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Dissertations / Theses on the topic 'Longshore currents'
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1
Church, John Casey. "Topics in longshore currents." Thesis, Monterey, Calif. : Naval Postgraduate School, 1993. http://catalog.hathitrust.org/api/volumes/oclc/29749880.html.
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Gutierrez, Enrique. "Effects of longshore currents on rip currents." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0004905.
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Soares, Costa Ventura Carlos Manuel da. "Vertical profiles of longshore currents." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305319.
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Smallegan, Stephanie M. "Longshore currents near Cape Hatteras, NC." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43719.
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As part of a beach erosion field experiment conducted at Cape Hatteras, NC in February 2010, this study focuses on quantifying longshore currents, which are the basic mechanism that drives longshore sediment transport. Using video imagery, the longshore currents in view of a video camera are estimated with the Optical Current Meter technique and the nearshore morphology is estimated by analyzing breaking wave patterns in standard deviation images.
During a Nor‟easter storm event on February 12 and 13, 2010, the video longshore currents are compared to in situ data and it is found that the currents are most affected by the angle of incidence of incoming waves, increasing in magnitude as the angle becomes more oblique due to a larger component of radiation stress forcing in the longshore direction. The magnitude of the radiation stress forcing, which is at least an order of magnitude larger than the surface wind stress, increases as wave height increases or tide level decreases, which causes more wave breaking to occur. The normalized standard deviation images show wave breaking occurring at an inshore and offshore location, corresponding closely to the locations of an inner and outer bar indicated in survey data.
Using two profiles from the survey data, one profile that intersects a trough and one that intersects a terrace, the video currents are also compared to currents simulated in one-dimension using the circulation module, SHORECIRC, and the wave module, REF/DIF-S, as part of the NearCoM system. Although the simulated currents greatly underpredict the video currents when the flow is only driven by radiation stresses, a mean water level difference between the two profiles creates a longshore pressure gradient. Superimposing a pressure gradient forcing term into the longshore momentum balance that assumes an equilibrium state of the flow, the magnitude of the simulated currents are much larger than the magnitude of the video estimated currents. Using analytical solutions of simplified forms of the mass and momentum equations to determine the effects of accelerations on the flow, it is seen that the acceleration term greatly affects the flow due to the relatively large mean water level difference that acts over a relatively short distance. Therefore, the pressure gradient forcing term is modified to include the effects of accelerations. By including the two-dimensional effects of the acceleration in the one-dimensional model through the modified pressure gradient, the quasi two-dimensional model simulated currents are very similar to the video estimated currents, indicating that the currents observed in the video may be pressure gradient driven.
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Brown, Susan Jayne 1967. "Longshore currents on seawall-protected beaches." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39079.
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Restrepo, Juan M., and Shankar Venkataramani. "Stochastic longshore current dynamics." ELSEVIER SCI LTD, 2016. http://hdl.handle.net/10150/621938.
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We develop a stochastic parametrization, based on a 'simple' deterministic model for the dynamics of steady longshore currents, that produces ensembles that are statistically consistent with field observations of these currents. Unlike deterministic models, stochastic parameterization incorporates randomness and hence can only match the observations in a statistical sense. Unlike statistical emulators, in which the model is tuned to the statistical structure of the observation, stochastic parametrization are not directly tuned to match the statistics of the observations. Rather, stochastic parameterization combines deterministic, i.e physics based models with stochastic models for the "missing physics" to create hybrid models, that are stochastic, but yet can be used for making predictions, especially in the context of data assimilation. We introduce a novel measure of the utility of stochastic models of complex processes, that we call consistency of sensitivity. A model with poor consistency of sensitivity requires a great deal of tuning of parameters and has a very narrow range of realistic parameters leading to outcomes consistent with a reasonable spectrum of physical outcomes. We apply this metric to our stochastic parametrization and show that, the loss of certainty inherent in model due to its stochastic nature is offset by the model's resulting consistency of sensitivity. In particular, the stochastic model still retains the forward sensitivity of the deterministic model and hence respects important structural/physical constraints, yet has a broader range of parameters capable of producing outcomes consistent with the field data used in evaluating the model. This leads to an expanded range of model applicability. We show, in the context of data assimilation, the stochastic parametrization of longshore currents achieves good results in capturing the statistics of observation that were not used in tuning the model.
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Whitford, Dennis James. "Wind and wave forcing of longshore currents across a barred beach." Thesis, Monterey, Calif. : Naval Postgraduate School, 1988. http://catalog.hathitrust.org/api/volumes/oclc/52803820.html.
