Increase in the resolution of the reflection coefficient Fourier-transform method by spectrum extrapolation based on the method of the minimum duration principle

An approach is proposed to increasing the resolution of a technique for synthesizing the time reflection characteristics of a dielectric layered structure using extrapolation of the measured frequency dependence of the reflection coefficient based on solving the optimization problem using nonquadratic regularization. The problem is solved under the assumption of a finite support of the time response and the presence of an error in measured frequency data. In order to minimize the time response, the minimum duration method is used.     

油膜压力测量传感器动力学特性研究

用有限元分析软件ANSYS对一种改进的测量油膜压力的传感器进行了动力学分析,包括固有振动特性分析、谐响应特性分析和瞬态响应特性分析。通过固有振动特性分析,得到振动系统的前4阶固有频率;通过谐响应分析,得到传感器在承受随时间按正弦规律变化的载荷时的稳态响应;通过瞬态响应特性分析,得到传感器在承受实际的油膜载荷作用下的响应特性。分析表明,传感器具有较高的一阶固有频率和良好的动态响应特性。     

Electromechanical system frequency response equilization using three different methods

The frequency response of different electromechanical systems like sensors and actuators is in many cases the most important parameter for their evaluation. In some cases, when a short time delay does not play an important role and the flatness of frequency response is more important, an approximate of inverse system for frequency response compensation can be used. We equalized the frequency response of a non-minimum phase linear time-invariant electromechanical system using a digital finite impulse response (FIR) filter. Three different deconvolution methods for determination of the approximate of inverse filter impulse response were used and the results of the compensation using three different inverse filters are compared. The first method is based on the solution of the system of linear equations, while the second method is based on a simple direct inverse Fourier transformation. The third method uses an active noise control algorithm based on a least mean square adaptive algorithm. The results of all three methods can be applied in a FIR filter realized on DSP boards to perform real time compensation. The theoretical simulations are compared with experiments. Compensation of arbitrary systems is an interesting subject and it can be applied in numerous different fields from sensors and actuators to measurement and acoustics.     

Analysis of sensitivity and robustness of forced response for nonlinear dynamic structures

An effective method is developed for calculation of the sensitivity and robustness of the forced response levels for strongly nonlinear structures. The sensitivity coefficients are determined with respect to parameters of friction contact interfaces, parameters of linear components of an assembled structure, frequency and level of excitation forces.Equations for determination of first- and second-order sensitivity coefficients of the forced response are derived analytically from a nonlinear multiharmonic equation of motion. The analytical derivation allows accurate and fast evaluation of the sensitivity coefficients. The sensitivity coefficients are calculated in frequency domain for each excitation frequency over the frequency range analysed simultaneously with the force response levels. The developed highly efficient method allows calculation of sensitivity characteristics without a noticeable increase of the computation time in addition to the time required for the forced response calculation.A measure of the forced response robustness is introduced. Sensitivity-based method for assessment of the forced response robustness for given ranges of uncertainty of structural and operating parameters is proposed.The methodology developed is illustrated on a set of problems including cases of forced response analysis for realistic strongly nonlinear gas-turbine structures.     

Dynamic response-based characterization of ring-based vibratory angular rate sensors

Dynamic response behaviour of a rotating ring is investigated in order to better understand the achievable performance improvements as well as system limitations. For this purpose, the governing equations that represent the transverse as well as the tangential in-plane motion of a rotating ring are derived via the Hamilton’s principle. These equations are then discretized to represent a two-degree-of-freedom time-varying gyroscopic system. The asymmetry effects are considered important and are included by considering mass mismatch in the system mass matrix. In order to predict dynamic behaviour of a ring system subjected to external excitation and body rotation, time and frequency response analyses are performed. The natural frequency variations due to the gyroscopic coupling presented in the system are first characterized for varying input angular rates. The effects of system parameters such as damping and mass mismatch on the sensor sensitivity and operating range are quantified via suitable time and frequency response analyses.     

电涡流传感器的脉冲激励与双参数检测

采用矩形脉冲作为激励信号,对电涡流传感器在位移检测过程中谐振频率及谐振阻尼的变化情况进行了研究分析.建立了以现场可编程门阵列(FPGA)为核心芯片的检测系统,用于产生所需要的矩形脉冲激励信号以及对传感器响应信号的欠采样.利用8 mm直径的电涡流线圈,对0～10 mm范围内碳钢目标靶的位移响应特性进行了测量,借助短时傅里叶变换分析了响应信号中频率成分的分布情况,同时获得了谐振频率及谐振阻尼的测量值.验证了通过脉冲激励同时获取电涡流传感器双参数检测的可行性.为研制基于电涡流效应的位移传感器及无损探伤传感器提供了一种新思路.     

Phase correction for frequency response function measurements

In modal testing, an impulse is often used to excite the structure and a linear transducer is used to measure the response. For these impact tests, two signals are measured: the impulsive force and the vibration response. Any lack of synchronization in the time domain acquisition of the two signals results in a frequency-dependent phase error in the frequency response function, or FRF. However, knowledge of the time delay may be used to correct the corresponding phase error. In this research, tests were conducted to measure the frequency-dependent phase error for a capacitive sensor and a frequency domain technique is proposed to correct the FRF. The method was validated using an FRF measurement of a cylindrical artifact mounted in a milling machine spindle.     

