Wave Transmission Below Breakwaters with Semi

Coastal Engineering Proceedings

The wave field around a rectangular submerged breakwater is investigated by means of an experiment in numerical wave flume. The results were compared with those obtained making use of the Boundary Element Method. The numerical experiment is carried out to determine the share of the incident wave energy that are reflected, dissipated over the roof of the breakwater, and transmitted in the lee. The wave field before the breakwater (i.e. the quasi standing field) obtained with the CFD simulations is quite similar to that obtained with the BEM. Some relevant differences between the two models arise in the lee of the breakwater, because the wave motion is strongly affected by the dissipation occuring over the breakwater roof by friction and wave breaking. They cannot be foreseen with BEM, being the motion ideal. Their analysis show that the dissipation is more than halves the transmission of energy, despite the relevant submergence of the considerated breakwater.

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...

Journal of Marine Science and Engineering

Submerged and low-crested breakwaters are nearshore barriers with an underwater or slightly emergent crest, designed to reduce the energy of wave attacks and, consequently, to protect the coast from erosion and flooding. Their performance in reducing the wave energy can be evaluated by the value of the wave transmission coefficient, which thus requires accurate prediction. In the last few decades, several experimental investigations allowed the development of several formulae to predict this coefficient that agreed well within the given range of validity. In the present study, a comprehensive review of the existing formulae has been reported and the influence of input design variables has been highlighted. Moreover, an extensive set of experimental data has been collected and critically examined and re-analyzed to obtain a homogenous up-to-date database. Special attention has been addressed to the assessment of the reliability of each existing formula for and to evaluate its perform...

The wave transmission over submerged breakwaters is investigated using existing formulae and wave models. The objective is to assess their performance and pinpoint research paths for their improvement. Application was made on a case study with two submerged detached breakwaters. It was found that some of the recent relations give satisfactory results of the transmission coefficient, while the predictability of the models tested depends on the wave breaking formulation assumed. In general, wave breaking and porosity of the structure are the most crucial factors that need further study for the improvement of the prediction of wave transmission over submerged breakwaters.

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.

2017

Various breakwaters have been developed to protect coastal areas from the force of waves. The majority of the breakwaters are gravity-type structures withstanding the wave energy by their effective masses. The construction of these gigantic structures is costly and the use of materials is substantial. This research study attempted to cope with the aforementioned problems by investigating wave attenuation performance of five submerged breakwaters that were made of multiple pipes in different configurations by the means of physical modelling. A series of experiments were conducted in a wave flume to study the wave transmission characteristics of the submerged breakwaters of different designs under regular waves. Wave attenuation efficiency of the breakwaters were expressed in terms of wave transmission coefficient Ct. The relationships between Ct and wave steepness Hi/L, relative breakwater width B/L and relative breakwater draft h/d were ascertained through a systematic experimental ...

Computation, 2020

In this paper, we investigate the wave damping mechanism caused by the presence of submerged bars using the Shallow Water Equations (SWEs). We first solve these equations for the single bar case using separation of variables to obtain the analytical solution for the wave elevation over a rectangular bar wave reflector with specific heights and lengths. From the analytical solution, we derive the wave reflection and transmission coefficients and determine the optimal height and length of the bar that would give the smallest transmission coefficient. We also measure the effectiveness of the bar by comparing the amplitude of the incoming wave before and after the wave passes the submerged bar, and extend the result to the case of n-submerged bars. We then construct a numerical scheme for the SWEs based on the finite volume method on a staggered grid to simulate the propagation of a monochromatic wave as it passes over a single submerged rectangular bar. For validation, we compare the t...

Journal of Hydraulic Research, 2005

In the present study the hydrodynamic interaction of regular and irregular waves with floating breakwaters (FBs) in shallow and intermediate waters is examined experimentally in a large-scale facility. The experiments were conducted in the CIEM flume of the Catalonia University of Technology, Barcelona. The influence of incident wave characteristics and certain geometric characteristics, such as the width and the draught of the structure, on its efficiency is examined. Four different FBs configurations are examined: (a) single fixed FB, (b) heave motion FB, (c) single fixed FB with attached front plate (impermeable and permeable) and (d) double fixed FB. Results related to transmission, reflection, and energy dissipation of the incident (regular and irregular) waves on the structure are presented. For the single fixed FB, the efficiency of the structure is proportional to the width/wavelength and draught/water depth ratios. The single fixed FB operates in a highly reflective manner. On the other hand, the heave motion FB operates in a dissipative manner with much lower reflection. The attached plate in the front part of the FB significantly enhances the efficiency of the structure. No significant differences are observed between the impermeable and the permeable plate cases. Generally, the most efficient configuration has been the double fixed FB. However, with regard to cost-effectiveness, the configuration of the FB with the attached plate should be considered the most efficient for design purposes.

2009

This paper summarises an investigation undertaken by the Water Research Laboratory and International Coastal Management into wave transmission for low crested geotextile breakwater structures. Structures such as these are being used as an alternative to rock structures or as interim coastal protection structures. These low crested (submerged) detached breakwater structures are typically implemented to provide a milder nearshore wave climate, and to maintain or increase the beach width in the lee of the breakwater. The structures tested were built using a single layer of geotextile mega containers, and ranged in cross section from a single mega container of approximately 4 m width, up to three mega containers measuring approximately 12 m in total cross section width. The two-dimensional physical modelling investigated the various breakwater structures under a range of monochromatic wave conditions, with wave periods varying from 5 to 10 seconds and wave heights ranging from small unbroken waves, up to depth limited breaking waves of approximately 2.5 m height. The test results determined that under shorter period wave conditions, a significant reduction in transmitted wave height was achieved even with a breakwater of only 4 m cross section width. Further reductions in transmitted wave conditions were recorded by increasing the breakwater width to 8 m, however, little additional reduction was achieved by further increasing the width to 12 m. During longer period wave conditions and slightly deeper submergence, the narrow 4 m breakwater width provided very little wave reduction, with increases in breakwater width to 8 m and 12 m providing more modest reductions in transmitted wave height. Following the physical modelling study, a range of empirical equations for wave transmission have been applied with the same hydraulic conditions as the physical model tests, and the predicted wave transmission compared to the physical model results.

IOP Conference Series: Materials Science and Engineering

Breakwater is a structure that builds parallel to the coast, and located within some distance from the coastline. The breakwater that is currently and widely used is Rubble Mound Breakwater; a large dimension coastal structure with also come in high price. Due to this matter, a Hanging Sheet Pile type breakwater can be one of good solution. This research was conducted at Ocean Technology Laboratory, Faculty of Engineering, Universitas Hasanuddin, in a flume thank with 1:25 model scale, and equipped with wave generator and probes as measurement apparatus. The purpose of this study is to identify the effect of wave parameters (Hi/gT 2) and structure parameters (draft relative, s/d) on fluctuated wave transmission coefficients produced. The waves are in the form of irregular waves that generated using JONSWAP spectrum. There were 5 variations in wave height (H) and wave period (T), while variations of structure in the form of draft (s) are in 3 variations. The results of this study indicate that the value of Kt will decrease when Hi/gT 2 value increase; so that the greater the value of s/d, the smaller value of Kt will be.