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中文核心期刊

基于扩展多面体的离散单元法及其作用于圆桩的冰载荷计算

DILATED POLYHEDRA BASED DISCRETE ELEMENT METHOD AND ITS APPLICATION OF ICE LOAD ON CYLINDRICAL PILE

  • 摘要: 对于具有复杂几何形态的多面体单元,线性接触模型不能准确地计算不同接触模式下的作用力,且接触变形和作用力方向也不易判断.基于闵可夫斯基和(Minkowski sum)方法的扩展多面体单元能够准确描述非规则颗粒单元的几何形态,并可精确计算单元间的接触碰撞作用.该方法具有接触判断简单、计算效率高的特点.它将基本多面体和扩展球体相叠加以形成具有光滑棱边和角点的扩展多面体单元.考虑扩展多面体单元相互作用过程中角点、棱边和平面之间的不同接触模式,发展了相应的非线性黏弹性接触模型. 该接触模型将不同接触模型下的法向刚度统一表述为单元接触中接触点处等效曲率半径的函数;黏滞力和切向弹性力接触模型则借鉴球体单元非线性接触模型的处理方法. 为检验扩展多面体的可靠性,对碎冰区冰块对圆桩结构的冰载荷进行了离散元分析. 采用沃洛诺伊(Voronoi)切割算法获得了碎冰的初始随机分布状态,并考虑了海冰在运动过程中的海水浮力和拖曳力.计算表明该扩展多面体单元可描述海冰在海流拖曳下的运动过程以及圆桩结构的动冰力特性.在此基础上进一步分析了冰速和冰块尺寸对圆桩冰力的影响,并确定了冰力在圆桩上的分布规律. 最后,讨论了目前扩展多面体单元在计算冰载荷方面的局限性和改进方法.

     

    Abstract: With the polyhedron elements with complex geometric shapes, the linear contact force model cannot precisely obtain the contact force and its direction and the contact deformation under various contact patterns. Due that dilated polyhedral element can be generated with superposing one dilating sphere on the surface of one basic polyhedron in the Minkowski sum theory to construct the geometric shape of irregular particle accurately, and then its contact detection between particles can be calculated easily, considering di erent contact patterns between vertices, edges and planes of the dilated polyhedral elements, a unified nonlinear viscoelastic contact force model is developed. In this model, the equivalent radius of curvature is introduced to calculate the elastic contact sti ness in normal direction. Meanwhile, the viscous force and the elastic force in tangential direction are simplified based on the contact force model of spherical element. To simulate the sea ice floes in broken ice region, the sea ice elements are generated randomly with the Voronoi tessellation algorithm. The ice loads on a vertical cylinder pile are simulated with the dilated polyhedral elements considering the buoyancy and drag forces of current. Moreover, the influences of ice velocity and ice floe size on the ice of pile are determined, and the distribution of ice load around the cylindrical pile is obtained. Finally, the limitation of the present dilated polyhedral element and its further modification are discussed.

     

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