Ara Arabyan

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• Wang, K., Li, P., & Arabyan, A. (2013). Achieving quasi-isothermal air compression with multistage compressors for large-scale energy storage. ASME 2013 7th Int. Conf. on Energy Sustainability Collocated with the ASME 2013 Heat Transfer Summer Conf. and the ASME 2013 11th Int. Conf. on Fuel Cell Science, Engineering and Technology, ES 2013.
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  Abstract:The round trip efficiency of compressed air for energy storage is greatly limited by the significant increase in the temperature of the compressed air (and the resulting heat loss) in high-ratio adiabatic compression. This paper introduces a multi-stage compression scheme with low-compression-ratio compressors and inter-compressor natural convection cooling resulting in a quasi-isothermal compression process that can be useful for large-scale energy storage. When many low pressure ratio compressors work inline, a high overall compression ratio can be achieved with high efficiency. The quasi-isothermally compressed air can then be expanded adiabatically in turbines to generate power with the addition of thermal energy, from either fuel or a solar thermal source. This paper presents mathematical models of such an energy storage system and discusses its round-trip performance with different operating schemes. Copyright © 2013 by ASME.
• Bogosyan, S., & Arabyan, A. (2007). High-order, sliding-mode-based precise control of direct-drive systems under heavy uncertainties. Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering, 221(5), 791-805.
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  Abstract: The high-performance control of direct-drive (DD) systems requires the full system dynamic effects to be taken into account owing to the eliminated gear mechanism. The actuator dynamics and structural flexibilities become of increased importance, particularly when highspeed, high-accuracy operation of lightweight structures is aimed for; however, in most related literature, these effects are neglected to avoid increased computational complexity at the expense of compromising the tracking accuracy of the system in the transient and steady state. As a solution to the problem, in this study, high-order, sliding-mode (HOSM) controllers (HOSMCs) are developed, which exploit the robustness properties of sliding-mode controllers (SMCs) while also increasing accuracy by reducing chattering effects. Different from standard HOSMCs, which are derived by artificially increasing the system order, the third-order HOSM (3-HOSM) control laws in this study are derived by including the actuator dynamics and structural flexibilities in the control design process. Two HOSMCs are developed for this purpose: one with a discontinuous input and one with a continuous input aimed at reducing chattering. The performance of the novel HOSMCs is tested by simulations for the precise position and tracking control of a one-degree-of-freedom (IDOF) DD weapon-positioning system as an example of a direct-drive system under heavy uncertainties and external disturbances. The improved accuracy obtained, particularly with the novel continuous-input 3-HOSMC, motivates the implementation of the schemes for demanding control applications under heavy uncertainties. © IMechE 2007.
• Arabyan, A., Chemishkian, S., & Meroyan, E. (1999). Limits of vibration suppression in flexible structures. Dynamics and Control, 9(3), 223-246.
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  Abstract: A method is described for the determination of limits of vibration suppression in an elastic structure by means of a given number of control actuators. The method is based on a theorem, described and proved herein, that defines the lower limit of residual deformations for specified disturbances and a given map of placement of actuators which can produce finite control forces. The new method can identify regions of placement which result in acceptable residual deformations, thus making control design easier and reduces the cost of searching for optimal actuator positions. Unlike traditional methods used to solve this class of problems, the new method does not require knowledge about the excitation states of various deformation modes. The method is demonstrated by applying it to a simply supported beam and a plate.
• Chemishkian, S., & Arabyan, A. (1999). Intelligent algorithms for H_∞-optimal placement of actuators and sensors in structural control. Proceedings of the American Control Conference, 3, 1812-1816.
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  Abstract: Four algorithms are described to search and find spatial configuration for the placement of a finite number of actuators and sensors on a continuous flexible structure to reduce deformations in the structures to a minimum in H∞ sense. The computational cost of the optimal mapping search is reduced through four techniques. First, the computationally expensive goal function based on the complete H∞ design is replaced by a two-step hybrid function, which performs a computationally inexpensive pass-fail test and proceeds to the complete H∞ design only if the test was passed. Second a target H∞ norm used in the mentioned pass-fail test is adjusted based on the already evaluated mappings in order to increase the number of failed tests and reduce the number of complete H∞ designs. Third, the exhaustive search as the basic search technique is replaced by a more intelligent genetic algorithm. Finally, the search is implemented on a parallel computer. The algorithms are benchmarked for two test cases: a model of a simply supported beam, and a model of the UCLA Large Space Structure.
• Koshland, G. F., Marasli, B., & Arabyan, A. (1999). Directional effects of changes in muscle torques on initial path during simulated reaching movements. Experimental Brain Research, 128(3), 353-368.
