Recent Submissions

  • Real-Time Testing of Synchrophasor-Based Wide-Area Monitoring System Applications Acknowledging the Potential Use of a Prototyping Software Toolchain

    Kumar, Lalit; Ahmed, Shehab; Vanfretti, Luigi; Kishor, Nand (International Transactions on Electrical Energy Systems, Hindawi Limited, 2022-07-30) [Article]
    This article presents a study on real-time testing of synchrophasor-based “wide-area monitoring system’s applications (WAMS application).” Considering the growing demand of real-time testing of “wide-area monitoring, protection, and control (WAMPAC)” applications, a systematic real-time testing methodology is formulated and delineated in diagrams. The diagrams propose several stages through which an application needs to be assessed (sequentially) for its acceptance prior to implementation into a production system. However, only one stage is demonstrated in this article which comprises the use of a prototyping software toolchain and whose potential is assessed as sufficient for preliminary real-time testing (PRTT) of WAMS applications. The software toolchain is composed of two components: the MATLAB software for application prototyping and other open-source software that allows ingesting prerecorded phasor measurement unit (PMU) signals. With this software toolchain, a PRTT study is presented for two WAMS applications: “testing of the PMU/phasor data concentrator (PDC)” and “testing of wide-area forced oscillation (FO) monitoring application.”
  • Effect of Winding Design on The Performance of Predictive Current Control of Six-Phase Induction Machine-Based Propulsion Systems

    Shawier, Abdullah; Abdel-Majeed, Mahmoud; Abdel-Azim, Wessam E.; Abdel-Khalik, Ayman S.; Hamad, Mostafa S.; Ahmed, Shehab; Hamdan, Eman; Elmalhy, Noha A. (IEEE Access, Institute of Electrical and Electronics Engineers (IEEE), 2022-07-29) [Article]
    Electric propulsion based on six-phase machines in marine propulsion and automotive traction applications are undergoing rapid development due to its high capacity, fault tolerance, reduced size, and reduced torque pulsations. Among different control techniques of six-phase machines, direct controllers, such as finite control set model predictive control (FCS-MPC), have extensively been studied in recent literature. One of the main problems of this controller type is the relatively poor current quality due to circulating xy current components. This problem has been tackled in literature through enhanced control techniques and/or winding design. Following both approaches, this paper extends a previous study to deeply investigate the effect of winding design on the performance of the model predictive control applied to a six-phase induction machine (SPIM). Three six-phase winding layouts have been compared, namely, dual-three phase (D3P), asymmetrical (A6P) and symmetrical (S6P) configurations. The main objective of this study is to investigate the effect of winding chording when standard three-phase stator frames are employed on the current quality of different winding configurations under classical predictive current control (PCC). A 1.5Hp prototype system has been used for this experimental comparative study.
  • DC-Signal Injection for Stator-Resistance Estimation in Symmetrical Six-Phase Induction Motors Under Open-Phase Fault

    Yepes, Alejandro G.; Abdel-Majeed, Mahmoud; Che, Hang Seng; Abdel-Khalik, Ayman S.; Ahmed, Shehab; Doval-Gandoy, Jesus (IEEE Transactions on Industrial Electronics, Institute of Electrical and Electronics Engineers (IEEE), 2022-07-26) [Article]
    Multiphase machines are often chosen due to their enhanced fault tolerance. Six-phase ones are especially convenient because they may be fed by off-the-shelf three-phase converters. In particular, those with symmetrical windings offer superior postfault capabilities. On the other hand, estimation of the stator resistance is important for purposes such as thermal monitoring and preserving control performance. Resistance estimation by dc-signal injection provides low sensitivity to parameter deviations compared with other techniques. It has previously been shown that the dc signal can be added in the non-torque-producing (x-y) plane of a six-phase machine to avoid the torque disturbances that typically arise in three-phase machines. However, extending this method to the case of an open-phase fault (OPF) is not straightforward, because of the associated current restrictions. This paper addresses dc-signal injection in a symmetrical six-phase induction motor with an OPF. It is shown that, in contrast to healthy operation, the postfault dc injection should be carefully performed so that minimum copper loss, peak phase current and zero-sequence braking torque are achieved. A solution that attains optimum performance in all these aspects simultaneously is proposed. Adapted controller and resistance estimation are also presented. Experimental results confirm the theory.
  • Inverting passive margin stratigraphy for marine sediment transport dynamics over geologic time

