Rankine time-domain method with application to side-by-side gap flow modeling

•The seakeeping problem of two ships in side-by-side configuration is investigated.•Wave resonance effects in the gap between the two ships are observed.•Time domain method presented convergence problems for the resonant frequencies.•Introduction of a damping lid improves the numerical convergence of the method.•Results show that the damping lid also improves the numerical predictions.

The performance of a time domain Rankine panel method applied to the seakeeping problem of two ships in side-by-side configuration is investigated in this article. Benchmark data for the numerical results are provided by fundamental seakeeping tests carried out in the towing tank of the CEHINAV-Technical University of Madrid. The multi-body system was composed by a barge and a prismatic geosim, which were subjected to regular head waves in two different gap distances. The motions of the geosim model were restricted to surge, heave and pitch, whereas the barge model was kept fixed. This set-up was adopted so as to guarantee that the gap width remained constant during the tests, providing a favorable situation for the numerical modeling of the system. Comparison between measurements and numerical results illustrates the limitation of potential flow solvers concerning the modeling of this hydrodynamic problem. Numerical wave resonance in the gap led to wave elevations and body motions much larger than those observed during the tests. In addition, the time domain method also presented convergence problems for a range of frequencies associated to the gap resonance phenomenon. In order to overcome these problems, an external damping factor was introduced in the time domain simulations, bringing a significant improvement to the numerical convergence of the method. Moreover, despite the simplicity of the damping model adopted, the results showed that this technique was indeed able to improve the computational predictions, leading to a closer agreement between the experiments and the numerical results.