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VIBRATION OF FLUID-FILLED MULTI-WALLED CARBON NANOTUBES SEEN VIA NONLOCAL ELASTICITY THEORY

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Acta Mechanica Solida Sinica 2014年第6期27卷 568-578页

作者： Qingtian Deng Zhichun YANG School of Science Chang'an University School of Aeronautics Northwestern Polytechnical University

Vibration characteristics of fluid-filled multi-walled carbon nanotubes axe studied by using nonlocal elastic Fliigge shell model. Vibration governing equations of an N-layer carbon nanotube are formulated by considering the scale effect. In the numerical simulations, the effects of different theories, small-scale, variation of wavenumber, the innermost radius and length of double- walled and triple-walled carbon nanotubes are considered. Vibrational frequencies decrease with an increase of scale coefficient, the innermost radius, length of nanotube and effects of wall number are negligible. The results show that the cut-off frequencies can be influenced by the wall number of nanotubes.

关键词： vibration multi-walled carbon nanotubes fluid-filled nonlocal elastic theory

Suppressing nonlinear aeroelastic response of laminated composite panels in supersonic airflows using a nonlinear energy sink

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Chinese Journal of Aeronautics 2021年第2期34卷 376-385页

作者： Jian ZHOU Minglong XU Zhichun YANG Yingsong GU State Key Laboratory for Strength and Vibration of Mechanical Structures School of Aerospace EngineeringXi'an Jiaotong UniversityXi'an 710049China School of Aeronautics Northwestern Polyteclmical UniversityXi'an 710072China

This paper proposes using a Nonlinear Energy Sink(NES) to suppress the nonlinear aeroelastic response of laminated composite panels in supersonic airflows. Relevant aeroelastic equations are established using Hamilton’s principle and a finite element approach, drawing upon Von Karman’s large deflection theory and first order piston theory. The idea of the NES suppression region is proposed and the effects of NES parameters on the NES suppression region are studied in detail. The results show that the nonlinear aeroelastic responses of the panel can be completely suppressed by the Transient Resonance Capture(TRC);the appropriate NES parameter values can increase the critical dynamic pressure for flutter and suppress the nonlinear aeroelastic response effectively. Increasing the mass ratio of the NES can improve the NES suppression region;the nonlinear stiffness coefficient and damping of the NES within a specific range can suppress the nonlinear aeroelastic response. The most effective installation position for a NES is in a specific region behind the center-line of the panel in the direction of the airflow.

关键词： Aeroelasticity Laminated composite panel Nonlinear dynamics Nonlinear energy sink Panel flutter Passive suppression

Wind tunnel test of gust load alleviation for a large-scale full aircraft model

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Chinese Journal of Aeronautics 2023年第4期36卷 201-216页

作者： Dongqiang ZHAO Zhichun YANG Xianang ZENG Jinge YU Yining GAO Guoning HUANG School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China AVIC The First Aircraft Institute Xi’an 710089China AVIC Aerodynamics Research Institute Harbin 150001China

Wind tunnel test is an important way to test the performance of Gust Load Alleviation(GLA).At present,some component-level wind tunnel tests have been carried out in big aviation countries,but there is a lack of full aircraft model GLA tests.In this study,a set of large-scale GLA test system in low-speed wind tunnel is developed,which includes a gust generator,a five-degree-of-freedom suspension system,a full elastic aircraft model with control system,and gust load measuring devices.Two control schemes based on closed-loop feedback control and open-loop feed forward control are respectively designed and verified by the full-model GLA tests in the wind tunnel.The experimental results show that the designed gust generator can generate a stable wideband,wide-area gust wind field;the suspension support system can sustain static and dynamic stability during wind tunnel test,and enables the model moving in the horizontal,vertical,pitching,rolling and yawing directions.The results show that the closed-loop feedback control can obtain good control performance of reducing the peak values of elastic vibration response induced by gust excitation,but has little effect on suppressing the rigid body motion excited by low-frequency gust,while the open-loop feed forward control presents superior performance in allevi-ating the high-frequency elastic vibration as well as the low-frequency rigid body motion with more than 40%overall reduction rate.

