The Experts below are selected from a list of 22257 Experts worldwide ranked by ideXlab platform

Hao Liu - One of the best experts on this subject based on the ideXlab platform.

  • flexible flapping wings with self organized microwrinkles
    Bioinspiration & Biomimetics, 2015
    Co-Authors: Hiroto Tanaka, Hao Liu, Hiroyuki Okada, Yosuke Shimasue
    Abstract:

    Bio-inspired flapping wings with a wrinkled wing membrane were designed and fabricated. The wings consist of carbon fibre-reinforced plastic frames and a polymer film with microscale wrinkles inspired by bird feathers and the corrugations of insect wings. The flexural and tensile stiffness of the wrinkled film can be controlled by modifying the orientations and waveforms of the wrinkles, thereby expanding the design space of flexible wings for micro flapping-wing aerial robots. A self-organization phenomenon was exploited in the fabrication of the microwrinkles such that microscale wrinkles spanning a broad wing area were spontaneously created. The wavy shape of these self-organized wrinkles was used as a mould, and a Parylene film was deposited onto the mould to form a wrinkled wing film. The effect of the waveforms of the wrinkles on the film stiffness was investigated theoretically, computationally and experimentally. Compared with a flat film, the flexural stiffness was increased by two orders of magnitude, and the tensile stiffness was reduced by two orders of magnitude. To demonstrate the effect of the wrinkles on the actual deformation of the flapping wings and the resulting Aerodynamic forces, the fabricated wrinkled wings were tested using a tethered electric flapping mechanism. Chordwise unidirectional wrinkles were found to prevent fluttering near the trailing edge and to produce a greater Aerodynamic Lift compared with a flat wing or a wing with spanwise wrinkles. Our results suggest that the fine stiffness control of the wing film that can be achieved by tuning the microwrinkles can improve the Aerodynamic performance of future flapping-wing aerial robots.

  • flapping wings and Aerodynamic Lift the role of leading edge vortices
    AIAA Journal, 2007
    Co-Authors: Wei Shyy, Hao Liu
    Abstract:

    AEROSPACE LETTERS are brief communications (approximately 2000 words) that describe new and potentially important ideas or results, including critical analytical or experimental observations that justify rapid publication. They are stringently prescreened, and only a few are selected for rapid review by an Editor. They are published as soon as possible electronically and then appear in the print version of the journal.

J Guan - One of the best experts on this subject based on the ideXlab platform.

  • numerical simulation and analysis of the effects of water film morphological changes on the Aerodynamic Lift of stay cables
    Journal of Fluids and Structures, 2014
    Co-Authors: J Wang, Chun Bao, J Guan
    Abstract:

    Abstract The cables in cable-stayed bridges can vibrate at large amplitudes during rain and windy conditions, a phenomenon known as rain-wind induced vibration (RWIV). Previous studies have demonstrated that the formation and oscillation of rivulets on stay cable surfaces play an important role in RWIV.This paper presents a new numerical method for simulating the evolution of rivulets on stay cable surfaces based on a combination of the gas–liquid two-phase theory and the volume of fluid method (VOF method), which allows for the straightforward determination of the cables’ Aerodynamic Lift when RWIV occurs. To verify the accuracy of this method and analyze the effects of wind velocity on the water film and the Aerodynamic Lift around the cable, three cases with different loadings were investigated using the computational fluid dynamics (CFD) software CFX. To verify the method’s accuracy, the Aerodynamic Lifts calculated from these cases were applied to the cable to obtain its vibrational response. In accordance with the experimental results, the numerical results demonstrated that an upper rivulet with a periodic oscillation was formed at a specific wind speed, causing the Aerodynamic Lift to change with a similar periodicity. The Aerodynamic Lift’s frequency was approximately the cable’s natural frequency, and induced large vibrations in the cable. No obvious upper rivulets were formed at sufficiently low wind speeds. The frequency of an Aerodynamic Lift that was significantly larger than the cable’s natural frequency induced small vibrations in the cable. When the wind speed was sufficiently high, despite the eventual formation of a continuous upper rivulet, the frequencies of the upper rivulet’s oscillation and the Aerodynamic Lift remained distinct from the natural frequency, and the cable continued to exhibit small-amplitude vibrations. These observations confirmed the conclusion that periodic variations in the water film morphology could lead to periodic changes in the Aerodynamic Lift that would induce RWIV.

