scholarly journals Sensitivity of LES-based harmonic flame response model for turbulent swirled flames and impact on the stability of azimuthal modes

2015 ◽  
Vol 35 (3) ◽  
pp. 3355-3363 ◽  
Author(s):  
M. Bauerheim ◽  
G. Staffelbach ◽  
N.A. Worth ◽  
J.R. Dawson ◽  
L.Y.M. Gicquel ◽  
...  
Keyword(s):  
Response Model ◽  
Flame Response ◽  
The Stability ◽  
Swirled Flames

NEGATIVE FEEDBACK DYNAMICS AND OSCILLATORY ACTIVITIES IN REGULATORY BIOLOGICAL NETWORKS

2007 ◽  
Vol 15 (02) ◽  
pp. 123-138 ◽  
Author(s):  
SHIWEI YAN
Keyword(s):  
Negative Feedback ◽  
Biological Networks ◽  
Feedback Loop ◽  
Biological Network ◽  
Network Motif ◽  
Radiation Environment ◽  
Negative Feedback Loop ◽  
Response Model ◽  
Model Equations ◽  
The Stability

The recent experiments on the dynamics of a common biological network motif, p53 and Mdm2 feedback loop, have shown the oscillatory behaviors for the activities of p53 and Mdm2 proteins in response to DNA damage. Exploiting the nonlinear dynamics in the negative feedback loop, we propose a statistical signal-response model with an aim to describe the p53-Mdm2 interaction under certain radiation environment. We discuss the existence of Hopf bifurcation, the stability of the solutions of model equations and their sensitivity to the changes of the parameters incorporated in the model. The proposed mathematical method may have the significance in the problems where the negative and/or positive feedback dynamics, as well as the time delay have the characteristic physical and biological background.

Impact of Swirl Fluctuations on the Flame Response of a Perfectly Premixed Swirl Burner

2009 ◽  
Author(s):  
Thomas Komarek ◽  
Wolfgang Polifke
Keyword(s):  
Heat Release ◽  
Axial Position ◽  
Strong Impact ◽  
Time Lags ◽  
Swirl Number ◽  
Swirl Generator ◽  
Flame Response ◽  
Combustion Technology ◽  
Swirling Flames ◽  
The Stability

Combustion instabilities represent a long known problem in combustion technology. The complex interactions between acoustics and turbulent swirling flames are not fully understood yet, making it very difficult to reliably predict the stability of new combustion systems. For example, the effects of fluctuations of swirl number on the heat release of the flame have to be investigated in more detail. In this paper a perfectly premixed, swirl stabilized burner with variable axial position of the swirl generator is investigated. In experiments, the position of the swirl generator has a strong impact on the dynamic flame response, although it does not influence the time-averaged distribution of the heat release significantly. This phenomenon is further investigated, using computational fluid dynamics combined with system identification. The generation of fluctuations of swirl number, their propagation to the flame, and their effect on the dynamic flame response are examined. A simple model based on convective time lags is developed, showing good agreement with experiments.

scholarly journals Demand Response Model for Duck Curve on Pv Dominated System using Support Vector Machines Based Multistage Modelling

2019 ◽  
Vol 9 (1) ◽  
pp. 5272-5283
Keyword(s):  
Power Generation ◽  
Solar Energy ◽  
Demand Response ◽  
Solar Irradiation ◽  
Support Vector ◽  
Response Model ◽  
Solar Pv ◽  
Peak Demand ◽  
Levelized Cost Of Electricity ◽  
The Stability

Solar Photovoltaic (PV) generation systems have a less Levelized cost of electricity (LCoE). As such, when solar energy is available, the demand response is scheduled in such a way that maximum utilization of solar energy is practised.But the power generation from a solar PV system is highly uncertain and unpredictable due to irregular solar irradiation. Also, the power generation is limited to a time fraction of a day.The impact of these negative traits in a power system is studied with the help of an analytical curve called “Duck curve”. “Solar Duck curve” is a graphical representation of time scaled imbalances between a SPV generation to peak demand. A steep or rugged part in a duck curve indicates sudden shortcoming of SPV generation with respect to the peak demand. Hence, during this period, the loads are shifted between solar PV sources and the main grid with respect to the insufficiency of solar power from peak demand. The proposed system is a machine learning-based multistage demand response system for meeting demand response of a SPV dominant duck curve. The model has four layers/stages.The primary layer is used to analyse the behaviour of the duck curve with the help of a Support Vector regression algorithm and the second layer is used for determining theoperating parameters based on the economic constraints imposed. The third layer is a demand response model based on the previous layer, and the fourth layer is aadaptive signal-processing model used to improve the stability of the system.The obtained demand response model is updated continuously in an adaptive manner so as to improve the stability of the system.A hardware experimental setup is made with eighteen numbers of 24V/2kW interconnected solar PV realtime system which is used for validating and analysing the method.

