ABSTRACT

This paper presents the results of the wind loads on typical offshore vessels at model scale 1:250 obtained with CFD simulations. A FPSO, shuttle tanker and two membrane/moss type LNG carriers have been investigated, as well as the side-by-side configuration of FPSO and shuttle tanker with a gap of 4m. The results are compared with the wind tunnel tests carried out within the Offloading Operability 2 JIP. The CFD code ReFRESCO is used. In this study, the simulations are carried out as a steady state problem and the k-ω SST model is used as turbulence model.

In order to efficiently solve every incidence angle from 0 to 360 with 15 degrees intervals, a cylindrical numerical domain is used. The numerical uncertainty has been determined using four consecutively refined grids. The results for the FPSO, shuttle tanker and membrane LNGC show a good agreement with experiments. For these vessels, the flow separation point is geometrically defined. The moss type LNGC is more difficult to compute accurately since the separation points on hemispherical tanks are difficult to capture.

The side-by-side configuration with the FPSO and shuttle tanker has 4m gap between the vessels. The calculated coefficients agree well with the experiments and the overall trends are nicely captured, except for a slight deviation for the yaw moments from 135 to 180 degrees. From the results presented in this paper, we conclude that the wind loads on offshore vessels in side-by-side configuration can be predicted with reasonable accuracy with CFD.

INTRODUCTION

Wind loads on operating vessels and offshore structures play an important part in ship motions, maneuvering situations and mooring of offshore constructions at sea. The function and safety of floating vessels is dependent upon an accurate prediction of the wind loads at the design stage. The impact of wind loads is increasingly important as vessels become larger and operating speed increases (Andersen, 2012). Wind loads can reach around 20% of the total loads, and there is a large decrease of the vessel speed and an increase in the required horsepower when it is rough weather (Lee et al, 2013; Fujiwara et al, 2006).

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