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1
Oost, W. A. "The wind profile in a wave flume". Journal of Wind Engineering and Industrial Aerodynamics 37, n. 2 (marzo 1991): 113–21. http://dx.doi.org/10.1016/0167-6105(91)90067-7.
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2
Tsoukala, V. K., e C. I. Moutzouris. "Gas transfer under breaking waves: experiments and an improved vorticity-based model". Annales Geophysicae 26, n. 8 (31 luglio 2008): 2131–42. http://dx.doi.org/10.5194/angeo-26-2131-2008.
Testo completoAbstract (sommario):
Abstract. In the present paper a modified vorticity-based model for gas transfer under breaking waves in the absence of significant wind forcing is presented. A theoretically valid and practically applicable mathematical expression is suggested for the assessment of the oxygen transfer coefficient in the area of wave-breaking. The proposed model is based on the theory of surface renewal that expresses the oxygen transfer coefficient as a function of both the wave vorticity and the Reynolds wave number for breaking waves. Experimental data were collected in wave flumes of various scales: a) small-scale experiments were carried out using both a sloping beach and a rubble-mound breakwater in the wave flume of the Laboratory of Harbor Works, NTUA, Greece; b) large-scale experiments were carried out with a sloping beach in the wind-wave flume of Delft Hydraulics, the Netherlands, and with a three-layer rubble mound breakwater in the Schneideberg Wave Flume of the Franzius Institute, University of Hannover, Germany. The experimental data acquired from both the small- and large-scale experiments were in good agreement with the proposed model. Although the apparent transfer coefficients from the large-scale experiments were lower than those determined from the small-scale experiments, the actual oxygen transfer coefficients, as calculated using a discretized form of the transport equation, are in the same order of magnitude for both the small- and large-scale experiments. The validity of the proposed model is compared to experimental results from other researchers. Although the results are encouraging, additional research is needed, to incorporate the influence of bubble mediated gas exchange, before these results are used for an environmental friendly design of harbor works, or for projects involving waste disposal at sea.
3
Wei, Chengxun, Shenghui Li e Haiying Mao. "Development of a Wind–Wave Coherence Function Based on Numerical Studies". Water 16, n. 17 (9 settembre 2024): 2552. http://dx.doi.org/10.3390/w16172552.
Testo completoAbstract (sommario):
The synchronization and intensity of fluctuating wind speeds and wave surfaces in wind–wave joint propagation processes are affected by the coherence of the marine ambient factors of fluctuating wind and random waves. This coherence further affects the precise calculations of wind–wave joint actions on marine structures. Therefore, a wind–wave joint propagation numerical flume was established based on the numerical simulation of random waves and fluctuating wind fields. A series of numerical simulations of wind–wave joint propagations were carried out. Based on the numerical results, the influences and influence laws of factors such as wind speed position height, significant wave height and wave spectrum peak frequency on the wind–wave coherence values were studied. According to the influence characteristics of these factors, a function of wind–wave coherence values for random wind–wave joint propagation was calculated. The coherence function takes frequency as the variable, while parameters include significant wave height, wind speed position height and wave spectrum peak frequency. Through a series of numerical simulation results, data fitting was used to calculate the parameter coefficients of the coherence function. The established random wind–wave coherence function can be described using the wind–wave joint fields of marine structures and the computational analyses of structural wind–wave joint actions.
4
Syamsidik, Syamsidik, Benazir Benazir, Nadri Pratama, Arifullah Arifullah, Eldina Fatimah, Nazaruddin Nazaruddin, Tarmizi Tarmizi, Ibrahim Ibrahim e Ikramullah Zein. "A New Multi-Purposes Flume Experiments Facility: Challenges and Opportunity for Tsunami and Coastal Engineering in Indonesia". International Journal of Disaster Management 6, n. 3 (24 marzo 2024): 345–54. http://dx.doi.org/10.24815/ijdm.v6i3.34568.
Testo completoAbstract (sommario):
Physical modelling for tsunami engineering is rather difficult to conduct due to lack of comprehensive and advanced facilities to do so. Large number of simulations of the tsunami impacts were performed numerically. In early 2023, a new advanced tsunami flume facility has been completed at Tsunami and Disaster Mitigation Research Center (TDMRC) of Universitas Syiah Kuala. This flume has 60 m in length, 2.5 m in width, and 1.7 m in height. The flume is also equipped with a number of wave, pressure, and current sensors, Particle Image Velocimetery (PIV) Camera, and a laser bed profiler. Beside of the tsunami generator, this flume is also capable to generate wind-driven waves (with two large wind turbines), regular and irregular waves, and currents. The flume provides new opportunities as well as challenges for tsunami scientists and engineers in Indonesia to collaborate and to perform novel researches in tsunami mitigation. This article is aimed at elucidating technical challenges and opportunities in performing tsunami physical models with the large tsunami flume. we performed a series numerical models using DualSPHysic. The results show that composite beach slopes inside the flume has succesfully mimic shallow coast effects that later deformed the incoming tsunami waves into breaking, bores, and runup. Challenges were identified in absorbing tsunami waves with more than one incoming wave to the observation area. In the future, this facility will be accessible for scientists and engineers to collaborate in tsunami science and engineering researches.
5
Zavadsky, A., D. Liberzon e L. Shemer. "Statistical Analysis of the Spatial Evolution of the Stationary Wind Wave Field". Journal of Physical Oceanography 43, n. 1 (1 gennaio 2013): 65–79. http://dx.doi.org/10.1175/jpo-d-12-0103.1.
Testo completoAbstract (sommario):
Abstract Detailed investigation of wind-generated water waves in a 5-m-long wind wave flume facility is reported. Careful measurements were carried out at a large number of locations along the test section and at numerous airflow rates. The evolution of the wind wave field was investigated using appropriate dimensionless parameters. When possible, quantitative comparison with the results accumulated in field measurements and in larger laboratory facilities was performed. Particular attention was given to the evolution of wave frequency spectra along the tank, distinguishing between the frequency domain around the spectral peak and the high-frequency tail of the spectrum. Notable similarity between the parameters of the evolving wind wave field in the present facility and in field measurements was observed.
6
Deng, Sijia, Ming Qin, Dezhi Ning, Lin Lin, Songxiong Wu e Chongwei Zhang. "Numerical and Experimental Investigations on Non-Linear Wave Action on Offshore Wind Turbine Monopile Foundation". Journal of Marine Science and Engineering 11, n. 4 (21 aprile 2023): 883. http://dx.doi.org/10.3390/jmse11040883.
Testo completoAbstract (sommario):
Monopiles are commonly utilized in offshore wind farms but are prone to non-linear wave loads and run-ups, significantly affecting their engineering design. Therefore, it is crucial to pursue a complete understanding of the non-linear wave action on monopile foundations. Both numerical and experimental investigations on the non-linear wave loads and run-ups on an offshore wind turbine monopile foundation are performed in this paper. The experiment is carried out at a scale of 1/30 in a wave flume at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, in which the wave loads and run-ups along the monopile are measured. Based on the second-order potential flow model and time-domain higher-order boundary element method (HOBEM), the related numerical tests are conducted to study the non-linear effects further. It is found that the present non-linear potential theory is sufficient for the simulation of wave force and run-ups on the monopile in the range of wave slope kA < 0.15 before wave breaking. “W” type distribution of wave run-up along the monopile is found, in which the peak value occurs at the frontward side (i.e., θ =180°) and is the maximum due to full reflection; the two symmetrical minimum amplitudes lie in the zones of (45° ≤ θ ≤ 90°) and (270° ≤ θ ≤ 315°), whose positions shift downward with the increase of wave non-linearity. Energy transfer among the fundamental wave component and higher-order components is also found, which is most apparent on the backward side. Besides, the transverse resonance occurs in the wave flume due to the wavelength being near the flume width, which induces the wave run-up at the backward position larger than that at the frontward position.
7
KAWASAKI, Koji, e Masami KIKU. "PROPOSAL OF NUMERICAL WAVE FLUME FOR WAVE OVERTOPPING ANALYSIS CONSIDERING WIND EXTERNAL FORCE". Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) 67, n. 2 (2011): I_58—I_63. http://dx.doi.org/10.2208/jscejoe.67.i_58.
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8
Kiku, Masami, e Koji Kawasaki. "PROPOSAL OF NUMERICAL WAVE FLUME FOR WAVE OVERTOPPING COMPUTATION CONSIDERING WIND EXTERNAL FORCE". Coastal Engineering Proceedings 1, n. 34 (30 ottobre 2014): 8. http://dx.doi.org/10.9753/icce.v34.waves.8.
