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Littérature scientifique sur le sujet « Waves/low frequency currents interractions »

Auteur : Grafiati

Publié le 11 janvier 2025

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Articles de revues sur le sujet "Waves/low frequency currents interractions"

Elgar, Steve, et Britt Raubenheimer. « Field Evidence of Inverse Energy Cascades in the Surfzone ». Journal of Physical Oceanography 50, n^o 8 (1 août 2020) : 2315–21. http://dx.doi.org/10.1175/jpo-d-19-0327.1.

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AbstractLow-frequency currents and eddies transport sediment, pathogens, larvae, and heat along the coast and between the shoreline and deeper water. Here, low-frequency currents (between 0.1 and 4.0 mHz) observed in shallow surfzone waters for 120 days during a wide range of wave conditions are compared with theories for generation by instabilities of alongshore currents, by ocean-wave-induced sea surface modulations, and by a nonlinear transfer of energy from breaking waves to low-frequency motions via a two-dimensional inverse energy cascade. For these data, the low-frequency currents are not strongly correlated with shear of the alongshore current, with the strength of the alongshore current, or with wave-group statistics. In contrast, on many occasions, the low-frequency currents are consistent with an inverse energy cascade from breaking waves. The energy of the low-frequency surfzone currents increases with the directional spread of the wave field, consistent with vorticity injection by short-crested breaking waves, and structure functions increase with spatial lags, consistent with a cascade of energy from few-meter-scale vortices to larger-scale motions. These results include the first field evidence for the inverse energy cascade in the surfzone and suggest that breaking waves and nonlinear energy transfers should be considered when estimating nearshore transport processes across and along the coast.

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Fioranelli, Massimo, Maria Grazia Roccia, Aroonkumar Beesham, Dana Flavin, M. Ghaeni et Faissal AZIZ. « A model for considering effects of extremely low frequency electromagnetic fields on quail embryonic cells ». AIMS Biophysics 9, n^o 3 (2022) : 198–207. http://dx.doi.org/10.3934/biophy.2022017.

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<abstract> <p>Previous experiments have shown that extremely low frequency electromagnetic fields could cause serious effects on the evolution of cells. We propose a mathematical model which confirms those results. In our model, electromagnetic waves could cause the motions of ions and charges and the emergence of some currents around and in the interior of cells. These currents produce some waves which interact with the DNAs and remove or attach some repressors. Consequently, some genes could be turned on or off, and cells could obtain some properties or lose them. The frequency of the external waves should be close to the frequency of the exchanged waves between the repressors and DNAs or even bigger than them. We test this idea and did some experiments on quail embryonic cells. We connected a sample of these cells to a battery and considered their evolution. We observed that after connecting the battery and the production of electrical current, some rings around the quail embryonic cells emerged. Maybe, these rings are the response of the cells to changes in electromagnetic waves and electrical currents.</p> </abstract>

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Johnson, E. R. « Boundary Currents, Free Currents and Dissipation in the Low-Frequency Scattering of Shelf Waves ». Journal of Physical Oceanography 19, n^o 9 (septembre 1989) : 1291–300. http://dx.doi.org/10.1175/1520-0485(1989)019<1291:bcfcad>2.0.co;2.

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Torres, Hector S., Patrice Klein, Jinbo Wang, Alexander Wineteer, Bo Qiu, Andrew F. Thompson, Lionel Renault et al. « Wind work at the air-sea interface : a modeling study in anticipation of future space missions ». Geoscientific Model Development 15, n^o 21 (7 novembre 2022) : 8041–58. http://dx.doi.org/10.5194/gmd-15-8041-2022.

