16,697 research outputs found
Local strain redistribution corrections for a simplified inelastic analysis procedure based on an elastic finite-element analysis
Strain redistribution corrections were developed for a simplified inelastic analysis procedure to economically calculate material cyclic response at the critical location of a structure for life prediction proposes. The method was based on the assumption that the plastic region in the structure is local and the total strain history required for input can be defined from elastic finite-element analyses. Cyclic stress-strain behavior was represented by a bilinear kinematic hardening model. The simplified procedure predicts stress-strain response with reasonable accuracy for thermally cycled problems but needs improvement for mechanically load-cycled problems. Neuber-type corrections were derived and incorporated in the simplified procedure to account for local total strain redistribution under cyclic mechanical loading. The corrected simplified method was used on a mechanically load-cycled benchmark notched-plate problem. The predicted material response agrees well with the nonlinear finite-element solutions for the problem. The simplified analysis computer program was 0.3% of the central processor unit time required for a nonlinear finite-element analysis
On local total strain redistribution using a simplified cyclic inelastic analysis based on an elastic solution
Strain redistribution corrections were developed for a simplified inelastic analysis procedure to economically calculate material cyclic response at the critical location of a structure for life prediction purposes. The method was based on the assumption that the plastic region in the structure is local and the total strain history required for input can be defined from elastic finite element analyses. Cyclic stress-strain behavior was represented by a bilinear kinematic hardening model. The simplified procedure has been found to predict stress-strain response with reasonable accuracy for thermally cycled problems but needs improvement for mechanically load cycled problems. This study derived and incorporated Neuber type corrections in the simplified procedure to account for local total strain redistribution under cyclic mechanical loading. The corrected simplified method was exercised on a mechanically load cycled benchmark notched plate problem. Excellent agreement was found between the predicted material response and nonlinear finite element solutions for the problem. The simplified analysis computer program used 0.3 percent of the CPU time required for a nonlinear finite element analysis
Ultracold neutron depolarization in magnetic bottles
We analyze the depolarization of ultracold neutrons confined in a magnetic
field configuration similar to those used in existing or proposed
magneto-gravitational storage experiments aiming at a precise measurement of
the neutron lifetime. We use an extension of the semi-classical Majorana
approach as well as an approximate quantum mechanical analysis, both pioneered
by Walstrom et al. [Nucl. Instr. Meth. Phys. Res. A 599, 82 (2009)]. In
contrast with this previous work we do not restrict the analysis to purely
vertical modes of neutron motion. The lateral motion is shown to cause the
predominant depolarization loss in a magnetic storage trap. The system studied
also allowed us to estimate the depolarization loss suffered by ultracold
neutrons totally reflected on a non-magnetic mirror immersed in a magnetic
field. This problem is of preeminent importance in polarized neutron decay
studies such as the measurement of the asymmetry parameter A using ultracold
neutrons, and it may limit the efficiency of ultracold neutron polarizers based
on passage through a high magnetic field.Comment: 18 pages, 6 figure
Calculation of geometric phases in electric dipole searches with trapped spin-1/2 particles based on direct solution of the Schr\"odinger equation
Pendlebury [Phys. Rev. A , 032102 (2004)] were
the first to investigate the role of geometric phases in searches for an
electric dipole moment (EDM) of elementary particles based on Ramsey-separated
oscillatory field magnetic resonance with trapped ultracold neutrons and
comagnetometer atoms. Their work was based on the Bloch equation and later work
using the density matrix corroborated the results and extended the scope to
describe the dynamics of spins in general fields and in bounded geometries. We
solve the Schr\"odinger equation directly for cylindrical trap geometry and
obtain a full description of EDM-relevant spin behavior in general fields,
including the short-time transients and vertical spin oscillation in the entire
range of particle velocities. We apply this method to general macroscopic
fields and to the field of a microscopic magnetic dipole.Comment: 11 pages, 4 figure
Unified constitutive material models for nonlinear finite-element structural analysis
Unified constitutive material models were developed for structural analyses of aircraft gas turbine engine components with particular application to isotropic materials used for high-pressure stage turbine blades and vanes. Forms or combinations of models independently proposed by Bodner and Walker were considered. These theories combine time-dependent and time-independent aspects of inelasticity into a continuous spectrum of behavior. This is in sharp contrast to previous classical approaches that partition inelastic strain into uncoupled plastic and creep components. Predicted stress-strain responses from these models were evaluated against monotonic and cyclic test results for uniaxial specimens of two cast nickel-base alloys, B1900+Hf and Rene' 80. Previously obtained tension-torsion test results for Hastelloy X alloy were used to evaluate multiaxial stress-strain cycle predictions. The unified models, as well as appropriate algorithms for integrating the constitutive equations, were implemented in finite-element computer codes
Develop and test fuel cell powered on-site integrated total energy systems: Phase 3, full-scale power plant development
A 25 cell stack of the 13 inch x 23 inch cell size (about 4kW) remains on test after 6000 hours, using simulated reformate fuel. A similar stack was previously shut down after 7000 hours on load. These tests were carried out for the purpose of assessing the durability of fuel cell stack components developed through the end of 1983. In light of the favorable results obtained, a 25kW stack that will contain 175 cells of the same size is being constructed using the same technology base. The components for the 25kW stack have been completed. A methanol steam reformer with a design output equivalent to 50kW has been constructed to serve as a hydrogen generator for the 25kW stack. This reformer and the balance of the fuel processing sub system are currently being tested and debugged. The stack technology development program focused on cost reduction in bipolar plates, nonmetallic cooling plates, and current collecting plates; more stable cathode catalyst support materials; more corrosion resistant metal hardware; and shutdown/start up tolerance
Develop and test fuel cell powered on-site integrated total energy systems
On-going testing of an 11 cell, 10.7 in. x 14 in. stack (about 1 kW) reached 2600 hours on steady load. Nonmetallic cooling plates and an automated electrolyte replenishment system continued to perform well. A 10 cell, 10.7 in. x 14 in. stack was constructed with a modified electrolyte matrix configuration for the purpose of reducing cell IR loss. The desired effect was achieved, but the general cell performance level was irregular. Evaluation is continuing. Preparations for a long term 25 cell, 13 in. x 23 in. test stack (about 4 kW) approached completion. Start up in early May 1984 is expected
Magnetic models on Apollonian networks
Thermodynamic and magnetic properties of Ising models defined on the
triangular Apollonian network are investigated. This and other similar networks
are inspired by the problem of covering an Euclidian domain with circles of
maximal radii. Maps for the thermodynamic functions in two subsequent
generations of the construction of the network are obtained by formulating the
problem in terms of transfer matrices. Numerical iteration of this set of maps
leads to exact values for the thermodynamic properties of the model. Different
choices for the coupling constants between only nearest neighbors along the
lattice are taken into account. For both ferromagnetic and anti-ferromagnetic
constants, long range magnetic ordering is obtained. With exception of a size
dependent effective critical behavior of the correlation length, no evidence of
asymptotic criticality was detected.Comment: 21 pages, 5 figure
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