Appropriate Rigid Body Correction for Analyzing the Dynamics of Rotating Structures Using 3D Digital Photogrammetry

Abstract

Stereophotogrammetry techniques have been used to measure high-speed dynamic systems for several years and are now being used to measure the motion of rotating systems, such as wind turbines and helicopter rotors. The blade vibratory motion of these systems is often considerably smaller than their rigid body dynamics, and to better understand the hidden structural dynamics of these structures, the extraneous movements can be subtracted from the collected data using rigid body correction (RBC) algorithms. Unfortunately, performing rigid body corrections on rotating systems is not always straightforward and the incorrect use of these algorithms can distort the measured dynamics of a system. Dynamic measurements have previously been taken on a rotating turbine and a RBC was performed on all rotor measurement points yielding unexpected dynamic behavior. This behavior was observed by processing the data using all measurement points on the turbine and observing the displacement versus time data for a single measurement point at the tip of one of the blades. A second RBC was performed using only the hub measurement points and the resulting processed dynamic behavior was very different. To better understand how RBC can affect the measured dynamics of rotating systems, a sensitivity study was conducted on the same rotating turbine. The results of this sensitivity study are presented within this work and conclusions on the size of the measurement point region that can be used in the RBC for this particular turbine and measurement point layout are made.