气体波动引起的弯曲流道气波机振荡管结构动态响应研究

弯曲流道气波制冷机内气体波动引起的振动行为复杂，而二维数值计算不能对其进行真实的模拟，且实验过程中难以采集气波机的振动信号。为了解决以上问题，对弯曲流道振荡管结构动态响应进行了研究。首先，基于流固耦合数值模拟方法，开发了双开口弯曲流道气波机波转子三维非定常流体流动模型，并对模型进行了可靠性验证；然后，采用傅里叶变换技术提取了振荡管内不规则压力激励载荷，分析了非定常流体激励载荷时域和频域分布规律；最后，分析了波动压力下振荡管结构的动态位移场和应力场，计算了气波机波转子系统固有频率，与相同参数下的直流道振荡管进行了对比。研究结果表明：相对于直流道振荡管，弯曲流道气波机振荡管的最大振幅增加了1.74倍，不利于结构安全运行，但幅值在10^-2 mm以下，满足工程设计要求；虽然，振荡管插片振动频率与流激力载荷频率相近，但远离波转子结构的固有频率，因此不会引发结构共振和激烈的强迫振动，能够确保气波机安全平稳地运行。     

Z形折叠薄膜充气管充气展开过程仿真

展开过程仿真是评估空间充气折叠结构展开力学行为的重要工具,仿真结果可以进一步指导折叠方案和展开构型的设计改进。笔者基于控制体积法和有限元法,建立了多次Z形折叠充气管的有限元模型,阐明了折叠管充气展开仿真计算的基本原理和建模处理方法。通过对比研究不同充气速率条件下充气管在展开过程中各参数的动态变化规律,表明充气速率是影响Z形折叠充气管展开性能中至关重要的因素。充气速率越快,展开越快捷。但充气速率过高,展开过程对母体的扰动力也越大,并且带来展开后期管体自身的严重振荡。适当选择充气速率,可以有效降低扰动载荷峰值,并且有利于展开后期管体自身振荡的迅速衰减。适当增加充气管薄膜的厚度,虽然增加了对母体的扰动力,但可以有效降低管体展开后期的振荡速度。     

基于经验模态分解的电力系统机电振荡模式识别方法研究

当前机电振荡模式识别多采用粒子滤波算法，此方法易受到信号高频成分波动影响，导致识别准确性较低。为此，提出了基于经验模态分解的电力系统机电振荡模式识别方法。该方法对原始振荡信号进行去噪处理，还原真实信号，采用经验模态分解算法分解信号，并提取振荡参数，通过设计阈值门限准则，抑制高频波动，以此为依据，计算求取不同振荡模式下的状态参数，由此实现机电振荡模式的识别。对比实验结果表明，在电力系统机电振荡模式识别中，该方法具有更高的识别准确性。     

谈谈高频感应加热设备的使用与维护(下)

三、正确选择振荡管的“阻抗匹配”所谓“阻抗匹配”(匹配即相等的意思),就是说:在工作中要使负载(即被加热的工件)阻抗,近似相等干振荡管的等效匹配电阻(振荡管的内阻,在工作时不是常数,但存在着一个等效的匹配电阻),使负载能获得最     

沟道超精研机振荡机构的优化设计

振荡机构设计是否合理，对超精研机的使用性能至关重要，也是超精研机设计的重点和难点之一。介绍了利用机械优化设计方法对沟道超精研机振荡机构的优化设计方法。附图2幅，表2个。     

振荡管式密度计测量精度的影响因素分析

原油及不透明样品中存在的气泡对振荡管式密度计的测试结果有较大影响。本研究通过对比试验,分析了气泡位置、样品密度、气泡体积3个因素对测量结果影响的原因。结果表明:振荡管存在测量敏感区,气泡越靠近敏感区测量偏差越大,样品密度越大气泡导致的测量偏差越大,在振荡管样品进出口区域气泡体积对测量结果的偏差影响不大。     

