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Frequency domain a9ctive vibration control of a flexible plate based on neural networks

Jinxin LIU, Xuefeng CHEN, Zhengjia HE

《机械工程前沿（英文）》 2013年第8卷第2期页码 109-117 doi: 10.1007/s11465-013-0252-z

摘要：

A neural-network (NN)-based active control system was proposed to reduce the low frequency noise radiation of the simply supported flexible plate. Feedback control system was built, in which neural network controller (NNC) and neural network identifier (NNI) were applied. Multi-frequency control in frequency domain was achieved by simulation through the NN-based control systems. A pre-testing experiment of the control system on a real simply supported plate was conducted. The NN-based control algorithm was shown to perform effectively. These works lay a solid foundation for the active vibration control of mechanical structures.

关键词： active vibration control (AVC) neural network (NN) low frequency noise frequency domain control multi-frequency control

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Integrated virtual-design methods for forecasting radiated noise of single cylinder diesel block

GUO Lei, HAO Zhiyong, XU Hongmei, LIU Lianyun

《能源前沿（英文）》 2008年第2卷第4期页码 416-421 doi: 10.1007/s11708-008-0097-z

摘要： The two cycle dynamical results, such as the bearing load, the piston thrust, and the load spatial distribution etc., were obtained by hybrid dynamical simulation of the flexible assembly of the block and crank-train. The finite element model of the block was validated by modal test. The frequency response of the block was calculated using the finite element method (FEM). Finally, the radiated noise such as sound power level and efficiency in the out sound field were obtained using the direct boundary element method (BEM).

关键词： bearing dynamical frequency response dynamical simulation hybrid dynamical

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Electromagnetic interference modeling and suppression techniques in variable-frequency drive systems

Le YANG, Shuo WANG, Jianghua FENG

《机械工程前沿（英文）》 2018年第13卷第3期页码 329-353 doi: 10.1007/s11465-018-0466-1

摘要：

Electromagnetic interference (EMI) causes electromechanical damage to the motors and degrades the reliability of variable-frequency drive (VFD) systems. Unlike fundamental frequency components in motor drive systems, high-frequency EMI noise, coupled with the parasitic parameters of the trough system, are difficult to analyze and reduce. In this article, EMI modeling techniques for different function units in a VFD system, including induction motors, motor bearings, and rectifier-inverters, are reviewed and evaluated in terms of applied frequency range, model parameterization, and model accuracy. The EMI models for the motors are categorized based on modeling techniques and model topologies. Motor bearing and shaft models are also reviewed, and techniques that are used to eliminate bearing current are evaluated. Modeling techniques for conventional rectifier-inverter systems are also summarized. EMI noise suppression techniques, including passive filter, Wheatstone bridge balance, active filter, and optimized modulation, are reviewed and compared based on the VFD system models.

关键词： variable-frequency drive (VFD) electromagnetic interference (EMI) motor drive modeling EMI noise suppression

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Wavelet-based iterative data enhancement for implementation in purification of modal frequency for extremely

Hassan YOUSEFI, Alireza TAGHAVI KANI, Iradj MAHMOUDZADEH KANI, Soheil MOHAMMADI

《结构与土木工程前沿（英文）》 2020年第14卷第2期页码 446-472 doi: 10.1007/s11709-019-0605-8

摘要： The main purpose of the present study is to enhance high-level noisy data by a wavelet-based iterative filtering algorithm for identification of natural frequencies during ambient wind vibrational tests on a petrochemical process tower. Most of denoising methods fail to filter such noise properly. Both the signal-to-noise ratio and the peak signal-to-noise ratio are small. Multiresolution-based one-step and variational-based filtering methods fail to denoise properly with thresholds obtained by theoretical or empirical method. Due to the fact that it is impossible to completely denoise such high-level noisy data, the enhancing approach is used to improve the data quality, which is the main novelty from the application point of view here. For this iterative method, a simple computational approach is proposed to estimate the dynamic threshold values. Hence, different thresholds can be obtained for different recorded signals in one ambient test. This is in contrast to commonly used approaches recommending one global threshold estimated mainly by an empirical method. After the enhancements, modal frequencies are directly detected by the cross wavelet transform (XWT), the spectral power density and autocorrelation of wavelet coefficients. Estimated frequencies are then compared with those of an undamaged-model, simulated by the finite element method.