    Shobe, Charles M.; Braun, Jean; Yuan, Xiaoping; Campforts, Benjamin; Gailleton, Boris; Baby, Guillaume Jean Baptiste; Guillocheau, François; Robin, Cécile (Basin Research, Wiley, 2022-07-24) [Article]
    Passive margin stratigraphy contains time-integrated records of landscapes that have long since vanished. Quantitatively reading the stratigraphic record using coupled landscape evolution and stratigraphic forward models (SFMs) is a promising approach to extracting information about landscape history. However, there is no consensus about the optimal form of simple SFMs because there has been a lack of direct tests against observed stratigraphy in well constrained test cases. Specifically, the extent to which SFM behavior over geologic space and time scales should be governed by local (downslope sediment flux depends only on local slope) versus nonlocal (sediment flux depends on factors other than local slope, such as the history of slopes experienced along a transport pathway) processes is currently unclear. Here we develop a nonlocal, nonlinear SFM that incorporates slope bypass and long-distance sediment transport, both of which have been previously identified as important model components but not thoroughly tested. Our model collapses to the local, linear model under certain parameterizations such that best-fit parameter values can indicate optimal model structure. Comparing 2-D implementations of both models against seven detailed seismic sections from the Southeast Atlantic Margin, we invert the stratigraphic data for best-fit model parameter values and demonstrate that best-fit parameterizations are not compatible with the local, linear diffusion model. Fitting observed stratigraphy requires parameter values consistent with important contributions from slope bypass and long-distance transport processes. The nonlocal, nonlinear model yields improved fits to the data regardless of whether the model is compared against only the modern bathymetric surface or the full set of seismic reflectors identified in the data. Results suggest that processes of sediment bypass and long-distance transport are required to model realistic passive margin stratigraphy, and are therefore important to consider when inverting the stratigraphic record to infer past perturbations to source regions.
  • Technical Evaluation of Conformance Improvement Technology with Anionic Surfactant-Stabilized Microemulsions in Porous Media

    Pal, Nilanjan; Alzahid, Yara; AlSofi, Abdulkareem; Ali, Muhammad; Zhang, Xuan; Hoteit, Hussein (Elsevier BV, 2022-07-22) [Preprint]
    The application of microemulsion-assisted conformance improvement technology (ME-CIT) has the potential to significantly reduce the water-to-oil production ratio and operational costs during oilfield stimulation/production. However, the efficacy of this process is dependent on workflow planning and validation from an experimental viewpoint. The current article aims to develop a functional ME-CIT route and propose a viable microemulsion fluid system, based on this approach. Initially, the liquid-liquid phase behavior was classified using the ternary phase diagram. A phase envelope was identified to separate the multi-phase (2- and 3-phase) region from the uneconomical one-phase region. ME droplets were characterized via dynamic light scattering tests to understand the aggregation behavior of micelles and the extent of salt on coalescence. Relative phase volume investigations revealed the existence of Winsor I at low salinities upto 20,000 ppm total dissolved salts (TDS) content. The first phase transition occurred at 25,000 ppm TDS to exhibit a Winsor III system and continued till the salinity reached 40,000 ppm. At 50,000 ppm, the Winsor III changed into Winsor II phase behavior. In addition, the steady-state shear viscosity of ME fluids does not alter markedly with time, irrespective of their salt content. Viscosity plots show the pseudoplastic or shear-thinning flow behavior of MEs. The ME rheology can be discussed in terms of two opposing interaction effects: electro-shielding and micelle deformation. The viscosity is, therefore, a function of salinity-induced phase behavior on a macroscopic level and micelle morphology on a microscopic scale. Viscosity versus salinity plots at 7.34 s-1 depicts a unique ‘M’ shape with increasing salinity, characterized by an initial increase, followed by a decrease, then an increase, and finally a near-constant viscosity. Flow displacement tests of optimized ME slug illustrated a favorable pressure drop response after water-flood, which is accompanied by a significant decrease in water cut. Based on the physicochemical evaluation and subsequent displacement testing, the proposed laboratory workflow model contributes to a potentially useful method of optimizing and designing surfactant-based ME fluid systems for conformance improvement.
  • Red sea evaporites: Formation, creep and dissolution

