【作者】 胡小舟；

【导师】 刘少军；

【作者基本信息】 中南大学 ， 机械电子工程， 2011， 博士

【摘要】 深海采矿系统的布放是深海采矿作业顺利进行的基础,按照系统的动力学特性,布放过程可分为两个部分,第一部分为集矿机从采矿船上吊起到集矿机入水,在集矿机入水时将出现复杂的气-固-液三相耦合过程,集矿机底部将承受瞬间出现的巨大砰击载荷,这将会影响到布放机构的工作,在极端的海况下甚至导致布放的失败；第二部分是从集矿机完全浸没在海水中开始到集矿机到达海底,在这个布放过程中,受到波浪等海洋环境以及船舶的随波运动的影响,布放中的系统处于不稳定状态,浸没在水下的设备总质量将越来越大,巨大的质量在水中随着采矿船运动,可能导致采矿系统与采矿船连接部分承受很大的载荷。因此,深海采矿系统的布放和水动力问题研究是我国深海采矿研究领域中非常重要但又涉及较少的内容,本文以中国深海采矿1000米海试系统为研究对象,采用计算流体力学方法对采矿系统在布放中的关键阶段的动力学和水动力特性进行了探索性研究。本文的主要研究成果分为以下几个部分：1、在RANSE (Reynolds-Averaged Navier-Stokes Equations)基础上,采用Fluent软件构建了二维数值波浪水槽。在数值水槽的左端采用摇臂法进行造波,而在水槽的右端则设置一段消波区域采用多孔介质法用来消散波浪,减少波浪的反射。在数值方法上,选择有限体积法,并用VOF(Volume of fluid)法追踪二维自由液面的波动。通过适当选择多孔介质特征参数,可以造出理想的规则线性波,二阶Stokes波以及基于海浪谱的随机波。着重对多孔介质特征参数的选择进行了研究,得到不同波高下多孔介质参数选择的方法。通过选择合适的仿真参数得到的波浪仿真结果与1000m海试布放回收作业海洋环境下的波浪十分吻合,为集矿机模型在波浪影响下入水的研究奠定基础。2、对集矿机在垂直方向的静水砰击进行了仿真研究。按照入水速度性质的不同,静水砰击分为匀速入水和自由落体入水两种情况。考虑到集矿机的主要外部特征,将其简化为平底物体,得到了在不同入水速度下,集矿机匀速入水最大砰击压力、砰击压力分布及砰击持续时间,分析了入水速度对最大砰击压力和砰击持续时间的影响；对集矿机的自由落体情况进行了研究,得到了最大砰击压力、砰击压力分布、砰击持续时间、砰击时最大加速度、最大速度等,分析了两个主要的特征参数——高度比率与质量比率的变化趋势,并与匀速入水的情况进行了比较。静水砰击研究结果可以与集矿机在波浪影响下的入水砰击进行比较。3、在构建完成数值波浪水槽和集矿机入静水研究的基础上,对集矿机在波浪影响下入水进行了研究。首先对集矿机静止悬挂在海面上的工况进行了仿真,其结果表明,其底部砰击力主要由波面水粒子的瞬时加速度决定；其次,根据在集矿机模型入静水研究所总结的理论,分析了集矿机入水时,底部砰击压力可能出现最大值的时间点和位置。在理论分析的基础上进行了仿真,得到不同海况和不同位置入水时,集矿机底部的最大砰击压力时间历程、压力分布情况以及砰击持续时间等要素,其结果与集矿机模型入静水研究进行了比较,得到了波浪的影响,并分析了影响产生的原因；观察到了集矿机在波浪影响下的入水与楔形体垂直入水的相似性。4、对深海采矿系统各主要部件水动力特性进行了研究。采用数值方法计算了各主要部件的附加质量系数：第一种方法是根据势流理论,在面元法的基础上使用FORTRAN语言编写计算程序的算法；另一种方法是在用牛顿第二定律分析集矿机模型在流场中运动的基础上,利用F1uent软件得到仿真结果后再进行处理。两种方法所得的结果可以相互验证。5、对深海采矿系统布放进行了研究。这里主要指集矿机从完全浸没在海水中开始到集矿机到达海底之前的布放,管道系统可视为垂直悬挂于安装在采矿船上的布放装置上,在集矿机的牵引下逐渐放入海水中。分析了不同海况和不同布放速度对布放作业各个过程的影响,还针对考虑集矿机附加质量和不考虑附加质量两种情况,对作用在集矿机上的拉力变化进行了讨论。6、在六自由度实验平台和水池中进行了结构物垂直入静水实验。设计了试验装置和试验模型,测试了模型以不同速度匀速入水时模型底部所受的砰击压力。通过比较表明实验结果与仿真结果相当吻合,可验证采用计算流体力学软件F1uent研究物体入水砰击问题以及仿真中所编制的仿真程序的正确性与可信性。更多还原

