Effect of liquid layer on the motion of particle during oblique wet collision

Collisions between particles and the wall covered by a liquid layer play an important role in many different industrial processes (e.g., chemical, pharmaceutical, and transportation). Understanding the rebound motion law of the collision between particles and the wall covered by a liquid layer is vital to ensure the high efficiency of processes such as wet granulation and fluid catalytic cracking. In the present study, we investigated the influence of different collision angles on the liquid bridge geometry, particle motions, particle energy, and other collision details based on the oblique collisions between particles and the target plate covered by a liquid layer. Results showed that the collision angle of particles has a great effect on the liquid bridge geometry. Moreover, the liquid bridge caused by different collision angles initially increases the particle deflection angle difference and then decreases, and this influence gradually increases with the increase of the collision angle. In addition, the collision angle greatly affects the particle’s energy.     

Radiation and dynamics of a nanoparticle in equilibrium background radiation upon translational–rotational motion

We have obtained general expressions for the intensity of radiation and tangential force of a small polarizable particle in the process of translational–rotational motion in equilibrium radiation background (thermalized photon gas) of a certain temperature at an arbitrary relative orientation of the linear and angular velocity vectors. It is shown that, in a cold vacuum background, the translational velocity of particle is independent of time and the intensity of its spontaneous emission is determined by the angular velocity and imaginary part of the particle polarizability.     

Experimental investigation of bubble and particle motion behaviors in a gas-solid fluidized bed with side wall liquid spray

Bubble and particle motion behaviors are investigated experimentally in a gas solid fluidized bed with liquid spray on the side wall. The particles used in the experiment are classified as Geldart B particles. The results reveal that when the fluid drag force is less than the liquid bridge force between particles, liquid distribute all over the bed. Bubble size increases as the increase of inter-particle force, then decreases owing to the increase of particle weight with increasing liquid flow rate. When the fluid drag force is greater than the liquid bridge force, liquid mainly distribute in the upper part of the bed. And it is difficult for the wet particles to form agglomerates. Bubble size decreases with increasing liquid flow rate due to the increasing of minimum fluidization velocity. Besides, the acoustic emission (AE) measurements illustrate that the liquid adhesion and evaporation on particles could enhance the particles motion intensity. Consequently, the bubble and particle behaviors change due to the variation in fluidized gas velocity and liquid flow rate should be seriously considered when attempting to successfully design and operate the side wall liquid spray gas solid fluidized bed.     

Magnetic Field Analysis and Dynamic Characteristic Prediction of AC Permanent-Magnet Contactor

This paper reports a thorough investigation into the magnetic field of an ac permanent-magnet contactor and its control principles. Such contactors offer many advantages over conventional electromagnetic contactors in terms of energy saving and reliability. The simulation model, which couples the interaction of the magnet, circuit, and motion, is synthesized using MATLAB software. In order to speed up the simulation process, the model computes the nonlinear relationships of displacement, flux linkage, and current separately, using the finite-element method. We report simulation results for various phase angles of current flowing in the full bridge rectifier at full voltage. We have validated the calculated static force and the dynamic simulation experimentally.      

Influence of interparticle forces on selective wet agglomeration

The influence of interparticle forces between primary particles, which include interaction force between dispersed particles in liquid calculated by DLVO theory and two kinds of forces caused by a liquid bridge of bridging liquid between particles, on selective wet agglomeration was investigated on the basis of the relationships between the results of separation efficiency obtained in author’s previous study and these interparticle forces. The first step of selective wet agglomeration is the collision between bridging liquid droplets and objective particles to be agglomerated. This collision is mainly influenced by the interparticle force calculated by DLVO theory. Incorporation of two objective particles, the second step in the agglomeration process, is influenced by liquid bridge force between objective particles. Growth to pellet-type agglomerates, the third step in the agglomeration process, is thought to be influenced mainly by aggregation force in the agglomerates by entry suction potential. The results of this study showed that selective wet agglomeration under the experimental conditions used in this study is influenced greatly by liquid bridge force and entry suction potential, which play major roles in the second step and third step, respectively, of the selective wet agglomeration process.     

