The applicability of SWASH model for wave transformation and wave overtopping: A case study for the Flemish coast (original) (raw)
2011
https://doi.org/10.13140/2.1.4232.7045
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Abstract
T. S uzuki1'2' , T. V erw aest1, W. H assan1, W. V e a le 1'2, J. R eyn s1'3, K. T rouw 1'4, P. Troch2 and M. Z ijlem a5
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Journal of Fluid Mechanics, 2002
The swash zone is that part of a beach over which the instantaneous shoreline moves back and forth as waves meet the shore. This zone is discussed using the nonlinear shallow water equations which are appropriate for gently sloping beaches. A weakly three-dimensional extension of the two-dimensional solution by Carrier & Greenspan (1958) of the shallow water equations for a wave reflecting on an inclined plane beach is developed and used to illustrate the ideas. Thereafter attention is given to integrated and averaged quantities. The mean shoreline might be defined in several ways, but for modelling purposes we find the lower boundary of the swash zone to be more useful. A set of equations obtained by integrating across the swash zone is investigated as a model for use as an alternative boundary condition for wave-resolving studies. Comparison with sample numerical computations illustrates that they are effective in modelling the dynamics of the swash zone and that a reasonable representation of swash zone flows may be obtained from the integrated variables. The longshore flow of water in the swash zone is in many ways similar to the Stokes' drift of propagating water waves. Further averaging is made over short waves to obtain results suitable as boundary conditions for longer period motions including the effect of incident short waves. In order to clearly present the work a few simplifications are made. The main result is that in addition to the kinematic type of boundary condition that occurs on a simple, e.g. rigid, boundary two further conditions are found in order that both the changing position of the swash zone boundary and the longshore flow in the swash zone may be determined. Models of the short waves both outside and inside the swash zone are needed to complete a full wave-averaged model; only brief indication is given of such modelling.
Improvements in wave overtopping analysis: the EurOtop overtopping manual and calculation tool
This paper describes the new Wave Overtopping Manual developed in UK, the Netherlands and Germany. This new manual extends and updates the EA's Overtopping Manual (W178) edited by Besley (1999), the Netherlands TAW manual edited by Van der Meer (2002), and the German Die Küste (EAK, 2002). Considerable research on overtopping processes and prediction methods since those publications has prompted the production of an updated and extended manual combining European expertise. The new manual will cover more types of sea and shoreline defence structures, will give more details on overtopping responses, and will include a wider choice of how to calculate those responses. The manual will be supported by a Calculation Tool that guides the user through a series of steps to establish empirical overtopping predictions as described in the manual.
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Onshore wind significantly affects wave run-up and overtopping, thereby representing a major variable to account for in the design process. The aim of this study is to analyze the ability of numerical models to properly reproduce the wind effect on the overtopping at vertical seawall and to use them to understand how the wind influences the overtopping process as well. We use the RANS model, FLOW-3D, and the NLSW model, SWASH; both model the action of wind through the shear stress that it exerts on the sea surface. Although a simplified modelling of wind has been adopted, the CFD model has led to physically consistent results. On the other hand, SWASH seems to be unsuitable for reproducing the enhancement of the overtopping rate due to wind. CFD numerical results show that the wind affects only the lower overtopping regime (i.e., q < 1 l/s/m); as the mean overtopping discharge decreases, the influence of wind increases. Specifically, wind plays a key role in pure “white overtoppi...
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This paper describes methods and results of research for incorporating four different parameterized wave breaking and dissipation formulas in a coastal wave prediction model. Two formulations assume the breaking energy dissipation to be limited by the Rayleigh distribution, whereas the other two represent the breaking wave energy by a bore model. These four formulations have been implemented in WABED, a directional spectral wave model based on the wave action balance equation with diffraction, reflection, and wave-current interaction capabilities. Four parameterized wave breaking formulations are evaluated in the present study using two high-quality laboratory data sets. The first data set is from a wave transformation experiment at an idealized inlet entrance, representing four incident irregular waves in a slack tide and two steady-state ebb current conditions. The second data set is from a laboratory study of wave propagation over a complex bathymetry with strong wave-induced currents. Numerical simulation results show that with a proper breaking formulation the wave model can reproduce laboratory data for waves propagating over idealized or complicated bathymetries with ambient currents. The extended Goda wave breaking formulation with a truncated Rayleigh distribution, and the Battjes and Janssen formulation with a bore model produced the best agreement between model and data.
