TY - JOUR TI - Impingement heat transfer on a target plate with film cooling holes AU - Ekkad, S.V. AU - Huang, Y. AU - Han, J.-C. T2 - Journal of thermophysics and heat transfer AB - Detailedheat-transferdistributionsarepresentedforanarray ofjetsimpinging onatargetplatewithastaggered array of e lm cooling holes. The e ow impinges on the target plate through a row of impingement holes and exits the channel from the sides and through the e lm holes. The top plate has 12 rows of impingement holes, and the target platehas11 rows ofe lm holes. Theimpingementholes and the e lm holes have thesame diameterandarestaggered such that the air from the impingement hole does not exit directly through the e lm hole. The setup is typical of an impingement/transpiration cooled gas turbine airfoil. Additional to the e ow exiting through the e lm holes, there is an exit for crosse ow after impingement. The exit opening of the impingement channel is changed to provide three different spent air exit directions. The detailed heat-transfer coefe cient distributions were measured using a transient liquid crystal technique. Results are presented for a range of jet Reynolds numbers between 0.4 ££ 10 3 and 2.0 ££ 10 4 with different exit e ow orientations. Heat-transfer results for the target plate with e lm holes are compared with those without e lm holes under the same e ow conditions. Film extraction reduces crosse ow effects on jet impingement heat transfer. However, overall averaged heat-transfer rates on the target surface appear less affected by presence of e lm hole for cases where the crosse ow is generated in only one direction. DA - 1999/// PY - 1999/// DO - 10.2514/2.6471 VL - 13 IS - 4 SP - 522-528 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033355454&partnerID=MN8TOARS ER - TY - JOUR TI - Heat transfer distributions on a cylinder with simulated thermal barrier coating spallation AU - Ekkad, S.V. AU - Han, J.-C. T2 - Journal of Thermophysics and Heat Transfer AB - Detailed heat transfer distributions are presented over a turbine blade leading-edge model with simulated thermal barrier coating spoliation. The blade leading-edge region is simulated by a cylinder in a crossflow with a tailboard. The heat transfer measurements are presented only on one side of the front half of the cylinder. The simulated spoliation cavities are rectangular in shape and have rounded corners. The effect of a spallation cavity is studied at four different locations (0-20, 10-30, 20-40, and 35-55 deg). Two different cavity depths are studied at each location to understand the effect of spallation depth on local heat transfer distributions. The effect of free stream turbulence on detailed heat transfer is also presented for each case. Detailed heat transfer measurements are obtained using a transient liquid crystal technique. Detailed heat transfer distributions present the local high-heat transfer and low-heat transfer regions inside and outside the spallation. Results show that spallations can enhance heat transfer up to two times compared with that for a smooth surface. Results also show that the spallation location and depth have a strong effect on local heat transfer distributions on the leading edge. An increase in freestream turbulence further increases the heat transfer coefficients caused by the spallation. Tt Tu Tw = Too = t = Nomenclature DA - 1999/// PY - 1999/// DO - 10.2514/2.6403 VL - 13 IS - 1 SP - 76-81 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032739395&partnerID=MN8TOARS ER - TY - JOUR TI - Effect of unsteady wake with trailing edge coolant ejection on film cooling performance for a gas turbine blade AU - Du, H. AU - Ekkad, S.V. AU - Han, J.-C. T2 - Journal of Turbomachinery AB - The effect of unsteady wakes with trailing edge coolant ejection on surface heat transfer coefficients and film cooling effectiveness is presented for a downstream film-cooled turbine blade. The detailed heat transfer coefficient and film effectiveness distributions on the blade surface are obtained using a transient liquid crystal technique. Unsteady wakes are produced by a spoked wheel-type wake generator upstream of the five-blade linear cascade. The coolant jet ejection is simulated by ejecting coolant through holes on the hollow spokes of the wake generator. For a blade without film holes, unsteady wake increases both pressure side and suction side heat transfer levels due to early boundary layer transition. Adding trailing edge ejection to the unsteady wake further enhances the blade surface heat transfer coefficients particularly near the leading edge region. For a film-cooled blade, unsteady wake effects slightly enhance surface heat transfer coefficients but significantly reduces film effectiveness. Addition of trailing edge ejection to the unsteady wake has a small effect on surface heat transfer coefficients compared to other significant parameters such as film injection, unsteady wakes, and grid generated turbulence, in that order. Trailing edge ejection effect on film effectiveness distribution is stronger than on the heat transfer coefficients. DA - 1999/// PY - 1999/// DO - 10.1115/1.2841337 VL - 121 IS - 3 SP - 448-455 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032704069&partnerID=MN8TOARS ER - TY - CONF TI - Influence of cross-flow induced swirl and impingement on heat transfer in an internal coolant passage of a turbine airfoil AU - Ekkad, S.V. AU - Pamula, G. AU - Acharya, S. C2 - 1999/// C3 - American Society of Mechanical Engineers, Heat Transfer Division, (Publication) HTD DA - 1999/// VL - 364-1 SP - 227-233 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033313153&partnerID=MN8TOARS ER - TY - JOUR TI - Cold forging tribo-test based on variation of deformation patterns at the tool-work piece interface AU - Ngaile, Gracious AU - Saiki, Hiroyuki T2 - Journal of tribologist and lubrication engineers (STLE) DA - 1999/2// PY - 1999/2// SP - 23–31 ER - TY - CONF TI - Multidiscipline Analysis of a Fatal LPG Tank Rupture AU - Ross, B. AU - Lange, C. AU - Eischen, J.W. T2 - Meeting of the Society for Machinery Failure Prevention Technology C2 - 1999/// C3 - Proceedings of the 53rd Meeting of the Society for Machinery Failure Prevention Technology CY - Virginia Beach, VA DA - 1999/// PY - 1999/4/19/ ER - TY - CONF TI - The Mechanics of Removing Staple Crimp AU - Bauer-Kurz, I. AU - Eischen, J.W. T2 - Gordon Research Conference C2 - 1999/7/4/ CY - New London, NH DA - 1999/7/4/ PY - 1999/7/4/ ER - TY - JOUR TI - Compression fatigue of a cellular Al alloy AU - Sugimura, Y AU - Rabiei, A AU - Evans, A.G AU - Harte, A.M AU - Fleck, N.A T2 - Materials Science and Engineering: A AB - The cyclic compression of a cellular Al alloy has been evaluated. Plastic compression occurs beyond a critical number of cycles, NT. At NNT, strain accumulates rapidly and preferentially within deformation bands, until the densification strain has been reached. The bands form preferentially from large cells in the ensemble. Such cells develop plastically buckled membranes which experience large strains upon further cycling, which lead to cracks. The cracks, once formed, result in rapid cyclic straining. This feature controls the fatigue life. DA - 1999/8// PY - 1999/8// DO - 10.1016/s0921-5093(99)00147-1 VL - 269 IS - 1-2 SP - 38-48 J2 - Materials Science and Engineering: A LA - en OP - SN - 0921-5093 UR - http://dx.doi.org/10.1016/s0921-5093(99)00147-1 DB - Crossref KW - cellular Al alloy KW - foam KW - fatigue KW - compression KW - strain mapping ER - TY - JOUR TI - Microstructure, deformation and cracking characteristics of thermal spray ferrous coatings AU - Rabiei, A AU - Mumm, D.R AU - Hutchinson, J.W AU - Schweinfest, R AU - Rühle, M AU - Evans, A.G T2 - Materials Science and Engineering: A AB - The microstructure and local mechanical characteristics of thermal spray ferrous coatings have been determined. The emphasis has been on coatings made by the high velocity oxyfuel (HVOF) process, especially the role of Al alloy additives. The oxide phase present in the material and preferred pathways for local cracking and separation have been determined. Thin