Using Time-Periodicity for Inducing Energy Transfer Between Vibration Modes

2013 ◽  
Author(s):  
Fadi Dohnal ◽  
Aleš Tondl
Keyword(s):  
Energy Transfer ◽  
Degrees Of Freedom ◽  
Vibrational Energy ◽  
Low Frequency ◽  
Vibration Modes ◽  
Present Contribution ◽  
Multiple Degrees Of Freedom ◽  
Time Periodicity ◽  
The Many ◽  
And Control

Introducing time-periodicity in system parameters may lead, in general, to a dangerous and well-known parametric resonance. In contrast to such a resonance, a properly tuned time-periodicity is capable of transferring energy between vibration modes. Time-periodicity in combination with system damping is capable of efficiently extracting vibrational energy from the system and of amplifying the existing damping affecting transient vibrations. Operating the system at such a specific time-periodicity, the system is tuned at a parametric anti-resonance. The basic principle of this concept has been studied theoretically and was proven experimentally. The physical interpretation of this concept was proposed in “Damping by Parametric Stiffness Excitation: Resonance and Anti-Resonance”, Journal of Vibration and Control, 2008, for a multiple degrees of freedom system. The present contribution highlights those findings on a multiple degrees of freedom system. It is illustrated that a parametric anti-resonance is connected to inducing an energy transfer between two of the many vibration modes of the underlying system with constant coefficients. The induced energy transfer can be utilized to transfer the vibration energy from low frequency to high frequency or vice versa or, in case of system damping, to a more efficient dissipation of vibrational energy. The achievable energy dissipation is most significant if an energy transfer is induced between a lightly damped mode and a strongly damped mode.

Nonlinear generation of non-acoustic modes by low-frequency sound in a vibrationally relaxing gas

2010 ◽  
Vol 88 (4) ◽  
pp. 293-300 ◽  
Author(s):  
Anna Perelomova
Keyword(s):  
Degrees Of Freedom ◽  
Vibrational Energy ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Dynamic Equations ◽  
Thermal Mode ◽  
Acoustic Source ◽  
Frequency Sound ◽  
Acoustic Modes ◽  
Relaxing Gas

Two dynamic equations referring to a weakly nonlinear and weakly dispersive flow of a gas in which molecular vibrational relaxation takes place, are derived. The first one governs an excess temperature associated with the thermal mode, and the second one describes variations in vibrational energy. Both quantities refer to non-wave types of gas motion. These variations are caused by the nonlinear transfer of acoustic energy into thermal mode and internal vibrational degrees of freedom of a relaxing gas. The final dynamic equations are instantaneous; they include a quadratic nonlinear acoustic source, reflecting the nonlinear character of interaction of low-frequency acoustic and non-acoustic motions of the fluid. All types of sound, periodic or aperiodic, may serve as an acoustic source of both phenomena. The low-frequency sound is considered in this study. Some conclusions about temporal behavior of non-acoustic modes caused by periodic and aperiodic sound are made. Under certain conditions, acoustic cooling takes place instead of heating .

Study of Targeted Energy Transfer Inside Three-Dimensional Acoustic Cavity by Two Nonlinear Membrane Absorbers and an Acoustic Mode

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Xian Wu ◽  
Jianwang Shao ◽  
Bruno Cochelin
Keyword(s):  
Energy Transfer ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Low Frequency ◽  
Nonlinear Energy Sink ◽  
Acoustic Mode ◽  
Targeted Energy Transfer ◽  
Working Zone ◽  
Acoustic Cavity ◽  
Acoustic Cavities

As a new approach to passive sound control in low-frequency domain, the targeted energy transfer (TET) phenomenon has been investigated inside a three-dimensional (3D) acoustic cavity by considering a two degrees-of-freedom (DOF) system with an acoustic mode and a membrane nonlinear energy sink (NES). The beginning of TET phenomenon of the 2DOF system and the desired working zone for the membrane NES have been defined. In order to enhance the robustness and the effective TET range in acoustic cavities, a 3DOF system with two membranes and one acoustic mode is studied in this paper. We consider two different membranes and two almost identical membranes to analyze the TET phenomenon, respectively. The desired working zone which was obtained by the 2DOF system is applied to analyze the 3DOF system. We observe that two membranes can enlarge the desired working zone.

