Resolving the Role of Dynamic Pressure on Positional State Changes of Submerged Objects

Military activity around the United States has led to over 10 million underwater acres potentially containing weapons, i.e., munitions. These munitions are difficult to locate, capable of sudden movement, and a danger to marine life and the public. Improved understanding of their mobility in underwater environments is vital for safe and cost-effective munition recovery. A pressure-mapped model munition (PMM) was designed and fabricated to resolve the role of dynamic pressure gradients on munition mobility. The PMM is an untethered instrument, capable of detecting and measuring surface pressure gradients, orientation and positional changes.

The surface pressure mapping was accomplished using an array of sixteen 3mm-diameter, diaphragm pressure sensors. Orientation changes were recorded using an Inertial Measurement Unit. The PMM was evaluated through several full-scale laboratory and field experiments to determine its accuracy in detecting hydrostatic pressure changes, orientation changes, passing waves, and environmental changes, such as being submerged in a sand bed. The PMM was able to resolve both the overlying progressive wave signal, and deviations due to vortex shedding around the cylinder.

The PMM design was modified, and further testing was conducted at both the Piscataqua River mouth in Kittery, Maine, and a beach in Rye, New Hampshire. PMM motion is correlated to wave and vortex pressure gradient peaks. This is commensurate with the Sleath parameter criterion for incipient motion. The results of this research suggest that vortex shedding may significantly contribute to the burial of free-standing objects. Additionally, these results can be more broadly applied to relationships between sediment and fluid structures.