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Faria, Antonio Fernando Garcez. "A simple quasi-three dimensional model of longshore currents over arbitrary profile." Thesis, [Monterey, Calif. : Naval Postgraduate School], 1995. http://catalog.hathitrust.org/api/volumes/oclc/35646712.html.
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Check, Lindsay A. (Lindsay Anne). "Analysis of Longshore Sediment Transport on Beaches." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4886.
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The present study investigates longshore sediment transport for a variety of bathymetric and wave conditions using the National Oceanic Partnership Program (NOPP) NearCoM Model. The model is used to determine the effects of wave shape and bathymetry changes on the resulting longshore sediment transport. The wave drivers, REF/DIF 1 and REF/DIF S, are used to assess the effects of monochromatic and spectral waves on longshore sediment transport, respectively. SHORECIRC is used as the circulation module and four different sediment transport models are used. Longshore transport comparisons are made with and without skewed orbital velocities in the shear stress and current velocities. It is found that the addition of skewed orbital velocities in shear stress and transport formulations increases longshore sediment transport by increasing time-varying effective shear stress. The addition of skewed orbital velocities greatly increases the transport due to advection by waves.
The localized longshore sediment transport is calculated using a generic physics based method and formulas by Bagnold, Bailard, and Bowen, Watanabe, and Ribberink. The transport results for each scenario are compared to the total transport CERC, Kamphuis, and GENESIS formulas. The bathymetries tested include an equilibrium beach profile, cusped beach profiles, and barred beach profiles with different bar locations. The longshore transport on an equilibrium beach profile is modeled for a 0.2 mm and 0.4 mm grain size and transport is compared to the CERC formula. The longshore sediment transport for d=0.2 mm is larger than d=0.4 mm when wave power is small, but as wave power increases the transport for the larger grain size dominates. The transport is also affected by the addition of cusps and bars on an equilibrium beach profile. The barred beach is modified to compare transport between waves breaking at the bar, before the bar, and after the bar. The features affect the transport when the wave powers are small, but as wave heights increase the cusp and bar features induce little change on the longshore sediment transport.
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Agarwal, Arpit. "Time-averaged model for longshore current and sediment transport in the surf and swash zones." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 4.62 Mb , 106 p, 2005. http://wwwlib.umi.com/dissertations/fullcit/1428092.
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11
Burnette, Carolina. "Analysis of a Long-Term Record of Nearshore Currents and Implications in Littoral Transport Processes." UNF Digital Commons, 2016. http://digitalcommons.unf.edu/etd/647.
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A seasonal and long-term analysis of the vertical structure of currents in the nearshore is conducted to determine the role of the wind in driving currents and consequently affecting littoral transport processes. Approximately ten years (January, 2002 – October, 2011) of nearshore current profiles are examined using the data collected with an Acoustic Doppler Current Profiler (ADCP) installed off of Spessard Holland North Beach Park located in Melbourne Beach, Florida. Additionally, wind data collected with a directional anemometer from September, 2002, until October, 2008, are used to further characterize the long-term hydrodynamic forcing. With the shoreline oriented nominally 17o west of magnetic north, both the current profiles and the wind vectors have been rendered into longshore and cross-shore components. The water level record from a NOAA tide station located at the Trident Pier at nearby Port Canaveral is utilized in establishing the water depth and conditioning the data for statistical analysis. Monthly mean vertical profiles reveal that during the winter months the surface currents are usually toward the south, and toward the north in the summer. In spring and fall, they are mixed, demonstrating a clear seasonality in both direction and intensity of the longshore current. Subjecting the longshore and cross-shore current data to Empirical Orthogonal Function Analysis reveals that the first spatial Eigenfunction accounts for more than 98% of the variability in the vertical profile of the longshore current, and more than 86% of the variability in the profile of the cross-shore current. However, there is a rotation of the current to the right (clockwise) with the rotation angle increasing and the variance decreasing with depth below the surface. The spiral structure of the water column follows a surface Ekman veering, but for very shallow water. The upper layer of the current is almost aligned with the direction of the wind. Monthly correlations between 2-hour average time series of longshore current and 2-hour average time series of wind speed reveal the seasonal patterns of the wind and longshore current in which the upper layer of the water column is highly correlated with the longshore component of the wind speed for most of the year and slightly less correlated for the lower layer of the water column. Most importantly, on average, wave height (Hmo) is larger when the longshore current is heading to the south (Hmo=0.95 m) than when the current is going to the north (Hmo=0.73 m). Additionally, there is a stronger correlation between southerly directed currents and incident wave energy flux than northerly directed currents and wave energy flux. These results indicate that the net long-term north-to-south sediment transport known to characterize the region is heavily influenced by wind-driven currents.
