Investigation of wind and smoke concentration effects on thermal instability of cylindrical tanks with fixed roof subjected to an adjacent fire

摘要

Fire loading on structures generally involves considerable degrees of uncertainties due to surrounding environmental conditions. Therefore, a reliable structural analysis depends on a proper evaluation of fire disturbing parameters such as wind and smoke concentrations. Wind intensity and direction could affect the heat flux distribution on the structures. Also, smoke (soot) concentration would decrease radiation intensity. Fair prediction of such uncertainties requires multi-physics structural and fluid dynamic approaches, which will be more complicated in the case of structural instability problems. In this research, for the first time, the effect of wind and soot concentration on thermal instability of cylindrical tanks is studied through fire simulation and nonlinear structural analysis. The Large Eddy Simulation (LES) approach is implemented for the fire dynamics analysis, and the Arc-length method is exploited in the case of structural stability calculations. In the Computational Fluid Dynamics (CFD) model, the wind intensity and direction and soot concentrations are considered as disturbing parameters. By conducting LES simulations, heat flux distribution on the fire exposing surfaces of the cylindrical tanks has been estimated. Afterward, the obtained data is transferred into Abaqus/heat transfer, and ultimately, the nonlinear Arc-length structural analyses are conducted. The results reveal that normal direction wind against the container could escalate the heat flux up to 25 times of the windless condition. Also, it is observed that there is a wind speed domain, in which the thermal stability threshold would be maximized. Moreover, the Heat Release Rate (HRR) of fire plays an important role in agitating the instability, while its effects on thermal instability threshold and corresponding mode shapes are negligible.