Current Research Projects

Research Experience and Mentoring (REM) Supplement to EFRI NewLAW: Nonreciprocity in Acoustic Systems with Nonlinear Hierarchical Internal Structure and Asymmetry

Funded by an NSF EFRI REM grant

The EFRI REM supplemental support provides pre-program training; research experiences to two high school students with their STEM Teacher, and five undergraduate students; and post-program mentoring activities at the University of Illinois. These mentoring activities are socio-economically and culturally relevant to our research participants. Team-based research projects are performed, focusing on nonlinear, non-reciprocal dynamics. Moreover, the supplemental support will allow us to validate the viability of this approach and share results within the community through publication. We are uniquely positioned to accomplish this task at the University of Illinois due to several factors: (i) Experienced and committed principal investigators and research collaborators with a wealth of teaching and student mentoring experience and track records; (ii) a strong, in-place group of REM administrative and support professionals that is highly experienced in working with our target audience; (iii) long and established partnership with multiple educational units targeting minority Urbana – Champaign District 4 high school and local community college students, aiming towards a unique opportunity to integrate multiple organizations’ efforts in a comprehensive way; and (iv) students that are increasingly interested in STEM outreach and continue to request additional mentoring and outreach opportunities.

Mr. Joseph Muskin is the educational coordinator of this project; this work is in collaboration with Profs. S. Tawfick, K. Matlack and A. Wissa of the University of Illinois at Urbana-Champaign.


Modeling and Analysis of Mechanical Systems with Non-smooth Nonlinearities

Funded by a Fellowship from the China Scholarship Council

The research focuses on the use of analytical and computational techniques to analyze flexible mechanical systems with non-smooth nonlinearities, such as dry friction and clearances. We aim towards stability analysis of these systems under transient and periodic loads, leading to predictive design of these systems. The study will be computationally intensive and will be based on advanced algorithms of computational mechanics. Moreover, asymptotic techniques will be applied to this problem, in order to gain insight into the complex nonlinear modal interactions that occur in these systems.

This project is in collaboration with Profs. Jinhua Zhang and Jun Hong, Xi’an Jiaotong University, PR China, and Prof. Malte Krack, University of Stuttgart, Germany.


Nonlinear System Identification and Reduced-Order Modeling of Structures and Material Systems

Funded by a Fellowship from the University of the Philippines, Diliman, and a supplemental Fellowship of the Department of Mechanical Science and Engineering of the University of Illinois

We develop and apply powerful new methods for nonlinear system identification and reduced-order modeling of flexible structures and soft material systems. Particular emphasis will be to account for geometric nonlinearities and their effects on the stiffness and damping characteristics, and to study the strongly nonlinear modal interactions that are induced by these nonlinearities. Moreover, the approach is data-driven and relies to as few ad hoc assumptions as possible. The systems considered include (but are not limited to) a model plane with nonlinear stores and material systems in shear. The project involves analytical, computational and experimental methods.

This project is in collaboration with Prof. Melih Eriten, University of Wisconsin at Madison.


Targeted Energy Transfer by Nonlinear Energy Sink with Strongly Nonlinear Stiffness and Nonlinear Damping

Funded by a Fellowship from the China Scholarship Council

Concerning the research on nonlinear energy sinks – NESs, and targeted energy transfer – TET, most studies consider NESs with pure stiffness nonlinearities. This project will explore the effects of nonlinear damping and its effects on targeted energy transfers between linear oscillators and nonlinear damped attachments. The effects of nonlinear damping will also be studied on the dynamics of linear, nondispersive elastic media coupled to local nonlinear spring–dashpot pairs under harmonic excitations. The parameters of the attachments should be predicted to maximize mode complexity and enhance the interplay of vibrations and acoustics in these systems. Also, the slow invariant manifold – SIM approach will be explored to study the strongly nonlinear dynamical responses of these systems.

This project is in collaboration with Prof. Guoping Chen, Nanjing University of Aeronautics and Astronautics, PR China.


Nonlinear Wave Propagation in Granular Media

Funded by a Fellowship from the China Scholarship Council

Ordered granular media exhibit very rich and complex dynamics, and so they find applications in numerous fields. Wave propagation in granular media is a complex problem and many factors should be taken into consideration. In previous studies, much consideration has been given to the dynamics of simple granular media like one-dimensional granular chains, under idealized boundary conditions such as rigid boundaries and impulse excitation, while the physical problems, considering their potential applications, are much more complex. This project will explore complex granular networks with flexible boundary conditions in an effort to computationally study the nonlinear acoustics of granular interfaces. Computational and experimental studies are planned.

This project is in collaboration with Prof. Wei Li, Huazhong University of Science and Technology (HUST), PR China.


