Cage slip characteristics of a cylindrical roller bearing with a trilobe-raceway

Based on dynamic analysis of rolling bearings, the nonlinear dynamic differential equations of a cylindrical roller bearing with a trilobe-raceway were established and solved by the GSTIFF (gear stiff) integer algorithm with a variable step. The influences of structural parameters and the tolerance of the trilobe-raceway, working conditions of the bearing, and the outer ring installation method on cage slip characteristics were investigated. The results show that: (i) The cage slip ratio and bearing rating life of a cylindrical roller bearing with a trilobe-raceway would reduce when the low-radius (radius of the outer raceway contour at the lowest point) and D-value (difference value between the high and low points of the outer raceway contour) decrease, and the former (low-radius) contributes more significantly. (ii) The cage slip ratio of a cylindrical roller bearing with a trilobe-raceway rises with the increase of the bearing speed, and decreases with the increase of the radial force; the variation range increases with the increase of the low-radius. (iii) When the installation angle of the outer ring increases in a period, the cage slip ratio remains unchanged while the bearing rating life rises up a little. Therefore, when installing a cylindrical roller bearing with a trilobe-raceway, the location of the maximum radius shall be under that of the radial force to improve the bearing rating life. (iv) With the increase of the roundness of the base circle where the radius of the lowest points of the trilobe-raceway contour locates, the cage slip ratio rises gradually and the bearing rating life decreases.     

四轮驱动汽车牵引力控制系统控制策略

针对四轮驱动汽车整车动力性和横向稳定性的问题,提出新的目标滑转率计算和修正方法的牵引力控制系统综合控制策略。首先,建立车辆系统各主要部件的数学模型;然后,针对不同工况,利用模糊PID控制技术建立以发动机节气门开度控制、轴间扭矩分配控制和驱动轮制动控制为一体的牵引力控制系统综合控制策略;在车轮目标滑转率的选取方面,提出了最优纵向滑转率查表法,并根据车速以及轮胎侧偏角的大小对目标滑转率进行实时修正;最后,在典型工况下使用MATLAB/Simulink对四轮驱动汽车牵引力控制系统进行离线仿真研究。结果表明：本文所提出的牵引力控制系统控制策略能有效地抑制驱动轮的过度滑转,充分利用路面附着条件,提高汽车纵向驱动稳定性。     

基于时间序列相似性原理的雷达信号识别

从密集复杂的信号环境中分选和识别出特定雷达辐射源信号,是信号处理领域的重要内容之一。利用威胁复杂雷达信号的先验信息,引入数据挖掘领域时间序列相似性快速匹配原理及其滑窗技术,提出了一种适于复杂体制雷达信号快速匹配识别方法。实验表明,该方法识别速度快、适应环境能力强,具有良好的应用前景。     

微通道内亲疏水壁面特性对入口段长度的影响

针对水力直径为200μm的微尺度通道,采用数值模拟的方法研究了壁面亲疏水特性产生的速度滑移对微尺度通道入口段长度的影响,建立了包含滑移长度影响的入口段长度修正计算公式.研究表明:相同流量下,速度滑移的存在使得微尺度通道充分发展段的最大速度减小,从而缩短了入口段长度,且在低雷诺数区域,入口段的缩短效应更为显著.针对不同的...     

航天器太阳电池阵驱动机构导电滑环真空充放电实验研究

太阳电池阵驱动机构部分暴露在航天器舱体外,其内部导电滑环容易成为充放电效应的侵害对象,利用90Sr-90Y β放射源模拟中高地球轨道的高能电子环境,实验研究不同辐照强度下导电滑环的充放电过程。结果显示：辐照初始阶段发生幅值较小的放电,多数为表面放电;随着电位升高,深层充电导致材料内部积累大量电子,超过一定阈值之后,发生击穿放电。导电滑环在2.4 pA/cm2通量的电子辐照下,其充电平衡电位达到-3600 V;而在0.1 pA/cm2通量下,平衡电位仅为-300 V。建议增加3 mm厚防护铝板以降低高能电子通量,预防导电滑环因充放电造成故障。在辐照实验过程中,同时监测导电滑环工作状态,未发现异常,说明在短时间辐照中发生的放电对导电滑环工作性能没有影响。     

