Medical Ultrasound Used for Hydrodynamics Study and Eroded Surface Mapping in Physical Simulation of Density Currents

Obtaining data with non-intrusive techniques is a great challenge in the context of physical simulation of density currents. An alternative for recording flows is the use of ultrasonic imaging equipment, which allows the acquisition of data with good quality and resolution, even in conditions of higher concentrations or when using sediments that have unfavorable pigmentation (e.g. mineral coal).

Experiments performed in the laboratory at the Density Currents Research Center (NECOD), Institute of Hydraulic Research of the Federal University of Rio Grande do Su, showed that the images obtained by a medical ultrasound could provide good qualitative and quantitative data. The first application, the simulation of density currents in a flume (15 x 0.4 x 0.6 m), ultrasound images indicated that there was a relationship between the different current strata and the velocity and concentration profiles measured during the experiments. In another experimental condition (basin tank: 2.5 x 2.0 x 0.6 m), a density currents eroded a slope and the equipment was abled to measure and map the evolution of such slope profile, suggesting that the equipment may be used to obtain bathymetric data.

Based on that, this work aims to present the applications for the use of the medical ultrasound to obtain hydrodynamic parameters of density currents (flume) and for bathymetric mapping (tank). . Applying image-processing techniques implemented in a Matlab code, numerical values were assigned for the different shades of gray scale recorded during the passage of the current through an observation window. These values allowed obtaining spectra of density and mass flow when correlated with the measured velocity (UVP) and concentration (UHCM) data as well as visualization and quantification of the internal layer dynamics of the simulated currents (e.g. bipartite flows).

Aiming to map the evolution of the slope profile on the tank, the images were treated to obtain thickness values of the eroded surface during the experiment and the mapping of the erosion produced by the knickpoint migration. The outcome of this analysis is a record of the slope evolution during the erosion process in the experiment.