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9
Kandaurov, Alexander, Daniil Sergeev, Yuliya Troitskaya e Olga Ermakova. "Investigation of the mechanisms of sea spray generation induced by wind-wave interaction in laboratory conditions". EPJ Web of Conferences 213 (2019): 02036. http://dx.doi.org/10.1051/epjconf/201921302036.
Testo completoAbstract (sommario):
The paper presents the results of investigations of the mechanisms of spray of droplets generation within wind wave interaction obtained under laboratory conditions on the High-speed Wind-Wave Flume of the Institute of Applied Physics of the Russian Academy of Sciences. For the research, a multi-angle high-speed video system used together shadow method, including underwater illumination. The results allowed for the classification of mechanismsleading to the formation of droplets. Three main types of phenomena responsible for the generation of the spume droplets near the wave crest were specified: breakage of liquid ligaments, bursting of large submerged bubbles, and bag breakup. The last and less known mechanism claims to be dominant for high wind speeds and it was described in detail.
10
Chowdhury, S. De, J. G. Zhou, L. Qian, D. Causon, C. Mingham, T. Pullen, K. Hu et al. "WIND EFFECTS ON OVERTOPPING DISCHARGE AT COASTAL DEFENCES". Coastal Engineering Proceedings, n. 36v (31 dicembre 2020): 40. http://dx.doi.org/10.9753/icce.v36v.papers.40.
Testo completoAbstract (sommario):
Wind effects on wave overtopping over fully impermeable vertical sea defence is studied in a shallow water flume based on a physical model for the Livermeade defence system. The investigation is mainly focused on impulse type wave interaction with the sea defence, when the overshooting jet is high during overtopping. We are able to identify distinct types of overtopping flows where moderate wind speed is not found to be affecting uniformly in all cases. We try to find explanation of this behaviours by studying the standing waves at the defence and complementary CFD simulations.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/byRz_N9zoXk
11
Yang, Ray-Yeng, Hsin-Hung Chen, Hwung-Hweng Hwung, Wen-Pin Jiang e Nian-Tzu Wu. "EXPERIMENTAL STUDY ON THE LOADING AND SCOUR OF THE JACKET TYPE OFFSHORE WIND TURBINE FOUNDATION". Coastal Engineering Proceedings 1, n. 32 (21 gennaio 2011): 25. http://dx.doi.org/10.9753/icce.v32.structures.25.
Testo completoAbstract (sommario):
A 1:36 scale model tests were carried out in the Medium Wave Flume (MWF) and Near-shore Wave Basin (NSWB) at the Tainan Hydraulics Laboratory (THL) with the jacket type offshore wind turbine foundation located in the test area. The loading of typhoon wave with current on the jacket type offshore wind turbine foundation was investigated in the MWF with fixed bed experiment. Meanwhile, the scour around the jacket type offshore wind turbine foundation exposed to wave and current was conducted in the NSWB with the moveable bed experiment. Two locations (water depth 12m and 16m) of the foundations are separately simulated in this study. Based on the analysis from the former NSWB experimental results, the suitable scour protection of a four-layer work around the foundation is also proposed to the impact of scour. Finally, a four-layer scour protection is tested and found to be effective in preventing scour around jacket type foundation of offshore wind turbines at water depth 12m and 16m.
12
Kahma, Kimmo K., e Mark A. Donelan. "A laboratory study of the minimum wind speed for wind wave generation". Journal of Fluid Mechanics 192 (luglio 1988): 339–64. http://dx.doi.org/10.1017/s0022112088001892.
Testo completoAbstract (sommario):
The minimum wind speed for wind wave generation has been investigated in a laboratory wind-wave flume using a sensitive slope gauge to measure the initial wavelets about 10 μm high. The growth at very low wind speeds was higher than predicted by the viscous shear-flow instability theory. Assuming that the growth is exponential, the inception wind speed at which the growth rate becomes positive can be defined. It occurred at (friction velocity) u* ≈ 2 cm/s, somewhat lower than the u* ≈ 4–5 cm/s predicted by shear-flow instability theory. However, the observed growth rates were close to the theory at higher wind speeds when the waves were higher than 1 mm. The effect of temperature on the wind speed at which the waves become readily visible is shown to be appreciable and in keeping with the temperature dependent viscous damping. Other sources of growth are discussed. Our estimates show that the Phillips resonance mechanism might be sufficiently effective to generate the observed growth at very low wind speeds.
13
Rusakov, N. S., G. A. Baydakov e Yu I. Troitskaya. "A COMPOSITE MODEL OF MICROWAVE SCATTERING FROM WATER SURFACE IN EXTREME WIND SPEED CONDITION". Доклады Российской академии наук. Науки о Земле 513, n. 1 (1 novembre 2023): 139–45. http://dx.doi.org/10.31857/s2686739723601710.
Testo completoAbstract (sommario):
Experiments were carried out in the wind-wave flume of Large Thermo-Stratified Wind-Wave Tank of IAP RAS aimed at studying the mechanisms of cross-polarized microwave radiation scattering from water surface under conditions of extremely high wind speeds. It is shown that the normalized radar cross-section (NRCS) can be represented as the result of an incoherent addition of contributions from breaking wave crests and from non-breaking wind waves. The effect of smoothing the water surface after passing the breaking crest made it possible to measure the NRCS of the breaking area on cross-polarization, while no dependence of the NRCS on wind speed and incidence angle was revealed. NRCS on non-breaking wind waves was calculated within the framework of the small slope approximation (SSA) using experimentally measured wind wave spectra. It is shown that the NRCS on cross-polarization increases monotonically with increasing wind speed, including hurricane conditions. In this case, the contribution of non-breaking wind waves to the NRCS saturates at wind speeds above 25 m/s. The monotonous increasing NRCS at higher wind speeds is associated with a breaking area increasing. A composite model of microwave radiation scattering from wave-covered water surface has been constructed, which has been verified on the basis of comparison with measurement data. The possibility of constructing a geophysical model function for ocean conditions based on the proposed composite model is shown, which can be used for remote sensing of sea storms and hurricanes.
14
Jiang, Changbo, Yang Yang e Bin Deng. "Study on the Nearshore Evolution of Regular Waves under Steady Wind". Water 12, n. 3 (3 marzo 2020): 686. http://dx.doi.org/10.3390/w12030686.
Testo completoAbstract (sommario):
We present a study on regular wave propagation on a sloping bed under the action of steady wind, which is of a great significance to complement and replenish the interaction mechanisms of nearshore wave and wind. Physical experiments were conducted in a wind-wave flume, and the corresponding numerical model was constructed based on the solver Waves2FOAM in OpenFOAM, with large-eddy simulation (LES) used to investigate the turbulent flow. The comparisons between the measured and calculated results of the free surface elevation and flow velocity indicated that the numerical model could predict the associated hydrodynamic characteristics of a nearshore wave regardless of the presence or absence of wind. The results showed that wind had a significant impact on nearshore wave evolution. It was found that under the same wind speed coverage constraint, wave breaking occurred ahead of time. The smaller the surf similarity ξ 0 was, the higher the dispersion degree of wave breaking locations would be, and the breaker index of H b / h b increased with wind speed under the same incident wave height. The main components of analysis for turbulent flow were the results of the cross-spectrum, the TKE (turbulent kinetic energy), and TDR (turbulent dissipation rate). The cross-spectrum illustrated that wind enhanced the degree of coherence of the residual velocity components and aggravated turbulence. The TKE indicated that in regions near the water surface, wind speed made it considerably larger and the average level rapidly decreased with depth. The TDR exhibited that the significant effect of wind was merely imposed after breaking, wherein the turbulence penetrated the deeper flow and the average level generally rose. The velocity profile on the slope showed that the wind accelerated the undertow, and the moment statistics indicated that the velocity distribution deviated gradually from the Gaussian distribution to the right.
15
Sullivan, Peter P., Michael L. Banner, Russel P. Morison e William L. Peirson. "Turbulent Flow over Steep Steady and Unsteady Waves under Strong Wind Forcing". Journal of Physical Oceanography 48, n. 1 (gennaio 2018): 3–27. http://dx.doi.org/10.1175/jpo-d-17-0118.1.
