Showing papers on "Wave flume published in 1993"

Sediment Transport by Currents and Waves

Abstract: Mathematical and experimental modelling of sediment transport processes in the coastal environment is presented. The convectiondiffusion equation for suspended sediment particles has been used to compute the vertical distribution of the time-averaged concentrations. The computed results are compared with measured values of laboratory and field experiments (surf zone Dutch coast).

Numerical simulation of wave motion on and in coastal structures

Abstract: A 2-dimensional program for simulation of wave motion on coastal structures is described. The program is based on the Volume Of Fluid method and is able to describe fully plunging waves on all kind of structures.

Intercomparison of Coastal Profile Models

Abstract: The present paper briefly presents 6 different models for short term coastal profile modelling for direct incoming waves. The models have been tested against measured profile evolutions from a large wave flume. Features such as wave height distribution, cross shore current profiles and sediment transport are compared and discussed.

Entrainment and transport of fine sand by combined waves and current: an experimental study

Abstract: Experiments have been performed in a large wave flume in order to measure sediment transport rate of fine sand under combined regular waves and current. Instantaneous velocities and concentrations are measured using ultrasonic velocimeters and optical turbidity probes. Suspended transport rates, as obtained from vertical integration of measured fluxes, are decomposed into a mean current and an oscillatory wave components. Under waves only, the wave contribution is in the direction of wave propagation. Under combined waves and current, the wave contribution is found to systematically oppose the direction of superimposed mean current.

Sand transport under grouping waves

Abstract: Laboratory experiments as well as numerical modeling were conducted for sand transport under non-breaking grouping waves. Experiments showed that the direction of net transport of fine sand was onshore under grouping waves although it was offshore under monochromatic waves with equivalent wave height. It was also revealed that the long wave bounded to wave group plays an important role in particular for suspended load. A numerical model was developed on the basis of the second-order Stokes wave theory and one-dimensional diffusion equation of sand concentration. The validity of the model was confirmed with experimental data.

Laboratory tests on the interaction between nonlinear long waves and submerged breakwaters

Abstract: This paper deals with the use of submerged detached breakwaters as beach protection, a use that today has become quite popular. This type of structure has been largely studied both theoretically and through experimental analyses in recent years, however its behaviour has not been completely understood, specially if related to the real irregular wave attacks. In particular some laboratory studies carried out by the authors have pointed out some interesting phenomena associated with the interaction between the nonlinearities of wave transformations in shallow water and submerged breakwaters. Aiming at discerning between the phenomena related to the structure (beach and breakwater) and flume geometry, a new series of laboratory tests have been carried out in a 50 m long wave flume; these tests and the results obtained are described in this work. Besides the study of the behaviour of submerged structures related to the bounded-long-waves, some current velocities have also been measured during this research through directional micro-propeller fluid meters.

LIP11D Delta flume experiments

Abstract: This note reports simulations carried out to simulate wave transformation along the flume following the initial beach profile and the wave conditions given in Roelvink(1993). Parametric spectral and wave-by-wave approaches are compared. An estimation of the distribution of the skewness of the bottom orbital velocity along the flume is also given.

Interaction of nonlinear waves with coastal structures

Abstract: Interaction of transient nonlinear waves (modeled by solitary waves with moderate wave height) with submerged breakwater has been studied both numerically and experimentally. The emphasis is on the comparison between the numerical solution and the laboratory experiments on the wave transformation and the water particle velocity of the induced flow field. For the numerical analysis, the Boundary Element Method (BEM) has been used for analyzing the wave field induced by the coastal structure. For the laboratory experiments the wave profiles are obtained by resistance type wave gauge; the two dimensional water particle velocities are obtained by a four-beam Laser Doppler Velocimeter (LDV) equipped with frequency shifting and with a fiber optics system. The LDV measurements are directed to obtain the detail of the wave kinematic properties important for ascertaining the dynamics of the modified wave field in the vicinity of the submerged breakwater. This serves as a critical check for the validity of the numerical computations. Results of the numerical model have been found to compare well with the experimental data for the conditions studied in both the wave profiles and the water particle velocities beneath the waves as they interact with the breakwater.

