Thermoelastohydrodynamic analysis of misaligned bearings with texture on journal surface under high-speed and heavy-load conditions

Hydrodynamic journal bearings are used to support the planetary gears in the transmission system of a Geared Turbo Fan engine, and they operate under severe working conditions, such as misalignment, high speed, and heavy load. Surface texture is regarded as an effective approach to improve mechanical properties under severe working conditions. However, the effects of surface texture on misaligned journal bearings under severe conditions have not been well studied. Therefore, a thermoelastohydrodynamic(TEHD) lubricating model with a textured and misaligned journal is presented in this study. Solid deformation, heat transfer between oil and the bearing, and heat convection between air and the bearing are considered in the model. The effects of cavitation and viscosity-temperature are also taken into account. The impacts of surface texture parameters and the misalignment angle on lubricating properties are investigated in the model. Results indicate that the bearing lubricating performance is greatly improved by optimal surface texture considering journal misalignment. The maximum oil film pressure and load-carrying capacity of a journal bearing increase with journal misalignment. Meanwhile, the oil film temperature increases sharply while considering misalignment.     

Aircraft engine fault detection based on grouped convolutional denoising autoencoders

Many existing aircraft engine fault detection methods are highly dependent on performance deviation data that are provided by the original equipment manufacturer. To improve the independent engine fault detection ability, Aircraft Communications Addressing and Reporting System (ACARS) data can be used. However, owing to the characteristics of high dimension, complex correlations between parameters, and large noise content, it is difficult for existing methods to detect faults effectively by using ACARS data. To solve this problem, a novel engine fault detection method based on original ACARS data is proposed. First, inspired by computer vision methods, all variables were divided into separated groups according to their correlations. Then, an improved convolutional denoising autoencoder was used to extract the features of each group. Finally, all of the extracted features were fused to form feature vectors. Thereby, fault samples could be identified based on these feature vectors. Experiments were conducted to validate the effectiveness and efficiency of our method and other competing methods by considering real ACARS data as the data source. The results reveal the good performance of our method with regard to comprehensive fault detection and robustness. Additionally, the computational and time costs of our method are shown to be relatively low.     

面向精准工程湍流模型的理论研究

长期以来,工程湍流模型建立在量纲分析和经验修正的基础上,绝对预测能力不足而且模型参数的意义不明确。关于湍流边界层的理论研究一直平行地在两条路线上前行,或是经验性地构造有关平均速度或动能的分布,或是利用数值模拟等技术对于湍流脉动结构进行精细刻画。二者之间的分割导致对湍流边界层物理图像的不完整,从而限制了对一系列相似性关系的揭示。新近发展的结构系综理论,立足于探索由于固壁对于流场的雷诺应力各个分量所表现的拉伸对称性约束,完成了一个对于平均速度和动能剖面的统一描述,从而形成了一个构建工程湍流模型的新思路:一方面,理论指导如何开展湍流DNS(Direct Numerical Simulation)和LES(Large Eddy Simulation)的大数据分析,提炼对定量描述复杂流动有物理意义的多层结构参数;另一方面,指导开发物理图像清晰、定量描述精确的新型湍流(代数)模型。结构系综理论揭示了壁湍流所共有的普适多层结构,完整地刻画了边界层湍流的雷诺数、马赫数相似性,有望推动理论空气动力学研究进入一个定量化、精确化的新阶段。     

Z源NPC三电平变换器恒功率并网控制策略研究

Z源中点钳位式(NPC)三电平变换器把逆变和升压两种环节结合在一起,结构简单、工作效率高,但是针对这种结构输出的无功功率研究较少。提出了一种Z源NPC三电平变换器的恒功率并网控制策略。首先对这种变换器的结构及原理进行分析;再把恒功率控制引入到这种变换器的并网控制中,并采用空间矢量脉宽调制(SVPWM)实现了变换器的并网控制。MATLAB/Simulink软件仿真结果证明了这种变换器能够提高电压升压比。该控制策略可使变换器输出的有功功率、无功功率稳定于设定值,且并网电流谐波较低。     

封严篦齿特征参数对其密封性能影响的数值分析

利用软件CFX对直通型篦齿的内部流动进行模拟,研究了直通型篦齿齿距、转速对其泄漏量的影响.计算结果表明:篦齿泄漏量随齿距的增大而减少,篦齿转速对篦齿泄漏量的影响很小.另外,本文提出一种变齿距直通型篦齿,研究变齿距对篦齿泄漏量的影响,并对变齿距齿形所处位置对泄漏量的影响进行研究.     

