Wave reflection and transmission by curtainwall–pile breakwaters using circular piles

This paper presents a mathematical model which computes the hydrodynamic characteristics of a curtainwall–pile breakwater (CPB) using circular piles, by modifying the model developed for rectangular piles by Suh et al. [2006. Hydrodynamic characteristics of pile-supported vertical wall breakwaters. Journal of Waterway, Port, Coastal and Ocean Engineering 132(2), 83–96]. To examine the validity of the model, laboratory experiments have been conducted for CPB with various values of draft of curtain wall, spacing between piles, and wave height and period. Comparisons between measurement and prediction show that the mathematical model adequately reproduces most of the important features of the experimental results. The mathematical model based on linear wave theory tends to over-predict the reflection coefficient as the wave height increases. As the draft of the curtain wall increases and the porosity between piles decreases, the reflection and transmission coefficient increases and decreases, respectively, as expected. As the relative water depth increases, however, the effect of porosity disappears because the wave motion is minimal in the lower part of a water column for short waves.     

Alternative placement technique for antifer blocks used on breakwaters

In this study, a placement technique named as “alternative placement technique” was developed for antifer blocks and the results of its application to a breakwater model were presented. This placement technique was compared with the existing techniques such as the “regular placement technique”, the “irregular placement technique” and the “sloped wall placement technique” by experiments. The comparison was carried out considering armor layer stability, prototype placement, clarity of the placement technique’s definition, armor layer cost, and wave runup. As a result of this investigation the “alternative placement technique” was found to be superior to the other existing placement techniques.     

Wave interaction with one or two rows of closely spaced rectangular cylinders

Experimental results are reported on the wave reflection from and transmission through one row or two rows of closely spaced rectangular cylinders. An empirical expression is proposed for the friction factor which models the head loss due to closely spaced rectangular cylinders. Algebraic expressions are presented to calculate the reflection and transmission coefficients of regular waves for a single slotted wall or double slotted walls. The model is validated by the published and present experimental results. The proposed method can be used for the preliminary design of slotted-wall breakwaters.     

Wave-induced mean flows in vertical rubble mound structures

Waves impinging on rubble mound breakwaters and seawalls induce a mean flow within the breakwater, analogous to the so-called undertow within the surf zone. Here, using a plane wave approximation (kh<1.5), a second-order problem is solved for an idealized breakwater with a rectangular cross-section to show the origin and the nature of the mean flow within the porous structure. The mean flow is expressed in terms of a mean stream function analytically derived, obtained based on the mass flux balance between the incident, reflected and transmitted waves. Furthermore, the evolution of other second-order magnitudes such as mean water level and mass flux is analyzed under different incident wave conditions, structure geometry and porous material characteristics. Results show that the evolution of the different mean quantities is controlled mainly by reflection and consequently depends highly on structure geometry and porous material characteristics. Furthermore, it is shown that the return flow is stronger with increasing mass flux decay. Some qualitative experiments to show the described mechanism are also presented.     

Empirical orthogonal function analysis of shoreline changes behind two different designs of detached breakwaters

This paper compares the shoreline responses immediately shoreward of two adjacent schemes of segmented shore parallel rubble mound breakwaters undergoing the same forcing by waves and tides. Scheme one consists of four longer, emergent breakwaters that have produced tidal tombolos in their lee. Scheme two consists of five shorter, lower breakwaters that are submerged at higher tides with salients in the breakwater's lee. Empirical orthogonal function analysis was used to decompose a video derived shoreline dataset into the dominant modes of shoreline change for both schemes. The two schemes showed similar modes of change. The primary mode of change for both schemes was the cross-shore growth and shrinking of the salients/tombolos. The secondary mode of change was the longshore movement of the salients/tombolos. For all modes of change, the dominant length scale was dictated by the breakwater dimensions and locations. A new manifestation of hydrodynamic parameters is introduced: the cumulative integral of the de-meaned parameters. This parameterisation allowed for meaningful correlation of the temporal EOF components with forcing parameters and identification of the important influence of the tide on observed morphodynamic change. Clear differences were observed between the shoreline responses measured in schemes one and two; including differences in bay erosion/accretion; and the longshore translation of salients/tombolos. The beaches in scheme two showed behavioural patterns similar to unprotected beaches which were not observable in scheme one. It is postulated that these differences are caused both by the different breakwater designs and by variation in longshore sediment supply.     

Experimental study of a sloping float breakwater

The aim of this study was to evaluate the performance of a sloping float (or inclined pontoon) breakwater with respect to expected wave climate for protection of small commercial vessels and yatch marinas. A two-dimensional model study was carried out for regular waves in intermediate water depths. The experimental results showed that the transmission coefficient was relatively insensitive to wave height and that it consistently increased as the wave period decreased. The performance of this type of breakwater was found to be promising for intermediate water depths.     

Neural network modelling of wave overtopping at coastal structures

A method has been developed to estimate wave overtopping discharges for a wide range of coastal structures. The prediction method is based on Neural Network modelling. For this purpose use is made of a data set obtained from a large number of physical model tests (collected within the framework of the European project CLASH, see e.g. [Steendam, G.J., Van der Meer, J.W., Verhaeghe, H., Besley, P., Franco, L. and Van Gent, M.R.A. (2004). The international database on wave overtopping. World Scientific, Proc. 29th ICCE, vol. 4, pp. 4301–4313, Lisbon, Portugal.]). Moreover, a method was developed to obtain confidence intervals for the overtopping predictions of the neural network.     

Violent breaking wave impacts. Part 1: Results from large-scale regular wave tests on vertical and sloping walls

As part of an investigation into the detailed characteristics of wave impacts, experimental data are presented for the impact pressures and forces generated by waves up to 1.7 m high breaking onto a vertical wall and a wall inclined at 27° to the vertical. Particular attention is given to the influence of entrained and entrapped air and, by selecting regular wave conditions that produce impacts, trends are identified for highly variable phenomena that could easily be missed when masked by the even greater variability associated with irregular waves.