scholarly journals Forced synchronization of periodic and aperiodic thermoacoustic oscillations: lock-in, bifurcations and open-loop control

2018 ◽  
Vol 838 ◽  
pp. 690-714 ◽  
Author(s):  
Karthik Kashinath ◽  
Larry K. B. Li ◽  
Matthew P. Juniper
Keyword(s):  
Periodic System ◽  
Systems Approach ◽  
Numerical Study ◽  
Dominant Frequency ◽  
Open Loop ◽  
Response Amplitude ◽  
Loop Control ◽  
Acoustic Forcing ◽  
Lock In ◽  
Thermoacoustic Oscillations

Synchronization is a universal concept in nonlinear science but has received little attention in thermoacoustics. In this numerical study, we take a dynamical systems approach to investigating the influence of harmonic acoustic forcing on three different types of self-excited thermoacoustic oscillations: periodic, quasi-periodic and chaotic. When the periodic system is forced, we find that: (i) at low forcing amplitudes, it responds at both the forcing frequency and the natural (self-excited) frequency, as well as at their linear combinations, indicating quasi-periodicity; (ii) above a critical forcing amplitude, the system locks in to the forcing; (iii) the bifurcations leading up to lock-in and the critical forcing amplitude required for lock-in depend on the proximity of the forcing frequency to the natural frequency; (iv) the response amplitude at lock-in may be larger or smaller than that of the unforced system and the system can exhibit hysteresis and the jump phenomenon owing to a cusp catastrophe; and (v) at forcing amplitudes above lock-in, the oscillations can become unstable and transition to chaos, or switch between different stable attractors depending on the forcing amplitude. When the quasi-periodic system is forced at a frequency equal to one of the two characteristic frequencies of the torus attractor, we find that lock-in occurs via a saddle-node bifurcation with frequency pulling. When the chaotic system is forced at a frequency close to the dominant frequency of its strange attractor, we find that it is possible to destroy chaos and establish stable periodic oscillations. These results show that the open-loop application of harmonic acoustic forcing can be an effective strategy for controlling periodic or aperiodic thermoacoustic oscillations. In some cases, we find that such forcing can reduce the response amplitude by up to 90 %, making it a viable way to weaken thermoacoustic oscillations.

Active Control of Combustion Instabilities in a Matrix Burner Using Primary and Pilot Fuel and Acoustic Forcing

2010 ◽  
Author(s):  
Dieter Bohn ◽  
Nils Ohlendorf ◽  
Frank Weidner ◽  
James F. Willie
Keyword(s):  
Heat Release ◽  
Mass Flow ◽  
Gas Turbines ◽  
Open Loop ◽  
Nox Emissions ◽  
Combustion Instabilities ◽  
Loop Control ◽  
First Case ◽  
Pilot Fuel ◽  
Acoustic Forcing

Lean premixed flames applied in modern gas turbines leads to reduce NOx emissions, but at the same time they are more susceptible to combustion instabilities than diffusion flames. These oscillations cause pressure fluctuations with high amplitudes and unacceptable noise as well as the risk of component or even engine failure. They can lead to pockets of fuel being formed in the mixing chamber and to bad mixing, which leads to increase in emissions. This paper reports the successful decoupling of the pressure and heat release inside the combustion chamber of a matrix burner using two actuation techniques. This led to the successful attenuation of the dominant instability modes occurring inside the combustor of the matrix burner. In the first case, acoustic forcing was used to decouple the pressure and the heat release inside the combustor. This was achieved by using a loudspeaker to modulate the primary air mass flow. This was followed by using acoustic forcing in CFD to decouple the pressure and heat release inside the combustor. For the action of the loudspeaker, sinusoidal forcing was used to mimic the modulation action of the diaphragm of the loudspeaker. In the second case, a fast gaseous “on-off” injector was used to modulate the primary fuel mass flow. After this, pilot fuel modulation was used to stabilize the flame. The control law governing the primary and pilot fuel modulation is discussed in details. The effect of open loop control on NOx emissions in the burner is also reported and discussed.

Open-loop control of compensation for optical propagation through a turbulent shear flow

1998 ◽  
Author(s):  
C. Truman ◽  
Lenore McMackin ◽  
Robert Pierson ◽  
Kenneth Bishop ◽  
Ellen Chen
Keyword(s):  
Shear Flow ◽  
Open Loop ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Open Loop Control ◽  
Loop Control ◽  
Optical Propagation

scholarly journals Sensuator: A Hybrid Sensor–Actuator Approach to Soft Robotic Proprioception Using Recurrent Neural Networks

Actuators ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 30
Author(s):  
Pornthep Preechayasomboon ◽  
Eric Rombokas
Keyword(s):  
Neural Networks ◽  
Recurrent Neural Networks ◽  
Linear Models ◽  
Open Loop ◽  
Proof Of Concept ◽  
State Estimator ◽  
Loop Control ◽  
Practical Applications ◽  
Soft Actuator ◽  
The Cost

Soft robotic actuators are now being used in practical applications; however, they are often limited to open-loop control that relies on the inherent compliance of the actuator. Achieving human-like manipulation and grasping with soft robotic actuators requires at least some form of sensing, which often comes at the cost of complex fabrication and purposefully built sensor structures. In this paper, we utilize the actuating fluid itself as a sensing medium to achieve high-fidelity proprioception in a soft actuator. As our sensors are somewhat unstructured, their readings are difficult to interpret using linear models. We therefore present a proof of concept of a method for deriving the pose of the soft actuator using recurrent neural networks. We present the experimental setup and our learned state estimator to show that our method is viable for achieving proprioception and is also robust to common sensor failures.

scholarly journals Numerical Study of an Oscillating-Wing Wingmill for Ocean Current Energy Harvesting: Fluid-Solid-Body Interaction with Feedback Control

2020 ◽  
Vol 9 (1) ◽  
pp. 23
Author(s):  
David Balam-Tamayo ◽  
Carlos Málaga ◽  
Bernardo Figueroa-Espinoza
Keyword(s):  
Energy Harvesting ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Ocean Current ◽  
Control Synthesis ◽  
Dimensionless Number ◽  
Control Law ◽  
Loop Control ◽  
Power Extraction ◽  
Current Energy

The performance and flow around an oscillating foil device for current energy extraction (a wingmill) was studied through numerical simulations. OpenFOAM was used in order to study the two-dimensional (2D) flow around a wingmill. A closed loop control law was coded in order to follow a reference angle of attack. The objective of this control law is to modify the angle of attack in order to enhance the lift force (and increase power extraction). Dimensional analysis suggests a compromise between the generator (or damper) stiffness and actuator/control gains, so a parametric study was carried out while using a new dimensionless number, called B, which represents this compromise. It was found that there is a maximum on the efficiency curve in terms of the aforementioned dimensionless parameter. The lessons that are learned from this fluid-structure and feedback coupling are discussed; this interaction, combined with the feedback dynamics, may trigger dynamic stall, thus decreasing the performance. Moreover, if the control strategy is not carefully selected, then the energy spent on the actuator may affect efficiency considerably. This type of simulation could allow for the system identification, control synthesis, and optimization of energy harvesting devices in future studies.

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