scholarly journals Experimental sensitivity analysis and control of thermoacoustic systems

2015 ◽  
Vol 787 ◽  
Author(s):  
Georgios Rigas ◽  
Nicholas P. Jamieson ◽  
Larry K. B. Li ◽  
Matthew P. Juniper
Keyword(s):  
Growth Rate ◽  
Sensitivity Analysis ◽  
Passive Control ◽  
Control Strategies ◽  
Control Device ◽  
Linear Regime ◽  
Adjoint Methods ◽  
Rijke Tube ◽  
Theoretical Predictions ◽  
And Control

In this paper, we report the results of an experimental sensitivity analysis on a thermoacoustic system – an electrically heated Rijke tube. We measure the change of the linear stability characteristics of the system, quantified as shifts in the growth rate and oscillation frequency, that is caused by the introduction of a passive control device. The control device is a mesh, which causes drag in the system. The rate of growth is slow, so the growth rate and frequency can be measured very accurately over many hundreds of cycles in the linear regime with and without control. These measurements agree qualitatively well with the theoretical predictions from adjoint-based methods of Magri & Juniper (J. Fluid Mech., vol. 719, 2013, pp. 183–202). This agreement supports the use of adjoint methods for the development and implementation of control strategies for more complex thermoacoustic systems.

scholarly journals Are Numerical Simulations Reliable? Proposed Improvements and Tests

1987 ◽  
Vol 117 ◽  
pp. 279-279
Author(s):  
F. R. Bouchet
Keyword(s):  
Growth Rate ◽  
Dispersion Relation ◽  
Numerical Experiments ◽  
Linear Growth ◽  
Numerical Dispersion ◽  
Linear Growth Rate ◽  
Linear Regime ◽  
Grid Spacing ◽  
Gravitational Clustering ◽  
Theoretical Predictions

When one builds a code to simulate numerically a process, the first concern is the range of validity of the results. This can be accessed empirically, though the results can be misleading if the tests are too naive. For particle-mesh codes simulating the gravitational clustering, an analytical theory has been proposed in Bouchet et al. 1985. It yields the numerical dispersion relation of the system in the linear regime, and thus describes how the linear growth rate is affected by the discretisation. The theoretical predictions are in agreement with the results of actual numerical experiments: both show that the results of standart particle-mesh codes should not be trusted at distances smaller than 6 to 8 grid-spacing Δx (depending on the detail of the algorithm).

Growth, Reproductive Potential, and Control Strategies for Deeproot Sedge (Cyperus entrerianus)

2012 ◽  
Vol 26 (1) ◽  
pp. 122-129 ◽  
Author(s):  
Charles T. Bryson ◽  
Richard Carter
Keyword(s):  
Growth Rate ◽  
Field Study ◽  
Control Strategies ◽  
Reproductive Potential ◽  
Field Studies ◽  
Growth Chamber ◽  
Chamber Studies ◽  
Growth Chamber Studies ◽  
And Control ◽  
Achene Production

Greenhouse, growth chamber, and field studies were conducted at Stoneville, MS, in 2000 to 2008, to determine the growth rate, reproductive and overwintering potential, and control of deeproot sedge. In growth chamber studies, deeproot sedge growth rate (ht) and plant dry wt were greatest at 25/35 C (night/day temperatures), when compared with regimes of 5/15, 15/25, and 20/30 C. Based on the average number of scales (fruiting sites per spikelet), spikelets per inflorescence, and culms per plant, deeproot sedge reproductive potential was 2.6-, 6.2-, and 17.4-fold greater than Surinam, green, and knob sedges, respectively. A single deeproot sedge plant produced an average of 85,500 achenes annually. Mowing at 15-cm ht weekly prevented achene production but did not kill deeproot sedge plants. The average number of inflorescences produced on mowed plants was 1.2 to 4 times greater in 2- and 1-yr-old deeproot sedge plants, respectively, when compared with unmowed plants. Mature deeproot sedge achenes were produced between monthly mowings. In a 3-yr field study, glyphosate, glufosinate, hexazinone, and MSMA provided more than 85% control of deeproot sedge, and above the soil, live deeproot sedge plant dry wt was reduced by 50, 64, 68, 72, 86, and 93% by dicamba, halosulfuron-methyl, MSMA, hexazinone, glufosinate, and glyphosate, respectively. All (100%) deeproot sedge plants 1 yr old or older overwintered at Stoneville, MS, at 33°N latitude.

