Impedance Tomography Research Articles

Electrical resistivity tomography inversion combining deep variational autoencoder and stochastic adaptive sampling

Geophysical methods, such as electrical resistivity tomography (ERT), can be used to imaging the near-surface electrical resistivity as field measurements depend on the subsurface porosity, water saturation and fluid salinity. ERT has been widely applied to investigate mineral and groundwater resources, and in archaeological, environmental, and engineering studies. The prediction of subsurface electrical conductivity from ERT data requires solving a geophysical inverse problem. For near-surface characterization studies, this is often accomplished with deterministic inverse methods. These methods linearize the problem around an initial solution, and their smoothness depends on an imposed a priori spatial regularization term. Depending on this parameterization, these methodologies might struggle to capture the natural variability of the subsurface. Moreover, deterministic solutions have limited capabilities for uncertainty assessment. On the contrary, stochastic inverse methods can assess uncertainties by predicting multiple model realizations that fit similarly the recorded ERT data. However, they are often more computationally expensive than deterministic solutions. Deep learning algorithms based on deep generative models have been used to re-parametrize model and data spaces into low-dimensional domains and efficiently solve geophysical inverse problems. However, within this context, uncertainty assessment is challenging. We propose a deep convolutional variational autoencoder (VAE) coupled with stochastic adaptive optimization to perform stochastic ERT inversion. Geostatistical simulations of electrical resistivity are used as training data set of the VAE. After training, the VAE generates electrical resistivity models that reproduce the statistics and spatial continuity patterns of the training data set. Then, the VAE latent space is iteratively perturbed and updated with adaptive stochastic sampling based on the misfit between observed and predicted ERT data. The proposed methodology is illustrated in two-dimensional synthetic and real data sets to illustrate the ability of the proposed method to predict reliable electrical resistivity models while generating multiple possible scenarios for uncertainty assessment.

Resistor Network for Forward Calculation in Electrical Resistance Tomography of Carbon Fiber-Reinforced Composites

Resistor Network for Forward Calculation in Electrical Resistance Tomography of Carbon Fiber-Reinforced Composites

The Effect Characterization of Lens on LNAPL Migration Based on High-Density Resistivity Imaging Technique

Light non-aqueous phase liquids (LNAPLs), which include various petroleum products, are a significant source of groundwater contamination globally. Once introduced into the subsurface, these contaminants tend to accumulate in the vadose zone, causing chronic soil and water pollution. The vadose zone often contains lens-shaped bodies with diverse properties that can significantly influence the migration and distribution of LNAPLs. Understanding the interaction between LNAPLs and these lens-shaped bodies is crucial for developing effective environmental management and remediation strategies. Prior research has primarily focused on LNAPL behavior in homogeneous media, with less emphasis on the impact of heterogeneous conditions introduced by lens-shaped bodies. To investigate the impact of lens-shaped structures on the migration of LNAPLs and to assess the specific effects of different types of lens-shaped structures on the distribution characteristics of LNAPL migration, this study simulates the LNAPL leakage process using an indoor two-dimensional sandbox. Three distinct test groups were conducted: one with no lens-shaped aquifer, one with a low-permeability lens, and one with a high-permeability lens. This study employs a combination of oil front curve mapping and high-density resistivity imaging techniques to systematically evaluate how the presence of lens-shaped structures affects the migration behavior, distribution patterns, and corresponding resistivity anomalies of LNAPLs. The results indicate that the migration rate and distribution characteristics of LNAPLs are influenced by the presence of a lens in the gas band of the envelope. The maximum vertical migration distances of the LNAPL are as follows: high-permeability lens (45 cm), no lens-shaped aquifer (40 cm), and low-permeability lens (35 cm). Horizontally, the maximum migration distances of the LNAPL to the upper part of the lens body decreases in the order of low-permeability lens, high-permeability lens, and no lens-shaped aquifer. The low-permeability lens impedes the vertical migration of the LNAPL, significantly affecting its migration path. It creates a flow around effect, hindering the downward migration of the LNAPL. In contrast, the high-permeability lens has a weaker retention effect and creates preferential flow paths, promoting the downward migration of the LNAPL. Under conditions with no lens-shaped aquifer and a high-permeability lens, the region of positive resistivity change rate is symmetrical around the axis where the injection point is located. Future research should explore the impact of various LNAPL types, lens geometries, and water table fluctuations on migration patterns. Incorporating numerical simulations could provide deeper insights into the mechanisms controlling LNAPL migration in heterogeneous subsurface environments.

