Closure to “A Lagrangian drifter for surveys of water surface roughness in streams” by CHRISTIAN NOSS, KAAN KOCA, PEGGY ZINKE, PIERRE-YVES HENRY, CHRISTY USHANTH NAVARATNAM, JOCHEN ABERLE and ANDREAS LORKE, J. Hydraulic Res.

2021 ◽  
Vol 59 (1) ◽  
pp. 178-179
Author(s):  
Christian Noss ◽  
Kaan Koca ◽  
Peggy Zinke ◽  
Pierre-Yves Henry ◽  
Christy Ushanth Navaratnam ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Water Surface ◽  
Lagrangian Drifter

A Lagrangian drifter for surveys of water surface roughness in streams

2019 ◽  
Vol 58 (3) ◽  
pp. 471-488 ◽  
Author(s):  
Christian Noss ◽  
Kaan Koca ◽  
Peggy Zinke ◽  
Pierre-Yves Henry ◽  
Christy Ushanth Navaratnam ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Water Surface ◽  
Lagrangian Drifter

Laboratory studies of wind–wave interactions

1968 ◽  
Vol 34 (1) ◽  
pp. 91-111 ◽  
Author(s):  
Jin Wu
Keyword(s):  
Surface Roughness ◽  
Wind Stress ◽  
Water Surface ◽  
Wind Wave ◽  
Wave Drag ◽  
Average Height ◽  
Drift Current ◽  
Stress Coefficient ◽  
Wide Range ◽  
Wind Velocities

The present study consists of wind profile surveys, drift current measurements and water surface observations for a wide range of wind velocities in a wind–wave tank. It is confirmed that the velocity distribution essentially follows the logarithmic law near the water surface and the velocity-defect law toward the outer edge of the boundary layer. The wind stresses and surface roughnesses calculated from these distributions are divided into two groups separated by the occurrence of the wave-breaking phenomenon. For low wind velocities the surface roughness is dictated by ripples, and the wind-stress coefficient varies with U0−½, where U0 is the free-stream wind velocity. The surface roughness is proportional to the average height of the basic gravity wave at higher wind velocities; the stress coefficient is then proportional to U0. In addition, it is found that Charnock's expression (k ∝ u*2/g) holds only at high wind velocities, and that the constant of proportionality determined from the present experiment correlates very well with field observations. A new technique, involving the use of various-sized surface floats to determine the drift current gradient and the surface drift current, has been developed. A good agreement is shown between the gradients obtained from the measured currents and those determined from the wind stresses. Finally, the wind-stress coefficient is shown to be larger than the friction coefficient for turbulent flow along a solid rough surface; the difference is shown to be the wave drag of the wind over the water surface.

scholarly journals Simulation Effects of Surface Geometry and Water Optical Properties on Hydrographic Lidar Returns

2020 ◽  
Vol 237 ◽  
pp. 08020
Author(s):  
Song Yang ◽  
Qian Sun ◽  
Yongchao Zheng
Keyword(s):  
Surface Roughness ◽  
Optical Properties ◽  
Water Surface ◽  
Signal To Noise Ratio ◽  
Surface Geometry ◽  
Signal To Noise ◽  
Noise Ratio

. Water LiDAR model was applied to simulate the returned waveforms of hydrographic LiDAR considering the effects of surface geometry and water optical properties. The signal to noise ratio(SNR) of bottom returned peak was considered as a criterion for performance of hydrographic LiDAR. The behavior of LiDAR was sensitive to water optical properties and it was insensitive to water surface roughness.

scholarly journals Flow and Turbulence driven Water Surface Roughness and Gas Exchange Velocity in Streams

2018 ◽  
Vol 40 ◽  
pp. 05018
Author(s):  
Christian Noss ◽  
Pascal Bodmer ◽  
Kaan Koca ◽  
Andreas Lorke
Keyword(s):  
Surface Roughness ◽  
Gas Exchange ◽  
Water Surface ◽  
River Flow ◽  
Surface Flow ◽  
Mountain Stream ◽  
Particle Image Velocimetry System ◽  
Flux Chamber ◽  
Acceleration Sensors ◽  
Flow Hydraulics

