Table of Content

30 October 2024, Volume 30 Issue 5

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Bending deformation and continuum model of 2D lattice metamaterials

HE Linghui

2024, 30(5):  777-789.  doi:10.12066/j.issn.1007-2861.2608

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2D lattice metamaterials composed of beams or rods are widely used in different technical fields. An important feature of such materials is that, through structural design of the unit cells, they can exhibit many unique mechanical behaviors that traditional materials do not have. In this review, recent advances in the study of bending deformation of lattice metamaterials are briefly summarized, with emphasis on the unconventional bending modes and dominant mechanisms, as well as the corresponding theoretical models of the continuum. The main problems and challenges in future research are also prospected.



Progress in turbulent boundary layer over the porous media wall

LIU Yulu1, 2, 3 , MA Yupeng4 , WANG Chao4 , TAO Yizhou3 , LI Jiahua5 , XIA Yuxian4 , QIU Xiang1, 2, 3

2024, 30(5):  790-801.  doi:10.12066/j.issn.1007-2861.2612

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The permeability of porous media wall enhances the momentum and energy transport near the interface, leading to the increase of complexity of flow in the turbulent boundary layer over porous media wall. The porous media wall affects the space-time evolution of turbulent structure directly, generation mechanism and transport characteristics of various physical quantities in the turbulent boundary layer. This paper summarizes the state of the art of statistical and turbulent structure characteristics of boundary layers over porous media wall. Firstly, the properties of porous media substrates have a direct relationship with turbulent boundary layer characteristics, as demonstrated by mean statistical quantum, the wall friction coefficient and characteristics of coherent structures. The structure characteristics of turbulent in the turbulent boundary layer over porous walls are closely related to the Kelvin-Helmholtz (KH) instability induced by porous media. Secondly, the paper discusses the modulation effect of large-scale turbulent structures on small-scale turbulent structures near wall region in porous wall boundary layers. Finally, we outline future research directions.



Development and application of classical and machine learning interatomic potential

ZHAO Haoran1 , SHEN Qiang2 , WANG Peng2

2024, 30(5):  802-812.  doi:10.12066/j.issn.1007-2861.2603

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This study reviewed the history of several classical and machine learning (ML) potential functions and focused on the recent developments and applications of these potential functions in metal and covalent-bond materials. A comprehensive analysis of the advantages and disadvantages of ML and traditional potential functions was provided and a perspective on the development of more effective interatomic potentials was offered.



Application of molecular dynamics simulation in the study of nucleosomes

MU Xuetao, LI Zhenhai

2024, 30(5):  813-825.  doi:10.12066/j.issn.1007-2861.2606

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Nucleosomes are the fundamental units of the chromatin structure and the smallest units of gene storage in eukaryotes. They consist of a histone octamer and DNA wrapped around it. The dynamic nucleosome structure can regulate interactions between DNA and binding proteins by hiding or exposing the binding sites on DNA, eventually governing gene expression. Experimental methods can be used to study the interactions between nucleosomes and binding proteins at the molecular level but cannot provide mechanistic explanations at the atomic level. Molecular dynamics simulations provide a highresolution method at the atomic level for studying nucleosomes, enabling the visualization of nucleosome behavior and serving as a powerful complement to experimental methods. Herein, the study reviewed the progress in molecular dynamics simulations of the nucleosome structure, regulation of nucleosome function by histone tails, and interactions between nucleosomes. Additionally, the applications of the three acceleration algorithms of molecular dynamics simulations in nucleosome research were discussed.



Progress on physical mechanics of van der Waals layered materials MoSi2N4 and their heterostructures

LI Xuanhao1, 2 , YU Jin1, 2

2024, 30(5):  826-837.  doi:10.12066/j.issn.1007-2861.2601

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Two-dimensional materials have attracted considerable attention because they exhibit various novel physical properties that differ from their three-dimensional parent materials. In 2020, MoSi2N4, a new van der Waals layered material without a corresponding parent material, was synthesized experimentally via chemical vapor deposition. Its advantages, such as high carrier mobility, excellent mechanical strength, high light transmittance, and good environmental stability, have attracted the interest of researchers. Moreover, because graphene/h-BN, MoS2/black phosphorus, and other heterostructures show intrinsic physical properties superior to those of the individual material, exploring the physical properties of MoSi2N4-based heterostructures has gradually become the focus of research. This paper focuses on recent research on this type of heterostructure. In particular, the regulation of its electronic properties under mechanical strain, which provides a guiding basis to improve the understanding of their physical and mechanical mechanisms and exploring the research on the van der Waals family MA2Z4 and its heterostructures.



