Longitudinal Vibrations Analysis Of Lifting Pipe In Deep-sea Mining

With the decrease of land mineral resources,many countries have divert their attentions to marine mineral resources.At present,the mining equipment and pipeline lifting system are mainly used to mine marine mineral resources.The lifting pipe is subjected to various forces in a complex marine environment and undergoes very complex deformation.In addition,the heave motion of the mining vessel will lead to the longitudinal vibration of the lifting pipe,affecting the service life of the mining pipe and even causing major accidents.In order to solve the above problems,this study separately made static analysis and dynamic analysis on two different pipes--equal diameter pipe and stepped pipe,and used additional vibration absorber to suppress the vibration of the pipes.The work operates as follows:First,the lifting sub-system is simplified to obtain the physical model of the lifting sub-system.The force analysis of the lifting pipe is then carried out,and the relevant knowledge of mechanics is used to get the values of gravity,buoyancy and the gravity of the pump and the intermediate ore bin in the seawater;The linear Airy wave theory is selected to analyze the ocean waves and the Morrison equation is used to get the value of hydrodynamic forces generated by the ocean waves and currents on the lifting pipe.Then,the finite element method is used to do static analysis of the lifting pipe.The ABAQUS software is used to calculate lateral displacements and bending moment of the equal diameter pipe and the stepped pipe when the mining ship is stationary and towing at different uniform speeds under the interactive Effects of wave and current.Subsequently,the finite element theory is applied to analyze the net elongation,axial force and axial stress of the lifting pipe.The relations between the net elongation,the axial force and the axial stress of the two kinds of pipes with the depth of sea water is present by MATLAB.Based on the previous analyses,the amplitude of the heave motion of the mining vessel is confirmed,and then the finite element method is used to analyze.The longitudinal vibration equation of the lifting pipe is set up,and the central difference method is used to calculate the vibration amplitude of the lifting pipe and the axial stress changing with time.4 points on the pipeline is selected to draw the corresponding curve.After knowing the changing relationship between the amplitude and the axial stress with time,because huge amplitude will affect the stability and service life of the pipeline,the author used additional dynamic vibration absorber to study the vibration reduction of the pipeline.In this study,the relation that the vibration amplitudes of the two kinds of pipelines will change with time is got by assuming that the dynamic vibration absorbers are attached to the intermediate ore bin.In this study,the relation of the amplitude between the lifting pipes mentioned above.