Evolution of mesoscale structure in fluidized beds with non-spherical dry and wet particles

Fluidized beds with non-spherical dry and wet particles are widely used in industrial processes, and the mesoscale structure in the bed has an important influence. In this study, CFD-DEM simulations are performed to evaluate the flow behaviors and mesoscale structure in fluidized beds with non-spherical dry and wet particles. The accuracy of the model is validated by comparison with the results of the particle image velocimetry experiment. The force distributions at bubble boundaries are analyzed to explain the influence mechanism of different shapes of bubbles in non-spherical dry and wet particle systems. The factor analysis indicates the interaction of particle shape and viscous liquid on the translational and rotational kinetic energy of particles. When the bed height is low, as the particle aspect ratio increases, the bubble equivalent diameter gradually increases. In addition, as the liquid viscosity increases, the particle and bubble granular temperature gradually decrease, indicating the reduction of particle velocity fluctuate and the decrease of turbulent kinetic energy of bubble. These findings have guiding significance for the fluidization of non-spherical dry and wet particles and can be used to optimize related industrial processes.     

近断层地震作用下曲线桥碰撞效应及影响试验研究

为明晰近断层地震动作用下曲线梁桥碰撞效应及其影响,以某小半径带坡匝道桥为对象,设计制作1/10缩尺模型及可调式碰撞测试装置,选取同次地震中近断层和远场地震动输入,完成了单向和双向激励条件下试验模型桥的振动台试验。结果表明:与远场地震动相比,近断层地震动作用下曲线梁桥的碰撞效应(碰撞次数和碰撞力)有较为显著的增加,而碰撞效应的增大会增大支座的位移响应,进而增加支座失效或落梁风险,且双向地震动影响更大;碰撞对边墩和中墩沿碰撞力方向的切向位移峰值增加显著,对碰撞力方向上试验模型桥的墩顶有效均方根位移响应均有放大作用,碰撞会增加试验模型桥桥墩的破坏风险。曲线桥抗震设计中应考虑近断层地震动诱发的碰撞效应影响。     

Direct measurement of particle–particle interaction using micro particle interaction analyzer (MPIA)

Direct particle–particle contact force measurement was successfully conducted for realistic parameter determination to support discrete element method (DEM) simulation by using a newly developed force measurement of micro particle interaction analyzer (MPIA). In this system particle-to-particle distance and deformation can be controlled by nanometer accuracy. The system can be used for measuring not only short-distance deformation but also long-distance deformation that was validated by both elastic contact and liquid bridge interaction including rupture distance, respectively. Then, the system was applied to obtain plastic normal deformation characteristics such as coefficients of restitution of the spherical granules at low loading force less than 0.5 mN. Granules were prepared from two-stage pressure swing granulation (PSG) technique in a fluidized bed.     

横向撞击力对铁路桥梁及行车影响的模型实验研究

高速铁路高架桥梁很多,跨越公路的桥墩被汽车撞击所引起的振动会影响列车运行安全。本文利用车—轨—桥耦合动力试验平台,通过模型试验研究了横向撞击力对桥梁及桥上车辆运行安全的影响规律。试验过程中采集了撞击处撞击力时程、桥墩底部动应变、墩顶动位移、墩顶加速度时程,梁1/4,1/2,3/4处的横向动位移和加速度时程,以及车辆的三向车体加速度时程,计算得到桥墩自振频率等振动特性。分析了车桥系统有无撞击力作用时的动力响应,以及撞击力对桥梁及桥上运行车辆的影响规律。结果表明,横向撞击使桥梁的动力响应大幅度增加,并对车辆运行安全有很大的影响。最后根据撞击力时程探讨了瞬态撞击力的等效静力计算方法并验证,为工程设计提供参考。     

Effect of reciprocating motions around working points on levitation force of superconductor-magnet system

In order to simulate vibration around working points in practical operation of superconducting levitation system, magnet in a simple superconductor-magnet system are conducted reciprocating motions around static height in this study. Two YBCO cylindrical samples with different grain orientations are used to investigate the effect of reciprocating motions of magnet on superconducting magnetic force. The c-axis of sample S1 is perpendicular to the top surface while sample S2 is parallel to the top surface. The initial cooling processes for the superconductors include zero-field-cooled (ZFC) and filed-cooled (FC). Compared to the levitation force before reciprocating motions, the ZFC levitation force at static height becomes smaller after reciprocating while the FC force presents opposite phenomenon. It is found that levitation force at static height tends to be stable after several times of reciprocating under ZFC and FC conditions and its time-decay phenomenon is suppressed in some extent, which is meaningful for the practical application of superconducting levitation system. Based on vortex dynamic, some physical discussions are presented to the experimental results.     

