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.
Highlights
As the Second Generation Intact Stability Criteria (SGISC) are in the final phase, it is the appropriate time to verify if existing simulation tools are ready for a Level 3 assessment, called Direct Stability Assessment
A number of basis criteria have been defined by the International Maritem Organization (IMO) Intact Stability Correspondence Group [1], and finalised during a session of the IMO sub-committee on Ship Design and Construction (SDC-7) [2], but these criteria do not guarantee the certain accuracy of the simulations versus the results of experiments
Quite some effort was spent on measuring the roll damping, since this is a critical parameter in parametric roll predictions, and, in most of the SGISC failure modes
Summary
As the Second Generation Intact Stability Criteria (SGISC) are in the final phase, it is the appropriate time to verify if existing simulation tools are ready for a Level 3 assessment, called Direct Stability Assessment. A number of basis criteria have been defined by the International Maritem Organization (IMO) Intact Stability Correspondence Group [1], and finalised during a session of the IMO sub-committee on Ship Design and Construction (SDC-7) [2], but these criteria do not guarantee the certain accuracy of the simulations versus the results of experiments. Work has been done in the Cooperative Research Ships (CRS) [3] consortium, which has focused on three out of five stability failure modes: parametric roll, loss of stability and dead ship. As in the earlier publication, the results of different simulation programs have been compared to the results of experiments
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