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Bandgap formation and low-frequency structural vibration suppression for stiffened plate-type metastructure with general boundary conditions

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Chinese Journal of Aeronautics 2023年第10期36卷 210-228页

作者： tian zhao Zhichun YANG Yanlong XU Wei tian School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China

Metastructures with unique mechanical properties have shown attractive potential application in vibration and noise ***,most of the metastructures deal with the vibration bandgap properties of infinite structures without considering specific boundary condition and dynamic behaviors,which cannot be directly applied to the engineering *** this research,we design a Stiffened Plate-type Metastructure(SPM)composed of a plate with periodic stiffeners and cantilever beam-type resonators subjected to general boundary conditions for low-frequency vibration *** effects of boundary conditions and the number and orientation of the stiffeners on Locally Resonant(LR)type bandgap properties in SPM are further *** analytical modeling framework is developed to predict the bandgap formations and vibration behaviors of SPMs in finite-size *** governing equations of the SPM reinforced by various arrangements of stiffeners are derived based on the first-order shear deformation theory and Hamilton’s principle,and a Fourier series combined with auxiliary functions is employed to satisfy the arbitrary boundary *** element analysis and experimental investigations of vibration behaviors for the SPM are carried out to validate the accuracy and reliability of the present analytical *** practical designs of the SPMs with specific boundary conditions,it is found that there exist optimal numbers of stiffeners and resonators which can produce the significant LR-type bandgap ***,various arrangements of stiffeners and resonators are explored for different boundary conditions by breaking the requirement of spatially *** is shown that for the designed SPM,the vibration modes of its host structure should be considered to widen the frequency range in which the resonators transfer and store energy,and hence improve the performance of low-frequency vibration *** present work can pro

关键词： Bandgap Locally resonant Metastructure Stiffened plate Vibration suppression

Supersonic flutter control and optimization of metamaterial plate

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Chinese Journal of Aeronautics 2021年第11期34卷 15-20页

作者： Wei tian tian zhao Yingsong GU Zhichun YANG School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China

A metamaterial plate is designed by embedding a periodic array of local nonlinear resonators for its supersonic flutter *** on the von Karman large deformation theory and supersonic piston aerodynamic theory,the nonlinear aeroelastic equations of the metamaterial plate are obtained by using the Hamilton *** comparisons for aeroelastic behaviors of the metamaterial plate and pure plate show that the proposed metamaterial plate can lead to an enlarged flutter boundary and lower vibration ***,a parametric optimization strategy for local nonlinear resonators is proposed to improve the nonlinear flutter behaviors of the metamaterial plate,and a significant enhancement of passive control performance can be achieved through optimization *** present study demonstrates that the design of the metamaterial plate can provide an effective approach and potential application for nonlinear flutter suppression of supersonic plate.

关键词： Local resonators Metamaterial plate Nonlinear aeroelastic responses Parametric optimization design Supersonic flutter control

The duality of internal energy of ideal gas

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Science Bulletin 2015年第15期60卷 1355-1358页

作者： tian zhao Zengyuan Guo Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering MechanicsTsinghua University

This contribution starts with the discussion on the classification of energy, and then the behaviors of various thermodynamic processes are analyzed, accompanying with the comparison of the adiabatic compression process of an ideal gas and an elastic rod. All these analyses show that the internal energy of ideal gases exhibits the duality of thermal energy–mechanical energy, that is,the internal energy acts as the thermal energy during the isochoric process, while the internal energy acts as the mechanical energy during the isentropic process. Such behavior of the internal energy is quite different from other types of energy during the energy conversion process because the internal energy of ideal gases exhibits the duality of thermal energy–mechanical energy. Because of this duality, the internal energy of ideal gas is proposed to be refered to as thermodynamic energy rather than thermal energy as indicated in some literature, although it consists of kinetics of the microscopic random motion of particles and can be expressed as the function of temperature only.

