Conditions Of Partial Saturation Research Articles

Data-Driven Constraint Handling in Multi-Objective Inductor Design

This paper analyses the multi-objective design of an inductor for a DC-DC buck converter. The core volume and total losses are the two competing objectives, which should be minimised while satisfying the design constraints on the required differential inductance profile and the maximum overheating. The multi-objective optimisation problem is solved by means of a population-based metaheuristic algorithm based on Artificial Immune Systems (AIS). Despite its effectiveness in finding the Pareto front, the algorithm requires the evaluation of many candidate solutions before converging. In the case of the inductor design problem, the evaluation of a configuration is time-consuming. In fact, a non-linear iterative technique (fixed point) is needed to obtain the differential inductance profile of the configuration, as it may operate in conditions of partial saturation. However, many configurations evaluated during an optimisation do not comply with the design constraint, resulting in expensive and unnecessary calculations. Therefore, this paper proposes the adoption of a data-driven surrogate model in a pre-selection phase of the optimisation. The adopted model should classify newly generated configurations as compliant or not with the design constraint. Configurations classified as unfeasible are disregarded, thus avoiding the computational burden of their complete evaluation. Interesting results have been obtained, both in terms of avoided configuration evaluations and the quality of the Pareto front found by the optimisation procedure.

Unsaturated Hydraulic Conductivity in Composite Porous Media

Determining the constitutive properties that describe the incipient hydraulic behavior of the materials, including the matrix domains and the distribution of macro and micropores, is crucial to analyzing the preferential water flow in saturated soils, ks, and unsaturated, ku. This study focused on determining the hydraulic conductivity in porous media under total and partial saturation conditions. The infiltration characteristics of three reconstituted soils were evaluated using five suction ranges employing conventional permeameters, an automated dual system, and mini-disk infiltrometers. The experimental cycles were carried out in granular soils with mixtures of diatomaceous soils, iron oxide (Fe2O3), and calcium carbonate (CaCO3) in 5–40% proportions. The differences between the granular microstructures of each material and the different hydraulic interaction mechanisms (suctione levels) significantly affected the values of ks and ku and the coupling between the pore domains and the defined water regime. Additionally, a lower impact was observed in the data set exposed to higher percentages of Fe2O3 and CaCO3 in different suction ranges, mainly due to a tension effect (meniscus) generated by suction in the granular skeleton. Since both parameters are mutually correlated and have a similar impact between methods and soil cores, ks and ku must be optimized simultaneously in each mechanism analyzed. The main findings of this work result in the confirmation that the unsaturated permeability decreases as suction is imposed on the sample. As well as the addition of different materials with Particle Size Distribution finer than the base sample, it also reveals a reduction in hydraulic conductivity, both saturated and unsaturated.

Mechanical Behavior of Low-Density Polyethylene Waste Modified Hot Mix Asphalt

The use of polymeric waste in the modification of asphalt binders for the construction of road pavements is a technique studied several years ago. However, the use of these materials involves high temperatures close to 190 °C, which generate large environmental impacts due to their emissions. In this study, an asphalt cement (AC) with low-density polyethylene (LDPE) residue contents of 5%, 7%, and 10% with respect to the mass of the AC was modified by the wet method. The modification was carried out using a temperature of 150 °C with the aim of preventing the oxidation of the AC and reducing the emissions generated at high temperatures. Based on the physical-rheological properties of the modified asphalt binder, it was found that 5% LDPE produces the best performance. Subsequently, a hot-mix asphalt type HMA-19 control without a modified asphalt binder and another with a modified asphalt binder were manufactured in order to evaluate the mechanical behavior by means of the Marshall test, an indirect tensile strength (ITS) test, resilient modulus (RM) testing, resistance to fatigue testing, permanent deformation testing, and the Cantabro test. Additionally, the asphalt mixtures were tested under the conditions of short-term aging (STOA, Short-Term Oven Aging), long-term aging (STOA + LTOA, Long-Term Oven Aging), and partial saturation with water (STOA + LTOA + water). Based on the results, an ANOVA analysis of variance was performed to assess whether the changes in the mechanical response of the modified mixture are statistically significant with respect to the control mixture. As a general conclusion, it is reported that mixtures with LDPE can be used for thick layers in high-temperature climates in order to control rutting.