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Abstract. Wind work at the air-sea interface is the transfer of kinetic energy between the ocean and the atmosphere and, as such, is an important part of the ocean-atmosphere coupled system. Wind work is defined as the scalar product of ocean wind stress and surface current, with each of these two variables spanning, in this study, a broad range of spatial and temporal scales, from 10 km to more than 3000 km and hours to months. These characteristics emphasize wind work's multiscale nature. In the absence of appropriate global observations, our study makes use of a new global, coupled ocean-atmosphere simulation, with horizontal grid spacing of 2–5 km for the ocean and 7 km for the atmosphere, analyzed for 12 months. We develop a methodology, both in physical and spectral spaces, to diagnose three different components of wind work that force distinct classes of ocean motions, including high-frequency internal gravity waves, such as near-inertial oscillations, low-frequency currents such as those associated with eddies, and seasonally averaged currents, such as zonal tropical and equatorial jets. The total wind work, integrated globally, has a magnitude close to 5 TW, a value that matches recent estimates. Each of the first two components that force high-frequency and low-frequency currents, accounts for ∼ 28 % of the total wind work and the third one that forces seasonally averaged currents, ∼ 44 %. These three components, when integrated globally, weakly vary with seasons but their spatial distribution over the oceans has strong seasonal and latitudinal variations. In addition, the high-frequency component that forces internal gravity waves, is highly sensitive to the collocation in space and time (at scales of a few hours) of wind stresses and ocean currents. Furthermore, the low-frequency wind work component acts to dampen currents with a size smaller than 250 km and strengthen currents with larger sizes. This emphasizes the need to perform a full kinetic budget involving the wind work and nonlinear advection terms as small and larger-scale low-frequency currents interact through these nonlinear terms. The complex interplay of surface wind stresses and currents revealed by the numerical simulation motivates the need for winds and currents satellite missions to directly observe wind work.

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Berthelier, A., J. C. Cerisier, J. J. Berthelikr et L. Rnzeau. « Low-frequency magnetic turbulence in the high-latitude topside ionosphere : low-frequency waves or field-aligned currents ». Journal of Atmospheric and Terrestrial Physics 53, n^o 3-4 (mars 1991) : 333–41. http://dx.doi.org/10.1016/0021-9169(91)90117-p.

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Matsumoto, Michio, Kazuo Sakai et Satoshi Takeuchi. « Low Frequency Waves with Azimuthal Currents in a Weakly Magnetized Positive Column ». Journal of the Physical Society of Japan 61, n^o 3 (15 mars 1992) : 844–48. http://dx.doi.org/10.1143/jpsj.61.844.

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Yao, S. T., Q. Q. Shi, Q. G. Zong, A. W. Degeling, R. L. Guo, L. Li, J. X. Li et al. « Low-frequency Whistler Waves Modulate Electrons and Generate Higher-frequency Whistler Waves in the Solar Wind ». Astrophysical Journal 923, n^o 2 (1 décembre 2021) : 216. http://dx.doi.org/10.3847/1538-4357/ac2e97.

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Abstract The role of whistler-mode waves in the solar wind and the relationship between their electromagnetic fields and charged particles is a fundamental question in space physics. Using high-temporal-resolution electromagnetic field and plasma data from the Magnetospheric MultiScale spacecraft, we report observations of low-frequency whistler waves and associated electromagnetic fields and particle behavior in the Earth’s foreshock. The frequency of these whistler waves is close to half the lower-hybrid frequency (∼2 Hz), with their wavelength close to the ion gyroradius. The electron bulk flows are strongly modulated by these waves, with a modulation amplitude comparable to the solar wind velocity. At such a spatial scale, the electron flows are forcibly separated from the ion flows by the waves, resulting in strong electric currents and anisotropic ion distributions. Furthermore, we find that the low-frequency whistler wave propagates obliquely to the background magnetic field ( B 0), and results in spatially periodic magnetic gradients in the direction parallel to B 0. Under such conditions, large pitch-angle electrons are trapped in wave magnetic valleys by the magnetic mirror force, and may provide free perpendicular electron energy to excite higher-frequency whistler waves. This study offers important clues and new insights into wave–particle interactions, wave generation, and microscale energy conversion processes in the solar wind.

