Browsing by Author "Barry, Oumar"

Now showing 1 - 20 of 21
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    Analysis of an Anti-vibration Glove for Vibration Suppression of a Steering Wheel
    Alabi, Oreoluwa Adekolade (Virginia Tech, 2022-01-11)
    Exposure to severe levels of hand-arm vibration can lead to hand-arm vibration syndrome. Towards curbing the development of hand-arm vibration syndrome, studies have shown that anti-vibration gloves effectively reduce the transmission of unwanted vibration from vibrating equipment to the human hand. However, most of these studies have focused on the study of anti-vibration gloves for power tools such as chipping hammers, and not much work has been done to design anti-vibration gloves for steering wheels. Also, as most of these studies are based on experimental or modeling techniques, the level of effectiveness and optimum glove properties for better performance remains unclear. To fill this gap, the dynamics of the hand-arm system, with and without gloves, coupled to a steering wheel is studied analytically in this work. A lumped parameter model of the hand-arm system with hand-tool interaction is modeled as a linear spring-damper system. The model is validated by comparing transmissibility obtained numerically to transmissibility obtained from experiments. The resulting governing equations of motion are solved analytically using the method of undetermined coefficients. Parametric analysis is performed on the biomechanical model of the hand-arm system with and without a glove to identify key design parameters. It is observed that the effect of glove parameters on its performance varies based on the frequency range. This observation further motivates us to optimize the glove parameters, using multi-objective optimization, to minimize the overall transmissibility in different frequency ranges.
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    Analytical and Spectro-Spatial Analyses of Nonlinear Metamaterials for Vibration Control, Energy Harvesting, and Acoustic Non-Reciprocity
    Bukhari, Mohammad Abdulbaqi (Virginia Tech, 2021-06-23)
    This dissertation investigates the nonlinear wave propagation phenomena in nonlinear metamaterials with nonlinear chains and nonlinear resonators using analytical and spectro-spatial analyses. In the first part of the thesis, the nonlinear metamaterials are modeled as a chain of masses with multiple local resonators attached to each cell. The nonlinearity stems from the chain's stiffness in one case and the local resonator's stiffness in another. Analytical approximates solutions are obtained for each case using perturbation techniques. These results are validated through numerical simulations and the results show good agreement. To further demonstrate the nonlinear wave propagation characteristics, spectro-spatial analyses are conducted on the numerical integration data sets. The wave profiles, short-term Fourier transform spectrograms, and contour plots of 2D Fourier transform show the presence of solitary waves for both sources of nonlinearity. In addition, spectro-spatial features demonstrate the presence of significant frequency shifts at different wavelength limits. indent The second part of the thesis studies a nonlinear electromechanical metamaterial and examines how the electromechanical coupling in the local resonator affects the wave propagation. Numerical examples indicate that the system can be used for simultaneous energy harvesting and vibration attenuation without any degradation in the size of bandgaps. Spectro-spatial analyses conducted on the electromechanical metamaterial also reveal the presence of solitons and frequency shifts. The presence of solitary wave in the electromechanical metamaterial suggests a significant improvement in energy harvesting and sensing techniques. The obtained significant frequency shift is employed to design an electromechanical diode, allowing voltage to be sensed and harvested only in one direction. Design guidelines and the role of different key parameters are presented to help designers to select the type of nonlinearity and the system parameters to improve the performance of acoustic diodes. indent The last part of this thesis studies the passive self-tuning of a metastructure via a beam-sliding mass concept. The governing equations of motions of the holding structure, resonator, and sliding mass are presented and discretized into a system of ODEs using Galerkin's projection. Given that the spatial parameters of the system continuously change over time (i.e., mode shapes and frequencies), instantaneous exact mode shapes and frequencies are determined for all possible slider positions. The numerical integration is conducted by continuously updating the spatial state of the system. The obtained exact mode shapes demonstrate that the resonance frequency of the resonator stretches over a wide frequency band. This observation indicates that the resonator can attenuates vibrations at a wide frequency range. Experiments are also conducted to demonstrate the passive self-tunability of the metastructure and the findings colloborate the analytical results.