Effect of pore fluid on ultrasonic S-wave attenuation in partially saturated tight rocks

S-wave attenuation in porous media is affected by the presence and properties of saturating fluids. We measured the ultrasonic S-wave velocities of three types of tight rocks (siltstone, dolomite, and sandstone) under partial fluid saturation conditions using the pulse-transmission technique. The S-wave attenuation is estimated by the centroid frequency shift and spectral-ratio methods. The fluid-saturated test results show that the attenuation of most water-saturated dolomites is stronger than that of gas- or oil-saturated dolomites, whereas no apparent relationship exists between attenuation and fluid type in siltstone. The attenuation of siltstone and dolomite increases with increasing porosity and permeability, as well as with clay content for siltstone with clay contents less than 6%. The maximum attenuation of rocks partially saturated with gas and water occurs at high water saturation (55%–100%) in most siltstones. The attenuation of most dolomites shows an increasing trend with water saturation, but remains nearly unchanged in partially saturated sandstone. The attenuation of rocks partially saturated with oil and water is strongest at the partial saturation state in siltstone, but remains essentially constant with water saturation in dolomite. A squirt flow model is used to predict the S-wave attenuation of the fluid-saturated sample. Based on rock property and microstructure analyses, wave attenuation in the fluid-saturated rocks measured in this study can be explained by squirt flow mechanisms and the scattering effect owing to heterogeneities of water patches and grain clusters.

NMR Fluid Substitution–A New Method of Reconstructing T2 Distributions Under Primary Drainage and Imbibition Conditions

Most nuclear magnetic resonance (NMR)-based petrophysics models, such as pore structure characterization and permeability prediction, were developed using T2 distributions measured at fully water-saturated conditions (i.e., Sw = 1). The downhole implementation of those models across the hydrocarbon zones is disputable due to partial saturation (Sw < 1) conditions; hence, a correction to such effects on T2 distributions is required. This paper provides a critical review of the fluid substitution methods currently available in the industry and presents an improved method for enhanced formation evaluation. In the new method presented, an effective irreducible water saturation model is used to account for the pore structure and capillary pressure effects, which were barely considered by the currently available NMR fluid substitution methods. For water-wet reservoir rocks, the typical NMR T2 distribution at the partial saturation condition displays a clear separation between the wetting and nonwetting phases. The water phase can be classified as irreducible and movable fluid volumes. Then, using a T2 mapping relationship and a total porosity constraint, the T2 distribution of movable water at Sw < 1 is shifted and amplified to determine the T2 distribution of movable water at Sw = 1. To validate the new method, NMR measurements were conducted on sandstone samples at Sw = 1 as well as Sw < 1. The reconstructed T2 distribution at Sw = 1 was compared with the measured T2 distribution at Sw = 1. Results showed that the reconstructed T2 distribution matched very well with the T2 distribution measured at Sw = 1, confirming the robustness of the new technique. Parameters used in the reconstruction methodology are observed to be a good indicator of pore connectivity. During desaturation, the water T2 in large pores shifts to a shorter T2 because of the enhanced surface relaxation as the water volume decreases while the surface area remains constant. Therefore, the amplitude at the short T2 increases. The increased amplitude was remapped to large pores in reconstructing T2 spectra of full saturation.

Coda and Intrinsic Attenuations From Ultrasonic Measurements in Tight Siltstones

AbstractWe have performed ultrasonic measurements on tight siltstone samples to obtain thePwave coda and intrinsic attenuations using a single isotropic scattering model and the spectral ratio method. The results indicate that attenuation is predominantly caused by scattering. Intrinsic attenuation increases with gas saturation and permeability and decreases with grain size, whereas coda attenuation is stronger under partial saturation conditions and increases with grain size. Porosity and mineral composition do not have significant effects on attenuation. The triple‐porosity and scattering models are used to simulate the intrinsic and scattering attenuations, respectively. The results show that the intrinsic attenuation is predominately caused by wave‐induced fluid flow between microcracks/micropores and intergranular pores. The model incorporating the scattering effects of microcracks underestimates the scattering loss in the coda, which may thus be better explained by heterogeneities in the clustering structure of grains.

