Experimental and Numerical Analysis of the Hydrodynamics around a Vertical Cylinder in Waves

Sara Corvaro,Andrea Cimarelli,Francesco Marini,Alessandro Mancinelli,Andrea Crivellini,Loris Capitanelli

doi:10.3390/jmse7120453

Abstract

The present study provides an extensive analysis on the hydrodynamics induced by a vertical slender pile under wave action. The authors carried out the study both experimentally and numerically, thus enabling a deep understanding of the flow physics. The experiments took place at a wave flume of the Università Politecnica delle Marche. Two different experimental campaigns were performed: In the former one, a mobile bed model was realized with the aims to study both the scour process and the hydrodynamics around the cylinder; in the latter one, the seabed was rigid in order to make undisturbed optical measurements, providing a deeper analysis of the hydrodynamics. The numerical investigation was made by performing a direct numerical simulation. A second order numerical discretization, both in time and in space, was used to solve the Navier–Stokes equations while a volume of fluid (VOF) approach was adopted for tracking the free surface. The comparison between experimental and numerical results is provided in terms of velocity, pressure distributions around the cylinder, and total force on it. The analysis of the pressure gradient was used to evaluate the generation and evolution of vortices around the cylinder. Finally, the relation between scour and bed shear stresses due to the structure of the vortex pattern around the pile was assessed. It is worth noting that the physical understanding of this last analysis was enabled by the combined use of experimental data on scour and numerical data on the flow pattern.

Highlights

The knowledge of the hydro- and morphodynamics induced by a slender vertical pile is very important for the design of marine structures, such as offshore platforms or wind farms
The combined use of direct numerical simulation and experimental data proved to be fundamental for a deep understanding of the hydrodynamics around a vertical cylinder under wave action
The convergence of the numerical simulation with experiments was achieved and its validation was performed by means of all the major hydrodynamic quantities

Summary

Introduction

The knowledge of the hydro- and morphodynamics induced by a slender vertical pile is very important for the design of marine structures, such as offshore platforms or wind farms. The pioneering work of Morison [1] started an extensive series of studies on the forces over vertical piles under waves. From the 1990s, several studies on the hydrodynamics have been realized [4,5,6,7], mostly focusing on the analysis of the scour process and the formation of vortices. The focus was on the analysis of the hydrodynamics around a vertical slender cylinder subjected to wave forcing only, by making use of both the experimental and numerical models. The combined analysis focused on the pressure distributions around the pile and on the evaluation of the total force on it at different wave phases. In the present paper the authors exploited the different information provided by the numerical and experimental approaches in order to shed light on relevant physical processes which would be otherwise difficult to understand by using solely experimental or numerical data

Experimental Setup

Discussion and Conclusions