颗粒物质斜槽流动和双仓振动的动态特性研究

发布时间：2018-07-24 19:14

【摘要】：颗粒物质是大量的宏观粒径大于微米的固体颗粒的聚集,是与连续态物质相区别的另一大类物质形态,往往表现出体系内部异质不均结构、整体对力非线性响应等特点,并发生无序到无序、unjam到jammed等结构变化,是凝聚态物理前沿研究领域和新增长点。颗粒体系为远离平衡态的耗散体系,其造成系统能量损失的主要原因是：颗粒之间的相互作用以非弹碰撞和摩擦为主。因此维持体系的运动就要依靠外部的能量输入,常见的驱动形式有重力、撞击、激振、剪切等。在这些外加的作用下,系统会呈现出类似于固体、液体及气体的特性,而颗粒物质自身离散的特性又使它们跟连续介质形态有很大的差异。以至于有的学者建议将颗粒物质看做除了传统的固体、液体、气体以外的“第四种物质聚集形态”。颗粒物质的系统尺度可以从微米以上跨越六个量级,因此在自然界、工程实践和人类生产生活中广泛存在。颗粒物质的研究涉及多个领域：工农业、建筑业、制造业、医药食品业等。许多自然现象(山体滑坡、浮冰流、雪崩等)和工业生产过程(散态物质的输运、加工等)也与颗粒物质的运动规律密切相关。因此,对颗粒物质的运动规律的探究具有重要的社会效益和经济价值。本文主要针对颗粒物质类液和类气特性设计了颗粒流动和振动试验,并通过试验观察、理论建模和计算模拟相结合的手段对其特性进行分析。希望对理解颗粒物质在非静态条件下的物理特性提供一些有益的借鉴,对工程上颗粒物质的管道输送、多道汇聚、流量优化等问题提供一些理论性的指导。本文的主要研究内容有：考虑到实际的颗粒运输管道往往是受多个瓶颈的制约(比如出口收缩、管道拐弯等),我们设计了双瓶颈斜槽流实验,用来研究多瓶颈对系统相变和流量的影响。实验中,系统发生了稀疏流一密集流的相转变。在相变过程中,出现了一个稀疏态和密集态都可能存在的双稳区域。我们对双稳现象出现的原因进行了研究。我们发现是入口初始流量波动和上下瓶颈共同作用的结果。我们引入了复杂网络方法对初始储料仓内堆积颗粒的力网络进行分析,发现疏松堆积和密集堆积对系统初始流量的影响。再通过对上下瓶颈进行离散元模拟,成功得到双稳发生的范围,模拟结果跟实验结果一致。最后,我们研究了槽道倾角对系统的影响,并给出优化系统流量的建议。颗粒流与车辆交通流有许多相似的物理特性,我们做了一个双道汇聚的颗粒斜槽实验,来类比车辆交通中匝道进入主道的情形。通过主(侧)道比侧(主)道宽两组不同的对比实验,发现两道的入口流量不同可以使系统发生从稀疏到密集的相转变,并且存在四个相态。这点跟车辆交通流中的匝道系统有相似之处。对双道流量变化进行分析,发现两组不同情况下,出口流量会出现一次或两次流量突降,这种现象在交通流中未被发现,可能是颗粒流的独特现象。通过实验,我们还发现汇聚区域存在一个发生稀疏流到密集流转变的临界体积分数(?)＝0.63±0.03。两道汇聚的研究希望对多道(N3)颗粒流汇聚问题的研究提供一定的借鉴。颗粒物质受激振动会表现出类气特性,系统内颗粒之间碰撞频繁,非线性、耗散性尤为突出,其中一种具体表现是颗粒聚簇(clustering)和颗粒时钟(GranularClock)现象。我们先对之前学者关于颗粒气体双仓振动体系的研究进行概述,接着介绍我们新发现的颗粒双仓振动中的聚簇一颗粒时钟(GC-Clustering)共存现象。当我们把双仓容器宽度增大以后,系统出现了水平偏析现象,并且此偏析存在两种不同模式,导致系统出现颗粒时钟态或者聚簇态。这两种状态是在同一个振动强度下随机发生的,从实验观察结果来看呈现一种“跳跳停停”的现象。我们对此问题进行了细致的研究,通过改变颗粒数目比、半径比、盒子宽度等试验条件找出了聚簇一颗粒时钟现象的存在区域,并引入了一个单位时间转换概率P修正了一般的颗粒双仓系统的Flux Model,定性的重现了该实验现象。此部分工作对颗粒气体非线性特性和颗粒系统的随机性进行了有益的探索。本文研究了颗粒物质的流动和振动两个主要方面的动态特性问题,较侧重于颗粒物质的独特动态行为和其非线性物理特性。通过本文的研究,进一步加深了对颗粒物质系统复杂性机理的认识,并对自然界和实际工程中涉及的颗粒物质的加工和输运问题提供有益的借鉴。
[Abstract]:Particulate matter is the aggregation of a large number of solid particles with a macro particle size larger than the micron. It is another large type of substance which is different from the continuous state matter. It often shows the heterogeneity of the structure in the system, the overall response to the force nonlinear response, and the disorder to disorder, unjam to jammed, and so on. It is the research of the condensed matter physics. The field and the new growth point. The particle system is a dissipative system which is far from the equilibrium state. The main cause of the system energy loss is that the interaction between particles is dominated by non elastic collisions and friction. Therefore, the movement of the maintenance system depends on the external energy input, and the common driving forms are gravity, impact, excitation, shear, etc. In addition, the system presents the characteristics similar to the solid, liquid and gas, and the discrete characteristics of the particles make them very different from the continuous medium. Some scholars suggest that the particles be regarded as the "fourth substance aggregation forms" other than the traditional solid, liquid and gas.
The systematic scale of particulate matter can span six orders of magnitude above the micron, so it exists widely in nature, engineering practice and human life. The research of particulate matter involves many fields: industry, agriculture, construction, manufacturing, medicine and food. Many natural phenomena (landslides, floating ice flows, avalanches, etc.) and industrial processes The movement of particulate matter is closely related to the movement of particulate matter. Therefore, it is of great social and economic value to explore the movement of particulate matter.
In this paper, the particle flow and vibration test are designed for the liquid and gas like properties of particles. The characteristics are analyzed by means of experimental observation, theoretical modeling and calculation simulation. It is hoped to provide some useful reference for understanding the physical properties of granular materials under non static conditions, and to the particle material in engineering. It provides some theoretical guidance for pipeline transportation, multi-channel convergence and flow optimization.
