Abstract
The safety of underwater operation depends on the accuracy of its speed logs which depends on the location of its probe and the calibration thoroughness. Thus, probes are placed in areas where the flow of water is smooth, continuous, without high velocity gradients, air bubbles, or vortical structures. In the present work, the flow around two different submarines is numerically described in deep-water and near-surface conditions to identify hull zones where probes could be installed. First, the numerical setup of a multiphase solver supplied with OpenFOAM v7 was verified and validated using the DARPA SUBOFF-5470 submarine at scaled model including the hull and sail configuration at H/D=5.4 and Fr=0.466. Later, the grid sensitivity of the resistance was assessed for the full-scale Type 209/1300 submarine at H/D=0.347 and Fr=0.194. Free-surface effect on resistance and flow characteristics was evaluated by comparing different operational conditions. Results shows that the bow and near free-surface regions should be avoided due to high flow velocity gradient, pressure fluctuations, and large turbulent vortical structures. Moreover, free-surface effect is stronger close to the bow nose. In conclusion, the probe could be installed in the acceleration region where the local flow velocity is 15% higher than the navigation speed at surface condition. A 4% correction factor should be applied to the probe readings to compensate free-surface effect.
Highlights
Submarines are the most powerful underwater marine vehicles used to guarantee the maritime sovereignty of nations, their operational safety depends on several mechanical and electronic equipment
Following current numerical hydrodynamics practices used for surface vessels, this study adopted a Volume of Fluid (VOF) method, implemented in the interFoam solver, to capture free-surface evolution when the submarine is navigating at near-surface and deep-water depth conditions
Results for Defense Advanced Research Projects Agency (DARPA) SUB-OFF geometry demonstrate that the numerical methodology used in this work is reliable at the engineering level when 4,500,000 cells are used in the simulations
Summary
Submarines are the most powerful underwater marine vehicles used to guarantee the maritime sovereignty of nations, their operational safety depends on several mechanical and electronic equipment. One of the viable options for submarines navigating completely submerged are EM logs with flush or protruding probes that estimate the local speed of water by measuring the amplitude of the electrical signal and whose accuracy relays on the probe protruding distance from the hull, flow linearity, turbulence intensity at the probe location, and sensor calibration thoroughness. The procedure to determinate the probe installation location requires to have an insight into the physics of the water flowing around the full-scale submarine’s light hull considering every hydrodynamic variable available in deep-water and near-to-surface conditions. These flow characteristics depend on fluid properties, hull geometry, appendage distribution, vessel motion orientation, and free-surface proximity. The probe calibration procedure could include free-surface effects using CFD results after a proper verification and validation procedure [1,2] is performed using experimental data from towing tank experiments or sea trials measurements
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