The dynamic characteristics of a high speed angular-contact ceramic ball bearing are studied and compared with that of the steel ball bearing. According to rolling bearing analysis theory, the bearing dynamic equation...The dynamic characteristics of a high speed angular-contact ceramic ball bearing are studied and compared with that of the steel ball bearing. According to rolling bearing analysis theory, the bearing dynamic equations are established and are solved based on Hook-Jeeves's optimization theory on the computer. The results show that the bearing dynamic characteristics mainly depend on the rotational speed and ball material property at high speed. The bearing stiffness, initially decreases obviously and then increases with the increase of rotational speed. The ceramic ball bearing gains significant advantages over the steel ball bearing in high speed applications, such as lower contact stress, smaller deformation, less altering amount of contact angle, decreasing extent of variation of axial and radial stiffness and higher performance stability.展开更多
A novel general purpose sense amplifier based flip flop is proposed.Compared to other flip flops,the proposed flip flop has faster operating speed under the approximately same power consumption,and needs fewer tr...A novel general purpose sense amplifier based flip flop is proposed.Compared to other flip flops,the proposed flip flop has faster operating speed under the approximately same power consumption,and needs fewer transistors and consumes smaller area.Moreover,it eliminates the glitch problem.By using pseudo PMOS dynamic technique,its performance is further improved.展开更多
The surface properties of PAN-based carbon fibers electrochemically treated in aqueous ammonium bicarbonate before and after treatment were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microsc...The surface properties of PAN-based carbon fibers electrochemically treated in aqueous ammonium bicarbonate before and after treatment were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Dynamic Contact Angle Analysis (DCAA). The results of characterization indicated that the oxygen and nitrogen contents in carbon fiber surface were significantly increased by electrochemical treatment, and amide groups was introduced onto it, which was related with the electrolyte. The AFM photographs illustrated that the roughness of the fiber surface was also increased. The wettibality of the fibers was improved after treatment because the surface energy especially the polar part of it was increased.展开更多
The contact angle is one of important parameters to simulate droplet spreading and impingement phenomena on the surface. In the most numerical research, it is assumed constant value and it is implemented as boundary c...The contact angle is one of important parameters to simulate droplet spreading and impingement phenomena on the surface. In the most numerical research, it is assumed constant value and it is implemented as boundary condition. However, contact angle is changed according to contact line velocity and time. Hence, for accurate simulation, dynamic contact angle which has various values as time elapsed is adopted. In the present study, the numerical analysis is performed on the droplet spreading phenomena considering dynamic contact angle function which is obtained from single droplet spreading experiment on the flat and bare surface. The CIP （cubic interpolated pseudo-particle） method by Yabe is used for analysis of interface between liquid and gas phases. The numerical results considering contact angle function which newly modeled as time and contact angle are compared with numerical results considering Hoffman＇s function and experimental data for range of Weber number which are 4.427 and 11.334. In contrast of numerical result considering Hoffman＇s function, the numerical result shows good agreement with experimental data as time elapsed in contact angle evolution, deformation of droplet spreading radius and height. Indeed, overall, the results display the increasing maximum spreading radius and the decreasing height as Weber numbers increased.展开更多
Wheel/rail rolling contact is a highly nonlinear issue affected by the complicated operating environment(including adhesion conditions and motion attitude of train and track system),which is a fundamental topic for fu...Wheel/rail rolling contact is a highly nonlinear issue affected by the complicated operating environment(including adhesion conditions and motion attitude of train and track system),which is a fundamental topic for further insight into wheel/rail tread wear and rolling contact fatigue(RCF).The rail gauge corner lubrication(RGCL)devices have been installed on the metro outer rail to mitigate its wear on the curved tracks.This paper presents an investigation into the influence ofRGCL on wheel/rail nonHertzian contact and rail surface RCF on the curves through numerical analysis.To this end,a metro vehicle-slab track interaction dynamics model is extended,in which an accurate wheel/rail non-Hertzian contact algorithm is implemented.The influence of RGCL on wheel/rail creep,contact stress and adhesion-slip distributions and fatigue damage of rail surface are evaluated.The simulation results show that RGCL can markedly affect wheel/rail contact on the tight curves.It is further suggested that RGCL can reduce rail surface RCF on tight curves through the wheel/rail low-friction interactions.展开更多
A comprehensive method to predict wear in planar mechanical systems with clearance joints is presented and discussed in this paper.This method consists of a system dynamic analysis and a joint wear prediction.As the s...A comprehensive method to predict wear in planar mechanical systems with clearance joints is presented and discussed in this paper.This method consists of a system dynamic analysis and a joint wear prediction.As the size and shape of the clearance are dictated by wear and evolve with the dynamic response of the system,the contact between the journal and bearing could be conformal or non-conformal,which makes the contact conditions in clearance joints quite complicated.Therefore a modified contact force model is employed to evaluate the joint reaction force in this study.As the nonlinear stiffness coefficient is related to the physical and geometrical properties of contact bodies and varies with the deformation,this contact force model is applicable to different contact conditions between the journal and bearing.Furthermore,based on the Archard’s wear model,the amount of wear can be quantified in the joint.And the geometry is updated to reflect the evolving contact boundary.Then,the wear process and the contact force model are integrated into the motion equations of the system to perform coupled iterative analyses between system dynamic response and joint wear prediction.In addition,a slider-crank mechanism is simulated as an example to demonstrate efficiency of the proposed method and to carry out a parametric study on mechanical systems considering joint wear.The influence of clearance size and driving power are discussed and compared respectively.The index of concordance is introduced to quantify contributions of contact pressure and sliding distance to wear rate under different types of journal motion.This study could help to predict joint wear in mechanical systems with clearances and optimize mechanisms in design.展开更多
基金TheNaturalScienceFoundationofJiangsuProvince (No .BK2 0 0 2 0 5 9) theKeyTechnologiesR&DProgramofJiangsuProvinceDuringthe 10thFive YearPlanPeriod (No .BE2 0 0 3 0 71) .
