非球形催化剂颗粒撞击构件的数值计算分析

研究催化裂化过程中壁面遭受磨损的问题。采用有限元方法建立单颗和多颗催化剂颗粒撞击构件壁面的有限元模型,运用ABAQUS有限元分析软件作为前处理器,并将颗粒形态设定为非球形(椭球形)。在有限元模型中选取相应的材料本构模型,模拟不同参数(入射速度、撞击角度和撞击次数)的催化剂颗粒撞击构件壁面的过程,建立构件壁面的质量损失与催化剂颗粒参数间的关系,并对模拟结果进行分析。撞击过程中的不同参数对构件壁面的磨损量会产生较大的影响,构件壁面的磨损量随着入射速度、撞击角度和撞击次数的增大而增大,且催化剂颗粒以45°的形态撞击所造成的构件壁面磨损量最小。构件壁面在使用过程中很容易被冲击而造成磨损,且颗粒在不同情况下造成的磨损状况不同。     

颗粒流撞击壁面的离散元模拟

为了解决催化裂化装置中催化剂颗粒的磨损、撞碎等问题,首要解决催化剂颗粒的运动特性问题,为此将离散元数值模拟的技术应用到催化剂颗粒撞击壁面的模型中,简化了催化剂颗粒撞击壁面的模型为颗粒流撞击壁面模型,开展了颗粒流撞击壁面的离散元分析;建立了颗粒流中随机标记颗粒的速度与时间、位移与时间的关系,及整个颗粒流的动能与时间的关系;追踪了标记颗粒的运动轨迹,解释了颗粒流撞击壁面产生不规则分布的原因;提出了分段区间随机取样求得壁面平均应力的方法,在不同入射速度下对壁面产生的平均应力大小进行了对比分析。研究结果表明,入射颗粒流的速度对壁面应力的影响呈不稳定性,不同的入射速度影响壁面的平均应力大小,且在一定范围内入射速度越大,壁面的应力越大。     

基于有限元法催化剂颗粒撞击壁面的数值模拟

为解决催化裂化装置中的许多构件因为催化剂颗粒长期不断冲击而导致失效等的问题,将有限元法应用到其模拟仿真中,分析了单颗催化剂颗粒参数(角度、速度、材料)对不同壁面材料的撞击而造成壁面磨损的影响,建立了催化剂颗粒撞击壁面的数值分析模型,研究了催化剂颗粒以不同的速度、撞击角度,以及不同的催化剂颗粒的材料撞击不同材料的壁面对壁面造成的影响,并分析了催化剂颗粒变形对壁面磨损的影响,根据计算的结果,对催化剂颗粒参数进行了优化控制,提出了减少催化剂颗粒变形和构件磨损的技术措施.研究结果表明,该方法能够使催化裂化装置长期安全稳定地运行.     

软性磨粒流磨粒入射壁面过程及其加工特性研究

针对利用两相流模型无法计算高浓度固—液两相流固相颗粒撞击壁面时颗粒速度的问题,提出一种边界层内颗粒运动轨迹计算模型,基于Mixture两相流模型和Realizable k-ε湍流模型仿真计算结果,通过分析提取颗粒入射前速度、计算边界层厚度、建立边界层内速度场和颗粒运动分析可以得到颗粒撞击壁面时的速度和入射角度。分析加工表面动压力分布和磨粒体积分数分布,结合两种结构约束流道验证仿真结果与加工效果的对应关系。通过对试验结果的分析,为约束模块的设计提供依据。研究结果表明:磨粒入射速度、磨粒体积分数和加工表面所受动压力大小直接影响工件加工效果,并与材料去除量成正相关关系;在本次试验中选择的工艺参数导致加工材料去除量小,适合初始粗糙度低的工件表面加工,对于此次试验的初始粗糙度应在0.2μm以下;约束模块的设计除了要考虑磨粒流流场特性之外,还要对加工表面的原始加工痕迹作详细了解,为约束模块的设计及加工工艺参数提供参考。     

混凝土泵送中管壁磨损过程的离散元模拟研究

建立了混凝土离散元模型,并通过L箱流动实验校核了该模型,得到了计算参数。采用该模型及得到的参数对混凝土泵送过程进行数值模拟,其中,以颗粒对管壁的冲击力和平均力表征壁面磨损程度,对泵送过程中管壁磨损过程进行研究。分析了泵送速度、弯管角度等因素对管壁磨损分布的影响,预测了最易磨损位置。结果表明：弯管管壁磨损随着泵送速度的增大而增大,随着弯管角度的增大而增大,模拟结果与实际泵送过程中观测到的最易磨损位置吻合较好。     

耦合DEM-CFD法双入口磨粒流动力学模拟及加工试验

针对单入口磨粒流加工装置光整不均匀问题,提出了双入口磨粒流加工装置,为了解决传统CFD软件不能跟踪颗粒撞击壁面问题,结合DEM和CFD方法,通过耦合PFC和CCFD软件,利用DMP颗粒运动模型和标准k-ε湍流模型来模拟磨粒在流场中的运动.仿真中,通过PFC记录磨粒撞击壁面的速度和次数,通过CCFD记录流场运动状态,并应用Abaqus中Johnson-Cook模型分析了撞击速度和撞击次数对靶材质量损失的影响.数值模拟结果表明,双入口装置内两股流体撞击使得磨粒运动更为无序,磨粒撞击壁面次数大大增加,同时撞击壁面速度大于40 m/s的次数达到1 382次,远大于单入口的563次,使得加工面的材料去除速度更快.加工试验结果表明,加工30 h后,双入口装置加工的工件表面粗糙度Ra=0.35 μm,单入口装置工件表面粗糙度Ra=0.65 μm,加工效率明显提高.     

