Scanning Curves Research Articles

A simple method for predicting the hydraulic properties of unsaturated soils with different void ratios

Reliable estimates of the unsaturated soil hydraulic properties are needed in many research and engineering projects. The void ratio or bulk density is an important factor affecting the unsaturated soil hydraulic properties. The bulk density of one soil can change considerably due to the influences of rain, irrigation, and traffic compaction. It remains a difficult task to accurately describe the hydraulic hysteresis of the unsaturated soil with different void ratios or bulk densities. The aim of this study was to evaluate hydraulic hysteresis behavior and permeability of unsaturated soil with different void ratios or bulk densities based on the normalized soil water retention curves (SWRCs) method. After the normalization, the normalized main drying and wetting SWRCs are independent of the void ratio or bulk density. The hysteresis behavior between the normalized main drying and wetting SWRCs can be described by referring to the existing void ratio independent hysteresis model. Additionally, a simple estimation method to simulate the effects of the void ratio or bulk density on the relative permeability coefficient of unsaturated soils is proposed. The approach proposed here requires no additional parameters. The results show that the proposed hysteresis model can be used to describe the arbitrary main drying, wetting, and scanning curves at arbitrary void ratios over a wide suction range, and the predictions for the relative permeability coefficient with different void ratios by the proposed permeability model can match the experimental data well.

Deformation Inspection and Safety Assessment Method of Buried Flexible Pipeline in Service

The working performance of buried flexible pipelines is connected with the pipe- soil interaction; the weak stiffness of backfill leads to large long-term pipeline deformation and even structural failure. Spangler’s formula is a theory for macroscopic evaluation of pipeline deformation, which cannot reflect the deformation state of various parts around the pipe from a microscopic view. A large number of engineering practices have shown that when the macro radial deformation of the flexible pipe is not large, it is also possible that the local geometric size of the pipeline may change suddenly in the microscopic view. Combining with a diversion project, a laser scanning and piecewise elliptic curve fitting combined method was proposed to measure the empty pipeline deformation in this paper. The deformation pattern of the flexible pipeline was analysis. And then, the analysis results were verified by the elastic wave test and material test data. Based on the deformation inspections, the internal force and related reliability of pipe structure were calculated. Finally, the structural safety of each pipe was assessed to guide the replacement, repair and reinforcement of pipeline.

Modelling the hydraulic/mechanical behaviour of an unsaturated completely decomposed granite under various conditions

Because the hydraulic/mechanical behaviour of unsaturated soil is more complicated than that of saturated soil, one of the most important issues in modelling unsaturated soil is to properly couple its stress-strain relationship with its water retention characteristics. Based on the results of a series of tests, the stress-strain relationship and the changes in suction and saturation of unsaturated completely decomposed granite (CDG, also called Masado) vary substantially under different loading/hydraulic conditions. To precisely model the hydraulic/mechanical behaviour of unsaturated Masado, in this study, the superloading concept was firstly introduced into an existing saturated/unsaturated constitutive model to consider the structural influences. Then a water retention curve (WRC) model considering the volumetric change in the soil, in which the skeleton and scanning curves of the water retention characteristics were assumed to shift in parallel in accordance with the change in the void ratio, was proposed. The proposed WRC model was incorporated into the constitutive model, and the validity of the newly proposed model was verified using the results of tests conducted on unsaturated Masado, including water retention, oedometer and triaxial tests. The accuracy of the proposed model in describing the stress-strain relationship and the variations in suction and saturation of unsaturated Masado is satisfactory.

Undrained Seismic Compression of Unsaturated Sand

Unsaturated soils in engineered geostructures like embankments or retaining walls may experience seismic compression during earthquakes due to particle rearrangement associated with large-strain cyclic shearing. Although previous studies have investigated volume changes during drained cyclic shearing of unsaturated soils, undrained cyclic shearing presents a more complex situation. During undrained cyclic shearing, changes in total volume, matric suction, degree of saturation, effective stress, shear modulus, and damping ratio may occur that have complex coupling effects that affect seismic compression. To better understand these coupling effects, this study performed a series of undrained cyclic simple shear tests on unsaturated sand specimens. Contractile volumetric strain after 200 cycles in these tests was found to vary nonlinearly with degree of saturation. The largest volumetric contraction occurred at a degree of saturation of 0.4 and coincided with the largest decrease in mean effective stress. The sand specimens followed a wetting-path scanning curve during shearing, with small changes in matric suction. The decrease in mean effective stress during cyclic shearing for all specimens followed the same linear relation with the accumulation of volumetric strain.

