The purpose of the moonpool in a drillship is to provide a sheltered and protected access to the sea for the safe and easy deployment of equipment used for drilling, diving, etc. However, in certain wave conditions, this function is impaired due to a hydrodynamic resonance that can lead to significant amplification of the wave elevation inside the moonpool. Beside the impact on operability, this amplification can result in large pressures that must be accounted for in the design of the vessel. Usually for the direct computation of hydrodynamic pressures, potential flow theory is employed, which is based on the assumption of a perfect fluid. This approach is known to overpredict the wave elevations close to the moonpool resonance frequencies, as it neglects viscous effects that in reality play a major role in limiting the wave kinematics. Thus, applying potential theory, without special treatment, may induce undesired over conservatism in the scantling of the structural elements in the moonpool region. As an alternative to potential flow, modelling techniques based on the solution of Navier Stokes equations (CFD) can potentially provide accurate results. The main drawback of these tools is that they are costly solutions and their application should be practically limited to a number of selected critical cases. This paper will present the results obtained from the assessment of wave elevations / hydrodynamic pressures on the moonpool of a drillship using CFD computations in calm water for calibrating a potential flow model.

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