An Experimental Investigation on the Tribological Behaviour of Nominally Flat Quartz Grains with Gouge Material in Dry, Partial Saturated and Submersed Conditions

We examined the normal and tangential contact behaviour of gouge materials between nominally flat quartz grains using micromechanical experiments. Primary mixtures of plastic clay (montmorillonite) and non-plastic silt (crushed aggregates) were used as gouges to focus the investigation on the tribological behaviour of gouge materials at dry, partial saturation and submersion conditions. The presence of gouges resulted in a decreased normal stiffness and frictional strength compared to pure quartz surfaces, and complex crushing behaviour. From cyclic shearing tests, montmorillonite showed the lowest secant stiffness and maximum energy losses, which were more pronounced at lower normal loads. Montmorillonite in its plastic and semi-solid states indicated that variation of post-peak softening and friction coefficient depend on the normal load at a given partial saturation level. In the sudden submersion simulation tests, both before and after the start of shearing, montmorillonite showed a significant decrease in the coefficient of friction (compared to dry gouge), unlike non-plastic silt.

New insights into tracer propagation in partially saturated porous media

This work deals with the influence of partial saturation on the transport process of a passive tracer. Transport experiments were done in a water-wet glass micromodel combined with specific optical techniques. Full water saturation was achieved by injecting initially the background solution and then the tracer, whereas for the partial saturation conditions, the micromodel was initially saturated with oil, and then sequential the background solution and the tracer were injected at the same flow rate. We have shown that in the investigated range of water saturations it exists a transition in the oil ganglia structure and size. For high water saturations oil ganglia have one or two pores in size, however for lower water saturations they comprise an important number of pores. Transport strongly depends on the size distribution of the oil ganglia as they create large percolating paths and stagnant zones. We also showed the existence of two different types of stagnant zones: zones accessible by diffusion into pores and zones only accessible by spatially limited diffusion in films. The major advantage of using glass micromodels lies in the fact that dispersion coefficients can be computed from concentrations averaged over the pore space or from concentrations at the outlet and simultaneously from spatial concentration profiles. Curves were fitted using the Advection–Dispersion Equation (ADE) with adequate boundary conditions. The fitting quality of the temporal evolution of the average and outlet concentration was very good. However, fitting of the concentration profiles could only be done for the higher water saturations. This is due to the fact that the Representative Elementary Volume (REV) of lower water saturations is larger than the micromodel. The results show that fitting the breakthrough curve in order to determine the dispersion coefficient in a partially saturated porous medium might be misleading. Indeed, when fitting the breakthrough curves we were able to compute a dispersion coefficient even in the case where the REV of the water saturation is larger than the micromodel. Consequently, the knowledge of the local concentration profiles as a function of time is necessary as it provides an additional information on the spatio-temporal behavior of the transport process and therefor a supplementary constraint of the fitting procedure. Finally, we observed a time dependent dispersion coefficient in the regime where oil ganglia comprise several pores. This fact might be attributed to the non-Gaussian nature of the transport.

Geotechnical aspects in the restoration of Insula dei Casti Amanti in Pompeii

This paper deals with the geotechnical aspects of the restoration of the Insula dei Casti Amanti (IX-12), in the ancient town of Pompeii, Italy. Such works include the restoration of some archaeological ruins, the stabilisation of artificial slopes realised during archaeological excavations and the replacement of the actual roofing system with a single-span covering. Remedial measures for excavation fronts will be adopted by re-profiling them with variable slope angles, taking advantage of the conditions of partial saturation in the pyroclastic surge. The system of roofing will be replaced by a unique, single-span covering equipped with seismic isolators and supported by steel columns founded on circular embedded foundations. Seismic site response analyses, carried out to predict the seismic behaviour of the new covering, reveal that, depending on the frequency content of the seismic excitation, a ‘double resonance’ between the seismic input, the subsoil and the ancient architecture may occur.

