Fluidic low-frequency oscillator with vortex spin-up time delay

2015 ◽  
Vol 90 ◽  
pp. 6-15 ◽  
Author(s):  
Václav Tesař ◽  
Emil Smyk
Keyword(s):  
Time Delay ◽  
Low Frequency ◽  
Frequency Oscillator

scholarly journals BeiDa Imaging Electron Spectrometer observation of multi-period electron flux modulation caused by localized ultra-low-frequency waves

2020 ◽  
Vol 38 (4) ◽  
pp. 801-813
Author(s):  
Xingran Chen ◽  
Qiugang Zong ◽  
Hong Zou ◽  
Xuzhi Zhou ◽  
Li Li ◽  
...  
Keyword(s):  
Time Delay ◽  
Electron Flux ◽  
Particle Interaction ◽  
Energetic Electron ◽  
Low Frequency ◽  
Particle Energy ◽  
Energy Change ◽  
Electron Spectrometer ◽  
Resonance Theory ◽  
Energy Channels

Abstract. We present multi-period modulation of energetic electron flux observed by the BeiDa Imaging Electron Spectrometer (BD-IES) on board a Chinese navigation satellite on 13 October 2015. Electron flux oscillations were observed at a dominant period of ∼190 s in consecutive energy channels from ∼50 to ∼200 keV. Interestingly, flux modulations at a secondary period of ∼400 s were also unambiguously observed. The oscillating signals at different energy channels were observed in sequence, with a time delay of up to ∼900 s. This time delay far exceeds the oscillating periods, by which we speculate that the modulations were caused by localized ultra-low-frequency (ULF) waves. To verify the wave–particle interaction scenario, we revisit the classic drift-resonance theory. We adopt the calculation method therein to derive the electron energy change in a multi-period ULF wave field. Then, based on the modeled energy change, we construct the flux variations to be observed by a virtual spacecraft. The predicted particle signatures well agree with the BD-IES observations. We demonstrate that the particle energy change might be underestimated in the conventional theories, as the Betatron acceleration induced by the curl of the wave electric field was often omitted. In addition, we show that azimuthally localized waves would notably extend the energy width of the resonance peak, whereas the drift-resonance interaction is only efficient for particles at the resonant energy in the original theory.

Flame Transfer Function for Swirled LPP Combustion From Experiments and CFD

2004 ◽  
Author(s):  
Carol A. Armitage ◽  
Alex J. Riley ◽  
R. Stewart Cant ◽  
Ann P. Dowling ◽  
Simon R. Stow
Keyword(s):  
Time Delay ◽  
Transfer Function ◽  
Gas Turbines ◽  
Transfer Functions ◽  
Low Frequency ◽  
Analytical Models ◽  
Delay Spread ◽  
Good Representation ◽  
Atmospheric Conditions ◽  
Spread Model

Combustion oscillations that arise in gas turbines can lead to plant damage. One method used to predict these oscillations is to analyse the acoustics using a simple linear model. This model requires a transfer function to describe the response of the heat release to flow perturbations. A transfer function has been obtained for a swirled premixed combustion system using experiments under atmospheric conditions and CFD. These results have been compared with analytical models. The experimental and computational transfer functions both indicate a low frequency zero. A time-delay spread model gives a good representation of the computational transfer function. The experimental transfer function is described well by a model that combines a time-delay spread with a constant gain.

Design and Numerical Analysis of an Electrostatic Energy Harvester With Impact for Frequency Up-Conversion

2020 ◽  
Vol 15 (5) ◽  
Author(s):  
R. Lensvelt ◽  
R. H. B. Fey ◽  
R. M. C. Mestrom ◽  
H. Nijmeijer
Keyword(s):  
Power Generation ◽  
High Frequency ◽  
Energy Harvester ◽  
Low Frequency ◽  
Electrostatic Energy ◽  
Computational Time ◽  
Ambient Vibrations ◽  
Frequency Oscillator ◽  
Low Frequency Power ◽  
Frequency Power

Abstract Integration of vibration energy harvesters (VEHs) with small-scale electronic devices may form an attractive alternative for relatively large batteries and can, potentially, increase their lifespan. However, the inherent mismatch between a harvester's high-frequency resonance, typically in the range 100−1000 Hz, relative to the available low-frequency ambient vibrations, typically in the range 10–100 Hz, means that low-frequency power generation in microscale VEHs remains a persistent challenge. In this work, we model a novel electret-based, electrostatic energy harvester (EEH) design. In this design, we combine an out-of-plane gap-closing comb (OPGC) configuration for the low-frequency oscillator with an in-plane overlap comb configuration for the high-frequency oscillator and employ impact for frequency up-conversion. An important design feature is the tunability of the resonance frequency through the electrostatic nonlinearity of the low-frequency oscillator. Impulsive normal forces due to impact are included in numerical simulation of the EEH through Moreau's time-stepping scheme which has, to the best of our knowledge, not been used before in VEH design and analysis. The original scheme is extended with time-step adjustments around impact events to reduce computational time. Using frequency sweeps, we numerically investigate power generation under harmonic, ambient vibrations. Results show improved low-frequency power generation in this EEH compared to a reference EEH. The EEH design shows peak power generation improvement of up to a relative factor 3.2 at low frequencies due to the occurrence of superharmonic resonances.

