泄漏同轴电缆在智能高速公路中的研究与应用

在分析原有智能高速公路移动通信系统的基础上,用时域有限差分（FDTD）方法计算和仿真了泄漏同轴电缆在移动通信系统的性能,分析了泄漏同轴电缆在槽口处的电磁场分布,仿真了系统中不同位置的电场,为了得到更精确的结果,在网格剖分上采用了非均匀网格技术,仿真结果表明泄漏同轴电缆在智能高速公路移动通信系统中可以起到信息发送、传输和接收的作用,在日常通信频段内可以为公路上的机动车提供无盲区的宽频、高速传输的移动通信,为未来智能高速公路的发展与应用提供了理论依据。     

双回特高压交流输电线路电场沿高度的非单调变化特性分析

采用模拟电荷法,计算了三维特高压交流双回输电线路模型在6种相序布置下的空间电场强度分布。通过分析空间电场强度的分布特性发现,对于同塔双回输电线路,采用不同相序布置时,在线路档距中央垂直于地面的对称轴线上某一点的电场强度值基本不变;并且,采用不同相序布置时,沿高度方向空间电场变化的单调特性不同,即电场强度随高度增加或减小。由此提出了对于需要降低空间不同位置电场强度的问题,应选择不同相序布置的思想;并根据不同相序空间电场强度的分布特性,给出了选择最优相序的方法。文中计算结果对于线路交叉跨越等需要降低空间电场强度的问题具有参考意义。     

核主成分分析法的MIG焊电弧声信号特征选择

以不同焊接状态电弧声信号识别为目的,从MIG焊平板对接射流过渡电弧声信号入手,探寻电弧声产生机理和传播特性.提出电弧声是气体放电的伴生物,是等离子体集体振荡以波形方式传播的结果,也是声源和声道共同作用的产物,其频谱特性主要取决于声道的频率响应.在此基础上,采用线性预测分析技术,提取了表征焊缝熔透状态的10维电弧声信号特...     

Melting and resolidification of a subcooled metal powder particle subjected to nanosecond laser heating

Melting and resolidification of a subcooled spherical metal powder particle subjected to nanosecond laser heating are investigated analytically. The problem is divided into three stages: preheating, melting and resolidification, and thermalization. The temperature distributions in the liquid and solid regions and the location of the solid–liquid interface are obtained using an integral approximate method. The effects of the laser intensity and pulse width, initial subcooling, and particle radius on the melting and resolidification of powder particles were investigated. The Selective Laser Sintering (SLS) process for a pulsed laser can be simulated by repeating the three stages but varying the initial conditions.     

基于反演法的导弹姿态控制律设计

提出一种应用反演法来设计导弹的姿态控制律,该控制律能够提高非线性系统的鲁棒性。在设计过程中,首先介绍了反演设计方法从第1步到第n步的设计步骤;然后,将导弹姿态角度作为提出的姿态控制律的控制对象,并根据给定的俯仰角、偏航角和滚转角作为参考信号,得到相应的舵偏输入,使导弹能够按照给定姿态角度确定的轨迹飞行;最后非线性仿真结果证明该控制律的设计可行。     

基于PSO-AMLS的数据拟合方法在红外辐射计校准中的应用

针对红外辐射计标定中的数据拟合问题,提出了一种基于PSO-AMLS算法的数据拟合方法。该方法结合了粒子群算法(PSO)和自适应移动最小二乘法(AMLS)。采用的PSO算法可以实现自适应移动最小二乘法中参数的最优化,提高了红外辐射计的校准精度。区别于传统的应用于红外辐射计校准中的数据拟合方法,文中提出的基于局部近似的PSO-AMLS数据拟合方法,不仅可以得到红外辐射计输出电压与准直辐射源辐射之间的对应关系,而且在数据处理中通过灵活的数据处理机制,可以降低因拟合数据不均匀分布对拟合结果产生的不利影响。实验结果表明,文中提出的PSO-AMLS数据拟合方法,优于红外辐射计校准中所用的传统数据拟合方法,可以提高数据拟合精度。     

