The flow dynamics in a moonpool is evaluated through analysis of experimental and numerical time series of surface elevations. Experimental results are obtained in the context of the interaction of irregular waves with the barge. The excitation of natural sloshing and piston modes is investigated as well as wave transmission in the bay. Dedicated numerical simulations of extinction tests of piston and sloshing modes are also performed, using a time domain potential flow solver. Three-dimensional effects are pointed out and a good agreement is found between experimental, numerical and analytical estimations of the moonpool natural frequencies.
Recent studies on flow dynamics in moonpools of FPSOs or barges showed that 3D effects cannot be neglected, (Maisondieu & Le Boulluec 2001), and are to be investigated, especially when the bay is large compared to the size of the floating unit itself. Natural sloshing and vertical modes in the bay, which can be considered as a bottomless tank, may be excited by pressure fluctuations along the hull induced by the travelling waves or by the motions of the barge. Such water motions in the moonpool can alter the response of the floating structure and possible coupling, mostly with heave, roll and pitch motions are likely to occur. Evaluation of the flow in the bay and below is also of major interest for the design and the distribution of the aircans fixed to the upper part of the risers as tensionning floats. Decay tests of the piston and sloshing modes in the moonpool are performed and natural periods are compared to analytical solutions and experimental results.
Tests were carried out on a model of the Wellhead Barge (WHB®), which is designed with an unusually large moonpool. The experimental set-up is described in Maisondieu & Le Boulluec, 2001.