scholarly journals Sensitivity Analysis for Coupled Structural-Acoustic System with Absorbing Material Using FEM/BEM

2021 ◽  
Vol 34 (1) ◽  
Keyword(s):  
Sensitivity Analysis ◽  
Acoustic System ◽  
Absorbing Material

scholarly journals Development of a Combined-Ritz Method for Modeling 3D Acoustics in Candu Fuel Sub-Channels

2021 ◽  
Author(s):  
David Villero
Keyword(s):  
Equations Of Motion ◽  
Ritz Method ◽  
Axial Direction ◽  
Acoustic System ◽  
Lagrange Equations ◽  
Acoustic Wave Propagation ◽  
Absorbing Material ◽  
Acoustic Pressure Wave ◽  
System Equations ◽  
Triangular Elements

A combined finite element-Ritz method is developed to effectively model the 3D lowfrequency acoustics in CANDU fuel sub-channels. The complex acoustic behavior of CANDU fuel sub-channels in the cross section is captured using the six-node isoparametric triangular elements; and the acoustic wave propagation in the axial direction is modeled using the polynomials of order n. The Lagrange equations are utilized to formulate the system equations of motion. The acoustic system considered in this study consists of pipe-like medium (water) with rigid and smooth walls. At the inlet of the fuel channel acoustic system, an acoustic pressure wave is prescribed to simulate the pulsation induced by the main feeder pumps. At the outlet, the acoustic system is assumed to interact with a reacting and absorbing material with prescribed acoustic impedance. The method was tested for several scenarios of interest. Numerical results obtained are in excellent agreement with the analytical and ANSYS solutions.

scholarly journals Global modes, receptivity, and sensitivity analysis of diffusion flames coupled with duct acoustics

2014 ◽  
Vol 752 ◽  
pp. 237-265 ◽  
Author(s):  
Luca Magri ◽  
Matthew P. Juniper
Keyword(s):  
Growth Rate ◽  
Sensitivity Analysis ◽  
Heat Release ◽  
Slot Width ◽  
Adjoint Equations ◽  
Flame Velocity ◽  
Acoustic System ◽  
Duct Acoustics ◽  
Structural Sensitivity ◽  
Global Modes

AbstractIn this theoretical and numerical paper, we derive the adjoint equations for a thermo-acoustic system consisting of an infinite-rate chemistry diffusion flame coupled with duct acoustics. We then calculate the thermo-acoustic system’s linear global modes (i.e. the frequency/growth rate of oscillations, together with their mode shapes), and the global modes’ receptivity to species injection, sensitivity to base-state perturbations and structural sensitivity to advective-velocity perturbations. Some of these could be found by finite difference calculations but the adjoint analysis is computationally much cheaper. We then compare these with the Rayleigh index. The receptivity analysis shows the regions of the flame where open-loop injection of fuel or oxidizer will have the greatest influence on the thermo-acoustic oscillation. We find that the flame is most receptive at its tip. The base-state sensitivity analysis shows the influence of each parameter on the frequency/growth rate. We find that perturbations to the stoichiometric mixture fraction, the fuel slot width and the heat-release parameter have most influence, while perturbations to the Péclet number have the least influence for most of the operating points considered. These sensitivities oscillate, e.g. positive perturbations to the fuel slot width either stabilizes or destabilizes the system, depending on the operating point. This analysis reveals that, as expected from a simple model, the phase delay between velocity and heat-release fluctuations is the key parameter in determining the sensitivities. It also reveals that this thermo-acoustic system is exceedingly sensitive to changes in the base state. The structural-sensitivity analysis shows the influence of perturbations to the advective flame velocity. The regions of highest sensitivity are around the stoichiometric line close to the inlet, showing where velocity models need to be most accurate. This analysis can be extended to more accurate models and is a promising new tool for the analysis and control of thermo-acoustic oscillations.

scholarly journals Sensitivity analysis of a time-delayed thermo-acoustic system via an adjoint-based approach

2013 ◽  
Vol 719 ◽  
pp. 183-202 ◽  
Author(s):  
Luca Magri ◽  
Matthew P. Juniper
Keyword(s):  
Growth Rate ◽  
Sensitivity Analysis ◽  
Heat Release ◽  
Passive Control ◽  
Feedback Mechanism ◽  
Control Element ◽  
Acoustic System ◽  
Hot Wire ◽  
Small Oscillations ◽  
Structural Sensitivity

AbstractWe apply adjoint-based sensitivity analysis to a time-delayed thermo-acoustic system: a Rijke tube containing a hot wire. We calculate how the growth rate and frequency of small oscillations about a base state are affected either by a generic passive control element in the system (the structural sensitivity analysis) or by a generic change to its base state (the base-state sensitivity analysis). We illustrate the structural sensitivity by calculating the effect of a second hot wire with a small heat-release parameter. In a single calculation, this shows how the second hot wire changes the growth rate and frequency of the small oscillations, as a function of its position in the tube. We then examine the components of the structural sensitivity in order to determine the passive control mechanism that has the strongest influence on the growth rate. We find that a force applied to the acoustic momentum equation in the opposite direction to the instantaneous velocity is the most stabilizing feedback mechanism. We also find that its effect is maximized when it is placed at the downstream end of the tube. This feedback mechanism could be supplied, for example, by an adiabatic mesh. We illustrate the base-state sensitivity by calculating the effects of small variations in the damping factor, the heat-release time-delay coefficient, the heat-release parameter, and the hot-wire location. The successful application of sensitivity analysis to thermo-acoustics opens up new possibilities for the passive control of thermo-acoustic oscillations by providing gradient information that can be combined with constrained optimization algorithms in order to reduce linear growth rates.

scholarly journals Development of a Combined-Ritz Method for Modeling 3D Acoustics in Candu Fuel Sub-Channels

2021 ◽  
Author(s):  
David Villero
Keyword(s):  
Equations Of Motion ◽  
Ritz Method ◽  
Axial Direction ◽  
Acoustic System ◽  
Lagrange Equations ◽  
Acoustic Wave Propagation ◽  
Absorbing Material ◽  
Acoustic Pressure Wave ◽  
System Equations ◽  
Triangular Elements

A combined finite element-Ritz method is developed to effectively model the 3D lowfrequency acoustics in CANDU fuel sub-channels. The complex acoustic behavior of CANDU fuel sub-channels in the cross section is captured using the six-node isoparametric triangular elements; and the acoustic wave propagation in the axial direction is modeled using the polynomials of order n. The Lagrange equations are utilized to formulate the system equations of motion. The acoustic system considered in this study consists of pipe-like medium (water) with rigid and smooth walls. At the inlet of the fuel channel acoustic system, an acoustic pressure wave is prescribed to simulate the pulsation induced by the main feeder pumps. At the outlet, the acoustic system is assumed to interact with a reacting and absorbing material with prescribed acoustic impedance. The method was tested for several scenarios of interest. Numerical results obtained are in excellent agreement with the analytical and ANSYS solutions.

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