Transformation of sliding motion to rolling during spheres collision

In this research, we have investigated the three-dimensional elastic collision of two balls, based on friction in the tangential plane. Our aim is to offer analytical closed form relations for post collision parameters such as linear and angular velocities, collision time and tangential and normal impulse in three dimensions. To simplify the problem, stick regime is not considered. In other words, balls have a low tangential coefficient of restitution. Sliding, sliding then rolling, and rolling at the beginning of contact are three cases that can occur during impact which have been considered in our research. The normal interaction force is described by the Hertz contact force and dimensionless analysis is used for investigating normal interaction force; furthermore, Coulomb friction is considered during sliding. Experimental data for collisions show when sliding exists through the impact, tangential impulses can be taken as frictional impulses using the Coulomb law if the dynamic regime is not stick regime. To identify transformation of sliding motion to rolling or sticking during the impact process, linear and trigonometric functions are considered as an approximation for the normal interaction force. Afterwards, we have obtained the condition for the possibility of this transformation; moreover, we can estimate the duration of sliding and rolling or sticking. We have obtained an analytical solution for maximum force and deformation, collision time, impulses and post-collision linear and angular velocities in three dimensions.     

Vibrational Diver

The paper is concerned with dynamics of light solid in cavity with liquid subjected to rotational vibration in the external force field. New vibrational phenomenon – diving of a light cylinder to the cavity bottom is found. The experimental investigation of a horizontal annulus with a partition has shown that under vibration a light body situated in the upper part of the layer is displaced in a threshold manner some distance away from the boundary. In this case the body executes symmetric tangential oscillations. An increase of the vibration intensity leads to a tangential displacement of the body near the external boundary. This displacement is caused by the tangential component of the vibrational lift force, which appears as soon as the oscillations lose symmetry. In this case the trajectory of the body oscillatory motion has the form of a loop. The tangential lift force makes stable the position of the body on the inclined section of the layer and even in its lower part. A theoretical interpretation has been proposed, which explains stabilization of a quasi-equilibrium state of a light body near the cavity bottom in the framework of vibrational hydromechanics.     

A compartment based population balance model for the prediction of steady and induction granule growth behavior in high shear wet granulation

This paper presents a predictive modeling approach of the high shear wet granulation process, quantifying the difference between the steady and induction granule growth behavior. The spatial heterogeneity in liquid binder distribution and shear rate is simulated using a compartmental population balance model. The granulator is divided into two compartments based on particle motion, which consists of a circulation compartment, and an impeller compartment. In the circulation compartment, a viscous dissipation dependent coalescence kernel is adapted for the aggregation process. In the impeller compartment a shear rate dependent aggregation kernel is implemented. The model was calibrated and validated using the dynamic evolution of granule mean size (d₅₀). The granulation dynamics are studied with respect to change in impeller speed, liquid to solid ratio, wet massing time, initial porosity, and binder viscosity. The transition from induction growth to steady growth regime with changing process conditions is demonstrated using the model. It is observed that the model captures the effect of process parameters and spatial heterogeneity on the dynamic evolution of d₅₀.     

DEM simulations: mixing of dry and wet granular material with different contact angles

In solid mixing the raw materials typically differ at least in one material property, such as particle size, solid density and wetting properties, which in turn influence particle mobility. For example, smaller particles can percolate through the voids of larger ones under the influence of strain and gravity. This may produce fine particle accumulation at the bottom of the mixing vessel which results in undesired, inhomogeneous final products. When wet particles with different wetting properties need to be mixed, heteroagglomeration may occur as another segregation mechanism. We present a new capillary bridge force model to study segregation in moist cohesive mixing processes using DEM. New analytical equations of best fit are derived by solving the Young–Laplace equation and performing a regression analysis, in order to investigate discontinuous mixing processes of dry and moist materials with different particle sizes and different contact angles. Compared to a dry mixing process, mixing efficiency is improved by the addition of a small amount of liquid. While percolating segregation is reduced, heteroagglomerates occur in the wet mixing process.     

基于整船整桥模型的船桥碰撞数值仿真

桥梁在船舶碰撞时受到的动力载荷和响应是复杂的动力非线性问题。近代非线性有限元技术为该问题的求解提供了有效的工具。简述了该技术的基本原理,并基于整船整桥模型对一艘4万吨实船与桥梁的碰撞过程进行了计算。仿真结果显示了船艏结构损坏、碰撞力演变、能量传递和桥墩内部应力变化的详细情景,讨论了船-桥碰撞的力学特征。演示的方法比传统的经验公式和简化解析法提供更为精确的结果。所提供的桥墩应力状态对桥梁的设计与碰撞后的损伤评估有重要参数价值。     

