The Experts below are selected from a list of 15033 Experts worldwide ranked by ideXlab platform

Jun Kobayashi - One of the best experts on this subject based on the ideXlab platform.

  • large force generation and control method of manipulator exploiting its Oscillatory Motion using van der pol oscillator
    International Journal of Control Automation and Systems, 2010
    Co-Authors: Jun Kobayashi
    Abstract:

    In this study, the effect of exploiting an Oscillatory Motion of a manipulator on large force generation is demonstrated using simulations. Firstly, a natural frequency approximation method is devised, and a preferable posture of the manipulator is selected based on the approximation. The preferable posture is a posture in which the natural frequency of the manipulator is low. Since, in general, high frequency vibration is considered to be an undesirable phenomenon for mechanical systems, the manipulator should be operated in the preferable posture. Secondly, a method to oscillate the manipulator is proposed, and its performance is investigated using simulations. The method capitalizes on the Oscillatory Motion of the manipulator for efficient large force generation. Specifically, the method uses Van der Pol (VDP) oscillator to exploit an Oscillatory Motion of the manipulator. A force reference signal, which is a command to make the manipulator oscillate, is produced by the VDP oscillator. Due to the entrainment property of the VDP oscillator, the force reference signal can synchronize with the Motion of the manipulator. The efficient large force generation is attained by the synchronization. Thirdly, a force control system that enables you to obtain the desired amount of force is designed based on the force generation method. By adjusting the natural frequency of the VDP oscillator, the purpose of the force control system is realized. Finally, a theoretical proof of the entrainment property of the VDP oscillator coupled with a linear mechanical system is established with an averaging method, and simulations exemplify the validity of the proof.

  • weeding manipulator exploiting its Oscillatory Motion for force generation verification of the effectiveness by simulations using open dynamics engine
    Robotics and Biomimetics, 2009
    Co-Authors: Jun Kobayashi
    Abstract:

    This paper addresses a weeding manipulator exploiting its Oscillatory Motion to generate a large force efficiently. To justify the exploitation, some simulations were conducted based on a manipulator model and a weed model created using Open Dynamics Engine (ODE), which is a high performance library for simulating rigid body dynamics. The simulation results illustrated that the exploitation of an Oscillatory Motion is effective on force generation by a manipulator. Furthermore, it was shown that a manipulator drive method using Van der Pol (VDP) oscillator has better performance than a method using a sinusoidal wave function, because of an entrainment property of the VDP oscillator.

  • ROBIO - Weeding manipulator exploiting its Oscillatory Motion for force generation: Verification of the effectiveness by simulations using Open Dynamics Engine
    2008 IEEE International Conference on Robotics and Biomimetics, 2009
    Co-Authors: Jun Kobayashi
    Abstract:

    This paper addresses a weeding manipulator exploiting its Oscillatory Motion to generate a large force efficiently. To justify the exploitation, some simulations were conducted based on a manipulator model and a weed model created using Open Dynamics Engine (ODE), which is a high performance library for simulating rigid body dynamics. The simulation results illustrated that the exploitation of an Oscillatory Motion is effective on force generation by a manipulator. Furthermore, it was shown that a manipulator drive method using Van der Pol (VDP) oscillator has better performance than a method using a sinusoidal wave function, because of an entrainment property of the VDP oscillator.

  • force control system with nonlinear oscillator for manipulator in Oscillatory Motion
    Robotics and Biomimetics, 2007
    Co-Authors: Jun Kobayashi, F Onkawa
    Abstract:

    A force control system for a manipulator equipped with a spring as the end-effector is presented in this paper. The manipulator exploits its Oscillatory Motion, applying a force through the spring. It has been investigated that the manipulator driven by the van der Pol oscillator can generate a large force efficiently. In this paper, the authors design a force control system to control the amplitude of a force generated by the manipulator. The force control system achieves the desired force by adjusting the natural frequency of the van der Pol oscillator. The performance of the force control system is evaluated using simulations.

  • ROBIO - Force control system with nonlinear oscillator for manipulator in Oscillatory Motion
    2007 IEEE International Conference on Robotics and Biomimetics (ROBIO), 2007
    Co-Authors: Jun Kobayashi, F Onkawa
    Abstract:

    A force control system for a manipulator equipped with a spring as the end-effector is presented in this paper. The manipulator exploits its Oscillatory Motion, applying a force through the spring. It has been investigated that the manipulator driven by the van der Pol oscillator can generate a large force efficiently. In this paper, the authors design a force control system to control the amplitude of a force generated by the manipulator. The force control system achieves the desired force by adjusting the natural frequency of the van der Pol oscillator. The performance of the force control system is evaluated using simulations.

Véronique Roig - One of the best experts on this subject based on the ideXlab platform.

