Stress generation during anisotropic lithiation in silicon nanopillar electrodes: A reactive force field study

Models that are developed to investigate lithiation-induced stress in high-volume-change electrodes are often based on continuum approaches with simplifying assumptions. In this work, we investigate stress generation during the first lithiation of crystalline silicon electrodes solely using atomistic simulations with chemo-mechanical fidelity. We use a 〈100〉-oriented silicon nanopillar as a model system and perform molecular statics simulations with a reactive force field. The simulation approach incorporates the key physical feature of the lithiation – anisotropic formation and migration of an atomistically-sharp phase boundary. The resulting stress fields show the development of hoop tension near the nanopillar surface, which drives surface fracture at angular sites between two adjacent {110} facets. This work links the atomic-level physics of the lithiation directly with the stress generation and accounts for the geometric effect of the sharp phase boundary.     

Thermal transport in lithium-ion battery: A micro perspective for thermal management

In recent years, lithium ion (Li-ion) batteries have served as significant power sources in portable electronic devices and electric vehicles because of their high energy density and rate capability. There are growing concerns towards the safety of Li-ion batteries, in which thermal conductivities of anodes, cathodes, electrolytes and separator play key roles for determining the thermal energy transport in Li-ion battery. In this review, we summarize the state-of-the-art studies on the thermal conductivities of commonly used anodes, cathodes, electrolytes and separator in Li-ion batteries, including both theoretical and experimental reports. First, the thermal conductivities of anodes and cathodes are discussed, and the effects of delithiation degree and temperature of materials are also discussed. Then, we review the thermal conductivities of commonly used electrolytes, especially on solid electrolytes. Finally, the basic concept of interfacial thermal conductance and simulation methods are presented, as well as the interfacial thermal conductance between separator and cathodes. This perspective review would provide atomic perspective knowledge to understand thermal transport in Li-ion battery, which will be beneficial to the thermal management and temperature control in electrochemical energy storage devices.     

锂离子电池用具有分级三维离子电子混合导电网络结构的纳微复合电极材料

文章评述了分级三维离子电子混合导电网络结构和具有该结构的纳微复合电极材料在锂离子电池中的应用等方面的最新研究工作进展.首先介绍了纳微复合电极结构相关概念及其优缺点,然后列举了一些运用此概念设计并构筑出的电极材料实例.研究证明,此新型电极结构能够大幅提高锂离子电池电极材料的储锂性能,并且该结构设计还可推广到其他电化学储能...     

耦合界面力的两相流相场格子Boltzmann模型

提出了一种改进的基于相场理论的两相流格子Boltzmann模型.通过引入一种新的更加简化的外力项分布函数,使得此模型克服了前人工作中界面力尺度与理论分析不一致的问题,并且通过Chapman-Enskog多尺度分析表明,所提出的模型能够准确恢复到追踪界面的Cahn-Hilliard方程和不可压的Navier-Stokes方程,并且宏观速度的计算更为简化.利用所提模型对几个经典两相流问题,包括静态液滴测试、液滴合并问题、亚稳态分解以及瑞利-泰勒不稳定性进行了数值模拟,发现本模型可以获得量级为10^-9极小的虚假速度,并且这些算例获取的数值解与解析解或已有的文献结果相吻合,从而验证了模型的准确性和可行性.最后,利用所发展的两相流格子Boltzmann模型研究了随机扰动的瑞利-泰勒不稳定性问题,并着重分析了雷诺数对流体相界面的影响.发现对于高雷诺数情形,在演化前期,流体界面出现一排“蘑菇”形状,而在演化后期,流体界面呈现十分复杂的混沌拓扑结构.不同于高雷诺数情形,低雷诺数时流体界面变得相对光滑,在演化后期未观察到混沌拓扑结构.     

A study of detonation diffraction and failure for a model of compressible two-phase reactive flow

A two-phase model of heterogeneous explosives, with a reaction rate that is proportional to the gas-phase pressure excess above an ignition threshold, is examined computationally. The numerical approach, a variant of Godunov's method designed to accommodate nonconservative terms in the hyperbolic model, extends previous work of the authors to two-dimensional configurations. The focus is on the behavior of an established detonation as it rounds a 90° corner and undergoes diffraction. The dependence of the post-diffraction conduct on the reaction rate is explored by varying the reaction-rate prefactor and the ignition threshold. The aim is to determine whether the model, as postulated, can capture dead zones, which are pockets of unreacted or partially reacted explosive observed in the vicinity of the corner in diffraction experiments. Results of this study are compared with those of a similar investigation on the one-phase ignition-and-growth model.     

A two-phase diffuse-interface model for Hele-Shaw flows with large property contrasts

A novel two-phase diffuse-interface model is used to simulate flows inside a Hele-Shaw cell. The model assumes that the two phases coexist inside the diffuse interface, with different velocities and properties. A separate equation is used to calculate the slip velocity between the two phases inside the diffuse interface. It is shown that for one-dimensional flows parallel to the diffuse interface, the results are independent of the diffuse-interface width, regardless of the magnitude of the density and viscosity contrasts between the phases. This two-phase approach is coupled with a phase-field equation for calculating the interface motion. The model is applied to a buoyancy-driven two-phase flow involving a Rayleigh-Taylor instability and validated through a comparison with available sharp-interface results. The flows and interface topology changes are investigated for large density and viscosity contrasts between the phases. The convergence of the results with respect to the interface width is examined in detail. It is shown that the two-phase model converges better than a standard diffuse-interface model that assumes the presence of a single velocity inside the diffuse interface. Remaining interface width dependencies can be attributed to the capillary stress term in the momentum equation.     

