scholarly journals An adaptive sparse grid rational Arnoldi method for uncertainty quantification of dynamical systems in the frequency domain

2021 ◽  
Author(s):  
U. Römer ◽  
M. Bollhöfer ◽  
H. K. Sreekumar ◽  
C. Blech ◽  
S. C. Langer
Keyword(s):  
Dynamical Systems ◽  
Uncertainty Quantification ◽  
Frequency Domain ◽  
Sparse Grid ◽  
Arnoldi Method

scholarly journals Methods for the Calculation of Thermoacoustic Stability Margins and Monte Carlo-Free Uncertainty Quantification

2017 ◽  
Author(s):  
Georg A. Mensah ◽  
Luca Magri ◽  
Jonas P. Moeck
Keyword(s):  
Monte Carlo ◽  
Factor Analysis ◽  
Risk Factor ◽  
Uncertainty Quantification ◽  
Frequency Domain ◽  
Gas Turbines ◽  
Network Models ◽  
System Stability ◽  
Risk Factor Analysis ◽  
Model Parameters

Thermoacoustic instabilities are a major threat for modern gas turbines. Frequency-domain based stability methods, such as network models and Helmholtz solvers, are common design tools because they are fast compared to compressible CFD computations. Frequency-domain approaches result in an eigenvalue problem, which is nonlinear with respect to the eigenvalue. Nonlinear functions of the frequency are, for example, the n–τ model, impedance boundary conditions, etc. Thus, the influence of the relevant parameters on mode stability is only given implicitly. Small changes in some model parameters, which are obtained by experiments with some uncertainty, may have a great impact on stability. The assessment of how parameter uncertainties propagate to system stability is therefore crucial for safe gas turbine operation. This question is addressed by uncertainty quantification. A common strategy for uncertainty quantification in thermoacoustics is risk factor analysis. It quantifies the uncertainty of a set of parameters in terms of the probability of a mode to become unstable. One general challenge regarding uncertainty quantification is the sheer number of uncertain parameter combinations to be quantified. For instance, uncertain parameters in an annular combustor might be the equivalence ratio, convection times, geometrical parameters, boundary impedances, flame response model parameters etc. Assessing also the influence of all possible combinations of these parameters on the risk factor is a numerically very costly task. A new and fast way to obtain algebraic parameter models in order to tackle the implicit nature of the eigenfrequency problem is using adjoint perturbation theory. Though adjoint perturbation methods were recently applied to accelerate the risk factor analysis, its potential to improve the theory has not yet been fully exploited. This paper aims to further utilize adjoint methods for the quantification of uncertainties. This analytical method avoids the usual random Monte Carlo simulations, making it particularly attractive for industrial purposes. Using network models and the open-source Helmholtz solver PyHoltz it is also discussed how to apply the method with standard modeling techniques. The theory is exemplified based on a simple ducted flame and a combustor of EM2C laboratory for which experimental validation is available.

Frequency domain conditions for the robust stability of linear and nonlinear dynamical systems

1991 ◽  
Vol 38 (4) ◽  
pp. 389-397 ◽  
Author(s):  
S. Dasgupta ◽  
P.J. Parker ◽  
B.D.O. Anderson ◽  
F.J. Kraus ◽  
M. Mansour
Keyword(s):  
Dynamical Systems ◽  
Frequency Domain ◽  
Robust Stability ◽  
Nonlinear Dynamical Systems ◽  
Nonlinear Dynamical ◽  
Linear And Nonlinear
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