Acta Mechanica Sinica
     Acta Mechanica Sinica
  Acta Mechanica Sinica--2019, 35 (4)   Published: 15 August 2019
FLUID MECHANICS
Boundary layer structure in turbulent rayleigh-bénard convection in a slim box
Hong-Yue Zou, Wen-Feng Zhou, Xi Chen, Yun Bao, Jun Chen, Zhen-Su She
Abstract

Logarithmic boundary layers have been observed in different regions in turbulence. However, how thermal plumes correlate to the log law of temperature and how the velocity profile changes with pressure gradient are not fully understood. Here, we perform three-dimensional simulations of turbulence in a slim-box without the front and back walls with aspect ratio, $\mathrm{width}:\mathrm{depth}:\mathrm{height}=L:D:H=1:1/6:1$ (respectively corresponding to $x$, $y$ and $z$ coordinates), in the Ra...

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Linear optimal control of transient growth in turbulent channel flows
Yang Song, Chunxiao Xu, Weixi Huang
Abstract

The suppression of linear transient growth in turbulent channel flows via linear optimal controls is investigated. The control algorithms are the LQR control based on full information of flow fields and the LQG control based on the information measured at walls. The influence of these controls on the development of small-scale and large-scale perturbations are considered respectively. It is found that the energy amplification of large-scale perturbations is suppressed significantly by both LQ...

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Numerical study on shock-dusty gas cylinder interaction
Jingyue Yin, Juchun Ding, Xisheng Luo, Xin Yu
Abstract

The interaction of a planar shock wave with a dusty-gas cylinder is numerically studied by a compressible multi-component solver with an adaptive mesh refinement technique. The influence of non-equilibrium effect caused by the particle relaxation, which is closely related to the particle radius and shock strength, on the evolution of particle cylinder is emphasized. For a very small particle radius, the particle cloud behaves like an equilibrium gas cylinder with the same physical properties ...

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Numerical study on shock-accelerated heavy gas cylinderswith diffusive interfaces
Dongdong Li, Ben Guan, Ge Wang
Abstract

Interactions of shock wave and heavy gas cylinders with different diffusive interfaces are numerically investigated. Comparisons among these interfaces are made in terms of cylinder morphology, wave system evolution, fluids mixing, and circulation generation. Navier-Stokes equations are solved in the present work to simulate the complex multi-fluid flow. The fifth-order weighted essentially non-oscillatory scheme is used to compute the numerical flux. The influence of interface diffusion is r...

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SOLID MECHANICS
Dynamic experimental studies of a6n01s-t5 aluminum alloy material and structure for high-speed train
Zishang Liu, YangyangYu, Zhe Yang, Yanpeng Wei, Junshuang Cai, Maohui Li, Chenguang Huang
Abstract

In this study, we focus on the dynamic failure property of A6N01S-T5 aluminum alloyusing for high-speed train. The method of SHBT+3D DIC was put forward to figure out the dynamic mechanical properties and dynamic failure strain of A6N01S-T5 aluminum alloy,and on the basis of this, Johnson-Cook model constitutive parameters and dynamic failure strain parameters were obtained through a series of static and dynamic tests.An important character of this methodwas that the sandwich structure from t...

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Effects of marine sediment on the response of a submerged floating tunnel due to p- wave incidence
Heng Lin, Yiqiang Xiang, Zhengyang Chen, Ying Yang
Abstract

Submerged floating tunnel (SFT) is a novel type traffic structure for crossing long strait and deep lakes. To investigate the dynamic pressure acting on an SFT under compression (P) wave incidence, a theoretical analysis model considering marine sediment effect has been proposed. Based on displacement potential functions, the reflection and refraction coefficients of P wave in different media are derived. Numerical examples are employed to illustrate the effects of the thickness of sediment l...

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Study on the damage-softening constitutive model of rock and experimental verification
Sheng-Qi Yang, Bo Hu, Peng Xu
Abstract

A damage-softening model is presented to describe the stress-strain curve of rock. By comparing the Hoek-Brown (H-B) and Mohr-Coulomb (M-C) yield criterion, the equivalent M-C yield criterion is selected as the strength criterion in this model. To better characterize the rock damage and failure processes with considering the relationship between damage and deformation, the concept of yield stress ratio is introduced to describe the yield strengthening deformation before rock peak stress. Dama...

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Effects of nano-voids and nano-cracks on the elastic properties of a host medium: xfem modeling with level-set function and free surface energy
M.R. Kired, B.E. Hachi, D. Hachi, M. Haboussi
Abstract

This work deals with the influences of nano-heterogeneities in the form of voids/cavities or cracks on the elastic (please confirm which word is correct. effective or elastic? According to the title of paper, I choose elastic.) properties of a host medium. With a relatively large ratio of apparent-surface to volume and particularly strong physical interactions with the surrounding medium at nano-scale, nano-heterogeneities can potentially affect the elastic(effective or elastic?) properties o...

