INVESTIGATIONS ON SCOUR DEVELOPMENT AT TRIPOD FOUNDATIONS FOR OFFSHORE WIND TURBINES: MODELING AND APPLICATION

Arne Stahlmann, Torsten Schlurmann

Abstract


Regarding offshore constructions, there is still a lack in knowledge of scour progression for complex structures like foundations for offshore wind energy converters at present, which is however necessary for its dimensioning. As an example of such complex structure types, tripod foundations are constructed in German offshore wind farms at present. In order to describe physical processes and influencing factors on scour progression from a scientific point of view, comprehensive investigations on the scouring phenomena for tripod foundations have been carried out and will be partly presented here. The overall investigation method consists of a combination of 1:40 small and 1:12 large scale physical model tests in wave flumes, numerical simulations using CFD methods and in-situ measured scour data. For the numerical modeling part, a sediment transport model formulation has been implemented into OpenFOAM software code. The results show a general variability of scour depending on the load boundary conditions and structural parameters. Scours occur both at the foundation piles and directly under the structure, which in this form could not be predicted using standard approaches, but which has to be taken into account when regarding the soil mechanical stability and the final dimensioning of the foundations.

Keywords


Scour, numerical modeling, physical modeling, tripod

References


DHI. 2007. Borkum West - Hydrographische Standortbedingungen. Modellierung und Statistische Analyse. Syke.

van Driest, E.R. 1956. On turbulent flow near a wall. J. Aeronaut. Sci. 23, 1007-1011, 1036.

Engelund & Fredsøe. 1976. Sediment Transport Model for Straight Alluvial Channels. Nordic Hydrology, 7(5):293-306.

Fredsøe, J., Deigaard, R. 1992. Mechanics of Coastal Sediment Transport. Advanced Series on Ocean Engineering - Volume 3. World Scientific.

Garcia, M.H. 1999. Sedimentation and Erosion Hydraulics. Hydraulic Design Handbook, Chapter 6, Larry Mays, ed., McGraw-Hill, Inc.

Göthel, O. 2008. Numerical modeling of flow and wave induced scour around vertical circular piles.

Institut für Strömungsmechanik und Elektronisches Rechnen im Bauwesen der Leibniz Universität Hannover, Bericht 76/2008, Hanover.

Hansen, M. et al. 2011. Probabilistic Safety Assessment of Offshore Wind Turbines. Annual Report 2010, Hanover.

Hildebrandt, A., Schlurmann, T. 2012. Breaking Wave Kinematics, local Pressures and Forces on a Tripod Support Structure, Proceedings of the Coastal Engineering Conference, No. 33, Santander.

Hoffmans, G.J.M.C., Verheij, H.J. 1997. Scour Manual. Balkema, Rotterdam.

Jacobsen, N.G., Fredsøe, J. 2011. A Full Hydro- and Morphodynamic Description of Breaker Bar Development. Ph.D. thesis, Department of Mechanical Engineering, Technical University of Denmark.

Jacobsen, N.G., Fuhrmann, D.R., Fredsøe, J. (in print). A Wave Generation Toolbox for the Open-Source CFD Library: OpenFoam. Int. J. Numerl. Meth. Fluids.

Jasak, H. 1996. Error Analysis and Estimation for the Finite Volume Method with Application to Fluid Flows. Ph.D. thesis, Imperial College of Science, Technology and Medicine. London.

Kovacs, A., Parker, G. 1994. A New Vectorial Bedload Formulation and Its Application to the Time Evolution of Straight River Channels. Journal of Fluid Mechanics, 267:153-183.http://dx.doi.org/10.1017/S002211209400114X"

Menter, F. 2003. The SST Turbulence Model with Improved Wall Treatment for Heat Transfer Predictions in Gas Turbines. Proceedings of the International Gas Turbine Congress (2003). Tokyo: November 2-7.

Roulund, A., Sumer, B.M., Fredsøe, J. 2005. Numerical and experimental investigation of flow and scour around a circular pile. Journal of Fluid Mechanics, 534:351-401.http://dx.doi.org/10.1017/S0022112005004507

Soulsby, R.L. 1997. Dynamics of marine sands. Thomas Telford Ltd. London.

PMCid:1343100

Stahlmann, A., Schlurmann, T. 2010. Physical Modeling of Scour around Tripod Foundation Structures for Offshore Wind Energy Converters, Proceedings of the Coastal Engineering Conference, No. 32, Shanghai.

Stahlmann, A., Schlurmann, T. 2012. Investigations on Scour at Tripod Foundations [Kolkbildung an komplexen Gründungsstrukturen für Offshore-Windenergieanlagen: Untersuchungen zu Tripod-Gründungen in der Nordsee]. Bautechnik 89(5):293-300.http://dx.doi.org/10.1002/bate.201200009

Sumer, B.M., Fredsøe, J. 2002. The Mechanics of Scour in the Marine Environment. World Scientific Publishing Co. Pte. Ltd.

Wilms, M., Stahlmann, A., Schlurmann, T. 2012. Investigations on Scour Development around a Gravity Foundation for Offshore Wind Turbines, Proceedings of the Coastal Engineering Conference, No. 33, Santander.

Zanke, U.C.E., Hsu, T.-W., Roland, A., Link, O., Diab, R. 2011. Equilibrium scour depths around piles in noncohesive sediments under currents and waves. Coastal Engineering, Vol. 58, 986-991.http://dx.doi.org/10.1016/j.coastaleng.2011.05.011


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