    Smith, Joshua E.; Santamarina, Carlos (Earth-Science Reviews, Elsevier BV, 2022-07-21) [Article]
    Evaporite deposition and seafloor spreading are two salient geological processes in the geological history of the Red Sea. We piece together the available evidence about rift evolution and evaporite formation to constrain the deposition history, analyze creep, and advance a plausible explanation for the preservation of these soluble formations. At the end of evaporite deposition before the Indian Ocean flooded the Red Sea through the Bab al-Mandab's strait, the salt thickness must have exceeded ~1.5 times the current thickness. Reported plate rotation, rift rates and the presence of a salt suture zone in the central Red Sea allow us to estimate an effective large-scale viscosity of 1018 Pa·s. Thinned salt along the southern Red Sea flows up to 5 mm/yr, creep cannot keep up with seafloor spreading and oceanic crust remains exposed. Vast alluvial fans and carbonate platforms cause salt withdrawal; corresponding seafloor settlement rates can exceed ~10 mm/yr and overtake coral reef production. Salt dissolution leaves behind a residual sediment cap made of insoluble minerals that gradually retards further dissolution, i.e., self-armoring. New experimental evidence and the numerical solution of diffusion with a moving boundary show that self-armoring by selective dissolution controls early evaporite dissolution while background sedimentation dominates sediment accumulation over long time scales. Armoring-delayed evaporite dissolution prevents the formation of a vast regional brine pool.
  • HATCHFRAC: A fast open-source DFN modeling software

    Zhu, Weiwei; Khirevich, Siarhei; Patzek, Tadeusz (Computers and Geotechnics, Elsevier BV, 2022-07-19) [Article]
    This paper introduces a comprehensive C++ software package, HATCHFRAC, for stochastic modeling of fracture networks in two and three dimensions. The inverse cumulative distribution function (CDF) and acceptance–rejection methods are applied to generate random variables from the stochastic distributions commonly used in discrete fracture network (DFN) modeling. The multilayer perceptron (MLP) machine learning approach, combined with the inverse CDF method, generates random variables following any sampling distribution. We extend the Newman–Ziff algorithm to determine clusters in the fracture networks and make the code faster. When combined with the block method, the coding efficiency is further enhanced. The software generates the T-type fracture intersections in the network by simulating a fracture growth process, which can be used in applications involving fracture growth or incorporating geomechanics. Three applications of HATCHFRAC are introduced to demonstrate the versatility of our software: percolation analysis, fracture intensity analysis, and flow and connectivity analysis.
  • Impacts of fracture properties on the formation and development of stimulated reservoir volume: A global sensitivity analysis

