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4 resultados encontrados para: AUTOR: Oumeraci, Hocine
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1.
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Drag and inertia forces on a branched coral colony of Acropora palmata
Osorio Cano, Juan D. ; Osorio, Andrés F. (coaut.) ; Alcérreca Huerta, Juan Carlos (coaut.) ; Oumeraci, Hocine (coaut.) ;
Contenido en: Journal of Fluids and Structures Vol. 88 (July 2019), p. 31-47 ISSN: 0889-9746
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Some branched corals are capable of surviving in wave/current exposed areas with moderate to high energy environments, where their branches, their geometry and the global and rigid structure of their colonies play an important role for wave damping due to bottom friction and wave energy dissipation due to turbulence. Constant frictional coefficients are commonly used within wave propagation models to consider reef roughness but without accounting for the type of coral species, its topological characteristics, form and distribution over the reef surface. In this sense, this study aims to improve the understanding of near-bed hydrodynamics in coral reefs by examining the drag and inertia coefficients of branched coral colonies of Acropora palmata. Laboratory tests were carried out considering steady and oscillatory flow conditions. In-line forces, flow velocities and water surface elevations over 3-D models of Acropora palmata were recorded for both a single coral colony and a group of corals. Additionally, the validated open source CFD (Computational Fluid Dynamics) toolbox OpenFOAM⃝R was used to simulate the hydrodynamic performance over the coral structures for a wide range of wave heights and periods. The results show that under steady flow conditions, the drag coefficient (CD) can be well represented as a function of the Reynolds number (Re) by means of a power law equation as CD = aReb+c. Also, under oscillatory flow conditions, it was found that the inertia force (FM) dominates over the drag component (FD), explaining more than 84% of the total force exerted on the coral structure.

Prediction formulas were developed and validated with the laboratory test to predict the resistance coefficients (drag and inertia) as function of Keulegan and Carpenter number (KC) for the CD (R² = 0.89) and CM (R² = 0.92). The CFD modeling showed to be an alternative for the modeling of the hydrodynamic forces exerted over complex coral shapes and to analyze the fluid–structure interaction around natural structures.


2.
Artículo
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Reefs are known to provide coastal protection and important ecosystem services for many coastlines around the world. Physicalprocesses such as wave damping, sediment transport and nearshore hydrodynamics are closely related to the coastal protectionservices provided by reefs. The steep-fronted bathymetries of reefs cause abrupt wave transformations and wave dampingalongshore, while reef roughness has an important contribution to coastal protection. Five Latin-American case studies arepresented to illustrate the coastal protection offered by reefs and their contribution to wave damping. The methodologies applied(e.g. numerical modelling, field measurements) and reef conditions (e.g. reef degradation scenarios and contribution of reefroughness) are listed. Considerable efforts have been made towards diagnosing, understanding and modelling the hydrodynamictransformations induced by reefs. Based on physical and field surveys, roughness and friction parameters were derived in order toimplement calibrated and validated numerical models. Discussion on the advantages and disadvantages of the different modelsapplied in the study cases is provided as well as on the needs of highlighting physical processes and the analysis of reefhydrodynamics for supporting appropriate ecosystem-based management.


3.
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CFD modelling of wave damping over a fringing reef in the Colombian Caribbean
Osorio Cano, Juan D. ; Alcérreca Huerta, Juan Carlos (coaut.) ; Osorio, Andrés F. (coaut.) ; Oumeraci, Hocine (coaut.) ;
Contenido en: Coral Reefs Vol. 37, no. 4 (December 2018), p. 1093–1108 ISSN: 0722-4028
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The understanding of physical processes over submerged reefs represents an important ongoing research topic when considering wave energy dissipation and coastal protection that these environments provide. Detailed analyses are required to assess wave damping based on the contribution of reef roughness and wave breaking. For this purpose, the CFD (computational fluid dynamics) toolbox OpenFOAM® is applied to simulate the wave energy dissipation process over reefs with explicit accounting for the complexities of coral shape instead of commonly applied parameterized approaches for bottom roughness and wave breaking. Model validation was performed through comparison with field measurements over a reef profile of Tesoro Island in the Colombian Caribbean.


4.
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Soil stability analysis for wave-induced momentary liquefaction beneath porous bonded revetments
Alcérreca Huerta, Juan Carlos ; Oumeraci, Hocine (coaut.) ;
Contenido en: Coastal Engineering Vol. 138 (August 2018), p. 22-35 ISSN: 0187-7674
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The highly porous revetments made of Polyurethane Bonded Aggregates (PBA) are an ecologically friendly alternative to conventional revetments for protection against coastal erosion. No information has yet been reported for these structures on failures from field applications. However, a well-documented collapse of a PBA-revetment observed in large-scale tests (GWK tests) and a first stability analysis were reported by Oumeraci et al., 2010; 2012. Based on these results, a methodology is proposed for stability analysis of the embankment subsoil beneath PBA-revetments against momentary liquefaction, considering the results of the comprehensive parametric study (Alcérreca-Huerta, 2014) using a recently developed CFD-CSD (Computational Fluids Dynamics- Computational Solid Dynamics) model wavePoreGeoFoam (Alcérreca-Huerta and Oumeraci, 2016a; 2016b). It will be shown that the proposed stability analysis is able to reproduce the failure observed in the GWK tests, so that it can be applied for PBA-revetment under field conditions. In this paper, the failure observed in the GWK tests is first briefly reported, followed by a description of the numerical parametric study using the validated wavePoreGeoFoam model in order to extend the conditions tested in GWK. Then, the processes underlying soil liquefaction of PBA-revetments are outlined, showing that the excess pore pressure development in the sand core beneath PBA-revetments is crucial. The latter is therefore examined and a formula to predict excess pore pressures in terms of the wave conditions is developed. Moreover, a methodology for the stability analysis of the soil beneath the revetment against soil liquefaction is proposed and implemented to reproduce the failure observed in the GWK tests. Finally, the main results are summarized and implications for further research are drawn.