Testo completoAbstract (sommario):
AbstractTurbulent flow over strongly forced steep steady and unsteady waves is simulated using large-eddy simulation (LES) with time t and space x varying wave height h(x, t) imposed as a lower boundary condition. With steady waves, h(x, t) is based on measurements of incipient and active breaking waves collected in a wind-wave flume, while a numerical wave code is used to generate an unsteady evolving wave packet (group). Highly intermittent airflow separation is found in the simulations, and the results suggest separation near a wave crest occurs prior to the onset of wave breaking. The form (pressure) drag is most sensitive to the wave slope, and the form drag can contribute as much as 74% to the total stress. Wind and scalar profiles from the LES display log-linear variations above the wave surface; the LES wind profiles are in good agreement with the measurements. The momentum roughness increases as the water surface changes from wind ripples to incipient breaking to active breaking. However, the scalar roughness decreases as the wave surface becomes rougher. This highlights major differences in momentum and scalar transport over a rough wavy surface. For a rapidly evolving, strongly forced wave group, the form drag is highly correlated with the wave slope, and intermittent separation is found early in the packet evolution when the local wave slope −∂h/∂x(x, t) ≥ 0.22. The packet root-mean-square wave slope is 0.084, but the form drag fraction is 2.4 times larger than a comparably forced steady wave. Thus, a passing wave group can induce unsteadiness in the wind stress.
16
Wang, Guangsheng, Kai Zhang e Jian Shi. "The Effect of Different Swell and Wind-Sea Proportions on the Transformation of Bimodal Spectral Waves over Slopes". Water 16, n. 2 (15 gennaio 2024): 296. http://dx.doi.org/10.3390/w16020296.
Testo completoAbstract (sommario):
In the laboratory experiment, 1:25 scaled models are constructed to investigate the effect of different swell and wind-sea proportions on the wave transformation. The source of the wave spectrum is related to the wave conditions in the Gulf of Guinea. Swell from the westerlies and local wind-sea forms the bimodal spectral waves in the region. To better understand the transformation of bimodal spectral waves, a series of wave conditions are measured by the wave gauges in a wave flume. Based on the wave spectrum at the Bight of Benin, the wave transformation along the slopes and variations of different swell proportions are analyzed. The result of the wave height variations shows that the slope and swell proportion play a significant role in the maximum wave height, and the wave height has an upward trend with a large swell proportion. The analysis of wave nonlinearity is conducted, showing that the large swell proportion in the wave spectrum leads to a more significant nonlinearity before wave breaking. Combining the variations of wave height and wave nonlinearity, the influence of bimodal spectral waves on nearshore wave prediction, shoreline change, marine operations, and structure design is discussed.
17
Yuan, Zhen Zhong, Bhupendra Singh Chauhan e Hee Chang Lim. "Study of a Wave Absorber in Various Distance Placed in a Sinusoidal Propagate Wave". Applied Mechanics and Materials 302 (febbraio 2013): 326–31. http://dx.doi.org/10.4028/www.scientific.net/amm.302.326.
Testo completoAbstract (sommario):
Since there has been a rapid progress to understand the dynamics of an offshore floating body under an ocean environment, we undertake to generate the ocean waves in a lab-scale wind-wave flume. The study is aiming to observe and optimize the similar ocean environmental condition as input wave and to reduce the wall reflective wave. Several absorption methods are suggested to optimize the propagate wave by measuring the maximum and minimum of the standing wave envelope. There has been no optimized absorption method, as they highly depend on the wave period and the wave length. One of the methods - two fixed wave gauges measuring two wave heights and one wave phase - is applied in this study. In the present paper various approaches were used to analyze the results using the flume, by position of probes, with absorber and without absorber, different position, condition and angle of the wave absorber, This paper also focuses on the analysis of fundamental equations which describe the separating method of the incident and reflective wave, and finally we confirm that the wave absorber is highly efficient considering all the permutation and combination.From the study it is clear that there is a change in the wave amplitude at the receiving end then the generated end; wave absorber is a strong source to control the energy of the coming wave. With the changing the period of the wave, the reflectance is increasing when the period becomes larger.
18
Zhu, Li-Xin, SeYoung Kim e HeeChang Lim. "Study on the Surge Motion of a Circular Cylinder Placed in the Propagating Wave". International Journal of Advance Research and Innovation 2, n. 2 (2014): 125–29. http://dx.doi.org/10.51976/ijari.221419.
Testo completoAbstract (sommario):
With the rapid development of offshore wind turbines, research about the stability of floating structure comes to be significance. This study aims at observing the movement characteristics of a circular cylinder . To simulate ocean wave, the demonstrative experiment was performed in a small-scale wave flume combined with a wave generator and a wave absorber. Moreover, to precisely visualize the oscillation of the circular cylinder, we have prepared (1) water level gauge (CH-601, KENEK, operation range±100mm); (2) circular cylinder with a set of light emitting diode illuminators; (3) a high-speed charge-coupled device camera. Through the wave generator under a variety of wave conditions such as different wave heights and periods, this study as a fundamental research aims to observe surge motion of a circular cylinder placed in the propagating wave.
19
Liberzon, Dan, e Lev Shemer. "An Inexpensive Method for Measurements of Static Pressure Fluctuations". Journal of Atmospheric and Oceanic Technology 27, n. 4 (1 aprile 2010): 776–84. http://dx.doi.org/10.1175/2009jtecha1352.1.
Testo completoAbstract (sommario):
Abstract An application of a commercially available and inexpensive pressure probe and transducer, originally designed for pressure drop measurements in air conditioning conduits, is suggested for accurate and reliable measurements of static pressure fluctuations in airflow, with a particular application to wind interaction with water waves. It is demonstrated that this static pressure probe is a robust instrument that offers efficient dynamic pressure elimination while having low directional sensitivity and sufficiently high dynamic response. A series of measurements in a wind-wave flume was carried out to validate the characteristics of the sensor and of the pressure transducer.
20
Laxague, Nathan J. M., Brian K. Haus, David G. Ortiz-Suslow, Conor J. Smith, Guillaume Novelli, Hanjing Dai, Tamay Özgökmen e Hans C. Graber. "Passive Optical Sensing of the Near-Surface Wind-Driven Current Profile". Journal of Atmospheric and Oceanic Technology 34, n. 5 (maggio 2017): 1097–111. http://dx.doi.org/10.1175/jtech-d-16-0090.1.
Testo completoAbstract (sommario):
AbstractEstimation of near-surface current is essential to the estimation of upper-ocean material transport. Wind forcing and wave motions are dominant in the near-surface layer [within O(0.01) m of the surface], where the highly sheared flows can differ greatly from those at depth. This study presents a new method for remotely measuring the directional wind and wave drift current profile near to the surface (between 0.01 and 0.001 m for the laboratory and between 0.1 and 0.001 m for the field). This work follows the spectral analysis of high spatial (0.002 m) and temporal resolution (60 Hz) wave slope images, allowing for the evaluation of near-surface current characteristics without having to rely on instruments that may disturb the flow. Observations gathered in the 15 m × 1 m × 1 m wind-wave flume at the University of Miami’s Surge-Structure-Atmosphere Interaction (SUSTAIN) facility show that currents retrieved via this method agree well with the drift velocity of camera-tracked dye. Application of this method to data collected in the mouth of the Columbia River (MCR) indicates the presence of a near-surface current component that departs considerably from the tidal flow and may be steered by the wind stress. These observations demonstrate that wind speed–based parameterizations alone may not be sufficient to estimate wind drift and to hold implications for the way in which surface material (e.g., debris or spilled oil) transport is estimated when atmospheric stress is of relatively high magnitude or is steered off the mean wind direction.
21
Knobler, Sagi, Ewelina Winiarska, Alexander Babanin e Dan Liberzon. "Wave breaking probabilities under wind forcing in open sea and laboratory". Physics of Fluids 34, n. 3 (marzo 2022): 032122. http://dx.doi.org/10.1063/5.0084276.
Testo completoAbstract (sommario):
Water wave breaking represents one of the most arduous problems in fluid mechanics. Understanding the process of wave breaking and developing an ability to quantify the associated energy losses and redistribution are critical across a wide range of coastal oceanic applications, maritime navigation, and climate and hydrodynamic research. Naturally, waves become steeper toward the inception of breaking; however, there is still a lack of unanimity regarding the relationship between breaking probability statistics and wave steepness. Here, we present a detailed investigation of breaking vs non-breaking statistics estimated using a recently developed method for accurate detection of breaking waves, based on the phase-time approach to identify breaking-associated patterns in the instantaneous frequency variations of surface elevation fluctuations. The findings are based on data collected both in the open sea and in a laboratory wind wave flume. An in-depth examination of celerities and steepnesses of breaking and non-breaking waves is presented. The analysis, which involved wave-by-wave examination, produced skewed Gaussian-like steepness histograms, revealing that non-breaking waves and breaking waves can reach steeper profiles, above the Stokes limit. All extreme steepness values were investigated and are presented here.
