The Experts below are selected from a list of 54 Experts worldwide ranked by ideXlab platform
Zhong Peng - One of the best experts on this subject based on the ideXlab platform.
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evolution of wave shape over a low Crested Structure
Coastal Engineering, 2011Co-Authors: Zhong PengAbstract:This paper investigates the evolution of wave shape over a low-Crested Structure (LCS) using a 2-D RANS-VOF model. The model predictions of surface elevation and wave skewness and asymmetry are in good agreement with the recent measurements collected in a small scale wave channel at the University of Cantabria (UCA). The empirical formulae relating wave skewness and asymmetry to local Ursell number by Peng et al. (2009) have been extended to include the effect of wave reflection and the ramp in front of LCS and a wider range of Ursell number in the present study. In the presence of LCS, wave skewness decreases slightly above the seaward slope, then increases rapidly up to a maximum value above the Structure crest, and decreases drastically above the leeward slope. Wave asymmetry decreases sharply above the seaward slope to a negative minimum value at the Structure crest, and then increases rapidly to a positive value above the leeward slope. Our bispectral analysis indicates that sum interactions increase skewness and decrease asymmetry while difference interactions have opposite effects and that the former dominate above the seaward slope and on the Structure crest but the latter dominate above the leeward slope of LCS. The observed wave shape evolution over a LCS can be attributed to the changes in the interplay of sum and difference interactions. We found that incident wave height and wave period, relative Structure freeboard, Structure crest width and Structure porosity are the controlling factors for wave shape evolution over LCS. This study provides new insights on the role of wave skewness and asymmetry in the breakwaters stability and sediment transport around the Structure and on the beaches behind it.
Danielle Denise Dowding - One of the best experts on this subject based on the ideXlab platform.
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analysys of hydrodinamic transformation around a low Crested permeable Structure
2010Co-Authors: Danielle Denise DowdingAbstract:The aim of this research project was to increase the knowledge about the hydrodynamic processes that take place around a permeable Low-Crested Structure (LCS) when this Structure is under wave attack. Further, the intention is to place the hydrodynamic data garnered here within the context of the current state of scientific research related to permeable LCS so as to build on previous literature and works associated to the hydrodynamics of LCS. In order to carry out the research, physical modelling experiments were conducted in the wave flume at the Laboratori d'Enginyeria Maritima (LIM). These experiments were sponsored by the larger research project of related to Composite Modelling of the Interactions Between Beaches and Structures (CoMIBBS). It is hoped that the work here will be able to contribute in some way to the goals of the larger CoMIBBS project. It was indispensable to conduct the experiments related to permeable LCS making use of various wave attack scenarios including varied wave heights and wave slopes. Two types of Structures were tested in these experiments, emerged and submerged. All of the information about the research project and the facility specifics, as well as the Structure details, the wave scenarios, the recorder locations and data collection methods are detailed within Chapter 2. The results acquired from the experiments conducted were analysed in terms of the following aspects: • wave transmission characteristics • wave reflection characteristics • spectral changes • current velocities – magnitude variation and vertical distribution Trend analysis revealed aspects of the hydrodynamics which were considered more significant than others; it also aided in distinguishing the effects of certain parameters on other data. The results garnered were compared to existing formulas and categorizations relating to the hydrodynamic indicators considered paramount, which were (1) the transmission coefficient, (2) the reflection coefficient, and (3) the spectral energy distribution. The relationships between the results of the physical modelling and the calculated results of the formulas were established and examined for connective trends. This process ascertained the relevance of the formulas to the LCS under examination and the hydrodynamic patterns noted. 3 Another part of the thesis was to numerically simulate the water movement through the permeable LCS. This was done with the use of the LIMWAVE model developed at the Universitat Politecnica de Catalunya (UPC). With this model, it was attempted to determine the correlation between the physical modelling results and numerical modelling results. From these simulations, it was noted that the numerical model represented the water level on the leeside of the Structure fairly well, save for slight differences resulting from the piling up effect. The relation between the models of the water level on the seaward side of the Structure was dependent on whether or not reflection was activated, in which case, a standing wave was produced. The most important conclusions found from the works are as follows: 1. The coefficients Kt and Kr as well as the shape of the frequency spectra are linked to the wave steepness, which seems to be a very important yet often underestimated parameter. 2. The inclusion of the Structure’s permeability into the existing formulae for the prediction of the coefficients Kt and Kr will greatly increase the accuracy of the formula. This work has opened up many more aspects of the application of hydrodynamic observation and modelling. A set of research exercises should be carried out in order to complement this report and relate the findings in more practical applications. Additional tests related to highly permeable low-Crested Structures both as offshore breakwaters and as submerged offshore reefs are required to gain a better understanding of the effect of permeability on the transmission and reflection of waves. Further, these tests should be conducted on selected sites in order to truly understand the effects of permeable LCS in the field. From these test results it is recommended that a review of the existing formulas for the transmission coefficients should be made to include the permeability of the Structures. Also, an attempt should be made to examine in detail the relationship between the wave steepness and the various parameters under examination. The results of these findings can have several practical applications: the design of an improved Structure with less scouring which is more environmentally friendly, as well as the probably use of wave energy as a power source.
Barbara Zanuttigh - One of the best experts on this subject based on the ideXlab platform.
