Optimum Multi-Nozzle Configuration for Minimizing the Rayleigh Integral During High-Frequency Transverse Instabilities

2021 ◽  
Author(s):  
Vishal Acharya ◽  
Tim Lieuwen
Keyword(s):  
High Frequency ◽  
Transverse Mode ◽  
Acoustic Mode ◽  
Combustion Stability ◽  
Circular Distribution ◽  
Transverse Modes ◽  
Fixed Set ◽  
Circular Configuration ◽  
Swirling Strength ◽  
The Stability

Abstract This paper develops a formalism for optimizing nozzle location/configuration with respect to combustion stability of high-frequency transverse modes in a can combustor. The stability of these acoustically non-compact flames was assessed using the Rayleigh Integral (RI). Several key control parameters influence RI - flame angle, swirling strength, nozzle location, as well as nozzle location with respect to the acoustic mode shape. In this study, we consider a N-around-1 configuration such as typically used in a multi-nozzle can system and study the overall stability of this system for different natural transverse modes. Typically, such nozzles are distributed in a uniformly circular manner for which we study the overall RI and for cases where RI>0, we optimize the nozzle distribution that can reduce and minimize RI. For a fixed geometry such a circular configuration, the analysis shows how the flame's parameters must vary across the different nozzles, to result in a relatively stable system. Additionally, for a fixed set of flame parameters, the analysis also indicates the non-circular distribution of the N nozzles that minimizes RI. Overall, the analysis aims to provide insights on designing nozzle locations around the center nozzle for minimal amplification of a given transverse mode.

Optimum Multi-Nozzle Configuration for Minimizing the Rayleigh Integral During High-Frequency Transverse Instabilities

2021 ◽  
Author(s):  
Vishal Acharya ◽  
Timothy Lieuwen
Keyword(s):  
High Frequency ◽  
Transverse Mode ◽  
Acoustic Mode ◽  
Combustion Stability ◽  
Circular Distribution ◽  
Transverse Modes ◽  
Fixed Set ◽  
Circular Configuration ◽  
Swirling Strength ◽  
The Stability

Abstract This paper develops a formalism for optimizing nozzle location/configuration with respect to combustion stability of high-frequency transverse modes in a can combustor. The stability of these acoustically non-compact flames was assessed using the Rayleigh Integral (RI). Several key control parameters influence RI – flame angle, swirling strength, nozzle location, as well as nozzle location with respect to the acoustic mode shape. In this study, we consider a N-around-1 configuration such as typically used in a multi-nozzle can system and study the overall stability of this system for different natural transverse modes. Typically, such nozzles are distributed in a uniformly circular manner for which we study the overall RI and for cases where RI > 0, we optimize the nozzle distribution that can reduce and minimize RI. For a fixed geometry such a circular configuration, the analysis shows how the flame’s parameters must vary across the different nozzles, to result in a relatively stable system. Additionally, for a fixed set of flame parameters, the analysis also indicates the non-circular distribution of the N nozzles that minimizes RI. Overall, the analysis aims to provide insights on designing nozzle locations around the center nozzle for minimal amplification of a given transverse mode.

Identification of High-Frequency Transverse Acoustic Modes in Multi-Nozzle Can Combustors

2020 ◽  
Author(s):  
J. Kim ◽  
W. Gillman ◽  
D. Wu ◽  
B. Emerson ◽  
V. Acharya ◽  
...  
Keyword(s):  
High Frequency ◽  
Gas Turbines ◽  
Least Squares Method ◽  
Flame Temperature ◽  
Three Dimensional ◽  
Transverse Mode ◽  
Nodal Line ◽  
Acoustic Mode ◽  
Mitigation Measures ◽  
Mode Shapes