Wetting Scanning Curve for Soil and Its Expression

Wetting Scanning Curve for Soil and Its Expression

The development and application of the test system for the silicon pixel modules in HEPS-BPIX

HEPS-BPIX is a prototype of photon counting pixel detector developed for the High Energy Photon Source. It consists of 16 silicon pixel modules which should be tested individually to ensure the function and performance. Due to various factors such as the non-uniformity of the processes and voltage drop, the response of each pixel in the silicon pixel module is not identical completely. The response difference of pixels can be minimized by the threshold calibration. This system is developed for the quality test and calibration of the silicon pixel modules. The system consists of a mother board, a control board and a data acquisition (DAQ) system. The mother board provides necessary resources including power supplies and the fanout of calibration signals. Besides, it can be used to test the connectivity by monitoring the power states. The control board reads data out and provides the clock, trigger and configuration data for the silicon pixel module. The DAQ system sends the control commands and receives the readout data through an Ethernet link. Compared with the previous readout system, this designed system has a lower noise level and better scanning curves making the calibration more accurate. And it has been successfully applied to the comparison experiments of the through silicon via and wire-bonding silicon pixel modules. The results show that this test system can be used to the quality test and calibration of the silicon pixel modules. In addition, the system can be adapted to the measurement of different pixel array detector modules.

Predictive Modeling of Relative Permeability Using a Generalized Equation of State

Summary Reliable simulation of enhanced oil recovery (EOR) processes depends on an accurate description of fluid transport in the subsurface. Current empirical transport models of rock-fluid interactions are fit to limited experimental data for specific rock types, fluids, and boundary conditions. In this paper, a general equation-of-state (EoS) approach is developed for relative permeability (kr) based on a set of geometric state parameters: normalized Euler characteristic (connectivity) and saturation. Literature data and pore network modeling (PNM) simulations are used to examine the functional form of the EoS. Our results show that the new kr-EoS matches experimental data better than the conventional Corey form, especially for highly nonlinear relative permeabilities at low saturations. Using hundreds of PNM simulations, relative permeability scanning curves show a locus of residual saturation and connectivity that defines an important limit for the physical kr region. The change of this locus is also considered for two contact angles. PNM data further allow for the estimation of the relative permeability partial derivatives that are used as inputs in the EoS. Linear functions of these partials in the connectivity-saturation space renders a quadratic response of kr, which shows excellent predictions. Unlike current empirical models that are based on only one residual saturation, the state function approach allows for dynamic residual conditions critical for capturing hysteresis in relative permeability.

On-machine noncontact scanning of high-gradient freeform surface using chromatic confocal probe on diamond turning machine

Inspecting a high-gradient freeform surface is a challenging task in manufacturing automation due to its complexity of the surface and high-aspect-ratio. On-machine measurement has shown remarkable achievements in ultra-precision manufacturing. In this paper, an on-machine noncontact scanning method using chromatic confocal probe for high-gradient freeform surface is proposed. First, a coordinate sampling model of scanning based on an ultra-precision diamond turning machine is established. Then, the steepness angle is defined to guide the scanning curves distribution, and global mesh scanning lines are generated by controlling planning deviations. Segmented motion trajectory of the probe is designed considering the vector direction of optical axis and sensor offset error. Finally, the scanning parameters are determined and the NC inspection program is generated. The proposed method can make a balance between accuracy and efficiency. Its effectiveness is verified by the on-machine inspection experiments.