scholarly journals Calculation of the Thermoacoustic Stability of a Main Stage Thrust Chamber Demonstrator

2020 ◽  
pp. 235-247
Author(s):  
Alexander Chemnitz ◽  
Thomas Sattelmayer
Keyword(s):  
Transfer Function ◽  
Injection Pressure ◽  
Scattering Matrix ◽  
Main Stage ◽  
Stability Prediction ◽  
Mean Flow ◽  
Linearized Euler Equations ◽  
Thrust Chamber ◽  
Flame Response ◽  
The Stability

Abstract The stability behavior of a virtual thrust chamber demonstrator with low injection pressure loss is studied numerically. The approach relies on an eigenvalue analysis of the Linearized Euler Equations. An updated form of the stability prediction procedure is outlined, addressing mean flow and flame response calculations. The acoustics of the isolated oxidizer dome are discussed as well as the complete system incorporating dome and combustion chamber. The coupling between both components is realized via a scattering matrix representing the injectors. A flame transfer function is applied to determine the damping rates. Thereby it is found that the procedure for the extraction of the flame transfer function from the CFD solution has a significant impact on the stability predictions.

Dynamics of a Transversely Excited Swirling, Lifted Flame: Part I — Experiments and Data Analysis

2013 ◽  
Author(s):  
Michael Malanoski ◽  
Michael Aguilar ◽  
Vishal Acharya ◽  
Tim Lieuwen
Keyword(s):  
High Speed ◽  
Acoustic Excitation ◽  
Response Model ◽  
Combustion Instabilities ◽  
Excitation Field ◽  
Azimuthal Mode ◽  
Flow Response ◽  
Flame Response ◽  
Swirling Flame ◽  
Helical Mode

This paper is the first of two parts, and describes measurements of the response of a transversely forced, single nozzle, swirling flame. This study is motivated by combustion instabilities coupling with azimuthal combustor modes. Two different forcing configurations are applied, where the flame/nozzle are located at a pressure node and anti-node, respectively. High speed velocimetry and chemiluminescence measurements were made of the forced and unforced flow in multiple orthogonal planes, revealing both the axial and azimuthal development of the unsteady flow. Spectra and azimuthal mode decompositions of these data show the dominance of the m = 1 helical mode in the unforced flow. Depending upon the nature of the forcing, the flow response at the forcing frequency can be dominated by the axisymmetric, m = 0 mode, or the m = 1 mode. These results clearly show that the dominant fluid mechanic structures exciting flames during transverse instabilities varies from nozzle to nozzle, depending upon the phase characteristics of the acoustic excitation field. Part II of this paper uses these time averaged and fluctuating measurements as inputs to a flame response model of the unsteady global heat release fluctuations.

Solution of Thermoacoustic Eigenvalue Problems With a Noniterative Method

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Philip E. Buschmann ◽  
Georg A. Mensah ◽  
Franck Nicoud ◽  
Jonas P. Moeck
Keyword(s):  
Eigenvalue Problems ◽  
Contour Integration ◽  
Complex Eigenvalue ◽  
Combustion Dynamics ◽  
Element Discretization ◽  
Nonlinear Eigenvalue Problems ◽  
Flame Response ◽  
The Stability ◽  
Thermoacoustic Oscillations ◽  
Nonlinear Eigenvalue

Abstract Gas turbine combustors are prone to undesirable combustion dynamics in the form of thermoacoustic oscillations. Analysis of the stability of thermoacoustic systems in the frequency domain leads to nonlinear eigenvalue problems (NLEVP); here, “nonlinear” refers to the fact that the eigenvalue, the complex oscillation frequency, appears in a nonlinear fashion. In this paper, we employ a noniterative strategy based on contour integration in the complex eigenvalue plane, which returns all eigenvalues inside the contour. An introduction to the technique is given, and is complemented with guidelines for the specific application to thermoacoustic problems. Two prototypical nonlinear eigenvalue problems are considered: a network model of the classical Rijke tube with an analytic flame response model and a finite element discretization of an annular model combustor with an experimental flame transfer function (FTF). Computation of all eigenvalues in a domain of interest is vital to assess stability of these systems. We demonstrate that this is generally challenging for iterative strategies. An eigenvalue solver based on contour integration, in contrast, provides a reliable, noniterative method to achieve this goal.

