@article{jenkins_atay_buckner_bryant_2021, title={Genetic Algorithm-Based Optimal Design of a Rolling-Flying Vehicle}, volume={13}, ISSN={["1942-4310"]}, DOI={10.1115/1.4050811}, abstractNote={
 This work describes a design optimization framework for a rolling-flying vehicle consisting of a conventional quadrotor configuration with passive wheels. For a baseline comparison, the optimization approach is also applied for a conventional (flight-only) quadrotor. The vehicle range is maximized using a hybrid multi-objective genetic algorithm in conjunction with multi-physics system models. A low Reynolds-number blade element momentum theory aerodynamic model is used with a brushless DC motor model, a terramechanics model, and a vehicle dynamics model to simulate the vehicle range under any operating angle-of-attack and forward velocity. To understand the tradeoff between vehicle size and operating range, variations in Pareto-optimal designs are presented as functions of vehicle size. A sensitivity analysis is used to better understand the impact of deviating from the optimal vehicle design variables. This work builds on current approaches in quadrotor optimization by leveraging a variety of models and formulations from literature and demonstrating the implementation of various design constraints. It also improves upon current ad-hoc rolling-flying vehicle designs created in previous studies. Results show the importance of accounting for oft-neglected component constraints in the design of high range quadrotor vehicles. The optimal vehicle mechanical configuration is shown to be independent of operating point, stressing the importance of a well-matched, optimized propulsion system. By emphasizing key constraints that affect the maximum and nominal vehicle operating points, an optimization framework is constructed that can be used for RFVs and conventional multi-rotors.}, number={5}, journal={JOURNAL OF MECHANISMS AND ROBOTICS-TRANSACTIONS OF THE ASME}, author={Jenkins, Tyler and Atay, Stefan and Buckner, Gregory and Bryant, Matthew}, year={2021}, month={Oct} }
 @article{atay_jenkins_buckner_bryant_2020, title={Energetic analysis and optimization of a bi-modal rolling-flying vehicle}, volume={4}, ISSN={["2366-598X"]}, DOI={10.1007/s41315-020-00119-2}, number={1}, journal={INTERNATIONAL JOURNAL OF INTELLIGENT ROBOTICS AND APPLICATIONS}, author={Atay, Stefan and Jenkins, Tyler and Buckner, Gregory and Bryant, Matthew}, year={2020}, month={Mar}, pages={3–20} }
 @article{jenkins_bryant_2020, title={Pennate actuators: force, contraction and stiffness}, volume={15}, ISSN={["1748-3190"]}, DOI={10.1088/1748-3190/ab860f}, abstractNote={Hierarchical actuators are comprised of multiple individual actuator elements arranged into a system, resulting in improved and expanded performance. Natural muscle tissue is a complex and multi-level example of hierarchical actuation, with its hierarchy spanning from the micrometer to the centimeter scale. In addition to a hierarchical configuration, muscle tissue exists in varying geometric arrangements. Pennate muscle tissue, denoted by its characteristic fibers extending obliquely away from the muscle tissue line of action, leverages geometric complexity to transform the relationship between fiber inputs and muscle tissue outputs. In this paper, a bioinspired hierarchical pennate actuator is detailed. This work expands on previous pennate actuator studies by deriving constitutive force, contraction, and stiffness models for a general pennate actuator, where the constituent fibers can be constructed from any linear actuator. These models are experimentally validated by studying a pennate actuator with McKibben artificial muscles constituting the actuator fibers. McKibben artificial muscles are used because they have a high force-to-weight ratio and are inexpensive to construct, making them an attractive candidate for hierarchical actuators and mobile robotics. Using the derived constitutive models, general pennate actuator performance is better understood by analyzing the transmission ratio, blocked force, and free contraction. Loaded contractions and stiffness during isotonic and isobaric contractions are also explored. The results allow for informed design decisions and an understanding of the associated tradeoffs when recreating the remarkable properties of pennate musculature. Future work will leverage the results of this paper to create an adaptive pennate actuator that is capable of changing configuration in response to force, contraction and stiffness demands.}, number={4}, journal={BIOINSPIRATION & BIOMIMETICS}, author={Jenkins, Tyler and Bryant, Matthew}, year={2020}, month={Jul} }
 @article{jenkins_bryant_2019, title={Variable stiffness soft robotics using pennate muscle architecture}, volume={10965}, ISBN={["978-1-5106-2585-3"]}, ISSN={["1996-756X"]}, DOI={10.1117/12.2514265}, abstractNote={Biological pennate muscles, denoted by muscle fibers arranged obliquely relative to the line of action, have shown the ability to passively regulate the effective transmission ratio coupling fiber contraction to overall muscle contraction. In this paper, a model for a bio-inspired variable-stiffness pennate actuator is developed. The pennate topology observed in natural musculature is leveraged to create an actuator capable of varying stiffness based on its mutable configuration. Variable Stiffness Actuators (VSA’s) are useful for roboticists and engineers because they enable features atypical of traditional, stiff kinematic linkages, such as energy storage or increased human-interactive safety. Typically, VSA’s are constructed of rigid materials, such as motors and springs. However, by utilizing non-rigid actuators in a pennate configuration, a pliable, soft VSA can be conceived. Previous studies have experimentally utilized McKibben artificial muscles and Twisted Coil Polymer wires in lieu of muscle fibers to recreate the pennate muscle architecture. This paper expands on previous pennate actuator studies by providing a general modeling framework, allowing roboticists to make informed design decisions and understand associated tradeoffs when recreating the remarkable properties of pennate musculature. Theoretical case studies are performed to better understand the design tradeoffs. The Variable Stiffness Pennate Actuator is a promising actuator configuration that can readily integrate with other bio-inspired actuator technologies, such as orderly recruitment.}, journal={BIOINSPIRATION, BIOMIMETICS, AND BIOREPLICATION IX}, author={Jenkins, Tyler and Bryant, Matthew}, year={2019} }