On calculation method for dangerously hydrated loess soil with consideration for elastic-plastic soil properties

On account of the flow theory of plastically compressible media formulas based on moisture-elasticity and plasticity model for strain analysis of dangerously hydrated loess ground are presented. For derivation of the constitutive equations of moisture transfer P. Ya. Polubarinova-Kochina's formula, Darcy's law for filtration rate and S.F. Averyanov to calculate the parameters at partial water saturation were considered. To estimate stress strain behaviour in subsiding building foundations, a finite element method and iterative methods are applied. The constitutive equation for plastic straining of dilating media is given. At each iterative step a linear problem is solved for soil ground with variable stress-strain properties that depend on a stress-strain state from the previous step. The parameters of matrix for stress-strain properties can be calculated during stabilometrical field tests or by processing the statistical relationship between strain and strength properties. The results of numerical studies and large-scale field tests, performed on experimental area of collapsible loess soil are compared. It is indicated that nonlinearly strained loess foundations of buildings must be regarded under partial saturation conditions, during dangerous hydration process and during stress field and humidity interaction in the course of moisture transfer.

Dynamics of ionic liquids in poly(vinyl alcohol) porous scaffold. Low field NMR study

In this study molecular dynamics of ionic liquids in poly(vinyl alcohol) scaffolds were investigated. The binary poly(vinyl alcohol) – ionic liquid (PVA-IL) compound was prepared from initial solutions of water, ionic liquid (IL) and poly(vinyl alcohol) (PVA) at different concentrations. Subsequently water was evaporated under open conditions, leaving the scaffold/IL system of interest. Low field nuclear magnetic resonance (NMR) relaxation and diffusion measurements, as well as 2D T1-T2 correlated NMR experiments were performed to determine specific local and translational dynamics properties at different time scales. Data suggest that during water evaporation, partial demixing of IL from the polymeric matrix leaves the remaining solvent confined in the porous structure formed by the PVA polymer. The results show that the translational diffusion, as well as the local rotational molecular dynamics is comparable to the bulk liquid state. Moreover, in partial saturation conditions, diffusion shows enhancements relative to the bulk.

Solvent diffusion and dispersion in partially saturated porous media: An experimental and numerical pore-level study

Recent research on unlocking the solvent dispersion as a physical blending process in porous media has been mainly focused on core-scale observations. Pore-level studies of multiphase displacements can help to develop models that correlate rock macro-scale characteristics with its small-scale features, particularly for unsaturated rocks where the intricate fluid arrangements cause dynamic events to be localized in preferential pathways. In this work, to draw new insights into the physics of pore-level interfaces and crystallize the role of small-scale phenomena on the efficiency of solvent-aided bitumen recovery processes, numerical simulations coupled with experiments are conducted in pore-level domains. We simulate fluid flow and transport phenomena through millimeter-sized three-dimensional slabs of consolidated and unconsolidated packings of grains representing the geological rock types of the McMurray formation. We propose a robust numerical workflow for simulation of miscible-floods in unsaturated porous media and investigate the impact of matrix heterogeneity, connate water, cementation, and injection velocity on the longitudinal dispersion coefficient. In particular, primary drainage is simulated at low capillary numbers resulting in two-phase fluid occupancies through pore space domains. Finite element simulations are then carried out in order to solve the mixing advection-diffusion equations within the water-free pore space, and lastly, the effluent history is analyzed to predict the dispersion coefficient in both fully- and partially-saturated conditions and evaluate the efficiency of miscible displacements in the presence of microheterogeneities. A new analytical model for calculation of dispersivity, together with the numerical simulation results, is utilized to adjust a general model for the prediction of longitudinal dispersion coefficient in unsaturated sandy porous media of either uniform or non-uniform grains. Moreover, miscible-flood experiments at low to high injection velocities are conducted in a transparent glass micromodel. According to the results, rock micro-heterogeneities and immobile water both increase the longitudinal dispersion coefficient, and two-phase equilibria control the velocity field by creating connected regions of brine and low resistance oil-filled channels and consequently influence the solute transport and mixing processes. The effect of viscosity contrast on the longitudinal dispersion coefficient is also noteworthy, as the viscous fingering at unfavorable viscosity ratios widens the mixing zone.

