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2021年 第42卷 第8期    刊出日期：2021-08-01

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论文

Nonlocal vibration and buckling of two-dimensional layered quasicrystal nanoplates embedded in an elastic medium

Tuoya SUN, Junhong GUO, E. PAN

2021, 42(8):  1077-1094.  doi:10.1007/s10483-021-2743-6

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A mathematical model for nonlocal vibration and buckling of embedded two-dimensional (2D) decagonal quasicrystal (QC) layered nanoplates is proposed. The Pasternak-type foundation is used to simulate the interaction between the nanoplates and the elastic medium. The exact solutions of the nonlocal vibration frequency and buckling critical load of the 2D decagonal QC layered nanoplates are obtained by solving the eigensystem and using the propagator matrix method. The present three-dimensional (3D) exact solution can predict correctly the nature frequencies and critical loads of the nanoplates as compared with previous thin-plate and medium-thick-plate theories. Numerical examples are provided to display the effects of the quasiperiodic direction, length-to-width ratio, thickness of the nanoplates, nonlocal parameter, stacking sequence, and medium elasticity on the vibration frequency and critical buckling load of the 2D decagonal QC nanoplates. The results show that the effects of the quasiperiodic direction on the vibration frequency and critical buckling load depend on the length-to-width ratio of the nanoplates. The thickness of the nanoplate and the elasticity of the surrounding medium can be adjusted for optimal frequency and critical buckling load of the nanoplate. This feature is useful since the frequency and critical buckling load of the 2D decagonal QCs as coating materials of plate structures can now be tuned as one desire.



Typical transient effects in a piezoelectric semiconductor nanofiber under a suddenly applied axial time-dependent force

Wanli YANG, Yuxing LIANG

2021, 42(8):  1095-1108.  doi:10.1007/s10483-021-2761-9

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Based on the mechanical motion equation, Gauss’s law, and the current continuity condition, we study a few typical transient effects in a piezoelectric semiconductor (PS) fiber to realize the startup and turning-off functions of common piezotronic devices. In this study, the transient extensional vibration induced by a suddenly applied axial time-dependent force is examined in a cantilevered n-type ZnO nanofiber. Neither the magnitude of the loadings nor the doping concentration significantly affects the propagation caused by disturbance of the axial displacement. However, both of the factors play an important role in the propagation caused by disturbance of the electron concentrations. This indicates that the electromechanical coupling effect can be expected to directly determine the electronic performance of the devices. In addition, the assumption of previous simplified models which neglect the charge carriers in Gauss’s law is discussed, showing that this assumption has a little influence on the startup state when the doping concentration is smaller than 10²¹ m^-3. This suggests that the screening effect of the carriers on the polarized electric field is much reduced in this situation, and that the state is gradually transforming into a pure piezoelectric state. Nevertheless, the carriers can provide a damping effect, which means that the previous simplified models do not sufficiently describe the turning-off state. The numerical results show that the present study has referential value with respect to the design of newly multifunctional PS devices.

Microstructural evolution and mechanical properties of FeCoCrNiCu high entropy alloys: a microstructure-based constitutive model and a molecular dynamics simulation study

Gangjie LUO, Li LI, Qihong FANG, Jia LI, Yuanyuan TIAN, Yong LIU, Bin LIU, Jing PENG, P. K. LIAW

2021, 42(8):  1109-1122.  doi:10.1007/s10483-021-2756-9

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High entropy alloys (HEAs) attract remarkable attention due to the excellent mechanical performance. However, the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed. Here, using a microstructure-based constitutive model and molecular dynamics (MD) simulation, we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation. Due to the interaction between the dislocation and solution, the high dislocation density in FeCoCrNiCu leads to strong work hardening. Plentiful slip systems are stimulated, leading to the good plasticity of FeCoCrNiCu. The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops. The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of $\frac{a}{6}$ [112] and $\frac{a}{6}$ [112], which interact with each other, and then emit along the h111i slip direction. In addition, the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model, which is identified according to the evolution of the dislocation density and the stress-strain curve. Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu, and improve the strength. Therefore, the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu. These results accelerate the discovery of HEAs with excellent mechanical properties, and provide a valuable reference for the industrial application of HEAs.

