Effect of position of radial air injection plane on control of thermo-acoustic instability using active closed-loop method

2021 ◽  
pp. 107754632110501
Author(s):  
Nilaj N Deshmukh ◽  
Afzal Ansari ◽  
Praseed Kumar ◽  
Allen V George ◽  
Febin J Thomas ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Structural Damage ◽  
Closed Loop ◽  
Control Method ◽  
Heat Waves ◽  
Air Injection ◽  
Rocket Engines ◽  
Acoustic Instability ◽  
Loop Method ◽  
Short Time

Thermo-acoustic instability occurs when self-excited oscillations are generated due to the coupling between unsteady heat release and acoustics. This phenomenon can result in an increased rate of vibration, structural damage, and produces unwanted emissions. Thermo-acoustic instability occurs in rocket engines, gas turbines, combustors, and furnaces. When thermo-acoustic instability occurs, many modes are developed naturally at a specific point. Some waves are unstable and some are stable. So, to study this phenomenon the most unstable waves are considered and a technique is developed to suppress these unstable waves. A radial air injector as a closed-loop active control method is used for breaking the coupling between the heat waves and acoustics inside the 1D combustion chamber. The distance between the burner and the air injector is varied for the fixed position of the burner with respect to the Rijke tube, that is, x/L = 0.01125, 0.0075, and 0.00375. This closed-loop method works based on the feedback acquired from a microphone. The control method is built using DAQ and Arduino with the LabVIEW as interface for Arduino (LIFA). An air flow rate controller setup is developed to control and measure air required for suppressing the thermo-acoustic instability. Thermo-acoustic instability is effectively suppressed with the help of radial injection in the form of micro-jets at the downstream of the burner as the closed-loop controlling method. It is concluded that when the radial micro-jet air injection plane is closer to the burner head, the thermo-acoustic instability gets suppressed in a short time and with a lesser quantity of air.

Influence of Boundary Layer Air Injection on Flashback of Premixed Hydrogen-Air Flames

2016 ◽  
Author(s):  
Vera Hoferichter ◽  
Payam Mohammadzadeh Keleshtery ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer ◽  
Yoshikazu Matsumura
Keyword(s):  
Boundary Layer ◽  
Mass Flow ◽  
Carbon Dioxide Emissions ◽  
Gas Turbines ◽  
Structural Damage ◽  
Alternative Fuels ◽  
Air Injection ◽  
Current Standard ◽  
Reference Case ◽  
Flame Flashback

Alternative fuels like hydrogen are presently discussed as one possibility to reduce carbon dioxide emissions from gas turbines. Premixed lean combustion is a current standard to minimize nitrogen oxide emissions. However, the early mixing of fuel and oxidizer upstream of the combustion chamber opens up the possibility of upstream flame propagation, referred to as flame flashback. Flame flashback in gas turbines has to be prevented as it leads to immediate engine shut down or even structural damage. Due to high burning velocities and low quenching distances, flashback is especially critical in premixed hydrogen flames. In particular, the low velocity region near the burner wall promotes flashback. Diluting the mixture near the wall by fluid injection is one approach to counteract this phenomenon and to enhance the safe operating range of a gas turbine burner. This article presents an experimental study on the effect of air injection on flame flashback investigated at a channel burner configuration. Different injection mass flow rates, positions and angles are compared to a reference case without injection regarding their flashback limits. The effectiveness of the injection increases with the injected mass flow rate. The resulting flashback limits can be correlated with the equivalence ratio at the wall by concepts taken from film cooling. However, the fluid injector is a source of boundary layer disturbances leading to an initial penalty regarding flashback resistance. This penalty increases the closer the injector is located to the burner exit. Furthermore, the penalty increases for lower injection angles as the area of the injector and the corresponding boundary layer disturbances increase.

scholarly journals Closed-Loop Identification of Hammerstein Systems with Application to Gas Turbines

2014 ◽  
Vol 47 (3) ◽  
pp. 493-498 ◽  
Author(s):  
Chad M. Holcomb ◽  
Raymond A. de Callafon ◽  
Robert R. Bitmead
Keyword(s):  
Gas Turbines ◽  
Closed Loop ◽  
Hammerstein Systems ◽  
Closed Loop Identification

An Optimal Sensitivity-Enhancing Feedback Control Approach via Eigenstructure Assignment for Structural Damage Identification

