Numerical modeling of electromagnetic coupling effects for phase correction in borehole EIT measurements

Spectral Electrical Impedance Tomography (EIT) allows obtaining images of the complex electrical conductivity for a broad frequency range (mHz to kHz). It has recently received increased interest in the field of near-surface geophysics and hydrogeophysics because of the relationships between complex electrical properties and hydrogeological and biogeochemical properties and processes observed in the laboratory with Spectral Induced Polarization (SIP). However, these laboratory results have also indicated that a high measurement accuracy is required for the phase angle of the complex electrical conductivity because many soils and sediments are only weakly polarizable and show small phase angles between 1 and 20 mrad only. It is challenging to achieve this phase accuracy in a broad frequency range for EIT measurements in the field. In the case of borehole EIT measurements, electrode chains with a length of 10 meters or more are typically used. This may lead to undesired inductive coupling between the electric wires used for current injection and potential measurement and capacitive coupling between the electrically conductive cable shielding and the soil. Depending on the measured transfer impedances, both coupling effects can cause large phase errors that have typically limited the frequency bandwidth of field EIT measurements to the mHz to Hz range. So far, potentially useful information from the high frequency range (up to kHz) could not be reliably measured in the field using EIT. Within this context, the aim of this PhD thesis was to develop correction procedures for inductive and capacitive coupling effects in borehole EIT measurements to enable more accurate phase measurements in the kHz frequency range. Throughout the thesis, an enhanced field EIT measurement system with 40 channels was used. In addition, custom-made electrode chains with eight electrode modules with a spacing of 1 m and a cable length of 25 m were initially used to develop the correction methods. Each electrode module of the electrode chain was equipped with a brass ring electrode, an integrated amplifier for potential measurement, and an integrated switch for current injection. In general, borehole EIT measurements can be divided into two different cases according to the electrode arrangement. In the first case, EIT measurements are performed in a single borehole. Here, a correction procedure was developed to determine the inductive coupling between the wires (i.e. the mutual inductance) in a single electrode chain using a calibration measurement. In this calibration measurement, all electrodes of the chain were short-circuited and the shield was used as the return line, so that the pure mutual inductance between the wire pairs could be measured indirectly. In the second case, EIT measurements are performed in two boreholes. Here, a correction procedure was developed that combines calibration measurements to determine the mutual inductance between wires close to each other (i.e. inside one electrode chain) with model-based estimates of the mutual inductances between wires far from each other (i.e. in two different electrode chains). In addition, a pole-pole matrix formulation was developed to efficiently describe mutual inductances inside and between electrode chains. To separate parasitic inductances associated with the grounding wire and the wire used for short-circuiting the electrodes in the calibration measurement from the mutual inductance associated with the electrode chains, a second calibration measurement with both electrode chains was used. This second calibration was required because these parasitic inductances cannot be compensated in the calculation of the mutual inductance when two electrode chains are used. A correction procedure was also developed to remove the effects of capacitive coupling. Since a priori correction of borehole EIT measurements as in the case of inductive coupling was not possible, this correction procedure relies on the integration of discrete capacitances in the electrical forward model describing the borehole EIT measurements. The developed correction methods for inductive and capacitive coupling were successfully verified with test measurements under controlled conditions. For EIT measurements with a single electrode chain, a phase accuracy of better than 1 mrad was achieved for frequencies up to 10 kHz. In the case of EIT measurements with two electrode chains, a phase accuracy of 1 mrad was achieved up to 1 kHz. A field evaluation of borehole EIT measurements at the Krauthausen test site also showed a considerable improvement of the phase accuracy by applying the correction methods. Here, it was observed that inductive coupling had a much stronger effect on the phase measurement than capacitive coupling. The complex electrical resistivity determined from 1D inversions of the borehole EIT measurements matched well with the general stratigraphy of the test site. The correction procedures outlined above were developed specifically for the custom-made EIT system and electrode chains. In a final step, the applicability of the correction procedures to commercially available electrode chains was explored. In particular, the possibility of performing accurate borehole EIT measurements using passive unshielded and shielded electrode chains was evaluated. In addition to the inductive and capacitive coupling, the use of this type of electrode chains requires the consideration of the capacitive load of the cables. It was shown that the phase errors due to the internal structure of the passive shielded electrode chains can be estimated using electrical circuit simulation. It was found that the phase error of the passive shielded electrode chains was about 1.5 mrad bigger as for the custom-made active electrode chains due to different capacitances between the electrode chains and the soil (in a conductive environment). Therefore, borehole EIT measurements with passive shielded electrode chains resulted in a reasonable phase accuracy of 3 mrad at 1 kHz. Finally, it was also confirmed that unshielded electrode chains are not suitable for accurate phase measurements at high frequencies because the induced phase errors cannot be predicted. Although the results presented in this thesis are promising, there still is room to further improve the correction procedures. In this study, the electromagnetic response of the underground was neglected because of the small size of the electrode layouts in the field measurements and the used frequencies (up to 1 kHz). If a further expansion of the frequency range is required or when longer electrode arrays will be used, this effect will also need to be considered. The modeling of capacitive effects can also be improved. In particular, the spatial resolution of the meshes used for finite element modeling was limited by available computational resources, which could have caused a certain degree of inaccuracy in the modeling. Furthermore, the calibration procedure to determine the additional parasitic inductance of the short-circuiting wires by using a calibration measurement on two nearly identical electrode chains was complex and should be simplified. Overall, it can be concluded that the developed correction methods for borehole EIT measurements resulted in a high phase accuracy (about 1 mrad at 1 kHz) when the custom-made EIT measurement system was used with active electrode chains. It was also shown that the correction methods to account for inductive and capacitive coupling can be applied to passive shielded electrode chains with a significant improvement in accuracy (about 3 mrad at 1 KHz). Therefore, this work opens up new research avenues where broadband EIT measurements can be used for improved characterization of hydrogeological and biogeochemical properties and processes in the field

