Acta Mechanica Sinica
The Journal covers all disciplines in the field of theoretical and applied mechanics, including solid mechanics, fluid mechanics, dynamics and control, and biomechanics. It explores analytical, computational and experimental progresses in all areas of mechanics. The Journal also encourages research in interdisciplinary subjects, and servess...
CN 11-2063/O3
ISSN 0567-7718(Print)
ISSN 1614-3116(Online)
Editors-in-Chief:
Professor Tian Jian Lu
Professor Wei Shyy
Professor Zhigang Suo
Impact Factor: 1.324
Citation: Acta Mech. Sin.
Frequency: Bimonthly
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Acta Mechanica Sinica--2018, 34 (3)   Published: 20 June 2018
FLUID MECHANICS
Instability waves and low-frequency noise radiation in the subsonic chevron jet
Lingke Ran, Chuangchao Ye, Zhenhua Wan, Haihua Yang, Dejun Sun
Abstract

Spatial instability waves associated with low-frequency noise radiation at shallow polar angles in the chevron jet are investigated, which are compared to the round counterpart. The Reynolds-averaged Navier-Stokes (RANS) equations are solved to obtain the mean flow fields, which serve as the baseflow for linear stability analysis. The chevron jet has more complicated instability waves than the round jet, where three kinds of instability modes are identified in the vicinity of the nozzle, corr...

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Density enhancement mechanism of upwind schemes for low Mach number flows
Bo-xi Lin, Chao Yan, Shu-sheng Chen
Abstract

Many all-speed Roe schemes have been proposed to improve performance in terms of low speeds. Among them, the F-Roe and T-D-Roe schemes have been found to get incorrect density fluctuation in low Mach flows, which is expected to be with the square of Mach number. The asymptotic analysis presents the mechanism of how density fluctuation problem relates to the incorrect order of term in the energy equation$\widetilde{p}\widetilde{a}\widetilde{U}\bigtriangleup{U}$. It is known that changing the u...

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Hydrodynamic studies on two wiggling hydrofoils in an oblique arrangement
Xingjian Lin, Guoyi He, Xinyi He, Qi Wang, Longsheng Chen
Abstract

The propulsive performance of an oblique school of fish is numerically studied using an immersed boundary technique. The effect of the spacing and wiggling phase on the hydrodynamics of the system is investigated. The hydrodynamics of the system is deeply affected by the spacing between each fish in the school. When the horizontal separation is smaller than the length of the fish body, the downstream fish exhibits a larger thrust coefficient and greater propulsive efficiency than the isolated...

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The spanwise spectra in wall-bounded turbulence
Hong-Ping Wang, Shi-Zhao Wang, Guo-Wei He
Abstract

The pre-multiplied spanwise energy spectra of streamwise velocity fluctuations are investigated in this paper. Two distinct spectral peaks in the spanwise spectra are observed in low-Reynolds-number wall-bounded turbulence. The spectra are calculated from direct numerical simulation (DNS) of turbulent channel flows and zero-pressure-gradient boundary layer flows. These two peaks locate in the near-wall and outer regions and are referred to as the inner peak and the outer peak, respectively. T...

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SOLID MECHANICS
The dimension split element-free Galerkin method for three-dimensional potential problems
Z. J. Meng, H. Cheng, L. D. Ma, Y. M. Cheng
Abstract

The paper presents the dimension split element-free Galerkin (DSEFG) method for three-dimensional potential problems, and the corresponding formulae are obtained. The main idea of the DSEFG method is that a three-dimensional potential problem can be transformed into a series of two-dimensional problems. For these two-dimensional problems, the improved moving least-squares (IMLS) approximation is applied to construct the shape function, which uses an orthogonal function system with a weight fu...

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Zero group velocity longitudinal modes in an isotropic cylinder
Takasar Hussain, Faiz Ahmad, Muhammad Ozair
Abstract

Zero group velocity (ZGV) modes are studied in an isotropic cylinder. The L(0, 2) mode behaves anomalously for the materials having value of the bulk velocity ratio, k, in the range, √2 < k < 2.64 and normally otherwise. All higher modes, except first few ones, have no ZGV point for all isotropic materials. These facts are explained analytically by finding the slope of phase velocity dispersion curves of modes first when phase velocity equals k and then at their initial s...

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Partition method and experimental validation for impact dynamics of flexible multibody system
J.Y. Wang, Z.Y. Liu, J.Z. Hong
Abstract

The impact problem of flexible multibody system is a non-smooth, high-transient and strong-nonlinear dynamic process with variable boundary. How to model the contact/impact process accurately and efficiently is one of the main di?culties in many engineering applications. The numerical approaches being used widely in impact analysis are mainly from two fields: multibody system dynamics (MBS) and computational solid mechanics (CSM). Approaches based on MBS provides a more e?cient yet less accur...

