Sergey V Shkarayev
- Professor, Aerospace-Mechanical Engineering
- Member of the Graduate Faculty
Dr. Sergey Shkarayev is a Professor in the Department of Aerospace and Mechanical Engineering and a Director of Micro Air Vehicles Laboratory at the University of Arizona. His research interests include unsteady aerodynamics, structural mechanics, and designing of unmanned aerial vehicles. Dr. Shkarayev has coauthored 5 books, 5 original chapters in the scholarly books, and more than 80 journal papers. The University of Arizona Micro Air Vehicles Team, lead by Dr. Shkarayev, won several International Competitions.
- Award for excellence at the student interface
- College of Engineering, UA, Spring 2018
No activities entered.
Advanced DynamicsAME 550 (Spring 2022)
Aerospace Engineering DesignAME 422 (Spring 2022)
Aerospace Engr DesignAME 522 (Spring 2022)
Directed ResearchAME 492 (Spring 2022)
ResearchAME 900 (Spring 2022)
Directed ResearchAME 492 (Fall 2021)
Master's ReportAME 909 (Fall 2021)
ResearchAME 900 (Fall 2021)
Advanced DynamicsAME 550 (Spring 2021)
Aerospace Engineering DesignAME 422 (Spring 2021)
Aerospace Engr DesignAME 522 (Spring 2021)
Master's ReportAME 909 (Spring 2021)
ResearchAME 900 (Spring 2021)
Advanced DynamicsAME 550 (Fall 2020)
AerodynamicsAME 320 (Fall 2020)
ResearchAME 900 (Fall 2020)
Aerospace Engineering DesignAME 422 (Spring 2020)
Aerospace Engr DesignAME 522 (Spring 2020)
ResearchAME 900 (Spring 2020)
ThesisAME 910 (Spring 2020)
Advanced DynamicsAME 550 (Fall 2019)
AerodynamicsAME 320 (Fall 2019)
ResearchAME 900 (Fall 2019)
AerodynamicsAME 320 (Spring 2019)
Aerospace Engineering DesignAME 422 (Spring 2019)
Aerospace Engr DesignAME 522 (Spring 2019)
Directed ResearchAME 492 (Spring 2019)
ResearchAME 900 (Spring 2019)
ThesisAME 910 (Spring 2019)
Advanced DynamicsAME 550 (Fall 2018)
ResearchAME 900 (Fall 2018)
ThesisAME 910 (Summer I 2018)
AerodynamicsAME 320 (Spring 2018)
Aerospace Engineering DesignAME 422 (Spring 2018)
Aerospace Engr DesignAME 522 (Spring 2018)
Independent StudyAME 699 (Spring 2018)
ResearchAME 900 (Spring 2018)
ThesisAME 910 (Spring 2018)
Advanced DynamicsAME 550 (Fall 2017)
Independent StudyAME 599 (Fall 2017)
ThesisAME 910 (Fall 2017)
AerodynamicsAME 320 (Spring 2017)
Aerospace Engineering DesignAME 422 (Spring 2017)
Aerospace Engr DesignAME 522 (Spring 2017)
Independent StudyAME 599 (Spring 2017)
ResearchAME 900 (Spring 2017)
Advanced DynamicsAME 550 (Fall 2016)
Directed ResearchAME 492 (Fall 2016)
Independent StudyAME 599 (Fall 2016)
ResearchAME 900 (Fall 2016)
ThesisAME 910 (Fall 2016)
AeroelasticityAME 423 (Spring 2016)
AeroelasticityAME 523 (Spring 2016)
Aerospace Engineering DesignAME 422 (Spring 2016)
Aerospace Engr DesignAME 522 (Spring 2016)
Independent StudyAME 599 (Spring 2016)
ThesisAME 910 (Spring 2016)
- Kumar, R., Randall, R., Silin, S., & Shkarayev, S. (2014). Chapter 2: Insect-inspired Micro Air Vehicles. In Handbook of Biomimetics and Bioinspiration: Biologically-driven Engineering of Materials Processes, Devices and Systems(pp 623-649). World Scientific.More infoWorld Scientific Series in Nanoscience and Nanotechnology (3 vols).E. Jabbari, D.-H. Kim, L. P. Lee, A. Ghaemmaghami, and A. Khademhosseini (Eds.)
- Footohi, P., Bouskela, A., & Shkarayev, S. V. (2020). Aerodynamic Characteristics of the Blended-Wing-Body VTOL UAV. Journal of Aerospace Engineering and Mechanics, Vol 4(Issue 1), Pages 187-200,.
- Shkarayev, S. V., & Zhao, L. (2019). Characterization of Ducted Contra-rotating Propellers. International Journal of Micro Air Vehicles.
- Shkarayev, S. V., Zhao, L., & Su, E. (2018). AERODYNAMICS OF A WING WITH A WINGTIP FLAPPER. Fluids, 29.
- Shkarayev, S. V., Su, E., Randall, R., & Wilson, L. (2017). Visualization of Vortical Flows around a Rapidly-Pitching Wing and Propeller. International Journal of Micro Air Vehicles.
- Kumar, R., & Shkarayev, S. (2013). Kinematics and aerodynamic responses of locusts in sideslip. 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013.More infoAbstract: Effects of the sideslip angle on the wing-kinematics and the aerodynamic forces and moments generated by the locusts were investigated in a low-speed wind tunnel. Three locusts (Schistocerca americana) were tested at tunnel speeds of 0, 2, and 4 m/s at three body angles of attack (0°, 3° and 7°) and three sideslip angles (0°, -10° and -20°) at each angle of attack. A sensitive custom-built microbalance was used to measure the forces and moments. Simultaneous high- speed videos were taken to record the wing kinematics. Results in the form of normalized stroke-averaged forces and moments are presented and a correlation with the wing kinematics has been investigated. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Shkarayev, S., Maniar, G., & Shekhovtsov, A. V. (2013). Experimental and computational modeling of the kinematics and aerodynamics of flapping wing. Journal of Aircraft, 50(6), 1734-1747.More infoAbstract: High-speed videography is used in measuring the kinematic and deformation parameters of the flapping wing. Based on these data, a theoretical analysis of the underlying physics is performed using computational fluid dynamics simulations. The time varying of the pitching angle in the chordwise directions exhibits a significant second harmonic. Results suggest the mechanics of membrane deformations during a flapping cycle is analogous to the buckling of a bistable structure. Noticeably, with an increase in the freestreamspeed, the downstroke duration increases. The solution to the three-dimensional fluid dynamics problem is constructed using two-dimensional solutions obtained for several sections of the wing by the improved discrete vortex method. The inertial component is dominant in the normal force coefficient, and hence, added mass is the main mechanism in aerodynamic force production for the studied problem. A normal component of the acceleration of the wing's trailing edge taken with a negative sign is introduced as a kinematic parameter that is essential in flapping-wing aerodynamics. The results show a satisfactory agreement in trends of the acceleration and force coefficients. From the analysis of kinematical changes, it follows that synchronization of acceleration and of the pitching angle is important for achieving maximum values of the vertical force coefficients. © 2012 AIAA.
