Numerical model for wave action on and in coastal structures

In the MAST-G6-S program numerical models will be developed for the description of wave motion on and in coastal structures. The most accurate one will probably be the SKYLLA model. That model uses the two-dimensional Navier-Stokes equations. For a description, see Broekens and Petit (1991). After it has been developed for structures with an impermeable slope (dikes), the porous flow has to be implemented for application for permeable structures. Adapted Navier-Stokes equations for the modelling of the porous flow are described by Van Gent (1991). The implementation of the porous flow is important for rubble mound breakwaters and Berm-breakwaters because there is an important interaction between the flow on the structure and the flow in the structure. Parallel to the development of the SKYLLA model, other models will be developed within the MAST-G6-S program. These models have to describe the flow on and in coastal structures. This means that a hydraulic model has to be coupled to a porous flow model. This will be done in a way so that the model can be used as an "Engineering Tool". The model described in this report is based on a one dimensional description of the flow (which does not mean that it can not give a two-dimensional impression of the flow). It means that the model uses some simplifications that make the results of the model deviate from reality but in such a way that the results do not deviate too much and will give a rather good impression of the movement of the water on and in a coastal structure.Civil Engineering and Geoscience

SKYLLA: Wave motion in and on coastal structures, gebruikers handleiding

In de voor u liggende gebruikers handleiding vindt u een beschrijving van de van in- en uitvoer files en practische overwegingen die het gebruik van het programma SKYLLA kunnen vereenvoudigen. Opgemerkt moet worden dat het programma SKYLLA nog in ontwikkeling is zodat wat vandaag in de gebruikers handleiding geschreven wordt morgen reeds verouderd kan zijn. Bovendien bestond bij het schrijven van deze tekst de neiging om ook dat reeds op te nemen wat nog niet in de code gerealizeerd was maar wel gerealizeerd zou worden. Een en ander maakt het begrijpelijk dat de gebruikers handleiding pas aan het eind van het SKYLLA project een definitieve vorm kan krijgen. Het programma SKYLLA lost de twee-dimensionale Navier-Stokes vergelijkingen met konstante viscositeit op. Aan zowel de linker- als de rechterrand kan een zwak reflecterende randvoorwaarde gebruikt worden die de gebruiker in staat stelt om golven het model binnen te laten komen. Golven die bijvoorbeeld na reflectie op een konstructie weer naar de zwak reflecterende rand toe bewegen moeten hier het model kunnen verlaten. De niet lineaire golven die het model binnen komen, worden bepaald door het Rieneker en Fenton model. SKYLLA kan echter ook met lineare golftheorie verkregen golven het model laten binnenkomen. De huidige (1994) versie van SKYLLA is in staat om de vloeistofbeweging op een ondoorlatend glad talud te modelleren. Dit talud mag zowel stijgende als dalende delen hebben. Het programma is bovendien in staat om de stroming door stortsteenconstructies te modelleren. Hierbij is de vorm van de constructie geheel aan de gebruiker. Het aantal soorten stortsteen dat bij het numerieke modelleren gebruikt wordt is beperkt tot tien.Golfoploop - TAW/EN

Water- en zandbeweging in golven en stroom

The purpose of the investigation which is described in this report, is to contribute to the study of the motion of water and sand in waves and currents. A one-dimensional (vertical) numerical model of oscillatory turbulent flow is used to determine velo city distributions. The so called k-\u80 model is applied to oscillatory flow over a flat bed, with and without a steady current. Velo city, turbulent energy, dissipation of turbulent energy, eddy viscosity and shear stress distributions are presented. For determining the watermotion a coefficient is used to describe the mixing processes caused by turbulent motions. In the k-\u80 model this coefficient, the eddy viscosity, is obtained out of equations concerning the energy which is present in eddies. The eddy viscosity describes the vertical exchange of horizontal momentum. The model is also used to investigate the possibility to determine concentration distributions out of the watermotion. The coefficient which describes the exchange of sediment by the turbulent motion is taken equal to the coefficient which describes the exchange of momentum. As far as the prediction of concentration distributions is concerned, the model fails; considerable differences appear when the results are compared with measurements. An explanation for the differences is given: Exchange of momentum in the vertical direction is assumed to be less than the exchange of mass in the vertical direction. The approximation which is used to describe the transport in the vertical direction can also cause deviations (transport is related to the local velo city gradient). The model pro duces reliable velo city distributions but the concentration distributions deviate from measured distributions. These deviations are explicable. To gain better understanding of the processes, more research concerning the transport of mass must be carried out.Environmental Fluid DynamicsHydraulic EngineeringCivil Engineering and Geoscience

Odiflocs: Computations for a berm breakwater

Computations made with the numerical model Odyflocs and compared with Skylla computations. Water pressures and water movements near the surface of a berm breakwater are computed.Berm Breakwater

Wave interaction with berm breakwaters

Wave interaction with berm breakwaters is studied by means of a physical model and a numerical model. The physical-model tests have been used to verify the wave motion as calculated by the numerical model. The numerical model based on finite-amplitude shallow-water wave equations is capable of simulating the wave motion both on and inside the structure. This model for normally incident waves has been extended with a new morphological model for cross-structure transport, which resulted in a wave load-response model capable of simulating the reshaping process of the seaward slopes of dynamic coastal structures such as berm breakwaters and gravel beaches. The combined wave-morphological model has been verified with small-scale laboratory tests and with prototype data. Trends observed in physical model tests, such as the influence of wave height, wave period, and stone diameter on the reshaped seaward slopes, are also reproduced properly.Berm Breakwater

Wave Interaction with Permeable Coastal Structures

Civil Engineering and Geoscience

Numerical modelling of wave interaction with dynamically stable structures

Wave interaction with dynamically stable structures is simulated by means of a numerical model based on fmite-amplitude shallow-water wave equations. The model can simulate wave motion on and inside permeable structures. For dynamically stable structures, including berm breakwaters, reef-type structures and gravel beaches, a procedure is developed to simulate the natural response to wave attack. This procedure is extended, for instance by implementing effects of grading and effects of seawalls, to increase the applicability for practical applications.Berm Breakwater