According to the dimensional tolerances on hydrodynamic journal bearing system, a nonlinear oil film force model was established,and the Reynolds' equation was solved by adopting finite difference method. In order...According to the dimensional tolerances on hydrodynamic journal bearing system, a nonlinear oil film force model was established,and the Reynolds' equation was solved by adopting finite difference method. In order to fulfill different dimensional tolerances in the system,adopting 2kfactor design and using the eccentricity ratio corresponding to the stability critical curve,the effects of the friction power loss brought by the dimensional tolerances of the dynamic viscosity,bearing width,bearing diameter and journal diameter were analyzed. The effect on dynamic characteristics of the hydrodynamic journal bearing system was quantitatively analyzed,and the nonlinear dynamic analysis, modeling and calculation methods were studied while considering the manufacturing tolerances. The results show that in contrast to the impacts of the tolerances in journal diameter,dynamic viscosity and bearing width,the bearing diameter tolerance would lead to the rise in the power loss, and the dimensional tolerances have different degrees of impacts on the journal bearing system. The friction power loss decreased as the eccentricity ratio increased, and when the eccentricity ratio was 0. 695 the power loss came to the minimum.The investigation would find the best solution and reduce energy consumption,then control varieties of nonlinear dynamical behavior effectively,and provide a theoretical basis for hydrodynamic journal bearing system in parameter design.展开更多
By monitoring the line voltage and current of the driving motor during linear friction welding （ LFW） of GH4169 superalloy, the frictional power of the rubbing interface between two components to be joined was detec...By monitoring the line voltage and current of the driving motor during linear friction welding （ LFW） of GH4169 superalloy, the frictional power of the rubbing interface between two components to be joined was detected. The data was recorded by a data acquisition card and processed by the LabVIEW software. By analyzing the evolution of frictional power, the joint formation mechanism was discussed. The curves of the measured basic variables （frictional power, axial shortening, interfacial temperature and axial pressure） reflected the characteristics of the LFW process and offered an effective way for welding parameter optimization.展开更多
We consider small vortices, such as tornadoes, dust devils, whirlpools, and small hurricanes at low latitudes, for which the Coriolis force can be neglected. Such vortices are (at least approximately) cylindrically sy...We consider small vortices, such as tornadoes, dust devils, whirlpools, and small hurricanes at low latitudes, for which the Coriolis force can be neglected. Such vortices are (at least approximately) cylindrically symmetrical about a vertical axis through the center of a calm central region or eye of radius . In the region fluid (gas or liquid) circulates about the eye with speed . We take to be the outer periphery of the vortex, where the fluid speed is reduced to that of the surrounding wind field (in the cases of tornadoes, dust devils, and small hurricanes at low latitudes) or deemed negligible (in the case of whirlpools). If , angular momentum is conserved within the fluid itself;if , angular momentum must be exchanged with Earth to ensure conservation of total angular momentum. We derive the steepness and upper limit of the pressure gradients in vortices. We then discuss the power and energy of vortices. We compare the kinetic energy of atmospheric vortices and the power required to maintain them against frictional dissipation with the same quantities for Earth’s atmosphere as a whole. We explain why the kinetic energy of atmospheric vortices must be replaced on much shorter timescales than is the case for Earth’s atmosphere as a whole. Brief comparisons of cyclostrophic flow with geostrophic and friction-balanced flows are then provided. We then consider an analogy that might be drawn, at least to some extent, with gravitational systems, considering mainly spherically-symmetrical and cylindrically-symmetrical ones. Generation of kinetic energy at the expense of potential energy in fluid vortices, in geostrophic and friction-balanced flows, and in gravitational systems is then briefly discussed. We explain the variations of pressure and gravitational gradients corresponding to generation of kinetic energy exceeding, equaling, and falling short of frictional dissipation. In the Appendix, we describe a simple method for maximizing power extraction from environmental fluid (air or water) flows. In summary, we provide an overview of features and energetics of Earth’s environmental fluid flows and of gravitational analogies thereto that, even though mostly semiquantitative, hopefully may be helpful.展开更多
By using a generalized Langevin equation to describe the vertieal oscillations of a general relativistic disk subjected to a memory-damped friction and a stochastic force, we derive the power spectrum density （PSD） ...By using a generalized Langevin equation to describe the vertieal oscillations of a general relativistic disk subjected to a memory-damped friction and a stochastic force, we derive the power spectrum density （PSD） of accretion disk oscillating luminosity by the method of Laplace transform, and discuss the influence of the system parameters on the resonant behavior in PSD curves. The results show that as the damping strength a and memory time τ of the friction increase, the variation of PSD with spectrum frequency f from monotonous decreasing to occurring maximums, and the phenomenon of a general stochastic resonance （SR） with a single peak and multi-peaks can be found in PSD curves. The radial distance parameter n, the mass M, and spin parameter a, of the black hole determine the inherent frequency of vertical oscillations in the disk, and they have significant influences on the SR phenomena in a system of black hole binaries.展开更多
基金National Natural Science Foundations of China(No.11272100,No.50865001)
文摘According to the dimensional tolerances on hydrodynamic journal bearing system, a nonlinear oil film force model was established,and the Reynolds' equation was solved by adopting finite difference method. In order to fulfill different dimensional tolerances in the system,adopting 2kfactor design and using the eccentricity ratio corresponding to the stability critical curve,the effects of the friction power loss brought by the dimensional tolerances of the dynamic viscosity,bearing width,bearing diameter and journal diameter were analyzed. The effect on dynamic characteristics of the hydrodynamic journal bearing system was quantitatively analyzed,and the nonlinear dynamic analysis, modeling and calculation methods were studied while considering the manufacturing tolerances. The results show that in contrast to the impacts of the tolerances in journal diameter,dynamic viscosity and bearing width,the bearing diameter tolerance would lead to the rise in the power loss, and the dimensional tolerances have different degrees of impacts on the journal bearing system. The friction power loss decreased as the eccentricity ratio increased, and when the eccentricity ratio was 0. 695 the power loss came to the minimum.The investigation would find the best solution and reduce energy consumption,then control varieties of nonlinear dynamical behavior effectively,and provide a theoretical basis for hydrodynamic journal bearing system in parameter design.
