Search Results

Advanced search parameters have been applied.
open access

Flaw identification from forced vibration testing

Description: A continuous system approach to the vibration characteristics of a symmetrically slotted beam has been developed. The beam was modelled as a Bernoulli-Euler beam with a reasonable stress distribution associated with the slots. The equation of motion was developd and resonant frequencies obtained from Rayleigh's Quotient. An experimental study of an aluminum beam with symmetrical slots was performed. The resonant frequency and apparent mass (a measure of damping) were measured. Reasonably good c… more
Date: January 1, 1988
Creator: Rogers, J. D. & Hollingshead, J. R.
Partner: UNT Libraries Government Documents Department
open access

Perturbation treatment of the longitudinal coupling impedance of a toroidal beam tube

Description: A simple analytical expression for the longitudinal coupling impedance of a toroidal beam tube below the resonance region has been derived by expanding the electromagnetic fields of the toroidal beam tube in a power series in curvature and substituting directly into Maxwell's equations. The resulting expression consists of the impedance of the straight beam pipe plus a correction terms due to the curvature. It has been verified that this result gives excellent agreement to the exact solution be… more
Date: January 1, 1991
Creator: Hahn, H. & Tepikian, S.
Partner: UNT Libraries Government Documents Department
open access

Some strategies for enhancing the performance of the block Lanczos method

Description: The block Lanczos method is used to calculate the eigenfunctions for a generalized eigenvalue problem constructed for a finite element solution to a 2-dimensional Schr/umlt o/dinger equation on the surface of a hypersphere. This equation results from a treatment of the 3-dimensional reactive scattering problem using Adiabatically adjusting. Principal axes Hyperspherical (APH) coordinates. Three stategies are considered with respect to increasing the CPU performance of the block Lanczos (with se… more
Date: January 1, 1988
Creator: Kress, J.D.; Woodruff, S.B.; Parker, G.A. & Pack, R.T.
Partner: UNT Libraries Government Documents Department
open access

Mathematical Modeling of Cation Contamination in a Proton-exchange Membrane

Description: Transport phenomena in an ion-exchange membrane containing both H+ and K+ are described using multicomponent diffusion equations (Stefan-Maxwell). A model is developed for transport through a Nafion 112 membrane in a hydrogen-pump setup. The model results are analyzed to quantify the impact of cation contamination on cell potential. It is shown that limiting current densities can result due to a decrease in proton concentration caused by the build-up of contaminant ions. An average cation conce… more
Date: September 11, 2008
Creator: Weber, Adam & Delacourt, Charles
Partner: UNT Libraries Government Documents Department
open access

The evolution of HOBO

Description: HOBO is a free-Lagrangian hydrodynamics code which has been under development at Los Alamos for several years. It was based on free-Lagrangian tracer points and finite difference approximations to the equations of motion for fluid flow. This method will be reviewed briefly here. The use of an independent time step at each point is also described. This technique increases the speed of the code by factors of 10 to 20. How the code has been modified to achieve energy and momentum conservation and … more
Date: April 1, 1987
Creator: Clark, R. A.
Partner: UNT Libraries Government Documents Department
open access

A fully nonlinear characteristic method for gyrokinetic simulation

Description: We present a new scheme which evolves the perturbed part of the distribution function along a set of characteristics that solves the fully nonlinear gyrokinetic equations. This nonlinear characteristic method for particle simulation is an extension of the partially linear weighting scheme, and may be considered an improvement of existing {delta} f methods. Some of the features of this new method are: the ability to keep all of the nonlinearities, particularly those associated with parallel acce… more
Date: July 1, 1992
Creator: Parker, S. E. & Lee, W. W.
Partner: UNT Libraries Government Documents Department
open access

