基于分形盒维数的汽轮机转子振动故障诊断的实验研究

汽轮机转子是汽轮机故障预测及诊断问题的一个重要方面.利用振动信号或状态量对设备进行诊断,是设备故障诊断中最有效、最常用的方法.本文在Bently实验台上进行了实验,模拟电站汽轮机转子的不对中、不平衡、碰摩和轴承松动4种故障的振动过程.根据汽轮机故障的分形特征,采用分形盒维数方法进行了不同故障试验数据的分形盒维数研究计算.结果表明:碰摩状况下的轴心轨迹最为混乱且呈现雪花状,其对应的分形盒维数也最大;不平衡时的轴心轨迹较为平滑,其对应的分形盒维数最小;不对中故障及松动故障的分形盒维数居中.因此,分形盒维数在进行汽轮机转子故障类型诊断时有更好的区分度.     

Robust feature learning for online discriminative tracking without large-scale pre-training

Owing to the inherent lack of training data in visual tracking, recent work in deep learning-based trackers has focused on learning a generic representation offline from large-scale training data and transferring the pre-trained feature representation to a tracking task. Offline pre-training is time-consuming, and the learned generic representation may be either less discriminative for tracking specific objects or overfitted to typical tracking datasets. In this paper, we propose an online discriminative tracking method based on robust feature learning without large-scale pre-training. Specifically, we first design a PCA filter bank-based convolutional neural network (CNN) architecture to learn robust features online with a few positive and negative samples in the high-dimensional feature space. Then, we use a simple soft-thresholding method to produce sparse features that are more robust to target appearance variations. Moreover, we increase the reliability of our tracker using edge information generated from edge box proposals during the process of visual tracking. Finally, effective visual tracking results are achieved by systematically combining the tracking information and edge box-based scores in a particle filtering framework. Extensive results on the widely used online tracking benchmark (OTB-50) with 50 videos validate the robustness and effectiveness of the proposed tracker without large-scale pre-training.     

Optimal layout of internal stiffeners for three-dimensional box structures based on natural branching phenomena

Thin-wall box structures combine an outer wall and internal stiffeners. These stiffeners can improve the stiffness of box structures. The adaptive growth method based on natural branching phenomena is applied to solve this layout optimization problem, in which techniques of ground structure construction, stiffener growth direction control, ‘seeding-line’ selection and sensitivity filtering are studied. First, the ground structure with solid and shell elements is established. Then, an iteration formula based on Karush–Kuhn–Tucker optimum conditions is derived. Stiffeners start at the seeding line and grow gradually according to the design sensitivities. Finally, an optimum stiffener layout is obtained. Draft manufacturing constraints are also included in the design procedure. The validity of the method is verified by several design examples. An actual machine tool bed is redesigned, and the performance comparison between the original and optimized beds shows the superiority of the suggested method.     

灰色聚类应用于钻床齿轮变速箱优化设计的研究

灰色聚类是研究灰色系统的一种分析、判断方法,对于求解多目标优化问题,较一般的其他方法更具合理性及实用性。通过对灰色系统、灰色聚类方法的研究,在钻床齿轮变速箱多目标优化设计问题传统解法的基础上,利用灰色聚类,求出了该问题的最满意解,使解得到了进一步的优化。     

桥式起重机箱形主梁焊缝疲劳寿命研究

以某桥式起重机箱型主梁为研究对象,利用ANSYS软件对其进行静态分析,结果表明该起重机静强度以及静刚度均满足设计要求。依据英国标准BS7608,采用FE-SAFE疲劳软件,对主梁翼缘焊缝疲劳寿命进行分析,得出该起重机主梁下翼缘板与主腹板连接处的翼缘焊缝处疲劳寿命最低。并对该处采用不等边角焊缝模型进行对比分析,结果显示适当增加角焊缝一边的长度,且长边位于翼缘板上时,同一焊缝上两条焊趾处的疲劳寿命均有所提高,有助于改善焊接结构件的抗疲劳性能。     

