At MARIN, we think that it is time for a change and consequently, we are making substantial investments to improve our ser- vices related to ART design. The objective is to provide accurate advice to our clients in the early design phase, based on up-to- date knowledge and tools.
Numerical tools upgrade Firstly, our RANS-CFD Code ReFRESCO has undergone a major update and now takes free surface flow into account. With the latest version of ReFRESCO, it is possible to simulate the water motions inside an ART under pre- scribed regular and irregular motions in the six degrees of freedom. The Code computes the flow inside the tank, as well as the associated reaction forces. A key feature of the upgrade is that the internal arrangement of the ART can be accounted for in detail (see Figure 1). Consequently, it is possible to compare different tank layouts and internal arrangements, in order to reach the optimal configuration. In parallel with the ReFRESCO developments, a coupling was established between the time domain simulation code FREDYN and the CFD Code COMFLOW (see Figure 2). This coupling enables MARIN to conduct a time domain calculation of the ship motions in a given sea state, which accounts for the reaction forces of the ART. The main advantage of the coupling lies in the fact that the actual tank geometry, loca- tion and filling level, are taken into account in the prediction of the reaction forces in a more accurate way than in the past. A further extension of the coupling method to other software available at MARIN is currently under discussion.
Anti Roll Tank Facility In addition to upgrading the numerical tools, the model testing capabilities were also extended significantly. In the first place, the Anti Roll Tank Facility officially came into service. This facility consists of an oscillating table, the design of which was largely reconsid- ered in order to provide a modern tool for assisting in ART design, as well as bench testing for the validation of our software. It provides a relatively inexpensive way of conducting a comparative design study at model scale. Several parameters such as vertical location or filling height can be adjusted to reach the optimal solution. The associated post-processing tool has also
Figure 2: 2D simulation of the flow inside a U-type ART
been modernised and now facilitates an easy coupling of the measured response with most of our seakeeping software. Besides the Anti Roll Tank facility, the recently ac- quired hexapod system, which can generate all translations and rotations, will be used as a tool to better understand the influence of ship motions and coupling effects. In the light of these developments, model tests featuring free-sailing models fitted with ART should not be forgotten. Through the years, MARIN has built up a great deal of experience in testing free surface and U-type ART in wave basins. Suggested test programmes include specific tests
resulting in a complete description of the ART per formance, in combination with tests representing realistic wave conditions at zero speed and in transit in various head- ings. During the tests, the risk of adverse performance - in other words worse rolling behaviour ith the ART fitted than without - is also assessed.
The fully modernised experimental set-up and numerical tools will be made available to clients in the coming half year. Currently, the first results are being reported and they will be published next year.
report 13
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