使用光纤放大器的频分复用光纤传输系统

报道了一个使用光纤放大器的两路非相干频分复用光纤传输实验系统。系统采用国产ＤＦＢ激光器作光源，用意大利生产的光纤放大器作在线放大器，用自制的光学谐振腔作光学滤波器和解复用器，采用ＦＳＫ调制制式，将１４０Ｍｂ／ｓ非归零伪随机码传输了５０公里，得到了很好的眼图。在频道间距为１０ＧＨｚ情况下，未观测到邻道干扰和光纤放大器的非线性现象。     

FDM系统的重要工艺参数及其控制技术研究

FDM快速成型系统的工艺过程中，有很多因素影响着FDM工艺的原型精度和成型时间，其中工艺参数的影响是主要因素之一。论文着重分析了8个最重要的工艺参数对FDM工艺的原型精度和成型时间的影响。在FDM系统实验调试阶段和FDM工艺过程中，实现对这8个重要工艺参数的控制具有非常重要的实际意义。论文详细地论述了FDM系统实现对这些重要工艺参数进行控制的控制技术。实践证明，通过这些控制技术可以自由地设置调节工艺参数，通过选择合理的工艺参数达到最佳的工艺效果。     

有限差分法在二维位场延拓的应用

采用第一类边界值条件下有限差分矩形等距网格法,对位场求解区进行网格剖分,探讨有限差分方程的建立、建模和计算原理。在同一种模型建立的差分方程下,使用Jacobian迭代和全选主元高斯消去法进行求解,统计计算时间和迭代次数,比较两者的均方误差。不同模型计算结果显示,两者求解结果基本吻合。     

CFD在熔融沉积成型挤出头性能分析中的应用

对两种丝料型熔融沉积快速成型(FDM)技术的挤出头进行性能比较分析,所用成型材料为生物可降解塑料聚乳酸(PLA)。应用计算流体动力学软件(CFD)Star CCM+进行挤出头各部件传热以及PLA在挤出头内流道熔融和流动情况的模拟,建立挤出头性能评判指标分别为进料阻力、熔融段长度、能量利用率和准备时间四部分。建立适当的模型和边界条件进行模拟,并监控所需参数,最后通过实验进行进料阻力模拟结果准确性验证,说明用CFD模拟的方法进行3D打印挤出头进料性能对比研究是可行的。     

Effect of MgO sintering additive on mullite structures manufactured by fused deposition modeling (FDM) technology

An optimized recipe for 3D printing of Mullite-based structures was used to investigate the effect of MgO sintering additive on the processing stages and final ceramic properties. To achieve dense 3:2 mullite, ceramic filaments were prepared based on an alumina powder, a methyl silicone resin, EVA elastomeric binder and MgO powder. Using 1 wt% MgO and a dwell time of 5 h at 1600 °C, a dense mullite structure could be obtained from filaments with a diameter of 1.75 mm. Ceramic structures with and without sintering additive were printed in vertical and horizontal direction, to investigate the effect of printing direction on mechanical strength after sintering. Using four-point bending test, it was demonstrated that by using MgO, the printing orientation did not affect the mechanical strength significantly anymore. The low Weibull modulus could be explained by the closed porosity that emerge during the degassing of the preceramic polymer due to cross-linking.     

基于FDM进丝系统的通信技术研究

提出了一种采用PC机与单片机通信的方法，解决了FDM进丝系统的控制信息与反馈信息的传输问题。该方法有有连接与无连接两种传输模式，采用自定义的协议进行通信，可分别适用于数据量大、精确度要求高和数据量小、实时性要求高的情况。采用该方法后，FDM进丝系统的稳定性大大提高，并且由此提高了成型精度。     

STUDY ON NUMERICAL SIMULATION OF CASTING THERMAL STRESSES BASED ON FDM

A system for the numerical simulation of 3D temperature and stress fields during casting process was studied, developed and practiced based on finite difference method (FDM) in this paper. An approach where the stress/strain and the heat transfer analysis use the same computational domain was presented, which avoided transferring temperature data between FDM and FEM nodes and elements. A slot-board steel casting was simulated and the calculated results are in agreements with those obtained from practical producing.     

集中式MIMO雷达研究进展：正交波形设计与信号处理

集中式多输入多输出（Multiple Input Multiple Output,MIMO）雷达通常利用正交波形增加发射波形自由度,采用数字阵列拓展空间收发自由度,使得雷达接收机的天线孔径获得明显扩展,最终带来空间分辨率、测角精确度、杂波抑制能力等大幅度提升。但是,这些性能提升的前提是发射波形具有正交特性。事实上,在实际应用中,在不牺牲时域/频域资源情况下,受限于时宽带宽积,无法获得完全正交的波形集合,从而限制了MIMO雷达系统性能。本文对集中式MIMO雷达正交波形复用的技术原理进行了系统回顾,分别归纳了三种快时间发射波形设计方法：时分复用（Time Division Multiplexing, TDM）、码分复用（Code Division Multiplexing,CDM）和频分复用 （Frequency Division Multiplexing, FDM）,以及两种慢时间发射波形设计方法：多普勒分复用（Doppler Division Multiplexing,DDM）和随机相位编码波形,并对其优缺点进行对比。同时,对快时间MIMO和慢时间MIMO的信号处理流程进行归纳综合,给出基于匹配滤波的集中式MIMO雷达统一信号处理框架。为了展示不同波形对成像性能的影响,本文给出了基于三维匹配滤波的MIMO雷达成像结果。最后,结合实际应用问题,指出当前MIMO雷达面临的技术难点和发展趋势。     

Additive Manufacturing of Porous Structures for Unmanned Aerial Vehicles Applications

Unmanned aerial vehicles (UAVs) have shown promising benefits in many applications. This has been enabled by the emergence of additive manufacturing (AM), which give the designers a large amount of geometrical freedom. In this paper, a novel design process of fused deposition modeling (FDM) combining both topology and infill optimization is introduced for AM of high performance porous structures. Tensile testing of FDM printed samples is first carried out to study the effect of the build orientation on the mechanical properties of acrylonitrile butadiene styrene (ABS) samples. It is found that samples built perpendicular to the load axis are the weakest with a tensile strength of 29 MPa and Young's modulus of 1960 MPa. The materials properties are fed to the finite elements analysis (FEA) for geometrical topology optimization, aiming to maximize stiffness and reduce weight of those parts. Afterwards, an infill optimization is carried out on the topology optimized parts using different mesostructures such as honeycomb, triangular, and rectangular to achieve high structural performance. The results showed that triangular pattern with 50% infill density had the lowest developed stresses, less mass, and strain energy when compared to other structures. Optimum UAVs parts of a quadcopter are successfully manufactured, assembled, and tested.

     

图像去噪中的有限元求解方法

提出一种图像去噪中的有限元求解方法.从P-M模型出发,利用双线性插值得到图像在任意点的灰度值,将该值作为初始条件,采用有限元法对模型进行分析求解.在相同的时间间隔与迭代次数的条件下,该方法的求解结果与传统的有限差分法相比,平滑去噪和保持边界的效果更好,峰值信噪比有较大提高.