Transom stern hydrodynamics.

The use of a transom stern on marine vehicles introduces many difficulties for the designer to predict performance characteristics. Particularly, the speed range in which the transom is partially wet is difficult to model for a full-scale ship. In this thesis the hydrodynamics of a transom stern vessel are studied experimentally and numerically by examining the two-dimensional canonical problem of a backward-facing step with a free-surface (BFSFS). Comparisons are made with transom stern destroyer model tests, including the effects of a stern flap, to evaluate the merit of the BFSFS. The first ever reported experiments are conducted on the two-dimensional problem in a low-turbulence water channel by measuring the free-surface by several methods including laser induced fluorescence, wire-capacitance wave probes, and a sonic probe. Additionally, velocity surveys are conducted using a pitot-tube and a special pressure-transducer apparatus which minimizes temperature and surface tension influences on very low speed velocity measurements. Numerically, an unsteady Navier-Stokes solver is used with the Level Set method for interface tracking to simulate the BFSFS. The Spalart-Allmaras one-equation turbulence model is implemented. The results from both experiments and numerical simulation are used to describe the free-surface in the context of four distinct flow regimes. Comparisons between the present work and inviscid theories show that viscosity, and surface tension effects are important in predicting the wave slope. The wave-length behind the body is much shorter than predicted by linear theory. A previous stream-function bi-linear shear current theory is used to account for the viscous wake effect on the wave-length. A frequency analysis is performed that identifies a dominant vortex street occurring at a Strouhal number of 0.2. The process of transom un-wetting is described for the canonical problem and compared to the un-wetting of the destroyer stern-flap model tests by means of assuming the pressure on the transom is hydrostatically dominated.Ph.D.Applied SciencesMechanical engineeringOcean engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125702/2/3208503.pd