- Kumar, R., & Shkarayev, S. (2012). Effects of yaw angle on aerodynamic response in locusts. 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition.More infoAbstract: Aerodynamic forces and moments produced by locusts (Schistocerca americana) were investigated in a low-speed wind tunnel. The experimental setup included locusts mounted on a sensitive six-component microbalance using a sting. Tests were conducted at tunnel speeds of 0, 2, 3, 3.5 and 4 m/s at two body angles of attack and five positive yaw angles at each body angle of attack. The experimental results are presented for stroke-averaged forces and moments normalized using the insect body weight and length. Locusts generated more lift at higher velocities and at higher angles of attack, but none of locust generated lift greater than its weight. They generally produced net thrust at lower velocities and lower angles of attack and net drag at higher velocities, as expected. Interestingly, locusts responded to yaw by generating more positive side force, yawing moment and negative rolling moment. The lift force and pitching moment were largely insensitive to yaw. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Kumar, R., Chan, R., Shkarayev, S., & Gabbiani, F. (2012). Force measurements on locusts during visually-evoked collision avoidance maneuvers. International Journal of Micro Air Vehicles, 4(3), 227-249.More infoAbstract: The collision avoidance behavior of the locust, Schistocerca americana, in response to simulated approaching objects, also called looming stimuli, was investigated in a low speed wind tunnel. The animals were mounted using a sting on a sensitive six-component microbalance custom-designed for the experiments. Forces and moments were measured as a function of time during the simulated approach and interpreted in the context of collision avoidance behaviors. The stimuli presented from the side effectively evoked robust and discernible collision avoidance responses. Locusts attempted to avoid collision by either flying over or under the looming object, or alternatively by steering around it. These efforts appeared in the form of changes in aerodynamic forces and moments as a function of time. It was also observed that the locusts increased the wing flapping frequency in response to the stimulus.
- Maniar, G., Randall, R., Shkarayev, S., Goff, Z., & Beran, P. (2012). Kinematics of free-flight ornithopters. 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition.More infoAbstract: Ornithopters are flapping-wing aircraft that mimic natural fliers; their wings flap, twist and deform during flight. This study was conducted to improve the kinematic understanding of such vehicles. Three experimental models were used with wingspans of 15, 25 and 74 cm. The wings consist of a sheet of material connected to a span-wise leading edge spar. The sheet of material is supported by two to four ribs on each side of the wing. Free-flight and ground tests were conducted using reflective markers whose positions were tracked using a Vicon™ system. In total, ten ground and thirteen free-flight tests were conducted using various flapping frequencies ranging from 5 to 25 Hz. The study found that flapping-induced oscillations exist for all measured body and wing kinematic parameters, and those oscillations occur at the same frequency as flapping. Roll oscillation amplitude is significantly greater than that of either pitch or yaw due, in part, to the low roll-inertia of small flapping-wing vehicles. For a flapping membrane-batten wing with chordwise ribs, pitching angle phase is virtually independent of spanwise position and pitching angle amplitude increases with spanwise distance from the wing-root. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
- Randall, R., Shkarayev, S., Abate, G., & Babcock, J. (2012). Longitudinal aerodynamics of rapidly pitching fixed-wing micro air vehicles. Journal of Aircraft, 49(2), 453-471.More infoAbstract: Some fixed-wing vertical-takeoff-and-landing aircraft can transition between two flight modes: forward flight and near-hover. This study was conducted to improve the transition performance of such vehicles. The experimental model consists of a rigid Zimmerman wing and a propulsion system with contra-rotating propellers. It was rapidly pitched about its aerodynamic center at an average freestream Reynolds number of 86,000. Five nondimensional pitching rates were used, along with two elevator deflections and three propulsive settings. The model was tested statically, and several observations were made. At constant throttle setting, from 20 to 70 deg, both advance ratio and thrust coefficient increase linearly with angle of attack. Higher throttle setting results in greater stall delay, causing the maximum lift coefficient to increase. When throttle setting increases, lift and drag coefficients increase throughout the tested angle-of-attack domain. Rapid-pitching tests showed that nose-up pitching delays stall and nose-down pitching hastens it. Lift and drag coefficients generally increase with positive pitching rate and decrease with negative pitching rate. Wing aerodynamic efficiency is virtually independent of throttle setting, elevator deflection, and pitching rate between 30 and 70 deg angle of attack. The propulsion system is not sensitive to rapid pitching with regard to thrust, normal force, or propulsive moment. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.
- Randall, R., Wilson, L., & Shkarayev, S. (2012). Flow interactions around a rapidly-pitching MAV wing. 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition.More infoAbstract: This study was conducted to visually investigate flows related to fixed-wing vertical-takeoff-and-landing micro air vehicles, using the smoke-wire technique. In particular, the study examines transition between forward flight and near-hover. The experimental model consists of a rigid Zimmerman wing and a propulsion system with contra-rotating propellers arranged in a tractor configuration. The model was pitched about the wing's aerodynamic center at approximately constant rates using a five-axis robotic arm. Constant-rate pitching angles spanned 20 to 70 degrees. Five pitching-rates were used, along with three propulsive settings. Several observations were made. Contra-rotating slipstreams generally cause a delay in the onset of trailing-edge vortex-shedding within their vicinities. Higher nose-up pitching-rates generally lead to greater trailing-edge vortex-shedding frequency. Nose-up pitching without a slipstream can lead to the development of a traditional dynamic-stall leading-edge vortex (LEV), delaying stall and increasing wing lift. During nose-up pitching a slipstream can drive periodically-shed leading-edge vortices into a larger vortical-structure that circulates over the upper-surface of a wing in a fashion similar to that of a traditional dynamic-stall LEV. At lower nose-up pitching-rates LEVs form at lower angle of attack. As a slipstream strengthens a few things occur: separation wakes diminish, separation occurs at a higher AOA and downward flow-deflection increases. Similar effects are observed for nose-up pitching, while nose-down pitching produces the opposite effects. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
- Shkarayev, S., & Silin, D. (2012). Measurements of aerodynamic coefficients for flapping wings at 0-90 angles of attack. AIAA Journal, 50(10), 2034-2042.More infoAbstract: This paper addresses the aerodynamics of membrane flapping wings. In a series of wind-tunnel experiments on the 25 and 74-cm-wingspan models, the stroke-averaged lift and horizontal force were measured at an angle of attack that varied from 0 deg (horizontal) to 90 deg (hovering position). The flapping frequency was held constant, and freestream velocity was varied with the advance ratio range 0-1.2. For high angles of attack, flapping wings do not exhibit a typical abrupt stall seen with fixed wings. This feature in flapping wings allows a smooth transition from a level flight to hovering and back. The angle of attack, corresponding to a balance of forces in the horizontal direction, decreases exponentially with advance ratio. Aerodynamic coefficients are defined using a reference velocity as a vector sum of a freestream velocity and a stroke-averaged wing-tip flapping velocity. The lift and drag coefficients obtained using this procedure collapse well for the studied advance ratios, especially at lower angles of attack. Polynomial approximations for aerodynamic coefficients are proposed that can be used in flight-performance analysis. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Shkarayev, S., Maniar, G., & Shekhovtsov, A. V. (2012). Experimental and computational modeling of the kinematics and aerodynamics of membrane flapping wings. 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition.More infoAbstract: High-speed videography is utilized in measuring kinematic and deformation parameters of the flapping wing. Based on these data, a theoretical analysis of the underlying physics is performed using computational fluid dynamics simulations. The time-varying angle of incidence in chordwise directions exhibits a significant second harmonic. Results suggest the mechanics of membrane deformations during a flapping cycle is analogous to the buckling of a bistable structure. Noticeably, with an increase in the freestream speed, the downstroke duration increases. The solution to the three-dimensional fluid dynamics problem is constructed using two-dimensional solutions obtained for several sections of the wing by the improved discrete vortex method. The inertial component is dominant in the normal force coefficient, and hence, added mass is the main mechanism in aerodynamic force production for the studied problem. A normal component of the acceleration of the wing's trailing edge taken with a negative sign is introduced as a kinematic parameter that is essential in flapping wings aerodynamics. Results show a satisfactory agreement in trends of the acceleration and force coefficients. From analysis of kinematical changes it follows that synchronization of acceleration and angle of incidence is important for achieving maximum values of vertical force coefficients. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.
