A. James Clark School of Engineering
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Item Hinge-Bill Orientation Techniques for Automated Oyster Processing(1977) Gird, John; Wheaton, F.W.; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)The width and thickness dimensions of oysters and an inclined V-shaped trough were studied as means for achieving end orientation. Two series of experiments were conducted on 2,430 oysters sampled from three different locations in the Chesapeake Bay. Both width and thickness were measured every 0.2 inch along the oyster length from the hinge to the bill end. A width to thickness ratio was found to be the best dimensional combination for distinguishing between the hinge and bill ends. Less than 0.50 percent of all oysters failed the ratio test conditions. Statistical analysis on five width to thickness ratio tests with failure rates between 0.25 and 0.49 percent showed there to be no differences in the percent oyster failure over all bars and across all tests. Results indicate that comparable oyster orienting efficiencies can be attained by width to thickness ratios with orienting points located 0.4 to 1.0 inches in from the oyster ends. Negative results occurred when an inclined V-shaped trough was used for orienting oysters. There were significant differences in the proportion of hinge and bill leading oysters exiting the trough for each trough loading position over all bars and oyster axes. The tendency for the oyster axes to behave differently explained some of the differences in the trough's orienting efficiency. However, there were no significant relationships between orienting efficiency and oyster axes.Item Local Atomic Arrangments and Solution Strengthening of Ta-Mo and Ta-Nb Alloys(1975) Predmore, Roamer Edward; Arsenault, Richard J.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Ta-Nb alloys are shown to form random solid solutions by x-ray diffuse scattering measurements. These alloys have equal size atoms in their pure state with lattice parameters that are invariant in composition, obey Vegard's law, and exhibit an absence of solid solution hardening and an absence of fracture embrittlement at high solute concentrations. Ta-Mo atoms of about 5% difference in atomic size form short range ordered solid solutions with large atomic displacement effects. The Ta-Mo, and Ta-W, Nb-Mo and Nb-W alloys have in common a lattice parameter that varies in composition with a negative deviation from Vegard's Law. There is also a negative heat of mixing which is well correlated with short range order. In addition, all these alloys show linear solid solution hardening to high solute concentrations at room temperature and fracture embrittlement at high solute concentrations. Diffuse ex-ray scattering measurements on Ta-Mo alloys give the short range order parameters and atomic size displacements. The hardening is attributed to a combination of size effect induced substitutional solid solution hardening and short range order induced hardening.Item Kinetic Parameters of the University of Maryland Reactor by the Interval-Distribution Method(1976) Simonson, Simon Christian III; Munno, Frank J.; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The Rossi alpha of the University of Maryland Reactor was measured at criticality and at shutdown by the Babala interval-distribution method. At criticality, α= 188.8 ± 4.7 sec^-1, and at shutdown, α= 1026.6 ± 4.1 sec^-1. The shutdown reactivity was found to be ρ/β = -4.44 ± 0.14 dollars.Item Reactivity Measurements on the University of Maryland Reactor by Conventional Methods and Statistical Processes and Comparison with Calculational Methods(1970) Zubieta, Agustin Diaz; Duffey, Dick; Nuclear Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The accurate experimental determination of nuclear reactor core physics parameters is of great importance for its safe operation. In particular, the accurate determination and prediction of criticality during the initial fuel loading of a nuclear reactor are essential for a safe nuclear reactor startup. Also, the degree of subcriticality or shutdown margin of a nuclear core with its control rods inserted is an important parameter for the operation of a nuclear reactor throughout the core operating lifetime. There are several methods utilized to determine both the criticality and the shutdown margins. All of these methods depend on measuring the response of neutron detectors and the calibration of the control rods. However, neutron detectors respond only to the neutron flux in the cor e in the vicinity of the nuclear detectors. During initial reactor core fuel loading, the reactivity of the core is determined from the multiplication of the neutrons of the startup source by the addition of nuclear fuel. Reactivity is determined from the multiplication factor by a constant which is related to the source-detector geometry in the core. In this research a method was studied which allowed the determination of reactivity independent of the source-detector geometry. Reactivity measurements of the 10 kw University of Maryland pool training reactor (UMR) were made by conventional methods and by a statistical process, the variance-to-mean ration method, and the results were compared with calculational methods. The theoretical method selected to determine the UMR core reactivity was based on the multigroup, multiregion, diffusion theory. The accuracy of the theoretical model was determined for the just critical UMR core. Agreement to within 0.2% ΔK/K was obtained between the control rod measured and the calculated reactivity for the UMR full core, and smaller UMR supercritical cores. The statistical technique of the variance-to-mean ratio of the number of counts for various counting gate openings, as a means to determine the degree of subcriticality, or shutdown margin, has been proven to be an effective method. A