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New Combined CFD and Model Testing Technique for Identification of Wave Impact Loads on a Semisubmersible

[+] Author Affiliations
Csaba Pakozdi, Anders Östman, Bjørn C. Abrahamsen, Ole D. Økland

SINTEF Ocean, Trondheim, Norway

Tone M. Vestbøstad, Gunnar Lian

Statoil, Stavanger, Norway

Carl T. Stansberg

Ctstansberg Marinteknikk, Trondheim, Norway

Paper No. OMAE2017-62643, pp. V001T01A089; 10 pages
doi:10.1115/OMAE2017-62643
From:
  • ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 1: Offshore Technology
  • Trondheim, Norway, June 25–30, 2017
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-5763-2
  • Copyright © 2017 by ASME

abstract

A procedure is presented describing how to estimate realistic loads using combined numerical and model test data. Measured platform motions are imposed on the structure during the CFD analysis. The combination of the wave matching procedure with the imposed measured platform motion gives a very good numerical reproduction of the observed extreme event. The numerical reproduction of model test events provide all necessary information on the hydrodynamic loads for further structure analysis. This represents an improvement in industry design applications.

Imposing the measured motion from regular wave model test into CFD simulation is validated by comparison of relative wave height time series. This comparison shows a very good agreement between the measured and the simulated time series. Existing model test data from irregular model test and CFD generated numerical wave are compared. A wave matching procedure has been developed, which shows very promising results with respect to reproducing critical hydrodynamic conditions observed during the model tests. This paper presents a case study how CFD can be used to enhance model test data in an efficient way to provide the critical hydrodynamic conditions for structure analysis. Comparison of the measured free surface elevation of the calibrated waves with the time series of the numerical waves, as well as the measured and simulated relative wave probes time series and the slamming load time series show that the applied numerical wave events show similar physical conditions as those observed in the model test. The effect of the platform motion on the impact force is identified by comparison of the impact force time series of the simulation with and without platform motion against model test time series. The results demonstrate that the approach provides a clear improvement compared to numerical or model testing alone. The observed steep wave events are numerically reproduced in a simplified manner, instead of trying to reproduce measured events directly. This approach significantly reduces the computational time, as well as computational costs, to an industrially acceptable level. Traditional load estimation is not able to provide such reliable detailed local load history for structural design purpose at areas exposed to wave impacts. This new procedure, where CFD simulates realistic breaking waves with coupling to measured vessel motion, offers new possibilities for the design of structures subject to risk of wave impact loading.

Copyright © 2017 by ASME

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