毫米波有源相控阵天线热设计

针对高功率毫米波有源相控阵天线的热设计问题,研究了一种理论估算和热仿真的方法。通过对某天线热设计,分析结果表明,优化流道布局和流道形状可以有效地解决这类电子设备的热设计问题。最后经过实物试验的验证,证实了该方法的可行性。     

PERFORMANCE IMPROVEMENT OF CENTRIFUGAL FAN BY MEANS OF NUMERICAL SIMULATION

Numerical simulation is used to investigate the flow field in a model centrifugal fan for steam power stations in order to improve the performance. During testing the model fan, it is found that the efficiency is only 62.5% with inlet box, without it the efficiency is 83%. In addition, the strong vibration of test rig is observed with inlet box. It would be highly desirable if the aerodynamics of the fan could be studied. Therefore, numerical simulation is carried out to investigate the internal flow characteristics of a model fan with inlet box. The results from CFD analysis show that the whole region of the inlet box is occupied by a spiral vortex rotating inversely as the rotor's direction, which significantly affect the most flow region inside the fan. For this reason, a dummy plate is arranged in the inlet box to impede the generation of the spiral vortex, the results from CFD after the reform demonstrate that the modification is quiet effective, the former large spiral vertex has been destroyed effectively, the large one is superseded in favor of two small vortexes. However, two small vortexes have little effect on the inner flow of the rotor and the following parts. Finally, the efficiency of the model fan is improved by the test and the strong vibration of the test rig disappears. This type of modification has been used in steam power stations, the fan efficiency raises to 84% successfully.     

铝板带轧制乳化液作用分析

介绍铝板带热轧制乳化液的特性和作用。     

矿用掘进机机电设备智能诊断系统的研究

针对目前掘进机机电设备故障率高、故障排除时间长影响正常掘进作业的现状,总结了掘进机机电设备的常见问题,建立了矿用掘进机机电设备智能诊断系统,并针对性地提出了系统维护方案,为提高掘进机机电设备可靠性、降低故障排除时间奠定了基础,有效提升了掘进机的使用可靠性.     

轮式智能车动-静随机障碍物避障研究

针对智能车传统A*算法存在拐点较多,不平滑,易发生碰撞问题,提出一种A*与DWA融合改进随机避障方法.在A*优化算法中通过计算节点间斜率,选择关键节点,剔除冗余节点,改进了评价函数,提高A*算法速度和路径平滑性.针对A*优化算法无法规避随机障碍物及DWA算法存在速度与安全不兼顾问题,提出一种兼顾速度与安全性的优化DWA...     

Dual Material Rapid Prototyping Techniques for the Development of Biomedical Devices. Part 1: Space Creation

Polymeric drug delivery devices play an important role in drug administration. However, the current polymeric drug delivery device fabrication methods lack precision. This impairs the quality of the devices, resulting in a decrease in the efficiency and effectiveness of drug delivery. The concept of building parts layer by layer out of powdered raw materials makes selective laser sintering (SLS) a suitable process for fabricating polymeric matrix drug delivery devices. The current SLS process is not capable of processing two or more materials separately. This work explores the possibilities of SLS per-forming a dual material operation by developing two process models. These two processes can then be integrated to form a dual or expanded multimaterial fabrication technique and act as a foundation for future work in multimaterial applications such as polymeric drug delivery device fabrication. Accord-ingly, two papers are presented. In this paper, Part 1, the focus is on the first process, which is a "space" creation technique in which a "space" is created by varying the density of a first representative material using heat during sintering. Three methods – one based on a vacuum and a place method, and the other two based on two variations of a laser compacting method – were tested. Results have shown that by varying the laser power during sintering, it is possible to create channels in which a second material can be deposited.     

Analysis of radiowave propagation in a four-layered anisotropicforest environment

Propagation of electromagnetic waves in forest environments is examined in which both the transmitting and receiving points are located in the trunk layer of a four-layered anisotropic forest model. This propagation model considers the forest as a horizontally stratified, anisotropic media of canopy and trunk, bounded by ground below and air above. The electromagnetic fields are obtained using dyadic Green's functions in their eigenfunction expansion forms for an anisotropic four-layered geometry. Analytical results are found for the fields, which consist primarily of three wave modes: a direct wave, multiply reflected waves, and lateral waves. These field constituents are compared, and their domains of preponderance are calculated; it is found that the lateral wave plays a major role in communication at large distances. Radio losses for typical forest are calculated to illustrate numerical application of the forest model     

数字音频压缩技术研究

音频信号数字化后的数据量相当惊人,不利于传输和存储,在日益广泛应用的数字技术中,数字音频的压缩成为其中的关键技术之。文中介绍了国内外现有的一些音频压缩技术,对其中重要的压缩算法进行了研究分析。