2007 ◽  
Vol 129 (6) ◽  
pp. 771-783 ◽  
Author(s):  
L. J. Jiang ◽  
J. Tang ◽  
K. W. Wang
Keyword(s):  
Feedback Control ◽  
Frequency Shift ◽  
Natural Frequency ◽  
Structural Damage ◽  
Closed Loop ◽  
Damage Identification ◽  
Frequency Measurement ◽  
Sensitivity Enhancement ◽  
Stiffness Reduction ◽  
Structural Damage Identification

The concept of using sensitivity-enhancing feedback control to improve the performance of frequency-shift-based structural damage identification has been recently explored. In previous studies, however, the feedback controller is designed to alter only the closed-loop eigenvalues, and the effect of closed-loop eigenvectors on the sensitivity enhancement performance has not been considered. In this research, it is shown that the sensitivity of the natural frequency shift to the damage in a multi-degree-of-freedom structure can be significantly influenced by the placement of both the eigenvalues and the eigenvectors. A constrained optimization problem is formulated to find the optimal assignment of both the closed-loop eigenvalues and eigenvectors, and then an optimal sensitivity-enhancing control is designed to achieve the desired closed-loop eigenstructure. Another advantage of this scheme is that the dataset of frequency measurement for damage identification can be enlarged by utilizing a series of closed-loop controls, which can be realized by activating different combinations of actuators in the system. Therefore, by using this proposed idea of multiple sensitivity-enhancing feedback controls, we can simultaneously address the two major limitations of frequency-shift-based damage identification: the low sensitivity of frequency shift to damage effects and the deficiency of frequency measurement data. A series of case studies are performed. It is demonstrated that the sensitivity of natural frequency shift to stiffness reduction can be significantly enhanced by using the designed sensitivity-enhancing feedback control, where the optimal placement of closed-loop eigenvectors plays a very important role. It is further verified that such sensitivity enhancement can directly benefit the damage identification accuracy and robustness.

scholarly journals The Adaptive Neural Control for a Class of High-Order Uncertain Stochastic Nonlinear Systems

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
Xiaoyan Qin
Keyword(s):  
Nonlinear Systems ◽  
Neural Control ◽  
Closed Loop ◽  
Control Method ◽  
High Order ◽  
Stochastic Nonlinear Systems ◽  
Closed Loop System ◽  
Adaptive Neural Control ◽  
Control Scheme ◽  
Approximation Capability

This paper studies the problem of the adaptive neural control for a class of high-order uncertain stochastic nonlinear systems. By using some techniques such as the backstepping recursive technique, Young’s inequality, and approximation capability, a novel adaptive neural control scheme is constructed. The proposed control method can guarantee that the signals of the closed-loop system are bounded in probability, and only one parameter needs to be updated online. One example is given to show the effectiveness of the proposed control method.

Discrete Time-Delay Optimal Control Method for Experimental Active Chatter Suppression and Its Closed-Loop Stability Analysis

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Xingwu Zhang ◽  
Ziyu Yin ◽  
Jiawei Gao ◽  
Jinxin Liu ◽  
Robert X. Gao ◽  
...  
Keyword(s):  
Optimal Control ◽  
Closed Loop ◽  
Control Method ◽  
Trial And Error ◽  
Stability Lobe Diagram ◽  
Weighting Matrix ◽  
Chatter Suppression ◽  
Stability Lobe ◽  
Optimal Control Method ◽  
Discrete Time Delay

Chatter is a self-excited and unstable vibration phenomenon during machining operations, which affects the workpiece surface quality and the production efficiency. Active chatter control has been intensively studied to mitigate chatter and expand the boundary of machining stability. This paper presents a discrete time-delay optimal control method for chatter suppression. A dynamical model incorporating the time-periodic and time-delayed characteristic of active chatter suppression during the milling process is first formulated. Next, the milling system is represented as a discrete linear time-invariant (LTI) system with state-space description through averaging and discretization. An optimal control strategy is then formulated to stabilize unstable cutting states, where the balanced realization method is applied to determine the weighting matrix without trial and error. Finally, a closed-loop stability lobe diagram (CLSLD) is proposed to evaluate the performance of the designed controller based on the proposed method. The CLSLD can provide the stability lobe diagram with control and evaluate the performance and robustness of the controller cross the tested spindle speeds. Through many numerical simulations and experimental studies, it demonstrates that the proposed control method can make the unstable cutting parameters stable with control on, reduce the control force to 21% of traditional weighting matrix selection method by trial and error in simulation, and reduce the amplitude of chatter frequency up to 78.6% in experiment. Hence, the designed controller reduces the performance requirements of actuators during active chatter suppression.

