滚动轴承最佳工作游隙的确定及分析

滚动轴承的工作游隙与载荷分布系数之间存在关联,当载荷分布系数为0.7~0.8时,轴承能够获得较长的疲劳寿命,因此使轴承载荷分布系数在最佳范围时的工作游隙为最佳状态。分析了影响工作游隙的重要因素(配合、温度、材料等),基于上述分析,根据6σ准则建立了计算轴承工作游隙的理论计算模型。最后,结合实例介绍了轴承工作游隙的计算方法。     

MSF海水淡化装置喷射器性能分析

结合蒸汽动力函数和热力学分析方法,建立蒸汽喷射器的数学模型,分析最佳引射系数的影响因素,引射系数随混合蒸汽出口压力的关系及引射压力随工作蒸汽压力和混合蒸汽出口压力的关系。分析指出,工作条件一定时,最佳引射系数是固定值;在达到极限值前,引射系数随混合蒸汽出口压力的增大而降低,达到极限值时,引射系数不随出口蒸汽压力的变化而变化;引射压力在设计范围内随工作蒸汽压力的升高而降低,随混合蒸汽出口压力的升高而升高。     

用相似理论分析涡轮流量计与旋涡流量计的流量系数

一、前言蜗轮流量计与旋蜗流量计的流量系数随被测介质的物理性质而变化,因而出厂前用水在标准设备上对流量系数标定后,使用单位不得不根据被测介质的物理性质重新标定。这项工作需要标准设备,技术性强,工作繁重,许多用户宁愿降低仪表的使用精度,也不标定流量系数。为了免于重新标定又不降低使用精度,本文用相似论推导出其流量系数表达式,结论是:流量系数仅是雷诺数的函数。使用这一结论建立出流量系数与雷诺数的关系图(表),可供用户选取准确的流量系数,而不必重新标定,从而保证了仪器原有的测量精度。二、涡轮流量计流量系数分析     

机床主传动系统齿轮变动工作用量系数的简化算法

本文首次提出了变动工作用量系数的概念,分析并推导了其简化计算公式,以此公式为依据,经上机计算与相应的数据处理后,给出了相应系数的取值表。利用变动工作用量系数对额定载荷进行修正,即可得出变载荷的当量载荷,从而可以采用国标进行机床齿轮强度计算。     

基于工作环境的电动汽车输出扭矩控制方案

本文主要针对汽车在不同的天气和路况中,汽车风阻系数、轮胎滚动阻尼系数不同问题,提出了一种基于汽车工作环境改变的电动汽车输出扭矩控制方案。该方案主要根据汽车的工作环境,将其定义为几种常见的工作模式。各模式主要对在不同环境中对应的阻尼系数进行研究,并将对应的模式下的阻尼系数反馈给电动汽车动力传递系统。并以冰雪环境为例,与无扭矩控制电动汽车进行比较,证明该方案具有一定的进步意义。     

一种电梯平衡系数测量装置的研制

在当前测量电梯平衡系数的实际工作中,存在劳动强度大、测量方法复杂、工作效率低的缺点.文中介绍了一种新型电梯平衡系数测量装置的原理、设计和测量方法,具有便于携带、安装方便、操作简单、劳动强度低、工作效率高、测量结果准确的优点,适用于绝大多数电梯的平衡系数的测量.     

4个1R2T绳牵引并联机构的工作空间质量之比较

引入比例系数、质量系数和全局质量系数来衡量工作空间的大小和形状，针对4个1R2T机构，比较了动平台处于相同2个姿态时工作空间的大小和形状。结果表明：绳与滑轮(或动平台)的连接点重合时，通常会增大转动工作空间；以转动工作空间的大小为准．发现了1R2T的完全约束定位机构中最好的构型；m=2n的冗余约束定位机构对大的转角提供一个大的平动工作空间。     