关键词： ambient vibration test high level noise iterative signal enhancement wavelet cross and autocorrelation of wavelets

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Comparative study of oscillating flow characteristics of cryocooler regenerator at low temperatures

Yonglin JU , Qingqing SHEN ,

《能源前沿（英文）》 2009年第3卷第1期页码 80-84 doi: 10.1007/s11708-009-0008-y

摘要： A brief review is presented on previous experimental results and correlations on the friction factor of cryocooler regenerators operating at oscillating flow and pulsating pressure conditions, for different mesh sizes of packed woven screens, focusing on the effects of different operating frequencies ranging from 20 to 80 Hz, at room and cryogenic temperatures. A comparison of the friction factor data with those of other studies is presented to clarify the reason for the difference. Finally, a new oscillating flow correlation of regenerators, in terms of several non-dimensional parameters, is discussed and compared.

关键词： friction factor regenerator oscillating flow high frequency

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Improving retrieval precision of NO

Jinpeng YANG

《机械工程前沿（英文）》 2009年第4卷第1期页码 92-96 doi: 10.1007/s11465-009-0001-5

摘要： The NO density error retrieved by the traditional method of differential optical absorption spectroscopy (DOAS) was analyzed. The technique for reducing the error is proposed and used to obtain the NO density of Chengdu through DOAS.

关键词： absorption structure low-frequency structure absorption cross-section NO₂ density

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Analysis and design of pulse frequency modulation dielectric barrier discharge for low power applications

Tang-tang GUO,Xing-liang LIU,Shi-qiang HAO,Chi ZHANG,Xiang-ning HE

《信息与电子工程前沿（英文）》 2015年第16卷第3期页码 249-258 doi: 10.1631/FITEE.1400185

摘要： For low power dielectric barrier discharge (DBD) used in small-size material treatment or portable devices, highstep transformer parasitic capacitance greatly influences the performance of the resonant converter as it is of the same order of magnitude as the equivalent capacitance of DBD load. In this paper, steady-state analysis of the low power DBD is presented, considering the inevitable parasitic capacitance of the high-step transformer. The rectifier-compensated first harmonic approximation (RCFHA) is applied to linearize the equivalent load circuit of DBD at low frequency and the derived expressions are accurate and convenient for the analysis and design of the power supply. Based on the proposed linear equivalent load circuit, the influence of transformer parasitic capacitance on the key parameters, including the frequency range and the applied electrode voltage, is discussed when the power is regulated with pulse frequency modulation (PFM). Also, a design procedure is presented based on the derived expressions. A prototype is constructed according to the design results and the accuracy of the design is verified by experimental results.

关键词： Dielectric barrier discharge Rectifier-compensated first harmonic approximation Parasitic capacitance Power converter design

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基于变压器CMOS超宽带毫米波电路分析与设计综述 Review Articles

Yi-ming YU, Kai KANG

《信息与电子工程前沿（英文）》 2020年第21卷第1期页码 97-115 doi: 10.1631/FITEE.1900491

摘要：近年来，由于大量毫米波无线应用的产生，具有更强通用性的宽带毫米波电路和系统引起广泛关注。总结了4种基于片上变压器结构超宽带毫米波电路的理论分析、设计方法和综合性能。其一为毫米波低噪声放大器，采用基于变压器的跨导增强和极点调谐技术；通过采用这两种技术，该电路同时实现了较大工作带宽、低噪声系数和良好功率增益。其二为毫米波注入锁定三倍频器，采用注入电流增强技术，有效拓展了倍频器的锁定带宽。进一步，采用类似注入锁定技术结合变压器高阶谐振腔方案，实现了一款超宽带毫米波注入锁定分频器。最后，介绍了一款E波段上混频器，其采用两路跨导并联结构和基于变压器的多极点负载，实现了优异线性度和较大工作带宽。