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Deguchi, Ichiro, Mamoru Arita et Takumi Yoshii. « FLUCTUATION OF RIP CURRENT MEASURED IN SHALLOW WATER REGION WITH SMALL TIDAL RANGE ». Coastal Engineering Proceedings 1, n^o 32 (25 janvier 2011) : 44. http://dx.doi.org/10.9753/icce.v32.currents.44.

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Disappearance and formation processes of rip channel are discussed based on the field measurements of wave height, current velocity, bottom topography and flow pattern of near-shore current. Sudden increase in wave height together with the change in the wave direction took place during a half day caused these phenomena and rip current rose and fell according to the transition of the bottom topography. Furthermore, flow pattern of rip current was not steady but transformed itself with low frequency fluctuations of the period of few minutes. It is found that such low frequency fluctuations are caused by the intrinsic fluctuations of the incident waves (grouping waves) through the numerical simulations.

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Stepanov, D. V., et V. V. Novotryasov. « Sub-inertial modulation of nonlinear Kelvin waves in the coastal zone ». Nonlinear Processes in Geophysics 20, n^o 3 (7 juin 2013) : 357–64. http://dx.doi.org/10.5194/npg-20-357-2013.

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Abstract. Observational evidence is presented for interaction between nonlinear internal Kelvin waves at the ωt,i (where the ωt is the semidiurnal frequency and the ωi is the inertial frequency) and random oscillations of the background coastal current at the sub-inertial Ω frequency in the Japan/East Sea. Enhanced coastal currents at the sum ω+ and difference ω-frequencies ω±=ωt,i ± Ω have properties of propagating Kelvin waves, which suggests permanent energy exchange from the sub-inertial band to the mesoscale ω± band. This interaction may be responsible for a greater-than-predicted intensification, steepening and breaking of boundary-trapped Kelvin waves. The problem of interaction between the nonlinear Kelvin wave at the frequency ω and the low-frequency narrowband noise with representative frequency Ω&ll;ω is investigated using the theory of nonlinear weak dispersion waves.

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Van Dongeren, Ap, Ryan Lowe, Andrew Pomeroy, Trang Minh Duong, Dano Roelvink, Graham Symonds et Roshanka Ranasinghe. « MODELLING INFRAGRAVITY WAVES AND CURRENTS ACROSS A FRINGING CORAL REEF ». Coastal Engineering Proceedings 1, n^o 33 (15 décembre 2012) : 29. http://dx.doi.org/10.9753/icce.v33.currents.29.

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Low-frequency (infragravity) wave dynamics on a fringing coral reef were investigated using the numerical model XBeach (Roelvink et al, 2009). First, the skill of the one-dimensional model was evaluated based on its predictions of short waves (0.04-0.2 Hz), infragravity waves (0.004-0.04 Hz) and water level measurements (tidal and wave setup) obtained during a 2009 field study at Ningaloo Reef in Western Australia. The model calibration was sensitive to friction coefficients for short waves and current / infragravity bed friction, which were assumed independent in this model study. The infragravity waves were found to be generated primarily in the surf zone through the breakpoint generation mechanism rather than through offshore forcing. The infragravity waves were strongly also modulated over the reef by tidal depth variations, primarily due to the variability in frictional dissipation rates when the total water depth over the reef varied. The results reveal that short waves dominated bottom stresses on the fore reef and near the reef crest; however, inside the lagoon, infragravity waves become increasingly dominant, accounting up to 50% of the combined bottom stresses

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Thèses sur le sujet "Waves/low frequency currents interractions"

Bella, Adrien. « Étude de l’impact des interactions entre ondes de marée interne et circulation basse fréquence sur le budget énergétique de la marée interne à l’aide d’une simulation numérique à haute résolution sur l’Atlantique Nord ». Electronic Thesis or Diss., Université de Rennes (2023-....), 2024. http://www.theses.fr/2024URENS046.

