Hydrodynamic Performance Improvement of Double-Row Floating Breakwaters by Changing the Cross-Sectional Geometry

This paper is presented to develop the hydrodynamic performance of double-row floating breakwater (FBW) by changing cross-sectional geometry in the high wave periods. The ANSYS-AQWA software is employed for the present calculations, which is a potential-based boundary element method (BEM). The rectangular moored pontoons in the single- and double-row types are selected, and the results of the wave transmission coefficient and response amplitude operator (RAO) are presented and compared. The numerical results showed good agreement with experimental data at different wavelengths, wave height, and the distance between double-row FBWs. Then, the performance results of FBWs for five shapes (rectangular, π-shaped, plus-shaped, triangular-shaped, and box-shaped) in the wave transmission coefficient, RAO, and mooring line tension are presented and compared to each other. The results showed that the plus-shaped FBW has a better performance in reducing wave transmission than other shapes. In waves with long periods, the performance of π-shaped, triangular-shaped, and box-shaped FBWs is reduced, and the rectangular FBW loses its efficiency. Overall, the plus-shaped FBW has preferable performance regarding RAO response, mooring tension, and wave transmission.

Application of a sound-conducting polymer foil for calibration of hydrophones by optical interferometry

Modern calibration of hydrophones at megahertz frequencies is based on the method of optical interferometry, in which the vibrational velocity of an acoustic wave is measured using a thin sound-transparent polymer foil (membrane), metallized on one side to improve light reflection and installed in an ultrasonic field, followed by its replacement with a hydrophone to be calibrated. The main problem of implementing this calibration method is to assess the adequacy of tracking vibrations of the metallized side of the foil to vibrational displacements of water particles under the action of a sound wave incident on the opposite side of the foil. On the basis of the simplified theory of acoustic plane waves passing through layers of dissimilar materials, methods for measuring the speed of sound in the applied foil and an algorithm for calculating the frequency dependence of the sound wave transmission coefficient (in terms of vibrational velocity) from water through the foil to water or air, introduced as a correction to the results of hydrophone calibration, were developed. The uncertainty of the introduction of this correction is estimated.

Numerical Investigation on Wave Transmission by a Submerged Reef Using MIKE 3 WAVE FM

Wave transmission of a 1:10 gradient slope submerged reef is studied using MIKE 3 WAVE FM software. The study focuses on the effect of wave steepness and relative submergence depth over the reef on the wave transmission for three water levels. The results from the numerical analysis are compared with published literature on wave transmission of submerged structures. The results from the numerical analysis using MIKE 3 WAVE FM software show that the wave steepness and relative submergence depth over the reef have strong dependence on the wave transmission of submerged reef. The wave transmission coefficient shows a decreasing trend with increasing wave steepness.

THE PERFORMANCE OF NARROW AND BROAD-CRESTED SUBMERGED BREAKWATERS IN DISSIPATING WAVE HEIGHTS

The main objective of this paper is to determine the wave transmission coefficient of an improved submerged breakwater called WABCORE. The objective is further explored to assess the effect of various parameters such as wave steepness, Hi/L, relative freeboard, R/d, and relative width of the top crest, B/L on wave transmission coefficient, KT. In general, as wave steepness increases, the wave transmissions decrease. Moreover wave transmission increases as relative freeboard increases. This is due to the fact that higher relative freeboard contains greater wave energy and hard to dissipate. As B/L increases, KT decreases. The effect of relative top crest width is insignificant as the freeboard increases. The transmission coefficient, KT derived from this study can be equated as , valid for certain ranges. This study concludes that WABCORE is capable to dissipate wave energy.

Straightening of light in a one dimensional dilute photonic crystal

Light transport in a dilute photonic crystal is considered. The analytical expression for the transmission coefficient is derived. Straightening of light under certain conditions in a one-dimensional photonic crystal is predicted. Such behavior is caused by the formation of a localized state in transversal motion. The main contribution to the central diffracted wave transmission coefficient is due to states, that either close to the conductance band’s bottom or deeply localized in the forbidden gap. Both these states suppress mobility in the transverse direction and force light to be straightened. Straightening of light in the optical region along with small reflection make these systems very promising for use in solar cells.

MODEL TESTS ON WAVE TRANSMISSION COEFFICIENT FOR RUBBLE MOUND STRUCTURES WITH SUPERSTRUCTURES

The coastal structures, such as breakwaters, are constructed to provide the calm basin for ships and to protect the harbor facilities. The adequate design and the evaluation of design parameters are indispensable. The determination of crest height of coastal structures is one of the most important design process among all procedures. The allowable wave overtopping, the relative crest height (Rc/Hs) and the wave transmission could be applied to design the crest height of structures. The previous studies on the wave transmission coefficients were mainly conducted about the low crested structures. The previous design method could not cover the conventional breakwaters with superstructures. In this study, the wave transmission coefficient for rubble mound structures with superstructures would be investigated with hydraulic model tests.

Modelling and Simulation of Waves in Three-Layer Porous Media

The propagation of gravity waves in an emerged three-layerporous medium is considered in this paper. Based onthe assumption that the flow can be described by Darcy’sLaw, an asymptotic theory is developed for small amplitudelong waves. This leads to a weakly nonlinear Boussinesq-typediffusion equation for the wave height, with coefficientsdepend on the conductivities and depths of each layer. In thelimit of equal conductivities of all layers, the equation reducesto the single layer result recorded in the literature. Themodel equations are numerically integrated in the case of anincident monochromatic wave hitting the layers. The resultsexhibit dissipation and also a downstream net height rise atinfinity. Wave transmission coefficient in three layer porousmedia with conductivity of mangrove is discussed. Numerically,propagation of an initial solitary wave through a porousmedium show the emergence of wave reflection and transmissionthat both evolve as permanent waves. Additionallywe examine the impact of a solitary gravity wave on a porousmedium breakwater.