Recent progress in fire simulations using NMF and automatic translation to IDa

The simulation of temperature and pressure development in the ventilation systems of an offshore oil platform during the initial phase of afire has been carried out using the IDA solver (IDA 1991). This paper focuses on the utility shaft and its ventilation system. The simulations are part of a project for the Norwegian oil company Statoil. That project is a total analysis of the situations in case of afire, with the objectives to decide the strategies of smoke control during the early stage of the fire. Different scenarios are analyzed and the simulation results are used together with lab measurements, CFD modelling, and experiences from real fires. The simulations are strongly aided by automatic translation from the Neutral Model Format (NMF) (Bring, Salhin and Sowell 1992) to IDA. The translator (NEUTRAN), which supports the current NMF definition, creates all the necessary FORTRAN code for IDA and also generates an input file. The connections among the components and the handling of the initial values are achieved by a simple system definition language. Some important effects that arise under a fire, such as stack effects and the effects caused by air expansion, are usually not modelled in a conventional air flow program. However, both have significant influence on pressure development in tall constructions and may cause undesired pressure differences during afire. The effects of air expansion cause a considerable pressure rise in the air enclosures only seconds after the fire begins and may even make the air flow change direction at the inlet; modelling this change of direction is quite a comprehensive task using one of the currently available modular simulation programs. The problem is solved in a crude way in the presented study, creating anew model each time the air flow rate crosses zero in any part of the system. This causes one simulation to become a series of simulations, each starting at the end state of the previous. The method can be used with any modular simulation program. This paper presents one of the scenarios from the fire simulations and shows the different problems that arise and how they are solved using NMF in combination with IDA and NEUTRAN.