This paper describes an experimental and numerical study on the effect of bilge keels on a specific offshore vessel. Forced roll and free decay experiments were carried out at MARINTEK in a joint project between VARD, DNV GL and MARINTEK during Nov. 2012. The 1:25 ship model was tested both with and without bilge keels. 19 forced roll periods were tested at 4 roll angles (2, 4, 6 and 10deg). Free decay tests were performed for initial roll angles 2, 4, 6, 10 and 15deg. Damping was extracted and compared with numerical simulations from a potential flow strip theory program (VERES) and a commercial CFD tool (StarCCM+).
Both qualitative and quantitative agreement between the experimentally and numerically obtained damping parameters was documented. Discrepancies were identified and discussed. The three different methods of investigation gave together a basis for discussing the effect of bilge keels. From the present study, it is recommended that both experimental and numerical work in combination, for both forced roll and free decay tests, should be performed to assess the damping efficiency of bilge keels.
A vessel traveling across the sea experiences waves. The waves produce forces on the vessel resulting in added resistance. The forces are caused by the combination of wave and vessel motion. A variety of methods for prediction of added resistance in waves exists. The complexity and accuracy varies significantly. This paper focuses on numerical solution of the problem when the waves are high compared to the vessel size. The commercial software Star-CCM+ is used to solve the Navier-Stokes equations by use of Reynolds averaging and a VOF model. This implies that all kind of nonlinearities are accounted for. Accurate numerical propagation of a 5th order Stokes wave is achieved. A study on the mesh and time step sensitivity of the added resistance is presented. The numerical results are validated by custom made model test. A numerical comparison of two alternative surge restrictions (constant speed or constant force) shows insignificant differences in results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.