This EDB-DNV-IPP project deals with the optimal design problem of the offshore wind support structure system. An iterative optimization approach utilizes in designing a 3-legged jacket substructure (Fig. 1), followed by detailed dynamic and stability assessments of the design in comparison to the reference 4-legged jacket substructure (Fig. 2) are done.
Results showed that the 3-legged jacket substructure can be a more cost-efficient support structure design in the transition water depth as it reduces approximately 17% of the structural mass requirement as well as featuring a 25% less number of welded joints. The jacket joints also fulfilled all the design FLS and ULS requirements, while the leg side of the mud-brace joint was found to be the critical joint in the design process. The members were also not exposed to column buckling failure albeit some of the members were in the column buckling zone. In the eigen analysis, the natural frequencies of the design jacket models were within the safe operating limits, away from resonance conditions.
On-going study includes a gradient based optimization framework to solve this dynamic constrained optimization problem with several key features include:
- the dynamic analysis in time domain, while including a comprehensive list of limit state functions (Eigenfrequency, ULS and FLS) as required by the industry standards in the design process.
- The sensitivity analysis in a semi-analytical manner using the Direct Differentiation Method (DDM).
- Chew, Kok Hon; Muskulus, Michael; Zwick, Daniel; Ng, E.Y.K; Tai, Kang, "Structural Optimization and Parametric Study of Offshore Wind Turbine Jacket Substructure”, pp. 203-210, The Proceedings of 23rd International Ocean and Polar Engineering Conference, Anchorage, Alaska, USA, Jun 30- Jul 5 2013, www.isope2013.org. ISBN 978-1-880653-99–9 (Set); ISSN 1098-6189 (Set)
- K.H. Chew, Michael Muskulus, Daniel Zwick, E.Y.K. Ng, K. Tai, “Offshore Wind Turbine Jacket Substructure-A Comparison Study between Four-Legged and Three-Legged Designs”, Journal of Ocean and Wind Energy, ISOPE, Vol 1, No 2, (2014), pp. 74-81.
- Chew, K.H., Tai, K., Ng, E.Y.K. and Muskulus, M. “Optimization of Offshore Wind Turbine Support Structures Using Analytical Gradient-Based Method”, 12th Deep Sea Offshore Wind R&D Conference, EERA DeepWind’15 Conference. Trondheim, Norway, 4 – 6 February 2015. Selected paper for Energy Procedia, 2015 (ISSN: 1876-6102, Elsevier, www.elsevier.com/locate/procedia). See also “NTNU Open” http://brage.bibsys.no/xmlui/handle/11250/223328, Technical Report number: BAT/MB/OW-R01/2015, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
- K.H. Chew, Michael Muskulus, Srikanth Narasimalu, K. Tai, Ng E.Y.K. “Fatigue Sensitivity Analysis of Offshore Wind Turbine Structures”, Proceedings of 11th World Congress on Structural and Multidisciplinary Optimisation 07th -12th, June 2015, Sydney Australia