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    Applications of Vibration-Based Occupant Inference in Frailty Diagnosis through Passive, In-Situ Gait Monitoring
    Goncalves, Rafael dos Santos (Virginia Tech, 2021-08-30)
    This work demonstrates an application of Vibration-Based Occupant Inference (VBOI) in frailty analysis. The rise of both Internet-of-Things (IoT) and VBOI provide new techniques to perform gait analysis via footstep-induced vibration which can be analyzed for early detection of human frailty. Thus, this work provides an application of VBOI to passively track gait parameters (e.g., gait speed) using floor-mounted accelerometers as opposed to using a manual chronometer as it is commonly performed by healthcare professionals. The first part of this thesis describes the techniques used for footstep detection by measuring the power of the footstep-generated vibration waves. The extraction of temporal gait parameters from consecutive footsteps can then be used to estimate temporal features such as cadence and stride time variation. VBOI provides many algorithms to accurately detect when a human-induced vibration event happened, however, spatial information is also needed for many gait parameters used in frailty diagnosis. Detecting where an event happened is a complicated problem because footsteps waves travel and decay in different ways according to the medium (floor system), the number of people walking, and even the walking speed. Therefore, the second part of this work will utilize an energy-based approach of footstep localization in which it is assumed that footstep waves decay exponentially as they travel across the medium. The results from this approach are then used to calculate spatial and tempo-spatial parameters. The main goal of this study is to understand the applicability of VBOI algorithms in gait analysis for frailty detection in a healthcare setting.
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    Control of Vibration Systems with Mechanical Motion Rectifier and their Applications to Vehicle Suspension and Ocean Energy Harvester
    Xiong, Qiuchi (Virginia Tech, 2020-05-08)
    Vibration control is a large branch in control research, because all moving systems may induce desired or undesired vibration. Due to the limitation of passive system's adaptability and changing excitation input, vibration control brings the solution to change system dynamic with desired behavior to fulfill control targets. According to preference, vibration control can be separated into two categories: vibration reduction and vibration amplification. Lots of research papers only examine one aspect in vibration control. The thesis investigates the control development for both control targets with two different control applications: vehicle suspension and ocean wave energy converter. It develops control methods for both systems with simplified modeling setup, then followed by the application of a novel mechanical motion rectifier (MMR) gearbox that uses mechanical one-way clutches in both systems. The flow is from the control for common system to the control design for a specifically designed system. In the thesis, active (model predictive control: MPC), semi-active (Skyhook, skyhook-power driven damper: SH-PDD, hybrid model predictive control: HMPC), and passive control (Latching Control) methods are developed for different applications or control performance comparison on single system. The thesis also studies about new type of system with switching mechanism, in which other papers do not talk too much and possible control research direction to deal with such complicated system in vibration control. The state-space modeling for both systems are provided in the thesis with detailed model of the MMR gearbox. From the simulation, it can be shown that in the vehicle suspension application, the controlled MMR gearbox can be effective in improving vehicle ride comfort by 29.2% compared to that of the traditional hydraulic suspension. In the ocean wave energy converter, the controlled MMR WEC with simple latching control can improve the power generation by 57% compared to the passive MMR WEC. Besides, the passive MMR WEC also shows its advantage on the passive direct drive WEC in power generation improvement. From the control development flow for the MMR system, the limitation of the MMR gearbox is also identified, which introduces the future work in developing active-MMR gearbox by using an electromagnetic clutch. Some possible control development directions on the active-MMR is also mentioned at the end of the thesis to provide reference for future works.
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    Data driven modeling and MPC Based control for Pathological Tremors
    Samal, Subham Swastik (Virginia Tech, 2024-12-19)
    Pathological tremor is a common neuromuscular disorder that significantly affects the quality of life for patients worldwide. With recent developments in robotics, rehabilitation exoskeletons serve as one of the solutions to alleviate these tremors. For improved performance of such devices, we need to solve a few problems, which include developing a model for pathological tremors, and a safe control system that can conveniently incorporate constraints on the wrist's range of motion and it's input force/torque. Accurate predictive modeling of tremor signals can be used to provide alleviation from these tremors via various currently available solutions like adaptive deep brain stimulation, electrical stimulation and rehabilitation orthoses. Existing methods are either too general or too simplistic to accurately predict these tremors in the long term, motivating us to explore better modeling of tremors for long-term predictions and analysis. We explore towards the prediction of tremors using artificial neural networks using EMG signals, leveraging the 20- 100 ms of Electromechanical Delay. The kinematics and EMG data of a publicly available Parkinson's tremor dataset is first analyzed, which confirms that the underlying EMGs have similar frequency composition as the actual tremor. 2 hybrid CNN-LSTM based deep learning architectures are then proposed to predict the tremor kinematics ahead of time using EMG signals and tremor kinematics history, and the results are compared with baseline models. This is then further extended by adding constraints-based losses in an attempt to further improve the predictions. Then, we explore the application of model-based predictive control (MPC) for the full wrist exoskeleton designed in our lab for the alleviation of tremors. The main motivation for using MPC here relies on its ability to incorporate state and input constraints, which are crucial for the user's safety. We employ a linear MPC methodology, in which the forearm-exoskeleton model is successively linearized at each time sample to obtain a linear state space model, which is then used to obtain the optimal input by minimizing a convex quadratic cost function. This is then integrated with the tremor model developed via BMFLC and neural networks to provide tremor suppression. Simulation studies are provided to demonstrate the effectiveness of the control schemes. The numerical simulations suggest that the MPC framework is capable of accurate trajectory tracking while providing better tremor suppression than a PD controller without using any tremor model, while the neural network model outperforms the frequency-based BMFLC model. The findings could set up for devising physics-based Neural networks for pathological tremor modeling and experimentally evaluate the performance of the developed framework.
