the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Feb 2024
Structural Design Optimization of Laminated Composites for Vertical Axis Wind Turbine Blades: A Single Objective Approach
Abstract. Vertical-axis wind turbines are considered a proper solution for today's energy needs. To make it affordable for domestic usage, this requires a reduction in the turbine cost, blade weight, and an increase in blade life. The challenge in VAWT blade design is fatigue and blade life prediction, besides surviving centrifugal force and repeated load pattern effects. The paper focuses on the blade structure modelling and optimization to assess the design for integrity, fatigue, life, sustainability, and cost. The presented model can examine varied materials, including new biodegradable materials, while reducing computation time and resources. The structure analysis is based on classical lamination theory (CLT) and polynomial failure theory (Tsai-Hill and Tsai-Wu). Fatigue analysis and blade life are based on damage evaluation using Miner’s rule for loading steps, evaluated stresses and strains, and loading cases. The approximation model simplifies the dynamic and fatigue analysis procedures to make the model integrable with the optimization method. The beam element method is used to approximate the fundamental frequencies of blade structure. The genetic algorithm is the optimization method used for single objective function, non-linear constrained, mixed integer problem. Decision variables vary according to the scope of optimization which includes the five main composite structure parameters: lamina thickness, orientation, volume fraction, and material selection for resin and fiber. However, in the case of pre-defined laminae materials, only the thickness, orientation, and selection index are used. The commercial finite element software ANSYS is used to validate results.
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RC1: 'Comment on wes-2024-1', Steffen Czichon, 20 Feb 2024
The paper presents a methodology to optimize laminate thickness, layup/ orientation and choice of material for a VAWT rotor blade. The method is clearly described and seems reasonable, except for some minor flaws (see attached pdf with more comments).
However, it is unclear how the presented approach provides novelty and brings benefit to the scientific community, especially since the paper does not include any experimental validation. To the reviewer, it seems like a solid engineering excercise. The results of the study do not provide any thought provoking insights.
If possible, the authors should clearly identify where the paper provides added value to the scientific community and center the paper around this.-
AC1: 'Reply on RC1', Ahmed Geneid, 23 Apr 2024
Dear Prof Steffen
Thanks very much for your precious comments.
All the comments cited within text were adjusted in the final version. The reply for these comments is attached in the supplement (this is not the final version of the manuscript).
Concerning the novelty and the contribution to scientific community, please find the following points:
- The paper presents a simple fatigue model to predict blade life. The presented life prediction model could be easily be integrated into optimization approach.
- The paper presents a single objective function optimization model to easily compare the effect of the blade’s life prediction OBF. The comparison between four objective functions shows that blade life has significant effect on the final design, as compared to mass, cost and natural frequency.
- The paper suggests that the study of blade life in the structure optimization problem be implemented using multi-objective functions approach.
- The presented model is very easy to implement and reduces computational time to great extent.
Consequently, the paper presents novelty in using simple fatigue model to present blade life prediction model that could be used in optimizing the blade structure design problem. The need for modeling this objective is clarified by comparing the optimization results of single objective problem. the comparison includes mass, cost, life and natural frequency. This shows that life has significant effect on improving optimized results compared to other objectives.
Hence, the main scientific contributions are the presentation of life prediction model and explaining the significance of the objective using the SOBF (Single Objective Function) comparison. Another indeed finding, the paper recommends the implementation of MOBF (Multi Objectives Functions).
Thanks & Regards
Citation: https://doi.org/10.5194/wes-2024-1-AC1
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AC1: 'Reply on RC1', Ahmed Geneid, 23 Apr 2024
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RC2: 'Comment on wes-2024-1', Anonymous Referee #2, 25 Mar 2024
General Comments
- Scientific significance
- The manuscript provides limited scientific significance in the area of structural design optimisation. The application of genetic algorithm-based optimisation to a vertical axis wind turbine blade is of relevance to the WES community, but the manuscript fails to adequately highlight the main areas of novelty in the presented research.
- The introduction section of the paper in particular fails to identify the gaps in research in this area and where the manuscript adds novelty or advances the state-of-the-art.
- Scientific quality
- The methods are well presented overall, however, there are several important gaps left in the methodology that make the manuscript difficult to fully assess. These include: considerations for the manufacturability of the optimised blade structures, the reasoning behind the definition of the objective functions, adequate descriptions of the structural design of the blade, and adequate descriptions of the FEA model and aerodynamic model used.
- Presentation quality
- The missing elements from the methods section mean the full scope of the conclusions cannot be assessed (e.g. the discussions of the comparison between the FEA and CLT models).
- The abstract presents an appropriate overview of the manuscript, and the figures/tables throughout are appropriately chosen. However, the quality of the images and descriptions of their relevance within the body of the text should be improved. There are several instances of imprecise or incorrect language used throughout the manuscript.
Specific Comments
- See the attached reviewed manuscript for specific comments.
Technical Corrections (typing errors, etc.)
- See the attached reviewed manuscript for highlighting of technical corrections.
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AC2: 'Reply on RC2', Ahmed Geneid, 23 Apr 2024
Dear Professor,
Thanks very much for your precious comments.
Please find the attached supplement containing reply on comments within text.
All the comments were counted in the final version.
Scientific significance: the research gap and the novelty were clarified in the final version according to recommendation by reviewers.
Scientific quality: the following points were clarified in the methodology according to the reviewer comments:
- The manufacturability.