BF3, thermal neutron proportional detector, with a sensitivity of 12.1 counts/sec per n/cm2/sec, was placed inside of an eleven feet long aluminum tubing. The end of the tubing containing the detector was inserted in the center Glory Hole of the UMR core. The current pulses from the proportional detector was amplified and fed to a TMC 1024-channel pulse analyzer. The pulses were counted for different Δt gate openings from 10-4 seconds to 10 seconds. For each Δt gate opening, 1023 samples were taken. The printed output from the TMC-1024 was collected, giving the number of counts received per Δt, as well as the integral of all the counts received during a period of time, equal to 1023 x Δt seconds. From the integrated value for the number of counts the average count c for the gate opening Δt was obtained. The printed output was transferred to IBM cards acceptable to a "Reactor Noise" code written for the IBM-7090. This code calculated the average value, c, for each Δt (which gave a check on the validity of the data transferred to the IBM cards by comparing it with the value obtained during the measurement), the standard deviation o, and the variance-to-mean ratio for all the data taken for each Δt seconds gate opening. Plots of the values of the variance-to-mean ratio versus gate openings were obtained for several UMR full core with the rods banked at various degrees of insertion (shutdown margins), and also for various UMR subcritical cores. Measurements of the shutdown margins by the variance-to-mean technique were in agreement with the values obtained from the rod calibration for negative reactivities of less than -1. 00% ΔK/K, and within ten percent for negative reactivities of approximately -2. 0% ΔK/K. Measurements of the reactivity of small UMR cores indicated that for UMR core conditions of 0. 5% ΔK/K subcritical, experiment and theory for 1-Keff were found to be only 6 parts in 100 apart, and for 2. 0% ΔK/K subcritical, experiment and theory were found to be only 8 parts in 100 apart. The variance-to-mean technique was compared to the inverse multiplication method for determination of criticality during the UMR fuel loading, and was found to be a more accurate method, primarily, because of its independence of the source-detector geometry effects. The system utilized for the statistical data processing is exact, however cumbersome, due to the amount of data to process and the amount of peripheral hardware utilized in the reduction of the data. It appears from this study that greater overall counting efficiency for the same amount of statistical data would permit more accurate measurements at larger degrees of subcriticality, perhaps, in the region of -4. 0% ΔK / K to -5. 0% ΔK / K . A system is proposed in this study to measure negative reactivity continuously, and directly, by means of a small computer capable of accepting the output of a multichannel scaler. The computer would have a fixed internal logic capable of calculating reactivity from the variance-to-mean analysis of the neutron detector counts.Item Navier Stokes Solutions for Chemical Laser Flows: Steady and Unsteady Flows(1979) Kothari, Ajay Prasannajit; Anderson, John D. Jr; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)This work consists of an overall effort to apply a detailed and accurate computational fluid dynamic technique to the solution of practical high energy laser flows. In particular, a third generation of super sonic diffusion chemical laser analysis is introduced, namely, the complete solution of the Navier-Stokes equations for the laminar, super sonic mixing flow fields fully coupled with chemical kinetics for both the hot and cold reactions for HF. Multicomponent diffusion is treated in a detailed fashion. Solutions are obtained, firstly, for "cold flows", where the effects of chemical reactions and vibrational relaxation are not included. Although such a situation is purely artificial, the results do isolate some of the fluid dynamic aspects of chemical laser flows, and provide a set of data to be compared later with hot flow calculations. A set of numerical experiments using four different time dependent finite difference schemes show that relatively minor changes in the differencing procedure can lead to major variations in the results. A modification of the well-known Maccormack approach appears to be the best suited for mixing flows associated with chemical lasers. A comparison is next made between cold flows (with fully coupled chemical kinetics). the results show that temperature distributions are affected the most and velocity distributions the least by chemical energy heat release. The results have an impact on the interpretation of cold flow aerodynamic experiments in the laboratory, and their proper extrapolation to the real chemical laser flows. also, comparisons between the present Navier Stokes results and other, more approximate, existing calculations are made. Gradients are calculated as a natural part of the Navier Stokes solutions. Results are given for steady flows with large pressure gradients where advantages of the Navier Stokes solutions are delineated. In addition, the effect of unsteady fluctuations intentionally introduced at the cavity inlet are studied. Specifically, sinusoidal fluctuations in one stream and then both streams (primary and secondary) in various quantities e.g. pressure, density, u velocity and v velocity were simulated. Of these, the oscillations in v velocity with approximate frequency and amplitude produced a remarkable improvement in mixing. Such unsteady fluctuations also yielded peak laser gain which were larger by almost a factor of two compared to the steady case. the flow at which the upstream boundary has so far, in the above mentioned cases been assumed to be uniform with real effects like Boundary Layer and Base Flow having been neglected. For comparison purposes these effects are next included. the boundary layer profile and velocity at the inlet is shown to feed production of gain substantially. Base flow calculations were attempted but were not successfulItem An Experimental Investigation of the Effects of Leading Edge Modification on the Post-Stall Characteristics of an NACA 0015 Wing(1979) Saini, Jugal Kishore; Jones, Everett; Winkelmann, Allen E.