天线阻抗特性对开关振荡器输出脉冲的影响

以单锥天线和螺旋天线作为开关振荡器辐射天线为例,采用等效电路模型和商业电磁仿真软件,分别对天线末端电压振荡信号和辐射电场脉冲进行了研究。研究结果表明:采用行波天线或者电长度与振荡器一致的振子天线作为辐射天线,都能够产生中心频率与振荡器本征频率一致的电磁脉冲信号;但采用振子天线时,振荡信号持续时间较短(Q值较低),频谱上能量较分散,带宽较宽,而采用行波天线则脉冲持续时间较长(Q值较高),频谱上能量较集中,带宽较窄。     

气流动态特征管内迁移研究

空调环境的动态化是对传统空调的改进,而送风动态化是实现空调环境动态化的一个途径。气流紊动特性是影响建筑热环境和人体舒适性的重要因素之一。利用FLUENT软件对速度入口呈模拟自然风波动的气流在管道中的流动进行了模拟,选择k-ε模型求解,分析其动态特征的变化。分别为:湍流强度、速度概率分布偏斜度、频谱分布。计算结果表明了几种典型的送风管道管件出口处湍流强度、风速概率分布偏斜度、功率谱密度曲线的变化情况;人体敏感区域(0.01—1Hz)区间双对数功率谱密度曲线的负斜率增大。这种方法为管道入口的送风提供了参考依据。     

1.6μm相干激光测风雷达的速度标定研究

介绍了相干激光测风雷达系统中用转盘进行速度标定的方法,在实验室搭建了激光雷达速度标定装置。采用1.645μm种子注入单频脉冲激光器,在激光中心频率相对种子光移频量约62MHz、转盘直径300mm、转盘速度-47.12～47.12m/s可调、激光出射方向和转盘线速度方向夹角为36°时,采用相干探测的方法测出了多普勒频移并反演出了测量速度;数据处理过程中分别采用最大值频谱估计法和频谱对齐法计算多普勒频移和转盘速度。实验结果显示,频谱对齐法相对于最大值频谱估计法能够提高36.3%的测速精度,因此在激光雷达测风系统中采用频谱对齐法相对于常用的最大值频谱估计法测量的风速精度更高,这对提高相干激光雷达测风的风速精度提供了实验依据和参考标准,验证了频谱对齐法在激光雷达测风的数据处理中的可行性。     

送风与辐射组合末端供冷舒适性与均匀性研究

利用CFD仿真技术,对卧式明装风机盘管与辐射地板的空调末端组合进行了供冷模拟研究,分析了风机盘管送风状态、辐射末端表面温度等参数对室内温湿度环境、均匀度及舒适性的影响规律。模拟结果表明:送风与地板辐射末端组合在保证室内符合国家标准的舒适度要求时,能维持较好的热环境均匀度;送风风速不宜过大,否则会造成吹风感强烈;为防止结露和保证舒适性,送风相对湿度要低于70%;送风温度增加导致室内温度增加幅度较大,地板表面温度增加导致室内温度增加幅度较小,即室内温度对送风温度变化更加敏感;当地板表面温度增加时,室内温度和相对湿度的均匀性得到改善,舒适性提高,且结露风险大大降低,因此在满足舒适性要求的情况下,建议适当增加地板表面温度。     

基于统计方法的自然风风向预测模型

自然界中的风力机受变化风向的影响,探究偏航工况下风向的变化规律对风力机的影响意义重大。本文依据激光雷达测风系统实测自然风数据,对风向变化规律进行分析;依据马尔可夫链模型等理论对自然风况条件下的风向进行数学建模,构建了呼和浩特某地自然风风向变化的状态转移概率矩阵模型;基于该模型生成随机时间序列对其进行验证,从而预测当地短时间内的风向变化。该方法考虑了自然风风向的随机特性及时序特性,并通过与实测风向序列数据进行对比,为风向变化的相关研究提供参考。     

