Irregular Wave Overtopping Research Articles

Numerical Simulation of Spatial Distribution of Wave Overtopping on Non-reshaping Berm Breakwaters

This study presents the results of a 2D numerical modeling investigation on the performance of non-reshaping berm breakwaters with a special look at the spatial distribution of irregular wave overtopping using FLOW-3D CFD code. The numerical model is based on Reynolds-Averaged Navier-Stokes solver (RANS) and volume of fluid (VOF) surface capturing scheme (RANS-VOF). The numerical model has been validated using experimental data. The armor and core porosities have been used as calibration factors to reproduce the wave overtopping distribution. The computed distributions of wave overtopping behind the structure agree well with the measurements for a non-reshaping berm breakwater. A formula is derived to relate the spatial distribution of wave overtopping water behind non-reshaping berm breakwaters to non-dimensional forms of wave height, wave period, berm width, berm height, and armor freeboard based on numerical results. This formula model agreed reasonably well with numerical model results.

Experimental investigation on non-breaking wave forces and overtopping at the recurved parapets of vertical breakwaters

This paper aims at investigating the intensity of the load applied by non-breaking waves on the recurved parapet wall of vertical breakwaters. For this purpose, 2-D experiments were carried out on a simple vertical breakwater physical model with four different geometries of the parapet (with an “exit angle” of recurve of 0°, 45°, 60° and 90°), under both regular and irregular waves.The tests showed the presence of loads of a quasi-static nature and loads with a typical church roof impulsive behaviour, depending on the (non breaking) wave characteristics and on the shape of the parapet. This impulsive force resulted significantly larger than the quasi-static load of the pure vertical wall case. The maximum measured total force under regular waves was compared with the one obtained by a numerical model based on IHFOAM.For irregular waves with Hs equal to 80% of the freeboard, the maximum measured horizontal load on a 90° recurved wall is equivalent to the force applied by a constant pressure of order 5 ρgHs. It was found, by analysing waves near the leading edge of a wave-group, that history effects are important, i.e., in certain circumstances, a high wave preceded by lower waves generated a larger force than if it had been preceded by waves of the same height. For regular tests, the largest impulsive forces occurred basically at the beginning of the tests, during the initial transient ramp-up period.The irregular wave overtopping was also measured, showing good agreement with the existing predictive formulae and confirming the significant reduction of mean discharge with increasing exit angle and overhanging extension of the parapet.

Numerical simulation of irregular wave overtopping against a smooth sea dike

Based on the filtered Navier-Stokes equations and Smagorinsky turbulence model, a numerical wave flume is developed to investigate the overtopping process of irregular waves over smooth sea dikes. Simulations of fully nonlinear standing wave and regular wave’s run-up on a sea dike are carried out to validate the implementation of the numerical wave flume with wave generation and absorbing modules. To model stationary ergodic stochastic processes, several cases with different random seeds are computed for each specified irregular wave spectrum. It turns out that the statistical mean overtopping discharge shows good agreement with empirical formulas, other numerical results and experimental data.

The new wave overtopping database for coastal structures

Significant effort has been made to generate a homogeneous database on wave overtopping consisting of more than 10,000 irregular wave overtopping tests from more than 160 independent projects or test series, each described by means of 31 parameters. Many coastal structures, including dikes, rubble mound breakwaters, berm breakwaters, caisson structures and combinations have been considered and have been schematised for inclusion in the database. All these overtopping tests are represented by over 300,000 numbers in the database. Within the framework of the CLASH-project specific overtopping tests on missing parameters and structures (white spots) in the database have been performed, as well as prototype overtopping measurements and small scale overtopping simulations. The results of these tests have enlarged and homogenized the database. White spot tests concentrated on the roughness of all kind of armour units and on the influence of oblique wave attack. These tests were performed by the University of Edinburgh (UK) and Aalborg University (DK), respectively. Prototype measurements were performed at Ostia (IT), Samphire Hoe (UK) and Zeebrugge (BE). The small scale simulation tests were performed by most of the partners in CLASH. The database has been created in such a way that particular and confidential information on actual projects is not present. This creates the opportunity to finally release the database to all interested people. The database was created as a first step and as basis for the generic prediction method on wave overtopping. The latter has been described in Van Gent [Van Gent, M.R.A., Van den Boogaard, H.F.P., Pozueta, B., Medina, J.R., 2007. Neural network modelling of wave overtopping at coastal structures, Coastal Engineering, Vol. 54, Issue 8, pp. 586–593]. But the database can also be applied on its own. Furthermore, the minimum set of hydraulic and structural parameters to describe a test is very useful in creating other databases and could be considered as essential parameters to be described in each test report on physical model investigation of coastal structures. The paper describes: • the gathering of the data • the screening of the data • the development of parameters to describe each individual test • the parameters required for an artificial neural network prediction method • a parameter analysis of the total database • the application of the database for design purposes

Direct Numerical Simulation of Wave Overtopping of Upright Seawall with Permeable Wave Chamber in Irregular Wave Field

There are mainly two ways to compute wave overtopping phenomena. One of them is a numerical method which employsa non-linear wave transformation equation combined with an overtopping formula. Another is a direct numericalmethod for solving Navier-Stokes equation. Only a few numerical studies with the direct numerical method have so farbeen made on irregular wave overtopping. In the present study, the applicability of the CADMAS-SURF, which is basedon the VOF method, for the numerical simulation of irregular wave overtopping of an upright seawall has been verifiedby comparison with the hydraulic model experiments. Moreover, some consideration for calculating irregular waves hasbeen shown.