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    Design and Control of an Ergonomic Wearable Full-Wrist Exoskeleton for Pathological Tremor Alleviation
    Wang, Jiamin (Virginia Tech, 2023-01-31)
    Activities of daily living (ADL) such as writing, eating, and object manipulation are challenging for patients suffering from pathological tremors. Pathological tremors are involuntary, rhythmic, and oscillatory movements that manifest in limbs, the head, and other body parts. Among the existing treatments, mechanical loading through wearable rehabilitation devices is popular for being non-invasive and innocuous to the human body. In particular, a few exoskeletons are developed to actively mitigate pathological tremors in the forearm. While these forearm exoskeletons can effectively suppress tremors, they still require significant improvements in ergonomics to be implemented for ADL applications. The ergonomics of the exoskeleton can be improved via design and motion control pertaining to human biomechanics, which leads to better efficiency, comfort, and safety for the user. The wrist is a complicated biomechanical joint with two coupled degrees of freedom (DOF) pivotal to human manipulation capabilities. Existing exoskeletons either do not provide tremor suppression in all wrist DOFs, or can be restrictive to the natural wrist movement. This motivates us to explore a better exoskeleton solution for wrist tremor suppression. We propose TAWE - a wearable exoskeleton that provides alleviation of pathological tremors in all wrist DOFs. The design adopts a 6-DOF rigid linkage mechanism to ensure unconstrained natural wrist movements, and wearability features without extreme tight-binding or precise positioning for convenient ADL applications. When TAWE is equipped by the user, a closed-kinematic chain is formed between the exoskeleton and the forearm. We analyze the coupled multibody dynamics of the human-exoskeleton system, which reveals a few robotic control problems - (i) The first problem is the identification of the unknown wrist kinematics within the closed kinematic chain. We realize the real-time wrist kinematic identification (WKI) based on a novel ellipsoidal joint model that describes the coupled wrist kinematics, and a sparsity-promoting Extended Kalman Filter for the efficient real-time regression; (ii) The second problem is the exoskeleton motion control for tremor suppression. We design a robust adaptive controller (IO-RAC) based on model reference adaptive control and inverse optimal robust control theories, which can identify the unknown model inertia and load, and provide stable tracking control under disturbance; (iii) The third problem is the estimation of voluntary movement from tremorous motion data for the motion planning of exoskeleton. We develop a lightweight and data-driven voluntary movement estimator (SVR-VME) based on least square support vector regression, which can estimate voluntary movements with real-time signal adaptability and significantly reduced time delay. Simulations and experiments are carried out to test the individual performance of robotic control algorithms proposed in this study, and their combined real-time performance when integrated into the full exoskeleton control system. We also manufacture the prototype of TAWE, which helps us validate the proposed solutions in tremor alleviation exoskeletons. Overall, the design of TAWE meets the expectations in its compliance with natural wrist movement and simple wearability. The exoskeleton control system can execute stably in real-time, identify unknown system kinematics and dynamics, estimate voluntary movements, and suppress tremors in the wrist. The results also indicate a few limitations in the current approaches, which require further investigations and improvements. Finally, the proposed exoskeleton control solutions are developed based on generic formulations, which can be applied to not only TAWE, but also other rehabilitation exoskeletons.