弯管缺陷形状与位置对超声导波传播特性影响*

基于超声数值模拟,研究椭圆形冲蚀缺陷的几何尺寸和位置与接收端超声波能量之间的关系。通过控制椭圆形冲蚀缺陷几何尺寸,研究缺陷在弯管θ= 0°且ψ= 20°位置处,不同几何尺寸的缺陷对接收端压电传感器(PZT)时域信号能量的影响。此外,为研究相同几何尺寸的椭圆形冲蚀缺陷位于弯管不同位置时,对接收端时域信号能量的影响,椭圆形冲蚀缺陷位于弯管以下位置：ψ= 20°且θ取值范围为0°~ 30°,每间隔2.5°取一个值;θ= 0°且ψ取值范围为15°~ 45°,每间隔2.5°取一个值。数值模拟结果表明：缺陷位于弯管θ= 0°且ψ= 20°位置处,随着缺陷面积增加,接收端上侧PZT时域信号能量减少;随着缺陷深度和缺陷深度与面积都增加的两种情况下,上侧PZT时域信号能量均出现先减小,当缺陷深度达到弯管厚度的75%(6 mm)时,上侧PZT时域信号能量再增加;相同几何尺寸的缺陷位于弯管θ= 0°,随着ψ增加,上侧PZT时域信号能量先减小后增加;相同几何尺寸的缺陷位于弯管ψ= 20°,随着θ增加,θ与 呈现出单调递增的关系。通过上述结果可知,椭圆形冲蚀缺陷的几何尺寸和位置与接收端时域信号能量之间存在相关性,基于此可通过能量变化实现对缺陷几何尺寸大小和位置的评估。     

室外风和加压送风综合驱动对防烟效果和烟气运动的影响

本文在相似原理基础上,开展1/3缩尺寸试验,通过改变室外风和加压送风量改变试验条件,研究了室外风和加压送风综合驱动对前室防烟效果和疏散走道烟气运动的影响。通过疏散走道烟气形态和前室门处烟气温度和气流速度等参数,定量分析了不同室外风条件下的临界送风量。试验结果表明,室外风增大时,烟气紊乱程度增大,临界送风量增大,当室外风为4.0 m/s时,烟气层完全紊乱,单独使用加压送风不能满足有效防烟。通过疏散走道各测点的烟气温度,分析了室外风和加压送风对烟气层高度和烟气温度的影响。试验结果表明,当加压送风量一定时,室外风增大会导致烟气层高度下降和烟气温度升高。当室外风一定时,送风量增大会导致烟气层高度升高,但当送风量大于前室5000 m~3/h、楼梯间10000 m~3/h时,加压送风会导致前室门附近烟气层高度下降;送风量越大,烟气温度越低。     

低温送风空调系统的经济性分析

低温送风空调由于其在经济上优势,与蓄冷技术结合成为暖通空调领域的研究热点。从室内设计参数、送风温度、风机水泵的能耗和末端装置等方面探讨了对空调系统经济性的影响,并通过工程实例验证了低温送风技术的经济性优势。     

四程放大激光系统输出能量稳定性研究

 根据原型装置主放大系统组合式四程放大结构的特点,计算分析了放大过程中注入能量、放大增益及损耗的微小起伏对系统输出能量稳定性的影响。根据原型装置集成实验结果,分析了目前原型装置单路输出能量稳定性水平。研究结果表明：注入能量越大,其变化对输出能量影响越小;小信号增益系数对输出能量的影响明显大于注入能量;系统输出能量稳定性对腔内光学元件的透过率变化要求高于腔外光学元件。在3 ns基频光输出达标点处要使输出能量不稳定性控制在5%以内,注入能量起伏要低于10%,腔内放大片小信号增益系数起伏要低于1%,腔内光学系统损耗起伏要低于2%。     

开关振荡器特性阻抗选取对输出波形影响

开关振荡器是宽带高功率电磁脉冲的重要产生方式之一,以开关激励同轴振荡器为例,采用理论计算和电磁仿真为主要手段,从传输线特性阻抗与开关振荡器储能、传输线特性阻抗与天线阻抗关系及传输线特性阻抗和开关导通阻抗关系三个方面进行了研究。研究结果表明:传输线阻抗越小,振荡器储能越高;天线阻抗与传输线阻抗比值越大,输出信号品质因数越大,频谱上能量越集中,带宽越小,能量效率随比值增大呈现先增大后减小趋势;传输线特性阻抗很小时,开关阻抗对输出振荡信号影响增大,此时随特性阻抗减小,输出信号中心频率降低,品质因数减小,频谱上能量分散,带宽较宽。     