Hybrid optimization for DC resistivity imaging via intelligible-in-time logic and the interior point method.

Geophysical DC resistivity imaging is crucial in subsurface exploration, environmental studies, and resource assessment. However, traditional inversion techniques face challenges in accurately resolving complex subsurface features because of the inherent nonlinearities in geophysical data. To overcome these challenges, we propose a hybrid optimization approach that combines incomprehensible but intelligible-in-time (IbI) logic with the interior point method (IPM). The IbI logic framework leverages complexity and temporal intelligibility, allowing for a dynamic interpretation of subsurface phenomena. By integrating IbI with IPM, our approach benefits from global exploration and local refinement, leading to improved convergence speed and solution quality. The objective function formulated for the inversion process includes data misfit and model regularization terms, which promote accurate and smooth solutions. Our methodology involves the use of the IbI logic algorithm (ILA) for initial global search, which identifies promising regions in the search space. This is followed by the application of IPM for local optimization. This synergy between the two algorithms ensures robustness and efficiency in handling large datasets and complex geological models. We conducted tests using synthetic and real DC resistivity data to validate our approach. The synthetic test demonstrated the accurate reconstruction of subsurface anomalies, whereas the real data test successfully identified fault zones, which is consistent with previous studies. The hybrid optimization algorithm significantly improves the resolution of subsurface structures and enhances geophysical data inversion practices. It balances the exploration and refinement phases effectively, optimizing the computation time and ensuring precise model delineation.

Exploration of Bituminous Materials Using 2D Electrical Resistivity Imaging, Kurdistan Region, NE Iraq

Solid bituminous materials are widely spread in the Iraqi Kurdistan Region, they are filled so many locations, such as fracture zones, fault planes, and bedding planes. These materials can be used in several industries like pavement road, roofing, bituminous paint and waterproof, etc. The study aims to find an economical quantity of these materials by using 2D resistivity imaging in three locations that are different in geology and tectonic settings. These locations are Alla Syaw, Mera De, and Nasalih villages. The data are collected using Syscal R1 plus resistivity meter, for the sake of following up horizontal and vertical extension of these materials Wenner-Schlumberger array is used with 72 electrodes and a spacing interval of 5 m. Three profiles were conducted for each location, which have lengths equal to 360 m. The data processing was carried out by using the RES2DINV, and the smoothness was performed using finite difference forward modeling. The results show that all the bituminous materials are detected in shallow depths and only in the sandstone layers of the Tanjero, Gercus, and Injana formations filling the fracture zones and fault planes. This is also attributed to the more brittle behavior of the sandstone layer than other layers of these formations which deforms easily by applying external stresses. In the Tanjero Formation bituminous body is detected at a depth of about 10 m, which has an extension of more than 50 m from profile-1 to profile-2 (this is a lateral extension). The average width and height of the body are about 8m and 20 m, so it forms an approximate total volume equal to 8000 m3. The study concludes that the preliminary estimation of the total volume of the detected bituminous bodies is about 20000 m3, which has great importance as raw material for different industries. The bituminous material has a high resistivity value in most of the profiles reaching more than 200 ohm.m.

