The impact of free surface modelling on hydrodynamic forces for ship navigating in inland waterways: water depth, drift angle, and ship speed effect

Simulations of standard manoeuvring tests require a good estimation of the hydrodynamic derivatives. These are extracted from the hydrodynamic forces applying on the ship. The present work focuses on the investigation of the importance of free surface assessment on the estimation of the hydrodynamic forces, particularly, in the presence of the ship–bottom interaction and when certain parameters are varied, including the ship’s speed and the drift angle. This investigation aims, in particular, to mark off the confidence Interval of neglecting free surface deformation hypothesis by comparing the results of static drift test with and without considering this assumption. The study was carried on a 135 m inland containership at a scale ratio of 1:25 undergoing static drift tests. In order to recreate the ship–bottom interaction, the depth to draft ratio (h/T) is varied to obtain four channel configurations. The tests are performed by numerical code under the commercial software Ansys Fluent by solving Reynolds Averaged Navier Stokes Equations(RANSE) coupled to a \(k -\omega\) SST turbulence model. To investigate the effect of free surface modelling, the hydrodynamic forces are compared when the free surface separating air and water is considered, using Volume Of Fluid (VOF) method, and when the free surface is neglected. The simulations are carried out for various ship speeds and various drift angles.