An improved real-time cycle slip correction algorithm based on Doppler-aided signals for BDS triple-frequency measurements

Doppler, which is an instantaneous GNSS observable signal, has been proven effective in determining velocity and acceleration due to its high availability and accuracy. We propose a real-time triple-frequency cycle slip correction (CSC) method based on Doppler-aided signals because Doppler shift is time-independent and immune to cycle slips. When the sampling interval is less than 1 s, cycle slips on triple-frequency can be detected and repaired using pure Doppler data with high reliability; however, this method cannot be used when the sampling interval exceeds 1 s because the integral cumulative error of Doppler increases significantly. For such cases, a modified triple-frequency CSC approach has been developed based on the raw phase and smoothed code data that was refined using the Doppler signal. To suppress the effect of the integral Doppler error, a balance factor is introduced to adjust the contributions of the raw code and Doppler observables. After the refinement of the GNSS data, three independent combinations need be selected to detect and repair cycle slips with triple-frequency observations. Four constrained criteria have been proposed to select optimal combinations that can reduce the residual ionospheric delay (RID) and measurement noise to a low level. Finally, experiments were carried out to test the performance of the new method using real triple-frequency BDS observations (GPST: 3:15:00–5:55:00, March 23, 2018). The results show that pure Doppler can detect and repair cycle slips effectively with small intervals, and modified Hatch-Melbourne-Wübbena (HMW) method based on Doppler-aided signals can achieve 99.7% success rate in cycle slip correction with large intervals (up to 30 s).     

单轴拉伸和压缩镁合金各滑移系的Schmid因子计算

针对单轴拉伸和压缩条件下的镁合金,计算了不同滑移系（基面滑移、柱面滑移、锥面滑移、锥面滑移）在整个取向空间中的Schmid因子分布.计算结果表明,基面滑移、柱面滑移和锥面滑移系的Schmid因子在取向空间中都有0.5的极大值;而锥面滑移系的Schmid因子普遍较低,当θ在80°左右,ψ在70°左右时的最大值仅为0.383.计算结果为镁合金变形机制的分析提供基础.     

Thin structure of temporal profiles of solar flares January 15, 17 and 20, 2005 by data of AVS-F apparatus onboard CORONAS-F satellite

The count rate temporal profiles and energy spectra of the solar flares January 15, 17, 20 2005 in hard X-ray and gamma energy bands by data of AVS-F apparatus onboard CORONAS-F satellite are discussed. The energy spectra of these solar flares contain positron line and neutron capture line. Solar flares of January 17 and 20 spectra also contain some nuclear lines. Thin structure with characteristic timescales of 33–92 s is presented on flares temporal profiles in energy bands corresponding to the observed spectral features, which are confirmed by periodogram analysis (confidence level is 99%).     

机场着陆排序的一种滑动窗优化算法

对交通拥挤时的终端区进场飞机进行合理的排序,是空中交通流量管理的一个重要研究内容。当降落飞机架次较多时,目前的各种算法因计算量太大而实时性不好。基于飞机进场时位置的调整受一定限制,通过分析窗体的大小与位置限制和步长的关系,对计算量的影响提出了滑动窗的方法,并给出了通过采用滑动窗方法可以减少运算量的理论证明。最后通过仿真对该方法进行了验证。     

镜面蒙皮拉形工艺参数研究

滑移带是导致飞机镜面蒙皮报废的主要原因之一。通过分析镜面蒙皮拉形中变形程度、拉形速度、毛料几何尺寸、润滑与操作方式对滑移带的影响,确定了临界变形程度和拉形应变速率的合理范围。毛料几何尺寸的影响,反映在悬空段板料的宽长比值上,宽长比值增加,变形趋向于平面应变状态,易出现滑移带。良好的润滑方式有利于改善板料变形的均匀性,增加成形面内材料的变形程度。操作方式的选择,应充分考虑模具拉胀的作用,严格控制夹钳预拉量和补拉量,避免冲击和阶跃式的加载方式。