A Comparison of Numerical Simulations and Model Experiments on Parametric Roll in Irregular Seas

Abstract

The recently finalised Second Generation Intact Stability Criteria (SGISC), produced by the International Maritime Organisation (IMO), contain a level 3 assessment, the so-called Direct Stability Assessment (DSA). This assessment can be carried out using either model experiments or simulations. The fact that such a choice is given implies that the methods are equivalent in accuracy. This assumption has been verified, for one case, by the Cooperative Research Ships (CRS) community. The verification was based on new model experiments and calculated results, using four different programs owned by different CRS members. Results of the verification of the parametric roll failure mode in regular waves were published before, but this study concerns results in irregular seas. The experimental and numerical results are compared in both probabilistic and deterministic manners. The probabilistic comparison showed that the simulation programs considered are sometimes conservative and sometimes non-conservative in the prediction of the probability of an extreme value. The deterministic comparison in head seas showed that parametric roll events were predicted in the simulations in a wave train that showed no sign of important roll events in the measurement. The deterministic comparison in the following seas, on the other hand, showed an accurate fit of experimental and numerical results. It is suggested that predictions could possibly be improved by adding non-linear diffraction forces to the numerical model.

Implementation of the IMO Second Generation Intact Stability Guidelines

“…Of note is the work by [23], which focused on the physics that need to be considered to perform a successful numerical simulation of parametric rolling-importance for both direct assessments, but also the level 2 PR time domain requirement. While the state-of-the-art in experimental and computational methods does show promise in providing analysis methods appropriate for direct stability assessments [24], it remains far less practical in terms of numerical sensitivity, availability of knowledge, and cost, for application to a wide range of vessels, especially when variations in environment or loading condition are included [11]. There also exists concern about the successful validation of such tools [22].…”

Accuracy Analysis of the Measurement of Centre of Gravity and Moment of Inertia with a Swing

“…The position of the centre of gravity as well as the moment of inertia are essential input for the simulation of motions and forces of floating devices. CG is especially important for ships [17,18] and floating structures [19] including falling lifeboats [20] or floating wind turbines [21]. New and refitted ships are typically investigated with an inclination test [22,23] to ensure the precise location of the CG and that the desired stability is achieved.…”