Hydrodynamics and Roughness of Irregular Boundaries

Abstract

LONG-TERM GOALSThe research goals of the work target accurate parameterization and modeling of nearshore waves, currents and turbulence in complex reef environments. A central theme of this work is the response of steady and oscillating flow to highly irregular, broad-banded roughness. Previous ONR supported study by the PI's group have quantified reef roughness, examined the hydrodynamic response to a variable roughness at small scales and explored the relationship between hydrodynamic and physical roughness. OBJECTIVESSpecifically, the work aims to examine methods for quantifying physical roughness scales in reef environments using an autonomous underwater vehicle (AUV) and to determine the hydrodynamically relevant roughness scales for wave and current flow.The work underway is also enabling development of a series of practical applications including examination of the relationship between measured roughness and sidescan imagery, exploration of AUV-based ADCP observations for resolution of steady flow boundary layer dynamics, and implementation of new tools for measurement of turbulent stresses in wavy environments. In addition high-resolution reef morphology data will enable further study on the correlation between roughness and other measurable reef characteristics including coral color, health and species. APPROACHTo achieve the objectives detailed above, we are conducting a series of focused field experiments targeting resolution of flow hydrodynamics over a range of reef environments in varying wave and current conditions, with concurrent high resolution roughness mapping. The first series of observations are being carried out at the Kilo Nalu Observatory on the south shore of Oahu (Pawlak et al, 2009; www.soest.hawaii.edu/OE/KiloNalu/). A second set of observations is also being carried out in Guam in October, 2010 leveraging funding from the Army Corps of Engineers in collaboration with Mark Merrifield (UH Oceanography). A third set of field observations is targeted for the north shore of Oahu for winter, 2011.