scholarly journals Real-Time Anticipation and Prevention of Hot Spots by Monitoring the Dynamic Conductance of Photovoltaic Panels

2021 ◽  
Author(s):  
William Lamb ◽  
Dallon Asnes ◽  
Jonathan Kupfer ◽  
Emma Lickey ◽  
Jeremy Bakken ◽  
...  
Keyword(s):  
Real Time ◽  
Hot Spots ◽  
Structural Damage ◽  
Reverse Bias ◽  
Control Method ◽  
Physical Damage ◽  
Operating Current ◽  
A Cell ◽  
Real Time Simulations ◽  
Dynamic Conductance

<div>Hot spotting in photovoltaic (PV) panels causes physical damage, power loss, reduced lifetime reliability, and increased manufacturing costs. The problem arises routinely in defect-free standard panels; any string of cells that receives uneven illumination can develop hot spots, and the temperature rise often exceeds 100°C in conventional silicon panels despite on-panel bypass diodes, the standard mitigation technique. Bypass diodes limit the power dissipated in a cell subjected to reverse bias, but they do not prevent hot spots from forming. An alternative control method has been suggested by Kernahan [1] that senses in real time the dynamic conductance |dI/dV| of a string of cells and adjusts its operating current so that a partially shaded cell is never forced into reverse bias. We start by exploring the behavior of individual illuminated PV cells when externally forced into reverse bias. We observe that cells can suffer significant heating and structural damage, with desoldering of cell-tabbing and discolorations on the front cell surface. Then we test PV panels and confirm Kernahan’s proposed panel-level solution that anticipates and prevents hot spots in real time. Simulations of cells and panels confirm our experimental observations and provide insights into both the operation of Kernahan’s method and panel performance.</div>

scholarly journals Transient amplitude modulation of alpha-band oscillations by short-time intermittent closed-loop tACS

2020 ◽  
Author(s):  
G. Zarubin ◽  
C. Gundlach ◽  
V. Nikulin ◽  
A. Villringer ◽  
M. Bogdan
Keyword(s):  
Individual Differences ◽  
Visual System ◽  
Amplitude Modulation ◽  
Closed Loop ◽  
Alternating Current ◽  
Stimulation Protocol ◽  
Spatial Filters ◽  
Alpha Oscillations ◽  
Transcranial Alternating Current Stimulation ◽  
Short Time

AbstractNon-invasive brain stimulation techniques such as transcranial alternating current stimulation (tACS) have recently become extensively utilized due to their potential to modulate ongoing neuronal oscillatory activity and consequently to induce cortical plasticity relevant for various cognitive functions. However, the neurophysiological basis for stimulation effects as well as their inter-individual differences are not yet understood. In the present study we used a closed-loop EEG transcranial alternating current stimulation protocol (EEG-tACS) to examine the modulation of alpha oscillations generated in occipito-parietal areas. In particular, we investigated the effects of a repeated short-time intermittent stimulation protocol (1 s in every trial) applied over the visual cortex (Cz and Oz) and adjusted according to the phase and frequency of visual alpha oscillations on the amplitude of these oscillations. Based on previous findings, we expected higher increases in alpha amplitudes for tACS applied in-phase with ongoing oscillations as compared to an application in anti-phase and this modulation to be present in low-alpha amplitude states of the visual system (eyes opened) but not high (eyes closed).Contrary to our expectations, we found a transient suppression of alpha power in inter-individually derived spatially specific parieto-occipital components obtained via the estimation of spatial filters by using the common spatial patterns approach. The amplitude modulation was independent of the phase relationship between tACS signal and alpha oscillations, and the state of the visual system manipulated via closed- and open-eye conditions. It was also absent in conventionally analyzed single-channel and multi-channel data from an average parieto-occipital region.The fact that the tACS modulation of oscillations was phase-independent suggests that mechanisms driving the effects of tACS may not be explained by entrainment alone, but rather require neuroplastic changes or transient disruption of neural oscillations. Our study also supports the notion that the response to tACS is subject specific, where the modulatory effects are shaped by the interplay between the stimulation and different alpha generators. This favors stimulation protocols as well as analysis regimes exploiting inter-individual differences, such as spatial filters to reveal otherwise hidden stimulation effects and, thereby, comprehensively induce and study the effects and underlying mechanisms of tACS.

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