静液传动系统数学模型和系数计算方法

引言常见的静液传动系统数学模型都是基于Wilson理论的系数模型。所以这些模型的精度主要取决于模型系数与实际物理现象的一致性与系数计算方法的精确性。实验表明这些模型系数如Cs、Cd和Cf等均随工作条件有较大变化,因而采用常系数或线性系数的模型必然精度较低。为了改善精度就必须引入一些物理意义含混的附加项。MaCandlish等     

液力偶合器充液量对其特性的影响分析

液力偶合器以工作液体为介质传递动力,工作腔充液量的多少直接影响偶合器泵轮力矩系数和过载系数等特性,通过对充液量与偶合器特性的研究,旨在为偶合器的稳定运行提供可靠地保证。     

绕管式换热器壳侧液体降膜流传热特性分析北大核心CSCD

为研究绕管式换热器壳侧传热特性,建立了以丙烷为模拟工质的三维液体降膜流传热模型,进行了不同流动工况下液体降膜流的传热数值模拟,分析了雷诺数、液相入口温度、换热管壁温、壳侧工作压力对绕管式换热器传热性能的影响。结果表明,流动工况对绕管式换热器的传热性能有显著影响;对于液体降膜流,传热膜系数随着雷诺数增大而增大,同时相同雷诺数时,随着换热管管层下降传热膜系数逐减减小;当液相入口温度升高时,传热膜系数增大,液相入口温度升高0.2 K时,平均传热膜系数升高约15%;当管壁温度与饱和温度间的温差较小时,升高管壁温度传热膜系数有明显增加,当管壁温度与饱和温度温差较大时,传热膜系数变化不显著。对于丙烷,工作压力增大时,液体降膜流的传热膜系数减小,当工作压力从0.2 MPa增大到0.3 MPa时,传热膜系数降低10%~15%,当工作压力从0.3 MPa增大到0.4 MPa时,传热膜系数降低约5%。所得结果可为绕管式换热器工艺设计提供参考。     

The influence of non-newtonian oil film short journal bearings on the stability of a rigid rotor

The stability behaviour of rotors supported in plain cylindrical cavitated non-Newtonian fluid film journal bearings is investigated. Expressions for the journal force due to the fluid film are developed for the short bearing approximate solution to the modified form of Reynolds' equation. Linearised fluid film coefficients are used for the stability analysis. The results show that the dynamic fluid film coefficients for non-Newtonian lubricants are different from Newtonian coefficients and that they have a strong influence on the stability of rotor-bearing systems.     

Frequency Effects in Tilting-Pad Journal Bearing Dynamic Coefficients

This paper examines the effects of damped vibrational frequencies on the linear reduced dynamical stiffness and damping coefficients of tilting-pad journal bearings. The frequency ratio (damped frequency/running speed) can be used to judge the accuracy of employing synchronously reduced linear coefficients in rotordynamic stability analyses. The use of these coefficients can result in simpler formulations of the system dynamical equations of motion and solution techniques as well as reduced computational and analysis time. Results presented here indicate that synchronously reduced bearing dynamical coefficients are generally adequate for stability analyses with positively preloaded tilting-pad bearings. Plots of dynamic coefficients are included for a five-pad bearing.     

脉动流诱发振动系统稳定性分析

建立了脉动流诱发振动转子密封系统的振动模型的一次近似方程,分析了系统的平衡点稳定性问题。从脉动流诱发振动的角度,建立转子密封系统的振动模型的一次近似方程为线性周期系数系统的方程。脉动流诱发振动转子密封系统的振动模型的稳定性判别,采用微分方程稳定性理论当中的线性周期系数系统的稳定性判据,讨论了系统的平衡点稳定性问题。研究表明,系统满足一定情况时能实现零解稳定性。     

Robust stability criterion for fractional-order systems with interval uncertain coefficients and a time-delay

This study investigates the robust stability of fractional-order systems with interval coefficients and a time-delay. By the Minkowski Sum, the vertices of value set with respect to the characteristic function of the investigated fractional-order system are offered, avoiding the calculations of the redundant vertices. Meanwhile, a function depending on the obtained vertices is defined to represent the position relationship between the origin and the value set. Based on the zero exclusion principle, we propose sufficient and necessary conditions to determine the robust stability of fractional-order systems with interval uncertain coefficients and a time-delay. Finally, illustrative examples are offered to verify the effectiveness of the proposed robust stability criterion.     