  • Oscillatory Motion and wake of a bubble rising in a thin gap cell
    Journal of Fluid Mechanics, 2015
    Co-Authors: Audrey Filella, Patricia Ern, Véronique Roig
    Abstract:

    We investigate the characteristics of the Oscillatory Motion and wake of confined bubbles freely rising in a thin-gap cell (h=3.1 mm width). Once the diameter d of the bubble in the plane of the cell is known, the mean vertical velocity of the bubble Vb is proportional to the gravitational velocity [...], where g is the gravitational acceleration. This velocity is used to build the Reynolds number [...] that characterizes the flow induced by the bubble in the surrounding liquid (of kinematic viscosity ν), and which determines at leading order the mean deformation of the bubble given by the aspect ratio χ of the ellipse equivalent to the bubble contour. We then show that in the reference frame associated with the bubble (having a fixed origin and axes corresponding to the minor and major axes of the equivalent ellipse) the characteristics of its Oscillatory Motion in the plane of the cell display remarkable properties in the range 1200Oscillatory Motion of sufficiently confined bubbles. We observe that vortex shedding occurs for a maximal transverse velocity Vt of the bubble, corresponding to a maximal drift angle of the bubble. Furthermore, the measured vorticity of the vortex at detachment corresponds to the estimation [...] of the vorticity produced at the bubble surface. Three stages then emerge concerning the evolution in time of the wake generated by the bubble. For one to two periods of oscillation Tx following the release of a vortex, a rapid decay of the vorticity of the released vortex is observed. Meanwhile, the released vortex located initially at a distance of approximately one diameter from the bubble centre moves outwards from the bubble path and expands. At intermediate times, the vortex street undergoes vortex pairing. When viscous effects become predominant at a time of the order of the viscous time scale τν=[...], the vortex street becomes frozen and decays exponentially in place.

  • Oscillatory Motion and wake of a bubble rising in a thin-gap cell
    Journal of Fluid Mechanics, 2015
    Co-Authors: Audrey Filella, Patricia Ern, Véronique Roig
    Abstract:

    We investigate the characteristics of the Oscillatory Motion and wake of confined bubbles freely rising in a thin-gap cell (h=3.1 mm width). Once the diameter d of the bubble in the plane of the cell is known, the mean vertical velocity of the bubble Vb is proportional to the gravitational velocity [...], where g is the gravitational acceleration. This velocity is used to build the Reynolds number [...] that characterizes the flow induced by the bubble in the surrounding liquid (of kinematic viscosity ν), and which determines at leading order the mean deformation of the bubble given by the aspect ratio χ of the ellipse equivalent to the bubble contour. We then show that in the reference frame associated with the bubble (having a fixed origin and axes corresponding to the minor and major axes of the equivalent ellipse) the characteristics of its Oscillatory Motion in the plane of the cell display remarkable properties in the range 1200

Shih-yuin Lin - One of the best experts on this subject based on the ideXlab platform.

  • Quantum radiation by an Unruh-DeWitt detector in Oscillatory Motion
    Journal of High Energy Physics, 2017
    Co-Authors: Shih-yuin Lin
    Abstract:

    Quantum radiated power emitted by an Unruh-DeWitt (UD) detector in linear Oscillatory Motion in (3+1)D Minkowski space, with the internal harmonic oscillator minimally coupled to a massless scalar field, is obtained non-perturbatively by numerical method. The signal of the Unruh-like effect experienced by the detector is found to be pronounced in quantum radiation in the highly non-equilibrium regime with high averaged acceleration and short Oscillatory cycle, and the signal would be greatly suppressed by quantum interference when the averaged proper acceleration is sufficiently low. An observer at a fixed angle would see periods of negative radiated power in each cycle of Motion, while the averaged radiated power over a cycle is always positive as guaranteed by the quantum inequalities. Coherent high harmonic generation and down conversion are identified in the detector's quantum radiation. Due to the overwhelming largeness of the vacuum correlators of the free field, the asymptotic reduced state of the harmonics of the radiation field is approximately a direct product of the squeezed thermal states.

  • Radiation by an Unruh-DeWitt Detector in Oscillatory Motion
    arXiv: High Energy Physics - Theory, 2016
    Co-Authors: Shih-yuin Lin
    Abstract:

    Quantum radiated energy flux emitted by an Unruh-DeWitt (UD) detector, with the internal harmonic oscillator coupled to a massless scalar field, in linear Oscillatory Motion in (3+1) dimensional Minkowski space is studied by numerical methods. Our results show that quantum interference can indeed suppress the signal of the Unruh effect if the averaged proper acceleration is sufficiently low, but not in the regime with high averaged acceleration and short Oscillatory cycle. While the averaged radiated energy flux over a cycle is always positive as guaranteed by the quantum inequalities, an observer at a fixed angle may see short periods of negative radiated energy flux in each cycle of Motion, which indicates that the radiation is squeezed. This reveals another resemblance between the detector theory and the moving-mirror model.