Coastal Engineering, 2009
The note extends and completes the analysis carried out by . Shoreline motion in nonlinear shallow water coastal models. Coastal Eng. 56(5-6) (doi:101016/j. coastaleng.2008.10.008), 495-505.] on the performance of a state of the art Non-Linear Shallow Water Equations solver in common coastal engineering applications. The case of bore-generated overtopping of a truncated plane beach is considered and the performance of the model is assessed by comparing with the Peregrine and Williams [Peregrine, D., Williams, S.M., 2001. Swash overtopping a truncated beach. J. Fluid Mech. 440, 391-399.] analytical solution. In particular the influence of shoreline boundary conditions is investigated by considering the two best performing approaches discussed in Briganti and Dodd . Shoreline motion in nonlinear shallow water coastal models. Coastal Eng. 56(5-6) (doi:101016/j.coastaleng.2008.10.008), 495-505.]. Different distances of the edge of the beach from the bore collapse point are tested. For larger distances, the accuracy of the overtopping modelling decreases, as a consequence of the error in modelling the tip of the swash lens and, consequently, the run-up. A sensitivity analysis using the numerical resolution is carried out. This reveals that the approach in which cells shallower than a prescribed threshold are drained and wave propagation speeds for wet/dry Riemann problem are used at the interface between a wet and a dry cell (referred as Option 2ea in . Shoreline motion in nonlinear shallow water coastal models. Coastal Eng. 56(5-6) (doi:101016/j. coastaleng.2008.10.008), 495-505.]) performs consistently better than the other.
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The advances in computational fluid dynamics have made numerical modeling a reliable complementary tool to the traditional physical modeling in the study of the wave overtopping phenomenon. This paper addresses overtopping on a seawall by combining the numerical models XBeach (non-hydrostatic and Surfbeat modes) and IH2VOF, and the Mase formulas. This work is structured in two phases: (i) phase I assesses the performance of numerical models and formulas in modeling wave run-up and overtopping on a seawall for a solid profile bottom and representative hydro-morphologic conditions of a study site in the Portuguese west coast; (ii) phase II investigates the effect of the profile bottom variation in the overtopping phenomenon for extreme maritime storm field conditions of the study site, considering a solid bottom and a varying sandy bottom. The results indicate that XBeach underestimates the wave energy, and the frequency and intensity of the overtopping occurrences predicted by IH2VOF...
A numerical model based on the Boussinesq equations was developed to simulate wave transformation in the nearshore zone with emphasis on describing the effects of wave breaking. Two different formulations for estimating additional momentum due to depth-limited wave w breaking, namely one proposed by Watanabe and Dibajnia Watanabe, A., . A numerical model of wave deformation in the surf zone. Proceedings of the 21st Coastal x w Engineering Conference, ASCE, pp. 578-587 and another one by Schaffer et al. Schaffer, H.A.,M adsen, P.A., Deigaard, R., 1993. A Boussinesq model for waves breaking in shallow water.
Simulation of random wave overtopping by a WCSPH model
Applied Ocean Research, 2021
In this work the Weakly Compressible SPH-based (WCSPH) model DualSPHysics has been validated and applied to study the random wave overtopping of dike-promenade layout in shallow water conditions. Data from physical model tests carried out in a small-scale wave flume have been used for model validation. The results have been compared in terms of water surface elevation, mean discharges and individual overtopping volumes distribution. The selected geometrical layout is representative of the coastal area of Premià de Mar, in Catalonia (Spain). This stretch of the coast presents both railways and a bike path very close to the shore and therefore exposed to possible sea storms. For the first time an SPH-based model has been employed to reproduce long-lasting wave overtopping tests, made of time series of 1000 irregular waves, which are representative of real sea states. The density diffusion scheme and the modified Dynamic Boundary Conditions have been applied in the present simulations. By employing standard setup for SPH modelling of wave-structure interaction problems of a very long duration, stable simulations and accurate results have been attained.
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