A study on the determination of optimal reference spectrum for random vibration control in environmental vibration test

For random vibration control in environmental vibration test it is desired that the spectra at the specimen attachment points coincide with the specified reference spectrum. However, this goal is seldom achieved because of the dynamic characteristics of shaker, fixture, and specimen and of the interactions between them in the test frequency ranges. This paper proposes a method for the determination of the optimal reference spectrum which minimizes the spectral deviations between the specified reference spectrum and spectra at the specimen attachment points. The least square method is used for this purpose. This method requires only the measured FRFs at the control point and specimen attachment points in pre-vibration test and is shown through theoretical and experimental results to be effective.     

A control system for the 3-mm-wavelength band spectral radiometer

An IBM PC-based control system for the multichannel modulation-type radiometric receiver with the series-parallel filtering spectral analysis in theK _a band is developed. A special-purpose instrument interface with a single-board controller linked to the computer via ISA bus is used for controlling receiver components and transferring data. Primary attention is drawn to the electromagnetic compatibility of the control system and receiver. Appropriate circuit designs and test results are provided.     

功率谱密度约束下多频激励的非线性失真研究

多频激励信号通过放大器后产生的非线性失真对测量准确性具有较大影响。本文对功率谱密度约束下的多频激励信号产生的非线性失真进行了定量和定性的研究,给出了不同谱线间隔、非线性阶数、谐波相位和频率分布下的数值计算结果,并从三个方面进一步阐释了非线性失真的作用机制。首先,通过仿真发现,二阶非线性时,由具有 Schroeder 相位的多频激励信号产生的二类失真分量的相位为随机分布,而不是和一类失真分量反相。其次,通过计算一类失真分量、二类失真分量以及总失真的变化,解释了通过对多个具有随机相位的多频激励信号产生的非线性失真求平均来减小二类失真分量影响的测量方法。最后,发现了具有 Schroeder 相位的多频激励信号所产生非线性失真的特殊分布机制。本文的研究对准确评估和深入理解非线性失真具有重要意义。     

A study on the reduction of uncertainty in the measurement of power tool vibration

To increase accurateness and reliability of the evaluation of power tool vibration transmitted to an operator, it is necessary to measure the grip and feed forces during the measurement of hand-transmitted vibration. In the study a system was invented to measure the vibration and the grip and/or feed force, which consists of a measurement handle and a PC with a data acquisition system and the corresponding software. Strain gages and an accelerometer were mounted on the handle surface for the simultaneous measurement of the forces and the vibration. The program in the system makes it possible to monitor the grip and feed force during the tool operation so that the operator keeps the applying forces within the pre-determined range. Investigating the vibration total values, frequency-weighted root-mean-square accelerations at the handle, obtained in repetition for each power tool with control of the grip and feed force showed more consistency than those measured without force control. By using the system the experimenter can reduce uncertainty in measurement of hand-held power tool vibration.     

Parametric study on a collocated PZT beam vibration absorber and power harvester

The parametric effects of a PZT beam that is simultaneously used as a vibration absorber and a power harvester were investigated in this study. A cantilever beam paved with PZT layers and with added tip mass has been widely used as a harvester or sometimes as a Dynamic vibration absorber (DVA). However, the beam is rarely considered a collocated device. In this study, the first step was theoretical derivation of a distributed beam covered with bimorph PZT layers. Then, the beam was attached to a 1DOF vibratory main system. Two indicators for vibration absorption and power harvesting were defined. Numerical results demonstrated that the lumped mass ratio favored both of the abilities, but that the DVA mass ratio influenced these two abilities in exactly the opposite way. The conjunction of a harvester circuit into a DVA shifted its resonance frequency up to 5 % (an extreme case of open circuit R→∞). Simultaneous power harvesting diminished the absorption capability up to 35 % for each set of mass ratios. To achieve the maximum degree of power harvesting, a corresponding load resistance that somewhat increases with the lumped mass ratio is applied. Experimental results verified the existence of the best load resistance, but the measured harvested curve was lower than the theoretical calculation because of structure damping and deviations of PZT material properties.     

变压器有载分接开关振动测试系统设计与开发

为实现电力变压器有载分接开关运行状态在线监测和故障判别,本文基于虚拟仪器技术通过二次开发研制了变压器有载分接开关振动测试系统.通过由传感模块、CompactRIO系统和上位机系统组成的硬件构架以及自行编写封装的分析函数模块,系统集成了数据精确采集和数据在线分析两大功能,从而实现有载开关运行状态的实时判别.为验证系统有效性,对一台实际有载开关进行了现场测试,结果表明,测试系统运行稳定,提出的振动数据分析方法可有效地识别有载分接开关的故障隐患,分析和评估其运行状态.此外,测试系统操作界面友好,扩展性好,便于操作人员使用和实现在线监测.     