关键词： Alleviation Full model Gust generator Suspension system Wind tunnel

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 control.Based 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 principle.The 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 amplitude.Furthermore,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 design.The 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

Boundary condition modelling and identification for cantilever-like structures using natural frequencies

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Chinese Journal of Aeronautics 2019年第6期32卷 1451-1464页

作者： Wei LIU Zhichun YANG Le WANG Ning GUO School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China Xi’an Aerospace Propulsion Institute Xi’an 710100China

The actual boundary conditions of cantilever-like structures might be non-ideally clamped in engineering practice, and they can also vary with time due to damage or aging. Precise modelling of boundary conditions, in which both the boundary stiffness and the boundary mass should be modelled correctly, might be one of the most significant aspects in dynamic analysis and testing for such structures. However, only the boundary stiffness was considered in the most existing methods. In this paper, a boundary condition modelling and identification method for cantilever-like structures is proposed to precisely model both the boundary stiffness and the boundary mass using sensitivity analysis of natural frequencies. The boundary conditions of a cantilever-like structure can be parameterized by constant mass, constant rotational inertia,constant translational stiffness, and constant rotational stiffness. The relationship between natural frequencies and boundary parameters is deduced according to the vibration equation for the lateral vibration of a non-uniform beam. Then, an iterative identification formulation is established using the sensitivity analysis of natural frequencies with respect to the boundary parameters. The regularization technique is also used to solve the potential ill-posed problem in the identification procedure.Numerical simulations and experiments are performed to validate the feasibility and accuracy of the proposed method. Results show that the proposed method can be utilized to precisely model the boundary parameters of a cantilever-like structure.

关键词： Boundary condition identification Boundary condition modelling Iterative method Natural frequency Sensitivity analysis

Positive and negative effects of graphite flake and monolayer graphene oxide templates on protein crystallization

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Particuology 2023年第8期79卷 27-34页

作者： zhichun Lin Wenqing Tian yang Su Vikash Kumar Yadav Huaiyu yang Department of Chemical Engineering Loughborough UniversityLoughboroughLE113TUUK Institute of Materials Research Tsinghua Shenzhen International Graduate SchoolTsinghua UniversityShenzhen518055China Human Sciences Research Centre University of DerbyDE221GBUK

Heterogeneous template-induced nucleation is a promising way to regulate protein crystallization events and could be employed for purification processes and crystallographic studies.Protein crystallization process with graphite and graphene oxide,as heterogeneous templates,were investigated.More than 640 hanging drops with different concentrations of Lysozyme(30,50,70,100 mg/mL)and NaCl(0.7,0.9,1.1,1.3,1.5 M)were crystallised at 4 ℃ with or without graphite/graphene oxide templates.The induction times and crystallization process were observed under the microscope.The lysozyme in the solutions with graphite flakes nucleated faster under all the conditions than the lysozyme with equal experimental conditions without templates.The crystals preferred to grow around the edge of graphite flakes than on the flat surfaces.In the droplets with monolayer graphene oxide,more crystals appeared around gra-phene oxide particles,and the faster or slower nucleation processes with templates were dependent on the lysozyme and NaCl concentrations.Graphene oxide templates strongly inhibited nucleation at high lysozyme concentrations but promoted nucleation at low lysozyme concentrations.Both heterogeneous templates changed the crystal morphology and the crystallization kinetics.More crystals were observed in the solution with graphite templatesthan with graphene oxide templates and without any template.

