The modal characteristics of the transverse vibration of an axially moving roller chain coupled with lumped mass were analyzed.The chain system was modeled by using the multi-body dynamics theory and the governing equ...The modal characteristics of the transverse vibration of an axially moving roller chain coupled with lumped mass were analyzed.The chain system was modeled by using the multi-body dynamics theory and the governing equations were derived by means of Lagrange's equations.The effects of the parameters,such as the axially moving velocity of the chain,the tension force,the weight of lumped mass and its time-variable assign position in chain span,on the modal characteristics of transverse vibration for roller chain were investigated.The numerical examples were given.It is found that the natural frequencies and the corresponding mode shapes of the transverse vibration for roller chain coupled with lumped mass change significantly when the variations of above parameters are considered.With the movement of the chain strand,the natural frequencies present a fluctuating phenomenon,which is different from the uniform chain.The higher the order of mode is,the greater the fluctuating magnitude and frequency are.展开更多
Dynamic investigations revealed that lower order harmonic resonance phenomenon exists in the three ring gear transmission. That is, when the input speed is close to 1/3, 1/6, 1/9,…, 1/3 n of the primary natural frequ...Dynamic investigations revealed that lower order harmonic resonance phenomenon exists in the three ring gear transmission. That is, when the input speed is close to 1/3, 1/6, 1/9,…, 1/3 n of the primary natural frequency of the transmission, the loads on the bearings and gears are especially high. This paper explained this phenomenon from the viewpoint of parametric resonance in terms of perturbation technique. A conclusion was drawn that the basic reason for this phenomenon is the primary resonance caused by forcing excitation and parametric resonance caused by parametric change.展开更多
Seismic safety of underground structures is one of the main concerns in underground space exploitation. As the first step for dynamic seismic response analysis, the free vibration of long large cross-section undergrou...Seismic safety of underground structures is one of the main concerns in underground space exploitation. As the first step for dynamic seismic response analysis, the free vibration of long large cross-section underground structures is studied in the present paper. The general free transverse vibration motion equation of long large cross-section underground structure is derived with the comprehensive consideration of internal and external damping, effects of shear, cross-sectional rotational inertia and axial force, and a twoparameter soil model. In this way, Timoshenko's beam theory is extended. Two limit cases of free transverse vibration of underground structures are discussed. Parameter study shows that in general wave propagation velocities in structures increase with soil elastic parameters. However the influence of Winkler's parameter k is significant while the effect of the second soil elastic parameter gp is insignificant. The free vibration frequency of underground structures increases with relative wave number and soil elastic parameters. Unlike the influence of soil elastic parameters on wave propagation velocities, the influence of soil elastic parameters k and gp on the vibration frequency of underground structures have the same order; therefore the influence of the second soil parameter gp on the free vibration of underground structures should not be neglected in dynamic seismic analysis of underground structures展开更多
基金Project(50605060) supported by the National Natural Science Foundation of ChinaProject(20050056058) supported by the Research Fund for the Doctoral Program of Higher Education of ChinaProject(06YFJMJC03300) supported by the National Science Foundation of Tianjin,China
文摘The modal characteristics of the transverse vibration of an axially moving roller chain coupled with lumped mass were analyzed.The chain system was modeled by using the multi-body dynamics theory and the governing equations were derived by means of Lagrange's equations.The effects of the parameters,such as the axially moving velocity of the chain,the tension force,the weight of lumped mass and its time-variable assign position in chain span,on the modal characteristics of transverse vibration for roller chain were investigated.The numerical examples were given.It is found that the natural frequencies and the corresponding mode shapes of the transverse vibration for roller chain coupled with lumped mass change significantly when the variations of above parameters are considered.With the movement of the chain strand,the natural frequencies present a fluctuating phenomenon,which is different from the uniform chain.The higher the order of mode is,the greater the fluctuating magnitude and frequency are.
基金Partly supported by the Open Fund of theState Key Lab.of Mechanical TransmissionChongqing U niv
文摘Dynamic investigations revealed that lower order harmonic resonance phenomenon exists in the three ring gear transmission. That is, when the input speed is close to 1/3, 1/6, 1/9,…, 1/3 n of the primary natural frequency of the transmission, the loads on the bearings and gears are especially high. This paper explained this phenomenon from the viewpoint of parametric resonance in terms of perturbation technique. A conclusion was drawn that the basic reason for this phenomenon is the primary resonance caused by forcing excitation and parametric resonance caused by parametric change.
基金Financial support from the Beijing Natural Science Foundation (No. KZ200810016007)the National 973 Key Program (No. 2010CB732003)the National Science Foundation of China(NSFC) (No. 50825403) is gratefully acknowledged
文摘Seismic safety of underground structures is one of the main concerns in underground space exploitation. As the first step for dynamic seismic response analysis, the free vibration of long large cross-section underground structures is studied in the present paper. The general free transverse vibration motion equation of long large cross-section underground structure is derived with the comprehensive consideration of internal and external damping, effects of shear, cross-sectional rotational inertia and axial force, and a twoparameter soil model. In this way, Timoshenko's beam theory is extended. Two limit cases of free transverse vibration of underground structures are discussed. Parameter study shows that in general wave propagation velocities in structures increase with soil elastic parameters. However the influence of Winkler's parameter k is significant while the effect of the second soil elastic parameter gp is insignificant. The free vibration frequency of underground structures increases with relative wave number and soil elastic parameters. Unlike the influence of soil elastic parameters on wave propagation velocities, the influence of soil elastic parameters k and gp on the vibration frequency of underground structures have the same order; therefore the influence of the second soil parameter gp on the free vibration of underground structures should not be neglected in dynamic seismic analysis of underground structures