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This and the next 3 images are from:
Abdullah Mahmoud, “Analysis and design of spirally welded thin-walled steel tapered cylindrical shells under bending with application to wind turbine towers”, PhD dissertation, Johns Hopkins University, Baltimore, 2017
ABSTRACT: An important obstacle restricting the growth of wind-generated energy is the production of taller towers for wind turbines that can harvest energy from the steadier, stronger winds at higher elevations. Currently, the need to transport wind turbine tower sections to the construction site constrains the diameter of the section, which then limits the height of the tower. This limitation can be avoided if the tower sections are made on-site, and one potential method for on-site manufacturing is automated spiral welding. This thesis, which focuses largely on computational modeling for design, is part of a larger research effort to advance the application of spirally welded tubes (SWTs) in wind tower structures. With the new manufacturing technique, a wider range of tower diameters and thicknesses, and potentially more optimal thin-walled sections can be employed. Thin-walled shells are one of the most advanced and efficient forms of large structures; however, their behavior can be unstable and extremely sensitive to imperfections. For decades, the structural design of such shell structures relied on elastic buckling “knockdown factors” obtained from experimental results, but with the expansion in the capabilities of computational modeling, today design is working to leverage the power of shell finite element models that are geometrically and materially nonlinear with imperfections included (i.e. “GMNIA” analysis models). This thesis explores the analysis and design of spirally welded tapered cylindrical steel shells and complements experimental results conducted as a companion to this effort within the larger SWT effort. The thesis includes an introduction and historical background on the development of research on thin shells; a summary of relevant experimental work completed in the literature and in the SWT project; careful examination of geometric imperfections in the world of shells in general and spirally welded shells in particular; provides a practical finite element modeling protocol for predicting the flexural strength and collapse behavior of thin-walled spirally welded tapered steel tubes; validates the proposed modeling protocols for GMNIA models with SWT test results; extends the results to provide standard “reference resistance” curves that can be used for future GMNIA analyses by structural designers; and highlights the application to an archetype 3MW wind turbine tower using both classical and new analysis-based.
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