Localized Nonuniformity Research Articles

Visualization of localized deformation of external thermal insulation composite systems during aging

• The deformation at different hygrothermal aging stages is tested. • The localized non-uniformity of displacement and strain field is highly correlated with the initiation and evolution of cracks in the finish layer. • The influence of temperature and rainfall on the crack expansion and contraction and local non-uniform deformation of the finish layer is analyzed. The localized deformation of finish coat materials occurs due to hygrothermal aging under harsh service conditions, which adversely impacts the thermal performance and safety of the external thermal insulation composite systems (ETICS). In this study, digital images of the ETICS finish coat were obtained using an industrial digital camera under artificially generated harsh aging environment. Both local deformation field and strain field as well as the surface crack initiation and evolution process of the ETICS finish coat were assessed by the digital image correlation method. The calculation results revealed that the phenomena associated with the occurrence of a localized non-uniform displacement field and strain field of the ETICS finish coat during aging are very significant especially at the cracks, with obvious regional boundaries. The localization of the strain field is highly correlated with the initiation and evolution of cracks with a significant local distribution band. The maximum horizontal displacement and vertical displacement during the resting phase after being exposed to rain were reduced by 77.14 and 57.69%, respectively compared with those at high temperature. The massive expansion and shrinkage resulted in the cracking of the finish coat. When the cracked finish coat expands at high temperature or shrinks when exposed to rain, the cracks also expand or shrink accordingly, so that the localized non-uniformity level of the displacement field decreases or increases, and the strain on the reference line presents uniform change or sudden change. The non-uniform deformation of the finish coat caused by the cyclic action of aging factors such as high temperature and rainfall eventually becomes more and more significant. The characteristic index for non-uniform deformation was proposed and its evolution laws with the aging time were systematically analyzed. Taken as the next research focus, it can provide a reference for analyzing the deformation and deterioration process of the ETICS and ensuring the operation safety.

Autoignition and detonation development induced by temperature gradient in n-C7H16/air/H2O mixtures

The effects of water vapor dilution on autoignition and detonation development induced by an ignition spot with thermal non-uniformity in an n-C7H16/air mixture are numerically investigated. Zero-dimensional homogeneous ignition under constant-volume conditions is studied first. It is found that excitation time increases, whereas total heat release decreases with a H2O vapor mole fraction. Moreover, the role of H2O vapor diluents as a third body considerably influences the critical temperature gradient. One-dimensional autoignition and detonation development caused by temperature gradients in ignition spots is then studied. Three different autoignition modes are identified: (I) supersonic deflagrative wave, (II) detonative wave, and (III) subsonic deflagrative wave. It is found that H2O dilution has a slightly better performance on detonation suppression than CO2 dilution. The chemistry–acoustics interactions during autoignition development are weakened when the H2O mole fraction is increased. Besides, H2O vapor dilution can delay the detonation initiation and reduce detonation intensity. Furthermore, typical autoignition processes induced by a hotspot and the chemical effects of water vapor diluent are discussed. It is seen that the chemical effects of H2O dilution do not affect the lower limits of detonation development curves. Besides, the third body effect from the H2O vapor diluent is important in suppressing the detonation development for the investigated ignition spot size. Finally, the effects of equivalence ratios and ignition spot sizes on the autoignition modes of n-C7H16/air/H2O mixtures are studied. It is observed that the water vapor diluted mixtures with the fuel-lean condition are advantageous in inhibiting detonation from localized thermal non-uniformity.

Scattering of Extremely Low Frequency Electromagnetic Waves by a Localized Seismogenic Ionospheric Perturbation: Observation and Interpretation

AbstractA significant anomaly in the extremely low frequency (ELF) spectra of Schumann resonance (SR) was discovered for the 1999 Chi‐Chi earthquake (EQ) in Taiwan as observed in Japan. Similar phenomena were confirmed for other EQs remote from the observer by a few megameters. An additional effect was detected for nearby EQs. The anomalies were explained by ELF radio wave scattering from a seismogenic disturbance. The global thunderstorms serve as the source positioned at the equator, and the localized seismogenic perturbation was placed above the EQ epicenter. We evaluate a seismic impact on SR power spectra using the realistic conductivity profile of atmosphere. The nonuniformity above EQ epicenter is axially symmetric varying along the radius according to Gaussian law whose scale depends on the magnitude. We use the complex characteristic heights relevant to the regular and disturbed cavities. These are substituted into the two‐dimensional telegraph equation (2DTE) for electric and magnetic fields. Deviations from the regular spectra are the seismogenic modifications that depend on the EQ magnitude. Computations indicate that a distant localized seismogenic nonuniformity provides a noticeable impact when the EQ magnitude exceeds the M = 7 threshold. The effect is also modeled of the nearby (up to 500 km) moderate (magnitude 5.5) EQs. The resonance spectra of disturbed fields become elevated as a whole. The distance dependence of field disturbance repeats seismogenic modifications in the characteristic heights above the observer. Model computations are compared with available observations.

