Robust adaptive control for a single-machine infinite-bus power system with an SVC

In this paper, a new control synthesis framework is developed to solve a robust stabilization problem for a single-machine infinite-bus power system with a static var compensator (SVC). The uncertainties in the infinite bus voltage and the internal and external reactances to the generating station are considered. First, control inputs for the excitation and the SVC are obtained via immersion and invariance (I&I). Then, the controller is redesigned using a parameter update law and a filter using indirect I&I adaptive control and a two-time-scale technique. The transient and steady-state performances are enhanced by introducing class K functions. The simulation results show that the developed controller improves the system performance.     

A newly-designed fault diagnostic method for transformers via improved empirical wavelet transform and kernel extreme learning machine

In order to solve the problems of unsatisfactory diagnosis performance and unstable model of conventional fault diagnosis methods for transformers, a new approach based on improved empirical wavelet transform (IEWT) and salp swarm algorithm (SSA) optimized kernel extreme learning machine (KELM) is proposed in this study. Firstly, IEWT is used to adaptively decompose the vibration signal to obtain a set of empirical wavelet functions (EWFs). Secondly, the first n-order components with high correlation coefficient are collected. Thirdly, the mean value, variance, kurtosis, refine composite multiscale entropy (RCMSE), and time-frequency entropy(TFE) of these n-order components are calculated to construct a fusion feature vector. Finally, a two-level diagnostic model based on SSA-KELM is established. The first-level of it is applied to identify normal and abnormal states, and the second-level is selected to identify fault categories in the abnormal states. The proposed method can effectively diagnose the existing fault categories in the training set and accurately identify the unknown categories of faults. Experimental results show that the proposed method can efficiently extract features of different vibration signals and identify the faults, with an average classification accuracy of 96.25%. It is better than other methods, such as wavelet packet energy spectrum analysis-KELM and EWT-fisher.     

不利围岩条件下施工期调压井的动力有限元分析

调压井作为一种地下薄壁结构,其动力特性对于围岩地质条件十分敏感。本文结合一工程实例,运用瞬态动力学方法,在进行调压井自振特性分析的基础上,按照单纯考虑水平地震荷载作用及考虑水平与竖向地震荷载组合作用两种计算工况,对不利围岩地质条件下施工期调压井的动力响应特性进行了有限元仿真分析。结果表明:在水平与竖向地震荷载组合作用下,衬砌结构位移及应力的分布规律与单纯水平地震荷载作用情况基本相同,但其位移及应力均有所增大。由此说明,地震组合作用增加了衬砌结构的动力反应,竖向地震作用也会影响衬砌结构水平方向的动力反应。因此,在进行调压井结构的抗震设计时,考虑水平与竖向地震的组合作用是必要的。     

碾压混凝土拱坝温度应力场仿真研究

拱坝是固结于基岩的空间壳体结构,体型较为复杂。针对拱坝易存在的温度裂缝问题,结合碾压混凝土拱坝的施工特点及进度计划,采用三维有限元浮动网格法进行温控仿真研究计算。计算结果表明：在高温月份控制碾压部位坝体混凝土的入仓温度,对不同区域碾压的混凝土进行初期、中期和后期冷却,最大温差和最大应力均可满足拱坝温控设计要求。计算结果为预防坝体混凝土开裂提供了重要理论依据。     

多肋式梁桥在全过程中应力重分布研究

为了考察多肋式梁在全过程中受力性能,利用非线性实体退化壳单元理论研究了多肋式梁的应力重分布规律.混凝土和普通钢筋采用分层壳单元模拟,预应力钢筋采用组合壳单元模拟,推导了预应力钢筋对组合壳单元刚度矩阵的贡献和统一的非线性壳单元模式.利用Owen屈服准则、Hinton压碎准则和弹塑性强化模型考虑了混凝土和钢筋的非线性效应,有效模拟了预应力混凝土多肋式梁的开裂、屈服和失效全过程,并编制了相应的三维非线性全过程计算程序.结合破坏性试验资料可知,理论计算结果与试验数据吻合良好,并对预应力钢筋应力发展规律进行研究.结果表明,用实体退化壳单元模拟预应力混凝土多肋式梁是合适的,研制的非线性单元和非线性程序是正确的.     

