Recent Submissions

  • Hybrid broadband ground motion simulations in the Indo-Gangetic basin for great Himalayan earthquake scenarios

    Jayalakshmi, S.; Dhanya, J.; Raghukanth, S. T. G.; Mai, Paul Martin (Bulletin of Earthquake Engineering, Springer Science and Business Media LLC, 2021-04-19) [Article]
    This study presents broadband ground motions for the Indo-Gangetic basin, a large sedimentary basin in India, for potential future great (Mw 8.5) Himalayan earthquakes. We use a recently developed 3D earth structure model of the basin as an input to simulate low-frequency ground motion (0–0.5 Hz). These ground motions are further combined with high-frequency scattering waveforms by using a hybrid approach, thus yielding broadband ground motions (0–10 Hz). We calibrate the 3D model and scattering parameters by comparing the simulated ground motions against available recorded data for two past earthquakes in Himalaya. Our approach accounts for the physics of interaction between the scattered seismic waves with deep basin sediments. Our results indicate that the ground motion intensities exhibit frequency-dependent amplification at various basin depths. We also observe that in the event of a great earthquake, the ground motion intensities are larger at deep basin sites near the source and exhibit an attenuating trend over distance similar to the ground motion models. The extreme ground motion simulations performed in our study reveal that the national building codes may not provide safe recommendations at deep basin sites, especially in the near field region. The period-dependent vertical-to-horizontal spectral ratio deviates from the code-recommended constant 2/3 at least up to 6 s at these sites.
  • Wavefield reconstruction inversion via physics-informed neural networks

    Song, Chao; Alkhalifah, Tariq Ali (arXiv, 2021-04-14) [Preprint]
    Wavefield reconstruction inversion (WRI) formulates a PDE-constrained optimization problem to reduce cycle skipping in full-waveform inversion (FWI). WRI often requires expensive matrix inversions to reconstruct frequency-domain wavefields. Physics-informed neural network (PINN) uses the underlying physical laws as loss functions to train the neural network (NN), and it has shown its effectiveness in solving the Helmholtz equation and generating Green's functions, specifically for the scattered wavefield. By including a data-constrained term in the loss function, the trained NN can reconstruct a wavefield that simultaneously fits the recorded data and satisfies the Helmholtz equation for a given initial velocity model. Using the predicted wavefields, we rely on a small-size NN to predict the velocity using the reconstructed wavefield. In this velocity prediction NN, spatial coordinates are used as input data to the network and the scattered Helmholtz equation is used to define the loss function. After we train this network, we are able to predict the velocity in the domain of interest. We develop this PINN-based WRI method and demonstrate its potential using a part of the Sigsbee2A model and a modified Marmousi model. The results show that the PINN-based WRI is able to invert for a reasonable velocity with very limited iterations and frequencies, which can be used in a subsequent FWI application.
  • Review on space energy

    Zhang, Tao; Li, Yiteng; Chen, Yin; Feng, Xiaoyu; Zhu, Xingyu; Chen, Zhangxing; Yao, Jun; Zheng, Yongchun; Cai, Jianchao; Song, Hongqing; Sun, Shuyu (Applied Energy, Elsevier BV, 2021-04-07) [Article]
    Energy resources in outer space, also known as space energy, has been recognized as a promising supplement to conventional energy supplies on Earth, as well as an irreplaceable energy provision for future space explorations. A critical review is conducted in this paper, to identify the most potential space energy resources, to conclude on the current exploitation technologies and to suggest on the challenges and future directions. Space solar power station, also known as SSPS, is presented first as a well-known utilization of space energy, and we go through the international progress, evolution of the collection systems and the thermophotovoltaic systems. The main technical gaps hampering the practical application of SSPS is concluded then to inspire future investigations. Energy on Mars is presented afterwards as a representative ISRU(In Situ Resource Utilization)-type energy resource, and we select three potential resources on Mars worth exploitation: solar energy, geothermal energy and wind energy. A model describing the global solar irradiance on Mars is concluded, typical applications of geothermal energy is analyzed, the phase equilibrium of geothermal fluids is established and the wind turbine is designed. Furthermore, the review on energy on Moon is started with the discussion on lunar geology relevant with energy resources, and an example of feature detection using Convolutional Neural Networks is illustrated as an example to demonstrate the application of deep learning techniques in space energy exploitation. Solar energy is always taken into account in space activities, and we are more focusing on the discussion of Helium-3, a promising resource for nuclear fusion. The material for nuclear fission, Uranium, has also been detected on Moon. A summary is provided in the end with concluding remarks.
  • Rock Triaxial Tests: Global Deformation vs Local Strain Measurements—Implications

