Projects

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♦   Elastic Wave Transmission in Metastable Modular Metastructures
♦   Lattice Reconfiguration and Phononic Bandgap Adaptation via Origami Folding
♦   Uncovering the Dynamics of Generic Origami Structures and Materials
♦   Fluidic Origami: A Plant-Inspired Innovation
♦   Muscle: Inspiration for a New Class of Engineered Adaptive System
♦   Earthworm-Inspired Metameric Robot Locomotion
♦   Harnessing Complex Dynamics of Mechanical-Electrical System for Energy Harvesting
♦   Structural Health Monitoring via Bistable and Adaptive Piezoelectric Circuitry
♦   Faster-Than-Real-Time Simulation for Powertrain Controls


Elastic Wave Transmission in Metastable Modular Metastructures 

Asymmetric and non-reciprocal wave transmissions have been demonstrated with great promise in applications such as ultrasonic imaging, sonars, noise absorbing devices, and impact and blast protection. For engineered structures/materials, the wave features are intricately related to the underlying architecture. This indicates that changes in topology, symmetry, and component composition could drastically alter the wave propagation characteristics. Therefore, adaptive structures/materials capable of on-demand reconfiguration presents the exciting potential to uncover new wave transmission features, and elevate nonconventional wave control to a new level in that such adaptivity would open new doors for systems to respond to environmental changes, maximize performance, enhance safety, and optimize operation. However, the opportunities to selectively leverage the breadth of exceptional unconventional wave transmission characteristics in an on-demand or tunable manner are not well understood and insufficiently elucidated. 

(a) Schematic of a six-module metastructure showing four different topological variations for the same overall global shape (length) exhibiting different mechanical properties. (b) Six-module prototype with local bistability achieved using embedded permanent magnets.

Therefore, in this research, we aim to create new foundations for reconfigurable structures invested with massively adaptive, asymmetric elastic wave propagation properties by building upon concepts of non-reciprocal wave transmissions integrated with our recent breakthroughs in nonlinear metastable modular structures. Metastability indicates a coexistence of metastable states, which are combinations of internal configurations/states that possess unique properties. Thus, transitions among coexisting metastable states yields a fundamental adaptation of properties, providing means for bandgap tuning in the context of wave transmission. Overall, we will facilitate non-reciprocal wave propagations by exploiting the metastable modular architecture through the nonlinearity and asymmetry of strategically configured constituents, and achieve adaptive wave motion via metastable state control through switching the internal configurations. An example metastable module containing a bistable constituent connected with a mono-stable elastic element and a multi-module assembly are illustrated in Figure. By assembling these modules in an asymmetric manner and strategically switching amongst the metastable states, one could realize significant spatial asymmetry and mechanical property changes, which will in turn enable non-reciprocal wave propagation and its on-demand adaptivity.

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Lattice Reconfiguration and Phononic Bandgap Adaptation via Origami Folding

We introduce a framework of utilizing origami folding to redistribute the inclusions of a phononic structure to achieve significant phononic bandgap adaptation. Cylindrical inclusions are attached to the vertices of Miura-Ori sheet, whose one degree-of-freedom rigid-folding can enable fundamental reconfigurations in the underlying periodic architecture via switching between different Bravais lattice‑types. Such reconfiguration can drastically change the wave propagation behavior in terms of bandgap and provide a scalable and practical means for broadband wave tailoring.

Figure: Different folding configurations of origami metastructure. (a-c) and (d-f) are top and iso-metric views of origami metastructure at 0degree, 55 degree and 70 degree folding angles respectively. The green polygons in the top view identify different lattice patterns and show that the lattice transforms from a (b) hexagon to a (c) square and to a (d) hexagon when the folding angle is shifted from (b) 0 degree to (c) 55 degree and to (d) 70 degree. In the iso-views (d‑f), different parts of the construction are labelled and a close up view of origami sheet at 0o, 55 degree and 70 degree folding configurations are given. In (d-f), the bandgap structure of different folding configuration calculated via plane wave expansion method is given that demonstrate broadband bandgap adaptation.

Such research outcomes can be used to design adaptive sonic barriers for effective noise control.  See video below.

