Safety analysis of deep-sea mining pipeline deployment operations considering internal solitary waves

Abstract

Internal solitary waves bring great challenges to the safety of deep-sea mining pipeline deployment operations. The three-dimensional finite element model of deep-sea mining pipeline system under the action of internal solitary waves is established and solved. The shape, tension, stress, upper rotation, offset, and transient response of the pipe string during the deployment process of the deep-sea mining system under the internal solitary wave environment are analysed, and dangerous stages and risk factors are obtained. The envelopes of deployment operations under different internal solitary waves are calculated, and the technical measures to enlarge the operation envelope are discussed. The results show that the upper rotation and offset at moon pool position are more easily affected by internal wave energy relative to stress and tension, and they are the main factors affecting the safety of operation. The stage that the mining vehicle passes through the high-velocity zone of internal solitary waves is the high-risk stage. The operation envelope is the smallest when the IW-OC direction angle is 0°, and is the largest when the angle is 180°. Strengthening the upper restraint has limited effect on improving the operation envelope, in contrast, turning on the propellers of mining vehicle to resist the internal wave when necessary can effectively expand the operation envelope.