Abstract High frequency thermoacoustic instabilities are problematic for lean-premixed gas turbines. Identifying which acoustic mode is being excited is important, in that it provides insight into potential mitigation measures and mechanical stress/life. However, the frequency spacing between modes becomes quite close for high frequency instabilities in a can combustor. This makes it difficult to distinguish between the modes (e.g., the first transverse mode vs. a higher order axial/mixed mode) based upon frequency calculations alone, which inevitably have uncertainties in boundary conditions, temperature profiles, and combustion response. This paper presents a methodology to simultaneously identify the acoustic mode shapes in the axial and azimuthal directions from acoustic pressure measurements. Multiple high temperature pressure transducers, located at distinct axial and azimuthal positions, are flush mounted in the combustor wall. The measured pressure oscillations from each sensor are then used to reconstruct the pressure distributions by using a least squares method in conjunction with a solution of a three dimensional wave equation. In order to validate the methodology, finite element method (FEM) calculations with estimated post-flame temperature is used to provide the candidate frequencies and corresponding mode shapes. The results demonstrate the reconstructed mode shapes and standing/spinning character of transverse waves, as well as the associated frequencies, both of which are consistent with the FEM predictions. Nodal line location was also extracted from the experimental data during the instabilities in the pressure data.

scholarly journals Delay compensation based controller for rotary electrohydraulic servo system

2021 ◽  
Author(s):  
Zakarya Omar ◽  
Xingsong Wang ◽  
Khalid Hussain ◽  
Mingxing Yang
Keyword(s):  
High Frequency ◽  
Dead Time ◽  
Sliding Mode ◽  
Servo System ◽  
Smith Predictor ◽  
Delay Compensation ◽  
Mechanical Parts ◽  
System Output ◽  
Electrohydraulic Servo System ◽  
The Stability

AbstractThe typical power-assisted hip exoskeleton utilizes rotary electrohydraulic actuator to carry out strength augmentation required by many tasks such as running, lifting loads and climbing up. Nevertheless, it is difficult to precisely control it due to the inherent nonlinearity and the large dead time occurring in the output. The presence of large dead time fires undesired fluctuation in the system output. Furthermore, the risk of damaging the mechanical parts of the actuator increases as these high-frequency underdamped oscillations surpass the natural frequency of the system. In addition, system closed-loop performance is degraded and the stability of the system is unenviably affected. In this work, a Sliding Mode Controller enhanced by a Smith predictor (SMC-SP) scheme that counts for the output delay and the inherent parameter nonlinearities is presented. SMC is utilized for its robustness against the uncertainty and nonlinearity of the servo system parameters whereas the Smith predictor alleviates the dead time of the system’s states. Experimental results show smoother response of the proposed scheme regardless of the amount of the existing dead time. The response trajectories of the proposed SMC-SP versus other control methods were compared for a different predefined dead time.

scholarly journals The Effect of RME-1-Butanol Blends on Combustion, Performance and Emission of a Direct Injection Diesel Engine

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2941
Author(s):  
Wojciech Tutak ◽  
Arkadiusz Jamrozik ◽  
Karol Grab-Rogaliński
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Direct Injection ◽  
Specific Energy Consumption ◽  
Combustion Process ◽  
Constant Load ◽  
Combustion Stability ◽  
Performance And Emission ◽  
Energy Share ◽  
The Stability

The main objective of this study was assessment of the performance, emissions and combustion characteristics of a diesel engine using RME–1-butanol blends. In assessing the combustion process, great importance was placed on evaluating the stability of this process. Not only were the typical COVIMEP indicators assessed, but also the non-burnability of the characteristic combustion stages: ignition delay, time of 50% heat release and the end of combustion. The evaluation of the combustion process based on the analysis of heat release. The tests carried out on a 1-cylinder diesel engine operating at a constant load. Research and evaluation of the combustion process of a mixture of RME and 1-butanol carried out for the entire range of shares of both fuels up to 90% of 1-butanol energetic fraction. The participation of butanol in combustion process with RME increased the in-cylinder peak pressure and the heat release rate. With the increase in the share of butanol there was noted a decrease in specific energy consumption and an increase in engine efficiency. The share of butanol improved the combustion stability. There was also an increase in NOx emissions and decrease in CO and soot emissions. The engine can be power by blend up to 80% energy share of butanol.

scholarly journals Supernova constraints on an axion-photon-dark photon interaction

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Anson Hook ◽  
Gustavo Marques-Tavares ◽  
Clayton Ristow
Keyword(s):  
Longitudinal Mode ◽  
Transverse Mode ◽  
The Other ◽  
Unusual Feature ◽  
Dark Sector ◽  
Longitudinal Modes ◽  
Dark Photon ◽  
Transverse Modes ◽  
Weakly Coupled ◽  
Photon Coupling

