Implementation of a particle-in-cell method for the energy solver in 3D spherical geodynamic modeling

The thermal evolution of the Earth’s interior and its dynamic effects are the focus of Earth sciences.However,the commonly adopted grid-based temperature solver is usually prone to numerical oscillations,especially in the presence of sharp thermal gradients,such as when modeling subducting slabs and rising plumes.This phenomenon prohibits the correct representation of thermal evolution and may cause incorrect implications of geodynamic processes.After examining several approaches for removing these numerical oscillations,we show that the Lagrangian method provides an ideal way to solve this problem.In this study,we propose a particle-in-cell method as a strategy for improving the solution to the energy equation and demonstrate its effectiveness in both one-dimensional and three-dimensional thermal problems,as well as in a global spherical simulation with data assimilation.We have implemented this method in the open-source finite-element code CitcomS,which features a spherical coordinate system,distributed memory parallel computing,and data assimilation algorithms.

Simulation of incompressible multiphase flows with complex geometry using etching multiblock method

The incompressible two-phase flows are simulated using combination of an etching multiblock method and a diffuse interface （DI） model, particularly in the com- plex domain that can be decomposed into multiple rectangular subdomains. The etching multiblock method allows natural communications between the connected subdomains and the efficient parallel computation. The DI model can consider two-phase flows with a large density ratio, and simulate the flows with the moving contact line （MCL） when a geometric formulation of the MCL model is included. Therefore, combination of the etch- ing method and the DI model has potential to deal with a variety of two-phase flows in industrial applications. The performance is examined through a series of numerical exper- iments. The convergence of the etching method is firstly tested by simulating single-phase flows past a square cylinder, and the method for the multiphase flow simulation is vali- dated by investing drops dripping from a pore. The numerical results are compared with either those from other researchers or experimental data. Good agreement is achieved. The method is also used to investigate the impact of a droplet on a grooved substrate and droplet generation in flow focusing devices.

A method and device for online magnetic resonance multiphase flow detection

Most multiphase flow separation detection methods used commonly in oilfields are low in efficiency and accuracy,and have data delay.An online multiphase flow detection method is proposed based on magnetic resonance technology,and its supporting device has been made and tested in lab and field.The detection technology works in two parts:measure phase holdup in static state and measure flow rate in flowing state.Oil-water ratio is first measured and then gas holdup.The device is composed of a segmented magnet structure and a dual antenna structure for measuring flowing fluid.A highly compact magnetic resonance spectrometer system and intelligent software are developed.Lab experiments and field application show that the online detection system has the following merits:it can measure flow rate and phase holdup only based on magnetic resonance technology;it can detect in-place transient fluid production at high frequency and thus monitor transient fluid production in real time;it can detect oil,gas and water in a full range at high precision,the detection isn’t affected by salinity and emulsification.It is a green,safe and energy-saving system.

Preparation of micro-nano hollow multiphase ceramic microspheres containing MnFe_2O_4 absorbent by self-reactive quenching method

Fe–Fe2O3–MnO2–sucrose–epoxy resin and O2 as reaction system and feed gas,separately,were used to prepare micro-nano hollow multiphase ceramic microspheres containing MnFe2O4absorbent by self-reactive quenching method which is integrated with flame jet,selfpropagating high-temperature synthesis(SHS),and rapidly solidification.The morphologies and phase compositions of hollow microspheres were studied by scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),and energy dispersive spectroscopy.The results show that the quenching products are regular spherical substantially with hollow structure,particle size is between few hundreds nanometers and 5 lm.Phase compositions are diphase of Fe3O4,Mn3O4,and MnFe2O4,and the spinel soft magnetic ferrite MnFe2O4 with microwave magnetic properties is in majority.Collisions with each other,burst as well as‘‘refinement’’of agglomerate powders in flame field may be the main reasons for the formation of micro-nano hollow multiphase ceramic microspheres containing MnFeOabsorbent.

A Multiphase Mixed Methods Approach to the Internationalization of Higher Education in South Africa:Outline of a Discursive Research Framework

Higher education internationalization(HEI)has become an important priority for global decision makers and education providers.Persuaded by globalization,HEI is a political strategy and economic prospect for countries,governments,and universities to position themselves in global markets.The purpose of this paper is to provide a methodological pathway to develop a dynamic,reformed South African HEI framework based on the transformative drive(i.e.,adjustment of change,learning,shared knowledge,internationalization,globalization an institutionalized memory)of HEI in China.The interpretivist paradigm constitutes the basic research approach.Quantitative and qualitative data will be collected,analyzed,and integrated using a multiphase mixed methods approach.This approach consists of three phases including content analysis(Phase I),in-depth interviews(Phase II),and surveys(Phase III),which answers the focal research question.The significance of this research includes creating a better understanding of South African higher education(HE)policy issues from a transformational perspective,contributing to theory on how internationalization affects HE’s position in economic and social development and broadening knowledge and understanding of the unique circumstances and challenges of HEI in developing countries,particularly in countries seeking to position themselves in the globalized knowledge economy.

