector（ATV） technique and coupled boundary element model and finite element model （BEM-FEM） approach.Analyses of vibration exciting loads,computing structural dynamic characteristics and dynamic responses have led to theoretical results,which are tested on an L6 diesel engine to validate this proposed technique in engineering practice.
基金supported by the project (51425804) of the National Science Fund for Distinguished Young Scholars of Chinathe National Natural Science Foundation of China (NSFC) under grants U1234201, U1334203, and 51378439
文摘Stiffness is one of the basic performance parameters for railway track. The efficient and accurate stiffness measurement has been considered as the foundation for further development of railway engineering, and therefore has great theoretical and practical significance. Based on a summary of the connotation and measurement of track stiffness, the state of the art of measurement methods for track stiffness was analyzed systematically. The standstill measurement of track stiffness can be performed with the traditional jack-loading method, impact hammer method, FWD （falling weight deflectometer） method, and track loading vehicle method. Although these methods can be adopted in stiffness measurement for a section of railway track, they are not desirable owning to small range and low efficiency. In the recent 20 years, researchers have proposed many methods like unbalancedloading laser displacement method, deflection basin deformation rate method, and eccentricity excitation method to continuously measure track stiffness; however, these methods have drawbacks like poor accuracy, low speed, and insufficient data analysis. In this work, the merits and demerits of these methods were summarized, and optimization suggestions were presented. Based on the wave transmission mechanism and principle of vibration energy harvesting, an overall conception on continuous measurement of stiffness and long-term stiffness monitoring for special sections was proposed.
基金the National Natural Science Foundation of China(Grant Nos.11704093 and 11705008)Beijing Institute of Technology Research Fund Program for Young Scholars,China.
文摘We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polarontransformed Redfield equation combined with full counting statistics.The steady state heat currents are obtained via this unified approach over a wide region of system–bath coupling,and can be analytically reduced to the Redfield and nonequilibrium noninteracting blip approximation results in the weak and strong coupling limits,respectively.A giant heat amplification phenomenon emerges in the strong system–bath coupling limit,where transitions mediated by the middle thermal bath are found to be crucial to unravel the underlying mechanism.Moreover,the heat amplification is also exhibited with moderate coupling strength,which can be properly explained within the polaron framework.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11704093,11775159,and 11935010)the Natural Science Foundation of Shanghai,China(Grant Nos.18ZR1442800 and 18JC1410900)the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology.
文摘Counter-rotating-wave terms(CRWTs)are traditionally viewed to be crucial in open small quantum systems with strong system–bath dissipation.Here by exemplifying in a nonequilibrium qubit–phonon hybrid model,we show that CRWTs can play the significant role in quantum heat transfer even with weak system–bath dissipation.By using extended coherent phonon states,we obtain the quantum master equation with heat exchange rates contributed by rotating-waveterms(RWTs)and CRWTs,respectively.We find that including only RWTs,the steady state heat current and current fluctuations will be significantly suppressed at large temperature bias,whereas they are strongly enhanced by considering CRWTs in addition.Furthermore,for the phonon statistics,the average phonon number and two-phonon correlation are nearly insensitive to strong qubit–phonon hybridization with only RWTs,whereas they will be dramatically cooled down via the cooperative transitions based on CRWTs in addition.Therefore,CRWTs in quantum heat transfer system should be treated carefully.