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)The effects of leading edge modifications on the stalling characteristics of an NACA 0015 panel wing model were investigated in a series of low speed wind tunnel tests. The modification typically consisted of adding a 14% Clark Y glove onto a portion of the leading edge. Six-component balance data, pressure distribution measurements and oil flow visualization tests were completed at a Reynolds number based on chord of 2.0 x 10^6 for increasing and decreasing angles of attack from 0° to 50°. The leading edge modifications produce stabilizing vortices at stall and beyond. These vortices have the effect of fixing the stall pattern of the wing such that various portions of the wing upper surface stall nearly symmetrically. This results in a higher lift on the modified wing as compared to the lift on the unmodified wing in the post-stall region. The lift curve slope of the modified and unmodified wings remained essentially constant at 0.071 per degree. Two lift-coefficient peaks were obtained for the baseline NACA 0015 wing at angles of attack of 17° and 30°. The twin-peak behavior of the lift curve was also observed on the modified wings. The drag coefficient obtained with several modified configurations was smaller than the drag coefficient of the baseline NACA 0015 wing in the pre-stall region. Also a smaller center of pressure shift with angle of attack was observed with several modified configurations. Considering a smoother variation of lift, pitching moment, rolling moment at stall and a smaller drag and center of pressure movement to be desired criteria, the best configuration tested consisted of placing the glove on the entire leading edge except for a gap at 25% to 50% of the semispan.Item Bleaching Kinetics of Visual Pigments(1977) Resnik, Judith Arlene; Zajac, Felix E. III; Electrical & Computer Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)A rapid scanning microspectrophotometer (RMSP) has been developed and utilized to study the photoproducts resulting from the bleaching of rhodopsin in the isolated retina of the frog. The RMSP is capable of measuring absorption spectra at multiple wavelengths within the milliseconds and longer time domain. The unusual characteristic of the instrument is the use of a special cathode ray tube as a measuring light source. Spectral scanning is accomplished electronically, with a sampling interval of 600 microseconds for each waveband. A lock-in amplifier system enables the RMSP to be utilized as either a single or dual beam instrument. The results discussed in this dissertation have shown that hydrogen ion availability is a primary cofactor in determining the relative concentration of the metarhodopsin III photoproduct, with less appearing, in lieu of greater free retinal formation, at low pH levels. Metabolic factors have also been shown to influence the pathways of photoproduct decay. The most significant effect has been observed in nonacidic intracellular environments, with deficiencies in metabolic energy production also favoring the direct formation of free retinal from metarhodopsin II. The half-times of formation and decay of metarhodopsin III have also been observed to vary, depending on the extracellular environment of photoreceptor cells. In general, both halftimes tend to be greater when proportionately more metarhodopsin III 1s formed. The ratio of the two half-times, however, remains relatively constant, except in anoxic conditions, in which the decay half-time is significantly prolonged with respect to the formation half-time. Several problems associated with the control of experimental conditions have been discussed as they relate to photoproduct sequence and kinetics. The elimination of as many metabolic, ionic, and other insufficiently controlled conditions as possible has been pointed out as a necessary requirement for obtaining meaningful quantitative results. In addition, the baseline magnitude of the optical density of the retina, which is, in part, a quantification of light scattering, has been shown to be significantly larger in conditions of low intracellular pH or insufficient substrate supply. The utilization of this parameter as an indirect indicator of the probably sequence of photoproducts has been discussed. In conclusion, this research has provided a greater insight into the mechanisms affecting the later, slow photoproduct processes in isolated retinas. In particular, the interaction of hydrogen ions and metabolic factors influences the pathways of photoproduct decay in isolated retinas, subsequent to metarhodopsin II. The results and methods described here should be useful in establishing a context in which to study the faster mechanisms involved in photochemical and electrical transduction in photoreceptor cells. In addition, these results may become important in understanding the normal and pathological functionings of the eye.Item Numerical Solutions for Two- and Three-Dimensional Non-Reacting Flowfields in an Internal Combustion Engine(1977) Griffin, Michael Douglas; Anderson, John D. Jr; Jones, Everett; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The numerical solution for the flowfield established in a spark- ignition internal combustion engine during the four-stroke (intake, compression, power, exhaust) cycle is considered. Only fluid-dynamic effects are treated with combustion simulated by constant- volume heat addition near top-dead-center on the compression stroke. The working fluid is assumed to