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Dans cette thèse, le cycle de vie de la marée interne et sa perte de cohérence par ses interactions avec les courants sont étudiés dans l’Atlantique Nord à l’aide d’une simulation d’un océan réaliste à haute résolution. Une décomposition en mode verticaux est utilisée pour obtenir le budget d’énergie des différentes échelles de la marée interne. La dispersion topographique est dominante à l’échelle du bassin et aux niveaux des reliefs, tandis que les interactions entre la marée interne et la circulation basse fréquence signent au niveau du Gulf Stream, de son prolongement Nord Atlantique et dans le Nord du Bassin. Enfin, une décomposition en partie cohérente/incohérente est utilisée. Les causes de la perte de cohérence de la marée sur des échelles de un à trois mois sont l’advection de la marée interne par l’écoulement lentement variable et le cisaillement horizontal de ce dernier. Cette perte de cohérence se fait majoritairement sans changement d’échelle pour la marée
The life cycle of the internal tide and its loss of coherence due to its interactions with currents are studied over the North Atlantic basin using a high-resolution simulation of a realistic ocean. A vertical mode decomposition is used to obtain the energy budget of the different scales of the internal tide. Topographic scattering is dominant at the basin scale and around topographic features, while interactions between the internal tide and the low-frequency circulation are significant in the Gulf Stream, its North Atlantic extension and in the northern part of the basin. Finally, a coherent/incoherent decomposition is used. The causes of the internal tide loss of coherence on scales of one to three months are the advection of the internal tide by the slowly varying current and the horizontal shear of the latter. Most of this loss of coherence occurs without any change of scale for the internal tide

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Chapitres de livres sur le sujet "Waves/low frequency currents interractions"

Lin, Y., et L. C. Lee. « Generation of Region 1 and Mantle Field-Aligned Currents by the Secondary Rotational Discontinuity ». Dans Solar Wind Sources of Magnetospheric Ultra-Low-Frequency Waves, 213–21. Washington, D. C. : American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm081p0213.

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Song, Yan, Robert L. Lysak et Naiguo Lin. « Control of the Generation of Field-Aligned Currents and Transverse ULF Waves by the Magnetic Helicity Input ». Dans Solar Wind Sources of Magnetospheric Ultra-Low-Frequency Waves, 223–30. Washington, D. C. : American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm081p0223.

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Garrett, Steven L. « One-Dimensional Propagation ». Dans Understanding Acoustics, 453–512. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-44787-8_10.

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Abstract Having already invested in understanding both the equation of state and the hydrodynamic equations, only straightforward algebraic manipulations will be required to derive the wave equation, justify its solutions, calculate the speed of sound in fluids, and derive the expressions for acoustic intensity and the acoustic kinetic and potential energy densities of sound waves. The “machinery” developed to describe waves on strings will be sufficient to describe one-dimensional sound propagation in fluids, even though the waves on the string were transverse and the one-dimensional waves in fluids are longitudinal. These results are combined with the thermal and viscous penetration depths to calculate the frequencies and quality factors in standing wave resonators. The coupling of those resonators to loudspeakers will be examined. The introduction of reciprocal transducers that are linear, passive, and reversible will allow absolute calibration of transducers using only electrical measurements (i.e., currents and voltages) by the reciprocity method, if the acoustic impedance that couples the source and receiver is calculable. Reflection and transmission at junctions between multiple ducts and other networks will be calculated and applied to the design of filters. The behavior of waves propagating through horns will provide useful impedance matching but introduce a low-frequency cut-off.

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Hayden, Bruce P., et Nils R. Hayden. « Decadal and Century-Long Changes in Storminess at Long-Term Ecological Research Sites ». Dans Climate Variability and Ecosystem Response in Long-Term Ecological Research Sites. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195150599.003.0026.

