Session: 01-06-01 CFD Modeling and Offshore Applications

Submission Number: 177747

Assessment of Wind Gust Effects on the Flow Around Offshore Helidecks Using RANS Simulations 

Helicopters play an important role in supporting offshore platform operations, providing crew transportation, equipment delivery, and, in critical situations, emergency evacuation and search-and-rescue missions. Despite their versatility, their operations in offshore environments can be very challenging. Among various contributing factors, airwake turbulence has been identified as a major source of operational risks during offshore landing.

Offshore helidecks are highly exposed structures, directly subjected to unsteady aerodynamic loads generated by turbulent winds. During helicopter landing and take-off operations, wind gusts can produce large and sudden variations in local flow velocity, leading to strong velocity fluctuations above the deck and surrounding structures. Understanding and quantifying these effects are essential for ensuring safe operating conditions and defining reliable design standards.

To ensure safer and less restrictive operations, regulatory agencies, such as the Civil Aviation Authority (CAA) and NORSOK, have proposed turbulence-based criteria to be considered in the design of helidecks and superstructures on offshore platforms. These criteria are based on vertical velocity fluctuations or turbulence kinetic energy (TKE) encountered at specific control points positioned above the helideck. 

Within this context, the present study aims to contribute to the ongoing effort to analyze the flow dynamics around a generic HVDC converter offshore platform, with particular attention to regions critical for helicopter operations. This platform features an octagonal helideck, two cranes, three box-shaped structures, and a turret positioned on top of one of the boxes. The analysis is conducted through full-scale unsteady RANS simulations in STAR-CCM+, using the k-ω SST turbulence model. An overset mesh approach is adopted to facilitate simulations at various inflow angles and velocity distributions, under both steady and unsteady conditions.

In fact, the simulations incorporate time-varying inlet profiles that reproduce wind gusts measured in the Baltic Sea during an offshore installation campaign. The recorded gusts are characterized by amplitude and frequency parameters derived from field measurements, enabling the numerical model to reproduce realistic unsteady wind conditions acting on the helideck.

The study provides a practical framework for simulating these gusty wind conditions using RANS models, balancing computational efficiency and physical accuracy.

Validation was carried out under steady inflow conditions using model-scale experiments conducted in the low-turbulence wind tunnel at the Hamburg University of Technology (TUHH). For steady inflow, a highly complex flow field emerges, characterized by the interaction of multi-scale vortical structures. For the same inflow velocity, the highest values of TKE are predicted at wind directions, for which the shear layer detached from the neighboring superstructures interacts with the vortical structures separating at the helideck’s edges.

The simulations for unsteady inflow conditions extend this analysis, providing a quantitative description of how gusts modify the TKE distribution and local flow organization above the helideck. The study evaluates the extent to which steady-state analyses may underestimate unsteady aerodynamic effects and identifies the inflow angles and gust characteristics most critical for helicopter operations.

The outcomes of this work will ultimately support the development of design guidelines and operational standards for offshore helidecks, enhancing safety margins for helicopter operations in offshore environments.

The paper complements a companion study that focuses on the acquisition, modeling, and experimental reproduction of wind gusts from the data collected in the Baltic Sea. Together, they aim to establish an integrated methodology that unites field measurements, data-driven modeling, experimental, and numerical campaigns to characterize offshore wind gusts and evaluate their impact on offshore installations and their operational safety.

Presenting Author: Ginevra Rubino Hamburg University of Technology (TUHH)

Presenting Author Biography: Dr. Ginevra Rubino is a postdoctoral researcher in the Fluid Dynamics and Ship Theory group at the Hamburg University of Technology. She received her Bachelor's degree in Mathematics from Università La Sapienza in Rome in 2015. She then obtained her Master's degree in Mathematical Engineering from the Polytechnic of Turin in 2017 and an M2 in Computational Mechanics from the Ecole Centrale Nantes in the same year. In 2021, Dr. Rubino successfully defended her Ph.D. at the Ecole Centrale Nantes. Her doctoral research focused on laminar-to-turbulence transition modeling for incompressible flows in a RANS framework. Her main research interests revolve around turbulence and transition modeling.

Authors:

Ginevra Rubino Hamburg University of Technology (TUHH)
Jochen Schoop-Zipfel Ingenieurbüro Dr.-Ing. Schoop GmbH
Ahmed Sahab Hamburg University of Technology (TUHH)
Moustafa Abdel-Maksoud Hamburg University of Technology (TUHH)