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《工程热物理学报》2020,(8)
根据光线透过盐水溶液产生衰减原理,利用流场内密度与光照强度的对比关系,提出通过图像灰度确定流场内密度分布特征的测试方法。采用这种实验方法,结合单一点源羽流条件下卷吸作用,模拟由热压产生的置换流动和混合流动。对于无热源的置换流动实验,当出口面积保持在5.1 cm~2时,进口面积由28.9 cm2增加到52.7 cm~2并不会显著增加体积流量。这表明对于置换通风,当进出口面积相差较大时,流量由进出口中较小的面积开口确定。对于有热源条件下置换流动,随着有效开口面积增加,热分层高度增加,且上部分层高度内的密度降低。实验数据显示,卷吸系数α取0.13时理论预测与实验结果一致。在有固定热羽流条件下进行了混合流动实验,确定流量修正系数ε等于2.21,该系数与开口大小和盐水密度无关,反映固定浮力通量与变浮力通量条件下通过开口流量的比值。通过理论分析和实验结果对比,证明了利用光学衰减原理确定盐水浓度的方法是一种有效的实验测试方法。 相似文献
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序列图像中运动目标的自动提取方法 总被引:2,自引:2,他引:0
针对目标检测与跟踪领域中的运动目标自动提取问题,提出了一种新的运动目标自动提取方法.利用已有的图像帧滤波后初始化背景,并在运动目标检测过程中,利用检测结果,不断地自动更新背景.使用背景差法检测运动区域,并对差分图像进行动态阈值分割,以及边缘链接,使其边缘处于基本连续状态.在得到的二值图上,提取轮廓,并根据目标大小选择面积阈值,剔除由于噪音或者背景提取不干净造成的虚假轮廓,将得到的轮廓掩模图像与原图像做逻辑与运算,提取出目标.实验结果表明,该方法可以有效地提取出刚体或非刚体运动目标. 相似文献
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为了实现视频序列图像中运动人体肢体的检测,提出了一种基于积分图像和类哈尔特征的检测方法,类哈尔特征(Haar like feature)因其固有的特点,适用于检测矩形或类矩形的图像区域,积分图像的特点是可以利用类哈尔特征快速定位人体肢体在图像中的位置。积分图像用于表示视频中的原始图像,边缘检测模板与原始视频每一帧进行卷积之后,通过累加计算可以得到该图像的积分图像,然后利用类哈尔算子,根据设定的阈值,即可以准确定位人体肢体位置。实验结果表明:该方法较背景减除法检测人体肢体准确。 相似文献
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提出了一种基于红外图像的建筑物墙体空鼓检测方法,不但可以远距离、无损地对建筑物空鼓等缺陷进行定性检测,还能对建筑物热工缺陷进行定量分析;采用一种红外图像处理方法来消除墙体温度分布中梯度干扰的影响;通过自适应地调整参数对红外图像进行图像增强处理,有效地排除了环境干扰;通过基于空鼓缺陷边缘轮廓的连通域计算,可直接得到空鼓面积的大小数据;建筑物缺陷现场检测实验结果表明,提出的检测方法既能快速定位出建筑物空鼓等缺陷位置又能以78.3%的精度检测出空鼓面积大小,具有较高的工程应用性。 相似文献
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利用图像的非接触检测螺纹是一种高效的检测方法。检测中,精准的获取到螺纹图像的牙型边界是检测的关键,而现有的图像处理技术并不能消除由于螺纹旋线对螺纹图像的影响。针对螺纹图像中牙型边界被遮挡的问题,从圆锥螺纹的几何空间关系分析图像产生误差的原因,建立圆锥螺纹数学模型,得到误差的方程。最后再设计了图像检测系统,根据误差方程修正螺纹图像、提取参数,经验证,此方法可以提高螺纹的检测精度,且通用在圆锥螺纹与圆柱螺纹中。 相似文献
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Pressure reducing valves are widely used to maintain the pressure of gas reservoirs to specific values. In a normal valve,
supply pressure is decompressed with an orifice structure. When compressed air passes through the orifice structure, considerable
noise occurs at the downstream side. In this paper, we have developed a radial slit structure that can reduce pressure without
noise. The noise is reduced by changing the orifice structure into the radial slit structure. The radial slit structure valve
reduces pressure without noise by suppressing the generation of turbulence and shock wave at the downstream. The analysis
of the flow in radial slit structure was achieved by CFD2000 software. The flow rate and pressure distribution were simulated
and compared with the experimental result. To confirm the generation of shock wave, the flow of orifice and radial slit structure
at the downstream was visualized by Schlieren photography method. A shock wave was generated in the orifice structure, but
no shock wave was generated in the radial slit structure. Noise reduction efficiency was investigated by the experiment. The
experiment apparatus was set up to JIS standards. The experimental results indicated that the noise level decreased by approximately
40 dB in the slit structure. It is confirmed that the radial slit structure has effectiveness for low noise in the pressure
reducing flow. And, it is expected that it can be applied to various kinds of industrial fields. 相似文献
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K.A. El-Shorbagy 《Applied Acoustics》1983,16(3):169-181
Flow control valve noise has been investigated, both analytically and experimentally, for two cases of variable orifice area and variable mass flow rate. The analysis is based on Lighthill's acoustic analogy, together with Curle's theory for noise generation from fluid-solid boundary interactions. Results indicate that monitoring sound levels of valve noise could be useful as a feasible means for flow rate measurements and on-line automatic flow control in pipes. 相似文献
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The use of the mechanical energy (ME) equation for fluid flow, an extension of the Bernoulli equation, to predict the aerodynamic loading on a two-dimensional finite element vocal fold model is examined. Three steady, one-dimensional ME flow models, incorporating different methods of flow separation point prediction, were compared. For two models, determination of the flow separation point was based on fixed ratios of the glottal area at separation to the minimum glottal area; for the third model, the separation point determination was based on fluid mechanics boundary layer theory. Results of flow rate, separation point, and intraglottal pressure distribution were compared with those of an unsteady, two-dimensional, finite element Navier-Stokes model. Cases were considered with a rigid glottal profile as well as with a vibrating vocal fold. For small glottal widths, the three ME flow models yielded good predictions of flow rate and intraglottal pressure distribution, but poor predictions of separation location. For larger orifice widths, the ME models were poor predictors of flow rate and intraglottal pressure, but they satisfactorily predicted separation location. For the vibrating vocal fold case, all models resulted in similar predictions of mean intraglottal pressure, maximum orifice area, and vibration frequency, but vastly different predictions of separation location and maximum flow rate. 相似文献
