Numerical simulation of complex multi-phase fluid of casting process and its applications

The fluid of casting process is a typical kind of multi-phase flow. Actually, many casting phenomena have close relationship with the multi-phase flow, such as molten metal filling process, air entrapment, slag movement, venting process of die casting, gas escaping of lost foam casting and so on. Obviously, in order to analyze these phenomena accurately, numerical simulation of the multi-phase fluid is necessary. Unfortunately, so far, most of the commercial casting simulation systems do not have the ability of multi-phase flow modeling due to the difficulty in the multi-phase flow calculation. In the paper, Finite Different Method (FDM) technique was adopt to solve the multi-phase fluid model. And a simple object of the muiti-phase fluid was analyzed to obtain the fluid rates of the liquid phase and the entrapped air phase.

A proposed NMR solution for multi-phase flow fluid detection

In the petroleum industry,detection of multi-phase fluid flow is very important in both surface and down-hole measurements.Accurate measurement of high rate of water or gas multi-phase flow has always been an academic and industrial focus.NMR is an efficient and accurate technique for the detection of fluids;it is widely used in the determination of fluid compositions and properties.This paper is aimed to quantitatively detect multi-phase flow in oil and gas wells and pipelines and to propose an innovative method for online nuclear magnetic resonance(NMR)detection.The online NMR data acquisition,processing and interpretation methods are proposed to fill the blank of traditional methods.A full-bore straight tube design without pressure drop,a Halbach magnet structure design with zero magnetic leakage outside the probe,a separate antenna structure design without flowing effects on NMR measurement and automatic control technology will achieve unattended operation.Through the innovation of this work,the application of NMR for the real-time and quantitative detection of multi-phase flow in oil and gas wells and pipelines can be implemented.

Multi-phase computer modeling and laboratory study of dust capture by an inertial Vortecone scrubber

Dust generated in mining and tunneling activities is hazardous to health of persons and safety of operations. These projects employ pick-milling machines to extract minerals and rock by mechanical breakage.The machines are equipped with flooded-bed scrubbers that encase dust particles within fine water films as particles encounter a flooded wire-mesh screen. A major disadvantage is that the screen gets clogged when particles become trapped within the wire mesh, reducing airflow through the scrubber and increasing ambient dust concentrations. Thus, the system requires frequent maintenance or replacement. The application of a Vortecone scrubber as an improved alternative to conventional fibrous type scrubbers is investigated. A Vortecone forces dust-laden air and water to follow a complex, rapidly swirling motion.The momentum drives dust particles towards the periphery where they are captured by the water film.The operating characteristics of a reduced-scale physical model of a Vortecone, with its primary axis mounted in the horizontal orientation, was analyzed numerically and experimentally. Computational fluid dynamics(CFD) models depicting the spraying action and multi-phase air/water flows using the volume of fraction(VOF) approach, are presented. Experimental results, utilizing an optical particle counting technique to establish the dust-cleaning capabilities of the model, are also described.

A Hybrid Scheme of Level Set and Diffuse Interface Methods for Simulating Multi-Phase Compressible Flows

We propose a hybrid scheme combing the level set method and the multicomponent diffuse interface method to simulate complex multi-phase flows.The overall numerical scheme is based on a sharp interface framework where the level set method is adopted to capture the material interface,the Euler equation is used to describe a single-phase flow on one side of the interface and the six-equation diffuse interface model is applied to model the multi-phase mixture or gas-liquid cavitation on the other side.An exact Riemann solver,between the Euler equation and the six-equation model with highly nonlinear Mie-Gr¨uneisen equations of state,is developed to predict the interfacial states and compute the phase interface flux.Several numerical examples,including shock tube problems,cavitation problems,air blast and underwater explosion applications are presented to validate the numerical scheme and the Riemann solver.

