Sotaro Masanobu

A Model Experiment of a Free Standing Riser in the Deep-Sea Basin

An experiment using a 1/70 reduced scale model of a Free Standing Riser (FSR) was carried in the Deep-Sea Basin of the National Maritime Research Institute in Japan. For instance, the model’s vertical pipe was about 32m long and the jumper was about 8m long. The FSR model had several measurement stations attached along the vertical pipe, subsurface buoy and jumper; and the motion of each station was measured in 3D by the Visual Measurement System. During the experiment, the effects of the jumper’s top end oscillation on the whole system were investigated. In this case, the top oscillation had propagated along the jumper; however the top oscillation had a reduced effect on the dynamics of the subsurface buoy and vertical pipe. In another experimental case, a current was generated in order to investigate the Vortex Induced Motion (VIM) on the FSR’s Subsurface Buoy. The VIM experiment was repeated for two different buoy models (a smooth cylinder and a cylinder with 3-start heli-coidally strakes) and the results were compared. In this article, some of the experimental results are presented and discussed.Copyright

Experimental Studies of Pressure Loss in Inclined Pipe in Slurry Transport for Subsea Mining

For subsea mining, the estimation of pressure loss in the pipe of lifting system and the flexible pipe to connect the mining tool and the lifting system is important to design the mining system. The configuration of flexible pipe is expected to have an inclined part.In the present paper, the authors carried out the experiment to measure the pressure loss in inclined pipes using alumina beads to investigate the effect of inclination angle of pipe on the pressure loss. Furthermore, a mathematical model to estimate the pressure loss in inclined pipes was proposed and validated through the experiments. As the result of the validation, it was confirmed that the proposed model could be applied to the pressure loss estimation in inclined pipes.Copyright

Evaluation of Wearing Pipe for Subsea Mining With Large Particles in Slurry Transportation

For a fundamental understanding of pipe wear under hydraulic transportation of deep-sea mining, a small scale test is conducted because there are many restrictions in conducting a full scale test. The small scale test apparatus are set up using the pipes of about 80mm in diameter and the rocks of which maximum particle diameters are about 20mm are used. In the test, the pipe materials and the pipe inclination are changed to evaluate the differential of the amount of pipe material loss. Furthermore, the amount of the pipe material loss in full scale is estimated based on the small scale test results.Copyright

Simulation of a Free Standing Riser Model and Validation With Experimental Results

In this article, we present the numerical analysis of a Free Standing Riser. The numerical simulation was carried out using a commercial riser analysis software suit. The numerical model’s dimensions were the same of a 1/70 reduced scale model deployed in a previous experiment. The numerical results were compared with experimental results presented in a previous article [1]. Discussion about the model and limitations of the numerical analysis is included.Copyright

A Numerical Model for Environmental Impact on Marine Organisms for Seafloor Resources Development

The exclusive economic zone (EEZ) of Japan has a very wide area due to a lot of islands in the Japanese Archipelago. Recently, the development of power generation facilities, food production facilities, and the natural resources in the Japanese EEZ are planned. As the worldwide supply and demand of mineral resources are being tight, the technology for effective exploitation and the use of mineral resources in the EEZ will become a key for sustainable development in the Japanese industry. Prior to development of marine mineral resources, it is necessary to evaluate its environmental impact on the water column and seafloor of ocean. However, the environmental evaluation method for open ocean has not been established yet. Then, we are developing the environmental impact prediction model for the seafloor mineral resources development in deep sea area with the consideration of benthic organisms. This model can estimate the impacts of excavating seafloor and sedimentation of particles on marine organisms using an ecosystem model. In addition, the influence of an increase in dissolved oxygen on bacteria caused by the discharging of oxygen-rich waste water at seafloor, is considered in this model. The ecosystem in this model includes benthic organisms, zooplankton, bacteria, particulate organic matter and dissolved oxygen as the components. This paper introduces the calculation case using the prototype model.Copyright

Study on Grinding Technology for Seafloor Mineral Processing

Seafloor Massive Sulfides (SMSs), which are formed by precipitates from hydrothermal fluids vented from seafloor, have been expected as one of mineral resources to be developed. The authors have proposed the concept of seafloor mineral processing for SMS mining, where valuable minerals contained in SMS ores are separated on seafloor. To apply a ball mill to the grinding unit for seafloor mineral processing, grinding experiments were carried out using a small-scale ball mill applicable to high-pressure condition. In the experiments, wet grinding and water-filled grinding of size-classified silica sands were carried out at three rotation rates to compare the grinding performance in both cases. In both cases, the silica sands were finely ground. The measurement of particle size of samples from the experiments showed that water-filled grinding had comparable grinding performance to wet grinding while the suitable rotation rate for water-filled grinding shifted to higher than that for wet grinding. This result suggests the possibility of water-filled grinding for seafloor mineral processing. If water-filled grinding can be employed for the grinding unit, the structure of the grinding unit would be simplified in comparison with wet grinding that leads to the saving of grinding costs.Copyright

Study on Seafloor Mineral Processing for Mining of Seafloor Massive Sulfides

Seafloor Massive Sulfides (SMSs), which were formed by deposition of precipitates from hydrothermal fluids vented from seafloor, has been expected as one of unconventional mineral resources on deep seafloors in the oceans. The authors have proposed the concept of seafloor mineral processing for SMS mining, where valuable minerals contained in SMS ores are separated on seafloor while gangue minerals are disposed on seafloor in appropriate ways. To confirm the applicability of column flotation, which is one of conventional mineral processing methods, to seafloor mineral processing, the authors carried out experiments simulating column flotation under the pressure conditions corresponding to the water depths down to 1000m in maximum using ore samples containing copper, iron, zinc and lead. In the experiments, formation of fine bubbles suitable to flotation and overflow of froth layer were observed at high pressures. The contents of copper and zinc in the concentrates recovered in the experiments at 1MPa were higher than those in the feed ores while the contents of silicon and calcium in the concentrates were lower than those in the feed ores. These results suggest that column flotation would be applicable to seafloor mineral processing.Copyright