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    Development of Comprehensive Experimental, Analytical and, Numerical Methods for Predicting Rubber Friction and Wear under Thermomechanical Conditions
    Shams Kondori, Mehran (Virginia Tech, 2021-10-07)
    Viscoelastic materials have been used widely in different applications, such as constructing tires, artificial joints, shoe heels, and soles. A study on the different characteristics of viscoelastic materials has always been a matter of interest in order to improve their properties for various applications. In the automotive industry, rubber, as a viscoelastic material, has been used in several subsystems, such as vehicle interior, suspension, steering joints, and tires. The tire and terrain's contact characteristics are among the essential factors for assessing the performance of the tire and the vehicle in general. Friction and tread wear are two of these contact characteristics. Considering the tire's functionality, for most applications, it is desired to have higher friction to have better traction and a lower wear rate to minimize the material loss of the tread. The friction coefficient and the rubber's wear rate depend on various parameters such as rubber material properties, terrain characteristics, temperature (tread and the environment), and the load. To obtain the wear rate and friction of a viscoelastic material, three approaches have been used for this study: Experimental, Analytical, and Numerical. The results obtained using these approaches have been compared and validated. Several test setups have been designed and implemented to study the wear and friction of the rubber experimentally. Also, a new linear friction tester has been designed and manufactured by the author to achieve this project's objectives. The new test setup has several advantages over existing test setups in this field, such as covering a higher range of velocities while maintaining high precision. The designed Linear Friction tester and the modified dynamic friction tester at the CenTiRe laboratory at Virginia Tech were used to measure the rubber's friction and wear for different testing conditions such as different normal loads, different velocities, and various surfaces such asphalt and sandpaper. The data collected by the experiment will later be used for the validation of the developed models. In order to obtain the wear rate of the rubber using the analytical approach, the real contact area and friction of the rubber were calculated using Persson's model. The simulation has created the surface to obtain the friction coefficient and the real contact area. After obtaining the friction coefficient and the real contact area, the rubber's wear rate was calculated using a novel approach by combining the Persson Powdery Rubber Wear model with the Crack Propagation model. The results from the improved model compare well with the results from the original model. For the last step of this project, a Finite Element approach was used for modeling a tread block and round rubber sample. A new semi-empirical model for wear was developed by improving the Archard wear model. The novel approach was implemented to Abaqus by using the Umeshmotion subroutine and adaptive mesh motion (ALE) and subroutine UFric and UFric_Coef in two categories: The Node base method and the Ribbon base method. For finite element modeling, the visco-hyper elastic material model has been used to define the rubber's material properties.
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    Dynamic Modeling and Lateral Stability Analysis of Long Combination Vehicles
    Zhang, Zichen (Virginia Tech, 2022-10-28)
    This study provides a comprehensive modeling evaluation of the dynamic stability of Long Combination Vehicles (LCVs) that are commonly operated on U.S. highways, using multibody dynamic simulations in MATLAB/Simulink®. The dynamic equations for a tractor with two trailers connected by an A-frame converter dolly (A-Dolly) are developed. The dynamic model is used for running MATLAB® simulations, with parameters that are obtained through measurements or obtained from other sources. The simulation results are verified using track test data to establish a baseline model. The baseline model is used for parametric studies to evaluate the effect of trailer cargo weight, center of gravity (CG) longitudinal location, and trailer wheelbase. The dynamic model is further used to analyze both single-trailer and double-trailer trucks through nondimensionalization. The nondimensionalization method has the added advantage of enabling studies that can more broadly apply to various truck configurations. The simulation results indicate that increasing the trailer wheelbase reduces rearward amplification due to the damping effect of the longer wheelbase. A larger momentum ratio due to increased trailer gross weight increases rearward amplification. The detailed models of pneumatic disc and drum brakes in LCVs, including the airflow delay and thermal characteristics, are also developed and are coupled with the articulated vehicle dynamic models. The disc and drum brake braking performance are evaluated and compared in straight-line braking and combined steering and braking at a 150-ft J-turn maneuver. In straight-line braking, the simulation results indicate that disc brakes provide significantly shorter braking distance than drum brakes at highway speeds on a dry road, mainly due to their larger braking torque. On a slippery road surface, however, the greater braking torque causes more frequent wheel lockup and ABS activation at higher speeds, and disc brakes do not provide a substantially shorter braking distance than drum brakes. The simulations also point out that the disc brakes' cooling capacity is higher than the drum brake, with the cooling efficiency heavily dependent on the airflow speed. At higher driving speeds, the airflow accelerates to a turbulent flow and increases the convection efficiency. For braking in-turn maneuvers, at higher entering speeds, disc brakes decelerate the vehicle slightly sooner and then scrub speed faster, resulting in better roll stability when compared with drum brakes.
