73 research outputs found

    Chapter 3 An introduction to OpenFOAM

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    Chapter 3 is an introduction to OpenFOAM, as the most popular CFD tool in effluent discharge modelling. A decade ago, OpenFOAM was only an academic tool for studying complex fluid mechanics problems. However, it has grown quickly in recent years and has found its way into industry as well (e.g., many consulting firms have invested in creating their own solvers for the particular problems they often solve). This book covers the fundamentals of OpenFOAM related to effluent discharge modeling: the choice of available solvers and differences between them, mesh generation options and methodology in OpenFOAM and postprocessing the numerical results

    Spatiotemporal Scouring Processes around a Square Column on a Sloped Beach Induced by Tsunami Bores

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    Tsunamis continue to pose an existential threat to life and infrastructure in many coastal areas around the world. One of the risks associated with tsunamis is the formation of deep scour holes around critical infrastructure and other coastal buildings, compromising their structural integrity and stability. Despite its importance, tsunami-induced scour is still given limited and simplified consideration in design guidelines for coastal structures. To further improve the understanding of tsunami-induced scour processes, and thus provide the basis for safer design of coastal structures, novel large-scale laboratory experiments have been conducted. The experiments featured a unique combination of boundary conditions, including a square coastal structure on a sloping and dry sandy beach. Single broken solitary waves were used to simulate tsunami bores. The spatiotemporal scour development directly at the square column was monitored by a high-resolution camera system, allowing a detailed description of the highly dynamic flow and scour process. Differences in the scour process between the wave runup and drawdown phases are described, and maximum and final scour depths are given as a function of inundation depth, wave height, and distance of the column from the shoreline. The scour process is characterized by several distinct phases of varying intensity and scour rate, the sequence of which varies depending on the location on the sides of the column. It is shown that the drawdown phase has a large influence on the overall scour development, adding up to 58% to the scour depth obtained during the wave runup phase. As a result of significant sediment infilling during the drawdown phase, the maximum scour depths achieved during the drawdown phase are up to twice the final scour depths at the end of a test. This discrepancy between final and maximum scour depths is greater than in previous studies using a flat sediment bed. The results of this study therefore help to interpret scour depths measured during field investigations after a tsunami event and provide a basis for extending design guidelines for coastal structures

    Conservative characteristic-based schemes for shallow flows

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    Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2005-2006Les équations en eaux peu profondes, encore appelées équations de Saint-Venant, sont utilisées dans de nombreux cas importants comme les fleuves, les lacs, les estuaires et les océans. La conservation de certaines quantités est une propriété importante qui est habituellement désirée pour assurer la précision des simulations à long terme et également pour le cas des écoulements complexes avec présence d'ondes de choc. Cette thèse examine tout d'abord la formulation de schémas semi-Lagrangiens, qui sont bien connus pour demeurer stables pour des nombres très élevés de CFL. Cependant, ces schémas perdent leur propriété de stabilité lorsque la conservation totale des quantités, qui est cruciale pour une simulation correcte les ondes de chocs, est imposée. Un schéma semi- Lagrangien entièrement conservatif est développé ici et ce dernier demeure stable pour des nombres élevés de CFL. L'approche proposée est ensuite étendue à la méthode des caractéristiques (MOC) et une version conservative du schéma MOC est développée. Contrairement au schéma MOC original, qui ne peut pas simuler correctement les ondes de choc à cause du manque de conservation, le schéma proposé les simule avec succès. De plus, le nouveau schéma présente des avantages sur le plan numérique, tant pour la diffusion et la dispersion que pour la stabilité. Le cas 2D est ensuite considéré, et la méthode de volume finie est utilisée à cause de son conservation inhérente. Le cas 2D est ensuite considéré, et la méthode de volumes finis est utilisée à cause de ses qualités inhérentes de conservation. La plupart des méthodes numériques disponibles sont sensibles au problème du déséquilibre entre les termes source et de flux, particulièrement en présence d'un maillage non structuré. D'autre part, la plupart des schémas numériques disponibles (par exemple les schémas HLL et ENO) induisent un niveau élevé de diffusion numérique en simulant des écoulements tourbillonnaires. Trois approches différentes, applicables sur des maillages non structurés sont développées ici. Elles peuvent simuler des conditions complexes d'écoulement comprenant les topographies variables, les écoulements tourbillonnaires, trans-critiques et discontinus. Finalement plusieurs méthodes de volumes finis upwind sont utilisées, via une analyse de type Fourier, pour évaluer le niveau d`amortissement des modes de Rossby. Contrairement aux bons résultats habituellement obtenus par les méthodes de volumes finis upwind dans iii le cas d'écoulements dominés par la convection, on remarque ici que les ondes de Rossby sont amorties de manière excessive.Shallow water equations arise in many important cases such as in rivers, lakes, estuaries and oceans. Conservation is an important property which is usually desired to ensure the accuracy of the long term simulations and also for the case of complex flows with shockwaves. This thesis begins with semi-Lagrangian schemes, which are well known to remain stable for very high CFL numbers. However, they lose their high stability property when the fully conservative property, which is crucial for a correct simulation of shock waves, is imposed. An inherently fully conservative semi-Lagrangian scheme is developed here which remains stable for high CFL numbers. The proposed approach is then extended to the method of characteristics (MOC) and a conservative extension of MOC is developed. Contrary to the original MOC, which is unable to simulate shockwaves due to the lack of conservation, the proposed scheme easily simulates them. Further, the new scheme presents favorable features in terms of numerical diffusion and dispersion. The 2D case is then considered, and the finite volume method is employed due to its inherent conservation properties. Most available numerical methods face the problem of imbalance between the source and flux terms, particularly when unstructured grids are used. On the other hand, most available numerical schemes (such as the HLL and the ENO schemes) induce a high level of numerical diffusion in simulating recirculating flows. Three different approaches using unstructured grids are successfully developed here. The new schemes can simulate complex flow conditions including recirculating, trans-critical and discontinuous flows over variable topographies. Finally, the performance of the upwind finite volume schemes, for Rossby waves, is studied using a Fourier analysis approach. Contrary to the usual good results obtained for those schemes in the case of convection dominated flows, it is observed here that they lead to an excessive damping of the Rossby modes

