VTechWorks Repository :: Browsing by Author "Liang, Chen"

Browsing by Author "Liang, Chen"

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The constitutive modeling of shape memory alloys
Liang, Chen (Virginia Tech, 1990-08-15)
This dissertation presents a one-dimensional thermomechanical constitutive model for shape memory alloys based on basic concepts of thermodynamics and phase transformation kinetics. Compared with other developed constitutive relations, this thermomechanical constitutive relation not only reflects the physical essence of shape memory alloys, i.e., the martensitic phase transformation involved, but also provides an easy-to-use design tool for engineers. It can predict and describe the behavior of SMA quantitatively. A multi-dimensional constitutive relation for shape memory alloys is further developed based on the one-dimensional model. It can be used to study the mechanical behavior including shape memory effect of complex SMA structures that have never been analytically studied, and provide quantitative analysis for many diverse applications of shape memory alloys. A general design method for shape memory alloy actuators has also been developed based on the developed constitutive relation and transient thermal considerations. The design methodology provides a quantitative approach to determine the design parameters of shape memory alloy force actuators, including both bias spring SMA force actuators and differential SMA force actuators.
Coupled electro-mechanical system modeling and experimental investigation of piezoelectric actuator-driven adaptive structures
Zhou, Su-Wei (Virginia Tech, 1994)
Of primary importance to the design and application of adaptive structures is a modeling method to allow for performance prediction and parametric optimization of the integrated system. The statics-based modeling approaches have been applied to model piezoelectric (PZT) actuator-driven adaptive structures. The dynamic interaction between the actuators and their host structures has been ignored, and the system energy conversion can’t be predicted. As a matter of fact, PZT actuator-driven smart structures are complex electromechanical coupling systems in which electrical energy is converted into mechanical energy and vice-versa. The actuator outputs and the system energy conversion are dominated by the complex electro-mechanical impedance of the system. The entire actuator/substrate system can thus be essentially represented by a coupled impedance-based system model. This research presents such an impedance-based electro-dynamics analytical method and the experimental investigation for integrated PZT/substrate systems. When compared with the conventional static models, the system modeling method has revealed the physical essence and the interconnections among the intelligent elements and supporting structures. The frequency-dependent behaviors of the actuator and the dynamic response of the integrated system are accurately predicted. The theoretical model was developed for generic PZT actuator-driven active structures. The actuation force was evaluated as a result of the dynamic interaction between the actuator and the host structure. The model was then extended to include the electrical parameters of the PZT actuator such that the power flow and consumption of the integrated system can be predicted. The system dissipative power was then treated as the equivalent generation source to evaluate a temperature rise and thermal damage of the actuator. To examine the utility and generality of the system modeling method, the developed model was applied to typical two-dimensional structures such as thin plates and thin shells, and to one-dimensional structures such as the circular rings and beams. The design-related mechanical and thermal stress characteristics of the actuators were also specifically investigated. In addition to the theoretical work, experiments were conducted. The PZT actuator-driven simply-supported plate was built and tested. The velocity response of the integrated plate and the dynamic strain of the PZT actuators were measured. The coupled electromechanical admittance of the real system was also directly measured using an impedance analyzer. The predicted solutions agree with the experimental results in all of the tested cases, verifying the theoretical model.
Dynamic analysis of piezoelectric actuator-driven circular rings using an impedance approach
Rossi, Anna; Liang, Chen; Rogers, Craig A. (Acoustical Society of America, 1994-09-01)
This paper presents a dynamic model for the response of a circular ring excited by piezoelectric transducer (PZT) actuators bonded on the ring surface. The dynamic response is determined based on the dynamic interaction between the PZT actuators and the structure using an impedance approach. Compared with the conventional static approach, in which a statically determined ''equivalent force'' of the actuator is used as the forcing function in the dynamic analysis, the impedance approach cannot only capture the physics of the actuator/structure interaction, but also accurately predict the structural dynamic response. Experiments have also been conducted to verify the theoretical model. The predicted dynamic response using the impedance approach agrees very well with the experimental results. Comparison of the conventional static approach and the impedance model has also been presented.