Modeling of the quasi-steady magnetotail

Description: The three-dimensional theory of the quiet magnetotail is reviewed and updated. The most advanced formulation of the theory allows one to solve the magnetohydrodynamic (MHD) equations including field-aligned flow by reduction to a set of ordinary differential equations and an ordinary integral. These solutions represent lowest order solutions of an asymptotic expansion of the MHD equations for small electric field and weak time dependence. Applications to the magnetotail configuration are presen… more
Date: January 1, 1989
Creator: Birn, J. (Los Alamos National Lab., NM (USA)) & Schindler, K. (Ruhr-Univ., Bochum (Germany, F.R.))
Partner: UNT Libraries Government Documents Department
open access

CSQII: a two-dimensional Eulerian code for computation of material motion in two dimensions

Description: CSQII is a general-purpose code with a wide variety of options: rectangular or cylindrical coordinates, up to ten materials, allowance for void, elestic-plastic or distended material, inclusion of energy sources or gravity. The basic solution scheme integrates the Lagrangian form of the conservation equations through a time step and then explicity rezones back to the Eulerian grid. The following aspects are treated in some detail: equation of state, momentum balance, energy balance, rezoning, a… more
Date: January 1, 1980
Creator: McGlaun, J. M. & Thompson, S. L.
Partner: UNT Libraries Government Documents Department
open access

Parabolic approximation method for the mode conversion-tunneling equation

Description: The derivation of the wave equation which governs ICRF wave propagation, absorption, and mode conversion within the kinetic layer in tokamaks has been extended to include diffraction and focussing effects associated with the finite transverse dimensions of the incident wavefronts. The kinetic layer considered consists of a uniform density, uniform temperature slab model in which the equilibrium magnetic field is oriented in the z-direction and varies linearly in the x-direction. An equivalent d… more
Date: July 1, 1987
Creator: Phillips, C. K.; Colestock, P. L.; Hwang, D. Q. & Swanson, D. G.
Partner: UNT Libraries Government Documents Department
open access

Electromagnetic Penetration Through Narrow Slots in Conducting Surfaces and Coupling to Structures on the Shadow Side

Description: Electromagnetic field penetration through a curved narrow slot in a planar conducting surface and coupling to a curved, loaded thin wire on the shadow side are determined in the time domain (TD) and the frequency domain (FD) by integral equation methods. Coupled integral equations are derived and solved numerically for the equivalent magnetic current in the slot and the electric current on the wire, from which the field that penetrates the slotted surface is determined. One employs a piecewise … more
Date: July 1, 1990
Creator: Reed, Erik K. & Butler, Chalmers M.
Partner: UNT Libraries Government Documents Department
open access

Focus wave modes in homogeneous Maxwell's equation - TE-mode

Description: Mathematical formulations are presented for TE-mode, three-dimensional, solitary electromagnetic pulses propagating in free space. The pulses are required to satisfy the homogeneous Maxwell's equations, have a three-dimensional pulse structure, have no charge, move at light velocity in straight lines, have nondispersive pulses for all time, and have finite electromagnetic energy. (LEW)
Date: January 1, 1982
Creator: Brittingham, J.N.
Partner: UNT Libraries Government Documents Department
open access

Theory of the tune shift due to linear coupling

Description: The presence of skew quadrupole fields will linearly couple the x and y motions. The x and y motion can then be written as the sum of two normal modes which have the tunes {nu}{sub 1},{nu}{sub 2}, in the absence of the skew quadrupole fields. New beta functions, {Beta}{sub 1} and {Beta}{sub 2}, can be defined which are the beta functions of the normal modes and which are different from {Beta}{sub x} and {Beta}{sub y}, the beta functions of the unperturbed accelerator. This paper presents analyt… more
Date: July 1, 1991
Creator: Parzen, G.
Partner: UNT Libraries Government Documents Department
open access

Spectral evolution equation for the sideband instability in a free-electron laser oscillator

Description: Assuming that the light remains in the optical system while the electrons pass through and are lost, we have derived the evolution equation for an arbitrary optical spectrum in a free-electron laser oscillator. The resulting integrodifferential equation includes the effects of linear optical system losses (due to either mirror reflectivity or clipping), the usual small signal gain term, and a quadratic nonlinear term that includes the effects of saturation and coupling to sideband modes. The ef… more
Date: January 1, 1987
Creator: Channell, P.J.
Partner: UNT Libraries Government Documents Department
open access

