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Moment stability for a predator–prey model with parametric dichotomous noises

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Chinese Physics B 2015年第6期24卷 177-183页

作者：靳艳飞 department of mechanics Beijing Institute of Technology

In this paper, we investigate the solution moment stability for a Harrison-type predator-prey model with parametric dichotomous noises. Using the Shapiro-Loginov formula, the equations for the first-order and second-order moments are obtained and the corresponding stable conditions are given. It is found that the solution moment stability depends on the noise intensity and correlation time of noise. The first-order and second-order moments become unstable with the decrease of correlation time. That is, the dichotomous noise can improve the solution moment stability with respect to Gaussian white noise. Finally, some numerical results are presented to verify the theoretical analyses.

关键词： dichotomous noise a Harrison-type predator-prey model moment stability

Targets capture by distributed active swarms via bio-inspired reinforcement learning

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Science China(Physics,mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 210-221页

作者： Kun Xu Yue Li Jun Sun Shuyuan Du Xinpeng Di Yuguang Yang Bo Li Institute of Biomechanics and Medical Engineering Applied Mechanics Laboratory Department of Engineering MechanicsTsinghua University Institute of Nuclear and New Energy technology Tsinghua University Shanghai Aerospace Control technology Institute Shanghai Key Laboratory of Aerospace Intelligent Control technology College of Automation Engineering Nanjing University of Aeronautics and Astronautics

Natural swarms arranged from cells to herds are usually decentralized but display intriguing collective intelligence in coordinating individuals across large scales to efficiently achieve their common goals. Learning from nature may provide new strategies for controlling collective dynamics of synthetic swarms to accomplish specific functions. Here, we present a bioinspired computational framework that steers distributed active swarms to collectively capture and merge targets via reinforcement learning. We exploit collective milling structures of natural herds to cage the targets, and adopt a switching control policy inspired by sperms' chiral dynamics to optimize the trajectories of individuals, through which the active swarms can selforganize to enclose single or multiple distant targets in a dynamical, adaptive and scalable manner. There exists a critical swarm size, beyond which the excessive competition between agents would generate large mechanical forces, leading to capture instability but enabling the transition from short-distance to long-distance merging capture of multiple targets. This work provides physical insights into distributed active swarms and could offer a multilevel, decentralized strategy toward controlling swarm robotics in wide applications such as bio-medical devices, machine immunity, and target clearance.

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REGULARIZATION OF NEARLY SINGULAR INTEGRALS IN THE BOUNDARY ELEMENT METHOD OF POTENTIAL PROBLEMS

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Applied Mathematics and mechanics(English Edition) 2003年第10期24卷 1208-1214页

作者：周焕林牛忠荣王秀喜 department of mechanics University of Science and Technology of China department of Engineering mechanics Hefei University of Technology

A general algorithm is applied to the regularization of nearly singular integrals in the boundary element method of planar potential problems. For linear elements, the strongly singular and hypersingular integrals of the interior points very close to boundary were categorized into two forms. The factor leading to the singularity was transformed out of the integral representations with integration by parts, so non-singular regularized formulas were presented for the two forms of integrals. Furthermore, quadratic elements are used in addition to linear ones. The quadratic element very close to the internal point can be divided into two linear ones, so that the algorithm is still valid. Numerical examples demonstrate the effectiveness and accuracy of this algorithm. Especially for problems with curved boundaries, the combination of quadratic elements and linear elements can give more accurate results.

关键词： boundary element method (BEM) nearly singular integral regularization potential problem

Surface effects on large deflection of nanowires

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Journal of Central South University 2015年第6期22卷 2060-2065页

作者：杨帆 department of mechanics Xi'an University of Science and Technology department of Engineering mechanics Xi'an Jiaotong University

Surface effects play an important role in the mechanical behavior of nanosized structural elements owing to the increased ratio of surface area to volume. The surface effects on the large deflection of nanowires were considered. Both geometric nonlinearity in finite deformation and surface effects at nanoscale were taken into account to analyze the bending of nanowires subjected to a concentrated force. For simply supported beams and clamped-clamped beams, the influence of surface effects and geometric nonlinearity were discussed in detail. It is found that both surface effects and geometric nonlinearity tend to decrease the deflection of bending nanowires and thus increase the effective elastic modulus of nanowires. Surface effects yield the size dependent behavior of nanowires.

