Author: Yiren Qin
Date/Time: June 19th, 2025 at 11:00 AM – 1:00 PM EST | Zoom: Meeting ID: 437 810 4474 Passcode: DZ24RZ
Location: JMP 3106B, J.M. Patterson
Committee Members:
- Dr. Arnaud Trouvé, Chair
- Dr. Cinzia Cirillo, Dean’s Representative
- Dr. Fernando Raffan-Montoya
- Dr. Peter Sunderland
- Dr. Shuna Ni
- Dr. Stanislav Stoliarov
Title of Dissertation: A Physics-Based Eulerian Framework for Modeling Firebrand Showering in Regional-Scale Wildland and Wildland-Urban Interface Fire Simulations
Abstract: Landscape-scale fire risk modeling plays a vital role in fire management as global wildfire activity continues to escalate. The objective of this dissertation is to extend the capabilities of an existing landscape-scale wildland fire spread simulation tool, ELMFIRE, to simulate conflagrations that propagate across Wildland–Urban Interface (WUI) communities. ELMFIRE employs a level-set formulation to describe flame spread and accounts for surface and crown fire dynamics in wildland environments. Recent extensions include ignition of structures and structure-to-structure fire propagation in the WUI via thermal radiation and direct flame contact.
Particular attention is devoted to modeling firebrand processes—specifically, generation, atmospheric transport, and spot ignition. The firebrand generation model employs an empirical correlation based on the local heat release rate, with separate generation rates estimated for biomass and structural fuels. A numerically robust algorithm is proposed and verified to ensure that the number of firebrands generated is independent of the simulation time step.
The firebrand transport model uses prescribed statistical distributions for ember flight distance and incorporates a simplified flight time formulation. A series of verification tests using MATLAB were conducted in one- and two-dimensional academic configurations. These tests demonstrate that the firebrand models are numerically converged—i.e., they remain stable under varying grid and time resolutions—provided the wind-based Courant–Friedrichs–Lewy (CFL) number remains below a defined threshold.
The firebrand ignition model assumes two consecutive time delays: the first represents the smoldering-to-flaming transition and is governed by an empirically derived probability of ignition; the second models flame growth using a $t$-squared law. Additional verification cases were performed to evaluate numerical accuracy. A firebrand consumption model is also proposed to account for the finite lifetime of deposited firebrands, which can influence ignition dynamics.
These firebrand models were coupled with the surface and WUI fire spread models to simulate multi-mechanism fire spread in WUI environments. The combined framework was tested in the MATLAB-based one-dimensional setting to analyze firebrand-driven structure-to-structure fire spread under varying wind speeds, building sizes, and separation distances. The results include a sensitivity analysis of spatial and temporal discretization and criteria for successful firebrand-induced ignitions.
The complete modeling framework—including the proposed firebrand models and WUI fire spread mechanisms—was integrated into ELMFIRE. A comprehensive preprocessing pipeline was developed to generate ELMFIRE-compatible GIS inputs using publicly available datasets and tools, including LANDFIRE, RTMA, the Microsoft Building Footprint dataset, WindNinja for wind field upscaling, and the NFDRS4 model for fuel moisture estimation. This pipeline automates data acquisition and processing to support reproducible simulation workflows.
The full framework was finally applied to reconstruct the 2017 Thomas Fire to evaluate sensitivity to both model improvements and input data quality. Results demonstrate that the proposed model improves predictive fidelity while offering physically interpretable insights. The study highlights the importance of future research on subgrid-scale modeling in WUI areas and the use of higher-resolution, dynamically consistent input datasets.