- Randall, R., Hoffmann, C., & Shkarayev, S. (2011). Longitudinal aerodynamics of a vertical takeoff and landing micro air vehicle. Journal of Aircraft, 48(1), 166-176.More infoAbstract: The research and development efforts outlined in this paper address the aerodynamic design of micro air vehicles that are capable of vertical takeoff and landing, as well as hovering. The effect of a propulsive slipstream on a wing's quasi-steady aerodynamics is investigated as an early step toward improving existing vertical takeoff and landing designs and control algorithms. Wind-tunnel testing was conducted on a propulsion system with contrarotating propellers, a wing, and the combined wing and propulsion system. Aerodynamic coefficient definitions are discussed with regard to vertical takeoff and landing micro air vehicles, and modified definitions are presented. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Shkarayev, S., & Silin, D. (2010). Applications of actuator disk theory to membrane flapping wings. AIAA Journal, 48(10), 2227-2234.More infoAbstract: This study addresses the aerodynamics of elastic membrane flapping wings. Several applications of the actuator disk theory to the flapping wings of insects and birds are reviewed. In previous studies, to account for spatial and temporal variance in the wake behind the flapping wings, empirical corrections were proposed for the induced velocity and power. In the present paper, a new procedure for determination of the correction factor is proposed, using membrane-type flapping-wing devices. Wind-tunnel experiments were conducted and the stroke-averaged propulsive thrust was measured on 25-cm-wingspan (flat and 9% camber) and 74-cm-wingspan flapping-wing models. Either flapping frequency or input power was held constant during the tests. Obtained thrust forces werecompared to theoretical values predicted by the actuator disk theory. Empirical correction factors to the actuator disk theory were determined, providing a best fit to the experimental data when the flapping axis aligned with freestream velocity. It is noteworthy that the numerical value for the correction factor for the 25 cm cambered wing agrees with the results obtained on large insects. The theoretical corrections for angle of attack of the flapping wing give satisfactory agreements with the experimental data only for relatively low forward speeds.
- Shkarayev, S., Silin, D., Abate, G., & Albertani, R. (2010). Aerodynamics of cambered membrane flapping wings. 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition.More infoAbstract: The aerodynamics of cambered membrane flapping wings is the focus of this paper. A cambered airfoil was introduced into the wing by shaping metal ribs attached to the membrane skin of the 25-cm-wing-span model. Tests in still air of the flapping wings oriented horizontally and vertically with respect to the gravitational field show no effects on generated aerodynamic forces. The thrust force generated by a 9% camber wing is found to be 30% higher than that of the same size flat wing. The aerodynamic forces and pitching moment generated by flapping wings were measured in a wind tunnel with the flapping wing angle of attack varying from horizontal to vertical. Cambered wings show significantly higher lift and thrust in comparison with flat wings. Adding a dihedral angle to the wings and keeping the flapping amplitude constant improved the cambered wing's performance even further. The aerodynamic coefficients are defined using a reference velocity as a sum of two components: a free stream velocity and a stroke-averaged wing tip flapping velocity. The lift, drag, and pitching moment coefficients obtained using this procedure collapse well for studied advance ratios, especially at lower angles of attack. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.
- Shkarayev, S., & Silin, D. (2009). Aerodynamics of flapping-wing micro air vehicles. 47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition.More infoAbstract: The research study outlined in the paper addresses the aerodynamic features of flexible flapping wings used in micro air vehicles called ornithopters. Aerodynamic force measurements were conducted for the 25-cm and 74-cm-wing-span models at different airflow velocities and flapping frequencies. A series of experiments were conducted on the 25-cm flapping-wing model without free stream airflow. In order to study the effect of a dihedral on generated thrust and normal force, the model was modified to accommodate three values of dihedral angle. It appeared that the thrust force is higher for higher dihedral angle. Effects of a wing's bending stiffness and of the wing root constraint on the generated thrust force and required power were investigated. The aerodynamic forces on flapping wings were studied with the stroke plane angle varied from horizontal to vertical. An important result was found that flapping wings do not exhibit a typical, abrupt stall seen with the fixed wings. Experimental results were analyzed in the framework of the momentum theory. The results of this study were realized in micro ornithopter designs that was successfully flight tested. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.
- Krashanitsa, R. Y., Silin, D., Shkarayev, S. V., & Abate, G. (2008). Flight dynamics of flapping-wing air vehicle. AIAA Atmospheric Flight Mechanics Conference and Exhibit.More infoAbstract: The research and development efforts presented in this paper address the flight dynamics of a flapping-wing air vehicle (ornithopter). The 74-cm wing span ornithopter was equipped with the automatic control system that provides the stability augmentation and navigation of the vehicle, and flight data acquisition. Wind tunnel tests were conducted with the control surfaces fixed in neutral position and flapping motion of the wings activated by a motor at a constant throttle setting. Coefficients of a lift, drag, and pitching moment were determined at a free stream velocity of 7.2 m/sec and the angle of attack varied from 0 to 41 degrees. In addition, variations of derivatives of aerodynamic coefficients with the freestream velocity were investigated. A series of flight tests were conducted with fixed controls demonstrating ornithopter stability in all axes. Proportional control laws were programmed into the autopilot for the closed-loop controls. A number of test flights of the autonomous ornithopter were conducted with the telemetry acquisition. During the autonomous flights, the autopilot performed waypoint and altitude navigation demonstrating stable performance. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc.
- Moschetta, J., Bataillé, B., Thipyopas, C., & Shkarayev, S. (2008). On fixed-wing micro-air vehicles with hovering capabilities. 46th AIAA Aerospace Sciences Meeting and Exhibit.More infoAbstract: The present paper investigates the possibility to improve the aerodynamic performance of a fixed-wing micro air vehicle (MAV) concept so as to simultaneously allow high cruise speed for covertness and hovering flight for stable image transmission. Two fixed-wing MAV configurations were tested and compared: a tilt-wing concept powered by two non-coaxial counter-rotating propellers and a tilt-body concept based on a coaxial rotor. The different configurations were separately analyzed based on wind tunnel experiments. The tilt-wing concept, although superior to the tilt-rotor concept, does not provide a significant benefit over an equivalent tilt-body MAV configuration. Finally, two tilt-body coaxial prototypes were designed and successfully flight tested to demonstrate the capability of fixed-wing MAV configurations to lift off, sustain hover flight and perform transition between forward and hover flight. Special attention was paid to the coaxial tail-sitter concept for which the propellers slipstream guarantees aerodynamic efficiency over the whole flight envelope. Side-by-side comparison of a mini- and a micro-sized coaxial tail-sitter model was carried out and discussed. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc.
