Design Of Spherical Joint Between Lifting Pipes Of Deep-Sea Mining System And Analysis Of Lateral Motion Of Pipe System

The merits and faults of connection device in deep sea mining system are summarized in this dissertation. Because of the influence of both marine environment and work condition, substantial moment is applied to lifting pipes. In order to relieve of its harmful effect, a neotype connection device—spherical joint is designed in the paper. And it has the features of free of welds, high strength and convenient dismounting; moreover, it can be used many times in deep sea mining. With this kind of joint, the moment will be removed from the lifting pipes, so the pipes can be regarded as flexible ones.Detailed performance analysis of spherical joint is developed in this paper, including stress analysis and safety check of key components, anticorrosion performance and thread seal effectiveness studied with energy loss method and thread slip stress with finite element method. The results indicated that the spherical joint can meet the work condition of 1000 meters'pilot-scale mining system in China.On the basis of 3D contact problem of spherical joint, computational method of 3D contact stress is investigated in the paper. Two rigidity equations of both spherical surfaces are derived from variation principle and virtual work principle. Furthermore, the contact conditions under four contact states are added in order to solve the rigidity equations. Surface to surface contact element is used as analysis element. With regard to the friction on the contact surfaces, the simplified ideal stick-slip friction model is built to simulate it. Finally distribution map of 3D contact stress on the contact surfaces of spherical joint is obtained.Hydrodynamic force under different conditions, including marine conditions band 4 and 6, is studied based on Normal Depth 2D Small Amplitude Linear Wave Theory and Modified Morison Equation. All the data are got by numerical integration method. The relationship among three variable parameters, which are hydrodynamic force, sea water depth and time, is presented in visual pictures.To study the performance of mining system assembled with spherical joints, static analysis model and dynamic characteristics variation mathematic model are built in the paper, both for thread-connected system and spherical joints connected system respectively. The lateral displacement characteristics of thread-connected system are compared with that of spherical joint connected system by FEM and virtual simulation technology. During the simulation of the first system, pipe element is chosen to simulate lifting pipe. Steady-state lateral displacement shape of lifting system is obtained under different conditions. The maximum lateral displacement is yield at the bottom of lifting pipes, which is 2.1m for band 4 marine conditions and 3.3m for band 6 marine conditions. And the deviation angle is 0.14 and 0.21 for each. Moreover, the displacement is increased with the increase of sea water depth. During the simulation of the second system, the hydrodynamic force is fitted with sinusoidal curve. Its deviation exhibits periodic property with the increase of time. The analysis result is that: under band 4 marine conditions, periodicity is about 50 seconds, its displacement is 6.3m and the deviation angle is 0.40 . While under band 6 marine conditions, the counterpart values are 57 seconds, 5.9m and 0.38 .Although the lateral displacement of thread-connected lifting pipes system is smaller, the pipes are subjected to immense moment, which is unfavorable to strength safety and reliability. The pipes of spherical joint connected lifting pipes system are free of moment and only subjected to axial forces, but the lateral displacement of the system is relatively larger. Nevertheless, the overall deviation angle is still small. If a given angle is allowed during spherical joint design, then the spherical joint connected lifting pipes system can meet the specification of 1000m deep sea mining system. According to this point, spherical joints can be widely applied in 1000 meters'pilot-scale mining system in China.To examine and certify the precision of analysis, two relevant experiments have been carried out in this paper: one is 1:100 model motion state experiment of 1000m lifting pipes, the other is 1:1 model tension test of designed spherical joint. The results of computation are consistent with those from experiments on the whole. Therefore, the spherical joints can be applied in the deep sea mining system of China.