intersplat oxide layers emerge as preferential sites. These oxides are amorphous and the cracks extend along the oxide/α–Fe interfaces with low local fracture toughness, in the range 0.2–1 MPa√m. These low toughness pathways govern coating deterioration. DA - 1999/8// PY - 1999/8// DO - 10.1016/s0921-5093(99)00132-x VL - 269 IS - 1-2 SP - 152-165 J2 - Materials Science and Engineering: A LA - en OP - SN - 0921-5093 UR - http://dx.doi.org/10.1016/s0921-5093(99)00132-x DB - Crossref KW - thermal spray coating KW - local fracture toughness KW - indentation test KW - high velocity oxyfuel process KW - plasma transfer wire arc process KW - atomic force microscopy ER - TY - CONF TI - Feedback control of a planar manipulator with an unactuated elastically mounted end effector AU - Reyhanoglu, M. AU - Cho, S. AU - McClamroch, N.H. T2 - 1999 IEEE International Conference on Robotics and Automation AB - We study feedback control laws that can stabilize an equilibrium position of an underactuated planar PPR robot manipulator. The manipulator operates in a horizontal plane, and it consists of two actuated prismatic links, an actuated revolute link, and an unactuated end effector that is elastically mounted on the third link. The fact that the end effector is unactuated and is elastically mounted on the manipulator, and thus can be controlled only through coupling with the manipulator dynamics, provides a major obstacle to control design for this problem. The control objective is to design a feedback controller that can achieve arbitrary positioning and arbitrary attitude of the end effector while suppressing any motion of the end effector relative to the third link. A nonlinear control model is constructed for this underactuated manipulator and a time-invariant discontinuous feedback law is constructed that achieves the objectives with exponential convergence rates. The effectiveness of the proposed feedback law is illustrated through simulations. C2 - 1999/// C3 - Proceedings 1999 IEEE International Conference on Robotics and Automation CY - Detroit, MI DA - 1999/// PY - 1999/5/10/ DO - 10.1109/ROBOT.1999.774022 VL - 4 SP - 2805–2810 PB - IEEE ER - TY - CONF TI - Feedback stabilization for a special class of underactuated mechanical systems AU - Reyhanoglu, M. AU - Cho, S. AU - McClamroch, N.H. T2 - 38th IEEE Conference on Decision and Control AB - We study feedback controllers that can stabilize the equilibrium of a special class of underactuated mechanical systems, namely mechanical systems with several directly actuated degrees of freedom and a single unactuated degree of freedom that must be controlled through the system coupling. Theoretical controllability and stabilizability results for a large class of such underactuated mechanical systems have been developed in our previous work. Here we propose feedback controllers so that a closed loop equilibrium is globally attractive. The proposed construction procedure depends on selection of a scalar configuration variable corresponding to a directly actuated degree of freedom so that the dynamics of the unactuated degree of freedom, after a rational coordinate transformation, has a special form. The construction procedure is introduced, and a number of possible modifications are suggested. This construction procedure unifies controllers that we have developed for particular examples, including an underactuated ship, a planar rigid body containing an unactuated internal degree of freedom, a planar manipulator with an unactuated elastically mounted end effector, and an aerospace vehicle with an unactuated internal degree of freedom. C2 - 1999/// C3 - Proceedings of the 38th IEEE Conference on Decision and Control CY - Phoenix, AZ DA - 1999/// PY - 1999/12/7/ DO - 10.1109/CDC.1999.830262 VL - 2 SP - 1658–1663 PB - IEEE ER - TY - CONF TI - Feedback control for planar maneuvers of an aerospace vehicle with an unactuated internal degree of freedom AU - Reyhanoglu, M. AU - Cho, S. AU - McClamroch, N.H. T2 - 1999 American Control Conference AB - We study feedback control laws that enable an aerospace vehicle to perform planar maneuvers. We make several key assumptions including: (1) maneuvers are planar, (2) a complete set of vehicle control forces and moments is available, (3) the vehicle is a rigid body with a single unactuated internal degree of freedom. The control objective is to design a feedback controller so that the controlled vehicle accomplishes a given planar maneuver, that is a change in the translational velocity vector and the attitude of the vehicle, while rapidly attenuating any relative motion of the internal degree of freedom. A time-invariant discontinuous feedback law is constructed that achieves these control objectives with exponential convergence rates. The effectiveness of the proposed feedback law is illustrated through a simulation example. C2 - 1999/// C3 - Proceedings of the 1999 American Control Conference (Cat. No. 99CH36251) CY - San Diego, CA DA - 1999/// PY - 1999/6/2/ DO - 10.1109/acc.1999.782402 PB - IEEE SN - 0780349903 UR - http://dx.doi.org/10.1109/acc.1999.782402 ER - TY - CONF TI - Fluid-structure-thermal interaction using a loose coupling algorithm and adaptive unstructured grids AU - Lohner, R. AU - Yang, C. AU - Cebral, J. AU - Baum, J.D. AU - Mestreau, E. AU - Luo, H. AU - Pelessone, D. AU - Charman., C. T2 - International Symposium on Computational Methods for Fluid-Structure Interaction A2 - Kvamsdal, T C2 - 1999/// C3 - Computational methods for fluid-structure interaction : proceedings from the International Symposium on Computational Methods for Fluid-Structure Interaction, 15-17 February 1999 CY - Trondheim DA - 1999/// PY - 1999/2/15/ DO - 10.2514/6.1998-2419 SP - 109–120 PB - Tapir Press ER - TY - JOUR TI - Dynamics and control of a class of underactuated mechanical systems AU - Reyhanoglu, M. AU - van der Schaft, A. AU - Mcclamroch, N.H. AU - Kolmanovsky, I. T2 - IEEE Transactions on Automatic Control AB - This paper presents a theoretical framework for the dynamics and control of underactuated mechanical systems, defined as systems with fewer inputs than degrees of freedom. Control system formulation of underactuated mechanical systems is addressed and a class of underactuated systems characterized by nonintegrable dynamics relations is identified. Controllability and stabilizability results are derived for this class of underactuated systems. Examples are included to illustrate the results; these examples are of underactuated mechanical systems that are not linearly controllable or smoothly stabilizable. DA - 1999/// PY - 1999/// DO - 10.1109/9.788533 VL - 44 IS - 9 SP - 1663-1671 J2 - IEEE Trans. Automat. Contr. OP - SN - 0018-9286 UR - http://dx.doi.org/10.1109/9.788533 DB - Crossref KW - controllability KW - mechanical systems KW - nonlinear control KW - stabilizability KW - underactuated ER - TY - JOUR TI - The mechanism of two-dimensional pocket formation in lean premixed methane-air flames with implications to turbulent combustion AU - Chen, J.H. AU - Echekki, T. AU - Kollmann, W. T2 - Combustion and Flame AB - The mechanism of unburnt pocket formation in an unsteady two-dimensional premixed lean methane-air flame is investigated using direct numerical simulations. Theoretical results for nonlinear diffusion equations combined with analytical examples are used to interpret some of the results. Flame structure and propagation show three distinct stages of pocket formation: (1) flame channel closing involving head-on quenching of flames, (2) cusp recovery, and (3) pocket burnout. The flame channel closing and subsequent pocket burnout are mutual annihilation events that feature curvature, diffusion normal to the flame front, unsteady strain rate effects, and singularities in flame propagation and stretch rate. The results show that during channel closing and pocket burnout thermo-diffusive and chemical interactions result in the acceleration of the flames prior to annihilation; the time scales associated with the final stage of mutual annihilation and the initial stage of cusp recovery are significantly smaller than diffusive and convective