Trans RINA, Vol 152, Part A4, Intl J Maritime Eng, Oct-Dec 2010 EXPERIMENTAL AND NUMERICAL STUDY ON PROGRESSIVE FLOODING
IN FULL-SCALE (DOI No: 10.3940/rina.2010.a4.195)
P Ruponen, Napa Ltd, Finland P Kurvinen, Aalto University School of Science and Technology, Finland I Saisto, VTT, Finland J Harras, Finnish Naval Research Institute, Finland
SUMMARY
A series of full-scale flooding tests was performed with a decommissioned fast attack craft. Various flooding scenarios were investigated and the floating position and progress of the floodwater were carefully measured. Also air compression inside a flooded tank was studied. The results were used to validate a state-of-the-art numerical flooding simulation tool. A comprehensive analysis of the experimental and numerical results is presented. A good correlation is found, especially when the applied permeabilities and discharge coefficients are properly selected. Finally, the stability of the flooded ship was studied by comparing the results of an inclining experiment and calculations with the lost buoyancy method.
1. INTRODUCTION
A breach in the hull of the ship, due to a collision or grounding,
results in flooding of the damaged
compartments. Passenger ships and navy vessels usually have a complex internal subdivision. Thus progressive flooding, even within a single watertight compartment, can result in a dangerous situation due to transient asymmetric
flooding can only be assessed with a approach.
flooding. These intermediate phases of time-domain
Flooding and damage stability have been studied in numerous model tests throughout the years, for example in [1], [2] and [3], to mention just a few. Recently the increased computing capacity has allowed also detailed numerical analyses, and various time-domain simulation tools for progressive flooding have been developed. The experimental results have been used to validate the calculation methods, for example in the recent ITTC benchmark studies, [4].
Flooding of a real full-scale ship involves factors that are difficult, or even impossible, to take into account in model tests. One of these is the air compression inside a damaged tank with a limited ventilation level. Previously, e.g. Palazzi and de Kat [2] have reported model tests, where also the air compression was included. The problem is that in model scale air is much stiffer and the compression does not follow Froude’s scaling law. A depressurized towing tank is one solution for avoiding this problem, but
still some full-scale
experiments were considered to be necessary in order to get a better insight into the flooding characteristics of a tank with restricted ventilation.
The real permeability of the flooded compartments can differ notably from the model test arrangements, where impermeable blocks are often used to model the large equipment, such as engines, [4]. Also thicker decks and
©2010: The Royal Institution of Naval Architects
Flooding of two watertight compartments was allowed. A butterfly valve with a diameter of 250 mm was installed on the side shell of the starboard side empty tank (Figure. 2), about 1.1 m below the waterline. The valve was opened by a diver in order to let the water flood in. The flooded compartments consist of empty tanks, pump room, equipment room and an empty store. An additional opening was installed on the transverse
A-197 bulkheads are needed in model scale for structural
reasons. On the other hand, the stiffeners and small equipment are completely ignored. Also the flow through various openings can be different due to the scale effects.
In order to provide further information on the different flooding mechanisms and to validate a numerical time- domain flooding simulation code, a national research project was carried out in Finland. A decommissioned vessel of the Finnish Navy provided a unique opportunity for the full-scale flooding tests. The experiments were performed by the Finnish Naval Research Institute. VTT (Technical Research Centre of Finland) carried out the measurements while Napa Ltd and Aalto University (former Helsinki University of Technology) were responsible for the planning of the tests, numerical simulations [5] and the final analysis of the results.
In this paper the test arrangement and measurements are presented. The main emphasis is on the comparison of experimental and numerical results.
2. TEST ARRANGEMENT 2.1 FAC TURKU
The vessel that was used in the tests is a decommissioned Fast Attack Craft Turku of the Finnish Navy (Figure. 1). The principal dimensions of the vessel are listed in Table 1. The weapon systems had been removed and additional weights were used to compensate this.
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