Experimental Observation on a Controllable Underwater Towed Vehicle With Vertical Airfoil Main Body

2015 ◽  
Author(s):  
Jiaming Wu ◽  
Jian Chen ◽  
Ying Xu ◽  
Xiaodong Jin ◽  
Lihua Lu ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Main Body ◽  
Control Mechanisms ◽  
Attitude Stability ◽  
Multiple Degrees Of Freedom ◽  
Structural Style ◽  
Alternative Type ◽  
And Control ◽  
Righting Moment ◽  
Ducted Propellers

An alternative type of controllable underwater towed vehicle is proposed. The vehicle is composed of horizontal fixed main wing, adjustable wing flap, and a vertical airfoil main body above which two torpedo-shaped buoyant cylinders are symmetrically fixed. The adjustable wing flap serves as an actuator for deflection of the horizontal fixed main wing to produce enough downward lifting force to the towed vehicle running at a required water depth. Principal function of the torpedo-shaped buoyant cylinders is to create a righting moment or a favorite roll damping for attitude stability of the vehicle during towing operation. Meanwhile two ducted propellers are installed at the sterns of the buoyant cylinders to provide an induced turning moment for the vertical airfoil main body, which in turn produce a driving force for the vehicle in lateral motion. Results of our laboratory experiments indicate that flexible attitude and trajectory manipulations to the vehicle in multiple degrees of freedom can be achieved with the structural style and control mechanisms of the proposed vehicle. The manipulations to the vehicle with the proposed control mechanisms are accomplished by a joint operation of controlling the rotational speeds and directions of the ducted propellers and/or adjusting the deflection of the wing flap. By means of the proposed structural style and control manner, difficulty in designing control system of the vehicle can be reduced greatly, and stronger self stability of the vehicle during its survey towing can be guaranteed.

scholarly journals On Differential Mechanisms for Underactuated, Lightweight, Adaptive Prosthetic Hands

2021 ◽  
Vol 15 ◽  
Author(s):  
Geng Gao ◽  
Mojtaba Shahmohammadi ◽  
Lucas Gerez ◽  
George Kontoudis ◽  
Minas Liarokapis
Keyword(s):  
Degrees Of Freedom ◽  
Experimental Validation ◽  
Minimal Set ◽  
Prosthetic Devices ◽  
Multiple Degrees Of Freedom ◽  
Prosthetic Hands ◽  
Promising Application ◽  
End Effectors ◽  
Critical Components ◽  
And Control

Over the last decade underactuated, adaptive robot grippers and hands have received an increased interest from the robotics research community. This class of robotic end-effectors can be used in many different fields and scenarios with a very promising application being the development of prosthetic devices. Their suitability for the development of such devices is attributed to the utilization of underactuation that provides increased functionality and dexterity with reduced weight, cost, and control complexity. The most critical components of underactuated, adaptive hands that allow them to perform a broad set of grasp poses are appropriate differential mechanisms that facilitate the actuation of multiple degrees of freedom using a single motor. In this work, we focus on the design, analysis, and experimental validation of a four output geared differential, a series elastic differential, and a whiffletree differential that can incorporate a series of manual and automated locking mechanisms. The locking mechanisms have been developed so as to enhance the control of the differential outputs, allowing for efficient grasp selection with a minimal set of actuators. The differential mechanisms are applied to prosthetic hands, comparing them and describing the benefits and the disadvantages of each.

scholarly journals Deformation model and experimental evaluation of a contractable and bendable wire-pulling mechanism with embedded soft tubes for a robotic tongue