Dynamic transduction characterization of magnetostrictive actuators
Ackerman, Anthony E. (Virginia Tech, 1993-12-06)
The objective of this thesis is to develop an analysis approach for formulation of transduction or input/output representations for magnetostrictive actuators. This transduction model is developed through application of an electro-magneto-mechanical impedance modeling approach which combines both the mechanical dynamics and coupled behavior of the actuator device. Lumped and continuous mechanical impedance elements model the actuator dynamics and the constitutive relationships for Terfenol-D characterize the electro-magneto-mechanical interaction. Experimental analysis of a Terfenol-D actuator serves to verify the developed models and provides an indication of actuator non-linearity. The developed transduction model allows for various device behavior analysis including dissipative power consumption, force and stroke output, and efficiency as a transducer. An actuator design strategy based upon the dynamics of the actuator and a driven external system is presented and allows for analysis of various actuator behaviors in terms of device parameters. The Terfenol-D actuator as a collocated actuator/sensor is also made possible with the transduction model.
Electro-dynamic analysis of stack actuators and active members integrated within truss structures
Flint, Eric Michael (Virginia Tech, 1994-08-15)
In this thesis, a method of predicting the steady state, dynamic, electromechanical behavior of stack actuators (both electrostrictive and piezoelectric) integrated within complex structures is developed and experimentally verified. This research was motivated by a need to accurately predict transmission force, velocity output, and power consumption for a wide range of applications both terrestrial and space based. The relevant transduction equation / parameters are derived from basic principles. These results are experimentally verified with a PZT stack active member. The derivations are then extended to incorporate the effects of integrating the actuator within a host structure. Specifically, the equations needed to predict actuator output force, resulting velocity and drawn current are derived. To implement and test these results in a structure, the equivalent host structure impedance must be determined. This is done experimentally for a complex truss structure representative of a small satellite. These results are then used to prepare theoretical predictions which compare well with experimentally measured output force. Finally, the derivations are extended to the electrical behavior of active members integrated within truss structures. It is now possible to predict the electrical load imposed by the active member on the power supply system including the effects of coupling with the host structure dynamic boundary conditions. Two implications of this are considered. First, the required power demands directly influence the design and sizing of amplifiers, applied voltage levels and power systems. Second, the dissipative power from actuation losses contributes directly towards raising the internal temperature of an operating stack actuator.
Enhanced induced strain actuator performance through discrete attachment to structural elements
Chaudry, Zaffir Ahmed (Virginia Tech, 1992-07-02)
In intelligent structures, structural deformation is generally controlled by either embedding or surface bonding the induced strain actuator to the structure. With bonded or embedded actuators used for inducing flexure, the developed in-plane force contributes indirectly through a locally-generated moment. Control authority in this configuration is thus limited by actuator offset distance. The focus of this research was to investigate a new concept in which the actuator, as opposed to being bonded, is attached to the structure at discrete points. This configuration is fundamentally different from the bonded/embedded configuration in that the actuator and the structure between the two discrete points can deform independently; and the in-plane force of the actuator, which contributes only indirectly in the case of bonded actuator, can directly influence out-of-plane displacements of the structure. Additionally, the actuator offset distance can be optimized with respect to actuator force/strain saturation for increased authority. Two implementations of this concept as applied to beam structures were investigated. In the first, the actuator (e.g., shape memory alloy actuator wire) does not possess any flexural stiffness; and therefore, remains straight between the two attachment points. In the second implementation, the actuator (PZT's and electrostrictive) possesses flexural stiffness, and bends with the structure. The formulation and experimental results for both implementations are presented. Enhanced authority is demonstrated by comparing the static response of the discretely attached actuator beam systems with their bonded counterpart systems.