A Geophysical Investigation in Which 3D Electrical Resistivity Tomography and Ground-Penetrating Radar Are Used to Determine Singularities in the Foundations of the Protected Historic Tower of Murcia Cathedral (Spain)

This study presents a procedure in which 3D electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) were used to determine singularities in the foundations of protected historic towers, where space is limited due to their characteristics and location in highly populated areas. This study was carried out on the Tower of the Cathedral “Santa Iglesia Catedral de Santa María” in Murcia, Spain. The novel distribution of a continuous nonlinear profile along the outer and inner perimeters of the Tower allowed us to obtain a 3D ERT model of the subsoil, even under its load-bearing walls. This nonlinear configuration of the electrodes allowed us to reach adequate investigation depths in buildings with limited interior and exterior space for data collection without disturbing the historic structure. The ERT results were compared with GPR measurements and with information from archaeological excavations conducted in 1999 and 2009. The geometry and distribution of the cavities in the entire foundation slab of the Tower were determined, verifying the proposed procedure. This methodology allows the acquisition of a detailed understanding of the singularities of the foundations of protected historic towers in urban areas with limited space, reducing time and costs and avoiding the use of destructive techniques, with the aim of implementing a more efficient and effective strategy for the protection of other tower foundations.

Woody Encroachment Modifies Subsurface Structure and Hydrological Function

ABSTRACTWoody encroachment—the expansion of woody shrubs into grasslands—is a widely documented phenomenon with global significance for the water cycle. However, its effects on watershed hydrology, including streamflow and groundwater recharge, remain poorly understood. A key challenge is the limited understanding of how changes to root abundance, size and distribution across soil depths influence infiltration and preferential flow. We hypothesised that woody shrubs would increase and deepen coarse‐root abundance and effective soil porosity, thus promoting deeper soil water infiltration and increasing soil water flow velocities. To test this hypothesis, we conducted a study at the Konza Prairie Biological Station in Kansas, where roughleaf dogwood (Cornus drummondii) is the predominant woody shrub encroaching into native tallgrass prairie. We quantified the distribution of coarse and fine roots and leveraged soil moisture time series and electrical resistivity imaging to analyse soil water flow beneath shrubs and grasses. We observed a greater fraction of coarse roots beneath shrubs compared to grasses, which was concurrent with greater saturated hydraulic conductivity and effective porosity. Half‐hourly rainfall and soil moisture data show that the average soil water flow through macropores was 135% greater beneath shrubs than grasses at the deepest B horizon, consistent with greater saturated hydraulic conductivity. Soil‐moisture time series and electrical resistivity imaging also indicated that large rainfall events and greater antecedent wetness promoted more flow in the deeper layers beneath shrubs than beneath grasses. These findings suggest that woody encroachment alters soil hydrologic processes with cascading consequences for ecohydrological processes, including increased vertical connectivity and potential groundwater recharge.

Application of Combined Geoelectrical Techniques for Groundwater Exploration at Federal University Gusau, Zamfara and its Environ, Northwest Nigeria