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Nobutsuna Endo
Keyword(s):  
Degrees Of Freedom ◽  
Physical Models ◽  
Deformation Model ◽  
Soft Body ◽  
Piecewise Constant ◽  
Multiple Degrees Of Freedom ◽  
Human Tongue ◽  
Drive And Control ◽  
Deformation Tests ◽  
And Control

AbstractFew physical models of oral and laryngeal systems for human speech movement exist for computer or mechanical simulators. In particular, a robot tongue mechanism that fully reproduces the deformation motion of the human tongue is lacking. The human tongue is an aggregate of muscles that is devoid of a skeleton. It possesses only a small hyoid. A mechanism that can drive and control the deformation of a soft body, such as the human tongue, along multiple degrees of freedom has not been realized to date. To solve this problem, a wire-pulling mechanism with embedded soft tubes is proposed. Using this mechanism, a flexible tongue that can be deformed along multiple degrees of freedom without breaking the wire is achieved. A prototype planar mechanism with two degrees of freedom that is capable of contraction and bending was fabricated. A deformation model that assumes a piecewise constant curvature (PCC) was formulated. Deformation tests confirmed that the prototype is capable of contraction and bending movements that are consistent with those of the model. Variations in the error with respect to the hardness of the deformable part are discussed, and the limits of the deformation model based on the PCC assumption are presented.

scholarly journals A Pendulum-Like Low Frequency Electromagnetic Vibration Energy Harvester Based on Polymer Spring and Coils

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3380
Author(s):  
Yunjia Li ◽  
Xinyi Wang ◽  
Shuhan Zhang ◽  
Chenyuan Zhou ◽  
Dayong Qiao ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Output Voltage ◽  
Degrees Of Freedom ◽  
Energy Harvester ◽  
Vibrational Energy ◽  
Low Frequency ◽  
Open Circuit ◽  
Vibration Energy ◽  
Vibration Energy Harvester ◽  
Circuit Output

This paper presents a low-frequency electromagnetic vibrational energy harvester (EVEH) with two degrees of freedom and two resonant modes. The proposed EVEH is based on a disc magnet suspended in a pendulum fashion by a polymeric spring between two sets of polymer coil stacks. The fabricated EVEH is capable of harvesting vibration energy on two directions with an extended bandwidth. With a sinusoidal acceleration of ±1 g on Z direction, a peak-to-peak closed-circuit output voltage of 0.51 V (open-circuit voltage: 1 V), and an output power of 35.1 μW are achieved at the resonant frequency of 16 Hz. With a sinusoidal acceleration of ±1.5 g on X direction, a peak-to-peak output voltage of 0.14 V and power of 2.56 μW are achieved, at the resonant frequency of 20 Hz.

Low-frequency interior noise in prop-driven aircrafts: Sources and control methodologies

2017 ◽  
Vol 48 (7-8) ◽  
pp. 94-98 ◽  
Author(s):  
Fathollah Ommi ◽  
Mohammadreza Azimi
Keyword(s):  
Conflicts Of Interest ◽  
Health Hazard ◽  
Low Frequency ◽  
Sound Field ◽  
Interior Noise ◽  
Low Frequencies ◽  
Modern Times ◽  
Propeller Noise ◽  
The Many ◽  
And Control

Nowadays, noise has turned into one of the most important among the environmental factors on which industry sets down a big part of its efforts and concerns. The recognition of noise as a serious health hazard is a development of modern times. Too much noise obviously impairs our physical and mental existence and therefore it is reasonable to pursue Technology Assessment concerning noisy technologies. The conflicts of interest associated with noise that arise from the operation of airports are well known. Propeller noise is most dominant at low frequencies (below 500 Hz) where traditional passive treatments have only little effect. The many factors contributing to the sound field inside propeller aircraft have led to extensive research directed toward identifying and improving techniques for interior noise reduction.

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