    Perbawa, Andika; Gramajo, Eduardo; Finkbeiner, Thomas; Santamarina, Carlos (Rock Mechanics and Rock Engineering, Springer Nature, 2021-04-05) [Article]
    Accurate stress–strain measurements in triaxial tests are critical to compute reliable mechanical parameters. We focus on compliance at the interfaces between the specimen and endcaps, and test specimens under various triaxial conditions using different instrumentation protocols. The tested materials include aluminum, Eagle Ford shale, Berea sandstone, and Jubaila carbonate. Results obtained following common practice reveal that surface roughness at the specimen-endcap interfaces leads to marked seating effects, affects all cap-to-cap based measurements and hinders ultrasonic energy transmission. In particular, cap-to-cap deformation measurements accentuate hysteretic behavior, magnify biases caused by bending and tilting (triggered by uneven surfaces and misalignment), and affect the estimation of all rock parameters, from stiffness to Biot’s α-parameter. Higher confining pressure diminishes seating effects. Local measurements using specimen-bonded strain gauges are preferred (Note: mounting strain gauges on sleeves is ill-advised). We confirm that elastic moduli derived from wave propagation measurements are higher than quasi-static moduli determined from local strain measurements using specimen-bonded strain gauges, probably due to the lower strain level in wave propagation and preferential high-velocity travel path for first arrivals.
  • PINNtomo: Seismic tomography using physics-informed neural networks

    Waheed, Umair bin; Alkhalifah, Tariq Ali; Haghighat, Ehsan; Song, Chao; Virieux, Jean (arXiv, 2021-04-04) [Preprint]
    Seismic traveltime tomography using transmission data is widely used to image the Earth's interior from global to local scales. In seismic imaging, it is used to obtain velocity models for subsequent depth-migration or full-waveform inversion. In addition, cross-hole tomography has been successfully applied for a variety of applications, including mineral exploration, reservoir monitoring, and CO2 injection and sequestration. Conventional tomography techniques suffer from a number of limitations, including the use of a smoothing regularizer that is agnostic to the physics of wave propagation. Here, we propose a novel tomography method to address these challenges using developments in the field of scientific machine learning. Using seismic traveltimes observed at seismic stations covering part of the computational model, we train neural networks to approximate the traveltime factor and the velocity fields, subject to the physics-informed regularizer formed by the factored eikonal equation. This allows us to better compensate for the ill-posedness of the tomography problem compared to conventional methods and results in a number of other attractive features, including computational efficiency. We show the efficacy of the proposed method and its capabilities through synthetic tests for surface seismic and cross-hole geometries. Contrary to conventional techniques, we find the performance of the proposed method to be agnostic to the choice of the initial velocity model.
  • Synergy processing of diverse ground-based remote sensing and in situ data using the GRASP algorithm: applications to radiometer, lidar and radiosonde observations

    Lopatin, Anton; Dubovik, Oleg; Fuertes, David; Stenchikov, Georgiy L.; Lapyonok, Tatyana; Veselovskii, Igor; Wienhold, Frank G.; Shevchenko, Illia; Hu, Qiaoyun; Parajuli, Sagar (Atmospheric Measurement Techniques, Copernicus GmbH, 2021-04-01) [Article]
    Abstract. The exploration of aerosol retrieval synergies from diverse combinations of ground-based passive Sun-photometric measurements with collocated active lidar ground-based and radiosonde observations using versatile Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm is presented. Several potentially fruitful aspects of observation synergy were considered. First, a set of passive and active ground-based observations collected during both day- and nighttime was inverted simultaneously under the assumption of temporal continuity of aerosol properties. Such an approach explores the complementarity of the information in different observations and results in a robust and consistent processing of all observations. For example, the interpretation of the nighttime active observations usually suffers from the lack of information about aerosol particles sizes, shapes and complex refractive index. In the realized synergy retrievals, the information propagating from the nearby Sun-photometric observations provides sufficient constraints for reliable interpretation of both day- and nighttime lidar observations. Second, the synergetic processing of such complementary observations with enhanced information content allows for optimizing the aerosol model used in the retrieval. Specifically, the external mixture of several aerosol components with predetermined sizes, shapes and composition has been identified as an efficient approach for achieving reliable retrieval of aerosol properties in several situations. This approach allows for achieving consistent and accurate aerosol retrievals from processing stand-alone advanced lidar observations with reduced information content about aerosol columnar properties. Third, the potential of synergy processing of the ground-based Sun-photometric and lidar observations, with the in situ backscatter sonde measurements was explored using the data from KAUST.15 and KAUST.16 field campaigns held at King Abdullah University of Science and Technology (KAUST) in the August of 2015 and 2016. The inclusion of radiosonde data has been demonstrated to provide significant additional constraints to validate and improve the accuracy and scope of aerosol profiling. The results of all retrieval setups used for processing both synergy and stand-alone observation data sets are discussed and intercompared.
  • Machine-driven earth exploration: Artificial intelligence in oil and gas

