Cooperative Research Navies continues code improvement and validation 20 years on


In 2010 the Cooperative Research Navies (CRN)


group celebrates its 20th anniversary. This milestone seemed a good opportunity to outline recent projects.


Frans van Walree f.v.walree@marin.nl


CRN mainly focuses on the prediction and validation of extreme motions and capsize risk assessment through the use of the FREDYN simulation program. CRN members include DSTO (Australia), DMSS (Canada), DGA (France), DMKM (Netherlands), MARIN, MoD-DES (UK), NSWCCD (USA) and USCG (USA). Associated members include DRDC (Canada), BEC (France), NAVSEA (USA) and Qinetiq (UK).


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Water on deck project Ships with a relatively low freeboard operating in heavy seas may be subject to extensive deck wet- ting which can drastically reduce stability. In order to better predict the relative wave height at the deck edge, Fredyn has been extended with a module that accounts for the wave disturbance by the ships forward speed and wave diffraction. Simulations showed that the midship wave trough at (high) forward speed especially reduces the occurrence and extent of deck wetting. Comparisons with the model tests in heavy seas (see Figure 1) indeed prove that the capsize risk can be reduced significantly when water on deck can be accounted for more accurately, see Figure 2.


Figure 1: High roll motion without capsize and very low amount of green water in stern quartering seas


Flooding of damaged ships While the flooding method was already validated for relatively small damage openings, some- times these openings can be large and the resulting process often appears chaotic. In order to investigate this, DSTO conducted model tests at the Australian Maritime College. A generic destroyer hull form and compartment arrangement was subject to flooding tests in calm water and in waves. Tests were performed with constrained,


2002 16 16


Full-scale CFD validation in EFFORT-project


Figure 2: Capsize risk in stern quartering seas with and without correction for wave disturbance. Note that except for the second 18 kt case, the experimental capsize risk is essentially zero.


Figure 3: Comparisons between predicted and experimental compartment water levels


forced and free model motions. Figure 3 shows the experimental and simulated water height in a compartment when the model is subject to forced motions. This figure also shows the relevance of experi- mental uncertainty associated with flooding model tests.


For more information see the news item on the 11th International Ship Stability Workshop in this Report.


2003


First PIV flow measurements


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