be air of constant specific heat, with both viscous and inviscid models considered. Two- and three-dimensional engine models are examined, with the three-dimensional models including both rectangular and cylindrical geometries. The difficulties associated with obtaining numerical solutions in cylindrical coordinates for three-dimensional non-axisymmetric problems when the centerline is included in the region of interest are discussed. A new method which avoids the coordinate- singularity problems associated with such cases is presented and used to obtain the first known four-stroke inviscid-flow solution for a three- dimensional cylindrical engine model. Similar results are presented for a three-dimensional rectangular model, and for the first known two-dimensional four-stroke calculation for a viscous fluid. The inviscid three-dimensional results are compared with each other and with previously obtained two-dimensional inviscid-flow calculations. The use of two-dimensional models is found to be justified for the non- reacting flowfields considered, since the results obtained from a two-dimensional calculation in the valve plane are apparently not strongly dependent on the flowfield perpendicular to the valve plane. It is found that significant flowfields do exist in all I.C. engine models considered. It is shown that the unit-cell-Reynolds-number criterion limits viscous flow calculations to Reynolds numbers of approximately one ten-thousandth the realistic value, and that this produces flowfields which are strongly piston-dominated. In contrast, inviscid results show marked circulatory patterns, which are more realistic. The velocity patterns which develop in the three-dimensional cylindrical engine model are shown to exhibit a marked swirl in planes parallel and perpendicular to the cylinder axis.Item An Investigation of Blast Waves Generated by Constant Velocity Flames(1977) Luckritz, Robert Thomas; Marchello, Joseph M.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The relevant flow field parameters associated with the generation and propagation of blast waves from constant velocity flames were systematically studied through numerical integrations of the non-steady equations for mass, momentum, and energy. The flow was assumed to be that of an adiabatic inviscid fluid obeying the ideal gas law and the flame was simulated by a working fluid heat addition model. The flame velocity was varied from infinitely fast (bursting sphere) through velocities characterized by the nearly constant pressure deflagration associated with low Mach number laminar flames. The properties noted included peak pressure, positive impulse, energy distribution, and the blast wave flow field. Results were computed for the case of a methane-air mixture assuming an energy density, q = 8.0, an ambient specific heat ratio, Yo = 1.4 and a specific heat ratio behind the flame, Y4 = 1.2. In the source volume, as the flame velocity decreased to Mach 4.0 the overpressure increased. For flame velocities below Mach 4.0 the overpressure decreased, and approach the acoustic solution originally developed by Taylor. In the far field the overpressure curves for supersonic flame velocities coalesced to a common curve at approximately 70% of Baker's pentolite correlation. Far field overpressures for subsonic flame velocities decreased as the flame velocity decreased. For the flame velocities investigated the near field impulse was greater than the impulse from Baker's pentolite correlation. In the far field the flame generated impulse decreased to 60 to 75% of the pentolite impulse. In cases where the flow was expected to reduce to a self-similar solution and/or show Rayleigh line behavior it did. The calculations showed that the flow field behaved normally where expected, and for flow velocities where steady state behavior is not expected, non-steady behavior was observed.Item Thermal Displacement in Copper-Gold Alloys(1971) Gilmore, Charles M.; Bolsaitis, P.; Skolnick, L.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The thermal displacements and Debye temperatures are determined for single crystals of copper and Cu-Au solid solutions including Cu3Au of four degrees of long range order (0.0, 0.53; 0.8, .98). Other solid solution compositions studied were .91Cu-.09Au and .2Cu-.8Au. At the .91Cu-.09Au composition a one week anneal produced a nonequilibrium structure. After a one month anneal the thermal displacements decreased to a value nearly equal to the value for pure Cu. The thermal displacements in the quenched .75Cu-.25Au crystal were also nearly equal to the value for pure Cu, but the thermal displacements increased as the Cu3Au crystal approached the equilibrium condition of full order. In the Cu3Au crystals, which were partially or fully ordered, the thermal displacements of the individual Cu and Au atoms were determined. It was observed that the vibration amplitudes of the Cu atoms are not isotropic in this diatomic cubic crystal. The vibrations of the Au atoms are equal in the [110] and [001] directions within experimental uncertainty. Also, the thermal displacements decrease as the crystal is changed from fully ordered to fully disordered. This is consistent with calculations of the vibrational spectrum for ordered and disordered Cu3Au. The static displacements for the partially ordered S = .80 crystal were also determined from the same experiments as the thermal displacements. An Einstein model was developed to calculate thermal displacements and Einstein frequencies from interatomic potentials. The calculated thermal displacements are 10 to 20 percent less than the experimental values. This is due to the simplifying assumptions in the model. The model calculation and the experimental results do agree on the changes in the thermal displacements with alloying. The Einstein model is also used to calculate the vibrational entropy in alloys.