The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations ...The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations need coefficients and parameters that, usually, must be experimentally estimated. This work uses a resistive electric SG （strain gage） to dynamically determine strains produced in the shaft due to harmonic oscillatory motion under multiaxial loading. This movement is simulated on a prototype specially developed for this purpose. It comprises a pulley attached to the end of a stepped cantilevered shaft, which is clamped at the opposite end. In this configuration, a cam generates a torque to the system, springs regulate the stiffness and the damping coefficient of the assembly, as well as they can be suitably adjusted to produce an underdamped condition. The main advantage, highlighted in this study, refers to a major simplification. Although the system under study shows multiple degrees of freedom （torsion and bending）, the shape and the positioning of linking SGs with the resistor bridge （Wheatstone Bridge）, allow ＂to evaluate the loading effects independently, as if only one degree of freedom of the system exists at a time domain. Strains graphs for two forms of cyclic torsional oscillation, analytical and experimental, were successfully generated.展开更多
It is of great importance to improve the energy performance of the air-conditioning system for building energy conversation. Entransy provides a novel perspective to investigate the losses existing in the air-conditio...It is of great importance to improve the energy performance of the air-conditioning system for building energy conversation. Entransy provides a novel perspective to investigate the losses existing in the air-conditioning system. The progress of entransy analysis in the air-conditioning system is comprehensively investigated in the present study. Firstly missions and characteris- tics of the air-conditioning system are analyzed with emphasis on heat or mass transfer process. It is found that reducing the temperature difference, i.e. reducing the entransy dissipation helps to improve the performance. Entransy dissipations and thermal resistances of typical transfer processes in the air-conditioning system are presented. Characteristics of sensible heat transfer process and coupled heat and mass transfer processes are researched in terms of entransy dissipation analysis. Reasons leading to entransy dissipation are also clarified with the help of unmatched coefficient 4. Principles for reducing the entransy dissipation and constructing a high temperature cooling system are summarized on the basis of case studies in typical handling processes. It＇s recommended that reducing mixing process, improving match properties are main approaches to reduce the entransy dissipation. The present analysis is beneficial to casting light on the essence of the air-conditioning system and proposing novel approaches for performance optimization.展开更多
文摘The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations need coefficients and parameters that, usually, must be experimentally estimated. This work uses a resistive electric SG （strain gage） to dynamically determine strains produced in the shaft due to harmonic oscillatory motion under multiaxial loading. This movement is simulated on a prototype specially developed for this purpose. It comprises a pulley attached to the end of a stepped cantilevered shaft, which is clamped at the opposite end. In this configuration, a cam generates a torque to the system, springs regulate the stiffness and the damping coefficient of the assembly, as well as they can be suitably adjusted to produce an underdamped condition. The main advantage, highlighted in this study, refers to a major simplification. Although the system under study shows multiple degrees of freedom （torsion and bending）, the shape and the positioning of linking SGs with the resistor bridge （Wheatstone Bridge）, allow ＂to evaluate the loading effects independently, as if only one degree of freedom of the system exists at a time domain. Strains graphs for two forms of cyclic torsional oscillation, analytical and experimental, were successfully generated.
基金supported by National Natural Science Foundation of China(Grant Nos.51422808&51521005)the National Science&Technology Pillar Program during the 12th Five-year Plan Period(Grant No.2014BAJ02B01)the China Postdoctoral Science Foundation(Grant No.2015M570107)
文摘It is of great importance to improve the energy performance of the air-conditioning system for building energy conversation. Entransy provides a novel perspective to investigate the losses existing in the air-conditioning system. The progress of entransy analysis in the air-conditioning system is comprehensively investigated in the present study. Firstly missions and characteris- tics of the air-conditioning system are analyzed with emphasis on heat or mass transfer process. It is found that reducing the temperature difference, i.e. reducing the entransy dissipation helps to improve the performance. Entransy dissipations and thermal resistances of typical transfer processes in the air-conditioning system are presented. Characteristics of sensible heat transfer process and coupled heat and mass transfer processes are researched in terms of entransy dissipation analysis. Reasons leading to entransy dissipation are also clarified with the help of unmatched coefficient 4. Principles for reducing the entransy dissipation and constructing a high temperature cooling system are summarized on the basis of case studies in typical handling processes. It＇s recommended that reducing mixing process, improving match properties are main approaches to reduce the entransy dissipation. The present analysis is beneficial to casting light on the essence of the air-conditioning system and proposing novel approaches for performance optimization.