影响风机盘管换热器传热性能的因素分析

从设计和生产工艺两方面阐述了影响风机盘管换热器传热性能的主要因素,针对风机盘管机组在运行中换热器的常见问题,分析原因并提出了相应的解决措施。     

结霜工况风量对风冷热泵性能影响的研究

针对一台名义制冷量为50kW的风冷热泵冷热水机组,实验研究了迎面空气流量变化对机组结霜工况性能的影响。实验结果表明,结霜条件下,迎面空气流量降低促使机组工作性能大幅降低;迎面空气流量的变化对V型换热器表面霜层分布没有影响。空气流量的降低只是造成换热器表面结霜量的增多,适当提高风机转速具有抑制结霜、有效提高机组运行性能的作用;来流风速的不均匀分布对结霜以及霜层的分布有重要影响。     

Improvement of ventilation flow inside a large factory building using PIV velocity field measurements

Air movement in workplaces, whether resulting from a forced ventilation system or natural airflow, has a significant impact on occupational health. In a huge building of shipbuilding factory, typical harmful factors such as fume or vaporized gas from welding and cutting of steel plates give an unpleasant feeling. From field data survey, the yearly dominant wind directions around the factory building tested were north-west, north-east and south-east. Among the three wind directions, the ventilation improvement was the worst for the north-eastern wind. This study was focused on modification of opening vents in order to utilize the natural ventilation flow effectively. Instantaneous velocity fields inside the 1/1000 scale-down factory building model were measured using a 2-frame cross-correlation PIV method. The factory model was embedded in an atmospheric boundary layer simulated in a wind tunnel. The modified vents improved the internal ventilation flow with increasing the flow speed more than two times, compared with that of present vents.     

Positive and negative sawtooth signals applied to a DBD plasma actuator – influence on the electric wind

The influence of the electric signal shape applied to a surface dielectric barrier discharge (DBD) actuator is investigated in order to optimise the produced electric wind. This report also gives insights on the mechanisms involved in the electro-fluido-dynamic (EFD) operated by actuators based on atmospheric non-thermal discharges in air. The parameters of the electric signal that maximises the produced electric wind in quiescent air are investigated with a positive and negative sawtooth waveforms. The induced airflow properties are observed with a particle image velocimetry (PIV) set-up. The positive sawtooth waveform results in a more filamentary discharge and generates an electric wind with maximum velocities close to the active air exposed electrode. This contrasts with the negative sawtooth waveform that does not create as many filaments and induces electric wind velocities more homogeneously distributed along the dielectric surface. Even though the velocities values are of the same order, the shape of the vortex generated above the air exposed electrode is very dependant on the waveform.     

Aerodynamic vibrations of a maglev vehicle running on flexible guideways under oncoming wind actions

This paper intends to present a computational framework of aerodynamic analysis for a maglev (magnetically levitated) vehicle traveling over flexible guideways under oncoming wind loads. The guideway unit is simulated as a series of simple beams with identical span and the maglev vehicle as a rigid car body supported by levitation forces. To carry out the interaction dynamics of maglev vehicle/guideway system, this study adopts an onboard PID (proportional-integral-derivative) controller based on Ziegler-Nicholas (Z-N) method to control the levitation forces. Interaction of wind with high-speed train is a complicated situation arising from unsteady airflow around the train. In this study, the oncoming wind loads acting on the running maglev vehicle are generated in temporal/spatial domain using digital simulation techniques that can account for the moving effect of vehicle's speed and the spatial correlation of stochastic airflow velocity field. Considering the motion-dependent nature of levitation forces and the non-conservative characteristics of turbulent airflows, an iterative approach is used to compute the interaction response of the maglev vehicle/guideway coupling system under wind actions. For the purpose of numerical simulation, this paper employs Galerkin's method to convert the governing equations containing a maglev vehicle into a set of differential equations in generalized systems, and then solve the two sets of differential equations using an iterative approach with the Newmark method. From the present investigation, the aerodynamic forces may result in a significant amplification on acceleration amplitude of the running maglev vehicle at higher speeds. For this problem, a PID+LQR (linear quadratic regulator) controller is proposed to reduce the vehicle's acceleration response for the ride comfort of passengers.     

