Throughout the years, the Structural Dynamics and Controls Lab (SDCL; Wang’s group) has created new paradigms, pioneered innovative and bold directions, and made significant contributions to the basic research field as well as to industrial applications. Some of the achievements are highlighted below.
a. The SDCL has pioneered a new class of adaptive structures via piezoelectric transducer circuitry networks and cross-field electromechanical tailoring for structural control and identification. Such ideas have created broad opportunities, generated original approaches and achieved unprecedented outcomes that impacted various areas in structural and system dynamics significantly, such as vibration and noise control, actuation, sensing and damage identification:
- New energy redistribution methods for vibration delocalization of mistuned periodic structures – The SDCL was the first to explore piezoelectric transducer circuitry networks for this class of problems to reduce localized vibration that is detrimental to periodic structures, such as bladed disks in turbo machinery. Novel network architecture and rigorous analytical tools to synthesize the circuitry have been created and significant modal de-localization has been demonstrated. The methodology was then further developed to synthesize a unique absorber configuration with networking that can concurrently suppress multiple spatial harmonic excitations that cannot be achieved traditionally. Through working with Air Force and NASA, the SDCL’s work has paved the path to ultra-low vibration intelligent gas turbine engines, which significantly improves the fuel economy, durability and safety of future air vehicles and transportation.
New active-passive network topology and concurrent design methods for vibration control – The SDCL has created methodologies that can simultaneously tailor the active authority amplification and passive damping characteristics of piezoelectric transducer circuitry networks for structural vibration control. With such tools, one can achieve much more vibration reduction with much less control power as compared to classical vibration control approaches. The SDCL has developed a rigorous simultaneous left-right eigen-structure assignment method that can optimally assign vibration modes and at the same time, assign left eigenvectors that are orthogonal to excitations (disturbance rejection). With piezoelectric circuitry networking, one can significantly increase the system degrees of freedom such that eigenvector admissible space can be greatly increased and better eigen-structures can be synthesized. Unique and effective schemes are created for the general class of vibration isolation problems and structural acoustic reduction problems.
- Structural damage identification enhancement via tunable piezoelectric circuitry network and feedback control – The SDCL has transformed the vibration-based structural damage detection methods; maintaining the advantages (simplicity) while overcoming the critical shortcomings (serious underdetermined problem with low sensitivity). One focus is to synthesize piezoelectric transducer tunable circuitry to favorably alter the dynamics of the system. By introducing additional resonant frequencies (provide more information) in desired frequency band (provide higher sensitivity), the method allows one to more completely and accurately capture the system dynamic response variations due to damage. To further enhance the detection sensitivity, a bistable piezoelectric circuitry and a sensitivity-enhancing eigenvector assignment control are developed, which directly benefited the damage identification accuracy and robustness. Such methods have created transformative opportunities for structural damage identification.
Piezoelectric-hydraulic topology and control for automotive drivetrain – The SDCL was the first to introduce this new concept of piezo-hydraulic topology and control into the automotive industry through working with Ford Motor Company. This technology is addressing the key demands for cost-effective, energy efficient, reliable and durable transmission systems with improved shift quality. By combining the advantages of piezoelectric transducers (high power density and large load authority) and hydraulic systems (large stroke), this stand-alone hybrid device is much simpler, smaller, and lighter as compared to the current automotive actuation systems. The traditional hydraulic control assembly can be eliminated, significantly reducing complexity and cost; oil pump can be downsized for improved efficiency. This technology revolutionizes future drivetrain design without complex hydraulic systems, which is especially ideal in a hybrid drivetrain. It significantly impacts the fuel economy, durability and comfort of the next generation of ground vehicles.
b. The SDCL has launched and led new multidisciplinary research directions in adaptive structures utilizing emerging knowledge and technologies, such as biology and nano-scale-materials. Such innovations have created a new paradigm with high impact and initiated path-breaking new directions that many followed.
- Plant cell inspired multifunctional adaptive structures – By leading a group of researchers with multidisciplinary expertise including engineering and biology, Dr. Wang’s team was the first to explore such a new class of adaptive structures and has achieved results that opened up new possibilities in structural dynamics. Their research has developed the ability to concurrently achieve large and stealth distributed actuation, autonomous property change, and self-reconfiguration and healing; which has long been the dream of adaptive structure researchers for the past two decades.
The program first aimed to create high authority active cellular elements by exploring the mechanical, chemical, and electrical properties of plant cells. Inspired by the fibrillar network in plant cell walls, a high mechanical advantage actuator cell was created based on fluidic flexible matrix composites (F2MCs). Through fiber-matrix tailoring with ultra-high anisotropy, one can cause the cellular element to actuate in various directions when pressurized. This concept is combined with a novel ion transport mechanism to regulate pressure, inspired by the ion transport and volume control feature of plant cells. The approach has significant advantages over current actuators, such as large stroke/force, and activation with stealth operation and no moving parts. The investigation was then expanded to develop cells that can achieve several orders of magnitude tunable mechanical stiffness properties. By taking advantage of the high anisotropy of the cells and the high bulk modulus of working fluids, one can obtain large changes in structural stiffness through valve control.
Advancing from the F2MC concept, a new idea of Fluidic Origami (FO) was further developed. The FO has all the features of a F2MC structure (multi-dimensional actuation and property adaptation), plus pressure-controlled multistability and can be fabricated into various scales and complex shapes. An adaptive metamaterial concept was then investigated for its potential of achieving multi-functionalities simultaneously through circulation control of F2MC- or FO-based cellular networks. This class of structural systems consists of a string of fluidic-connected cells with different properties. Synthesis methods were developed with multiple performance targets, where actuation authority, variable stiffness ratio, multi-stability characteristics and spectral dynamics were considered concurrently. With these innovations and working with industry, SDCL has developed ideas for a wide variety of applications, ranging from soft robotics to aircraft morphing control surfaces and engine inlet, to automobile shock absorption safety components.
- Engineering metamaterials with muscle-like characteristics – Inspired by the multi- functionality and versatility of muscle’s architectural composition, the SDCL was the first to investigate a new paradigm of modular structure-material development to achieve significant system adaptivity by utilizing building blocks possessing metastability. Combining adaptable supporting structure, large compliance, and intricate energy management, skeletal muscle is a natural system that exhibits numerous attractive characteristics. Recent mechanical modeling of muscle suggested some of the intriguing macroscale features are due to the assembly of nanoscale, metastable cross-bridge constituents. A modular metastable building block was created to emulate the effective passive functionality of muscle’s cross-bridge. Analytical and experimental results revealed that metamaterials assembled from the metastable modules supply unique changes in reaction force when global displacement is prescribed, adapting not only the magnitude of force but also the direction, in addition to yielding a multitude of globally stable topologies. The investigations provided clear evidence that such metamaterials would realize orders of magnitude change in stiffness for a constant system shape and enable the variation in required energy expense to globally deform the system in multiple directions, as well as effective and efficient energy trapping and release. The metastructural design framework represents a major leap forward in adaptive multifunctional materials and structural systems.
Ultra-high damping light-weight composites with carbon nanotube fillers – The SDCL was the first to develop computation tools and experimental methods to analyze, synthesize and evaluate composites with nanotube chains for energy dissipation or damping. Such composites have ultra-high and well-tailored damping characteristics, through utilizing the nanotube ultra-large surface area the will generate strong interfacial frictional damping due to nanotube-resin interaction. These are bold initiatives in non-traditional damping, which have created significant breakthroughs and generated a new multi-scale, multidisciplinary research direction in structural dynamics and control.