scholarly journals A NOTE ON THE DEVELOPMENT OF WIND WAVES IN AN EXPERIMENT

1966 ◽  
Vol 1 (10) ◽  
pp. 5
Author(s):  
Tokuichi Hamada ◽  
Akihiko Shibayama ◽  
Hajime Kato
Keyword(s):  
Boundary Condition ◽  
Tangential Stress ◽  
Water Surface ◽  
Physical Mechanism ◽  
Wind Waves ◽  
Air Flow ◽  
Wave Momentum

This is a note paper of experiment in an air-water experimental waterway. Two cases of the uniform depth of water 50 cm and of the uniform depth of water 15 cm are examined. The boundary condition for air flow is not changed. In a condition of almost the same discharge of air flow on the water surface, the development of wind waves is investigated. The properties of wind waves are slightly different in each case, but the analysis of physical mechanism of the development suggests that almost the same mechanism is active throughout both cases. Stillmore the portion of tangential stress, which is apparently transfered to wave momentum, is numerically obtained, and it is not so different in both cases of depth of water.

Power Generation Potential of a VLFS Equipped With OWC Type WECs and Damper Effects on Elastic Motion

2015 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Yuka Watanabe ◽  
Hiroaki Eto ◽  
Chang-kyu Rheem ◽  
...  
Keyword(s):  
Power Generation ◽  
Boundary Condition ◽  
Wave Energy ◽  
Water Surface ◽  
Free Water ◽  
Vertical Displacement ◽  
Air Pressure ◽  
Linear Potential ◽  
Floating Structure ◽  
Free Water Surface

This paper describes potential of PTO (Power Take-Off) and the damper effect of motion in a large scale pontoon type floating structure on which lots of oscillating water column (OWC) type wave energy convertors (WEC) are installed. It is enable to use upper space for utilizing marine renewable energy such as wind power, tidal power, wave power generation farm using large pontoon structure. Due to the concept, it should reduce cost of maintenance as well. For investigation of PTO and elastic motion behaviours of large floating structures, we calculated three types of models on which OWC devices were installed differently. We examined how much reduction was possible when including elastic motion effects and the fixed type which radiation wave was not taken into account. In this paper, a boundary condition in order to give effect of a free water surface with air pressure is theoretically modeled. We can directly consider influence of wave energy absorption to hydrodynamic forces and wave exciting forces on the floating structure with the Green’s function method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and vertical displacement within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement. As a result, performance of PTO and hydroelastic motion of the floating structure increased when including elastic motion effect. In addition, expected value of annual PTO was about 4.4MW with 146 OWCs.

Experimental study of the initial stages of wind waves' spatial evolution

2011 ◽  
Vol 681 ◽  
pp. 462-498 ◽  
Author(s):  
DAN LIBERZON ◽  
LEV SHEMER
Keyword(s):  
Energy Transfer ◽  
Growth Rates ◽  
Water Surface ◽  
Wind Waves ◽  
Pressure Fluctuations ◽  
Theoretical Models ◽  
Small Scale ◽  
Wave Flume ◽  
Spatial Growth ◽  
The Mean

Despite a significant progress and numerous publications over the last few decades a comprehensive understanding of the process of waves' excitation by wind still has not been achieved. The main goal of the present work was to provide as comprehensive as possible set of experimental data that can be quantitatively compared with theoretical models. Measurements at various air flow rates and at numerous fetches were carried out in a small scale, closed-loop, 5 m long wind wave flume. Mean airflow velocity and fluctuations of the static pressure were measured at 38 vertical locations above the mean water surface simultaneously with determination of instantaneous water surface elevations by wave gauges. Instantaneous fluctuations of two velocity components were recorded for all vertical locations at a single fetch. The water surface drift velocity was determined by the particle tracking velocimetry (PTV) method. Evaluation of spatial growth rates of waves at various frequencies was performed using wave gauge records at various fetches. Phase relations between various signals were established by cross-spectral analysis. Waves' celerities and pressure fluctuation phase lags relative to the surface elevation were determined. Pressure values at the water surface were determined by extrapolating the measured vertical profile of pressure fluctuations to the mean water level and used to calculate the form drag and consequently the energy transfer rates from wind to waves. Directly obtained spatial growth rates were compared with those obtained from energy transfer calculations, as well as with previously available data.

scholarly journals Searching for chaotic deterministic features in laboratory water surface waves

2000 ◽  
Vol 7 (1/2) ◽  
pp. 37-48 ◽  
Author(s):  
M. Joelson ◽  
Th. Dudok de Wit ◽  
Ph. Dussouillez ◽  
A. Ramamonjiarisoa
Keyword(s):  
Surface Waves ◽  
Water Surface ◽  
Wind Waves ◽  
Theoretical Models ◽  
Resonant Interactions ◽  
Mechanical Waves ◽  
Random Character ◽  
Nonlinear Features ◽  
Low Dimensional ◽  
Laboratory Water

Abstract. The dynamic evolution of laboratory water surface waves has been studied within the framework of dynamical systems with the aim to identify stochastic or deterministic nonlinear features. Three different regimes are considered: pure wind waves, pure mechanical waves and mixed (wind and mechanical) waves. These three regimes show different dynamics. The results on wind waves do not clearly support the recently proposed idea that a deterministic Stokes-like component dominate the evolution of such waves; they are more appropriately described by a similarity-like approach that includes a random character. Cubic resonant interactions are clearly identified in pure mechanical waves using tricoherence functions. However, detailed aspects of the interactions do not fully agree with existing theoretical models. Finally, a deterministic motion is observed in mixed waves, which therefore are best described by a low dimensional nonlinear deterministic process.

