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- Title
- A COMPARATIVE-STUDY OF TOOLS FOR ASSESSING THE EFFECTS OF FORCED PERIODIC OPERATION OF CATALYTIC REACTORS
- Creator
- Ozgulsen, F., Rigopoulos, K. R., Cinar, A.
- Date
- 1992
- Publisher
- GORDON BREACH SCI PUBL LTD
- Description
-
Two methods for assessing the effects of forced periodic catalytic reactor operation are presented. The vibrational control method is an...
Show moreTwo methods for assessing the effects of forced periodic catalytic reactor operation are presented. The vibrational control method is an analytical technique which evaluates the effects of high frequency forcing of system parameters by the method of averaging. The second technique is a numerical tool based on a shooting algorithm. These methods are capable of handling multiple input forcing and various shapes of forcing functions. Both methods are applied to isothermal, adiabatic and nonadiabatic operation of an internal recycle reactor in which the catalytic oxidation of ethylene takes place. The basic features of both techniques are discussed and the results obtained by using these methods are compared. Effects of single and multiple input parameter forcing are investigated. Experimental verification of the theoretical results is also performed for the isothermal case.
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- Title
- Development of Powered Resonance-tube Actuators for Aircraft Flow Control Applications
- Creator
- Raman, G., Mills, A., Kibens, V.
- Date
- 2004-12
- Publisher
- American Inst Aeronaut Astronaut
- Description
-
The present paper addresses both active-flow-control actuator technology development and the demonstration of the effectiveness of actuators...
Show moreThe present paper addresses both active-flow-control actuator technology development and the demonstration of the effectiveness of actuators that could be easily integrated into practical aircraft applications. The actuator used is an adaptation of the Hartmann oscillator. Demonstration experiments that illustrate the effectiveness of this actuator include cavity tone suppression at transonic speeds and the reduction of jet-impingement tones. The actuator concept is based on a high-speed jet aimed at the mouth of a cylindrical tube closed at the other end. The result is a high-amplitude self-sustaining fluctuating field accompanied by an intense narrowband tone, all in the region between the supply jet and the resonance tube. Using unsteady pressure sensors and flow visualization, we explored the effect of varying actuator parameters such as the spacing between the power jet and the resonance tube, supply pressure, resonance-tube depth, diameter, shape, and lateral spacing. By varying the depth of the tube, the frequency could be varied from about 1.6 kHz to over 10 kHz and amplitudes as high as 156 dB (microphone location dependent) were obtained in the vicinity of actuation. To integrate this concept into practical aircraft applications, two generations of a more complex version of this device known as the powered resonance-tube bank (PRTB) were developed and demonstrated. Results indicate that by using high-frequency excitation at 5-kHz suppression levels in excess of 20 dB were consistently obtained over a range of operating conditions in both cavity and impingement flow situations. Based on our results, we have grounds to believe that a properly designed PRTB has significant advantages over conventional actuators such as acoustic, piezo, and oscillatory microstructures.
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- Title
- VIBRATIONAL STABILIZATION OF A CHEMICAL REACTOR - AN EXPERIMENTAL-STUDY
- Creator
- Cinar, A., Deng, J., Meerkov, S. M., Shu, X. S.
- Date
- 1987-04
- Publisher
- IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
- Description
-
Vibrational control is a method for modification of dynamic properties of linear and nonlinear systems by introduction of fast, zero-average...
Show moreVibrational control is a method for modification of dynamic properties of linear and nonlinear systems by introduction of fast, zero-average oscillations in a system's parameters. It has been previously shown that forced oscillations introduced in the reactant flow rates to a continuous stirred tank reactor (CSTR) cause a modification of theS- shaped steady-state curve. In the present note experimental evidence is given to show that this modification leads to the operation the CSTR at an asymptotically stable periodic regime located near an unstable steady-state of the reactor system having fixed flow rates. For a given average stabilized state, such a stabilizing mechanism results in a higher production rate or lower energy expenditure compared to a steady operation with shifted input conditions.
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- Title
- Jet Impingement Tone Suppression Using Powered Resonance Tubes
- Creator
- Sarpotdar, Shekhar, Raman, Ganesh, Sharma, S. D., Cain, Alan B.
- Date
- 2007-05
- Publisher
- American Inst Aeronaut Astronaut
- Description
-
This work is an experimental study of high subsonic jet impingement tone suppression. We begin by documenting the characteristics of the...
