Submerged Ordnance and Unrestrained Cylinder Movement in Coastal Zone

Abstract

Laboratory experiments were conducted in a wave flume to measure wave conditions (height, period, and kinematics) that caused movement of submerged ordnance and cylinders. Laboratory results were analyzed and two empirical theories were developed for predicting movement based on wave conditions and ordnance/cylinder characteristics: (1) modified Shields parameter approach comparing ordnance and cylinder parameters with a wave Shields parameter to identify critical regimes for ordnance/cylinder movement; and (2) Keulegan-Carpenter number (KC) approach comparing the ratio of maximum orbital velocity at the ordnance/cylinder surface and ordnance/cylinder diameter with relative water depth. Evaluation of these two approaches with the laboratory data indicated that the best predictive technique appeared to be the modified Shields parameter approach. A field deployment of two drogue cylinders instrumented with acoustic pingers was conducted to further investigate ordnance movement using acoustic tracking procedures. Measured wave conditions and cylinder characteristics were used in the modified Shields parameter approach and indicated that the cylinders would be mobile. The field deployment of two cylinders verified the prediction results showing net movements of 15 and 13 m, respectively.