Measurements of emission spectra from hot,dense germanium plasma in short pulse laser experiments

Heating of thin foil targets by an high power laser at intensities of 10¹⁷–10¹⁹ W/cm² has been studied as a method for producing high temperature, high density samples to investigate X-ray opacity and equation of state. The targets were plastic (parylene-N) foils with a microdot made of a mixture of germanium and titanium buried at depth of 1.5 μm. The L-shell spectra from the germanium and the K-shell spectra from the titanium were taken using crystal spectrometers recording onto film and an ultra fast X-ray streak camera coupled to a conical focussing crystal with a time resolution of 1 ps. The conditions in the microdot were inferred by comparing the measured spectra to synthetic spectra produced by the time-dependent collisional–radiative (CR) models FLY and FLYCHK. The data were also compared to simulated spectra from a number of opacity codes assuming local thermodynamic equilibrium (LTE). Temperature and density gradients were taken into account in the comparisons. The sample conditions were inferred from the CR modelling using FLYCHK to be 800 ± 100 eV and 1.5 ± 0.5 g/cc. The best fit to the LTE models was at a temperature 20% lower than with the CR model. Though the sample departs from LTE significantly useful spectral comparisons can still be made. The results and comparisons are discussed along with improvements to the experimental technique to achieve conditions closer to LTE.     

Simulation of X-ray scattering diagnostics in multi-dimensional plasma

X-ray scattering is a powerful diagnostic technique that has been used in a variety of experimental settings to determine the temperature, density, and ionization state of warm dense matter. In order to maximize the intensity of the scattered signal, the x-ray source is often placed in close proximity to the target plasma. Therefore, the interpretation of the experimental data can become complicated by the fact that the detector records photons scattered at different angles from points within the plasma volume. In addition, the target plasma that is scattering the x-rays can have significant temperature and density gradients. To address these issues, we have developed the capability to simulate x-ray scattering for realistic experimental configurations where the effects of plasma non-uniformities and a range of x-ray scattering angles are included. We will discuss the implementation details and show results relevant to previous and ongoing experimental investigations.     

Comparison of fatigue effects in simulated and actual earthquakes

One of the unresolved aspects of simulated earthquake testing concerns the amount of low-cycle fatigue produced by a series of single-frequency-vibration tests compared to random-motion excitation. The recommended sinebeat vibration input using 5 cyc/beat at each measured equipment natural frequency is considered conservative because it can produce more fatigue damage than the most severe earthquake being postulated. A computer-aided analysis has been made of simple mass-spring-damper systems representing the uncoupled structure and equipment response to well-known acceleration-time histories available for both the El Centro-1940 and San Fernando-1971 earthquakes. In the proposed testmachine simulation, the comparable sine-beat-vibration input was adjusted to duplicate the building-floor response at the base of the equipment, which was represented as a series of oscillators geometrically spaced in the 1 to 25-Hz range of damaging earthquake effects. Both large- and small-strain ranges have been compared, but these values are assumed for convenience and cannot be used as actual seismic effects in specific pieces of equipment.     

Interfacial separation between elastic solids with randomly rough surfaces: Comparison between theory and numerical techniques

We study the distribution of interfacial separations at the contact region between two elastic solids with randomly rough surfaces. An analytical expression is derived for the distribution of interfacial separations using Persson's theory of contact mechanics, and is compared to numerical solutions obtained using (a) a half-space method based on the Boussinesq equation, (b) Green's function molecular dynamics technique and (c) smart-block classical molecular dynamics. Overall, we find good agreement between all the different approaches.     

Comparison between the relaxation spectra obtained from homogenization models and finite elements simulation for the same composite

The objective of this work is to determine the relaxation spectrum of spherical particles reinforced viscoelastic and isotropic composites from 3D Finite Elements (FE) simulations of the microstructure. The matrix and the reinforcements are assumed to be incompressible and Maxwellian. The spectra obtained from the FE simulations are compared with those obtained from analytical homogenization models. This paper presents the procedure used for generating the FE models as well as the procedure used for obtaining relaxation spectra meeting the thermodynamics requirements imposed on linear viscoelastic materials. It seems that the relaxation spectrum for the microstructure studied in this paper is composed of a negligible continuous part and a discrete part of higher intensity. In any case, the resulting material does not have a Maxwellian behavior.     

