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Title: Cessation of Screech in Underexpanded Jets
Creator: Raman, G.
Date: 1997-04-10
Publisher: Cambridge Univ Press
Description: In significantly underexpanded jets, screech inherently ceases to exist. This paper studies screech cessation in a supersonic rectangular jet...
Show moreIn significantly underexpanded jets, screech inherently ceases to exist. This paper studies screech cessation in a supersonic rectangular jet and provides an explanation for its occurrence. Experimental data are presented for fully expanded Mach numbers, M-j, ranging from 1.1 to 1.9. Screech becomes unsteady beyond M-j = 1.65 and ceases to exist beyond M-j = 1.75. The reason for this cessation has remained a mystery, and this paper examines three suspects: (i) the theory of a frequency mismatch between screech tones and the band of the most-amplified jet instability waves, (ii) the notion that Mach disk formation disrupts the shock-cell structure and weakens the screech-producing shocks, and (iii) the idea that acoustic feedback and receptivity diminish at high levels of underexpansion. A thorough interrogation of experimental data shows that (i) is not the main cause of screech cessation here, (ii) plays an insignificant role, and (iii) appears to have been largely responsible for screech cessation. Cessation occurs because feedback to the jet lip is diminished due to excessive expansion of the jet boundary. Further, since the jet lip now reflects and scatters low intensity sound, the end result is poor receptivity at the initial shear layer. This theory is substantiated by the re-activation of screech when the nozzle lip thickness is made larger than the expanded jet boundary. Finally, increasing lip thickness is seen to produce a systematic shift (to higher M-j) of the onset of cessation. The results of this study are of direct relevance to the sonic fatigue problem in aircraft structures, because understanding screech helps prevent such damage.
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Title: HACCP with multivariate process monitoring and fault diagnosis techniques: application to a food pasteurization process
Creator: Tokatli, F., Cinar, A., Schlesser, J. E.
Date: 2005-06
Publisher: ELSEVIER SCI LTD
Description: Multivariate statistical process monitoring (SPM), and fault detection and diagnosis (FDD) methods are developed to monitor the critical...
Show moreMultivariate statistical process monitoring (SPM), and fault detection and diagnosis (FDD) methods are developed to monitor the critical control points (CCPs) in a continuous food pasteurization process. Multivariate SPM techniques effectively use information from all process variables to detect abnormal process behavior. Fault diagnosis techniques isolate the source cause of the deviation in process variable(s). The methods developed are illustrated by implementing them to monitor the critical control points and diagnose causes of abnormal operation of a high temperature short time (HTST) pasteurization pilot plant. The detection power of multivariate SPM and FDD techniques over univariate SPM techniques is shown and their integrated use to ensure the product safety and quality in food processes is demonstrated.
Endnote format citation for DOI:10.1016/j.foodcont.2004.04.008
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Title: Jet-cavity Interaction Tones
Creator: Raman, G., Bencic, Tj, Envia, E.
Date: 2002-08
Publisher: American Inst Aeronaut Astronaut
Description: A fundamental study of resonant tones produced by jet-cavity interaction over a wide range of flow conditions covering both subsonic and...
Show moreA fundamental study of resonant tones produced by jet-cavity interaction over a wide range of flow conditions covering both subsonic and supersonic speeds is described. Two significant findings emerge. For the jet-cavity configurations investigated, a suitably defined reduced frequency parameter allows for a global classification of all jet-cavity tones into two main types. For the first type, the reduced frequency depends on the jet Mach number, whereas for the second type, the reduced frequency is independent of the jet Mach number. We propose simple correlations for the frequency of both types of tones. Based on earlier research, we had expected that the traditional classifications of cavity flows into the open, transitional, or closed variety would be insensitive to small changes in Mach number and would depend primarily on the cavity's LID ratio. However, use of the novel high-resolution photoluminescent pressure sensitive paint shows that these classifications are actually quite sensitive to the jet Mach number for jet-cavity interactions. However, these classifications provide no guidance for determining tone type, amplitude, or frequency.
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Title: Controller performance assessment by frequency domain techniques
Creator: Kendra, S. J., Cinar, A.
Date: 1997-06
Publisher: ELSEVIER SCI LTD
Description: A system identification based method for assessing the performance of closed-loop systems is proposed, utilizing measures which coincide...
Show moreA system identification based method for assessing the performance of closed-loop systems is proposed, utilizing measures which coincide naturally with classical and modern frequency domain design specifications. Standard robust control system design methodologies seek to maximize closed-loop performance, subject to strict robustness requirements and include specifications for bandwidth and peak magnitude of the sensitivity and complementary sensitivity functions. Estimates of these transfer functions can be obtained by exciting the reference input with a zero mean, pseudo random binary sequence, observing the process output and error response, and developing a closed-loop model. Performance assessment is based on the comparison between the observed frequency response characteristics and the design specifications. Selection of appropriate model structures, experiment design, and model validation which will ensure reasonable estimates of the closed-loop transfer functions are considered in this paper. A case study involving the performance assessment of a packed bed tubular reactor control system is presented.
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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: Static and dynamic behavior of autocatalytic replicators in reactor networks
Creator: Tatara, E., Birol, I., Teymour, F., Cinar, A.
Date: 2004-07-07
Publisher: AMER CHEMICAL SOC
Description: The static and dynamic behavior of the autocatalytic reaction R + 2P --> 3P with decay P --> D is studied in networks of coupled continuous...