time scales. As in earlier one-dimensional studies, the acceleration is attributed to enhanced diffusion and reaction rates, modifications to species profiles leading to shifts in balance between diffusion and reaction, and vanishing species and thermal gradients at the location in the channel where the pocket pinches off. Flame propagation and stretch rate are singular at this location. Enhanced radical production is initiated by a reversal of diffusion of H2 towards the reaction zone during the early stages of thermo-diffusive interactions. Peak radical concentrations resulting from flame channel closing and pocket burnout exceed peak laminar values by as much as 25%. After the merging of the fuel consumption layers, radical production and flame structure shifts more towards an H2/CO/O2 system at the expense of hydrocarbon reactions. Species thermodiffusive interaction times are shorter than the unstrained one-dimensional counterpart due to unsteady strain and convection. Curvature effects on the flame propagation are prominent during pocket burnout and cusp recovery. The recovery stage shows strong dependence on diffusion of radicals left from the channel closing stage. This diffusion is amplified by the strong curvature of the flame cusp. DA - 1999/// PY - 1999/// DO - 10.1016/S0010-2180(98)00026-1 VL - 116 IS - 1-2 SP - 15-48 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0004781216&partnerID=MN8TOARS ER - TY - JOUR TI - Analysis of the contribution of curvature to premixed flame propagation AU - Echekki, T. AU - Chen, J.H. T2 - Combustion and Flame AB - Modern spark ignition internal combustion (IC) engines rely on highly diluted fuel-air mixtures to achieve high brake thermal efficiencies. To support this, new engine designs have introduced high stroke-to-bore ratios and cylinder head designs that promote high tumble flow and turbulence intensities. However, mixture dilution through exhaust gas recirculation (EGR) is limited by combustion instabilities manifested in the form of cycle-to-cycle variability. Propane has been observed to have superior EGR dilution tolerance than gasoline, which makes it a very competitive low-carbon fuel for the new IC engines without sacrificing efficiency. Two-dimensional direct numerical simulations (DNS) are performed with detailed chemistry to study and contrast the effect of turbulence intensity and dilution on propane and iso-octane premixed flames at high pressure conditions similar to those in-cylinder. A new reduced mechanism for propane consisting of 53 transported species and 17 quasi-steady state species is developed based on a previously published mechanism and used in these simulations. Three levels of turbulence intensity and two levels of exhaust gas dilution are chosen based on conditions relevant to IC engine operation. The DNS results are analyzed based on the evolution of the flame surface area and the statistics of its driving terms, which are found to be similar for both fuels when there is no dilution but considerably different under high dilution. The analysis of the DNS data provides fundamental insights into the underlying mechanisms for improved stability under dilution. DA - 1999/// PY - 1999/// DO - 10.1016/S0010-2180(99)00006-1 VL - 118 IS - 1-2 SP - 308-311 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032912357&partnerID=MN8TOARS ER - TY - JOUR TI - The numerical simulation of strongly unsteady flow with hundreds of moving bodies AU - Lohner, R AU - Yang, C AU - Baum, JD AU - Luo, H AU - Pelessone, D AU - Charman, CM T2 - INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS AB - A methodology for the simulation of strongly unsteady flows with hundreds of moving bodies has been developed. An unstructured grid, high-order, monotonicity preserving, ALE solver with automatic refinement and remeshing capabilities was enhanced by adding equations of state for high explosives, deactivation techniques and optimal data structures to minimize CPU overheads, automatic recovery of CAD data from discrete data, two new remeshing options, and a number of visualization tools for the preprocessing phase of large runs. The combination of these improvements has enabled the simulation of strongly unsteady flows with hundreds of moving bodies. Several examples demonstrate the effectiveness of the proposed methodology. Copyright © 1999 John Wiley & Sons, Ltd. DA - 1999/9/15/ PY - 1999/9/15/ DO - 10.1002/(sici)1097-0363(19990915)31:1<113::aid-fld958>3.0.co;2-q VL - 31 IS - 1 SP - 113-+ SN - 0271-2091 KW - moving bodies KW - numerical simulation KW - unsteady flows ER - TY - JOUR TI - Gliding arc gas discharge AU - Fridman, A AU - Nester, S AU - Kennedy, LA AU - Saveliev, A AU - Mutaf-Yardimci, O T2 - PROGRESS IN ENERGY AND COMBUSTION SCIENCE AB - The sliding arc discharge starts at the shortest distance between the electrodes, then moves with the gas flow at a velocity of about 10 m/s and the length l of the arc column increases together with the voltage. When the length of the gliding arc exceeds its critical value lcrit, heat losses from the plasma column begin to exceed the energy supplied by the source, and it is not possible to sustain the plasma in a state of thermodynamic equilibrium. As a result, a fast transition into a non-equilibrium phase occurs. The discharge plasma cools rapidly to a gas temperature of about T0=1000 K and the plasma conductivity is maintained by a high value of the electron temperature Te=1 eV (about 11 000 K). After this fast transition, the gliding arc continues its evolution, but under non-equilibrium conditions (Te≫T0). The specific heat losses Wcrit in this regime are much smaller than in the equilibrium regime (numerically about three times less). The discharge length increases up to a new critical value of l≅3lcrit. The main part of the gliding arc power (up to 75–80%) can be dissipated in the non-equilibrium zone. After the decay of the non-equilibrium discharge, the evolution repeats from the initial break-down. This permits the stimulation of chemical reactions in regimes quite different from conventional combustion and environmental situations. It provides an alternative approach to addressing energy conservation and environmental control. In the first part of this paper, the gas discharge physics are described. The second part reviews the chemical reaction in the gliding arc plasma and some possible applications. DA - 1999/// PY - 1999/// DO - 10.1016/s0360-1285(98)00021-5 VL - 25 IS - 2 SP - 211-231 SN - 0360-1285 ER - TY - JOUR TI - Cloning and expression of guinea pig MUC2 and MUC5AC genes. AU - Li, Y. AU - Greenfeder, S. AU - Martin, L. D. AU - Minnicozzi, M. AU - Voynow, J. A. AU - Adler, K. B. T2 - American Journal of Respiratory and Critical Care Medicine DA - 1999/// PY - 1999/// VL - 159 SP - A852 ER - TY - JOUR TI - Precision cylindrical face grinding AU - Shih, AJ AU - Lee, NL T2 - PRECISION ENGINEERING-JOURNAL OF THE AMERICAN SOCIETY FOR PRECISION ENGINEERING AB - The mathematical models and experimental validations of precision cylindrical face grinding using a narrow ring superabrasive wheel are presented. The high pressure seal in diesel engine fuel systems demands the μm-scale form tolerance specifications and has driven the development of precision face grinding using the superabrasive wheel. Two mathematical models were developed: one was applied to predict the convex or concave face profile and another was used to simulate the abrasive trajectories, which become the cross-hatch grinding marks on the ground face. Cylindrical face grinding experiments were conducted. Experimental measurements of face profile and abrasive trajectories were used to validate the theoretical results. For high-pressure sealing surfaces, the height of face profile and grinding trajectories were two critical characteristics for design and manufacturing. Two design tools, a linear approximate solution for the profile height and an atlas for grinding trajectories, were developed to assist the selection of process parameters for the machine setup. DA - 1999/7// PY - 1999/7// DO - 10.1016/S0141-6359(99)00008-2 VL - 23 IS - 3 SP - 177-184 SN - 0141-6359 KW - precision grinding KW - cylindrical grinding KW - face grinding ER - TY - CHAP TI - Dynamic grid adaption and grid quality AU - McRae, D. S. AU - Laflin, K. R. T2 - Handbook of grid generation A2 - J. F. Thompson, B. Soni A2 - Weatherill, N. P. CN - QA377 .H3183 1999 PY - 1999/// SP - 34/1-3433 PB - Boca Raton, FL: CRC Press ER - TY - JOUR TI - Evaporative air conditioning in a manufacturing facility AU - Brown, CD AU - Leach, JW AU - Terry, SD T2 - ENERGY ENGINEERING AB - ABSTRACT A case study evaluates the economics of installing a staged evaporative cooling system in a factory in the southeastern USA. The effective temperature at the plant floor is predicted for each working hour from typical meteorological year data. The analysis accounts for internal loads and moisture evaporated by the manufacturing process. Worker productivity is estimated from the effective temperature. Several building loads and evaporative cooling system designs are considered. The results show that evaporative air conditioning can improve worker productivity and profit margins in manufacturing facilities that have high internal loads, high ventilation requirements, or other plant-specific conditions that would make conventional air conditioning uneconomical. DA - 1999/// PY - 1999/// DO - 10.1080/01998595.1999.10530467 VL - 96 IS - 4 SP - 40-58 SN - 0199-8595 ER - TY - JOUR TI - Estimation of the effective permeability in magnetorheological fluids AU - Simon, TM AU - Ito, K AU - Banks, HT AU - Reitich, F AU - Jolly, MR T2 - JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES AB - Magnetorheological (MR) fluids constitute examples of controllable ("smart") fluids, whose Theological properties vary in response to an applied magnetic field. These fluids typically consist of micron-sized, magnetizable particles dispersed in a nonpermeable carrier fluid. The essential characteristic of MR fluids is that they may be continuously and reversibly varied from a state of free flowing liquids in the absence of an applied magnetic field to that of stiff semi-solids in a moderate field. Understanding the magnetic properties of MR fluids is crucial to the design of MR fluid-based devices and it also provides valuable insight into the character of the microstructure responsible for their field-dependent rheology. Prediction of the overall magnetic properties of MR composites is a challenging task, however, due to the highly nonlinear and strongly spatially variable nature of the magnetization of the constituents. In this paper we propose a model for this behavior that is based on the mathematical theory of homogenization. We derive effective equations that govern the magnetic response of (periodically arranged) particle-chains through magnetic saturation. Comparisons of numerical results for these equations with experimental data show good agreement which suggests that our approach could be useful in the design of improved MR fluids. DA - 1999/11// PY - 1999/11// DO - 10.1106/6KW6-7V12-NRQ3-BW6V VL - 10 IS - 11 SP - 872-879 SN - 1045-389X ER - TY - JOUR TI - Study of transient effects on the extinction limits of an unsteady counterflow diffusion flame AU - Decroix, ME AU - Roberts, WL T2 - COMBUSTION SCIENCE AND TECHNOLOGY AB - Extinction strain rates in unsteady methane- and propane-air counterflow diffusion flames were experimentally measured as a function of initial strain rate, oscillation frequency, and amplitude of the imposed fluctuation. The maximum strain rate was found to occur at a temporal phase corresponding to the maximum velocity for the diluted methane flame. However, for the propane flame the maximum strain rate occurred when the imposed velocity fluctuation was zero and decreasing. Above an oscillation frequency of 100 Hz, the diluted methane flame was able to survive peak strain rates exceeding the steady extinction strain rate. The minimum air velocity in the pure methane and propane flames was negative for all cases studied, which is most likely responsible for flame extinction at low frequencies and initial strain rates. However, at high initial strain rates and forcing frequencies peak unsteady strain rates at extinction approached the steady extinction strain rate and flow reversal was much less significant. DA - 1999/// PY - 1999/// DO - 10.1080/00102209908924208 VL - 146 IS - 1-6 SP - 57-84 SN - 0010-2202 ER - TY - JOUR TI - Influence of the grinding wheel in the ductile grinding of brittle materials: Development and verification of kinematic based model AU - Miller, MH AU - Dow, TA T2 - JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME AB - Empirical evidence has shown that grinding wheel characteristics significantly affect performance in the grinding of brittle materials. In this research a grit depth of cut model was developed based on a kinematic simulation of the grinding process. The model describes the relationships between grinding wheel parameters (grit size, concentration, binder modulus) and chip thickness and area. It was corroborated by the measurement of number of cutting grits in tests using a fly wheel with small abrasive area. Based on this grit depth of cut model, the “critical depth of cut” model for the grinding of brittle materials was modified to include wheel parameter effects. The new critical depth of cut model was tested using “crossfeed” experiments. Although the theoretical and experimental results show less agreement than for the grit depth of cut model, the model equations provide guidelines for choosing wheel specifications. DA - 1999/11// PY - 1999/11// DO - 10.1115/1.2833087 VL - 121 IS - 4 SP - 638-646 SN - 1087-1357 ER - TY - JOUR TI - Weighted-residual discretization for uniform damping and uniform stiffening of structural systems AU - Silverberg, L AU - Washington, G T2 - JOURNAL OF GUIDANCE CONTROL AND DYNAMICS DA - 1999/// PY - 1999/// DO - 10.2514/2.7638 VL - 22 IS - 4 SP - 614-618 SN - 0731-5090 ER - TY - JOUR TI - Simulations of particle dynamics in magnetorheological fluids AU - Ly, HV AU - Reitich, E AU - Jolly, MR AU - Banks, HT AU - Ito, K T2 - JOURNAL OF COMPUTATIONAL PHYSICS AB - We present particle dynamics simulations for the response of magnetorheological (MR) fluids upon application of a magnetic field. The particles motion is considered to be governed by magnetic, hydrodynamic, and repulsive interactions. Fluid-particle interactions are accounted for via Stokes' drag while inter-particle repulsions are modeled through approximate hard-sphere rejections. In accordance with their greater significance, on the other hand (linear) magnetic interactions are fully simulated. The time evolution is considered to be magnetically quasi-static and magnetostatic forces are derived from the solution of (steady) Maxwell's equations, recomputed at each instant in time. For this we use a potential theoretic formulation where the boundary integral equations are solved with a fast multipole approach. We show that the resulting numerical codes can be effectively used to study a number of experimental observables such as effective magnetic permeabilities and response time-scales which are of crucial importance in the design of MR fluids. DA - 1999/10/10/ PY - 1999/10/10/ DO - 10.1006/jcph.1999.6335 VL - 155 IS - 1 SP - 160-177 SN - 1090-2716 KW - particle dynamics KW - fast multipole method KW - MR fluids KW - effective permeability KW - response time scale ER - TY - JOUR TI - Pendeo-epitaxy versus lateral epitaxial overgrowth of GaN: A comparative study via finite element analysis AU - Zheleva, T. S. AU - Ashmawi, W. M. AU - Jones, K. A. T2 - Physica Status Solidi. A, Applications and Materials Science DA - 1999/// PY - 1999/// VL - 176 IS - 1 SP - 545-551 ER - TY - JOUR TI - Paraboloidally shaped antenna possessing pointing and beam-width control AU - Stanley, RJ AU - Silverberg, LM T2 - JOURNAL OF SPACECRAFT AND ROCKETS AB - Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields. DA - 1999/// PY - 1999/// DO - 10.2514/2.3487 VL - 36 IS - 5 SP - 736-744 SN - 0022-4650 ER - TY - JOUR TI - Ferroelectric properties of new chemical solution derived SBT thin films for non-volatile memory