Affine particle-in-cell method for two-phase liquid simulation

Background The interaction of gas and liquid can produce many interesting phenomena,such as bubbles rising from the bottom of the liquid.The simulation of two-phase fluids is a challenging topic in computer graphics.To animate the interaction of a gas and liquid,MultiFLIP samples the two types of particles,and a Euler grid is used to track the interface of the liquid and gas.However,MultiFLIP uses the fluid implicit particle(FLIP)method to interpolate the velocities of particles into the Euler grid,which suffer from additional noise and instability.Methods To solve the problem caused by fluid implicit particles(FLIP),we present a novel velocity transport technique for two individual particles based on the affine particle-in-cell(APIC)method.First,we design a weighed coupling method for interpolating the velocities of liquid and gas particles to the Euler grid such that we can apply the APIC method to the simulation of a two-phase fluid.Second,we introduce a narrowband method to our system because MultiFLIP is a time-consuming approach owing to the large number of particles.Results Experiments show that our method is well integrated with the APIC method and provides a visually credible two-phase fluid animation.Conclusions The proposed method can successfully handle the simulation of a two phase fluid.

A pseudopotential-based multiple-relaxation-time lattice Boltzmann model for multicomponent/multiphase flows

In this paper, a pseudopotential-based multiplerelaxation-time lattice Boltzmann model is proposed for multicomponent/multiphase flow systems. Unlike previous models in the literature, the present model not only enables the study of multicomponent flows with different molecular weights, different viscosities and different Schmidt numbers, but also ensures that the distribution function of each component evolves on the same square lattice without invoking ad- ditional interpolations. Furthermore, the Chapman-Enskog analysis shows that the present model results in the correct hydrodynamic equations, and satisfies the indifferentiability principle. The numerical validation exercises further demonstrate that the favorable performance of the present model.

FEM Modeling of Crack Propagation in a Model Multiphase Alloy

In this paper, several widely applied fracture criteria were first numerically examined and the crack-tip-region Jntegral criterion was confirmed to be more applicable to predict fracture angle in an elastic-plastic multiphase material. Then, the crack propagation in an idealized an elastic-plastic finite element method. The variation dendritic two-phase AI-7%Si alloy was modeled using of crack growth driving force with crack extension was also demonstrated. It is found that the crack path is significantly influenced by the presence of α-phase near the crack tip, and the crack growth driving force varies drastically from place to place. Lastly, the simulated fracture path in the two-phase model alloy was compared with the experimentally observed fracture path.

Quasi-static simulation of droplet morphologies using a smoothed particle hydrodynamics multiphase model

Numerical simulation of the morphology of a droplet deposited on a solid surface requires an efficient description of the three-phase contact line. In this study, a simple method of implementing the contact angle is proposed, combined with a robust smoothed particle hydrodynamics multiphase algorithm (Zhang 2015). The first step of the method is the creation of the virtual liquid-gas interface across the solid surface by means of dummy particles, thus the calculated surface tension near the triple point serves to automatically modulate the dynarnic contact line towards the equilibrium state. We simulate the evolution process of initially square liquid lumps on fiat and curved surfaces. The predictions of droplet profiles are in good agreement with the analytical solutions provided that the macroscopic contact angle is accurately implemented. Compared to the normal correction method, the present method is straightforward without the need to manually alter the normal vectors. This study presents a robust algorithm capable of capturing the physics of the static welling. It may hold great potentials in bio-inspired superhydrophobic surfaces, oil displacement, microfluidics, ore floatation, etc.

Lattice Boltzmann model for interface capturing of multiphase flows based on Allen–Cahn equation

A phase-field-based lattice Boltzmann model is proposed for the interface capturing of multi-phase flows based on the conservative Allen–Cahn equation(ACE).By adopting the improved form of a relaxation matrix and an equilibrium distribution function,the time derivative?t(φ)induced by recovering the diffusion term in ACE is eliminated.The conducted Chapman–Enskog analysis demonstrates that the correct conservative ACE is recovered.Four benchmark cases including Zalesak’s disk rotation,vortex droplet,droplet impact on thin film,and Rayleigh–Taylor instability are investigated to validate the proposed model.The numerical results indicate that the proposed model can accurately describe the complex interface deformation.

