AN ANALYTICAL INVESTIGATION OF THE DIRECT MEASUREMENT METHOD OF ESTIMATING THE ACOUSTIC IMPEDANCE OF A TIME-VARYING SOURCE

This paper presents an analytical investigation of the direct method of measurement of the source impedance of a linear time-variant source. The direct method yields a frequency-dependent effective source impedance which is routinely used in a time-invariant analysis to determine the insertion loss of two different acoustic loads applied to the same source. In such an analysis the strength of the source is assumed to be invariant with load. It is shown here that there is generally no precise correspondence between the effective source impedance as given by the direct method and the characteristics of the actual source. Furthermore, it is shown that the effective source impedance values given by the direct method are functions of the acoustic load and the location of the injected signal as used in the measurement. However, the effective source resistance is always found to be positive, in accordance with experimental measurements. In this regard the direct method is an improvement on the indirect method, where physically implausible negative resistance values are often found. Finally, it is shown that the effective impedance values as given by the direct method when used with a time-invariant analysis give rise to very accurate predictions of insertion loss, even when the strength of the actual time-variant source is allowed to vary with the acoustic load.     

On the selection of loads in the multiload method for measuring the acoustic source parameters of duct systems

The in-duct source can be characterized by two acoustical parameters such as the source strength and the source impedance, which permit the prediction of radiated sound pressure or insertion loss of the whole duct system. One-port acoustic characteristics of an in-duct source can be measured by the multiload method using an overdetermined set of open pipes or side-branch pipes with different lengths as applied loads. The input data, viz. load pressure and load impedance, are usually contaminated by measurement error in the actual measurements, which result in errors in the calculated source parameters. In this paper, the effects of the errors in the input data on the results have been studied numerically, varying the number of loads and their impedances in order to determine what combination of the loads will yield the best result. It is noted that, frequently, only a set of open pipes is used when applying the multiload method to the internal combustion engine sources. A set of pipe lengths, which cause the calculated results to be least sensitive to the input data error, can be found when using open pipe loads. The present work is intended to produce guidelines for preparing an appropriate load set in order to obtain accurate source properties of fluid machines.     

On the causes of negative source impedance in the measurement of intake and exhaust noise sources

In order to evaluate the acoustic field within a duct system some knowledge is required about the acoustic source, which is characterized by frequency-dependent values of both strength and impedance. However, in using various experimental techniques for various types of source to obtain these values, negative real parts of the source impedance have been measured. Negative source resistance is physically implausible. In some instances, one measurement method gives positive values of source resistance where another gives negative values. This paper reviews the possible causes of the problem, with reference to experimental and theoretical results, in an attempt to clarify the issue. Various possible origins of a negative source resistance have been investigated. It is noted that, for the time being, the violation of the assumption of a time-invariant source and the defect in the inherent algorithm of the load method are the most probable origins of the negative source resistance.     

Out-of-equilibrium admittance of single electron box under strong Coulomb blockade

We study admittance and energy dissipation in an out-of-equilibrium single electron box. The system consists of a small metallic island coupled to a massive reservoir via single tunneling junction. The potential of electrons in the island is controlled by an additional gate electrode. The energy dissipation is caused by an AC gate voltage. The case of a strong Coulomb blockade is considered. We focus on the regime when electron coherence can be neglected but quantum fluctuations of charge are strong due to Coulomb interaction. We obtain the admittance under the specified conditions. It turns out that the energy dissipation rate can be expressed via charge relaxation resistance and renormalized gate capacitance even out of equilibrium. We suggest the admittance as a tool for a measurement of the bosonic distribution corresponding collective excitations in the system.     

The Green’s function in a channel with a sound-absorbing cover in the case of a uniform flow

We study the modal structure of an acoustic field of a point source as function of channel wall admittance in the case of a two-dimensional channel. The characteristic equation for determining the eigen-values corresponding to the boundary problem is studied in the form of this equation??s dependence on the admittance, which varies in the entire complex plane. All modes, without exception, existing in the channel and forming the source field are classified based on the obtained topography of the characteristic equation. The expressions that describe the amplitudes and spatial distribution of the hydrodynamic modes, attenuation rate (for stable modes), or increment (for unstable modes) were obtained as functions of the wall admittance and flow velocity. It is shown that in addition to the hydrodynamic unstable modes existing downstream from the source, hydrodynamic unstable modes exist upstream from the source at any admittance. They appear only when the admittance has an elastic character. It is shown that hydrodynamic modes are induced only in the case when the source is located close to the wall or on the wall. The amplitude of these modes decreases exponentially with distance from the wall.     

外界条件在电磁脉冲对GaAs赝高电子迁移率晶体管损伤过程中的影响

结合器件仿真软件Sentaurus TCAD,建立了GaAs赝高电子迁移率晶体管器件的电磁脉冲损伤模型.基于此模型,从信号参数和外接电阻两个方面出发讨论了外界条件对器件电磁脉冲损伤效应的影响.结果表明,信号参数的改变能够显著影响器件的损伤时间:信号幅度通过改变器件的吸收能量速度来影响器件的损伤效应,其与器件损伤时间成反比;信号上升时间的改变能够提前或延迟器件的击穿点,其与器件损伤时间成正比.器件外接电阻能够减弱器件的电流沟道,进而延缓器件的损伤进程,且源极外接电阻的影响更加明显.     

