Optimisation of wind turbine foundations

[摘要] ENGLISH ABSTRACT: This study seeks to optimize the foundations of tall wind turbine support structures inSouth Africa. It is postulated that the concrete quantity can be reduced in gravity based foundations by incorporating the backfill material into the foundation design.The study was based on the development of finite element models consisting of gravity based foundation embedded in a founding material and connected to a wind turbine tower. Three main analyses were computed namely; Static non-linear push over analysis,Cyclic load analysis and Structural eigenvalue analysis. The purpose of the study was to investigate (a) soil-structure interaction in order to assess the infinite vs. finite soil stiffness effect on the natural frequency of the structure, (b) the stress distribution in the foundation in order to replace under-stressed parts with backfill material yet maintaining the same structural stiffness and vibrational behaviour that complies with thesoft-stiff structural vibration frequency domain, (c) the feasibility of using high density concrete towards foundation size reduction, as well as water usage reduction. Finally, a structural performance and cost comparison is drawn between a conventional andalternative foundation systems. A conceptual design guideline for the foundation system is also created for both geotechnical and structural design of the foundation.The study concludes that soil-structure interaction does influence the natural frequency of the wind turbine tower. Stiff soils result in higher natural frequency and less stiff soils result in a lower natural frequency. Secondly the critical sections that require structural concrete in a gravity based foundation are the section directly below the tower base and also the base of the foundation. The rest of the concrete is primarily for rotational stiffnessas a counterweight. Lastly, volumetric aggregate replacement is a feasible solution towardsincrease in the density of concrete and consequently reducing the concrete foundation size.The feasibility being based on the mechanical behaviour of the concrete material. The study recommends that finite element analysis be used in order to develop an optimum wind turbine foundation design.

[发布机构] Stellenbosch University