A General Moving Mesh Framework in 3D and its Application for Simulating the Mixture of Multi-Phase Flows

In this paper, we present an adaptive moving mesh algorithm for meshesof unstructured polyhedra in three space dimensions. The algorithm automaticallyadjusts the size of the elements with time and position in the physical domain to resolvethe relevant scales in multiscale physical systems while minimizing computationalcosts. The algorithm is a generalization of the moving mesh methods basedon harmonic mappings developed by Li et al. [J. Comput. Phys., 170 (2001), pp. 562-588, and 177 (2002), pp. 365-393]. To make 3D moving mesh simulations possible,the key is to develop an efficient mesh redistribution procedure so that this part willcost as little as possible comparing with the solution evolution part. Since the meshredistribution procedure normally requires to solve large size matrix equations, wewill describe a procedure to decouple the matrix equation to a much simpler blocktridiagonaltype which can be efficiently solved by a particularly designed multi-gridmethod. To demonstrate the performance of the proposed 3D moving mesh strategy,the algorithm is implemented in finite element simulations of fluid-fluid interface interactionsin multiphase flows. To demonstrate the main ideas, we consider the formationof drops by using an energetic variational phase field model which describesthe motion of mixtures of two incompressible fluids. Numerical results on two- andthree-dimensional simulations will be presented.

基于Moldflow的交流接触器外壳注射成型模拟研究

运用UG三维造型技术对交流接触器外壳进行实体建模,并运用Moldflow软件进行注射成型模拟.分析塑料件的最佳浇口位置,选取不同的浇口数目,通过对塑料件注射成型过程的流动模拟,预测塑料熔体注射成型的填充性、填充时间、压力降、熔体流动前沿温度、熔接痕、气穴等,得到合理的注射成型工艺参数.为模具设计与制造提供可靠的设计数据,减少了试模时间,降低了制造成本,提高了模具企业的市场竞争力.

纳米多孔介质中的流体流动

Fluid flow at nanoscale is closely related to many areas in nature and technology(e.g.,unconventional hydrocarbon recovery,carbon dioxide geo-storage,underground hydrocarbon storage,fuel cells,ocean desalination,and biomedicine).At nanoscale,interfacial forces dominate over bulk forces,and nonlinear effects are important,which significantly deviate from conventional theory.During the past decades,a series of experiments,theories,and simulations have been performed to investigate fluid flow at nanoscale,which has advanced our fundamental knowledge of this topic.However,a critical review is still lacking,which has seriously limited the basic understanding of this area.Therefore herein,we systematically review experimental,theoretical,and simulation works on single-and multi-phases fluid flow at nanoscale.We also clearly point out the current research gaps and future outlook.These insights will promote the significant development of nonlinear flow physics at nanoscale and will provide crucial guidance on the relevant areas.

Wellbore drift flow relation suitable for full flow pattern domain and full dip range

Aiming at the simulation of multi-phase flow in the wellbore during the processes of gas kick and well killing of complex-structure wells(e.g.,directional wells,extended reach wells,etc.),a database including 3561 groups of experimental data from 32 different data sources is established.Considering the effects of fluid viscosity,pipe size,interfacial tension,fluid density,pipe inclination and other factors on multi-phase flow parameters,a new gas-liquid two-phase drift flow relation suitable for the full flow pattern and full dip range is established.The distribution coefficient and gas drift velocity models with a pipe inclination range of-90°–90°are established by means of theoretical analysis and data-driven.Compared with three existing models,the proposed models have the highest prediction accuracy and most stable performance.Using a well killing case with the backpressure method in the field,the applicability of the proposed model under the flow conditions with a pipe inclination range of-90°–80°is verified.The errors of the calculated shut in casing pressure,initial back casing pressure and casing pressure when adjusting the displacement are 2.58%,3.43%,5.35%,respectively.The calculated results of the model are in good agreement with the field backpressure data.