- Poinsot, D., Bérard, C., Krashanitsa, R., & Shkarayev, S. (2008). Investigation of flight dynamics and automatic controls for hovering micro air vehicles. AIAA Guidance, Navigation and Control Conference and Exhibit.More infoAbstract: The present work describes the development of an automatic control system and the investigation of the flight dynamics of fixed-wing micro air vehicles (MAVs) with vertical take-off and landing (VTOL) capabilities. Specifically, the hovering phase of the flight was studied in detail. A state-space model was formulated and used in a control law design. The effects of propeller slip stream impinging on the airframe are discussed in the context of control design. Feedback control laws based on a proportional, integral, and derivative (PID) control design were developed and programmed into the autopilot. The development and evaluation of two VTOL MAVs with wingspans of 65 and 31 cm are presented. A number of test flights of vehicles with attitude stabilization and altitude hold were conducted with telemetry acquisition. Despite the difference in size, similarities were noted in the dynamic response for both aircraft. The actuation delays in the propulsion systems caused a systematic error in an altitude. Average amplitudes of rotational oscillations in all three axes were also about the same for both aircraft. Higher roll rates can be explained by lower inertia in roll axis. © 2008 by the American Institute of Aeronautics and Astronautics, Inc.
- Shkarayev, S., Moschetta, J., & Bataille, B. (2008). Aerodynamic design of micro air vehicles for vertical flight. Journal of Aircraft, 45(5), 1715-1724.More infoAbstract: The research and development efforts outlined in this paper address the aerodynamic design of micro air vehicles with hovering and vertical takeoff and landing capabilities. The tilt-body configuration of the vertical takeoff and landing micro air vehicle is proposed based on a propulsion system consisting of two coaxial contrarotating motors and propellers. Values of thrust, torque, power, and efficiency of this propulsion system were measured in pusher and tractor arrangements of propellers and compared against single motor-propeller propulsion. With comparable efficiency, the developed propulsion system has very little propeller torque. Hot-wire measurements have been conducted to investigate the velocity profile in slipstream. The lower average velocity and significant decrease in velocity in the core of the slipstream found in the tractor arrangement are mostly due to the parasite drag caused by the motors. It causes the decrease of the thrust force observed for the tractor arrangement in comparison with the pusher arrangement. Wind-tunnel testing was conducted for a motor, a wing, and an arrangement of a wing with a motor. The drag force on the wing is produced by two mixing airflows: freestream and propeller-induced pulsating slipstream. The zero-lift drag coefficient increases by about 4 times with propeller-induced speed increased from 0 to 7.5 m/s. The results of this study were realized in the design of a vertical takeoff and landing micro air vehicle prototype that was successfully flight tested. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Brion, V., Aki, M., & Shkarayev, S. (2006). Numerical simulations of low Reynolds number flows around micro air vehicles and comparison against wind tunnel data. Collection of Technical Papers - AIAA Applied Aerodynamics Conference, 4, 2485-2504.More infoAbstract: Micro air vehicles (MAVs) have grown as an increasingly important field of study in aeronautics research throughout the world for the past few years. The low speed and the small aspect ratio of wings of these airplanes generate a particular flow regime that is still not well understood. The present study uses the commercial software Fluent to consecutively investigate the aerodynamics of airfoils, wings, fuselage, and entire MAVs for angles of attack up to stall. It enlightens the requirements for the proper meshing of the fluid domain and settings of the simulations. Obtained numerical results give an insight on the development of separation as angle of attack increases accounting for the stability of the MAV near the stall. Further investigations give an overview on the propeller, fuselage and wing interactions. Effects of low aspect ratio and planform of wings were studied and were confirmed by wind tunnel testing.
- Krashanitsa, R., Platanitis, G., Silin, B., & Shkarayev, S. (2006). Aerodynamics and controls design for autonomous micro air vehicles. Collection of Technical Papers - 2006 Atmospheric Flight Mechanics Conference, 2, 1277-1293.More infoAbstract: Due to their small size, micro air vehicles (MAVs) demonstrate intrinsically unsteady behavior with high frequency oscillations, disturbing the usefulness of their applications. An enhanced automatic flight control system is in a great need for the progress of MAV technology. This paper presents an approach for simultaneous aerodynamics and closed-loop control design for MAVs including the determination of stability and control derivatives, simulation of flight dynamics of a vehicle with open- and closed-loop control, and analysis of the telemetry from flight tests of autonomous vehicles. Aerodynamic stability and control derivative coefficients of the MAV were determined for various parameters (angle of attack, roll rate, pitch rate, etc.) using the MAV geometry and airfoil characteristics. These coefficients were integrated with the geometric, mass, and inertial data to produce the longitudinal and lateral equations of motion. Closed-loop control laws were determined via root-locus methods and the closed-loop system simulated. The effects of varying the center of gravity and changing dihedral angle on the stability are discussed in detail. The proposed approach was applied in the development and evaluation of two autonomous micro air vehicles with wingspans of 12 and 23 inches. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Krashanitsa, R., & Shkarayev, S. (2005). Computational study of dynamic response and flow behavior of damaged ceramics. Collection of Technical Papers - AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 1, 573-580.