    Alkhalifah, Tariq Ali; Almomin, Ali; Naamani, Ali (The Leading Edge, Society of Exploration Geophysicists, 2021-04) [Article]
    Artificial intelligence (AI), specifically machine learning (ML), has emerged as a powerful tool to address many of the challenges we face as we try to illuminate the earth and make the proper prediction of its content. From fault detection, to salt boundary mapping, to image resolution enhancements, the quest to teach our computing devices how to perform these tasks accurately, as well as quantify the accuracy, has become a feasible and sought-after objective. Recent advances in ML algorithms and availability of the modules to apply such algorithms enabled geoscientists to focus on potential applications of such tools. As a result, we held the virtual workshop, Artificially Intelligent Earth Exploration Workshop: Teaching the Machine How to Characterize the Subsurface, 23–26 November 2020.
  • Characterization and microfabrication of natural porous rocks: from micro-CT imaging and digital rock modelling to micro-3D-printed rock analogs

    Song, Rui; Wang, Yao; Sun, Shuyu; Liu, Jianjun (Journal of Petroleum Science and Engineering, Elsevier BV, 2021-04) [Article]
    Tests on standard rock specimens with controlled and identical pore structure are critical to validating the analytical and numerical models. However, it is usually difficult to acquire two natural samples with the same internal structure for the destructive laboratory tests, for the sake of the heterogeneity of natural rock which is caused by the complex diagenetic processes. Three-dimensional (3D) printing technology provides an alternative approach to produce geometry-identical, features-controllable, and lab-testable analogs of natural rock from digital data in a faster and more cost-effective way. This paper presents a customized workflow of 3D-printed rock analogs from micro-CT images combining with digital rock modelling. Three types of natural rock specimens are imaged by micro-CT and processed as inputs for two types of 3D printing techniques. Rock analogs are printed at multiple magnifications from original CT volume in five curable resin materials. Petrophysical parameters of 3D-printed rock analogs are acquired through helium pycnometry (HP) and mercury intrusion porosimetry (MIP). The accuracy of 3D-printed rock analogs is evaluated by comparing the measured results with the benchmark data derived from the digital rock modelling. Both the advantages and the current challenges to reproduce the real pore structure of natural rock by the 3D-printed analogs are discussed. The results indicate that the gypsum-based printed analogs are prior to modelling the surface roughness and wettability properties to natural rock grains, while the resin-based printed analogs owe advantages on reproducing pore structure. As the first effort in literature, this study investigates the inherent relationship between digital rock and 3D-printed rock analogs via comprehensive comparison on petrophysical properties. The results approve that the 3D printing technique is a novel, feasible, and alternative approach for laboratory test to generate rock analogs from the digital model of the natural rock. However, it is still difficult to print the pore structure of the rock at the original dimension.
  • The Effect of the Oleophobicity Deterioration of a Membrane Surface on Its Rejection Capacity: A Computational Fluid Dynamics Study

    Salama, Amgad; Alyan, Adel; El-Amin, Mohamed F.; Sun, Shuyu; Zhang, Tao; Zoubeik, Mohamed (Membranes, MDPI AG, 2021-03-31) [Article]
    In this work, the effects of the deteriorating affinity-related properties of membranes due to leaching and erosion on their rejection capacity were studied via computational fluid dynamics (CFD). The function of affinity-enhancing agents is to modify the wettability state of the surface of a membrane for dispersed droplets. The wettability conditions can be identified by the contact angle a droplet makes with the surface of the membrane upon pinning. For the filtration of fluid emulsions, it is generally required that the surface of the membrane is nonwetting for the dispersed droplets such that the interfaces that are formed at the pore openings provide the membrane with a criterion for the rejection of dispersals. Since materials that make up the membrane do not necessarily possess the required affinity, it is customary to change it by adding affinity-enhancing agents to the base material forming the membrane. The bonding and stability of these materials can be compromised during the lifespan of a membrane due to leaching and erosion (in crossflow filtration), leading to a deterioration of the rejection capacity of the membrane. In order to investigate how a decrease in the contact angle can lead to the permeation of droplets that would otherwise get rejected, a CFD study was conducted. In the CFD study, a droplet was released in a crossflow field that involved a pore opening and the contact angle was considered to decrease with time as a consequence of the leaching of affinity-enhancing agents. The CFD analysis revealed that the decrease in the contact angle resulted in the droplet spreading over the surface more. Furthermore, the interface that was formed at the entrance of the pore opening flattened as the contact angle decreased, leading the interface to advance more inside the pore. The droplet continued to pass over the pore opening until the contact angle reached a certain value, at which point, the droplet became pinned at the pore opening.
  • Near-surface real-time seismic imaging using parsimonious interferometry

