Background Noise Effects on Combustor Stability

2002 ◽  
Author(s):  
Tim Lieuwen ◽  
Andrzej Banaszuk
Keyword(s):  
Acoustic Waves ◽  
Background Noise ◽  
Noise Sources ◽  
Turbulent Fluctuations ◽  
Number Systems ◽  
Damping Rate ◽  
Parametric Noise ◽  
High Reynolds ◽  
The Stability ◽  
Stability Limits

This paper considers the effects of background turbulent fluctuations upon a combustor’s stability boundaries. Inherent turbulent fluctuations act as both additive and parametric (also called multiplicative) excitation sources to acoustic waves in combustors. While additive noise sources exert primarily quantitative effects upon combustor oscillations, parametric noise sources can exert qualitative impacts upon its dynamics; particularly of interest here is their ability to destabilize a “nominally” stable system. The significance of these parametric noise sources increases with increased background noise levels and, thus, may play more of a role in realistic, high Reynolds number systems than experiments on simplified, lab scale combustors might suggest. The objective of this paper is to determine whether and/or when these effects might be significant. The analysis considers the effects of fluctuations in damping rate, frequency and combustion response. It is found that the effects of noisy damping and frequency upon the combustor’s stability limits is quite small, at least for the fluctuation intensities estimated here. The effects of a noisy combustion response, particularly of a fluctuating time delay between flow and heat release perturbations, can be quite significant, however, in some cases for turbulence intensities as low as <(u′/u¯)2>1/2∼5–10%. These results suggest that deterministic stability models calibrated on low turbulence intensity, lab scale combustors may not adequately describe the stability limits of realistic, highly turbulent combustors.

Stability as a constraint in sagittal plane human force exertion modeling

1998 ◽  
Vol 1 (1) ◽  
pp. 23-39
Author(s):  
Carter J. Kerk ◽  
Don B. Chaffin ◽  
W. Monroe Keyserling
Keyword(s):  
Muscle Strength ◽  
Ankle Joint ◽  
Coefficient Of Friction ◽  
Sagittal Plane ◽  
Biomechanical Model ◽  
Whole Body ◽  
The Stability ◽  
Joint Center ◽  
Static Conditions ◽  
Stability Limits

The stability constraints of a two-dimensional static human force exertion capability model (2DHFEC) were evaluated with subjects of varying anthropometry and strength capabilities performing manual exertions. The biomechanical model comprehensively estimated human force exertion capability under sagittally symmetric static conditions using constraints from three classes: stability, joint muscle strength, and coefficient of friction. Experimental results showed the concept of stability must be considered with joint muscle strength capability and coefficient of friction in predicting hand force exertion capability. Information was gained concerning foot modeling parameters as they affect whole-body stability. Findings indicated that stability limits should be placed approximately 37 % the ankle joint center to the posterior-most point of the foot and 130 % the distance from the ankle joint center to the maximal medial protuberance (the ball of the foot). 2DHFEC provided improvements over existing models, especially where horizontal push/pull forces create balance concerns.

Stability and instability of some nonlinear dispersive solitary waves in higher dimension

1996 ◽  
Vol 126 (1) ◽  
pp. 89-112 ◽  
Author(s):  
Anne de Bouard
Keyword(s):  
Solitary Waves ◽  
Acoustic Waves ◽  
Vries Equation ◽  
Three Dimensional ◽  
Higher Dimension ◽  
Ion Acoustic Waves ◽  
Stability And Instability ◽  
Ion Acoustic ◽  
De Vries ◽  
The Stability

We study the stability of positive radially symmetric solitary waves for a three dimensional generalisation of the Korteweg de Vries equation, which describes nonlinear ion-acoustic waves in a magnetised plasma, and for a generalisation in dimension two of the Benjamin–Bona–Mahony equation.

scholarly journals Modeling and Mapping of Combined Noise Annoyance for Aircraft and Road Traffic Based on a Partial Loudness Model

2021 ◽  
Vol 18 (16) ◽  
pp. 8724
Author(s):  
Wonhee Lee ◽  
Chanil Chun ◽  
Dongwook Kim ◽  
Soogab Lee
Keyword(s):  
Background Noise ◽  
Road Traffic ◽  
Noise Source ◽  
Transportation Systems ◽  
Masking Effect ◽  
Noise Sources ◽  
Noise Annoyance ◽  
Short And Long Term ◽  
Loudness Model

Complex transportation systems often produce combined exposure to aircraft and road noise. Depending on the noise source, the annoyance response is different, and a masking effect occurs between the noise sources within the combined noise. Considering these characteristics, partial loudness was adopted to evaluate noise annoyance. First, a partial loudness model incorporating binaural inhibition was proposed and validated. Second, short- and long-term annoyance models were developed using partial loudness. Finally, the annoyance of combined noise was visualized as a map. These models can evaluate the annoyance by considering both the intensity and frequency characteristics of the noise. In addition, it is possible to quantify the masking effect that occurs between noise sources. Combined noise annoyance maps depict the degree of annoyance of residents and show the background noise effect, which is not seen on general noise maps.

