With respect to the validation of numerical tools – the main basis for the validation are scaled model tests。 Within SinSee computer controlled  model test techniques are used and further developed to allow for more detailed studies of dangerous phe- nomena in model testing on the one hand, and the generation of synchronized data for waves and ship motions for validation purposes on the other。 Model tests are quite intense with respect to time and costs, thus the test conditions should be well chosen。 With respect to dangerous roll angles two conditions are of major interest: 1。 The performance of the ves- sel in resonance conditions (not necessarily extreme),

2。the performance of the vessel in extreme condi- tions。 Based on the tests from the Roll-S project, quite some experience is available for the modelling of extreme conditions, e。g。 extreme wave groups em- bedded in regular or random seaways。 When assess- ing resonance phenomena the testing condition need to be tuned to the inpidual ship characteristics。 For the latest test series numerical simulations were successfully used to pre-select interesting conditions。 This new approach will be further developed。 Based on these findings further developments are planed to also re-model conditions measured in full scale in nu- merical or tank environments。

These links between numerical simulations, model tests and full scale measurements are vital for the further development of safer ships and as basis for future decision support systems。

Numerical  assessments

Several numerical motion simulation programs exist worldwide ranging from rather simplified linearized tools to sophisticated non-linear tools。 All simula- tion methods use underlying assumptions in their mathematical model, in order to reduce the comput- ing time。 Still some of the highly non-linear methods have longer computing times than simulated time, which strongly reduces their practical applicability for safety assessments。 For practical applications (i。e。 safety assessments, design evaluations, etc。) of- ten specialized tools are in use。

All numerical simulation programs require a thor- ough validation of their results and have restrictions regarding their applicability depending on the un- derlying assumptions and models。 Unfortunately no common criteria and methods for quality and accu-

racy control exist。

In SinSee three goals are targeted with respect to numerical simulations:

1。dedicated model tests are carried out in order to produce reliable and suitable data for the validation of numerical methods。 For the val- idations purpose as such different approaches are used to identify different weaknesses (i。e。 in the wave or force model respectively)。

2。existing numerical tools are being further de- veloped based on the findings。 These models are developed to support the ship design pro- cess, therefore it is necessary that the numeri- cal tools are fast and robust at sufficient relia- bility。

3。methodologies are being developed to assess the safety of ship’s with respect to intact sta- bility。 Results from this part of the project are also presented at this conference by Kru¨ger et al。

Design evaluation and optimization based on numerical simulations

In order to improve the sea keeping characteristics of a design it is important to identify, evaluate and un- derstand the deficiencies a design might have。 Fig。 1 shows a plot of the roll angle and the wave eleva- tion versus time, of a situation were a container ship encounters extreme angles of roll due to parametric excitation。

Figure 1: Roll angle and wave elevation versus time for a containership encountering parametric excita- tion

Such detailed simulations are used to study the phe- nomena endangering the respective vessel in detail and develop possible design alternatives。 While for design comparisons and the evaluation of the ship’s seakeeping performance usually the results from nu- merous simulations are summarized in polar plots。