Gas exchange velocity in streams and rivers controls fluxes of atmospheric gases across the air-water interface and is commonly related to the turbulence at the water side. Similarly, river flow hydraulics influences the water surface roughness, which is frequently used (in terms of surface flow types) for eco- and morphological mapping of spatial variations of hydraulic conditions. We investigated the relationships between gas exchange velocity, water surface roughness and flow hydraulics for different surface flow types in a low-mountain stream. We used the flux chamber-method to estimate exchange velocity, a freely floating sphere (equipped with acceleration sensors) to measure water surface roughness, as well as a field-particle image velocimetry system for flow and turbulence measurements. The results demonstrate that the gas exchange velocity in smooth and rippled flows followed the same universal dependence on turbulent dissipation rates (with an empirical scaling coefficient at the upper limit) as observed in wind-driven systems. More rough flows were anisotropic and gas exchange velocity was stronger related to vertical components of turbulence parameters. We further explored the potential of using surface flow type evaluations and water surface roughness measurements for estimating gas exchange velocities at the reach scale and beyond.

scholarly journals Internal boundary layer development over lake surface in case of very young waves

2021 ◽  
Author(s):  
Gabriella Lükő ◽  
Péter Torma ◽  
Tamás Weidinger ◽  
Tamás Krámer ◽  
Zeljko Vecenaj ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Wind Speed ◽  
Land Surface ◽  
Momentum Flux ◽  
Water Surface ◽  
Roughness Length ◽  
Internal Boundary Layer ◽  
Internal Boundary ◽  
Lake Surface ◽  
Wave State

<p>An internal boundary layer (IBL) may develop above lakes due to surface roughness change. The water surface has significantly less resistance to wind flow compared to the aerodynamically rough land surface. As a result, the wind speed increases along the fetch in the IBL over the lake surface. Consequently, the wind shear stress, which is the main driving force of waves and currents in lakes, also varies along the fetch. Measurements were carried out for six weeks in 2018 within a Croatian-Hungarian observational campaign in Lake Balaton in order to explore the IBL characteristics and establish a simple but reliable IBL model that can reproduce wind shear stress variability over the lake. One wind measurement station was installed on land and three over the lake along the fetch of the prevailing wind direction. On the landside, the wind profile was observed by a sodar from which characteristic land surface roughness lengths were derived by logarithmic profile fitting. On the waterside, momentum fluxes were measured with eddy-covariance (EC) technique at fetches of ~0.1, ~3.5, and ~6 km. To describe the water surface roughness dynamics, waves were simultaneously recorded with an underwater acoustic surface tracking at the middle station. An analytic IBL model is fitted to the measured wind speed and stress data employing wind speed classes. In the model, the wind stress development is dynamically coupled with the wave state by a wave age dependent roughness length function which is valid for highly fetch limited conditions and very young wave ages of ~2-15. The model is able to quantitatively reproduce wind speed, wind stress, and wave state development over the lake surface based on land observation of wind speed if the land roughness length is also known. Based on our model and measurements, we found a considerable spatial variability of momentum flux due to the change of wave state and wind speed along the fetch. The variation of momentum flux also influences the evolving sensible heat flux, which was also compared to the EC measurements.</p>

scholarly journals Air entrainment by inclined circular plunging water jets with various impingement heights

2020 ◽  
Vol 20 (8) ◽  
pp. 3478-3486
Author(s):  
Yiyi Ma ◽  
Luchen Zhang ◽  
Yu Yang ◽  
Ping Wei
Keyword(s):  
Experimental Study ◽  
Surface Roughness ◽  
Water Surface ◽  
Jet Impingement ◽  
Air Entrainment ◽  
Entrainment Rate ◽  
Water Jets ◽  
Air Entrainment Rate ◽  
Jet Breakup ◽  
Early Increase

Abstract This paper presents an experimental study on air entrainment by inclined circular plunging water jets issued from long nozzles with various jet impingement heights up to 6.1 m. Particular attention was paid to the jets having a large impingement height, and which disintegrated into small droplets before reaching the water surface. The dominant sizes and velocities of the droplets generated by jet breakup were 1–4 mm and 4–9 m/s. The results show that for plunging water jets having the same hydraulic head, the air entrainment rate increased as the jet impingement height at first grew, then dropped as the jet impingement height kept increasing. The early increase in the air entrainment rate was due to the growth of jet surface roughness, while the later decrease was caused by the water jet disintegration. The momentum of the plunging jet decreased dramatically due to the reduced mass and the significant energy dissipation through the atmosphere caused by jet disintegration. This led to a much smaller penetration depth and air entrainment rate compared to with a continuous jet.

scholarly journals The effect of water surface roughness on the measurement of radiated ship noise

2020 ◽  
Author(s):  
He Tengjiao ◽  
Victor F. Humphrey ◽  
Shiqi Mo ◽  
Erzheng Fang
Keyword(s):  
Surface Roughness ◽  
Water Surface ◽  
Effect Of Water
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