22
Zhang, Xin Zhou, Xi Ping Dou, Xiao Dong Zhao, Xiang Ming Wang e Xiang Yu Gao. "3D Numerical Simulation of Current and Sediment Transport in Estuary and Coast". Advanced Materials Research 779-780 (settembre 2013): 899–902. http://dx.doi.org/10.4028/www.scientific.net/amr.779-780.899.
Testo completoAbstract (sommario):
In estuarine and coastal area, due to the colligated function of tide, runoff, wind and wave, suspended sediment profile in main flow direction varies from the inland river. Thus, combined with massive data sets from experiments in flume and observations in field, the study on the profile of concentration of suspended sediment are carried out in the thesis. Finally, 3D numerical model of turbulent sediment is established in estuarine and coastal area to carry out a simulation research on current and sediment movement in Yangtze River estuary.
23
BANNER, MICHAEL L., e WILLIAM L. PEIRSON. "Tangential stress beneath wind-driven air–water interfaces". Journal of Fluid Mechanics 364 (10 giugno 1998): 115–45. http://dx.doi.org/10.1017/s0022112098001128.
Testo completoAbstract (sommario):
The detailed structure of the aqueous surface sublayer flow immediately adjacent to the wind-driven air–water interface is investigated in a laboratory wind-wave flume using particle image velocimetry (PIV) techniques. The goal is to investigate quantitatively the character of the flow in this crucial, very thin region which is often disrupted by microscale breaking events. In this study, we also examine critically the conclusions of Okuda, Kawai & Toba (1977), who argued that for very short, strongly forced wind-wave conditions, shear stress is the dominant mechanism for transmitting the atmospheric wind stress into the water motion – waves and surface drift currents. In strong contrast, other authors have more recently observed very substantial normal stress contributions on the air side. The availability of PIV and associated image technology now permits a timely re-examination of the results of Okuda et al., which have been influential in shaping present perceptions of the physics of this dynamically important region. The PIV technique used in the present study overcomes many of the inherent shortcomings of the hydrogen bubble measurements, and allows reliable determination of the fluid velocity and shear within 200 μm of the instantaneous wind-driven air–water interface.The results obtained in this study are not in accord with the conclusions of Okuda et al. that the tangential stress component dominates the wind stress. It is found that prior to the formation of wind waves, the tangential stress contributes the entire wind stress, as expected. With increasing distance downwind, the mean tangential stress level decreases marginally, but as the wave field develops, the total wind stress increases significantly. Thus, the wave form drag, represented by the difference between the total wind stress and the mean tangential stress, also increases systematically with wave development and provides the major proportion of the wind stress once the waves have developed beyond their early growth stage. This scenario reconciles the question of relative importance of normal and tangential stresses at an air–water interface. Finally, consideration is given to the extrapolation of these detailed laboratory results to the field, where the present findings suggest that the sea surface is unlikely to become fully aerodynamically rough, at least for moderate to strong winds.
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Aartsen, M. W. "MODEL STUDY ON THE IMPACT OF WAVES". Coastal Engineering Proceedings 1, n. 6 (29 gennaio 2011): 45. http://dx.doi.org/10.9753/icce.v6.45.
Testo completoAbstract (sommario):
The problem to be investigated is the structural strength of a sluice gate under the influence of wave attack. The gate was designed in view of the hydraulic forces in quasi permanent conditions The fact, however, that the gate is exposed to wave attack, necessitates an investigation of:
1) the transient forces due to impact,
2) the possibilities of modificating the shape of the gate in order to avoid, or at least to diminish, the chance on the occurrence of impacts.
As the mechanism of wave attack is influenced by the hydrodynamic properties of the oncoming waves, the tests are being carried out in a flume in which the waves are generated by wind in order to simulate the expected extreme natural conditions as close as possible.
25
Riha, Jaromir, e Miroslav Spano. "The Influence of Current on the Height of Wind Wave Run-Up: A comparison of experimental results with the Czech National Standard". Journal of Hydrology and Hydromechanics 60, n. 3 (1 settembre 2012): 174–84. http://dx.doi.org/10.2478/v10098-012-0015-2.
Testo completoAbstract (sommario):
The Influence of Current on the Height of Wind Wave Run-Up: A comparison of experimental results with the Czech National StandardOne of the basic questions related to the safety of dikes and river levees is the size of the freeboard. One of the important parameters for freeboard design is the height of waves and wave run-up on levee slopes. Routine and standardised calculations of wave run-up deal with the freeboards of dams where wind waves originate on the still water of the reservoir. In the case of running water in streams (thereinafter only "currents") the effect of wave and current interaction on wave run-up is usually not taken into account due to the lack of reliable knowledge regarding the phenomenon. In the Czech Republic this question is topical in the case of large rivers such as the Elbe, the Vltava and the Morava. Within the framework of the projects Hydralab III and NAZV QI 92A139, hydraulic research and further analysis focused on wave run-up as a result of the combination of current and wind wave parameters were performed. The laboratory research was carried out in a hydraulic flume with a wavemaker on the right bank and a levee with a slope of 1:3 installed on the left bank opposite the wavemaker. Waves were generated both perpendicular and oblique to the levee axis; the angle of oblique wave attack varied within the range of ± 30°. The aim of this paper is to compare the results of the mentioned research with recommendations mentioned in the Czech National Standard CSN 75 0255Calculation of wave effects on water structuresand to quantify the effect of current on the wave run-up height.
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Shim, Kyu-Tae, e Kyu-Han Kim. "A Study on the Characteristics of Beach Profile Evolution According to the Particle Size Variation of Beach Nourishment". Water 15, n. 16 (16 agosto 2023): 2956. http://dx.doi.org/10.3390/w15162956.
Testo completoAbstract (sommario):
This study investigated the beach nourishment effect and topographical changes when using nourishment sand with relatively large particle diameters to perform beach nourishment on a beach subject to erosion. A physical model test was conducted in a 2D wave flume with an installed wind tunnel. The experiment examined the sediment transport mechanism under conditions with wind and waves. Although applying nourishment sand with large particle diameters attenuated sediment transport, the increase in particle diameter was not always proportional to the reduction in topographical changes. Increasing the particle diameter of the nourishment sand increased the friction force between particles, resulting in large-scale erosion and accretion around the coastline, and this trend increased with winds. Also, with wind, the wave run-up height increased, the undertow became stronger, and large-scale scouring occurred at the boundary between the nourishment sand and the existing beach. Increasing the particle diameter of the nourishment sand played a role in reducing the run-up phenomenon (d50: 1.0 mm with 24–50%, d50: 5.0 mm with 59–83%), and the range of particles moved by winds also decreased (d50: 1.0 mm with 10–38%, d50: 5.0 mm with 5–37%).
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Sergeev, Daniil, e Alexander Kandaurov. "Experimental investigation of multiphase hydrodynamics of the ocean-atmosphere boundary layer within laboratory modelling". EPJ Web of Conferences 269 (2022): 01052. http://dx.doi.org/10.1051/epjconf/202226901052.
Testo completoAbstract (sommario):
Laboratory modelling of the processes of interaction between the atmosphere and ocean in the boundary layers is one of the most interesting from the point of view of the features of the hydrophysical experiment. The main characteristics that need to be controlled in these experiments include, first of all, the air velocity field over the rough surface waves and the underwater flow, as well as the shape of the free surface. However especial features as spray of droplets, the bubbles in the water and foam generated during the breaking of waves should also be taken into account when modelling extreme weather conditions associated with strong winds. Thus, from the point of view of experimental hydrodynamics, we are dealing with a multiphase turbulent flow with a free boundary. For purpose of experimental study on the wind-wave flume, an integrated approach is required that allows simultaneous measurements of the velocity flow fields, the sizes of droplets and bubbles, the shape of waves and parameters of foam coverage. Contact methods often do not allow for universality. This review study describes developing approaches to the use of optical methods for performing these studies. Presented results were obtained in experiments carried out on several wind-wave flumes. To study the processes of fragmentation of the water surface leading to the formation of droplets an foam, high-speed multi-angle video taking is used in combination with the shadow imaging method.