Three-dimensional orthotropic nonlinear transient moisture simulation for wood: analysis on the effect of scanning curves and nonlinearity

This paper introduces, with the development of user-subroutines in the finite-element software Abaqus FEA®, a new practical analysis tool to simulate transient nonlinear moisture transport in wood. The tool is used to revisit the calibration of moisture simulations prior to the simulation of mechanical behaviour in bending subjected to climate change. Often, this calibration does not receive sufficient attention, since the properties and mechanical behaviour are strongly moisture dependent. The calibration of the moisture transport simulation is made with the average volumetric mass data experimentally obtained on a paired specimen of Norway spruce (Picea abies) with the dimensions 30times 15times 640, {mathrm{mm}}^{3}. The data, from a 90-day period, were measured under a constant temperature of 60 °C and systematic relative humidity cycles between 40 and 80%. A practical method based on analytical expressions was used to incorporate hysteresis and scanning behaviour at the boundary surface. The simulation tool makes the single-Fickian model and Neumann boundary condition readily available and the simulations more flexible to different uses. It also allows for a smoother description of inhomogeneity of material. The analysis from the calibration showed that scanning curves associated with hysteresis cannot be neglected in the simulation. The nonlinearity of the analysis indicated that a coherent set of moisture dependent diffusion and surface emission coefficient is necessary for the correct description of moisture gradients and mass transport.

Simple functions for describing soil water retention and the unsaturated hydraulic conductivity from saturation to complete dryness

Many applications require accurate soil hydraulic functions that can describe the dynamics of water in variably saturated systems from full saturation to complete dryness. Current functions considering zero water content at the dry end involve the summation of capillary and adsorption functions. This study proposes relatively simple yet complete soil hydraulic functions from full saturation to oven dryness that can be incorporated into existing models. The proposed water retention model is constructed by scaling the saturation function of Fredlund and Xing (1994) to describe capillary and adsorptive water retention as well as zero water content at oven dryness. To describe the hydraulic conductivity due to capillary and film flow, the model of Wang et al. (2018) is used. We further incorporated hysteresis in the water retention function of Wang et al. (2018). Testing on 241 hydraulic property data sets covering a wide range of soil textures from sands to clays, shows good agreement with laboratory observations, especially for coarse-textured soils. The proposed model accounts for the following processes: hysteretic capillary and adsorptive water retention, hysteretic hydraulic conductivity as a function of pressure head, non-hysteretic hydraulic conductivity as a function of water content, the effects of entrapped air, and closed scanning curves. This paper successfully derives the parameters of the main wetting curve from the main drying curve. Using the proposed functions for soil water flow modelling should lead to improved dynamic flow predictions, especially for drying soil conditions.

Variation of Small-Strain Shear Modulus of Unsaturated Silt under Successive Cycles of Drying and Wetting

A new framework is developed to extend an existing small-strain shear modulus (Gmax) model to determine Gmax of unsaturated silty soils along different paths of the soil water retention curve (SWRC) including the scanning loops. The suitability of the proposed framework is validated against experimental results of a series of bender-element tests performed in this study and data reported in literature. Measured values of Gmax showed a slight hysteresis in the Gmax measurements along the scanning curves of the SWRC, with lower values along the wetting scanning paths. However, results indicated that the value of Gmax was recovered once the main drying path was reached. Results of this study also indicated that Gmax behavior of the silty specimen along the scanning curves was stress dependent. The model was observed to follow the experimental data along different paths of the SWRC including scanning curves.

Estimation of the wetting scanning curves for sandy soils

It is known that the soil-water characteristic curve (SWCC) of unsaturated soils is hysteretic. The engineering properties of unsaturated soils during the drying process are different from those during the wetting process, and the difference can be related to the hysteresis of the SWCC. Therefore, understanding the hysteresis of the SWCC is crucial in engineering practices. In this paper, both the “rain-drop” and “ink-bottle” effects on the hysteresis of the SWCC are quantified with mathematical equations. In the proposed equations, it is assumed that soil volume changes during the drying and wetting processes are negligible, which is a reasonable assumption for most sandy soils. Based on the proposed theory, the wetting scanning curves were estimated from the main drying curves. The results from the method proposed in this paper have been compared with experimental data from the published literature. Satisfactory agreements were found between the measured and estimated wetting scanning curves. Consequently, the method for estimating the wetting scanning curves from the fitting parameters of the SWCC by using the equations proposed in this paper is recommended.

