Experimental study of a cylinder towed through natural mud

With the rapid increase in ship size, the definition of the nautical bottom is becoming more crucial for ports and waterways authorities worldwide. Previous theoretical and experimental research has demonstrated that under certain conditions it is possible to sail through fluidized mud. However, in most numerical models, the complex rheological behaviour of the natural mud is simplified and treated as a Newtonian fluid. To better understand the behaviour of natural mud from the nautical point of view, a series of towing tests with a 0.2 m diameter cylinder moving through natural mud and seawater were performed, for use as reference data for 2D CFD simulations. Different under keel clearances (UKC) with respect to the mud layer thickness were tested for a tow velocity ranging from 0 to 0.5 m/s. A state-of-the-art experimental setup equipped with load cells and pressure sensors recorded the hydrodynamic forces and pressure acting on the cylinder. The mud layer was constantly monitored with a series of pressure probes and pore pressure sensors installed in the flume tank, along with local sampling for rheological characterization. Drag force plots for the first tested condition (the main fluid consisted of only natural mud) demonstrate an initial rigidity followed by a quadratic tendency similar to a Bingham fluid. However, experimental results with mud and water reveal a clear velocity dependency. At low velocities, a jet flow between the cylinder and the mud creates a high-intensity turbulent wake behind the cylinder, generating larger drag forces and more turbidity. A clear mud-water interface is defined as the velocity increases, reducing the overall drag. This series of experiments will be used to validate a new mud rheology model implemented in CFD, that will be used in manoeuvring simulations in muddy environments.

Jaar van publicatie:2022

Toegankelijkheid:Closed