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frequency domain analysis of pre-stressed elastomeric vibration isolators

Defence Technology（防务技术） 2023年第7期25卷 33-47页

作者： S.Somanath R.Marimuthu Shankar Krishnapillai Indian Space Research Organisation Anthariksh BhavanNew BEL RoadBengaluru560231India STR/VSSC Indian Space Research OrganisationThiruvananthapuram695022India Department of Mechanical Engineering IIT MadrasChennai600036India

Two types of elastomeric vibration isolators used for equipment vibration isolation in aerospace vehicles are considered for the present study. These isolators are constructed using elastomers mounted in steel encasings. These isolators are initially deformed statically and dynamic loads are applied on the deformed configuration. To capture the static deformation, equivalent static load corresponding to its load rating and specified displacements are created. Static deformation is computed using Finite Element methods with four node axi-symmetric element which include the geometric non-linear effect for steel and with standard Yeoh hyper-elastic material model for elastomers(Muhammed and Zu, 2012) [1]. Yeoh material constants are derived from uni-axial tension test data of the elastomer specimen. These isolators are subjected to harmonic and random excitations in the pre-deformed state. For numerical analysis, elastomeric constants at dynamic conditions are obtained as complex function of frequency using Dynamic Mechanical Analyzer(DMA) for a range of frequencies. The standard material model of Yeoh is modified incorporating frequency dependant material characteristics and damping in the range of frequencies of interest. A multiplicative non-separable variables law is derived for Yeoh material model to include the effect of static pre-stress, based on the methodology given in literature(Nashif et al.,1985;Beda et al., 2014) [2,3]. The modifications of Yeoh model suitable for frequency domain analysis is the novelty in the present study. In the analysis, while dynamic loads are applied, the configuration is updated considering initial static loading. The frequency response of the isolators is computed using material properties evaluated at progressive dynamic strains until a match in natural frequency is observed. Appropriate damping corrections are then incorporated to match the test observed transmissibility. Then updated material properties are used to compute the

关键词： Elastomer Isolator Axi-symmetric frequency Random Response Strain amplitude Complex modulus Transmissibility

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frequency comparative study of coal-fired fly ash acoustic agglomeration

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Journal of Environmental Sciences 2011年第11期23卷 1845-1851页

作者： Jianzhong Liu Jie Wang Guangxue Zhang Junhu Zhou Kefa Cen State Key Laboratory of Clean Energy Utilization Zhejiang UniversityHangzhou 310027China Institute for Energy Engineering China Jiliang UniversityHangzhou 310018China

Particulate pollution is main kind of atmospheric *** fine particles are seriously harmful to human health and *** agglomeration is considered as a promising pretreatment technology for fine particle *** mechanisms of acoustic agglomeration are very complex and the agglomeration efficiency is affected by many *** most important and controversial factor is *** studies between high-frequency and low-frequency sound source to agglomerate coal- fired fly ash were carried out to investigate the influence of frequency on agglomeration *** agglomeration theoretical analysis,experimental particle size distributions （PSDs） and orthogonal design were *** results showed that the 20 kHz high-frequency sound source was not suitable to agglomerate coal-fired fly *** within the size ranging from 0.2 to 0.25 μm the particles agglomerated to adhere together,and the agglomerated particles were smaller than 2.5 μ*** application of low-frequency （1000–1800 Hz） sound source was proved as an advisable pretreatment with the highest agglomeration efficiency of 75.3%,and all the number concentrations within the measuring range *** design L16 （4） 3 was introduced to determine the optimum frequency and optimize acoustic agglomeration *** to the results of orthogonal analysis,frequency was the dominant factor of coal-fired fly ash acoustic agglomeration and the optimum frequency was 1400 Hz.

关键词： coal-fired fly ash acoustic agglomeration frequency agglomeration kernel orthogonal design

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frequency control of future power systems: reviewing and evaluating challenges and new control methods

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Journal of Modern Power Systems and Clean Energy 2019年第1期7卷 9-25页

作者： Zeyad Assi OBAID Liana M.CIPCIGAN Lahieb ABRAHIM Mazin T.MUHSSIN College of Engineering University of Diyala Institute of Energy School of Engineering Cardiff University School of Engineering South Wales University College of Engineering Mustansiriyah University

Integration of more renewable energy resources introduces a challenge in frequency control of future power *** paper reviews and evaluates the possible challenges and the new control methods of frequency in future power *** types of loads and distributed energy resources(DERs) are reviewed.A model representation of a population of the water heater devices for the demand side frequency response is considered.A model representation of a population of battery energy storage system(BESS)-based DERs such as smart electric vehicles(EVs) charging, large-scale BESSs, and residential and non-residential BESSs, are *** simplified Great Britain power system and the 14-machine South-East Australian power system were used to demonstrate the effectiveness of the new methods in controlling power system frequency following a *** new methods are effective in recovering the fallen frequency response and present a great potential in controlling the frequency in future power systems.