Dynamics and response reshaping of nonlinear predator-prey system undergoing random abrupt disturbances

Lei XIA, Jiaojiao SUN, Zuguang YING, Ronghua HUAN, Weiqiu ZHU

2021, 42(8):  1123-1134.  doi:10.1007/s10483-021-2755-8

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An actual ecological predator-prey system often undergoes random environmental mutations owing to the impact of natural disasters and man-made destruction, which may destroy the balance between the species. In this paper, the stochastic dynamics of the nonlinear predator-prey system considering random environmental mutations is investigated, and a feedback control strategy is proposed to reshape the response of the predator-prey system against random abrupt environmental mutations. A delayed Markov jump system (MJS) is established to model such a predator-prey system. A novel first integral is constructed which leads to better approximation solutions of the ecosystem. Then, by applying the stochastic averaging method based on this novel first integral, the stochastic response of the predator-prey system is investigated, and an analytical feedback control is designed to reshape the response of the ecosystem from the disturbed state back to the undisturbed one. Numerical simulations finally illustrate the accuracy and effectiveness of the proposed procedure.

Vibration absorption of parallel-coupled nonlinear energy sink under shock and harmonic excitations

Jian'en CHEN, Wei ZHANG, Jun LIU, Wenhua HU

2021, 42(8):  1135-1154.  doi:10.1007/s10483-021-2757-6

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Nonlinear energy sink (NES) can passively absorb broadband energy from primary oscillators. Proper multiple NESs connected in parallel exhibit superior performance to single-degree-of-freedom (SDOF) NESs. In this work, a linear coupling spring is installed between two parallel NESs so as to expand the application scope of such vibration absorbers. The vibration absorption of the parallel and parallel-coupled NESs and the system response induced by the coupling spring are studied. The results show that the responses of the system exhibit a significant difference when the heavier cubic oscillators in the NESs have lower stiffness and the lighter cubic oscillators have higher stiffness. Moreover, the efficiency of the parallel-coupled NES is higher for medium shocks but lower for small and large shocks than that of the parallel NESs. The parallel-coupled NES also shows superior performance for medium harmonic excitations until higher response branches are induced. The performance of the parallel-coupled NES and the SDOF NES is compared. It is found that, regardless of the chosen SDOF NES parameters, the performance of the parallel-coupled NES is similar or superior to that of the SDOF NES in the entire force range.

Radial integral boundary element method for simulating phase change problem with mushy zone

Hongxiao YAO, Weian YAO, Chong ZUO, Xiaofei HU

2021, 42(8):  1155-1170.  doi:10.1007/s10483-021-2760-8

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A radial integral boundary element method (BEM) is used to simulate the phase change problem with a mushy zone in this paper. Three phases, including the solid phase, the liquid phase, and the mushy zone, are considered in the phase change problem. First, according to the continuity conditions of temperature and its gradient on the liquid-mushy interface, the mushy zone and the liquid phase in the simulation can be considered as a whole part, namely, the non-solid phase, and the change of latent heat is approximated by heat source which is dependent on temperature. Then, the precise integration BEM is used to obtain the differential equations in the solid phase zone and the non-solid phase zone, respectively. Moreover, an iterative predictor-corrector precise integration method (PIM) is needed to solve the differential equations and obtain the temperature field and the heat flux on the boundary. According to an energy balance equation and the velocity of the interface between the solid phase and the mushy zone, the front-tracking method is used to track the move of the interface. The interface between the liquid phase and the mushy zone is obtained by interpolation of the temperature field. Finally, four numerical examples are provided to assess the performance of the proposed numerical method.

Interfacial instability of ferrofluid flow under the influence of a vacuum magnetic field

Mingjun LI, Li ZHU

2021, 42(8):  1171-1182.  doi:10.1007/s10483-021-2758-7

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This study is to numerically test the interfacial instability of ferrofluid flow under the presence of a vacuum magnetic field. The ferrofluid parabolized stability equations (PSEs) are derived from the ferrofluid stability equations and the Rosensweig equations, and the characteristic values of the ferrofluid PSEs are given to describe the ellipticity of ferrofluid flow. Three numerical models representing specific cases considering with/without a vacuum magnetic field or viscosity are created to mathematically examine the interfacial instability by the computation of characteristic values. Numerical investigation shows strong dependence of the basic characteristic of ferrofluid Rayleigh-Taylor instability (RTI) on viscosity of ferrofluid and independence of the vacuum magnetic field. For the shock wave striking helium bubble, the magnetic field is not able to trigger the symmetry breaking of bubble but change the speed of the bubble movement. In the process of droplet formation from a submerged orifice, the collision between the droplet and the liquid surface causes symmetry breaking. Both the viscosity and the magnetic field exacerbate symmetry breaking. The computational results agree with the published experimental results.