关键词： Graphite Graphene oxide Protein crystallization Adsorption Heterogeneous nucleation Template technology

Trees species’ dispersal mode and habitat heterogeneity shape negative density dependence in a temperate forest

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森林生态系统:英文版 2023年第5期10卷 589-596页

作者： Lishunan yang Daniel J.Johnson Zhichun YANG Xiaochao yang Qiulong Yin Ying Luo Zhanqing Hao Shihong Jia School of Ecology and Environment Northwestern Polytechnical UniversityXi’anShaanxi710072China Shaanxi Key Laboratory of Qinling Ecological Intelligent Monitoring and Protection Northwestern Polytechnical UniversityXi’anShaanxi710072China School of Forest Fisheriesand Geomatics SciencesUniversity of FloridaGainesvilleFLUSA School of Geography and Tourism Shaanxi Normal UniversityXi’anShaanxi710062China

Conspecific negative density dependence(CNDD)is a potentially important mechanism in maintaining species diversity.While previous evidence showed habitat heterogeneity and species’dispersal modes affect the strength of CNDD at early life stages of trees(e.g.,seedlings),it remains unclear how they affect the strength of CNDD at later life stages.We examined the degree of spatial aggregation between saplings and trees for species dispersed by wind and gravity in four topographic habitats within a 25-ha temperate forest dynamic plot in the Qinling Mountains of central China.We used the replicated spatial point pattern(RSPP)analysis and bivariate paircorrelation function(PCF)to detect the spatial distribution of saplings around trees at two scales,15 and 50 m,respectively.Although the signal was not apparent across the whole study region(or 25-ha),it is distinct on isolated areas with specific characteristics,suggesting that these characteristics could be important factors in CNDD.Further,we found that the gravity-dispersed tree species experienced CNDD across habitats,while for wind-dispersed species CNDD was found in gully,terrace and low-ridge habitats.Our study suggests that neglecting the habitat heterogeneity and dispersal mode can distort the signal of CNDD and community assembly in temperate forests.

关键词： Biodiversity Conspecific negative density dependence Dispersal Replicated point patterns Temperate forest Topographic habitat

Recent progress on flutter‐based wind energy harvesting

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International Journal of Mechanical System Dynamics 2022年第1期2卷 82-98页

作者： Zhiyuan Li Shengxi Zhou Zhichun YANG School of Aeronautics Northwestern Polytechnical UniversityXi'anChina Research&Development Institute in Shenzhen Northwestern Polytechnical UniversityShenzhenChina

Wind energy harvesting technology can convert wind energy into electric energy to supply power for microelectronic devices.It has great potential in many specific applications and environments,such as remote areas,sea surfaces,mountains,and so on.Over the past few years,flutter‐based wind energy harvesting,which generates electric energy based on the limit cycle oscillation created by structural aeroelastic instability,has received increasing attention,and as a consequence,different energy harvesting structures,theories,and methods have been proposed.In this paper,three types of flutter‐based energy harvesters(FEHs)including airfoil‐based,flat plate‐based,and flexible body‐based FEHs are reviewed,and related concepts and theoretical models are introduced.The recent progress in FEH performance enhancement methods is classified into structural improvement and optimization,the introduction of nonlinearity,and hybrid structures and mechanisms.Finally,the main FEH challenges are summarized,and future research directions are discussed.

关键词： dynamics flutter performance enhancement wind energy harvesting working principle

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 reduction.Typically,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 structures.In 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 suppression.The effects of boundary conditions and the number and orientation of the stiffeners on Locally Resonant(LR)type bandgap properties in SPM are further investigated.An analytical modeling framework is developed to predict the bandgap formations and vibration behaviors of SPMs in finite-size configuration.The 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 conditions.Finite element analysis and experimental investigations of vibration behaviors for the SPM are carried out to validate the accuracy and reliability of the present analytical model.For 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 behaviors.Furthermore,various arrangements of stiffeners and resonators are explored for different boundary conditions by breaking the requirement of spatially periodicity.It 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 suppression.The present work can provide a significant theoretical guidance for the

关键词： Bandgap Locally resonant Metastructure Stiffened plate Vibration suppression