A fundamental relationship between the relaxation spectra and the tangent distribution function in the theory of linear viscoelasticity

The tangent distribution function (TDF) is analyzed within the theory of linear viscoelasticity on mechanical properties. A proof is given that both the relaxation and retardation spectra can be derived from the TDF, through a Fredholm integral equation. Furthermore, the relaxation strength can be calculated as a consequence of this relationship. Finally, as an example, the relationship is applied to discrete spectra.     

Theoretical and experimental analysis of iron-exchanged X-zeolite catalyst for SI engine emission control

The fuel economy potential of lean-burn gasoline engines can be utilized without any adverse effect on the environment, only if a suitable catalytic system for converting NO_x in an oxidizing atmosphere is available. Selective catalytic reduction of NO_x over metal-exchanged zeolite can be one of the solutions for reducing NO_x in automobile exhaust containing excess oxygen. Iron-exchanged X-zeolite catalyst (Fe–X) has been developed and tested in the exhaust of an actual SI engine over a wide range of air–fuel ratio, space velocity (SV) and catalyst temperature. Maximum conversion efficiencies of 55.8% and 57.4% were recorded for NO_x and CO, respectively. The catalyst also maintains its high performance through a wide range of temperatures. A mathematical model has been developed as well for predicting the performance of the catalytic converter containing Fe–X catalyst and the numerical solutions are presented. The predicted results agree well with the experimental results and are within the experimental uncertainty limits. The absolute average deviations are found to be within 6% and 5% of the predicted conversion efficiencies for NO_x and CO, respectively.     

Comparison of electrical and laser spark emission spectroscopy for fuel concentration measurements

Emission spectra from electrical and laser sparks in flowing methane–air mixtures of various compositions have been collected and analysed. The differences and similarities between the electrical and laser sparks in the context of their emission are discussed. The emission spectra from the laser spark were characterized by a weak continuum, onto which several strong atomic lines and some molecular bands were superimposed, in contrast to the spectra of electrical spark where a strong continuum, few atomic lines and several strong molecular bands were evident, making thus the laser spark spectroscopy a more accurate technique to measure hydrocarbon concentration. For both types of spark, the total intensity of the CN chemiluminescence around 388 nm was found to correlate almost linearly with fuel concentration in methane–air mixtures.     

Generating line spectra from experimental responses. Part II: Storage and loss functions

A computer algorithm is described which allows the determination of a discrete distribution of relaxation times from simulated or smoothed storage or loss modulus data, or of retardation times from simulated or smoothed storage or loss compliance data. The distributions faithfully reproduce the input data and are suitable for data storage as well as for generating any other response curves.     

Theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains

One of the major problems in structural fatigue life analysis is establishing structural load spectra under actual operating conditions.This study conducts theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains.The quasistatic load series that corresponds to quasi-static deformation modes are identified according to the structural form and bearing conditions of high-speed train bogie frames.Moreover,a force-measuring frame is designed and manufactured based on the quasi-static load series.The load decoupling model of the quasi-static load series is then established via calibration tests.Quasi-static load–time histories,together with online tests and decoupling analysis,are obtained for the intermediate range of the Beijing—Shanghai dedicated passenger line.The damage consistency calibration of the quasi-static discrete load spectra is performed according to a damage consistency criterion and a genetic algorithm.The calibrated damage that corresponds with the quasi-static discrete load spectra satisfies the safety requirements of bogie frames.     

Effect of an electric field on the nitrogen oxide emission and structure of a laminar propane diffusion flame

The effect of an electric field E on the structure and nitrogen oxide NO_x emission of an individual laminar propane diffusion flame is experimentally investigated. The current-voltage characteristics of the flame, its deformation, the fuel-air ratio and the NO_x emission are determined for positive and negative burner polarities. A reduction in NO_x emission (up to 30% with respect to the emission index) is demonstrated in the case of negative burner polarity. A cause-and-effect relationship between the processes in the flame is proposed: the presence in the flame of positively charged ions and soot particles; the motion of the ions in the E field and the onset of an induced electrohydrodynamic flow directed towards the negatively charged burner; the retention and increase in the concentration of soot particles in the lower region of the flame, which leads to an increase in soot particle radiation and hence to a decrease in the temperature of the flame front and a corresponding reduction in NO_x emission. The electrohydrodynamic aspects of the problem are subjected to a qualitative analysis.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 13–23, March–April, 1995.     