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Freeman, Elizabeth, Kristen Splinter e Ron Cox. "FLOATING BREAKWATERS AS PUBLIC PLATFORMS – IMPACT ON POSTURAL STABILITY". Coastal Engineering Proceedings, n. 36 (30 dicembre 2018): 63. http://dx.doi.org/10.9753/icce.v36.structures.63.
Testo completoAbstract (sommario):
Floating Breakwaters are used extensively to provide cost effective protection from wind and vessel waves. Floating breakwaters are commonly multitasked, being used as a point of mooring for vessels or simply an access way to other pontoons in a small boat harbour, as well as their main function as wave dissipators. A floating breakwater does not completely stop the incident wave; rather it partially transmits, partially reflects and partially dissipates the wave energy. Cox et al (2007) completed wave flume testing of a number of floating breakwaters and reported on performance in irregular waves with particular emphasis on wave transmission and reflection, energy dissipation and restraining forces. Motion measurements were limited by the instrumentation. This paper discusses the results from a further series of laboratory experiments on the dynamic motions of an active floating breakwater system. The performance is related to wave attenuation, wave reflection and energy dissipation as well as safety considerations for standing persons based on high resolution measurements of accelerations in all six degrees of freedom.
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Troitskaya, Yu, D. Sergeev, A. Kandaurov, M. Vdovin e S. Zilitinkevich. "The Effect of Foam on Waves and the Aerodynamic Roughness of the Water Surface at High Winds". Journal of Physical Oceanography 49, n. 4 (aprile 2019): 959–81. http://dx.doi.org/10.1175/jpo-d-18-0168.1.
Testo completoAbstract (sommario):
AbstractThis paper models the impact of the presence of foam on the short-wave component of surface waves and momentum exchange in the atmospheric boundary layer at high winds. First, physical experiments were carried out in a wind-wave flume in which foam can be artificially produced at the water surface. Tests were conducted under high-wind-speed conditions where equivalent 10-m wind speed ranged from 12 to 38 m s−1, with measurements made of the airflow parameters, the frequency–wavenumber spectra of the surface waves, the foam coverage of the water surface, and the distribution of the foam bubbles. Analysis of the resulting data indicates that the surface drag coefficient correlates with the fraction of foam coverage and the mean square slope (MSS) of the water surface, and that, at a certain wind speed, the MSS decreases with an increase in the fraction of foam coverage. Based on these results, we suggest a simple model for eddy viscosity in the turbulent boundary layer over a fractionally foam-covered wave surface. The measurements in a laboratory environment are shown to be in good agreement with the predictions of a quasi-linear model of the atmospheric boundary layer over a waved water surface that adopts this eddy viscosity. Adaptation of the proposed model to field conditions is discussed, and the synergetic effect of foam at the water surface and spray in the marine atmospheric boundary layer on ocean surface resistance at high winds is estimated so as to be able to explain the observed peaking dependence of the surface drag coefficient on the 10-m wind speed.
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LIBERZON, DAN, e LEV SHEMER. "Experimental study of the initial stages of wind waves' spatial evolution". Journal of Fluid Mechanics 681 (24 giugno 2011): 462–98. http://dx.doi.org/10.1017/jfm.2011.208.
Testo completoAbstract (sommario):
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.
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Zhao, Z., L. Zhang, L. Yuan e TJ Bouma. "Saltmarsh seeds in motion: the relative importance of dispersal units and abiotic conditions". Marine Ecology Progress Series 678 (11 novembre 2021): 63–79. http://dx.doi.org/10.3354/meps13891.
Testo completoAbstract (sommario):
Propagule dispersal is fundamental to the colonization of new habitats, metapopulation connectivity, and gene flow and thus enables saltmarsh species to cope with global change. In this study, mesocosm and flume experiments were used to quantify the effects of different dispersal units (i.e. seed, spikelet, inflorescence, and plant fragment-containing seeds) and abiotic conditions on the dispersal processes of 4 globally distributed saltmarsh species: Salicornia europaea, Scirpus maritimus, Spartina anglica, and Elymus athericus. The results showed that (1) moving seawater has a species-specific effect on buoyancy, leading to prolonged floatability of high tidal-flat species E. athericus and reduced floatability of pioneer species; (2) tidal currents increase dispersal speed, whereas wind can have additive or antagonistic effects on current-dominated dispersal speed depending on its direction; (3) wave action reduces dispersal speed, but this effect becomes smaller with increasing wave magnitudes and/or applied co-directional wind; (4) dispersal speed may vary depending on the physical forcing and type and morphology of the dispersal units, but the largest species effect is related to the period in which units remain buoyant; and (5) the dispersal potential of saltmarsh species in wind wave-dominated coastal environments can be ordered as follows: E. athericus > S. maritimus > S. anglica > S. europaea. This study provides valuable guidance for future numerical hydrodynamic models of saltmarsh dispersal and establishment, allowing more accurate prediction of the distributional responses of saltmarsh species to climate change, thereby supporting appropriate management and restoration strategies.
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Li, Zhiyue, Guoliang Dai, Shuo Du, Haoran Ouyang, Tao Hu, Hongbo Liu e Zhongwei Li. "Local Scour Depth Prediction of Offshore Wind Power Monopile Foundation Based on GMDH Method". Journal of Marine Science and Engineering 11, n. 4 (31 marzo 2023): 753. http://dx.doi.org/10.3390/jmse11040753.
Testo completoAbstract (sommario):
In recent years, Chinese offshore wind farms have experienced varying degrees of foundation scour since their completion. The maximum scour depth of pile foundations has far exceeded the design scour depth, which seriously threatens the safety of wind turbines. Among the current scour depth prediction formulas, the values calculated by the Chinese specification 65-1, 65-2 formula are small and the prediction results are on the dangerous side. The calculated value of the American Hec-18 formula is safe but conservative. The prediction formula of other specifications has a large deviation from the actual situation. Based on the available test data, the main factors influencing the local scour depth of pile foundations, the gauge analysis method, and the group method of data handling (GMDH), this paper proposes a prediction formula for the local scour depth of monopile foundation under the action of wave–current. In addition, monopile scour flume experiments were conducted. Combining the experimental data of the flume test and the scour monitoring data of the Rudong wind farm in Jiangsu, the calculated values of the depth prediction equation in this paper and the Chinese code equation, DNV code equation, HEC-18 equation, Rudolph equation, and Raaijmakers equation were compared and analyzed. The results show that the relative error, mean relative error, variance, and normalized variance between the predicted and measured values of this paper’s formula are smaller than those of other prediction formulas. The formula in this paper has a high calculation accuracy and practical application value.
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Toffoli, A., A. V. Babanin, M. A. Donelan, B. K. Haus e D. Jeong. "Estimating Sea Spray Volume with a Laser Altimeter". Journal of Atmospheric and Oceanic Technology 28, n. 9 (1 settembre 2011): 1177–83. http://dx.doi.org/10.1175/2011jtecho827.1.
Testo completoAbstract (sommario):
Abstract Down-looking laser altimeters are commonly used to measure the sea surface elevation. However, because the laser radiation is attenuated by spray droplets suspended along the transmission path, it is presumed that altimeters may also provide an indirect measure of the sea spray volume. Here, this conjecture is discussed by means of laboratory experiments, which have been conducted in a wind-wave flume. A large number of wind conditions were considered between equivalent 10-m wind speeds of 20 and 60 m s−1 in order to generate different spray volumes above the water surface. The facility was equipped with a laser and side-looking camera system to estimate the spray volume as well as a nearby down-looking laser altimeter. Results confirm that there is a robust degradation of the laser intensity for increasing wind speed and hence the amount of spray droplets above the water surface. A simple regression model to extract spray volume from the average intensity of the laser radiation is presented, demonstrating the promise of laser altimeters for making in situ spray observations. Additional observations will be required to calibrate the altimeters for applications in the open ocean marine environment.
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Han, Mengmeng, e Chien Ming Wang. "Efficiency and Wave Run-Up of Porous Breakwater with Sloping Deck". Journal of Marine Science and Engineering 10, n. 12 (5 dicembre 2022): 1896. http://dx.doi.org/10.3390/jmse10121896.
