【作者】 刘静；

【导师】 李海旺；

【作者基本信息】 太原理工大学 ， 结构工程， 2009， 硕士

【摘要】 筒仓是储存散粒状物料的筒状或柱状构筑物,广泛运用于粮食、煤炭、矿产、建材等行业。筒仓属于特种结构,其仓壁受静态和动态荷载作用,特别是动态压力随仓壁形状、贮料颗粒大小、输送速度以及上层压力等因素而改变,所以,正确确定动态压力的大小和分布成为筒仓设计的关键。目前国内外有关筒仓规范中,关于动态压力的确定均以静态压力的Janssen公式为基础,采用修正系数的方法来估算动态压力。显然,这种方法缺少科学性和真实性,故正确确定筒仓仓壁动态压力具有广泛的工程意义。本文以山西省一裤型漏斗型钢贮煤筒仓为研究对象,利用颗粒流程序PFC2D对该煤仓在装卸料过程中散料对仓壁的静、动态压力进行模拟研究,重点研究仓壁动态压力的分布及变化规律,通过研究得到超压系数的大小及最大动态压力出现的位置和分布情况,并与国家规范(GB50077-2003)和ISO提供的计算方法进行比较分析,其结果表明,用PFC2D确定的仓壁动态压力更科学更符合实际。具体开展以下几个方面的工作:1.贮煤筒仓仓壁静态压力的研究:首先,建立一缩尺模型,通过增大模型仓内颗粒重力密度使模型仓和原型仓具有相同的重力场,从而通过模型仓得出原型仓仓壁压力的分布情况。其次,为了能仿真模拟煤仓实际装料过程,本文采用分层法编制颗粒流程序逐层生成筒仓内散料颗粒。数值模拟结果表明:①用缩尺模型筒仓是可以反映原型筒仓的实际受力情况的,说明采用这种研究方法具有一定的科学性;②筒仓装料时,该煤仓上部直壁压力根据ISO计算,下部裤型漏斗壁压力按静模拟取值。2.贮煤筒仓仓壁动态压力的研究:按照生产工艺的要求,模拟时,使该煤仓两个漏斗交替卸料相同的时间,直至仓内贮料全部卸完。研究结果表明:①用离散元模拟筒仓卸料过程,能获得模型实验和现场实验所不能取得的信息,如颗粒流动的力场、速度场,还能通过设置不同层次的颗粒不同的颜色,以观测卸料时颗粒的流型变化;②筒仓卸料时,该煤仓上部直壁动态侧压力按国家现行规范计算而侧壁摩擦力根据动态模拟取值,其超压系数分别在1.093～1.870和1.088～1.514之间;下部裤型漏斗的法向力和切向力均取动模拟值,其超压系数分别为1.000～1.870和1.000～1.746;③在计算筒仓压力时,应考虑卸料过程的特点,特别是在上部直壁仓与漏斗交接处以及筒仓几何形状突变部位,其超压现象更加突出,故筒仓设计时要对压力取值留有充分余地。3.从杨森曾采用的平衡条件和常系数假定出发,本文用分段法推导裤型漏斗直壁和曲壁的贮料压力计算公式。通过PFC2D模拟分析表明:漏斗内贮料的竖向压力及漏斗直壁和漏斗曲壁的法向压力均呈非线性递减变化趋势,在截面突变处有严重的压力集中现象。更多还原

【Abstract】 A silo is a cylindrical structure for storing granular materials, such as grains, coals, cement , etc . The silo is a kind of special structure, and static load and dynamic load act on the wall of silo. Dynamic pressure on the wall alters as the change of the shape of silo, the magnitude of granular, the speed of transportation and the pressure from upper load. So the key factor of silo structural design is to determine and calculate correctly the pressure developed in silos. At present, many national standards including Chinese introduce a modified coefficient into Janssen formula to estimate the dynamic pressure. The calculating method apparently lacks science and authenticity, so it is very important to confirm the dynamic pressure on the wall of silo for the practical project.This paper presents the research on the charging and discharging pressure distribution of granular coal on the wall of a special silo with trouser- shape funnel built in Shanxi province by the particle flow code PFC2D. Dynamic pressure distribution and variation are the primary research part. The value of overpressure coefficient, the position and distribution of maximal dynamic pressure can be obtained from modeling research. The modeling result is compared with those of computation methods offered by national code (GB50077-2003) and ISO. The results indicate that it is more scientific and authentic to calculate the pressure on the wall of silo with PFC2D. The contents of the thesis are following:1. Research on the static pressure of coal silo: First, a reduced scale model silo is created. In order to make the model silo and the full size silo have the same grave field, the grave density of granular coal in the model silo is increased. So the pressure distribution on the wall of full size silo is gained by testing pressure on the wall of model silo. Second, layered method is adopted to work out particle flow code. The granular coal in the model silo is created layer by layer so as to simulate the actual charging process of coal silo. The numerical simulation results acquired could be adapted to instruct the design of the silo. A method that the actual pressure on the wall of full size silo can be obtained by testing reduced scale model silo is scientific to research the pressure of silo. The results show that when charging the static pressure on the upper silo’s straight coal silo wall could be computed by the ISO method, but the static pressure upon the funnel wall should be presented by modeling with PFC2D.2. Research on the dynamic pressure of coal silo: According to the requirement of product technique, when simulating the two funnels of coal silo discharge the same time in turn until the granule in silo flow out completely. The results indicate that the message which cannot be obtained from model and spot test is gained by simulating the discharging process of silo with discrete element method , and that when discharging the flowing manner of granule in silo can be observed by setting different layer granular with different color . It is found that when discharging the dynamic pressure on the upper silo’s straight coal silo wall could be computed by national code, but the dynamic pressure upon the funnel wall should be presented by modeling with PFC2D, and the overpressure coefficients of them respectively ranges 1.093～1.870 and 1.088～1.514; and that the normal force and tangential force of the trouser-shape funnel would accept dynamic modeling values , and the overpressure coefficients of them ranges 1.000～1.870 and 1.000～1.746 respectively. It is necessary to consider the discharging characteristic when calculating pressure on the wall of silo. Because the overpressure phenomenon is extraordinary prominence on the junction of upper silo’s straight coal silo and funnel wall and on the geometric mutation wall , so it is very important to keep enough the value of pressure when designing silo .3. This paper derives the pressure formula of granular for trouser-shape funnel from equilibrium condition and assumption with constant coefficient ever adopted by Janssen. It is founded that the variable trend of vertical pressure for granular in funnel and normal pressure of the wall of straight funnel and hyperbolic funnel are all nonlinear degression, and the phenomenon of pressure concentration is more obvious at the geometric mutation section simulated with PFC2D.更多还原