Abstract
A numerical model was developed to predict mobility and burial of seafloor cylindrical objects. The model contains four components: 1) object's physical parameters such as diameter, length, mass, and rolling moment; 2) dynamics of rolling cylinder around its major axis; 3) empirical sediment scour model; and 4) seabed environmental characteristics such as currents, waves (peak period, significant wave height), sediment density, and medium sediment grain size. Under the sponsorship of the Department of Defense Strategic Environmental Research and Development Program, a field experiment was conducted from April 21 to May 23, 2013 off the coast of Panama City, FL, USA to measure both objects' mobility using sector scanning and pencil beam sonars and simultaneous environmental time-series data of the boundary layer hydrodynamics and sediment transport conditions for driving mobility. Comparison between modeled and observed data shows the model capability. Future work needs to consider more realistic object shapes and motions such as pitch and yaw, and wavy seabed.
Highlights
P REDICTION of the mobility and burial of a rigid object on the seafloor is confounded by the influence of environmental characteristics such as waves, currents, sediment dynamics, and seafloor morphology
The 6-degrees of freedom (DoF) model is based on the approach previously developed to predict sea mine impact burial, named IMPACT35, which predicts the trajectory of a mine through air and water, in addition to the amount of burial that occurs upon impact with the seafloor [4]–[6]
It consists of four parts: 1) cylindrical object model with the burial percentage Shields parameter; 2) sediment scour model with sediment Shields parameter; 3) input data such as object’s physical parameters (D, So, M, Io), and environmental variables such as near seabed ocean currents, bottom wave orbital velocity (Ubr) water depth (h), wave peak period (TP), significant wave height (HS), sediment characteristics; 4) model output such as the burial percentage pB, and the object’s displacement
Summary
P REDICTION of the mobility and burial of a rigid object on the seafloor is confounded by the influence of environmental characteristics such as waves, currents, sediment dynamics, and seafloor morphology. A model to predict objects’ mobility and burial on sandy seafloor has been developed in this study based on the following four assumptions: 1) cylindrical munition with a large aspect ratio (length L much larger than diameter D, L>>D); 2) roll dominating the motion of the long cylinder (L >> D) with no yaw and pitch; 3) burial depth (B) smaller than half of the diameter (B < D/2) [10]; 4) flat seabed. It consists of four parts: 1) cylindrical object model with the burial percentage Shields parameter (θopb); 2) sediment scour model with sediment Shields parameter (θsed); 3) input data such as object’s physical parameters (D, So, M, Io), and environmental variables such as near seabed ocean currents, bottom wave orbital velocity (Ubr) water depth (h), wave peak period (TP), significant wave height (HS), sediment characteristics; 4) model output such as the burial percentage pB, and the object’s displacement.
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