基于NI ELVIS的超声换能器参数测量系统设计

为了满足超声换能器快速筛选的要求,在对超声换能器参数导纳圆法测量原理进行分析的基础上,利用NI ELVIS平台搭建了一种结构简单的超声换能器参数测量系统。采用点频法实现高精度、快速的导纳测量,采用最小二乘法拟合得到导纳圆,进而完成超声换能器诸参数的计算。基于LabVIEW软件平台编写了相应的软件系统。针对40 kHz超声换能器的测试表明,所设计的超声换能器参数测量系统精度高、处理速度快,且结构简单、便于使用。     

Acoustical source characterization studies on a multi-cylinder engine exhaust system

It is well known that the characterization of the acoustic source in an exhaust muffler system is of utmost importance in the proper evaluation of the acoustic performance of the muffler. However, in the literature, there are very few experimental studies on source characterization of a multi-cylinder internal combustion engine. This paper describes the use of a transfer function method (with a random excitation source) for measurement of the internal source impedance of an eight-cylinder engine under running conditions. The results obtained agree well with those obtained by the standing wave method by earlier investigators. The studies include the effect on the measured internal source impedance caused by variation of engine speed and load. The source impedance results obtained for the engine in operation are compared with those for the engine not in operation. The use of these results in the overall modeling of the exhaust system is described in an accompanying paper.     

Approximate method for obtaining source quantities for calculation of structure-borne sound transmission into lightweight buildings

An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average.     

混响声场条件下水声互易传递函数的测量及应用

对不规则的混响声场情况的互易测量方法进行了理论研究,对相关测量误差提出了修正方法。通过测量结果的空间平均和混响环境对声能密度影响的评估,修正了声源体积速度的计算值,并在水中进行了试验验证。经修正后的互易测量结果与正向实测结果基本一致。表明混响声场不影响互易原理有效性的成立,但影响了声源体积速度的计算,进而影响了应用互易原理对传递函数的测量。提出的修正方法在不规则的混响声场情况下简单有效,结论为今后基于互易原理的工程应用提供了参考和依据。      

ITER聚变功率关闭系统的一种阀门箱 结构的有限元分析

用ANSYS软件对ITER聚变功率关闭系统(FPSS)的一种阀门箱的结构在ITER各种典型荷载组合下的应力和应变进行了有限元分析，并遵照ASME及ITER标准对分析结果进行了评判。结果表明这种阀门箱结构能够满足ITER的设计要求。     

Dynamic simulation of a tilting-disc valve with clearance in pulsatile channel flow

Abstract  

In this study, a fully coupled fluid–structure interaction (FSI) software system for a pulsatile flow across a moving tilting-disc valve with clearance is developed. Unsteady pulsatile flow coupled with induced valve motion has been examined in details. State-of-the-art computational fluid dynamics (CFD) methods are adopted in the present flow solver development. To account for nonstationary valve motion, the meshes surrounding the valve are generated and updated in each time-marching step using hybrid grid method. A single-degree-of-freedom rotational valve model is integrated simultaneously with the CFD adaptive time-stepping. It is found in the present study that, on both side of the occluder, strong shedding vortices occur and persist in the valve closing phase. These closure vortices show great influence on the prediction of the regurgitate flow characteristics and the subsequent valve opening dynamics as well. Based on the present software system, the results obtained from quasi-steady simulations performed at various instants of interest with prescribed valve motion are critically evaluated to assess whether simplified flow and valve conditions may lead to erroneous conclusions.     

同轴电缆连续波电磁辐照的终端负载响应

为了揭示设备互连电缆在连续波电磁辐照条件下的耦合响应规律,以典型射频同轴电缆为受试对象,将电缆终端连接的设备（系统）等效为负载,通过对其进行连续波电磁辐照效应试验研究,分析了受试电缆长度、终端负载状态等对同轴电缆终端负载响应规律的影响。结果表明:同轴电缆对电磁辐照响应具有选频特性,终端负载响应电压的峰值出现在电缆相对长度为1/2整数倍的频点;同轴电缆受到连续波电磁辐照后,感应皮电流通过转移阻抗转化为芯线与屏蔽层之间的差模感应电压,而这一感应电压源的内阻就是同轴电缆的特性阻抗;同轴电缆终端负载阻值的变化不会对其连续波辐照响应曲线的变化规律产生影响,终端负载与等效感应电压源内阻上的电压响应满足分压原理; 同轴电缆皮电流处于谐振状态时,两波节之间的分布感应电压同向,可等效为一个感应电压源,对同轴电缆终端负载响应起直接作用的电压源是最靠近终端负载的等效感应电压源。     

Application and measurement of underwater acoustic reciprocity transfer functions in reverberant sound field

The reciprocity measurement theory in anomalous reverberant sound fields was investigated.An improved method Was proposed due to the interrelated errors.The source volume velocity Was corrected by spatial average of measurement results and evaluation of the reverberant sound field influence on acoustic energy density.The result was validated in underwater experiment,corrected reciprocity measurement results were almost the same as direct measurement results.It indicates that reverberant sound field does not affect the validitv of the principle,but influences the obtainment of source volume velocity,then influences the measurement of transfer functions with the principle.The proposed method is simple and effective in anomalous reverberant sound fields.The study mav be valuable for the applications which are based on the principle.     