活化凹凸棒石对多级孔分子筛合成种类和孔道结构的影响EI北大核心CSCD

采用不同方法活化的凹凸棒石为前驱体,在模板剂四乙基氢氧化铵(TEAOH)作用下一步法合成多级孔分子筛。研究不同硅铝比条件下活化凹凸棒石对分子筛合成种类和孔道层次结构的影响。结果表明:不同活化凹凸棒石作为前驱体合成的分子筛种类存在差异;XRD结果显示:当以碱焙烧酸微波凹凸棒石(HM-NC-ATP)、酸微波凹凸棒石(HM-ATP)和酸水热凹凸棒石(HH-ATP)为前驱体时,相同条件下分别获得ZSM-5,ZSM-12和ZSM-11分子筛,且硅铝比不同导致合成产物的形貌和孔道结构不一。此外,以HM-NC-ATP,HH-ATP为前驱体,合成产物孔道层次结构因子(HF)与硅铝比变化呈线性相关;HM-ATP为前驱体时,合成产物的孔道层次因子HF值最小,约为0.105,说明此时有利于介孔孔道构筑。     

面向影像金字塔的四叉树空间索引算法

基于线性四叉树提出一种面向影像金字塔的空间索引算法。在分析线性四叉树拓扑关系的基础上,设计一个具有方向一致、层次递进特性的编码方式,建立影像金字塔与线性四叉树的映射方案,给出一个按照经度纬度自然增长的邻域查找算法,并构建一个全球多分辨率虚拟地形环境对编码和算法进行测试。实验结果表明,该算法能够明显地缩小空间影像的检索时间,具有较高的编码效率和查找效率。     

Research on intelligent assembly method of aero-engine multi-stage rotors based on SVM and variable-step AFSA-BP neural network

The quality of the aero-engine rotors assembly determines the overall performance of the engine. Aiming at the problems of rotors assembly with different plane types, we proposes a rotor plane classification method based on SVM by using the profile data of PCA dimension reduction. Meanwhile, for the unilateral-tilt plane rotors, the three-objective rotors assembly method of coaxiality, unbalance amount and perpendicularity based on the rigid rotor model is established. For the hyperbolic paraboloid rotors, an intelligent assembly method based on AFSA-BP neural network for coaxiality, unbalance amount and perpendicularity is established. The experiment is based on the double-column ultra-precision measuring instrument and V4L vertical balancing machine and HL5UB horizontal balancing machine to measure rotors geometry and unbalance data. The experimental results show that the plane type classification accuracy can reach 99 %. The prediction error of the coaxiality of the unilateral-tilt plane rotors assembly is 5.1 μm, the prediction error of the unbalance amount is 196 g·mm, and the prediction error of the perpendicularity is 0.6 μm. The average prediction error of the coaxiality of the hyperbolic paraboloid rotors assembly is 0.9 μm, and the average prediction error of the unbalance amount is 73 g·mm, and the average prediction error of the perpendicularity is 0.2 μm. Our method provides a reliable assembly solution for aero-engine rotors assembly and meets actual assembly requirements.     

膜分离过滤过程中膜相内扩散动力学研究

基于与传统膜分离技术对物质进行分离过滤的共性,对这种便捷的迁移过程进行了动力学方程的推导,考察了物质穿过膜相的扩散作用和膜相内的运移规律,并用菲克第一定律建立了动力学方程。在此研究中,假定整个体系是瞬时和稳态的反应。最后,对膜相过滤过程的总压力损失和各部分压力损失的关系做了简要的介绍。     

Tb(Ⅲ)Transport in Dispersion Supported Liquid Membrane System with D2EHPA as Carrier in Kerosene

The transport of Tb(Ⅲ)in dispersion supported liquid membrane(DSLM)with polyvinylidene fluoride membrane(PVDF)as the support and dispersion solution including HCI solution as the stripping solution and di(2-ethylhexyl)phosphoric acid(D2EHPA)dissolved in kerosene as the membrane solution,has been studied.The effects of pH value,initial concentration of Tb(Ⅲ)and different ionic strength in the feed phase,volume ratio of membrane solution to stripping solution,concentration of HCl solution,concentration of carrier,different stripping agents in the dispersion phase on the transport of Tb(Ⅲ)have also been investigated,respectively.As a result,the optimum transport conditions of Tb(Ⅲ)were obtained,i.e.,the concentration of HCI solution was 4.0 mol/L,the concentration of D2EHPA was 0.16 mol/L,the volume ratio of membrane solution to stripping solution was 30:30 in the dispersion phase and pH value was 4.5 in the feed phase.Ionic strength had no obvious effect on the transport of Tb(Ⅲ).Under the optimum conditions,the transport percentage of Tb(Ⅲ)was up to 96.1% in a transport time of35 min when the initial concentration of Tb(Ⅲ)was 1.0×10-4 mol/L.The diffusion coefficient of Tb(Ⅲ)in the membrane and the thickness of diffusion layer between feed phase and membrane phase were obtained and the values were 1.82×10-8 m2/s and 5.61 μm,respectively.The calculated results were in good agreement with the literature data.