Continuum modeling of interlayer tangential entropy forces in 2D materials

ZHU Fangyan1, 2 , JIANG Jinwu1, 2 , CHANG Tienchong1, 2

2024, 30(5):  838-846.  doi:10.12066/j.issn.1007-2861.2609

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The interlayer interactions significantly affect the interfacial mechanical behavior of two-dimensional (2D) materials. In particular, under the condition of mechanicalthermal coupling, the interlayer tangential entropic forces in the lap-joint contact con- figuration of 2D materials have important applications in the design of nanodevices. In this study, we develop a continuum model based on the vibration theory of thin plates combined with the equipartition theorem to describe the interlayer tangential entropic forces in layered structures. This model reveals the intrinsic relationship between the tangential forces induced by thermal vibration gradients under different conditions. This study provides novel insights into tangential entropic forces in 2D materials and establishes a theoretical foundation for the design of thermomechanical nanodevices.



Diffusion behavior of polymer chain in a periodic nanoparticle array: a dissipative particle dynamics simulation

HU Jianglin1, 2, 3 , LU Yu1, 2, 3 , HU Guohui1, 2, 3

2024, 30(5):  847-857.  doi:10.12066/j.issn.1007-2861.2520

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Polymer nanocomposites (PNCs) have shown excellent mechanical properties owing to their combinations of nanoparticle (NP) and polymer properties, and they are now of significant interest in the fields of materials and soft matter science. Considering the difficulties in determining their multiscale dynamic characteristics, predicting the diffusion behaviors of polymers in polymer nanocomposites remains an open problem. In this study, the diffusion processes of polymers with different chain lengths in PNCs are numerically simulated via the dissipative particle dynamics (DPD) method, and the diffusion behaviors of polymer chains are described by a key dimensionless constraint factor χ, which is the ratio of the distance Lee from the first end of the polymer chain to the effective free diffusion length Lf. By analyzing the effects of the concentration of NPs, the lengths of polymer chains, and the interactions between polymer NPs on polymer diffusion, a scaling rate for the effective diffusivity of polymer chains is proposed with respect to the confinement factor χ, and it is confirmed that this scaling law can accurately predict the numerical results with a low confinement factor χ. This study provides a guide for the theoretical development and application of PNCs.



Steady-state thermal analysis of ellipsoidal inhomogeneities embedded in a bimaterial or semi-infinite domain

YANG Yuanpeng, WU Chunlin

2024, 30(5):  858-874.  doi:10.12066/j.issn.1007-2861.2602

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This study performed a steady-state thermal analysis of ellipsoidal inhomogeneities embedded in a bimaterial or semi-infinite domain. Because of the Green’s function of the bimaterial, the continuity conditions for the temperature and heat flux of the interface were mathematically involved. Through proper modification of the material properties, the Green’s function of the bimaterial could be reduced to semi-infinite and infinite. This study proposed the use of Eshelby’s equivalent inclusion method to simulate ellipsoidal inhomogeneities, which replaced the inhomogeneity of the matrix material containing a continuously distributed polynomial-form eigen-temperature gradient field. Based on the analytical ellipsoidal integral with polynomial density functions, the disturbance caused by inhomogeneities was analytically evaluated using the domain integrals of the eigentemperature gradient and Green’s function of the bimaterial. The eigen-temperature gradient for each inhomogeneity was described by a Taylor series expanded at the geometric center, which could then be evaluated by solving the equivalent heat flux conditions. A fi- nite element method (FEM) was used to verify the accuracy of the semi-analytical method.The study showed that mesh-free solutions to multiple ellipsoidal inhomogeneities in the bimaterial/semi-infinite domain could be achieved.



Interval model updating of a butted cylindrical shell structure based on Chebyshev polynomials and interval overlap ratio

CHEN Yifeng, WEI Sha, LI Xulong, DING Hu, CHEN Liqun

2024, 30(5):  875-889.  doi:10.12066/j.issn.1007-2861.2600

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An interval model updating method based on Chebyshev polynomials and the interval overlap ratio is used to study the model updating of a butted cylindrical shell structure. First, the natural frequencies of the structure are obtained through modal test, and the interval ranges of the natural frequencies are determined using the kernel density estimation method. The thin-layer element method is next used to simulate the boltconnected components, and a finite element model of the butted cylindrical shell structure is established to analyze the modal characteristics of the structure. A deterministic model updating method is then employed to update the material parameters of the cylindrical shell and flange. Finally, an interval model updating method based on the Chebyshev polynomials and the interval overlap ratio is used to update the uncertain parameters in the thin-layer elements. Results show that the errors in the upper and lower bounds of the updated parameter intervals satisfy engineering accuracy requirements. The updated output space aligns well with the experimental output space, confirming the feasibility and effectiveness of the interval model updating method.