Analysis of surface finish in milling by power spectral density measurement

The power spectral densities (psd) of surface profiles of milled steel samples have been determined by analogue measurement techniques, ie by a spectral analyser. The recorded psd curves indicate the presence in the surface profiles of some periodic components. Increase of cutting speed during milling causes the spectral density values to decrease. By psd measurement it was possible: to distinguish between surface profiles with the same R_a value, but milled under different cutting conditions; and to detect axial run-out of the milling cutter, which results in waviness of machined surfaces.     

A study on free vibration of a spinning disk

Without a logical jump, we have derived the governing equation for free vibration of a spinning circular disk by using the variational formulation based upon the Kirchhoff plate theory and von Karman strain one. It has been found during the derivation that the governing equation is theoretically valld under the assumption that in plane deflections are steady and axisymmetric, and that internal forces are linearized while the strains remain nonlinear. The natural frequencies and the critical speeds of a freely spinning disk are obtained approximately and their dependencies on the spinning speed, mode number, and natural freqeuncy of the stationary disk are analyzed.     

基于灵敏度分析的振动试验夹具优化设计

研究了固有频率对设计变量的灵敏度,设计了一个典型的汽车电器振动试验夹具,在进行灵敏度分析的基础上对夹具结构进行了优化设计.最后,进行了试验模态分析,验证了此方法的有效性.     

Extraction the unbalance features of spindle system using wavelet transform and power spectral density

Identification of the spindle unbalance is very important for the ultra-precision machining tools. In the first part, the frequency information for the spindle system is computed by two methods. In the second part, the results between the modal information of the spindle and the error frequency of the measured workpiece surface which processed by wavelet transform and power spectral density is compared, the signal feature in the waviness which is consistent with the spindle unbalance frequency is extracted. In the last part, the identified result is compared, it proves the extraction and identification method for the spindle unbalance of the machine tool is correctness and validity.     

周期弹簧振子结构振动带隙及隔振特性研究

无限周期弹簧振子结构具有和声子晶体类似的振动(弹性波)带隙,带隙频率范围内的振动(弹性波)在该结构 中无法进行传播。在计算无限周期弹簧振子结构振动(弹性波)带隙的基础上,采用数值方法计算并讨论了有限周 期弹簧振子结构的振动传输特性及隔振特性,最后以双质量周期弹簧振子结构为例,对其振动传输特性及隔振特 性进行了试验验证。     

A study on the design of a new power transmission for wind turbines

The single-rotor wind turbine remains the dominant design for energy production. However, this design requires improvements to overcome some of its limitations. The introduction of the dual rotor system regarded as improvement over the single-rotor system in Korea due to its high efficiency, despite Korea’s low wind quality. Many researchers have attempted to devise different dual rotor machines and assess their power production capabilities under similar wind conditions to those in Korea. Existing power transmissions for dual-rotor wind turbines have issues with the complexity of design, difficulty in manufacturing, high costs and low efficiencies. Therefore, the aim of this study was to design a new power transmission for the dual-rotor wind turbine with an alternative to the bevel-planetary system by using a planetary system. This new method is dependent on the torque ratio and not the gear ratio as in common gear systems. The design and analysis of each part, such as the gears, shafts, bearings and control mechanisms are included in this study. The design is based on the power transmission of a motor vehicle. A prototype of the design is manufactured to verify the proposed method. The experimental results show that the new planetary-type gear box incurs fewer energy losses, has a high efficiency and low manufacturing costs. It is anticipated that the proposed design might be suitable for use with commercial wind turbines.     

Reduction of system order using power spectral density function-generalization of liaw's dispersion analysis

The method of model reduction based on dispersion analysis and the continued fraction is extended to treat the system which has multiple poles or has simple or multiple poles on the imaginary axis. Using the power spectral density function and preserving the dynamic modes with large power contibutions, the denominator of the reduced model is obtained and its numerator is obtained by using the continued-fraction method. This method is proved to give better approximation to an original system through examples than other methods.     

