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Mechanical properties of bimrocks with high rock block proportion 被引量:1
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作者 LIN Yue-xiang PENG Li-min +2 位作者 LEI Ming-feng YANG Wei-chao LIU Jian-wen 《Journal of Central South University》 SCIE EI CAS CSCD 2019年第12期3397-3409,共13页
For the investigation of mechanical properties of the bimrocks with high rock block proportion,a series of laboratory experiments,including resonance frequency and uniaxial compressive tests,are conducted on the 64 fa... For the investigation of mechanical properties of the bimrocks with high rock block proportion,a series of laboratory experiments,including resonance frequency and uniaxial compressive tests,are conducted on the 64 fabricated bimrocks specimens.The results demonstrate that dynamic elastic modulus is strongly correlated with the uniaxial compressive strength,elastic modulus and block proportions of the bimrocks.In addition,the density of the bimrocks has a good correlation with the mechanical properties of cases with varying block proportions.Thus,three crucial indices(including matrix strength)are used as basic input parameters for the prediction of the mechanical properties of the bimrocks.Other than adopting the traditional simple regression and multi-regression analyses,a new prediction model based on the optimized general regression neural network(GRNN)algorithm is proposed.Note that,the performance of the multi-regression prediction model is better than that of the simple regression model,owing to the consideration of various influencing factors.However,the comparison between model predictions indicates that the optimized GRNN model performs better than the multi-regression model does.Model validation and verification based on fabricated data and experimental data from the literature are performed to verify the predictability and applicability of the proposed optimized GRNN model. 展开更多
关键词 block-in-matrix-rock high rock block proportion resonance frequency test general regression neural network
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Design of Robust Controller for LFC of Interconnected Power System Considering Communication Delays
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作者 T. Jesintha Mary P. Rangarajan 《Circuits and Systems》 2016年第6期794-804,共11页
The usage of open communication infrastructure for transmitting the control signals in the Load Frequency Control (LFC) scheme of power system introduces time delays. These time delays may degrade the dynamic performa... The usage of open communication infrastructure for transmitting the control signals in the Load Frequency Control (LFC) scheme of power system introduces time delays. These time delays may degrade the dynamic performance of the power system. This paper proposes a robust method to design a controller for multi-area LFC schemes considering communication delays. In existing literature, the controller values of LFC are designed using time domain approach which is less accurate than the proposed method. In proposed method, the controller values are determined by moving the rightmosteigenvalues of the system to the left half plane in a quasi-continuous way for a preset upper bound of time delay. Then the robustness of the proposed controller is assessed by estimating the maximumtolerable value of time delay for maintaining system stability. Simulation studies are carried out for multi-area LFC scheme equipped with the proposed controller using Matlab/simulink. From the results, it has been concluded that the proposed controller guarantees the tolerance for all time delays smaller than the preset upper bound and provides a bigger delay margin than the existing controllers. 展开更多
关键词 Continuous Pole Placement Technique Delay Margin Delay-Dependent Stability Analysis Frequency Sweeping test Load Frequency Control with Time Delays Output Feedback Control
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Influence factors on natural frequencies of composite materials 被引量:1
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作者 Bo WANG Feng ZHAO +1 位作者 Zixu ZHAO Kunpeng XU 《Frontiers of Mechanical Engineering》 SCIE CSCD 2020年第4期571-584,共14页
Compared with traditional materials, composite materials have lower specific gravity, larger specific strength, larger specific modulus, and better designability structure and structural performance. However, the vari... Compared with traditional materials, composite materials have lower specific gravity, larger specific strength, larger specific modulus, and better designability structure and structural performance. However, the variability of structural properties hinders the control and prediction of the performance of composite materials. In this work, the Rayleigh–Ritz and orthogonal polynomial methods were used to derive the dynamic equations of composite materials and obtain the natural frequency expressions on the basis of the constitutive model of laminated composite materials. The correctness of the analytical model was verified by modal hammering and frequency sweep tests. On the basis of the established theoretical model, the influencing factors, including layers, thickness, and fiber angles, on the natural frequencies of laminated composites were analyzed. Furthermore, the coupling effects of layers, fiber angle, and lay-up sequence on the natural frequencies of composites were studied. Research results indicated that the proposed method could accurately and effectively analyze the influence of single and multiple factors on the natural frequencies of composite materials. Hence, this work provides a theoretical basis for preparing composite materials with different natural frequencies and meeting the requirements of different working conditions. 展开更多
关键词 composite material hammering and frequency sweep test structural parameter natural frequency
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Large-scale frequent testing and tracing to supplement control of Covid-19 and vaccination rollout constrained by supply
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作者 Lia Humphrey Edward W.Thommes +5 位作者 Roie Fields Laurent Coudeville Naseem Hakim Ayman Chit Jianhong Wu Monica G.Cojocaru 《Infectious Disease Modelling》 2021年第1期955-974,共20页