Long-term in situ observations on typhoon-triggered turbidity currents in the deep sea

This work is supported by the National Science Foundation of China (grants 91528304, 41576005, and 41530964). We thank J. Li, X. Lyu, P. Li, K. Duan, J. Ronan, Y. Wang, P. Ma, and Y. Li for cruise assistance; G. de Lange and J. Hinojosa for editing an early version of manuscript; and E. Pope and two anonymous reviewers for their reviews.Peer reviewedPublisher PD

Model-Checking an Ecosystem Model for Decision-Aid

International audience—This work stems on the idea that timed automata models and model-checking techniques may bring much in a decision-aid context when dealing with large and interacting qualitative models. In this paper, we focus on two key issues when facing the interpretation and explanation of behavior in real-world systems: the model building and its exploration using logic patterns. We illustrate this approach in the ecological domain with the modeling and exploration of a fisheries ecosystem

Understanding the Hydrodynamics in a 2-Dimensional Downer by CFD-DEM Simulation

The gas-solid flows in a 2-dimensional downer were simulated using a CFD-DEM method. The predicted macro-scale flow structure had good agreement with the experiments. The distinct clustering phenomena at meso-scale were revealed throughout the downer. Influences of the collision properties of the wall and the particles on the hydrodynamics in downer were investigated

RS5M: A Large Scale Vision-Language Dataset for Remote Sensing Vision-Language Foundation Model