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    Effect of electromechanical coupling on locally resonant quasiperiodic metamaterials
    LeGrande, Joshua; Bukhari, Mohammad; Barry, Oumar (AIP Publishing, 2023-01)
    Electromechanical metamaterials have been the focus of many recent studies for use in simultaneous energy harvesting and vibration control. Metamaterials with quasiperiodic patterns possess many useful topological properties that make them a good candidate for study. However, it is currently unknown what effect electromechanical coupling may have on the topological bandgaps and localized edge modes of a quasiperiodic metamaterial. In this paper, we study a quasiperiodic metamaterial with electromechanical resonators to investigate the effect on its bandgaps and localized vibration modes. We derive here the analytical dispersion surfaces of the proposed metamaterial. A semi-infinite system is also simulated numerically to validate the analytical results and show the band structure for different quasiperiodic patterns, load resistors, and electromechanical coupling coefficients. The topological nature of the bandgaps is detailed through an estimation of the integrated density of states. Furthermore, the presence of topological edge modes is determined through numerical simulation of the energy harvested from the system. The results indicate that quasiperiodic metamaterials with electromechanical resonators can be used for effective energy harvesting without changes in the bandgap topology for weak electromechanical coupling.
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    An Evaluation of Laboratory and Test Road Environments and Electric Vehicle Warning Sounds and Systems
    Beard, Michael Hansen (Virginia Tech, 2022-08-23)
    The number of electric vehicles on the road is increasing rapidly every year. Due to the decreased sound produced by these vehicles at low speeds, there is significant concern that pedestrians and bicyclists will be at increased risk of vehicle collisions. This is particularly true for those with vision impairment who cannot rely on visual cues to alert them of an approaching vehicle. This thesis explores pedestrian aural detectability of six electric vehicle additive sounds produced by two additive sound systems: a modified version of the factory equipped system and a prototype exciter transducer-based system. All additive sounds and systems were first evaluated for regulatory compliance at stationary, 10 km/h, and 20 km/h conditions and then pedestrian detectability was assessed using 16 blind folded participants and on-road drive by tests. Participant drive by tests were then replicated using 3D sound field recordings played in a high-fidelity immersive reality lab. Results were used to verify the accuracy of lab environment and its potential applicability to future testing. The exciter transducer acoustic warning system was found to created more uniform sound levels on the passenger and drivers' sides of the vehicle than the factory system but produced lower sound levels on the front side of the vehicle. Additive sound modulation rate was not determined to be a key differentiator in pedestrian detectability and low frequency emphasis sounds were found to have the highest level of pedestrian detectability. As expected, vehicle speed played a critical role in participant detection with the 20 km/h speed condition producing higher average detection distances. The immersive reality lab was found to not replicate on-road environment however a perceived linear offset was observed between the two environments.
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    Experimental Evaluation of Roll Stability Control System Effectiveness for A-double Commercial Trucks
    Van Kat, Zachary Robert (Virginia Tech, 2022-01-05)
    Some of the results of an extensive track testing program at the Center for Vehicle Systems and Safety (CVeSS) at Virginia Tech for evaluating the roll stability of commercial trucks with 33-ft A-double trailers are evaluated. The study includes straight-rail trailers with heavy and light loading conditions. Commercial trucks are more susceptible to rollovers than passenger cars because of their higher center of gravity relative to their track width. Multi-trailer articulated heavy vehicles, such as A-doubles, are particularly prone to rollovers because of their articulation and rearward amplification. Electronic stability control (ESC) has been mandated by the National Highway Safety Administration (NHSTA) for Class 8 trucks and busses since 2017. When detecting oversteer or understeer, ESC automatically activates the brakes at the correct side of the steer and/or drive axle(s) to regain steering stability. ESC, however, often cannot sense the likelihood of trailer rollover in multi-trailer articulated heavy vehicles because of the articulation between the trailers and tractors. As a result of this, trailers are often equipped with roll stability control (RSC) systems to mitigate speed-induced rollovers. Sensing the trailer lateral acceleration, RSC activates the trailer brakes to reduce speed and lower the likelihood of rollover. However, a limited number of past studies have shown that the trailer roll angle may provide an earlier indication of a pending rollover than the lateral acceleration. This study intends to provide further analysis in this regard in an effort to improve the effectiveness of RSC systems for trailers. An extensive amount of data from track testing with a 33-ft A-double under heavy and light loading is evaluated. Particular attention is given to lateral accelerations and trailer roll angles prior to rollover and relative to RSC activation time. The study's results indicate that the trailer roll angle provides a slightly earlier indication of rollover than lateral acceleration during dynamic driving conditions, potentially resulting in a timelier activation of RSC. Of course, detecting the roll angle is often more challenging than lateral acceleration, which can be detected with an accelerometer. Additionally, the roll angle measurement may be subjected to errors and possibly unwanted RSC engagement. The study's results further indicate that the trailer-based RSC systems effectively mitigate rollovers in both quasi-steady-state and dynamic driving conditions.
