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Title: Shock-induced Flow Resonance in Supersonic Jets of Complex Geometry
Creator: Raman, G.
Date: 1999-03
Publisher: American Inst Physics
Description: Jets with complex shock-cell structures exist in numerous technological applications. This paper describes a fundamental study of shock...
Show moreJets with complex shock-cell structures exist in numerous technological applications. This paper describes a fundamental study of shock-induced flow resonance (commonly referred to as "jet screech") in supersonic jets with spanwise nonuniform shock-cell structures. Experiments that involve flow visualization and detailed mapping of the near field reveal unsteady aspects of shock-induced flow resonances, mode transitions, and directivity of the radiated noise. The following important results about the role of spanwise nonuniform shock-cells emerged: (1) It is possible to have two coexisting, independent feedback loops at nonharmonically related frequencies and different spanwise modes. (2) The same type of spanwise asymmetric mode was produced by two entirely different source configurations. (3) Nozzle geometry significantly altered the intensity and directivity of screech and broadband shock noise. The results presented here provide considerable insight into the fluid dynamics and acoustics of jets with spanwise oblique shock-cell structures and provide grounds for believing that shock-induced noise can be controlled by tailoring nozzle geometry. (C) 1999 American Institute of Physics. [S1070-6631(99)00103-8].
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Title: Resonant interaction of a linear array of supersonic rectangular jets: An experimental study
Creator: Raman, G, Taghavi, R
Date: 1996-11-10
Publisher: CAMBRIDGE UNIV PRESS

Title: What's Congress Doing on Twitter?
Creator: Hemphill, Libby, Otterbacher, Jahna, Shapiro, Matthew A.
Date: 2013-10-23, 2012-10-23
Description: As Twitter becomes a more common means for officials to communicate with their constituents, it becomes more important that we understand how...
Show moreAs Twitter becomes a more common means for officials to communicate with their constituents, it becomes more important that we understand how officials use these communication tools. Using data from 380 members of Congress’ Twitter activity during the winter of 2012, we find that officials frequently use Twitter to advertise their political positions and to provide information but rarely to request political action from their constituents or to recognize the good work of others. We highlight a number of differences in communication frequency between men and women, Senators and Representatives, Republicans and Democrats. We provide groundwork for future research examining the behavior of public officials online and testing the predictive power of officials’ social media behavior.
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Title: INITIAL TURBULENCE EFFECT ON JET EVOLUTION WITH AND WITHOUT TONAL EXCITATION
Creator: Raman, G, Zaman, Kbmq, Rice, Ej
Date: 1989-07
Publisher: AMER INST PHYSICS

Title: Powered Resonance Tubes: Resonance Characteristics and Actuation Signal Directivity
Creator: Sarpotdar, S., Raman, G., Cain, A. B.
Date: 2005-12
Publisher: Springer
Description: The powered resonance tube (PRT) actuator and its variants are new developments in active flow control (AFC) technology. The PRT is attractive...
Show moreThe powered resonance tube (PRT) actuator and its variants are new developments in active flow control (AFC) technology. The PRT is attractive because it has no moving parts and can produce acoustic tones that have amplitudes greater than 150 dB over a large frequency bandwidth. The first part of this paper deals with the resonance characteristics of the PRT as a function of the operating parameters such as jet-to-tube spacing (Sp), tube depth (d), and nozzle pressure ratio (NPR). It was found that: (1) at low NPR (3.33), the PRT resonates at discrete combinations of spacing and depth. (2) Using theoretical estimates for predicting shock cell lengths, one could observe a correlation between the theoretical prediction for shock cell length and the spacing at which the PRT resonates. (3) At high NPR (4.29), for a fixed depth, the PRT resonates at virtually all spacings. (4) The frequency at which the PRT resonates remains approximately constant, regardless of spacing. The second part of the study focused on examining the directivity of the acoustic radiation from the PRT-significant for developing orientation strategies of the PRT with respect to the target flow in the end application. The directivity of the fundamental PRT tone and that of its harmonics were studied for a variety of resonance frequencies, both separately as well as cumulatively. It was found that the fundamental part of the actuation signal radiated predominantly in the downstream direction of the jet for low resonance frequencies. As the resonance frequency was increased from 3 to 12 kHz, the directivity changed from downstream of the jet to vertically upward, and finally upstream of the jet at the higher frequencies.
http://dx.doi.org/10.1007/s00348-005-0041-5
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Title: Intelligent real-time performance monitoring and quality prediction for batch/fed-batch cultivations
Creator: Undey, C., Tatara, E., Cinar, A.
Date: 2004-02-19
Publisher: ELSEVIER SCIENCE BV
Description: Supervision of batch bioprocess operations in real-time during the progress of a batch run offers many advantages over end-of-batch quality...
Show moreSupervision of batch bioprocess operations in real-time during the progress of a batch run offers many advantages over end-of-batch quality control. Multivariate statistical techniques such as multiway partial least squares (MPLS) provide an efficient modeling and supervision framework. A new type of MPLS modeling technique that is especially suitable for online real-time process monitoring and the multivariate monitoring charts are presented. This online process monitoring technique is also extended to include predictions of end-of-batch quality measurements during the progress of a batch run. Process monitoring, quality estimation and fault diagnosis activities are automated and supervised by embedding them into a real-time knowledge-based system (RTKBS). Interpretation of multivariate charts is also automated through a generic rule-base for efficient alarm handling. The integrated RTKBS and the implementation of MPLS-based process monitoring and quality control are illustrated using a fed-batch penicillin production benchmark process simulator.