scholarly journals A Critical Review of Stall Control Techniques in Industrial Fans

2013 ◽  
Vol 2013 ◽  
pp. 1-18 ◽  
Author(s):  
Stefano Bianchi ◽  
Alessandro Corsini ◽  
Anthony G. Sheard ◽  
Cecilia Tortora
Keyword(s):  
Control Systems ◽  
Passive Control ◽  
Control Strategies ◽  
Warning System ◽  
Detection Methods ◽  
Stall Inception ◽  
Stall Margin ◽  
Control Techniques ◽  
Control Technologies ◽  
And Control

This paper reviews modelling and interpretation advances of industrial fan stall phenomena, related stall detection methods, and control technologies. Competing theories have helped engineers refine fan stability and control technology. With the development of these theories, three major issues have emerged. In this paper, we first consider the interplay between aerodynamic perturbations and instability inception. An understanding of the key physical phenomena that occurs with stall inception is critical to alleviate stall by design or through active or passive control methods. We then review the use of passive and active control strategies to improve fan stability. Whilst historically compressor design engineers have used passive control techniques, recent technologies have prompted them to install high-response stall detection and control systems that provide industrial fan designers with new insight into how they may detect and control stall. Finally, the paper reviews the methods and prospects for early stall detection to complement control systems with a warning capability. Engineers may use an effective real-time stall warning system to extend a fan’s operating range by allowing it to operate safely at a reduced stall margin. This may also enable the fan to operate in service at a more efficient point on its characteristic.

scholarly journals Uncertainty and sensitivity analysis of control strategies using the benchmark simulation model No1 (BSM1)

2009 ◽  
Vol 59 (3) ◽  
pp. 491-499 ◽  
Author(s):  
Xavier Flores-Alsina ◽  
Ignasi Rodriguez-Roda ◽  
Gürkan Sin ◽  
Krist V. Gernaey
Keyword(s):  
Growth Rate ◽  
Sensitivity Analysis ◽  
Monte Carlo ◽  
Carbon Source ◽  
Simulation Model ◽  
Correction Factor ◽  
Control Strategies ◽  
Hydrolysis Rate ◽  
External Carbon Source ◽  
Uncertainty And Sensitivity Analysis

The objective of this paper is to perform an uncertainty and sensitivity analysis of the predictions of the Benchmark Simulation Model (BSM) No. 1, when comparing four activated sludge control strategies. The Monte Carlo simulation technique is used to evaluate the uncertainty in the BSM1 predictions, considering the ASM1 bio-kinetic parameters and influent fractions as input uncertainties while the Effluent Quality Index (EQI) and the Operating Cost Index (OCI) are focused on as model outputs. The resulting Monte Carlo simulations are presented using descriptive statistics indicating the degree of uncertainty in the predicted EQI and OCI. Next, the Standard Regression Coefficients (SRC) method is used for sensitivity analysis to identify which input parameters influence the uncertainty in the EQI predictions the most. The results show that control strategies including an ammonium (SNH) controller reduce uncertainty in both overall pollution removal and effluent total Kjeldahl nitrogen. Also, control strategies with an external carbon source reduce the effluent nitrate (SNO) uncertainty increasing both their economical cost and variability as a trade-off. Finally, the maximum specific autotrophic growth rate (μA) causes most of the variance in the effluent for all the evaluated control strategies. The influence of denitrification related parameters, e.g. ηg (anoxic growth rate correction factor) and ηh (anoxic hydrolysis rate correction factor), becomes less important when a SNO controller manipulating an external carbon source addition is implemented.

