Wave reflection from partially perforated-wall caisson breakwater

Coastal Engineering, 2001

An analytical model has been developed that predicts the reflection of irregular waves normally incident upon a perforatedwall caisson breakwater. To examine the predictability of the developed model, laboratory experiments have been conducted for the reflection of irregular waves of various significant wave heights and periods impinging upon breakwaters having various wave chamber widths. For frequency-averaged reflection coefficients, though the overall agreement is fairly good between measurement and calculation, the model somewhat over-predicts the reflection coefficients at larger values, and under-predicts at smaller values. The model also underestimates the energy loss coefficients as wave reflection becomes larger. These differences occur because the model neglects the evanescent waves near the breakwater, which increase the energy loss at the perforated wall. The frequency-averaged reflection coefficient shows a minimum when the wave chamber width is approximately 0.2 times the significant wavelength, and it decreases with increasing wave steepness. Finally, it is shown that the reflection of irregular waves from a perforated-wall caisson breakwater depends on the wave frequency, so that the reflected wave spectrum shows a frequency dependent oscillatory behavior. D

Encyclopedia of Artificial Intelligence, 2009

IOP Conference Series: Earth and Environmental Science, 2020

Waves towards the shore that have a porous breakwater building will experience reflection and transmission, to determine the height of reflection and transmission wave is needed a study by the process of generating waves on the flume with a porous breakwater building, the effect of wave changes in its propagation requires an experiment in the laboratory. This study was aimed to determine the height ratio of reflection and transmission wave by using a model of pipe structure as a wave reducer by adding the friction plane of the roughness of the walls in the pipe. A method of laboratory experiment on the wave generation flume has several variations consisting of 3 periods (T; 1,0 seconds, T; 1,1 seconds, T; 1.2 seconds) and 3 water depth (d) are 15, 30 and 36 cm, stroke to regulate the flap motion that determines the wave height (H) as a wave generator that is 4, 5 and 6 by comparing the model that uses pipe wall roughness and without roughness. The result of testing indicates that th...

2017

Submerged breakwaters are a special type of breakwater associated with low wave reflection. They can also save large quantities of engineering resources from the view of economics. Although there have been previous investigations on the interaction between waves and rubble mound low-crested breakwaters, performance of impermeable submerged breakwater is somehow different from rubble mound structures. Thus, the accurate estimation of reflection and transmission coefficients is essential in designing of this kind of structures in near shore zone. In this paper, performance of impermeable trapezoidal submerged breakwater was investigated experimentally using regular waves. In the experimental plan, for three submergence depths of breakwaters different wave groups were used to measure transmission and reflection coefficients. Based on the test results, empirical expressions were formulated to describe the transmission and reflection coefficients for solid submerged breakwater under regu...

IRANIAN JOURNAL OF MARINE TECHNOLOGY, 2016

Perforated breakwaters are newer generation of vertical breakwaters in which somehow the problems of high wave reflection and forces exerted to the structure have been solved. In this paper the effect of hole shapes of Vertical Perforated Breakwaters on reflection of Solitary Wave s was investigated using numerical method. A single and double walls vertical breakwater with four different hole shapes and four different front wall porosity were considered. The breakwater was modeled in 3D using FVM method of FLOW-3D ® Software. The free surface was modeled using VOF method while RNG k-ε was used to model turbulent effect. The results show that in single wall breakwater as porosity increases the wave reflection increases as well so that a 40% porous wall reflects 90% of incident waves. Furthermore, the reflection coefficient has a fluctuating nature as non-dimensional ratio of B/L increases (B is width of caisson and L is incident wave length). Moreover, double wall breakwater is able to damp wave energy up to 20 to 25% greater than that of the single wall.

2007

Experimental tests on interaction between a wave and a submerged rubble-mound breakwater were performed in wave flume at University of Napoli Federico II. Different incident wave conditions were tested, including both non-breaking and breaking waves over the barrier. In cases of breaking, different breaker types at structure were described and classified according to hydraulic-morphological criteria. Experimental results show, according to early literature, that wave breaking induces a saturation in non-linear processes that characterize wave-structure interaction. Effect of saturation on 2 nd order transmitted free waves amplitude was investigated, and a best-fit formula was derived. A simple approximate method for wave profile prediction leeward of the barrier is finally proposed.

2014

The recent developments in the study of hydrodynamic characteristics of various coastal structures are reviewed in this paper. The method to determine the wave reflection coefficient using two fixed probe method is also demonstrated with an example. The physical model studies were conducted in a wave tank to compute the reflection coefficient of corrugated perforated beach and vertical upright breakwater with different heights. Some recent works published are reviewed here with a hope that these works can be beneficial to other researchers working in this area.

Low crested breakwaters are used to protect beaches from wave action. A series of large scale 3D laboratory experiments were carried out to investigate the effects in wave characteristics (disturbance) around a system of two non-parallel, permeable, low crested breakwaters by oblique wave incidence. The transmission and reflection coefficients were calculated and compared to existing formulae. The existing formulae, for both phenomena, transmission and reflection, had good relation in some cases. The angle of wave incidence did not show important influence for the wave transmission while is affected the wave reflection. The influence of wave period must be investigated in wave transmission and the influence of wave height in wave reflection.

Journal of Coastal Research, 2008

A slotted breakwater is a kind of perforated breakwater with vertical slots in the front wall of the structure. It can provide a sheltered area for loading and unloading of ships and crafts. In this study, a modified model to the one proposed by SUH et al. (2001) was developed to calculate the frequency-averaged reflection coefficient by means of the velocity potential. Using this model, the reflected energy spectrum from slotted breakwaters for normal incident waves can be calculated. A comparison with experimental and analytical works shows that this model can accurately predict frequency-averaged reflection from this type of breakwater. This model can provide a good trend to predict frequencyaveraged reflection and is a powerful tool for predicting the reflected energy spectrum from slotted breakwaters. The effect of effective parameters such as relative wave chamber width, relative significant wave height, significant wave period, and porosity of the slotted wall was also considered on the frequency-averaged reflection and reflected energy spectrum in this model. One of the most important results is the calculation of frequencies in the reflected spectrum that have a minimum energy close to zero, denoted as zeroth frequency points. This means that a large part of the wave energy in such frequencies is absorbed by the structure of the breakwater.

Coastal Engineering, 2007

The paper presents a series of analytical and numerical investigations of oblique wave transmission at low-crested breakwaters. For a smooth breakwater, two important features of wave height and direction are analyzed to establish the generic nature of the wave transmission process at oblique incidence. The proposed framework of research is validated against laboratory data from the EU-sponsored project, DELOS. The numerical simulations exhibit a significant decrease of the transmission coefficient with increasingly oblique incidence at a smooth breakwater. The roles of wave-breaking, nonlinearity, wave-induced currents and set-up in determining the characteristics of oblique wave transmission are demonstrated in the paper. It is found that both the amplitude-dependent phase velocity and the decrease of mean wave period contribute to the change of mean wave direction on the transmission side. An attempt has also been made to qualitatively explain the different behaviour of oblique wave transmission at a rubble-mound breakwater.