静止式气波制冷机振荡特性的实验研究

静止式气波制冷机是依靠附壁射流的原理,籍着装在喷嘴两侧的振荡源的压力脉动改变方向,使高速射流依次间隔地射入各振荡管内,通过激波和膨胀波的运动产生制冷效应.因此,其制冷效率的高低在很大程度上取决于振荡特性的好坏,而且,通过研究振荡特性也可以进一步改进机器的结构.以控制管为振荡源对气波制冷机的振荡特性进行了详细的研究,结果表明,当振荡源为控制管时,一般来说,振荡频率仅与控制管管长有关;控制管适合于较低频率的场合使用;在同一射流作用下,在不同振荡管中产生的入射激波强度并不相同,最外侧两管内波的强度较弱,而中间管内波的强度高.     

静止式气波制冷机控制管内振荡特性的数值实验研究

静止式气波制冷机的性能主要取决于射流振荡,而射流振荡又取决于振荡源,因此,研究振荡源的振荡特性显得非常重要.以控制管为振荡源,在分析了控制管内流动特性的基础上,首先采用数值模拟的方法,分析了射流附壁切换与控制管内流动特性间的关系,结果表明,射流的切换与控制口处的流量变化几乎无关,而是由于两个控制口处的瞬时压力差造成的.对控制管内振荡特性的实验研究结果表明,控制管内实测频率、振荡管内实测频率与计算频率是一致的,当管长较长时,其只是控制管长的函数,且控制管内只有低幅压缩波和膨胀波运动.     

分流劈距对静止式气波制冷机性能影响的实验研究

分流劈距是静止式气波制冷机设计的一个重要参数.通过实验的方法研究了分流劈距对静止式气波制冷机性能的影响.当分流劈距较小时,射流发生了切换,当分流劈距较大时,射流未发生切换.振荡频率几乎不受分流劈距的影响,它只是振荡管长的函数.分流劈距的大小对制冷效率有直接的影响,随着分流劈距的增大制冷效率逐渐减小.对应不同的操作条件,分流劈距都有其最合理的值.     

冲击射流离散频率噪声的特性及机理

为探索冲击射流离散频率噪声的产生机理，系统地研究了冲击射流离散频率噪声的特性。发现对于给定的喷嘴和冲击距离，存在一个压比临界点，当压比高于此临界点值时，流场振荡和离散频率噪声被显著抑制乃至消失。解释了此压比临界值的机理：气流的出口膨胀阻遏了反馈声波对喷嘴唇口的激发，从而抑制了反馈环的形成。研究了射流倾斜冲击平板时反馈环以及相应的离散频率噪声，推测此压比临界点值与冲击距离、射流倾斜角度有关。实验表明：压比临界点值随冲击距离在一定范围内的增加而增高，随喷嘴偏离垂直角度增加而减低。     

一种射流振荡式微通道流量计的设计与仿真

以射流振荡技术为基础,设计了一种用于测量微通道内液体流量的射流振荡式流量计.通过对微通道射流流量计结构模型的FLUENT数值仿真,研究流体流动过程的振荡特性及振荡原理,进而优化结构参数,建立微通道内液体流速与振荡频率的特性关系.最终的仿真结果表明,射流振荡式流量计附壁稳定,切换灵敏,斯特劳哈尔数恒定,在一定程度上为微通道射流流量计的设计及优化提供了有效的途径.     

静止式气波制冷机出口结构模拟及实验研究

为进一步提高静止式气波制冷机效率及优化气体出口流场,通过数值模拟与实验结合的方法,比较分析了膨胀比分别为2和3时,单侧垂直、单侧前倾斜、双侧垂直和双侧前倾斜4种出口结构的气体泄漏率和气波管的制冷效率随射流频率的变化。模拟结果表明:膨胀比为2和3时,射气阶段不同出口结构的气体泄漏率随射流频率的增加呈现上下波动的变化趋势;气波管制冷效率随射流频率的增加呈现波动增加的变化规律,双侧前倾斜出口时气波管的制冷效率最高。以单管型气波机进行实验研究,对比之下能明显看出双侧前倾斜出口时气波管的制冷效率升高显著。     

气波制冷机振荡管外强化换热的试验研究

在膨胀比ε＝２～６范围内，对气波制冷机振荡管（接受管）外有、无翅片两种情况进行了比较性试验。结果表明：强化管外换热能显著提高振荡管的制冷效率，并对管内振荡流特性产生影响     

振荡管结构对气波制冷机制冷性能影响的研究

振荡管是入射气体与管内循环气进行能量交换的场所，是气波制冷机的一个重要组成部分。其结构形式的不同对管内流动产生很大的影响，进而影响气波制冷机的制冷性能。在分析了各种结构振荡管对气波制冷机性能的影响的基础上，着重分析了双开口振荡管的结构及制冷原理、管内的流动并通过实验研究了其对气波制冷机性能的影响。结果表明，采用双开口振荡管不仅能消除反射激波提高制冷效率，而且大大地优化了整机的结构，使体积仅为原来的十分之一左右。     

