Adhesive bonded towers for wind turbines: Design, Optimization and Cost Analysis

In an increasingly competitive energy market, the cost of a wind power plant has become more important. A tubular steel tower supporting a wind turbine can amount to up to 20% of the overall turbine costs and its optimization may lead to substantial savings with regard to the costs and the use of materials. One important aspect of the design is connections between the tower’s sections and between the cans. The towers usually consist of steel segments, made of several welded cans (conical subsections), which are further connected by welded flanges. The welded connections have high risk of fatigue failure leading to the thick tower wall. Also, the flanges are very expensive. This research is focused on improving wind turbine towers by using adhesive bonded joints instead of welded joints and flanges. This idea is investigated and the principles of bonded connection are presented. Fatigue resistance is treated as the main discerning factor between the existing design and the proposed solution in this study. The first part of the project focuses on providing a design solution for replacing the bottom-most flange with the bonded joints. A comparative cost study of the proposed solution is also provided in this project. In the second part, optimization of the thickness has been investigated for the entire tower when the cans are bonded circumferentially using adhesives instead of welds. For the cost analysis of the proposed solution, an 80m reference tower was designed based on the stability and the fatigue assessment of the welds. The approach is use a reference 3MW wind turbine model in GH Bladed. The proposed bonded joint is a tubular-single lap joint based on implementation of simple analytical Volkersen Model. A design guideline for the adhesive bonded joint is presented. Furthermore, particular focus was given to the factors affecting a joint strength and their behavior in a bonded joint. Finally, the benefits in terms of fatigue strength, design simplicity, and cost savings are addressed in detail. According to this study, the replacement of the bottom-most flanges with an adhesive bonded joint provides a maximum cost reduction of 17%. This seems to be an economically feasible assembly solution. For the bonding of entire cans in the tower, only the top two cans can be bonded economically, keeping the remaining cans to be welded to each other. The replacement of welds in the entire tower by bonded joints is possible, however, in comparison to the existing solution it is not a feasible solution in terms of material and cost saving.

Subject

Windenergy

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Student theses

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master thesis

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