scholarly journals Derived Interaction Parameters for the TSAI-WU Tensor Polynomial Theory of Strength for Composite Materials

2001 ◽  
Author(s):  
Steven J. DeTeresa ◽  
Gregory J. Larsen
Keyword(s):  
Hydrostatic Pressure ◽  
Fiber Composite ◽  
Strength Criterion ◽  
Test Methods ◽  
Standard Test ◽  
Transverse Compression ◽  
Strength Parameters ◽  
Carbon Fiber Composite ◽  
The Stability ◽  
Stability Limits

Abstract It is shown that the two interactive strength parameters in the Tsai-Wu tensor polynomial strength criterion for fiber composites can be derived in terms of the uniaxial or non-interacting strength parameters if the composite does not fail under practical levels of hydrostatic pressure or equal transverse compression. Thus the required number of parameters is reduced from seven to five and all five of the remaining strength terms are easily determined using standard test methods. The derived interactive parameters fall within the stability limits of the theory, yet they lead to open failure surfaces in the compressive stress quadrant. The assumptions used to derive the interactive parameters were supported by measurements for the effect of hydrostatic pressure and unequal transverse compression on the behavior of a typical carbon fiber composite.

One-dimensional model for the Rijke tube

1989 ◽  
Vol 202 ◽  
pp. 83-96 ◽  
Author(s):  
C. Nicoli ◽  
P. Pelcé
Keyword(s):  
Heat Transfer ◽  
Transfer Function ◽  
Dimensional Model ◽  
Unsteady Heat Transfer ◽  
Order Unity ◽  
Rijke Tube ◽  
Thermoacoustic Instability ◽  
One Dimensional ◽  
The Stability ◽  
Stability Limits

We develop a simple model in which longitudinal, compressible, unsteady heat transfer between heater and gas is computed in the small-Mach-number limit. This calculation is used to determine the transfer function of the heater, which plays an important role in the stability limits of the thermoacoustic instability of the Rijke tube. The transfer function is determined analytically in the limit of small expansion parameter γ, and numerically for γ of order unity. In the case ρμ/cp = constant, an analytical solution can be found.

Prediction of pressure-generated earth motion using optimum filters

1975 ◽  
Vol 65 (3) ◽  
pp. 637-650
Author(s):  
E. J. Douze ◽  
G. G. Sorrells
Keyword(s):  
Atmospheric Pressure ◽  
Acoustic Waves ◽  
Background Noise ◽  
Single Channel ◽  
Pressure Variation ◽  
Long Period ◽  
System A ◽  
The Earth ◽  
Multichannel Filtering ◽  
Time Trace

abstract The performance of long-period seismographs is often seriously degraded by atmospheric pressure variation; the problem is particularly severe at periods greater than 20 sec. The pressure variations associated with wind-generated turbulence and acoustic waves are sufficient to deform the surface of the Earth, thus adding to the background noise level recorded by the seismometer. If microbarographs are operated together with the seismograph system, a large percentage of the atmospherically generated noise can be eliminated by the use of optimum filters. The filters are designed based on the least-mean-squares criterion, with the seismograph time trace as the desired output and the microbarographs as the inputs. Single-channel filters, using only one microbarograph, located at the seismometer vault are used to attenuate wind-generated noise. In order to attenuate the noise on windless days from other pressure sources, multichannel filtering is usually necessary and therefore an array of microbarographs is required. The filters used to predict the wind-generated noise are shown to be stable despite the complicated source. The performance of the multichannel varies widely depending on the structure of pressure variations predominating in the atmosphere.

Investigation of Gyroscopic Effect on the Stability of High Speed Micromilling via Bifurcation Analysis

2021 ◽  
Vol 5 (4) ◽  
pp. 130
Author(s):  
Rinku K. Mittal ◽  
Ramesh K. Singh
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Multistep Method ◽  
Gyroscopic Effect ◽  
High Rotational Speed ◽  
Micro Tool ◽  
The Stability ◽  
Delay Differential ◽  
Stability Limits ◽  
Micro Tools

Catastrophic tool failure due to the low flexural stiffness of the micro-tool is a major concern for micromanufacturing industries. This issue can be addressed using high rotational speed, but the gyroscopic couple becomes prominent at high rotational speeds for micro-tools affecting the dynamic stability of the process. This study uses the multiple degrees of freedom (MDOF) model of the cutting tool to investigate the gyroscopic effect in machining. Hopf bifurcation theory is used to understand the long-term dynamic behavior of the system. A numerical scheme based on the linear multistep method is used to solve the time-periodic delay differential equations. The stability limits have been predicted as a function of the spindle speed. Higher tool deflections occur at higher spindle speeds. Stability lobe diagram shows the conservative limits at high rotational speeds for the MDOF model. The predicted stability limits show good agreement with the experimental limits, especially at high rotational speeds.

