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Stability of Resonator Configurations in the Presence of Free-Electron Laser Interactions

Description: The stability of empty resonators (or cold cavities) has been widely studied, and is well understood. Here we consider the stability of symmetric resonator systems when there is a free-electron laser (FEL) interaction present within the cavity. We first construct a linear thick-lens model of the FEL and analytically study the dependence of resonator stability on its geometry. Next, we employ a nonlinear, three-dimensional FEL oscillator code to study the dependence of FEL performance on the cavity configuration. The analytic and numerical approaches are compared and it is shown that they agree quite well. It is found that the region of stability is shifted toward longer cavities, and beyond the concentric configuration. Between the confocal and the concentric configurations, where the empty-resonator analysis predicts stability, there now appear regions of instability. We find that operation near the concentric configuration is preferable, and operation very near the confocal should be avoided.
Date: November 1, 1992
Creator: Krishnagopal, S. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Fractal analysis of pressure transients in the Geysers Geothermal Field

Description: The conventionally accepted models for the interpretation of pressure transient tests in naturally fractured reservoirs usually involve simplistic assumptions regarding the geometry and transport properties of the fractured medium. Many single well tests in this type of reservoirs fail to show the predicted behavior for dual or triple porosity or permeability systems and cannot be explained by these models. This paper describes the application of a new model based on a fractal interpretation of the fractured medium. The approach, discussed elsewhere [2], [6], is applied to field data from The Geysers Geothermal Field. The objective is to present an alternative interpretation to well tests that characterizes the fractured medium in a manner more consistent with other field evidence. The novel insight gained from fractal geometry allows the identification of important characteristics of the fracture structure that feeds a particular well. Some simple models are also presented that match the field transient results.
Date: January 1, 1992
Creator: Acuna, J.A.; Ershaghi, I. & Yortsos, Y.C.
Partner: UNT Libraries Government Documents Department

Determining the 3-D fracture structure in the Geysers geothermal reservoir

Description: The bulk of the steam at the Geysers geothermal field is produced from fractures in a relatively impermeable graywacke massif which has been heated by an underlying felsite intrusion. The largest of these fractures are steeply dipping right lateral strike-slip faults which are subparallel to the NW striking Collayomi and Mercuryville faults which form the NE and SW boundaries of the known reservoir. Where the graywacke source rock outcrops at the surface it is highly sheared and fractured over a wide range of scale lengths. Boreholes drilled into the reservoir rock encounter distinct ''steam entries'' at which the well head pressure jumps from a few to more than one hundred psi. This observation that steam is produced from a relatively small number of major fractures has persuaded some analysts to use the Warren and Root (1963) dual porosity model for reservoir simulation purposes. The largest fractures in this model are arranged in a regular 3-D array which partitions the reservoir into cubic ''matrix'' blocks. The net storage and transport contribution of all the smaller fractures in the reservoir are lumped into average values for the porosity and permeability of these matrix blocks which then feed the large fractures. Recent improvements of this model largely focus on a more accurate representation of the transport from matrix to fractures (e.g. Pruess et al., 1983; Ziminerman et al., 1992), but the basic geometry is rarely questioned. However, it has long been recognized that steam entries often occur in clusters separated by large intervals of unproductive rock (Thomas et al., 1981). Such clustering of fixtures at all scale lengths is one characteristic of self-similar distributions in which the fracture distribution is scale-independent. Recent studies of the geometry of fracture networks both in the laboratory and in the field are finding that such patterns are ...
Date: January 1, 1992
Creator: Sammis, Charles G.; An, Linji & Ershaghi, Iraj
Partner: UNT Libraries Government Documents Department

Optimizing Reinjection Strategy at Palinpinon, Philippines Based on Chloride Data

