二维驱动机构的机电一体化谐振问题探讨

谐振是机电一体化的普通现象,致其产生的因素有很多,其中最为常见的是电机与负载之间的力矩传递。谐振的发生不仅会损害本体,还会对安装平台造成不良影响,甚至恶化平台上其他仪器的性能。以二维驱动机构的机电一体化谐振问题为例,通过高频(100kHz)采样伺服电机相电流及角度传感器的信号,分析了电机三相电流和角度传感器的频谱成份,提出采用双反馈控制和notch数字滤波器改变系统的频谱特性,从而消除机械谐振,提高伺服跟踪精度,使之满足工程型号的要求。此方法对解决机电一体化的谐振问题具有重要意义。     

钛合金钣金件脉冲电流辅助热压成形精度控制

针对钛合金钣金件冷加工成形精度低、热成形机成形成本高的问题,提出一种采用脉冲电流辅助热压成形工艺。以TC1钛合金U型件为对象,研究了脉冲电流辅助热压成形工艺对钛合金钣金件的缺陷、尺寸精度及力学性能的影响。结果表明,脉冲电流加热可提高成形效率,当脉冲电流密度为9.2A/mm^2,合模速度为15mm/s时,补偿了成形过程的热量损失,使钛合金钣金件保持在良好的成形温度区间,增加其成形极限,得到零件表面质量良好、无裂纹。在成形过程中,随着成形压力、保压时间、模具预热温度的升高,零件的尺寸精度逐渐提高,当成形压力10t、保压时间10s、模具不预热时,零件的尺寸精度即可达到±0.2mm。脉冲电流辅助热压成形后零件的晶粒尺寸比热成形机成形的细小,且力学性能也较好。     

航空发动机起动过程摩擦阻力矩计算分析

扭矩特性分析是航空发动机起动仿真数学模型建立的重要环节,其中摩擦阻力矩因缺少相应的经验公式难以确定。为了得到起动过程的摩擦阻力矩,借助于某型发动机台架试车数据,根据转速变化率与扭矩的关系,在冷态和热态2种条件下分别对转速变化率和阻力矩进行计算,得到了冷、热态下发动机起动过程摩擦阻力矩,并分析了大气温度对冷态阻力矩的影响规律。以此建立起动过程数值仿真模型,完成了摩擦阻力矩对起动过程转速的影响分析。计算结果表明:摩擦阻力矩随着发动机转速的增加呈减小趋势;在冷态条件下,随着大气温度的降低,摩擦阻力矩逐渐增大;起动过程转速变化率随之减小。     

1.5级大子午扩张涡轮非定常流动和传热特性分析

大子午扩张涡轮端壁二次流与热负荷之间的关系,对于端壁冷却非常重要。本文采用几何约化法,对某1.5级大子午扩张涡轮进行数值模拟,研究了大子午扩张涡轮上端壁非定常流动和传热特性。计算结果表明：大子午扩张涡轮上通道涡尺度较大且位置发生改变,沿径向向下移动约20%叶高;R1出口泄漏涡、通道涡和尾迹是造成S2流动和传热非定常性的主要因素;传热与二次流密切相关,对传热研究必须与流动相结合。研究结果将有助于提高对大子午扩张涡轮端壁非定常流动和传热特性的认识。     

高低压转子弹性支承振动应力信号的LMD切片谱分析与时频分布

针对传统的频谱分析方法不能很好地辨识航空发动机转子振动特征频率的问题,采用局部均值分解（Local Mean Decompo? sition, LMD）,结合切片谱的频谱分析方法,对航空发动机转子振动信号进行自适应模态分解与峰值频率辨识;对转子振动信号进行时 频分析,得到其时频分布。将该方法应用于某航空发动机高、低压转子的弹性支承振动应力信号分析中。结果表明：相比于发动机振 动正常状态,在发动机振动异常状态下,高、低压转子弹性支承振动应力信号的LMD切片谱中除了存在高、低压转子的基频和倍频成 分,还存在高、低压转子间的调制频率,且在异常状态下F分量的时变特征更加明显。采用LMD切片谱分析方法获取了发动机振动正 常状态和异常状态下的振动频谱特征和时频分布,可为航空发动机转子振动特征提取与状态判别提供参考。     

7YSZ coating prepared by PS-PVD based on heterogeneous nucleation

Plasma spray-physical vapor deposition (PS-PVD) as a novel coating process based on low-pressure plasma spray (LPPS) has been significantly used for thermal barrier coatings (TBCs). A coating can be deposited from liquid splats, nano-sized clusters, and the vapor phase forming different structured coatings, which shows obvious advantages in contrast to conventional technologies like atmospheric plasma spray (APS) and electron beam-physical vapor deposition (EB-PVD). In addition, it can be used to produce thin, dense, and porous ceramic coatings for special applications because of its special characteristics, such as high power, very low pressure, etc. These provide new opportunities to obtain different advanced microstructures, thus to meet the growing requirements of modern functional coatings. In this work, focusing on exploiting the potential of gas-phase deposition from PS-PVD, a series of 7YSZ coating experiments with various process conditions was performed in order to better understand the deposition process in PS-PVD, where coatings were deposited on different substrates including graphite and zirconia. Meanwhile, various substrate temperatures were investigated for the same substrate. As a result, a deposition mechanism of heterogeneous nucleation has been presented showing that surface energy is an important influencing factor for coating structures. Besides, undercooling of the interface between substrate and vapor phase plays an important role in coating structures.     

