Review and Verification of Numerical Wave Models for Near Coastal Areas - Part 1: Review of Mild Slope Equation, Relevant Approximations, and Technical Details of Numerical Wave Models PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Ocean wave propagation is heavily affected by bathymetric variation, particularly in the nearshore areas. In this report, the theoretical basis behind the mild slope equation, which is often used for modeling wave propagation, is discussed. In particular, the theory and technical details of the models REF/DIF1, REF/DIF-S, and RCPWAVE are defined. (REF/DIF-S is an irregular wave version of REF/DIF1.) Two different modifications of the mild slope equation that simplify the modeling of wave propagation for general areas: the parabolic approximation, which is used in the model REF/DIF1 and REF/DIF-S; and the eikonal-transport equations, used in RCPWAVE are examined. The consequences of using either modification is also discussed. Incorporation of relevant physical effects (e.g., wave breaking, bottom friction, etc.) that affect wave propagation in the nearshore area is illustrated.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Ocean wave propagation is heavily affected by bathymetric variation, particularly in the nearshore areas. In this report, the theoretical basis behind the mild slope equation, which is often used for modeling wave propagation, is discussed. In particular, the theory and technical details of the models REF/DIF1, REF/DIF-S, and RCPWAVE are defined. (REF/DIF-S is an irregular wave version of REF/DIF1.) Two different modifications of the mild slope equation that simplify the modeling of wave propagation for general areas: the parabolic approximation, which is used in the model REF/DIF1 and REF/DIF-S; and the eikonal-transport equations, used in RCPWAVE are examined. The consequences of using either modification is also discussed. Incorporation of relevant physical effects (e.g., wave breaking, bottom friction, etc.) that affect wave propagation in the nearshore area is illustrated.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
This report details the validation of the numerical wave models REF/DEF1 and REF/DIF-S. The monochromatic model REF/DIF1 is used to test most model physics, while the irregular wave model REF/DIF-S is used to investigate model applicability to realistic situations. Comparisons of the models to available analytical solutions, synthetic cases, and laboratory and field scenarios are performed. Where applicable, we also compare the two models to the wave model RCPWAVE, which is based on a different formulation. We find that the REF/DIF models are reasonably accurate in most of the situations tested. The REF/DIF models also outperform RCPWAVE in most of the instances where the models can be compared. In particular, it is found that the RCPWAVE model under predicts the effect of wave diffraction. Model robustness to bathymetric uncertainty is also tested. It is found that neither REF/DIF1 nor REF/DIF-S is overly sensitive to bathymetric uncertainty. In areas where the diffraction effect is large, the REF/DIF-S model tends to have more robust characteristics than the monochromatic model, due primarily to its irregular nature. Details of the modified spectral input program used in this study appear in the appendix.
Author: W. E. Rogers Publisher: ISBN: 9781423565499 Category : Languages : en Pages : 108
Book Description
This report details the validation of the numerical wave models REF/ DEF1 and REF/DIF-S. The monochromatic model REF/DIF1 is used to test most model physics, while the irregular wave model REF/DIF-S is used to investigate model applicability to realistic situations. Comparisons of the models to available analytical solutions, synthetic cases, and laboratory and field scenarios are performed. Where applicable, we also compare the two models to the wave model RCPWAVE, which is based on a different formulation. We find that the REF/DIF models are reasonably accurate in most of the situations tested. The REF/DIF models also outperform RCPWAVE in most of the instances where the models can be compared. In particular, it is found that the RCPWAVE model under predicts the effect of wave diffraction. Model robustness to bathymetric uncertainty is also tested. It is found that neither REF/DIF1 nor REF/DIF-S is overly sensitive to bathymetric uncertainty. In areas where the diffraction effect is large, the REF/DIF-S model tends to have more robust characteristics than the monochromatic model, due primarily to its irregular nature. Details of the modified spectral input program used in this study appear in the appendix.
Author: Bruce A. Ebersole Publisher: ISBN: Category : Languages : en Pages : 163
Book Description
The numerical model documented here, RCPWAVE, can be used to solve wave propagation problems over arbitrary bathymetry. The governing equations solved in the model are the mild slope equation for linear, monochromatic waves, and the equation specifying irrotationality of the wave phase function gradient. Finite difference approximations of these equations are solved to predict wave propagation outside the surf zone. Inside the breaker zone, an empirical method is used to predict wave transformation. This method is based on a hydraulic jump representation of the entire surf zone. The model is verified using laboratory and field data. A user's manual section is provided to aid potential users. This documentation describes job control language files, job submission procedures, sample input and output files, and execution costs.
Author: Zeki Demirbilek Publisher: ISBN: Category : Languages : en Pages : 124
Book Description
This report describes a new wave-prediction model called CGWAVE. CGWAVE is a genetal-purpose, state-of-the-art wave prediction model. It is applicable to estimation of wave fields in harbors, open coastal regions, coastal inlets, around islands, and around fixed or floating structures. Both monochromatic and spectral waves can be simulated with the CGWAVE model. While CGWAVE simulates the combined effects of wave refraction-diffraction included in the basic mild-slope equation, it also includes the effects of wave dissipation by friction, breaking, nonlinear amplitude dispersion, and harbor entrance losses. CGWAVE is a finite-element model that is interfaced to the Corps of Engineers' Surface-water Modeling System (SMS) for graphics and efficient implementation (pre-processing and post-processing). The classical super-element technique and a new parabolic approximation method developed recently are used to treat the open-boundary condition. An iterative procedure (conjugate gradient method) is used to solve the discretized equations, thus enabling the modeler to deal with large-domain problems. A detailed derivation of the basic theory of the CGWAVE model is provided in Sections 2 and 3. Sections 4 through 6 provide the details of how this theory is implemented numerically. A step-by-step user's guide is provided in Section 7 to ensure safe and efficient usage of the CGWAVE model for practical applications. Example applications used in the development, testing, and validation of CGWAVE are presented in Section 8 of this report.
Author: World Meteorological Organization Publisher: Secretariat to World Meteorological Organization ISBN: Category : Science Languages : en Pages : 174
Author: David R. Michalsen Publisher: ISBN: Category : Borrow pits Languages : en Pages : 260
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: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The choice of a particular wave model for use in nearshore wave climate forecasting or hindcasting is usually contingent upon the site to be considered and the processes to be modeled. Phase averaged spectral models such as SWAN, WAM or STWAVE are source based energy models which treat the wave field as a stochastic phenomenon. This particular formulation allows for the consideration of wind wave generation, among other source terms. These models (particularly STWAVE and SWAN) are able to simulate irregular wave propagation over coastal areas relatively efficiently; however, the propagation terms in these models are derived from ray theory and do not handle bathymetrically induced diffraction, which may be important in coastal areas. (It should be noted that STWAVE does not contain some accounting for diffraction as a diffusion of wave energy in the source terms). Phase resolving models such as REF/DIF1, REF/DIF-S and RCPWAVE by contrast, treat the wave field deterministically, tracing the free surface evolution over the domain. The irregular nature of the wave field can be accounted for by running several wave frequencies/directions through the model and calculating the statistics from the model results. This is often done by discretizing an input spectrum into frequency and direction bins, calculating the waveheight in each bin and then running them through the model. This formulation is most useful in the case of complex bathymetry and predominantly swell like conditions. Models in this latter class cannot account for wind wave generation.
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Author: W. E. Rogers
Author: Bruce A. Ebersole
Author: Zeki Demirbilek
Author: World Meteorological Organization
Author: James Thornton Kirby
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Author: David R. Michalsen
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