Wind Turbine Blade Test Method

From PDI

A method to test very large, compliant wind turbine blades utilizing a combination of forced displacement (direct attached actuators) and resonance actuators.

Existing Methods:

Patent US 2006/0037402A1 Resonance Test System This patent describes a method to use a linear hydraulic actuator attached to a wind turbine blade. Operation of the actuator with a mass attached to the piston rod excites the blade at resonance. The patent also shows excitation of the blade in the edgewise direction by means of a strut and bell crank connected to an actuator which is attached to the ground. The flapwise (resonance) test and edgewise tests do not run at the same frequency.

U.S. Patent Application Serial No. 10/520,011 Title: “Resonance Test System” Inventors: Musial, et al. Filing Date: December 29, 2004 This describes and improved method for applying uniaxial resonance.

Force displacement methods (direct attachment of an actuator to the test piece) are well known, but for large blades, the velocity and displacement demand on the actuator leads to expensive equipment and high energy demand. This problem is largely solved by the use of resonant test devices as described in the patents referenced above.

Problem with existing methods: For very long blades, it is difficult to get sufficient loading into a blade via the resonant test method. This potentially requires the use of additional resonant devices and may compromise the quality of the test.

Description The testing method uses a combination of force displacement testing and resonant testing in the same axis of motion. The resonant device and the forced actuation device are controlled in a coordinated fashion such that the frequency and phase relationship between devices is maintained.

In the most typical arrangement, 1 or more actuators are used near the root of the blade to impose loads at reasonably small displacements and velocities while one or more resonant devices are used further from the blade root. This combination of direct loading and resonant loading imposes greater energy into the blade with minimal equipment and provides the test designer with the ability to match the test amplitude more closely to the desired moment distribution.

The direct connected actuators (force displacement) and resonant actuators must be controlled to find and remain on the resonant frequency of the blade.

Details of Operation The connection of the forced displacement and resonant actuators is presented in both patents and other public domains.

The control of the system requires a blade resonant control test system which can search and find the blade resonance and hold the resonance during changes in the blade produced by blade degradation of environmental effects.

The master control is via the resonant test control system in conjunction with the resonant test actuator(s). An output of the resonant control system must include a signal indicating the frequency and phase of the blade resonance. This information is used to generate the input signal to the forced displacement actuator(s). The amplitude of the each of the input devices is controlled independently or in a coordinated fashion.

With this method testing of very long blades is possible with the greatest amount of test control using the least amount of equipment. In particular fewer resonant test devices (UREX/CRM)are needed for the test.