    Zhu, Weiwei; He, Xupeng; Li, Yiteng; Lei, Gang; Santoso, Ryan; Wang, Moran (Journal of Petroleum Science and Engineering, Elsevier BV, 2022-07-15) [Article]
    Stimulated reservoir volume (SRV), the highly permeable fracture network created by hydraulic fracturing, is essential for fluid production from low-permeable reservoirs. However, the configuration of SRV and its impacting factors are largely unknown. In this work, we adopt the stochastic discrete fracture network method to mimic natural fractures in subsurface formations and conduct a global sensitivity analysis with the Sobol method. The sensitivity of different fracture properties, including geometrical properties (fracture lengths, orientations, and center positions), mechanical properties (fracture roughness and fracture strength), fracture sealing properties (probabilities of open fractures and segment lengths), and the fracture intensity, are investigated in two and three-dimensional fracture networks. JRC-JCS model is adopted to identify critically stressed fractures. We find that critically stressed fractures compose the backbone of SRV, while partially open fractures can significantly enlarge the size of SRV by connecting more critically orientated fractures. The fracture roughness is the most influential factor for the total length (area) of critically stressed fractures. For the relative increase of SRV (RI) in 2D/3D fracture networks, the probability of open fractures is the most significant factor. The fracture lengths and center positions are essential factors for RI in 2D fracture networks but insignificant in 3D fracture networks. This work provides a realistic scenario of the subsurface structure and systematically investigates the influential factors of SRV, which is useful for estimating the size of SRV and predicting shale gas reservoirs’ production in an accurate and physically meaningful way.
  • A Three-Phase Non-Isolated Pseudo Six-Phase-Based Integrated Onboard Battery Charger for Electric Vehicles

    Abdel-Majeed, Mahmoud; Shawier, Abdullah; Habib, Abdelrahman; Abdel-Khalik, Ayman S.; Hamad, Mostafa S.; Ahmed, Shehab; Elmalhy, Noha A. (IEEE Transactions on Transportation Electrification, Institute of Electrical and Electronics Engineers (IEEE), 2022-07-14) [Article]
    The trending modern designs of electric vehicle motors are concerned with maximizing the machine torque density while offering a fault tolerance capability. Among different available stator winding layouts, the so-called pseudo-six-phase winding has recently been proposed, which offers an improved torque density and fault tolerance over conventional six-phase distributed winding. An integrated onboard battery charger (IOBC) has also been proposed as a new leading technology that employs the propulsion components of the EV in the charging process to achieve the highest possible charging current with zero machine torque production. In this context, this paper proposes a new pseudo six-phase-based IOBC system. Two different controllers have been investigated, namely, conventional proportional resonant (PR)-based current control and predictive current control (PCC) techniques. Under charging mode, the control objectives aim at achieving a balanced three-phase grid current while nullifying machine torque production. To this end, the sequence stator currents are regulated to ensure a balanced xy current while both the αβ and 0+0- current components are controlled to zero. Furthermore, a novel postfault controller using a PR-based current controller has been proposed which ensures balanced grid line currents under one open phase fault. A comparative experimental study has been carried out under different controllers for both vehicle to grid (V2G) and grid to vehicle (G2V) modes using a 2 Hp prototype machine.
  • Fluid-Driven Instabilities in Granular Media: From Viscous Fingering and Dissolution Wormholes to Desiccation Cracks and Ice Lenses

    Liu, Qi; Santamarina, Carlos (Frontiers in Mechanical Engineering, Frontiers Media SA, 2022-07-08) [Article]
    Single and multi-phase fluids fill the pore space in sediments; phases may include gases (air, CH4, CO2, H2, and NH3), liquids (aqueous solutions or organic compounds), and even ice and hydrates. Fluids can experience instabilities within the pore space or trigger instabilities in the granular skeleton. Then, we divided fluid-driven instabilities in granular media into two categories. Fluid instabilities at constant fabric take place within the pore space without affecting the granular skeleton; these can result from hysteresis in contact angle and interfacial tension (aggravated in particle-laden flow), fluid compressibility, changes in pore geometry along the flow direction, and contrasting viscosity among immiscible fluids. More intricate fluid instabilities with fabric changes take place when fluids affect the granular skeleton, thus the evolving local effective stress field. We considered several cases: 1) open-mode discontinuities driven by drag forces, i.e., hydraulic fracture; 2) grain-displacive invasion of immiscible fluids, such as desiccation cracks, ice and hydrate lenses, gas and oil-driven openings, and capillary collapse; 3) hydro-chemo-mechanically coupled instabilities triggered by mineral dissolution during the injection of reactive fluids, from wormholes to shear band formation; and 4) instabilities associated with particle transport (backward piping erosion), thermal changes (thermo-hydraulic fractures), and changes in electrical interparticle interaction (osmotic-hydraulic fractures and contractive openings). In all cases, we seek to identify the pore and particle-scale positive feedback mechanisms that amplify initial perturbations and to identify the governing dimensionless ratios that define the stable and unstable domains. A [N/m] Contact line adhesion.
  • A Software Toolchain for Real-Time Testing of Synchrophasor Algorithms in MATLAB