Scattering of ELF radio waves by a localized non-uniformity in the lower ionosphere

We numerically model the ELF radio wave scattering by a localized non-uniformity in the mesosphere conductivity characterized by a 25–30 km reduction of conventional profile from 70 to 80 km altitude. The disturbance is axially symmetric; it depends on the radius according to the Gaussian law of 1 Mm scale. The complex characteristic electric and magnetic heights are found by solving the Riccati equation. These heights are used in the 2D (two dimensional) telegraph equations (2DTE) when computing the ELF fields in the Earth–ionosphere cavity. The field source is located at the point (10° S; 0° E), the non-uniformity is positioned above the North Pole, and the observer moves across the entire surface of the Earth. Spatial distributions were computed of the vertical electric field amplitude in both regular and non-uniform cavity. Comparison of these data allowed us to single out the reflections from the localized non-uniformity. It is shown that interference takes place at an arbitrary observation point between direct wave and the wave reflected from the non-uniformity. Computational data might be interpreted by secondary currents induced in the non-uniformity by the incident radio wave. There are two types of secondary sources. The first one is a “monopole” radiating symmetrically in all directions. Spatial distribution of the field from this source coincides with the distribution of corresponding Schumann resonance mode at a particular frequency. The other secondary source is of “dipole” type, which has a cosine radiation pattern with the maximum oriented along the source – non-uniformity line. Its spatial distribution coincides with the derivative of the corresponding Schumann resonance mode eigen-function on the distance. Model data obtained will facilitate interpretation of experimentally observed seismogenic Schumann resonance signals.

Growth Rates and Spontaneous Navigation of Condensate Droplets Through Randomly Structured Textures.

Dropwise condensation is a phenomenon of common occurrence in everyday life, the understanding and controlling of which is of great interest to applications ranging from technology to nature. Scalable superhydrophobic textures on metals are of direct relevance in improving phase change heat transport in realistic industrial applications. Here we reveal important facets of individual droplet growth rate and droplet departure during dropwise condensation on randomly structured hierarchical superhydrophobic aluminum textures, that is, surfaces with a microstructure consisting of irregular re-entrant microcavities and an overlaying nanostructure. We demonstrate that precoalescence droplet growth on such a surface can span a broad range of rates even when the condensation conditions are held constant. The fastest growth rates are observed to be more than 4 times faster as compared to the slowest growing droplets. We show that this variation in droplet growth on the hierarchical texture is primarily controlled by droplet growth dynamics on the nanostructure overlaying the microstructure and is caused by condensation-induced localized wetting nonuniformity on the nanostructure. We also show that the droplets nucleating and growing within the microcavities are able to spontaneously navigate the irregular microcavity geometry, climb the microtexture, and finally depart from the surface by coalescence-induced jumping. This self-navigation is realized by a synergistic combination of self-orienting Laplace pressure gradients induced within the droplet as it dislodges itself and moves through the texture, as well as multidroplet coalescence.

Four Metrics to Evaluate Heterogeneous Multicores

Semiconductor device scaling has made single-ISA heterogeneous processors a reality. Heterogeneous processors contain a number of different CPU cores that all implement the same Instruction Set Architecture (ISA). This enables greater flexibility and specialization, as runtime constraints and workload characteristics can influence which core a given workload is run on. A major roadblock to the further development of heterogeneous processors is the lack of appropriate evaluation metrics. Existing metrics can be used to evaluate individual cores, but to evaluate a heterogeneous processor, the cores must be considered as a collective. Without appropriate metrics, it is impossible to establish design goals for processors, and it is difficult to accurately compare two different heterogeneous processors. We present four new metrics to evaluate user-oriented aspects of sets of heterogeneous cores: localized nonuniformity , gap overhead , set overhead , and generality . The metrics consider sets rather than individual cores. We use examples to demonstrate each metric, and show that the metrics can be used to quantify intuitions about heterogeneous cores.

Fluid flow and convective heat transfer to fluids at supercritical pressure

The feature of fluids at pressures just above the critical value which makes them of particular interest is that they change in a continuous manner from being liquid-like to gas-like with increase of temperature at constant pressure. As a consequence of the extreme dependence of fluid properties on temperature, non-uniformity of density can lead to important effects on the mean flow and turbulence fields and heat transfer effectiveness. When the author and his colleagues first commenced research on supercritical pressure fluids many years ago it was decided to begin with a novel experiment specifically designed to include effects of strong non-uniformity of fluid properties whilst avoiding other complications associated with the temperature dependence of density. This fundamental experiment on stably stratified turbulent flow of supercritical pressure carbon dioxide between two horizontal planes, with the upper one heated and the lower one cooled, in such a way that there was no net heat transfer to the fluid, yielded evidence of a special mechanism for enhancement of turbulent mixing. Later, experiments with uniformly heated vertical tubes using carbon dioxide at pressures very near to the critical value gave results, which exhibited further striking features. Severe localized non-uniformity of heat transfer developed in the case of upward flow, but was not found with downward flow. Gravitationally induced motion caused effects on heat transfer which could only be explained by postulating drastic modification of turbulence. Such results stimulated the development of physically based ideas concerning the mechanisms which might be involved and led to the development of a semi-empirical model of buoyancy-influenced turbulent flow and heat transfer. The main aim of this paper is to show how such early work is now providing a basis for correlating experimental data and enabling the complicated phenomena encountered in those early experiments to be properly accounted for in thermal design procedures.

