Effect of Noise and Nonlinearities on Thermoacoustics of Can-Annular Combustors

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
G. Ghirardo ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Background Noise ◽  
Noise Intensity ◽  
Stochastic Simulations ◽  
Linear Regime ◽  
Good Match ◽  
Mode Localization ◽  
Nonlinear Solution ◽  
Turbine Inlet ◽  
Flame Response ◽  
Linearized System

Abstract Can-annular combustors consist of N distinct cans setup symmetrically around the axis of the gas turbine. Each can is connected to the turbine inlet by means of a transition duct. At the turbine inlet, a small gap between the neighboring transition ducts allows acoustic communication between the cans. Thermoacoustic pulsations in the cans are driven by the respective flames, but also the communication between neighboring cans through the gap plays a significant role. In this study, we focus on the effect of the background noise intensity and of the nonlinear flame saturation. We predict how usually clusters of thermoacoustic modes are unstable in the linear regime and compete with each other in the nonlinear regime, each cluster consisting of axial, azimuthal and push-pull modes. Since linear theory cannot predict the nonlinear solution, stochastic simulations are run to study the nonlinear solution in a probabilistic sense. One outcome of these simulations is the various pulsation patterns, which are in principle different from one can to the next. We recover how not only a stronger flame response in one can gives rise to the phenomenon of mode localization, but also how the nonlinearity of the flame saturation and the competition between modes have an effect on the nonlinear mode shape. We finally predict the coherence and phase between cans on the linearized system subject to noise, and compare the predictions with engine measurements, in terms of spectra of amplitude in each can and coherence and phase, observing a good match.

Effect of Noise and Nonlinearities on Thermoacoustics of Can-Annular Combustors

2019 ◽  
Author(s):  
G. Ghirardo ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Rotational Symmetry ◽  
Turbine Rotor ◽  
Stochastic Simulations ◽  
Linear Solution ◽  
Mode Localization ◽  
Turbine Inlet ◽  
Flame Response ◽  
Linearized System ◽  
Set Up ◽  
The Individual

Abstract Can-annular combustors consist of N distinct cans set up symmetrically around the axis of the gas turbine rotor. Each can is connected to the turbine inlet by means of a transition duct. At the turbine inlet a small gap between the neighbouring transition ducts allows acoustic communication between the individual cans. Thermoacoustic pulsations in the cans are driven by the respective flames, but also the communication between neighbouring cans through the gap plays a significant role. In this study we focus in particular on the effect of the background noise intensity and of the nonlinear flame saturation. We predict how usually clusters of thermoacoustic modes are unstable in the linear regime and compete with each other in the nonlinear regime, with each cluster consisting of axial, azimuthal and push-pull modes. Since linear theory cannot predict the nonlinear solution, stochastic simulations are run to study the non-linear solution in a probabilistic sense. One outcome of these simulations are the various pulsation patterns, which are in principle different from one can to the next. This is done for several configurations, with a focus on the effect of a loss of rotational symmetry of the system. We recover how a stronger flame response in one can give rise to the phenomenon of mode localization, but also how the nonlinearity of the flame saturation and the competition between modes have an effect on the nonlinear average mode shape. We finally predict the coherence and phase pattern between cans on the linearized system subject to stochastic noise, and compare the predictions with direct engine measurements, both in terms of spectra of pulsation amplitude in each can and coherence and phase between different cans, observing a good match.

Thermoacoustics of Can-Annular Combustors

2018 ◽  
Author(s):  
G. Ghirardo ◽  
C. Di Giovine ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Experimental Work ◽  
Rotational Symmetry ◽  
Acoustic Response ◽  
Open Area ◽  
Mode Localization ◽  
Downstream Side ◽  
Upstream Side ◽  
Turbine Inlet ◽  
Adjacent Transition ◽  
Thermoacoustic Oscillations

Can-annular combustors consist of a set of independent cans, connected on the upstream side to the combustor plenum, and on the downstream side to the turbine inlet, where a transition duct links the round geometry of each can with the annular segment of the turbine inlet. Each transition duct is open on the sides towards the adjacent transition ducts, so that neighbouring cans are acoustically connected through a so called cross-talk open area. This theoretical, numerical and experimental work discusses the effect that this communication has on the thermoacoustic frequencies of the combustor. We show how this communication gives rise to axial and azimuthal modes, and that these correspond to particularly synchronised states of axial thermoacoustic oscillations in each individual can. We show that these combustors typically show clusters of thermoacoustic modes with very close frequencies and that a slight loss of rotational symmetry, e.g. a different acoustic response of certain cans, can lead to mode localization. We corroborate the predictions of azimuthal modes, clusters of eigenmodes and mode localization with experimental evidence.