Soot Formation in the Methane Partial Oxidation Process under Conditions of Partial Saturation with Water Vapor

The effect of saturation of methane with water vapor on soot formation at different saturation levels has been studied on a test facility of noncatalytic high-temperature partial oxidation of methane with syngas capacity of 8 Nm3/h. Relationship between the synthesis gas composition and the H2O/CH4 ratio has been revealed, as well as the qualitative and quantitative relations of the formation of soot agglomerates to the degree of saturation of pure methane or natural gas with water vapor. The structural features of the soot formed have been investigated by scanning and transmission electron microscopy and X-ray diffraction analysis.

Mechanical response of asphalt mixtures under partial saturation conditions

Quantifying the impact of environmental conditions on the mechanical properties and performance of hot mix asphalt (HMA) materials is a necessary task to achieve high-quality pavement structures. Although the influence of temperature in the behaviour of these viscoelastic materials has been well determined, there is still a lack of information regarding the impact of moisture on the mechanical response of HMA. Studies in this direction should consider that under actual field conditions, these mixtures are usually in a partial saturation state. Within this context, this work evaluates the mechanical response of an HMA through the quantification of the axial tension, axial compression and shear moduli of the mixture, after subjecting it to different relative humidity environments. The experimental plan was conducted using the recently developed Hollow-Cylinder Tester for Asphalt Mixtures equipment, and the results demonstrate that partial saturation strongly influences the rheological properties of these mixtures.

Advanced characterisation of cement-stabilised lateritic soils to be used as road materials

ABSTRACTLaterites or lateritic soils are located in tropical and subtropical regions. Identifying the conditions under which these local materials could be used as part of road infrastructure projects is particularly critical in regions where high-quality unbound aggregates are limited or unavailable. Previous works conducted on this material have suggested that hydraulic cement stabilisation improves its properties, making it suitable for the construction of low-volume roads. This work investigates the impact of cement stabilisation at three different doses (i.e. 2, 4 and 6% by weight of soil) on a Colombian laterite granular material located in the Orinoquia region. The study included the characterisation of the basic properties of this laterite (e.g. gradation, Atterbergh limits, specific gravity and Los Angeles abrasion test), and the advanced characterisation of the cement-stabilised material through the determination of its resilient modulus at different partial saturation conditions, and its compressive and tensile strengths. The impact of stabilisation was further studied through the determination of the mechanical properties and fatigue degradation of cement-stabilised lateritic mortars, which were fabricated at equivalent cement doses and tested under torsional conditions using a rheometer. The results suggest that cement stabilisation at doses ranging between 2 and 6% by weight of soil efficiently improves the mechanical properties of this laterite, allowing its used as part of low- and eventually medium-volume roads.

Supported lithium hydroxide for carbon dioxide adsorption in water-saturated environments

Rebreather-type personal protective equipment requires efficient removal of CO2 from the air that the user exhales. The required operating conditions of low CO2 partial pressure, low temperature, and water saturation create a challenging environment for developing high capacity CO2 adsorbents. Biphasic adsorbents of lithium hydroxide supported on high surface area carbons were synthesized and tested for CO2 capacity under water-saturated conditions. The LiOH phase provides high CO2 capacity through chemisorption while the porous carbon structure helps prevent the formation of diffusion barriers that limit the effectiveness of pure LiOH pellets. Several carbons with different pore morphology were tested, and it was determined that the ideal support has a high degree of mesoporosity that balances the need for high surface area without excess blockage of pore volume upon deposition of LiOH. The activated carbon Norit SX Ultra was chosen based on this criterion. It was found that the maximum achievable loading of LiOH on Norit SX Ultra was 30 wt%, and the highest CO2 capacity under water-saturated conditions at atmospheric pressure with one mole percent CO2 in the gas phase was 3.4 mol/kg.