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Prevedel, Lloyd Massimo. "Longshore current variations, Guyana, South America." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ30974.pdf.
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Marquez, André Lanfer. "Estudo de agitação, correntes induzidas por ondas e balanço sedimentar da região do Porto de Tubarão e Praia de Camburi, Vitória/ES." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/21/21133/tde-05082011-110336/.
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Os ambientes costeiros podem ser caracterizados por sua grade dinâmica, onde existe o embate entre o continente e o mar. A dinâmica sedimentar da linha de costa constitui conhecimento básico em obras de engenharia e na compreensão do ambiente costeiro. Buscou-se compreender os mecanismos do funcionamento dinâmico da região em torno do Porto de Tubarão, Vitória-ES, através de análises de marés, de clima de ondas, agitação marítima, de correntes induzidas por ondas e transporte sedimentar. Os resultados permitiram algumas interpretações tanto de curtíssimo prazo como de longo prazo. As correntes de marés são particularmente importantes, sobretudo próximo as bocas dos canais de Vitória e da Passagem atingindo valores de até 0,.7m/s. As ondas atingem a área com alturas significativas variadas, dependendo do grau de exposição. Na praia de Camburi as ondas dificilmente ultrapassam 1 metro de altura significativa, enquanto na praia Mole ondas de 2.5m de altura significativa ocorrem com certa freqüência. A direção da corrente na praia Mole está diretamente relacionadas com as direções de incidência das ondas variando de NE até SW, enquanto sua intensidade está relacionada com as alturas e períodos, variando de 0 até 0.44 m/s. A praia de Camburi, por sua vez apresenta correntes rumo ENE independente da direção de propagação das ondas ao largo da Baia do Espírito Santo. As velocidades médias variam entre 0 e 0,3 m/s. O porto de tubarão serve de abrigo às ondas, influenciando na direção média do fluxo de energia nas praias adjacentes. A longo prazo a tendência da praia de Camburi é de sofrer uma rotação acentuando os processos erosivos na porção ocidental.The coastal zones can be characterized by the huge dynamic battle, continent forces against the ocean forces. The sedimentary dynamic of the coast line is a basic knowledge necessary to carry out engineering features and to understand the natural coastal environment. This work tried to understand the mechanisms that control those dynamics in the region near to the Tubarão Harbour, Vitória- ES. The effects of the tides, wind generated wave clima, wave induced currents and sedimentary transport was analyzed in short and long terms. In short terms, tide currents are specially important near the estuaries mouth (Vitória and Passagem channels), with velocities reaching 0.7m/s. The waves reach the coast line with different significant wave heights, depending on the each site expositions to in coming waves. At Cambury beach the waves hardly gets significant wave height over 1meter, in other hand, at Mole beach, waves with 2,5m significant wave height are quite often. At Mole beach, wave induced currents directions are directly correlated with the wave direction in outside zones, oscillating between NE and SW directions. The current velocities, which depends on wave height and wave period, presents values between 0 and 0,44 m/s. At Cambury beach the currents always goes to ENE, independent of outside wave directions. The velocities varies between 0 and 0,3 m/s. The Tubarão harbour acts like a wall creating shadows for the incident waves in the beaches behind. In long terms, the Mole beach seems to be stable and Cambury Beach seems to rotate some degrees of it mean direction, with the intensifications of the erosional process in the oriental portion of the beach.
14
van, Gaalen Joseph F. "Longshore Sediment Transport From Northern Maine To Tampa Bay, Florida: A Comparison Of Longshore Field Studies To Relative Potential Sediment Transport Rates Derived From Wave Information Study Hindcast Data." Scholar Commons, 2004. https://scholarcommons.usf.edu/etd/1280.
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This paper examines the regional longshore sediment transport pattern of the seaward coast of the United States and Gulf of Mexico from northern Maine to Tampa Bay, Florida. From previous studies it is known that along the coast there are variations in direction of sediment transport known as nodal zones as well as variations in sediment transport rate. Wave Information Study (WIS) hindcast data for the interval 1976 through 1995 (United States Army Corps of Engineers, 2003) provide a spatially continuous model of the regional longshore current directions in the study area.
