@article {bnh-6819, title = {Physics-based simulation of firebrand and heat flux on structures in the context of AS3959}, number = {560}, year = {2020}, month = {04/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Firebrand is known as one of the most dangerous airborne components of wildfires having the potential to ignite structures in Wildland-Urban Interface (WUI). Quantifying the firebrand and heat flux on structures is essential to determine the wildfire risks and prepare strategic plans to mitigate the hazard. We endeavor to use a physics-based model, Fire Dynamic Simulator (FDS) to map firebrand and heat flux to determine the vulnerability of structures in WUI. In this study, we have validated FDS{\textquoteright} tree burning and firebrand transporting sub-models against the experiment conducted in no wind condition at the National Institute of Standards and Technology (NIST). The experimental data of firebands were processed to use as inputs in the numerical simulation and the grid convergence was appraised in terms of mass loss rate (MLR). The intial velocity and direction of firebrands, the number of generations were determined as model inputs by a reverse analysis through comparing firebrand distribution with the experiment. As the FDS{\textquoteright} sub-models were validated, we attempted to quantify the heat flux and firebrand risk on a structure at three different driving wind velocities. Increasing wind speed showed more firebrands transported towards the structure but none of them landed on the house because of the low height of the tree and insufficiency of fire-induced buoyancy to lift them enough to carry a longer distance by the wind field. Similarly, heat flux computed on the structure is well below Australian building standard AS3959{\textquoteright}s bushfire attack level (BAL). it is due to the low heat release by single tree burning instead of a 100m wide fire line assumed in the standard. In future study, simulations will be conducted with a cluster of taller trees (100m wide) to quantify the heat flux and firebrand hazard on structures to apprise AS3959.

}, keywords = {firebrand, heat flux, physics simulation, structures}, issn = {560}, author = {Amila Wickramasinghe and Nazmul Khan and Khalid Moinuddin} } @article {bnh-7242, title = {The effect of ignition protocol on grassfire development}, journal = {International Journal of Wildland Fire}, volume = {29}, year = {2019}, month = {11/2019}, pages = {70-80}, abstract = {

The effect of ignition protocol on the development of grassfires is investigated using physics-based simulation. Simulation allows measurement of the forward rate of spread of a fire as a function of time at high temporal resolution. Two ignition protocols are considered: the inward ignition protocol, where the ignition proceeds in a straight line from the edges of the burnable fire plot to the centre of the plot; and the outwards ignition protocol, where the ignition proceeds from the centre of the burnable fire plot to the edges of the plot. In addition to the two ignition protocols, the wind speed, time taken for the ignition to be completed and ignition line length are varied. The rate of spread (R) of the resultant fires is analysed. The outwards ignition protocol leads to an (approximately) monotonic increase in\ R, whereas the inward ignition protocol can lead to a peak in\ R\ before decreasing to the quasi-equilibrium\ R. The fires simulated here typically take 50 m from the ignition line to develop a quasi-equilibrium\ R. The results suggest that a faster ignition is preferable to achieve a quasi-equilibrium\ R\ in the shortest distance from the ignition line.

}, keywords = {grassfire, ignition, physics simulation}, doi = {https://doi.org/10.1071/WF19046}, url = {https://www.publish.csiro.au/WF/WF19046}, author = {Duncan Sutherland and Jason J. Sharples and Khalid Moinuddin} }