文摘The dynamic characteristics of a high speed angular-contact ceramic ball bearing are studied and compared with that of the steel ball bearing. According to rolling bearing analysis theory, the bearing dynamic equations are established and are solved based on Hook-Jeeves's optimization theory on the computer. The results show that the bearing dynamic characteristics mainly depend on the rotational speed and ball material property at high speed. The bearing stiffness, initially decreases obviously and then increases with the increase of rotational speed. The ceramic ball bearing gains significant advantages over the steel ball bearing in high speed applications, such as lower contact stress, smaller deformation, less altering amount of contact angle, decreasing extent of variation of axial and radial stiffness and higher performance stability.
文摘A novel general purpose sense amplifier based flip flop is proposed.Compared to other flip flops,the proposed flip flop has faster operating speed under the approximately same power consumption,and needs fewer transistors and consumes smaller area.Moreover,it eliminates the glitch problem.By using pseudo PMOS dynamic technique,its performance is further improved.
基金Sponsored by the Scientific Research Foundation of Harbin Institute of Technology(Grant No. HIT. 2003.57)
文摘The surface properties of PAN-based carbon fibers electrochemically treated in aqueous ammonium bicarbonate before and after treatment were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Dynamic Contact Angle Analysis (DCAA). The results of characterization indicated that the oxygen and nitrogen contents in carbon fiber surface were significantly increased by electrochemical treatment, and amide groups was introduced onto it, which was related with the electrolyte. The AFM photographs illustrated that the roughness of the fiber surface was also increased. The wettibality of the fibers was improved after treatment because the surface energy especially the polar part of it was increased.
文摘The contact angle is one of important parameters to simulate droplet spreading and impingement phenomena on the surface. In the most numerical research, it is assumed constant value and it is implemented as boundary condition. However, contact angle is changed according to contact line velocity and time. Hence, for accurate simulation, dynamic contact angle which has various values as time elapsed is adopted. In the present study, the numerical analysis is performed on the droplet spreading phenomena considering dynamic contact angle function which is obtained from single droplet spreading experiment on the flat and bare surface. The CIP （cubic interpolated pseudo-particle） method by Yabe is used for analysis of interface between liquid and gas phases. The numerical results considering contact angle function which newly modeled as time and contact angle are compared with numerical results considering Hoffman＇s function and experimental data for range of Weber number which are 4.427 and 11.334. In contrast of numerical result considering Hoffman＇s function, the numerical result shows good agreement with experimental data as time elapsed in contact angle evolution, deformation of droplet spreading radius and height. Indeed, overall, the results display the increasing maximum spreading radius and the decreasing height as Weber numbers increased.
基金supported by the National Key Research and Development Program of China(Grant No.2020YFA0710902)the National Natural Science Foundation of China(Grant Nos.51735012,52072317,and UJ9A20110)the State Key Laboratory of Traction Power(Grant No.202JTPL-T08).
文摘Wheel/rail rolling contact is a highly nonlinear issue affected by the complicated operating environment(including adhesion conditions and motion attitude of train and track system),which is a fundamental topic for further insight into wheel/rail tread wear and rolling contact fatigue(RCF).The rail gauge corner lubrication(RGCL)devices have been installed on the metro outer rail to mitigate its wear on the curved tracks.This paper presents an investigation into the influence ofRGCL on wheel/rail nonHertzian contact and rail surface RCF on the curves through numerical analysis.To this end,a metro vehicle-slab track interaction dynamics model is extended,in which an accurate wheel/rail non-Hertzian contact algorithm is implemented.The influence of RGCL on wheel/rail creep,contact stress and adhesion-slip distributions and fatigue damage of rail surface are evaluated.The simulation results show that RGCL can markedly affect wheel/rail contact on the tight curves.It is further suggested that RGCL can reduce rail surface RCF on tight curves through the wheel/rail low-friction interactions.
基金supported by the National Natural Science Foundation of China(Grant No.11272171)Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20120002110070)
文摘A comprehensive method to predict wear in planar mechanical systems with clearance joints is presented and discussed in this paper.This method consists of a system dynamic analysis and a joint wear prediction.As the size and shape of the clearance are dictated by wear and evolve with the dynamic response of the system,the contact between the journal and bearing could be conformal or non-conformal,which makes the contact conditions in clearance joints quite complicated.Therefore a modified contact force model is employed to evaluate the joint reaction force in this study.As the nonlinear stiffness coefficient is related to the physical and geometrical properties of contact bodies and varies with the deformation,this contact force model is applicable to different contact conditions between the journal and bearing.Furthermore,based on the Archard’s wear model,the amount of wear can be quantified in the joint.And the geometry is updated to reflect the evolving contact boundary.Then,the wear process and the contact force model are integrated into the motion equations of the system to perform coupled iterative analyses between system dynamic response and joint wear prediction.In addition,a slider-crank mechanism is simulated as an example to demonstrate efficiency of the proposed method and to carry out a parametric study on mechanical systems considering joint wear.The influence of clearance size and driving power are discussed and compared respectively.The index of concordance is introduced to quantify contributions of contact pressure and sliding distance to wear rate under different types of journal motion.This study could help to predict joint wear in mechanical systems with clearances and optimize mechanisms in design.
