Steady-state Line Research Articles

Analyse de la liquéfaction et du comportement non drainé des sables du delta de Kenamu (Projet ADFEX)

Jointly sponsored by France, Norway, and Canada, the ADFEX project (Artic Delta Failure Experiment) aims at triggering a full-scale submarine slide. For that purpose, a delta is destabilized by blasting to induce instantaneous liquefaction of the delta front. The selected site is the delta of Kenamu River at Melville Lake (Labrador), located approximately 40 km northeast of Goose Bay. The delta sediments are angular fine silty sands constituted mainly of quartz. A series of consolidated isotropically and undrained triaxial tests was performed on specimens of reconstituted loose sands to establish the boundaries between the contracting and dilating behaviours (steady state line or F line) and the upper and lower limits of the boundaries within the bidimensional diagram void ratio – mean effective stress. A soil state above this boundary region constitutes a necessary condition to liquefaction. The results of the triaxial tests are used to evaluate the liquefaction potential of Kenamu delta. Key words : liquefaction, sand, steady state, triaxial test, undrained, delta.

Influence of fines on the collapse of loose sands

A study has been carried out to investigate the influence of fines and gradation on the skeletal collapse behaviour of loosely prepared sand samples. Loose sand samples, formed by moist tamping and consolidated to the same effective stress level, were prepared with varying percentages of both plastic and non-plastic fines (< 74 μm) and non-plastic fine sand (> 74 μm). Samples were isotropically consolidated and subjected to monotonic undrained triaxial compression. Results indicate that increased percentages of fines (< 74 μm) have a pronounced effect on the monotonic undrained behaviour at large strains (> 0.5%). This change is represented by a decreased strain softening behaviour and a shifting of the steady-state line. Variation of the gradation of the host sand appears to have little effect on the monotonic undrained behaviour. A supplemental study, involving use of the scanning electron microscope, was carried out to evaluate the findings of the test program in terms of sand fabric. Key words : collapse, monotonic undrained behaviour, scanning electron microscope, fabric.

Physical modeling in sand

Small-scale testing under 1 g conditions as well as in the centrifuge presupposes that a model and prototype have comparative behavior. The chief condition for agreement between model and prototype is that the initial soil states of both must be at equal proximity to the steady state line. Then, when stresses are normalized to the initial mean stress, the model will in all aspects behave similarly to the prototype. Scaling rules are presented that indicate the relations between stress, strain, and displacement for the model and the prototype in terms of geometric scale and stress scale. An obvious limit of scales is imposed by that the soil in the model can be no looser than the maximum void ratio. Similarly, it must not be denser than a value that corresponds to a prototype soil at the minimum void ratio. Three main areas of application of the approach in engineering practice are identified: design of representative 1 g small-scale model tests; reanalysis of data from conventional small-scale tests; and improving the versatility of centrifuge facilities in recognition of the fact that the centrifuge test does not need to be performed at equal levels of stress, when designed according to the new approach. Key words : physical modeling, sand, scaling relations, steady state, centrifuge testing.

Effects of lubricant compressibility on the film thickness in EHL line and circular contacts

As a first step towards generalized (non-closed-form coefficients in Reynolds' equation) lubricant behaviour, this paper describes the incorporation of the Jacobson and Vinet density pressure equation in a multilevel solver for the pressure and the film thickness in an EHL contact. However, the use of this model is also of interest on its own account, as compression experiments (Jacobson and Vinet, Ramesh) have indicated limitations to the applicability of the widely used Dowson and Higginson equation. In this paper, results of the isothermal steady-state line and circular contact are presented and compared with results obtained assuming an incompressible lubricant and with results employing lubricant compressibility according to the Dowson and Higginson equation. The observed phenomena are traced back to Reynolds' equation, and it is shown that the reduction of the central film thickness due to compressibility can be predicted easily, regardless of the type of density pressure equation used. In addition it is shown that, using the Jacobson and Vinet equation, the minimum film thickness in a line contact, beyond a certain load, may occur in the centre of the contact, instead of at the exit. This phenomenon is analysed theoretically, and it is shown to be very unlikely to occur in the circular-contact problem.

Uniqueness of steady state and liquefaction potential

A given sand is presumed to have a unique steady-state line. The proximity of an initial state to the steady-state line is considered to be a measure of liquefaction potential. This line of reasoning and application in practice is based on data obtained predominantly from triaxial tests in compression-mode loading. In such tests, relative orientations of bedding plane and principal stress directions remain fixed while stress states along actual failure surfaces may range from active to passive. This study examines the uniqueness of the steady state relative to the mode of loading, form of consolidation, and initial anisotropy as induced by bedding orientation. A sample-preparation method was developed to form triaxial samples with different bedding orientations. Steady states of a uniform sand reached under compressional and extensional modes of triaxial undrained loading of samples with different bedding orientation are compared. Effects of isotropic and anisotropic consolidation are examined. The results indicate the steady-state line obtained for compression-mode loading is different from and does not apply for extension-mode loading. Use of a compression side steady-state line for extension-mode failure states would result in overestimation of steady-state strengths and unconservative stability evaluations. Key words : anisotropy, compression, extension, liquefaction, sand, steady state, triaxial.