devices AU - Kim, SH AU - Kim, DJ AU - Im, J AU - Kim, CE AU - Kingon, AI T2 - JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY DA - 1999/10// PY - 1999/10// DO - 10.1023/A:1008748718231 VL - 16 IS - 1-2 SP - 57-63 SN - 1573-4846 KW - ferroelectricity KW - chemical solution KW - alkanolamine KW - SBT KW - imprint KW - fatigue ER - TY - JOUR TI - Electric current-induced stresses at the crack tip in conductors AU - Cai, GX AU - Yuan, FG T2 - INTERNATIONAL JOURNAL OF FRACTURE DA - 1999/// PY - 1999/// DO - 10.1023/A:1018670829822 VL - 96 IS - 3 SP - 279-301 SN - 0376-9429 ER - TY - JOUR TI - Analytical investigation of forced convection from a flat plate enhanced by a porous substrate AU - Kuznetsov, AV T2 - ACTA MECHANICA DA - 1999/// PY - 1999/// DO - 10.1007/bf01179210 VL - 137 IS - 3-4 SP - 211-223 SN - 0001-5970 ER - TY - JOUR TI - Studies on lifted jet flames in coflow: The stabilization mechanism in the near- and far-fields AU - Brown, CD AU - Watson, KA AU - Lyons, KM T2 - FLOW TURBULENCE AND COMBUSTION DA - 1999/// PY - 1999/// DO - 10.1023/A:1009925500084 VL - 62 IS - 3 SP - 249-273 SN - 1386-6184 KW - combustion KW - lifted flame KW - stabilization KW - coflow KW - turbulent ER - TY - JOUR TI - Relation between non-uniform hemodynamics and sites of altered permeability and lesion growth at the rabbit aorto-celiac junction AU - Buchanan, , JR AU - Kleinstreuer, C AU - Truskey, GA AU - Lei, M T2 - ATHEROSCLEROSIS AB - Using the rabbit's aorto-celiac junction as a representative atherosclerotic model, the hemodynamics of a bifurcating blood vessel are numerically simulated and three hemodynamic parameters are compared. The wall shear stress (WSS), the oscillatory shear index (OSI), and the spatial wall shear stress gradient (WSSG) are considered in this study. Locally enhanced wall permeabilities and intimal macrophages are generally considered to be involved in atherogenesis, and here the primary concern is with the hemodynamic influence on these early stages of the disease process. In comparing the segmental averages of the indicator functions and previously published intimal white blood cell densities, only the WSSG shows a statistically significant correlation. All three indicators have selective strengths in determining sites of early lesion growth around the aorto-celiac flow divider. At the proximal end of the flow divider on the lateral side of the orifice, there are elevated values of the OSI as well as WSSG and low WSS values. Regions of elevated wall permeabilities compare with the regions of elevated WSSG along the lateral and distal portions of the flow divider. Largely dependent upon the present input pulse with reverse flow, the OSI indicates relatively high values throughout the flow domain, however, it is important when utilized in conjunction with low WSS regions. This study presents a rationale for further quantitative correlative studies in the rabbit model based on additional histological data sets. DA - 1999/3// PY - 1999/3// DO - 10.1016/S0021-9150(98)00264-0 VL - 143 IS - 1 SP - 27-40 SN - 1879-1484 KW - computational simulation KW - aorto-celiac junction KW - hemodynamic parameters KW - enhanced wall permeability KW - WBC uptake KW - atherosclerotic lesion growth ER - TY - JOUR TI - Parametric study of macrosegregation in the horizontal strip casting process for different cooling rates and different casting speeds AU - Kuznetsov, AV T2 - HEAT AND MASS TRANSFER DA - 1999/8// PY - 1999/8// DO - 10.1007/s002310050314 VL - 35 IS - 3 SP - 197-203 SN - 0042-9929 ER - TY - JOUR TI - High-temperature wear of cemented tungsten carbide tools while machining particleboard and fiberboard AU - Sheikh-Ahmad, JY AU - Bailey, JA T2 - JOURNAL OF WOOD SCIENCE AB - Published research on the wear processes of cemented tungsten carbide tools used for machining reconstituted wood products was reviewed, and the current state of knowledge in this area was evaluated. Underlying assumptions and conclusions regarding high-temperature oxidation/corrosion wear during machining were examined in view of known reaction kinetics of cemented tungsten carbide alloys in oxidative and corrosive environments at temperatures that may occur at the cutting edge. This examination indicated that some wear mechanisms other than high-temperature oxidation/corrosion are likely to be rate-controlling when machining reconstituted wood products such as particleboard and fiberboard. DA - 1999/// PY - 1999/// DO - 10.1007/BF00538952 VL - 45 IS - 6 SP - 445-455 SN - 1611-4663 KW - cemented tungsten carbide KW - machining KW - wear mechanism KW - particleboard KW - fiberboard ER - TY - JOUR TI - Fluid mechanics and heat transfer in the interface region between a porous medium and a fluid layer: A boundary layer solution AU - Kuznetsov, A. V. T2 - Journal of Porous Media DA - 1999/// PY - 1999/// DO - 10.1615/jpormedia.v2.i3.70 VL - 2 IS - 3 SP - 309-321 ER - TY - JOUR TI - The wear characteristics of some cemented tungsten carbides in machining particleboard AU - Sheikh-Ahmad, JY AU - Bailey, JA T2 - WEAR AB - This work is focused on developing an understanding of the wear mechanisms of cemented tungsten carbide tools in machining particleboard. Cutting experiments were conducted on several grades of cemented tungsten carbide tools using a high speed lathe, and their wear characteristics were determined. It was found that wear occurred predominantly on the clearance face of the tools for most grades tested. It was also found that the amount of wear after the same cutting distance correlates well with the bulk hardness of the tool material. The amount of wear generally decreased with an increase in hardness, a decrease in grain size and a decrease in binder content of the cutting tool material. Examination of the worn surfaces inside a scanning electron microscope showed that the cutting edge was worn by preferential removal of the metal binder phase from between the tungsten carbide grains. It is suggested that removal of the binder weakens the bond between the tungsten carbide grains leading to their mechanical removal from the clearance face. It is concluded that the main wear mechanism for cemented tungsten carbide tools in machining particleboard is the removal of the binder phase by plastic flow and micro-abrasion, which is followed by fragmentation and dislodging of the WC grains. DA - 1999/4// PY - 1999/4// DO - 10.1016/s0043-1648(98)00361-5 VL - 225 SP - 256-266 SN - 1873-2577 KW - tungsten carbide KW - wear KW - particleboard ER - TY - JOUR TI - Suppression of NF-kappa B-Dependent proinflammatory gene expression in human RPE cells by a proteasome inhibitor AU - Wang, X. C. AU - Jobin, C. AU - Allen, J. B. AU - Roberts, W. L. AU - Jaffe, G. J. T2 - Investigative Ophthalmology and Visual Science DA - 1999/// PY - 1999/// VL - 40 IS - 2 SP - 477-486 ER - TY - JOUR TI - Scalar and velocity field measurements in a lifted CH4-air diffusion flame AU - Watson, KA AU - Lyons, KM AU - Donbar, JM AU - Carter, CD T2 - COMBUSTION AND FLAME AB - Experiments have been performed to investigate the leading edge of a lifted jet diffusion flame. The first portion of this study is a simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) investigation of a lifted methane flame. The simultaneous technique is an approach for establishing the 2-D velocity field in conjunction with the flame front location indicated by laser-induced fluorescence from CH radicals within the reaction zone. The results show that the lifted flame stabilizes in a region of relatively low incoming gas velocity. Furthermore, the radial movement of large-scale vortices appears to play a crucial role in local flame extinction. The second set of experiments involves a simultaneous CH and OH PLIF investigation of the same lifted flame. The relative positions of the two radical fields have remarkable agreement. The CH profile is indicative of the fuel-rich region of the reaction zone and closely follows the inner edge of the OH profile. Furthermore, the OH zone is more than three times as thick as the CH zone, and the structures in both images support the radial motion of vortices established