Generating line spectra from experimental responses. Part I: Relaxation modulus and creep compliance

We describe a recursive computer algorithm which generates line spectra from relaxation modulus or creep compliance data without producing negative spectrum lines. We apply the algorithm here to data read from mathematical models for the relaxation modulus. Since these data were thus free of the usual experimental error, we could use a relatively simple form of the basic algorithm that is applicable also to smoothed data. The spectra faithfully reproduced the input functions and may serve for data storage as well as for predicting other experimental responses.     

An experimental study of the adhesion between clay and steel

Many practical problems in Soil Mechanics require a detail knowledge of the shearing resistance to relative sliding at the interface between soils and structural materials. This study presents a complete set of parameters for the shearing resistance between two different clays and a smooth steel surface. Results are given for the behaviour of clay samples tested in the shear box under quick undrained, consolidated undrained and consolidated drained conditions. These parameters are compared with those obtained for the internal shear strength.The drained and undrained results for both clays show that clay to steel initially has a higher shear strength than clay.to clay. Its subsequent behaviour depends upon whether the clay is over or normally consolidated. Some adhesion factors are suggested.     

Comparison of experimental and theoretical results for the hydrostatic bulging of circular sheets

Incremental and total-strain theories have recently been used by the authors to obtain numerical solutions for the hydrostatic bulging of circular diaphragms. These solutions have incorporated the effects of anisotropy in the direction of the thickness of the sheet. This investigation was conducted to obtain test data on aluminum-killed steel sheets which contain the above mentioned anisotropy and to compare these data with the predictions of the incremental and total-strain theories solutions. The results show that the incremental theory is in better agreement with test data than the total-strain theory. Strain-path data for several volume elements shows that each volume element follows an approximately proportional strain path. However, the strain paths obtained from the total-strain theory are in gross disagreement with the data.     

Comparison of slamming and whipping loads by fully coupled hydroelastic analysis and experimental measurement

This paper proposes a numerical method for analyzing whipping using a fully coupled hydroelastic model. The numerical analysis method utilizes a 3-D Rankine panel method, 1-D/3-D finite element methods, and a 2-D generalized Wagner model, which are strongly coupled in the time domain. The computational results were compared with those of a model test of an 18 000-TEU containership. The slamming pressures and whipping responses to regular waves for bow flare and stern slamming were compared. Furthermore, the slamming pressure was decomposed into its dynamic and static components. The numerical and experimental models produced similar results. In addition, the effects of the discretization and geometric approximation of the 2-D slamming sections were investigated.     

Stability of a supersonic flat-plate wake (Comparison of numerical and experimental results)

The stability of the wake downstream of a plat plate with a blunt trailing edge is numerically investigated at a supersonic freestream velocity. The calculated stability characteristics are compared with the experimental data.     

An experimental study of two-phase flow in simulated reduced-gravity condition: dispersed droplet to slug flow transition and slug flow

The results from an experimental study of reduced-gravity two-phase flows are reported in this paper. The experiments were conducted in simulated reduced-gravity conditions in a ground-based test facility with a circular test section of 25 mm inner diameter. The flow conditions for which data were acquired lie in the dispersed droplet to slug flow transition and slug flow regime. Local data were acquired for 17 different flow conditions at three axial locations. The acquired data complement and extend those discussed in an earlier paper by the authors (Vasavada et al. in, Exp Fluids 43: 53–75, 2007). The radial profiles and axial changes in the local data are analyzed and discussed in this paper. The area-averaged data, in conjunction with the local data, are discussed to highlight important interaction mechanisms occurring between fluid particles, i.e., drops. The data clearly show the effect of progressive coalescence leading to formation of slug drops. Furthermore, the shape of slug drops in reduced-gravity conditions was observed to be different from that in normal-gravity case. The analyses presented here show the presence of drop coalescence mechanisms that lead to the formation of slug drops and transition from dispersed droplet flow to the slug flow regime. The most likely causes of the coalescence mechanism are random collision of drops driven by turbulence eddies in the continuous phase and wake entrainment of smaller drops that follow preceding larger drops in the wake region. Data from flow conditions in which the breakup mechanism due to impact of turbulent eddies on drops illustrate the disintegration mechanism.