Testo completoAbstract (sommario):
In order to protect fragile shoreline and coastal assets during extreme storms, a combined floating breakwater-windbreak has been proposed to reduce both wind and wave energies in the sheltered area. The 1 km-long breakwater has a porous hull with internal tubes to allow free passage of water; thereby further dissipating wave energy. The deck of the structure is designed to have a slope of 25 degrees facing the upstream side, and arrays of cylindrical tubes are placed on the sloping deck to form a windbreak. A reduced-scale (1:50) model test was carried out in a wave flume to examine wave sheltering performance under significant wave heights Hs = 3.0 m to 7.5 m and peak wave periods Tp = 9.4 s to 14 s sea states. Both regular and random wave conditions with different wave heights were considered. It is found that transmission coefficients ranging from 0.4 to 0.6 can be achieved under tested wave conditions. Porous breakwater hull increases the wave dissipation coefficients and is effective in reducing the wave reflection at the upstream side. The wave run-up length is dependent on the Iribarren number if the reduction induced by vertical freeboard is considered. Based on experimental data, empirical formulae have been proposed to predict the wave run-up responses in regular waves, probability of non-zero wave run-up occurrence, modified Weibull distribution of the wave run-up peaks and extreme wave run-up in random waves.
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Yamashiro, Masaru, Akinori Yoshida e Yasuhiro Nishii. "PRACTICAL MEASURES AGAINST SEA SALT PARTICLES FROM AN EXISTING VERTICAL WALL". Coastal Engineering Proceedings 1, n. 32 (31 gennaio 2011): 31. http://dx.doi.org/10.9753/icce.v32.structures.31.
Testo completoAbstract (sommario):
At Waku fishing port, facing to Japan Sea, in Yamaguchi prefecture, Japan, a vertical type breakwater was constructed in front of the mouth of the port to protect the inside against incoming waves about 10 years ago. Residents in the area have been troubled with heavy seawater spray and much smaller sea salt particles caused at the breakwater by sever waves and strong winds ever since. To reduce the generation of and the damage from the seawater spray and the sea salt particles, three different types of measures were proposed: (a) covering the breakwater with wave dissipating blocks, (b) construction of a low crested offshore breakwater some distance ahead of the breakwater, and (c) construction of an artificial reef some distance ahead of the breakwater. Laboratory experiments using a wave flume with a wind tunnel were conducted to compare the effects of suppressing the water spray generation. The results of the comparative experiments showed that the covering with the wave dissipating blocks (Plan (a)) is the most effective means.
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Zhu, Jiangfeng, Yuguang Cao, Yuanyuan Liu, Chenyi Ren e Qiankun Zhao. "Study on structural design and hydrodynamic response law of new floating wind power fishery integration". Science and Technology for Energy Transition 78 (2023): 39. http://dx.doi.org/10.2516/stet/2023025.
Testo completoAbstract (sommario):
The new lattice floating wind turbine integrated system (also known as Dot Matrix Floating wind turbine, and hereinafter referred to as DMF) is proposed as a new concept. It is a design scheme that combines multiple wind turbines into a polygonal floating foundation in the form of a lattice arrangement, which can meet the research and development requirements of higher power generation equipment in the future. More far-reaching, it has obvious advantages over the traditional floating wind turbine scheme in terms of structural cost and motion stability, which provides a new idea for the development of offshore wind power energy. Firstly, the structural parameters and mechanical model of DMF are analyzed to determine the feasibility and superiority of the overall scheme of the new lattice foundation. Combined with the traditional OC4 semi-submersible wind turbine system, the hydrodynamic simulation under wind, wave, and current load is carried out, and the hydrodynamic response law of DMF under the different environmental factors is summarized and analyzed. It is concluded that the stability of DMF in pitching motion is 70% higher than that of traditional OC4 system. In order to further verify the feasibility of the DMF system and the accuracy of the theoretical model, based on the similarity theory, this study carried out the small-scale prototype processing of DMF and the simulation experiment of wind wave flume. The test results are in good agreement with the simulation data. Finally, aiming at the problem of the large amplitude of swaying motion response of DMF in the simulation results, a mooring optimization scheme suitable for the new DMF is proposed, which provides 47% stability compared with the traditional catenary mooring through comparative analysis. This study provides a reference and theoretical basis for the research and development of offshore multi-wind turbine combined equipment and hydrodynamic stability optimization. It has certain theoretical guiding significance and economic development value.
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Song, Juhun, e Hee-Chang Lim. "Study of Floating Wind Turbine with Modified Tension Leg Platform Placed in Regular Waves". Energies 12, n. 4 (21 febbraio 2019): 703. http://dx.doi.org/10.3390/en12040703.
Testo completoAbstract (sommario):
In this study, the typical ocean environment was simulated with the aim to investigate the dynamic response under various environmental conditions of a Tension Leg Platform (TLP) type floating offshore wind turbine system. By applying Froude scaling, a scale model with a scale of 1:200 was designed and model experiments were carried out in a lab-scale wave flume that generated regular periodic waves by means of a piston-type wave generator while a wave absorber dissipated wave energy on the other side of the channel. The model was designed and manufactured based on the standard prototype of the National Renewable Energy Laboratory (NREL) 5 MW offshore wind turbine. In the first half of the study, the motion and structural responses for operational wave conditions of the North Sea near Scotland were considered to investigate the performance of a traditional TLP floating wind turbine compared with that of a newly designed TLP with added mooring lines. The new mooring lines were attached with the objective of increasing the horizontal stiffness of the system and thereby reducing the dominant motion of the TLP platform (i.e., the surge motion). The results of surge translational motions were obtained both in the frequency domain, using the response amplitude operator (RAO), and in the time domain, using the omega arithmetic method for the relative velocity. The results obtained show that our suggested concept improves the stability of the platform and reduces the overall motion of the system in all degrees-of-freedom. Moreover, the modified design was verified to enable operation in extreme wave conditions based on real data for a 100-year return period of the Northern Sea of California. The loads applied by the waves on the structure were also measured experimentally using modified Morison equation—the formula most frequently used to estimate wave-induced forces on offshore floating structures. The corresponding results obtained show that the wave loads applied on the new design TLP had less amplitude than the initial model and confirmed the significant contribution of the mooring lines in improving the performance of the system.
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Troitskaya, Yu, A. Kandaurov, O. Ermakova, D. Kozlov, D. Sergeev e S. Zilitinkevich. "The “Bag Breakup” Spume Droplet Generation Mechanism at High Winds. Part I: Spray Generation Function". Journal of Physical Oceanography 48, n. 9 (settembre 2018): 2167–88. http://dx.doi.org/10.1175/jpo-d-17-0104.1.
Testo completoAbstract (sommario):
AbstractThis paper describes the results of an experimental and theoretical investigation into the mechanisms by which spume droplets are generated by high winds. The experiments were performed in a high-speed wind-wave flume at friction velocities between 0.8 and 1.5 m s−1 (corresponding to a 10-m wind speed of 18–33 m s−1 under field conditions). High-speed video of the air–water interface revealed that the main types of spray-generating phenomena near the interface are “bag breakup” (similar to fragmentation of droplets and jets in gaseous flows at moderate Weber numbers), breakage of liquid ligaments near the crests of breaking surface waves, and bursting of large submerged bubbles. Statistical analysis of these phenomena showed that at wind friction velocities exceeding 1.1 m s−1 (corresponding to a wind speed of approximately 22.5 m s−1), the main mechanism responsible for the generation of spume droplets is bag breakup fragmentation of small-scale disturbances that arise at the air–water interface under the strong wind. Based on the general principles of statistical physics, it was found that the number of bags arising at the water surface per unit area per unit time was dependent on the friction velocity of the wind. The statistics obtained for the bag breakup events and other data available on spray production through this type of fragmentation were employed to construct a spray generation function (SGF) for the bag breakup mechanism. The resultant bag breakup SGF is in reasonable agreement with empirical SGFs obtained under laboratory and field conditions.
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Weaver, Robert J., e Abigail L. Stehno. "Mangroves as Coastal Protection for Restoring Low-Energy Waterfront Property". Journal of Marine Science and Engineering 12, n. 3 (9 marzo 2024): 470. http://dx.doi.org/10.3390/jmse12030470.
