The research objective of this project is to integrate novel dynamic experimental measurements and computational modeling to predict the total spatial response and most importantly, how internal structural members respond to externally induced dynamic loads. For many complex composite structures (e.g. wind turbine, helicopter blades and other large flexible structures), mechanical failure is not externally apparent and typically occurs at the interfaces between the structure's surface and the internal ribs or stiffening members. Unfortunately, the interior dynamic response due to time-varying environmental, aerodynamic, and operating loads is not currently predictable from measured data. The proposed research will examine the use of analytical shape expansion functions for a large number of measured distributed points while rotating to predict interior dynamic stress-strain information at intricate joint interfaces, where failure often occurs. Such an approach will also enable the estimation of the externally applied distributed forces that are currently not measurable. The modeling approach can be applied to virtually any structure that has intricate joint interfaces by using a reduced number of measured degrees of freedom to interrogate or monitor a structure?s integrity. The proposed research is a new technology that will enable full-field dynamic measurement of rotating structures in operation, resulting in an improved understanding of the structural response of blades in flight. Both graduate and undergraduate students involved will gain an appreciation for current research areas important to industry and academia. The analytical tools can be used to create visually stimulating data that connects the effect of design decisions to the vibration response, and examples from music and sports can be tailored to the interest of different audiences to show how scientific research can contribute to our everyday lives. A strong outreach effort, building on previous successes, will be implemented using the animated image correlation data to motivate women and K-12 students to become interested in science and engineering.
PI: Christopher Niezrecki Awardee: University of Massachusetts Lowell Award Number: 0900534 Award Expires: 08/31/2012 Program Officer Name: Eduardo A. Misawa Program Officer Email Address: emisawa@nsf.gov Program Officer Phone Number: (703)292-8360 The research objective of this project was to integrate novel dynamic experimental measurements and computational modeling to predict the total spatial response and most importantly, how internal structural members respond to externally induced dynamic loads. For many complex composite structures (e.g. wind turbine, helicopter blades and other large flexible structures), mechanical failure is not externally apparent and typically occurs at the interfaces between the structure’s surface and the internal ribs or stiffening members. Unfortunately, the full-field and interior dynamic response due to time-varying environmental, aerodynamic, and operating loads is not currently predictable from measured data. The research conducted examined the use of analytical shape expansion functions for a large number of measured distributed points while rotating to predict full field and interior dynamic stress-strain information at intricate joint interfaces, where failure often occurs. The modeling approach can be applied to virtually any structure that has intricate joint interfaces by using a reduced number of measured degrees of freedom to interrogate or monitor a structure’s integrity. The proposed research is a new approach that will enable full-field dynamic measurement of rotating structures in operation, resulting in an improved understanding of the structural response of blades in flight. Both graduate and undergraduate students involved have gained an appreciation for current research areas important to industry and academia. The investigators and students working on the project have presented the results at numerous conferences and written several conference and peer-reviewed journal papers. This research has led to: 1) an understanding of how to measure small vibratory motions in combination with large displacements on rotating structures in operation, thus enhancing the capability of digital image correlation (DIC) to make spatially rich, full-field, dynamic measurements. (2) an understanding of the appropriate set of expansion functions necessary to provide accurate predictions of structural dynamic response using experimentally acquired data. (3) empirical validation that the expansion method can be used to predict full-field dynamic stress-strain information for complex heterogeneous structures that have intricate joint interfaces. As a result of the modeling and testing performed, it was found that proper analytical models can be developed if care and attention is directed towards material characterization and during fabrication. For structures with complex shapes (e.g. composite wind turbine blades) and orthotropic properties, attention to geometry, mass distribution, and physical material properties is important for full-field dynamic stress-strain prediction using the appropriate expansion functions. In stereophotogrammetry, rigid body correction (RBC) calculates best-fit coordinate systems for selected points in each data frame (or image set) and performs the required translations and rotations necessary to maintain a static coordinate system across all frames referencing the first frame. It was shown that improper RBC can distort the extracted measurement data. The results of this work can be used to determine the appropriate size of the measurement point region used in the RBC to examine the true structural dynamic response with respect to a rigid region of the structure. The graduate and undergraduate students working on the project have gained an appreciation for conducting research to achieve a goal without a closed form solution or direct path. The graduate students have helped to train undergraduate students in using the advanced equipment and in performing structural dynamic testing. All students have gained an appreciation that research methods must be properly employed in order to understand results obtained from any testing or modeling activities undertaken. The students have learned that in a research environment, one must always be willing to interpret and accept outcomes as opposed to originally envisioned results. This methodology is critical so that a researcher’s results are not tainted by preconceived expectations. The development and extension of the real time operating data expansion technique has been a significant breakthrough in the utilization of limited sets of sparsely populated operating data to develop full field dynamic stress-strain information. The main work of this project is validate the concept and to extend the techniques further to determine if this full field response can be used as a structural health monitoring tool, depicting changes in response characteristics due to load redistribution. The ability to appropriately make experimental measurements on rotating structures is significant. Measuring operating data on rotating structures (e.g. rotor blades and turbines) had historically been difficult. The new measurement approach will likely have a significant impact on better understanding the structural dynamics of helicopter rotors and wind turbines as well as their fluid-structure interaction.