基金The work is supported by the National Natural Science Foundation of China （51005180） , the Fok Ying-Tong Education Foundation for Young Teachers in the Higher Education Institutions of China （131052） and Fundamental Research Fund of Northwestern Polytechnical University （JC201233）.
文摘By monitoring the line voltage and current of the driving motor during linear friction welding （ LFW） of GH4169 superalloy, the frictional power of the rubbing interface between two components to be joined was detected. The data was recorded by a data acquisition card and processed by the LabVIEW software. By analyzing the evolution of frictional power, the joint formation mechanism was discussed. The curves of the measured basic variables （frictional power, axial shortening, interfacial temperature and axial pressure） reflected the characteristics of the LFW process and offered an effective way for welding parameter optimization.
文摘We consider small vortices, such as tornadoes, dust devils, whirlpools, and small hurricanes at low latitudes, for which the Coriolis force can be neglected. Such vortices are (at least approximately) cylindrically symmetrical about a vertical axis through the center of a calm central region or eye of radius . In the region fluid (gas or liquid) circulates about the eye with speed . We take to be the outer periphery of the vortex, where the fluid speed is reduced to that of the surrounding wind field (in the cases of tornadoes, dust devils, and small hurricanes at low latitudes) or deemed negligible (in the case of whirlpools). If , angular momentum is conserved within the fluid itself;if , angular momentum must be exchanged with Earth to ensure conservation of total angular momentum. We derive the steepness and upper limit of the pressure gradients in vortices. We then discuss the power and energy of vortices. We compare the kinetic energy of atmospheric vortices and the power required to maintain them against frictional dissipation with the same quantities for Earth’s atmosphere as a whole. We explain why the kinetic energy of atmospheric vortices must be replaced on much shorter timescales than is the case for Earth’s atmosphere as a whole. Brief comparisons of cyclostrophic flow with geostrophic and friction-balanced flows are then provided. We then consider an analogy that might be drawn, at least to some extent, with gravitational systems, considering mainly spherically-symmetrical and cylindrically-symmetrical ones. Generation of kinetic energy at the expense of potential energy in fluid vortices, in geostrophic and friction-balanced flows, and in gravitational systems is then briefly discussed. We explain the variations of pressure and gravitational gradients corresponding to generation of kinetic energy exceeding, equaling, and falling short of frictional dissipation. In the Appendix, we describe a simple method for maximizing power extraction from environmental fluid (air or water) flows. In summary, we provide an overview of features and energetics of Earth’s environmental fluid flows and of gravitational analogies thereto that, even though mostly semiquantitative, hopefully may be helpful.
基金supported by the National Natural Science Foundation of China(Grant No.11045004)the Key Program of the Scientific Research Foundation of the Education Bureau of Hubei Province,China(Grant No.D20132603)
文摘By using a generalized Langevin equation to describe the vertieal oscillations of a general relativistic disk subjected to a memory-damped friction and a stochastic force, we derive the power spectrum density （PSD） of accretion disk oscillating luminosity by the method of Laplace transform, and discuss the influence of the system parameters on the resonant behavior in PSD curves. The results show that as the damping strength a and memory time τ of the friction increase, the variation of PSD with spectrum frequency f from monotonous decreasing to occurring maximums, and the phenomenon of a general stochastic resonance （SR） with a single peak and multi-peaks can be found in PSD curves. The radial distance parameter n, the mass M, and spin parameter a, of the black hole determine the inherent frequency of vertical oscillations in the disk, and they have significant influences on the SR phenomena in a system of black hole binaries.