Show moreThis work is an experimental study of high subsonic jet impingement tone suppression. We begin by documenting the characteristics of the impingement tone for various Mach numbers and standoff (nozzle exit to ground plate) distances. The results revealed frequency staging and the presence of two types of impingement tones. A novel feature of our work is the use of four miniature high-frequency actuators known as powered resonance tubes that were located circumferentially around the main jet nozzle. The powered resonance tubes were capable of producing high amplitude acoustic excitation over a range of frequencies, up to 17.5 kHz. Our target excitation frequency range was about 3-5 times that of the natural flow instability. Using high-frequency excitation, tonal suppression levels as high as 20 dB and broadband suppression levels as high as 5-10 dB were obtained. The mass addition rate from the powered resonance tubes was of the order of 2% of the mass flow rate from the main jet. Mass flow reductions could be obtained under conditions when the powered resonance tube resonated strongly. Our results suggest that appropriately designed miniature powered resonance tube actuators have potential for use in flow control applications.
http://dx.doi.org/10.2514/1.15818
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- Title
- ENHANCED MIXING OF MULTIPLE SUPERSONIC RECTANGULAR JETS BY SYNCHRONIZED SCREECH
- Creator
- Taghavi, R, Raman, G
- Date
- 1994-12
- Publisher
- AMER INST AERONAUT ASTRONAUT
- Title
- Tweeting Vertically? Elected Officials’ Interactions with Citizens on Twitter
- Creator
- Otterbacher, Jahna, Shapiro, Matthew A., Hemphill, Libby
- Date
- 2012-12-05, 2012
- Description
-
Enthusiasts propose that social media promotes vertical political communication, giving citizens the opportunity to interact directly with...
Show moreEnthusiasts propose that social media promotes vertical political communication, giving citizens the opportunity to interact directly with their representatives. However, skeptics claim that politicians avoid direct engagement with constituents, using technology to present a façade of interactivity instead. This study explores if and how elected officials in three regions of the world are using Twitter to interact with the public. We examine the Twitter activity of 15 officials over a period of six months. We show that in addition to the structural features of Twitter that are designed to promote interaction, officials rely on language to foster or to avoid engagement. It also provides yet more evidence that the existence of interactive features does not guarantee interactivity.
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- Title
- Nozzle-Orientation Effects and Nonlinear Interactions Between Twin Jets of Complex Geometry
- Creator
- Joshi, R, Panickar, P, Srinivasan, K, Raman, G
- Date
- 2006-04
- Publisher
- American Inst Aeronaut Astronaut
- Description
-
In this paper we focus on understanding the behavior of twin nozzles of complex geometry in various yaw orientations. To the best of our...
Show moreIn this paper we focus on understanding the behavior of twin nozzles of complex geometry in various yaw orientations. To the best of our knowledge there are no published studies addressing the effects of nozzle orientation on the coupling of twin jets of complex exit geometry. We study the behavior of 1) uniform-exit rectangular nozzles, 2) single-beveled nozzles in a codirected configuration, and 3) single-beveled nozzles in a contradirected configuration. Experiments were carried out at fully expanded Mach numbers ranging from 1.28 to 1.72. Bevel angles of 10 and 30 deg were considered, and microphones located at the nozzle exit plane quantified the coupling using both linear and nonlinear spectral-analysis methods. Nonlinear characteristics were quantified using the nonlinear interaction density metric with a cross-bicoherence cut-off threshold of 0.4. The following interesting results emerged from this study: 1) When nozzles having uniform rectangular exits are yawed, the sound-pressure levels in the internozzle region reduce as the yaw angles are increased, and, at a very high yaw angle, the symmetric coupling regime that existed at the high fully expanded Mach number range (without yaw) is replaced by an antisymmetric coupling regime in the same range. 2) Geometrically similar exits from uniform-exit rectangular nozzles and beveled nozzles in the contradirected configuration showed similar characteristics when studied using linear techniques. However, they revealed information that was hitherto unknown when studied using nonlinear spectral-analysis techniques. It is believed that the results presented in this paper will provide benchmark data to those simulating/designing complex-geometry nozzle systems.
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- Title
- FORCED PERIODIC CONTROL OF AN EXOTHERMIC CSTR WITH MULTIPLE INPUT OSCILLATIONS
- Creator
- Rigopoulos, K., Shu, X. S., Cinar, A.
- Date
- 1988-12
- Publisher
- AMER INST CHEMICAL ENGINEERS
- Description
-
Interaction among various oscillating inputs may result in significant modifications in the behavior of a system under forced periodic control...
