Study on the Change in Fluid Dynamic Characteristics due to the Recess Deck inside the Drillship Moonpool

Abstract A drillship is a floating offshore structure used to perform drilling operations, marking the initial stage of oil field development. At the center of the drillship is a moonpool, through which the drilling riser is lowered to conduct drilling activities. Violent flows often occur inside the moonpool due to moonpool resonance, and these abnormal oscillations can directly affect operator safety and increase operational downtime. Therefore, minimizing violent flow within the moonpool is crucial for ensuring safety and maximizing operational efficiency. To achieve this objective, optimization of the recess deck geometry is essential in moonpool design. This study investigates the fluid dynamic characteristics inside the moonpool under variations in recess deck height. Changes in free-surface elevation and flow behavior were closely examined at specific locations within the moonpool for with and without recess deck configuration. Furthermore, the study compares and analyzes the impact forces and flow characteristics acting on the splash plate with and without the recess deck. Results show that variations in recess deck height lead to significant changes in the internal flow pattern. From the comparative analysis of free-surface elevation, an optimal recess deck height that effectively mitigates violent flow inside the moonpool is proposed. Additionally, model test results reveal distinct differences in fluid impact forces on the splash plate between configurations with and without a recess deck. Overall, this study provides valuable experimental and numerical data and fundamental insights for optimizing the moonpool geometry of drillships.