关键词： Internal energy Mechanical energy Ideal gas Duality

Experimental study and cellular automata simulation of corrosion behavior of ferritic stainless steel in molten aluminum

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Journal of Iron and Steel Research International 2022年第9期29卷 1485-1494页

作者： Ji-yin Long tian-tian zhao Mei-yi Yuan Yi-tao Yang School of Materials Science and Engineering Shanghai UniversityShanghai 200444China

The corrosion behavior of feritic stainless steel(446)after being immersed in molten Al alloy at 750℃ for 1,2,4,and 8 h has been investigated experimentally and *** microstructure and composition distribution at the corrosion interface were characterized using the optical microscope,scanning electron microscope,and energy dispersive *** results showed that Cr and Si synergistically delay the progress of corrosion at the interface of the intermetallic compounds(IMC).In the early stage of corrosion,Si element was enriched at the interface of IMC1 and IMC2,and the diffusion channels of Al element were occupied by ***,as the corrosion progresses,Cr and Si gradually gather to form a band-like structure and coarsen,causing their hindering effect to be *** the corrosion time increases,the banded structure was further aggregated and coarsened,and the inhibitory effect of Cr and Si elements on corrosion was strongly *** addition,based on the cellular automata dynamics model of reaction-diffusion,the corrosion process of ferritic stainless steel in aluminum alloy melts was *** is demonstrated that if there is no stabilizing effect of Cr element,the thickness of IMC will be doubled.

关键词： Stainless steel Molten Al alloy Intermetallic Diffusion-Cellular automata

Microstructure evolution and corrosion behavior of Nb-alloyed cast heat-resistant steel during different aging treatments

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Journal of Iron and Steel Research International 2020年第12期27卷 1456-1465页

作者： Lv-dan Teng tian-tian zhao Teng-fei Cheng Yi-tao Yang School of Materials Science and Engineering Shanghai UniversityShanghai 200444China

The microstructure evolution of heat-resistant cast stainless steels aged at 600, 700, 800 and 900 ℃ for 2 h was investigated by scanning electron microscopy and X-ray diffraction. Potentiodynamic polarization curves were applied to study the effects of Nb addition and aging temperature on corrosion resistance. The results demonstrated that eutectoid decomposition of the ferritic phase (δ → σ + γ2) was observed at 700-900 ℃. The content of σ-phase first increased and then decreased in the steels, where the maximum content was obtained at 800 ℃, indicating that the highest hardness occurred at 800 ℃ accordingly. The hardness of Nb-containing steels was significantly higher than that of Nb-free steels. The corrosion resistance of heatresistant cast steels in various aging temperatures was different due to the formation of σ-phase. Both Cr-rich carbides and σ-phase were harmful to the corrosion resistance, while Cr-rich carbides were the main factor. Nb-containing heat-resistant cast steels exhibited superior corrosion resistance, as Cr-rich carbides were reduced and the corrosion products of Nb-rich slowed down the formation of steady-state pits.

关键词： Nb addition Aging temperature σ-phase Polarization Pitting corrosion

A Correction Factor-Based General Thermal Resistance Formula for Heat Exchanger Design and Performance Analysis

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Journal of Thermal Science 2021年第3期30卷 892-901页

作者： HAO Junhong CHEN Qun LI Xia zhao tian Key Laboratory of Power Station Energy Transfer Conversion and System of Ministry of Education School of Energy Power and Mechanical EngineeringNorth China Electric Power UniversityBeijing 102206China Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering MechanicsTsinghua UniversityBeijing 100084China

Methods for the analysis of heat exchangers with various flow arrangements modeling,design,and performance are essential for heat transfer system modeling and its integration with other energy system *** paper proposes the use of the linear-transfer law for the heat exchanger design and performance analysis as a function of the thermal resistance related to the ratio of a linear temperature difference to the total heat transfer ***,we derived a correction factor that represents the influence of the flow arrangement on the heat transfer performance by the effective thermal conductance,as a function of correction factor,heat transfer coefficient,and surface *** on the effective thermal conductance,we propose the hot-end NTU and cold-end NTU for deriving a standardized and general thermal resistance formula for different types of heat exchangers by the combination of the correction factor with linear-transfer ***,for parallel-flow,cross-flow,and 1-2 Tubular Exchanger Manufacturers Association(TEMA)E shell-and-tube heat exchangers,we derived and obtained alternative correction factor expressions without introducing any *** cases about heat exchanger design and performance analysis show that the calculation processes using the correction factor-based general thermal resistance are straightforward without any iteration and the calculation results are ***,the experimental validation shows that the general thermal resistance formula is appropriate for analyzing the heat transfer *** is,the correction factor-based general thermal resistance formula provides a standardized model for heat exchanger analysis and heat transfer/integrated energy system modeling using the heat current method.