Description: One of the guidelines established for the safe and efficient management of the Palinpinon Geothermal Field is to adopt a production and well utilization strategy such that the rapid rate and magnitude of reinjection fluid returns leading to premature thermal breakthrough would be minimized. To help achieve this goal, sodium fluorescein and radioactive tracer tests have been conducted to determine the rate and extent of communication between the reinjection and producing sectors of the field. The first objective of this paper is to show how the results of these tests, together with information on field geometry and operating conditions were used in algorithms developed in Operations Research to allocate production and reinjection rates among the different Palinpinon wells. Due to operational and economic constraints, such tracer tests were very limited in number and scope. This prevents obtaining information on the explicit interaction between each reinjection well and the producing wells. Hence, the chloride value of the producing well, was tested to determine if use of this parameter would enable identifying fast reinjection paths among different production/reinjection well pairs. The second aim, therefore, of this paper is to show the different methods of using the chloride data of the producing wells and the injection flow rates of the reinjection wells to provide a ranking of the pair of wells and, thereby, optimize the reinjection strategy of the field.
Date: March 24, 1992
Creator: Urbino, Ma. Elena G. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

A cubic matrix-fracture geometry model for radial tracer flow in naturally fractured reservoirs

Description: This study presents a general solution for the radial flow of tracers in naturally fractured reservoirs, with cubic blocks matrix-fracture geometry. Continuous and finite step injection of chemical and radioactive tracers are considered. The reservoir is treated as being composed of two regions: a mobile where dispersion and convection take place and a stagnant where only diffusion and adsorption are allowed. Radioactive decay is considered in both regions. The model of this study is thoroughly compared under proper simplified conditions to those previously presented in the literature. The coupled matrix to fracture solution in the Laplace space is numerically inverted by means of the Crump algorithm. A detailed validation of the model with respect to solutions previously presented and/or simplified physical conditions solutions (i.e., homogeneous case) or limit solutions (i.e., naturally fractured nearly homogeneous) was carried out. The influence of the three of the main dimensionless parameters that enter into the solution was carefully investigated. A comparison of results for three different naturally fractured systems, vertical fractures (linear flow), horizontal fractures (radial flow) and the cubic geometry model of this study, is presented.
Date: January 1, 1992
Creator: Ramirez-Sabag, Jetzabeth & V., Fernando Samaniego
Partner: UNT Libraries Government Documents Department

Hydraulic fracture design optimization

Description: This research and development investigation, sponsored by US DOE and the oil and gas industry, extends previously developed hydraulic fracture geometry models and applied energy related characteristic time concepts towards the optimal design and control of hydraulic fracture geometries. The primary objective of this program is to develop rational criteria, by examining the associated energy rate components during the hydraulic fracture evolution, for the formulation of stimulation treatment design along with real-time fracture configuration interpretation and control.
Date: January 1, 1992
Creator: Lee, Tae-Soo & Advani, S.H.
Partner: UNT Libraries Government Documents Department

The Torus Does Not Have a Hyperbolic Structure

Description: Several basic topics from Algebraic Topology, including fundamental group and universal covering space are shown. The hyperbolic plane is defined, including its metric and show what the "straight" lines are in the plane and what the isometries are on the plane. A hyperbolic surface is defined, and shows that the two hole torus is a hyperbolic surface, the hyperbolic plane is a universal cover for any hyperbolic surface, and the quotient space of the universal cover of a surface to the group of automorphisms on the covering space is equivalent to the original surface.
Date: August 1992
Creator: Butler, Joe R.
Partner: UNT Libraries

1992 annual report to the National Science Foundation

Description: The Geometry Center research program has a number of different aspects. This report documents the work of the past year. The activities described here are organized under intertwined areas: manifold geometry and associated group theory; optimal geometries; dynamical systems; and computational geometry and computer graphics.
Date: December 31, 1992
Partner: UNT Libraries Government Documents Department

Development of singularities in Riemann Invariants

Description: Shocks form in finite time in systems of quasilinear hyperbolic equations in one space variable which are genuinely nonlinear. The authors write down a simple geometric construction for systems of two equations, and use it to obtain a priori estimates for the growth of the derivatives. They also find realistic bounds on the maximum and minimum time of existence of smooth solutions for large amplitude waves in a model system of an unusual type.
Date: May 22, 1992
Creator: Keyfitz, B.L.
Partner: UNT Libraries Government Documents Department

