Numerical Modeling of Nearshore Morphological Changes Under Current-wave Field PDF Download

Author: Taerim Kim
Publisher:
ISBN:
Category : Beach erosion
Languages : en
Pages : 142

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Author: Dano J A Roelvink
Publisher: World Scientific
ISBN: 9814465127
Category : Science
Languages : en
Pages : 291

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Book Description
Process-based morphodynamic Modeling is one of the relatively new tools at the disposal of coastal scientists, engineers and managers. On paper, it offers the possibility to analyse morphological processes and to investigate the effects of various measures one might consider to alleviate some problems. For these to be applied in practice, a model should be relatively straightforward to set up. It should be accurate enough to represent the details of interest, it should run long enough and robustly to see the real effects happen, and the physical processes represented in such a way that the sediment generally goes in the right direction at the right rate. Next, practitioners must be able to judge if the patterns and outcomes of the model are realistic and finally, translate these colour pictures and vector plots to integrated parameters that are relevant to the client or end user. In a nutshell, this book provides an in-depth review of ways to model coastal processes, including many hands-on exercises.

Author: Santiago Alfageme
Publisher:
ISBN:
Category : Ocean waves
Languages : en
Pages : 148

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Author: David R. Michalsen
Publisher:
ISBN:
Category : Borrow pits
Languages : en
Pages : 260

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Book Description
Steep bathymetric anomalies in the beach profile, such as offshore borrow pits, submerged breakwaters, and nearshore canyons can significantly transform the wave climate through the effects of refraction, diffraction, and reflection. When located in the nearshore region the modified wave climate can also substantially change the location of breaking and has been observed to impact the shoreline morphology. The current study focuses on the borrow pit case and attempts to explain how limitations in existing methodologies may impact the predictions in both the wave field modification and shoreline response. Recent analytical methods by Bender (2003) have successfully explained the wave transformation near pits. However, these models are only capable of modeling bathymetries of constant depth surrounding the anomaly. Therefore in order to investigate cases without this restriction, this often requires numerical solutions following Berkhoff's (1972) mild-slope equation (MSE). However, a significant limitation of these model types is the accuracy suffers for steep bathymetric features. Booij (1983) demonstrates this for slopes larger than 1:3 (rise:run). Furthermore, these models often rely on Radder's (1979) parabolic approximation to the MSE which restricts the ability to include wave reflection which can be substantial in the case of a borrow pit. These limitations and their effects on shoreline response are investigated in the current study. By utilizing a form of the modified mild-slope equation (MMSE) originally derived by Massel (1993) the limitation of the MSE in representing steep features is removed. Additionally, a numerical model following Lee et al. (1998) is employed to investigate wave transformation around borrow pits of arbitrary depth. The formulation of the model is of hyperbolic form; therefore, the reflected waves generated by a borrow pit are included. The models accuracy is validated through a rigorous set of tests showing that the model compares well with previous analytical solutions for steep features. To estimate the importance of wave reflection, information from documented borrow sites is gathered. Using dimensionless parameters relating the incident waves and the pit geometry, an estimate of the amount of reflection generated by each borrow pit is calculated. It is shown that upward of 30% of the wave energy can be reflected by a borrow pit. Additionally, it is shown as wave frequency increases (or kh located in the intermediate depth region), the MSE's inaccuracy in predicting reflection is enhanced. Expanding on this conclusion, a parametenzation analysis is performed. The analysis describes conditions under which resonance inside the trench capable of producing large reflection is reached. The study serves as preliminary design guidance which can be used to avoid borrow pit geometries that are capable of producing a large amount of reflection. It is also of interest to describe how the effects of reflection affect the regions far shoreward of the pit. Employing a form of the MMSE model, the evolution of the wave field is analyzed. It was found that although the effects of reflection are strong near the borrow pit, as the distance leeward of the pit increases the effects of refraction and diffraction outweigh the impacts of reflection. Thus, the result using a wave model including reflection would not substantially differ from that of using a model that neglects the reflected waves when investigating the impacts on shoreline evolution. Finally, the last part of the study looks at the validity of utilizing current shoreline response models for this particular problem. Wave height and direction at breaking dictate how one-line models predict shoreline response. However, these models fail to include the effect that longshore gradients in wave height have on generating mean water level (MWL) gradients. MWL gradients in wave height are capable of producing longshore currents which can significantly alter the sediment transport trends. Coupling the MMSE wave model with a 2DH nearshore circulation model shows that MWL gradients have a significant impact on current generation. Results indicate that incipient rip currents result from the converging currents associated with the MWL gradients. The presence of these currents would thereby dictate a new sediment transport trend, possibly transporting sediment offshore instead of in the theorized salient formation predicted by one-line models.