关键词：硅基集成电路；毫米波；超宽带；变压器；低噪声放大器；倍频器；分频器；混频器

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解决未来低惯量电力系统的频率控制难题——英国视角 Perspective

洪启腾, Md Asif Uddin Khan, Callum Henderson, Agustí Egea-Àlvarez, Dimitrios Tzelepis, Campbell Booth

《工程（英文）》 2021年第7卷第8期页码 1057-1063 doi: 10.1016/j.eng.2021.06.005

摘要：

为实现全球艰巨的脱碳目标，电力系统需大规模整合可再生能源发电，这大大降低了系统惯量。除了系统惯量的降低，英国的输电系统还有一些特有的难题：其容量相对较小，同时又与其他输电系统分离，并且可再生资源在整个系统中的分布很大程度上不均匀。本文聚焦英国的输电系统，就低惯量系统中频率控制的相关挑战以及可能的解决方案提出了见解和建议。本文重点讨论了在不同时间尺度上发挥作用的三种主要技术：同步调相机、惯量模拟和快速频率响应。文中借鉴了英国最近的研究和开发项目，评估了其相对优势和局限性及其在解决未来低惯量系统频率控制难题方面的作用。

关键词：快速频率控制惯量模拟同步补偿低惯量系统

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Improvement to observability measures of LFO modes in power systems with DFIGs

Shenghu LI

《能源前沿（英文）》 2021年第15卷第2期页码 539-549 doi: 10.1007/s11708-019-0617-z

摘要： Observation of the low-frequency oscillation (LFO) modes in power systems is important to design the damping scheme. The state equations of the power system with the doubly-fed induction generators (DFIGs) are derived to find the LFO modes related to the synchronous generator (SGs) and the DFIGs. The definition of the observability measure is improved to consider the initial output and the attenuation speed of the modes. The sensitivities of the observability measures to the control parameters are derived. The numerical results from the small and large-disturbance validate the LFO modes caused by the DFIGs, and different observability measures are compared. Adjustment of the control parameters is chosen based on the sensitivity model to improve the observability and damping ratio of the LFO mode, and the stability of the wind power system.

关键词： wind power system low-frequency oscillation (LFO) observability measure sensitivity doubly-fed induction generator (DFIG)

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极低频探地工程——无线电磁法

陆建勋, 卓贤军, 刘勇, 赵国泽, 底青云

《工程（英文）》 2022年第10卷第3期页码 13-20 doi: 10.1016/j.eng.2021.12.003

关键词：工程成就

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Design of noise-reduction seats for high-speed trains

Xiaojun DENG, Yanju ZHAO, Haijin ZHANG, Renzhong SHUAI, Leiwei ZHU

《机械工程前沿（英文）》 2018年第13卷第3期页码 385-389 doi: 10.1007/s11465-017-0438-x

摘要：

Noise-reduction seats have been successfully used in concert halls, theaters, and other places that reduce noise. In this study, a new noise-reduction seat design was proposed for high-speed trains, which have unique interior noise spectral characteristics. First, before the noise-reduction seat models were fabricated, the parameters of high-performance sound-absorbing materials and perforated plates were selected by conducting a standing-wave tube test. The sound-absorption effects of the noise-reduction seats and normal seats were investigated and compared in a reverberation chamber. Test results showed that, compared with normal seats, the noise-reduction seats obtained a significantly improved sound-absorption coefficient in the entire frequency band. Furthermore, the test results were used to establish a simulation model for calculation, and the simulation results proved that the noise-reduction seats substantially reduced the noise in an entire train car. Finally, the noise-reduction seats were fabricated and installed in a full train car of an actual high-speed train. The test results showed that, compared with the normal seats, the noise-reduction seats decreased the noise level at a standard point in the passenger car by 1.5 dB. Therefore, the noise-reduction seats are effective in noise reduction.