Collaborative Research: A new nonlinear modal updating framework for soft, hydrated materials

Funded by an NSF research grant

The mechanical properties of soft, hydrated materials have long been of interest to the scientific community. Increasingly, a particular area of interest has been on the high-rate response of soft materials due to their many applications in robotics, materials and the biomedical sciences. Most soft and hydrated materials (e.g., biomaterials) exhibit broadband nonlinear mechanical behavior that is challenging to quantify due to measurement uncertainties, mechanical anisotropy and inhomogeneity. High-rate dynamic testing, broadband rheometry, and acoustic force radiation/ultrasound techniques are commonly utilized for measuring high-rate responses of bio-tissues, however, they do not allow for independent control of the excitation amplitude and frequency. Therefore, there is a need for accurate characterization of these materials over the full spectrum of strain rates and finite deformations. To address these critical needs, a new nonlinear dynamics-based model identification and updating methodology is proposed. It starts with measured response time series and construction of transitions in a frequency-energy plot (FEP) of a soft-tissue tester and sample system. Then, the dynamics of an underlying conservative system (i.e., with no dissipative effects) modeling the tester is correlated with the measured response. In the conservative system model, soft tissues are modeled as highly flexible elements with stiffness and damping nonlinearities. The reconciliation of the measured and simulated responses in the FEP is utilized to estimate the broadband dissipative properties of the soft tissues. Preliminary work has focused on constructing a model updating framework for localized stiffness-type nonlinearities. In order to achieve the main objective, the following aims will be completed: (i) Understand and study the nonlinear broadband dynamic responses of soft materials; (ii) Construct the modal updating framework based on a computational benchmark model; and (iii) Experimentally validate the proposed model updating framework with a soft material characterization benchmark. The findings of this research have the potential to drastically increase the accuracy, cost-efficiency and accessibility of broadband soft material characterization, and, as such, it can be transformative in diverse interdisciplinary areas, such as soft robotic design, micro and nanoindentation measurements, soft tissue feedback during surgery, and modeling of the impact dynamics of the brain. This project will provide training and mentoring opportunities for a diverse group of K12, undergraduate and graduate research students. The PIs are committed in diversity as evidenced by the fact that the teams of the PIs consist of members of underrepresented groups actively serving as role models in different organizations, which will facilitate recruitment of underrepresented individuals. To engage the interest of the public in this scientific issue, an interactive demonstration of the developed experimental research benchmark will be displayed at the New Jersey State Science Festival. Partnerships with local high-schools to provide summer internships to students in under-represented and under-privileged communities are also planned.

This work is performed in collaboration with Professor Mehmet Kurt of the Stevens Institute of Technology.


EFRI NewLAW: Non-reciprocity in Acoustic Systems with Nonlinear Hierarchical Internal Structure and Asymmetry

Funded by an NSF Emerging Frontiers Research Initiative Award

This research program will investigate new theoretical and practical knowledge on the application of nonlinearity, asymmetry, and mixed scales to design and fabricate ground-breaking materials and devices. The approach will yield materials which overcome traditional bounds on time-reversal symmetry and acoustic reciprocity. These transformative reciprocity-breaking materials and systems are expected to find wide application in diverse fields, including noise-mitigating transportation systems; medical ultrasound devices; atomic force microscope (AFM) sensing; acoustic filters and logic devices; sonar; and energy control and redirection. The research will also broadly impact education through planned curriculum development and outreach activities aimed at increasing exposure of engineering students, and the public, to the exciting physics of acoustic materials. At the same time, these activities will promote interest in science, technology, engineering, and mathematics. Planned activities will include a multidisciplinary collaborative course on non-traditional acoustic materials; broadening opportunities with outreach organizations on campus by inviting high school students and teachers to develop lab modules and earn continuing education credits; a collaboration with Clark Atlanta University to engage faculty and underrepresented undergraduate students in research tasks; and industrial collaboration with the Hughes Research Laboratory to enhance and facilitate technology transfer. This research investigates a new class of reciprocity-breaking acoustic systems characterized by nonlinear internal structures, asymmetry and mixed scales. These systems exhibit directed cross-scale energy transfers which break time reversibility and reciprocity both locally (within each of the system subunits) and globally (for the entire system viewed a whole). Non-reciprocal, large-to-small scale energy transfers mimic analogous nonlinear energy transfer cascades in nature (e.g., turbulence). The research aims to be transformative in the field of nonlinear acoustics, promoting a new paradigm for predictive design with nonlinear non-reciprocity through (i) the theoretical and experimental understanding of acoustic systems with nonlinear hierarchical internal structures; (ii) the uncovering of the combined role of asymmetry, disorder, nonlinearity and cross-scale directed energy transfers on non-reciprocity; (iii) the development of new approaches for fabricating, characterizing and experimentally testing non-reciprocal lattice materials combining multiple macro-to-nano scales; and (iv) the translation of these materials to new technologies and acoustic devices that exploit and showcase transformative capabilities.

This work is performed in collaboration with Professor Michael Leamy of the Georgia Institute of Technology, Professor Chiara Daraio of the California Institute of Technology, and Professor Sameh Tawfick of the University of Illinois at Urbana-Champaign.