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Uncovering the Dynamics of Generic Origami Structures and Materials

Origami-based designs for engineering applications are gaining popularity due to their simplicity, scalability, and rich geometry. However, efforts to understand and explore origami features have mostly focused on the geometries and mechanics of origami, while dynamic characteristics remain largely unexplored. This research, for the first time, rigorously investigates the dynamics of origami-based structures in order to develop their potential for use in advanced engineered systems.

For example, we have found that a bistable stacked Miura-Ori exhibits a rich variety of dynamic responses under harmonic excitation, including small-amplitude intra-well oscillations, large-amplitude inter-well oscillations, and chaotic oscillations. Findings reveal that such bistable origami structures could be the basis for constructing mechanical metamaterials with embedded dynamic features such as vibration isolation and motion amplification, and the outcomes of this research are expected to lead to significant breakthroughs in the fields of adaptive origami structures and materials. 

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Fluidic Origami: A Plant-Inspired Innovation

The impulsive and recoverable movements in plants like the Venus flytrap have inspired scientists and engineers for more than a century.Even though the associated actuation mechanisms and physiological features of these movements have been relatively well studied, there have not been significant efforts to holistically apply the lessons from the plant kingdom to engineered multifunctional materials and structural systems. By combining the plant movement principles and paper folding topology, a novel adaptive structure concept called fluidic origami was invented in this research project. The idea is to combine different Miura-Ori sheets along their crease lines to form a three dimensional topology, which has naturally embedded tubular cells. Filling these cells with working fluid, one can strategically control their internal pressures and volumes to achieve multiple adaptive functions concurrently.

fluidic-origami

For example, fluidic origami can achieve distributed shape morphing according to the origami folding trajectory by actively changing the internal fluid volume (e.g. via pumping). Fluidic origami can also significantly tailor its stiffness properties by constraining the internal fluid volume via simple on-off valve control. In addition, fluidic origami structure is multi-stable, and the existence and shape of these stable configurations can be controlled by the fluid pressure. The performances of these unique adaptive functions are based on scale-independent geometric principles, and it’s highly programmable by tailoring the origami crease pattern.

Building upon these ideas, an integration of fluidic origami cells could lead to novel adaptive structures capable of distributed and rapid shape change based on the similar physical principles as the plant movements. Therefore, fluidic origami can have great potentials in various applications like high-performance morphing aircraft, kinetic architectures, and impulsive actuators.

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Muscle: Inspiration for a New Class of Engineered Adaptive System

Skeletal muscle possesses several features – such as properties adaptability, multi-functionality, robustness, and versatility – that are attractive for a broad range of scientific and engineering applications. Much of the engineering research focus to date has been on emulating the whole-muscle characteristics, leading to advanced concepts for actuation and locomotion mechanisms, but there has been a scarcity of investigations that take inspiration from the synergistic assembly of skeletal muscle’s microscale and nanoscale active and passive mechanical constituents. This research aims to develop new adaptive engineered systems by exploiting a more complete understanding of the micro- and macroscale mechanical constituents and compositions of muscle.

The research objectives include developing an understanding of one-dimensional mechanical modules designed to emulate muscle’s nanoscale cross-bridge constituent, and exploiting modularity to assemble these modules into larger systems, similar to the assembly of muscle cross-bridges into sarcomere contractile units. Investigations inspired by the asymmetric potential energy landscape of cross-bridges, and by their remarkable ability to effectively store and release energy to enable sudden motions and reduce the energetic cost of periodic motions have shown that mechanical systems may be strategically designed to exhibit similar characteristics, and incorporation of these behaviors into multi-dimensional structural and material systems enhances opportunities for properties adaptation and energy capture and release. The results of this research are expected to foster the development of new structural and material systems exhibiting multi-functionality, properties adaptability, and improved energy dissipation and recovery.