喷丸强化过程的有限元和离散元模拟

利用有限元法建立喷丸强化过程中单/多颗弹丸连续撞击靶材的数值分析模型,对于单弹丸撞击情况,探讨了弹丸参数(速度和角度)对靶材中残余应力场的影响,对于双弹丸连续撞击情况,探讨了第二颗弹丸速度对靶材中残余应力场的影响;建立了模拟喷丸强化过程的三维离散元模型并进行了数值试验研究,分析了喷丸强化过程的工艺参数(质量流速、初始速度、喷嘴攻角等)对颗粒流中弹丸间相互碰撞的影响;结合有限元和离散元计算结果,提出对喷丸强化工艺参数进行优化控制,提高喷丸强化的加工工艺水平,以实现更好的强化效果.     

航空钛合金Ti6Al4V的三维铣削加工有限元仿真

基于有限元技术的三维铣削仿真对于改善工艺参数、实现高效高质加工具有重要意义。以Ti6Al4V为工件材料,建立了接近实际铣削加工的有限元模型,成功模拟了切屑的形成过程,模拟的切屑形态与真实切屑形态相似;根据应力与温度分布云图对工件的应力场和温度场进行了分析;应用所建模型模拟了不同铣削速度时的3个方向切削力,分析了模拟结果,并进行了与模拟同样条件的测铣削力实验。通过对比切削力的模拟值与实验值,验证了铣削模型的正确性,此模型可用于优化铣削参数。     

单颗磨粒的冲击磨损理论及实验研究

针对螺旋式约束磨粒流抛光的机理研究,基于ANSYS建立了单颗磨粒的冲击模型,选用铝合金作为工件的材料,并建立相应的Johnson-Cook弹塑性模型,分析单颗磨粒对材料的冲击磨损情况,并对颗粒的冲击磨损特性进行了实验研究。结果表明:对于弹塑性金属材料,撞击初期主要是发生弹塑性变形,形成压坑与变形唇,经多次碰撞挤压后,最终以小块金属剥落而产生磨损。在一定冲击角度(颗粒冲击轨迹与水平面的夹角)下工件表面材料磨损量较高,随着磨粒碰撞速度和碰撞次数的增加材料磨损量增大。螺旋式约束磨粒流通过改变颗粒的冲击轨迹能有效提高工件表面的加工效率与质量。     

碳纤维复合材料麻花钻钻孔轴向力的数值模拟

针对碳纤维增强树脂基复合材料制孔质量差的问题,建立了麻花钻钻削该复合材料的有限元模型,应用ABAQUS软件对不同工艺参数下钻孔过程中的轴向力进行了数值模拟,并通过相同工艺下的钻削试验进行验证。结果表明:轴向力随着主轴转速的增大而减小,随着进给速度的增大而增大,且轴向力受进给量的影响较大;数值模拟结果与试验结果吻合度较好,证明了有限元模型的合理性。     

螺旋槽小孔节流动静压空气轴承颗粒冲蚀研究

为研究空气轴承在运转过程中细小颗粒对壁面冲蚀情况，借助三维建模工具建立动静压空气轴承模型，从连续方程、可压缩流体润滑方程、气体状态方程出发，推导出等温条件下稳态气体润滑Reynolds方程；结合离散相模型(DPM)颗粒平衡方程，分析颗粒运动轨迹和颗粒对壁面的最大冲蚀速率。借助Fluent仿真软件分析气源压力、主轴转速、粒径参数对气体轴承壁面冲蚀的影响。结果表明：随着粒径尺寸的增加，相同运行工况下，壁面冲蚀磨损速率呈现先增加后降低趋势；随着主轴转速的增加，壁面冲蚀磨损的面积在增加，但最大壁面冲蚀磨损速率在下降，同时壁面磨损面积向主轴正向旋转的方向延伸。     

Particle velocity and size effects in laboratory slurry erosion measurements OR… do you know what your particles are doing?

The major factors which determine the erodent particle impact wear process are described. Thus, particle impact velocity, impact angle and impact frequency are dictated by the slurry flow regime about the specimen. The influence of these factors on erosion rates (or on erosion–corrosion rates) can only be understood in terms of a quantitative model for slurry flow and particle impact and an assumption on the nature of the rate-controlling factor governing material loss. For erosion in the absence of corrosion, this latter has been taken to be the rate of dissipation of particle impact energy on the specimen surface. It is emphasised that material loss must be measured by changes in surface profile rather than mass loss, and that the best specimen form for this analysis is a cylinder. The effect of change of particle size on erosion rates is discussed. It is suggested that the application of these experimental and analytical techniques should provide a tool for the quantitative analysis of wastage in conditions of erosion–corrosion.     

