Application of Ultrasound Image Velocimetry (UIV) to cohesive sediment (fluid mud) flows

Ultrasound image velocimetry (UIV) is a technique that enables non-intrusive whole-flow field velocimetry measurements in opaque fluids. It gained interest in experimental fluid dynamics to study the flow mechanics of, amongst others, sediment-laden fluids. Further customisation of this technique is required to make it a reliable asset for experimental research involving high density cohesive sediments (fluid mud). Potential applications include rheological or settling experiments or experiments serving nautical research on the interaction between a ship, water and fluid mud forming the bottom of the navigation channel. This study presents experiments to validate the applicability of UIV in such dense cohesive sediments exhibiting non-Newtonian and thixotropic behaviour. During these experiments, an ultrasound transducer was moved through stationary mud at known velocities. Due to the viscosity of the mud, the zone of influence of the moving transducer is limited in depth. This enables the recording of the relative velocity between moving transducer and the undisturbed mud at greater depths. Medical ultrasound imaging equipment was used, as such equipment allows ultrasound imaging in the required frequency range and frame rate. A good correlation (accuracy  \(>95\) $>95$  %) was found between the imposed motion velocity of the transducer and the output of UIV. However, limitations were found in both depth and velocity, caused by the equipment, settings and mud properties.