Research

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.

 

Collaborative Research: Intentionally Nonlinear Design of High-Frequency Atomic Force Microscopy for Enhanced Material Characterization

Funded by an NSF research grant

Detailed analytical, computational and experimental studies are performed of a new, microcantilever beam design enabling higher-frequency nonlinear atomic force microscopy (AFM). Under dynamic mode operation an intentionally designed 1:n internal resonance between the two leading bending modes of the AFM microcantilever incorporating an inner Silicon paddle, leads to magnification of high-frequency harmonics in the paddle response, which is the basis for AFM of improved sensitivity. It is emphasized that although the cantilever-paddle design is linear, the intentional strongly nonlinear effect is activated through the nonlinear tip-sample interactions that occur during the AFM dynamic operation, that excite and nonlinearly couple the two bending modes in 1:n resonance. Preliminary theoretical and experimental measurements demonstrate the efficacy of this intentionally nonlinear design. Indeed, prototype tests of the proposed nonlinear AFM design applied on an inhomogeneous polymer sample consisting of a thin PDMS film with ~200 nm embedded polystyrene nanoparticles, indicated the capacity for simultaneous topography imaging and compositional mapping with as much as five-fold enhanced sensitivity This project will theoretically develop and fully document the significantly enhanced AFM measurements of sample material properties and topography, achieved through sensing of higher harmonics in the response. It is proposed to systematically study, optimize, extend and validate this promising concept. This will be achieved through theoretical studies to characterize the paddle’s response to different types of interaction forces, and an extended series of experimental tests to assess the sensitivity of high-order internal resonance designs to changes in topology and material properties. Moreover, multi-paddle AFM designs incorporating multiple simultaneous internal resonances will be analyzed for quantitative characterization, whereas related microfabrication issues will also be addressed. This work can be potentially transformative, since it can provide a new paradigm of intentionally nonlinear AFM technology based on higher-frequency sensing, and with capacity for drastically enhanced sensitivity and performance. The gained AFM sensing capability will be an incomparable tool in fields such as nano- and bio-sciences.

This work is performed in collaboration with Professor Hanna Cho of Ohio State University.

 

Nonlinear System Identification, Reduced Order Modeling, and Model Updating of the Effects of Mechanical Joints on Structural Dynamics

Funded by an NSF Graduate Fellowship (Keegan Moore)

Mechanical joints are present in nearly every structure, device, or vehicle in operation today. As these become ever more complicated the need for the classification and understanding of the nonlinear effects on structural dynamics grows ever more critical. I propose to apply recently developed nonlinear system identification methods, reduced order modeling and model updating techniques to characterize and model these nonlinear effects. The outcome of this research will be the development of models for use in standard finite element (FE) methods that capture the nonlinear effects of mechanical joints.

 

Nonlinear Dynamics of a Bluff Body with Nonlinear Internal Oscillating/Rotating Elements: Vortex-Induced Vibration Suppression, Partial Wake Stabilization, and Drag Reduction

Funded by an NSF research grant

Detailed computational and analytical studies are proposed of the nonlinear dynamics of vortex-induced vibration (VIV) of a linearly sprung circular cylinder with an internally attached, strongly nonlinear device (acting, in essence, as a nonlinear energy sink, or NES) in laminar or turbulent flow. The NES possesses oscillating and/or rotational components, and induces passive nonlinear targeted energy transfer to itself from the cylinder and flow over broad frequency ranges. Preliminary findings with a simple rotating NES or with a simple translating NES (in the latter case employing a spring with an essentially nonlinear stiffness), each with a linear viscous damper, indicate that an NES can effect dramatic suppression of VIV, significant symmetrization and stabilization of the wake with major associated drag reduction, chaotic oscillation of the cylinder and temporally chaotic flow at intermediate Reynolds numbers (Re), and interesting bifurcations resulting in multiple stable co-existing VIV solutions. It is proposed to extend these exciting and unexpected results by developing a new paradigm, wherein strongly nonlinear internal oscillating devices in a bluff body are designed to drastically suppress or enhance VIV, and to partially stabilize and symmetrize the wake. Fluid-structure interaction dynamics of the sprung cylinder having one or more internal NESs will be studied for intermediate and higher Re using slow/fast dynamical decompositions, invariant slow manifold considerations, nonlinear system identification, and reduced-order modeling techniques. High-fidelity fluid-structure interaction computations will be performed in the laminar, transitional, and turbulent regimes. As in the past, the aim will be to involve undergraduate and graduate students, especially from underrepresented groups. Participation in the G.A.M.E.S. (Girls Adventures in Mathematics, Engineering, and Science) summer camp organized for high-school girls by UIUC is planned, by building an educational experimental demonstration of fluid-structure interaction, where participants can perform their own physical experiments. Moreover, a dedicated educational web site capable of interactive VIV computational ‘experiments’ will be constructed and broadly disseminated to engage a variety of audiences.

This work is performed in collaboration with Professor Arne Pearlstein (University of Illinois).

 

Targeted Energy Transfer in Powertrains to Reduce Vibration-induced Energy Losses

Funded by an EPSRC grant (Principal Investigator Prof. Stephanos Theodossiades, Loughborough University, UK)

The project will develop the tools required to reduce energy losses associated with vibrations in power transmission systems, by implementing the state-of-the-art Targeted Energy Transfer (TET) technique. The research team comprises of internationally leading researchers from academe and industry, who can support the transition of this technology from the laboratory to engineering reality in an industrial setting. The aim of this research is to apply the TET method in automotive powertrains with the view of building sustainable vibration reduction technology and then assessing its potential to harvest energy for low-power system functions (e.g. wireless sensors). The above successful technique in systems under translational oscillations has not hitherto been applied systematically to rotating systems, which is the main novelty of the proposed research. The LNDVL team acts as International collaborator for this project.