Fluid dynamic mechanisms of particle flow causing ductile and brittle erosion

Traditional prediction of erosion focuses on the use of velocity and impact angle of particles as independent variables in analytically derived models. This approach is most suitable for numerical predictions of erosion in disperse flow fields where particle trajectories may easily be followed prior to impact. For dense particle flows, the prediction of individual particle or particle cluster movement is nearly never attempted by following trajectories. Instead, two-fluid Eulerian–Eulerian approaches are used in which a continuous particle fluid phase is considered.The present study shows that the impact velocity and angle of attack of particles at the eroding surface are difficult to obtain for dense flows, thus being difficult to consider as parameters for predicting erosion. Instead, it is proposed that the normal and the shearing components of the viscous dissipation of the particulate phase are more suitable as independent flow variables governing the erosion process. These variables describe deformation and cutting wear processes, respectively, and are readily derived from the flow field.Eulerian erosion models are proposed, based on these independent variables. It is possible to implement previous results and theories concerning the material–mechanical interaction between the abrasive and an eroding surface to achieve model improvements. In this work, only a simple model taking into account a threshold elastic strain limit is proposed, to more correctly model the deformation wear.The particle-flow boundary condition — a partial-slip condition — significantly influences the erosion process, particularly the cutting erosion. The boundary condition depends on parameters such as the local particle phase flow, the mean diameter and the sharpness of the abrasive as well as the surface roughness.A simple 2D test application — a jet stream of particles impinging a tilted plate — is presented, and the qualitative angular behaviour of ductile and brittle erosion is reproduced at the target position. A scheme is presented for determination of material constants and suitable boundary conditions to be used in the proposed erosion models.     

Analysis of boiler-tube erosion by the technique of acoustic emission Part I. Mechanical erosion

This paper investigates the mechanical erosion of the metal tubes in bagasse-fired boilers with the aid of the acoustic emission technique. By studying the material removal under various collision conditions, the paper analyzes the dependence of the erosion wear upon the impact angle, velocity, size and concentration of the particles. It was found that the material removal mechanisms were mainly dependent on the particle collision angle and fell into four regimes characterized by rubbing and scratching, cutting and cracking, forging and extrusion as well as sputtering and adhesion. The highest wear rate took place with the cutting and cracking mechanism when the particle collision angle was in the range of 20–30°. The variation of the acoustic emission energy confirmed the conclusions. Finally, three simple formulae were developed to show the dependence of the erosion wear upon the main erosion parameters.     

Wear Performance Forecasting of Chopped Fiber–Reinforced Polymer Composites: A New Approach Using Dimensional Analysis

Solid particle erosion of polymer matrix composites is a complex process in which wear occurs from the target surface by impingement of rigid sand particles in an air medium. The rate of material removal (RMR), also referred to as the erosion rate, mainly depends on target material parameters and the erosion conditions such as impact angle, impact velocity, and erodent size. A new semi-empirical model for prediction of the erosion rate of polymer matrix composites has been developed using a dimensional analysis technique based on Buckingham's π theorem. The predictive model analytically rests upon parameters related to chopped glass fiber composites, erodent (target material properties), and operating variables that mainly affect the erosion process of chopped glass fiber–vinyl ester resin composites. The forecasting ability of the predictive model has been assessed and verified by experimental investigations for chopped glass fiber–reinforced vinyl ester resin (VGF) composites. Validation of the theoretical erosion rates obtained from the predictive model showed that they were in good agreement with the experimentally determined erosion rates, where the average error range was estimated to be ～10 to ～20%.     

A coupled finite element and meshfree analysis of erosive wear

Erosive wear is a kind of material degradation, which is largely involved in many industries, and caused a series of serious problems and economic loss. Many theoretical models and numerical models have been established to study the erosion phenomena. In this study, a coupled finite element and meshfree model was developed for the simulation and prediction of erosive wear. By utilizing the meshfree technique, the error due to mesh distortion and tangling at impacted area in the finite element analysis could be effectively avoided. The fundamental mechanisms of erosion by solid particle impact were investigated as well. Comparison against the results of analytical erosion models and finite element model are made. It is shown that the predicted results are in agreement with reported results. The present study could be very useful and efficient in studying erosive wear.     

RV减速器摆线轮磨损量的数值计算与分析

基于Archard磨损模型和Hertz接触理论为理论基础,将摆线轮齿廓啮合区域离散化,建立了摆线轮磨损的计算模型;根据该计算模型分析了各啮合点处滑动系数、磨损率、磨损量与啮合相位角之间的关系,并进行曲线拟合。结果表明,建立的数值计算方法可以实现对不同修形方法、不同尺寸、不同工况条件下摆线针轮齿廓磨损量的定量计算。