Abstract
The air flow surrounding offshore helidecks is subjected to many perturbations and obstacles that may represent additional risks to helicopter operations. There are some standards and recommendations for offshore helidecks that establish some thresholds in terms of turbulence and temperature levels that are acceptable for helideck location during early stages of offshore platforms design (e.g.: CAP437 and NORSOK C-004). Nowadays it is usual to perform such evaluations by using Computational Fluid Dynamics (CFD) techniques. Although the hot gas plume evaluation through simulations is done by the temperature field evaluation directly, the turbulence parameter suggested by the standards is not straightforward to obtain from traditional turbulence modelling approaches adopted in CFD. As already discussed in previous publications, the turbulence criteria can be obtained as a function of the turbulent kinetic energy, which is available in traditional RANS (Reynolds Average Navier Stokes) models. This paper illustrates a systematic approach of turbulence and hot gas plume evaluation around offshore helidecks using CFD. The simulations were performed using real case studies for three different offshore unit concepts, namely a semi-submersible, a spread moored and turret moored FPSO (Floating, Production Storage and Offloading). The results are interpreted in terms of the expected risk levels for each key variables threshold. The temperature evaluation method is based on NORSOK C-004 Temperature Gradient Matrix (TGM) and for turbulence, this paper presents a similar and novel approach, called Turbulence Kinetic Energy Gradient Matrix (KGM) according to the standard deviation of vertical velocity levels cited in CAP-437.
