对现有的几种常用的无刷直流电动机(Brushless DC Motor,BLDCM)转速测量方法进行分析,研究一种基于霍尔传感器的BLDCM转速计算方法。在电动机运行时,测量出单个霍尔传感器一个周期波形的时间,实时计算其当前的转速,为转速闭环提供实际...对现有的几种常用的无刷直流电动机(Brushless DC Motor,BLDCM)转速测量方法进行分析,研究一种基于霍尔传感器的BLDCM转速计算方法。在电动机运行时,测量出单个霍尔传感器一个周期波形的时间,实时计算其当前的转速,为转速闭环提供实际转速反馈信息,并通过电路仿真试验验证该方法的可行性。相对于传统的测速方法,该方法不仅省去外部测速传感器,节约系统成本,还可以便捷地得到电动机的实时转速。展开更多
The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine t...The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine the effectiveness of offshore wind turbines.With different rotating speeds and blade length,the rotating blades generate various centrifugal stiffening effects.To directly analyze the centrifugal stiffening effect of blades,the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade,including the centrifugal stiffening effect and the axial force calculation formula.The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates.The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed,and then the fundamental frequency correction formula was built based on the rotating speed and the blade length.The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results.The error of calculation results between them is less than 0.5%.展开更多
Computational fluid dynamics-discrete element method(CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions...Computational fluid dynamics-discrete element method(CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank.Influences of operating conditions and physical properties of particles(i.e., particle diameter and density) on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied.The wide distribution of particle angular velocity ranging from 0 to 105r·min 1is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to understand the physics of particle movement in micro- to macro-scales in the solid suspension of a stirred tank.展开更多
文摘对现有的几种常用的无刷直流电动机(Brushless DC Motor,BLDCM)转速测量方法进行分析,研究一种基于霍尔传感器的BLDCM转速计算方法。在电动机运行时,测量出单个霍尔传感器一个周期波形的时间,实时计算其当前的转速,为转速闭环提供实际转速反馈信息,并通过电路仿真试验验证该方法的可行性。相对于传统的测速方法,该方法不仅省去外部测速传感器,节约系统成本,还可以便捷地得到电动机的实时转速。
基金Supported by the National Natural Science Foundation of China under Grant No.50708015the foundation of State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology
文摘The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine the effectiveness of offshore wind turbines.With different rotating speeds and blade length,the rotating blades generate various centrifugal stiffening effects.To directly analyze the centrifugal stiffening effect of blades,the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade,including the centrifugal stiffening effect and the axial force calculation formula.The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates.The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed,and then the fundamental frequency correction formula was built based on the rotating speed and the blade length.The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results.The error of calculation results between them is less than 0.5%.
基金Supported by the State Key Development Program for Basic Research of China （2013CB733600）, the National Natural Science Foundation of China （21036003, 20776074） and the Specialized Research Fund for the Doctoral Program of Higher Education of China （20090002110069）.
文摘Computational fluid dynamics-discrete element method(CFD-DEM) coupled approach was employed to simulate the solid suspension behavior in a Rushton stirred tank with consideration of transitional and rotational motions of millions of particles with complex interactions with liquid and the rotating impeller. The simulations were satisfactorily validated with experimental data in literature in terms of measured particle velocities in the tank.Influences of operating conditions and physical properties of particles(i.e., particle diameter and density) on the two-phase flow field in the stirred tank involving particle distribution, particle velocity and vortex were studied.The wide distribution of particle angular velocity ranging from 0 to 105r·min 1is revealed. The Magnus force is comparable to the drag force during the particle movement in the tank. The strong particle rotation will generate extra shear force on the particles so that the particle morphology may be affected, especially in the bio-/polymer-product related processes. It can be concluded that the CFD-DEM coupled approach provides a theoretical way to understand the physics of particle movement in micro- to macro-scales in the solid suspension of a stirred tank.