Study’s Excerpt Integrated approach combining Electrical Resistivity Tomography (ERT), Natural Electric Field (NEF) method, and Vertical Electrical Sounding (VES) is used to delineate groundwater potential in the study area. The results revealed that the water bearing aquifers in the study area are fractured basement layers at varying depths between 15 and 105 meters. This research provided a robust framework for groundwater exploration in arid and geologically complex terrains. Full Abstract The area of study is currently facing an acute water shortage due to the dominant lithological framework that underlies the region and its fragile climate condition. As such, this study aimed at unearthing the groundwater potential of the area using a combined three geoelectrical techniques. Techniques such as Electrical Resistivity Tomography (ERT), Natural Electric Field (NEF) method, and Vertical Electrical Sounding (VES) were employed in the delineation of the groundwater potential of the area. Using an ABEM SAS-4000 Resistivity meter and a PQWT-TC150 water-detector equipment, respectively. Wennar array was employed for the conduct of ERT while Schlumberger configuration was used for VES data collection. The measured apparent resistivity value was inputted into RES2DIV software and subjected to an inversion process to generate the resistivity structural image of the subsurface. However, IP2WIN software was used for the VES data interpretation. The result of the ERT method revealed two to three geoelectrical resistivity layers: an overburdened layer of topsoil/laterite with resistivity values ranging from 6.86 Ωm to 1095 Ωm and thicknesses of 1-13 meters, a weathered/fractured basement layer, interpreted as the aquifer unit, with resistivity values between 28.7 Ωm and 345 Ωm, and thicknesses ranging from 6 - 30 meters; and a fresh/slightly fractured basement layer with resistivity values from 367 Ωm to 6899 Ωm. NEF method revealed the thickness and depth of the aquiferous layer across the six profile lines to range between 15-60m, 30-90m, 15-85m, 20-80m, 45-105m, and 20-40m respectively, with points on profile five (5) identified as the most promising site with regards to groundwater development. VES result identifies weathered and fractured layers as the major aquiferous units with resistivity values ranging from 9.965 Ωm to 9651 Ωm and 21.7 Ωm to 859 Ωm respectively with fracture thickness reaching up to 60m in some instances. The result goes in line with the outcome of both NRF and ERT techniques. The geological interference of this lithology on groundwater exploration reveals both the weathered overburden and fractured basement as aquiferous units in the study area. The study identified several promising aquiferous zones at depths ranging from 15 to 105 meters, with fractured basement layers serving as primary reservoirs for groundwater development.

Deep geophysical investigations (DERT and Seismic Reflection) to unravel the Ferrara urban area geology

Exploring the ‘fragile crust of our planet’ is crucial for human survival holding an immense social and economic significance. Therefore, innovative approaches become of utmost importance for obtaining precise subsoil models in urban areas making the latter more resilient to natural disasters. Due to logistic issues and a high level of anthropogenic disturbance and related background noise, urban areas are usually intrinsically more problematic for applying geophysical prospecting methods. This work presents the results obtained by Deep Electrical Resistivity Tomography and P wave Seismic Reflection surveys performed along the Ferrara, north Italy, city walls documenting the adaptability of the geophysical surveys and how it is possible to obtain high-quality electrical resistivity and seismic data even in complex urban settings. The joint interpretation of geoelectrical and seismic data fully integrated with tectonic, geological and hydrogeological information allowed to reconstruct the stratigraphic evolution down to a depth of about 1.5 km. These results highlight the occurrence of a syndepositional Quaternary tectonic tilting associated with the growth of a fault-propagation fold.

Evaluating the deformation modulus at representative elementary volume using electrical resistivity tomography

The deformation modulus of rock mass is an essential parameter for evaluating the bearing capacity and deformations. A deformation modulus obtained through conventional approaches, including empirical equations and in situ tests, cannot present the deformation modulus at representative elementary volume (DREV) due to limited test coverage and technical difficulties in harsh geological or topographic conditions. This study utilized electrical resistivity (ER) tomography and numerical back-analysis to investigate DREV at the Asmari-Jahrum formation. We employed geoelectrical contrasts to detect proper locations for installing extensometers at excavated galleries. The deformations recorded by extensometer were used to back-calculate the DREV values by finite difference numerical modeling. We established a correlation between ER and DREV to predict DREV, which were 30–80 % more accurate than those obtained through conventional approaches at the study site. The tested area, anisotropy, creep, ER inaccuracies, and plastic deformations are evaluated as statistically significant factors that can influence DREV. Our methodology provides a systematical approach to assess DREV, which applies to geoengineering projects within the Asmari-Jahrum formation or similar sedimentary units (ER below 200 Ω⸱m). This methodology is also replicable for other geological formations with harsh geology or limited access without exposing an extreme financial burden or environmental issues.

