The steering committee, Matthew Brake (Rice), Malte Krack (Stuttgart), and Christoph Schwingshackl (Imperial), are seeking 12 graduate students or postdocs to participate in this year’s projects.
Project 1: Effects of Non-Unique Residual Traction on the Non-Repeatability of the Dynamics of Jointed Structures
The tangential friction force of a permanently sticking contact (residual traction) can have an arbitrary value within the limits given by the Coulomb cone. The actual residual traction depends on the load history and is generally unknown. This can lead to a variability of the resonant vibration level of 20 to 300 percent, as shown in experiments of structures with friction dampers. In this project, the effect of non-unique residual traction will be analyzed, for the first time, on the vibrations of a system with bolted joints. A simple assembly with two joints is considered, which are aligned under an angle so that there is structural coupling among the contacts’ tangential and normal directions. Different static loading and tightening sequences will be considered, and both experimental and numerical investigations will be pursued to assess to what extent the non-repeatability of the vibration response is due to the non-unique residual traction.
Project 2: Quantitative Measurements with Phase-Based Motion Magnification for Nonlinear Structures
Experimental insights into the physics of jointed structures have benefited significantly in recent years from the use of digital image correlation (DIC) techniques. However, DIC is limited by several factors, including the trade-off between physical resolution of displacements and the field of view (for instance, to study slip at an interface, the field of view usually can only include a small amount of material near the interface making it impractical to measure the motion of the structure simultaneously without multiple cameras at different magnifications). Phase-based motion magnification, on the other hand, is a promising video-based technique for amplifying structural motion. In this project, we will explore the application of phase-based motion magnification to jointed structures and the efficacy of combining it with DIC methods in order to make higher resolution measurements of the motion of jointed structures. In particular, the primary focus of this project will be on assessing applicability of this approach to a nonlinear (jointed) structure and validating the quantitative measurements of displacements across the structure’s interface using a second camera with a magnified field of view and a traditional DIC approach. This project will be co-mentored by Zhu Mao of Worcester Polytechnic Institute.
Project 3: System Identification with Multiple Data Sets
Often, system identification is performed on a single data set at a time. When multiple data sets exist, the present approach to considering them is to analyze the resulting identified parameters statistically (such as the average frequency, or 95% confidence interval of extracted parameters, etc.). If, however, a method was formulated to identify the parameters of a system based on data from multiple measurements, then this would potentially lead to an identified system model that is valid over a much larger operating range. This project proposes an approach in which the ensemble of data sets is considered in order to identify a system’s parameters. There are multiple approaches to address this problem in both statistics and applied mathematics, such as boot-strapping, stochastically driven optimization schemes, etc. Key to success for this project will be formulating a way to handle modeling errors (e.g., fitting a polynomial stiffness model to Coulombic friction or handling outliers), parameter initialization (such that any optimized models are able to avoid bad local minima), and assessing the quality of the resulting models. Students with expertise in system identification, statistics, or applied mathematics are sought to participate in this computational project. This project will be co-mentored by JP Noel of KU Leuven.