In chapter one, all available published field studies of longshore current direction and sediment transport directions and rates are compiled to create a description of the direction and, whenever possible, magnitude of longshore transport. A detailed compilation of regional and local published studies are provided in tables. An interpretation of sediment transport rates and directions is provided in eight regional maps of the study area.
In chapter two the results of the literature compilations are compared with gross and net potential sediment transport directions and rates modeled using WIS hindcast data. The WIS deep-water wave characteristics are used to predict the directions and rate of longshore sediment transport at local outer coast positions using the method of Ashton et al. (2003a). The WIS-derived transport directions, including nodal zones, generally agree with the published field studies, although there are a few local inconsistencies particularly near inlets, shoals and irregular bathymetry. Trends in longshore transport rates, such as increases and decreases in gross transport rates are well represented by the WIS-derived potential transport rates. The discrepencies between the published field studies and WIS results are apparently primarily due to assumptions in the WIS model, such as assuming shore-parallel bathymetric contours.
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Dubarbier, Benjamin. "Modélisation numérique de l'évolution des profils de plages sableuses dominées par l'action de la houle." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0365/document.
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Les barres sableuses pré-littorales ont un rôle fondamental en morphodynamique des plages soumises à l’action des vagues. Le déséquilibre permanent entre les flux sédimentaires induits vers laplage par les non linéarités des vagues et ceux induits vers le large par le courant de retour gouverne lamigration transversale des barres. Dans cette thèse, un nouveau modèle morphodynamique de profilde plage intégrant l’état de l’art des processus hydro-sédimentaires a été développé. Le faible coûten temps de calcul de ce modèle permet de réaliser des simulations à long terme, O(mois/années),de la morphologie de plages réelles ayant des caractéristiques variées (pente, type de déferlement,granularité). La simulation sur plusieurs jeux de données, de plages réelles et expérimentales, a permisd’identifier la contribution respective des principaux processus hydro-sedimentaires dans la dynamiquede la plage suivant les conditions de houle (e.g. Tempête, temps calme). Ces avancées scientifiques ontété intégrées à un modèle 2DH, ce qui a notamment permis de simuler pour la première fois sur des casacadémiques la formation d’une barre sableuse rectiligne à partir d’une plage parfaitement plane, suiviedu développement de corps sableux tridimensionnels. Ces résultats ouvrent la voie vers l’applicationde ce type de modèle aux plages naturelles soumises à une large variabilité de régimes de houleSandbars are ubiquitous patterns along wave-dominated sandy coastlines and are key elementsin the global evolution of beaches. Cross-shore sandbar migrations are the result of the permanentimbalance between sediment flux driven by wave non-linearity and mean return current. In this thesis,we developed a new process-based beach profile model integrating the recent scientific advancesin term of hydrodynamics and sediment transport developed for beach morphodynamics. The lowcomputing time allows for long-term morphodynamic simulations (O months/years) of natural beachprofiles of diverse characteristics (beach slope, sediment grain size or type of wave breaking). Modelvalidations on several data sets, encompassing natural and experimental beach profile evolutions,highlight the respective contribution of the main hydrodynamic and sediment transport processesinvolved in specific cross-shore sandbar evolution relative to various wave conditions. Finally, all thecross-shore physical processes were integrated in a 2DH morphodynamic model, resulting for the firsttime in the simulation of a quasi-complete down state sequence showing alongshore bar generationwith subsequent spontaneous formation of transverse bar and rip morphology. These very encouragingresults pave the way for using this model to simulate 3-Dimensional evolutions of natural beachesforced by irregular wave conditions
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Costa, Ventura Soares Carlos Manuel da. "Vertical profiles of longshore currents." 1995. http://catalog.hathitrust.org/api/volumes/oclc/35253647.html.
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lin, Li Ching, and 林立青. "Evaluation of longshore sediment transport resulted from threshold longshore current." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/77461258586348100294.