Prospection of faults on the Southern Erftscholle (Germany) with individually and jointly inverted refraction seismics and electrical resistivity tomography

As part of the Lower Rhein Embayment (LRE), the Southern Erft block is characterized by a complex tectonic setting that influences hydrological and geological conditions on a local as well as regional level. The study area is located in the south of North Rhine-Westphalia and traversed by several NW-SE-oriented fault structures. Since the tectonic structures were located by past studies based on a sparse foundation of geological data, the positions include considerable uncertainties. Therefore, it was decided to re-evaluate and refine the assumed fault locations by conducting geophysical measurements. Seismic Refraction Tomography (SRT) as well as Electrical Resistivity Tomography (ERT) was performed along seven measurement profiles with a length of up to 1.1 km. In addition to compiling individual resistivity and velocity models for all deduced measurements, ERT and SRT datasets were cooperatively inverted using the Structurally Coupled Cooperative Inversion (SCCI). This algorithm strengthens structural similarities between velocity and resistivity by adapting the individual regularizations after each model iteration. Previously assumed locations of the tectonic structures diverge from the new evidence based on ERT and SRT surveys. Especially in the western and eastern parts of the research area, differences between the survey results and formerly assumed locations are in the order of 100 m. Seismic and geoelectric measurements further indicate a fault structure in the southern part of the area, which remained undetected by past studies. The cooperative inversions do not improve the geophysical models qualitatively, since the individually inverted datasets already provide results of good quality and resolution.

A case study of canal seepage quantification using gain/loss method and electrical resistivity tomography in an intensively managed water resource system in the Treasure Valley, Idaho, United States

Monitoring groundwater-surface water (GW-SW) interactions is essential for effectively managing the available water resources in semi-arid and arid environments. The focus of this study was to quantify how much SW is being exchanged with the shallow GW aquifer in the Treasure Valley (TV), Idaho, USA. Previous water budgets estimated regional canal seepage without incorporating canal variability and flow measurement uncertainty. To address this, we applied both direct (gain/loss) and indirect (electrical resistivity tomography (ERT)) techniques. Direct seepage measurements were taken on canals capturing a range of different characteristics in the TV. The discrete measurements were then used to estimate the total seepage anticipated to be lost from these canals during the irrigation season. Our findings showed high seepage variability across the canals. The ERT inversion approach was utilized before and after the irrigation season by applying an advanced inversion scheme to better constrain the canal seepage spatial variability and uncertainty by quantifying changes in the saturated zone with 2D-ERT results. Temporal changes in the subsurface resistivity were observed due to the lateral flow from the nearby surface canal during the irrigation season. The combination of these approaches improves our understanding of SW-GW interactions in intensively managed irrigation systems.

Topographic ridges express late Quaternary faulting peripheral to the New Madrid seismic zone, intraplate USA: Their tectonic implications

Northeast-trending linear topographic ridges in Pliocene and Quaternary sediments adjacent to the New Madrid seismic zone (NMSZ), intraplate North America, have been long speculated to be neotectonic landforms related to reactivation of basement faults of the eastern Mississippi Valley Rift margin. Earthquake epicenters and paleoseismological studies show that eastern rift margin faults (ERMF) were active during late Quaternary south of a restraining bend in the Mississippi Valley Rift fault complex, but the ERMF zone north of the restraining bend (ERM-N) and underlying the linear ridges is seismically quiescent. A previous P-wave seismic reflection survey across the most prominent linear ridge (Rives lineament) revealed that it overlies a horst in Eocene sediment. To ascertain whether the Rives lineament could have been produced by surface faulting/folding, we collected electrical resistivity tomography (ERT) and ground penetrating radar (GPR) profiles to image the ridge's shallow subsurface features. We interpret shallow folding and faulting of late Pleistocene sediment in our ERT and GPR images. Additionally, convexity of multiple topographic profiles of scarps along margins of the Rives lineament was quantified and compared to the convexity of profiles of known neotectonic scarps and of fluvial terrace riser profiles within the region. Comparison of these profiles reveals a high degree of similarity between the scarps along the Rives lineament margins and the Holocene Reelfoot thrust scarp. When combined, our results strongly suggest late Pleistocene or Holocene folding and faulting created this ridge despite its current seismic quiescence, and thus they provide useful insight for assessing the seismic hazard potential of quiescent faults in strike-slip systems in general. We conclude that the late Quaternary series of movements documented on the Reelfoot thrust was initiated to accommodate crustal shortening after transpressional fault movements on the ERM-N became inactive in late Pleistocene or early Holocene and that movement along the ERM-N may resume if the Reelfoot thrust has an interval of inactivity in the future. Our results suggest how fault interactions within a strike-slip system can change, making faults with significant amounts of seismic potential appear as though they are inactive.