Optimization of Journal Bearing Profile for Higher Dynamic Stability Limits

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Rodrigo Nicoletti
Keyword(s):  
Journal Bearing ◽  
Optimization Procedure ◽  
Control Points ◽  
Time Domain Simulation ◽  
Rotating System ◽  
Stability Margins ◽  
Dynamic Coefficients ◽  
The Stability ◽  
Stability Limits ◽  
Improve Stability

This work presents an optimization procedure to find bearing profiles that improve stability margins of rotor-bearing systems. The profile is defined by control points and cubic splines. Stability margins are estimated using bearing dynamic coefficients, and obtained solutions are analyzed as a function of the number of control points and of the Sommerfeld number at optimization. Results show the feasibility of finding shapes for the bearing that significantly improve the stability margins. Some of the obtained solutions overcome the stability margins of conventional bearings, such as the journal bearing and preloaded bearings with 0.5 and 0.67 preload. A time domain simulation of a flexible shaft rotating system supported by such bearings corroborates the results.

Stability of non-parabolic flow in a flexible tube

1999 ◽  
Vol 395 ◽  
pp. 211-236 ◽  
Author(s):  
V. SHANKAR ◽  
V. KUMARAN
Keyword(s):  
Reynolds Number ◽  
Velocity Profile ◽  
Asymptotic Analysis ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Flexible Tube ◽  
Developing Flow ◽  
Parabolic Flow ◽  
High Reynolds ◽  
The Stability

Flows with velocity profiles very different from the parabolic velocity profile can occur in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the temporal stability of such ‘non-parabolic’ flows in a flexible tube in the limit of high Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile contains both axial and radial components, the flow is assumed to be locally parallel in the stability analysis. The fluid is Newtonian and incompressible, while the flexible wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis shows that the non-parabolic velocity profiles can become unstable in the inviscid limit. This inviscid instability is qualitatively different from that observed in previous studies on the stability of parabolic flow in a flexible tube, and from the instability of developing flow in a rigid tube. The results of the asymptotic analysis are extended numerically to the moderate Reynolds number regime. The numerical results reveal that the developing flow could be unstable at much lower Reynolds numbers than the parabolic flow, and hence this instability can be important in destabilizing the fluid flow through flexible tubes at moderate and high Reynolds number. For flow in a slightly converging tube, even small deviations from the parabolic profile are found to be sufficient for the present instability mechanism to be operative. The dominant non-parallel effects are incorporated using an asymptotic analysis, and this indicates that non-parallel effects do not significantly affect the neutral stability curves. The viscosity of the wall medium is found to have a stabilizing effect on this instability.

scholarly journals ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction: Part II—Influence of the Acoustic Models

Acoustics ◽  
2020 ◽  
Vol 2 (3) ◽  
pp. 617-649
Author(s):  
Sébastien Guérin ◽  
Carolin Kissner ◽  
Pascal Seeler ◽  
Ricardo Blázquez ◽  
Pedro Carrasco Laraña ◽  
...  
Keyword(s):  
Analytical Methods ◽  
Acoustic Waves ◽  
Power Spectra ◽  
Low Frequency ◽  
Broadband Noise ◽  
Experimental Results ◽  
Acoustic Analogy ◽  
Noise Sources ◽  
Acoustic Models ◽  
The Impact

A benchmark dedicated to RANS-informed analytical methods for the prediction of turbofan rotor–stator interaction broadband noise was organised within the framework of the European project TurboNoiseBB. The second part of this benchmark focuses on the impact of the acoustic models. Twelve different approaches implemented in seven different acoustic solvers are compared. Some of the methods resort to the acoustic analogy, while some use a direct approach bypassing the calculation of a source term. Due to differing application objectives, the studied methods vary in terms of complexity to represent the turbulence, to calculate the acoustic response of the stator and to model the boundary and flow conditions for the generation and propagation of the acoustic waves. This diversity of approaches constitutes the unique quality of this work. The overall agreement of the predicted sound power spectra is satisfactory. While the comparison between the models show significant deviations at low frequency, the power levels vary within an interval of ±3 dB at mid and high frequencies. The trends predicted by increasing the rotor speed are similar for almost all models. However, most predicted levels are some decibels lower than the experimental results. This comparison is not completely fair—particularly at low frequency—because of the presence of noise sources in the experimental results, which were not considered in the simulations.

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