【作者】 李艳洁；

【导师】 徐泳；

【作者基本信息】 中国农业大学 ， 固体力学， 2005， 硕士

【摘要】 离散元法是分析散体力学行为的有效数值方法,但许多研究者习惯于只做离散元模拟而忽视用实验证明其合理性。只有少数研究能给出模拟预测的结果并与实验进行比较分析,其参数的给定都通过实验测出。对给定参数交代不清会导致理论上的不确定性从而限制其实际应用。在诸多离散元模型中,基于圆球接触力学的模型无疑更合理,但迄今尚未得到任何实验的验证。为了评估离散元模型的可行性及可应用性,本文通过模拟与实验研究系统地分析了基于接触力学的球颗粒模型(无粘干颗粒模型为主)的堆积问题,比较不同堆积情况下的休止角和堆的外形。堆积模拟采用的型式包括单层拟二维(SL2D)、拟二维(Q2D)和空间堆积。研究主要包括如下方面:(1) 、 单层拟二维颗粒堆积的初步模拟,分析了影响休止角的参数。发现颗粒表面的摩擦系数是影响休止角的主要因素,颗粒与底板间的摩擦系数也影响自由堆积的休止角,因此需限制颗粒在底板边界上的滚动。(2) 、 发展了一种简单适用的实验测量摩擦系数的方法和装置,并测出了磨砂玻璃球等颗粒材料的颗粒间和颗粒-壁面间的摩擦系数。此外还分析了磨砂玻璃板接触面积与摩擦系数的关系。(3) 、 利用测出的磨砂玻璃球摩擦系数结果进行了完全相同条件下磨砂玻璃球拟二维和空间堆积工况的DEM模拟与实验比较,并做了几种其他颗粒材料的堆积实验研究。模拟和实验的对比证实了基于圆球接触力学的模型表明该离散元模型和算法是合理的。本论文的创新点可概括为两点:一是提出了测量球颗粒表面摩擦系数的简易实验方法和堆积实验方法及其结果被证明是可靠的;二是首次用实验事实验证了所论离散元模型和算法是合理的因此具有很高的可应用性。更多还原

【Abstract】 The particulate Discrete Element Method has become a powerful numerical method in analyzing behaviors of granular materials. However, many researchers used to do DEM simulations utilizing different models without experimental validation, only a small number of studies contributed their predicted results in comparison with laboratorial ones with a full set of specified parameters. The ambiguous parameter specification leads to theoretical uncertainty and thus constrains its use in application. Among the various models the model based on classical contact mechanics between two spheres is undoubtedly reasonable, but up to date there has not any experimental evidence to prove.hi this thesis a comprehensive study on the particle piling with sphere elements utilizing the contact-mechanics-based model, mainly for without adhesive dry particles, is presented by means of both numerical and experimental manners in order to give physical evidence for evaluation the feasibility and the applicability of the model. The results in terms of repose angles and visual profiles are compared and analyzed. The particle assembles in simulations are classified as single-layer two-dimensional (SL2D), quasi-two-dimensional (Q2D) and three dimensional for geometrical arrangements, and following approaches are presented:(1) Primary tests were carried out with SL2D simulations, where the parameters affecting the repose angle in piling were analyzed. It shows that, friction between particle surfaces is a main factor affecting the repose angle, and friction between particles and baseboard also affects free piling significantly therefore free rolling along the board needs to be restrained.(2) An easy-to-use method for measuring particle-particle friction and particle-wall friction was developed, with the method the measurement of friction for coarse glass beads and other materials reported with a simple experimental apparatus. Besides, the relationship between the contacting area and the glide friction was analyzed and discussed.(3) A comparative study on piling of coarse glass beads with DEM simulations (both Q2D and 3D) and matching experiments, together with piling experiments of other granular materials were carried out, it shows that the contact-mechanics-based model and the related algorithm are accurate and rational.The main contribution of this thesis can be concluded on two aspects: one is the proposed easy-to-use method for measuring particle friction coefficient and the piling experimental method are quite reliable, though further improvement is needed, the other is the proposed model is firstly proved with reliable evidences so it has a high applicability.更多还原