Thermoacoustics of Can-Annular Combustors

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
G. Ghirardo ◽  
C. Di Giovine ◽  
J. P. Moeck ◽  
M. R. Bothien
Keyword(s):  
Experimental Work ◽  
Rotational Symmetry ◽  
Acoustic Response ◽  
Open Area ◽  
Mode Localization ◽  
Downstream Side ◽  
Upstream Side ◽  
Turbine Inlet ◽  
Adjacent Transition ◽  
Thermoacoustic Oscillations

Can-annular combustors consist of a set of independent cans, connected on the upstream side to the combustor plenum and on the downstream side to the turbine inlet, where a transition duct links the round geometry of each can with the annular segment of the turbine inlet. Each transition duct is open on the sides toward the adjacent transition ducts, so that neighboring cans are acoustically connected through a so-called cross-talk open area. This theoretical, numerical, and experimental work discusses the effect that this communication has on the thermoacoustic frequencies of the combustor. We show how this communication gives rise to axial and azimuthal modes, and that these correspond to particularly synchronized states of axial thermoacoustic oscillations in each individual can. We show that these combustors typically show clusters of thermoacoustic modes with very close frequencies and that a slight loss of rotational symmetry, e.g., a different acoustic response of certain cans, can lead to mode localization. We corroborate the predictions of azimuthal modes, clusters of eigenmodes, and mode localization with experimental evidence.

Evaluation Method for Complex Electromagnetic Environment

2019 ◽  
Vol 23 (5) ◽  
pp. 891-897
Author(s):  
Yan Li ◽  
Yigang He ◽  
Baiqiang Yin ◽  
◽  
Keyword(s):  
Background Noise ◽  
Noise Intensity ◽  
Evaluation Method ◽  
Electromagnetic Environment ◽  
Environmental Complexity ◽  
Training Time ◽  
Time Frequency ◽  
S Transform ◽  
Fast Convergence Rate ◽  
Learning Machine

To perform a complexity evaluation for an electromagnetic environment (EME), a new method based on the S-transform is proposed, which can simultaneously count the time occupancy, frequency occupancy, and energy occupancy in the time–frequency domain. The frequency coincidence, modulation similarity, and background noise intensity are selected as important evaluation indices, and their physical interpretations are analyzed and calculated. The Extreme Learning Machine (ELM) method is adopted to evaluate the environmental complexity. The proposed method (S-ELM) requires less training time and has a fast convergence rate. The simulation and experimental results confirm that the proposed method is accurate and efficient.

Spatial Receptive Fields of Primary Auditory Cortical Neurons in Quiet and in the Presence of Continuous Background Noise

1998 ◽  
Vol 80 (5) ◽  
pp. 2417-2432 ◽  
Author(s):  
John F. Brugge ◽  
Richard A. Reale ◽  
Joseph E. Hind
Keyword(s):  
Receptive Field ◽  
Cortical Neurons ◽  
Background Noise ◽  
Noise Intensity ◽  
Receptive Fields ◽  
Virtual Space ◽  
Spatial Gradients ◽  
Firing Strength ◽  
Continuous Background ◽  
Acoustic Space

Brugge, John F., Richard A. Reale, and Joseph E. Hind. Spatial receptive fields of primary auditory cortical neurons in quiet and in the presence of continuous background noise. J. Neurophysiol. 80: 2417–2432, 1998. Spatial receptive fields of primary auditory (AI) neurons were studied by delivering, binaurally, synthesized virtual-space signals via earphones to cats under barbiturate anesthesia. Signals were broadband or narrowband transients presented in quiet anechoic space or in acoustic space filled with uncorrelated continuous broadband noise. In the absence of background noise, AI virtual space receptive fields (VSRFs) are typically large, representing a quadrant or more of acoustic space. Within the receptive field, onset latency and firing strength form functional gradients. We hypothesized earlier that functional gradients in the receptive field provide information about sound-source direction. Previous studies indicated that spatial gradients could remain relatively constant across changes in signal intensity. In the current experiments we tested the hypothesis that directional sensitivity to a transient signal, as reflected in the gradient structure of VSRFs of AI neurons, is also retained in the presence of a continuous background noise. When background noise was introduced three major affects on VSRFs were observed. 1) The size of the VSRF was reduced, accompanied by a reduction of firing strength and lengthening of response latency for signals at an acoustic axis and on-lines of constant azimuth and elevation passing through the acoustic axis. These effects were monotonically related to the intensity of the background noise over a noise intensity range of∼30 dB. 2) The noise intensity-dependent changes in VSRFs were mirrored by the changes that occurred when the signal intensity was changed in signal-alone conditions. Thus adding background noise was equivalent to a shift in the threshold of a directional signal, and this shift was seen across the spatial receptive field. 3) The spatial gradients of response strength and latency remained evident over the range of background noise intensity that reduced spike count and lengthened onset latency. Those gradients along the azimuth that spanned the frontal midline tended to remain constant in slope and position in the face of increasing intensity of background noise. These findings are consistent with our hypothesis that, under background noise conditions, information that underlies directional acuity and accuracy is retained within the spatial receptive fields of an ensemble of AI neurons.

scholarly journals Adaptive Auditory Alerts for Smart In-Vehicle Interfaces

2019 ◽  
Vol 63 (1) ◽  
pp. 1545-1549
Author(s):  
Edin Šabić ◽  
Daniel Henning ◽  
Justin MacDonald
Keyword(s):  
Reaction Time ◽  
User Experience ◽  
Background Noise ◽  
Noise Intensity ◽  
Background Music ◽  
Intensity Level ◽  
Best Interest ◽  
Noise Condition ◽  
Auditory Alerts

