Violent axial vibration of a vehicle engine crankshaft might lead to multiple defects to the engine.Much research on mechanism and control measures has been done on engines,such as using the dynamic stiffness matrix m...Violent axial vibration of a vehicle engine crankshaft might lead to multiple defects to the engine.Much research on mechanism and control measures has been done on engines,such as using the dynamic stiffness matrix method,rayleigh differential method,and system matrix method.But the source of axial vibration has not been identified clearly because there are many excitation factors for the axial vibration of a crankshaft,such as coupled torsional-axial vibration and coupled bending-axial vibration,etc.In order to improve the calculation reliability and identify the excitation source of axial vibration of in vehicle engine crankshafts,this paper presents a method to identify the axial vibration excitation source of crankshafts for high speed diesel engines based on an auto-regressive and moving average（ARMA） model.Through determining initial moving average variables and measuring axial /bending/torsional vibrations of a crankshaft at the free-end of a 4-cylinder diesel engine,autoregressive spectrum analysis is applied to the measured vibration signal.The results show that the axial vibration of the crankshaft is mainly excited by coupled bending vibration at high speed.But at low speed,the axial vibration in some frequencies is excited primarily by torsional excitation.Through investigation of axial vibration source of engine crankshafts,calculation accuracy of vibration can be improved significantly.展开更多
Borehole-to-surface electrical imaging （BSEI） uses a line source and a point source to generate a stable electric field in the ground. In order to study the surface potential of anomalies, three-dimensional forward ...Borehole-to-surface electrical imaging （BSEI） uses a line source and a point source to generate a stable electric field in the ground. In order to study the surface potential of anomalies, three-dimensional forward modeling of point and line sources was conducted by using the finite-difference method and the incomplete Cholesky conjugate gradient （ICCG） method. Then, the damping least square method was used in the 3D inversion of the formation resistivity data. Several geological models were considered in the forward modeling and inversion. The forward modeling results suggest that the potentials generated by the two sources have different surface signatures. The inversion data suggest that the low- resistivity anomaly is outlined better than the high-resistivity anomaly. Moreover, when the point source is under the anomaly, the resistivity anomaly boundaries are better outlined than when using a line source.展开更多
The uniform speed of the magnetic field is directly influenced by the quality of the exciting signals for time grating sensors,which determines the measurement accuracy of the time grating sensors.Therefore,the highqu...The uniform speed of the magnetic field is directly influenced by the quality of the exciting signals for time grating sensors,which determines the measurement accuracy of the time grating sensors.Therefore,the highquality exciting signals are of great significance to the measurement accuracy improvement of the time grating sensors.Regarding the high requirements on quadrature exciting signal sources for linear time grating sensors,a direct digital frequency synthesis technique is employed to design the quadrature exciting signals.In addition,an active band-pass filter is designed to eliminate the interference and improve the signal quality.The frequency and the phase of the proposed quadrature exciting signal sources can easily adjust,and the precision of the signals is high.The exciting signal sources and the signal processing circuits are integrated into one FPGA chip,which greatly decrease the size of the circuit board and improve the reliability.Simulation and experiment results prove the validity.This design method can be widely applied into many applications which require high quality of exciting signal sources.展开更多
A robust optimization design method is proposed to investigate the influence of the hook position on the vertical vibration(bending)of an automobile exhaust system.A block diagram for the robustness analysis of the ex...A robust optimization design method is proposed to investigate the influence of the hook position on the vertical vibration(bending)of an automobile exhaust system.A block diagram for the robustness analysis of the exhaust system is initially constructed from the major affecting factors.Secondly,the second-order inertia force is set as the vibration excitation source of the exhaust system and the displacement of four hooks of the exhaust system is selected as the variable factor.Then tests are carried out to investigate the resulting vertical bending considering four influencing factors and three levels of analysis.Finally,a variance analysis of the vertical bending is performed.The present study provides a set of guidelines to control the key factors affecting the vibration of vehicle exhaust systems while proposing an effective method to reduce vehicle vibration and improve noise analysis。展开更多
Miniaturization of photoacoustic microscopy(PAM)to portable and wearable levels requires special design of scanning,detection,acquisition,and excitation units.Now the first three can be minimized to gram and millimete...Miniaturization of photoacoustic microscopy(PAM)to portable and wearable levels requires special design of scanning,detection,acquisition,and excitation units.Now the first three can be minimized to gram and millimeter levels,but the excitation sources usually remain bulky and also face different challenges,including low pulse energy,wide pulse width,limited wavelength,or high cost.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 509060605)China Postdoctoral Science Foundation (Grant No. 201003295)
文摘Violent axial vibration of a vehicle engine crankshaft might lead to multiple defects to the engine.Much research on mechanism and control measures has been done on engines,such as using the dynamic stiffness matrix method,rayleigh differential method,and system matrix method.But the source of axial vibration has not been identified clearly because there are many excitation factors for the axial vibration of a crankshaft,such as coupled torsional-axial vibration and coupled bending-axial vibration,etc.In order to improve the calculation reliability and identify the excitation source of axial vibration of in vehicle engine crankshafts,this paper presents a method to identify the axial vibration excitation source of crankshafts for high speed diesel engines based on an auto-regressive and moving average（ARMA） model.Through determining initial moving average variables and measuring axial /bending/torsional vibrations of a crankshaft at the free-end of a 4-cylinder diesel engine,autoregressive spectrum analysis is applied to the measured vibration signal.The results show that the axial vibration of the crankshaft is mainly excited by coupled bending vibration at high speed.But at low speed,the axial vibration in some frequencies is excited primarily by torsional excitation.Through investigation of axial vibration source of engine crankshafts,calculation accuracy of vibration can be improved significantly.