Johansson L. Christoffer - One of the best experts on this subject based on the ideXlab platform.

  • Data from: Body Lift, drag and power are relatively higher in large-eared compared to small-eared bat species
    2017
    Co-Authors: Håkansson Jonas, Jakobsen Lasse, Hedenström Anders, Johansson L. Christoffer
    Abstract:

    Bats navigate the dark using echolocation. Echolocation is enhanced by external ears, but external ears increase the projected frontal area and reduce the streamlining of the animal. External ears are thus expected to compromise flight efficiency, but research suggests that very large ears may mitigate the cost by producing Aerodynamic Lift. Here we compare quantitative Aerodynamic measures of flight efficiency of two bat species, one large-eared (Plecotus auritus) and one small-eared (Glossophaga soricina), flying freely in a wind tunnel. We find that the body drag of both species is higher than previously assumed and that the large-eared species has a higher body drag coefficient, but also produces relatively more ear/body Lift than the small-eared species, in line with prior studies on model bats. The measured Aerodynamic power of P. auritus was higher than predicted from the Aerodynamic model, while the small-eared species aligned with predictions. The relatively higher power of the large-eared species results in lower optimal flight speeds and our findings support the notion of a trade-off between the acoustic benefits of large external ears and Aerodynamic performance. The result of this trade-off would be the eco-morphological correlation in bat flight, with large-eared bats generally adopting slow-flight feeding strategies

  • Body Lift, drag and power are relatively higher in large-eared than in small-eared bat species
    'The Royal Society', 2017
    Co-Authors: Håkansson Jonas, Jakobsen Lasse, Hedenström Anders, Johansson L. Christoffer
    Abstract:

    Bats navigate the dark using echolocation. Echolocation is enhanced by external ears, but external ears increase the projected frontal area and reduce the streamlining of the animal. External ears are thus expected to compromise flight efficiency, but research suggests that very large ears may mitigate the cost by producing Aerodynamic Lift. Here we compare quantitative Aerodynamic measures of flight efficiency of two bat species, one large-eared (Plecotus auritus) and one small-eared (Glossophaga soricina), flying freely in a wind tunnel. We find that the body drag of both species is higher than previously assumed and that the large-eared species has a higher body drag coefficient, but also produces relatively more ear/body Lift than the small-eared species, in line with prior studies on model bats. The measured Aerodynamic power of P. auritus was higher than predicted from the Aerodynamic model, while the small-eared species aligned with predictions. The relatively higher power of the large-eared species results in lower optimal flight speeds and our findings support the notion of a trade-off between the acoustic benefits of large external ears and Aerodynamic performance. The result of this trade-off would be the ecomorphological correlation in bat flight, with large-eared bats generally adopting slow-flight feeding strategies

Xinyan Deng - One of the best experts on this subject based on the ideXlab platform.

  • resonance principle for the design of flapping wing micro air vehicles
    IEEE Transactions on Robotics, 2017
    Co-Authors: Jian Zhang, Xinyan Deng
    Abstract:

    Achieving resonance in flapping wings has been recognized as one of the most important principles to enhance power efficiency, Lift generation, and flight control performance of high-frequency flapping wing micro air vehicles (MAVs). Most work on the development of such vehicles have attempted to achieve wing flapping resonance. However, the theoretical understanding of its effects on the response and energetics of flapping motion has lagged behind, leading to suboptimal design decisions and misinterpretations of experimental results. In this work, we systematically model the dynamics of flapping wing as a forced nonlinear resonant system, using both nonlinear perturbation method and linear approximation approach. We derived an analytic solution for steady-state flapping amplitude, energetics, and characteristic frequencies including natural frequency, damped natural frequency, and peak frequency. Our results showed that both Aerodynamic Lift and power efficiency are maximized by driving the wing at natural frequency, instead of other frequencies. Interestingly, the flapping velocity is maximized at natural frequency as well, which can lead to an easy experimental approach to identify natural frequency and validate the resonance design. Our models and analysis were validated with both simulations and experiments on ten different wings mounted a direct-motor-drive flapping wing MAV. The result can serve as a systematic design principle and guidance in the interpretations of empirical results.