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Ecological disturbances at Long-Term Ecological Research (LTER) sites are often the result of extreme meteorological events. Among the events of significance are tropical storms, including hurricanes, and extratropical cyclones. Extratropical storms are low-pressure systems of the middle and high latitudes with their attendant cold and warm fronts. These fronts are associated with strong, horizontal thermal gradients in surface temperatures, strong winds, and a vigorous jet stream aloft. These storms and their attendant fronts generate most of the annual precipitation in the continental United States and provide the lifting mechanisms for thunderstorms that, on occasion, spawn tornadoes. Off the United States West and East Coasts, extratropical storms generate winds, wind waves, wind tides, and long-shore currents that rework coastal sediments, alter landscape morphology, and change the regional patterns of coastal erosion and accretion (Dolan et al. 1988). Although extratropical storms do not match hurricanes in either precipitation intensity or in the strength of the winds generated, they are much larger in size and have a more extensive geographic impact. On occasion, extratropical storms will intensify at an extraordinary rate of 1 millibar (mb) per hour for 24 hours or more. Such storms are classed as “bomb” and are comparable to hurricanes. Extratropical storms occur in all months of the year but are most frequent and more intense in winter when the north-south temperature contrast is large and dynamic support for storm intensification from the stronger jet stream aloft is great. In this chapter, we will explore the history of storminess for those LTER sites in the continental United States at which more than a century of data on storms and their storm tracks are readily available. Specifically, we will look at the record of changes in storminess at both the regional and national scales. During the 1990s, significant storms along the U.S. West Coast and droughts and fires in Florida in an El Niño year led to a hypothesis that El Niño and La Niña conditions were associated with a modulation in the frequency of storms. In addition, it has been suggested that the frequency of El Niño and La Niña events and, by inference, storminess, has increased during the past century.

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Actes de conférences sur le sujet "Waves/low frequency currents interractions"

Jena, Parthasarathi, Lin Li, Sverre Haver et Xu Xiang. « Low Frequency Energy in Measured Waves in a Narrow Norwegian Fjord ». Dans ASME 2024 43rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/omae2024-126795.

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Abstract The E39 Coastal Highway Route project undertaken by Norwegian Public Roads Administration aims at replacing existing ferry crossings by constructing permanent road connections using bridges along the western coast of Norway. One of the bridge designs being developed is a beam bridge resting on floating pontoons. In contrast to conventional bridges, a floating bridge rests on pontoons floating on the water surface and are affected to a much greater extent by waves and currents in the waters it spans. In order to have a solid basis for taking the environmental loads into account in the bridge design a wave measurement campaign was initiated at the bridge fabrication location. The wave measurement was carried out using a small diameter wave buoy with a proven track record in the offshore industry. The location of the wave measurement campaign is a narrow fjord surrounded by relatively high terrain. The fjord, being sheltered from swells from the North Sea and considering the available fetch length, it was expected that the measured waves would consist of purely wind generated waves with peak wave period, Tp, between 2s to 7s. However, the observed wave signal showed spurious long period waves with Tp in the range of 20s to 30s interspersed seemingly at random throughout the measured data. This paper discusses possible reasons for the observed low frequency energy. Harbor resonance in the fjord, resonance in the mooring system of the buoy, and passing ship interaction with the buoy were investigated as possible reasons for the presence of the low frequency energy. A method for identifying the low frequency energy and filtering them out using wavelet analysis of buoy heave signal is proposed.

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Абрамян, Владимир Казаросович, Валентин Эдуардович Гель, Александр Сергеевич Дворников et Андрей Игоревич Жирохов. « EMISSION OF ELECTROMAGNETIC WAVES (EMW) OF THE RADIO-FREQUENCY RANGE IN LOW-VOLTAGE ELECTRIC CIRCUITS WITH QUASISTATIONARY CURRENTS ». Dans Высокие технологии и инновации в науке : сборник избранных статей Международной научной конференции (Санкт-Петербург, Май 2022). Crossref, 2022. http://dx.doi.org/10.37539/vt197.2022.95.51.006.

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Представлена методика оценки параметров электромагнитных волн (ЭМВ), источниками которых являются элементы цепи низкочастотного переменного тока. Она позволяет оценить их роль в создании помех для нормального функционирования средств связи в радиочастотном диапазоне. An engineering technique has been developed for estimating the parameters of electromagnetic waves (EMW), the sources of which are elements of a low-frequency alternating current circuit. It allows you to evaluate their role in creating interference for the normal functioning of communications in the radio frequency range.