关键词： Battery energy storage system(BESS) Distributed energy resource(DER) Electric vehicle Home-based BESS Large-scale BESS aggregation Demand side response frequency control Markov chain

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frequency Analyses for Mechanism Research of Unsteady Flow Inside Three Dimensional Compressor Cascade

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Journal of Thermal Science 2004年第3期13卷 207-212页

作者： Sheng Zhou Hongbin Wu Xinqian Zheng Beijing Univ Aeronaut & Astronaut Natl Key Lab Aircraft Engine Beijing 100083 Peoples R China

Numerical simulations are carried out for unsteady flow field of certain kind of 3D compressor cascade. Emphasis is laid on vortex shedding and frequency analysis in a compressor cascade. Numerical simulations using unsteady Reynolds-averaged viscous turbulent equations are carried out. The results show that the flows in separated areas and wake areas are characterized as periodic or quasi-periodic vortex shedding and the frequencies of vortex shedding vary with incidences and Mach number. At the same Mach number, the frequency of vortex shedding will decrease as the incidence increases. Yet, the frequency will increase as the Mach number increases at the same incidence. In the same computation case, the frequency of vortex shedding will vary along the span of blade. The frequency is smaller at the middle of the span than that at the hub.

关键词： axial flow compressor cascade unsteady flow separated flow frequency of vortex shedding.

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frequency and Similarity-Aware Partitioning for Cloud Storage Based on Space-Time Utility Maximization Model

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Tsinghua Science and Technology 2015年第3期20卷 233-245页

作者： Jianjiang Li Jie Wu Zhanning Ma Department of Computer Science and Technology University of Science and Technology Beijing Department of Computer and Information Sciences Temple University

With the rise of various cloud services, the problem of redundant data is more prominent in the cloud storage systems. How to assign a set of documents to a distributed file system, which can not only reduce storage space, but also ensure the access efficiency as much as possible, is an urgent problem which needs to be solved. Space-efficiency mainly uses data de-duplication technologies, while access-efficiency requires gathering the files with high similarity on a server. Based on the study of other data de-duplication technologies, especially the Similarity-Aware Partitioning （SAP） algorithm, this paper proposes the frequency and Similarity-Aware Partitioning （FSAP） algorithm for cloud storage. The FSAP algorithm is a more reasonable data partitioning algorithm than the SAP algorithm. Meanwhile, this paper proposes the Space-Time Utility Maximization Model （STUMM）, which is useful in balancing the relationship between space-efficiency and access-efficiency. Finally, this paper uses 100 web files downloaded from CNN for testing, and the results show that, relative to using the algorithms associated with the SAP algorithm （including the SAP-Space-Delta algorithm and the SAP-Space-Dedup algorithm）, the FSAP algorithm based on STUMM reaches higher compression ratio and a more balanced distribution of data blocks.

关键词： de-duplication cloud storage redundancy frequency

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frequency-specified EOF analysis and its application to Pacific decadal oscillation

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Science China Earth Sciences 2017年第2期60卷 341-347页

作者： LIAN Tao TANG YouMin State Key Lab of Satellite Ocean Environment Dynamics Second Institute of Oceanography Environmental Science and Engineering University of Northern British Columbia

t A frequency-specified empirical orthogonal function （FSEOF） analysis is proposed in this study. The aim of FSEOF is to specify a prescribed-band of frequency in leading principal components with less information losing at the ends of the data, thus well characterizing the signals of interest. The FSEOF can well capture prescribed variability in leading modes, and has intrinsic merits in resolving frequency-related modes, especially those associated with low frequency oscillations. An application of the FSEOF to the tropical and northern Pacific sea surface temperature shows that this new method can successfully separate Pacific decadal oscillation （PDO） mode from the El Nino-Southern oscillation mode, and clearly detect all regime shifts of PDO in the past century.

关键词： frequency EOF PDO

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frequency Loss and Recovery in Rolling Bearing Fault Detection

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Chinese Journal of Mechanical Engineering 2019年第2期32卷 145-156页

作者： Aijun Hu Ling Xiang Sha Xu Jianfeng Lin Department of Mechanical Engineering North China Electric Power University

Rolling element bearings are key components of mechanical equipment. The bearing fault characteristics are a ected by the interaction in the vibration signals. The low harmonics of the bearing characteristic frequencies cannot be usually observed in the Fourier spectrum. The frequency loss in the bearing vibration signal is presented through two independent experiments in this paper. The existence of frequency loss phenomenon in the low frequencies, side band frequencies and resonant frequencies and revealed. It is demonstrated that the lost frequencies are actually suppressed by the internal action in the bearing fault signal rather than the external interference. The amplitude and distribution of the spectrum are changed due to the interaction of the bearing fault signal. The interaction mechanism of bearing fault signal is revealed through theoretical and practical analysis. Based on mathematical morphology, a new method is provided to recover the lost frequencies. The multi-resonant response signal of the defective bearing are decomposed into low frequency and high frequency response, and the lost frequencies are recovered by the combination morphological filter(CMF). The e ectiveness of the proposed method is validated on simulated and experimental data.

