Olav H. Slaattelid

A rational approach to wave-current friction coefficients for rough, smooth and transitional turbulent flow

Abstract The wave-current friction coefficients and the phase lead of the bottom shear stress over the free-stream oscillatory velocity for rough, smooth and transitional smooth-to-rough turbulent flow are presented. The analogy between wave boundary layer flow and planetary boundary layer flow is utilized by using similarity theory. The turbulent current is described by using a simple eddy viscosity representation. An approximation for the friction coefficients by disregarding the phase is also presented. Comparisons are made with experiments for rough and smooth turbulent flow.

Seabed shear stresses under random waves : Predictions vs estimates from field measurements

Abstract The paper discusses the seabed shear stresses under random waves, and compares model predictions with results from field measurements near the seabed in the Strait of Juan de Fuca, Washington State, and at EDDA, North Sea. The model predictions as well as the interpretation of data are based on three different representative measures of random wave velocities within 12 minute records: root-mean-square, significant and maximum values. From the two locations the best agreement is found for the Strait of Juan de Fuca data regardless of the random velocity measure used. This agreement is attributed to the absence of suspended sediment at this location.

Wave boundary layer in flow measurements near the seabed

Abstract Analysis of data near the seabed in the Strait of Juan de Fuca, Washington state, in 18 m water depth and EDDA, North Sea, in 70 m water depth gives estimates of large wave boundary layers. Such wave boundary layer data are not available in the open literature and are relatively scarce. Although the physical bottoms in the two locations are different, the general character of the boundary layer, which includes a velocity overshoot, was similar. However, in general the data demonstrate large variability in the detailed velocity profile. Published semi-empirical formulas for wave boundary layer characteristics show good agreement with the analysis results from these measurements. Consistency is also found between the analysis results from these field data and large and small scale laboratory tests with sinusoidal oscillations.

Effects of sea roughness and atmospheric stability on wind wave growth

The paper considers the effects of sea roughness and atmospheric stability on the wind wave growth by using the logarithmic boundary layer profile including a stability function, as well as adopting Toba et al.s [J. Phys. Ocean. 34 (1990) 705] significant wave height formula combined with some commonly used sea surface roughness formulations. The wind wave growth is represented by the non-dimensional total wave energy relative to that for neutral stability used by Young [Coast. Engng 34 (1998) 23]. For a given velocity at the 10 m elevation, spectral peak period and stability parameter, the wind wave growth is determined.

Bottom shear stresses and velocity profiles in stratified tidal planetary boundary layer flow from similarity theory

The paper presents the bottom shear stresses and velocity profiles in stratified tidal planetary boundary layer flow by using similarity theory. For a given seabed roughness length, free stream current velocity components, frequency of tidal oscillation, Coriolis parameter and stratification parameter, the maximum bottom shear stress is determined for flow conditions in the rough, smooth and transitional smooth-to-rough turbulent regime. Further, the direction of the bottom shear stresses and the velocity profiles are given. Comparison is made with data from field measurements of time-independent as well as tidal planetary boundary layer flow for neutral conditions, and the agreement between the predictions and the data is generally good. Further, an example of application for stable stratification is given, and qualitatively the predictions show, as expected, that the bottom shear stress and the thickness of the boundary layer become smaller for stable than for neutral stratification. Other features of the tidal planetary boundary layer flow are also discussed.

Note on air drag on sea ice in stably stratified flow

Abstract We consider the air-ice drag coefficient for stably stratified flow by using the logarithmic velocity profile. The stability function containing a non-dimensional universal constant is included to represent stratification effects. In this study three values of the universal constant are used; of which one is obtained here as the best fit to data. Comparison between the air-ice drag coefficients using these three values and data is presented.