基于装卸料过程能量转换的筒仓动态超压机理研究

It is well known that the dynamic lateral pressure generated by storage material during emptying is greater than the static ones, and which is the main load for silo design as well. However, the mechanism for the overpressure is not clear so far. Currently, many silo design codes in the world, including China, are based on the static pressure and modified in different ways. Therefore, exploring the main mechanism and developing calculating method for the dynamic pressure has been an important issue to be solved in the silo field. Both the silo wall and the storage materials are considered as a whole system, according energy conversion during filling and emptying, the interaction between them is studied, and the mechanism of overpressure is explored. It is proposed that the silo wall release the strain energy absorbed in the filling process during emptying, and the dynamic pressure be in passive state，so it is larger than the static ones. Next, a mechanical model will be established for calculating the dynamic pressure, a simplified calculation method of dynamic pressure will be developed. Last, taking the advantage of DEM to analyze particles, a three dimension numerical simulation model will be set up, which considering about deformation of the silo wall and is same to the experimental condition. With the model, the flow pattern will be simulated, and the law of value for dynamic lateral pressure and the range of the maximum overpressure coefficient will be obtained, and it will be verified by the model test. To provide the effective method to calculate the dynamic lateral pressure for the silo design.

筒仓在卸料过程中散体对仓壁的压力是筒仓设计的主要荷载,此动态压力大于静态压力已被大家所公认,但其增大机理尚不清楚,所以,目前包括中国在内的许多国家筒仓设计规范都是在静态压力的基础上采用不同的修正方法来考虑动态压力的。因此，探索动态压力增大机理和计算方法一直是筒仓领域亟待解决的重要基础研究课题。本项目考虑装卸料过程中仓壁和仓内贮料二者之间能量的相互转换，研究二者之间的相互作用,探索动态压力增大机理。提出在卸料过程中,仓壁释放其在装料过程中吸收的应变能, 根据仓壁的位移情况等,此时散料对仓壁的压力为被动压力,由此解释动态压力增大机理；建立筒仓动态压力计算的力学模型,推导其简化计算方法；利用离散元分析颗粒的优势,建立与试验条件相同的、考虑仓壁变形的三维数值模型,模拟仓内散料流态,得出动态侧压力的大小规律和最大超压系数范围,并通过试验验证其有效性,为筒仓设计确定侧向动压力提供有效方法。

项目利用室内模型试验、数值分析和理论分析进行了如下研究：（1）研究一种带流槽侧壁卸料筒仓，该筒仓具有缓解动态超压、基本实现分层有序自动卸料、节约能源等优点。利用PFC3D 建立与试验条件相同的三维颗粒流数值模型，模拟静、动态侧压力的大小及分布规律，计算出动态超压系数，并与试验结果进行对比分析；（2）采用了数值模拟与实仓试验相结合的方法探讨筒壁双侧卸料方式下高径比（1.1 和2.2）不同的筒仓的静、动态侧压力大小，探究最大动态压力的分布位置，对比两种筒仓在双侧壁卸料方式下的超压系数；（3）采用室内模型试验法和离散单元法，通过改变筒仓高径比来研究贮料在静态储粮状态和卸料过程中的力学行为，从宏观流态和细观颗粒层次研究贮料颗粒物质的力学行为及二者的本质联系；（4）基于室内粮食筒仓卸料模型试验，利用高速摄像仪拍摄筒仓中心卸料的全过程，运用图像处理技术分析贮料的流动形式，并测量卸料过程中产生的动态侧压力。在此试验的基础上，利用颗粒流程序PFC3D（particle flow code in 3 dimensions）进行数值模拟，追踪特定颗粒的运动情况。通过比较试验与数值模拟结果，从流态方面探索深仓中心卸料时超压现象产生的机理；（5）分析筒仓装卸料过程中仓壁和仓内贮料两者之间能量的相互转换，深入研究两者是如何进行能量的转化与转移并且探究仓壁动态压力的增大机理，筒仓卸料的进程中，仓壁的应变得以恢复也即是释放了储存的应变能，筒仓内部的平衡被打破，仓壁受到贮料的压力为被动压力，以此来解释动态压力增大机理，在此基础上运用能量原理推导公式并且进行理论分析。