Analytical and numerical investigation of the interaction energy between the dislocations and inhomogeneous inclusions

DING Gaowen1, 2 , LI Zhiyuan1, 2 , LI Yang1, 2, 3

2024, 30(5):  890-903.  doi:10.12066/j.issn.1007-2861.2604

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Eshelby’s equivalent inclusion method (EIM) were used to address the inhomogeneous inclusion problem while considering the effects of the intrinsic eigenstrain. The interaction energy between screw/edge dislocations and inhomogeneous inclusions were explicitly derived. To validate the model, the results of dislocation-void interactions were compared with the results of molecular dynamics (MD) simulations. The model’s capacity were fully evaluated and the effects of inclusion parameters were discussed, including the intrinsic eigenstrain and elastic constant.



Atomistic simulation of the effect of helium bubbles on interface tensile yield strength of Cu/Nb layered material

ZHANG Yaning1, 2, 3 , LU-CHEN Yangtao ¨ 1, 2, 3 , CHU Haijian1, 2, 3

2024, 30(5):  904-912.  doi:10.12066/j.issn.1007-2861.2523

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The interfacial tensile yield strengths of Cu/Nb layered materials containing helium bubbles are investigated via molecular dynamics simulations. Specifically, the effects of helium bubble internal pressure, bubble size, and layer thickness on the interface tensile yield strength and deformation mechanism of Cu/Nb layered materials are investigated. Results show that interface helium bubbles can induce interface dislocation nucleation, change the microstructural evolution, and significantly reduce the interface tensile yield strength of Cu/Nb layered materials. The effect of helium bubbles on the interface tensile yield strength weakens as the helium bubble size increases resulting in apparent size effect. Compared with the case without helium bubbles, the interface tensile yield strength reduced by approximately 12% and 33% for the models containing 3 and 6 nm helium bubbles, respectively. Additionally, the layer thickness minimally affects the upper yield stress of the Cu/Nb-layered materials, whereas it significantly affects the lower yield stress. The former is attributed to the structure symmetry of the Cu/Nb interface and the loading symmetry, which render the interface stress and dislocation nucleation stress insensitive to the layer thickness. The latter is due to the increased layer thickness, which provides more space for dislocation motion and evolution, thus resulting in rapid stress reduction during the yield period.



Stability and controllability of unswept-wing flying-wing aircraft

LI Zhikai1 , WEI Sha1, 2, 3 , DING Hu1, 2, 3 , CHEN Liqun1, 2, 3

2024, 30(5):  925-937.  doi:10.12066/j.issn.1007-2861.2605

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Flying-wing aircraft are known for their high aerodynamic efficiency and are often utilized in solar-powered aircraft. However, they generally exhibit poor stability and controllability. Unswept-wing flying-wing aircraft, also called “flying planks”, possess aerodynamic characteristics that differ from swept-wing flying-wing designs. This study utilizes the vortex lattice method to calculate the aerodynamic coefficients and derivatives of a lightweight, small-scale, unswept-wing flying-wing unmanned aerial vehicle (UAV). The study analyzes the longitudinal static stability, longitudinal and lateral-directional dynamic stability under varying angles of attack (AoAs) and climb angles as well as the effects of the centre of gravity (CG) position below the wing on the stability of the UAV.An aeromodel is constructed and test-flown to validate the findings. Results show that the longitudinal stability of the unswept-wing flying-wing aircraft differs from that of conventional configurations. These aircraft show almost no tendency for dutch-roll, and maintain lateral-directional stability without stability augmentation. Lowering the CG position can alter the trimmed AoAs, and enhance the pitch stability at positive AoAs and deteriorates the pitch stability at negative AoAs or large climbing angles; it also narrows the flight envelope. Unswept-wing flying wings possess various unconventional characteristics during flight and need further investigation.