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Experimental verification of the quasi-steady approximation for aerodynamic sound generation by pulsating jets in tubes 总被引:3,自引:0,他引:3
Zhang Z Mongeau L Frankel SH 《The Journal of the Acoustical Society of America》2002,112(4):1652-1663
Voice production involves sound generation by a confined jet flow through an orifice (the glottis) with a time-varying area. Predictive models of speech production are usually based on the so-called quasi-steady approximation. The flow rate through the time-varying orifice is assumed to be the same as a sequence of steady flows through stationary orifices for wall geometries and flow boundary conditions that instantaneously match those of the dynamic, nonstationary problem. Either the flow rate or the pressure drop can then be used to calculate the radiated sound using conventional acoustic radiation models. The quasi-steady approximation allows complex unsteady flows to be modeled as steady flows, which is more cost effective. It has been verified for pulsating open jet flows. The quasi-steady approximation, however, has not yet been rigorously validated for the full range of flows encountered in voice production. To further investigate the range of validity of the quasi-steady approximation for voice production applications, a dynamic mechanical model of the larynx was designed and built. The model dimensions approximated those of human vocal folds. Airflow was supplied by a pressurized, quiet air storage facility and modulated by a driven rubber orifice. The acoustic pressure of waves radiated upstream and downstream of the orifice was measured, along with the orifice area and other time-averaged flow variables. Calculated and measured radiated acoustic pressures were compared. A good agreement was obtained over a range of operating frequencies, flow rates, and orifice shapes, confirming the validity of the quasi-steady approximation for a class of relevant pulsating jet flows. 相似文献
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The purpose of this study was to develop an analysis system for studying the relationship between vocal fold vibration and the associated transglottal airflow. Recordings of airflow, electroglottography (EGG), oral air pressure, and acoustic signals were performed simultaneously with high-speed imaging at a rate of approximately 1900 frames/s. Inverse filtered airflow is compared with the simultaneous glottal area extracted from the high-speed image sequence. The accuracy of the synchronization between the camera images and the foot pedal synchronization pulse was examined, showing that potential synchronization errors increase with time distance to the synchronization pulse. Therefore, analysis was limited to material near the synchronization pulse. Results corroborate previous predictions that air flow lags behind area, but also they reveal that relationships between these two entities may be complex and apparently varying with phonation mode. 相似文献
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G. Benedek P. Nieto J. P. Toennies 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(2):237-249
The mechanism behind the intensity oscillations accompanying the flow of
solid helium through a micron-sized orifice into vacuum, called the geyser
effect, is investigated by measuring the pressure pulses at various
locations in the entire flow system. The new results reveal that the source
chamber pressure pulses have the same shape as the external detector pulses
monitored in the previous experiments [G. Benedek et al., Phys. Rev. Lett.
95, 095301 (2005)]. New experiments in which the external gas
reservoir is isolated from the pressure regulator provide direct information
on the mechanism of the collapse leading to the geyser pulses. Thus each
geyser pulse is triggered by the breakdown of a plug located upstream of the
source chamber. The flow of liquid through the orifice determines the shape
of the subsequent geyser pulse. 相似文献
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一台可工作在双向进气模式和小孔模式下的单级脉管制冷机,当双向进气方式采用并联双阀双向进气时,最低制冷温度为19.3K,50K以下的制冷量变化约为2W/K;当双向进气阀门关闭时,制冷机就工作在小孔模式下,最近的研究工作发现,当制冷机工作在小孔模式下时出现了一个新的现象-脉管冷端温度存在温度回路,该特点与脉管冷端的热负荷及小孔开度的调节方法有关,该现象的发现对于理解双向进气模式下温度不稳定问题提供了一个新的思路。 相似文献
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ACTIVE IMPACT CONTROL SYSTEM DESIGN WITH A HYDRAULIC DAMPER 总被引:1,自引:0,他引:1
We propose a new active impact control (or absorber) system that is able to respond to a highly rapid impact and a large flow rate. The system has advantage over a passive system regarding a feasible pressure and displacement regulation. The impact control system constructs both internal and external dampers, that is its orifice is placed inside and outside the hydraulic cylinder. The designed system has a set of logic valves, which respond rapidly to an external impact and are capable of discharging an instant excessive hydraulic flow, and a servo valve to control the pilot chamber of the logic valve. The impact control system is designed and fabricated based on an appropriate mathematical modelling and its dynamic analysis, and on various control performances. The control performance is verified by simulations and experiments. 相似文献