Show moreInteraction among various oscillating inputs may result in significant modifications in the behavior of a system under forced periodic control. Forced oscillations in the input flow rate and input concentrations of an exothermic continuous stirred tank reactor enable the stabilized operation of the CSTR in the unstable steady state region. Reactor temperature oscillations under forced periodic control are similar to the oscillations resulting from proportional-integral feedback or nonlinear (push-pull) feedback control, and under some operating conditions the oscillation amplitude is significantly lower. Theoretical and experimental studies illustrate the effects of forcing frequency and phase shift on reactor behavior.
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- Title
- Gerry-meandering: An Assessment of the Congressional District Model of Depository Allocation (preprint): AhrensGriffinfinalpreprint
- Creator
- Ahrens, Aric G., Griffin, Luke A.
- Date
- 2003-06
- Description
-
The preprint of a published article dealing with the effect of allocating Federal Depositories by Congressional district. Conclusions drawn...
Show moreThe preprint of a published article dealing with the effect of allocating Federal Depositories by Congressional district. Conclusions drawn include the fact that due to redistricting that occurs after each decennial census, over time some districts may have within their boundaries a greater number than the two depositories that Congressional district allocation was intended to produce. Likewise, over time shifting boundaries of districts have created districts that have no depositories whatsoever.
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- Title
- THE BIFURCATION BEHAVIOR OF AN AUTOTHERMAL PACKED-BED TUBULAR REACTOR
- Creator
- Adomaitis, R. A., Cinar, A.
- Date
- 1988
- Publisher
- PERGAMON-ELSEVIER SCIENCE LTD
- Description
-
The analysis of a chemical reactor by numerical bifurcation techniques can completely define the multiplicity and stability of its equilibrium...
Show moreThe analysis of a chemical reactor by numerical bifurcation techniques can completely define the multiplicity and stability of its equilibrium states and can give insights into the reactor's parametric sensitivity and dynamical behavior in the neighborhood of the chosen operating points. In this paper, we will present some of the numerical bifurcation techniques used and developed in analyzing an autothermal packed bed tubular reactor. The bifurcation behavior found will be cataloged over the range of relevant reactant inlet conditions, and an explanation for the isolated solution branches characteristic of this reactor will also be presented.
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- Title
- DISTURBANCE GROWTH TRIGGERED BY STEADY HEATING OF A JETS NOZZLE EXIT BOUNDARY-LAYER
- Creator
- Cornelius, D, Raman, G
- Date
- 1995-10
- Publisher
- AMER INST PHYSICS
- Description
-
Experiments were conducted to investigate how heating only the nozzle exit boundary layer of an axisymmetric jet, with an unheated potential...
Show moreExperiments were conducted to investigate how heating only the nozzle exit boundary layer of an axisymmetric jet, with an unheated potential core, affects disturbance growth in the initial shear layer. The exit boundary layer had a minimum density ratio of 0.74, was laminar, and had a constant momentum thickness (theta) for all levels of nozzle heating used in this study. The fluctuating velocity (u') and temperature (t') in the exit boundary layer increased monotonically with increasing nozzle temperature. Low-amplitude acoustic excitation produced a more rapid growth of coherent velocity fluctuations for the heated case than for the unheated. (C) 1995 American Institute of Physics.
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- Title
- A Toolkit for Reframing Services for a Diverse Group: a research study of international students at Illinois Institutions
- Creator
- Han, Yi, Piotrowski, Pattie
- Date
- 2015-11-06, 2015-11-06
- Title
- A morphologically structured model for penicillin production
- Creator
- Birol, G., Undey, C., Parulekar, S. J., Cinar, A.
- Date
- 2002-03-05
- Publisher
- JOHN WILEY & SONS INC
- Description
-
A morphologically structured model is proposed to describe penicillin production in fed-batch cultivations. The model accounts for the effects...
Show moreA morphologically structured model is proposed to describe penicillin production in fed-batch cultivations. The model accounts for the effects of dissolved oxygen on cell growth and penicillin production and variations in volume fractions of abiotic and biotic phases due to biomass formation. Penicillin production is considered to occur in the subapical hyphal cell compartment and to be affected by availability of glucose and oxygen. As it stands, the model provides a wide range of applicability in terms of operating conditions. The model has been tested for various conditions and has given satisfactory results. A series of glucose feeding profiles have been considered to demonstrate the capabilities of the proposed model. It is concluded that the model may be valuable for the interpretation of experimental data collected specifically for metabolic flux analysis during fed-batch cultivation because the elements of measured specific production rates are determined from measurements of the concentrations of the components and their mass balances. The proposed model may be further used for developing control strategies and model order reduction algorithms
Endnote format citation for DOI:10.1002/bit.10115
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- Title
- Flow characteristics of a rectangular multielement supersonic mixer-ejector
- Creator
- Taghavi, R, Raman, G
- Date
- 1996-04
- Publisher
- SPRINGER VERLAG
- Description
-
This study describes a technique that combines the benefits of focusing schlieren and phase conditioning. Focusing schlieren blurs and drops...