Author: J. H. Allender
Publisher:
ISBN:
Category : Coast changes
Languages : en
Pages : 150

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 15

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Book Description
Numerical models were developed to predict the propagation and transformation of the time-dependent wave field across the nearshore zone, nearshore circulation including longshore, undertow and rip currents, and instantaneous and mean water levels including wave runup and swash on beaches. The inclusion of time-dependence permitted the study of evolving wave and current fields, including the generation of low frequency waves and shear instability of the currents. The developed two-dimensional and three-dimensional models were extensively validated by comparison to laboratory experiments conducted in this project and available field experiments. Equipment purchases and upgrades allowed the laboratory studies of breaking waves, and the associated turbulence, bottom friction, undertow, swash, runup, overtopping, and overwash in the University of Delaware's Precision Wave Tank, Directional Wave Basin, and Sand Beach Wave Tank.

Author: Pablo Higuera
Publisher: World Scientific
ISBN: 981126547X
Category : Science
Languages : en
Pages : 208

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Book Description
This unique compendium introduces the field of numerical modelling of water waves. The topics included the most widely used water wave modelling approaches, presented in increasing order of complexity and categorized into phase-averaged and phase-resolving at the highest level.A comprehensive state-of-the-art review is provided for each chapter, comprising the historical development of the method, the most relevant models and their practical applications. A full description on the method's underlying assumptions and limitations are also provided. The final chapter features coupling among different models, outlining the different types of implementations, highlighting their pros and cons, and providing numerous relevant examples for full context.The useful reference text benefits professionals, researchers, academics, graduate and undergraduate students in wave mechanics in general and coastal and ocean engineering in particular.

Author: James Thornton Kirby
Publisher:
ISBN:
Category : Mathematical models
Languages : en
Pages : 182

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Book Description
This report represents a review and conclusion of several studies conducted at the University of Delaware with the aim of providing numerical model for calculating nearshore wave-induces currents and mean water level fluctuations. The purpose of constructing a numerical model rests on the need to extend our predictive capabilities into situations which lie beyond the scope of analytic methods. In the end, all numerical models, as well as analytical formulations, are limited in scope by the simplifying assumptions incorporated in their theoretical framework; in this regard, the present models represent an attempt to extend present analytic treatments to the case of a complex topography in two dimensions. The models do not consider the associated sediment transport problem, although this capability can be added. Also, the models require that the incident wave field be regarded as monochromatic, or, after some model modifications, narrow banded enough to be represented as a modulated wave train at a single carrier frequency.

Author: Peter B. Hale
Publisher:
ISBN:
Category : Beach erosion
Languages : en
Pages : 94

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Author: James T Kirby (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 171

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In this chapter the theoretical framework for the development of time averaged governing equations for the problem of waves and currents in the nearshore zone is outlined. The development of the numerical circulation models in either the 'linear' or 'nonlinear' form is then described in Chapter III based on the theoretical framework. In general, the development of each model has been described in previous technical reports; the linear model in Birkemeier and Dalrymple (1976), and the nonlinear model in Ebersole and Dalrymple (1979). For this reason, some of the derivations and intermediate steps needed to develop the governing equations are not described in detail in the present report. The reader can refer to the previous work for missing details. However, both models now include the option of calculating wave energy decay due to interaction with the bottom, which has not been included in previous reports. The theory and implementation of this option is described in detail. (Author).