Performing and Documenting Flow Simulations and Experiments of Roll-Decay Tests and the Comparison of their Results

Computational fluid dynamics (CFD) simulations of rolldecay tests are performed for roll amplitudes in the range 2^o < ϕ_a < 20^o of the KRISO Container Ship (KCS) ship with Froude number Fr = 0 without bilge keels. Investigations include the influence of grid- and time-step dependence, y⁺-value, model scale, degrees of freedom, k_xxvalue, location of center of gravity, appendages, initial roll amplitudes ϕ_init and disturbed initial conditions to investigate coupling effects. Recommendations are developed how to perform such flow simulations accurately. Additionally, challenges regarding experimental roll-decay tests and post-processing roll-decay results are discussed and illustrated based on results from NATO AVT-348 activity. Particularly, analysis methods to determine roll period and logarithmic decrement are reviewed and extended, and approaches to assess measurement offset and motion-coupling are proposed. Furthermore, it is investigated how toobtain conclusive comparison of results when experimental parameters, such as model scale or radius of gyration, differ. From these findings, recommendations are proposed regarding the documentation and comparison of results from roll-decay tests, applicable both to experiments and CFD simulations.