Hydrodynamic analysis of an underwater glider

Autonomous underwater gliders are underwater vehicles that can travel underwater by changing their buoyancy and center of gravity. This movement mechanism grant underwater gliders the longest mission endurance among all autonomous underwater vehicles with 6 to 12 months of active time. In this period, these vehicles can collect various kinds of ocean data over thousands of kilometers in range and transfer that data to a control center over satellite connection. The endurance, range of operation and variety of the collectable data makes underwater gliders one of the best tools for ocean observation. In this study, drag force on the axisymmetric torpedo shaped glider hulls are analyzed. Dimensions of tested forms are chosen by considering commercial and academic gliders. From there, basis dimensions for length and diameter are selected as 1.50m and 0.20m respectively. Thirteen different forms are generated for analyses. The forms include; 4 constant diameter forms with changing length (0.20m diameter with 0.50, 1.00, 2.00, 2.50 meter lengths), 5 constant length forms with changing diameter (1.5m length with 0.12, 0.16, 0.20, 0.24, 0.28m diameters) and 4 extra forms for comparison of flow separation of the forms with large diameter. Shape of the nose and back sections are chosen using Myring equations with length 0.20m nose and 0.30m back section. Nose and back sections are kept constant for all forms. The forms are analyzed in 4 different velocities (0.3, 0.6, 0.9, 1.2 m/s) and 6 different angles of attack (0, 2, 4, 6, 8, 10°) for a total of 312 analyses using the open source CFD software OpenFOAM. The results show that volume increase effects gliders more and more as angle of attack and glider velocity increases. However for glider with velocities ranging from 0.3 to 0.6 m/s the increase in the volume does not contribute drag force as much. Moreover it is important to do nose and back sections analyses to determine the dimensions of the nose and back sections because of the increase in separation with increasing angle of attack and velocity.