  • resonance principle for the design of flapping wing micro air vehicles
    Intelligent Robots and Systems, 2016
    Co-Authors: Jian Zhang, Xinyan Deng
    Abstract:

    Achieving resonance in flapping wings has been recognized as one of the most important principles to enhance power efficiency, Lift generation, and flight control performance of high-frequency flapping wing micro air vehicles (MAVs). Most of work on the development of such vehicles have attempted to achieve wing flapping resonance. However, the theoretical understanding of its effects on the response and energetics of flapping motion has lagged behind, leading to sub-optimal design decisions and misinterpretations of experimental results. In this work, we systematically model the dynamics of flapping wing as a forced nonlinear resonant system. Using linear approximation approach, we derived analytic solution for steady-state flapping amplitude, energetics, and characteristic frequencies including natural frequency, damped natural frequency, and peak frequency. Our results showed that both Aerodynamic Lift and power efficiency are maximized by driving the wing at natural frequency, instead of other frequencies. Interestingly, the flapping velocity is maximized at natural frequency as well, which can lead to an easy experimental approach to identify natural frequency and validate the resonance design. Our models and analysis were validated with both simulations and experiments on ten different wings mounted a direct-motor-drive flapping wing MAV. The result can serve as a systematic design principle and guidance in the interpretations of empirical results.

Manfred Morari - One of the best experts on this subject based on the ideXlab platform.

  • Real-Time Optimization and Adaptation of the Crosswind Flight of Tethered Wings for Airborne Wind Energy
    IEEE Transactions on Control Systems Technology, 2015
    Co-Authors: Aldo U Zgraggen, Lorenzo Fagiano, Manfred Morari
    Abstract:

    Airborne wind energy systems aim to generate renewable energy by means of the Aerodynamic Lift produced using a wing tethered to the ground and controlled to fly crosswind paths. The problem of maximizing the average power developed by the generator, in the presence of limited information on wind speed and direction, is considered. At constant tether speed operation, the power is related to the traction force generated by the wing. First, a study of the traction force is presented for a general path parametrization. In particular, the sensitivity of the traction force on the path parameters is analyzed. Then, the results of this analysis are exploited to design an algorithm to maximize the force, hence the power, in real-time. The algorithm uses only the measured traction force on the tether and the wing's position, and it is able to adapt the system's operation to maximize the average force with uncertain and time-varying wind. The influence of inaccurate sensor readings and turbulent wind are also discussed. The presented algorithm is not dependent on a specific hardware setup and can act as an extension of existing control structures. Both numerical simulations and experimental results are presented to highlight the effectiveness of the approach.

  • real time optimization and adaptation of the crosswind flight of tethered wings for airborne wind energy
    arXiv: Systems and Control, 2013
    Co-Authors: Aldo U Zgraggen, Lorenzo Fagiano, Manfred Morari
    Abstract:

    Airborne wind energy systems aim to generate renewable energy by means of the Aerodynamic Lift produced by a wing tethered to the ground and controlled to fly crosswind paths. The problem of maximizing the average power developed by the generator, in presence of limited information on wind speed and direction, is considered. At constant tether speed operation, the power is related to the traction force generated by the wing. First, a study of the traction force is presented for a general path parametrization. In particular, the sensitivity of the traction force on the path parameters is analyzed. Then, the results of this analysis are exploited to design an algorithm to maximize the force, hence the power, in real-time. The algorithm uses only the measured traction force on the tether and it is able to adapt the system's operation to maximize the average force with uncertain and time-varying wind. The influence of inaccurate sensor readings and turbulent wind are also discussed. The presented algorithm is not dependent on a specific hardware setup and can act as an extension of existing control structures. Both numerical simulations and experimental results are presented to highlight the effectiveness of the approach.