by the joint PIV/CH-PLIF measurements. DA - 1999/4// PY - 1999/4// DO - 10.1016/S0010-2180(98)00086-8 VL - 117 IS - 1-2 SP - 257-271 SN - 0010-2180 ER - TY - JOUR TI - Perturbation analysis of high strain-rate shear localization in BCC crystalline materials AU - Baucom, JN AU - Zikry, MA T2 - ACTA MECHANICA DA - 1999/// PY - 1999/// DO - 10.1007/BF01313148 VL - 137 IS - 1-2 SP - 109-129 SN - 0001-5970 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0033316049&partnerID=MN8TOARS ER - TY - JOUR TI - Systems approach for the ceramic thru-feed centerless grinding AU - Tricard, M AU - Gust, DJ AU - Shih, AJ T2 - MACHINING SCIENCE AND TECHNOLOGY AB - ABSTRACT An approach for simulation and production implementation of thru-feed centerless grinding of transformation toughened zirconia using vitreous bond diamond grinding wheels is presented. A set of grinding tests was designed and conducted to identify the effects of abrasive product (diamond grit size), work-material, and operational factors (stock removal, thru-feed rate, number of thru-feed passes and truing and dressing methods) on grinding performance. Evaluation parameters of surface finish, grinding forces and C-ratio were utilized to determine machine tool features. Very fine surface finishes, in the order of 0.05 to 0.1 u.m Ra range, could be achieved using vitreous bond micro-grit diamond wheels, without additional part processing. Such a level of surface finish on ground ceramics has traditionally been generated only by using resinoid bonded diamond wheels. These test results were used to design and manufacture a full-size composite or sandwiched diamond grinding wheel. This grinding wheel has been successfully applied in high-volume ceramic production, which in turn has verified the proposed approach. Lastly, the surface finish data is interpreted based on SEM and AFM observations and materials properties. DA - 1999/// PY - 1999/// DO - 10.1080/10940349908945690 VL - 3 IS - 2 SP - 201-219 SN - 1091-0344 ER - TY - JOUR TI - An experimental investigation of high velocity impact and penetration failure modes in textile composites AU - Flanagan, MP AU - Zikry, MA AU - Wall, JW AU - El-Shiekh, A T2 - JOURNAL OF COMPOSITE MATERIALS AB - The dynamic failure evolution of textile composites, which were subjected to impact velocities up to 1100 m/s, was investigated. Specialized machines were used to fabricate composites from combinations of Spectra®, Kevlara®, and Twaron® fibers and two- and three-dimensionally woven, braided, and needle-punched nonwoven fabrics. This control of fabrication and processing enabled us to characterize response as a function of areal density, fabric finish, and consolidation techniques. Failure was categorized in terms of material layers, debris mass, matrix cracking, fiber failure, and shear-plugging. Results indicate that shear-plugging occurs at velocities corresponding to decreases in debris mass. DA - 1999/// PY - 1999/// DO - 10.1177/002199839903301202 VL - 33 IS - 12 SP - 1080-1103 SN - 0021-9983 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0032668475&partnerID=MN8TOARS KW - textile laminate composite KW - high velocity impact KW - shear plugging KW - tensile and shear fiber failure KW - matrix cracking ER - TY - JOUR TI - A note on similarity measures between vague sets and between elements AU - Hong, DH AU - Kim, C T2 - INFORMATION SCIENCES AB - Recently, Chen (Fuzzy Sets and Systems 74 (2) (1995) 217–223; IEEE Trans. Syst. Man and Cybern., 27 (1) (1997) 153–158) proposed a set of methods for measuring the degree of similarity between vague sets and between elements, and presented some examples to illustrate the application of the said measures in handling behavior analysis problems. In this paper, we showed by examples that the similarity measures proposed by Chen do not fit well in some cases, and proposed a set of modified measures. Comparing the similarity degree of each measure, the modified similarity measures turned out to be more reasonable in more general cases than the previous one. DA - 1999/4// PY - 1999/4// DO - 10.1016/S0020-0255(98)10083-X VL - 115 IS - 1-4 SP - 83-96 SN - 0020-0255 ER - TY - JOUR TI - Single-point thermometry in high-pressure, sooting, premixed combustion environments AU - Brown, MS AU - Roberts, WL T2 - JOURNAL OF PROPULSION AND POWER AB - We have performed nonintrusive thermometry in the burnt gases of rich, pressurized ethylene/air flames using a frequency measurement based on laser-induced gratings. Light from a continuous-wav e probe beam is coherently scattered from a thermal or electrostrictive grating induced by a pair of crossed, pulsed pump beams. The measured Doppler shift of the signal beam is a function of the local speed of sound from which a temperature can be extracted. At equivalence ratios of 1.6, the transient grating temperature agreed with a corrected thermocouple temperature. At higher soot loading, it is necessary to account for the change in local gas composition caused by soot particle vaporization. Soot particles, acting as blackbody absorbers, were observed to generate thermal gratings of diagnostic value. DA - 1999/// PY - 1999/// DO - 10.2514/2.5400 VL - 15 IS - 1 SP - 119-127 SN - 0748-4658 ER - TY - JOUR TI - Local thermal nonequilibrium effects in forced convection in a porous medium channel: a conjugate problem AU - Nield, DA AU - Kuznetsov, AV T2 - INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER AB - Forced convection in a plane channel filled with a saturated porous medium, coupled with conduction in plane slabs bounding the channel, is investigated analytically on the basis of a two-temperature model allowing for local thermal nonequilibrium (LTNE). It is found that the effect of the finite thermal resistance due to the slabs is to reduce both the heat transfer to the porous medium and the degree of LTNE. An increase in value of the Péclet number leads to a decrease in the rate of exponential decay in the downstream direction but does not affect the value of a suitably defined Nusselt number. The dependence of the Nusselt number on a new solid–fluid heat exchange parameter, the solid/fluid thermal conductivity ratio, and the porosity, is investigated. The general two-temperature formulation of the thermal boundary conditions is discussed. DA - 1999/9// PY - 1999/9// DO - 10.1016/S0017-9310(98)00386-X VL - 42 IS - 17 SP - 3245-3252 SN - 0017-9310 ER - TY - JOUR TI - Understanding biases in the near-field region of LDA two-point correlation measurements AU - Benedict, LH AU - Gould, RD T2 - EXPERIMENTS IN FLUIDS DA - 1999/4// PY - 1999/4// DO - 10.1007/s003480050301 VL - 26 IS - 5 SP - 381-388 SN - 0723-4864 ER - TY - JOUR TI - Thermal mismatch stress relaxation via lateral epitaxy in selectively grown GaN structures AU - Zheleva, TS AU - Ashmawi, WM AU - Nam, OH AU - Davis, RF T2 - APPLIED PHYSICS LETTERS AB - A reduction in the dislocation density of 104–105 cm−2 has been achieved via lateral epitaxial overgrowth (LEO) of GaN films selectively grown from stripes etched in SiO2 masks deposited on GaN/AlN/6H–SiC(0001) heterostructures. The magnitudes and distribution of stresses generated in the LEO GaN layer and the SiO2, due primarily to differences in the coefficients of thermal expansion, were modeled using finite element (FE) analysis. These calculations showed that localized compressive stress fields of ≈3 GPa occurred at the edges of the LEO GaN in the vicinity of the GaN/SiO2 interface. Localized compression along the GaN substrate/SiO2 interface and tension along the 〈0001〉 direction were responsible for the change in shape of the SiO2 stripes from rectangular with flat sides to an airfoil shape with curved sides. The FE calculations also revealed that an increase in the width of the LEO GaN regions over the SiO2 or the reduction in the separation between the GaN stripes (all other dimensions being fixed) resulted in a slight reduction in the compressive stresses along the LEO GaN/SiO2 interface and an increase in the compressive stress along [0001]. An increase in the shear stress, at the corners of the LEO GaN near the LEO GaN/SiO2 interface, with