液-固流化床最小流态化速度的数值模拟与验证

为使用计算颗粒流体力学(CPFD)的数值模拟法代替实验法,建立单管的液-固两相流化床实验系统;实验测量5种颗粒的最小流化速度;应用CPFD方法对单管液-固流化床模型进行数值模拟,比较5种颗粒的最小流态化速度的实验值与模拟值,并进行误差分析,验证数值模拟方法的正确性。结果表明:5种实验颗粒的最小流态化速度实验值分别为0.0216、0.0367、0.0293、0.0555、0.0845 m/s;2种公式验算值与实验值的最大相对误差小于10%,平均相对误差小于5%,证明实验结果是可靠的;5种模拟颗粒的最小流态化速度模拟修正值分别为0.024、0.044、0.041、0.069、0.062 m/s;颗粒S_(1)、S_(2)、S_(4)、S_(5)的模拟修正值与颗粒E_(1)、E_(2)、E_(4)、E_(5)的实验值之间的最小流态化速度的误差分别为11.1%、19.9%、24.3%、26.6%,均为正向偏差且在工程允许范围内,证明CPFD数值模拟方法是可靠的;最小流态化速度随固体颗粒的密度和粒径的增大而增大。

基于SYCL的多相流LBM模拟跨平台异构并行计算研究

异构并行体系结构是当前高性能计算的重要技术趋势。由于各种异构平台通常支持不同的编程模型,跨平台性能可移植异构并行应用开发非常困难。SYCL是一个基于C++语言的单源跨平台并行编程开放标准。目前针对SYCL的研究主要集中于与其他并行编程模型的性能比较,对SYCL中提供的不同并行内核实现及其性能优化研究得较少。针对这一现状,基于SYCL编程模型对开源多相流数值模拟软件openLBMmflow实现跨平台异构并行模拟,通过对比基础并行版本、细粒度调优的ND-range并行版本以及计算到工作项多对一映射方法,系统总结了SYCL并行应用的性能优化方法。测试结果表明,在Intel Xeon Platinum 9242 CPU以及NVIDIA Tesla V100 GPU上,相比优化后的OpenMP并行实现,在不需要额外调优的情况下,基础并行版本在CPU上获得了2.91的加速比,表明了SYCL的开箱即用性能具备一定优势。以基础并行版本为基准,ND-range并行版本通过改变工作组大小及形状,在CPU与GPU上分别取得了最高1.45以及2.23的加速比。通过优化计算到工作项的多对一映射改变每个工作项处理的格子数量以及形状,与基础并行版本相比,在CPU与GPU上分别取得了最高1.57以及1.34的加速比。结果表明,SYCL并行应用在CPU上更适合采用计算到工作项多对一映射的优化方法,在GPU上更适合采用ND-range并行内核,以提高性能。

An efficient multi-resolution SPH framework for multi-phase fluid-structure interactions

Applying different spatial and temporal resolutions for different sub-systems is an effective approach to increase computational efficiency for particle-based methods. However, it still has many challenges in terms of achieving an optimized computational efficiency and maintaining good numerical robustness and accuracy for the simulation of multi-phase flows involving large density ratio and interacting with rigid or flexible structures. In the present work, based on the multi-resolution smoothed particle hydrodynamics(SPH) method [Zhang et al., JCP 429, 110028(2021)], an efficient multi-resolution SPH framework for multi-phase fluid-structure interactions(FSI) is proposed. First, an efficient multi-phase model, exploiting different density reinitialization strategies instead of applying different formulations to implement mass conservation to the light and heavy phases, respectively,is developed and the same artificial speed of sound for both phases can be used. Then, the transport velocity formulation is rewritten by applying temporal local flow state dependent background pressure to eliminate the unnatural voids, unrealistic phase separation and decrease the numerical dissipation. Finally, the one-sided Riemann-based solid boundary condition is modified to handle the FSI coupling in both single-and multi-resolution scenarios in the triple point. A set of examples involving multi-phase flows with high density ratio, complex interface and multi-phase FSI are studied to demonstrate the efficiency, accuracy and robustness of the present method.

基于事件驱动的集束型晶圆制造设备调度算法

为了有效利用集束型晶圆制造设备,并使其满足动态到达晶圆调度要求,在描述调度问题域及引入时间约束集概念的基础上建立了调度问题的数学模型,根据模型提出了一种基于事件驱动的调度算法,调度目标是使到达晶圆在最短时间内完成加工.对调度算法进行了仿真实验分析.结果表明,该算法有效且实用.

