Shear thinning of non-colloidal suspensions involving multi-scaled air bubbles is studied. It is observed that the presence of bubbles significantly affects the transition and equilibrium rheological behavior. Large bubbles enhance shear thinning of the system by increasing the particle loading at low shear rates, whereas nano-bubbles suppress shear thinning by introducing additional repulsive interactions between smooth solid spheres, which also hinder the shear thinning of the polymeric matrix at high shear rates. As to the transition behavior at low shear rates caused by the particle organization, nano-bubbles induce a more diffusive particle motion, leading to a larger critical strain accounting for the finish of the organization process. It shows that nano-bubbles shield the interaction between solid spheres. Therefore, a degassing process prior to the rheological experiment is essential in order to achieve reliable rheological properties of the two-phase suspension system.

During the harvesting of polymetallic nodules on the seabed, the sediment plume due to disturbance on the seabed impacts the benthic ecosystem. A numerical simulation based on the SPH (smooth particle hydrodynamics) method is used to estimate the time and length scale of the plume impact near the seabed during a small-scale harvesting process. The simulation result considerably agrees with the one from the lab-scale water-channel experiment. It is found that, in the sediment plume, the traced sub-plume with iso-surface of lower sediment concentration travels a longer distance, and spends a longer time to achieve the stable state. Moreover, with the increase of the releasing rate of the disturbed sediment, the sub-plume spreads over greater distance, which also needs more time to achieve the stable state.

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