Jinshi Chen

When waves break, the wave roller, an aerated region on the front face of a spilling wave, redistributes momentum into mean cross- and alongshore currents and wave setup (breaking wave induced mean water level increase), causing these responses to lag behind wave-energy dissipation. Because rollers are transient and highly unsteady, their properties are difficult to measure directly in laboratory or field settings, and existing parameterizations of roller shape and energy are largely empirical.

My research then used the two-phase (air & water) Reynolds-averaged Navier–Stokes (RANS) model waves2Foam, together with in situ pressure and current measurements, to directly quantify the cross-shore evolution of wave rollers over barred and unbarred beaches under different offshore wave conditions and to evaluate existing parameterizations.

Turbulence is ubiquitous in the ocean, and it is especially strong in surfzone due to breaking waves. Breaking-wave turbulence is responsible for mixing in the water column, transporting momentum cross-shore and downward, and dissipating wave energy. Accurately estimating turbulence strength and structure in surfzone is critical for estimating vertical structure of undertow and cross-shore wave transformation. Yet, two-equation RANS model relates turbulence structure with mean current stress, assuming maximum turbulence energy flux across length scales, leading to erroneous turbulent estimate in the model and subsequently unsatisfactory estimation of undertow.

For my research, I use in-situ field observation to directly estimate surfzone turbulence anisotropy (directional preference of turbulence Reynolds stresses) and relate that to bulk wave and mean current.

In the surf zone, undertow, an offshore-directed mean current below the wave trough, balances the onshore mass transport carried by breaking waves and rollers. Understanding the vertical structure of undertow is critical to accurately estimate the water column mixing, bottom shear stress and sediment transport rate, which has important implications for beach erosion and the transport of land-based pollutants and biota. However, the depth-dependent momentum forcing that controls undertow remains poorly understood.

My research uses the aforementioned two-phase RANS model to quantify the vertical structure of undertow and its forcing terms and to develop parameterizations based on bulk wave and bathymetric properties.

Surfzone eddies can transport sediment and biota offshore across the surfzone. One proposed generation mechanism is short-crested wave breaking, caused by directional wave spreading or alongshore-varying bathymetry. Uneven breaking produces strong forcing beneath each crest and weaker forcing between crest ends, generating vortex dipoles at the crest tips. These vortices may merge through an inverse cascade into larger eddies, with scales of approximately 10–100 m, that can propagate toward the inner shelf. However, the processes governing their cross-shore transport remain poorly quantified.

My research uses a simplified process model implemented in Dedalus to derive dimensionless relationships describing eddy advection over a slope as a function of slope and wave properties.

Winds and ocean surface waves often travel in different directions, particularly during storms with rapidly changing winds and in coastal regions where bathymetry influences wave propagation. Understanding these misaligned interactions is essential for predicting wind profiles, improving wave-forecasting models, and optimizing offshore wind-turbine performance.

My research employs two-phase direct numerical simulations (DNS) to resolve misaligned wind–wave interactions and develop physical frameworks and parameterizations applicable across a range of wind and wave conditions.