关键词： geometric nonlinearity nanowires bending nanowires bending surface effect

Effective electroelastic constants for three-phase confocal elliptical cylinder model in piezoelectric quasicrystal composites

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Applied Mathematics and mechanics(English Edition) 2018年第6期39卷 797-812页

作者： Yongbin WANG Junhong GUO department of mechanics Inner Mongolia University of Technology

A three-phase confocal elliptical cylinder model is proposed to analyze micromechanics of one-dimensional hexagonal piezoelectric quasicrystal （PQC） compos- ites. Exact solutions of the phonon, phason, and electric fields are obtained by using the conformal mapping combined with the Laurent expansion technique when the model is subject to far-field anti-plane mechanical and in-plane electric loadings. The effective elec- troelastic constants of several different composites made up of PQC, quasicrystal （QC）, and piezoelectric （PE） materials are predicted by the generalized self-consistent method. Numerical examples are conducted to show the effects of the volume fraction and the cross-sectional shape of inclusion （or fiber） on the effective electroelastic constants of these composites. Compared with other micromechanical methods, the generalized self- consistent and Mori-Tanaka methods can predict the effective electroelastic constants of the composites consistently.

关键词： piezoelectric quasicrystal (PQC) three-phase elliptical cylinder model effective constant generalized self-consistent method

ON THE INTERACTION BETWEEN A QUARTZ CRYSTAL RESONATOR AND AN ARRAY OF MICRO-BEAMS IN THICKNESS-SHEAR VIBRATIONS

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Acta Mechanica Solida Sinica 2015年第5期28卷 464-470页

作者： Lingcheng Kong Xuan Xie Jun Zhang Yuxi Wang Yuantai Hu department of mechanics Huazhong University of science and Technology

We studied the coupled dynamic behavior of a quartz-crystal-resonator （QCR）/micro- beams system in the thickness-shear motions. Through taking into account the couple stress in the dynamic equations of the quartz plate, both continuous conditions of shear force and bending moment at the resonator/micro-beams interface are realized. Frequency shift of the compound QCR system induced by micro-beams is studied in detail. The obtained results are useful in device design and frequency-stability analysis of quartz crystal resonators.

关键词： quartz crystal resonator couple stress frequency shift

Static deformation of a multilayered one-dimensional hexagonal quasicrystal plate with piezoelectric effect

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Applied Mathematics and mechanics(English Edition) 2018年第3期39卷 335-352页

作者： Tuoya SUN Junhong GUO Xiaoyan ZHANG department of mechanics Inner Mongolia University of Technology

Quasicrystals （QCs） are sensitive to the piezoelectric （PE） effect. This paper studies static deformation of a multilayered one-dimensional （1D） hexagonal QC plate with the PE effect. The exact closed-form solutions of the extended displacement and traction for a homogeneous piezoelectric quasicrystal （PQC）plate are derived from an eigensystem. The general solutions for multilayered PQC plates are then obtained using the propagator matrix method when mechanical and electrical loads are applied on the top surface of the plate. Numerical examples for several sandwich plates made up of PQC, PE, and QC materials are provided to show the effect of stacking sequence on phonon, phason, and electric fields under mechanical and electrical loads, which is useful in designing new composites for engineering structures.

关键词： quasicrystal (QC) piezoelectric (PE) effect multilayered plate exactsolution static deformation

A MICROMECHANICAL FRAMEWORK WITH AGGREGATE-MASTIC INTERFACE EFFECT FOR PREDICTING UNIAXIAL COMPRESSION CREEP OF ASPHALT MIXTURE

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Acta Mechanica Solida Sinica 2014年第3期27卷 306-314页

作者： Jun Wu Xinhua Yang Fan Bai department of mechanics Huazhong University of Science and Technology

According to the elastic-viscoelastic correspondence principle, an elastic microme- chanical framework taking the inclusion-matrix interface effect into account is extended for predicting viscoelastic properties of asphalt mixture, which is simply treated as elastic coarse aggregate inclusions periodically and isotropically embedded in a viscoelastic asphalt mastic matrix. The Burgers model is adopted for characterizing the matrix mechanical behavior, so that the homogenized relaxation modulus of asphalt mixture in compression creep is derived. After a series of uniaxial compression creep tests are performed on asphalt mastic in different temperature and stress conditions in order to determine the matrix constitutive parameters, the framework presented is validated by comparison with the experiment, and then some predictions of uniaxial compression creep behavior of asphalt mixture in different temperature and stress conditions are given.

关键词： asphalt mixture micromechanics elastic-viscoelastic correspondence principle compression creep

Effect of strain-gradients of surface micro-beams on frequency-shift of a quartz crystal resonator under thickness-shear vibrations

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Acta Mechanica Sinica 2015年第5期31卷 647-652页

作者： Ling-Cheng Kong Yuan-Tai Hu department of mechanics Huazhong University of Science and Technology

With introduction of the first-order strain-gradient of surface micro-beams into the energy density function,we developed a two-dimensional dynamic model for a compound quartz crystal resonator（QCR） system,consisting of a QCR and surface micro-beam *** frequency shift that was induced by micro-beams with consideration of strain-gradients is discussed in detail and some useful results are obtained,which have important significance in resonator design and applications.

关键词： Micro-beams Strain-gradient Quartz crystal resonator Frequency shift