navyspecial


parameters are changing very slowly to an almost stationary value. This could mani- fest itself in a run where the model has a constantly changing drift angle. Such an approach can lead to very strange trajecto- ries. Figure 2 shows a range of these tra- jectories as carried out with the naval combatant in MARIN’s Seakeeping and Manoeuvring Basin. The first figure shows a traditional rotating arm test, while the second figure shows a traditional PMM test. At the maximum transverse ampli- tude, the ship has achieved a rate of turn and this rate of turn is the value that is used in the mathematical model.


angle, with results obtained using traditional captive drift tests. The right hand figure shows the typical trajectory, while the left hand figure is showing the correspondence of the results. A near perfect match is achieved!


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The third figure gives the unconventional manoeuvres. Figure 3 shows how in one run through the Seakeeping and Manoeuvring Basin four radii are tested and hence, information is obtained on four steady states. A photograph is shown with the trajectory of the naval combatant in the Seakeeping and Manoeuvring basin. The captive connection between the towing carriage and the model can be seen. A yoke is mounted which allows the model to trim and sink during the tests. But the motions in all other directions are restricted, so that forces and moments can be measured.


Does it work?


So to the million-dollar question, do these results give the same answers as a tradi- tional approach? Figure 3 shows a sample of the results. It compares the results of a test with a continuously changing drift


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And the future? The range of applications goes further. Not only a continuously changing drift angle or rate of turn is possible, also a continu- ously changing combination of rate of turn and drift angle can be done. The results of these measurements are displayed and indeed, using fewer model tests, they provide a complete description of forces and moments for the creation of a mathe- matical model.


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