A three-dimensional solid-liquid two-phase turbulence model with the effect of vegetation in non-orthogonal curvilinear coordinates

A three-dimensional k-ε-Ap solid-liquid two-phase two-fluid model with the effect of vegetation is solved numerically with a finite-volume method on an adaptive grid to study water-sediment movements and bed evolution in vegetated channels. The additional drag force and additional turbulence generation due to vegetation are added to the relevant control equations for simulating the interaction between vegetation and flow. The flow structure and the bed-topography changes in a 60° partly vegetated channel be...     

A constitutive model of frozen soil with damage and numerical simulation for the coupled problem

Based on the microcosmic mechanics of composite materials, an elastic constitutive model for frozen soil with damage is presented. For frozen sandy soil with a range of ice contents and under a range of temperature conditions, quantitative results determined by this constitutive model agree with practically measured stress-strain curves. After numerically simulating the coupled water, temperature and stress fields of channel frozen and frozen roadbed using a self-developed finite-element routine, more accur...     

A Volume of Fluid Based Method for Fluid Flows with Phase Change

This paper presents a numerical method directed towards the simulation of flows with mass transfer due to changes of phase. We use a volume of fluid (VOF) based interface tracking method in conjunction with a mass transfer model and a model for surface tension. The bulk fluids are viscous, conducting, and incompressible. A one-dimensional test problem is developed with the feature that a thin thermal layer propagates with the moving phase interface. This test problem isolates the ability of a method to accurately calculate the thermal layers responsible for driving the mass transfer in boiling flows. The numerical method is tested on this problem and then is used in simulations of horizontal film boiling.     

A viscous continuum traffic flow model with consideration of the coupling effect for two-lane freeways

In this paper, the viscous continuum traffic flow model for a single lane is extended to the traffic flow for two-lane freeways. The proposed model is a higher-order continuum model considering the coupling and lane changing effects of the vehicles on two adjacent lanes. It results from integrating the Taylor series expansion of the viscous continuum traffic flow model proposed by Ge (2006 Physica A 371 667) into the multi-lane model presented by Daganzo (1997 Transpn. Res. B 31 83). Our proposed model may be used to describe non-anisotropic behaviour because of lane changing in multi-lane traffic. A linear stability analysis is given and the neutral stability condition is obtained. Also, issues related to lane changing, shock waves and rarefaction waves, local clustering and phase transition are investigated through a simulation experiment. The simulation results show that the proposed model is capable of explaining some particular traffic phenomena commonly observable in real world traffic flow.     

开放性边界条件下双车道元胞自动机交通流模型耦合效应研究

在一种改进的Nagel-Schrekenberg元胞自动机交通流模型的基础上，提出一个高速公路双车 道元胞自动机模型来模拟开放性边界条件下的车流运动，并考虑两车道之间左边界开放程度 的比例系数α及车辆加减速概率p的影响.计算机数值模拟结果表明，在车流状态的演化过程 中，通过确定车道耦合系数b来控制车流量，不同的b值车流量不同，对车辆运动出现堵塞项 的相变点有影响. 关键词： 元胞自动机 交通流模型 耦合效应     

A model for the interaction of near-infrared laser pulses with metal powders in selective laser sintering

A thermal model of the interaction of pulsed near-infrared laser radiation from a Nd:YAG laser was made, taking the measured powder properties such as reflectance, optical penetration depth and thermal conductivity into account. It allows an estimation of the evolution of two different temperatures: the average temperature of the powder (taken over the grains in a volume given by the laser beam diameter and the optical penetration depth) and the temperature distinction within a single grain. It showed that in pulsed mode consolidation can be achieved at much lower average power as the surface of the powder particles are molten but their cores remain at nearly room temperature. This leads to a much lower average temperature and therefore a dramatic decrease in residual thermal stresses in the finished piece. The results of the model were experimentally tested and confirmed. Received: 26 July 2001 / Accepted: 23 November 2001 / Published online: 23 January 2002     

SU(3) coupling schemes for odd-odd nuclei in the interacting boson – fermion – fermion model with both odd proton and odd neutron in natural parity orbits

The SU^BFF(3) dynamical symmetry limits of interacting boson – fermion – fermion model are identified and they are appropriate for heavy deformed odd – odd nuclei for configurations with both the odd proton and odd neutron occupying all the natural parity orbits in the corresponding valence shells. There are three symmetry limits and their correspondence with two quasi-particle (proton-neutron) Nilsson configurations is established; one of the limits mixes both Nilsson n_z's and Λ's and other two limits mix only Nilsson Λ's. The ¹⁹¹Ir (d,t) ¹⁹⁰Ir single nucleon transfer spectroscopic strengths are well described by one of the symmetry limits that mixes only Nilsson Λ's. Received: 22 June 1998     

A method for calculating the surface tension of a droplet in a lattice-gas model with long-range interaction

Since the droplet of the lattice-gas model with long-range interaction is not circular and is determined by the Wulff construction due to surface tension anisotropy, a calculation method of the surface tension of the droplet is proposed in this paper. The calculated surface tension is in good agreement with the surface tension measured by using the Laplace's formula in consideration of the surface thickness. Received 15 March 2000 and Received in final form 31 May 2000