Wind Turbine Blade Structural Member with Variable Stiffness
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Solution Overview
Problem
Wind turbine blades face challenges in managing deflection due to overlapping exciting frequencies and resonant frequencies, leading to increased fatigue loading and reduced annual energy production, as existing solutions either add excessive mass or compromise on material strain and tower clearance.
Innovation Solution
A structural member with a spar assembly comprising first and second stringers, rigid ties, and tension ties that pivotally secure the stringers, providing initial resistance to deflection and increasing resistance nonlinearly as the blade deflects, shifting shear loads to longitudinal loads and maintaining separation between spar caps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional mass is added to the blade to shift operating frequencies below exciting frequencies, then frequency overlap is avoided, but blade weight increases and fatigue loading increases
Solution Approach 1:
The patent applies passive dynamic control through spring elements and dampers that automatically adjust blade stiffness and damping characteristics in response to varying operational conditions. The spring elements (224, 226) and dampers (228, 230) create a dynamic system that adapts to different wind speeds and loading conditions, eliminating the need for additional mass while avoiding frequency overlap through real-time stiffness modulation.
Solution Approach 2:
The invention changes the stiffness parameter of the blade structure dynamically through the spring-damper mechanism. By varying the effective stiffness of the spar assembly through the spring elements, the blade's natural frequencies shift in response to operating conditions, preventing frequency overlap without requiring mass addition. The dampers simultaneously adjust damping parameters to control fatigue loads.
2Strength
If blade stiffness is increased to meet extreme load requirements, then tower clearance and material strain limits are satisfied, but fatigue loading increases and energy production decreases
Solution Approach 1:
The spring-damper system creates a dynamically adaptable stiffness characteristic that provides high stiffness when needed for extreme loads while allowing greater flexibility during normal operation. The spring elements (224, 226) engage preferentially under extreme loading conditions to provide additional stiffness, while the dampers (228, 230) dissipate energy to reduce fatigue loads during regular cycling, thereby maintaining both strength and productivity.
Solution Approach 2:
The spring elements act as beforehand cushioning by being pre-positioned to engage before extreme loads cause damage. The springs are configured to become active at specific deflection thresholds, providing progressive stiffness enhancement that protects the blade structure during extreme events while remaining inactive during normal operation to avoid unnecessary fatigue loading.
3Reliability
If operational constraints are applied to avoid overlapping frequencies, then resonance is prevented, but annual energy production is reduced
Solution Approach 1:
Instead of static operational constraints, the invention implements dynamic frequency adjustment through the spring-damper system. The varying stiffness provided by the spring elements (224, 226) continuously shifts the blade's natural frequencies to avoid overlap with exciting frequencies across the full operational range, eliminating the need for restrictive operational constraints and maximizing energy production while maintaining resonance avoidance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows wind turbine blades to deflect readily under lower loads, reducing stress and increasing fatigue life while preventing tower strikes and exceeding material strain limits by stiffening upon reaching a threshold deflection.
Implementation Method 1
A structural member with a spar assembly comprising first and second stringers, rigid ties, and tension ties that pivotally secure the stringers, providing initial resistance to deflection and increasing resistance nonlinearly as the blade deflects
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A wind turbine blade (12) having a structural member (10) including: a first stringer (40); a second stringer (42); a rigid tie (44) pivotally secured to the first stringer and pivotally secured to the second stringer; and a tension tie (46) secured to the first stringer and the second stringer and arranged to experience tension during increasing lateral displacement between the first stringer and the second stringer as the wind turbine blade bends in a first direction (48). Unlike a conventional wind turbine blade truss, the structural member (10) provides nonlinear resistance to bending of the blade.