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TU Berlin

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MAXWAVE – Rogue waves – Forecast and impact on marine structures

Prof. Dr.-Ing. Günther Clauss, Dr.-Ing. Christian Schmittner

Within the past 20 years at least 200 supercarriers have been lost, each more than 200 meters long. The causes of the accidents are in many cases believed to be 'rogue waves'. These are individual waves of exceptional height and/or abnormal shape. In this project properties and forecasting abilities of extreme individual waves and wave groups are investigated. New design criteria considering the impact of rogue waves on ships and offshore structures will be derived. The innovation is the combination of new oceanographic knowledge and ocean wave data resources with new approaches to the design and operation of vessels and marine structures.

The objective of workpackage 7 is to model extreme wave events numerically and at model scale in a physical wave tank, furthermore to investigate wave/structure interaction, e.g. a semisubmersible or FPSO encountering a high wave group.

Lupe

The animated figure above shows a nonlinear wave evolution in the physical wave tank. One can see that a dangerous freak wave can develop from a wave group containing several high but harmless waves.

At the TUB a numerical technique is currently being developed for optimizing two dimensional extreme transient design waves. The method is based on potential flow theory and applies the finite element method. This numerical approach allows the modeling and simulation of extreme waves. Furthermore freak waves will be simulated in a physical wave flume. The electrical control signals are generated with an optimization process using sequential quadratic programming and a numerical wave tank. The main advantage of this approach is that local parameters such as wave height, wave length and crest elevation can be taken into account.

Lupe

In addition measured dangerous ocean waves or wave groups are investigated to identify most dangerous wave systems. As a first example a semisubmersible of type GVA4000 was build in model scale 1:81 and tested in the wave tank. Furthermore the behavior of this semisubmersible was numerically simulated using a panel method program based on potential theory. Numerical and experimental results are presented e.g. at OMAE2002 and ISOPE2003. A key parameter for the seaworthyness of an offshore platform is the airgap left in extreme wave conditions (distance between wave crest and underside main deck). The airgap was also experimentally (using wave probes at different positions of the deck) and numerically investigated. The animated picture above gives you an impression of the selected semisubmersible in rogue waves.
If you want to see more of the model tests, you can download a video.

Förderung: The research project is funded by the European Commission under the Fifth Framework Programme: Sustainable Marine Ecosystems within the Energy, Environment and Sustainable Development Project Number: EVK:3-2000-00544

Laufzeit: 01.04.2001 - 31.03.2004

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