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Non-uniqueness of critical solid fraction considering boundary conditions and strain-rate effects

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Particuology 2021年第1期19卷 37-49页

作者： Mingze Xu Zixin Zhang Xin Huang Kevin J.Hanley Department of Geotechnical Engineering Tongji UniversityShanghai 200092China State Key Laboratory of Geotechnical Engineering Ministry of EducationTongji UniversityShanghai 200092China School of Engineering Institute for Infrastructure and EnvironmentThe University of EdinburghEdinburgh EH93JLUnited Kingdom

The critical solid fraction(ϕJ),which marks the transition between the solid and liquid phases in the jamming diagram,is influenced by several *** this study,the dependency ofϕJ on strain rate and boundary conditions is examined through discrete element method simulations considering a frictionless polydisperse granular *** approaches are used to determineϕ*** observed boundary effect is due to the nonuniform solid fraction distribution induced by the clustering of particles close to rigid-wall boundaries at high compression *** solid fraction distribution within the sample in the rigid-wall simulations approaches that in the periodic-boundary simulations as the compression rate *** increasing compression rate,the major force transmission network contains fewer mechanically stable particles and a less stable force transmission *** causes jamming of the granular assembly at a lower solid *** force transmission networks,however,are fragile and disintegrate quickly upon relaxation.

关键词： Jamming transition Jamming density Strain rate dependency boundary effects

Efficient and Reliable Nanoindentation Simulation by Dislocation Loop Erasing Method

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Acta Mechanica Solida Sinica 2020年第5期33卷 586-599页

作者： Fei Shuang Pan Xiao Yilong Bai LNM Institute of MechanicsChinese Academy of SciencesBeijing100190China Department of Mechanical and Aerospace Engineering University of FloridaGainesvilleFL32611USA

Nanoindentation is a useful technique to measure material properties at microscopic ***,the intrinsically multiscale nature makes it challenging for large-scale simulations to be carried *** is shown that in molecular statics simulations of nanoindentation,the separated dislocation loops(SDLs)are trapped in simulation box which detrimentally affects the plastic behavior in the plastic zone(PZ);and the long-distance propagation of SDLs consumes much computational cost yet with little contribution to the variation of tip *** tackle the problem,the dislocation loop erasing(DLE)method is proposed in the work to alleviate the influence of artificial boundary conditions on the SDL–PZ interaction and improve simulation *** results indicate that the force–depth curves obtained from simulations with and without DLE are consistent with each other,while the method with DLE yields more reasonable results of microstructural evolution and shows better *** new method provides an alternative approach for large-scale molecular simulation of nanoindentation with reliable results and higher efficiency and also sheds lights on improving existing multiscale methods.

关键词： Nanoindentation Dislocation loops boundary effects Molecular statics

Interaction potential of two nonidentical ground-state atoms

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Communications in Theoretical Physics 2023年第8期75卷 100-110页

作者： Yan Peng Shijing Cheng Wenting Zhou Department of Physics Synergetic Innovation Center for Quantum Effects and Applications and Institute of Interdisciplinary StudiesHunan Normal UniversityChangsha 410081China School of Physics and Information Engineering Shanxi Normal UniversityTaiyuan 030031China Department of Physics School of Physical Science and TechnologyNingbo UniversityNingbo 315211China

We study the interaction potential of two nonidentical ground-state atoms coupled to a scalar field in a vacuum by separately calculating the contributions of vacuum fluctuations and those of the radiation reaction of the *** cases of atoms in a free space and in parallel or vertical alignment to a reflecting boundary are *** the former case,we find that the leading-order interaction potential in the regionλA?L?λB exhibits the same separationdependence as that in the region L?λA?λB,where L,λA andλB are respectively the interatomic separation and the transition wavelengths of two atoms withλA?λ*** the latter case,we find that boundary-induced modifications are very remarkable when L?z,with z characterizing the separation between the two-atom system and the ***,when L further satisfies L?λA and L?λB,the interaction potential in the parallel-and the verticalalignment cases respectively scales as z4L-7 and z2L-5,the L-dependence of which is one order higher than those of two atoms in regions where L?z and meanwhile L?λA or/and L?λ*** results suggest that retardation for the interaction potential of two nonidentical atoms with remarkably distinctive transition frequencies happens only when the interatomic separation is much greater than the transition wavelengths of both atoms.

关键词： boundary effects interatomic interaction potential nonidentical atoms with remarkably distinctive transition frequencies

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Constrained oscillation of a bubble subjected to shock wave in microvessel

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Progress in Natural Science:Materials International 2009年第9期19卷 1109-1117页

作者： Farong Gao, Caihua Xiong *, Youlun Xiong Institute of Rehabilitation and Medical Robotics, State Key Lab of Digital Manufacturing Equipment and Technology, School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China Institute of Rehabilitation and Medical Robotics State Key Lab of Digital Manufacturing Equipment and Technology School of Mechanical Science and Engineering Huazhong University of Science and Technology Wuhan 430074 China

A three-phase coupled model of the gasliquid-solid oscillation system is established to analyze the oscillation characteristics of a bubble inside a micro blood vessel with various radii and its shape changes with different interface boundaries. The results show that unlike the spherical symmetric oscillation in an unbounded fluid, the oscillating bubble has significant asymmetric characteristics under the constraint of a fiexible microvessel, especially while its radius reduces to the same order of magnitude as that of the bubble. Moreover, the variation of microbubble motion, whether the geometric shape or oscillation feature, exhibits obvious differences in the micro blood vessel compared with the rigid wall. The reasons behind these phenomena are analyzed in this paper. The conclusions have significant importance in the understanding of the mechanism of microvessel injury in ultrasound therapy.

关键词： Asymmetric oscillation Microbubble Shock wave Micro blood vessel boundary effects

Preliminary study on the dynamic mechanism of the deep equatorial jets

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Acta Oceanologica Sinica 1994年第4期13卷 465-474页

作者： Wu Dexing (Received December 15, 1993 accepted March 7, 1994)(Institute of Physical OCeanography, Ocean University of Qingdao, Qingdao 266003, China)

Observations show that the deep equatorial circulation is surprisingly energetic, with alternating eastward adn westward zonal currents(these fkows are commonly referred to as the deep equatorial jets) between 1 000 and 3 000 m. This paper shows that the waves generated by an off-equatorial deep buoyancy oscillation, and their energy radiatin as well as the equatorial focus of waves energy are the viable dynamic mechanisms of forming the deep equatorial *** results of testinh the effects of vertical mixing coefficients on the jets show that as the coefficients increase, the jets become weaker and their zonal coherent scales become *** solutions for different periods of forcing indicate that lengthening the period of forcing results in the position of the core of the deep jets moving westward and also enhances the zonal coherent scales of the jets.

关键词： Deep equatorial jets buoyancy oscillation focus of waves energy boundary effects

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DIFFUSIVE LIMITS OF THE BOLTZMANN EQUATION IN BOUNDED DOMAIN

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Annals of Applied Mathematics 2020年第2期36卷 111-185页

作者： Raffaele Esposito Yan Guo Chanwoo Kim Rossana Marra International Research Center M&MOCS Univ.delVAquilaCistema di Latina(LT)0/012 Italy Division of Applied Mathematics Brown UniversityProvidenceRI 02812U.S.A. Department of Mathematics University of WisconsinMadison53706-1325 WIU.S.A. Dipartimento di Fisica and Unita INFN Universita di Roma Tor Vergata00133 RomaItaly

The goal of this paper is to study the important diffusive expansion via an alternative mathematical approach other than that in [21].

关键词： steady and unsteady Boltzmann equation hydrodynamics limits boundary effects

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