Application of electrical resistivity tomography for groundwater evaluation in Yirgacheffe Town and its environs, Main Ethiopian Rift

Exploring groundwater is crucial in areas with poor surface water quality, such as Yirgacheffe Town and its surroundings. This study aims to assess aquifer materials and groundwater potential using Electrical Resistivity Tomography (ERT) in the region,within the Main Ethiopian Rift. Four electrical resistivity profiles were gathered using a Wenner array with a WDA-1 digital resistivity and induced polarization meter from Chongqing, China. Each profile extended 236 m with 4-m electrode spacing. Data were analyzed and inverted with Res2DinV software and validated against lithological logs. The ERT inversion revealed three subsurface geoelectric layers: (1) massive rhyolite ignimbrite and basalt (>2000 Ωm); (2) weathered rhyolite ignimbrite and basalt (200–2000 Ωm); and (3) topsoil (4–200 Ωm). These results are key for effective water resource management and highlight ERT's utility in similar geological settings.

Effects of human and tectonic activities on groundwater in the upper Yellow River terraces of the loess Plateau

Terraces of the Yellow River are among the most crucial geomorphological landforms pertaining to human survival on the Loess Plateau. After more than half a century of surface flood irrigation, rapid rises in groundwater levels have led to frequent geological disasters, causing a rapid short-term evolution of Yellow River terraces, and an increasingly serious contradiction between this rapid evolution and human survival. However, the process by which water transfers through the thick loess vadose zone and causes a rapid groundwater response within months or years remains controversial. Using the Heitai platform of Yellow River terrace IV as an example, we found, on the basis of regional geological surveys, that at least 112 tectonically-induced cracks have developed in this area. We contend that the superimposed effects of earthquake ground motions from historical and ancient earthquakes since the Late Pleistocene have driven the development of such densely distributed cracks in the loess layer. These cracks, together with a series of fault planes generated by NE-directed extrusive stress at the regional scale, constitute a potential network of preferential channels for water transport within the Heitai platform. Combined with the results of a large-scale in situ ponding test and electrical resistivity tomography, we found that this network of cracks helps to establish catchment areas within the loess layer, thereby increasing soil saturation at a more extensive spatial scale, which may then increase the overall movement velocity of the wetting front. We semi-quantified the efficiency of the crack network in enhancing the recharge of surface water to groundwater, and suggested that the impact of human and tectonic activities substantially shortens the response time of groundwater to surface water, with the reduced time far exceeding one order of magnitude. The results of a field investigation of structural traces and terrace groundwater after the Ms 6.2 Jishishan earthquake on 18 December 2023 further emphasize that a causal mechanism of human and tectonic activities leading to the rapid short-term evolution of groundwater distribution patterns may be universally applicable to all Yellow River terraces on the Loess Plateau. This study mitigates the long-standing controversy concerning the mode of surface water infiltration, including piston flow and preferential flow, and the infiltration medium by which rapid surface water recharge to groundwater occurs in loess areas over short time periods.

