Field Measurements and Numerical Simulations of Deep-Draft Vessel-Wake Hydrodynamics in a Shallow-Bay System

Abstract

Large vessels traversing waterways and bays generate wakes that influence near- and far-field hydrodynamics as well as erosion and sedimentation. A better understanding of these dynamics is important for optimized ship channel management, erosion control, and smaller vessel safety. This study presents data analysis and numerical simulation results based on two field measurement campaigns conducted along the Houston Ship Channel (HSC) in Galveston Bay (GB), Texas, to investigate the far-field hydrodynamics of ship wakes in a shallow-bay system. The first field campaign included detailed hydrodynamic measurements over a 1-year period near a mixed-sediment embankment about 1.0 km away from the HSC. A second, 2-week-long field campaign added data in an unobstructed area of GB between 0.5 and 3.0 km from the HSC. Hydrodynamic data were collected using acoustic Doppler velocimeters and pressure transducers and correlated with vessel characteristics obtained from automatic identification system data, validated through video footage. FUNWAVE-TVD model, which is a numerical nonlinear Boussinesq model including a vessel module, was used to simulate generation and propagation of water free-surface fluctuations caused by deep-draft vessel transits through the HSC. FUNWAVE is used frequently by agencies, academia, and industry, but its vessel module has not been extensively vetted for deep-draft vessel transits in shallow-bay systems using in situ measured data. Model validation and parameter sensitivity analyses involved comparisons between simulated ship-wake data and measured samples at five distinct points. Results indicate that the FUNWAVE model effectively replicates primary deep-draft vessel wakes (including surge and drawdown) in both time and frequency domains but fails in capturing the high-frequency oscillations of the trailing transverse wakes at the far-field measuring locations. Suggestions for numerical model improvements are provided. The study also introduces a methodology to compute the spatial distribution of total ship-wake energy flux induced by individual vessel passages from numerical results through spectral analysis to help identify dissipation (and potentially erosion) hotspots. For the example vessel passages investigated, an average reduction in energy flux of 2.1% per 100-m distance from the channel was found.