Abstract We present the supernova constraints on an axion-photon-dark photon coupling, which can be the leading coupling to dark sector models and can also lead to dramatic changes to axion cosmology. We show that the supernova bound on this coupling has two unusual features. One occurs because the scattering that leads to the trapping regime converts axions and dark photons into each other. Thus, if one of the two new particles is sufficiently massive, both production and scattering become suppressed and the bounds from bulk emission and trapped (area) emission both weaken exponentially and do not intersection The other unusual feature occurs because for light dark photons, longitudinal modes couple more weakly than transverse modes do. Since the longitudinal mode is more weakly coupled, it can still cause excessive cooling even if the transverse mode is trapped. Thus, the supernova constraints for massive dark photons look like two independent supernova bounds super-imposed on top of each other.

An Efficient Galerkin BEM to Compute High Acoustic Eigenfrequencies

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Mario Durán ◽  
Jean-Claude Nédélec ◽  
Sebastián Ossandón
Keyword(s):  
Numerical Method ◽  
Integral Equations ◽  
High Frequency ◽  
High Accuracy ◽  
Integral Representations ◽  
Stability And Convergence ◽  
Symmetric Matrices ◽  
Frequency Interval ◽  
Numerical Treatment ◽  
The Stability

An efficient numerical method, using integral equations, is developed to calculate precisely the acoustic eigenfrequencies and their associated eigenvectors, located in a given high frequency interval. It is currently known that the real symmetric matrices are well adapted to numerical treatment. However, we show that this is not the case when using integral representations to determine with high accuracy the spectrum of elliptic, and other related operators. Functions are evaluated only in the boundary of the domain, so very fine discretizations may be chosen to obtain high eigenfrequencies. We discuss the stability and convergence of the proposed method. Finally we show some examples.

SiGe Heteroepitaxy for High Frequency Circuits

1998 ◽  
Vol 525 ◽  
Author(s):  
B. Tillack ◽  
D. Bolze ◽  
G. Fischer ◽  
G. Kissinger ◽  
D. Knoll ◽  
...  
Keyword(s):  
Heterojunction Bipolar Transistors ◽  
High Frequency ◽  
Defect Density ◽  
Process Capability ◽  
Chemical Vapor ◽  
Bipolar Transistors ◽  
Capability Indices ◽  
Data Points ◽  
B Doping ◽  
The Stability

ABSTRACTWe have determined the process capability of Low Pressure (Rapid Thermal) Chemical Vapor Deposition (LP(RT)CVD) of epitaxial Si/SiGe/Si stacks for heterojunction bipolar transistors (HIBTs). The transistor parameters primarily influenced by the epitaxial characteristics were measured for 600 identically processed 4” wafers. The results demonstrate that it is possible to control accurately the epitaxial process for a 25 nm thick graded SiGe base profile with 20 % Ge and very narrow B doping (5 nm). The pipe limited device yield of about 90 % for an emitter area of 104 μm2 indicates a very low defect density in the epitaxial layer stack. The process capability indices determined from about 40,000 data points demonstrate the stability and capability of the LP(RT)CVD epitaxy with regard to manufacturing requirements.

Discrete-Time H-Infinity Synthesis of Frequency-Shaped Sliding Mode Control for Suppression of Vibration With Multiple Peak Frequencies

2016 ◽  
Author(s):  
Minghui Zheng ◽  
Masayoshi Tomizuka
Keyword(s):  
High Frequency ◽  
Sliding Mode ◽  
Disk Drive ◽  
Sliding Surface ◽  
Surface Dynamics ◽  
H Infinity ◽  
High Frequencies ◽  
Multiple Peak ◽  
Significant Performance ◽  
The Stability

Vibration with multiple large peaks at high frequencies may cause significant performance degradation and have become a major concern in modern high precision control systems. To deal with such high-frequency peaks, it is proposed to design a frequency-shaped sliding mode controller based on H∞ synthesis. It obtains an ‘optimal’ filter to shape the sliding surface, and thus provides frequency-dependent control allocation. The proposed frequency-shaping method assures the stability in the presence of multiple-peak vibration sources, and minimizes the weighted H∞ norm of the sliding surface dynamics. The evaluation is performed on a simulated hard disk drive with actual vibration sources from experiments, and the effectiveness of large vibration peak suppression is demonstrated.

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