A Theoretical Approach for Passive Control of Thermoacoustic Oscillations: Application to Ducted Flames

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Luca Magri ◽  
Matthew P. Juniper
Keyword(s):  
Heat Release ◽  
Passive Control ◽  
Local Variation ◽  
Control Device ◽  
Adjoint Equations ◽  
Hot Wire ◽  
Adjoint Sensitivity ◽  
Cross Sectional ◽  
Rijke Tube ◽  
Thermoacoustic Oscillations

In this paper, we develop a linear technique that predicts how the stability of a thermoacoustic system changes due to the action of a generic passive feedback device or a generic change in the base state. From this, one can calculate the passive device or base state change that most stabilizes the system. This theoretical framework, based on adjoint equations, is applied to two types of Rijke tube. The first contains an electrically heated hot wire, and the second contains a diffusion flame. Both heat sources are assumed to be compact, so that the acoustic and heat release models can be decoupled. We find that the most effective passive control device is an adiabatic mesh placed at the downstream end of the Rijke tube. We also investigate the effects of a second hot wire and a local variation of the cross-sectional area but find that both affect the frequency more than the growth rate. This application of adjoint sensitivity analysis opens up new possibilities for the passive control of thermoacoustic oscillations. For example, the influence of base state changes can be combined with other constraints, such as that the total heat release rate remains constant, in order to show how an unstable thermoacoustic system should be changed in order to make it stable.

scholarly journals Analysis of Dynamic Characteristics and Control Strategies of a Solvent Dehydration Distillation Column in a Purified Terephthalic Acid Plant

Processes ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 125
Author(s):  
Xiuhui Huang ◽  
Jun Wang ◽  
Zeqiu Li
Keyword(s):  
Sensitivity Analysis ◽  
Dynamic Model ◽  
Control Strategy ◽  
Terephthalic Acid ◽  
Control Strategies ◽  
Plate Temperature ◽  
Dynamic Sensitivity ◽  
Purified Terephthalic Acid ◽  
And Control ◽  
Dynamic Sensitivity Analysis

In this study, a solvent dehydration column of purified terephthalic acid (PTA) plant was used as the research object. Based on a dynamic model of the solvent dehydration column, a dynamic sensitivity analysis of the key parameters was carried out using Aspen Dynamics. After the dynamic model reached stability, the reflux rate, methyl acetate concentration, and reflux temperature of the solvent dehydration column were adjusted and the changes of the key separation indexes under the corresponding disturbance were analyzed. According to the analysis results, a sensitive plate temperature controller was added to carry out the dynamic sensitivity analysis. In addition, the acetic acid (HAc) concentration of the bottom of the column was found to be unstable in the dynamic sensitivity analysis. Considering the HAc concentration controller of the column bottom, two control strategies were designed. By analyzing the dynamic response of the feed flow disturbance under different control strategies, a more suitable control strategy under different conditions was obtained. From this, a reasonable method could be derived to design the control strategy, thereby providing a theoretical basis for further real-time optimization and advanced control of solvent dehydration in a PTA plant.

Control Strategies of an Academic Rotor/Stator Cavity Through Sensitivity Analysis

2019 ◽  
Author(s):  
Matthieu Queguineur ◽  
Laurent Gicquel ◽  
Gabriel Staffelbach
Keyword(s):  
Sensitivity Analysis ◽  
Passive Control ◽  
Structural Integrity ◽  
Control Strategies ◽  
Unsteady Motion ◽  
Base Flow ◽  
Operating Conditions ◽  
Space Applications ◽  
Flow Modification ◽  
Set Up