Volume Behavior of a Soil of Capdevila Formation in Partial Saturation Conditions

Volume Behavior of a Soil of Capdevila Formation in Partial Saturation Conditions

Relations between electrical resistivity, carbon dioxide flux, and self-potential in the shallow hydrothermal system of Solfatara (Phlegrean Fields, Italy)

We present the results of an electric resistivity tomography (ERT) survey, combined with mappings of diffuse carbon dioxide flux, ground temperature and self-potential (SP) at Solfatara, the most active crater of Phlegrean Fields. Solfatara is characterized by an intense carbon dioxide degassing, fumarole activity, and ground deformation. This ensemble of methods is applied to image the hydrothermal system of Solfatara, to understand the geometry of the fluid circulation, and to define the extension of the hydrothermal plume at a high enough resolution for a quantitative modeling. ERT inversion results show Solfatara as a globally conductive structure, with resistivity in the range 1–200Ωm. Broad negative anomaly of self-potential in the inner part of Solfatara with a minimum in the area of Bocca Grande suggests a significant downward flow of condensing liquid water. Comparison between spatial variations of resistivity and gas flux indicates that resistivity changes at depth are related to gas saturation and fluid temperature. These variations delineate two plume structures: a liquid-dominated conductive plume below Fangaia mud-pool and a gas-dominated plume below Bocca Grande fumarole. The geometry of the Fangaia liquid-saturated plume is also imaged by a high resolution 3-D resistivity model. In order to estimate the permeability, we propose a 2-D axis-symmetric numerical model coupling Richards equation for fluid flow in conditions of partial saturation with the resistivity calculation as function of saturation only. Alternatively, we apply the Dupuit equation to estimate the permeability of the shallow layer. Using these two approaches we obtain the permeability of the shallow layer below Fangaia which ranges between (2–4)×10−14m2.

Seismoelectric wave propagation numerical modelling in partially saturated materials

To better understand and interpret seismoelectric measurements acquired over vadose environments, both the existing theory and the wave propagation modelling programmes, available for saturated materials, should be extended to partial saturation conditions. We propose here an extension of Pride's equations aiming to take into account partially saturated materials, in the case of a water-air mixture. This new set of equations was incorporated into an existing seismoelectric wave propagation modelling code, originally designed for stratified saturated media. This extension concerns both the mechanical part, using a generalization of the Biot-Gassmann theory, and the electromagnetic part, for which dielectric permittivity and electrical conductivity were expressed against water saturation. The dynamic seismoelectric coupling was written as a function of the streaming potential coefficient, which depends on saturation, using four different relations derived from recent laboratory or theoretical studies. In a second part, this extended programme was used to synthesize the seismoelectric response for a layered medium consisting of a partially saturated sand overburden on top of a saturated sandstone half-space. Subsequent analysis of the modelled amplitudes suggests that the typically very weak interface response (IR) may be best recovered when the shallow layer exhibits low saturation. We also use our programme to compute the seismoelectric response of a capillary fringe between a vadose sand overburden and a saturated sand half-space. Our first modelling results suggest that the study of the seismoelectric IR may help to detect a sharp saturation contrast better than a smooth saturation transition. In our example, a saturation contrast of 50 per cent between a fully saturated sand half-space and a partially saturated shallow sand layer yields a stronger IR than a stepwise decrease in saturation.

A probabilistic threshold for the onset of carbonation-induced corrosion

A large experimental investigation was conducted in order to assess the capability of electrochemical techniques to detect the effective onset of carbonation-induced corrosion. Specimens made with CEM I, CEM II and CEM III cement-based concrete with embedded steel bars were subjected to several exposure conditions (wet/dry cycles, partial saturation and outdoor conditions) and tested. At regular time intervals, the polarisation resistance and free corrosion potential were measured, as was the amount of corrosion product. From the data acquired, and considering the experimental uncertainties, the probabilities of right or wrong alarm were estimated depending on the alarm thresholds for the electrochemical measurements and the threshold of the effective onset of corrosion. Optimum values of these thresholds were proposed on the basis of the receiver-operating-characteristic curve concept.