机场跑道改性沥青混凝土抗冲击性能

为研究中高应变率下NRP和掺高粘剂的SBS两种改性剂对AC-13型沥青混凝土动力性能的影响,采用直径74 mm SHPB装置进行了4个气压下的冲击压缩试验,获得了不同种类改性沥青混凝土的破坏形态及应力-应变曲线。研究表明：沥青混凝土动态应力-应变曲线分为弹性变形、塑性强化和塑性破坏3个阶段,破坏形态分为裂缝、破损、块裂和碎裂4种;两种改性剂均能改善沥青混凝土的抗冲击性能,并且对峰值应力和冲击韧性的应变率敏感性有一定影响,在不同应变率范围内两种改性剂对冲击韧性增强作用不同,NRP对峰值应力增强作用优于掺高粘剂的SBS;应变率超过130/s时,沥青混凝土出现弹性模量退化现象,NRP对弹性模量有提高作用。     

火箭发动机涡轮典型结构形式对叶片低周疲劳寿命的影响研究

以某火箭发动机涡轮为对象,研究了涡轮叶片带冠、不带冠、带部分冠及叶片空心等典型结构形式对叶片低周疲劳寿命的影响。结果表明:叶片不带冠可以消除叶片顶部的疲劳损伤,但使叶背根部损伤增大,危险点位于叶背根部,叶片寿命与带冠叶片相当;带部分冠叶片在消除叶顶疲劳损伤的同时,还可以减缓叶背根部的低周疲劳,危险点位于前缘根部,寿命比原叶片高约116%;叶片空心结构可以有效降低叶片的应力应变水平,减缓叶片疲劳的效果最好,空心叶片危险点位于前缘根部,寿命比原叶片高约370%。     

基于解耦算法的化学非平衡流并行数值模拟

化学非平衡流的数值模拟需要求解化学反应源项,而详细化学反应机理中各个基元反应的时间尺度相差显著,因而导致空间离散后形成刚性常微分方程组,其求解计算量巨大。为此,在非结构有限体积法化学非平衡流解耦算法的基础上,进一步采用基于MPI的并行计算实现大规模化学非平衡流数值模拟的加速,从而为进一步求解复杂的工程应用建立条件。由于基于解耦算法的求解器中计算量最大的化学反应源项求解是基于各个单元格心变量实现,每个时间步求解时不需要进行交互,因此便于实现分区并行计算。经典的激波诱导振荡燃烧算例的数值模拟表明,开发的并行求解器具有较高的计算精度和良好的计算效率,并且由于其较低的内存需求,具备进一步开发图形处理器(GPU)计算能力的基础。     

深冲钢W08Al热轧模拟试验研究

在热模拟试验机上对 Ｗ ０８ Ａｌ深冲钢进行了热轧模拟试验,测量了材料在不同情况下的相变温度,考察了不同热轧工艺参数对晶粒尺寸和织构的影响。结果表明,铸坯经预先热变形后重新加热测量相变时,相变温度较低,而直接热变形后测量相变温度升高;在 Ａｒ３温度以上采用大变形量可以使晶粒细化,但在两相区终轧变形会造成混晶现象; Ａｒ３温度以上热变形所得的变形织构是弱的,进入两相区终轧变形则不利织构（１００）成分很快发展起来,并且织构的取向密度沿板厚方向明显不均匀。最后对 Ｗ ０８ Ａｌ热轧合理热轧工艺提出了建议。     

谐波传动齿啮式输出啮合参数的优化设计

根据谐波传动齿啮式输出刚柔轮齿的啮合特点,建立了一种同时考虑啮合侧隙和啮合效率的齿啮式输出啮合参数优化设计的数学模型。该模型有７个变量、２个目标函数、３个等式约束条件和７个不等式约束条件,优化方法采用罚函数法。文中对优化实例的结果进行了分析,得出了通过适当提高径向变位系数和他齿高可改善轮齿啮合性能的结论。文中提出的理论和方法为齿啮输出式谐波传动的啮合参数设计提供了依据。