SPONTANEOUS INITIATION OF DETONATIONS IN WHITE DWARF ENVIRONMENTS: DETERMINATION OF CRITICAL SIZES

Some explosion models for Type Ia supernovae (SN Ia), such as the gravitationally confined detonation (GCD) or the double detonation sub-Chandrasekhar (DDSC) models, rely on the spontaneous initiation of a detonation in the degenerate C/O material of a white dwarf. The length scales pertinent to the initiation of the detonation are notoriously unresolved in multi-dimensional stellar simulations, prompting the use of results of 1D simulations at higher resolution, such as the ones performed for this work, as guidelines for deciding whether or not conditions reached in the higher dimensional full star simulations successfully would lead to the onset of a detonation. Spontaneous initiation relies on the existence of a suitable gradient in self-ignition (induction) times of the fuel, which we set up with a spatially localized non-uniformity of temperature -- a hot spot. We determine the critical (smallest) sizes of such hot spots that still marginally result in a detonation in white dwarf matter by integrating the reactive Euler equations with the hydrodynamics code FLASH. We quantify the dependences of the critical sizes of such hot spots on composition, background temperature, peak temperature, geometry, and functional form of the temperature disturbance, many of which were hitherto largely unexplored in the literature. We discuss the implications of our results in the context of modeling of SNe Ia.

Separation of energy fractions of an electron beam by a localized nonuniformity of magnetic field in the collector region of gyrodevices

To separate the energy fractions of an electron beam, we propose that a ferromagnetic ring coaxial to the solenoid is inserted in the collector region, which can increase the efficiency of energy recovery in the case of electron deposition onto the multistage collector.

Mathematical Modeling of the Formation of Type IIId Solar Decameter Radio Bursts with Echo Components

Using numerical simulation, we investigate the possibility that echo components of type IIId solar decameter bursts can be produced through refraction of radio emission in a coronal plasma with large-scale regular electron density inhomogeneities. It is shown that the observed time profiles of radio burst intensity with three or four maxima can be related to the presence in the middle corona of streamers and a localized regular nonuniformity whose electron density exceeds background electron density by a factor of more than 3 – 4. The nonuniformity scale in this case is comparable with the optical diameter of the solar disk. The observed radio burst echo components with delays longer than 3 s are explained by the production of additional radio emission propagation modes within a “transverse" refraction waveguide arising between the localized electron density nonuniformity and deeper layers in the corona. As these additional modes are reflected from the streamers, they can reach the Earth. Calculations of the time profile of radio burst intensity take into consideration the influence of scattering by turbulent coronal inhomogeneities and of collisional absorption. Comparison of the modeling results with the observational data shows that the calculated values of some profile parameters differ from the observed values. One of the possible reasons is that the method used does not take into account the diffraction leakage of radio emission through the large-scale nonuniformity.

Flow structure from an oscillating cylinder with a localized nonuniformity: Patterns of coherent vorticity concentrations

Forced oscillation of a uniform cylinder with a localized, fluid-induced nonuniformity at its midspan, in the form of either blowing or suction, generates well-defined patterns of vorticity concentrations. The spanwise extent of these patterns abruptly grows to an order of magnitude larger than the initially induced nonuniformity. Such patterns exhibit ordered changes in the number, arrangement, and circulation of the vorticity concentrations as the magnitude of the nonuniformity is altered.

ELF radio wave propagation in a locally nonuniform Earth‐ionosphere cavity

The vertical electric field component of the ELF radio wave propagating in the spherical Earth‐ionosphere cavity with a localized nonuniformity is studied. The analysis is performed in the framework of Born's approximation of the perturbation theory applied to the Stratton‐Chu integral equation. Both the vertical electric dipole and the horizontal grounded wire antenna are considered as the ELF field sources. It is shown that different effects can arise within the nonuniform waveguide depending on the disturbance position between or beyond the endpoint of the propagation path that are conditioned by the vectorial nature of the radio wave. Backscatter is the prevailing effect in the case of impedance or height disturbances. A localized nonuniformity can bring forth pattern rotation of the horizontal wire antenna and at the same time an amplitude modification of its lobes.