Investigation on static grounding analysis model of non-pneumatic tire with nonlinear spokes
Liang, Chen; Wei, Wei; Mousavi, Hoda; Chen, Kun; Asafo-Duho, Bentil; Wang, Guolin (2021-01)
A static grounding analysis model of non-pneumatic tire (NPT) was built and presented in this paper. The proposed NPT analysis model considers the non-linearity of the spoke stiffness and is suitable for the performance exploration of various structures of the NPT. First, the shear band, rigid rim, and spoke structure of the NPT were simplified, the main structural parameters and mechanical parameters were extracted, and an analysis model was established. The model can describe the deformation of the NPT when it is subjected to external forces. On this basis, the different stiffness of the spokes during tension and compression was considered, an iterative method was used to compensate for the difference in the deformation caused by the difference in radial stiffness of the spokes, and an analysis model of NPT with nonlinear spokes was established. Then, the contact between the tire and the road surface was introduced to iteratively compensate for the reaction force of the road surface, and the deformation of the NPT with nonlinear spokes on the road surface was obtained. Finally, the finite element software ABAQUS was used to verify the accuracy of the model. This model contains more comprehensive structural parameters and material parameters, which can more realistically simulate the structural characteristics and static grounding behavior of the NPT.
Mechanism of CASK-linked ophthalmological disorders
Liang, Chen (Virginia Tech, 2018-09-21)
Calcium/calmodulin-dependent serine protein kinase (CASK) is a membrane-associated guanylate kinase (MAGUK) family protein, which is encoded by a gene of identical name present on the X chromosome. CASK may participate in presynaptic scaffolding, gene expression regulation, and cell junction formation. CASK is essential for survival in mammals. Heterozygous mutations in the CASK gene (in females) produce X-linked intellectual disability (XLID) and mental retardation and microcephaly with pontine and cerebellar hypoplasia (MICPCH, OMIM# 300749). CASK mutations are also frequently associated with optic nerve hypoplasia (ONH) which is the most common cause of childhood blindness in developed countries. Some patients with mutations in CASK have been also diagnosed with optic nerve atrophy (ONA) and glaucoma. We have used floxed CASK (CASKfloxed), CASK heterozygous knockout (CASK(+/-)), CASK neuronal knockout (CASKNKO) and tamoxifen inducible CASK knockout (CASKiKO) mouse models to investigate the mechanism and pathology of CASK-linked ONH. Our observations indicate that ONH occurs with 100% penetrance in CASK(+/-) mice, which also displayed microcephaly and disproportionate cerebellar hypoplasia. Further, we found that CASK-linked ONH is a complex developmental neuropathology with some degenerative components. Cellular pathologies include loss of retinal ganglion cells (RGC), astrogliosis, axonopathy, and synaptopathy. The onset of ONH is late in development, observed only around the early postnatal stage in mice reaching the plateau phase by three weeks of birth. The developmental nature of the disorder is confirmed by deleting CASK after maturity since CASKiKO mice did not produce any obvious optic nerve pathology. Strikingly the CASKfloxed mice expressing ~49% level of CASK did not manifest ONH despite displaying a slightly smaller brain and cerebellar hypoplasia indicating that ONH may not simply be an extension of microcephaly. We discovered that deleting CASK in neurons produced lethality before the onset of adulthood. The CASKNKO mice exhibited delayed myelination of the optic nerve. Overall this work suggests that CASK is critical for neuronal maturation and CASK-linked ONH is a pervasive developmental disorder of the subcortical visual pathway. Finally, in a side project, I also described a new methodology of targeting neurons using receptor-mediated endocytosis which would help target retinal neurons for therapeutic purposes in the future.
Modeling of distributed piezoelectric actuators integrated with thin cylindrical shells
Zhou, Su-Wei; Liang, Chen; Rogers, Craig A. (Acoustical Society of America, 1994-09-01)
The dynamic interaction between induced strain piezoelectric (PZT) actuators and their host structures is often ignored in the modeling of intelligent structures. A more realistic investigation of intelligent material systems must account for the dynamic behaviors of integrated actuator/substrate systems. In this paper, a generic method for the dynamic modeling of distributed PZT actuator-driven thin cylindrical shells has been developed using a mechanical impedance approach. The impedance characteristics of a cylinder corresponding to the excitation of a pair of pure bending moments have been developed, from which the dynamic output moments (or forces) of PZT actuators can be accurately predicted. Direct comparisons have been made between a conventional static modeling approach and the impedance method in order to identify the critical differences between these modeling methods for thin cylindrical structures. The case studies demonstrate that the mechanical impedance matching between PZT actuators and host structures has an impact on the output performance of the actuators. The dynamic essence of integrated PZT/substrate systems has thus been revealed.