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Dev, Arun Kr. « Viscous Drift Forces on a Semisubmersible in Waves and Currents ». Dans SNAME Maritime Convention. SNAME, 2022. http://dx.doi.org/10.5957/smc-2022-069.

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Starting from the early sixties and then in the early eighties, it was well established that second-order wave excitation forces exist for floating bodies in regular waves. This force is not only steady (mean) in nature; it also has a low-frequency (difference frequency) and a high-frequency (sum frequency) component force in irregular waves, e.g., in a wave envelope of irregular waves. While potential drift force calculations were entirely accurate for large body structures like tankers, FPSOs, and other bluff bodies, the potential theory-based drift force calculations fell far short (seriously under-predicted) for slender body offshore structures like a semisubmersible. The drift force in a regular wave is dominated by viscous effects resulting in the force itself becoming a function of the third order in the splash zone of the semisubmersible column. Experimental results have validated this. This happens at the low diffraction parameter (κD) and high viscous parameter (H/D). In a waves-only field, the potential drift force remains purely second-order in regular waves due to first-order and second-order pressure. The presence of currents with waves increases the potential drift forces with the additional contribution. The presence of currents along with waves increases the viscous drift force in the splash zone and increases viscous effects on the submerged zone of the semisubmersible like the pontoons and the part of the columns below the splash zone. As the semisubmersible consists of vertical columns (vertical cylinders) and submerged pontoons, extensive experimental works were conducted with a vertical cylinder (resembling the column of a semisubmersible) and with fully submerged pontoons. These tests provided a fundamental understanding of the physics and mechanism of viscous effects in drift forces on semisubmersibles. Finally, numerical works were done using some of the experimental findings. The prediction matched quite well with experimental results for a complete semisubmersible in waves and waves and currents. The prediction method is also helpful in calculating the higher-order environmental forces in station keeping, like static and dynamic mooring analysis, Dynamic Positioning (DP) calculations, especially in time domain DP predictions.

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Papadopoulos, K., Bengt Eliasson, X. Shao et A. S. Sharma. « Modeling pitch angle scattering of radiation belt particles by the injection of low frequency waves with F-region HF-driven ionospheric currents ». Dans 2011 XXXth URSI General Assembly and Scientific Symposium. IEEE, 2011. http://dx.doi.org/10.1109/ursigass.2011.6051068.

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Sagrilo, Lui´s Volnei Sudati, Marcos Queija de Siqueira, Thiago Aˆngelo Gonc¸alves de Lacerda, Gilberto Bruno Ellwanger, Edison Castro Prates de Lima et Elizabeth Frauches Netto Siqueira. « VIM and Wave-Frequency Fatigue Damage Analysis for SCRs Connected to Monocolumn Platforms ». Dans ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-79807.

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The large Vortex Induced Motion (VIM) due to current acting on a circular-shaped monocolumn platform induces low-frequency stress variations on the SCRs (Steel Catenary Risers) connected to it. These stresses together with stress variations associated to wave effects must be accounted for in the fatigue analysis of these risers. Normally, the joint statistics of waves and currents show that these environmental variables may be considered as statistically independent. Therefore, the number of global riser analyses necessary for the SCRs fatigue analysis becomes extremely high in order to consider a suitable number of combinations (including intensities and directions) of waves and currents. This paper describes a methodology for computing the fatigue damage in SCRs (Steel Catenary Risers) due to wave-frequency and VIM (Vortex Induced Motion) load effects based on a combination damage formula presented in DnV-OS-F204 [1]. The wave-frequency and VIM fatigue damages are calculated separately (by a time-domain rainflow approach) and the combined damage is evaluated by means of the DnV formula. This methodology reduces considerably the number of global riser analyses and consequently the computational burden associated to the fatigue analyses of SCRs connected to monocolumn-type platforms.