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Macroscopic damping model for structural dynamics with random polycrystalline configurations
Yantao Yang, Junzhi Cui, Yifan Yu, Meizhen Xiang
Abstract

SIn this paper the macroscopic damping model for dynamical behavior of the structures with random polycrystalline configurations at micro-nano scales is established. First, the global motion equation of a crystal is decomposed into a set of motion equations with independent SDOF (Single Degree Of Freedom) along normal discrete modes, and then damping behavior is introduced into each SDOF motion. Through the interpolation of discrete modes, the continuous representation of damping effects for ...

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A prediction model of effective thermal conductivity of nanofluids by considering agglomeration effect and radial distribution function of nanoparticles
Z. M. Zheng, B. Wang
Abstract

Conventional heat transfer fluids usually have low thermal conductivities, limiting their efficiency in many applications. Many experiments have shown that adding nano-size solid particles into conventional fluids could greatly enhance the thermal conductivity of the fluids. To explain this anomalous phenomenon, lots of theoretical investigations have been conducted in recent year. Some of these research have indicated that the agglomeration effect of particles that commonly existed in nanofl...

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Enriched Reproducing Kernel Particle Method for Fractional Advection-Diffusion Equation
Yuping Ying, Yanping Lian, Shaoqiang Tang, Wing Kam Liu
Abstract

The Reproducing Kernel Particle Method (RKPM) has been efficiently applied to problems with large deformations, high gradients and high modal density. In this paper, it is extended to solve a nonlocal problem modeled by a Fractional Advection-Diffusion Equation (FADE), which exhibits a boundary layer with low regularity. We formulate this method on a moving least-square approach. Via the enrichment of fractional-order power functions to the traditional integer-order basis for RKPM, leading te...

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Anhrmonic 1D actuator model including electrostatic and Casimir forces with fractional damping perturbed by an external force
Maryam Mansoori Kermani, Maryam Dehestani
Abstract

We modelled a one dimensional actuator including the Casimir and electrostatic forces perturbed by an external force with fractional damping. The movable electrode was assumed to oscillate by an anharmonic elastic force originated from Murrell-Mottram or Lippincott potential. The nonlinear equations have been solved via the Adomian decomposition method. The behavior of the displacement of the electrode from equilibrium position, its velocity and acceleration were described versus time. Also t...

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Loading direction-dependent shear behavior at different temperatures of single-layer chiral graphene sheets
Yang Zhao, Shuhong Dong, Peishi Yu, Junhua Zhao
Abstract

The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics (MD) simulations. Our results show that the shear properties (such as shear stress-strain curves, buckling strains and failure strains) of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformatio...

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A Timoshenko beam model for chiral materials
T.Y. Ma, Y.N. Wang, L. Yuan, J.S. Wang, Q.H. Qin
Abstract

Natural and artificial chiral materials such deoxyribonucleic acid (DNA), chromatin fiber, flagellar filament, chiral nanotube and chiral lattice material widely exist. Due to the chirality of intricately helical or twisted microstructures, chiral materials hold great promise for diverse applications in smart sensor and actuator, force prober in biomedical engineering, structural elements absorbing microwave and elastic wave, etc. In this paper, a Timoshenko beam model for chiral materials is...

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Nonlinear dynamic analysis of cantilevered piezoelectric energy harvesters under simultaneous parametric and external excitations
Fei Fang, Guanghui Xia, Jianguo Wang
Abstract

The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as the Euler-Bernoulli model with inextensible deformation. A nonlinear distributed parameter model of cantilevered piezoelectric energy harvesters is proposed using the generalized Hamilton’s principle. The proposed model includes geometric and inertia nonlinearity, but neglects th...

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LCP method for the planar passive dynamic walker based on the event-driven scheme
Xu-Dong Zheng, Qi Wang
Abstract

The main purpose of this paper is to present a linear complementarity problem (LCP) method for a planar passive dynamic walker with round feet based on the event-driven scheme. The passive dynamic walker is treated as a planar multi-rigid-body system. The dynamic equations of the passive dynamic walker are obtained by using the Lagrange equations of the second kind. The normal forces and frictional forces acting on the feet of the passive walker are described based on the modified Hertz conta...

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Non-contact tensile viscoelastic characterization of microscale biological materials
Yuhui Li, Yuan Hong, Guang-Kui Xu, Shaobao Liu, Qiang Shi, Deding Tang, Hui Yang, Guy M. Genin, Tian Jian Lu, Feng Xu
Abstract

Many structures and materials in nature and physiology have important “meso-scale” structures at the micron length-scale whose tensile responses have proven difficult to characterize mechanically. Although techniques such as atomic force microscopy and micro- and nano-identation are mature for compression and indentation testing at the nano-scale, and standard uniaxial and shear rheometry techniques exist for the macroscale, few techniques are applicable for tensile-testing at the...

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