Abstract Strong hydrodynamic instabilities are often observed in rotating cavities of turbomachinery in the aerospace industry for specific thermal and operating conditions. This highly unsteady motion of the flow, often referred to as ‘pressure bands’ phenomenon can be detrimental and jeopardize the structural integrity of aeronautical engines by damaging turbomachinery components or turbopumps in the context of space applications. In order to avoid this fluid structure interaction, a deeper understanding of the stability of the flow of rotating cavities becomes compulsory. A few studies enabled to point out the spatial distribution and origins of such multi-frequency flow. However control solutions have not yet been set up. In this context, an academic stator/rotor cavity is studied in this paper with a sensitivity analysis to base flow modification based on linear stability analysis. This latter points out the regions of the stator boundary layer of each mode where the flow should be modified. Possible passive control strategies are then proposed from the interpretation of the results. The more relevant solution being suction and injection actuators directly introduced on the stationary disk of the cavity.

scholarly journals Experimental sensitivity analysis via a secondary heat source in an oscillating thermoacoustic system

2017 ◽  
Vol 9 (4) ◽  
pp. 230-240 ◽  
Author(s):  
Nicholas P Jamieson ◽  
Georgios Rigas ◽  
Matthew P Juniper
Keyword(s):  
Sensitivity Analysis ◽  
Heat Source ◽  
Decay Rate ◽  
Linear Growth ◽  
Control Strategies ◽  
Linear Frequency ◽  
Theoretical Predictions ◽  
Stringent Test ◽  
The Stability ◽  
Thermoacoustic Oscillations

In this article, we report the results of an experimental sensitivity analysis on a vertical electrically heated Rijke tube. We examine the stability characteristics of the system due to the introduction of a secondary heat source. The experimental sensitivity analysis is quantified by measuring the shift in linear growth and decay rate as well as the shift in the linear frequency during periods of growth and decay of thermoacoustic oscillations. Linear growth and decay rate measurements agree qualitatively well with the theoretical predictions from adjoint-based methods. A discrepancy in the linear frequency measurements highlight deficiencies in the model used for those predictions and shows that the experimental measurement of sensitivities is a stringent test of any thermoacoustic model. The findings suggest that adjoint-based methods are, in principle, capable of providing industry with a cheap and efficient tool for developing optimal control strategies for more complex thermoacoustic systems.

scholarly journals Inter-provincial disparity of COVID-19 transmission and control in Nepal

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Buddhi Pantha ◽  
Subas Acharya ◽  
Hem Raj Joshi ◽  
Naveen K. Vaidya
Keyword(s):  
Growth Rate ◽  
Disease Transmission ◽  
Reproduction Number ◽  
Control Strategies ◽  
National Level ◽  
Effective Control ◽  
Data Set ◽  
Control Policies ◽  
Local Spread ◽  
And Control

AbstractDespite the global efforts to mitigate the ongoing COVID-19 pandemic, the disease transmission and the effective controls still remain uncertain as the outcome of the epidemic varies from place to place. In this regard, the province-wise data from Nepal provides a unique opportunity to study the effective control strategies. This is because (a) some provinces of Nepal share an open-border with India, resulting in a significantly high inflow of COVID-19 cases from India; (b) despite the inflow of a considerable number of cases, the local spread was quite controlled until mid-June of 2020, presumably due to control policies implemented; and (c) the relaxation of policies caused a rapid surge of the COVID-19 cases, providing a multi-phasic trend of disease dynamics. In this study, we used this unique data set to explore the inter-provincial disparities of the important indicators, such as epidemic trend, epidemic growth rate, and reproduction numbers. Furthermore, we extended our analysis to identify prevention and control policies that are effective in altering these indicators. Our analysis identified a noticeable inter-province variation in the epidemic trend (3 per day to 104 per day linear increase during third surge period), the median daily growth rate (1 to 4% per day exponential growth), the basic reproduction number (0.71 to 1.21), and the effective reproduction number (maximum values ranging from 1.20 to 2.86). Importantly, results from our modeling show that the type and number of control strategies that are effective in altering the indicators vary among provinces, underscoring the need for province-focused strategies along with the national-level strategy in order to ensure the control of a local spread.

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.

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