Riser lift system for deep sea mining

• Main Author: Mao, Haiying
• Other Authors: Romanoff, Jani, Insinööritieteiden korkeakoulu, Aalto-yliopisto, Aalto University
• Format: Master Thesis
• Language: English
• Published: 2018
• Subjects: riser lift system; deep sea mining; SIMA; dynamic response; limiting criteria; fatigue life; Mid-Atlantic Ridge; Svalbard
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/33662

The growing global demand for rare metals and the declining land mineral resources impel the research on exploring deep sea minerals resources. This thesis focuses on one case, which is within the Norwegian interest zone along the North-East part of the Mid-Atlantic Ridge outside Svalbard, the water depth is in excess of 3000 m. The objective of this master thesis is to explore the limitations of operating such a riser system at large water depths with focus on the dynamic behaviour of the system. In addition, based on the dynamic response and the limiting criteria, perform the fatigue analysis to find the fatigue life of the riser lift system. Then, comparing the difference of the dynamic behavior and fatigue life of the riser lift system under the two topside connection conditions. A case study was performed for representative sea states with regard to two working conditions by the Riflex module of SIMA. The results of this study indicated that the topside connection of the riser has a big impact on the riser. The bending moment and stress of the riser with fixed topside connection is much larger than it with pinned topside connection.In this case, the fatigue life of the riser is too short whatever the topside connection is. In general, it is difficult to apply a steel riser under these conditions, even if the vortex induced vibration is not considered in this study.