Comparison of methods measuring electrical conductivity in coastal aquifers

Coastal aquifers, the transition zone between freshwater and saltwater, show large salinity contrasts in the subsurface. Salinity is a key parameter to understand coastal groundwater flow dynamics and consequently also geochemical and microbial processes. For mapping porewater salinity, a variety of methods exists, mainly using electrical conductivity as a proxy. We investigate methods including hydrological/geochemical (well sampling, fluid logger) as well as geophysical method (direct push, geoelectrics) utilising measurements near the high-water line of a high-energy beach at the North Sea island of Spiekeroog. We compare the methods, discuss their benefits and limitations and assess their spatial and temporal resolution. One key to enable a comparison is the estimation of formation factors transforming bulk conductivity measured by geophysical tools in to fluid conductivities obtained from direct measurements. We derive depth-dependent formation factors derived from time-series measurements of fluid loggers and a vertical electrode installation. Using these formation factors, the vertical electrode chain proves to provide reliable salinities at high spatial and temporal dimension. Direct-push profiling data provide the highest vertical resolution. However, a careful calibration is needed to allow for salinity quantification. On the other hand, electrical resistivity tomography (ERT) exhibits the lowest spatial resolution, but can image two-dimensional salinity distributions. We found ERT to fit very well to all other methods, but the data analysis should be aimed at salinities instead of bulk conductivities, i.e. including formation factors and temperature models into the inversion process.

Experimental study of hydrodynamic characteristics in three-phase coarse particle fluidized flotation column

Understanding multiphase flow regimes and hydrodynamic characteristics in the three-phase coarse particle fluidized flotation column (TFC) is crucial in mineral processing. This study systematically investigated the influence of gas velocity (Ug) and water velocity (Uw) on the flow regimes in TFC, focusing on the identification and hydrodynamic characteristics of different flow regimes in the freeboard and bulk fluidized bed regions. Three distinct flow regimes (heterogeneous flow, pseudo-homogeneous flow and mono-homogeneous flow) and two transition water velocities (transitions from a heterogeneous flow regime to a pseudo-homogeneous flow (Ut1) and transitions from a pseudo-homogeneous flow to a mono-disperse homogeneous flow regime (Ut2)) were identified in the freeboard region based on the visual observation and bubble characteristic parameter acquisition system (BVW-2) monitoring the variations in the bubble size distribution. Visual observation combined with electrical resistance tomography (ERT) monitoring the solid concentration variations facilitated accurate determination of three flow regimes (fixed bed regime, agitated bed regime, and complete fluidization regime) and two transition points (minimum agitation water velocity (ULma) and minimum fluidization water velocity (ULmf)) in the bulk fluidized bed region. Furthermore, statistical and spectral methods were used to analyze pressure fluctuation signals and characterize fluidization behavior across different flow regimes, including the average pressure fluctuation (ΔP¯), the probability density function (PDF), normalized standard deviation (δ), kurtosis (K), skewness (S), autocorrelation function (ACF), power spectral density (PSD) and average cycle frequency (fc). The results indicated that it is the changes in dominant flow structures within the three-phase fluidized bed, such as variations in bubble behavior and particle movement under different Ug and Uw, that lead to differences in flow characteristics, thereby forming distinct flow regimes.

Comprehensive investigation of gas hold-up in a double coaxial mixer with shear-thinning fluids exhibiting yield stress: Experimental, numerical, and artificial neural network approaches

This study addresses the challenge of uneven gas dispersion in yield-stress, non-Newtonian fluids, commonly encountered in industries such as biopharmaceuticals, cosmetics, and food processing. While previous research demonstrated the advantages of dual coaxial mixers for pseudoplastic fluids, limited attention has been given to aerating yield-pseudoplastic fluids with higher aspect ratios. This study bridges that gap by investigating both local and global gas hold-up under various conditions, utilizing electrical resistance tomography and computational fluid dynamics. Key findings showed that increasing the anchor speed from stationary to 30 rpm significantly enhanced aeration efficiency (gas hold-up per specific power consumption), with improvements of 78 % in UP-CO mode and 25 % in UP-COUNTER mode at Nc = 350 rpm and Qg = 20 L/min. These results underscore enhanced gas dispersion under specific operating conditions, driving overall process intensification. To ensure accurate prediction of gas hold-up, both dimensional and dimensionless empirical correlations, along with an artificial neural networks (ANNs) model, were developed. The ANNs model exhibited superior accuracy, achieving R² values of 0.99 for both rotation modes, outperforming empirical models, which achieved R² values of 0.90 and 0.89 for UP-CO and UP-COUNTER modes, respectively.