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Study on establishment of standardized load spectrum on bogie frames of high-speed trains
Daoyun Chen, Qian Xiao, Minghui Mou, Shouguang Sun, Qiang Li
Abstract

Establishing structural load spectrum under actual operating conditions is a major problem in structural fatigue life analysis. This study introduces the load measuring method for the bogie frame structure. The load-measuring frame based on quasi-static can measure different load systems synchronously. The t-test method is employed to evaluate the least test time of deducing the parent distribution. In order to fit the load spectrum distribution accurately, the kernel density estimat...

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Finite element simulation of elastoplastic fieldnear crack tips and results for a central crackedplate of le-lhp material under tension
X. Ji, F. Zhu
Abstract

The elastoplastic field near crack tips is investigated through finite element simulation.A refined mesh model near the crack tip is proposed. In the mesh refining area, element size continuously varies from the nanometer scale to themicrometer scale and the millimeter scale. Graphics of the plastic zone, the crack tip blunting, and the deformed crack tip elements are given in the paper.Based on the curves of stress and plastic strain, closely near the crack tip, the stresssingularity index a...

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Dynamic crushingof cellular materials: a particle velocity-based analytical method and its application
Shilong Wang, Zhijun Zheng, Yuanyuan Ding, Changfeng Zhu, Jilin Yu
Abstract

Cellular material under high-velocity impacthas a typical feature oflayer-wise collapse.A cell-based finite element model is employed to simulate the direct impact of closed-cell foam, and one-dimensional velocity field distributionsareobtained to characterize thecrushing bandpropagating through a cellular material. An explicit expression of continuous velocity distribution is derivedbased on the features of velocity gradient distribution. The velocity distribution function is adopted to dete...

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Analysis on the velocity relationship and deceleration of long-rod penetration
W.J.Jiao, X.W. Chen
Abstract

The relationship between the average penetration velocity,$\bar{U}$,and the initial impact velocity, ${{V}_{\text{0}}}$,in long-rod penetration has been studied recently. Experimental and simulation results all show the linear relationship between $\bar{U}$ and ${{V}_{\text{0}}}$ over a wide range of ${{V}_{\text{0}}}$ for different combinations of rod and target materials. However, the physical essence has not been fully revealed.In this paper, the $\bar{U}-{{V}_{\text{0}}}$relationship is p...

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DYNAMICS, VIBRATION, AND CONTROL
Modelling and control of a spatial dynamic cable
Bo Tian, Subhrajit Bhattacharya
Abstract

We study the problem of dynamically controlling the shape of a cable that is fixed at one end and attached to an actuated robot at another end. This problem is relevant to unmanned aerial vehicles (UAVs) tethered to a base. While rotorcrafts, such as quadcopters, are agile and versatile in their applications and have been widely used in scientific, industrial and military applications, one of the biggest challenges with such UAVs is their limited battery life that make the flight time for a t...

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Free vibration analysis of a spinning piezoelectric beam with geometric nonlinearities
Wei Li, Xiao-Dong Yang, Wei Zhang, Yuan Ren, Tian-Zhi Yang
Abstract

The linear and non-linear free vibrations of a spinning piezoelectric beam are studied by considering geometric nonlinearities and electromechanical coupling effect. The non-linear differential equations of the spinning piezoelectric beam governing two transverse vibrations are derived by using two Euler angles transformation and extended Hamilton principle, wherein an additional piezoelectric coupling term and different linear terms are present in contrast to the traditional shaft model. Lin...

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Modeling and power performance improvement of a piezoelectric energy harvester for low-frequency vibration environment
Dongxing Cao, Yanhui Gao, Wenhua Hu
Abstract

A novel oscillator structure, bimorph piezoelectric cantilever beam with two-stepped variable thicknesses,is proposed to improve the energy harvestingperformance of the vibration energy harvester (VEH) under low-frequency vibration environment. Firstly, the piezoelectric cantilever is segmented to obtain the energy functions based on the Euler-Bernoulli beam assumptions, and the Galerkin approach is utilized to discretize the energy functions. Applying boundary conditions and continuity condi...

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Nonlinear vibration analysis of a circular composite plate harvester via harmonic balance
Tian-Chen Yuan, Jian Yang, Li-Qun Chen
Abstract

Alumped parameter transversevibration model of a composite plate harvester is analyzed via harmonic balance approaches. The harvester is mainly composed of a piezoelectriccircular composite clamped by two steel rings and a proof mass on the plate.The lumped parameter model is a 1.5 degree-of-freedom strongly nonlinear system with a higher order polynomial stiffness. Aharmonic balance approach is developed to analyze the system, and the resulting algebraic equations are numerically solved by a...

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Single-legweight limit of fixation model of simple supracondylar fracture of the femur
Guo-Yu Bai, Xiang-Hong Xu, Jin-Hui Wang, Ning Sun
Abstract

Postoperative early rehabilitation training for supracondylar fracture of femur aids in accelerating the healing of fractures with shorter recovery periods. Presently, clinical studies on post-operative early weight training are still in the nascent stages. The weight bearing capacity at different healing stages typically depends on clinical experience and there is a lack of standards to quantify the weight that would be conducive to the healing of fractures. In this paper, a 3D geometric mod...

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Correction to: spherical cavity-expansionmodel for penetration of reinforced-concrete targets
Y. J. Deng, W. J. Song, X. W. Chen
Abstract
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