- The objective functions reason.
- The description of structure design.
- The description of FEA model (validation).
- The aerodynamic model.
Presentation Quality:
- The comment about language were revised according to reviewers’ comment and edited in the final version.
- The quality of images was improved, the description within text was clarified in the final version.
- Added a comparison discussion about the FEA and CLT models.
In the end thanks very much for your precious comments that added great value for the final manuscript.
Thanks & Regards
Citation: https://doi.org/10.5194/wes-2024-1-AC2
- Scientific significance
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CC1: 'Comment on wes-2024-1', David Wood, 27 Mar 2024
The first sentence of the Abstract and the second sentence of the Introduction are highly contentious. Given the huge amount of rooftop solar photovoltaics around the world, wind energy is currently not the “proper solution for domestic usage” and the commercial implementation of vertical axis wind turbines (VAWTs) lags monumentally behind that of horizontal-axis wind turbines (HAWTs). There are important R & D programs designed to change these situations, such as the NREL distributed wind aeroelastic modeling program Distributed Wind Aeroelastic Modeling | Wind Research | NREL which includes VAWTs. Part of the technology barrier for VAWTs has been the lack of detailed aeroelastic modeling capability, but this is starting to change with the advent of the Sandia OWENS software Offshore Wind Energy Simulation (OWENS) – Licensing and Technology Transfer (sandia.gov) which can be used for onshore turbines. Nevertheless, common aeroelastic codes like OpenFAST do not include vertical-axis turbines and the current IEC standard for small turbines (IEC 61400-2) excludes them. This manuscript is aimed at improving the aeroelastic modeling of VAWTs, in particular, the design of the blade structure. This aim is desirable, and the methodology used appears to be appropriate in general, so I welcome the contribution. There are, however, several important issues that must be addressed before the manuscript can be accepted. These are:
- As suggested by the above, the manuscript does not properly describe the context of the study. The important statements in the first two paragraphs of the Introduction are given without references or justification. VAWTs do not experience “extreme” centrifugal loading (L80) because their typical operational tip speed ratio is significantly lower than that of HAWTs, even for small turbines. There is little information about the specific features of small turbines as indicated by the reference to the IEC standard for large ones, instead of to IEC 61400-2. There is no reference to Clausen et al. (2023, additional references below) which is relevant even though it focuses on HAWTs. The statement on L105 about the lack of procedures for fatigue design of composites is incorrect. The simplified loads model of IEC 61400-2 includes a fatigue case with specific instructions about the methodology to be used. It does not provide detailed guidance for all possible blade materials but it is a good starting place. Further work on small HAWT fatigue loads modeling is described in Evans et al. (2021). The last two paragraphs of the Introduction are repetitious.
- The description of the blade model and its loading is incomplete. We are not given any information about the composite layup or whether a spar is used or not. A spar is used in HAWT blades of all sizes to prevent buckling but this issue for VAWT blades is not discussed. The layup of small and large HAWT blades usually comprises unidirectional matting to withstand the radial centrifugal loads and “tri-ax” layers for torsional rigidity. These requirements will change for a VAWT blade so the layup is of major interest. No details are given of the fatigue loads. Most wind turbine fatigue loads are once-per-cycle loads of which the loads associated with the azimuthal variation in blade torque are likely to be critical for VAWTs. Again, no information is given. L226 describes the only validation of the blade model. This is against an Ansys simulation but no details are given. This deficiency is very important as we have no other way to assess the validity of the results.
- Several deficiencies in the presentation were noted above. Others include the forward referencing of equations, for example. Equation (2) is referred on L135 but not given until after L170. Equations should be placed in the sentence that naturally includes them. Many abbreviations, symbols and subscripts are not defined or explained and the subscripts and superscripts in Equation (4) are not aligned.
- The description and use of the genetic algorithm NSGA should be improved. The statement on L209 about each “iteration of the algorithm is wrong. The use of a random population is restricted to the first iteration. “Blade” is misspelt in figure 2 and the label for figure 3 should have “NSGA” not “NSDGA”. L229 and elsewhere mentions four objectives: mass, cost, natural frequency, and lifetime. Each objective was optimized separately, and no consideration was given to using a composite objective function. Composite objective functions have been used for small HAWT blades for a long time, eg Sessarego & Wood (2015) who also used the NSGA, and Pourrajabian et al. (2021). Exploring the use of one for VAWTs would be valuable.
Additional References
Clausen, P. D., Evans, S. P., & Wood, D. H. (2023). Design, manufacture, and testing of small wind turbine blades. In Advances in wind turbine blade design and materials (pp. 441-461). Woodhead Publishing.
Evans, S., Dana, S., Clausen, P., & Wood, D. (2021). A simple method for modelling fatigue spectra of small wind turbine blades. Wind Energy, 24(6), 549-557.
Pourrajabian, A., Dehghan, M., & Rahgozar, S. (2021). Genetic algorithms for the design and optimization of horizontal axis wind turbine (HAWT) blades: A continuous approach or a binary one? Sustainable Energy Technologies and Assessments, 44, 101022.
Sessarego, M., & Wood, D. (2015). Multi-dimensional optimization of small wind turbine blades. Renewables: Wind, Water, and Solar, 2, 1-11.
Disclaimer: this community comment is written by an individual and does not necessarily reflect the opinion of their employer.Citation: https://doi.org/10.5194/wes-2024-1-CC1
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