In an effort to improve offshore platform safety standards, oil giant BP Amoco is working with engineers from Fluent Europe Ltd. on the design of a new platform. The platform, which will be based in waters off Vietnam, is still in the design stage. Among the many safety issues to be examined are the environmental conditions in the vicinity of the helideck, which is used for helicopter landing and take-off.

In particular, the Fluent Europe team has focused on modeling the path of hot exhaust gases discharged from the gas turbine power generators, and how these gases are dispersed around the platform and helideck. The model predicts the temperature rise in the vicinity of the helideck as a result of the exhaust emissions. Helicopters engulfed by hot gas plumes could suffer a loss of lift, which in extreme circumstances could result in an uncontrolled descent and heavy landing.

The platform geometry, designed using CAD, was read into GAMBIT and embedded within a numerical mesh. The model was then solved for a range of wind speeds and wind directions to establish how often the helideck will be exposed to temperature rises greater than the 2° F threshold contained in the UK Civil Aviation Authority (CAA) guidelines in CAP 437. These guidelines are constantly reviewed and updated, most recently following a heavy-landing incident in 1995 on the Claymore Accommodation Platform when, during the final stages of approach to the helideck, a Sikorsky S61N helicopter was engulfed by a hot gas plume. The helicopter lost height and landed abruptly and heavily, resulting in considerable mechanical damage. If an offshore helideck does not satisfy the guidelines, it is recommended that the appropriate helicopter advisory board be notified, which may result in flying restrictions.

Platform model showing the flow path of gas from the gas turbine exhaust. Path lines are colored by the plume temperature, which falls as the hot gas mixes with the surrounding air.

Using Fluent's CFD simulations, BP and its partners on the project - Statoil, Petro Vietnam, PVEP, and ONGC Videsh Limited - have analyzed the effect of hot exhaust gases on helicopter operations at the proposed platform. Using CFD techniques, they have modeled many different conditions within a matter of weeks and provided immediate feedback to the design team. In addition, the FLUENT simulation has not only allowed the full path of the exhaust plume to be modeled, but also the full flow-field around the platform. This means that other ventilation and dispersion effects can also be assessed and understood.

Today, it is necessary to prove safety in order to meet the standards of the legislative body for the oil and gas industry. By using Fluent's engineering and CFD expertise, BP is aiming to exceed these standards.

Flow velocity vectors on a surface 1m above the floor. The simulations identify low-velocity regions behind process equipment that impact the ventilation and dispersion effects. Flow velocity vectors on a surface 1m above the floor. The simulations identify low-velocity regions behind process equipment that impact the ventilation and dispersion effects.

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