    Kumar, Lalit; Ahmed, Shehab; Vanfretti, Luigi; Kishor, Nand (IEEE, 2022-06-29) [Conference Paper]
    This article develops and demonstrates the software toolchain for real-time testing of synchrophasor based algorithms. Real-time testing procedure being the need of smart grid, requires to be hassle-free and easily accessible to the researchers. The developed software toolchain combines both MATLAB and open-source software. The toolchain requires recorded phasor measurement unit (PMU) or phasor data concentrator (PDC) signals, which are then played-back in real-time in the same computer using local sockets. The data is replayed using transmission control protocol/internet protocol (TCP/IP) sockets and the IEEE C37.111-2013 data transfer standard. The data is then retrieved and processed in real-time by any synchrophasor based algorithm in MATLAB. The toolchain is demonstrated with two examples, one that shows the main functionality by testing the connection with a PMU/PDC and another testing of a wide-area forced oscillation (FO) monitoring algorithm.
  • A robust fully Mixed Finite Element model for flow and transport in unsaturated fractured porous media

    Younes, Anis; Hoteit, Hussein; Helmig, Rainer; Fahs, Marwan (Advances in Water Resources, Elsevier BV, 2022-06-25) [Article]
    A fully mixed finite element (MFE) model is developed for nonlinear flow and transport in unsaturated fractured porous media with matrix-fracture and fracture-fracture fluid and mass exchanges. The model is based on the discrete fracture matrix (DFM) approach and assumes cross-flow equilibrium in the fractures. The MFE method is employed for the spatial discretization of both flow and transport on the 2D-matrix elements as well as on the 1D-fracture elements. An upwind scheme is employed to avoid unphysical oscillations in the case of advection dominant transport. The temporal discretization is performed using high-order time integration methods and efficient automatic time-stepping schemes via the MOL. Two test problems dealing with flow and mass transport in saturated and unsaturated fractured porous media are simulated to show the validity of the new model by comparison against (i) a 1D-2D Comsol finite element model and (ii) a 2D-2D Discontinuous Galerkin (DG) model where both fractures and matrix continua are discretized with small 2D mesh elements. The robustness and efficiency of the developed 1D-2D MFE model are then investigated for a challenging problem dealing with infiltration of contaminated water into an initially dry soil involving a fracture network. The new model yields stable results for advection-dominated and advection-dispersion transport configurations. Further, the results of the 1D-2D MFE model are in very good agreement with those of the 2D-2D DG model for both configurations. The simulation of infiltration of contaminated water into a dry fractured soil shows that the 1D-2D MFE model is within 15 times more efficient than the 2D-2D DG model, which confirms the high benefit of using robust and efficient DFM models for the simulation of flow and transport in fractured porous media.
  • Thermodynamic modeling of hydrogen–water systems with gas impurity at various conditions using cubic and PC-SAFT equations of state