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  PMID: 10501807;Abstract: Adults are able to reach for an object for the first time with appropriate direction, speed, and accuracy. The rules by which the nervous system is able to set muscle activities to accomplish these outcomes are still debated and, indeed, the sensitivity of kinematics to variations in muscle torques is unknown for complex arm movements. As a result, this study used computer simulations to characterize the effects of change in muscle torque on initial hand path. The same change was applied to movements towards 12 directions in the horizontal plane, and changes were systematically manipulated such that: (1) torque amplitude was changed at one joint, (2) timing of torque was changed at one joint, and (3) amplitude and/or timing was changed at two joints. Results showed that simultaneous changes in torque amplitude at shoulder and elbow joints affected initial speed uniformly across direction. These results add to conclusions from previous experimental and modeling work that the simplest rule to produce a desired change in speed for any direction is to scale torque amplitude at both joints. In contrast, all simulations showed nonuniform effects on initial path direction. For some regions of the workspace, initial path direction was little affected by either a ± 30% change in amplitude or a ± 100-ms change in timing, whereas for other regions the same changes produced large effects on initial path direction. These findings suggest that the range of possible torque solutions to achieve a particular initial path direction varies within the workspace and, consequently, the requirements for an accurate initial path will vary within the workspace.
• Arabyan, A., & Chemishkian, S. (1998). H_∞-optimal mapping of actuators and sensors in flexible structures. Proceedings of the IEEE Conference on Decision and Control, 1, 821-826.
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  Abstract: A computationally efficient method is described to search and find optimal spatial configurations for the placement (mapping) of a finite number of actuators and sensors on a continuous flexible structure to reduce the vibrations or deformations in the structure to a minimum in the H∞ sense. The method produces a feedback controller corresponding to the minimal H∞ norm of the disturbance-deformation operator. The computational cost of the optimal mapping search is reduced through two techniques. First, the computationally expensive goal function based on the complete H∞ synthesis is evaluated only for the mappings that pass a computationally inexpensive test. Second, the target norm is adjusted statistically based on the already evaluated mappings. Mapping optimization based on exhaustive search and genetic algorithms are presented and demonstrated on a 30-node finite-element model of simply supported beam.
• Arabyan, A., & Fei, W. u. (1998). An Improved Formulation for Constrained Mechanical Systems. Multibody System Dynamics, 2(1), 49-69.
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  Abstract: This paper presents an investigation of the advantages of a new formulation in the study of mechanical systems with holonomic and nonholonomic constraints. The formulation, originally proposed for systems of constrained particles, provides an efficient and robust means of simulating general multibody systems in the presence of redundant, degenerate and intermittent constraints. The structure of the formulation also allows the use of a dynamics code for pure kinematics analysis with a simple substitution. In addition, the formulation separates applied and constraint forces explicitly allowing recovery of constraint forces by straightforward means. Several examples are given to demonstrate the effectiveness of the formulation in special circumstances.
• Arabyan, A., & Jiang, Y. (1998). A consistent dynamic finite element formulation for a pipe using Euler parameters. Shock and Vibration, 5(2), 111-117.
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  Abstract: A pipe element developed earlier for the analysis of combined large bending and torsional deformations of blood vessels under static loading is extended to model behavior in the presence of large rotations and time-varying external forces. As in the case of the earlier element, the enhanced element supports ovalization and warping of its cross-section. The enhancements presented in this paper are comprised of a mass matrix and gyroscopic effects resulting from fast rotation rates and large deformations. The effectiveness of the element is demonstrated by two examples, which simulate the three-dimensional behavior of a highly flexible pipe under dynamic loading conditions.
• Arabyan, A., & Tsai, D. (1998). A distributed control model for the air-righting reflex of a cat. Biological Cybernetics, 79(5), 393-401.
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  PMID: 9851020;Abstract: A multisegment, multijoint model of a falling animal is presented to examine the effectiveness of a two-stage control scheme in a zero-momentum self-righting maneuver. The model contains a much larger number of degrees of freedom than is required to execute a self-righting maneuver and is thus capable of providing multiple solutions for the same task. The decentralized control scheme is designed to achieve gross turning in minimum time and to maintain a steady orientation relative to gravity after the turn has been achieved. The scheme is able to determine the sequence of steps necessary to execute the motor task and also incorporates learning features. Results from various simulations are presented and their implications discussed.
• Bogosyan, M., Gokasan, S., Arabyan, A., & Sabanovic, A. (1998). Sliding mode based controller for a flexible arm with a load. IECON Proceedings (Industrial Electronics Conference), 2, 1083-1087.