注塑成形模拟技术在模具设计中的应用

在一模多腔的注塑模具设计中,合理地设计分流道和浇口的尺寸,保证塑料熔体以相同的成形压力和温度,在同一时间充满型腔一直是设计的重点和难点。以非自然平衡浇注系统为重点,阐述了浇道和冷却系统的优化算法以及如何利用华塑三维模拟成形分析软件进行流动模拟和工艺优化。

湍流边界层拟序结构的大涡模拟研究

采用动力亚格子模型,利用大涡模拟方法模拟了雷诺数为13000的充分发展槽道湍流流动。从瞬时速度和脉动 速度场、脉动速度相关、均方根脉动涡量分布、以及瞬时涡量场等多个方面,对湍流边界层流动的拟序结构进行了分析, 包括近壁区小尺度湍流结构和瞬态过程,如条纹结构、喷射和扫掠过程、以及近壁旋涡结构等。

Progress in numerical simulation of cavitating water jets

This paper reviews recent progress made toward modeling of cavitation and numerical simulation of cavitating water jets. Properties of existing cavitation models are discussed and a compressible mixture flow method for the numerical simulation of high- speed water jets accompanied by intensive cavitation is introduced. Two-phase fluids media of cavitating flow are treated as a homo- geneous bubbly mixture and the mean flow is computed by solving Reynolds-Averaged Navier-Stokes （RANS） equations for com- pressible fluid. The intensity of cavitation is evaluated by the gas volume fraction, which is governed by the compressibility of bubble-liquid mixture corresponding to the status of mean flow field. Numerical results of cavitating water jet issuing from an orifice nozzle are presented and its applicability to intensively cavitating jets is demonstrated. However, the effect of impact pressure caused by collapsing of bubbles is neglected, and effectively coupling of the present compressible mixture flow method with the dynamics of bubbles remains to be a challenge.

Multi-scale HPC system for multi-scale discrete simulation—Development and application of a supercomputer with 1 Petaflops peak performance in single precision

A supercomputer with 1.0 Petaflops peak performance in single precision, designed and established by Institute of Process Engineering, Chinese Academy of Sciences, is introduced in this brief communication. A designing philosophy utilizing the similarity between hardware, software and the problems to be solved is embodied, based on the multi-scale method and discrete simulation approaches developed at Institute of Process Engineering （IPE） and implemented in a graphic processing unit （GPU）-based hybrid computing mode. The preliminary applications of this machine in areas of multi-phase flow, molecular dynamics and so on are reported, demonstrating the supercomputer as a paradigm of green computation in new architecture.

ELECTROMAGNETIC TOMOGRAPHY (EMT): THEORETICAL ANALYSIS OF THE FORWARD PROBLEM

Inductance-bared electromagnetic tomography (EMT) is a novel industrial process tomographic technique. Exact expressions of the magnetic field distribution in a two-dimensional object space were derived by analytically solving the forward problem for a particular two-component pow. The physical mechanisms within the sensor and the detectability limits of the EMT technique were quantitatively analyzed. Direct mathematical expressions for the field sensitivity and the sensitivity maps were established. To a certain extent, mathematical and theoretical bares are given for quantitative design of the sensor, detectability analysis of the EMT technique and image reconstruction of two-component processes based on the linear back-projection algorithm.

Numerical modeling of sediment transport based on unsteady and steady flows by incompressible smoothed particle hydrodynamics method

The purpose of the present paper is to introduce a simple two-part multi-phase model for the sediment transport problems based on the incompressible smoothed particle hydrodynamics（ISPH） method. The proposed model simulates the movement of sediment particles in two parts. The sediment particles are classified into three categories, including the motionless particles, moving particles behave like a rigid body, and moving particles with a pseudo fluid behavior. The criterion for the classification of sediment particles is the Bingham rheological model. Verification of the present model is performed by simulation of the dam break waves on movable beds with different conditions and the bed scouring under steady flow condition. Comparison of the present model results, the experimental data and available numerical results show that it has good ability to simulate flow pattern and sediment transport.