过氧化氢/醋酸法制备纳米纤维素

目的制备纤维素纳米晶体(CNCs),并对其性能进行表征,以促进纳米纤维素制备过程向绿色化、环保化转变,保证林业废弃物高效利用。方法以松木粉为原料,采用酸性过氧化氢和氢氧化钾进行化学预处理,去除木质素、半纤维素,采用机械方法进一步缩小木质纤维尺寸,改善分散性,最终制得CNCs。利用FT-IR,DSC,SEM,TEM对样品进行组分分析、性能检测及微观形貌观察。结果经过一次去木质素处理后,1636 cm^?1处的羰基(C=O)吸收峰消失;经KOH去半纤维素处理后,1720 cm^?1处的木聚糖羰基吸收峰消失。此外,综纤维素、纯化纤维素以及CNCs对应的DSC曲线形状相近,吸热峰峰值在125℃左右。结论经化学预处理与机械剪切处理后,最终成功制得了尺寸均匀、形貌清晰的CNCs,其径向尺寸集中在0~30 nm,轴向尺寸集中在100~300 nm。     

Cellulose aerogels from cellulose–NaOH/PEG solution and comparison with different cellulose contents

A green mild NaOH/polyethylene glycol solution was employed to dissolve the cellulose extracted from waste wheat straw. Subsequently combined with the freezing?thawing treatment, regeneration process and freeze drying, the cellulose aerogels with different cellulose contents were fabricated at mass ratios of 1∶100, 3∶100, 5∶100 and 7∶100 cellulose to the solution. Moreover, the influences of cellulose contents on the morphologies, crystal structures, crystallinity indexes, thermal stabilities and pore characteristic parameters of the aerogels were investigated by scanning electron microscope, X-ray diffraction, thermogravimetric analysis and nitrogen adsorption. Meanwhile, the oil adsorption properties of the aerogels with different cellulose contents were also surveyed; besides, for improving lipophilicity, the hydrophobic modifications of trimethylchlorosilane for the aerogels were carried out before the adsorption tests.     

Fatigue in laser welded titanium tubes intended for use in aircraft pneumatic systems

The pneumatic system conducts the pressurized hot air from the engine to the environmental systems of the aircrafts. In-service failures of arc-welded pneumatic parts have driven further developments of laser beam welding as an alternative method. Here, a fiber laser with 2 kW power had been employed to weld commercial purity titanium tubes with 0.5 mm wall thickness and 50 mm diameter. For comparison purposes, semiautomatic TIG welding was realized. The chosen parameters speed and laser power for laser welding were 200 W–2 m/min and 250 W–3 m/min. The laser welded tubes presented 1 mm wide weld beads composed by partially twinned α-Ti grains. The TIG welded tubes showed 5 mm wide beads composed by acicular α-grains. These observed differences had been associated with the cooling rates, which are ten times higher in the laser case. Both laser and TIG welded tubes were cycled 44,000 times in a pneumatic bench at 350 °C without failures or cracks that could release the internal pressure. After the pressurization tests, the tubes were tested for tensile and fatigue resistance. The yield stresses, tensile strengths and total elongation did not change comparing base material, TIG welded and laser welded cases. The condition 200 W–2 m/min presented superior fatigue resistance values compared to other welding conditions, and could be considered similar to the tubes in the unwelded condition. The microstructural and mechanical results had shown that the current laser technology can replace, with advantages, the arc welding for the joining of the titanium tubes.     

连续平压机伺服位置系统自适应滑模反步控制

针对连续平压热压机中执行机构存在的非线性问题、参数不确定和因板坯粘弹性对执行元件反作用力引起的外界干扰问题,采用了自适应滑模反步控制方法。对执行机构建立数学模型后,结合自适应滑模控制和反步法,有效降低了参数不确定、非线性和外界干扰对系统的影响,大大改善了控制系统的准确性。利用控制系统非线性数学模型的等价变换并选择合适的Lyapunov函数和中间虚拟量,完成了对系统稳定性的证明。仿真研究结果表明,所设计的自适应滑模反步控制器输出平稳,达到了快速准确的跟踪目的,同时对参数的变化具有较强鲁棒性。