Missing a message from an in-vehicle device can range in severity from annoying at best to dangerous at worst. The in-cab auditory environment can vary spontaneously, making some volume levels too loud while rendering others too quiet. It is in the best interest of system designers, both from a safety and user experience perspective, to ensure that users are able to adequately hear alerts, and that drivers do not have to alter their gaze or attention during a visually and attentionally demanding task such as driving. To this end, we propose a system for dynamically tracking the background noise intensity level immediately prior to alert presentation in order to present an alert at an appropriate loudness. Furthermore, we evaluated the proposed system across both behavioral (accuracy and reaction time) and subjective (questionnaire results) measures. Behavioral results showed that while the proposed system increased recognition in one noise condition (background music), it also led to slower responses in two other noise conditions (windows-down and windows-up noise).

MODE LOCALIZATION DUE TO SYMMETRY-BREAKING NONLINEARITIES

1991 ◽  
Vol 01 (02) ◽  
pp. 471-475 ◽  
Author(s):  
CHRISTOPHE PIERRE ◽  
STEVEN W. SHAW
Keyword(s):  
Nonlinear System ◽  
Symmetry Breaking ◽  
Linear Systems ◽  
Break Symmetry ◽  
Structural Systems ◽  
Mode Localization ◽  
Nonlinear Structural ◽  
Periodic Linear ◽  
Linearized System

We present some ideas regarding the occurrence of mode localization in nonlinear structural systems. Preliminary analytical and numerical findings indicate that even if the linearized system has perfect periodicity, and thus cannot feature localized behavior, severe localization may occur in the nonlinear system when nonlinear terms break symmetry. These symmetry-breaking nonlinear terms play the same role as disorder does in nearly periodic linear systems.

scholarly journals Noise Risk Assessment at Air Separation Plant PT. X Surabaya (Nitrogen, Oxygen, and Argon Plant)

2017 ◽  
Vol 1 (2) ◽  
pp. 70
Author(s):  
Hanif Rizqi Diniari ◽  
Tofan Agung Eka Prasetya ◽  
Erwin Dyah Nawawiwetu ◽  
Abdul Rohim Tualeka
Keyword(s):  
Background Noise ◽  
Noise Intensity ◽  
Intensity Measurement ◽  
Air Separation ◽  
Risk Level ◽  
Noise Sources ◽  
Separation Plant ◽  
Cross Sectional ◽  
Measurement Result ◽  
Descriptive Research

Background : Noise was one of the dangerous factors at a workplace which causes various effects on workers. Purpose :  The purpose of this research was to described the activity stages, identified the noise danger, and assessed the risk and its level at Air Separation Plant of PT. X. Methods : This research was a descriptive research with a cross sectional approach. The object of the research was the noise danger potential and the noise risk level assessment at Air Separation Plant of PT. X. Results : The result of this research showed that there were 12 identified noise danger points. These results consisted of 5 (42 %) noise risks with low category, 2 (16 %) with middle category, and another 5 (42 %) with high category. The highest noise intensity measurement result was found on Recycle Nitrogen Compressor (RNC) machine, which was 116,5 dBA.  Conclusion :  Based on this data, it can be concluded that there were 12 identified noise danger points and the highest noise intensity measurement result was found on Recycle Nitrogen Compressor (RNC) machine, which was 116,5 dBA. It is suggested for the related company to execute controls mostly in diminishing the noise sources.

Microdensitometer—computer correlation analysis of ultrastructural periodicity

1978 ◽  
Vol 36 (2) ◽  
pp. 32-33
Author(s):  
D.R. Ensor ◽  
C.G. Jensen ◽  
J.A. Fillery ◽  
R.J.K. Baker
Keyword(s):  
Correlation Analysis ◽  
Background Noise ◽  
Computer Control ◽  
Optical Diffraction ◽  
Screw Thread ◽  
Straight Line ◽  
Computer Storage ◽  
Correlation Process ◽  
Electron Microscope Image ◽  
Fixed Beam

Because periodicity is a major indicator of structural organisation numerous methods have been devised to demonstrate periodicity masked by background “noise” in the electron microscope image (e.g. photographic image reinforcement, Markham et al, 1964; optical diffraction techniques, Horne, 1977; McIntosh,1974). Computer correlation analysis of a densitometer tracing provides another means of minimising "noise". The correlation process uncovers periodic information by cancelling random elements. The technique is easily executed, the results are readily interpreted and the computer removes tedium, lends accuracy and assists in impartiality.A scanning densitometer was adapted to allow computer control of the scan and to give direct computer storage of the data. A photographic transparency of the image to be scanned is mounted on a stage coupled directly to an accurate screw thread driven by a stepping motor. The stage is moved so that the fixed beam of the densitometer (which is directed normal to the transparency) traces a straight line along the structure of interest in the image.

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