Investigation of droplet-mediated sensible and latent heat fluxes in a turbulent air flow over a waved water surface by direct numerical simulation

2020 ◽  
Author(s):  
Oleg Druzhinin
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Direct Numerical Simulation ◽  
Latent Heat ◽  
Water Surface ◽  
Air Flow ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Coupled Equations ◽  
Turbulent Air Flow

<p>The objective of the present study is to investigate sensible and latent heat transfer mediated by evaporating saline droplets in a turbulent air flow over a waved water surface by performing direct numerical simulation. Equations of the air-flow velocity, temperature and humidity are solved simultaneously with the two-way-coupled equations of individual droplets coordinates and velocities, temperatures and masses. Two different cases of air and water surface temperatures,T<sub>a</sub> = 27 <sup>0</sup>C, T<sub>s</sub> = 28 <sup>0</sup>C,  and T<sub>a</sub> = -10 <sup>0</sup>C, T<sub>s</sub> = 0 <sup>0</sup>C, are considered and conditionally termed as "tropical cyclone" (TC) and "polar low"  (PL) conditions, respectively. Droplets-mediated sensible and latent heat fluxes, Q<sub>S</sub> and Q<sub>L</sub>, are integrated along individual droplets Lagrangian trajectories and evaluated as distributions over droplet diameter at injection, d, and also obtained as Eulerian, ensemble-averaged fields. The results show that under TC-conditions, the sensible heat flux from droplets to air is negative whereas the latent heat flux is positive, and thus droplets cool and moisturize the carrier air. On the other hand, under PL-conditions, Q<sub>S</sub> and Q<sub>L</sub>  are both positive, and Q<sub>L</sub> – contribution is significantly reduced as compared to Q<sub>S</sub> - contribution. Thus in this case, droplets warm up the air. In both cases, the droplet-mediated enthalpy flux, Q<sub>S</sub><sub> </sub>+ Q<sub>L </sub>, is positive, vanishes for sufficiently small droplets (with diameters d ≤ 150 μm) and further increases with d. The results also show that the net fluxes are reduced with increasing wave slope.</p><p>This work is supported by the Ministry of Education and Science of the Russian Federation (Task No. 0030-2019-0020). Numerical algorithms were developed under the support of RFBR (Nos. 18-05-60299, 18-55-50005, 18-05-00265, 20-05-00322). Postprocessing was performed under the support of the Russian Science Foundation (No. 19-17-00209).</p>

Wind action on water standing in a laboratory channel

1966 ◽  
Vol 26 (4) ◽  
pp. 651-687 ◽  
Author(s):  
G. M. Hidy ◽  
E. J. Plate
Keyword(s):  
Water Surface ◽  
Wind Waves ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Wavy Surface ◽  
Recent Theory ◽  
Waves And Currents ◽  
Mean Wind Speed ◽  
Equilibrium Range ◽  
The Waves

The development of waves and currents resulting from the action of a steady wind on initially standing water has been investigated in a wind–water tunnel. The mean air flow near the water surface, the properties of wind waves, and the drift currents were measured as they evolved with increasing fetch, depth and mean wind speed. The results suggest how the stress on the water surface changes with an increasingly wavy surface, and, from a different viewpoint, how the drift current and the waves develop in relation to the friction velocity of the air. The amplitude spectra calculated for the wavy surface reflected certain features characteristic of an equilibrium configuration, especially in the higher frequencies. The observed equilibrium range in the high frequencies of the spectra fits the f−5 rule satisfactorily up to frequencies f of about 15 c/s. The wave spectra also revealed how the waves grow in the channel, both with time at a fixed point, and with distance from the leading edge of the water. These results are discussed in the light of recent theories for wave generation resulting from the action of pressure fluctuations in the air, and from shearing flow instabilities near the wavy surface. The experimental observations agree reasonably well with the predictions of the recent theory proposed by Miles, using growth rates calculated for the mechanism suggesting energy transfer to the water through the viscous layer in the air near the water surface.

A 3-Dimentional Numerical Analysis of Solar-Panel-Chimney for House Ventilation

2013 ◽  
Vol 483 ◽  
pp. 149-153
Author(s):  
Song Hao Wang ◽  
Chih Sheng ◽  
Huann Ming Chou ◽  
Shun Chih Yu
Keyword(s):  
Numerical Analysis ◽  
Solar Power ◽  
Physical Mechanism ◽  
Air Flow ◽  
Ventilation System ◽  
Solar Panel ◽  
Numerical Analyses ◽  
Flow Rates ◽  
Dimensional Parameters ◽  
Innovative Concept

3-dimentional CFD Numerical analyses were conducted. Major dimensional parameters were considered in the simulation and meaningful air flow rates were observed under normal conditions. to fully understand the physical mechanism of the phenomenon by air buoyancy. Based on the results of the study, the proposed solar panel chimney and its advantages are worth of further investigation. Based on this innovative concept, the rooftop solar panel could be re-arranged, grouped and boxed to form an effective solar panel chimney, to serve as passive ventilation system without much cost and fully utilize the solar power.

Modulation of short wind waves by a long surface wave: a mechanism for feedback with an air flow

1997 ◽  
Vol 8 (5) ◽  
pp. 305-327
Author(s):  
V. N. Kudryavtsev ◽  
K. Mastenbroek ◽  
V. K. Makin
Keyword(s):  
Surface Wave ◽  
Wind Waves ◽  
Air Flow
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