Showing papers on "Wave flume published in 1980"

Wave attenuation and wave set-up on a coastal reef

Abstract: In attempting to specify criteria for the design of structures on coastal reefs, it was found that no adequate method existed to derive those criteria from the deep water wave conditions. In order to fill the gap, a program of measurements and analysis was initiated at the University of Hawaii. The program consisted of prototype and laboratory measurements. Great emphasis was placed on reliable field data, which were collected on Ala Moana Reef, in Honolulu. Laboratory investigations on the behavior of waves on shallow reefs are subject to scale effects; verification from field observations is required to obtain reliable results. As a result of this study, a mathematical model was developed for the calculation of wave attenuation and wave set-up on a shallow reef, using the incident waves in the ocean as boundary conditions. This paper discusses the general behavior of waves approaching a shallow reef and presents some essential characteristics of the mathematical model. The study is limited to waves approaching the shoreline at right angles. The results of this study can be extended to breakwaters with wide, submerged berms.

Oscillation Sand Ripples Generated by Laboratory Apparatus

Abstract: Laboratory data on the geometry of oscillation ripples, collected by a number of investigators using a variety of experimental devices, have been compared to determine differences among oscillating bed, wave flume and water tunnel devices. Additional data have been obtained employing a wave flume that generates large waves. It was found that ripples formed in oscillating-bed devices do not correspond well with those developed under progressive waves in flumes and in water tunnels. The remaining vortex ripple data, the class of ripples primarily formed under ocean waves, are found to correspond to the linear relationship, = 0.65do, where is the ripple spacing and do is the near-bottom orbital diameter. The data depart from this relationship as the orbital diameter increases, the departure occurring at higher orbital diameters as the grain size increases. A tentative diagram is developed relating the maximum possible tipple spacing to the median sand diameter.

Laboratory Generated Waves and Wave Theories

Abstract: Tests are carried out in a wave tank to record the waves, the water pressures, and the horizontal and vertical water particle velocities. The water depth is such that the waves generated during the test cover the deep, intermediate and shallow water ranges. In the intermediate and shallow water range the soliton effects are observed. In deep water, the Airy wave theory is found to describe the water particle kinematics adequately. Stokes' 3rd order wave theory is found to be valid for higher waves in intermediate water depths. Stream function theory is found to agree reasonably with the test data in general. Based on these comparisons, a region of validity of various wave theories is described and compared with other predicted regions in the literature.

Mass transport in progressive waves of permanent type

Abstract: Mass transport phenomenon was first recognized by Stokes in 1847 using a Lagrangian description. Later, a basic theory for the mass transport in water waves in viscous fluid and of finite depth was derived by Longuet-Higgins in 1953. Theoretical solutions of mass transport in progressive waves of permanent type are subjected to the definitions of wave celerity in deriving the various finite amplitude wave theories. As it has been generally acknowledged that the Stokes wave theory can not yield a correct prediction of mass transport in the shallow depths, some new theories have been developed. Recently the authors(1974 § 1977) have derived a new finite amplitude wave theory in shallow water for quasi- Stokes and cnoidal waves by the so-called reductive perturbation method, in which the mass transport is formulated both in Lagrangian and Eulerian descriptions. On the experimental verification, Russell and 0sorio(1957) investigated and compared Longuet-Higgins' solution with experimental data of Lagrangian mass transport velocity obtained in a normal closed wave tank of finite length. Since then, many investigations, and nearly all of them, have employed the finite length of wave tank in carrying out their experiments. However, no experiment has yet been attempted at verifying the Stokes drift in progressive waves of permanent type in a wave tank of infinite length. It is not realistic nor economical in constructing such an infinitely long flume to investigate experimentally the mass transport velocity in progressive waves. Instead of using such an ideal wave tank, a new one incorporated with natural water re-circulation was equipped to carry out experiments by the authors(1978). It was confirmed from these experiments that mass transport in progressive waves of permanent type exists in the Same direction of wave propagation throughout the depth, and agrees with both the Stokes drift and the authors' new formulations, within the test range of experiments.

Surface Dispersion in Wave Flume

Abstract: The surface dispersion of a floating bead under wave action was investigated by measuring the Lagrangian characteristics using photographic techniques. The experiments were carried out with regular waves in a wave flume where the water depth and the wave period were kept constant, and the wave height was varied. In the experiments, trajectories of the floating bead were recorded as a function of time by a movie camera. The analysis was restricted to the component of dispersion in the transverse direction only. The motion of the beads in an oscillatory flow was shown to be governed by a linear second-order differential equation. Starting from the fundamental principles, dispersion coefficients were investigated; statistical descriptions of the displacement and velocity fluctuations were obtained in time and length scales.

Wave Transmission Characteristics of Fixed and Floating Breakwaters

Abstract: Transmission of regular waves past fixed breakwaters and floating breakwaters are studied in detail in a laboratory wave flume. The performance characteristics of these breakwaters are presented and discussed.