- Null, W., & Shkarayev, S. (2005). Effect of camber on the aerodynamics of adaptive-wing micro air vehicles. Journal of Aircraft, 42(6), 1537-1542.More infoAbstract: Four microair vehicle wind-tunnel models were built with 3, 6, 9, and 12% camber, all based upon the S5010-TOP24C-REF thin, cambered-plate airfoil. These models were tested in the Low Speed Wind Tunnel at angles of attack ranging from 0 to 35 deg and velocities of 5, 7.5, and 10 m/s, corresponding to mean aerodynamic chord Reynolds numbers of 5 × 104, 7.5 × 104, and 1 × 105, respectively. Aerodynamic coefficients CL, CD, CM and lift-to-drag ratio (L/D) were obtained and plotted vs angle of attack for all of the cambers at each velocity. Large positive, nose-up pitching moment coefficients were found with all cambers at the lowest Reynolds number. These results have been verified with flight tests of micro air vehicles utilizing these airfoils. The 3% camber wing gives the best lift-to-drag ratio of the four cambers and theoretically would be the optimal choice for high-speed, efficient flight. It is theorized that the 6 and 9% camber wings will give the best low-speed performance because of their high lift-to-drag ratios and mild pitching moments near their stall angles of attack. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Null, W., Noseck, A., & Shkarayev, S. (2005). Effects of propulsive-induced flow on the aerodynamics of micro air vehicles. Collection of Technical Papers - AIAA Applied Aerodynamics Conference, 1, 198-216.More infoAbstract: A propulsion system (DC electric motor and propeller) was installed on micro air vehicle wind tunnel models of 3, 6 and 9% camber. In one set of tests the motor was mounted in its typical location; in the next test set the motor was angled both toward and then away from the leading edge; and in the final set of tests the motor was extended 1/2 inch away from the leading edge from its usual location. All models had wingspans of 9" and wing areas of 60 in 2. The models were tested in the Low Speed Wind Tunnel, with the propulsion system activated (motor-on testing), at angles of attack ranging from 4 to 43° or 0 to 35.1°, depending on the test set, at velocities of 5, 7.5 and 10 m/s, corresponding to mean aerodynamic chord Reynolds numbers of 5×10 4,7.5×10 4, and 1×10 5, respectively. C L, C D, C M-c/4 and L/D were obtained and plotted versus angle of attack at each velocity. The aerodynamic coefficients obtained from the motor-on testing were compared to those obtained from a previous study that were completed without a propulsion system installed. In general, it was found that the propulsive-induced flow had a positive effect on the aerodynamics of the micro air vehicle models at higher angles of attack, particularly for low Reynolds number tests, and motors angled away from the leading edge. It was also found that relocating the motor forward from its usual mounting position increased both the lift and drag coefficients. However, due to the way that the aerodynamic coefficients were calculated, the effects in the aerodynamic coefficients are partly a mathematical phenomenon. In other words, at low Reynolds numbers there is an increase in the lift coefficient, but it is due to the way that the lift coefficient is calculated. Because this reduction in the Reynolds number is due to a reduction in speed, the actual lift produced at these low speeds may decrease faster than the lift coefficient increases. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Platanitis, G., & Shkarayev, S. (2005). Integration of an autopilot for a micro air vehicle. Collection of Technical Papers - InfoTech at Aerospace: Advancing Contemporary Aerospace Technologies and Their Integration, 3, 1428-1446.More infoAbstract: The integration of a commercially available autopilot, the MicroPilot MP2028g, is investigated for a 30-inch Zagi airframe. Analytical methods, including the Advanced Aircraft Analysis software from DARCorp, were used to determine the stability and control derivatives, and then validated through wind tunnel experiments. From this data, the linear, perturbed model about steady-state flight conditions was cast and transfer functions for the control and navigation systems were developed. Feedback control laws based on Proportional, Integral, and Derivative (PID) control design were developed to control the aircraft which may then be programmed into the autopilot. Flight tests were performed in remote control mode to evaluate handling, adjust trim, and test data logging for the Zagi with integrated MP2028g. Ground testing was performed to test GPS acquisition, data logging, and control response in autonomous mode. Technical difficulties and integration limitations with the autopilot prevented Fully autonomous flight from taking place, but the integration methodologies are, in general, applicable for unmanned air vehicles that use a PID control based autopilot. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Shkarayev, S., & Krashanitsa, R. (2005). Probabilistic method for the analysis of widespread fatigue damage in structures. International Journal of Fatigue, 27(3), 223-234.More infoAbstract: A probabilistic method was developed to model structural failure associated with widespread damage as a stochastic chain of crack initiation and growth, linkup, and final failure. The major feature of this method is that multiple sites (fastener holes) have individual crack-initiation and crack-growth characteristics. These individual characteristics are established by Monte Carlo simulation. Stress analysis of undamaged and cracked structures is performed incrementally using a finite element method incrementally and the crack length increment is determined at a given time increment by using an equation for crack growth. Consequent application of the Monte Carlo simulation results in empirical distributions for (a) life to crack initiation, (b) residual life and (c) total life of the structure. A worst-case scenario of multiple cracks is introduced by assigning equal cracks growing simultaneously with highest speed at all sites. This case establishes the threshold of residual life of a structure. Utilizing the threshold, Monte Carlo simulations are conducted in conjunction with a three-parameter lognormal probability distribution for the residual life of a structure. Numerical studies were performed for panels with rows of holes and for a panel stiffened by stringers. The proposed method makes it possible to assess the probability of occurrence of a structure's failure associated with widespread damage as a function of time. © 2004 Elsevier Ltd. All rights reserved.
- Krashanitsa, R., & Shkarayev, S. (2004). Theoretical study of the dynamic response of bars composed of dissimilar materials. Materials Science, 40(6), 795-808.More infoAbstract: We study the one-dimensional process of propagation of waves in a composite bar whose components have different cross sections and are made of dissimilar materials. The initial-boundary-value problem is posed for the key system of nonlinear equations for an arbitrary nonlinear elastic behavior of the materials. The developed numerical scheme is based on iterations and the finite-difference method. The shock compression of the split Hopkinson bar extensively used for the experimental investigation of the dynamic properties of materials is studied in detail. © 2005 Springer Science+Business Media, Inc.
- Null, W., & Shkarayev, S. (2004). Effect of camber on the aerodynamics of adaptive wing micro air vehicles. 2nd AIAA Flow Control Conference.More infoAbstract: Four micro air vehicle wind tunnel models were built with 3, 6, 9 and 12% camber, all based upon the S5010-TOP24C-REF thin, cambered plate airfoil. These models were tested in the Low Speed Wind Tunnel at angles of attack ranging from 0 to 35° and velocities of 5, 7.5 and 10 m/s, corresponding to chord Reynolds numbers of 5x104, 7.5x104 and 1x105, respectively. CL, CD, CM and L/D were obtained and plotted versus angle of attack for all the cambers at each velocity. Large positive, nose-up pitching moment coefficients were found with all cambers at the lowest Reynolds number. These results have been verified with flight tests of micro air vehicles utilizing these airfoils. The 3% camber wing gives the best lift-to-drag ratio of the four cambers and theoretically would be the optimal choice for high speed, efficient flight. It is theorized that the 9% camber wing will give the best low-speed performance due to its high lift-to-drag ratio and mild pitching moment near its stall angle of attack. © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
- Savruk, M. P., & Shkarayev, S. V. (2003). Analogy of stress singularity problems for material with linear and bilinear behaviours. Fiziko-Khimicheskaya Mekhanika Materialov, 39(6), 45-53.
- Savruk, M. P., & Shkarayev, S. V. (2003). Similarity of stress-singularity problems for materials with linear and bilinear behaviors. Materials Science, 39(6), 807-819.More infoAbstract: An analogy is established between the solutions of the problems of singularities of stresses in linear and bilinear elastic isotropic media. It is shown that the distributions of stresses and displacements in the vicinity of singular points on the boundary of the body (characterized by the singularities of stresses) are described, in both cases, by the same functional dependences on the space coordinates but with different characteristics of the material. We deduce expressions for the effective moduli of elasticity and Poisson's ratio of the bielastic medium including the parameter of hardening of the material. The solution of the problem of singularities of stresses in bilinear materials is obtained from the solution of the corresponding problem for the linear elastic medium by replacing the elastic constants with the corresponding effective values depending on the parameter of hardening of the material. The cases of wedge-shaped notches (for various boundary conditions imposed on their edges), two-component wedges, plane wedge-shaped cracks, and circular conic notches or rigid inclusions in the bielastic space are studied in detail.