基于主振模态预测的带锯振动主动抑制系统

针对带锯条振动引起的材料损失、锯条寿命降低、锯材尺寸精度及加工面质量变差的状况,设计了一种基于主振模态预测的带锯条振动主动抑制装置。该装置实时采集带锯条横向、纵向及扭转方向上的多维度振动信号,并采用基于EMD筛分方法的主振型模态识别算法,来构建振动信号关于主振型模态的预测模型,最后基于实时采得的数据及其预测模型的输出量,通过PID控制方法控制电液阻尼减振器。实验结果表明,该装置对带锯条横向、纵向及扭转方向上的抑振效果分别可达80%、66%、75%。     

Welch-type estimator for a spectral density function. Case of a continuous-time

A Welch-type estimator (an estimator obtained by averaging over the time shift) for the spectral density function of a stationary continuous-time random process is considered. The bias and variance of the statistical estimator are studied, and some recommendations concerning the choice of its parameters are formulated.     

A novel method for the optimal band selection for vibration signal demodulation and comparison with the Kurtogram

The narrowband amplitude demodulation of a vibration signal enables the extraction of components carrying information about rotating machine faults. However, the quality of the demodulated signal depends on the frequency band selected for the demodulation. The spectral kurtosis (SK) was proved to be a very efficient method for detection of such faults, including defective rolling element bearings and gears [1]. Although there are conditions, under which SK yields valid results, there are also cases, when it fails, e.g. in the presence of a relatively strong, non-Gaussian noise containing high peaks or for a relatively high repetition rate of fault impulses.In this paper, a novel method for selection of the optimal frequency band, which attempts to overcome the aforementioned drawbacks, is presented. Subsequently, a new tool for presentation of results of the method, called the Protrugram, is proposed. The method is based on the kurtosis of the envelope spectrum amplitudes of the demodulated signal, rather than on the kurtosis of the filtered time signal. The advantage of the method is the ability to detect transients with smaller signal-to-noise ratio comparing to the SK-based Fast Kurtogram. The application of the proposed method is validated on simulated and real data, including a test rig, a simulated signal, and a jet engine vibration signal.     

A counting method for density packed cells based on sliding band filter image enhancement

Cell loss and addition is an important biological event in pathology, and it usually provides central information to the changes of biological activity in the histological sections. To develop a reliable and accurate cell counting tools in tissue section, in this paper, we proposed a novel cell nuclei detecting method based on the sliding band filter which is a member of convergence index family. We evaluated the accuracy and performance of our method on density packed retinal outer nuclear layer cell confocal multivariate fluorescence microscopy image datasets. The results show our proposed method exhibited an excellent performance with its accuracy compared with human manual counting. It is worth noting that the proposed cell counting method can clearly benefit for retinal detachment and reattachment visual diagnostics close related to cell loss and addition.     

A rail vibration test and analysis method for the electromagnetic launching process

During the electromagnetic launching (EML) process, rail vibrations occur due to the electromagnetic force generated by an acute current. These vibrations result in a reduced launch velocity and decreased launch efficiency. To measure the vibration amplitude of a rail accurately and to analyze the internal relationships between current strength, rail material and vibrations, a small transient vibration in a strong electromagnetic field was studied in this paper. Related experiments were also performed on the test system. Fiber-optic displacement sensors were used to collect vibration data at key locations along the rail. Using virtual instrument technology, a software platform was designed that displayed the vibration waveform and analyzed the time, frequency domain and other parameters. We collected data on the vibration response and the modal parameters of the rail and determined the natural frequencies of the electromagnetic launch system by performing a modal analysis of its vibrations and dynamic responses that combined experimental and theoretical methods. Methods of optimizing the structure’s vibration and dynamic response and of assessing the damage to it could be studied further on the basis of the results described in this paper.     

短路条件下变压器振动特性研究

利用振动法对运行中的变压器进行诊断是一种新的趋势,但是到目前为止,振动法的效果仍然不够理想。变压器表面振动信号比较复杂,如何得到一个能正确反映实际振动的模型是研究的关键,针对如何简化模型的问题,提出了短路条件下变压器油箱表面的振动模型,该模型基于振动的产生和传递过程。该模型的参数由单相短路实验得到的数据计算得到。利用得到的模型,只需要根据输入电流值即可计算振动估计值。最后,采用三相短路实验验证了模型的正确性。实验结果表明,估计信号和实测信号基本一致,利用简化的绕组模型和传递模型是完全可行的。     

行星齿轮功率分流式无级变速器的设计研究

针对液力自动变速器传动效率低、油耗大、结构复杂的缺陷,提出了一种新型的行星齿轮功率分流式无级变速器,它取消了液力变矩器,在辛普森双行星排变速机构的基础上,通过功率分流并调节发电机输入功率来实现无级变速,该变速器结构简单,传动效率高,具有较高的实用价值。