    Alanazi, Amer; Bawazeer, Saleh; Ali, Muhammad; Keshavarz, Alireza; Hoteit, Hussein (Energy Conversion and Management: X, Elsevier BV, 2022-06-22) [Article]
    Hydrogen (H2) has emerged as a viable solution for energy storage of renewable sources, supplying off-seasonal demand. Hydrogen contamination due to undesired mixing with other fluids during operations is a significant problem. Water contamination is a regular occurrence; therefore, an accurate prediction of H2-water thermodynamics is crucial for the design of efficient storage and water removal processes. In thermodynamic modeling, the Peng–Robinson (PR) and Soave Redlich–Kwong (SRK) equations of state (EoSs) are widely applied. However, both EoSs fail to predict the vapor-liquid equilibrium (VLE) accurately for H2-blend mixtures with or without fine-tuning binary interaction parameters due to the polarity of the components. This work investigates the accuracy of two advanced EoSs: the Schwartzentruber and Renon modified Redlich–Kwong cubic EoS (SR-RK) and perturbed-chain statistical associating fluid theory (SAFT) in predicting VLE and solubility properties of H2 and water. The SR-RK involves the introduction of polar parameters and a volume translation term. The proposed workflow is based on optimizing the binary interaction coefficients using regression against experimental data that cover a wide range of pressure (0.34 to 101.23 MPa), temperature (273.2 to 588.7 K), and H2 mole fraction (0.0004 to 0.9670) values. A flash liberation model is developed to calculate the H2 solubility and water vaporization at different temperature and pressure conditions. The model captures the influence of H2-gas (CO2) impurity on VLE. The results agreed well with the experimental data, demonstrating the model's capability of predicting the VLE of hydrogen-water mixtures for a broad range of pressures and temperatures. Optimized coefficients of binary interaction parameters for both EoSs are provided. The sensitivity analysis indicates an increase in H2 solubility with temperature and pressure and a decrease in water vaporization. Moreover, the work demonstrates the capability of SR-RK in modeling the influence of gas impurity (i.e., H2–CO2 mixture) on the H2 solubility and water vaporization, indicating a significant influence over a wide range of H2–CO2 mixtures. Increasing the CO2 ratio from 20% to 80% exhibited almost the opposite behavior of H2 solubility compared to the pure hydrogen feed solubility. Finally, the work emphasizes the critical selection of proper EoSs for calculating thermodynamic properties and the solubility of gaseous H2 and water vaporization for the efficient design of H2 storage and fuel cells.
  • 3D digital outcrop model-based analysis of fracture network along the seismogenic Mt. Vettore Fault System (Central Italy): the importance of inherited fractures

    Panara, Yuri; Menegoni, Niccolò; Carboni, Filippo; Inama, Riccardo (Journal of Structural Geology, Elsevier BV, 2022-06-20) [Article]
    The Mt. Vettore area is located in the Central Apennines (Italy), a region characterized by intense seismic activity that has recorded multiple moderate-to-high magnitude seismic sequences. The seismic activity is due to the presence of normal fault systems, among which is the Mt. Vettore Fault System (VFS), which was last activated during the 2016-17 Central Italy seismic sequence. Moreover, the region has experienced three major tectonic phases over geological history, thus it is important to unravel their contribution to the current fracture network. Based on the integration of field observation with Unmanned Aerial Vehicle - Digital Photogrammetry data, we aim to analyze the fracture network on eight different outcrops located at different structural positions with respect to VFZ. Results show that the Late Miocene−Early Pliocene compressional phase deeply affected the present-day fracture pattern, which is especially related to the evolution of the Mt. Sibillini regional thrust and its related anticline. The present-day Quaternary extensional phase, and the associated normal faults, mostly reactivate some of the pre-existing fracture sets.
  • Modeling lost-circulation in natural fractures using semi-analytical solutions and type-curves