Characterizations of Some Combinatorial Geometries

Description: We give several characterizations of partition lattices and projective geometries. Most of these characterizations use characteristic polynomials. A geometry is non—splitting if it cannot be expressed as the union of two of its proper flats. A geometry G is upper homogeneous if for all k, k = 1, 2, ... , r(G), and for every pair x, y of flats of rank k, the contraction G/x is isomorphic to the contraction G/y. Given a signed graph, we define a corresponding signed—graphic geometry. We give a characterization of supersolvable signed graphs. Finally, we give the following characterization of non—splitting supersolvable signed-graphic geometries : If a non-splitting supersolvable ternary geometry does not contain the Reid geometry as a subgeometry, then it is signed—graphic.
Date: August 1992
Creator: Yoon, Young-jin
Partner: UNT Libraries

Estimated Critical Conditions for UO(Sub 2)F(Sub 2)-H(Sub 2)O Systems in Fully Water-Reflected Spherical Geometry

Description: The purpose of this report is to document reference calculations performed using the SCALE-4.0 code system to determine the critical parameters of UO{sub 2}F{sub 2}-H{sub 2}O spheres. The calculations are an extension of those documented in ORNL/CSD/TM-284. Specifically, the data for low-enriched UO{sub 2}F{sub 2}-H{sub 2}O spheres have been extended to highly enriched uranium. These calculations, together with those reported in ORNL/CSD/TM-284, provide a consistent set of critical parameters (k{sub {infinity}}, volume, mass, mass of water) for UO{sub 2}F{sub 2} and water over the full range of enrichment and moderation ratio.
Date: January 1, 1992
Creator: Jordan, W.C.
Partner: UNT Libraries Government Documents Department

Reducing Emissions from Uranium Dissolving

Description: This study was designed to assess the feasibility of decreasing NO{sub x} emissions from the current uranium alloy scrap tray dissolving facility. In the current process, uranium scrap is dissolved in boiling nitric acid in shallow stainless-steel trays. As scrap dissolves, more metal and more nitric acid are added to the tray by operating personnel. Safe geometry is assured by keeping liquid level at or below 5 cm, the depth of a safe infinite slab. The accountability batch control system provides additional protection against criticality. The trays are steam coil heated. The process has operated satisfactorily, with few difficulties, for decades. Both uranium and uranium alloys are dissolved. Nitric acid is recovered from the vapors for reuse. Metal nitrates are sent to uranium recovery. Brown NO{sub x} fumes evolved during dissolving have occasionally resulted in a visible plume from the trays. The fuming is most noticeable during startup and after addition of fresh acid to a tray. Present environmental regulations are expected to require control of brown NO{sub x} emissions. Because NO{sub x} is hazardous, fumes should be suppressed whenever the electric blower system is inoperable. Because the tray dissolving process has worked well for decades, as much of the current capital equipment and operating procedures as possible were preserved. A detailed review of the literature, indicated the feasibility of slightly altering process chemistry to favor the production of NO{sub 2}, which can be scrubbed and recycled as nitric acid. Methods for controlling the process to manage offgas product distribution and to minimize chemical reaction hazards were also considered.
Date: January 1, 1992
Creator: Griffith, W.L.
Partner: UNT Libraries Government Documents Department

Plasma-induced conversion of surface-adsorbed hydrocarbons

Description: Experimental results are reported for an electrical device for direct conversion of methane into higher hydrocarbons. A microchannel plate is excited with electrons from a photoemissive source, and electron impact ionization of methane on the inner surfaces of the microchannels creates an ion feedback process. The resulting low-density plasma creates higher hydrocarbons when charged particles impact the surfaces at grazing incidence. The production Of C{sub 2} to C{sub 8}-containing gases was noted, with a selectivity for C{sub 2} of 39% in one case. The proportions of converted products and the conversion rates depend upon the electrical voltage, the microchannel geometry, and the operating pressure. Conversion rates increase with operating pressure.
Date: January 1, 1992
Creator: Sackinger, W.M.
Partner: UNT Libraries Government Documents Department

CGVIEW: A program to generate isometric and perspective views of combinatorial geometries

Description: The prototype of a graphical debugger for combinatorial geometry (CG) is described. The prototype debugger consists of two parts: a FORTRAN-based view'' generator and a Microsoft Windows application for displaying the geometry. This document describes the code CGVIEW, which comprises the first part of the system. User-specified options permit the selection of an arbitrary viewpoint in space and the generation of either an isometric or perspective view. Additionally, any combination of zones, materials, or regions can be flagged as invisible to facilitate the inspection of internal details of the geometry. In the same manner, an arbitrary body can be cut away from the geometry to facilitate inspection and debugging. Examples illustrating the various options are described.
Date: July 1, 1992
Creator: Burns, T.J.
Partner: UNT Libraries Government Documents Department