Non-pharmaceutical interventions(NPI)were implemented all around the world in the fight against COVID-19:Social distancing,shelter-in-place,mask wearing,etc.to mitigate transmission,together with testing and contact-t... Non-pharmaceutical interventions(NPI)were implemented all around the world in the fight against COVID-19:Social distancing,shelter-in-place,mask wearing,etc.to mitigate transmission,together with testing and contact-tracing to identify,isolate and treat the infected.The majority of countries have relied on the former measures,followed by a ramping up of their testing and tracing capabilities.We present here the cases of South Korea,Italy,Canada and the United States,as a look back to lessons that can be drawn for controlling the pandemic,specifically through the means of testing and tracing.By fitting a disease transmission model to daily case report data in each of the four countries,we first show that their combination of social-distancing and testing/tracing have had a significant impact on the evolution of their first wave of pandemic curves.We then consider the hypothetical scenario where the only NPI measures implemented past the first pandemic wave consisted of isolating individuals due to repeated,country-scale testing and contact tracing,as a mean of lifting social distancing measures without a resurgence of COVID-19.We give estimates on the average isolation rates needed to occur in each country.We find that testing and tracing each individual of a country,on average,every 4.5 days(South Korea),5.7 days(Canada),6 days(Italy)and 3.5 days(US),would have been sufficient to mitigate their second pandemic waves.We also considered the situation in Canada to see how a frequent large-scale asymptomatic testing and contact tracing could have been used in combination with vaccination rollout to reduce the infection in the population.This could offer an alternative approach towards preventing and controlling an outbreak when vaccine supply is limited,while testing capacity has been increasingly enhanced. 展开更多
关键词 Pandemic modelling Pandemic evolution scenarios testing frequency policy modelling
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Effects of installations on the low frequency vibration response of specimens in acoustic fatigue tests
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作者 TIAN Jing(Institute of Acoustics , Academia SinicaBeijing 100080) 《Chinese Journal of Acoustics》 1991年第3期201-208,共8页
The low frequency vibration response of a specimen in acoustic fatigue tests depends not only on the dynamic characteristics and the boundary conditions of the specimen itself, but also on the test unit which couples ... The low frequency vibration response of a specimen in acoustic fatigue tests depends not only on the dynamic characteristics and the boundary conditions of the specimen itself, but also on the test unit which couples the specimen to a given sound field. Further, the latter can even be dominant instead the former in some circumstances. This fact is shown in the paper by using the experimental results and the theoretical analysis of the acoustic-induced vibration of a boundary clamped rectangular thin plate. In analysing the systems of acoustic fatigue test, an approach of electro-mechano-acoustical analogous circuit is used. The application of the approach can give an estimation of the effects on the low frequency vibration modes of various parameters in a system quantitatively. This supplies a theoretical basis and a means for the rational layout of acoustic fatigue tests. 展开更多
关键词 Effects of installations on the low frequency vibration response of specimens in acoustic fatigue tests
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Design and analysis of bidirectional deployable parabolic cylindrical antenna 被引量:1
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作者 Tian YU Fu-ling GUAN Lu DAI 《Journal of Zhejiang University-Science A(Applied Physics & Engineering)》 SCIE EI CAS CSCD 2014年第2期83-96,共14页
A bidirectional deployable parabolic cylindrical reflector for an L-band synthetic aperture radar is presented in this study, in which a self-deployed antenna with low weight was designed. The antenna consists of four... A bidirectional deployable parabolic cylindrical reflector for an L-band synthetic aperture radar is presented in this study, in which a self-deployed antenna with low weight was designed. The antenna consists of four curved surfaces formed from thin sheets of composite materials connected by hinges along the edges, and the reflective surface is provided by the front surface. The edge profiles of connecting lines were obtained through geometric analysis. A scaled model, including design and manufac- ture, was demonstrated to validate the process from the folded state to the fully deployed state. The non-contact synchronous vision measuring method was used to test the basic frequency of the scaled model, and the test results gave the verification of the analyses. Compared with the existing unidirectional deployable antenna, this new type of bidirectional deployable antenna can be applied to larger-size antennas and has better performance because the glass-woven tape connections were substituted with more reliable hinges. Static, modal, harmonic response, and transient response analyses of the full-sized reflector structure were mod- eled with the commercial finite element (FE) package ABAQUS. The modeling techniques were developed to predict the struc- tural dynamic behavior of the reflector and the results showed that the first natural frequency was 0.865 Hz, and the reflector structure had good stiffness in three directions. This proposed structure has very high stiffness-to-mass ratio because of its hollow solid construction. A preliminary simulation of radiation properties of the parabolic cylindrical antenna, fed by an off-set linear feed horn array, was conducted to obtain the radiation pattern of the feed and the reflector. 展开更多
关键词 Parabolic cylindrical antenna Geometric analysis Deploying and folding process Frequency test Structuralanalysis Radiation property
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VORTEX SHEDDING FREQUENCY DETERMINED BY SURFACE PRESSURE FLUCTUATIONS OF THREE EQUISPACED CYLINDERS
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作者 Dong Li yun, Xu You heng, Huang Dong qun Department of Mechanics and Engineering Science, Fudan University, Shanghai 200433, P.R.China 《Journal of Hydrodynamics》 SCIE EI CSCD 1999年第4期76-85,共10页
In his paper, the frequency of vortex shedding from three cylinders of the same diameter in equilateral triangular arrangement is determined experimentally by the spectrum analysis of surface pressure fluctuations at ... In his paper, the frequency of vortex shedding from three cylinders of the same diameter in equilateral triangular arrangement is determined experimentally by the spectrum analysis of surface pressure fluctuations at a Reynolds number of 3.0×10 4. For α=0°, there exists ‘bistable’ flow at the spacing 2.0. For α=30°, the vortex shedding of the front cylinder is found at small spacing less than 2.0. It is quite different from the case of two cylinders in tandem arrangement only. The side cylinder has great effects on the flow between the other two cylinders in close arrangement. For α=60°, there exists a critical spacing of about 2.5 that the frequency of each cylinders is nearly half of f s below this spacing and equal to f s above it respectively. The interference among three cylinders was negligible in the spacing range above 3.0 at α=0 and 60 deg., and each cylinder behaves as a single cylinder with the same vortex shedding frequency f s. In these small spacing (spacing<3.0), interference occurs seriously and has great effects in a complex fashion on the flow state around three cylinders. 展开更多
关键词 interference among three cylinders pressure fluctuation vortex shedding frequency. wind tunnel testing
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