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Tang, Hung-Jie, Ray-Yeng Yang et Chai-Cheng Huang. « Numerical Modelling of the Mooring Line Failure Induced Performance Changes of a Marine Fish Cage in Irregular Waves and Currents ». Dans ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-95730.

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Abstract This study aims to investigate the performance changes resulted from a mooring line failure of a marine fish cage exposed to irregular waves and current. A numerical model based on the lumped mass method and Morison equation was extended to simulate the mooring line failure scenario. In this study, the failed resulting changes were compared with its normal counterpart in both the time domain and the frequency domain. After one upstream anchor loss, the maximum tension on the remaining anchor has increased significantly, as well as the drift distance of the rearing part (net chamber, floating collar, and tube-sinker) of the fish cage. The resulting changes can also be seen in both the wave-frequency and the low-frequency region in the spectra, including mooring tensions and body motions.

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Ivanov, Leonid, Rafael Ramos et Drew Gustafson. « Energetics and Kinematics of Inertial Oscillations in the Central Northern GOM ». Dans Offshore Technology Conference. OTC, 2021. http://dx.doi.org/10.4043/31020-ms.

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Abstract Understanding the physics of generation, propagation, and dissipation of inertial currents is important from a variety of aspects. For the Gulf of Mexico, one such aspect is that these oscillations represent an uncertainty in the measurements and forecasting of the longer-period currents, such as those due to the Loop Current (LC) and meso-scale eddies. The Industry has a practice of applying an ‘uplift’ to estimates of current velocity to account for the effect of tidal and inertial currents in cases when observations or model estimates do not resolve the high-frequency current variability. The value of the ‘uplift’ is assumed to be proportional to the intensity of the low-frequency flow. Our analysis aims at testing whether this assumption is valid by providing a detailed description of the space-time variability, including seasonal changes, of inertial oscillations in the central northern Gulf of Mexico. From the analysis of long-term current profile observations and drifter data we found that, on average, near-inertial oscillations have higher amplitudes outside of the areas of strong low-frequency currents associated with a Loop Current Eddy (LCE). Within the upper 200m of the water column, periods characterized by the downward energy propagation dominate. In the layer below 200m, near-inertial waves propagate upward and downward, and the wave trains cannot be traced to a single source of energy. This suggests near-inertial waves within the main part of the water column are of ‘global’ rather than of ‘local’ origin. For most near-inertial wave generation events through wind forcing, the downward energy propagation could not be traced for any extended period of time and no deeper than approximately 200-m depth. The rate of downward energy propagation in the upper pycnocline is on the order of 10-12 m/day. For the near-inertial currents, the first two Empirical Orthogonal Functions (EOF) contribute only 40% into the total current variability for the period of LCE presence and 52% for the period of benign current conditions. The mode shapes vary within a wide range that, most likely, reflects a random distribution of mode shapes that depend on the lateral geometry of the forcing, mixed layer depth, and stratification.

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Barzegar Valikchali, Saeed, Mitchell Anderson, David Molyneux et Dean Steinke. « Estimating Second Order Wave Drift Forces and Moments for Calculating DP Capability Plots ». Dans ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-96307.

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Abstract The DP capability plot is a useful tool to show the limitations of a dynamic positioning system for ships or offshore structures under loading from wind, waves and ocean currents. At the preliminary design stage, it is desirable to use fast methods for calculating the forces and moments caused by the environment, preferably without the need for CFD simulations or model experiments. Empirical methods are available for predicting aerodynamic forces and moments, and hydrodynamic forces and moments from currents, but little is published for second order wave drift forces. Wave drift forces and moment calculations have been carried out using WAMIT, for a series of ship hulls from OSVs to VLCCs and the effects of wave direction and frequency on the Surge, Sway, and Yaw forces and moment have been studied. The presentation of the results allows the user to interpolate the resulting drift forces and moments as a function of wave direction for a given ship size. In terms of wave drift loads calculation, it is found that the very large vessels are dominant in the low frequency waves, while smaller size ships are in high frequencies. The wave frequency and direction in which maximum drift load occurs depends on the ship size.

