Failure analysis of wind turbine blade under critical wind loads
Highlights
► Wind turbine blades often exhibit surface delamination and cracks. ► Contributing factors in this damage and their mechanisms are investigated. ► Structural mechanics of wind turbine blade failure are constructed. ► The data provide a reference for improving risk management and disaster prevention.
Introduction
In September, 2008, super typhoon Jangmi caused significant damage in Taiwan. In wind turbines (WTs) located in the Changhua Coastal Industrial Park in Taichung, maximum wind speed readings exceeded 53.4 m/s. After the typhoon damage inspection and repair teams dispatched by the owners found that five wind power generators, #11, #12, #14, #15, and #23, exhibited damage, including cracks and surface delamination in seven blades (Fig. 1).
Specifically, the original supplier of the wind turbine determined that six of the seven blades were irreparable and that only one blade could be repaired and reinstalled. The damaged wind turbine blades were located in the Changhua Coastal Industrial Park located in northwest Taiwan (Fig. 2) approximately 5 km south of the Dadu River Estuary. This industrial park is divided into three sections, Xian Xi, Lun Wei, and Lu Gang. Notably, all the damaged wind turbine blades were located in the Lun Wei section.
To understand the mechanisms that trigger blade delamination and damage under strong winds, this study performed on-site inspections, material lab experiments, and a literature review. Based on the results, a model was constructed to facilitate understanding of the structural mechanics of WTs. After comprehensively analyzing potential causes, we identified the surface delamination mechanism, the primary causes of the incident, and strategies for preventing similar damage in the future.
Section snippets
Literature review
The Taiwan government has responded by passing the renewable energy development act on June 12, 2009, which was implemented in January, 2010. This policy is expected to increase domestically generated energy, promote diversification of energy sources, reduce greenhouse gas emissions, and facilitate development of the renewable energy industry [1]. Since wind power generation is a new government-supported energy industry, the contributing factors in accidents involving WTs must be examined to
Research procedure
Disaster damage incidents can result from the effects of one or more factors [16], [17]. Therefore, investigation procedures and required examinations of actual incident investigations must be performed using the divide-and-conquer approach as shown in Fig. 4. The process includes collecting relevant engineering data and historical cases, performing on-site inspections to determine the underlying causes of accidents, taking samples for lab experiment, and conducting relevant modeling to
Wind turbine design specifications
After reviewing the design drawings from the original manufacturer [21], a field survey of damaged blades was performed to determine the geometrical structure of WT blades and to facilitate subsequent model building. A single blade weighs approximately 6.5 tons (14,500 lb). Fig. 6 is a schematic diagram showing the dimensions of the blade. The length from the hub to blade tip is approximately 39.5 m, the maximum width of the blade is approximately 3.317 m, and the width of the tip is approximately
Geometric scan and model construction
The stress and strain on the wind turbine blade induced by different wind speeds were analyzed using the ANSYS finite element analysis software system. First, a geometric model of the blade structure constructed according to the actual dimensions was entered into the software for analysis. This enabled stress and strain modeling under set conditions. The analysis results could also be compared with the actual blade damage when calculating the critical wind-speed resulting in the blade damage.
To
Potential incident-causing factors
Based on the analysis of collected data and historical case review, three main causes of damage incidents were identified: (1) insufficient blade material strength, (2) wind frequency and resonance effects, and (3) human error during the installation stage.
Conclusions and suggestions
This work modeled blade behavior under varying wind-speed conditions. The analysis results indicated that the blades can resist forces induced by a wind-speed of 80 m/s, which exceeds the maximum instantaneous wind-speed of 53.4 m/s recorded during Typhoon Jangmi. Therefore, in the absence of other external forces, no blade failures would have occurred during the typhoon season.
In addition, a series of frequencies for local natural vibration modes were modeled. Recommendations in past related
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