Thermal-hydraulic and structural considerations on the gap variation between fuel bundle and hexcan

Description: One of the safety concerns in reactor operation is the temperature of the fuel elements, which are contained in a hexagonal duct, referred to as the hexcan. There are gaps between the fuel bundle and the hexcan, and the gaps somewhat affect thermal-hydraulic behavior of the fuel element. This paper investigates the impact of gap variations on the thermal-hydraulic responses of the fuel element as well as the possibility of fuel bundle and hexcan interaction. The gap variation between hex duct and fuel bundle is caused by differential thermal expansion, creep strain, and irradiation-induced swelling of fuel-cladding and hex duct, and it is a function of fuel burnup. The effects of gap variations on the thermal-hydraulic responses of typical driver subassemblies in the Experimental Breeder Reactor (EBR-II) are investigated. A structural analysis was performed to predict the in-reactor deformation behavior of fuel bundle and hex duct, and followed by a thermal-hydraulic analysis to determine the flow and temperature response due to gap changes. The effects of geometry variation on the thermal-hydraulic response are discussed. The study indicates that the effect of gap variation should not be ignored for subassembly designs.
Date: January 1, 1992
Creator: Chang, L.K.; Lee, M.J. & Ku, J.Y.
Partner: UNT Libraries Government Documents Department

Density equalizing map projections: A new algorithm

Description: In the study of geographic disease clusters, an alternative to traditional methods based on rates is to analyze case locations on a transformed map in which population density is everywhere equal. Although the analyst's task is thereby simplified, the specification of the density equalizing map projection (DEMP) itself is not simple and continues to be the subject of considerable research. Here a new DEMP algorithm is described, which avoids some of the difficulties of earlier approaches. The new algorithm (a) avoids illegal overlapping of transformed polygons; (b) finds the unique solution that minimizes map distortion; (c) provides constant magnification over each map polygon; (d) defines a continuous transformation over the entire map domain; (e) defines an inverse transformation; (f) can accept optional constraints such as fixed boundaries; and (g) can use commercially supported minimization software. Work is continuing to improve computing efficiency and improve the algorithm.
Date: February 1, 1992
Creator: Merrill, D.W.; Selvin, S. & Mohr, M.S.
Partner: UNT Libraries Government Documents Department

A dip-dependent divergence correction

Description: A divergence correction is conventionally applied to zero-offset data in an effort to preserved amplitude information. The conventional divergence correction compensates for the geometrical spreading of a point source in a horizontally layered medium where velocity varies with depth only. The dip-dependent divergence correction extends the conventional correction for improved amplitude processing of dipping beds. The dip-dependent divergence correction is computed by dynamic ray tracing, and applied to stacked data using a dip decomposition technique. This correction decreases amplitudes relative to the conventional correction for steep dips and late times. In a data example from the Gulf of Mexico, the conventional correction over- amplified the reflection off a salt dome flank by a factor of 1.6. High amplitudes near salt flanks are also associated with the presence of hydrocarbons. Applying the dip-dependent divergence correction ensures that bright spots'' are not due to over-amplification of steep dips by the conventional correction. In areas like the Gulf of Mexico, where the velocity function varies primarily with depth, and steep beds are commonplace, the dip-dependent divergence correction is an inexpensive way to improve the amplitude information in seismic images.
Date: January 1, 1992
Creator: Fazzari, F.
Partner: UNT Libraries Government Documents Department

