锥形光纤在空间光通信耦合系统中的应用

为了提高自由空间光通信的接收端耦合效率,将锥形光纤应用于光耦合,依据BPM算法的仿真结果使用熔融拉锥法制备了满足低损传输条件的锥形光纤。在实验上研究了锥形光纤和双锥形光纤模场传输特性。通过静态空间光-光纤耦合实验,对比了多/单模熔接光纤和锥形光纤光耦合效率和传输效率的差异,并研究了以上两种光纤结构耦合效率的横向偏移量容差。结果表明,锥形光纤的传输效率约为70%,具有低损传输特性、用于匹配后端单模光电子器件的良好滤波特性以及相比普通光纤更高的横向偏移量容差特性,因此可以广泛应用于自由空间光通信接收端光耦合、模式转换器等方面。     

锥形光纤的调制特性研究

将通信光纤的末端拉制成锥形能实现光纤之间的耦合,在锥形光纤耦合系统中,载波(被信号所调制的光波-光脉冲)在经过锥形光纤耦合后(连接与分束)其脉冲变化特性对锥形光纤通讯系统是十分重要的。在实验上检测了锥形光纤中光脉冲的调制特性,并从理论上引入脉冲归一化振幅,讨论色散和非线性效应对脉冲的影响,得出光脉冲在经过锥形光纤耦合传输后其形状保持不变的结论。     

湍流环境中光纤耦合效率的提高

在空间激光通信应用中,空间光与单模光纤的耦合效率是影响通信系统性能的重要因素。考虑大气湍流会降低激光与光纤的耦合效率,本文从湍流强度与光学系统分辨率之间的关系出发,研究了大气湍流对光纤耦合效率的影响,导出了接收口径、系统焦距、入射光波长、接收光纤半径、大气相干长度等与单模光纤耦合效率之间的关系。提出了两种在湍流环境中提高光纤耦合效率的方法。方法一是在外界湍流强度发生变化时,通过改变耦合系统焦距,使耦合效率保持在较高值;方法二则是采用锥状光纤接收来提高耦合效率。最后对提出的方法进行了分析、仿真和室外耦合效率测试,验证了所提出的改善耦合效率方法的有效性。     

马赫-曾德尔干涉集成化的全光纤磁场与温度传感器

为了简化光纤磁场与温度传感器的结构并提高传感器灵敏度,设计并制作了马赫-曾德尔干涉集成化的全光纤磁场与温度传感器。将单根光纤的马赫-曾德尔模间干涉结构和双臂马赫-曾德尔干涉结构结合:将总长度为1.2m的单模光纤部分制备成长度为2.7cm、锥腰直径为30.1μm的锥形微纳光纤,并得到了拉锥时间与锥腰直径的关系。将锥形微纳光纤放置尼龙槽内并包覆磁凝胶构成传感头,实现模间干涉的马赫-曾德尔磁场传感器;将磁场传感器通过两耦合比为50%∶50%的耦合器并联带有可调谐光衰减器的单模光纤形成马赫-曾德尔干涉的温度传感器。从理论上分析了光谱漂移对磁场和温度传感的特性关系,实验测得室温下磁场强度在25~50mT时,磁场传感的灵敏度为0.301 14nm/mT;在磁场强度为0,温度由25℃升高到30℃时,温度传感的灵敏度为0.518 86nm/℃。该传感器可广泛应用于电力系统放电检测、材料加工、安全监控等领域。     

808nm高亮度半导体激光器光纤耦合器件

针对单个808nm单管半导体激光器输出功率低,采用端面泵浦方式对光纤激光器进行泵浦时受到限制的问题,本文利用空间合束技术制成高亮度半导体激光器光纤耦合模块来提高808nm单管半导体激光器泵浦掺Nd3+双包层光纤激光器的效率。首先,通过微透镜对每个单管半导体激光器进行快慢轴准直;然后,使用反射棱镜对每个激光器发出的光进行空间合束;最后,利用自行设计的扩束系统将合束后的光束进行扩束,聚焦进入光纤,从而极大地提高光纤耦合模块的亮度。实验中将4只连续输出功率为5W的单管半导体激光器发出的光束耦合进芯径为105μm、数值孔径(NA)为0.2的光纤,当工作电流为5.8A时,通过光纤输出的功率为15.22W,耦合效率达到74%,亮度超过1.4MW/cm2.sr。     