新能源电力系统多模态振荡识别技术研究

在新能源电力系统振荡识别过程中，通常采用经验模态分解方法实现电力系统量测信号分解，但极易出现模式混叠的情况，导致多模态振荡识别的频率误差较大。因此，针对新能源电力系统，设计了一种新型多模态振荡识别技术。依托于多元经验模态分解策略，协同分解多通道电力系统量测信号，得到不同频率尺度的IMF（固有模态函数）分量。再计算每个IMF分量的能量权重，从中筛选出包含主导振荡模式的关键分量。运用Prony算法对关键IMF分量进行分析，得出振荡特征参数，基于此得出电力系统多模态振荡识别结果。实验结果表明，所提识别技术应用后可以得到较为准确的振荡特征参数，其中频率最大误差仅为1.8×10-3Hz。     

砂带的张紧与振荡

砂带的张紧与振荡是砂带磨床设计与调整的重要环节之一，尤其是砂带的振荡原理及结构，在世界各国都是作为专利加以保护的。由此可见，砂带的振荡在砂带磨床的设计和使用中所占的重要地位。当然，在砂带磨削的范筹内，既有不需张紧、也有不需振荡的。例如，意大利生产的皮革砂光机，它是将破带直接缠绕在磨辊上的，就无需张紧。又如，螺旋卷式，叶轮式，砂片式等破带制成工具，都不需张紧。不需要振荡机构的砂带机械工具就更多了，例如，手提式破带抛磨工具和破带宽度＜30Omm的破带磨床，一般都不设置振荡装置。如新乡机床厂生产的2MJ5810…     

电气自动控制中振荡现象

介绍了在设计控制电路中经常出现的振荡现象，并给出了解决方法。     

用大功率分米波振荡管替换ICP—AES中的射频大功率管

本文介绍用国产大功率分米波振荡管替换PLASMA-300型电感耦合等离子体发射光谱仪中射频大功率管的经验。     

The study on pressure oscillation and heat transfer characteristics of oscillating capillary tube heat pipe

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40 vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90°. the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.     

微型制冷机连杆轴承温度场分析

以某高速摆动工况下应用的微型制冷机连杆轴承为研究对象,对其进行受力分析,计算轴承的接触变形、载荷分布、摩擦力矩,并基于ABAQUS建立高速摆动工况下连杆-轴承摆动系统温度场模型,分析径向载荷、摆动频率及摆动角度对轴承最高温度的影响,结果表明:随径向载荷、摆动频率、摆动角度增大,轴承最高温度增大,与摆动系统试验台验证结果...     

Nanometer-scale layer modification of polycarbonate surface by scratching with tip oscillation using an atomic force microscope

This paper presents a simple and reliable technique for nanometer-scale layer modification of a polycarbonate (PC) surface using an atomic force microscope (AFM). The AFM tip, coated with amorphous carbon was made to oscillate vertically at its resonance frequency. With tip oscillating in tapping mode, it scan-scratched the PC surface to make the desired modification. This action carved the PC surface without distorting it. The bottom of the depression made by scan-scratching with the oscillating tip was obviously flat in comparison with the area scan-scratched without tip oscillation in contact mode. The depth of the scan-scratched depression was controlled by adjusting the amplitude of oscillation and the scanning speed of scratching. This technique is very interesting for microtribology and surface modification.     

S826叶型的非定场气动力特性的数值研究

利用自行开发的二维非定常Euler方程的求解程序模拟S826叶型的外部非定常绕流,分别研究了在俯仰振动、平振以及俯仰与平振耦合的情况下叶型的气动特性.研究表明,随着折合频率,振幅值的增大,迟滞效应增强;平振与俯仰振动耦合时,当-90°≤φ≤90°时,气动力是激振力;当90°＜φ＜270°时,气动力为阻尼力.     

