Current Research Projects
Characterization of Capacity for, and Rate of Energy Dissipation in Linear and Nonlinear Dissipative Oscillators via Action–Angle Variables
Funded by the Fulbright Program (Hungary)
The simplest representation of oscillatory systems is often achieved using action–angle variables. This project extends this framework to study the dissipative capacity and rate of energy dissipation in single- and multi-mode linear and nonlinear oscillatory systems. Our aim is to provide analytical expressions for effective dissipation measures such as bandwidth, storage time (time constant) and time-bandwidth product in these systems, with special attention given to multi-modal dynamical systems with closely spaced modes and non-classical damping distribution, and/or systems exhibiting nonlinear internal resonances and strongly nonlinear modal interactions.
This research is in collaboration with Mr. Csanád Árpád Hubay and Prof. Tamás Kalmár-Nagy, of the Budapest University of Technology and Economics.
Exploiting Impact-induced Intermodal Targeted Energy Transfer (IMTET) for Passive Mitigation of Resonant Vibrations of Rotationally Periodic Structures
Funded by the Deutsche Forschungsgemeinschaft (DFG), Germany
Without countermeasures, lightweight structures like turbine blades break under vibration loads. We investigate a new, fully passive concept for vibration mitigation, namely intermodal Targeted Energy Transfer (IMTET). To induce intense energy transfers, a small impactor is placed freely into a cavity of the host structure, achieving vibration mitigation by Impact Energy Scattering. More specifically, the collisions enable the participation of more system modes in the response and induce intense, almost irreversible nonlinear energy transfers from the critical low-frequency modes to high frequencies, where energy is dissipated more rapidly. Moreover, as vibration energy is transferred from low to high frequencies, the overall level of system vibration is reduced not by adding extra dissipative elements, but rather by redistributing energy to a much larger set of vibration modes (especially high-frequency ones). In other words, by IMTET we radically enhance the system’s inherent dissipative capacity in a predictable and robust way.
This project is in collaboration with Prof. Malte Krack of the University of Stuttgart, Germany.
Robust Stabilization of Subsea Power Cables using Nonlinear Energy Sinks
Funded by the National Offshore Wind Research and Development Consortium
We perform computational studies of passive vortex-induced-vibration (VIV) mitigation of undersea cables equipped with attached nonlinear energy sinks (NESs). Specifically, we model the nonlinear fluid-structure interaction of these cables with their undersea environment and show that the NESs are capable of mitigating cable vibrations over broad frequency ranges, under continuously varying, non-stationary loads from the undersea environment. Then we will proceed with optimization of the NES parameters in order to achieve most effective and robust cable vibration mitigation.
This project is in collaboration with Prof. Lei Zuo of the University of Michigan.
Prediction of Limit Cycle Oscillations of Fighter Aircraft with Store Nonlinearities
Funded by the Naval Innovative Science and Engineering (NISE) Program
Research will focus on the accurate and computationally economical prediction of limit cycle oscillation (LCO) amplitude, frequency, and onset speed for fighter aircraft carrying external stores with various nonlinearities. A generic fighter aircraft carrying stores with a freeplay nonlinearity at the wing-store connection, part of a KTH-NASA collaborative project focused on building a repository of LCO wind-tunnel data, will be studied using aeroelastic codes such as FUN3D and analytical methods. Experimental data from wind tunnel tests of a full-span model in the Transonic Dynamics Tunnel at NASA Langley Research Center will provide truth data to assist in the development of methodologies for LCO prediction. This research will aim to develop and refine methods for LCO prediction and identify and characterize LCO mechanisms.
This project is in collaboration with Dr. Walter Silva, NASA Langley Research Center.
Quantification of Dissipation in General Classes of Engineering Systems Based on Generalizations of the Notions of Bandwidth and Energy Storage
Funded by funds provided by the University of Illinois at Urbana-Champaign
We develop and apply generalizations of the classical notions of bandwidth and energy storage time, to quantify and engineer the dissipative capacity and the rate of energy dissipation in a general class of dynamical systems. We investigate the break of the classical time-bandwidth limit in these systems, and relate it to the design of resonators with tailored dissipation properties.