A Comparison of Driver Steering Activity during Motion on an Even and Uneven Road Surface

SUMMARY The paper presents results of simulation investigation on driver-vehicle motion on an even and uneven road. The 14 degrees of freedom vehicle model has been verified experimentally on an even road surface. The driver models were adopted to perform typical motion cases: circular steady state and stright line. Road irregularities were realizations of a random process and they represented four road categories. The driver steering activity measure was adopted to investigate the influence of road undulations. The performed simulation investigations indicate that there is a considerable influence of road irregularities on the driver-vehicle system behaviour during two typical motion cases.

The use of a spreadsheet for sinusoidal steady-state transmission line and optics problems

It is shown how a spreadsheet on a personal computer can be used for sinusoidal steady-state transmission line and optics problems. It gives students the experience of programming the equations rather than relying on special-purpose software written by someone else. At the same time, the students do not need to expend too much effort on coding in a standard computer language, and the numerical effort is accomplished by the computer rather than a hand-held calculator. >

Life Estimation of Cracked Stainless Steel Components Under Creep Conditions

Experimental investigations have been carried out to study the creep crack growth in types 316, 308 Cb, and 304 L stainless steel in the temperature range of 873–1073 K under plane stress condition. Testings have been carried out with both the base metal and the welded composite joints, because such joints are commonly used in nuclear power industries. Among the various parameters tried to correlate the creep crack growth, the energy rate line integral has been found to give the best description of the crack growth rate. The steady-state energy rate line integral has been found to correlate well with the rupture time. Based on this observation, life estimations are presented for thin components containing various initial defect sizes.

In situ tests in a sand dune

A field testing program using an electric piezocone penetrometer (CPTU) and a flat dilatometer (DMT) probe was carried out in a sand dune. The analysis of the field data in terms of relative density using current empirical correlations showed that significant differences were obtained at this site. It is suggested that any empirical correlation between relative density and CPT or DMT data obtained from calibration chambers should only be used for a sand that has the same slope of the steady-state line as the sand used in the calibration tests. Key words: sand, in situ density, field investigation, piezocone penetrometer, flat dilatometer, steady state.

CRACK TIP FIELDS UNDER NON‐STEADY CREEP CONDITIONS—I. ESTIMATES OF THE AMPLITUDE OF THE FIELDS

Abstract— Under non‐steady creep conditions, the stress and strain rate fields near the tip of a stationary crack can be described by the singular fields of Hutchinson, Rice and Rosengren for power‐law creeping materials. Estimation formulae are presented for describing the amplitude of these fields under load and displacement controlled boundary conditions. For constant loading, the formulae reduce to the result of Riedel and Rice for short times after load application and to the steady state line integral C* for long times. At intermediate times, the estimate is validated by detailed finite‐element computation. For displacement‐controlled loading, the amplitude of the near‐tip fields is shown to fall rapidly, consistent with finite‐element analysis. The implications of the results for data collection and defect assessments are discussed in a companion paper.

Steady State Testing of Loose Sands: Limiting Minimum Density

The steady state line (SSL) of a soil is defined as the relationship between a soil's void ratio (or density) and its residual ``steady state'' or critical state strength. Recent testing of very low density sand samples indicates that the steady state line approaches a limiting maximum void ratio, representing a considerable departure from the assumption of a linear relationship between the logarithm of steady state strength and void ratio employed in many constitutive models. This recent testing suggests that a limiting minimum density exists, below which a sample will show no steady state shear strength at all. Moreover, this limiting density appears to occur at a relative density of Dr=>0%–10%. This technical note presents data regarding this apparent limiting density, based on the results of laboratory testing performed by four researchers on three different sands.

Stress path and steady state

The effect of stress path on the steady state line of a liquefiable sand is investigated. Results from undrained triaxial compression and extension tests on water-deposited sands show that the steady state line of a given sand, though unique in the effective stress space, is not so in the void ratio – effective stress space. The sand is contractive over a much larger range of void ratios in extension than in compression. While a single steady state line emerges for compression loading, extension loading yields several lines, each characteristic to a given deposition void ratio. All these extension lines lie to the left of the compression line in void ratio – effective stress space. Thus at a given void ratio, steady state strength is smaller in extension than in compression, the difference increasing as the sand becomes looser. The implications of the results are discussed in relation to practical design. Key words: sand, liquefaction, steady state, stress path.