数値波動水路を用いた越波排水路を有する低天端護岸の不規則波越波計算とその有用性

A stepped seawall with drainage is one of the coastal structures for reducing wave overtopping. The accurate prediction of wave overtopping is of importance in order to design the seawall economically. However, the previous design diagrams for the estimation of wave overtopping rate cannot be used for the complex shape of a seawall.The main purpose of this paper is to investigate irregular wave overtopping process on a stepped seawall with drainage and verify the utility of a two-dimensional numerical wave flume “CADMAS-SURF” by implementing hydraulic experiments and numerical simulations. The comparison of the numerical and experimental results reveals that the CADMAS-SURF can appropriately reproduce wave overtopping phenomena under irregular wave actions.

Irregular Wave Overtopping of Revetments in Surf Zones

Twelve test runs were conducted to examine the overtopping processes of normally incident irregular waves over a revetment of a 1:2 rough impermeable slope fronted by a gentle, smooth slope and situated well inside the surf zone. The measured overtopping probability and average overtopping rate are affected noticeably by the spectral shape and wave grouping of the incident irregular waves measured immediately outside the surf zone. The empirical procedure for estimating these overtopping quantities is found to yield only order‐of‐magnitude estimates for this experiment. The measurements made for the 12 runs are used to calibrate and evaluate the existing one‐dimensional, time‐dependent numerical model, which is modified slightly to allow the spatial variation of the bottom friction factor. The calibrated numerical model is shown to be fairly capable of predicting the average overtopping rate and the depth of overtopping flow on the crest of the revetment. The measured and predicted time series and spectra of the flow depth including entrained air show the grouped nature of irregular wave overtopping events.

SEAWALL OVERTOPPING MODEL

Results from an extensive series of laboratory tests of irregular wave overtopping for a number of seawall and seawall/revetment configurations is presented. Data for 13 configurations has been collected and grouped into 7 data sets representing relatively similar geometrical characteristics. All data sets showed an approximately exponential relationship between the overtopping rate and a dimensionless freeboard parameter which is the ratio of the seawall freeboard to the local wave severity. This finding logically led to the development of three progressively more complex overtopping models. The models provide a relatively simple way to estimate overtopping rates and an objective way to evaluate the hydraulic performance of seawalls/revetments. Advantages and disadvantages of the models are discussed and their ability to predict overtopping rates is compared.

Discussion of “Irregular Wave Overtopping on Gravel Islands” by Nobuhisa Kobayashi and Allan M. Reece (November, 1983)

Discussion of “<i>Irregular Wave Overtopping on Gravel Islands</i>” by Nobuhisa Kobayashi and Allan M. Reece (November, 1983)

Closure to “ Irregular Wave Overtopping on Gravel Islands ” by Nobuhisa Kobayashi and Allan M. Reece (November, 1983)

Closure to “ <i>Irregular Wave Overtopping on Gravel Islands</i> ” by Nobuhisa Kobayashi and Allan M. Reece (November, 1983)

Irregular Wave Runup and Overtopping

A cumulative frequency distribution function for the runup elevation of irregular waves is useful in the design of many coastal structures. Such a relationship would help a designer to quantify trade offs between structure geometry and allowable overtopping. The work of Saville and Battjes suggests that a Rayleigh distribution is a reasonable but somewhat conservative dierstribution for irregular wave runup elevations. This note gives a simple technique for establishing a Rayleigh runup distribution for given wave and structure characteristics and then extends the technique to estimate irregular wave overtopping rates.

Expected Rate of Irregular Wave Overtopping of Seawalls

SYNOPSISThe overtopping rate of seawalls by irregular waves can be estimated as the expected value of overtopping rate with regular wave data weighted with the distribution of wave heights. The calculated rates for several model seawalls are in agreement with the measured rates under the action of irregular waves in laboratory. Diagrams for the estimation of the expected rate of wave overtopping have been prepared for seawalls with vertical faces and those with mounds of artificial concrete blocks. The overtopping rates of many coastal structures which were damaged by waves due to typhoons have been estimated with the above diagrams. The estimation reveals the existence of threshold overtopping rates for damage for respective types of structures.