    Albattat, Rami; AlSinan, Marwa; Kwak, Hyung; Hoteit, Hussein (Journal of Petroleum Science and Engineering, Elsevier BV, 2022-06-16) [Article]
    Drilling is a requisite operation for many industries to reach a targeted subsurface zone. During operations, various issues and challenges are encountered, particularly drilling fluid loss. Loss of circulation is a common problem that often causes interruptions to the drilling process and a reduction in efficiency. Such incidents usually occur when the drilled wellbore encounters a high permeable formation such as faults or fractures, leading to total or partial leakage of the drilling fluids. In this work, a semi-analytical solution and mud type-curves (MTC) are proposed to offer a quick and accurate diagnostic model to assess the lost-circulation of Herschel-Bulkley fluids in fractured media. Based on the observed transient pressure and mud-loss trends, the model can estimate the effective fracture conductivity, the time-dependent cumulative mud-loss volume, and the leakage period. The behavior of lost-circulation into fractured formation can be quickly evaluated, at the drilling site, to perform useful diagnostics, such as the rate of fluid leakage, and the associated effective fracture hydraulic properties. Further, derivative-based mud-type-curves (DMTC) are developed to quantify the leakage of drilling fluid flow into fractures. The developed model is applied for non-Newtonian fluids exhibiting yield-power-law (YPL), including shear thickening and thinning, and Bingham plastic fluids. Proposing rigorous dimensionless groups generates the dual type-curves, MTC and DMTC, which offer superior predictivity compared to traditional methods. Both type-curve sets are used in a dual trend matching, which significantly reduces the non-uniqueness issue that is typically encountered in type-curves. Usage of numerical simulations is implemented based on finite elements to verify the accuracy of the proposed solution. Data for lost circulation from several field cases are presented to demonstrate the applicability of the proposed method. The semi-analytical solver, combined with Monte Carlo simulations, is then applied to assess the sensitivity and uncertainty of various fluid and subsurface parameters, including the hydraulic property of the fracture and the probabilistic prediction of the rate of mud leakage into the formation. The proposed approach is based on a robust semi-analytical solution and type-curves to model the flow behavior of Herschel-Bulkley fluids into fractured reservoirs, which can serve as a quick diagnostic tool to evaluate lost-circulation in drilling operations.
  • A Geomechanical Model for Gas Hydrate Bearing Sediments Incorporating High Dilatancy, Temperature, and Rate Effects

    Zhou, Bohan; Sanchez, Marcelo; Oldecop, Luciano; Santamarina, Carlos (Energies, MDPI AG, 2022-06-10) [Article]
    The geomechanical behavior of methane hydrate bearing sediments (MHBS) is influenced by many factors, including temperature, fluid pressure, hydrate saturation, stress level, and strain rate. The paper presents a visco-elastoplastic constitutive model for MHBS based on an elastoplastic model that incorporates the effect of hydrate saturation, stress history, and hydrate morphology on hydrate sediment response. The upgraded model is able to account for additional critical features of MHBS behavior, such as, high-dilatancy, temperature, and rate effects. The main components and the mathematical formulation of the new constitutive model are described in detail. The upgraded model is validated using published triaxial tests involving MHBS. The model agrees overly well with the experimental observations and is able to capture the main features associated with the behavior of MHBS.
  • Cascaded Inverters Increasing the Number of Levels and Effective Switching Frequency in Output Using Coupled Inductors

    Khan, Ashraf Ali; Jamil, Mohsin; Khan, Usman Ali; Khan, Shahnawaz; Ahmed, Shehab (IEEE Journal of Emerging and Selected Topics in Power Electronics, Institute of Electrical and Electronics Engineers (IEEE), 2022-06-06) [Article]
    In this paper, a new coupled-inductor based modular multilevel cascaded inverter using a new phase-shift control is presented. The proposed inverter can generate a high output ac voltage using standard low voltage rating devices. The number of levels in the output pulse width modulation (PWM) voltage and the effective switching frequency of the output filter are increased using coupled inductors and phase-shift control. The switching signals of the cascaded units in the proposed inverter are phase-shifted by 360°/4n, where n is the number of cascaded units. The proposed phase-shift control results in (4n+1) levels in the output PWM voltage of the proposed inverter and increases the effective switching frequency of the output filter by 4n times of the actual switching frequency fsw. As a result, the output waveforms can be generated with better quality and less distortion. In addition, the output filter can be decreased dramatically in size. Besides, fewer coupled inductors are used to reduce the footprints, the number of inductors, and magnetic volume. Moreover, the proposed inverter is exceptionally reliable due to no short-circuit risk in the circuit.
  • A hybrid approach to seismic deblending: when physics meets self-supervision