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    An Exploration of Nonlinear Locally Resonant Metamaterials with Electromechanical and Topological elements
    Malla, Arun Lee (Virginia Tech, 2024-07-02)
    In recent years, the study of metamaterials has been a subject of much interest, with acoustic metamaterials being applied to a wide range of applications. This utility is in part due to the incorporation of various elements in their design. The addition of local resonators provides greater versatility in controlling vibrations. Nonlinear elements introduce features such as discrete breathers and frequency shift. Electromechanical metamaterials have been established to have great potential for use in simultaneous energy harvesting in addition to vibration control. Furthermore, metamaterials with quasiperiodic patterning have been shown to possess useful properties such as edge-localized modes. However, no works investigate the interaction between all these elements, especially in the nonlinear regime. In this work, we investigate a unique metamaterial with local resonators, nonlinearity, electromechanical elements, and quasiperiodicity. The proposed metamaterial is examined using both analytical and numerical techniques in order to firmly establish the effects of each element. First, a nonlinear metamaterial with electromechanical local resonators is studied using the perturbation method of multiple scales, wavepacket excitation and direct integration, and specto-spatial processing techniques. The effect of the electromechanical local resonators is established for both the linear and nonlinear regimes, notably including the addition of new bandgaps and pass bands. The influence of electrical parameters on the system dynamics is explored through parametric analysis, demonstrating their use in tuning the system response. It is also shown that nonlinear phenomena such as localized solitons and frequency shift are present in the voltage response of the electromechanical metamaterial. Next, a nonlinear metamaterial with local resonators and quasiperiodicity is investigated using the method of multiple scales as well as numerical solution of the method of harmonic balance. Topological features stemming from quasiperiodicity are observed in the linear and nonlinear regimes. The presence of local resonators is shown to result in an additional, topologically trivial bandgap. The influence of quasiperiodic parameters and the source of quasiperiodicity on the system's band structure and mode shapes are established in both the linear and nonlinear regimes. Nonlinearity is also shown to affect topological features such as edge modes, resulting in amplitude dependence that can affect the localization of these modes in the nonlinear regime. Finally, a metamaterial with nonlinearity, electromechanical local resonators, and quasiperiodic patterning is modeled and investigated. Multiple configurations are examined, including different shunt circuits coupled to the electromechanical resonators and different sources of quasiperiodic patterning. It is shown that electromechanical local resonators produce two topologically trivial bandgaps, compared to the single trivial bandgap of the purely mechanical resonator. The influence of mechanical, electrical, and quasiperiodic parameters is explored to establish the effects of these parameters on bandgap formation in the linear regime. The behavior of the metamaterial in the nonlinear regime was found to be consistent with a purely mechanical system, with no adverse effects from the presence of electromechanical elements. The impact of nonlinear and quasiperiodic phenomena on energy harvesting is also investigated. Through exploration of this unique metamaterial, it is shown that beneficial features from all elements can be present at once, resulting in a versatile metamaterial with great potential for numerous applications.
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    High-Speed Roll Stability Evaluation of A-Double Tractor-Trailers
    Zheng, Xiaohan (Virginia Tech, 2023-01-03)
    The effect of center of gravity (CG) height and lateral and longitudinal off-centering on high-speed roll stability of A-double tractor trailers with 28-ft and 33-ft straight-rail and drop-frame trailers is evaluated through simulation and track testing. The changes in CG position due to the type of trailer (straight-rail vs. drop-frame) and laterally and longitudinally off-centered loads are considered. The simulation results show that imbalanced trailer loading induces roll instability and increases the likelihood of trailer rollover. Additionally, for equal loading conditions, the drop-frame trailers exhibit better roll stability than straight-rail trailers because of the lower CG. The simulation evaluation of 28-ft A-doubles is complemented with track testing of 33-ft trailers in alike (Drop-Drop and Straight-Straight) and mixed (Drop-Straight and Straight-Drop) arrangements of front and rear trailers, for various steering maneuvers that represent highway driving, such as exit ramp, obstacle avoidance, etc. The test trailers include specially designed load frames for emulating a loaded trailer in various loading conditions, outriggers for preventing trailer rollover, and durability structures for withstanding the torsional and bending moments resulting from the tests. Various sensors, including GPS, LiDAR units, accelerometers, string pots, and pressure transducers, are used, along with an onboard data acquisition (DAQ) system, for collecting the necessary data for post-analysis. Analysis of the test data indicates that the Drop-Drop configuration exhibits higher roll stability than the Straight-Straight configuration. For mixed trailers, the Drop-Straight configuration exhibits higher roll stability in exit ramps, but lower obstacle avoidance stability. Equipping the trailers with a roll stability control (RSC) system improves roll stability in terms of increasing the rollover threshold speed and tolerating more aggressive lane change steering maneuvers for A-doubles in various conditions. The RSC performance increases further when the brake application is synchronized between the two trailers to account for any lateral dynamic delay that naturally occurs. A novel interconnected RSC system is proposed to eliminate the lag between the RSC modules with a new control logarithm. The proposed RSC system increases the trailers' roll stability by 16% when compared with independent RSC systems that are commonly used for A-doubles.
