1 1 Three-Dimensional Hydrodynamic Model for Prediction of Falling Cylinder Through Water Column

Abstract—A three dimensional hydrodynamic model based on triple coordinate systems is developed to predict translation and orientation of falling rigid cylinder through the water column: earth-fixed coordinate (E-coordinate), cylinder’s main-axis following coordinate (M-coordinate), and hydrodynamic force following coordinate (F-coordinate). Use of the triple coordinate systems and the transforms among them leads to the simplification of the dynamical system. The body and buoyancy forces and their moments are easily calculated using the E-coordinate system. The hydrodynamic forces (such as the drag and lift forces) and their moments are easily computed using the F-coordinate. The cylinder’s moments of gyration are simply represented using the M-coordinate. A recursive model is developed on the base of the triple coordinate transform to predict the cylinder’s translation and orientation. To evaluate the recursive model, a cylinder-drop experiment was conducted at the Naval Postgraduate School swimming pool in June 2001. Comparison between the modeled and observed results shows a great potential of using the triple coordinate transform. Key Words — Triple coordinate systems, momentum of cylinder, moment of momentum of cylinder, cylinder drop experiment (CIDEX)