Research Of Motion Response Of Deep-sea Mining System

As the development of human's science& technology, the world's demand of various kinds of metals, especially manganese and cobalt , are increasing day by day. However, the mineral reserve in the land is very limited, which is only able to meet human's requirement within a few decades now. And what's more, the cost for mining is increasing with the decline of the mineral's density. To sum up, it is urgent to look for new mineral resources. Deep in the bottom of the ocean, where we human haven't developed yet, there are enormous scale of minerals, including manganese nodule and cobalt crust, which attract the attention from all around the world. The two kinds of minerals have a plentiful store of manganese, cobalt, copper, nickel and other kinds of metallic elements, both the percentage and total storage of which are both several orders of magnitude of that in the land. The minerals deep in the ocean are able to meet human requirement in a quite long period. Therefore, deep-sea mining becomes a focal point of study for many countries in the world.This thesis begins with the development of deep-sea mining, a few mining programs classified by hoisting styles are introduced, then a mining system of combined mining vehicle and hydraulic hoisting is chosen and introduced in detail as well as studied from three sub-systems, which are collecting system, hoisting system and mother ship system. Function analysis is made for the collecting system. A relatively detailed design regarding size, arrangement, joint method and material is made for the hoisting system. Based on function analysis of the mother ship, the RAOs of the ship are calculated according to potential wave theory and dynamic equilibrium equation of six degree of freedom through HydroD software from Det Norske Veritas, and frequency-domain motion performance of the ship is therefore predicted briefly, of which the heave RAO provides reference for heave compensation system design.The significant difference of deep-sea mining hoisting pipe from common ocean platform pipes is that the lower end is free, which makes its motion response notable. So the rest part of the thesis focuses on the motion response of the hoisting system. Based on Morison equation, 5-order Stokes wave theory and dynamic equation of the hoisting pipe, a general-purpose finite element software Abaqus is chosen to simulate the system. This part is divided into mainly two aspects as follow.1. Different Working Condition During Mining OperationAs the impact of ocean current and waves, the riser is deformed. The most important parameters we care about are the horizontal offset of the mid-bin, maximum moment and axial stress, etc. The riser in different conditions such as working in a fixed position, mother ship shifting and installation progress are simulated, the parameters mentioned above are gained, as well as some conclusions regarding parameters'variation due to the change of environmental loads and restrains. And the material of the riser is checked through the calculations mentioned, thereby an optimal choice is made .2. Impact of The Design Parameters of The Hoisting SystemIn this part, the size of the hoisting pipe is assumed to be fixed. The variables are chosen to be the weight of the mid-bin, the installation of buoyancy bodies and the appliance of spherical joints. The influence of which to the response parameters of the hoisting pipe is simulated, the influence disciplines of the variables are summarized, and a method of using ball joint properly is proposed. The conclusions of this part is of reference value to the hoisting system design.To sum up, a relatively comprehensive study of the deep-sea mining system is made in this paper, including design, simulation and analysis. The main research contents can provide useful reference for the design of deep-sea mining system, the study of heave compensation system and actual deep-sea mining operations.