Stability,periodicity, and symmetries of certain second‐order fractional difference equation with quadratic terms via KAM theory

By using the Kolmogorov–Arnold–Moser theory, we investigate the stability of the equilibrium solution of the difference equation where A ,B ,D > 0,u _?1,u ₀>0. We also use the symmetries to find effectively the periodic solutions with feasible periods. Copyright © 2016 John Wiley & Sons, Ltd.     

航空发动机压气机叶片振动频率与温度的关系

以某型航空发动机压气机第六级叶片为例，研究了温度对叶片振动频率的影响。发现由于温度的升高导致了材料弹性模量的下降，而弹性模量的下降又导致了叶片在发动机一定的转速范围内，除一阶振动外，其余各阶振动的动频均小于静频，因此与通常的工程处理方法不同，研究压气机叶片的动频时，应考虑温度的影响。     

风扇叶片外物撞击监测识别试验

为开展基于非接触叶尖振动测量的风扇叶片外物撞击监测识别技术研究,设计搭建了风扇叶片外物撞击监测识别试验平台,开展了不同弹体质量、发射速度、风扇转速等工况下的外物撞击试验.利用高速摄像机对外物撞击识别结果进行了检验,初步给出了外物撞击判定准则.分析了不同弹体质量、转速条件下系统识别准确率的差异,以及不同撞击因素与叶尖振动之间的定性规律.分析得出:外物撞击监测识别系统能够准确识别出撞击事件以及撞击叶片编号;风扇转速在1 800～4 000 r/min范围内,当弹体质量大于2.90 g时,系统的识别准确率达到了100％,这为后续建立外物撞击智能监测识别方法提供了重要的试验数据和依据.     

基于立体视觉的直升机旋翼桨叶三维动态变形测量

针对直升机旋翼桨叶变形测量难度大的问题,构建了一种随旋翼旋转的立体相机系统;设计了一种快速精确组网测量旋翼桨叶变形量方案,提出了桨叶三维动态变形量测量方法。理论分析和仿真实验表明,提出的直升机桨叶摄像测量方法具有精度高、速度快、便携式特点,同时通过地面实验验证了该方法的可靠性和鲁棒性。在直升机定型试飞中,可以高速率、高精度获得直升机旋翼桨叶三维变形量和表面结构,具有较好的应用前景。     

Using a pseudo-functionally graded interlayer in order to improve the static and dynamic behavior of wind turbine blade T-bolt root joints

The large wind turbines blades with multi-ton composite structures are mostly connected to the peach-bearings flanges using T-bolt joints which induce shear and bearing stress fields around the cross bolts. The significant differences between the modulus of elasticity of metallic bolts and composite surrounding materials cause stress concentration around interfaced zones and, also, limit the load capacity of the joints. In the present research, a pseudo functionally graded material (PFGM) as an interlayer is used around the cross bolts to examine the reduction of the stress concentration. Some radial variation of the mechanical properties would be considered for this interlayer. The finite element method is used to analyze the structures. Loadings are applied to the center of the cross bolts analogous to the real cases. Both the static and dynamic loadings are studied. For the finite element of the functionally graded material interlayer, a multilayer alternative material with constant properties in each layer is used. The results show that using an isotropic single layer with an average modulus of elasticity and specific thickness decreases the stress concentration of the composite part up to 47%. The various property models for the interlayer also show that an appropriated model can decrease the stress concentration up to 55%. Dynamic transient analyses would be implemented over the joint structure and improved considering to the practical cases. Using the PFGM interlayer decreases the constant and variable parts of the stresses up to 55% and also causes significant increasing of the joint fatigue life.     

具有相交性质的近小扭转映射的不变环面的保持性

In this paper we investigate the nearly small twist mappings with intersection property. With a certain non-degenerate condition, we proved that the most of invariant tori of the original small twist mappings will survive afer small perturtations. The persisted invariant tori are close to the unperturbed ones when the perturbation are small. The orbits reduced by those mappings are quasi-periodic in the invariant tori with the frequences closing to the original ones.     

离心泵叶轮参数对进口回流的影响

本文对不同叶片进口角、叶片数、不同叶顶间隙的开式和闭式离心叶轮共12种叶轮的进口流场和回流发生情况进行了探针的动态测试和可视化观察．弄清了上述叶轮参数对进口回流初始流量和进口流场的影响．     

INVESTIGATION ON KANE DYNAMIC EQUATIONS BASED ON SCREW THEORY FOR OPEN-CHAIN MANIPULATORS

IntroductionDynamicsofroboticmanipulatorsisthebasisofdynamiccontrolandmechanicaldesignofroboticmanipulators.Dynamicanalysisofrobotscanemploytheapproachesoftheoreticalmechanicsanddynamicequationsofanalyticalmechanics,suchasNewton_Eulerdynamicequations,Lagrange_Eulerdynamicequations ,Routhequation ,Appellequation ,andKaneequations.Theultimateresultsarethesamewhenweinvestigateononekindofmotionsaboutoneobjectivebydifferentdynamicequations,butthespeedandquantitiesofcomputationoftheseequationsare…     

旋转锥镜散斑剪切术测量动态扭率和斜率

采用旋转锥镜技术，进行激光散斑剪切照相，测量变形物体的动态扭率和斜率，拍摄一幅散斑图可获得扭率和斜率动态变化的全过程。     

Atomic force microscopy and transmission electron microscopy of cellulose from Micrasterias denticulata; evidence for a chiral helical microfibril twist

Atomic force microscopy (AFM), tapping mode atomic force microscopy (TM-AFM) and transmission electron microscopy (TEM) have been used to image the cell wall, ultrathin sections of whole cells and cellulose microfibrils prepared from the green alga Micrasterias denticulata. Measurements of the microfibril dimensions are in agreement with earlier observations carried out by electron microscopy. Images at the molecular level of the surface of the microfibrils were obtained with AFM and show regular periodicities along the microfibril axis that correspond to the fibre and glucose repeat distances of cellulose. Twisted regions visible at intervals along the microfibrils dried down onto substrates were noted to be right-handed in over 100 observations by TEM, AFM and TM-AFM. This revised version was published online in August 2006 with corrections to the Cover Date.