An improved goal-oriented adaptive finite-element method for 3-D direct current resistivity anisotropic forward modeling using nested tetrahedra

We developed a novel adaptive finite element method (FEM) to address the problem of 3-D direct current (DC) resistivity forward modeling with complex surface topography and arbitrary conductivity anisotropy. The tetrahedra-based FEM and secondary virtual potential algorithm are first used to handle arbitrary complex geo-models. Then, to ensure the accuracy of the simulation solution, an improved goal-oriented adaptive mesh refinement (AMR) algorithm is proposed to realize an optimized mesh density distribution. To avoid the drawback of the traditional goal-oriented AMR algorithm for the DC forward modeling problem, we incorporate a volume-based weighting factor into the posterior error estimation procedure to further optimize the density distribution of the forward modeling grid. In addition, instead of traditional open source mesh generation software, we propose using the longest-edge bisection (LEB) algorithm to perform the mesh refinement process, which can preserve the topological structure between different-level meshes. Finally, the comprehensive test using a two-layered model and two complex 3-D models demonstrate the capability of our newly developed code to obtain highly accurate solutions even on relatively coarse initial grids. By incorporating the volume factor, our novel AMR algorithm achieves a more uniform and reasonable mesh density distribution during these experiments. The LEB refinement technique can generate a series of nested tetrahedral elements and provide fewer tetrahedral elements compared to the traditional Delaunay-based AMR method. The proposed 3-D DC forward modeling method has been implemented into an open source C++ code, which will contribute to the advancement of the 3-D DC resistivity imaging field.

Characterizing groundwater contamination flow-paths and heavy metal mobilization near a waste site in Southwestern Nigeria

This study investigates potential groundwater contamination near a waste disposal site in southwestern Nigeria. The area's complex geological setting, characterized by fractured rock formations, posed significant challenges for traditional monitoring methods. To address these challenges and comprehensively assess groundwater conditions, we employed a combined approach utilizing Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), and geochemical analysis of heavy metals and water conductivity. This approach enabled the investigation of groundwater levels, identification of potential contamination zones, and delineation of contaminant flow paths. GPR identified a shallow zone, termed the “shadow zone,” with conductive residues indicating contaminants with anomalous conductivity ranging from 1 to 1.5 m. An intermittent reflection zone at a depth of 1.5–3.5 m suggested the potential presence of leachate-impacted groundwater. ERT confirmed a shallow resistive layer at depths of 0–2 m, attributed to compacted waste and topsoil, around the abandoned main dumpsite. Below this layer, a zone of low resistivity, decreasing downward through a porous weathered zone, was observed. This corresponded to high water conductivity in well data, ranging from 21 to 147 mS/m (equivalent to 6.80 to 47.62 Ω-m), indicating a high conductive anomaly suspected to be a leachate plume at depths of 2–10 m in a sandy-gravelly weathered zone. Validation against ground truth data confirmed the correlation between radar signatures, geoelectrical imaging, and subsurface lithology. Analysis of well and soil samples revealed concerningly elevated concentrations of cadmium, mercury, lead, arsenic, and cobalt, ranging from 641 to 1175 ppb, exceeding established safety limits for drinking water. Additionally, soil samples showed elevated levels of nickel and chromium, generally ranging from <0 to <1 ppb. These findings highlight the significant risk of groundwater contamination due to the proximity of the leachate zone to the groundwater table in the weathered basement complex. This study demonstrates the effective integration of geophysical and geochemical methods for comprehensive mapping of contaminated zones and identification of preferential pathways for contaminant migration. The findings underscore the critical need for implementing comprehensive risk assessment methodologies in similar complex geological settings.