Testo completoAbstract (sommario):
Mangroves offer vital ecological advantages including air and water filtration, coastal and estuarine habitat provision, sediment stabilization, and wave energy dissipation. Their intricate root systems play a key role in safeguarding shorelines from tsunamis and erosive storms by dissipating wave energy. Moreover, mangroves shield against boat wakes and wind-waves, thus naturally bolstering shoreline defense. Wave dissipation is a function of forest width, tree diameter, and forest density. Restoration efforts of juvenile mangroves in Florida’s Indian River Lagoon (IRL) aim to reduce wave energy in areas vulnerable to erosion. Physical model testing of wave dissipation through mangroves is limited due to the complexity in representing the mangrove structure, where prop roots are non-uniform in both diameter and location. Previous studies have quantified wave-dissipating effects through the use of scaled and parameterized mangrove structures. This study measures the dissipation effects of live mangroves in a wave flume, forced by conditions representative of the IRL. These measurements are used to validate a parameterized dowel model. Error between wave attenuation factors for the live mangrove and dowel system was on average 2.5%. Validation of the modularized dowel system allowed for further parameterized testing to understand forest structure effects, such as sediment stabilization and wave attenuation. Maximum wave attenuation achieved in this study was 27–35% corresponding to a 40–60% reduction in wave energy depending on the configuration of the system. The wave reduction resulted in a 50–70% decrease in sediment erosion from the berm. The dowel tests indicate a target minimum thickness for mangrove root systems of 0.6 m for shoreline stabilization and restoration in the IRL.
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Venis, W. A. "DETERMINATION OF THE WAVE ATTACK ANTICIPATED UPON A STRUCTURE FROM LABORATORY AND FIELD OBSERVATIONS". Coastal Engineering Proceedings 1, n. 7 (29 gennaio 2011): 37. http://dx.doi.org/10.9753/icce.v7.37.
Testo completoAbstract (sommario):
Model tests have been carried out to obtain an insight into the magnitude of the wave-pressures in various situations. These tests showed, that sharp high pressure peaks occur in addition to the pressures caused by the reflecting of the waves, which pressures are quasi-static. As the structure can be compared with a multiple mass-spring system these pressure-peaks may cause the whole construction to vibrate. Wave-attack therefore can be expressed in terms of impact. Moreover, calculations revealed that the impact pressures were critical factors in determining the strength of the structure.
So many model tests were carried out to determine the design and location of the sluices. These tests involved numerous water-levels discharges and waves. Regarding the pressure-peaks a comparative study was made in the model, which led to the structure being designed in such a way that the occurrence of critical impacts was reduced to an acceptable minimum. As it was impossible to avoid the occurrence of impact pressures entirely it remained necessary to determine a basic load for the structure that takes care of the impact pressures. As it has not yet appeared possible physically to determine a theoretical maximum for the impact pressures, it has to be borne in mind that there is a probability that each pressure measured will be exceeded. So this paper describes, how the cumulative frequency curve of the impacts for the case mentioned in 1.1 sub a, which served as a basis for determining the basic load was arrived at by a certain combination of laboratory and field observations. The data used for this purpose were a. Results of wave-impact measurements on a model of the sluices. This model, built in accordance with the results of the comparative study, was situated in the wind-flume of the "de Voorst" hydraulic laboratory. b. Wave height measurements in the Haringvliet during 1957 and 1958. c. Wind-speed measurements on board the lightship Qoeree, likewise during 1957 and 1958. d. Tidal registrations at Hellevoetsluis from 1920 to 1960. e. Wind-force data from the Hook of Holland, likewise from 1920 to 1960.
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Shelushinin, Yuriy A. "Changes in the initial parameters of waves caused by distortions in the scale of a hydraulic model". Vestnik MGSU, n. 1 (gennaio 2022): 83–92. http://dx.doi.org/10.22227/1997-0935.2022.1.83-92.
Testo completoAbstract (sommario):
Introduction. The distorted scale method is often used to develop physical models of hydraulic structures. Notably, scientific researches concerning the methodology of distortions are quite rare, especially those that are focused on the modeling of wind waves. In the modern practice, scale distortions only affect the underwater topography and hydraulic structures. In this case, initial waves remain unchanged, and this can lead to errors in the wave mode at the control points of a model. Given the data on errors, the author considers the changes in the parameters of initial waves, if the scale of a physical model is distorted.
Materials and methods. The author used methods of physical and numerical modeling. Experimental studies were conducted in a wave flume and a wave pool that had a wavemaker. In the course of the experiments, the initial wave mode was changed and the parameters of waves were measured at the control points of distorted physical models. Numerical modeling was employed to analyze the computational patterns similar to the physical models.
Results. The author used physical models featuring varying degrees of distortion to obtain a collection of the wave mode data under the conditions of the wave transformation and diffraction. Physical and numerical modeling results are compared. The author provides an assessment of the results attained by changing the parameters of initial waves and distorted physical models.
Conclusions. The scale distortion triggers changes in the wave mode that may not be easy to control and correct. This fact must be taken into account when distorted hydraulic models are developed. This approach demonstrates varying efficiency if applied to different physical models featuring characteristic processes.
42
Zheng, Shuang, Guanlin Li, Qiang Fu, Kaiming Luo, Haodong Shi, Di Yang e Yingchao Li. "Analysis of the Factors Influencing the Trailing Infrared Characteristics of Underwater Vehicles under Surge Conditions Using the Orthogonal Method". Applied Sciences 13, n. 5 (2 marzo 2023): 3234. http://dx.doi.org/10.3390/app13053234.
Testo completoAbstract (sommario):
With its benefits of efficiency and speed, the orthogonal experimental design method is currently often employed in many domains for multi-factor experimental design. In this study, the wind–wave–flow multifunctional experimental flume was used to replicate surge circumstances using the orthogonal technique in order to investigate the contributing factors and their interactions on the sea surface IR characteristics of underwater vehicles’ wakes. According to the correlation analysis, the height of the swell and the surface temperature difference of the wake had only a weak negative correlation, while the dive depth of the underwater vehicle and the surface temperature difference of the wake had a significant negative correlation (p = −0.833). It was tentatively concluded that the surface temperature differential of the wake was found to be more sensitive to dive depth than to swell height. An investigation of the impact of trailing IR features can use this finding as a pertinent reference.
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Hu, Zhan, Simei Lian, Huaiyu Wei, Yulong Li, Marcel Stive e Tomohiro Suzuki. "Laboratory data on wave propagation through vegetation with following and opposing currents". Earth System Science Data 13, n. 10 (28 ottobre 2021): 4987–99. http://dx.doi.org/10.5194/essd-13-4987-2021.
Testo completoAbstract (sommario):
Abstract. Coastal vegetation has been increasingly recognized as an effective buffer against wind waves. Recent laboratory studies have considered realistic vegetation traits and hydrodynamic conditions, which advanced our understanding of the wave dissipation process in vegetation (WDV) in field conditions. In intertidal environments, waves commonly propagate into vegetation fields with underlying tidal currents, which may alter the WDV process. A number of experiments addressed WDV with following currents, but relatively few experiments have been conducted to assess WDV with opposing currents. Additionally, while the vegetation drag coefficient is a key factor influencing WDV, it is rarely reported for combined wave–current flows. Relevant WDV and drag coefficient data are not openly available for theory or model development. This paper reports a unique dataset of two flume experiments. Both experiments use stiff rods to mimic mangrove canopies. The first experiment assessed WDV and drag coefficients with and without following currents, whereas the second experiment included complementary tests with opposing currents. These two experiments included 668 tests covering various settings of water depth, wave height, wave period, current velocity and vegetation density. A variety of data, including wave height, drag coefficient, in-canopy velocity and acting force on mimic vegetation stem, are recorded. This dataset is expected to assist future theoretical advancement on WDV, which may ultimately lead to a more accurate prediction of wave dissipation capacity of natural coastal wetlands. The dataset is available from figshare with clear instructions for reuse (https://doi.org/10.6084/m9.figshare.13026530.v2, Hu et al., 2020). The current dataset will expand with additional WDV data from ongoing and planned observation in natural mangrove wetlands.
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Wang, Shi Ming, e Dao Tao Lei. "Design and Experimental Research of a New Horizontal Wave and Flow Generation Device". Applied Mechanics and Materials 404 (settembre 2013): 337–43. http://dx.doi.org/10.4028/www.scientific.net/amm.404.337.
Testo completoAbstract (sommario):
According to the current needs of the independent power supply to the offshore marine equipment and reefs, as well as the serious status of the world's energy crisis, environmental pollution, we design a miniaturized modular turbine marine energy generation device. With turbine which is circular evenly arranged vane typed as its wave flow capturing device,and through the spindle which fixedly mounted with the turbine, transmiting the captured energy directly to the generator which is mounted at the end of the spindle,eventually the entire device achieves single-stage transmission,and overcomes the problems such as low conversion efficiency and complicated structure in comparision with the traditional multi-stage conversion power generation device.The entire device achieves offshore running by buoys floating, anchor chain mooring and data remotely controlling .With the establishment of the program, 3D modeling and simulation,prototype production and processing, performance testing of key components and prototype flume tests,the project has got a lot grades.The device can extend to the multiple complementary power supply system with offshore wind, solar and so on,and achive integrated system to islands with low-cost power supply,desalination and sewage treatment,which has a good prospect.
