This project focused on a significant expansion of the high fidelity Eulerian two-phase model, SedFoam, to simulate mobility and burial dynamics of unexploded ordnance (UXO) driven by waves and currents. The main technical objective of this project, developing the next-generation Computational Fluid Dynamics model to simulate burial dynamics by resolving flowstructure- sediment interactions, is motivated by knowledge gaps identified by several field observations from SERDP sponsored studies. To address these knowledge gaps, the scientific objectives were to: Simulate self-burial processes in energetic conditions that often lead to full burial. Investigate the role of UXO density in the burial dynamics. Develop proper nondimensional parameters to describe energetic burial relevant to field observations.

The implementation of full object-sediment-fluid interaction capability with six-degree-offreedom into SedFoam was successful during the first half of the project. New benchmarks were established for simulating the mobility and burial dynamics of UXO via validating the model with a series of laboratory experiments on the initial motion behavior of a short cylinder driven by an accelerating current and various burial behaviors driven by oscillatory flows. Through communications with SERDP sponsored researchers in field observations and data-driven modeling, more than 30 high-fidelity numerical simulations were designed to fill the data gaps, particularly, to address the role of UXO density, wave intensity, wave period and wave angle on burial dynamics.

Simulation results reveal insight into self-burial by fluidization and a transitional regime, named rapid scour burial, between scour burial and fluidization. As burial by fluidization occurs within a timescale of a few wave periods, rapid scour burials can take place over a timescale of minutes and both processes can cause full burials. Generally, UXO density plays an important role leading to burial by fluidization while wave periods also control the transition. A 5-degree deviation from normal incidence is not sensitive to the resulting burial regimes, while for 45~90 degree wave angle, burial development becomes slower. To facilitate upscaling the high-fidelity simulation results, several nondimensional parameters are used to describe the occurrence of different UXO burial regimes or rolls away. Due to the inconsistencies in the wave period effect on self-burials (vortices dynamics) and boundary layer turbulence, the combined use of the mobility number and the KC number is recommended, as well as a normalized UXO density for parameterization.

Using large number of high-fidelity simulations, this study provides insight into self-burial processes observed in the energetic field conditions, which cannot be fully-understood based on existing laboratory experiments. Simulation results provide a regime map to describe the occurrence of different burial regimes based on simple but properly chosen nondimensional parameters that can be used in the real world setting. Simulation data are also available for SERDP-sponsored researchers that can guide the development of reduced-complexity data-driven predictive models. (Project Completion - 2025)