射流噪声测量中远场测量边界影响研究EI北大核心CSCD

射流噪声实验是射流噪声产生机理及降噪措施研究的最重要手段之一。为确保射流噪声远场测量数据可信,远场传声器的布置需在远场条件和最终数据的信噪比之间进行合理的选取。通过严格的射流噪声模拟装置,采用精细的声学测量及修正手段,系统的研究了射流噪声不同测量角度及位置、不同射流速度等因素对远场测量结果的影响规律,并对射流噪声频谱随距离的增加而变化的特性进行了机理分析。通过试验确定了射流噪声远场测量时的最小远场边界条件,对于不满足远场边界条件的远场噪声测量,给出了适当的修正的方法。     

气举用振荡脉冲射流破碎器的研究

本文着重研究了气举用振荡脉冲射流破碎器在淹没条件下的动态特性、冲蚀特性和现场试验情况。实验表明在淹没条件下振荡脉冲射流不仅具有强烈的动态脉动冲击特性，而且具有波动的径向流动（附壁流动）。在相同条件下振荡压力能破碎连续射流所不能破坏的土岩，而且能产生波动上举力；波动的径向流动使作用在破碎的土岩颗粒上的升力增大，使作用在土岩颗粒上的上举力大于压持力，导致土岩颗粒易于流动。在气举上使用脉冲射流喷嘴，其轴吸浓度稳定，提取的固液混合液浓度比采用连续射流喷嘴时的大。     

结晶器振动类型与特点分析

结晶器振动有几种类型，每种类型有其固有的优缺点。合理的正确使用相应的结构，能够降低投资，减少维修维护成本，进而提高经济效益。     

流动诱导空腔振荡频率方程的改进

研究了流动诱导空腔振荡的机理，并做了相应的实验。基于流动诱导空腔振荡的机理和小尺寸空腔(长深比L／D=4，2)的实验，对预测流动诱导空腔自由剪切层自激振荡模态的频率方程和声学模态的频率方程作了合理改进，实验结果表明，这一改进提高了流动诱导空腔剪切层自激振荡模态和声学模态的预测精度，并能用于工程计算。     

Measurement of the Effect of Thermal Noise on the Amplitude of Oscillation of a Maser Oscillator

Experimental verification of the effect of thermal noise on the oscillation amplitude of a maser is described. Two different masers are considered, the H maser with an homogeneous atomic line and the Rb maser with an inhomogeneous line. The effect is characterized by the spectral density of the relative amplitude fluctuations and this parameter is measured with a conventional superheterodyne AM receiver for various maser saturation factors. Experimental results show good agreement with theoretical predicted values. At high saturation factors, a peak appears with a maximum at a frequency close to the Rabi frequency. Observed values at high Fourier frequencies allow a measurement of the atomic power by the knowledge of the absolute temperature of the cavity and the prediction of the oscillator short-term frequency stability. Furthermore, the effect on amplitude and on frequency noise of an external feedback loop used to increase the cavity quality factor is discussed.     

机械振动对钎料润湿性的影响

钎料在钎焊金属上的润滑性在一定程度上表示它能否致密地填满钎缝的能力,本文 一套适于钎焊的机械振动系统,并测试了其传振性能,在此基础上初步研究了振地钎料润湿性的影响。     

Optimization of Mold Inverse Oscillation Control Parameters in Continuous Casting Process

This paper introduces an approach towards selection of optimum control parameters of mold oscillation in the continuous casting process. A new model was applied to optimize the control parameters of the inverse oscillation control model. Optimization was aimed at reducing the depth of oscillation marks and was performed within constraints imposed by process parameters that influence the quality and productivity of continuous casting. Optimization generated an optimum control parameter set that provided better performance than that offered by Baoshan Iron & Steel Co., Ltd., and was verified by testing results.     

Double-resonance quartz crystal oscillator and excitation of a resonator immersed in liquid media

In this work we propose a novel circuit design: a double-resonance oscillator. Its oscillation shows two oscillation modes: frequency locking to the quartz crystal resonance and LC resonance oscillation. Transition of the oscillation mode and the strength of oscillation are analyzed and reviewed for the fundamental mode in comparison with a Colpitts oscillator. The experimental results support the estimates of negative resistance for the double-resonance oscillator compared with the LC oscillator.     

Surface Oscillation of a Liquid Bridge Induced by Single and Multiple Vibrations

A three dimensional numerical model has been developed based on a level set algorithm to predict the surface oscillation behavior of a liquid bridge induced by single and multiple vibrations under space environment. By subjecting the liquid bridge to single lateral vibration, the surface resonance characteristics have been predicted numerically. Moreover, the controlling mechanism of the surface oscillation under multiple vibrations is also determined, and the results show the external vibrations at resonance frequency in lateral direction completely control the surface oscillation in horizontal direction.     

The new design of AGC circuit for the sinusoidal oscillator with wide oscillation frequency range

The typical automatic gain control (AGC) schemes are not suitable for the sinusoidal oscillator with wide oscillation frequency range. To solve this problem, the up-down counter, multiplying digital-to-analog converter, and high-speed comparators are employed to achieve the proposed AGC circuit, which corrects the complex roots of the overall system automatically to the imaginary axis of the complex frequency plane. The negative feedback technique with digital hardware is applied on the loop gain control. No low-pass filter is needed to detect the oscillation amplitude. Thus, this technique is suitable for the sinusoidal oscillator with wide oscillation frequency range. The oscillation frequencies ranging from 7 Hz to 1 MHz are tested with the proposed AGC circuit. The experimental results demonstrate the static characteristics and dynamic responses of the overall system.