Two-dimensional experimental and numerical investigations of parallel perforated plates in oscillating and orbital flows

Fredrik Mentzoni,Trygve Kristiansen

doi:10.1016/j.apor.2019.102042

Fredrik Mentzoni, Trygve Kristiansen

Open Access

https://doi.org/10.1016/j.apor.2019.102042

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Abstract

The hydrodynamic loads on two-dimensional perforated plates are investigated experimentally and numerically. Two parallel plate configurations, consisting of an upper perforated plate and a lower perforated plate, are studied. The difference between the two configurations is the gap distance between the upper and the lower plates, being 0.14 and 0.29 times the width of the plates. Comparisons are made between forced oscillation experiments and numerical simulations of oscillating and orbital flow conditions. The Keulegan–Carpenter (KC) number and period of oscillation are varied. Added mass and damping coefficients are presented. The coefficients are highly KC number dependent. There is in general small dependence on the period of oscillation. The force coefficients are in general somewhat larger for the largest gap distance. The hydrodynamic force on both configurations is dominated by damping. We find in general good agreement between the experimental and numerical results.Interaction effects between the plates of the parallel configurations are studied. The interaction effects increase with increasing KC number and depend on the distance between the two plates. Compared to the force on one single perforated plate, interaction effects influence the phase and magnitude of the force on the upper and lower plates in the parallel configurations. A reduction in hydrodynamic force, compared to that of one single plate, is found for both plates, in particular for the downstream plate.

Highlights

A reduction in hydrodynamic force, compared to that of one single plate, is found for both plates, in particular for the downstream plate. This is the second part of a study on the hydrodynamic loads on perforated plates in waves and oscillating and orbital flows
The focus in the second part is on the hydrodynamic interaction of two parallel perforated plates in oscillating and orbital flow
The total hydrodynamic force on these simplified subsea structures are typically dominated by the perforated plates; for example, we found almost no difference in the hydrodynamic coefficients of two perforated plates in parallel compared to two perforated plates in parallel with five cylinders in between [2]

Summary

Introduction

This is the second part of a study on the hydrodynamic loads on perforated plates in waves and oscillating and orbital flows. The focus in the second part is on the hydrodynamic interaction of two parallel perforated plates in oscillating and orbital flow. The first part of the study is on the hydrodynamic forces of single perforated plates in waves compared to oscillating and orbital flows [1]. The introduction, theory and method sections are included in both parts, such that they can be read separately. This part of the study is organized in six main sections. The structures and modules of subsea fields are lifted by cranes on vessels, lowered through the water, and installed on the seabed. There is a need for accurate estimates of the hydrodynamic forces that subsea structures are exposed to during the lifting and lowering phases in harsh environments

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