Applying micro-perforated panels in the measurement of sound source characteristics in a duct system

In order to measure the acoustic characteristics of the sound source in a duct system effectively without destroying the main duct,micro-perforated panel structures were applied in the new method by attaching the side branch tubes.The effect and influence to change the acoustical impedance of the loads in a duct system was analyzed and simulated for using one layer and double-layer micro-perforated panel and back cavities with different parameters such as panel thickness,hole diameter,perforation ration,back depth and so on.The results show that the load’s resistance can be changed efficiently by adjusting panel thickness,hole diameter, perforation ratio,the ratio of cross-section between ducts and tubes and other parameters;and the load’s reactance can be changed efficiently by adjusting back depth and distance between micro-perforated panel and main duct.It is also found that combinative usage of one layer and double-layer of these structures can change the reactance substantially in broad frequency domain.The method and the efficient performance of the structures with micro-perforated panel in the measurement were verified by the experiment under the situations of flow and no-flow. Finally,suggestions to design and apply these structures in the above-mentioned method in application were given.     

分析端接频变负载的多导体传输线FDTD新方法

提出了一种新的有效求解端接频变负载的时域有限差分法（FDTD）.该方法将频域导纳经矢量匹配后以有理式表示,通过逆傅里叶变换将其转换到时域,基于分段线性递归卷积法,推导出该导纳两端的电压和电流关系,将其代入到传输线FDTD模型中,得到了求解端接频变负载多导体（MTL）传输线FDTD的一般公式.对一典型电路进行了仿真,和以状态变量法求解任意负载的结果进行了对比,两者基本重合,说明该方法用来求解频变负载是有效的. 关键词： 多导体传输线 分段线性递归卷积 时域有限差分法 任意负载     

同轴交错膜片加载慢波线的分析

膜片加载圆波导是相对论行波管最主要的慢波结构,同轴结构的膜片加载波导可以拓宽带宽。利用变分法对同轴交错膜片加载的慢波结构（亦称同轴径向线）进行了理论分析,得到了色散方程并进行了数值计算。计算结果表明,它比非同轴结构的带宽有明显的增加。     

模糊PID在高精密球抛光机床压力控制中的应用

针对高精密球体抛光机床压力加载控制中,存在的加压精度低、抗干扰能力差等问题,提出了基于模糊PID控制策略的压力加载控制系统。分析了抛光机床的加压装置,并对机床整体控制系统进行设计;针对高精密抛光机床加压过程中存在的滞后性、非线性及时变性等特点,分析模糊PID控制器的设计过程及其软件实现;静态加载实验表明,运用模糊PID的控制系统可将静态加压误差控制在1%以内;同时,动态加工实验表明,动态误差可控制在4.2%以内。将模糊PID控制方法运用于高精密球体抛光压力控制中,提高了压力加载精度和稳定性,在实际加工中有较好的运用效果。     

一种测量高温中间包的蓝宝石光纤温度计

介绍了一种测量高温的蓝宝石光纤温度计.蓝宝石单晶光纤由于其极好的高温物理化学性能,适用于高温下光纤测温应用,可用作辐射型光纤温度传感器.蓝宝石光纤温度计采用激光加热小基座法生长出端部掺Cr3+的蓝宝石光纤荧光温度传感头.用激光加热小基座,把对荧光有温度反应的材料如红宝石晶体光纤生长在蓝宝石光纤上,制成具有结构紧凑,耐高温,功能稳定的传感探头.通过荧光寿命的检测,可以测量所对应的温度.根据表面温度,可以依据温度场得到内部温度,用于测量连铸炉中的中间包钢水温度,并给出了温度计的实验系统以及原始实验数据.实验数据表明,此结果精度高,可实现非接触测量.     

System for measuring optical admittance of a thin film stack

A new method based on the polarization interferometer structure has been applied to measure the optical admittance, the refractive index and thickness of a thin film. The structure is a vibration insensitive optical system. There is one Twyman-Green interferometer part to induce a phase difference and one Fizeau interferometer part to induce the interference in the system. The intensities coming from four different polarizers were measured at the same time to prevent mechanical vibration influence. Using the polarization interferometer, the optical admittance, the refractive index and thickness of a single layer of Ta₂O₅ thin film has been measured. The measurement results were compared with the results obtained by ellipsometer. The results meet reasonable values in both refractive index and thickness.