A Novel Approach Combining Bootstrapped Non-Intrusive Reducedorder Models and Unscented Transform for the Robust and Efficientcfd Analysis of Accidental Gas Releases in Congested Plants

The risk assessment for safety-critical, complex systems is avery challenging computational problem when it is performedwith high-fidelity models, e.g. CFD, like in the case of acci-dental gas releases in congested systems. Within this frame-work, a novel CFD approach, named Source Box AccidentModel, has been recently proposed to efficiently model suchphenomena by splitting the simulation of the gas release andits subsequent dispersion in the system in two steps. In thisview, the present paper proposes a non-intrusive, Proper Or-thogonal Decomposition-Radial Basis Functions reduced or-der model that exploits the two-step nature of the SBAM ap-proach, to mimic the behaviour of the original, long-runningCFD model code at a significantly lower computational cost.Moreover, the paper presents a methodology combining thebootstrap and unscented transform approaches to efficientlyassess the ROM uncertainty in the safety-critical simulationoutput quantities of interest, e.g. the flammable volume. Theresults obtained in a test case involving a high pressure, ac-cidental gas release in an off-shore oil&gas plant are in verysatisfactory agreement with those produced by CFD, with arelative error smaller than 10% and a reduction in the com-putational time of about three orders of magnitude