基于NI CompactRIO的晶闸管电源同步信号处理系统

HL-2A装置使用脉冲发电机组为装置极向场晶闸管电源供电以驱动线圈负载,晶闸管电源采用相控控制,因此同步信号的质量将直接影响电源的控制精度。HL-2A装置晶闸管电源同步信号取自同步变压器,脉冲发电机组带整流负载的供电方式使得同步信号不仅存在严重的波形畸变,同时还存在同步信号频率在大范围快速变化的特点。根据HL-2A装置晶闸管电源同步信号的特点,采用逐点巴特沃斯滤波器消除波形畸变,并通过实时频率计算和相位重建获得高质量同步信号。基于NI CompactRIO平台设计了晶闸管相控电源同步信号实时处理系统,实验结果表明该系统可有效解决同步信号畸变严重和频率宽范围快速变化的问题。     

高速气流对C/SiC复合材料激光烧蚀行为影响的实验研究

为了明确高速气流对C/SiC复合材料激光烧蚀行为的影响机制,开展了不同环境下强激光对C/SiC复合材料的烧蚀对比实验研究。利用激光器与高速风洞联合实验平台,完成了静态以及Ma 1.8,Ma 3.0,Ma 6.0气流环境下2D与3DN C/SiC复合材料激光烧蚀实验。结果表明,与静态环境相比,高速气流对C/SiC复合材料的激光烧蚀行为产生了显著的影响,气流的冲刷使得烧蚀坑呈现出更宽、更深、更光滑的变化趋势。随着气流速度的增长,线烧蚀速率与质量烧蚀速率逐渐增大,主要原因为当地静压降低引起的升华速率增大,以及动压增大引起的剥蚀速率增大。此外,通过实验对比了不同构型对C/SiC激光烧蚀行为的影响。结果表明：2D C/SiC复合材料由于厚度方向更低的导热能力、更低的孔隙率等原因,其在不同环境条件下抗烧蚀能力均强于3DN C/SiC复合材料。     

Shaping function models of the phonatory excitation signal

The phonatory excitation signal is the acoustic signal that is generated at the glottis by the vibrating vocal folds and pulsatile airflow. A shaping function model is a nonlinear memoryless input-output characteristic that transforms a simple harmonic into the desired output. The model can be fitted linearly to observed or simulated template cycles. The instantaneous values of the excitation cycle centroid, amplitude as well as length, and the cues for phonatory identity are set via distinct parameters. The synthetic phonatory excitation signal is zero on average, as well as identically zero when the glottal airflow rate is constant.     

Primary Break‐up of a Viscous Liquid Jet in a Cross Airflow

This article presents an experimental study of the primary break‐up of a viscous liquid jet interacting with a cross airflow. This experiment was carried out in an open circuit wind tunnel. The measurement test section was made of clear acrylic resin to allow optical access for visualizing and imaging the jet break‐up in the cross airflow. The working liquid used in the present experiment was the aero‐engine lubrication oil, which was injected at 90° into the airflow, via a nozzle from the top wall of the test‐section. The effects of liquid viscosity, and the jet and cross airflow velocities on the primary break‐up mechanisms of the jet were studied. The main results showed that different break‐up regimes were identified; column break‐up and bag break‐up separated by a transition zone, and new correlations have been proposed for predicting the jet transverse and streamwise penetrations before break‐up.     

基于自动跟踪LED驱动电压控制电路的创新设计

LED发光二极管在发光时约有80%以上的功率转化成了热能,导致LED发光二极管的PN结温度过高,这是影响LED发光二极管的发光效率与照明功能的主要因素。本文针对上述问题,结合现实情况,设计了一种自动跟踪LED驱动电压的控制电路,从串联稳流单元采样一个电压信号,与本控制电路中的基准电压相比较,产生一个控制信号,去控制所述串联稳流单元前级的开关稳压电源,使它的输出电压随LED灯的工作电压的变化而变化,不增加调整管的功耗。避免了常见的恒压驱动亮度变化大的缺陷,从而大幅度提高LED发光二极管的工作效率,该控制电路结构简单、成本低、损耗小与可靠性高。