Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection cu...Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection curved-compliant annulus-shaped flexure pivot composed of six curved beam flexure elements. It can offer more than lO^angular stroke theoretically. Firstly, main-motion pseudo-rigid-body method is introduced to establish the flexure pivot model. Although pseudo-rigid-body method can be used to analyze the large-deformation flexure pivot performance, the method is definitely a laborious and difficult task for designing this novel flexure pivot. In order to simply the designing process, dimension-design graphs based on the parametric models and finite element analysis is presented. Using the dimension-design method as a tool, the designers can determine the optimal geometry rapidly, based on the stiffness and rotation demands of an annulus-shaped flexure pivot. Finally, dimension-design graph examples are given whose primary design aims to achieve a rotation stroke of annulus-shaped flexure pivot. The finite element analysis results show that the relative designing error between anticipative rotation stroke and graph design result is less than 4%. The dimensionless method used in designing annulus-shaped flexure pivot can reduce design process in both time and complexity. The novel annulus-shaped flexure pivot and dimension-design method are helpful supplement to configuration and design method of large-deflection flexure pivot.展开更多
Common fluid film bearing issues(mainly high bearing temperature)preventing reliable operation of turbomachinery will be addressed.Atheoretical review of radial and thrust bearing performance will be included for a ba...Common fluid film bearing issues(mainly high bearing temperature)preventing reliable operation of turbomachinery will be addressed.Atheoretical review of radial and thrust bearing performance will be included for a basic understanding on how to handle the bearing issues.Some theoretical plots will be presented to demonstrate the effect of key bearing design parameters on bearing performance.Advanced bearing materials beyond babbitt will also be introduced as bearing upgrade options to overcome bearing issues.Case studies on radial and thrust bearing upgrades to mitigate or eliminate the bearing issues will be shared.Some of the common vibration problems preventing reliable operation of turbomachinery will also be described with suggestions on how to eliminate or mitigate the problems via changes to bearing design features or new bearing technology.A couple of case studies representing each vibration problem will be presented.展开更多
At the time of re-entry modules entering into the atmosphere from space,a small perturbation introduces dynamic oscillations on the vehicle because of their extreme traveling speed.The dynamic stability characteristic...At the time of re-entry modules entering into the atmosphere from space,a small perturbation introduces dynamic oscillations on the vehicle because of their extreme traveling speed.The dynamic stability characteristics of re-entry modules at hypersonic Mach numbers is of considerable relevance to their initial design.In the present paper,the dynamic stability of blunt cone model about 10◦is examined with wide range of design parameters such as nose bluntness,semi-vertex angle and center of rotation through theoretical and experimental methods.Theoretical approximations are made over a model based on the standard Newtonian theory.Experiments are conducted at 0.25m hypersonic wind tunnel at M=8.3 and the following trends are observed from the experimental analysis.Interestingly,the incremental higher nose bluntness,semi-vertex angle and center of rotation reduce the dynamic stability.At higher hypersonic Mach numbers(M>10),dynamic stability characteristics of the re-entry module are insensitive to the free stream Mach number.However,it is observed that the dynamic stability is increased in proportion to the vibration amplitude at hypersonic speeds.展开更多
基金supported by National Natural Science Foundation of China(Grant No. 50675007)Program for New Century Excellent Talents in University of China (Grant No. NCET-06-0165)
文摘Large-deflection flexure pivot is widely used in high precision rotation application, but there are less flexure configurations and simple and convenient design methods, This paper presents a novel large-deflection curved-compliant annulus-shaped flexure pivot composed of six curved beam flexure elements. It can offer more than lO^angular stroke theoretically. Firstly, main-motion pseudo-rigid-body method is introduced to establish the flexure pivot model. Although pseudo-rigid-body method can be used to analyze the large-deformation flexure pivot performance, the method is definitely a laborious and difficult task for designing this novel flexure pivot. In order to simply the designing process, dimension-design graphs based on the parametric models and finite element analysis is presented. Using the dimension-design method as a tool, the designers can determine the optimal geometry rapidly, based on the stiffness and rotation demands of an annulus-shaped flexure pivot. Finally, dimension-design graph examples are given whose primary design aims to achieve a rotation stroke of annulus-shaped flexure pivot. The finite element analysis results show that the relative designing error between anticipative rotation stroke and graph design result is less than 4%. The dimensionless method used in designing annulus-shaped flexure pivot can reduce design process in both time and complexity. The novel annulus-shaped flexure pivot and dimension-design method are helpful supplement to configuration and design method of large-deflection flexure pivot.
文摘Common fluid film bearing issues(mainly high bearing temperature)preventing reliable operation of turbomachinery will be addressed.Atheoretical review of radial and thrust bearing performance will be included for a basic understanding on how to handle the bearing issues.Some theoretical plots will be presented to demonstrate the effect of key bearing design parameters on bearing performance.Advanced bearing materials beyond babbitt will also be introduced as bearing upgrade options to overcome bearing issues.Case studies on radial and thrust bearing upgrades to mitigate or eliminate the bearing issues will be shared.Some of the common vibration problems preventing reliable operation of turbomachinery will also be described with suggestions on how to eliminate or mitigate the problems via changes to bearing design features or new bearing technology.A couple of case studies representing each vibration problem will be presented.
文摘At the time of re-entry modules entering into the atmosphere from space,a small perturbation introduces dynamic oscillations on the vehicle because of their extreme traveling speed.The dynamic stability characteristics of re-entry modules at hypersonic Mach numbers is of considerable relevance to their initial design.In the present paper,the dynamic stability of blunt cone model about 10◦is examined with wide range of design parameters such as nose bluntness,semi-vertex angle and center of rotation through theoretical and experimental methods.Theoretical approximations are made over a model based on the standard Newtonian theory.Experiments are conducted at 0.25m hypersonic wind tunnel at M=8.3 and the following trends are observed from the experimental analysis.Interestingly,the incremental higher nose bluntness,semi-vertex angle and center of rotation reduce the dynamic stability.At higher hypersonic Mach numbers(M>10),dynamic stability characteristics of the re-entry module are insensitive to the free stream Mach number.However,it is observed that the dynamic stability is increased in proportion to the vibration amplitude at hypersonic speeds.