High-temperature oxidation behavior and analysis of impedance spectroscopy of 7YSZ thermal barrier coating prepared by plasma spray-physical vapor deposition

Quasi-columnar structure 7YSZ(yttria stabilized zirconia) thermal barrier coatings(TBCs) are prepared by plasma spray-physical vapor deposition(PS-PVD) onto pretreated and un-pretreated bond coating, respectively. An isothermal oxidation experiment of 7YSZ TBCs is carried out in the atmosphere of 950 °C in order to simulate the high-temperature oxidation process of engine blades. The isothermal oxidation process of 7YSZ thermal barrier coatings is investigated systematically by impedance spectroscopy. The electrochemical physical model and equivalent circuit of columnar 7YSZ coatings are established. Results show that the isothermal oxidation kinetic curve of columnar 7YSZ thermal barrier coatings appears to follow the parabolic law. A pretreatment of bond coating can reduce the growth rate of the thermally grown oxide(TGO) layer, restraining the initiation and propagation of microcracks between YSZ and TGO layers. The oxidation rate constants of 7YSZ coatings with pretreated and un-pretreated bond coating are 0.101×10~(-12) cm~2·s~(-1) and 0.115 × 10~(-13) cm~2 ·s~(-1), respectively. Impedance analysis shows that the content of oxygen vacancies decreases and the density increases after the TGO layer is oxidized for 150 h. In addition, shrinkage microcracks formed by sintering during the oxidation process is the main reason for an increase of the capacitance and a decrease of the resistance in the grain boundary of YSZ.     

海陆交界非平稳场景星载ScanSAR扇贝效应抑制方法

扫描式合成孔径雷达(ScanSAR)因不受光线、天气影响,能够提供宽测绘带图像而被广泛应用在海洋监测领域。但ScanSAR图像的扇贝效应(Scalloping)和子带拼接效应(Inter-Scan Banding,ISB)严重地降低图像质量,尤其在海陆相接一类的非平稳场景下,干扰更为严重,影响图像的应用效能。针对上述问题,文章给出了一种基于图像分层和卡尔曼滤波的ScanSAR图像扇贝效应和子带拼接效应的抑制方法。针对非平稳场景,先进行图像分层处理使其满足线性卡尔曼滤波需求;然后,利用加性二维周期函数对子图层的扇贝效应和子带拼接效应进行建模;再将卡尔曼滤波器应用于条纹抑制;最后,对真实ScanSAR图像数据的有效处理结果验证了算法的有效性。     

单轴旋转捷联惯导系统误差分析与转位方案

对单轴旋转捷联惯导系统误差调制原理与旋转方案进行了研究,光纤陀螺作为惯性测量单元的主要传感器件,其误差主要包括常值漂移、标度因数误差、安装误差以及随机漂移误差,分析了单轴旋转调制对各项误差的补偿作用,给出了单轴单向连续旋转、两位置正反转停(大于360°）、四位置正反转停(小于360°）3种转动方案。在摇摆状态下综合考虑各项误差,并对其中的两种转位方案进行了长时间导航仿真,仿真结果表明：两位置转停方案与四位置转停方案长时间导航定位精度相当,四位置转停方案不需要加装导电滑环,实现起来更加简单,是一种最为有效的单轴旋转方式。在自行研制的单轴旋转捷联惯导系统上对四位置转停旋转方式进行了转台摇摆和车载环境验证实验,结果都能满足系统设计的指标。     

小波包与PNN在抖动控制电路故障诊断中的应用

抖动控制电路是激光陀螺仪的重要组成部分,电路一旦发生故障,激光陀螺仪的输出信息也会随之出现错误。因此,有必要对抖动控制电路的故障诊断技术进行研究。基于不同故障模式下各频段能量的改变,提出了基于小波包频带能量谱和概率神经网络(PNN）的故障诊断方法。采用小波包分解提取各频段的能量信号,将其作为故障特征向量,利用PNN强大的非线性映射能力,以PNN作为分类器,对实验样本进行学习和测试。实验结果证明,所提方法可以较高精度识别出实验中的12种故障模式。