    Luiken, Nick; Ravasi, Matteo; Birnie, Claire Emma (arXiv, 2022-05-30) [Preprint]
    To limit the time, cost, and environmental impact associated with the acquisition of seismic data, in recent decades considerable effort has been put into so-called simultaneous shooting acquisitions, where seismic sources are fired at short time intervals between each other. As a consequence, waves originating from consecutive shots are entangled within the seismic recordings, yielding so-called blended data. For processing and imaging purposes, the data generated by each individual shot must be retrieved. This process, called deblending, is achieved by solving an inverse problem which is heavily underdetermined. Conventional approaches rely on transformations that render the blending noise into burst-like noise, whilst preserving the signal of interest. Compressed sensing type regularization is then applied, where sparsity in some domain is assumed for the signal of interest. The domain of choice depends on the geometry of the acquisition and the properties of seismic data within the chosen domain. In this work, we introduce a new concept that consists of embedding a self-supervised denoising network into the Plug-and-Play (PnP) framework. A novel network is introduced whose design extends the blind-spot network architecture of [28 ] for partially coherent noise (i.e., correlated in time). The network is then trained directly on the noisy input data at each step of the PnP algorithm. By leveraging both the underlying physics of the problem and the great denoising capabilities of our blind-spot network, the proposed algorithm is shown to outperform an industry-standard method whilst being comparable in terms of computational cost. Moreover, being independent on the acquisition geometry, our method can be easily applied to both marine and land data without any significant modification.
  • Evaluation of Rwanda’s Energy Resources

    Favero Bolson, Natanael; Patzek, Tadeusz (Sustainability, MDPI AG, 2022-05-25) [Article]
    Energy flows in a fertile environment drive societal development and progress. To develop a country sustainably, striking balance between environmental management, natural resource use, and energy generation is a must. However, developing a country with limited access to energy and critical levels of environmental depletion is challenging. This description fits Rwanda, which faces a dual crisis of energy supply shortages and environment depletion. Overpopulation is driving urban and agricultural expansion which in turn unbalance biomass demand to supply the growing energy needs and exacerbate environmental damage. Just when urgent actions must be taken to overcome this current debacle, political aspirations seek to turn Rwanda into a middle- and subsequently high-income country. From our analysis, the available energy resources can only maintain current population in Rwanda as a low-income country. To become an average middle-income country, Rwanda needs an equivalent of 3 Mtoe /yr (≈20 Mbbl /yr) of oil imports, and must install a nominal capacity of 90 GW of solar photovoltaics (PV). For a high-income country, it is necessary to obtain an extra power input of 11.4Mtoe /yr (≈77 Mbbl /yr) of oil imports and to install a nominal capacity of 400 GW of solar PV. Comparing current power generation capacity in Rwanda against the extra power needed to achieve the middle-income and high-income status indicates a mismatch between available resources and developmental goals.
  • Hydrothermal metalliferous sediments in the Red Sea: Characterization and properties

    Modenesi, M. Clara; Santamarina, Carlos (Engineering Geology, Elsevier BV, 2022-05-19) [Article]
    Sediment accumulations within the Red Sea central deeps have unique genesis and properties. We piece together available information to understand their geological setting and formation history, and conduct an extensive sediment characterization study to assess their geotechnical properties in order to anticipate engineering/mining implications. The various sediment columns reflect slow-rate background sedimentation (biogenic and detrital particles – Valdivia deep) and hydrothermal metalliferous sediments that nucleate and grow within the overlying brine pools (primarily in the Atlantis II, as well as in the Wando deep, and to a lesser extent in Discovery deep). All sediments are fine-grained silt and clay-size particles; smaller particles tend to have higher specific gravity and define the metalliferous content. Hydrothermal sediments exhibit extreme properties when compared to sediments worldwide: they have uncharacteristically large maximum void ratio and compressibility, and their self-compaction is very different from background Red Sea sediments. Their unique self-compaction trends have a strong effect on remote acoustic characterization and sampling, and must be carefully accounted for during field studies and resource assessment. Three distinct properties of hydrothermal metalliferous sediments are relevant for separation and enrichment: high specific surface area, high specific gravity, and ferromagnetic signature. Small grains and low-density flocs have low terminal Stokes' velocities and their residency times may be extended in convective stratified brine pools; this observation affects the environmental analysis of mining operations and tailings disposal.

View more