A dynamic design and analysis of the flexible hose of the deepsea mining system

Abstract

Climate change is a recurring topic in the news and goes side by side with the energy transition. The energy transition focuses on using clean energy generated by resources like wind and water. Due to the increasing demand for technology that focuses on generating and storing clean energy, the demand for metals grows. These metals are currently extracted from landbased locations but are also found on the bottom of the ocean. Three types of resources are found on the
ocean floor: hydrothermal vents, cobalt crusts, and polymetallic nodules. To extract these resources from the ocean floor, a project called ”Blue Nodules was launched in 2020. This project addresses the challenge of creating a viable and sustainable value chain to retrieve the polymetallic nodules from the ocean floor. Royal IHC is one of the partners on this project and designed the seafloor nodule collector. The total mining system consists of a surface vessel, a vertical transport system, a flexible hose (jumper hose) and a seafloor nodule collector. In combination with a hose developing company, IHC designed the flexible hose. This design was projected on a prior design of the seafloor module collector. Since then, the seafloor module collector design has advanced, but the flexible hose design did not. Therefore the main objective of this master thesis is to design and analyse the flexible hose with its main focus on the dynamic behaviour.
The methodology for this thesis is addressed in the following manner. The old design of the flexible hose was investigated, and all relevant parameters were addressed. A static model was built to verify the parameters that modelled the hose with these parameters. The parameters of interest were: the length of the hose, the distance between crawler and vertical transport system in height and width, number of buoyancy modules, number of buoyancy modules per hose section, starting position of buoyancy nodules. This static model was used to perform a parameter study, resulting in an optimal set of parameters tested against design criteria.
The next stage was implementing the static design in a dynamic software packet called ”OrcaFlex”. Orcaflex is a software program for static and dynamic analysis of offshore systems. The static model is implemented end tested with this software. This resulted in a failure of the set of parameters and adjustment to the static model. After a redo of the parameter study, a new set of parameters was
extracted. This set is tested for an inline motion of the crawler compared to the vertical transport system and for a perpendicular motion. These motions expand in size until the flexible hose reaches its critical values. These tests resulted in a range around the VTS where the crawler could move in.
Results show that the crawler can move in this range for a selected set of parameters. Throughout the research, it is shown that the parameter set needs further development to complete the flexible connection design. It is recommended that some disregarded motions, parameters and environmental forces are further investigated and that the failure criteria that test the hose need to be expanded.