- Shkarayev, S. (2003). Theoretical modeling of crack arrest by inserting interference fit fasteners. International Journal of Fatigue, 25(4), 317-324.More infoAbstract: The repair technology under consideration involves drilling a number of holes along a crack in a metal part and inserting fasteners (bolts, rivets, or pins) into the holes with a predetermined interference fit. A fracture mechanics-based model is proposed to study the decrease in the crack growth rate after repair. A parametric analysis is performed to discover the effect of geometry and materials on crack retardation. Elastic-plastic contact stress distributions in the specimens during cyclic loading are determined by the finite element method. The results show that a significant enhancement of fatigue life until crack re-initiation can be achieved through an optimal set of parameters: number of fasteners, their material, and interference fit. The model is validated using a comparison of fatigue tests of the specimens. © 2003 Elsevier Science Ltd. All rights reserved.
- Shkarayev, S., & Mall, S. (2003). Computational modelling of shot-peening effects on crack propagation under fretting fatigue. Journal of Strain Analysis for Engineering Design, 38(6), 495-506.More infoAbstract: Recent experimental studies have demonstrated fretting fatigue life enhancement of titanium alloy Ti-6Al-4V specimens after treatment by shot-peening. Because of complexities in tracking crack growth under fretting conditions experimentally, the present work describes computational modelling for crack propagation behaviour in specimens with and without shotpeening. A crack growth model is combined with a finite element submodelling technique to assess the crack trajectory and crack propagation life in the specimens under fretting fatigue. A parametric numerical analysis has been performed to investigate crack trajectories and stress intensity factors along the crack path under different loading conditions. Obtained results revealed the features of the crack growth trajectory and stress intensity factors in the presence of residual stresses from shot-peening. These results also demonstrated a significant (2-3 times) increase in the crack propagation life of shot-peened specimens relative to virgin specimens (i.e. without shot-peening), which is in agreement with experimental observations.
- Shkarayev, S., Jouse, W., Null, W., & Wagner, M. (2003). Measurements and performance prediction of an adaptive wing micro air vehicle. Proceedings of SPIE - The International Society for Optical Engineering, 5054, 53-65.More infoAbstract: The mission space requirements imposed on the design of micro air vehicles (MAVs) typically consist of several distinct flight segments that generally conflict: the transit phases of flight require high speeds, while the loiter/surveillance phase requires lower flight velocities. Maximum efficiency must be sought in order to prolong battery life and aircraft endurance. The adaptive wing MAV developed at the University of Arizona features a thin, deformable flying wing with an efficient rudder-elevator control system. The wing camber is varied to accommodate different flight speeds while maintaining a constant total lift at a relatively low angle of attack. A new airfoil was developed from the Selig 5010 that features a small negative pitching moment for pitch stability. Wind tunnel tests were performed and stall angles and best lift-to-drag ratios were analyzed from the data. The wind tunnel data was used in a performance analysis in order to determine the flight speeds and throttle settings for maximum endurance at each camber, as well as the MAVs theoretical minimum and maximum flight speeds. The effectiveness of camber change on flight speed and endurance was examined with promising results; flight speed could be reduced by 25% by increasing the camber from 3 to 9% without any increase in power consumption.
- Shkarayev, S., Savastiouk, S., & Siniaguine, O. (2003). Stress and reliability analysis of electronic packages with ultra-thin chips. Journal of Electronic Packaging, Transactions of the ASME, 125(1), 98-103.More infoAbstract: This research concerns itself with a stress and reliability analysis of electronic packages with ultra-thin chips based on the finite element method. The effect of chip and substrate thickness, substrate material, presence of underfill, dimensions, and shape of the bump on stress reduction is analyzed. Obtained results clearly show that chip thinning, when used with an appropriate design of the entire package, can significantly decrease stresses and stress intensity factors and improve the reliability of the package. The developed software provides an effective design tool to quantify the reliability, stresses, and deflections of a package with ultra-thin chips.
- Null, W., Wagner, M., Shkarayev, S., Jouse, W., & Brock, K. (2002). Utilizing adaptive wing technology in the control of a micro air vehicle. Proceedings of SPIE - The International Society for Optical Engineering, 4698, 112-120.More infoAbstract: Evolution of the design of micro air vehicles (MAVs) towards miniaturization has been severely constrained by the size and mass of the electronic components needed to control the vehicles. Recent research, experimentation, and development in the area of smart materials have led to the possibility of embedding control actuators, fabricated from smart materials, in the wing of the vehicle, reducing both the size and mass of these components. Further advantages can be realized by developing adaptive wing structures. Small size and mass, and low airspeeds, can lead to considerable buffeting during flight, and may result in a loss of flight control. In order to counter these effects, we are developing a thin, variable-cambered airfoil design with actuators embedded within the wing. In addition to reducing the mass and size of the vehicle or, conversely, increasing its available payload, an important benefit from the adaptive wing concept is the possibility of in-flight modification of the flight envelope. Reduced airspeeds, which are crucial during loiter, can be realized by an in-flight increase in wing camber. Conversely, decreases in camber provide for an airframe best suited for rapid ingress/egress and extension of the mission range. To these ends, we are working on the design, integration, and testing of MAVs with adaptive wing structures. Our current airframe design is a composite design consisting of small-diameter carbon rods for the structure and a thin, flexible fiberglass/epoxy skin for the wing covering. The airfoil is a thin, variable-cambered plate design and actuators are embedded within the wing structure. Both shape memory alloy (SMA) wires and traditional micro servos are utilized in our adaptive wing designs. An effective shortening or lengthening of the wing chord produces camber variations in the wing. Bilaterally symmetric variations in trailing edge geometry affect the pitch of the vehicle, while asymmetric warping affects roll.
- Savruk, M. P., & Shkarayev, S. V. (2001). Stress singularities for three-dimensional corners using the boundary integral equation method. Theoretical and Applied Fracture Mechanics, 36(3), 263-275.More infoAbstract: The boundary integral equation method is developed to study three-dimensional asymptotic singular stress fields at vertices of a pyramidal notch or inclusion in an isotropic elastic space. Two-dimensional boundary integral equations are used for the infinite body with pyramidal notches and inclusions when either stresses or displacements are specified on its surface. Applying the Mellin integral transformation reduces the problem to one-dimensional singular integral equations over a closed, piece-wise smooth line. Using quadrature formulas for regular and singular integrals with Hilbert and logarithmic kernels, these integral equations are reduced to a homogeneous system of linear algebraic equations. Setting its determinant to zero provides a characteristic equation for the determination of the stress singularity power. Numerical results are obtained and compared against known eigenvalues from the literature for an infinite region with a conical notch or inclusion, for a Fichera vertex, and for a half-space with a wedge-shaped notch or inclusion. © 2001 Elsevier Science Ltd. All rights reserved.
- Shkarayev, S., Madenci, E., Ibnabdeljalil, M., & Savruk, M. P. (2001). Analytical stress singularities for a crack at a Bi- or triple junction of dissimilar materials with bilinear behavior. Engineering Fracture Mechanics, 68(4), 475-486.More infoAbstract: The reliability of electronic packages is strongly influenced by the interfacial thermo-mechanical stresses arising from temperature excursions during fabrication and operation. Understanding the mechanisms for relaxing these interfacial thermo-mechanical stresses through the use of appropriate material selection is critical to the enhancement of their reliability. Therefore, this study provides analytical solutions for the asymptotic stress field ahead of the interface crack tip emanating from the apex of a wedge composed of dissimilar materials exhibiting elastic and/or elastic-plastic deformations.