Maxwell-Vlasov equations as a continuous Hamiltonian system

Description: The well-known Maxwell-Vlasov equations that describe a collisionless plasma are cast into Hamiltonian form. The dynamical variables are the physical although noncanonical variables E, B, and f. We present a Poisson bracket which acts on these variables and the energy functional to produce the equations of motion.
Date: November 1, 1980
Creator: Morrison, P.J.
Partner: UNT Libraries Government Documents Department
open access

A Magnetically Switched Kicker for Proton Extraction

Description: The application of magnetic current amplification and switching techniques to the generation of precise high current pulses for switching magnets is described. The square loop characteristic of Metglas tape wound cores at high excitation levels provides excellent switching characteristics for microsecond pulses. The rugged and passive nature of this type pulser makes it possible to locate the final stages of amplification at the load for maximum efficiency. 12 refs., 8 figs.
Date: March 1, 1989
Creator: Dinkel, John & Biggs, James
Partner: UNT Libraries Government Documents Department
open access

Particle dynamics for motion in a non-planar accelerator

Description: The basic dynamics of a planar accelerator is extended to the non-planar case. This is done using the geometrical concept of torsion and extending the Hamiltonian formalism. A generalized non-planar reference orbit is adopted which introduces torsion in appropriately chosen drift spaces. The parameters of the reference orbit are associated with uncoupled and coupled betatron parameters currently in use.
Date: August 20, 1985
Creator: Antillon, A. & Month, M.
Partner: UNT Libraries Government Documents Department
open access

Semi-implicit spectral deferred correction methods for ordinary differential equations

Description: A semi-implicit formulation of the method of spectral deferred corrections (SISDC) for ordinary differential equations with both stiff and non-stiff terms is presented. Several modifications and variations to the original spectral deferred corrections method by Dutt, Greengard, and Rokhlin concerning the choice of integration points and the form of the correction iteration are presented. The stability and accuracy of the resulting ODE methods are explored analytically and numerically. The SISDC… more
Date: October 6, 2002
Creator: Minion, Michael L.
Partner: UNT Libraries Government Documents Department
open access

Adiabatic Hamiltonian Deformation, Linear Response Theory, and Nonequilibrium Molecular Dynamics

Description: Although Hamiltonians of various kinds have previously been used to derive Green-Kubo relations for the transport coefficients, the particular choice described is uniquely related to thermodynamics. This nonequilibrium Hamiltonian formulation of fluid flow provides pedagogically simple routes to nonequilibrium fluxes and distribution functions, to theoretical understanding of long-time effects, and to new numerical methods for simulating systems far from equilibrium. The same methods are now be… more
Date: May 28, 1980
Creator: Hoover, W. G.
Partner: UNT Libraries Government Documents Department
open access

Tranverse beam break up in a periodic linac

Description: The problem of cumulative beam break up in a periodic linac for a general impedance is discussed, with the effects of acceleration included. The transverse equations of motion for a set of identical point like bunches moving along the length of the linac are cast into a simple form using a smooth approximation. This results in a working formula that is used to analyze beam breakup. Explicit expressions for the transverse motion in the case of a single resonance impedance are found using saddle … more
Date: January 1, 1987
Creator: Decker, G. & Wang, J.M.
Partner: UNT Libraries Government Documents Department
open access

Chaotic Vibrations of Nonlinearly Supported Tubes in Crossflow

Description: By means of the unsteady-flow theory and a bilinear mathematical model, a theoretical study is presented for chaotic vibrations associated with the fluid-elastic instability of nonlinearly supported tubes in a crossflow. Effective tools, including phase portraits, power spectral density, Poincare maps, Lyapunov exponent, fractal dimension, and bifurcation diagrams, are utilized to distinguish periodic and chaotic motions when the tubes vibrate in the instability region. The results show periodi… more
Date: February 1992
Creator: Cai, Y. & Chen, Shoei-Sheng
Partner: UNT Libraries Government Documents Department
Back to Top of Screen