DEFECT FUNCTION MODELS FOR THE WAVE BOUNDARY LAYERS

The boundary layer flow induced by surface waves has been extensively investigated due to its significance in engineering applications such as sediment transport and hydrodynamic forces on subsea structures. Several forms of defect functions (referred to as DF hereafter) were developed in the past decades, e.g. Sleath (1970, 1982), Nielsen (1985, 2016) and etc., due to their good efficiency in the description of the velocity distribution in one dimensional wave boundary layer (WBL). In this work, two forms of DFs are proposed: (i) DF-I describes the velocity distributions and bottom shear stresses in phase space with 4 model parameters; (ii) DF-II describes the maximum WBL profile with 3 model parameters. A number of datasets to support the validation of the DFs were obtained through experimental and numerical tests. Two sets of experiments were conducted individually in a free-surface-wave flume located in Dalian University of Technology and an oscillating-flow flume located in the University of Western Australia. For the free surface wave tests, the velocity was measured.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/RK-z0Q8rTjk

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Unsteady free-surface wave-induced boundary-layer separation for a surface-piercing NACA 0024 foil: Towing tank experiments

Journal of Fluids and Structures ◽

10.1016/j.jfluidstructs.2005.09.004 ◽

2006 ◽

Vol 22 (1) ◽

pp. 77-98 ◽

Cited By ~ 16

Author(s):

B. Metcalf ◽

J. Longo ◽

S. Ghosh ◽

F. Stern

Keyword(s):

Boundary Layer ◽

Free Surface ◽

Surface Wave ◽

Boundary Layer Separation ◽

Towing Tank ◽

Layer Separation ◽

Free Surface Wave ◽

Wave Induced

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Towed Underwater SPIV Measurement of Flow Fields Around a Surface-Piercing Cylinder With Free Surface Effects

Volume 1A: Symposia, Part 2 ◽

10.1115/ajkfluids2015-20165 ◽

2015 ◽

Author(s):

Jeonghwa Seo ◽

Bumwoo Han ◽

Shin Hyung Rhee

Keyword(s):

Boundary Layer ◽

Free Surface ◽

Surface Wave ◽

Flow Field ◽

Cross Section ◽

Surface Effects ◽

Flow Fields ◽

Two Dimensional ◽

Two Dimensional Flow ◽

Wave Induced

Effects of free surface on development of turbulent boundary layer and wake fields were investigated. By measuring flow field around a surface piercing cylinder in various advance speed conditions in a towing tank, free surface effects were identified. A towed underwater Stereoscopic Particle Image Velocimetry (SPIV) system was used to measure the flow field under free surface. The cross section of the test model was water plane shape of the Wigley hull, of which longitudinal length and width were 1.0 m and 100 mm, respectively. With sharp bow shape and slender cross section, flow separation was not expected in two-dimensional flow. Flow fields near the free-surface and in deep location that two-dimensional flow field was expected were measured and compared to identify free-surface effects. Some planes perpendicular to longitudinal direction near the model surface and behind the model were selected to track development of turbulent boundary layer. Froude numbers of the test conditions were from 0.126 to 0.40 and corresponding Reynolds numbers were from 395,000 to 1,250,000. In the lowest Froude number condition, free-surface wave was hardly observed and only free surface effects without surface wave could be identified while violent free-surface behavior due to wave-induced separation dominated the flow fields in the highest Froude number condition. From the instantaneous velocity fields, Time-mean velocity, turbulence kinetic energy, and flow structure derived by proper orthogonal decomposition (POD) were analyzed. As the free-surface effect, development of retarded wake, free-surface waves, and wave-induced separation were mainly observed.

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Wind Profile and Drag Coefficient over Mature Ocean Surface Wave Spectra

Journal of Physical Oceanography ◽

10.1175/jpo2633.1 ◽

2004 ◽

Vol 34 (11) ◽

pp. 2345-2358 ◽

Cited By ~ 45

Author(s):

Tetsu Hara ◽

Stephen E. Belcher

Keyword(s):

Boundary Layer ◽

Surface Wave ◽

Drag Coefficient ◽

Analytical Model ◽

Wind Profile ◽

Momentum Conservation ◽

Wave Drag ◽

Wave Spectra ◽

Wave Boundary Layer ◽

Wave Boundary

Abstract The mean wind profile and the Charnock coefficient, or drag coefficient, over mature seas are investigated. A model of the wave boundary layer, which consists of the lowest part of the atmospheric boundary layer that is influenced by surface waves, is developed based on the conservation of momentum and energy. Energy conservation is cast as a bulk constraint, integrated across the depth of the wave boundary layer, and the turbulence closure is achieved by parameterizing the dissipation rate of turbulent kinetic energy. Momentum conservation is accounted for by using the analytical model of the equilibrium surface wave spectra developed by Hara and Belcher. This approach allows analytical expressions of the Charnock coefficient to be obtained and the results to be examined in terms of key nondimensional parameters. In particular, simple expressions are obtained in the asymptotic limit at which effects of viscosity and surface tension are small and the majority of the stress is supported by wave drag. This analytical model allows us to identify the conditions necessary for the Charnock coefficient to be a true constant, an assumption routinely made in existing bulk parameterizations.

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Estimating Turbulence and Shear Stress under Regular Waves from ADV Data

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.212-213.1083 ◽

2012 ◽

Vol 212-213 ◽

pp. 1083-1091

Author(s):

Zheng Xiao ◽

Chao Shen ◽

Zhi Xin Guan ◽

Yuan Li ◽

Rui Min Ji

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Bottom Boundary Layer ◽

Wave Flow ◽

Shear Stresses ◽

Coastal Morphology ◽

Bottom Boundary ◽

Sand Ripples ◽

Laboratory Flume ◽

Layer Flow

The boundary layer flow determines the bottom shear stresses, which is key point for sediment transport and thereby the evolution of coastal morphology. The structure of the bottom boundary layer in coastal seas has been of interest to oceanographers for many years. In the paper Acoustic Doppler velocimeter (ADV) technique is applied to measure the bottom boundary layer under cnoidal waves in a laboratory flume with 40-m-long, 0.5-m-wide, and 0.8-m-deep.. Based on the high frequency turbulence signal collected, statistic parameters of cnoidal wave flow are calculated, compared and analyzed. The turbulent structure over plain bed and sand ripples bed are carefully studied. The turbulence intensity of near-bed velocities changes along depth of several phases in a period is analyzed. Turbulent Kinetic Energy Method (TKE Method) is used to estimate near-bed shear stress on flat and slope.

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