Show moreThe static and dynamic behavior of the autocatalytic reaction R + 2P --> 3P with decay P --> D is studied in networks of coupled continuous stirred tank reactors (CSTRs). Numerical bifurcation studies of the system are performed, resulting in rich steady-state bifurcation structures with multiple steady states and isolas. The heterogeneity of the networks is influenced by the number of reactors as well as the network topology. It is shown that the number of steady states of the network increases with heterogeneity, thereby allowing those autocatalytic species to exist in the network that would normally not exist in the homogeneous environment of a single CSTR. Spatial patterns of stable steady states are evident in reactor networks. Dynamic simulation studies are performed to illustrate the transition from one stable state configuration to another or from stable steady states to periodic regimes.
Endnote format citation for DOI:10.1021/ie030802d
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Title: Flow characteristics of a rectangular multielement supersonic mixer-ejector
Creator: Taghavi, R, Raman, G
Date: 1996-10
Publisher: AMER INST AERONAUT ASTRONAUT

Title: Jet Thrust Vectoring Using a Miniature Fluidic Oscillator
Creator: Raman, G., Packiarajan, S., Papadopoulos, G.
Date: 2005-03
Publisher: Royal Aeronautical Soc
Description: This paper presents a new approach to vectoring jet thrust using a miniature fluidic actuator that provided spatially distributed mass...
Show moreThis paper presents a new approach to vectoring jet thrust using a miniature fluidic actuator that provided spatially distributed mass addition. The fluidic actuators used had no moving parts and produced oscillatory flow with a square wave form at frequencies up to 1(.)6kHz. A subsonic jet with an exit diameter of 3(.)81cm was controlled using single and dual fluidic actuators, each with an equivalent circular diameter of 1(.)06mm. The fluidic nozzle was operated at pressures between 20(.)68 and 165(.)47kPa. The objectives of the present work included documentation of the actuation characteristics of fluidic devices, assessment of the effectiveness of fluidic devices for jet thrust vectoring, and evaluation of mass flow requirements for vectoring under various conditions. Measurements were made in the flow field using a pitot probe for the vectored and unvectored cases. Some acoustic measurements were made using microphones in the near-field and for selected cases particle image velocimetry (PIV) measurements were made. Thrust vectoring was obtained in low speed jets by momentum effects with fluidic device mass flow rates of only 2 x 10(-4) kg/sec (0-6% of main jet mass flow per fluidic oscillator). Although a single fluidic device produced vectoring of the primary jet, the dual fluidic device configuration (with two fluidic devices on either side of the jet exit) produced mass flux enhancement of 28% with no vectoring. Our results indicate that fluidic actuators have the potential for use in thrust vectoring, flow mixing and industrial flow deflection applications.
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Title: Statistical Monitoring of Complex Chemical Processes Using Agent-Based Systems
Creator: Perk, Sinem, Teymour, Fouad, Cinar, Ali
Date: 2010-06-02
Publisher: AMER CHEMICAL SOC
Description: It is highly desirable to have a statistical process monitoring (SPM) system that detects the abnormalities in process operations quickly with...
Show moreIt is highly desirable to have a statistical process monitoring (SPM) system that detects the abnormalities in process operations quickly with as few missed and false alarms as possible while the process operates under various operating conditions An agent-based combined monitoring and fault detection framework is proposed in this study. In this framework, different SPM techniques compete with and complement each other to enhance detection speed and accuracy. SPM techniques from literature such as principal component analysis (PCA), multiblock PCA (MBPCA), and dynamic PCA (DPCA) techniques are implemented in this agent-based process supervision system An agent performance assessment and agent management layer provides dynamic adaptation of the supervision system and improves the performance of SPM The statistical information coming from each of the statistical techniques is summarized through a consensus mechanism The performance of the agent-based consensus mechanism using different consensus criteria is tested for system disturbances of various magnitudes The effectiveness of the proposed agent-based framework with different consensus criteria is evaluated based on fault detection times and missed alarm rates and the adaptation of the supervision system is illustrated
Endnote format citation for DOI:10.1021/ie901368j
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Title: Integration of multivariate SPM and FDD by parity space technique for a food pasteurization process
Creator: Kosebalaban, F., Cinar, A.
Date: 2001-03-15
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Description: Multivariate statistical process monitoring (MSPM), contribution plots, and parity space fault diagnosis (FD) techniques are used to detect...
Show moreMultivariate statistical process monitoring (MSPM), contribution plots, and parity space fault diagnosis (FD) techniques are used to detect abnormal operation of dynamic processes and diagnose sensor and actuator faults. The methods are illustrated by monitoring the critical control points (CCP) and diagnosing causes of abnormal operation of a pilot pasteurization plant. An empirical model of the process is developed by using subspace state space system identification methods and normal process data. The process data collected under the influence of different magnitude and duration of faults in sensors and actuators are used to validate the MSPM and FD techniques. T-2 and squared prediction error (SPEN) charts are used as MSPM charts. A parity space technique for dynamic stochastic systems and dynamic trends in contribution plots of T-2 and SPEN statistics are used for FD. The detection and FD by these techniques show significant improvements over univariate methods.
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Title: Diagnosis of process disturbances by statistical distance and angle measures
Creator: Raich, A., Cinar, A.
Date: 1997
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Description: Disturbance and fault diagnosis techniques that rely on statistical methods traditionally utilize distance based discrimination functions....
Show moreDisturbance and fault diagnosis techniques that rely on statistical methods traditionally utilize distance based discrimination functions. Complementary information is contained in the angular relations between data clusters representing process operations under various disturbances. A novel disturbance diagnosis approach is presented based on angle discriminants. The diagnosis method is successful in cases where distance based discrimination is not very accurate. The methodology is illustrated by diagnosing various disturbances in the Tennessee Eastman process and compared with the diagnosis utilizing distance based algorithms.
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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: 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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