Impact of Swirl Fluctuations on the Flame Response of a Perfectly Premixed Swirl Burner

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Thomas Komarek ◽  
Wolfgang Polifke
Keyword(s):  
Heat Release ◽  
Axial Position ◽  
Strong Impact ◽  
Time Lags ◽  
Swirl Number ◽  
Swirl Generator ◽  
Flame Response ◽  
Combustion Technology ◽  
Swirling Flames ◽  
The Stability

Combustion instabilities represent a long known problem in combustion technology. The complex interactions between acoustics and turbulent swirling flames are not fully understood yet, making it very difficult to reliably predict the stability of new combustion systems. For example, the effects of fluctuations of swirl number on the heat release of the flame have to be investigated in more detail. In this paper a perfectly premixed swirl stabilized burner with variable axial position of the swirl generator is investigated. In experiments, the position of the swirl generator has a strong impact on the dynamic flame response, although it does not influence the time-averaged distribution of the heat release significantly. This phenomenon is further investigated using computational fluid dynamics combined with system identification. The generation of fluctuations of swirl number, their propagation to the flame, and their effect on the dynamic flame response are examined. A simple model based on convective time lags is developed, showing good agreement with experiments.

Open discussion

1982 ◽  
Vol 99 ◽  
pp. 605-613
Author(s):  
P. S. Conti
Keyword(s):  
Buenos Aires ◽  
Large Mass ◽  
List Type ◽  
Common Phenomenon ◽  
Open Discussion ◽  
The Stability ◽  
Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

Symmetric Multistep Methods Revisited: II. Numerical Experiments

1999 ◽  
Vol 173 ◽  
pp. 309-314 ◽  
Author(s):  
T. Fukushima
Keyword(s):  
Multistep Methods ◽  
Computational Time ◽  
Integration Time ◽  
Implicit Methods ◽  
Symmetric Methods ◽  
Celestial Bodies ◽  
The Stability ◽  
Predictor Corrector ◽  
Symmetric Multistep Methods ◽  
Integration Errors

AbstractBy using the stability condition and general formulas developed by Fukushima (1998 = Paper I) we discovered that, just as in the case of the explicit symmetric multistep methods (Quinlan and Tremaine, 1990), when integrating orbital motions of celestial bodies, the implicit symmetric multistep methods used in the predictor-corrector manner lead to integration errors in position which grow linearly with the integration time if the stepsizes adopted are sufficiently small and if the number of corrections is sufficiently large, say two or three. We confirmed also that the symmetric methods (explicit or implicit) would produce the stepsize-dependent instabilities/resonances, which was discovered by A. Toomre in 1991 and confirmed by G.D. Quinlan for some high order explicit methods. Although the implicit methods require twice or more computational time for the same stepsize than the explicit symmetric ones do, they seem to be preferable since they reduce these undesirable features significantly.

Uniformity of Magnification from Different Electron Microscopes

1967 ◽  
Vol 25 ◽  
pp. 32-33
Author(s):  
Godfrey C. Hoskins ◽  
V. Williams ◽  
V. Allison
Keyword(s):  
Diffraction Grating ◽  
The Other ◽  
Carbon Replica ◽  
Electron Microscopes ◽  
The Stability

The method demonstrated is an adaptation of a proven procedure for accurately determining the magnification of light photomicrographs. Because of the stability of modern electrical lenses, the method is shown to be directly applicable for providing precise reproducibility of magnification in various models of electron microscopes.A readily recognizable area of a carbon replica of a crossed-line diffraction grating is used as a standard. The same area of the standard was photographed in Phillips EM 200, Hitachi HU-11B2, and RCA EMU 3F electron microscopes at taps representative of the range of magnification of each. Negatives from one microscope were selected as guides and printed at convenient magnifications; then negatives from each of the other microscopes were projected to register with these prints. By deferring measurement to the print rather than comparing negatives, correspondence of magnification of the specimen in the three microscopes could be brought to within 2%.

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