- Kay, N., Madenci, E., & Shkarayev, S. (1999). Global/local finite element analysis for singular stress fields near the junction of dissimilar elastic and elastic-plastic materials in electronic packages. Proceedings - Electronic Components and Technology Conference, 987-993.More infoAbstract: The global/local finite element method was extended to include elastic and/or plastic deformation. A global element stiffness matrix was constructed based on the analytical solution for a singular stress field near a junction of dissimilar materials with elastic and elastic-plastic behaviors. It was found that considering only the order of the singularity in predicting the failure site is not sufficient.
- Razi, H., Sergeev, B., Shkarayev, S., & Madenci, E. (1999). Analysis of sandwich panels with multiple-site damage. Engineering Fracture Mechanics, 64(2), 255-268.More infoAbstract: Hail impaction may cause multiple-site damage to sandwich panels used as a part of control surfaces and is therefore a major maintenance and repair concern for the airlines. A strength analysis of the damaged sandwich panels is essential to predict the influence of the multi-site damage, which is necessary for establishing allowable damage limits. The location of the damage sites in relation to each other and their size influence the stress field significantly. This study presents an analytical method to determine the stress distribution in sandwich panels with arbitrarily located damage, that is elliptical or circular in shape. The validity of this method is established by comparison against the three-dimensional finite element models of sandwich panels with multiple damage zones.
- Savruk, M. P., Madenci, E., & Shkarayev, S. (1999). Singular integral equations of the second kind with generalized Cauchy-type kernels and variable coefficients. International Journal for Numerical Methods in Engineering, 45(10), 1457-1470.More infoAbstract: A numerical solution method is presented for singular integral equations of the second kind with a generalized Cauchy kernel and variable coefficients. The solution is constructed in the form of a product of regular and weight functions. The weight function possesses complex singularities at the ends of the interval. The parameters defining the power of these singularities are obtained by solving for the characteristic equations. A Gauss-Chebychev quadrature formula is utilized in the numerical solution of the integral equations. Benchmark examples are considered in order to illustrate the validity of the solution method. Copyright © 1999 John Wiley & Sons, Ltd.
- Savruk, M. P., Shkarayev, S., & Madenci, E. (1999). Stress near apex of dissimilar material with bilinear behavior. Theoretical and Applied Fracture Mechanics, 31(3), 203-212.More infoAbstract: This study presents an analytical solution for the asymptotic stress field near the apex of a wedge composed of dissimilar materials exhibiting elastic and/or plastic deformation that can be described by a bilinear material model. Under the same assumptions, previous investigations resulted in eigenvalue differential equations that were not amenable to analytical integration. The present formulation avoids the numerical integration of such equations. After establishing its validity, the corner of the junction formed between a solder ball and a substrate was considered in order the study the effect of the hardening parameter on the strength of the singular stress field. Also, this formulation provides the exact form of the displacement field, which permits the construction of a global element to capture the correct strength of the singular stress field in regions with material and geometric discontinuities. © 1999 Elsevier Science B.V. All rights reserved.
- Madenci, E., Sergeev, B., & Shkarayev, S. (1998). Boundary collocation method for multiple defect interactions in an anisotropic finite region. International Journal of Fracture, 94(4), 339-355.More infoAbstract: The modified mapping collocation method is extended for the solution of plane problems of anisotropic elasticity in the presence of multiple defects in the form of holes, cracks, and inclusions under general loading conditions. The approach is applied to examine the stress and strain fields in an anisotropic finite region including an elliptical and a circular hole, an elliptical flexible inclusion, and a line crack. It can be readily incorporated into micro-mechanics modes, capturing the relative importance of the matrix, the fiber/matrix interface, and reinforcement geometry and arrangement while estimating the effective elastic properties of composite materials. The accuracy and robustness of this method is established through comparison with results obtained from finite element analysis.
- Madenci, E., Shkarayev, S., & Mahajan, R. (1998). Potential Failure Sites in a Flip-Chip Package with and Without Underfill. Journal of Electronic Packaging, Transactions of the ASME, 120(4), 336-341.More infoAbstract: In this study, the effect of underfill on the level of stress concentrations is investigated and possible failure sites are identified by using a global/local finite element approach. The global elements capture the exact singular behavior of the stresses near the geometric and material discontinuities. Application of the strain energy density criterion indicates the possible failure sites and how they shift due to the presence of underfill.
- Madenci, E., Shkarayev, S., & Sergeev, B. (1998). Thermo-mechanical stresses for a triple junction of dissimilar materials: Global-local finite element analysis. Theoretical and Applied Fracture Mechanics, 30(2), 103-117.More infoAbstract: Finite element analysis with conventional elements fails to provide convergent stresses in regions where a free edge with a bimaterial interface or a junction of dissimilar materials exists. However, these regions are characteristic of electronic devices, and they are the most critical locations for failure. A finite element analysis with global (special) and local (conventional) elements has been developed to provide an accurate description of the stress field at these locations. The global elements capture the singular nature of the stresses arising from geometric and material discontinuities. With this method, the designer can accurately evaluate the thermo-mechanical integrity of various electronic devices.
- Madenci, E., Shkarayev, S., Sergeev, B., Oplinger, D. W., & Shyprykevich, P. (1998). Analysis of composite laminates with multiple fasteners. International Journal of Solids and Structures, 35(15), 1793-1811.More infoAbstract: Fatigue-and fracture-related cracks are to be expected with the large number of fasteners present in aircraft structures. Therefore, contact stresses around the fastener holes and stress intensity factors associated with edge cracks are critical concerns in damage-tolerant designs. Mechanical joints consisting of many fasteners with a staggered pattern further complicate the already rather complex analysis for single-fastener joints. Load distribution among the fasteners significantly influences the failure load of multi-fastener joints. Most existing analyses are confined to single-fastener joints, and the data available for multi-fastener joints are rather limited. Very few experimental and/or analytical/numerical investigations of contact stresses for mechanical joints with staggered fasteners exist in the literature. Therefore, the accurate prediction of contact stresses (load distribution) and stress intensity factors associated with edge cracks is essential for the reliable design of such mechanical joints. This study concerns the development of an analytical methodology, based on the boundary collocation technique, to determine the contact stresses and stress intensity factors required for strength and life prediction of bolted joints with many fasteners. It provides an analytical capability for determining the contact stresses in mechanically fastened composite laminates while capturing the effects of finite geometry, presence of edge cracks, interaction among fasteners, material anisotropy, fastener flexibility, fastener-hole clearance, friction between the pin and the laminate, and by-pass loading. Also, it permits determination of the fastener load distribution, which significantly influences the failure load of a multi-fastener joint. © 1998 Elsevier Science Ltd.
