Abstract
Beam finite-element (FE) models have been instrumental in the predictive simulation of wind turbine blades. However, modern blades are challenging conventional design assumptions and analysis tools, due to large, non-linear deflections and the uptake of traditionally unexploited stiffness coupling coefficients.
More specifically, optimised turbine designs are featuring blades with greater radii and increased
compliance [1], thus deflections at ultimate loading are well within the non-linear elastic region and are incorrectly predicted by linear models [2]. In addition, such designs are exploring the benefits of aeroelastic tailoring either through geometric or material bend-twist coupling—hence accurate prediction of blade
loads in response to small changes in the twist of aerofoil sections, and vice versa, is imperative.
In this work, high-order finite beam elements [3], in both a linear and co-rotational non-linear
framework, are used to simulate the static test loading of an existing 7 MW wind turbine blade. The blade is an 83.5m swept blade [4], providing a good test case for predicting non-linear, coupled deflections. Additionally, a study into the convergence of high-order beam elements is presented to illustrate the
benefits that they provide for modelling of modern blade structures.
This study highlights the necessity of non-linear beams in accurately predicting deflections of modern wind turbine blades, as a linear beam severely underpredicts deflections in an ultimate loading scenario (i.e. linear beam tip deflection 9% lower than non-linear for flapwise load case). Additional findings from the convergence study illustrate that high-order beam elements result in converged beam states (e.g. coupled beam deflections and modal frequencies) with far fewer nodes than conventional two-node
elements. Given the large number of two-node elements required for convergence of this particular blade (Figure 1—121 nodes with 120 two-node elements vs 61 nodes with 30 three-node elements), it is clear that high-order beam elements can improve the computational efficiency of aero-elastic simulations. Furthermore, in an optimisation setting, the number of conventional two-node elements required for accurate structural modelling of large, tailored blades may even tend toward the impractical.
More specifically, optimised turbine designs are featuring blades with greater radii and increased
compliance [1], thus deflections at ultimate loading are well within the non-linear elastic region and are incorrectly predicted by linear models [2]. In addition, such designs are exploring the benefits of aeroelastic tailoring either through geometric or material bend-twist coupling—hence accurate prediction of blade
loads in response to small changes in the twist of aerofoil sections, and vice versa, is imperative.
In this work, high-order finite beam elements [3], in both a linear and co-rotational non-linear
framework, are used to simulate the static test loading of an existing 7 MW wind turbine blade. The blade is an 83.5m swept blade [4], providing a good test case for predicting non-linear, coupled deflections. Additionally, a study into the convergence of high-order beam elements is presented to illustrate the
benefits that they provide for modelling of modern blade structures.
This study highlights the necessity of non-linear beams in accurately predicting deflections of modern wind turbine blades, as a linear beam severely underpredicts deflections in an ultimate loading scenario (i.e. linear beam tip deflection 9% lower than non-linear for flapwise load case). Additional findings from the convergence study illustrate that high-order beam elements result in converged beam states (e.g. coupled beam deflections and modal frequencies) with far fewer nodes than conventional two-node
elements. Given the large number of two-node elements required for convergence of this particular blade (Figure 1—121 nodes with 120 two-node elements vs 61 nodes with 30 three-node elements), it is clear that high-order beam elements can improve the computational efficiency of aero-elastic simulations. Furthermore, in an optimisation setting, the number of conventional two-node elements required for accurate structural modelling of large, tailored blades may even tend toward the impractical.
Original language | English |
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Number of pages | 1 |
Publication status | Published - 20 Jun 2019 |
Event | Wind Energy Science Conference 2019 - University College Cork, Cork, Ireland Duration: 17 Jun 2019 → 20 Jun 2019 https://www.wesc2019.org/ |
Conference
Conference | Wind Energy Science Conference 2019 |
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Abbreviated title | WESC2019 |
Country/Territory | Ireland |
City | Cork |
Period | 17/06/19 → 20/06/19 |
Internet address |
Research Groups and Themes
- Bristol Composites Institute ACCIS
Keywords
- wind turbine blade
- non-linear
- finite element
- higher order