The enzyme rhodanese can be reactivated after denaturation in guanidinium chloride.

For the first time, the enzyme rhodanese has been refolded after denaturation in guanidinium chloride (GdmHCl). Renaturation was by either (a) direct dilution into the assay, (b) intermediate dilution into buffer, or (c) dialysis followed by concentration and centrifugation. Method (c) preferentially retained active enzyme whose specific activity was 1140 IU/mg, which fell to 898 IU/mg after 6 days. The specific activity of native enzyme is 710 IU/mg. Progress curves were linear for the dialyzed enzyme, and kinetic analysis showed it had the same Km for thiosulfate as the native enzyme, but apparently displayed a higher turnover number. Progress curves for denatured enzyme directly diluted into assay mix showed as many as three phases: a lag during which no product formed; a first order reactivation; and an apparently linear steady state. An induction period was determined by extrapolating the steady-state line to the time axis. The percent reactivation fell to 7% (t1/2 = 10 min) as the time increased between GdmHCl dilution and the start of the assay, independent of the presence of thiosulfate. The induction period, which decreased to zero as the incubation time increased, was retained in the presence of thiosulfate. There were no observable differences between native and renatured protein by electrophoresis or fluorescence spectroscopy. Previous reports of some refolding of urea-denatured rhodanese (Stellwagen, E. (1979) J. Mol. Biol. 135, 217-229) were confirmed, extended, and compared with results using GdmHCl. A working hypothesis is that rhodanese refolding involves intermediates that partition into active and inactive products. These intermediates may result from nucleation of the two rhodanese domains, which exposes hydrophobic surfaces that become the interdomain interface in the correctly folded protein.

Stability Limited Load Supply and Interchange Capability

Traditional load supply and interchange capabilities represent maximums based on steady state generation, line flow and voltage constraints. If the system cannot survive a list of transients when operated at these capabilities, the current computational algorithms do not provide a means for systematically determining alternative secure capabilities. In this paper, the recent results in direct stability methods are applied to give reasonably rapid solutions to this problem. The concept of a Potential Energy Boundary Surface (PEBS) is utilized to obtain transient energy stability margins and their sensitivity to load levels. The energy margins and their sensitivities are used to direct a systematic search for approximate stability limited capabilities.

Stability Limited Load Supply and Interchange Capability

Traditional load supply and interchange capabilities represent maximums based on steady state generation, line flow, and voltage constraints. If the system cannot survive a list of transients when operated at these capabilities, the current computational algorithms do no provide a means for systematically determining alternative secure capabilities. In this paper, the recent results in direct stability methods are applied to give reasonably rapid solutions to this problem. The concept of a potential energy boundary surface (PEBS) is utilized to obtain transient energy stability margins and their sensitivity to load levels. The energy margins and their sensitivities are used to direct a systematic search for approximate stability limited capabilities.

Steady-state response of a delay-constrained adaptive linear predictor filter to a sinusoid in white noise

An analysis is presented for the steady-state response of a delay-constrained adaptive linear predictor filter to a sinusoid in white noise. Expressions are derived for the steady-state adaptive weights, frequency response, and line suppression. A useful bound is also derived for the worst-case output signal-to-noise ratio as a function of normalized frequency and the order of the filter.

The line shape of a zero-field level-crossing effect in methyl fluoride

The line shape of the zero-field level-crossing effect that occurs when 13CH3F is irradiated by the 9P(32) CO2 laser has been recorded by an infrared laser Stark spectrometer operating under computer control. The level-crossing effect, which occurs as a narrow decrease in the absorption due to superposition of the m components of the Doppler-broadened R(4,3) transition in the ν3 band, has been recorded at several pressures. Comparison of the experimental line shapes with theoretically calculated curves leads to a value of 13.9±0.9 MHz/Torr for the pressure broadening parameter for this transition. An algebraic solution is given for the linear system that occurs in the density matrix treatment of the steady state line shape of a level crossing or level anticrossing effect. The modifications of the solution required to treat three-level double resonance or two-photon effects are also given.

Carbon dioxide sensitivity of aortic chemoreceptors in the cat

Steady state CO 2 sensitiviy in the aortic chemoreceptors was variable. For 70.3% of the steady state response lines to increasing CO 2 the slope was not significantly different from zero. For 24.3% it was significantly positive and for 5.4% significantly negative. In contrast, in 86.7% of cases the oscillating response to alternate breaths of high and low CO 2 suggested a transient response line which was significantly steeper than the steady state line. Removing CO 2 from a high CO 2 content inspirate for one breath caused a distinct drop in discharge on 83.3% of occasions. The significance of such transient CO 2 sensitivity in the absence of clear steady state sensitivity is discussed.