An oscillating cryo-knife reduces cutting-induced deformation of vitreous ultrathin sections

A new oscillating cryo‐knife for producing uncompressed vitreous sections is introduced. The knife is a modified cryo diamond knife that is driven by a piezo translator. Optimal setting for the oscillation was found to be in the inaudible frequency range of 20–25 kHz. Yeast cells and polystyrene spheres were used as model systems to describe compression in the vitreous sections. We found that compression could be reduced by a factor of about 2 when the knife was oscillating. When the oscillator was turned off, sections were compressed by 40–45%. However, only 15–25% compression was obtained when the knife was oscillating. In some cases completely uncompressed sections of yeast cells were produced. It was also found that the amount of compression depends on the specimen itself and on its embedding medium. With the results shown here, we demonstrate that the oscillating knife can produce high‐quality vitreous sections with minimum cutting artefacts.     

Flow visualization of oscillation characteristics of liquid and vapor flow in the oscillating capillary tube heat pipe

The two-phase How patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the How pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R-I42b was achieved.     

Fast scanning of a pulsed terahertz signal using an oscillating optical delay line

We describe a fast measurement of a pulsed terahertz signal generated by a femtosecond laser and a photoconductive antenna using an oscillating optical delay line. The method to measure the amplitude of the retroreflector in the oscillating optical delay line is proposed and the displacement of the retroreflector is exactly calculated to acquire the optical delay time in the fast scan mode. With the different oscillation frequency and amplitude of the retroreflector, the pulsed terahertz signals are measured and analyzed. The comparison of the temporal waveform and frequency spectrum between the fast scan mode and the slow scan mode shows a good agreement with the decrease in the scanning time from 60 to 1 s at a signal to noise ratio of 430.     

Vibration of a hydrostatic gas bearing due to supply pressure oscillations

The vibration of a statically loaded, inherently compensated hydrostatic journal bearing due to oscillating supply pressure is investigated. Both angular and radial vibration modes are analyzed. The time-dependent Reynolds equation governing the pressure distribution between the oscillating journal and the sleeve is solved numerically together with the journal equation of motion to obtain the response characteristics of the bearing. The Reynolds equation and the equation of motion are simplified by applying regular perturbation theory for small displacements. The results presented include Bode plots of bearing oscillation gain and phase for a particular bearing configuration for various combinations of parameters over a range of frequencies, including the resonant frequency. The results are compared with the results of an earlier study involving the response of a similar bearing to oscillating exhaust pressure.     

A theoretical study on the acoustically driven oscillating flow around small spherical particles

In order to study the oscillating flow induced by a high intensity acoustic field, a computer code which employs the two-dimensional, unsteady mass and momentum conservation equations for laminar flow in spherical coordinates has been developed. The displacement amplitude of the incident sound wave is large compared to the characteristic length of particles, and the acoustic Reynolds number based on the particle diameter and the velocity amplitude of the oscillating flow is less than about 100. Numerical solutions of these equations give the velocity field, axial pressure gradient, shear stress and flow separation angle around the particle for acoustically oscillating flow as a function of acoustic Reynolds number and Strouhal number. The axial pressure gradient, shear stress and separation angle are proportional to the magnitude of oscillating flow at low frequency (～50Hz) and can be approximated by the quasi-steady analysis. The effects of flow oscillation increase with increasing frequency (～2000Hz) due to combined effects of curvature and flow acceleration, giving different values of axial pressure gradient, shear stress and separation angle for different frequencies of 500, 1000 and 2000 Hz.     

阀门用波纹管爆破压力的有限元分析

作为阀门外密封元件的波纹管是影响阀门外密封性能的关键部件,掌握工作状态下的应力状况非常重要.基于有限元方法建立了阀门用波纹管的爆破压力分析方法,同时采用有限元计算和试验相结合的方法.分析了波纹管的爆破压力.研究结果表明,波纹管的爆破压力值为61.4MPa,有限元计算结果为59.44 MPa,二者数值和位置都基本吻合.波...