An Empirical Approach for Modeling Hysteresis Behavior of Pyroclastic Soils

For modeling physical and mechanical phenomena that occur in unsaturated soils, it is very important to identify the correct relationship between suction and water content. This relationship defines the soil water retention curve (SWRC). Its shape depends on numerous factors, including grain size composition, particles’ thickening state and, above all, the hydraulic and stress soil history. In particular, the SWRC in wetting phase differs from SWRC in drying phase, showing a hysteretic behavior. Hysteresis domain is defined by the main drying and wetting curves; when moving from one phase to another, relationship between suction and water content defines secondary curves within them. In this paper, a laboratory experiment was carried out to determine main wetting and drying curves of a pyroclastic ash sample from southern Italy. In same site of the sample collection, a monitoring station was installed that measured the suction and water content values. The experimental curves were compared with the data recorded on the site. In this paper, moreover, an empirical procedure is proposed to model secondary curves (or scanning curves) within the hysteresis domain. The scanning curves obtained with this method were compared with data collected by the in-situ monitoring network, revealing the ability to describe a situation realistically with a good adaptation. With this procedure, it is therefore possible to minimize errors since it covers a hysteretic behavior.

Temperature-driven migration of heavy metal Pb2+ along with moisture movement in unsaturated soils

Nonlinear coupled heat-moisture-contaminant transport equations are established to analyze the temperature-driven movement of moisture and migration of heavy metal Pb2+ in unsaturated soils. A new soil–water characteristic curve (SWCC) with hysteretic effects is constructed, which can directly give the scanning curve equations starting from any point on the boundary curves without introducing a new equation or new parameters. The theoretical results demonstrate good agreement with the results of laboratory tests in a soil column and satisfactorily verify the hysteretic effects of moisture movement induced by thermal cycling. Due to the obvious driving effect of the temperature gradient, the moisture in the soil column gradually moves to a distant point and develops a nonuniform distribution. Finally, the driving potential of the temperature gradient and the driving potential of the moisture content gradient reach a new equilibrium. In addition to the flow of liquid water, the movement of moisture also includes the transformation of liquid water to water vapor. With the movement of moisture, the migration distance of heavy metal Pb2+increases with increasing initial moisture content. Generally, kaolin clay with a high adsorption capacity has an obvious retardation effect on the migration of heavy metal contaminants.

Laser curve scanning forming process of laminated metal composite plate

To analyze the deformational behaviors of laminated metal composite plate under laser curve scanning, a numerical 3D nonlinear thermodynamic coupling model was constructed for a three-layer stainless steel composite plate, 06Cr19Ni10/1Cr17Mn6Ni5N/06Cr19Ni10. The effects of curvature M of the scanning path, laser power P, scanning velocity V, and the distance He from the scanning line to the free end on the forming process were investigated. The numerical model and research contents were experimentally verified. Results showed that the plate under laser curve scanning underwent double-curvature deformation. The deformational curvature of the free end of the plate increased with the curvature of the scanning curve. Plate forming accuracy could be improved by reasonably controlling laser power and scanning velocity. The bending angle of the plate was approximately in direct proportion to He. The crystal grains of the formed plate under optimized process parameters were refined without lamination phenomenon.

Approximation of Scalar Conservation Law with Hysteresis

We consider a scalar conservation law with hysteresis in which the flux function depends on the history of the evolution. The work is motivated by the need to account for hysteresis in important applications to transport with adsorption. To model hysteresis we use an auxiliary system of ODEs with constraints known as linear play combined with particularly chosen nonlinear truncation functions. A combination of these allows a quite general shape of hysteresis graph with piecewise linear primary and secondary scanning curves; this is distinct from the well-known Preisach model. We prove well-posedness of the model and stability of an explicit-implicit finite difference scheme. The challenge of history dependence requires auxiliary results in product spaces. Numerical results confirm convergence of linear or slower rate.