Show moreThis study describes a technique that combines the benefits of focusing schlieren and phase conditioning. Focusing schlieren blurs and drops contrast of non-critical features whereas phase conditioning emphasizes periodic flow features, and their combination produces unique results. The supersonic jets that we studied produced an intense tone referred to as screech. The measured screech tone signal was used as input to the phase conditioning circuit that adjusted the strobing light source to the vertical synchronization pulse of a CCD camera. The sharp video images obtained by this technique could either be frozen or continuously swept through one period of screech to acquire a slow motion video record of the jet unsteadiness. Two cases were visualized in this study: first, an underexpanded jet from a convergent rectangular nozzle at various fully expanded Mach numbers. Second, a supersonic jet emerging from a convergent-divergent rectangular nozzle at a design Mach number of 1.4, artificially excited by impingement tones. The results of this study illustrate the usefulness of this system in visualizing oscillatory flows.
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- Title
- Intelligent process monitoring by interfacing knowledge-based systems and multivariate statistical monitoring
- Creator
- Norvilas, A., Negiz, A., Decicco, J., Cinar, A.
- Date
- 2000-08
- Publisher
- ELSEVIER SCI LTD
- Description
-
An intelligent process monitoring and fault diagnosis environment has been developed by interfacing multivariate statistical process...
Show moreAn intelligent process monitoring and fault diagnosis environment has been developed by interfacing multivariate statistical process monitoring (MSPM) techniques and knowledge-based systems (KBS) for monitoring multivariable process operation. The real-time KBS developed in G2 is used with multivariate SPM methods based on canonical variate stare space (CVSS) process models. Fault detection is based on T-2 charts of state variables. Contribution plots in G2 are used for determining the process variables that have contributed to the out-of-control signal indicated by large T-2 values, and G2 Diagnostic Assistant (GDA) is used to diagnose the source causes of abnormal process behavior. The MSPM modules developed in Matlab are linked with G2. This intelligent monitoring and diagnosis system can be used to monitor multivariable processes with autocorrelated, cross-correlated, and collinear data. The structure of the integrated system is described and its performance is illustrated by simulation studies.
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- Title
- Statistical process monitoring and disturbance diagnosis in multivariable continuous processes
- Creator
- Raich, A., Cinar, A.
- Date
- 1996-04
- Publisher
- AMER INST CHEMICAL ENGINEERS
- Description
-
Detecting out-of-control status and diagnosing disturbances leading to the abnormal process operation early are crucial in minimizing product...
Show moreDetecting out-of-control status and diagnosing disturbances leading to the abnormal process operation early are crucial in minimizing product quality variations Multivariate statistical techniques are used to develop detection methodology for abnormal process behavior and diagnosis of disturbances causing poor process performance. Principal components and discriminant analysis ave applied to quantitatively describe and interpret step, ramp and random-variation disturbances. All disturbances require high-dimensional models for accurate description and cannot be discriminated by biplots. Diagnosis of simultaneous multiple faults is addressed by building quantitative measures of overlap between models of single faults and their combinations. These measures are used to identify the existence of secondary disturbances and distinguish their components. The methodology is illustrated by monitoring the Tennessee Eastman plant simulation benchmark problem subjected to different disturbances. Most of the disturbances can be diagnosed correctly, the success rate being higher for step and vamp disturbances than random-variation disturbances.
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- Title
- Reversal in Spreading of a Tabbed Circular Jet Under Controlled Excitation
- Creator
- Zaman, Kbmq, Raman, G.
- Date
- 1997-12
- Publisher
- American Inst Physics
- Description
-
Detailed flow field measurements have been carried out for a turbulent circular jet perturbed by tabs and artificial excitation. Two ''delta...