Modeling of shape memory alloy hybrid composites for structural acoustic control
Rogers, Craig A.; Liang, Chen; Fuller, Chris R. (Acoustical Society of America, 1991-01-01)
Experimental demonstration of active vibration and structural acoustic control using shape memory alloy (SMA) hybrid composites [C. A. Rogers, in Proceedings of the International Congress on Recent Developments in Air and Structure Borne Sound and Vibration (to be published)[ has provided the motivation for investigating new control schemes and developing more accurate models. This paper will briefly describe newly developed constitutive models for shape memory alloy actuators and the hybrid material system. A general dynamical model for laminated SMA hybrid composite beams and plates will be presented with several theoretical results. A new structural acoustic model for laminated composite plates [Liang et al., J. Sound Vib. (to be published)] will be briefly described and the potential for active structural acoustic control using SMA hybrid composites demonstrated by numerical simulation.
Non-Cell Autonomous Roles for CASK in Optic Nerve Hypoplasia
Kerr, Alicia; Patel, Paras A.; LaConte, Leslie E. W.; Liang, Chen; Chen, Ching-Kang; Shah, Veeral; Fox, Michael A.; Mukherjee, Konark (ARVO, 2019)
PURPOSE. Heterozygous mutations in the essential X-linked gene CASK associate with optic nerve hypoplasia (ONH) and other retinal disorders in girls. CASKþ/ heterozygous knockout mice with mosaic CASK expression exhibit ONH with a loss of retinal ganglion cells (RGCs) but no changes in retinal morphology. It remains unclear if CASK deficiency selectively affects RGCs or also affects other retinal cells. Furthermore, it is not known if CASK expression in RGCs is critical for optic nerve (ON) development and maintenance. METHODS. The visual behavior of CASKþ/ mice was assessed and electroretinography (ERG) was performed. Using a mouse line with a floxed CASK gene that expresses approximately 40% CASK globally in all cells (hypomorph) under hemizygous and homozygous conditions, we investigated effects of CASK reduction on the retina and ON. CASK then was completely deleted from RGCs to examine its cell-autonomous role. Finally, for the first time to our knowledge, we describe a hemizygous CASK missense mutation in a boy with ONH. RESULTS. CASKþ/ heterozygous mutant mice display reduced visual contrast sensitivity, but ERG is indistinguishable from wildtype. CASK hypomorph mice exhibit ONH, but deletion of CASK from RGCs in this background does not exacerbate the condition. The boy with ONH harbors a missense mutation (p.Pro673Leu) that destabilizes CASK and weakens the crucial CASK–neurexin interaction. CONCLUSIONS. Our results demonstrate that mosaic or global reduction in CASK expression and/or function disproportionately affects RGCs. CASK expression in RGCs does not appear critical for cell survival, indicating a noncell autonomous role for CASK in the development of ON.
