An Investigation on Turbulence Assessment Methods for the Offshore Helideck Availability Study

The aim of this study is to investigate methods of assessing the turbulence effect for the helideck availability study. Due to the limited space on offshore platforms, a helideck is normally positioned on cramped areas and this makes turbulence flows around the helideck. CAP 437, the representative standard for the offshore helideck design suggests various criteria for the helideck availability assessment and recommends a Standard Deviation of Vertical airflow Velocity (SDVV) value to be used for the turbulence effect assessment. Although there is a specific value of SDVV recommended in CAP 437, different interpretations are possible in the calculation of the value resulting in totally different assessment outcomes even under the same analysis condition. In this study, two different approaches are investigated and their results are compared. One approach is based on the spatial variation of the mean vertical velocity while the other utilizes the Turbulence Kinetic Energy (TKE) value from the Computational Fluid Dynamics (CFD) simulation. With a CFD tool, Kamelon FireEX (KFX), a couple of 3-dimensional simulations is performed and turbulence flows around an offshore semi-rig are obtained. SDVV values are calculated using both approaches and compared each other as well as with criteria recommended in CAP 437. It is hoped that the result of this study is helpful to engineers for understanding evaluation methods of turbulence effects in the helideck availability assessment.