Negative air gap and wave slamming load on the deck box of drilling semi-submersible units in severe storm have received a great deal of attention, due to the COSL Innovator accident in 2015. Equally important is vertical slamming load on the MODU underdeck, which is less reported in the literature. The present paper attempts to derive characteristic vertical slamming pressure on the deck bottom, based on an extensive model test program for a drilling semi-submersible unit, CM-SD1000. 
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The test program conducted a total of 96 wave impact tests including 4 sea states selected along the DNV steepness curve in 3 wave headings. Two critical sea states were identified and each was tested with 16 random realizations in 2 wave headings. 8 force panels were installed on the underdeck to capture vertical wave impact events. This allows us to derive the extreme vertical wave impact pressure in a statistical way. 
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Meanwhile, a linear radiation-diffraction analysis is performed using WAMIT to predict extreme values of upwell and relative vertical velocities. An attempt is tried to establish a correlation between the predicted relative vertical velocity and the wave slamming pressure. Such a correlation, if valid, would help structural scantling design for the deck bottom in the early project phase before model testing. &nbsp;&nbsp;

Underdeck Wave Slamming Model Tests for a Drilling Semi-Submersible Unit

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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