Optic Nerve Hypoplasia Is a Pervasive Subcortical Pathology of Visual System in Neonates
Liang, Chen; Kerr, Alicia; Qui, Yangfengzhong; Cristofoli, Francesca; Van Esch, Hilde; Fox, Michael A.; Mukherjee, Konark (ARVO, 2017-11)
PURPOSE. Optic nerve hypoplasia (ONH) is the most common cause of childhood congenital blindness in developed nations, yet the fundamental pathobiology of ONH remains unknown. The objective of this study was to employ a ‘face validated’ murine model to determine the timing of onset and the pathologic characteristics of ONH. METHODS. Based on the robust linkage between X-linked CASK haploinsufficiency and clinically diagnosed ONH, we hypothesized that heterozygous deletion of CASK (CASK(⁺/⁻)) in rodents will produce an optic nerve pathology closely recapitulating ONH. We quantitatively analyzed the entire subcortical visual system in female CASK(⁺/⁻) mice using immunohistochemistry, anterograde axonal tracing, toluidine blue staining, transmission electron microscopy, and serial block-face scanning electron microscopy. RESULTS. CASK haploinsuffiency in mice phenocopies human ONH with complete penetrance, thus satisfying the ‘face validity’. We demonstrate that the optic nerve in CASK(⁺/⁻) mice is not only thin, but is comprised of atrophic retinal axons and displays reactive astrogliosis. Myelination of the optic nerve axons remains unchanged. Moreover, we demonstrate a significant decrease in retinal ganglion cell (RGC) numbers and perturbation in retinothalamic connectivity. Finally, we used this mouse model to define the onset and progression of ONH pathology, demonstrating for the first time that optic nerve defects arise at neonatally in CASK(⁺/⁻) mice. CONCLUSIONS. Optic nerve hypoplasia is a complex neuropathology of the subcortical visual system involving RGC loss, axonopathy, and synaptopathy and originates at a developmental stage in mice that corresponds to the late third trimester development in humans.
Power consumption of piezoelectric actuators driving a simply supported beam considering fluid coupling
Stein, Steve C.; Liang, Chen; Rogers, Craig A. (Acoustical Society of America, 1994-09-01)
An electromechanical impedance model is applied to the case of a simply supported beam in an infinite rigid baffle with a fluid medium on one side. The effects of the fluid medium are included in the impedance analysis by considering fluid-structure interaction. The use of static and impedance model for structural acoustic analysis is discussed. Various power consumptions of PZT actuator-driven underwater beam structures will be quantified. The analysis discussed in this paper will be used to determine radiated structural acoustic power without using microphones. This work is the first step toward the determination of power requirements for underwater active structural acoustic control.
X-linked intellectual disability gene CASK regulates postnatal brain growth in a non-cell autonomous manner
Srivastava, Sarika; McMillan, Ryan P.; Willis, Jeffery; Clark, Helen R.; Chavan, Vrushali; Liang, Chen; Zhang, Haiyan; Hulver, Matthew W.; Mukherjee, Konark (BMC, 2016-03-31)
The phenotypic spectrum among girls with heterozygous mutations in the X-linked intellectual disability (XLID) gene CASK (calcium/calmodulin-dependent serine protein kinase) includes postnatal microcephaly, ponto-cerebellar hypoplasia, seizures, optic nerve hypoplasia, growth retardation and hypotonia. Although CASK knockout mice were previously reported to exhibit perinatal lethality and a 3-fold increased apoptotic rate in the brain, CASK deletion was not found to affect neuronal physiology and their electrical properties. The pathogenesis of CASK associated disorders and the potential function of CASK therefore remains unknown. Here, using Cre-LoxP mediated gene excision experiments; we demonstrate that deleting CASK specifically from mouse cerebellar neurons does not alter the cerebellar architecture or function. We demonstrate that the neuron-specific deletion of CASK in mice does not cause perinatal lethality but induces severe recurrent epileptic seizures and growth retardation before the onset of adulthood. Furthermore, we demonstrate that although neuron-specific haploinsufficiency of CASK is inconsequential, the CASK mutation associated human phenotypes are replicated with high fidelity in CASK heterozygous knockout female mice (CASK(+/-)). These data suggest that CASK-related phenotypes are not purely neuronal in origin. Surprisingly, the observed microcephaly in CASK(+/-) animals is not associated with a specific loss of CASK null brain cells indicating that CASK regulates postnatal brain growth in a non-cell autonomous manner. Using biochemical assay, we also demonstrate that CASK can interact with metabolic proteins. CASK knockdown in human cell lines cause reduced cellular respiration and CASK(+/-) mice display abnormalities in muscle and brain oxidative metabolism, suggesting a novel function of CASK in metabolism. Our data implies that some phenotypic components of CASK heterozygous deletion mutation associated disorders represent systemic manifestation of metabolic stress and therefore amenable to therapeutic intervention.

Browsing by Author "Liang, Chen"

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