Shingle beach profiles and wave kinematics

Abstract: An extensive experimental project has been undertaken, in two parts, to measure both the formation of shingle beach profiles due to wave attack and the wave velocity fields using the technique of Particle Image Velocimetry (PIV). The former was achieved with moveable beach experiments carried out in the wave basin at HR Wallingford, and the latter on models in the 9.75m wave flume in The University of Edinburgh. Waves of several JONSWAP spectra, reflecting storm conditions, were allowed to impinge normally on an initial slope of 1:7, the resulting profiles were found to reach dynamic equilibrium after about 3000 wave periods. These profiles were modelled at The University of Edinburgh for the wave velocity measurements using the relatively new technique of PIV. This technique has the benefit of providing very accurate, full-field, instantaneous velocity data. In these experiments monochromatic waves were measured on smooth, impermeable beaches although the extension to multi-frequency waves on rough, permeable beaches is planned for the near future. The effect of the increased backwash component typical of these steeper beaches is dealt with in some detail.

Numerical modelling of waves and currents with regard to coastal structures

Abstract: This paper describes a two-dimensional numercial model capable of simulating non-stationary flows. Special emphasis has been put on wave motion on and in porous structures, e.g. a rubble mound breakwater. Comparisons of numerical simulations with analytical solutions and model test results have confirmed the applicability of this model for studies of waves and currents with regard to coastal structures.

Transient propagation of waves in a flume

Abstract: A recently developed numerical method is applied to the study of transient, nonlinear wave propagation in a flume. The nonlinear free surface boundary conditions and the wave generator boundary condition are expanded about the corresponding equilibrium positions by perturbation expansions. The boundary conditions are then satisfied to second order by a numerical integration in time, and the field solution at each time step is obtained by an integral equation method based on Green's theorem. The propagation characteristics of regular, trichromatic and irregular waves are studied numerically, and the significance of nonlinear effects is highlighted.

Mass Transport in Mud Layer Induced by Wave Action

Abstract: This paper analyzes the mass transport velocity in a two layers system produced by wave action. In a previous paper, Piedra Cueva (1933), a theory for linear water waves propagating in a two layered viscoelastic fluid system was described. The mass transport in the mud layer and in the water boundary layer is obtained solving the momentum and mass conservation equations in the Lagrangian coordinate system. It was found that the Eulerian coordinate system is not appropriate because it does not guarantee the continuity of the mass transport velocity through the water-mud interface. The results show that the mass transport velocity can be increased one order of magnitude in relation to the velocity given by the rigid bed theory and can be opposite to the wave propagation direction, depending on the physical mud properties. This result is very important when considering near bed sediment transport.

Wave kinematics on sheared currents

Abstract: Whole-field kinematic measurements are presented for steep, steady waves travelling on strongly sheared currents, concentrating on the region between trough and crest level. For slab currents, the crest kinematics and wave parameters were found to be correctly obtained by using Doppler shifting and standard wave theories. When the current was sheared, the crest kinematics were found to be well predicted by adding the results of an irrotational model to the stretched current profile, although this approach did not yield good predictions in the trough. The average shear was found to be reduced, in the presence of waves, from the undisturbed value, in agreement with the findings and predictions of other authors.

Laboratory wave generation: A second-order theory for regular and irregular waves in wave channels

Abstract: The correct generation of a second order wave field in a laboratory wave tank is of importance in several experimental investigations, particularly those of nonlinear evolutions and sediment transport. In the present work, which was carried out under the MLTP (medium long-term planning) of DELFT HYDRAULICS for improving experimental techniques, expressions are found for the motion of a waveboard to generate a correct second order wave field. These expressions are valid for both regular and irregular waves. Two important features of the procedure adopted here are that the computing time for the motion of the waveboard is signifcantly smaller compared to a method based on the frequency domain and that the accuracy of the physical representation increases with decreasing spectral width. The assumption of a narrow band spectrum is sufficient for realistic sea states described by spectral shapes of JONSWAP and Pierson-Moskowitz types. Results of some experimental investigations into the performance of the software based on the wave generation theory are also included in the report. Although the overall agreement between the theory and the experiment is good, some discrepancies are apparent from the limited analysis carried out so far, all of which cannot be attributed to the wave generation theory. Further analysis (and possibly a set of new experiments) is required in order to resolve aH the discrepancies.

Transient wave propagation in a laboratory flume

Abstract: A recently developed numerical method is applied to the study of transient, nonlinear wave propagation in a laboratory flume. The nonlinear free surface boundary conditions and the wave generator boundary condition are expanded about the corresponding equilibrium positions by perturbation expansions. The Sommerfeld radiation condition applied on the downwave control surface is modified to incorporate a time-dependent celerity to account for transient effects. The boundary conditions are then satisfied to second order by a numerical integration in time, and the field solution at each time step is obtained by an integral equation method based on Green's theorem. The accuracy of the numerical solution is first assessed in term of the condition number. The propagation characteristics of regular and irregular waves are studied. To verify the numerical model, a series of laboratory tests have been performed. For the case of an irregular wave packet, the experimental results of the free surface elevations obtain...