    Buoyant Jets in Cross-Flows: Review, Developments, and Applications

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    Significant environmental effects from the use of marine outfall discharges have led to increased efforts by both regulatory bodies and research groups to minimize the negative impacts of discharges on the receiving water bodies. Understanding the characteristics of discharges under conditions representative of marine environments can enhance the management of discharges and mitigate the adverse impacts to marine biota. Thus, special attention should be given to ambient cross-flow effects on the mixing behaviors of jet discharges. A buoyant jet in cross-flow has different practical applications such as film cooling and dilution, and provide a higher mixing capability in comparison with free jets or discharges into stationary environments. The main reason for this is believed to be the existence of various complicated vortical structures including a counter-rotating vortex pair as the jet expands downstream. Although tremendous research efforts have been devoted to buoyant jets issuing into cross-flows over the past five decades, the mixing process of an effluent at the discharge point is not yet well understood because of the highly complex fluid interactions and dispersion patterns involved. Therefore, there is a need for a deeper understanding of buoyant jets in cross-flows in order to obtain better predictive methods and more accurate design guidelines. The main aims of this study were (i) to establish the background behind the subject of buoyant jets in cross-flows including the flow structures resulting from the interaction of jets and cross-flows and the impacts of current on mixing and transport behavior; (ii) to present a summary of relevant experimental and numerical research efforts; and finally, (iii) to identify and discuss research gaps and future research directions

    Selenium Removal from Water and Wastewater by Different Technologies: A Systematic Review

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    Background: Selenium (Se) is an essential element playing a vital role in the metabolism of organisms. Se can generally be discharged in the potable water through natural and anthropogenic activities. Both excess and shortage of Se can cause significant adverse health effects in humans. Excess values of se may stimulate toxici-ty, leading to selenosis and alkali disease in humans and grazing animals, respectively. Methods: A review search was systematically carried out from the databases Embase, PubMed/MEDLINE, Scopus, PubMed Central (PMC), Google Scholar, as well as medRxiv by using the following keywords: “waste water”, “bioremediation”, “selenium removal”, “adsorption”, and “drinking water”. This study provides a review of the recent literature covering the period between 2011 and 2021. After screening the full text of the articles, 27 papers were enrolled. This study reviews the reported techniques for Se removal from water and wastewater, including adsorption, biological treatment, microbial reduction, bioreactors, fungal bioreactor, algal treatment, phytoremediation, and photocatalysis. Results: Biological and bioremediation techniques, such as microbial reduction, biotransformation, and fluid-ized bed reactor have removal efficiency about 100. The highest Se concentration of 15-7600 µg/L was achieved in ground waters in Ethiopia and the lowest level of 0.07 µg /L in Finland. Conclusion: The combination of biological treatment with chemical or physical technologies is envisaged to optimize se elimination and to ensure ecological protection and human health safety

    Numerical Simulation of Flow in Parshall Flume Using Selected Nonlinear Turbulence Models

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    This study uses a computational fluid dynamics (CFD) approach to simulate flows in Parshall flumes, which are used to measure flowrates in channels. The numerical results are compared with the experimental data, which show that choosing the right turbulence model, e.g., v2−f and LC, is the key element in accurately simulating Parshall flumes. The Standard Error of Estimate (SEE) values were very low, i.e., 0.76% and 1.00%, respectively, for the two models mentioned above. The Parshall flume used for this experiment is a good example of a hydraulic structure for which the design can be more improved by implementing a CFD approach compared with a laboratory (physical) modeling approach, which is often costly and time-consuming

    Numerical Investigation of Tsunami Bore Effects on Structures, Part I: Drag Coefficients

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    Recent tsunami disasters caused devastating damage to non-engineered as well as engineered coastal infrastructure. In fact, previous design guidelines containing provisions for tsunami loading did not provide accurate estimations of tsunami loads in order to design structures capable of withstanding tsunami impacts. The drag coefficient plays a significant role in the calculation of tsunami hydrodynamic forces. This coefficient is traditionally calculated based on a steady flow analogy. However, tsunami-induced coastal inundation is a typical case of rapidly varying unsteady flows. The present study aims at investigating the tsunami forces exerted on structures with different geometries in order to provide realistic guidelines to estimate drag coefficients for unsteady flows. In this paper, a dam-break wave is used to investigate the tsunami-induced bore interaction with structures. A three-dimensional multiphase numerical model is implemented to study the tsunami loading on rectangular-shaped structures with various aspect ratios (width/depth) and orientations. The numerical model results are validated using measured forces and bore surface elevations from physical experiments previously carried out by some of the authors of this paper. A scaled-up domain is then modeled in order to assess the performance of the model and the induced tsunami loading at prototype scale. The drag coefficient relations for various structural geometries and bore depths are further provided. The calculated hydrodynamic forces and associated drag coefficients are compared with data in the existing literature and current design codes
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