多体系统的脉冲响应

本文介绍一种多体系统动力学的计算方法。利用脉冲响应,可在时间域和频率域进行计算分析。在此基础上开发了一般多体系统动力学分析程序DAGOMS及其FFT后续处理程序PTODA。以工业机器人为典型系统进行了实验模态分析,识别了接合面物理参数。用上述程序求得时域和频域数值解。理论分析与实验结果吻合较好。     

抖晃对振动脉冲频响特性估计的影响

以振动脉冲响应为例,研究抖晃对振动信号分析和估计的影响。应用傅里叶变换和贝塞尔函数,从理论上分析含抖晃振动脉冲频率响应和倒谱的特征;用仿真手段直观展示估计误差的分布、纳奎斯特图形态及抖晃初相的作用。分析和仿真表明:抖晃对振动脉冲频响干扰的数学表达是真实振动频率响应函数与复宗量贝塞尔系数加权旋转脉冲序列卷积的结果。抖晃现象对振动冲击响应的信号处理中的频率响应估计、纳奎斯特图形态和倒谱特征影响极大,所引入的估计误差在信号分析中不可被忽略。     

压电应变传感特性的理论分析与实验研究

提出了一种通过测量动态应变实现工程中低频振动监测的方法.在对动态应变压电传感特性进行理论分析的基础上,对压电传感元件在不同激振频率下(0.1~40.0Hz)的动态响应进行了实验研究,实验给出了较好的测量精度.结果表明,压电传感元件灵敏度高、频响范围宽、响应时间快,符合工程中低频振动测量的要求.     

DETERMINATION OF UNKNOWN IMPACT FORCE ACTING ON A SIMPLY SUPPORTED BEAM

This work presents a predictive model for determining the location and amplitude of an unknown impact force acting on a simply supported beam. Both time and frequency domain prediction methods are developed, respectively. The structural modal parameters can be first obtained by theoretical modal analysis (TMA) or by experimental modal analysis (EMA). The structural response at time and frequency domains due to an unknown impact force can then be measured and recorded. The predicted response can also be formulated and expressed as functions of amplitude and location of the impact force. The sum of square errors between the predicted and measured response is then defined as the objective function, while the amplitude and the location of the unknown impact force are defined as design variables. The optimisation problem is thereby constructed and can be solved for the amplitude of the impact force. The mode shape information associated to the location of the impact force can also be resolved and compared to the structural mode shapes to determine the location of the unknown impact force. Both numerical and experimental prediction results are presented. Results show that the predictive model is feasible and leads to the prediction of magnitude and location of the unknown impact force for arbitrary structures as well.     

时频非平稳地震动模型及结构随机振动应用

地震动具有显著的时域和频域非平稳性,传统的均匀调制地震动模型不能充分表征时频两域的非平稳性,并影响结构随机振动分析的精准度。为了克服上述不足,建立由多峰平滑包络和非平稳噪声信号点乘而成的非均匀调制地震动模型,该模型能够在时域上充分反映地震动的波动和衰减特性,同时其频谱特征也与真实信号相接近。在此基础上,建立同时以时间和频率为变量的非平稳地震动演变谱随机模型。分析结果表明,以上两种模型在时域和频域的合成精度上均优于均匀调制模型。针对以上地震动随机模型的形式和特点,对传统结构随机振动响应求解方法进行改进。通过算例证明,按照均匀调制模型计算结构随机响应不能充分获得结构时频域的非平稳特性且结果偏于不安全,而利用两种改进模型可以获得更精确的结构响应概率特征和更细致的非平稳性演变过程。     

一种新的预测铣刀刀尖频响函数的方法

为准确快速地预测铣刀刀尖点频响函数,提出一种基于逆响应耦合子结构分析（IRCSA）法辨识刀柄-刀具结合面参数的刀尖点频响函数预测方法。该方法通过建立计算刀柄末端频响函数矩阵和刀尖点频响函数矩阵的数学模型,利用逆响应耦合子结构分析法求取随频率变化的刀柄-刀具结合面参数。通过Cuckoo search算法及有限元分析确定刀尖点频响函数中对刀柄-刀具结合面复刚度矩阵变化最为敏感的固有频率,取该频率对应的结合面参数为刀柄-刀具结合面复刚度矩阵的辨识结果,由此计算出刀尖点频响函数。通过硬质合金圆柱棒、2刃铣刀和4刃铣刀进行验证,对比了所提预测方法、Cuckoo search优化算法预测的刀尖点频响函数与实测值三者之间的差异,实验结果表明该预测方法预测的刀尖点频响函数的固有频率和实测固有频率的误差在5%以内,所用时间约为Cuckoo search优化算法的1%,达到了较高的预测精度,并且更加省时、简便。     

Study of the frequency response of the thin film cold cathode electron source of a lighting element.