基金sponsored by the National Major Project(No.2016ZX05014-001)the National Natural Science Foundation of China(No.41172130 and U1403191)the Fundamental Research Funds for the Central Universities(No.2-9-2015-209)
文摘Borehole-to-surface electrical imaging （BSEI） uses a line source and a point source to generate a stable electric field in the ground. In order to study the surface potential of anomalies, three-dimensional forward modeling of point and line sources was conducted by using the finite-difference method and the incomplete Cholesky conjugate gradient （ICCG） method. Then, the damping least square method was used in the 3D inversion of the formation resistivity data. Several geological models were considered in the forward modeling and inversion. The forward modeling results suggest that the potentials generated by the two sources have different surface signatures. The inversion data suggest that the low- resistivity anomaly is outlined better than the high-resistivity anomaly. Moreover, when the point source is under the anomaly, the resistivity anomaly boundaries are better outlined than when using a line source.
基金funded by National Natural Science Foundation of China(No.51775075)Natural Science Foundation of Chongqing(No.cstc2016jcyj A0505)
文摘The uniform speed of the magnetic field is directly influenced by the quality of the exciting signals for time grating sensors,which determines the measurement accuracy of the time grating sensors.Therefore,the highquality exciting signals are of great significance to the measurement accuracy improvement of the time grating sensors.Regarding the high requirements on quadrature exciting signal sources for linear time grating sensors,a direct digital frequency synthesis technique is employed to design the quadrature exciting signals.In addition,an active band-pass filter is designed to eliminate the interference and improve the signal quality.The frequency and the phase of the proposed quadrature exciting signal sources can easily adjust,and the precision of the signals is high.The exciting signal sources and the signal processing circuits are integrated into one FPGA chip,which greatly decrease the size of the circuit board and improve the reliability.Simulation and experiment results prove the validity.This design method can be widely applied into many applications which require high quality of exciting signal sources.
基金science and technology projects of Jiangxi Provincial Education Department(GJJ161186).
文摘A robust optimization design method is proposed to investigate the influence of the hook position on the vertical vibration(bending)of an automobile exhaust system.A block diagram for the robustness analysis of the exhaust system is initially constructed from the major affecting factors.Secondly,the second-order inertia force is set as the vibration excitation source of the exhaust system and the displacement of four hooks of the exhaust system is selected as the variable factor.Then tests are carried out to investigate the resulting vertical bending considering four influencing factors and three levels of analysis.Finally,a variance analysis of the vertical bending is performed.The present study provides a set of guidelines to control the key factors affecting the vibration of vehicle exhaust systems while proposing an effective method to reduce vehicle vibration and improve noise analysis。
基金National Natural Science Foundation of China(62305274,62475222,62205163)NaturalScience Foundation of Xiamen Municipality(3502Z202371001,3502Z20227162)+1 种基金Natural Science Foundation of Fujian Province(2024J01056)Xiamen University(20720240025).
文摘Miniaturization of photoacoustic microscopy(PAM)to portable and wearable levels requires special design of scanning,detection,acquisition,and excitation units.Now the first three can be minimized to gram and millimeter levels,but the excitation sources usually remain bulky and also face different challenges,including low pulse energy,wide pulse width,limited wavelength,or high cost.
