Comparison of wind turbine tower failure modes under seismic and wind loads

This paper studies the structural responses and failure modes of a 1.5-MW horizontal-axis wind turbine under strong ground motions and wind loading. Ground motions were selected and scaled to match the two design response spectra given by the seismic code, and wind loads were generated considering tropical cyclone scenarios. Nonlinear dynamic time-history analyses were conducted and structural performances under wind loads as well as short- and long-period ground motions compared. The results show that under strong wind loads the collapse of the wind turbine tower is driven by the formation of a plastic hinge at the lower section of the tower. This area is also critical when the tower is subject to most ground motions. However, some short-period earthquakes trigger the collapse of the middle and upper parts of the tower due to the increased contribution of high-order vibration modes. Although long-period ground motions tend to result in greater structural responses, short-period earthquakes may cause brittle failure modes in which the full plastic hinge develops quickly in regions of the tower with only a moderate energy dissipation capacity. Based on these results, recommendations for future turbine designs are proposed

Nonlinear response history analysis and collapse mode study of a wind turbine tower subjected to tropical cyclonic winds

The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases

Numerical ABL Wind Tunnel Simulations with Direct Modeling of Roughness Elements through Immersed Boundary Condition Method

Reproduction of atmospheric boundary layer wind tunnel experiments by numerical simulation is achieved in this work by directly modeling with immersed boundary method the geometrical elements placed in the wind tunnel's floor to induce the desired characteristics to the boundary layer.The wind tunnel has a cross section of 2.2 m x 2.25 m, with an inlet region 14 m long and a working region 2 m long. Boundary layer development is shaped up with a series of cubical elements, 3 cm in side, placed in a regular staggered arrangement with a 15 cm spacement. Vortex induction, Standen spires type elements, of 13,4 cm height, and a wall of 31.5 cm height are placed at the inlet. This arrangement is used to reproduce a representative urban site boundary layer (figure 1).The numerical model is implemented on the basis of the open source modelcaffa3d.MBRi [Usera et al 2008], which uses a finite volume method over block structured grids, coupled with various LES approaches for turbulence modeling and parallelization through domain decomposition with MPI [Mendina et al 2013]. Simulations were setup with approximately 2 million cells per block, with a 26 block arrangement. The computational grid is horizontally uniform with a resolution of 1.04 cm x 1.04 cm and nonuniform in vertical direction with the grid points concentrated near the floor . The grid spacing is geometrically stretched away from the floor with a minimum value of 1mm. The time step is 0.1 second and the computation is distributed in 26 cores on the Cluster-FING infraestructure [www.fing.edu.uy/cluster]. The Immersed boundary method approach followed the work of [Liao et al 2009]. Numerical simulation results are compared to wind tunnel measurements for the mean velocity profiles (figure 2), rms profiles and spectrums, providing good overall agreement. We conclude that the Immersed Boundary Condition method is a promising approach to numerically reproduce ABL Boundary Layer development methods used in physical modeling.Agencia Nacional de Investigación e Innovació

Estimation of wind loading on trees for a vegetated building envelope: a multi-scale experimental study

With the sustainability movement, vegetated building envelopes are gaining more popularity, which requires special wind effect investigations both from sustainability and resiliency perspectives. This paper focuses on wind load estimation on small- and fullscale trees used as part of green roofs and balconies. The small-scale wind load assessment was carried out using the Politecnico di Milano wind tunnel. The large trees were investigated at the new 12-fan Wall of Wind facility, Florida international University. The effect of Reynold's number and shape change on the overall loads measured at the base of the trees (near the roots) has been investigated by testing at different modelscales and wind speeds. In addition, destructive tests were conducted to examine the security of the trees in soil and to assess the effectiveness of a proposed structural mitigation system