Stability Analysis on Rotor Systems Supported by Self-acting Tilting-pad Gas Bearings with Frequency Effects

The recent research on stability of gas bearing-rotor systems still mostly adopts the same method as in oil-lubricated bearing-rotor systems.The dynamic coefficients of gas bearings in the case that the perturbation frequencies are same as the rotating speed are used to carry out the stability analysis of rotor systems.This method does not contact the frequency characteristics of dynamic stiffness and damping coefficients of gas bearings with the dynamical behaviors of rotor systems.Furthermore,the effects ...     

Chatter stability prediction in milling using time-varying uncertainties

The chatter stability in milling severely affects productivity and quality of machining. Tool wear causes both the cutting coefficient and the process damping coefficient, but also other parameters to change with cutting time. This variation greatly reduces the accuracy of chatter prediction using conventional methods. To solve this problem, we consider the cutting coefficients of the milling system to be both random and time-varying variables and we use the gamma process to predict cutting coefficients for different cutting times. In this paper, a time-varying reliability analysis is introduced to predict chatter stability and chatter reliability in milling. The relationship between stability and reliability is investigated for given depths and spindle speeds in the milling process. We also study the time-varying chatter stability and time-varying chatter reliability methods theoretically and with experiments. The results of this study show that the proposed method can be used to predict chatter with high accuracy for different cutting times.     

螺旋槽小孔节流动静压气体轴承动态特性分析*

为进一步改善小孔节流动静压气体轴承的稳定性,对螺旋槽小孔节流动静压气体轴承的动态特性进行了研究。建立不定常工况下的动态雷诺方程,采用偏导数积分法求解动态特性系数。研究有无螺旋槽、涡动比、转速、供气压力以及槽宽和槽深对轴承动态特性的影响规律。结果表明:螺旋槽可以显著提高轴承的动态特性,增加轴承的稳定性;随涡动比的增大,直接刚度系数增加,交叉刚度系数和各阻尼系数都减小;随转速的增大,各刚度系数增加,而各阻尼系数减小;随供气压力的增大,各刚度和阻尼系数均增加;随槽宽的增大,直接刚度系数和阻尼系数呈先增加后减小趋势,交叉刚度系数和阻尼系数变化较小;随槽深的增大,直接刚度系数增加,交叉刚度系数和各阻尼系数先增加后减小。     

考虑间隙的平面四杆机构稳定性分析

应用李雅普诺夫第一方法及Floquet理论来分析具有间隙的平面四杆机构的稳定性,并讨论了阻尼对稳定性的影响。     

Dynamic characteristics and stability of a journal bearing in a non-laminar lubrication regime

A mathematical model to determine the stiffness and damping coefficients and the stability limit curves of a journal bearing in a non-laminar lubrication regime is described. The results show the flow regime influence on the dynamic characteristics of cylindrical bearings and on the stability of a rigid rotor on rigid supports.     

Stability of rotors supported in gas bearings with bushes mounted in air rings

When during the operation of rotors supported in gas bearings their rotational velocity reaches a sufficiently high value, the loss of steady-state stability occurs. This instability is caused by the loss of damping properties of the gas film, which leads to self-excited vibrations. These vibrations are the basic obstacle to a widespread application of gas bearings.The phenomenon of self-excited vibrations can be avoided by introducing an elastic supporting structure between the bearing bushes and the casing, characterised by properly selected stiffness and damping coefficients. In practice such a structure can have the form of an externally pressurised gas ring.In this paper we demonstrate, on the basis of selected examples, which ranges of the values of stiffness and damping coefficients of the gas ring make it possible to retain steady-state stability at practically any rotational velocity of the rotor. We also show a design of the ring structure, especially of its feeding system, which ensures the required values of stiffness and damping coefficients (with regard to the stability). Our investigations have been carried out by means of a numerical simulation method with the use of a mathematical model of the gas bearing, verified already many times.