计及液桥的湿颗粒液化机理及“海况-货物-船舶”耦合特性研究

Liquefaction of nickel ore carried by bulk ship may lead to cargo flow and collapse, which shifts the location of gravity center of ship. The ship stability decreases and then capsizes. The seepage of intergranular water is the root cause of onset of liquefaction. When the water content is low, the intergranular water exists in the form of liquid bridge. When the water content or the degree of saturation increases due to compaction and vibration, the contact probability will increase and the fusion of liquid bridges may happen. If the mass fused cannot keep the equilibrium, the liquid bridge will rupture, resulting in seepage and shaping the free surface, and hence the term ‘liquefaction’. However, the previous research mainly focused the formation and rupture, neglected the fusion and seepage of liquid bridge. Therefore, combining the theoretical derivation, numerical analysis and physical experiment, the capillary force kinetics model of formation, rupture and fusion is studied firstly. The formation, rupture, fusion and seepage of liquid bridges will be numerically simulated in a holistic manner. Based on this numerical model, this work will analyze the liquefaction characteristics of wetting particles with liquid bridge effect, and the coupling characteristics between sea, cargo and ship, which further reveal the liquefaction mechanism and provide the theoretical and experimental basis for the design of ship vessels, transportation safety and manipulation.

镍矿在运输过程中液化引起货物流动和坍塌，使船舶重心位置偏移，船舶稳定性下降进而导致船舶倾覆。孔隙间的液态水渗流是镍矿液化的主要原因。镍矿含水量较低时，颗粒间水分以液桥的形式存在，当含水率升高或由挤压、振动引起的饱和度增加时，液桥之间接触概率提高并有可能发生融合。如果液桥融合后的重量无法维持液桥的力平衡，液桥断裂并从颗粒孔隙中渗流形成自由液面，从而导致液化。然而，以往的研究主要关注颗粒间液桥的形成和断裂过程，而对液桥的融合和渗流考虑不足。本课题拟采用理论推导、数值开发和物理实验等多种手段开展工作，首先研究液桥形成、断裂、融合的毛细力动力学模型，建立颗粒间液桥形成、断裂、融合、渗流的整体数值计算方法。在此基础上，开展计及液桥的湿颗粒液化特性及“海况-货物-船舶”耦合特性研究，从而进一步揭示镍矿液化机理，为散货船设计、船舶运输安全及操控提供理论和实验依据。

镍、铁矿等固体散货在船舶运输过程中发生液化时所引起的货物滑移有可能导致船舶突然失去稳性并倾覆，已成为海上安全运输的重大事故隐患。目前，已有25艘装载镍矿和铁矿的散货船沉没并造成了大量的人员伤亡。本项目《计及液桥的湿颗粒液化机理及“海况-货物-船舶”耦合特性研究》为国家自然科学基金青年基金项目，项目的主要研究内容包括：液桥形成/断裂数值及实验研究；液桥融合/渗流数值及实验研究；计及液桥的湿颗粒液化特性及“海况-货物-船舶”耦合特性研究。项目的重要研究成果包括：1）基于Fortran语言建立了考虑毛细效应的颗粒-液桥二维耦合模型，开发了计及液桥的固-液-气三相耦合数值模拟方法，基于此方法开展了液桥的形成、断裂、融合及渗流数值模拟研究；2）搭建了可分析液桥拉伸、断裂、融合及渗流的实验平台，分析了静态颗粒不同布置条件下的持液规律，探究了颗粒相对运动过程中液桥演化至水分迁移的过程；3）建立了“海况-货物-船舶”耦合模型，揭示了不同海况条件下考虑货物滑移的船舶运动响应规律。1）-2）方面的研究成果从细观角度揭示了固体散货液化机理，3）方面的研究成果可拓展到大型散货船稳性评估当中。通过本项目的实施，课题组正与CCS规范所合作，为后续形成行业规范提供有效技术支撑。在研期间，国内外会议作报告2次；发表及录用SCI源期刊论文5篇，EI源期刊论文4篇；申请发明专利4项，登记软件著作权2项；培养硕士生毕业2人，硕士生2人在读。