Large amounts of data have been gathered in field and laboratory studies to reveal the mechanisms behind the motion of munitions. However, there are still knowledge gaps for the physical and deterministic explanation of observations. The objective of this project is to develop and utilize three-dimensional (3D) computational models to describe the details of physical processes on flow and transport around underwater unexploded ordnances (UXOs), which help to predict the initiation of motion, continuous movement, and final deposition of munitions. Modeling tools and capabilities achieved from this project, in conjunction with the physical insights gained, are important for site assessment and remediation actions.

The 3D models capture the key physical processes which control the motion of munitions, including turbulent flow, sediment transport and scour, granular material dynamics, and the rigid-body motion of munitions. Two models were developed by the project team. One is the 3D scour model which can capture the scour and erosion around UXOs. To deal with the complex geometry of UXOs, an innovative immersed boundary method was developed which can produce accurate and smooth wall shear. A new sand slide method was also invented to handle the sliding of sediment along steep slopes. The UXOs in the 3D scour model can be either fixed or move with some prescribed motion. The scour model is suitable for cases where UXOs are stationary, in-between movement steps, or moving at a much slower pace than the scour hole development. The second model is the 3D Smoothed Particle Hydrodynamics (SPH) model based on the open source DualSPHycis code. A multiphase approach for both phases of water and sediment has been used. The motion of munition is simulated with a 6-Degrees-of-Freedom rigid-body motion solver.

There are two key results. One is the advancement of UXOs modeling capability with the two new models. These models are valuable tools for the Munition Response program. They complement other research projects, especially those field and lab-based projects. The second key result is the physical insights gained through the case studies with the models. With the 3D scour model, the detailed physical processes and their implication for UXOs dynamics are revealed. This project specifically investigated the effects of munition shape and angle of attack, both of which play an important role. There are many other physical parameters which can be investigated in future research. To reduce the parameter space, a dimensional analysis was performed. A unified scour time scale was proposed and the scour hole development is well captured by a saturation-growth curve. With the 3D SPH model, the penetrometer experiment and munition movement on beach face were simulated. Both cases captured the bulk dynamics and produced information on forcing, which is difficult to measure in experiments. There are also many other simulated cases on various aspects of the UXOs problem.

One benefit is the availability of two powerful computer models which are previously not available. These models can benefit all other research projects supported in the program. The 3D SPH model has already been used to collaborate with other projects on penetrometer study and munition of beach face. In the future, these models, with careful calibrations, can be used to study many aspects of munition movement. Another benefit is that some of the findings, e.g. the scaling law, can be directly used in large scale prediction models.