an increase in the width of the LEO GaN region were also indicated. DA - 1999/4/26/ PY - 1999/4/26/ DO - 10.1063/1.123017 VL - 74 IS - 17 SP - 2492-2494 SN - 0003-6951 ER - TY - JOUR TI - Pendeo-epitaxy: A new approach for lateral growth of gallium nitride structures AU - Zheleva, T. S. AU - Smith, S. A. AU - Thomson, D. B. AU - Gehrke, T. AU - Linthicum, K. J. AU - Rajagopal, P. AU - Carlson, E. AU - Ashmawi, W. M. AU - Davis, R. F. T2 - MRS Internet Journal of Nitride Semiconductor Research DA - 1999/// PY - 1999/// VL - 4S1 IS - G3.38 ER - TY - JOUR TI - Observations on the leading edge in lifted flame stabilization AU - Watson, KA AU - Lyons, KM AU - Donbar, JM AU - Carter, CD T2 - COMBUSTION AND FLAME AB - The objective of this paper is to report some of the first experimental evidence for the “leading edge” flame as the stabilization mechanism in lifted jet diffusion flames 1, 2, 3, 4, 5. CH fluorescence has been used to indicate the flame front location (i.e., region of chemical reaction) and thereby characterize features of the stabilization region 5, 6. The “leading edge” flame phenomenon reported within refers to the outward-extending branch of CH fluorescence at the base of the streamwise CH zones. Whether the “leading edge” flame is a special case of the more general triple flame is a question which remains unanswered. It is evident from previous computational studies 7, 8 that the triple flame, when interacting with a vortex or pair of vortices, can take on characteristics of the “leading edge” flames introduced in the present study. Veynante et al. [8] illustrate the contortion of the premixed branches of the triple flame by the flowfield where the premixed branches are swept into the trailing diffusion flame. These simulated triple flame/vortex interactions are consistent with the results of this study which show a trailing diffusion flame and the leading edge reaction zone structure.The test conditions and measurement locations for this investigation are shown in Fig. 1. Download : Download high-res image (204KB)Download : Download full-size imageFig. 1. Test conditions and measurement locations for (a) the lowest flow rate and (b) the highest flow rate. The intermediate flow rate (not shown) corresponds to a methane velocity of 21.2 m/s while the bottom of the image region is 37.4 mm from the jet exit and includes both sides of the lifted flame. The axisymmetric burner consists of a 5-mm inner diameter fuel jet surrounded by a 150-mm i.d. coflow tube. Methane is delivered through the fuel jet, while low-speed air (∼0.15 m/s) passes through the coflow annulus. The stabilization regions of three lifted flames are investigated by varying the methane and air flow rates and adjusting the burner position accordingly so that the image region includes the leading edge of the reaction zone. The methane exit velocities are 15.8, 21.2, and 27.5 m/s, corresponding to jet Reynolds numbers of 4800, 6400, and 8300, respectively. Both sides of the lifted flame are imaged during the two lower flow rates (Fig. 1a) while the turbulent fluctuations and wider stabilization region resulting from the highest flow rate limit this case to one side of the flame (Fig. 1b). Fig. 1. Test conditions and measurement locations for (a) the lowest flow rate and (b) the highest flow rate. The intermediate flow rate (not shown) corresponds to a methane velocity of 21.2 m/s while the bottom of the image region is 37.4 mm from the jet exit and includes both sides of the lifted flame. The CH planar laser-induced fluorescence (CH-PLIF) technique has been described elsewhere 5, 6. The setup includes a Nd:YAG-pumped dye laser which excites the Q1(7.5) transition of the B2Σ−–X2π(0,0) band of CH at λ = 390 nm. Fluorescence from the A–X(1,1), (0,0) and B-X(0,1) bands between λ = 420 and 440 nm is recorded. This approach has resulted in acceptable CH signal levels and excellent image quality (i.e., spatial resolution and contrast), which the authors find superior to the 431.5 nm laser excitation employed in earlier studies 9, 10. The authors believe the excellent resolution resulting from the signal levels and laser sheet characteristics in this study are extremely important in uncovering the leading edge premixed branch, which is generally weaker in signal level than the trailing diffusion flame. It is likely that these stabilizing leading edge flame observations are not reported in studies with less spatial resolution or are possibly not at all detectable due to limitations in the specific CH excitation/detection scheme. Several diagnostic studies involving lifted flames present the lifted flame structure as a continuous flame surface, similar to a distorted cylindrical object, emanating from a ring-shaped structure where the flame is stabilized 4, 5, 11. Most previous work, however, does not give experimental evidence of the mechanism of lifted flame stabilization. Figure 2Download : Download high-res image (3MB)Download : Download full-size imageFig. 2. CH-PLIF images illustrating the leading edge phenomenon where the CH zone extends outward at the stabilization point. (a)–(c) are from the lowest Re = 4800 flow condition (Fig. 1a); (d)–(h) are from the intermediate Re = 6400 flow condition; (i)–(l) are from the highest Re = 8300 flow condition and only include the right side of the flame (Fig. 1b). consists of several instantaneous 35.1 mm × 23.4 mm CH-PLIF images which provide such evidence. The images clearly show a continuous vertical distribution of CH which represents the primary diffusion flame reported in many previous studies. In addition to the vertical trailing diffusion flame, a structure is witnessed near the flame base which curls toward the outside, or fuel-lean, portion of the reaction zone. In comparison to ideal, laminar tribrachial structures, evidence of both rich and lean branches of premixed flame is not present, only the one branch extending outward near the jet edge. However, the rich branch on the fuel side of the diffusion flame may be overlapped into the diffusion flame by the flowfield as illustrated by Veynante et al. [8]. It is believed that the branch in the CH zone is a leading edge flame, stabilized by opposing the flow in the relatively low-speed region (∼1.0 m/s) near the outside edge of the jet. Fig. 2. CH-PLIF images illustrating the leading edge phenomenon where the CH zone extends outward at the stabilization point. (a)–(c) are from the lowest Re = 4800 flow condition (Fig. 1a); (d)–(h) are from the intermediate Re = 6400 flow condition; (i)–(l) are from the highest Re = 8300 flow condition and only include the right side of the flame (Fig. 1b). This branch of CH is not obviously present in all of the data; it only appears in approximately 30% of the images. The authors reason that the leading edge phenomenon may not be present around all 360 degrees of the stabilizing “ring,” but only in a portion of the flame sufficient to generate enough thermal energy to stabilize the flame globally. The reader must keep in mind that while the laser imaging techniques allow one to investigate the flame in detail locally, global behavior, most notably out-of-sheet activity, may be dominant at any given instant. With the flow inherently three-dimensional and time-dependent 11, 12, sheet imaging techniques often provide data to support a theory, but rarely provide definitive evidence. Since the measurements only investigate the flowfield in one plane, it is feasible that the leading edge structure could be present outside the measurement slice during the instances when no premixed CH branch is witnessed. In addition, recent cross-sectional images of lifted flames near the stabilization zone clearly render three-dimensional lobed structures that are consistent with this theory 11, 12. The extent of mixing and the entrainment of ambient air into the fuel is of central importance to this problem. Based on comparisons with mixture fraction images presented by Stårner et al. [13], which illustrate that the portion at the base of a lifted methane flame has a flammable composition, the authors are confident that the leading edge flame lies