Resolving the Role of the Dynamic Pressure in the Burial, Exposure, Scour, and Mobility of Underwater Munitions
Dr. Diane Foster | University of New Hampshire
The overarching and long-term goal of this effort is to resolve the burial, exposure, and mobility of munitions commonly present in nearshore and inlet underwater test sites. The objectives specific to this project are focused on resolving the role of intermittent bed instability (i.e. momentary liquefaction, sheet flow, localized scour) on burial, exposure, and mobility processes. Evidence suggests that underwater munitions remain relatively stable with intermittent but significant mobility or sediment transport leading to burial or exposure. These intermittent and transient changes leading to a new positional state (burial, scour, mobility) suggest a series of threshold conditions induced by far field or near field hydrodynamic or sediment bed conditions.
The following three-pronged approach will lead to advancing the classification and detection of munitions positional state:
- Develop a theoretical formulation for the change in munitions positional state that can be used for predicting the burial, exposure, or mobility. The formulation will include the response to the dynamic pressure gradients and shear due to nonlinear surface waves and/or shed vortices and momentary bed liquefaction. This formulation will be evaluated with a number of existing and new observations and will provide guidance regarding the threshold conditions leading to changes in the positional state of munitions.
- Develop Pressure Mapping Munitions (PMMs) that will measure the orientation, rotation, and surface pressure surrounding munitions during threshold events leading to a new positional state. The 81 mm mortar and the 155 mm munitions will be instrumented as PMMs with 2 types of pressure sensors. Flexible surface mounted tactile pressure sensors will be evaluated with an array of flushmount imbedded piezoelectric sensors. The PMMs will also contain Inertial Measurement Units to measure munition orientation and an acoustic tracking device.
- Observe the motion and transport of PMM and other Smart munitions, bed stability, and near and far field hydrodynamics in three inner surf zones (two with higher energy and one with relatively low energy and a river mouth influence) and an estuary as part of comprehensive set of local field observations. A pore water pressure sensor array will provide observations of intermittent bed liquefaction, and the near-bed flow field will be resolved with an acoustic Doppler profiling velocimeter. Observations will be obtained for a 20 mm naval round, five inch and 155 mm munitions, 81 mm mortar, and a 100 lb bomb.
Results from this effort will improve classification and detection of munitions in the littoral zone. The proposed observations will build on PI Foster's existing boundary layer and sediment transport observational datasets by including 5 different munitions, mortar or bomb types. The PMMs will allow for an estimate of the dynamic pressure of buried munitions. The theoretical formulation will provide operational models guidance regarding when the wave dynamics or vortex shedding could influence munitions motion, burial or exposure.