Part mounting revisited

Description: Having been involved with single point diamond turning since the 1960's; I share with others of my age, a unique perspective of the craft. I am amazed at how the fundamentals seem to be forgotten or misplaced, and need to be re emphasized and re learned. Each new precision machine operator not only needs to re learn (many times the hard way), these fundamentals, but seems to inherit all the folklore; good and bad, from his predecessor. Let me explain. I spend some of my time as a consultant to the shops' division at the Los Alamos National Laboratory, at which there are five precision turning machines divided between two buildings. The main shop area houses an old friction way (hydrodynamic) turning Machine. The base of this turning machine is made from the base of an old Moore measuring machine. The air bearing spindle, a Red Head'' was made by the Heald Machine Tool Co. With the addition of an Allen-Bradley Numerical control system, this machine has become a work horse, used primarily to make smooth flat surfaces in the fly-cutting mode. Recently, I became involved in the evaluation and repair of the machine as it no longer produced smooth surfaces. Smooth surfaces are not the point of this narrative, accurate geometry however is.
Date: January 1, 1992
Creator: Hannah, P.R.; Garcia, F.P. & Stewart, D.D.
Partner: UNT Libraries Government Documents Department

Lewis number effects on turbulent premixed flame structure

Description: The influence of the Lewis number on turbulent flame front geometry is investigated in a premixed turbulent stagnation point flame. A laser tomography technique is used to obtain the flame shape, a fractal analysis of the multiscale flame edges is performed and the distribution of local flame front curvature is determined. Lean H[sub 2]/Air and C[sub 3]H[sub 8]/Air mixtures with similar burning rates were investigated with Lewis numbers of 0.33 and 1.85 respectively. At the conditions studied the laminar H[sub 2]/Air mixture is unstable and a cellular structure is observed. Turbulence in the reactant is generated by a perforated plate and the turbulent length scale (3mm) and intensity (7%) at the nozzle exit are fixed. The equivalence ratio is set so that the burning velocity is the same for all the cases. Results show clearly that the turbulent flame surface area is dependent on the Lewis number. For a Lewis number less than unity surface area production is observed. The shape of the flame front curvature distribution is not found to be very sensitive to the Lewis number. For the H[sub 2]/Air mixture the distribution is skewed toward the positive values indicating the presence of cusps while for the C[sub 3]H[sub 8]/Air mixture the distribution is more symmetrical. In both cases the average curvature is found to be zero, and if the local burning speed varies linearly with curvature, the local positive and negative burning velocity variations due to curvature will balance.
Date: September 1, 1992
Creator: Goix, P.J. (Centre National de la Recherche Scientifique (CNRS), 230 - Mont-Saint-Aignan (France). URA CORIA) & Shepherd, I.G. (Lawrence Berkeley Lab., CA (United States))
Partner: UNT Libraries Government Documents Department

The influence of the rib width on the performance of tubes with the separation and reattachment enhancement mechanism

Description: This paper presents numerically predicted turbulent heat-transfer and friction-factor results for tubes with transverse, rectangular ribs for different width-to-height ratios. The rib spacing was maintained at values where the separated flow over the rib reattached between adjacent ribs (i.e. the separation and reattachment enhancement mechanism). The mean Nusselt number was found to decrease slightly with an increase in the width to height ratio for low Prandtl number fluids (Pr = 0.71). However, the trend is more complex for higher Prandtl number fluids. The mean Nusselt number can either increase or decrease depending on the magnitude of the Prandtl number and rib spacing. The friction factors decreased with an increase in the width to height ratio and the magnitude of this decrease was somewhat Reynolds number dependent.
Date: January 1, 1992
Creator: Arman, B. & Rabas, T.J.
Partner: UNT Libraries Government Documents Department

(Mathematics and string theory)

Description: Over the past year our research activities concentrated around: (1) non-commutative differential geometry and its connections with quantum physics and (2) 2-dimensional(super) conformal quantum field theories and related non-linear {sigma}-models. This paper discusses these topics.
Date: January 1, 1992
Partner: UNT Libraries Government Documents Department

Understanding curved detonation waves

Description: A wave curve is the set of final states to which an initial state may be connected by a traveling wave. In gas dynamics, for example, the wave curve consists of the shock Hugoniot curve for compressive waves and the rarefaction curve for expansive waves. In this paper, we discuss the wave curve for an undriven planar detonation and for general planar detonations. We then extend the wave curve concept to detonations in converging and diverging geometry. We also discuss the application of these wave curves to the numerical computation of detonation problems.
Date: January 1, 1992
Creator: Bukiet, B.G. (New Jersey Inst. of Tech., Newark, NJ (United States). Dept. of Mathematics) & Menikoff, R. (Los Alamos National Lab., NM (United States))
Partner: UNT Libraries Government Documents Department