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  Abstract: This study is about the chattering-free sliding mode based control of a single link flexible arm with a mass at the endpoint. The model for this system is obtained using Lagrange's method and the control is developed aiming the angular position of the hub unit to follow a desired trajectory, while the strain is forced to be zero. Experimental results obtained on a DSP32 based single link arm system with and without control on the strain, demonstrate the improved performance caused by the strain control in terms of the transient and steady state and robustness.
• Gokasan, M., Bogosyan, O., Sabanovic, A., & Arabyan, A. (1998). Sliding mode observer and controller for a single link flexible arm. Proceedings of the IEEE Conference on Decision and Control, 4, 3625-3626.
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  Abstract: A sliding mode based controller was designed to achieve the end-point tracking of a flexible arm, with minimum transient and steady-state error. The information on deflection is derived through a sliding mode observer, providing data on the variables, q1 and q2 and their derivatives. The sliding mode technique utilized both for the observer and the controller provides robustness against the nonlinearities and uncertainties of the system.
• Jiang, Y., & Arabyan, A. (1996). A new pipe element for modeling three-dimensional large deformation problems. Finite Elements in Analysis and Design, 22(1), 59-68.
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  Abstract: A new straight pipe element that enables the efficient computation of large, three-dimensional deformations in pipes with circular cross-sections is presented. The new element, which supports rigid-body and constant-strain modes, is modeled using curvilinear shell coordinates and sinusoidal interpolation functions and captures all stresses except the normal stress across the shell thickness (i.e. small thickness is assumed). Euler parameters are used to describe rotational rigid-body modes and are incorporated into the element's vector of degrees of freedom. Under general loading (axial, transverse, bending and torsion), the element allows large ovalization of its cross-section and large, three-dimensional, angular changes in the orientation of its reference axis. The formulation used to derive the clement incorporates the nonlinear coupling between torsional and bending deformations. Results are presented for stresses and deformations produced by combined bending and torsional loads. A comparison of these results to corresponding quantities generated by ABAQUS using a large number of 24 degree-of-freedom shell elements indicates excellent agreement and significant gains in computational efficiency because of a reduction in number of degrees of freedom.
• Tsang, T. Y., & Arabyan, A. (1996). A novel approach to the dynamic analysis of highly deformable bodies. Computers and Structures, 58(1), 155-172.
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  Abstract: A method using element-fixed moving reference frames is introduced to compute the behavior of highly deformable bodies undergoing large and fast rotations. The use of reference frames attached to each finite element allows the correct computation of overall large deformations and the characterization of rigid-flexible coordinate coupling through the systematic incorporation of higher-order kinematic terms and time derivatives of coordinate transformation matrices. The approach is applied to planar rotating Bernoulli beams of various flexural rigidities and the results are compared to those obtained by other methods and ABAQUS. a nonlinear finite element package. The results indicate excellent agreement with published data and superior efficiency of compulation.
• Arabyan, A., & Chemishkian, S. (1995). SVD-based control of a beam figure. Proceedings of the American Control Conference, 2, 1413-1417.
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  Abstract: A beam figure control problem which is closely related to active optics concepts and vibration damping of structures is addressed. In view of this, an efficient scheme is developed to control the shape of a beam using only a small number of actuators and sensors. This scheme is modeled and designed using the MATLAB software.
• Flashner, H., Beuter, A., & Arabyan, A. (1988). Fitting mathematical functions to joint kinematics during stepping: Implications for motor control. Biological Cybernetics, 58(2), 91-99.
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  PMID: 3349116;Abstract: The present study extends past work on modeling and control of stepping. The relationship between joint space kinematic data and routine motor control (i.e., open loop) during human stepping is investigated. A model of open loop stepping control using joint kinematics is described. Different functional approximations are employed to simulate experimental joint kinematic data collected on a subject stepping repeatedly over an obstacle. Results indicate that joint kinematics can be characterized by a small number of functions yielding a simple analytical description of open loop motor control. The different basis functions used and their associated coefficients reflected the qualitative behavior of joint trajectories thus allowing flexibility in the formulation of system kinematics. This approach provides a tool to study movement pathologies and movement development by identifying the basis functions governing the kinematics of motion and their associated coefficients. The model presented here is helpful in studying the segmentation of multiarticular movements into their elementary components by analytically modeling the discrete organization of motor behavior. © 1988 Springer-Verlag.
• Arabyan, A., & Shiflett, G. R. (1987). METHOD FOR DETERMINING THE VARIOUS GEAR TRAINS THAT PROVIDE A SPECIFIC VELOCITY RATIO.. Journal of mechanisms, transmissions, and automation in design, 109(4), 475-480.
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  Abstract: The problem of determining the number of teeth on a set of meshing gears for the creation of a gear train is examined. A method is proposed for determining all the gear trains which yield identical velocity ratios and an algorithmic description of the method is provided. Several examples are included in which the results are compared to those of other methods.