Considering that the actual particle transport pipeline is often restricted by multiple bottlenecks (such as exit contraction, pipe turning, etc.), we designed a double bottleneck flow experiment to study the effect of multiple bottlenecks on the phase change and flow of the system. In the experiment, a phase transition of a dense flow of sparse flow is taken place in the experiment. In the process of phase transition, a dilute occurs. We have studied the causes of the bistable phenomenon. We find that the initial flow fluctuation and the upper and lower bottlenecks are the result of the joint effect. We introduce the complex network method to analyze the force network of the accumulated particles in the initial storage bin, and find loose accumulation and dense heap. The effect of the product on the initial flow of the system. Then through the discrete element simulation of the upper and lower bottlenecks, the range of the bistability is successfully obtained. The simulation results are in agreement with the experimental results. Finally, we study the influence of the slot angle on the system, and give a suggestion to optimize the flow of the system.
There are many similar physical characteristics between the particle flow and the vehicle traffic flow. We have done a double channel converged granular slots experiment to compare the ramp into the main road in vehicle traffic. Through the two different comparison experiments of the main (side) side (main) path width, it is found that the difference in the inlet flow of the two channels can cause the system to occur from sparse to dense. Phase transition, and there are four phase states. This is similar to the ramp system in the traffic flow. Analysis of the two channel flow changes shows that the flow rate will occur once or two times under the two different conditions. This phenomenon is not found in the traffic flow and may be a unique phenomenon of the particle flow. Through experiments, we It is also found that there is a critical volume fraction (?) (?) = 0.63 + 0.03. two channel convergence of a sparse flow to dense flow transition in the aggregation region, and hopes to provide some reference for the study of the problem of multichannel (N3) particle flow convergence.
The stimulated vibration of particulate matter will show gas like characteristics. The collisions between particles in the system are frequent, nonlinear and dissipative, and one of them is particle cluster (clustering) and particle clock (GranularClock). First, we summarize the previous scholars' research on the dual chamber vibration system of particle gas, and then introduce it. We found the coexistence of cluster and particle clock (GC-Clustering) in the newly discovered particle double chamber vibration. When we increase the width of the double chamber container, the system appears horizontal segregation phenomenon, and there are two different modes in the system, which leads to the emergence of the particle clock state or the cluster state. The two states are in the same vibration intensity. At random, we present a "jump stop" phenomenon from the experimental observation results. We have studied the problem in detail. By changing the particle number ratio, the radius ratio, the box width and other experimental conditions, we found the existence region of the cluster one particle clock phenomenon, and introduced a unit time conversion probability P correction. The Flux Model of the general particle double chamber system reproduces the experimental phenomenon qualitatively. This part of the work makes a useful exploration of the nonlinear characteristics of the particle gas and the randomness of the particle system.
In this paper, the dynamic characteristics of the two main aspects of the flow and vibration of particulate matter are studied, which are more focused on the unique dynamic behavior and the nonlinear physical properties of the particles. Through this study, the understanding of the complex mechanism of the granular material system is further deepened, and the particulate matter involved in the natural and practical engineering is also discussed. It provides a useful reference for the processing and transportation problems.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TB53

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