Endnote format citation for DOI:10.1016/j.jbiotec.2003.10.004
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Title: SYNTHESIS OF MODEL-BASED CONTROLLERS FOR AN AUTOTHERMAL REACTOR
Creator: Chylla, R. W., Cinar, A.
Date: 1990-08
Publisher: CANADIAN SOC CHEMICAL ENGINEERING
Description: Model-based controllers for a bench scale autothermal tubular packed-bed reactor have been formulated using the Internal Model Control (IMC)...
Show moreModel-based controllers for a bench scale autothermal tubular packed-bed reactor have been formulated using the Internal Model Control (IMC) approach. The Structural Dominance Analysis technique has been used in developing the reduced-order models. Controller performance at robust and sensitive steady states have been assessed through simulations and experiments. Both PI and model-based controllers can regulate reactor operation at robust steady states, but only third order IMC controllers are able to regulate reactor operation at the sensitive steady state.
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Title: DYNAMIC ESTIMATION OF TEMPERATURE AND CONCENTRATION PROFILES IN A PACKED-BED REACTOR
Creator: Windes, L. C., Cinar, A., Ray, W. H.
Date: 1989
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Description: A two-dimensional nonlinear distributed-parameter optimal state estimation algorithm has been developed and applied to an exothermic packed...
Show moreA two-dimensional nonlinear distributed-parameter optimal state estimation algorithm has been developed and applied to an exothermic packed bed catalytic reactor. Temperature and concentration profiles were estimated from limited temperature and/or concentration measurements. Orthogonal collocation was used to solve the differential sensitivity and filtering equations. Both simulations and on-line experiments with a pilot scale packed bed reactor for the partial oxidation of methanol have been used to study the effects of measurement choice, model parameter errors, and unmeasured process disturbances. Excellent tracking of the reactor profiles was achieved with only one or two properly placed temperature sensors.
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Title: Criteria for the Existence of Helical Instabilities in Subsonic Inpinging Jets
Creator: Panickar, Praveen, Raman, Ganesh
Date: 2007-10
Publisher: American Inst Physics
Description: Understanding instability modes in impinging jets is important for the design of advanced vertical takeoff and landing aircraft. Our initial...
Show moreUnderstanding instability modes in impinging jets is important for the design of advanced vertical takeoff and landing aircraft. Our initial experimental observations of helical modes in subsonic impinging jets were contrary to expectations based on published stability theory results. This paper focuses on the curious phenomenon of the occurrence of these, hitherto unexpected, helical modes in subsonic impinging jets and provides, both experimental and analytical proof for their existence. Past results, based on linear stability analysis, that call for an absence of helical modes in cold, subsonic impinging jets have been re-examined to reconcile new experimental data. Based on this re-examination, a new threshold Mach number has been proposed, above which helical modes are permissible. The revised theory put forth in this paper indicates that the threshold Mach number for the existence of the helical mode depends on the jet temperature and that this threshold decreases as the jet temperature increases. This threshold Mach number has been experimentally verified for unheated jets. Additionally, the experimental results reveal that the threshold Mach number also depends on the stand-off distance. Finally, it has been shown that the experimentally obtained mean Strouhal numbers for the helical mode show excellent agreement with the Strouhal number of the least dispersive wave of the same mode calculated at various Mach numbers. The results presented here offer hope for better understanding of impinging jet instability modes. (C) 2007 American Institute of Physics.
http://dx.doi.org/10.1063/1.2798804
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Title: Control of grade transitions in distributed chemical reactor networks - An agent-based approach
Creator: Tetiker, M. Derya, Artel, Arsun, Teymour, Fouad, Cinar, Ali
Date: 2008-09-26
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Description: Supervision of distributed manufacturing processes producing different grades of a product requires intelligent reconfiguration strategies...
Show moreSupervision of distributed manufacturing processes producing different grades of a product requires intelligent reconfiguration strategies during grade transition phases to minimize off-spec production. Agent-based approaches are ideal for such problems and they provide flexible, robust, and emergent solutions during dynamically changing process conditions. Three different multi-layered multi-agent, frameworks are proposed for the supervision of grade transitions in autocatalytic reactor networks. The first framework is the centralized framework and it is useful for small-scale grade transitions where only a small region of the network needs to be reconfigured. Alternatively, the other two frameworks use a decentralized approach. The first decentralized framework implements genetic algorithms and the second one uses self-organizing heuristics and auctions for large-scale grade transitions. The case studies demonstrate that as the complexity of the reconfiguration problem increases, decentralized solutions perform more efficiently.
Endnote format citation for DOI:10.1016/j.compchemeng.2008.02.008
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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: FLIP-FLOP JET NOZZLE EXTENDED TO SUPERSONIC FLOWS
Creator: Raman, G, Hailye, M, Rice, Ej
Date: 1993-06
Publisher: AMER INST AERONAUT ASTRONAUT
Description: An experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic...
Show moreAn experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic to supersonic. Unsteady velocity and pressure measurements were made using hot wires, piezoresistive pressure transducers, and pitot probes. In addition, smoke flow visualization using high-speed photography was used to document the oscillation of the jet. For the subsonic flip-flop jet, it was found that the apparent time-mean widening of the jet was not accompanied by an increase in the mass flux. Fluidically oscillated jets up to a Mach number of about 0.5 have been reported before, but to our knowledge there is no information on fluidically oscillated supersonic jets. It was found that it is possible to extend the operation of these devices to supersonic flows. The streamwise velocity perturbation levels produced by this device were much higher than the perturbation levels that could be produced using conventional excitation sources such as acoustic drivers. In view of this ability to produce high amplitudes, the potential for using a small-scale fluidically oscillated jet as an unsteady excitation source for the control of shear flows in full-scale practical applications seems promising.
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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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