Numerically, the problem of shallow water ship resistance is somewhat more complex that that of deep water resistance. In CFD the bottom needs to be regarded as an impermeable, non-slip wall, on which a boundary layer flow develops, just as it does on the surface of the hull. The boundary layer flow need sto be well captured, othervise the pressure drop along the gap between the hull and the bottom is not well predicted, which also leads to innacurate resistance evaluation.
Validating ship resistance in shallow water
We conducted a benchmark study to investigate the accuracy of our apporach in predicting shallow water ship resistance. In the benchmark we used the KCS model and experimental results available in Mucha et al. 2016 (https://izw.baw.de/e-medien/4th-mashcon/PDF/4th%20MASHCON.pdf). The study is performed for the draft to depth ratio of 1.2, at four different speeds. Total resistance and Under Keel Clearance are compared to experiental measurements.
Simulations were perfromed in full scale using the standard Cloud Towing Tank procedure for shallow water conditions, which includes special meshing in the gap between the keel and the bottom and alarger simulation domain. The results are scaled from full scale to model scale to allow a direct comparison agaisnt experimental measurements. Ship resistance differences range from 3.8 and 8.6 %, while the Under Keel Clearance differences range from 2.6 and 9.5 %. Compared against CFD results from Mucha et al. 2016 the present results correspond better then relative to experimental results, while at the highest speed the present approach gives slightly better prediction (see the graph below.)
Follow the link below for the full benchmark study with detailed discussion and data.