Acta Mechanica Sinica
     Acta Mechanica Sinica
  Acta Mechanica Sinica--2021, 37 (9)   Published: 30 September 2021
INVITED REVIEW
Review of Lagrangian stochastic models for turbulent combustion
Tianwei Yang · Yu Yin · Hua Zhou · Zhuyin Ren
Abstract
Predictive simulation of the combustion process in engine is crucial to understand the complex underlying physicochemical processes, improve engine performance, and reduce pollutant emissions. Key issues such as the physical modeling of the interaction between turbulence, chemistry and droplets, and the incorporation of the detailed chemistry in high-fidelity simulations of complex flows remain essential though challenging. This paper reviews the transported probability density function method f...
RAPID COMMUNICATION
Implementing fractional Fourier transform and solving partial differential equations using acoustic computational metamaterials in space domain
Zengyao Lv · Peng Liu · Yuanshuai Ding · Hangyu Li · Yongmao Pei
Abstract
Metamaterials can control incident waves in the sub-wavelength range through the design of artificial structures, and realize the functions that natural materials cannot achieve. The study of metamaterials has important theoretical value and application prospects. In recent years, the proposal of computational metamaterials has opened up a brand-new direction for analog computing, providing high-throughput, energy-free computing methods for special computing tasks. However, the development of ac...
EXTREME MECHANICS
Evolution of strong unsteady accompanying jet under dual conditions of high-speed rotation and transient depressurization
Duo Wang · Xu Zheng · Xiaodong Chen · Guoqing Hu
Abstract

Droplet-based micro uidics o ers unique advantages to create platforms that fabricate functionalized particles with increased accessibility, robustness, and simplicity. Herein we present a three-phase micro uidic device that can control the ow pattern to directly generate either core–shell or hole–shell microparticles. The major bene ts of this device are the ease of control- ling the morphology of the compound droplets by the ow rates and thus the microstructure of the synthesize...

Fracture mechanics of methane clathrate hydrates
Jinjie Liu · Ke Xu · Li Yang · Yanwen Lin · Tong Li · Xuezheng Gao· Zhisen Zhang · Jianyang Wu
Abstract

Fundamental mechanics of gas hydrates is of importance to evaluating geomechanical and geotechnical properties of gas hydrate deposits, but it remains largely unexplored yet due to insufficient direct experimental techniques and high-quality of gas hydrate samples. Here, classic molecular dynamic (MD) simulations are used to study the fracture mechanics of three main methane clathrate hydrates of sI, sII and sH types. The results show that the mechanical properties of those three methane clat...

Experimental study on hypersonic crossflow instability over a swept flat plate by flow visualization
Haibo Niu, Shihe Yi, Junjie Huo, Wenpeng Zheng, Xiaolin Liu
Abstract
An experimental study on the traveling crossflow instability over a 60° swept flat plate was conducted. The Mach number is 6, the angle of attack of the model is 5°. The traveling crossflow waves and the secondary instability of the traveling crossflow waves were visualized by nano-tracer-based planar laser scattering (NPLS) technique. In the spanwise NPLS images, the traveling crossflow waves appeared as regular strikes, and the secondary instability appeared as small eddies attached to strikes...
FLUID MECHANICS
Length and stiffness effects of the attached flexible plate on the flow over a traveling wavy foil
Lin Tian · Zhiye Zhao · Wenjiang Wang · Nansheng Liu
Abstract
Flow over a traveling wavy foil attached with a flexible plate has been numerically investigated using the lattice Boltzmann method combined with the immersed boundary method. The influence of the flexibility and length of the caudal fin on the locomotion of swimming fish through this simplified model, whereas the fish body is modeled by the undulating foil and the caudal fin by the plate passively flapping as a consequence of fluid-structure interaction. It is found that the plate flexibility d...
Machine learning for adjoint vector in aerodynamic shape optimization
Mengfei Xu · Shufang Song · Xuxiang Sun · Wengang Chen· Weiwei Zhang
Abstract
Adjoint method is widely used in aerodynamic design because only once solution of fow feld is required for it to obtain the gradients of all design variables. However, the computational cost of adjoint vector is approximately equal to that of fow computation. In order to accelerate the solution of adjoint vector and improve the efciency of adjoint-based optimization, machine learning for adjoint vector modeling is presented. Deep neural network (DNN) is employed to construct the mapping between ...
Effect of cooperative injection and suction jet on power extraction characteristics of semi-active flapping airfoil
Jianyang Zhu · Mingkang Zhu · Tinghai Cheng
Abstract
A novel cooperative injection and suction jet was employed in this work to improve the power extraction characteristics of a semi-active fapping airfoil (S-AFA). The combined Taguchi method and numerical simulations was used to optimize the characteristic parameters of the cooperative injection and suction jet that afect the power extraction characteristics of the S-AFA. Under the Reynolds number of 6× 104 and the pitching axis location at the center of the ellipse airfoil, the efects of jet pos...
SOLID MECHANICS
Wave propagation in graphene reinforced piezoelectric sandwich nanoplates via high?order nonlocal strain gradient theory
Biao Hu · Juan Liu · Yuxing Wang · Bo Zhang · Huoming Shen
Abstract
Αn analytical method is developed to explore the wave propagation characteristics of piezoelectric sandwich nanoplates in the present work. The sandwich nanoplates are composed of a graphene reinforced composite core layer with two piezoelectric surface layers exposed to electric feld. The material properties of the nanocomposite layer are given by the Halpin–Tsai model and mixture’s rule. The Euler–Lagrange equation of the nanoplates is obtained by Hamilton’s principle and frst-order shear defo...
DYNAMICS, VIBRATION, AND CONTROL
Nonlinear dynamical analysis of some microelectromechanical resonators with internal damping
Dongming Wei · Daulet Nurakhmetov · Christos Spitas · Almir Aniyarov · Dichuan Zhang
Abstract
In this paper, a new Kelvin-Voigt type beam model of a microelectromechanical resonator made of power-law materials taking into account internal strain-rate damping is proposed and the corresponding lumped-parameter model is derived. Analytical formulas of the lumped parameters in the model are presented. And the pull-in solution is analyzed based on the lumped-parameter model. It is demonstrated analytically and numerically that the internal damping plays an important rolein the pull-in solutio...
 
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