S. A. Ermakov

Investigation of damping of gravity-capillary waves (GCWs) in the presence of turbulence is a classical hydrodynamic problem which has important geophysical applications, one of which is related with

Wave tank experiments were performed to study features of microwave radar backscattering by strongly nonlinear gravity-capillary waves (GCWs). Backscattering by centimeter and partly decimeter GCW was found to be related to the microbreaking of GCWs and the generation of parasitic capillary ripples. The scattering of meter-scale GCWs was attributed to the effects of strong breaking, i.e., to the overturning of wave crests and the excitation of quasilinear (free) capillary ripples, while the scatterers for intermediate decimeter GCWs were both free and parasitic ripples.

We studied the time dynamics of a turbulent region excited by a moving surface vessel in a field experiment. The time dependences of the geometrical sizes of the turbulent region are obtained, and it is shown that the time dependence of the width of the turbulent wake at the initial stage is close to the power-law function with an exponent of 0.4 for different experiments (the depth of the wake remaining practically constant). In the semiempirical turbulence theory, we suggested a qualitative model describing the process of the initial expansion of a ship wake as a diffusion of a one-dimensional layer of turbulized liquid due to a pulsed source.

The physical influence of the intensification of decimeter waves on a water surface covered by a surfactant film is proposed. The damping of a long wave caused by the loss of its energy on the modulation of short (centimeter) wind waves is analyzed. The damping coefficient of waves of decimeter-meter lengths is calculated, and this coefficient is shown to decrease in the presence of a surfactant film. The strong suppression of the spectrum of centimeter wind waves in a film slick is the physical factor responsible for such a decrease. Due to a decrease in the damping coefficient of decimeter-meter waves, their intensity in the slick increases. Within the framework of a model of the spectrally local energy balance of wind waves, the results of calculations satisfactorily agree with the experiment.

The dynamics of a layer of turbulence excited by a ribbed oscillating grate in homogeneous and stratified fluids is investigated experimentally. The time dependences of the thickness of the region encompassed by turbulence in a homogeneous fluid are obtained. On the basis of a semiempirical turbulence theory, it is shown that the time dependence of the coordinate of the turbulent-front position can be described by a power function. A satisfactory agreement between the experimental and theoretical dependences is obtained. Different regimes of turbulent-layer dynamics in a fluid with salinity stratification are investigated. The results of numerical calculations of turbulent-layer dynamics in a stratified fluid that satisfactorily agree with experimental data are presented. The data obtained can be used to estimate the efficiency of mixing within the oceanic depth.

The mechanism of the resonance (Bragg) scattering of microwaves by gravity-capillary waves (GCWs) is checked experimentally. Resonant regularities of backscattered signal intensity are obtained as functions of frequency and GCW propagation direction. It is shown that the width of the resonance curves is determined by the width of the directivity pattern of the scatterometer’s antenna. The excitation of the GCW second harmonic and the spatial structure of the wave field at the GCW doubled frequency are investigated. The ratio of the amplitudes of the free wave and forced harmonic that originated during excitation of the primary wave is determined. The resonance curve is obtained for the second-order scattering of radio waves (on forced harmonics and free GCWs). The correction to the backscattering cross section is investigated in the second order of smallness relative to the Bragg term.