  • Unruh Effect under Non-equilibrium conditions: Oscillatory Motion of an Unruh-DeWitt detector
    Journal of High Energy Physics, 2013
    Co-Authors: Jason Doukas, Shih-yuin Lin, Robert B. Mann
    Abstract:

    The Unruh effect refers to the thermal fluctuations a detector experiences while undergoing linear Motion with uniform acceleration in a Minkowski vacuum. This thermality can be demonstrated by tracing the vacuum state of the field over the modes beyond the accelerated detector's event horizon. However, the event horizon is well-defined only if the detector moves with eternal uniform linear acceleration. This idealized condition cannot be fulfilled in realistic situations when the Motion unavoidably involves periods of non-uniform acceleration. Many experimental proposals to test the Unruh effect are of this nature. Often circular or Oscillatory Motion, which lacks an obvious geometric description, is considered in such proposals. The proper perspective for theoretically going beyond, or experimentally testing, the Unruh-Hawking effect in these more general conditions has to be offered by concepts and techniques in non-equilibrium quantum field theory. In this paper we provide a detailed analysis of how an Unruh-DeWitt detector undergoing Oscillatory Motion responds to the fluctuations of a quantum field. Numerical results for the late-time temperatures of the oscillating detector are presented. We comment on the digressions of these results from what one would obtain from a naive application of Unruh's result.

Audrey Filella - One of the best experts on this subject based on the ideXlab platform.

  • Oscillatory Motion and wake of a bubble rising in a thin gap cell
    Journal of Fluid Mechanics, 2015
    Co-Authors: Audrey Filella, Patricia Ern, Véronique Roig
    Abstract:

    We investigate the characteristics of the Oscillatory Motion and wake of confined bubbles freely rising in a thin-gap cell (h=3.1 mm width). Once the diameter d of the bubble in the plane of the cell is known, the mean vertical velocity of the bubble Vb is proportional to the gravitational velocity [...], where g is the gravitational acceleration. This velocity is used to build the Reynolds number [...] that characterizes the flow induced by the bubble in the surrounding liquid (of kinematic viscosity ν), and which determines at leading order the mean deformation of the bubble given by the aspect ratio χ of the ellipse equivalent to the bubble contour. We then show that in the reference frame associated with the bubble (having a fixed origin and axes corresponding to the minor and major axes of the equivalent ellipse) the characteristics of its Oscillatory Motion in the plane of the cell display remarkable properties in the range 1200Oscillatory Motion of sufficiently confined bubbles. We observe that vortex shedding occurs for a maximal transverse velocity Vt of the bubble, corresponding to a maximal drift angle of the bubble. Furthermore, the measured vorticity of the vortex at detachment corresponds to the estimation [...] of the vorticity produced at the bubble surface. Three stages then emerge concerning the evolution in time of the wake generated by the bubble. For one to two periods of oscillation Tx following the release of a vortex, a rapid decay of the vorticity of the released vortex is observed. Meanwhile, the released vortex located initially at a distance of approximately one diameter from the bubble centre moves outwards from the bubble path and expands. At intermediate times, the vortex street undergoes vortex pairing. When viscous effects become predominant at a time of the order of the viscous time scale τν=[...], the vortex street becomes frozen and decays exponentially in place.

  • Oscillatory Motion and wake of a bubble rising in a thin-gap cell
    Journal of Fluid Mechanics, 2015
    Co-Authors: Audrey Filella, Patricia Ern, Véronique Roig
    Abstract:

    We investigate the characteristics of the Oscillatory Motion and wake of confined bubbles freely rising in a thin-gap cell (h=3.1 mm width). Once the diameter d of the bubble in the plane of the cell is known, the mean vertical velocity of the bubble Vb is proportional to the gravitational velocity [...], where g is the gravitational acceleration. This velocity is used to build the Reynolds number [...] that characterizes the flow induced by the bubble in the surrounding liquid (of kinematic viscosity ν), and which determines at leading order the mean deformation of the bubble given by the aspect ratio χ of the ellipse equivalent to the bubble contour. We then show that in the reference frame associated with the bubble (having a fixed origin and axes corresponding to the minor and major axes of the equivalent ellipse) the characteristics of its Oscillatory Motion in the plane of the cell display remarkable properties in the range 1200

Robert B. Mann - One of the best experts on this subject based on the ideXlab platform.

  • Unruh Effect under Non-equilibrium conditions: Oscillatory Motion of an Unruh-DeWitt detector
    Journal of High Energy Physics, 2013
    Co-Authors: Jason Doukas, Shih-yuin Lin, Robert B. Mann
    Abstract:

    The Unruh effect refers to the thermal fluctuations a detector experiences while undergoing linear Motion with uniform acceleration in a Minkowski vacuum. This thermality can be demonstrated by tracing the vacuum state of the field over the modes beyond the accelerated detector's event horizon. However, the event horizon is well-defined only if the detector moves with eternal uniform linear acceleration. This idealized condition cannot be fulfilled in realistic situations when the Motion unavoidably involves periods of non-uniform acceleration. Many experimental proposals to test the Unruh effect are of this nature. Often circular or Oscillatory Motion, which lacks an obvious geometric description, is considered in such proposals. The proper perspective for theoretically going beyond, or experimentally testing, the Unruh-Hawking effect in these more general conditions has to be offered by concepts and techniques in non-equilibrium quantum field theory. In this paper we provide a detailed analysis of how an Unruh-DeWitt detector undergoing Oscillatory Motion responds to the fluctuations of a quantum field. Numerical results for the late-time temperatures of the oscillating detector are presented. We comment on the digressions of these results from what one would obtain from a naive application of Unruh's result.