关键词： high-speed train sound-absorbing materials perforated board noise-reduction seats

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Anovel approach of noise statistics estimate using H∞ filter in target tracking

Xie WANG,Mei-qin LIU,Zhen FAN,Sen-lin ZHANG

《信息与电子工程前沿（英文）》 2016年第17卷第5期页码 449-457 doi: 10.1631/FITEE.1500262

摘要： Noise statistics are essential for estimation performance. In practical situations, however, a priori information of noise statistics is often imperfect. Previous work on noise statistics identification in linear systems still requires initial prior knowledge of the noise. A novel approach is presented in this paper to solve this paradox. First, we apply the H∞ filter to obtain the system state estimates without the common assumptions about the noise in conventional adaptive filters. Then by applying state estimates obtained from the H∞ filter, better estimates of the noise mean and covariance can be achieved, which can improve the performance of estimation. The proposed approach makes the best use of the system knowledge without a priori information with modest computation cost, which makes it possible to be applied online. Finally, numerical examples are presented to show the efficiency of this approach.

关键词： Noise estimate H∞ filter Target tracking

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极低频探地（WEM）工程

卓贤军,陆建勋,赵国泽,底青云

《中国工程科学》 2011年第13卷第9期页码 42-50

摘要：

“极低频探地（WEM）工程”是国家发展和改革委员会批准的“十一五”国家重大科学技术基础设施建设项目之一，用于资源探测和地震预测及其他前沿科学研究。文章对工程项目背景、建设内容、关键技术和试验成果作了全面介绍，在此基础上，对工程的应用前景作了展望。

关键词： WEM法资源探测地震预测

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珊瑚岛礁环境噪声成像 Article

夏少红, 张昌榕, 曹敬贺

《工程（英文）》 2023年第25卷第6期页码 182-193 doi: 10.1016/j.eng.2021.09.022

摘要：

As valuable land in the ocean, coral islands are not only important bases for making use of marine resources and protecting marine rights and interests, but also important for breakthrough research in many fields of earth science. Hence, the economical and efficient determination of the underground structure of coral islands has become significant in coral island engineering geology, but remains challenging for traditional marine geophysical prospecting and drilling methods. While ambient noise tomography with dense arrays has been widely used in continental regions, its applicability to coral islands remains undetermined. In this study, based on the data recorded by a dense array on an isolated coral island in the South China Sea, we analyzed the ambient noise characteristics and obtained a 3D subsurface structure of the coral island using ambient noise tomography. We made the following findings: ① The ambient noise frequencies can be roughly categorized into three levels: < 1, 1–5, and > 5 Hz. The spectral characteristics of the noise below 5 Hz were consistent at different stations, but there were significant differences in the characteristics of the noise above 5 Hz. ② For ambient noise frequencies below 5 Hz, cross-correlation functions with high quality could be obtained with only 24 h of waveform data. However, it was difficult to extract meaningful cross-correlation functions for ambient noise frequencies above 5 Hz. ③ The S-wave velocity in the coral island was higher toward the sea and lower toward the lagoon, which was consistent with the high degree of cementation of the outer reef flat stratum on the seaward side. ④ There were two low-velocity horizons at 25–75 and 200–300 m, which were in good agreement with the high-porosity horizons that were revealed by drilling core samples, reflecting the weathering history of the reef. Our research demonstrates that ambient noise tomography is a potentially economical, efficient, and environmentally friendly method for the geological prospecting of coral reefs.

关键词： Coral island Ambient noise tomography Engineering geology South China Sea