1,720,998 research outputs found
Numerical Simulation Of Ski-Jump Hydraulic Behavior
No full textThe hydraulics of ski jumps is an issue of great importance in dam construction, the former being in practice the only existing solution as related to the dissipation of energy from high-speed spillway ows from large dams. Inspite of the fact that thousands of dams have been built all over the world in the years, and besides the reporting of specic case studies, the general hydraulic behavior of the ski jumps has been scarcely investigated. In the present work, the hydraulic behavior of ski jumps is investigated numerically using the OpenFOAM digital library [1]. A number of skijump cases has been simulated numerically following the RANS (Reynolds Averaged Navier-Stokes equations) approach, using the kappa-omega SST closure model [2] and ther VoF technique (Volume of Fluid) for the tracking of the ow free surface [3]. The numerical procedure appears to be a rather favourable option to overcome the complexities always associated to experimental measurements. Particular attention is given to the forces, to the pressure distribution in the zone of impact of the falling jet, and to the length of the jet itself. The issue of the length of the falling jet is particularly considered, as dened as the distance along the x- direction between the point of maximum dynamic pressure head in the zone of impact of the jet along the centerline of the tailwater channel, and the origin of the reference system. A chart is proposed, reporting the correlation lines (and correspondent formal expressions) between the approach Froude numbers and the lengths of the jets, in the limit of the range of other parameters tested. The chart may serve as a useful tool to determine the length of the jet taking o from the bucket, starting from the value of the approach Froude number
Numerical investigation of ski jump hydraulics
No full textThe hydraulics of ski jumps is an issue of utmost importance in dam construction, the former being in practice the only existing solution as related to the dissipation of energy from high-speed spillway flows. Despite the fact that thousands of dams have been built all over the world, and aside from the availability of specific case studies, the general hydraulic behavior of ski jumps deserves a more complete and systematic comprehension. In the present work, the issue of the hydraulics of ski jumps is addressed numerically. After a first phase of calibration of the numerical model against experimental results obtained by others, a number of ski jump cases are simulated with particular attention to the heads at the impact of the falling jet and to the length of the jet itself. The results clarify several aspects that characterize this subject in a systematic manner and may provide useful suggestions for those involved in dam construction and management. © 2020 American Society of Civil Engineers
Flow Resistance in Open Channel Due to Vegetation at Reach Scale: A Review
Full text linkVegetation on the banks and flooding areas of watercourses significantly affects energy losses. To take the latter into account, computational models make use of resistance coefficients based on the evaluation of bed and walls roughness besides the resistance to flow offered by vegetation. This paper, after summarizing the classical approaches based on descriptions and pictures, considers the recent advancements related to the analytical methods relative both to rigid and flexible vegetation. In particular, emergent rigid vegetation is first analyzed by focusing on the methods for determining the drag coefficient, then submerged rigid vegetation is analyzed, highlighting briefly the principles on which the different models are based and recalling the comparisons made in the literature. Then, the models used in the case of both emergent and submerged rigid vegetation are highlighted. As to flexible vegetation, the paper reminds first the flow conditions that cause the vegetation to lay on the channel bed, and then the classical resistance laws that were developed for the design of irrigation canals. The most recent developments in the case of submerged and emergent flexible vegetation are then presented. Since turbulence studies should be considered as the basis of flow resistance, even though the path toward practical use is still long, the new developments in the field of 3D numerical methods are briefly reviewed, presently used to assess the characteristics of turbulence and the transport of sediments and pollutants. The use of remote sensing to map riparian vegetation and estimating biomechanical parameters is briefly analyzed. Finally, some applications are presented, aimed at highlighting, in real cases, the influence exerted by vegetation on water depth and maintenance interventions
PROPER ORTHOGONAL FLOW MODES IN THE VISCOUS-FLUID WAVE-DIFFRACTION CASE
No full textThe diffraction of a wave of viscous fluid (water) impinging on a large-diameter vertical circular cylinder piercing a free surface is studied numerically. The three-dimensional time-dependent full Navier−Stokes equations in primitive variables are solved by following the Direct Numerical Simulation (DNS) approach, thus obtaining an accurate three-component velocity field through a number of time steps in the case at hand. The technique of the Karhunen−Loeve decomposition is then applied to the numerical database, and a "reduced" velocity field is reconstructed based on the three most energetic eigenfunctions of the decomposition. The results are compared with those obtained in terms of flow structures from the formerly simulated field, so unveiling the characteristics of the most energetic portion of the flow field in the case at hand
Wave-field flow structures developing around largediameter vertical circular cylinder
No full textIn this work the issue of wave-induced flow structures that develop around a large-diameter surface-piercing vertical circular cylinder is addressed. A strictly-linear wave case is considered and simulated numerically, solving the Euler equations in primitive variables, and the results are compared with those obtained from the corresponding close-form velocity-potential solution. Then, the swirling-strength criterion for flow-structure eduction is applied to the primitive-variable Euler-equations-derived velocity field. It is found that differently-shaped flow structures develop at the free surface and under the free surface, in particular at the cylinder wall. This field of structures is not detectable from the potential-derived velocity field, due to the purely mathematical nature of the latter
Recent Results from Analysis of Flow Structures and Energy Modes Induced by Viscous Wave around a Surface-Piercing Cylinder
Full text linkDue to its relevance in ocean engineering, the subject of the flow field generated by water waves around a vertical circular cylinder piercing the free surface has recently started to be considered by several research groups. In particular, we studied this problem starting from the velocity-potential framework, then the implementation of the numerical solution of the Euler equations in their velocity-pressure formulation, and finally the performance of the integration of the Navier-Stokes equations in primitive variables. We also developed and applied methods of extraction of the flow coherent structures and most energetic modes. In this work, we present some new results of our research directed, in particular, toward the clarification of the main nonintuitive character of the phenomenon of interaction between a wave and a surface-piercing cylinder, namely, the fact that the wave exerts its maximum force and exhibits its maximum run-up on the cylindrical obstacle at different instants. The understanding of this phenomenon becomes of crucial importance in the perspective of governing the entity of the wave run-up on the obstacle by means of wave-flow-control techniques.</jats:p
Simulazione numerica del moto di un fluido viscoso attorno a corpi cilindrici di sezione circolare e frattale
No full textWAVE-FIELD FLOW STRUCTURES DEVELOPING AROUND LARGE-DIAMETER VERTICAL CIRCULAR CYLINDER
No full textIn this work the issue of wave-induced flow structures that develop around a large-diameter surface-piercing vertical circular cylinder is addressed. A strictly-linear wave case is considered and simulated numerically, solving the Euler equations in primitive variables, and the results are compared with those obtained from the corresponding close-form velocity-potential solution. Then, the swirling-strength criterion for flow-structure eduction is applied to the primitive-variable Euler-equations-derived velocity field. It is found that differently-shaped flow structures develop at the free surface and under the free surface, in particular at the cylinder wall. This field of structures is not detectable from the potential-derived velocity field, due to the purely mathematical nature of the latter
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