Wave Variable Based Force Control

2007 ◽  
Author(s):  
J. Scot Hart ◽  
Gu¨nter Niemeyer
Keyword(s):  
Time Delay ◽  
Force Control ◽  
Time Delays ◽  
Communication Channel ◽  
Force Feedback ◽  
Low Frequency ◽  
Force Sensor ◽  
Wave Variable ◽  
Communication Time ◽  
Frictional Forces

Wave variable controllers maintain passive communication across time delays in telerobotics. As passive elements, wave variable controllers interact well with other passive elements, such as P.D. controllers and masses, and use a combination of force and velocity signals to apply force feedback. Currently we are exploring the use of wave variable controllers with large non-backdrivable industrial-type slave devices where dynamics are dominated by inertial and frictional forces. The objective is to integrate force sensor measurements into wave variable controllers to provide low frequency force feedback and hide the slave’s friction and inertia from the user in the presence of a communication time delay. This paper presents and uses a wave variable based approach to design force control. The resulting wave variable based force controller is converted to power variables and shown to be similar to traditional force controllers. A 1-DOF telerobotic system is used to experimentally show the wave variable based force control combines with the enhanced stability properties of the wave communication channel to produce robust slave side force control. The resulting system is better able to maintain force control with rigid environments then a traditional controller both with and without communication time delay.

Cascade controllers design based on model matching in frequency domain for stable and integrating processes with time delay

2022 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Mohd Atif Siddiqui ◽  
Md Nishat Anwar ◽  
Shahedul Haque Laskar
Keyword(s):  
Time Delay ◽  
Frequency Domain ◽  
Disturbance Rejection ◽  
Low Frequency ◽  
Cascade Control ◽  
Model Matching ◽  
Content Type ◽  
Proportional Integral ◽  
Load Disturbance ◽  
Wide Range

Purpose This paper aims to present an efficient and simplified proportional-integral/proportional-integral and derivative controller design method for the higher-order stable and integrating processes with time delay in the cascade control structure (CCS). Design/methodology/approach Two approaches based on model matching in the frequency domain have been proposed for tuning the controllers of the CCS. The first approach is based on achieving the desired load disturbance rejection performance, whereas the second approach is proposed to achieve the desired setpoint performance. In both the approaches, matching between the desired model and the closed-loop system with the controller is done at a low-frequency point. Model matching at low-frequency points yields a linear algebraic equation and the solution to these equations yields the controller parameters. Findings Simulations have been conducted on several examples covering high order stable, integrating, double integrating processes with time delay and nonlinear continuous stirred tank reactor. The performance of the proposed scheme has been compared with recently reported work having modified cascade control configurations, sliding mode control, model predictive control and fractional order control. The performance of both the proposed schemes is either better or comparable with the recently reported methods. However, the proposed method based on desired load disturbance rejection performance outperforms among all these schemes. Originality/value The main advantages of the proposed approaches are that they are directly applicable to any order processes, as they are free from time delay approximation and plant order reduction. In addition to this, the proposed schemes are capable of handling a wide range of different dynamical processes in a unified way.

Laser interferometer calibration system for extensometers

1968 ◽  
Vol 58 (5) ◽  
pp. 1379-1383
Author(s):  
G. Hade ◽  
M. Conner ◽  
J. T. Kuo
Keyword(s):  
Laser Interferometer ◽  
Michelson Interferometer ◽  
Low Frequency ◽  
Calibration Method ◽  
Linear Range ◽  
Laser Source ◽  
Calibration System ◽  
Frequency Oscillator ◽  
Transducer Output ◽  
Optical Calibration

Abstract A laser interferometer technique has been developed for calibrating extensometers at the Ogdensberg Station of Lamont Geological Observatory. It provides remotecontrolled calibration of both horizontal and vertical extensometers within the linear range of the transducer output. The present calibration system consists of an electromagnetic driving unit and a Michelson interferometer. The transducer end of the extensometer is displaced longitudinally with an electromagnetic driving unit, which is excited by a variable low-frequency oscillator with a bandwidth of 0.0005 to 60 kHz. The resultant displacement is detected by counting fringe displacements of the interferometer with an Ne-He laser source. With this calibration system, motion as small as 0.03 micron can be determined with excellent repeatability and with errors of less than 5 per cent, in comparison with errors of more than 40 per cent for the optical calibration method previously used.

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