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research-article

CFD Reproduction of Nonlinear Loads on a Vertical Column during Extreme Irregular Wave Events

[+] Author and Article Information
Erin E. Bachynski

Associate Professor, Dept. of Marine Technology,Norwegian University of Science and Technology (NTNU), Trondheim, Norway
erin.bachynski@ntnu.no

Csaba Pakozdi

Research Scientist, SINTEF Ocean (former MARINTEK), Trondheim, Norway
csaba.pakozdi@sintef.no

Anders Östman

Senior Research Scientist, SINTEF Ocean (former MARINTEK), Trondheim, Norway
anders.ostman@sintef.no

Carl Trygve Stansberg

Norwegian Marine Technology Research Institute (MARINTEK), Trondheim, Norway
ctstansberg.marinteknikk@gmail.com

1Corresponding author.

ASME doi:10.1115/1.4040442 History: Received October 19, 2016; Revised May 23, 2018

Abstract

Recently, a method for numerical reproduction of measured irregular wave events has been developed. The measured motion of the wave maker flaps defines the wave kinematics at the boundary of the numerical simulation in order to generate the waves. When such data are not available, the control signal of the wave maker can, instead, be generated from a given free surface elevation following the same procedure as in model tests. This procedure is applied to a model test case with extreme irregular wave events and resulting nonlinear global wave loads on a vertical cylinder, focusing on higher-order ringing excitation. The purpose of the investigation is two-fold: 1) to validate the wave reconstruction procedure, and 2) to validate the resulting CFD ringing loads with the given waves. In order to better understand the frequency content in the CFD-generated loads, wavelet analysis as well as the response of a single degree-of-freedom (SDOF) oscillator are examined and compared with the corresponding results for the 3rd order wave forcing based on the MacCamy-Fuchs (MF) and Faltinsen, Newman, Vinje (FNV) formulations. The results show generally good agreement between CFD and experiment both in the waves and in the loads; discrepancies found in the loads mainly originate from corresponding uncertainties in the wave reconstruction. Wave breaking may be one source of uncertainty. The MF+FNV formulation showed reasonable prediction of the maximum responses of an SDOF oscillator, but could not capture the loads well at all of the important frequencies.

Copyright (c) 2018 by ASME
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