• Flashner, H., Beuter, A., & Arabyan, A. (1987). Modeling of control and learning in a stepping motion. Biological Cybernetics, 55(6), 387-396.
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  PMID: 3567242;Abstract: In a previous study (Beuter et al. 1986) the authors modeled a stepping motion using a three-body linkage with four degrees of freedom. Stepping was simulated by using three task parameters (i.e., step height, length, and duration) and sinusoidal joint angular velocity profiles. The results supported the concept of a hierarchical control structure with open-loop control during normal operation. In this study we refine the dynamic model and improve the simulation technique by incorporating the dynamics of the leg after landing, adding a foot segment to the model, and preprogramming the complete step motion using cycloids. The equations of the forces and torques developed on the ground by the foot during the landing phase are derived using the Lagrangian method. Simulation results are compared to experimental data collected on a subject stepping four times over an obstacle using a Selspot motion analysis system. A hierarchical control model that incorporates a learning process is proposed. The model allows an efficient combination of open and closed loop control strategies and involves hardwired movement segments. We also test the hypothesis of cycloidal velocity profiles in the joint programs against experimental data using a novel curve-fitting procedure based on analytical rather than numerical differentiation. The results suggest multiob-jective optimization of the joint's motion. The control and learning model proposed here will help the understanding of the mechanisms responsible for assembling selected movement segments into goaldirected movement sequences in humans. © 1987 Springer-Verlag.
• Arabyan, A., & Shiflett, G. R. (1986). METHOD FOR DETERMINING ALL GEAR PAIRS WHICH SATISFY VELOCITY RATIO AND/OR CENTER DISTANCE CONSTRAINTS.. American Society of Mechanical Engineers (Paper).
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  Abstract: The problem of determining the number of teeth on two meshing external spur gears is examined when either a velocity ratio, a center distance, or a combination of the two is specified. A method is proposed for determining all possible combinations of tooth numbers in each case. The theory behind the method is developed first and the method itself is presented algorithmically. Several examples are provided in which the results are compared to those of other methods.
• Arabyan, A., & Shiflett, G. R. (1986). METHOD FOR DETERMINING ALL GEAR TRAINS THAT PROVIDE A SPECIFIC VELOCITY RATIO.. American Society of Mechanical Engineers (Paper).
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  Abstract: The problem of determining the number of teeth on a set of meshing gears for the creation of a gear train is examined. A method is proposed for determining all the gear trains which yield identical velocity ratios. An algorithmic description of the method is provided. Several examples are included in which the results are compared to those of other methods.
• Beuter, A., Flashner, H., & Arabyan, A. (1986). Phase plane modeling of leg motion. Biological Cybernetics, 53(5), 273-284.
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  PMID: 3697401;Abstract: Phase plane analysis of dynamical systems, in which variables are plotted against their time derivatives, has been recently emphasized as a general method for reconstructing system dynamics from data. The purpose of this experiment was to develop a model of leg movement in a stepping task using the phase plane approach. In this model, the leg is represented as a three-body linkage and the motion of the leg is assumed to be planar with four degrees of freedom. Experimental data was collected on one subject stepping six times, using a two dimensional videomotion analysis system with reflective markers placed on the lower limb joints. A computer program able to solve the equations of motion and compute the state of the system for a given task was implemented. This computer program was written to generate the motion of the leg for a given task using inverse kinematics and a preplanned foot path. Foot trajectories with cycloidal, constant acceleration/deceleration and sinusoidal velocity profiles were studied. From the results, an attempt was made to identify the variables which are measured and to determine the motion characteristics during stepping. The preliminary results support the concept of a hierarchical control structure with openloop control during normal operation. During routine activity there is no direct intervention of the Central Nervous System (CNS). The results support the existence of preprogramming and provide a starting point for the study of the development of control in multiarticulate movements. © 1986 Springer-Verlag.
• Arabyan, A., Shiflett, G. R., & Sun, C. Y. (1984). SIMPLIFIED, MICROCOMPUTER-BASED METHOD FOR SPUR GEAR DESIGN.. American Society of Mechanical Engineers (Paper).
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  Abstract: The design of a pair of gears given geometric constraints, power transmission requirements and other factors is an iterative process that can be time consuming if done by hand; however, much of the work may be automated. A new design algorithm has been developed based on computational techniques which significantly automate and improve the design process. One feature of the algorithm is that it is entirely based on procedures and standards recommended by the American Gear Manufacturers Association (AGMA). A computer program implementing this new algorithm has been developed to assist in the gear design procedure. The program, written in FORTRAN, is interactive and may be run on most personal computers.