Results from the SERDP SEED project MR20-1478 have presented promising evidence that the high fidelity two-phase numerical modeling framework, SedFoam, is capable of simulating several key coupling mechanisms between hydrodynamics, sediment transport, objects and seabed response through benchmarking with laboratory experiments and proof-of-concept simulations. The objectives of this project are to propose the full implementation of SedFoam in order to:

1. Investigate key physical processes responsible for the mobility, scour burial, and extreme burial of unexploded ordnance (UXO), including mechanisms triggering liquefaction, the effect of UXO density, and UXO-bedform interactions.

2. Develop parameterizations for liquefaction, burial depth, and mobility of UXO as a function of UXO density, initial burial depth and other non-dimensional flow parameters.

3. Carry out field-inspired scenario simulations to fill the parameter space and provide simulation data to train the existing expert system Underwater Munition Expert System (UnMES) for scour burial prediction.

The project team plans to carry out the full implementation and validation of the Eulerian two-phase model, SedFoam and apply the model to investigate the following two hypotheses critical to the understanding of munition mobility and burial dynamics:

Hypothesis I: While the mobility and the local burial of UXO depend on UXO density, extreme burial is also controlled by UXO density. For the latter, however, seabed liquefaction or combined liquefaction and shear-driven fluidization must first occur.

Hypothesis II: Many extreme burial events may also be caused by bedforms migration. The mobility of UXO is hindered by the presence of bedforms. The mobility of UXO is controlled by the competition between the timescales of burial and change of wave energy.

Five fully integrated tasks are suggested, which include improving the soil mechanics modeling in SedFoam to resolve liquefaction, implementing moving object and UXO-sediment-fluid interaction capabilities, model validation with laboratory/field experiments and an integrated investigation on the two hypotheses through scenario studies and model data synthesis. All simulation data will be made available for training the UnMES.

This project will provide a novel numerical modeling tool, complimentary to field observations, to improve the scientific understanding on a wide range of munition mobility, scour burial, and extreme burial problems. Simulation results, when integrated with probabilistic modeling, will also contribute to an improved munition site management. The work also lays a foundation for future model development for UXO mobility and burial dynamics for soil with different amounts of fines (silt/clay) and unsaturated soil.