Pre-trained Vision-Language Foundation Models utilizing extensive image-text paired data have demonstrated unprecedented image-text association capabilities, achieving remarkable results across various downstream tasks. A critical challenge is how to make use of existing large-scale pre-trained VLMs, which are trained on common objects, to perform the domain-specific transfer for accomplishing domain-related downstream tasks. In this paper, we propose a new framework that includes the Domain Foundation Model (DFM), bridging the gap between the General Foundation Model (GFM) and domain-specific downstream tasks. Moreover, we present an image-text paired dataset in the field of remote sensing (RS), RS5M, which has 5 million RS images with English descriptions. The dataset is obtained from filtering publicly available image-text paired datasets and captioning label-only RS datasets with pre-trained VLM. These constitute the first large-scale RS image-text paired dataset. Additionally, we tried several Parameter-Efficient Fine-Tuning methods on RS5M to implement the DFM. Experimental results show that our proposed dataset are highly effective for various tasks, improving upon the baseline by $8 \% \sim 16 \%$ in zero-shot classification tasks, and obtaining good results in both Vision-Language Retrieval and Semantic Localization tasks. \url{https://github.com/om-ai-lab/RS5M}Comment: RS5M dataset v

Hierarchical macro-nanoporous metals for leakage-free high-thermal conductivity shape-stabilized phase change materials

Impregnation of Phase Change Materials (PCMs) into a porous medium is a promising way to stabilize their shape and improve thermal conductivity which are essential for thermal energy storage and thermal management of small-size applications, such as electronic devices or batteries. However, in these composites a general understanding of how leakage is related to the characteristics of the porous material is still lacking. As a result, the energy density and the antileakage capability are often antagonistically coupled. In this work we overcome the current limitations, showing that a high energy density can be reached together with superior anti-leakage performance by using hierarchical macro-nanoporous metals for PCMs impregnation. By analyzing capillary phenomena and synthesizing a new type of material, it was demonstrated that a hierarchical trimodal macro-nanoporous metal (copper) provides superior antileakage capability (due to strong capillary forces of nanopores), high energy density (90vol% of PCM load due to macropores) and improves the charging/discharging kinetics, due to a three-fold enhancement of thermal conductivity. It was further demonstrated by CFD simulations that such a composite can be used for thermal management of a battery pack and unlike pure PCM it is capable of maintaining the maximum temperature below the safety limit. The present results pave the way for the application of hierarchical macro-nanoporous metals for high-energy density, leakage-free, and shape-stabilized PCMs with enhanced thermal conductivity. These innovative composites can significantly facilitate the thermal management of compact systems such as electronic devices or high-power batteries by improving their efficiency, durability and sustainabilit

A Mini Review on Sewage Sludge and Red Mud Recycling for Thermal Energy Storage

Sewage sludge and red mud, as common industrial waste, have become a research hotspot in the field of achieving carbon peaking and carbon neutrality, reducing carbon emissions, and solving environmental problems. However, their treatment and disposal have always been a difficult problem in the environmental field. Utilizing these two materials for thermal energy storage can not only improve energy utilization efficiency but also further reduce carbon emissions during their treatment process, providing a new approach for sustainable development in the industrial sector. This article summarizes the research progress for the resource recovery of sewage sludge and red mud for direct thermal energy recovery and composite phase change energy storage. After proper treatment, sludge and red mud can be directly used as energy storage materials. In addition, sludge and red mud can be combined with phase change materials to prepare composite materials with an excellent energy storage performance. This composite has broad application prospects in fields such as solar energy utilization and building energy efficiency. However, there are still some challenges and issues in this resource recovery and utilization, such as potential environmental pollution during the treatment process, the long-term stability of energy storage materials, and cost-effectiveness, which require further research and resolution. The purpose of this paper is to evaluate the potential of sewage sludge and red mud as energy storage materials, to explore their feasibility and advantages in practical applications, and to reveal the research progress, technical challenges, and future development directions of these two materials in the field of thermal energy storage

Pore scale modelling of Three-Phase Capillary Pressure Curves Directly in Uniformly-Wet Rock Images

Acknowledgments: The early stages of this research work were funded by the Research Council of Norway through the CLIMIT program, ConocoPhillips and the Ekofisk co-venturers, including TOTAL, ENI, Statoil and Petoro. Dr. Yingfang Zhou would like to acknowledge the support from State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Southwest Petroleum University), PLN201602, to finalize this work. Professor Dimitrios G. Hatzignatiou acknowledges financial support received from the University of Houston to complete the present work.Peer reviewedPublisher PD