- Madenci, E., Shkarayev, S., & Mahajan, R. (1997). Potential failure sites in a flip-chip package with and without underfill. American Society of Mechanical Engineers, Applied Mechanics Division, AMD, 222, 61-64.More infoAbstract: The thermal integrity of an electronic package depends on the strength of the interface between dissimilar materials. Due to high thermo-mechanical stress concentrations arising from large temperature excursions, electronic packages become prone to cracking at regions with geometric and/or material discontinuities. Thus, the accurate calculation of the thermo-mechanical stresses in regions of high stress concentrations is critical to achieving a reliable design. These high-stress-concentration regions pose a major concern, especially in the design of flip-chip packages. Understanding the mechanisms for relaxing the high stress concentrations through the use of appropriate material properties, bump and adhesive joint geometry, and filler size in a flip-chip package will aid in design improvements for ensuring the thermomechanical reliability of electronic packages. In this study, the effect of underfill on the level of stress concentrations is investigated and possible failure sites are identified by using a global/local finite element approach. The global elements capture the exact singular behavior of the stresses near the geometric and material discontinuities. Potential failure sites are established by applying concepts from fracture mechanics.
- Shkarayev, S. V., & Mover Jr., E. T. (1987). Edge cracks in stiffened plates. Engineering Fracture Mechanics, 27(2), 127-134.More infoAbstract: An analytical method for the determination of stress intensity factors in two-dimensional plane elastostatic problems is extended for the parametric study of edge cracks in stiffened panels. Two problems are studied: the case of a cracked panel reinforced with stringers and the case of two panels, connected by rivets, one of which contains a crack. The loading in each problem is uniform tensile stress applied normal to the crack plane. A parametric investigation of these problems is to discover the influence of geometric factors on the strength of the panels. The results show that the influence depends on the crack tip location relative to the reinforcement. The results for some examples are also compared with finite element calculations. © 1987.
- Shkarayev, S. V., & Mover Jr., E. T. (1987). The effect of shear and plasticity on crack arrest characteristics in stiffened panels. Engineering Fracture Mechanics, 27(2), 135-142.More infoAbstract: Elastic Mode 1 and 2 stress intensity factors for stiffened, cracked plates were calculated for panels loaded both in tension and shear by the finite element method. The influence of stringer thickness, rivet spacing and stringer stress intensity factors and stringer stresses were analyzed. The influence of plastic deformation was studied for the case of tensile loading. The J-integral values and stringer stresses were calculated. Contrary to the elastic case, the stiffeners failed to provide much protection for the panels and did provide crack arrest. © 1987.
- Bouskela, A., Kling, A., Shkarayev, S. V., & Thangavelautham, J. (2020, 11-12 May). Aerial Reconnaissance of Canyons and Craters on Mars Using Sailplanes. In Inter-Planetary Small Satellite Conference.
- Footohi, P., Shkarayev, S. V., & Heinemann, G. (2020, 15–19 June). Dynamics of Wingtip Vortex near Solid Surface. In 2020 AIAA AVIATION Forum.
- Shkarayev, S. V., & Bouskela, A. (2020, 11-12 May). Atmospheric Flight Mechanics on Other Planets. In Inter-Planetary Small Satellite Conference.
- Shkarayev, S. V., & Bouskela, A. (2020, 15–19 June). Modeling of Dynamic Soaring Maneuvers in the Atmospheres of Earth and Mars. In 2020 AIAA AVIATION Forum.
- Shkarayev, S. V., Schuler, T., Kalita, H., Moses, R., & Thangavelautham, J. (2020, 02/2020). GNC of Shape Morphing Microbots for Planetary Exploration. In AAS Guidance and Control Conference 2020.
- Shkarayev, S. V., Schuler, T., Kalita, H., Moses, R., & Thangavelautham, J. (2020, 02/2020). GNC of Shape Morphing Microbots for Planetary Exploration. In AAS Guidance and Control Conference.
- Thangavelautham, J., Shkarayev, S. V., Bouskela, A., & Schuler, T. (2020, 02/2020). Inflatable Aircrafts and Blimps for Long Duration Mars Exploration. In AAS Guidance and Control Conference 2020.
- Thangavelautham, J., Shkarayev, S. V., Kling, A., & Bouskela, A. (2020, 11-12 May). Aerial Reconnaissance of Canyons and Craters on Mars Using Sailplanes. In Interplanetary Small Satellite Conference.
- Thangavelautham, J., Shkarayev, S. V., Vilvanathan, V., Kukkala, K., & Schuller, T. (2020, 05/2020). Mars Exploratory Balloons (MEB) CubeSats. In Interplanetary Small Satellite Conference.
- Bouskela, A., Chandra, A., Shkarayev, S. V., & Thangavelautham, J. (2019, January). Attitude Control of an Inflatable Sailplane for Mars Exploration. In 42nd Annual AAS Guidance and Control Conference.
- Bouskela, A., Kling, A., Schuler, T., Shkarayev, S. V., & Thangavelautham, J. (2019, October). Planetary Exploration Using Cubesat Deployed Sailplanes. In International Astronautical Congress 2019.
- Footohi, P., Bouskela, A., & Shkarayev, S. V. (2019, January). Aerodynamic Design of Long-Range VTOL UAV. In AIAA Science and Technology Forum.
- Shkarayev, S. V., Thangavelautham, J., Kling, A., Bouskela, A., & Schuler, T. (2019, October). Planetary Exploration Using Cubesat Deployed Sailplanes. In 70th International Astronautical Congress.
- Shkarayev, S. V., & Kurnosov, V. (2017, June). Modification of Vortex Identification Method Based on Normalized Angular Momentum. In Aviation Forum, AIAA.
- Shkarayev, S. V., Kurnosov, V., Gomez, D., Moschetta, J., & Jardin, T. (2017, June). Flow Studies around a Small Propeller in Converting Maneuver. In Aviation Forum, AIAA.
- Shkarayev, S. V., Kranepuhl, R., & Planchenault, P. (2016, June). Wingtip Vortex Modifications Using Alternating Jets. In 34th AIAA Applied Aerodynamics Conference.
- Shkarayev, S. V., Su, E., & Zhao, L. (2016, June). Aerodynamics of Wing with Oscillating Wingtip Flapper, AIAA 2016-3119. In 34th AIAA Applied Aerodynamics Conference.
- Shkarayev, S., & Kumar, R. (2014, June 15-20). Kinematics and Inertial Effects in Flapping Wings. In 32nd AIAA Applied Aerodynamics Conference.
- Shkarayev, S., & Kumar, R. (2014, June 16-20). Instantaneous Forces in Locust Flapping Wings. In 32nd AIAA Applied Aerodynamics Conference.
- Shkarayev, S. V. (2020, March 2). Sailplane for Earth observation and Mars exploration. UA-Mexican Space Agency Workshop. UA.
- Shkarayev, S. V. (2019, August). UAV Projects at the University of Arizona. Unmanned Arizona Workshop. Phoenix.
- Shkarayev, S. V. (2018, May 10). Unmanned Aerial Vehicles Project. CubeSat Seminar, UA. UA.More infoUnmanned Aerial Vehicles Project
- Shkarayev, S. V. (2016, August). Micro Aerial Vehicles Project. AME Seminar.
- Shkarayev, S. V. (2014, ???). Hybrid UAVs. SCR. Phoenix, AS.