in a flammable mixture fraction region. Furthermore, fluctuations in the axial location of the leading edge, along with its orientation relative to the trailing diffusion flame, imply axial propagation into the unburned gas region. These observations imply that the physics of flame stabilization is likely a combination of multiple mechanisms based on premixedness, strain rate considerations 6, 14, and flame propagation into nonhomogeneous flowfields with flow separation, scalar gradients, and a range of mixture fractions [13]. DA - 1999/10// PY - 1999/10// DO - 10.1016/S0010-2180(99)00056-5 VL - 119 IS - 1-2 SP - 199-202 SN - 1556-2921 ER - TY - JOUR TI - Computational study of hypersonic transitional wake flow AU - Nance, RP AU - Hollis, BR AU - Horvath, TJ AU - Alter, SJ AU - Hassan, HA T2 - JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER AB - A study of transition and turbulence in hypersonic blunt-body wake flows is presented. The current approach combines the A>£ turbulence closure model with a newly developed transition prediction method. This method utilizes results from linear stability theory and treats transitional flows in a turbulence-like manner. As a result, the onset and extent of transition are determined as part of the solution. The model is used to study flows past two spherically blunted 70-deg cone geometries at Mach 6 and 10. Two mechanisms of instability are examined. Comparison between computation and experiment suggests that for the cases considered, transition is a result of the instability of the free shear layer emanating from the shoulder region. DA - 1999/// PY - 1999/// DO - 10.2514/2.6441 VL - 13 IS - 2 SP - 236-242 SN - 1533-6808 ER - TY - JOUR TI - A note on infinite fuzzy logic L-1 controllers AU - Hong, DH AU - Choi, CH T2 - FUZZY SETS AND SYSTEMS AB - In this note, we give a counterexample to show that the Theorem of Rastović (1995) is incorrect. DA - 1999/2/1/ PY - 1999/2/1/ DO - 10.1016/S0165-0114(98)00183-3 VL - 101 IS - 3 SP - 513-514 SN - 0165-0114 KW - universal fuzzy controller ER - TY - JOUR TI - The effect of thermal aging on the Mode-I interlaminar fracture behavior of a high-temperature IM7/LaRC-RP46 composite AU - Hutapea, P AU - Yuan, FG T2 - COMPOSITES SCIENCE AND TECHNOLOGY AB - High-temperature Mode-I interlaminar fracture tests have been conducted to evaluate the effect of thermal aging at various temperatures on the fracture behavior of IM7/LaRC-RP46 composites. Double cantilever beam specimens made of unidirectional laminates were used in the test program. The specimens were aged at high temperatures for times up to and including 6000 h. Changes in fracture behavior that occurred over periods of aging time and aging temperature have been measured and determined for variations of test temperature and loading rate. As expected, the crack growth at high temperature showed non-linear load–displacement response as a result of the rate-dependent nature of behaviour of the matrix. Present loading rates had no measurable effect on GIC values for unaged and aged specimens. High temperature increased GIC values of aged and unaged specimens at temperature near Tg and decreased at temperatures above Tg. Thermal aging for longer times also significantly reduced GIC initiation values for aged specimens. In contrast, thermal aging increased GIC propagation values as a result of the occurrence of increased fiber bridging, fiber breakage and microcracks, as deduced from SEM studies. Results also indicated that high temperatures slowed crack-growth rates. However, thermal aging and higher loading rates accelerated crack-growth rates. The effect of thermal aging and temperature on the crack growth rate, da/dt, can be correlated with the C* parameter in the power-law relationship. DA - 1999/// PY - 1999/// DO - 10.1016/S0266-3538(98)00164-X VL - 59 IS - 8 SP - 1271-1286 SN - 0266-3538 ER - TY - JOUR TI - Effect of unsteady stretch on spark-ignited flame kernel survival AU - Eichenberger, DA AU - Roberts, WL T2 - COMBUSTION AND FLAME AB - The chemistry–turbulence interaction remains one of the most important topics in combustion research. The ignition of premixed reactants in a highly turbulent environment is fundamentally coupled to this chemistry–turbulence interaction. The spark-ignition (SI) internal combustion (IC) engine relies on the ability of the flame kernel to survive the high-strain-rate, unsteady environment of a turbulent flowfield and successfully transition into a fully developed flame to operate cleanly and efficiently. If certain length and velocity scales within the turbulence spectrum are found to promote flame kernel growth, then by tailoring the flow passages and aerodynamics of the intake valves, piston, and combustion chamber, it may be possible to increase the efficiency and reduce the emissions of SI IC engines. This paper describes a novel experimental investigation of a spark-generated flame kernel interacting with a single vortex toroid with well-defined length and velocity scales. This experiment measured the ability of a vortex to quench a growing kernel in a very lean methane–air mixture at atmospheric pressure. The absence of superequilibrium OH concentrations, qualitatively determined by planar laser-induced fluorescence (PLIF), was used as in indicator of quenching. It was found that larger eddies are more effective at globally quenching the flamefront, requiring a lower strength, when compared to vortices with a smaller characteristic length. At the globally quenching condition, the maturity of the kernel was then increased incrementally until the vortex was no longer able to completely strain out the kernel. The result of this was surprising in that the larger vortices had a much narrower range of kernel maturity for which the vortex could still quench the growing kernel. DA - 1999/8// PY - 1999/8// DO - 10.1016/S0010-2180(98)00169-2 VL - 118 IS - 3 SP - 469-478 SN - 0010-2180 ER - TY - JOUR TI - Transition effects on heating in the wake of a blunt body AU - Hollis, BR AU - Perkins, JN T2 - JOURNAL OF SPACECRAFT AND ROCKETS AB - Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields. DA - 1999/// PY - 1999/// DO - 10.2514/2.3499 VL - 36 IS - 5 SP - 668-674 SN - 0022-4650 ER - TY - JOUR TI - Nonlinear spectral dynamics of hypersonic laminar boundary layer flow AU - Chokani, N. T2 - Physics of Fluids (Woodbury, N.Y.) DA - 1999/// PY - 1999/// VL - 11 IS - 12 SP - 3846-3851 ER - TY - JOUR TI - Effect of the suspension structure on equivalent suspension parameters AU - Kim, C AU - Ro, PI AU - Kim, H T2 - PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING AB - This paper examines the uncertainties in modelling a real suspension system that are due to the effect of suspension linkage layout (or structure) on the equivalent suspension parameters of a corresponding mathematical model. In most research on active suspension systems, a quarter-car model of two masses is very often used. However, without considering the influence of the suspension kinematic structure, the simple model may not be as effective as might be expected because of the uncertainties in the suspension parameters. Two sets of identified parameters for different suspension systems are compared to show the effect of suspension structure on the equivalent parameters. The relationships between specific parameters and changes in certain suspension linkage layouts are also investigated. The benefits of the parameter identification are demonstrated in the process of designing two active systems (one using a sky-hook control law and the other using a sliding mode control technique). The results show that suspension structure has a strong effect on the equivalent suspension parameters and this relationship becomes more important as the structure of suspension increases in complexity. The advantage of the identification process is crucial in designing both linear and non-linear active suspension systems. DA - 1999/// PY - 1999/// DO - 10.1243/0954407991527026 VL - 213 IS - D5 SP - 457-470 SN - 0954-4070 KW - active suspension KW - uncertainty KW - parameter identification KW - sliding mode ER -