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Earthworm-Inspired Metameric Robot Locomotion

Earthworms possess flexible body and strong locomotion capability in various environments, which have inspired researchers and engineers to develop earthworm-like robots. It is revealed that the metameric segmentation, the antagonistic muscle layout, and the setae are three important morphology features for the earthworm to perform effective locomotion, and the retrograde peristalsis wave is the key locomotion mechanism that the earthworm takes. Much of the research to date has been on the design of segmented robots, with major focus on the actuation mechanisms. However, there has been a scarcity of efforts that are devoted to the understanding and utilization of the earthworms’ locomotion mechanisms. As a result, this research project aims to develop control methods for generic metameric locomotion robots by exploiting the correlations among robot segment coordination and locomotion performance, and the earthworm’s peristaltic waves.

robot     

Building upon the metameric feature of the earthworm-like robot, generic mechanical models of the metameric robot are built. Two methods are developed to control the robot segments for effective locomotion. From a bio-inspiration perspective, a generic gait generation algorithm is proposed by mimicking the earthworm’s basic locomotion mechanism. From a robotics perspective, the robot segment actuations are coordinated by making use of their symmetry relationship. These two approaches, although are significantly different, converges toward the same finding that the peristalsis wave is an inherent mechanism of earthworm-like locomotion and can be adopted to effectively control the metameric robot locomotion. The concept of metameric architecture as well as the proposed control methods will advance the state of the art of the design and control of crawling robots.

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Harnessing Complex Dynamics of Mechanical-Electrical System for Energy Harvesting

While vibration energy harvesting is becoming more feasible, recent research outcomes show that it is critical that basic research issues be addressed before a high performance, high efficiency energy harvesting system can be realized for myriad applications. Vibration energy harvesting devices are generally a combination of electromechanical platform (e.g. piezoelectric beam) converting vibration energy to electrical power, and electrical impedance to which the platform is coupled (e.g. rectifying circuit) for energy capture and/or utilization. The state-of-the-art formulations of these devices exploit the nonlinearities in dynamics of either mechanical side (with unrealistic linear circuits) or electrical side (with simple linear mechanical devices) to enhance energy capture compared to linear devices, but do not exploit them in an integrated manner.

Schematic of base-excited piezoelectric cantilever coupled to one of various electrical circuits

This research aims to maximize the energy capture by formulating an integrated approach to leverage complex dynamics of nonlinear electromechanical platform and realistic nonlinear rectifying electrical circuitry. This research will create accurate, predictive analytical formulations for nonlinear, non-smooth, and multimodal dynamic systems. This will facilitate rich insight into their ideal integration and guide design for energy harvesting systems that yield high and robust energy capture performance. Experimental studies will validate the analytical findings and will investigate new piezoelectric energy harvesting systems identified by the theory that set electrical energy-capture benchmarks. The results of this research will guide development of energy harvesting systems that empower future generations of self-sufficient microelectronics, such as the prolific wireless structural health monitoring sensor networks that are otherwise reliant on unsustainable energy resources.

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Structural Health Monitoring via Bistable and Adaptive Piezoelectric Circuitry

Electromechanical impedance-based structural health monitoring (SHM) approaches have been extensively explored due to their excellent potential in identifying small structural defects, while maintaining simplicity in implementation. Available independent measurement data sets, however, are generally far fewer than the number of required system parameters to be identified. This results in a seriously underdetermined problem that undermines the reliability of damage prediction. This research aims to advance the state-of-art SHM techniques that can accurately identify the location and severity of structural damage.

(a) Bistable and adaptive piezoelectric circuitry, (b) damage identification with conventional method, and (c) damage identification with bistable and adaptive piezoelectric circuitry

Specifically, we explore a novel integration of the monitored structure with a bistable and adaptive circuitry network that (a) enables highly accurate measurement of damage-induced piezoelectric impedance variations against noise influences and (b) fundamentally improves the underdetermined inverse problem to reliably identify the location and severity of structural defects.

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Faster-Than-Real-Time Drivetrain Simulation for Powertrain Controls

Automotive powertrain control strategies are executed on onboard Powertrain Control Module (PCM) to determine control actions for both performance and efficiency, accounting for complex interactions between drivetrain hardware, vehicle states, and driver inputs. However, the consequences of these control actions are usually not understood in advance. The ability to constantly look ahead and examine multiple control alternatives on the fly will give the next-generation automotive powertrain systems significant advantages in robustly responding to driver actions, disturbances, and control sequences that are not covered by pre-programmed approaches. Motivated by this idea, our research develops models and methodologies that enable on-board faster-than-real-time simulations of drivetrain to predict consequences of multiple powertrain control alternatives & probable future driver actions, and to mitigate undesirable drivetrain responses in advance.

Proposed simulation and prediction framework

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