 @article{chapman_jenkins_bryant_2018, title={Design and analysis of electrohydraulic pressure systems for variable recruitment in fluidic artificial muscles}, volume={27}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665X/aadbff}, abstractNote={This paper investigates the energetics and performance of an electrohydraulic power system with variable recruitment fluidic artificial muscle (FAM) actuators. A coupled dynamic model of the system is developed and applied to study the implications of hydraulic power system architecture for both variable recruitment actuator bundles and equivalent single-muscle actuators. This analysis extends previous FAM literature by considering both actuator recruitment methodology as well as the complete electromechanical circuit and the interactions of these two subsystems. Specifically, for both single-muscle actuators and variable recruitment muscle bundles, hydraulic architectures with a continuously-operating motor and pump are compared with a system in which the motor is intermittently shut down and restarted based on accumulator pressure. The results reveal that variable recruitment offers bandwidth advantages over the single equivalent actuator regardless of the hydraulic power architecture that is selected. However, use of the intermittently-operating motor and pump system allowed the variable recruitment system to achieve efficiency advantages over the other configurations considered. A steady-state analytic solution for the operating envelopes of the variable recruitment and single-muscle systems, including force limits and flow rate limits, was also developed and used to investigate effects of pump displacement on system bandwidth and stroke. The results of these analyses provide tools for the selection of actuator configuration, system architecture, and component design in FAM-actuated electrohydraulic robots.}, number={10}, journal={SMART MATERIALS AND STRUCTURES}, author={Chapman, Edward M. and Jenkins, Tyler and Bryant, Matthew}, year={2018}, month={Oct} }
 @article{nabavi_chakrabortty_2017, title={Structured Identification of Reduced-Order Models of Power Systems in a Differential-Algebraic Form}, volume={32}, ISSN={0885-8950 1558-0679}, url={http://dx.doi.org/10.1109/tpwrs.2016.2554154}, DOI={10.1109/tpwrs.2016.2554154}, abstractNote={In a recent paper, we proposed a system identification method for constructing reduced-order models for the electro-mechanical dynamics of large power systems, divided into multiple coherent clusters, using Synchrophasors. Every cluster in the actual model was represented as an aggregate generator in the reduced-order model. An aggregate network graph connected one aggregate generator to another. In this paper, we extend this identification approach to differential-algebraic (DAE) models. First, every cluster is associated with a unique terminal bus, referred to as the pilot bus, that couples its internal network to the rest of the system. The proposed algorithm uses Synchrophasor measurements from the pilot buses to identify the dynamic model of the aggregate generator for each cluster using nonlinear least squares while retaining the identity of all the pilot buses. The resulting reduced-order model is in the form of a nonlinear electric circuit described by aggregate differential and algebraic equations. We illustrate our results using two case studies, one for the IEEE 9-bus power system and another for the IEEE 39-bus power system. We also discuss how these reduced-order DAE models may be useful for designing shunt controllers at the pilot buses by using Synchrophasor feedback.}, number={1}, journal={IEEE Transactions on Power Systems}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Nabavi, Seyedbehzad and Chakrabortty, Aranya}, year={2017}, month={Jan}, pages={198–207} }
 @inproceedings{chapman_jenkins_bryant_2016, title={Parametric study of a fluidic artificial muscle actuated electrohydraulic system}, DOI={10.1115/smasis2016-9044}, abstractNote={Fluidic artificial muscles have the potential for a wide range of uses; from injury rehabilitation to high-powered hydraulic systems. Their modeling to date has largely been quasi-static and relied on the operator to adjust pressure so as to control force output and utilization while little work has been done to analyze the kinematics of the driving-systems involved in their operation. This paper utilizes an established electro-hydraulic model to perform a study of the components of a fluidic artificial muscle actuated climbing robot. Its purpose is to determine the effect of the robotic subsystems on function and efficiency for a small-scale system in order to extrapolate more general design and analysis schemes for future use. Its results indicate that important aspects to consider in design of the hydraulic system are system payload, operating pressure, pump selection, and FAM construction.}, booktitle={Proceedings of the asme conference on smart materials adaptive}, author={Chapman, E. and Jenkins, T. and Bryant, M.}, year={2016} }