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ANALYSIS OF AN UNEXPECTED GROIN FAILURE AT A LOW Crested DEFENCE SCHEME
Coastal Engineering 2006, 2007Co-Authors: Luca Martinelli, Barbara Zanuttigh, M. Gabriella Gaeta, Alberto LambertiAbstract:This contribution analyses the structural failure of two groins that laterally confined a coastal defence scheme placed in Igea Marina beach (IT), where six emerged barriers were converted into one single low Crested Structure. \ud The site has been monitored since the works started. Recent results from bathymetric surveys, sediment samplings and geotechnical tests are presented. \ud The storm after which the groins failed is reconstructed and modeled by means of morphological simulations with MIKE 21. On the basis of the field surveys and of the computed bed level changes during the storm, it is concluded that the groin failure can not be justified only by currents induced local scour but it was also caused by a soil resistance decrease due to partial liquefaction
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WAVE TRANSMISSION AT LOW-Crested StructureS, INCLUDING OBLIQUE WAVE ATTACK
Coastal Engineering 2004, 2005Co-Authors: Jentsje Van Der Meer, Riccardo Briganti, Baoxing Wang, Barbara ZanuttighAbstract:A part of the DELOS research focused on wave transformation at low-Crested Structure and is summarised in this paper. Several flume tests have been carried out within the project to analyse wave transmission on rubble mound Structures and simultaneously an existing database has been extensively increased by receiving data from other researchers in the world. This new database consists of more than 2300 tests and has been used to come up with the best 2D wave transmission formula for rubble mound LCS. Oblique wave attack on LCS was a second objective within DELOS. Small scale model results were produced and analysed leading to new transmission formulae for smooth LCS and to conclusions on 3D effects for both rubble mound and smooth LCS.
Agustín Sánchez-arcilla - One of the best experts on this subject based on the ideXlab platform.
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Simulation of Wave Overtopping of Maritime Structures in a Numerical Wave Flume
Journal of Applied Mathematics, 2012Co-Authors: Tiago C. A. Oliveira, Agustín Sánchez-arcilla, X. GironellaAbstract:A numerical wave flume based on the particle finite element method (PFEM) is applied to simulate wave overtopping for impermeable maritime Structures. An assessment of the performance and robustness of the numerical wave flume is carried out for two different cases comparing numerical results with experimental data. In the first case, a well-defined benchmark test of a simple low-Crested Structure overtopped by regular nonbreaking waves is presented, tested in the lab, and simulated in the numerical wave flume. In the second case, state-of-the-art physical experiments of a trapezoidal Structure placed on a sloping beach overtopped by regular breaking waves are simulated in the numerical wave flume. For both cases, main overtopping events are well detected by the numerical wave flume. However, nonlinear processes controlling the tests proposed, such as nonlinear wave generation, energy losses along the wave propagation track, wave reflection, and overtopping events, are reproduced with more accuracy in the first case. Results indicate that a numerical wave flume based on the PFEM can be applied as an efficient tool to supplement physical models, semiempirical formulations, and other numerical techniques to deal with overtopping of maritime Structures.
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Quantification of changes in current intensities induced by wave overtopping around low-Crested Structures
Coastal Engineering, 2008Co-Authors: Iván Cáceres, Marcel J. F. Stive, Agustín Sánchez-arcilla, Le Hai TrungAbstract:The phenomenon of overtopping is traditionally studied for well-emerged harbour Structures and often focuses on safety and stability. In this paper laboratory tests are presented and analysed to sharpen the hypothesis that overtopping is capable of changing the horizontal circulation pattern around low-Crested Structures. A unique data set from laboratory experiments was acquired in the wave basin at Delft University of Technology. The experiments were performed using an emerged impermeable low-Crested Structure (three freeboards and three different wave conditions for each freeboard) and yielded nine different combinations of set-up and overtopping driving forces. Using this information it was possible to quantify the changes in cross-shore and longshore velocity induced by the overtopping and the set-up changes under the different freeboard and wave conditions described. It is found that overtopping enhances the outgoing flows (longshore velocities parallel to the Structure) away from the lee side of the Structure and dampens the water level gradient driven flow towards the Structure.
J.p. De Waal - One of the best experts on this subject based on the ideXlab platform.
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Wave Transmission: Spectral Changes and Its Effects on Run-Up and Overtopping
Coastal Engineering, 2001Co-Authors: J.w. Van Der Meer, E. Regeling, J.p. De WaalAbstract:Most research work on wave transmission over low-Crested Structures has been concentrated on establishing the wave transmission coefficient, i.e. the ratio between transmitted and incident significant wave height. It is clear that such Structures decrease the wave height, but there is more! Goda, Tanimoto et al. Raichlen et al. and Van. der Meer all conclude that also the mean period reduces to 0.4–1.0 of the incident mean period. The conclusion is that overtopping generates more waves. Further, Raichlen et al. and Lee give examples of measured spectra of transmitted waves. Both examples show the peak of the spectrum similar to the incident spectrum, but with much more energy at the higher frequencies. A good estimation of the wave height in front of a Structure is required for design or assessment of such a Structure. But also wave period and sometimes spectral shape may have influence on the design. Wave run-up, for example, depends largely on the wave period. In order to establish the required dike height for acceptable run-up, both wave height and period should be known. In situations where a low-Crested Structure in front of such a dike gives some protection, wave period and spectral changes should be studied. A local situation in the Netherlands was the reason for the research presented in this paper. Figure 1 gives a schematised layout. A large lake is situated on the west side (left side in the figure) and NW wind may generate waves up to a significant wave height of over 2 m. The dikes on the eastern side are partly protected by a system of various low-Crested Structures or dams, including some openings. The figure shows the results of a calculation on wave penetration. Such calculations were performed by Alkyon. Besides wave penetration, wave transmission is generated over the low-Crested dams. The area is about 1 km by 2.5 km. This means that with a fetch of more than 1 km also locally generated (short) waves will be present during extreme conditions. The wave climate in front of the dikes can be described as a combination of wave penetration, wave transmission and locally generated wind waves. This paper deals with wave transmission only, but the effect on the total wave climate is discussed at the end.