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Karatvuo, Helena, Michael Linde, Azam Dolatshah et Simon Mortensen. « Improved Climate Change Adaptation in Port of Brisbane Using a Digital Twin Cloud-Based Modelling Approach ». Dans ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/omae2022-79613.

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Abstract Due to their low-lying coastal location, ports are vulnerable to climate change induced increases to flooding, waves, extreme winds, and the associated costly damages to port infrastructure and operational disruptions. For these reasons, there is an increasing need for ports to undertake regular risk assessments of the vulnerability of their infrastructure and operations due to the impacts of climate change. A digital twin, cloud-based climate change modelling solution has been developed to enable in-house risk assessments of climate change vulnerability to be undertaken for any port. Once set-up, the system supports the continued sustainable operation of ports and enhancing stakeholder confidence in corporate sustainability strategies by allowing in-house re-evaluation of the ports climate risk as new predictions are released. The basis of the digital twin model of the port are numerical wave and hydrodynamic models, configured with the actual port geography and bathymetry enabling highly detailed simulations of the ports physical environment. The numerical model simulations are supplemented with observations of wind, rainfall, and sea level to identify trends and extreme event probabilities under the historic climate conditions. Scenarios describing the predicted impacts of climate change can be superimposed on the historical climate via a web-based interface where the user (port) selects a planning horizon (e.g., 2050), storm event frequency (e.g., 100-year storm), and climate change predictions (e.g. RCP8.5). The resulting climate change simulations shows great potential to enable port-specific predictions of future impacts of extreme occurrences of wind, waves, water levels, and currents. The ports asset portfolio is incorporated in the risk assessment through dynamic GIS layouts and damage curves identifying the damage cause and cost for each vulnerable port asset. As new climate science becomes available, this cloud-based digital twin model enables ports to rapidly complete updated risk assessments and respond to stakeholder queries and concerns. The capability of the tool was validated by comparing the model results against a large conventional study of the region, and a historical flood event of 2011. Both validation exercises displayed a reasonable agreement increasing confidence in the model’s capacity as a predictive tool. Additionally, six climate change scenarios were modelled for one of Australia’s fastest growing container ports, Port of Brisbane and the results were successfully incorporated in the ports overall sustainability strategy.

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Rapports d'organisations sur le sujet "Waves/low frequency currents interractions"

Unknown, Author. L51630 In-Line Detection and Sizing of Stress Corrosion Cracks Using EMAT Ultrasonics. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), avril 1990. http://dx.doi.org/10.55274/r0010616.

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The development of stress corrosion cracks (SCC) in buried gas pipelineshas posed a serious threat to pipeline integrity for many years. It can be reliably detected by magnetic particle techniques in the field or by laboratory studies using low frequency eddy currents. It is also possible to find and measure the depths of the cracks from the ID by careful scanning with an ultra-sonic angle beam probe but the transducer must be manipulated by a skilled operator. All of these approaches are not very satisfactory for in-line inspections because they are not suitable for covering the total area of a pipeline and they are too labor intensive to be automated. In order to address this problem with new technology, the PRCI requested proposals for any technique that seemed to be practical and the Electromagnetic Acoustic Transducer (EMAT) was suggested as very promising because it has already demonstrated operation in the environment of the inside of a gas pipeline. Magnasonics, Inc., of Albuquerque, New Mexico, was chosen from many respondents to conduct an in-vestigation of the use of EMATs for overcoming the problems expected to arise from in-line operation and to incorporate the latest developments in ultrasonic inspection with EMATs. The objective of the program described in this report was twofold. First, to apply the most recent developments in EMAT technology to the problem of detecting and sizing stress corrosion cracks (SCC) in operating gas pipelines and second to exploit the ability of EMATs to generate and detect a wide variety of ultrasonic waves in the walls of a pipeline under operating conditions.

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