基于CFD-DEM算法的气力输送气固两相流特性分析

超轻粉体颗粒由于质量较小,在运输过程中易受气流扰动而飘散,物料的管道气力输送过程不稳定,易发生堵塞。为了研究超轻粉体颗粒在旋流气力输送中气固两相流流动特性,采用计算流体力学与离散单元法(CFD-DEM),对Komax型静态混合器内气固两相流动特性进行数值模拟研究。研究发现,带有Komax型元件的水平管道可以改变颗粒的流动情况,改善了水平管道内颗粒堆积和分布不均匀的现象;分别从颗粒相和流体相的流动状态分析得到元件长径比Ar=3时为最优几何结构;通过正交实验极差分析得到影响气固两相流动特性的因素顺序:输送气速>颗粒质量流量>颗粒粒径。当元件Ar=3时,颗粒-颗粒和颗粒-管壁的碰撞次数与碰撞强度呈现负相关,结合出口颗粒流分散状态,优选输送气速为3~4m/s;主要考虑输送气速对管内压降的影响,提出了带有Komax型元件的水平管道气力运输过程中压降与输送气速和轴向位置的经验拟合式。

大数据税收征管对企业风险承担的影响研究

当前我国企业的风险承担处于较低水平,这给企业的可持续发展和国家的长期繁荣带来了极大的挑战。借助“金税三期”工程这一准自然实验,采用多期双重差分法研究了大数据税收征管对企业风险承担的影响及作用机制,研究表明:大数据税收征管对企业风险承担具有显著促进作用。机制检验发现,大数据税收征管通过抑制代理行为、缓解融资约束、增进税负公平、优化营商环境来促进企业风险承担。进一步的分析表明,大数据税收征管对非国有企业和有产业政策扶持企业风险承担的促进作用更大。

强制流动对Mg–9%Al合金定向凝固组织演化的模拟研究

基于欧拉多相流技术与元胞自动机方法构建了镁合金凝固组织预测模型,研究了无流动、x方向流动和y方向流动三种条件下Mg–9%Al合金定向凝固过程中的成分和组织演化过程.研究结果表明,无流动作用时镁合金枝晶呈现互为60°夹角生长,并在凝固后期出现与一次枝晶呈60°夹角二次枝晶形貌,凝固组织具有密排六方(HCP)晶体结构特征,验证了该模型的可靠性.由于x方向的流动作用下,与无流动结果相比较,迎流方向枝晶生长较快并出现发达的二次枝晶形貌,研究表明由于枝晶前端排出的溶质受流动影响被运输到枝晶后端区域,从而使前端区域具有更大的过冷度,提升了凝固驱动力.由于y方向流动的存在,枝晶呈现不对称生长,其中部分枝晶生长方向偏转约3°,研究表明迎流枝晶前沿的溶质被运输并富集在其他枝晶生长区域,最终使其发生了生长偏转;进一步分析枝晶生长前沿的流场和成分分布信息发现,枝晶生长过程中流动u1∇c1引起的值在固液界面处的不对称分布是导致枝晶生长发生偏转的主要原因.

基于元胞自动机方法与欧拉多相流技术的激光沉积IN718组织形貌模拟

为研究激光沉积过程中沉积层微观枝晶外延生长及转向机制,基于欧拉多相流技术与元胞自动机方法相结合,建立了激光沉积IN718二维熔化凝固模型;获得了沉积层温度场、流场以及微观凝固组织的演变过程,对比了模拟与实验所得沉积层枝晶外延生长区厚度,分析了顶部枝晶转向的机制。结果表明:温度场与流场相互影响,模型对沉积层厚度预测误差约为7.0%。沉积层顶部和中部晶体织构取向不同,枝晶的生长方向更偏向于局部热梯度方向,在沉积层顶部,局部热梯度的方向接近水平方向,枝晶的生长方向与局部热梯度偏角较小,因此,形成平行于激光扫描方向的枝晶区。

冰区船舶压载水舱吹泡防冻性能的模拟分析

文中通过建立压载舱三维模型,采用VOF模型和凝固融化模型分析气泡在压载舱内的运动规律和形态变化,探究舱内海水-海冰-气泡多相流的换热规律以及海水-海冰的相变过程.结果表明:未吹泡情况下舱壁附近温度降低至海水凝固温度273.15 K以下,会发生冻结;吹泡情况下温度降低至273.15 K后维持不变.