【Abstract】 Successful deployment of mining system is the basic and premise of deep sea mining operation. According to the dynamics characteristics of mining system, the deploying process can be divided into two parts:the first part is from beginning of deployment to water entry of mining tool when a complicated air-body-water coupling process occurs, and the bottom of mining tool would bear a huge impact force, exerting big influence on deploying equipment, which even results in failure of deployment in hostile ocean conditions; the second part is from the time that mining tool fully immerses in sea water to mining tool reaching to seafloor, because of the effect of sea wave and motion of mining vessel, the mining system in deploying process is in unstable state, and the whole mass of immersed parts of mining system is more and more big, leading to considerable large load in connecting parts between mining system and mining vessel. The study of deployment and hydrodynamic characteristics of deep sea mining system is an important but seldom concerned subject. Based on the 1000m sea pilot system of deep-sea mining tool of China, exploratory researches are conducted which focus on deployment and hydrodynamic characteristics of mining system in key process of deployment.Efforts have been made and the results are presented as follows:1. The two-dimensional (2D) numerical wave tank is developed using CFD code Fluent. A piston-type wave-maker is incorporated in the computational domain to generate the desired waves, including linear waves of different ocean conditions,2-order Stokes wave and random wave based on Pierson-Moskowitz spectrum. Towards the end of the computational domain, the porous media technology is applied to form an artificial damping zone so that the wave energy is gradually dissipated in the direction of wave propagation. To verify their applicability in two dimensions, the computational results are compared with analytical solutions, showing good agreement; the effect of permeability of porous media is discussed, a suggestion for choosing permeability of porous media is made. It is shown that an efficient method for the simulation of waves is successfully established for research of wave-structure interaction by CFD codes.2. The hydrodynamic problems of a two-dimensional model of seafloor mining tool entering still water vertically are analyzed based on the velocity potential theory. Two conditions are mainly discussed. The first is that mining tool enters still water in constant speed. Pressure distribution, maximum impact pressure, impact duration time during the water entry of mining tool are presented at various deploying velocity, the two peak pressures in impact process are observed, the relationship between maximum impact pressure and deploying velocity is obtained. The results are compared and verified with that based on other prediction theories and methods. The second condition is that mining tool enters water in free fall motion. The time histories of velocity and pressure during the impact process are obtained. Residual air entrained between the bottom of mining tool and free water surface is observed, and influence which exerts on impact is discussed. The concept of impact added mass is presented to express the coupled function between air-rigid body-water during water entry process. Two dimensionless ratios are determined which the drop simulations should comply with to simulate an average slam:drop height ratio and mass ratio. The relationships between dimensionless ratios and several important parameters derived from simulation results are discussed.3. Based on the studies of numerical wave tank and mining tool entering still water, the mining tool impacting with sea water with the influence of ocean waves are studied. The condition that the mining tool is suspended still above the water surface is considered, the simulation results show the impact pressures of this condition are mainly determined by the instant acceleration of water particles on wave surface. The second condition is that mining tool enters waves, the time points and positions of which the pressures on bottom of mining tool reaches to their maximum values are obtained, and the time histories of impact pressure of bottom of mining tool, the pressure distributions and impact durations are presented, those results are compared with that of still water entry of mining tool, thus the influence that waves exert on water entry of mining tool is obtained. The similarity between mining tool entering wave and wedged-shape body entering still water is observed.4. Two numerical methods for assessing the added mass of components of deep sea mining system are mainly proposed in this work. The first method is referred to as the Hess-Smith method which is based on surface panel method and potential theory. The second method is referred to here as a Fluent method which is a constant acceleration method based on the CFD software Fluent. The added mass coefficient of components of mining system which are acquired from the two methods are approximately equal, both are applicable for infinite flow field, while for the condition of free surface, including water entry, mining tool touching down the seafloor, the Fluent method is more suitable.5. Deployment of seafloor mining tool is studied with the effects of wave and motion of vessel considered. Four ocean conditions which are proper for deployment are considered, and the effect of deploying velocity is also researched. The results indicate that the ocean condition and the deploying velocity play an important role to determine the kinematic and dynamic condition of the deployment process of deep sea mining system, and the research results can provide basic information for the design of the heave compensation system and reduction of dynamics effects of riser system on seafloor mining tool during the deploying process.6. Experiments of still water entry of body are conducted by six dimension-of-freedom (DOF) experiment platform and water tank. The experimental model is designed and experimental equipment is constructed. The impact pressures which mining tool model bear when it enters still water in different constant velocities are obtained by measuring devices, The comparisons between simulation results and experimental results indicate that the two results are identical, thus the accuracy and dependablity of simulations of water entry study based on CFD code Fluent can be verified.更多还原