COMPARISON OF NUMERICAL MODELS FOR WAVE OVERTOPPING AND IMPACT ON A SEA WALL (original) (raw)
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Numerical Analysis of Wind Effect on Wave Overtopping on a Vertical Seawall
Water
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...
Wave Runup and Overtopping at Seawalls Built on Land and in Very Shallow Water
Journal of Waterway, Port, Coastal, and Ocean Engineering, 2013
The current study proposes prediction formulas both for random wave runup and mean overtopping discharge at seawalls constructed on land or in very shallow water. Although several existing formulas for runup and overtopping use the incident wave characteristics at the toes of seawalls, this study adopts the equivalent deepwater wave characteristics and an imaginary seawall slope for easy application of the formulas, especially in relation to seawalls constructed on land. The prediction formulas for overtopping use the predicted runup values. For the wave runup prediction formulas two sets of experimental data are used; i.e., a new set of data and the data obtained in a previous study. For the wave overtopping prediction formulas, the experimental data measured in a previous study are used. Comparisons with measurements show good performances of both new prediction methods.
Random Wave Overtopping of Simple Sea Walls: A New Regression Model
Proceedings of the ICE - Water Maritime and Energy, 1998
Sea walls are expensive, and fixing a seawall freeboard at too large a value has a financial penalty and is unnecessarily damaging to the natural environment owing to the increased impact of the structure on its surroundings. On the other hand, if the crest of a sea wall is set too low then there are potential problems with structural safety and flooding from wave overtopping. Hence, it is important to strike the correct balance between satisfying the structural and functional requirements of the project, avoiding unnecessary expense, and having undesirable impacts on the surrounding environment. The prediction of wave overtopping rates is usually based on empirical equations fitted to laboratory data. These equations do not have any theoretical basis. However, a new model has now been developed which, unlike existing expressions, accounts for the fact that no overtopping (apart from wind-blown spray) occurs if the sea-wall freeboard exceeds the maximum wave run-up on the face of the structure. This fact is of practical importance because allowable overtopping discharges to ensure the safety of people and property are quite small. This paper starts with a brief review of existing overtopping equations, then presents the new model, and concludes by giving an example of its practical implications. It is shown that, for some conditions, the new model predicts sea-wall freeboards which are several metres less than those predicted by the well-known expression given by Owen.
Coastal Engineering, 2000
A one-dimensional high-resolution finite volume model capable of simulating storm waves propagating in the coastal surf zone and overtopping a sea wall is presented. The model Ž. Ž. AMAZON is based on solving the non-linear shallow water NLSW equations. A modern upwind scheme of the Godunov-type using an HLL approximate Riemann solver is described which captures bore waves in both transcritical and supercritical flows. By employing a finite volume formulation, the method can be implemented on an irregular, structured, boundary-fitted computational mesh. The use of the NLSW equations to model wave overtopping is computationally efficient and practically flexible, though the detailed structure of wave breaking is of course ignored. It is shown that wave overtopping at a vertical wall may also be approximately modelled by representing the wall as a steep bed slope. The AMAZON model solutions have been compared with analytical solutions and laboratory data for wave overtopping at sloping and vertical seawalls and good agreement has been found. The model requires more verification tests for irregular waves before its application as a generic design tool.
Modeling Wave Overtopping on a Seawall with XBeach, IH2VOF, and Mase Formulas
Water
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...
Comparisons of wave overtopping at coastal structures calculated with AMAZON, COBRASUC and SPHYSICS
The use of numerical models to calculate the mean overtopping discharges is, nowadays, more frequent in preliminary design of coastal structures, since they are more flexible than both empirical/semi-empirical and physical models and, once calibrated and validated, they can be applied reliably to a large range of alternative structure geometries and wave conditions. There are different models that can be used to calculate the mean overtopping discharges over a structure. The paper compares the output from three numerical models used to predict the mean overtopping discharges: AMAZON [1], based on solving the non-linear shallow-water equations; and two models based on Reynolds averaged Navier-Stokes equations, COBRAS-UC [2], a Eulerian model using the volume of fluid (VoF) method for surface capturing, and SPHysics [3], a Lagrangian model based on Smoothed Particle Hydrodynamics (SPH). The numerical results are also compared with experimental data obtained at the National Civil Engin...
Wave overtopping models and seawall freeboards
Unless the maximum wave run-up, R max on the face of a seawall is greater than the freeboard of the structure, R c , then there is no overtopping (apart from wind-blown spray). This condition is satisfied in a new theoretical model of random wave overtopping developed by Hedges and Reis 1 .
Investigation of Wind Effects on Wave Overtopping at Sea Defences
Coastal structures, 2019
Quantitative assessments of wind effects on wave overtopping are carried out using CFD simulations with the open source solver OpenFOAM. The desired wind speeds are achieved efficiently by introducing artificial pressure gradient terms for desired zones inside the computational domain. A new run-time post processing utility has been developed to track the overtopping water over a sea defence. Numerical results are validated using (1) a past experimental study with simple sloped defence and (2) new experiments that were conducted at HR Wallingford with a more realistic structure. Several additional calculations with both small and large water depths reveal that with a high wind speed the overtopping volume can be increased by 30% compared to that without wind. The 2D code is then extended to wave overtopping at a semi-circular beach in the plane as a hypothetical 3D sea defence in order to investigate the 3D effect of wind speeds.