相关式油井液相计量系统研究与设计

针对现有油井计量方式自动化程度低,误差较大等问题,利用同轴线相位法含水率计设计了一种相关式油井液相计量系统,该系统以同轴线相位法含水率计为传感器构建了相关流量计,基于互相关法建立了计量模型,实现了流量与含水率的同步测量。通过对不同情况下上、下游含水率计信号的分析可知,两路信号之间具有相关性,满足相关流量计的使用条件。该系统在现场试验的测量结果与涡轮流量计相比,平均误差为11.36%。试验结果证明了相关式油井液相计量系统在实际应用中的可行性。

致密砂岩气藏注CO_(2)提高天然气采收率微观机理

中国致密砂岩气藏资源储量丰富,复杂的气水渗流关系和气水同产特征制约了单井产能的发挥和天然气采收率提高,注CO_(2)是提高气藏采收率(EGR)和实现碳埋存的双赢途径。为明确致密砂岩气藏CO_(2)驱替微观渗流和提高天然气采收率机理,指导致密砂岩气藏CO_(2)-EGR方案设计,基于格子玻尔兹曼方法(LBM)建立了孔隙尺度多相多组分流动模型,揭示了致密砂岩气藏储层微观气水分布特征和CO_(2)-EGR的微观渗流机理,并明确了CO_(2)-EGR的主控因素。研究结果表明:①驱动压差显著影响了致密砂岩气藏的气水微观分布和水锁程度,使得气水流动能力和气水相对渗透率特征不同;②CO_(2)-EGR微观渗流过程包括气水两相的非混相驱替和CO_(2)-CH_(4)的混相驱替,对应EGR机理为分别受生产压差和地层压力控制的黏性驱替和混相扩散;③注入的CO_(2)可有效缓解水锁现象和贾敏效应,与CH_(4)良好的混相能力能促进沟通分散气泡,微观驱气效率可达42%~94%;④含水饱和度、孔隙结构和驱动压差显著影响微观驱气的作用机制和驱气效率的改善幅度。结论认为,在进行致密砂岩气CO_(2)-EGR的方案设计时,可优先考虑中—低含水饱和度的区块作为试验靶区,并根据靶区储层孔隙结构特征,优化不同注气阶段的注采参数,可充分发挥CO_(2)对CH_(4)的黏性驱替和混相扩散作用。

基于格子Boltzmann方法的自由能密度模型

基于格子Boltzmann方法的多相流模型具有相界面自动演化、无需边界积分等优势,在模拟复杂多相流系统中获得广泛的研究和应用。本文引入自由能密度计算分子间的相互作用力,提出一种满足热力学一致性和伽利略不变性的多相流模型。使用该模型预测气液两相共存密度的结果与理论值吻合得很好,误差值为-0.01~0.01,并且在低温度下优于改进的伪势模型。同时该模型也可以模拟较大密度比的气液系统,液相与气相的密度比可达10^(7)以上。通过两相分离和液滴撞击液膜等一系列数值模拟,验证了该模型符合伽利略不变性。该模型物理清晰、易于实施,能够结合不同状态方程模拟多相流系统,具有较好的实用性和应用前景。

基于同轴聚焦微流控拓扑构造的双乳液滴生成机制数值模拟

采用流体体积(VOF)相界面追踪技术建立了同轴聚焦微通道内双乳液滴生成过程的数值计算模型。当内相、中间相和外相流体流速分别为0.01、0.011、0.04m/s时,该模型能够稳定形成单分散性较好、直径为500μm的双乳液滴。形成的双乳液滴适合药物领域的应用。在此基础上,分析了聚焦孔半径、聚焦孔颈长与聚焦孔颈角对三相流体的液滴驱动方式的影响,并讨论了微流道拓扑结构变化与双乳液滴生成机制及特性的内在联系与机理。结果表明,聚焦孔半径影响了Marangoni效应对内液滴局部扰动的程度,在改变生成液滴截面尺寸的同时,也使液滴生成频率发生相应的变化。聚焦孔颈长的改变决定了内外相流体的流型,限制了液膜断裂与脱离过程,从而对液滴生成方式产生根本性影响。聚焦孔颈角的变化影响了鞘液对外界面的剪切作用,通常情况下较大的角度使得局部流体阻力得以缓慢的释放,有利于生成液滴界面的稳定性。

Sparse identification-assisted exploration of the atomic-scale deformation mechanism in multiphase CoCrFeNi high-entropy alloys

This study investigated the atomic-scale deformation mechanism of multiphase CoCrFeNi high-entropy alloys(HEAs)at liquid helium,liquid nitrogen,and room temperatures.A million-atom multiphase HEA was prepared using molecular dynamics simulation involving melt and quench processes.The HEA exhibited high-density dislocations and some twins,consistent with experimental observations.Quantitative analysis revealed an inconsistent evolution of the microstructure under tensile deformation.In particular,the elastic and initial plastic stages exhibited an increase in the disordered structure at the expense of the face-centered cubic and hexagonal close-packed structures,followed by a subsequent transformation involving multiple structural rearrangements.Furthermore,through sparse identification,a model depicting microstructural evolution during tension was extracted for the CoCrFeNi HEA at three typical temperatures and three tensile rates.The model highlighted the importance of the body-centered cubic structure in the evolutionary process.