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    Investigation of a Mobile Damping Robot for Electric Transmission Lines
    Choi, Andrew C. (Virginia Tech, 2023-07-03)
    Electric transmission lines suffer from many hazards, including wind-induced vibrations (WIV), which can lead to fatigue failure of the transmission conductors. Current vibration mitigation methods do not adequately address WIV because they overwhelmingly rely on narrow-band fixed absorbers. A mobile damping robot (MDR) can overcome the limitations of these fixed absorbers by actively transporting them to locations of highest amplitude on the cable; i.e., antinodes. These antinodes are where the absorbers can most efficiently remove energy from the system. While analyses have been performed for vibration absorbers on transmission line conductors, they have not been in the context of a mobile damping robot (MDR). There is a need to investigate the potential impact of the MDR on a transmission line and the resulting implications for the MDR's development. In this thesis, we explore the dynamics of a power line conductor through finite element analysis (FEA) and modal testing. We perform numerical analysis in MATLAB using equations of motion obtained via Hamilton's Principle. We discuss the design and validation of an appropriate test bench and MDR prototype. We also experimentally investigate the ability of the MDR prototype to transport a mass along a conductor to antinode locations. Experimental results indicate that the damping robot is indeed able to navigate to cable locations of highest amplitude corresponding to antinodes. We then conclude and discuss future work. The insights gained from this research lay a foundation to guide further development of the MDR. Through this work, we are better able to define the operating conditions of the MDR, which will facilitate the creation of a more robust, adaptable control framework for expanded capability.
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    Modal Analysis of a Discrete Tire Model and Tire Dynamic Response Rolling Over Short Wavelength Road Profiles
    Alobaid, Faisal (Virginia Tech, 2022-09-19)
    Obtaining the modal parameters of a deflected and rolling tire represents a challenge due to the complex vibration characteristics that cause the tire's symmetry distortion and the natural frequencies' bifurcation phenomena. The modal parameters are usually extracted using a detailed finite element model. The main issue with full modal models (FEA, for example) is the inability to integrate the tire modal model with the vehicle models to tune the suspension system for optimal ride comfort. An in-plane rigid–elastic-coupled tire model was used to examine the 200 DOF finite difference method (FDM) modal analysis accuracy under non-ground contact and non-rotating conditions. The discrete in-plane rigid–elastic-coupled tire model was modified to include the contact patch restriction, centrifugal force, Doppler, and Coriolis effects, covering a range of 0-300 Hz. As a result, the influence of the contact patch and the rotating tire conditions on the natural frequencies and modes were obtained through modal analysis. The in-plane rigid–elastic-coupled modal model with varying conditions was created that connects any two DOFs around the tire's tread or sidewall as inputs or outputs. The vertical movement of the wheel was incorporated into the in-plane rigid–elastic-coupled tire modal model to extract the transfer function (TF) that connects road irregularities as an input to the wheel's vertical movement as an output. The TF was utilized in a quasi-static manner to obtain the tire's enveloping characteristics rolling over short wavelength obstacles as a direct function of vertical wheel displacement under varying contact patch length constraints. The tire modal model was implemented with the quarter car model to obtain the vehicle response rolling over short wavelength obstacles. Finally, a sensitivity analysis was performed to examine the influence of tire parameters and pretension forces on natural frequencies.
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    Modelling of a Bio-inspired Bistable Structure for Potential Application in Fish Telemetry Tags
    Bhalerao, Mrunal Vinay (Virginia Tech, 2025-01-13)
    Monitoring of aquatic life is important for assessing long-term impacts on activities associated with fish stock and migration. One promising approach for long-term monitoring involves the development of self-powered telemetry devices capable of powering themselves by harnessing energy from the fish body undulations using implanted devices or from fluid motions generated by fish swimming using external devices. One of the latter devices is a broadband low frequency nonlinear bistable energy harvester. This cost-effective harvester has been inspired from the doubly curved leaf blades of a Venus-fly trap. This work ex- amines the static behavior of such a bio-inspired bistable energy harvester by analyzing its force-displacement characteristics. The objective is to identify crucial design parameters to optimize the harvester's performance for potential application in self-powered fish telemetry tags. The unique characteristics of the hysteresis loop and snap-through discontinuity of the bistable structure are investigated using experimentation and finite element analysis. The finite element model is found to qualitatively replicate experimental observations. Addition- ally, geometrical and assembly parameters that affect the force-displacement behavior of the harvester are identified. A sensitivity analysis is performed to determine the effect of the aspect ratio, buckling displacement and thickness of the proposed harvester on the static force-displacement curve. The sensitivity analysis has highlighted that the assembly and geometric parameters of the bistable structure affect multiple aspects of the force-displacement behavior simultaneously. Hence, analytical modeling has been attempted using the theory of lateral torsional buckling to further investigate the complex influence of the said parameters.