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Nielsen, Anders, e Thor Petersen. "Onset of Motion of Sediment underneath Scour Protection around a Monopile". Journal of Marine Science and Engineering 6, n. 3 (29 agosto 2018): 100. http://dx.doi.org/10.3390/jmse6030100.
Testo completoAbstract (sommario):
The stability of scour protections is, potentially, an important issue during the design of fixed foundations for offshore wind turbines. One of the failure mechanisms observed at placed scour protection around offshore foundations is suction of sediment through the scour protection and subsequent sinking of the scour protection. Incipient motion of sediment and the initiation of suction underneath scour protections around piles in the marine environment were studied under waves, current and combined waves and current conditions. The motion of a thin layer of sediment underneath the scour protection was studied through the glass bottom of the test flume, which provided a clear view of the initiation of the motion of the sediment. The results show that the mobility depends on the Keulegan–Carpenter ( K C ) number for the pile, the ratio between waves and current flow and the ratio between the thickness of the scour protection and the base sediment. The critical mobility number is smaller for the wave-dominated situation compared to current-dominated conditions, which again are smaller than for combined waves and current conditions. Consequently, larger K C -numbers cause larger critical mobility numbers than smaller K C -numbers. Design diagrams are presented for the threshold of incipient motion of sediment underneath a scour protection in waves, current and combined waves and current.
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Yang, Can, Zhibin Hao, Huaqi Yuan, Xiaodong Bai, Zuohang Su, Hailong Chen e Lars Johanning. "Numerical Simulation on the Hydrodynamic Flow Performance and an Improve Design of a Circulating Water Channel". Journal of Marine Science and Engineering 10, n. 3 (15 marzo 2022): 429. http://dx.doi.org/10.3390/jmse10030429.
Testo completoAbstract (sommario):
A Circulating Water Channel (CWC) is an important piece of equipment for hydrodynamic tests in ocean engineering, the quality of the flow field produced by the CWC directly affects the accuracy of the experimental results. Optimizing the key parts of the CWC device can efficiently improve the velocity uniformity and helps to achieve a high-level flow performance. In this paper, a CWC flume is set up numerically, and a series of hydrodynamic tests were carried out to evaluate the flow uniformity by optimizing the turning vane and contraction section. The numerical model is solved based on the RANS equation by using the RNG model to simulate turbulence. The improved design of the CWC includes the investigations of the flow guiding vane at the turning corners and the contraction section in the flow acceleration zone. The turning vane cross-sectional shape, the straight-edged length of the wing, and the layout of the contraction transition section design were considered and verified. The obtained results show that the wing-type turning vane with appropriate straight-edged length can help to improve the velocity uniformity of the flow field. The Witozinsky transition curve could achieve better pressure gradient effects for CWC contraction section design, and the flow uniformity improved by increasing the contraction transition length. Based on the optimal design, the internal flow characteristics of the circulating water channel have been greatly improved, laying a solid foundation for wind-wave-current multifunction CWC equipment applications for future experiments.
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Tasaki, Ryo, e Akihiro Ogawa. "Two-Component Model for Crude Oil Evaporation and its Application to Weathering Prediction". International Oil Spill Conference Proceedings 1999, n. 1 (1 marzo 1999): 271–80. http://dx.doi.org/10.7901/2169-3358-1999-1-271.
Testo completoAbstract (sommario):
ABSTRACT The model approximates a crude oil as a mixture of an evaporating and non-evaporating component of which the physico-chemical properties are calculated by their composing fractions. The ordinary differential equation with separated variables derived from the model yields a concept of the evaporation time constant TQ that is defined by the initial oil properties and thickness, and the ambient temperature and wind speed. The evaporation ratios Q measured in flume tests on six types of Middle East crude oils are analyzed for the elapsed time non-dimensionalized by TQ. The measured values collapse well to a single straight line Q-log(t/TQ) for each type of oil, independently of emulsification and wave disturbance. A single line common to all the six types of oils is enough for rough estimation. A method using the common line or, more accurately, a line derived from the distillation test of each type of oil is proposed for evaporation prediction. Further analyses of the test results reveal the one-to-one correspondence between evaporation and properties (viscosity and density) of evaporated residual water-free oil. Formulae using the correspondence are suggested for estimating the properties of residual oil. The influences of substrates and thickness of an oil slick on evaporation and oil properties were examined in a small-scale laboratory. The laboratory tests are discussed as a useful procedure for obtaining basic prediction data.
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Fingas, Merv. "A Review of Natural Dispersion Models". International Oil Spill Conference Proceedings 2014, n. 1 (1 maggio 2014): 285471. http://dx.doi.org/10.7901/2169-3358-2014-1-285471.1.
Testo completoAbstract (sommario):
Natural dispersion occurs when fine droplets of oil are transferred into the water column by wave action or sea turbulence. Depending on oil conditions and the amount of sea energy available, natural dispersion can be insignificant or it can temporarily displace a portion of the oil. Current models predict the amount of oil entering the water column, but do not deal with their stability or how long these droplets stay in the water column. The most commonly-used model is by Delvigne, who carried out experiments in a flume. Delvigne measured the droplets entering the water column using a simplified procedure. These data were then converted to a model to predict the entry of droplets into the water column. Delvigne recommended procedures to calculate the resurfacing of the dispersed droplets but no models have implemented these. A review of the mathematics of this procedure show that the Delvigne model might be adjusted to be more unit consistent and to correctly incorporate oil viscosity. The other models used include the Audunson and Mackay models. These models are also reviewed. The Audunson model is simple and does not incorporate any inputs other than the wind speed. Further, the Audunson model predicts that most slicks will dissipate within a day or a few days. The Mackay model predicts little natural dispersion. Although the Mackay model incorporates a sea state function, the effect of this is not as great as in other models. Several issues have been noted about all natural dispersion models. These are: 1 In all cases natural dispersion models predicted the input of droplets into the water column and suggestions were made about predicting rise and resurfacing, but this important second part was never implemented by anyone,2 The natural dispersion predicted was measured as a temporary phenomenon - that is the instantaneous input of droplets into the water column. The persistence was not measured. The equation was designed to yield only the temporary transport in the water. Later workers assumed that the natural dispersion portion was permanently dispersed, and3 All models over-predict natural dispersion, especially in cases of low sea states.
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Xiong, Caiyi, Zilong Wang e Xinyan Huang. "Acoustic flame extinction by the sound wave or speaker-induced wind?" Fire Safety Journal 126 (dicembre 2021): 103479. http://dx.doi.org/10.1016/j.firesaf.2021.103479.
Testo completo
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Zhang, Qi, Lei Pang e Dachao Lin. "Numerical analysis of characteristics of the wind caused by methane-air explosion". Engineering Computations 31, n. 3 (28 aprile 2014): 490–500. http://dx.doi.org/10.1108/ec-12-2011-0161.
Testo completoAbstract (sommario):
Purpose – The high-velocity wind caused by a methane-air explosion is one of the important hazardous effects in explosion events of coal mines, and, however, until now it has not been received much attention from scientific works. The paper aims to discuss this issue. Design/methodology/approach – In consideration of the difficulties in observing particle velocities of high-velocity flows, this work presented a study to reveal the regularity during a methane-air explosion happening in the tunnel of coal mine through the numerical analysis approach. Findings – The strong wind caused by a methane-air explosion is a significant hazard and can cause damage in the accidents of methane-air explosion in underground coal mines, especially at structural opening, according to this work. Obtained results show that maximum particle velocity of the high-velocity wind occurs in the outside region of the premixed area, with a peak value of 400∼500 m/s, and the peak velocity of the high-velocity wind decreases exponentially with distance beyond the premixed area. Originality/value – The objective of this work was to examine the effect of wind caused by a methane-air explosion in a tunnel. Other information, such as shock wave and flame and temperature distribution, has been reported in the previous literatures. However, in the accidents of methane-air explosion in underground coal mines, some phenomena (structural opening is destroyed badly) can not be understood by using shock wave and flame and temperature distribution caused by the explosion. The strong wind caused by a methane-air explosion is another significant hazard and can cause damage in the methane-air explosion accidents in underground coal mines, especially at structural opening, according to this work.