Gravity waves interacting with a narrow jet‐like current

Abstract

[1] A unique experiment to investigate the transformation of near-linear gravity waves propagating across a narrow horizontally sheared jet-like current, typical of those found in the nearshore, coastal, and ocean regions, is described. A single wave condition was studied, propagating across the current orthogonally and at oblique incidence in both a following and opposing sense to the current. The length scale of the current shear layers was comparable to the incident wavelength. The experiment is the first attempt to assess the kinematics and dynamics of the interaction of regular waves and currents in three dimensions at a physically realistic scale. The resulting data set provides direct quantitative measurements of the spatial variation of the primary flow variables. Negligible reflection of the incident wave at the current shear layers was observed. Typical refraction behavior was observed: A following wave is refracted to a more current-parallel direction with an increased wavelength and reduced wave height as it moves onto the current, while the opposing wave becomes more current normal with a shortened wavelength and enhanced wave height. The experimental data are compared with predictions of a wave ray model, assuming a depth-averaged current and slowly varying horizontal shear, and a new model that incorporates the influence of vertical shear.

Surface current effects on the fetch‐limited growth of wave energy

“…On YD 361 there were fluctuations in the wave energy with fetch (Figure 8b) that were similar to the current normal laboratory observations of MacIver et al [2006]. However, the amount of energy increase was much less than that observed on YD 356 and was not significant at the 95% confidence level.…”

“…The amount of wave refraction over a sheared current will depend on the magnitude of ψ as determined by [ Kenyon , 1971] and in stronger currents the direction of wave propagation [ MacIver et al , 2006]. In these observations, ψ was continually varying and therefore the angle between the stress and the wind would change as well.…”

“… MacIver et al [2006] measured wave refraction on both horizontally and vertically sheared currents in the laboratory. Their results confirmed the basic structure predicted by ray theory based on the mild shear assumption.…”

Occurrence of extreme waves in three-dimensional mechanically generated wave fields propagating over an oblique current

“…Experimental results, though, have mainly been obtained in wave flumes, where only long-crested waves and a collinear current (i.e., one dimensional problem) can be considered. Fewer experiments have dealt with waves crossing oblique currents (see MacIver et al, 2006) but these have been confined to a study of kinematics and linear properties. For the present investigation, we accessed the directional wave basin facility at Marintek (Norway) in order to address the more general two-dimensional problem, where a multi-directional wave field propagates obliquely over a current field in partial opposition.…”

Shear Current Effects on Monochromatic Water Waves Crossing Trenches

“…Horizontally sheared currents such as those formed at river mouths, tidal inlets, and tidal races and around coastal structures are also one of the main factors of wave transformation [13]. However, even within the linear theory framework, the analysis of the water waves across a shear current is remarkably intractable.…”