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    Simultaneous Vibration Control and Energy Harvesting of Nonlinear Systems Applied to Power Lines
    Kakou, Paul-Camille (Virginia Tech, 2024-05-28)
    The resilience of power infrastructure against environmental challenges, particularly wind-induced vibrations, is crucial for ensuring the reliability and longevity of overhead power lines. This dissertation extends the development of the Mobile Damping Robot (MDR) as a novel solution for mitigating wind-induced vibrations through adaptive repositioning and energy harvesting capabilities. Through comprehensive experimental and numerical analyses, the research delineates the design, optimization, and application of the MDR, encompassing its dynamic adaptability and energy harvesting potential in response to varying wind conditions. The study begins with the development and validation of a linearized model for the MDR, transitioning to advanced nonlinear models that more accurately depict the complex interactions between the robot, cable system, and environmental forces. A global stability analysis provides crucial insights into the operational limits and safety parameters of the system. Further, the research explores a multi-degree-of-freedom system model to evaluate the MDR's efficacy in real-world scenarios, emphasizing its energy harvesting efficiency and potential for sustainable operation. Findings from this research show the clear promise for the development of the MDR with the consideration of the nonlinear dynamics in play between the robot, the cable, and the wind. This work lays a foundational framework for future innovations in infrastructure maintenance, paving the way for the practical implementation of mobile damping technologies in energy systems.
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    Towards A Mobile Damping Robot For Vibration Reduction of Power Lines
    Kakou, Paul-Camille (Virginia Tech, 2021-05-18)
    As power demand across communities increases, focus has been given to the maintenance of power lines against harsh environments such as wind-induced vibration (WIV). Currently, Inspection robots are used for maintenance efforts while fixed tuned mass dampers (FTMDs) are used to prevent structural damages. However, both solutions are facing many challenges. Inspection robots are limited by their size and considerable power demand, while FTMDs are narrowband and unable to adapt to changing wind characteristics, and thus are unable to reposition themselves at the antinodes of the vibrating loop. In view of these shortcomings, we propose a mobile damping robot (MDR) that integrates inspection robots' mobility and FTMDs WIV vibration control to help maintain power lines. In this effort, we model the conductor and the MDR by using Hamilton's principle and we consider the two-way nonlinear interaction between the MDR and the cable. The MDR is driven by a Proportional-Derivative controller to the optimal vibration location (i.e, antinodes) as the wind characteristics vary. The numerical simulations suggest that the MDR outperforms FTMDs for vibration mitigation. Furthermore, the key parameters that influence the performance of the MDR are identified through a parametric study. The findings could set up a platform to design a prototype and experimentally evaluate the performance of the MDR.
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    Towards Naturalistic Exoskeleton Glove Control for Rehabilitation and Assistance
    Chauhan, Raghuraj Jitendra (Virginia Tech, 2020-01-11)
    This thesis presents both a control scheme for naturalistic control of an exoskeleton glove and a glove design. Exoskeleton development has been focused primarily on design, improving soft actuator and cable-driven systems, with only limited focus on intelligent control. There is a need for control that is not limited to position or force reference signals and is user-driven. By implementing a motion amplification controller to increase weak movements of an impaired individual, a finger joint trajectory can be observed and used to predict their grasping intention. The motion amplification functions off of a virtual dynamical system that safely enforces the range of motion of the finger joints and ensures stability. Three grasp prediction algorithms are developed with improved levels of accuracy: regression, trajectory, and deep learning based. These algorithms were tested on published finger joint trajectories. The fusion of the amplification and prediction could be used to achieve naturalistic, user-guided control of an exoskeleton glove. The key to accomplishing this is series elastic actuators to move the finger joints, thereby allowing the wearer to deflect against the glove and inform the controller of their intention. These actuators are used to move the fingers in a nine degree of freedom exoskeleton that is capable of achieving all the grasps used most frequently in daily life. The controllers and exoskeleton presented here are the basis for improved exoskeleton glove control that can be used to assist or rehabilitate impaired individuals.