Details of the recent experimental and theoretical studies of the frequency characteristic of the field emission electron source of a lighting element are given. The response times at different frequencies (0.02-200 kHz) and applied gap fields, acting on cathode surface, have been studied. A correlation has been found to exist between the response time and the frequency of applied voltage pulse. The response time remains almost constant within a range of frequencies between 1 and 30 kHz, and it remains nearly constant with increasing applied gap field higher than the threshold field. Finally, the cutoff frequency of the electron source is found, and with the current design of the electron source, it can be as high as 40 kHz. An equivalent circuit model is proposed, and theoretical results based on this model agree well with experimental findings.     

一种适合于动态建模的信号参数模型

本文利用复指数模型作为瞬态信号的表示形式;系统的动态参数模型可由系统的输入与输出信号之间的关系建立;对实际窄带滤波器的阶跃响应的建模,表明了复指数信号模型是一种很有效的瞬态信号表示方法,只需截取很短的一段瞬态过渡信号,就可以得到信号参数的估计,系统模型的频域,时域回归效果较好.     

Hilbert-Huang Transform (HHT) transient analysis of composite panel undergoing high-velocity impact

Fast Fourier transform (FFT) has been widely used to analyze distribution patterns of frequency components in dynamic response signals. Given a stationary dynamic response signal, a fixed frequency distribution pattern can be obtained efficiently using FFT. If the system of concern is not stationary, however, the frequency distribution pattern varies with time, and the variation in that pattern cannot be effectively determined via FFT. To overcome this weakness, time-frequency dual-domain signal analysis methods such as wavelet transform and Hilbert-Huang transform (HHT) have been introduced. HHT has been shown to be particularly effective in analysis of non-stationary signals obtained from non-linear as well as linear systems. In the present study, the transient characteristics of a composite panel undergoing high-velocity impact were investigated. The composite panel, along with the colliding bullet, were modeled using the finite element method. To verify the reliability of the analysis model, an impact experiment was carried out, which proved that the model provides reliable, similar-to-experimental results.     

基于谐振式MEMS传感器的仪表开发关键技术

针对基于谐振式MEMS传感器开发数字智能仪器仪表的高精度、快响应频率测量技术展开研究。以一谐振式MEMS气压传感器为开发样件,其差分输出是两路40～70 kHz之间的正弦频率信号。对传统的频率测量方法进行阐述分析,提出一种新的结合传统测频方法各自优点的频率检测方法。设计实现相关软、硬件,搭建测试系统,实验结果表明该测频方案针对40～70 kHz的频率信号误差小于±0.02 Hz,响应时间为1 s以内。     

Frequency response similarity-based bolt clamping force prediction method using convolutional neural networks

This paper proposes a convolutional neural network (CNN)-based method with which to predict bolt clamping force using the frequency response of bolted structures. The dynamic characteristics of the bolted structure change with the bolt clamping force, which is predicted using a CNN trained with massive frequency response data. Big data required for training the CNN is constructed using prestressed frequency response analysis according to the clamping force of individual bolts. The numerical efficiency is increased using the Krylov subspace-based model order reduction (MOR) method. The frequency response for each set of bolt clamping forces calculated from the MOR method is converted into form of the magnitude and shape (MS) similarity spectrum by using the MS similarity function. Finally, an MS similarity map is generated by stacking the MS similarity spectrum at several output points. A CNN that is trained using massive MS similarity maps as training data, is used to predict the clamping force of bolted structures. To validate the efficiency and accuracy of a trained CNN in practical applications, the prediction results of the trained network in terms of computation time and accuracy were compared according to the size of the training input data.

     

Signature analysis of mechanical watch movements

This paper presents a new application of the signature analysis for mechanical watch movements. Contrary to the existing method, it analyzes the time–frequency features of a mechanical watch movement through a combination of two well-known techniques: reassigned time–frequency distributions (RTFD) and finite element analysis (FEA). By mapping the signal into a two-dimensional domain of time and frequency, RTFD reveals the frequency components at different time of the movement, while FEA gives the theoretical frequency response of the movements. By comparing the frequency components at different time of the movements to the theoretical frequency response of the movement, various malfunctions of the movement can then be detected. The effectiveness of the presented method is tested for some specific fault diagnosing examples. For completeness, a brief introduction of RTFD is given in the Appendix.     

新颖高频动圈式永磁直线电机的研究

针对常规动圈式永磁直线电机在电磁力、响应时间和响应速度等性能上的不足,从永磁体结构入手,对比单个永磁体不同的磁化技术和多个永磁体不同的阵列结构,提出了一种新颖八片瓦型有气隙Halbach磁化阵列动圈式永磁直线电机。对其静态磁场和瞬态磁场的分析以及实验结果表明,线圈与永磁体间的作用力能提高40%以上,仿真频宽接近350 Hz/-3 dB,响应时间为0.004 s。而实验频宽达到300 Hz/-3 dB,与仿真结果基本吻合,表明所设计的动圈式永磁直线电机具有高频和快速响应特性,能很好地满足高速电液比例控制系统的要求。