Detailed CFD Simulations for Near-Field Dispersion of Deep Sea Mining Plumes
Type:
Presented during:
WODCON XXII - Enhance the Harmony between Dredging and Ecology
Authors:
B. Decrop and T. De Wachter
Abstract
"A growing population, more than 9.7 billion people in 2050, and an urbanization trend of people seeking higher standard of living are expected to cause megatrends shaping the future. These megatrends can only be met by smarter infrastructure and advanced clean transportation means. Metals like cobalt, nickel and manganese will be essential in enabling this transformation and puts polymetallic nodules (PMN) from deep sea mining as an additional resource on the map. One of the environmental challenges is the management of sediment plumes generated while collecting these PMN. Accurate model predictions of plume dispersion is key to optimize the design and operations of the collector system thereby minimizing the sediment plume impact zone. Far-field plume dispersion models – based on ocean model downscaling methods – have been implemented in the past. Yet, in order to simulate the far-field plume dispersion accurately, knowledge of the near-field dispersion is of paramount importance. The large far-field models have a numerical mesh resolution of generally at least 150 m and are therefore not capable of resolving the small-scale dynamics of the turbulent dispersion in the vicinity of the collector at work (turbulent length scales in the order of centimeters). In order to determine the sediment dispersion near the collector, a separate model is set up to resolve the turbulent dispersion of the released sediments in the vicinity of the collector, called the near field. The near field ranges from the collector to about 100 to 200 m downstream, depending on the dynamics. The vertical distribution of sediment in the near field is subsequently imposed as a sediment source in the far-field models, leading to significant increase in accuracy of the latter. In the presented paper, the setup and application of a Computational Fluid Dynamics (CFD) model for near-field dispersion is described. Applications include determination of near-field sediment dispersion and optimization of an outflow diffusor and flow guidance structure to minimize sediment dispersion."
Keywords: Deep Sea Mining, Environmental Impact Assessment, Sediment plumes, Numerical modelling