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碩士國立交通大學
土木工程系
89
A new evaluation of longshore sediment transport resulted from threshold longshore was proposed in this paper. Longuet-Higgins’ (1970) theory of longshore current was chosen to calculate velocity distribution due to its explicit form. The threshold velocity of longshore current to start to move sands was decided by one-equation Shields parameter that was extended to the case of a sloping bed. The amount of longshore sediment was classified into bed-load and suspended load in this paper. The amount of bed-load and suspended load was estimated by the formula proposed by Bagnold (1956) and Van Rijn (1984), respectively. If the amount of littoral sand drift the was related with wave energy flux and a coefficient K, it is found that coefficient K depends on the beach slope, the wave steepness, and the sediment grain size. The average value of K is 0.53 and lies between those of Komar and Inmans’ (1970) and CERC’s (1977). Coefficient K was represented by a power law in terms of dimensionless environmental factors which are relative grain diameter, beach slope, and wave steepness. The value of K computed from the regressed formula is fairly close to the value of original K by error deviation within 27%. It is easy and accurate to obtain longshore sediment transport by the present formula when the offshore wave condition, sand size, and bottom slope is given.
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Suen, Pi-Feng, and 孫丕峰. "Longshore Current on Composite Beach Profiles." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/52240143358938912699.
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碩士國立交通大學
土木工程學系
84
Natural beaches tend to exhibit an equilibrium profile that is planar nearshore and nonplanar, concave-up offshore. Its analytical solution for the longshore current on composite beach profiles was given in this paper. The effects of the shape of bottom beach profile, lateral turbulent mixing stress, the location of the intersection between the planar and nonplanar profiles, and the landward limit of run-up on longshore current inside surf zone are discussed in the present paper. The rusults show that stronger effect of the composite beach profiles acts on longshore current inside surf zone than outside surf zone, and different beach profiles have their own longshore current. For composite beach profiles, the longshore current becomes stronger near the coast than far from the coast when lateral turbulent stresses increases. When the width of the planar beach face increases, the location of the maximum longshore current moves closer to the seaward. The landward limit of run-up has only effects on current near the nearshore but not for the outside of the location of profiles intersection.
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Lee, Pei-Jung, and 李培榮. "Data Measurement and Transmission System for Longshore Current Survey." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/04748329609150614479.
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碩士國立成功大學
電機工程學系碩博士班
91
This thesis presents a measuring and data transmission system for longshore current survey, which is mainly composed of the positioning sub-system, the data processing sub-system and the radio transmission sub-system. In the positioning sub-system, Global Positioning System (GPS) receiver is employed to locate ball position. A single-chip 8051 is used for data processing sub-system. Applying the software UART, we receive data from the GPS receiver and transmit GPS data to PC. Regarding the communication protocol, the hardware UART method is used to communicate between two balls and base station. In this thesis, the two balls are set to taking turns to transmit data per second. The radio transmission sub-system is a channel of the data transmits. The frequency band of radio transceiver is 433.92MHz, which is modulated by Frequency Shift Keying (FSK) method. The radio transceiver total output power is over 800mW. The sensitivity is over —80dBm. Finally, a PC-based information monitoring and storing sub-system is designed to collect the experimental data. The experimental results verify that the purpose of positioning and transmission is achieved.
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Cai, Zong-Wen, and 蔡宗文. "Wave deformation, set-up and longshore current on barred beaches." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/39637359650258622321.
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Lin, Jeng-Yih, and 林政毅. "A!Study of Formation of Bar Beach and its Longshose Current." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/07350878864916186252.
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碩士國立成功大學
水利及海洋工程學系
86
Equilibrium beaches are qualitatively decomposed into storm beaches andnormal beaches. A storm beach has recession near the shoreline and thedeposition of offshore bar built from the eroded material. The geometry ofbottom profile of a barred beach comprises a convex downward curve nearshoreand a concave upward curve offshore. Therefore, the previous proposed shapefunctions are monotonously decreasing which can not sufficiently describe theconfiguration of the storm beaches. In this paper beach profile data from bothlaboratory and field survey were used to examine a reliable shape function byregression analysis. The results showed that a fifth polynomial is applicableto present the profile of a barred beach. A general functional form relatedgeometric characteristic of a storm profile to various forcing parameters isderived on the basis of a wave dissipation model. The predictive model hasbeen developed to describe the shape of a barred beach and proven to favorablycompare with laboratory data. Meanwhile, the momentum and energy equationswere used to obtain wave deformation, set up and longshore current induced byan obliquely regular or irregular wave. The good agreement between the presentprediction and laboratory data gives the verification of the accuracy of thispredictive model. When the wave height, period and incidence angle and sandgrain size are given, the present model can give the profile of a barred beachand longshore current on the formed beach. The results showed that the wavebreaks before it reaches the bar crest and then wave height consequentlydecays during a short distance, but the maximum value of longshore currentoccurs at the bar crest.