关键词： Rolling element bearing Signal processing frequency loss Fault detection Morphological filter

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frequency dependence of plasma characteristics at different pressures in cylindrical inductively coupled plasma source

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Plasma Science and Technology 2019年第7期21卷 114-122页

作者： Zeyu HAO Jian SONG Yue HUA Gailing ZHANG Xiaodong BAI Chunsheng REN Key Laboratory of Materials Modification by Laser Ion and Electron Beams (Dalian University of Technology) Ministry of Education

The effects of driving frequency on plasma parameters and electron heating efficiency are studied in cylindrical inductively coupled plasma(ICP) source. Measurements are made in an Ar discharge for driving frequency at 13.56/2 MHz, and pressures of 0.4-1.2 Pa. In 13.56 MHz discharge, higher electron density(n_e) and higher electron temperature(T_e) are observed in comparison with 2 MHz discharge at 0.6-1.2 Pa. However, slightly higher n_e and T_e are observed in 2 MHz discharge at 0.4 Pa. This observation is explained by enhanced electron heating efficiency due to the resonance between the oscillation of 2 MHz electromagnetic field and electron-neutral collision process at 0.4 Pa. It is also found that the variation of T_edistribution is different in 13.56 and 2 MHz *** ICP at 13.56 MHz, T_eshows an edge-high profile at 0.4-1.2 Pa. For 2 MHz discharge, T_e remains an edge-high distribution at 0.4-0.8 Pa. However, the distribution pattern involves into a center-high profile at 0.9-1.2 Pa. The spatial profiles of n_e remain a center-high shape in both 13.56 and 2 MHz discharges, which indicates the nonlocal kinetics at low pressures. Better uniformity could be achieved by using 2 MHz discharge. The effects of gas pressure on plasma parameters are also examined. An increase in gas pressure necessitates the rise of n_e in both 13.56 and 2 MHz discharges. Meanwhile, T_e drops when gas pressure increases and shows a flatter distribution at higher pressure.

关键词： inductively coupled plasma driving frequency electron heating efficiency electron temperature electron density

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frequency Analysis and Anti-Shock Mechanism of Woodpecker＇s Head Structure

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Journal of Bionic Engineering 2014年第2期11卷 282-287页

作者： Zhaodan Zhu Chengwei Wu Wei Zhang State Key Lab of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian 116024 P. R. China

The mechanical properties of the skull and the anti-shock characteristics of woodpecker＇s head were investigated by ex- periment and numerical simulation. We measured the micro-Young＇s modulus of the skull by nano-indentation method and calculated the macro-equivalent Young＇s modulus of the skull at different positions using homogenization theory. Based on the Computerized Tomography （CT） images of woodpecker head, we then built complete and symmetric finite element models of woodpecker＇s skull and its internal structure and performed modal analysis and stress spectrum analysis. The numerical results show that the application of pre-tension force to the hyoid bone can increase the natural frequency of woodpecker＇s head. The first natural frequency under the pre-tension force of 25 N reaches 57 Hz, which is increased by 21.3% from the non-pre-tension state and is more than twice the working frequency of woodpecker （20 Hz 25 Hz）. On the application of impact force to the tip of beak for 0.6 ms, high magnitudes of stress component occur at around 100 Hz and 8,000 Hz, far away from both the working frequencies and the natural frequencies of woodpecker head. The large gaps among the natural, working and stress response frequencies enable the woodpecker to effectively protect its brain from the resonance injury.

关键词： woodpecker anti-shock frequency modal analysis stress spectrum

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frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in ^85Rb

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Chinese Physics Letters 2007年第7期24卷 1883-1885页

作者：刘璐郭涛邓科刘新元陈徐宗汪中 Laboratory for Quantum Information and Measurements School of Electronics Engineering and Computer Science Peking University Beijing 100871

An atomic clock system based on coherent population trapping （CPT） resonance in 85Rb is reported, while most past works about the CPT clock are in ST Rb. A new modulation method （full-hyperfine-frequency-splitting modulation） is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in SSRb. The experimental results show that the short-term frequency stability of the CPT clock in SSRb is in the order of 10^-10/s and the long-term frequency stability can achieve 1.5 × 10^-11/80000s, which performs as well as 87 Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of SSRb indicates that an atomic clock based on CPT in SSRb should be a promising candidate for making the chip scale atomic clock.

关键词： Population Resonance frequency

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