Dynamic simulation of rod-like and plate-like particle dispersed systems

A particle simulation method (PSM) is presented to simulate the dynamics of rod-like and plate-like particle dispersed systems. In this method, the particle is modeled with arrays of spheres connected by three types of springs. The motion of particles in flow is followed by solving the translational and rotational equations of motion for each constituent sphere. The mobility matrix for each particle is calculated to obtain the hydrodynamic force and torque exerted on each sphere. For the hydrodynamic interaction among particles, the near-field lubrication force is considered. The method was applied to the simulation of the transient behavior of particles in a shear flow by dispersing them into a cell with periodic boundaries. In semi-dilute to concentrated systems, the overshoot of viscosity was observed for rigid rod-like particle dispersed systems, but not for flexible ones. This was due to the transient change of the microstructure from the flow-directional orientation to the planar one of particles. The normal stress appeared in the flexible particle dispersed systems because of the deformation of particles. In the rectangular plate-like particle dispersed system, the planar orientation of particles was observed and furthermore the orientation of the major axis of particles in the shear direction appeared.     

Stress wave in monosized bead string with various water contents

Wet granular materials exhibit unique physical and mechanical properties, especially in relation to wave propagation, which is quite different from dry granular materials. In this paper, by introducing the capillary bridge force into the discrete element method, the stress wave in mono-sized bead string with various water content has been studied. First the vibration of two particles with liquid bridge has been analyzed. The presence of the liquid bridge force causes the kinetic response of the particles to exhibit completely different properties than that of the dry particles. The equilibrium position is affected by both the physical properties of the particles and the liquid bridge properties. Then the wave propagation behaviors in a mono-sized bead string have been analyzed. According to whether the liquid bridge volume has an effect on granular motion, the whole process can be divided into two stages. Stage I, particles are physically contacted with each other directly. The influence of liquid bridge force is independent of the bridge volume. Stage II, particles start to oscillate back and forth at their equilibrium positions, the influence of the liquid bridge force becomes related to the bridge volume. The kinetic energy dissipation first decreases and then increases. A U-shaped trend appears throughout the dissipation process. In our work, the mechanical properties of wet granular materials are studied from two levels: particle vibration and wave propagation, which will provide theoretical guidance for the application of granular materials in aqueous environment.     

Homogeneous cooling of hard ellipsoids

We study the homogeneous cooling of hard, smooth ellipsoids in three dimensions using event driven numerical simulation. The elongation of the particle has a strong effect on the cooling behavior. Weakly elongated ellipsoids display two distinct cooling regimes. For small times, the translational and rotational energy decay at a different rates. Once their ratio reaches a time-independent value (different from equipartition), the overall temperature of the system decays like t ^?2, as predicted by Haff??s law. For more elongated ellipsoids the translational and rotational temperatures rapidly reach a constant ratio near unity. The cooling behavior in the homogeneous state can be predicted from Haff??s law and the equilibrium collision rate.     

AUV水下对接系统设计与接驳控制方案研究

为了实现自主水下机器人（autonomous underwater vehicle,AUV）稳定、准确、高效地完成水下对接,提出一种导向罩开合式水下对接装置。针对该装置对接结构的特征所决定的AUV入坞运动的控制要求,考虑到在入坞阶段前向运动起主导作用,分别建立了在静对接、悬浮对接和拖曳动对接三种应用场景下AUV对接系统的动力学仿真模型,重点分析了AUV对接系统在对接时受到的水动力和碰撞力。基于ADAMS （automatic dynamic analysis of mechanical system,机械系统动力学自动分析）和控制仿真软件MATLAB/Simulink联合搭建的水下对接仿真系统,进行在不同接驳控制方案下静对接、悬浮对接和拖曳动对接效果的仿真分析与对比。分析结果表明：在位置-速度闭环控制下,对接能耗、碰撞次数和最大碰撞力均为最小,对接耗时比传统的位置闭环控制减少约50%;在拖曳动对接场景下,在位置-速度闭环控制下对接系统实现了良好的变速跟踪,有利于AUV快速对接。该AUV水下对接系统适用于不同的对接场景,方便无人艇搭载并对AUV进行布放与回收,有利于革新海洋无人系统跨域协同作业模式。     

Numerical simulation of particle motion in dense phase pneumatic conveying

A gas-solids two-dimensional mathematical model was developed for plug flow of cohesionless particles in a horizontal pipeline in dense phase pneumatic conveying. The model was developed based on the discrete element method (DEM). For the gas phase, the Navier-Stokes equations were integrated by the semi-implicit method for pressure-linked equations (SIMPLE) scheme of Patankar employing the staggered grid system. For the particle motion the Newtonian equations of motion of individual particles were integrated, where repulsive and damping forces for particle collision, the gravity force, and the drag force were taken into account. For particle contact, a nonlinear spring and dash pot model for both normal and tangential components was used. In order to get more realistic results, the model uses realistic pneumatic system and material values.