基于熵的自适应门限小波去噪股市价格预测

本文针对传统软阈值法小波去噪采用统一门限而引起的过平滑问题,根据熵的特性,在各层自适应调整去噪门限,提出一种改进的小波去噪算法,采用Hurst指数和盒维数作为判决准则抑制过平滑。最后将算法应用于股市价格时间序列去噪,并用BP神经网络对去噪后的深发展A近20年的收盘价格进行了分段预测。仿真表明,本文方法与传统方法相比,误差明显减小,预测结果更为理想。     

Effect of Powder Mixed Dielectric on Material Removal and Surface Modification in Microelectric Discharge Machining of Ti-6Al-4V

Microelectric discharge milling is one of the variants of microelectric discharge machining process which acquire the attention of researchers due to its unique ability to produce microchannels and three-dimensional structures in difficult-to-machine materials like titanium. In the present work, an experimental investigation has been performed in order to study the effect of SiC microparticle suspended dielectric on machining Ti-6Al-4V with tungsten carbide electrode. The effects of major electric discharge milling process parameters—voltage, capacitance, and powder concentration in dielectric—on responses—viz., material removal rate (MRR) and tool wear rate (TWR)—were studied. Experiments were designed and performed based on response surface methodology (RSM)-Box–Behnken statistical design and the significance of in put parameters were identified with the help of analysis of variance. From the results, it is recommended to use powder concentration of 5 g/L, capacitance of 0.1 µF, and voltage of 115 V for achieving high material removal and low tool wear rate. Finally, the studies were conducted to analyze the surface modification and the quality of machined surface.     

大连中山路地下通道结构力学特征分析

中山路地下通道位于大连市中山路和五惠路的交汇处,共有3个出入口,分别下穿中山路、五惠路,结构极其复杂。针对中山路地下通道的特殊性,利用有限单元法分别建立了二维和三维计算模型,分析了主通道和三向交叉口处的力学特征,结果发现三向交叉口处箱涵受力较为复杂,且箱涵转角处有明显的应力集中现象,据此根据箱涵的受力特征给出了相应的改善措施。论文所得到的结论,可为今后类似条件下地下通道工程的设计和施工提供相应的参考。     

预应力混凝土箱梁桥底板开裂机理及简化设计方法

针对悬臂施工预应力混凝土箱梁合龙过程中底板开裂问题,本文对其破坏的机理和防治进行研究。以某预应力混凝土连续箱梁桥为例,对该箱梁的施工过程进行模拟,通过考虑材料非线性对底板开裂的过程进行仿真分析,并对底板崩裂的机理进行分析,在此基础上根据规范提出防治措施供设计应用。结果表明,由于合龙束孔道的影响,孔肋为受力最不利区域,在径向力作用下,孔肋的斜裂缝和撕裂裂缝是导致箱梁破坏的主要原因。在今后箱梁设计中,底板横向除应满足抗剪承载力外,孔肋尚需满足最小孔道间距的要求。     

Unusual structural effects in a variable-depth box girder bridge: The Pujayo viaduct

The new Spanish highway bridge, the Pujayo Viaduct, has a single-cell box girder. Owing to the large width of 26.1 m, the box girder had to be stiffened by transverse upper and lower ribs, by haunches in the connection web-flange and by inclined webs. Together with the variable girder depth, a relatively complicated geometry was created that was analysed by means of finite-shell-element calculation. Several unusual secondary structural effects are identified and explained. The longitudinal axial force resulting from global bending causes deviation forces in the curved bottom slab, which are responsible for transverse bending in the bottom slab and axial forces in the webs. Shear lag deformation of the box section causes moderate horizontal bending of the transverse ribs. Global deflection of the bridge girder causes out-of-plane bending of inclined webs. Global bending of box girders causes local bending moment output in finite shell elements. A further conclusion is that three-dimensional finite-shell-element models are an exact and appropriate complement to the common beam-element calculation models.