塑料光纤微透镜耦合平头发光二极管

为了有效耦合平头发光二极管(LED),使用机械方法加工了锥球面塑料光纤(POF)微透镜。平头发光二极管由圆头发光二极管打磨掉聚光帽制得,其出光端面与芯片距离小于0.5mm。锥球面塑料光纤微透镜用数控机床加工制得。采用光线追迹法对耦合模型进行了分析。实验优化了锥球面光纤微透镜的参数、锥角、小球半径、工作距离和单端/双端模式,并理论分析了双端锥球面微透镜耦合的实验结果。当双端锥球面光纤微透镜锥角为140°、小球半径为0.15mm时,可带来20.4%的耦合效率增益。所用加工方法有利于微透镜参数优化,具有较好的加工精度和重现性,可以用于制作塑料光纤微透镜。     

负荷对整体齿轮增速式离心压缩机转子系统动力学特性的影响研究

整体齿轮增速式离心压缩机振动特性较单转子压缩机更为复杂,由于存在齿轮啮合作用,齿轮-转子-轴承系统耦合出新的频率、振动峰值。本文以一台在役的4轴6级整体齿轮增速式离心压缩机为研究对象,建立齿轮-转子-轴承系统的弯扭耦合有限元模型,分析在工作转速下不断提升负荷过程中耦合系统的动力学特性。模态分析表明:随着负荷增大,耦合频率中的单轴弯扭耦合频率增幅较大,并在75%负荷时与激振频率相交;不平衡响应分析表明:随着负荷增大,在80%负荷时出现临界负荷点,轴承处出现振动峰值。稳定性分析表明:随着负荷增大,单轴弯曲频率所对应的对数衰减率降低,单轴弯扭耦合频率所对应的对数衰减率部分增大、部分降低,多轴弯扭耦合频率所对应的对数衰减率增大。     

微型燃气轮机转轴振动特性分析

基于有限元法，针对某30 kW微型燃气轮机发电机组永磁转子物理模型，建立了该转子在不平衡量与转子弯曲耦合下的动力学响应方程。分析了不平衡力与转子弯曲力在不同夹角下对高速转子在升速过程中振动响应的影响情况。结果表明：不同夹角对转子振动响应影响差别较大。当两激励力所在平面夹角相差180°时，转子在升速过程中会出现“倒临界”现象，即经过临界转速时转子振幅会达到最小；整体而言，在耦合作用下转子的振幅较单激励力条件下有所增大。     

808 nm high brightness module of fiber coupled diode laser

针对单个808 nm单管半导体激光器输出功率低,采用端面泵浦方式对光纤激光器进行泵浦时受到限制的问题,本文利用空间合束技术制成高亮度半导体激光器光纤耦合模块来提高808 nm单管半导体激光器泵浦掺Nd3+双包层光纤激光器的效率.首先,通过微透镜对每个单管半导体激光器进行快慢轴准直;然后,使用反射棱镜对每个激光器发出的光进行空间合束;最后,利用自行设计的扩束系统将合束后的光束进行扩束,聚焦进入光纤,从而极大地提高光纤耦合模块的亮度.实验中将4只连续输出功率为5W的单管半导体激光器发出的光束耦合进芯径为105 μm、数值孔径(NA)为0.2的光纤,当工作电流为5.8A时,通过光纤输出的功率为15.22W,耦合效率达到74％,亮度超过1.4 MW/cm2·sr.     

风电叶片单点疲劳加载过程数值仿真与试验

设计了一套风电叶片单点疲劳加载系统,基于拉格朗日方程建立了振动耦合数学模型,对振动特征规律（叶片振幅、电机电流）分别进行数值仿真。当驱动频率与叶片固有频率偏差较小时,固存的机电耦合现象会导致叶片振幅稳定,若偏差增大,叶片振幅则发生剧烈波动。加载源电流跟随叶片振动产生周期性波动,且转速越大,等负载下的电流相对越大,共振时电流达到最大。建立了一套单点疲劳加载试验系统,对振动过程中的叶片振幅和电流进行测试。试验结果验证了数学模型与仿真模型的准确性,该结论为疲劳加载解耦控制算法的制定提供了理论依据。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.