Crude oil wax:A review on formation,experimentation,prediction,and remediation techniques

Wax deposition during crude oil production,transportation,and processing has been a headache since the early days of oil utilization.It may lead to low mobility ratios,blockage of production tubing/pipelines as well as fouling of surface and processing facilities,among others.These snags cause massive financial constraints increasing projects’turnover.Decades of meticulous research have been dedicated to this problem that is worth a review.Thus,this paper reviews the mechanisms,experimentation,thermodynamic and kinetic modeling,prediction,and remediation techniques of wax deposition.An overall assessment suggests that available models are more accurate for single than multi-phase flows while the kind of remediation and deployment depend on the environment and severity level.In severe cases,both chemical and mechanical are synergistically deployed.Moreover,future prospective research areas that require attention are proposed.Generally,this review could be a valuable tool for novice researchers as well as a foundation for further research on this topic.

PARTICLE METHODS FOR COMPLEX FLOWS IN CHEMICAL ENGINEERING ——THE PSEUDO-PARTICLE APPROACH

The multi-scale structures of complex flows in chemical engineering have been great challenges to the design and scaling of such systems, and multi-scale modeling is the natural way in response. Particle methods (PMs) are ideal constituents and powerful tools of multi-scale models, owing to their physical fidelity and computational simplicity. Especially, pseudo-particle modeling (PPM, Ge & Li, 1996; Ge & Li, 2003) is most suitable for molecular scale flow prediction and exploration of the origin of multi-scale structures; macro-scale PPM (MaPPM, Ge & Li, 2001) and similar models are advantageous for meso-scale simulations of flows with complex and dynamic discontinuity, while the lattice Boltzmann model is more competent for homogeneous media in complex geometries; and meso-scale methods such as dissipative particle dynamics are unique tools for complex fluids of uncertain properties or flows with strong thermal fluctuations. All these methods are favorable for seamless interconnection of models for different scales. However, as PMs are not originally designed as either tools for complexity or constituents of multi-scale models, further improvements are expected. PPM is proposed for microscopic simulation of particle-fluid systems as a combination of molecular dynamics (MD) and direct simulation Monte-Carlo (DSMC). The collision dynamics in PPM is identical to that of hard-sphere MD, so that mass, momentum and energy are conserved to machine accuracy. However, the collision detection procedure, which is most time-consuming and difficult to be parallelized for hard-sphere MD, has been greatly simplified to a procedure identical to that of soft-sphere MD. Actually, the physical model behind such a treatment is essentially different from MD and is more similar to DSMC, but an intrinsic difference is that in DSMC the collisions follow designed statistical rules that are reflection of the real physical processes only in very limited cases such as dilute gas. PPM is ideal for exploring the mechanism of complex flows ab initio. In final analysis, the complexity of flow behavior is shaped by two components on the micro-scale: the relative displacements and interactions of the numerous molecules. Adding to the generality of the characteristics of complex system as described by Li and Kwauk (2003), we notice that complex structures or behaviors are most probably observed when these two components are competitive and hence they must compromise, as in the case of emulsions and the so-called soft-matter that includes most bio-systems. When either displacement or interaction is dominant, as in the case of dilute gas or solid crystals, respectively, complexity is much less spectacular. Most PMs consist explicitly of these two components, which is operator splitting in a numerical sense, but it is physically more meaningful and concise in PPM. The properties of the pseudo-particle fluid are in good conformance to typical simple gas (Ge et al., 2003; Ge et al., 2005). The ability of PPM to describe the dynamic transport process on the micro-scale in heterogeneous particle-fluid systems has been demonstrated in recent simulations (Ge et al., 2005). Especially, the method has been employed to study the temporal evolution of the stability criterion in the energy minimization multi-scale model (Li & Kwauk, 1994), which confirms its monotonously asymptotic decreasing as the model has assumed (Zhang et al., 2005). Massive parallel processing is also practiced for simulating particle-fluid systems in PPM, indicating an optimistic prospect to elevate the computational limitations on their wider applications, and exploring deeper underlying mechanism in complex particle-fluid systems.