Shubhra Misra

The mean and turbulent flow structure of a weak hydraulic jump

The turbulent air–water interface and flow structure of a weak, turbulent hydraulic jump are analyzed in detail using particle image velocimetry measurements. The study is motivated by the need to understand the detailed dynamics of turbulence generated in steady spilling breakers and the relative importance of the reverse-flow and breaker shear layer regions with attention to their topology, mean flow, and turbulence structure. The intermittency factor derived from turbulent fluctuations of the air–water interface in the breaker region is found to fit theoretical distributions of turbulent interfaces well. A conditional averaging technique is used to calculate ensemble-averaged properties of the flow. The computed mean velocity field accurately satisfies mass conservation. A thin, curved shear layer oriented parallel to the surface is responsible for most of the turbulence production with the turbulence intensity decaying rapidly away from the toe of the breaker (location of largest surface curvature) wi...

An approach to determining nearshore bathymetry using remotely sensed ocean surface dynamics

This paper describes a spatially one-dimensional algorithm developed to estimate water depths from remotely sensed information of the water surface, using extended Boussinesq equations. Local phase speed estimates are obtained using a least-squares approach, from spatial profiles of surface elevation/orbital velocity lagged in time. Inversion algorithms have been developed for both linearized and fully nonlinear Boussinesq equations to calculate the depth. In all cases, synthetic input data are generated using a fully nonlinear time-dependent Boussinesq model. Wave conditions including monochromatic and irregular waves are simulated in the model. Mean flow effects are included in the inversion algorithm to account for currents. For monochromatic wave conditions, there is good agreement between the actual and estimated depth and particle kinematics. The fully nonlinear method, as compared to the linearized inversion, improves the depth prediction by 10% for the test case considered. Irregular wave conditions were simulated using time series generated for a TMA spectrum with varying values of the peak enhancement factor. The error in the inverted depths increased in the deeper part of the bathymetry as the wave train become more broad-banded. For monochromatic waves in the presence of weak currents, the modified algorithm (including mean flow effects) is seen to improve the inverted depth by 10%, over the original formulation.

TURBULENT INTERFACIAL BOUNDARY CONDITIONS FOR SPILLING BREAKERS

This paper presents experimental observations as well as theoretical formulations of the flow structure in the turbulent shear layer in spilling breakers. The theoretical model is developed within the framework of a three-layer system, with the top layer being the two-phase (air/water) turbulent surface layer, and the bottom layer comprising the single phase (water) irrotational flow. The model development in the single phase (water) turbulent shear layer is guided by and validated with PIV flow measurements of a turbulent hydraulic jump. The breaker shear layer is seen to resemble a classical mixing layer with entrainment of fluid into the reverse flow region localized about the mean surface. Preliminary results are reported on interfacial boundary conditions which account for the contributions from the surface layer as well as the evolution of turbulent and mean quantities in the breaker shear layer. Such interfacial boundary conditions can be incorporated into Reynolds-averaged Navier-Stokes numerical models for simulating the spatio-temporal evolution of the turbulent and mean flow in spilling breakers.

SURFACE GRAVITY WAVE INTERACTIONS WITH DEEP-DRAFT NAVIGATION CHANNELS – PHYSICAL AND NUMERICAL MODELING CASE STUDIES

number 368

Dynamic open contours using particle swarm optimization with application to fluid interface extraction

This paper describes a method for the estimation of a dynamic open contour by incorporating a modified particle swarm optimization technique. This scheme has been applied to a Particle Image Velocimetry experiment for the analysis of fluid turbulence during a hydraulic jump. Due to inter reflections within the medium and refractions across different media interfaces, the imagery contains spurious regions, which have to be eliminated prior to the estimation of turbulence statistics at the fluid surface. The PIV image sequences provide a strict test bed for the performance analysis of this estimation mechanism due to the occurrence of intense specularity and extreme non-rigid motion dynamics.