Propagation characteristics of the hydro-acoustic waves due to an oscillating source in an ice-covered ocean

YAN Xiangyi1, 2 , LU Dongqiang1, 2, 3, 4

2024, 30(5):  938-950.  doi:10.12066/j.issn.1007-2861.2607

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Based on the linear theory of potential flow, the propagation characteristics of ocean-based hydro-acoustic waves (also known as acoustic-gravity waves) are studied through the use of an elastic plate model to simulate an ocean-surface ice sheet, where the seawater is regarded as an inviscid compressible fluid with a rigid bottom. Approximate solutions for the displacement at the ice-water interface and the acoustic pressure in the ice-covered ocean under the pulsation of a single mass point source are derived. The effects of the thickness and lateral stress of the elastic ice sheet and the depth of fluid on the propagation of the hydro-acoustic waves are discussed. Results show that with the gradual increase in elastic ice sheet thickness, the displacements at the ice-water interface first increase, then decrease, and finally gradually approach zero, whereas the acoustic pressure of the ice-covered ocean initially remains unchanged and then gradually decreases. The lateral stress of the elastic ice sheet has little effect on both the displacement and acoustic pressure. With the increase in the depth of fluid, both the displacement and acoustic pressure tend to decrease.



Influence and analysis of cavitation flow on pipeline vibration

WU Zerong1 , WENG Peifen1 , DING Jue1 , LI Xiaowei2

2024, 30(5):  951-967.  doi:10.12066/j.issn.1007-2861.2471

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Pipe vibration induced by cavitating flow in a pipe system is an important factor that damages the pipe system. This paper focuses on the interaction between flow disturbance and cavitation, as well as its impact on pipeline vibration. Zwart-GerberBelamri (ZGB) cavitation model is used to study the dynamic evolution of the cavitation cloud with the cavitation number and Reynolds number under the influence of small perturbations. The cavitation cloud is found to cause an unbalanced force and flow pulsation in the pipeline. Furthermore, the cavitation cloud has amplitude modulation and frequency conversion characteristics, which aggravate the amplitude and change the frequency of the unbalanced force and flow pulsation. Based on this, an excitation source term, cavitation excitation, is introduced into the fluid structure coupling dynamic model, and an improved fluid structure coupling dynamic model for analyzing the mechanism of pipeline vibration induced by cavitation is established. The equations for the vibration of a pipeline under cavitation excitation are solved, and the critical cavitation number interval is determined. Moreover, the causes of pipeline vibrations induced by cavitation under small perturbations are revealed. The results are essential for studying vibration and noise reduction and the safe operation of pipeline systems.



Prediction method of combined guiding force of pre-bent BHA bit based on PSO-SVR algorithm

WANG Zhaobin1, 2 , YANG Heyuan1, 2 , WANG Wenchang1, 2 , CHEN Feng3 , DI Qinfeng1, 2

2024, 30(5):  968-979.  doi:10.12066/j.issn.1007-2861.2610

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The combined guiding force of pre-bent bottom hole assembly (BHA) bit is of paramount significance for well trajectory control, but the traditional calculation method is time-consuming and labor-intensive. A method based on particle swarm optimization and support vector regression is proposed to quickly predict the combined guiding force of prebent BHA bit. Firstly, the weighted margin method is used to solve the three-dimensional small deflection mechanical model of the BHA, and the bit combined guiding force is obtained, and the sample space of support vector regression is formed. Secondly, particle swarm optimization is used to optimize the support vector regression parameters, and the optimal values of penalty factor, kernel function parameters and insensitivity coefficient are obtained. Finally, combined with an example, particle swarm optimization is used to predict the bit combined guiding force, and the accuracy of the prediction results is analyzed and evaluated. The results show that the prediction accuracy of the combined guiding force of pre-bent BHA bit is high, and the coefficient of determination R 2 is 0.956 8.



Bendable-in-any-direction imprinted flexible thick electrodes for Li-ion batteries

ZHANG Bochang1, 2, 3, 4 , GAO Huadong1, 2, 3, 4 , XU Shenxin5 , BAO Yinhua1, 2, 3, 4 , LU Bo ¨ 1, 2, 3, 4

2024, 30(5):  980-988.  doi:10.12066/j.issn.1007-2861.2615

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A method of mechanical imprinting on semi-solid electrodes is proposed to prepare a imprinted flexible thick electrode for lithium-ion batteries (LIBs). This method balances the conflict between high energy storage performance and high flexibility without significantly altering the traditional wet preparation process of LIB electrodes. By introducing an imprinting step during the electrode drying stage, a network channel structure can be constructed in the electrode with hundreds of microns thickness. Consequently, the prepared electrode can bend in any direction. Further, based on finite element analysis, the critical bending radius of the imprinted thick electrode in different bending directions is determined. Additionally, the network channel structure introduced by imprinting enhances ion transport efficiency in the electrode, significantly improving its electrochemical performance at high C-rates. Meanwhile, the battery containing the flexible thick electrode maintains good and stable electrochemical performance in the bending state. The results of this paper provide a new path for the development of high-performance multi-functional energy storage batteries.