Show moreDetailed flow field measurements have been carried out for a turbulent circular jet perturbed by tabs and artificial excitation. Two ''delta tabs'' were placed at the nozzle exit at diametrically opposite locations. The excitation condition involved subharmonic resonance that manifested in a periodic vortex pairing in the near flow field. While the excitation and the tabs independently increased jet spreading, a combination of the two diminished the effect. The jet spreading was most pronounced with the tabs but was reduced when excitation was applied to the tabbed jet. The tabs generated streamwise vortex pairs that caused a lateral spreading of the jet in a direction perpendicular to the plane containing the tabs. The excitation, on the other hand, organized the azimuthal vorticity into coherent ring structures whose evolution and pairing also increased entrainment by the jet. In the tabbed case, the excitation produced coherent azimuthal structures that were distorted and asymmetric in shape. The self-induction of these structures produced an effect that opposed the tendency for the lateral spreading of the streamwise vortex pairs. The passage of the distorted vortices, and their pairing, also had a cancellation effect on the time-averaged streamwise vorticity field. These led to the reduction in jet spreading. [S1070-6631(97)03012-2].
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- Title
- Fault detection and diagnosis in a food pasteurization process with hidden Markov models
- Creator
- Tokatli, F., Cinar, A.
- Date
- 2004-12
- Publisher
- CANADIAN SOC CHEMICAL ENGINEERING
- Description
-
Hidden Markov Models (HMM) are used to detect abnormal operation of dynamic processes and diagnose sensor and actuator faults. The method is...
Show moreHidden Markov Models (HMM) are used to detect abnormal operation of dynamic processes and diagnose sensor and actuator faults. The method is illustrated by monitoring the operation of a pasteurization plant and diagnosing causes of abnormal operation. Process data collected under the influence of faults of different magnitude and duration in sensors and actuators are used to illustrate the use of HMM in the detection and diagnosis of process faults. Case studies with experimental data from a high-temperature-short-time pasteurization system showed that HMM can diagnose the faults with certain characteristics such as fault duration and magnitude.
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- Title
- Aeroacoustic Characteristics of a Rectangular Multi-element Supersonic Jet Mixer-ejector Nozzle
- Creator
- Taghavi, R., Raman, G.
- Date
- 1997-10-23
- Publisher
- Academic Press Ltd
- Description
-
This paper provides a unique, detailed evaluation of the acoustics and aerodynamics of a rectangular multi-element supersonic jet mixer...
Show moreThis paper provides a unique, detailed evaluation of the acoustics and aerodynamics of a rectangular multi-element supersonic jet mixer-ejector noise suppressor. The performance of such mixer-ejectors is important in aircraft engine applications for noise suppression and thrust augmentation. In contrast to most prior experimental studies on ejectors that reported either aerodynamic of acoustic data, the present work documents both types of data. Information on the mixing, pumping, ejector wall pressure distribution, thrust augmentation and noise suppression characteristics of four simple, multi-element, jet mixer-ejector configurations is presented. The four configurations included the effect of ejector area ratio (AR = ejector cross-sectional area/total primary nozzle area) and the effect of non-parallel ejector walls. The configuration that produced the best noise suppression characteristics has also been studied in detail. The present results show that ejector configurations that produced the maximum pumping (secondary (induced) flow normalized by the primary flow) also exhibited the lowest wall pressures in the inlet region, and the maximum thrust augmentation. When cases having the same total mass flow were compared, one found that noise suppression trends corresponded with those for pumping (per unit secondary area). Surprisingly, the mixing (quantified by the peak Mach number, and flow uniformity) at the ejector exit exhibited no relationship to the noise suppression at moderate primary jet fully expanded M-j (the Mach number that would have been attained under isentropic expansion). However, the noise suppression dependence on the mixing was apparent at M-j = 1.6. The above observations are justified by noting that the mixing at the ejector exit is not a strong factor in determining the radiated noise when noise produced internal to the ejector dominates the noise field outside the ejector. (C) 1997 Academic Press Limited.
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- Title
- Measuring complexity in reactor networks with cubic autocatalytic reactions
- Creator
- Tatara, E., Birol, I., Cinar, A., Teymour, F.
- Date
- 2005-04-13
- Publisher
- AMER CHEMICAL SOC
- Description
-
Systems with high steady-state multiplicity and rich dynamic behavior are difficult to investigate using conventional reductionist methods. A...
Show moreSystems with high steady-state multiplicity and rich dynamic behavior are difficult to investigate using conventional reductionist methods. A network of more than five reactors hosting cubic autocatalytic reactions may potentially have more than 101 steady states and many distinct dynamic regimes, all for the same parameter set. This paper discusses how the static complexity of such systems can be measured to give a holistic picture. To achieve this, stochastic simulations were performed to statistically determine the bifurcation structure of the system, and the gathered information is summarized using a measure akin to fractal dimension. With this measure, the growth of static complexity is investigated as a function of the network size.
Endnote format citation for DOI:10.1021/ie049246t
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