Horizontal convection in a rectangular enclosure driven by a linear temperature profile

Tianyong YANG, Bofu WANG, Jianzhao WU, Zhiming LU, Quan ZHOU

2021, 42(8):  1183-1190.  doi:10.1007/s10483-021-2754-5

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The horizontal convection in a square enclosure driven by a linear temperature profile along the bottom boundary is investigated numerically by using a finite difference method. The Prandtl number is fixed at 4.38, and the Rayleigh number Ra ranges from 107 to 1011. The convective flow is steady at a relatively low Rayleigh number, and no thermal plume is observed, whereas it transits to be unsteady when the Rayleigh number increases beyond the critical value. The scaling law for the Nusselt number Nu changes from Rossby’s scaling Nu~Ra^1/5 in a steady regime to Nu ～ Ra^1/4 in an unsteady regime, which agrees well with the theoretically predicted results. Accordingly, the Reynolds number Re scaling varies from Re~Ra^3/11 to Re~Ra^2/5. The investigation on the mean flows shows that the thermal and kinetic boundary layer thickness and the mean temperature in the bulk zone decrease with the increasing Ra. The intensity of fluctuating velocity increases with the increasing Ra.

Bio-Marangoni convection flow of Casson nanoliquid through a porous medium in the presence of chemically reactive activation energy

J. K. MADHUKESH, G. K. RAMESH, B. C. PRASANNAKUMARA, S. A. SHEHZAD, F. M. ABBASI

2021, 42(8):  1191-1204.  doi:10.1007/s10483-021-2753-7

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Bioconvection research is primarily focused on the augmentation of energy and mass species, which has implications in the processes intensification, mechanical, civil, electronics, and chemical engineering branches. Advanced bioconvection technology sectors include cooling systems for electronic devices, building insulation, and geothermal nuclear waste disposal. Hence, the present investigation is mainly discoursing the impact of Marangoni convention Casson nanoliquid flow under gyrotactic microorganisms over the porous sheet. The partial differential equations (PDEs) are re-structured into ordinary differential equations (ODEs) via suitable similar variables. These ODEs are numerically solved with the help of the spectral relaxation method (SRM). The numerical outcomes are illustrated graphically for various parameters over velocity, temperature, concentration, and bioconvection profiles. Three-dimensional (3D) views of important engineering parameters are illustrated for various parameters. The velocity of the Casson nanoliquid increases with increasing the Marangoni parameter but decreases against higher porosity parameter. The surface drag force enhances for enhancement in the Marangoni number. The rate of mass transmission is higher for reaction rate constraint but diminishes for activation energy parameter. The higher radiative values augment the rate of heat transmission.

Entropy generation approach with heat and mass transfer in magnetohydrodynamic stagnation point flow of a tangent hyperbolic nanofluid

Tiehong ZHAO, M. R. KHAN, Yuming CHU, A. ISSAKHOV, R. ALI, S. KHAN

2021, 42(8):  1205-1218.  doi:10.1007/s10483-021-2759-5

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This work examines the entropy generation with heat and mass transfer in magnetohydrodynamic (MHD) stagnation point flow across a stretchable surface. The heat transport process is investigated with respect to the viscous dissipation and thermal radiation, whereas the mass transport is observed under the influence of a chemical reaction. The irreversibe factor is measured through the application of the second law of thermodynamics. The established non-linear partial differential equations (PDEs) have been replaced by acceptable ordinary differential equations (ODEs), which are solved numerically via the bvp4c method (built-in package in MATLAB). The numerical analysis of the resulting ODEs is carried out on the different flow parameters, and their effects on the rate of heat transport, friction drag, concentration, and the entropy generation are considered. It is determined that the concentration estimation and the Sherwood number reduce and enhance for higher values of the chemical reaction parameter and the Schmidt number, although the rate of heat transport is increased for the Eckert number and heat generation/absorption parameter, respectively. The entropy generation augments with boosting values of the Brinkman number, and decays with escalating values of both the radiation parameter and the Weissenberg number.