Computational and experimental study of the influence of the free surface on rigid and deformable submerged structures
- Autores: Héctor Rubén Díaz Ojeda
- Directores de la Tesis: Leo Miguel González Gutiérrez (dir. tes.), Francisco J. Huera Huarte (codir. tes.)
- Lectura: En la Universidad Politécnica de Madrid ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Luis Perez Rojas (presid.), Ricardo Zamora Rodríguez (secret.), Jesús Valle Cabezas (voc.), Guillermo Artana (voc.), Miguel Ángel Fosas De Pando (voc.)
- Programa de doctorado: Programa de Doctorado en Ingenieria Naval y Oceánica por la Universidad Politécnica de Madrid
- Materias:
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- Resumen
The aim of this thesis is to evaluate to what extent the immersion depth affects the hydrodynamics of a submerged body. Two different geometries have been selected.
Firstly, a deformable splitter plate is attached to the base of a stationary circular cylinder, and an uniform flow is imposed on the system, in the laminar regime. This structure is submerged at different depths and the dependence on the Cauchy, Reynolds and Froude number are studied. The deformation and the drag forces acting on the structure are analysed in detail in order to understand the effects that the free surface has on the problem. It was observed that the amplitude of the tip of the splitter plate grows as the Reynolds, Froude and Cauchy numbers are increased. However, as the depth grows, and the structure moves away from the interface, all measurements tend to saturate. For lower depths, the free surface works as a damper for the plate dynamics, reducing the oscillations. The physical mechanism of deformation based on the pressure difference at both sides of the plate is studied, monitoring how the pressure difference decreases as the structure approaches the free surface. The drag coefficient of the global structure (cylinder and plate) increases linearly with depth, but decreases when the viscosity of the fluid is reduced.
Secondly, the flow normal to a rectangular flat plate with sharp angles in the presence of the free surface and gravity has been studied numerically, using a 3D Large Eddy Simulation (LES) methodology. Previous numerical studies on this geometry consider either periodic assumptions or the laminar regime Re around 1000. The numerical study described here, with a fully 3D simulation of the flat plate in the turbulent regime Re around 100000 has not been reported before. Important differences have been found with respect to the laminar case or when periodic boundary conditions are assumed. The simulations are initially validated using a reference case of a plate with sharp corners and a single phase 3D-periodic configuration. The time averaged drag force, the velocity and pressure fields are compared against the case of the plate with smooth corners. Finally, in the case of the two-phase 3D numerical simulations, the drag force and the vorticity fields in the near wake of the plate are compared to recent experimental work of Satheesh and Huera-Huarte (2019) Effect of the free surface on a at plate translating normal to the flow. Ocean Engineering 171, 458 - 468. These experiments were used as a guideline for the computational set-up, consequently the value of most of the dimensionless parameters are the same. A second scenario where the free surface is replaced by a solid wall is also considered. Two important observations show up from this research, first: the characteristic unsteady frequencies associated to the two periodic regimes in the case involving smooth corners, is missing in this scenario. Second, a critical submergence depth (distance) between the upper part of the plate and the free surface (or solid wall) has been found, where the drag force shows a maximum value. These observations are discussed in relation to the pressure distribution, the vortex structures formed at the wake and the gap flow formed between the plate and the free surface.
