Appropriate rigid body correction of stereophotogrammetry measurements made on rotating systems

Stereophotogrammetry has typically been used to measure the response of non-rotating dynamic systems. More recently, this technique has been used to measure the motion of both small and large rotating systems. Often, the rigid body motion (RBM) of these systems is orders of magnitude larger than the flexible motion of interest and it may be desirable to remove the RBM using a measurement point subset. In earlier work, stereophotogrammetry was used to collect operating data on a small rotating wind turbine. Two rigid body correction (RBC) schemes were applied to this data generating very different results at one of the blade tips. The purpose of this work is to mathematically describe RBC and present the results of a small wind turbine RBC sensitivity study. This study shows how the selection of the measurement point subset used in the RBC can affect measured system dynamics. The sensitivity study can be used to determine the appropriate size of the measurement point region used in the RBC to examine the flexible response with respect to a rigid region of the structure. Performing RBC on rotating systems is not always straightforward and the incorrect application of these algorithms can distort dynamic measurements.