Image Encryption Algorithm Based on Block Scrambling and Finite State Machine

To better protect the image information, an image encryption algorithm based on block scrambling and finite state machine is proposed. The method uses discrete wavelet transform (DWT) to divide the original image into four frequency bands. Secondly, chaotic sequences and zigzag scanning curve are used to construct a scrambling matrix to scramble the four frequency bands. Then combine the chaotic sequence, DNA coding, and automata to transform the state of the scrambled image. Finally, the key stream is used to diffuse the sequence to improve the security of cipher images further. Experimental results and security analysis show that the proposed encryption scheme can resist various attacks and ensure the secure transmission of images.

Reversible and Irreversible Processes in Drying and Wetting of Soil.

In this article, we provide a detailed description of a modeling technique for the capillary hysteresis in a soil-like porous material based on a Generalized Preisach Model. The identification of the reversible and irreversible Preisach distributions was performed with the first-order reversal curve (FORC) diagram technique, which is very popular now in magnetism and in other areas of science to give a fingerprint of the studied system. A special attention was given to the evaluation of the reversible component. In this case, we used a set of data published in 1965 by Morrow and Harris which has been used as a reference by many other researchers since. The advantage of this approach is that the experimental FORC distributions can be described with analytical functions and easily implemented in the mentioned Preisach-type model. Our research is also focused on the development of a characterization tool for the soil using the soil-moisture hysteresis. The systematic use of scanning curves provides a (FORC) diagram linked to the physical properties of the studied soil. The agreement between the experimental data and the Preisach model using the set of parameters found through the FORC technique is really noticeable and gives a good practical option to the researchers to use a method with a strong predictive capability.

Measurement of water vapor adsorption isotherms in mesoporous materials using the zero length column technique

Measurement of water adsorption isotherms is important for industrial applications and for the characterization of nanoporous materials. The zero-length column technique is used for the first time to measure the adsorption-desorption isotherm of water on a mesoporous adsorbent, SBA-15, up to 90% relative humidity at 298 K. The technique showed two key advantages; (a) The experimental flexibility for the measurement of continuous adsorption-desorption isotherms characterized by complex shapes and hysteresis loops; (b) The possibility to measure a complete set of adsorption-desorption isotherms and scanning curves in few days compared to several weeks needed with traditional gravimetric techniques. The adsorption isotherm measured was compared and validated against isotherms measured on a commercial gravimetric system designed for water vapor adsorption. For the system considered, the adsorption and desorption branches are very steep, and the zero-length column technique is shown to allow setting easily the starting point of the scanning curves.

Pore structural evolution of shale following thermochemical treatment

Abstract Shales experience heat treatment concurrent with the presence of water or steam during reservoir engineering interventions, such as high pressure water fracking and in-situ combustion of hydrocarbons. This work utilises a novel technique, which is a combination of gas sorption overcondensation and integrated mercury porosimetry experiments, not used before for any type of porous material, to study the pore structure of a shale rock, and its evolution following thermal treatment in the presence of water. Overcondensation allows the extension of gas sorption beyond the limits of conventional experiments to enable direct study of macroporosity. Scanning curve experiments, initiated from the complete boundary desorption isotherm, that can only be obtained for macropores by overcondensation experiments, has revealed details of the relative pore size spatial disposition within the network. In particular, it has been found that the new large voids formed by treatment are shielded by relatively much narrower pore windows. Use of a range of different adsorbates, with differing polarity, has allowed the chemical nature of the pore surface before and after treatment to be probed. Integrated rate of gas sorption and mercury porosimetry experiments have determined the level of the particular contribution to mass transport rates of the newly introduced porosity generated by thermal treatment. Combined CXT and mercury porosimetry have allowed the mapping of the macroscopic spatial distribution of even the new mesoporosity, and revealed the degree of pervasiveness of the new voids that leads to a thousand-fold increase in mass transport on thermal treatment.