关键词： general thermal resistance formula correction factor heat current model linear-transfer law heat exchanger

Load-balanced broadcast routing in wireless Ad-hoc networks

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The Journal of China Universities of Posts and Telecommunications 2007年第3期14卷 1-4,42页

作者： HU tian zhao Bao-hua Department of Computer Science and Technology University of Science and Technology of China Hefei 230027 China

In wireless Ad-hoc networks, where mobile hosts are powered by batteries, the entire network may be partitioned because of the drainage of a small set of batteries. Therefore, the crucial issue is to improve the energy efficiency, with an objective of balancing energy consumption. A greedy algorithm called weighted minimum spanning tree （WMST） has been proposed, in which time complexity is O（n^2）. This algorithm takes into account the initial energy of each node and energy consumption of each communication. Simulation has demonstrated that the performance of the proposed algorithm improves the load balance and prolongs the lifetime.

关键词： wireless Ad-hoc networks broadcast routing load balance lifetime

The framework of a geospatial semantic web-based spatial decision support system for Digital Earth

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International Journal of Digital Earth 2010年第2期3卷 111-134页

作者： Chuanrong Zhang tian zhao Weidong Li Department of Geography and Center for Environmental Sciences and Engineering University of ConnecticutStorrsCT 06269USA Department of Computer Science University of WisconsinMilwaukeeWI 53201USA College of Resources and Environment Huazhong Agricultural UniversityWuhan 430070China

While significant progress has been made to implement the Digital Earth vision,current implementation only makes it easy to integrate and share spatial data from distributed sources and has limited capabilities to integrate data and models for simulating social and physical *** achieve effectiveness of decisionmaking using Digital Earth for understanding the Earth and its systems,new infrastructures that provide capabilities of computational simulation are *** paper proposed a framework of geospatial semantic web-based interoperable spatial decision support systems(SDSSs)to expand capabilities of the currently implemented infrastructure of Digital *** technologies applied in the framework such as heterogeneous ontology integration,ontology-based catalog service,and web service composition were *** proposed a partitionrefinement algorithm for ontology matching and integration,and an algorithm for web service discovery and *** proposed interoperable SDSS enables decision-makers to reuse and integrate geospatial data and geoprocessing resources from heterogeneous sources across the *** on the proposed framework,a prototype to assist in protective boundary delimitation for Lunan Stone Forest conservation was implemented to demonstrate how ontology-based web services and the services-oriented architecture can contribute to the development of interoperable SDSSs in support of Digital Earth for decision-making.

关键词： spatial decision support system(SDSS) web services ontology geospatial semantic web Digital Earth

Correlation between Atmospheric Water Vapor and Diurnal Temperature Range over China

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Atmospheric and Oceanic Science Letters 2014年第4期7卷 369-375页

作者： zhao tian-Bao Key Laboratory of Regional Climate-Environment Research for East Asia Institute of Atmospheric Physics Chinese Academy of Sciences

Diurnal temperature range （DTR） is an im- portant measure in studies of climate change and variability. The changes of DTR in different regions are affected by many different factors. In this study, the degree of correlation between the DTR and atmospheric precipitable water （PW） over China is explored using newly homogenized surface weather and sounding observations. The results show that PW changes broadly reflect the geographic patterns of DTR long-term trends over most of China during the period 1970-2012, with significant anticorrelations of trend patterns between the DTR and PW, especially over those regions with higher magnitude DTR trends. PW can largely explain about 40% or more （re 0.40） of the DTR changes, with a d（PW）/d（DTR） slope of -2% to -10% K^-1 over most of northwestern and southeastern China, despite certain seasonal dependencies. For China as whole, the significant anticorrelations between the DTR and PW anomalies range from -0.42 to -0.75, with a d（PW）/d（DTR） slope of-6% to -11% K^-1. This implies that long-term DTR changes are likely to be associated with opposite PW changes, approximately following the Clausius-Clapeyron equation. Furthermore, the relationship is more significant in the warm season than in the cold season. Thus, it is possible that PW can be considered as one potential factor when exploring long-term DTR changes over China. It should be noted that the present study has a largely statistical focus and that the underlying physical processes should therefore be examined in future work.

关键词： atmospheric water vapor precipitable water diurnal temperature range anticorrelation China