    Hanafy, Sherif M.; Hoteit, Hussein; Li, Jing; Schuster, Gerard T. (Scientific Reports, Springer Nature, 2021-03-30) [Article]
    AbstractResults are presented for real-time seismic imaging of subsurface fluid flow by parsimonious refraction and surface-wave interferometry. Each subsurface velocity image inverted from time-lapse seismic data only requires several minutes of recording time, which is less than the time-scale of the fluid-induced changes in the rock properties. In this sense this is real-time imaging. The images are P-velocity tomograms inverted from the first-arrival times and the S-velocity tomograms inverted from dispersion curves. Compared to conventional seismic imaging, parsimonious interferometry reduces the recording time and increases the temporal resolution of time-lapse seismic images by more than an order-of-magnitude. In our seismic experiment, we recorded 90 sparse data sets over 4.5 h while injecting 12-tons of water into a sand dune. Results show that the percolation of water is mostly along layered boundaries down to a depth of a few meters, which is consistent with our 3D computational fluid flow simulations and laboratory experiments. The significance of parsimonious interferometry is that it provides more than an order-of-magnitude increase of temporal resolution in time-lapse seismic imaging. We believe that real-time seismic imaging will have important applications for non-destructive characterization in environmental, biomedical, and subsurface imaging.
  • Automatic seismic phase picking based on unsupervised machine learning classification and content information analysis

    Valero Cano, Eduardo; Akram, Jubran; Peter, Daniel B. (GEOPHYSICS, Society of Exploration Geophysicists, 2021-03-29) [Article]
    Accurate identification and picking of P- and S-wave arrivals is important in earthquake and exploration seismology. Often, existing algorithms lack in automation, multi-phase classification and picking, as well as performance accuracy. A new fully-automated fourth-step workflow for efficient classification and picking of P- and S-wave arrival times on microseismic datasets is presented. First, time intervals with possible arrivals on the waveform recordings are identified using the fuzzy c-means clustering algorithm. Second, these signal intervals are classified as corresponding to P, S, or unidentified waves using the polarization attributes of the waveforms contained within. Third, the P-, S-, and unidentified-waves arrival times are picked using the Akaike information criterion picker on the corresponding intervals. Fourth, unidentified waves are classified as P or S based on the arrivals moveouts. The application of the workflow on synthetic and real microseismic datasets shows that it yields accurate arrival picks for both high and low signal-to-noise ratio waveforms.
  • Editorial: Advanced modeling and simulation of flow in subsurface reservoirs with fractures and wells for a sustainable industry

    Sun, Shuyu; Edwards, Michael; Frank, Florian; Li, Jingfa; Salama, Amgad; Yu, Bo (Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, EDP Sciences, 2021-03-26) [Article]
    Flow in subsurface reservoirs is a crucial process in a wide range of applications at different time and space scales, such as petroleum exploration and recovery, groundwater contamination, subsurface carbon sequestration, and geothermal reservoir engineering. As an effective method, modeling and simulation of flow in subsurface reservoirs become essential components of many scientific and engineering applications in recent years. Significant advances have been made in this area, but accurate modeling and efficient, robust simulation still remain a challenging problem, especially for flow and transport in subsurface reservoirs with fractures and wells. To facilitate the exchange and dissemination of original research results and state-of-the-art reviews pertaining to flow in subsurface reservoirs with fractures and wells efficiently, we organized a special issue on “Advanced modeling and simulation of flow in subsurface reservoirs with fractures and wells for a sustainable industry” within Oil & Gas Science and Technology.
  • Interseismic deformation from Sentinel-1 burst-overlap interferometry: Application to the southern Dead Sea fault

    Li, Xing; Jonsson, Sigurjon; Cao, Yunmeng (Wiley, 2021-03-26) [Preprint]
    Interferometric Synthetic Aperture Radar (InSAR) data are increasingly being used to map interseismic deformation with ascending and descending-orbit observations allowing for resolving for the near-east and vertical displacement components. The north component has, however, been difficult to retrieve due to the limited sensitivity of standard InSAR observations in that direction. Here we address this problem by using time-series analysis of along-track interferometric observations in burst-overlap areas of the TOPS imaging mode of the Sentinel-1 radar satellites. We apply this method to the southern part of the near-north striking Dead Sea transform fault to show that the ~5 mm/year relative motion is well recovered. Furthermore, the results indicate the locking depth of the fault decreases towards the south as it enters the transtensional Gulf of Aqaba basin. Our results show that time-series analysis of burst-overlap interferometric observations can be used to obtain meaningful interseismic deformation rates of slow-moving and northerly-striking faults.
  • Coastal circulation and water transport properties of the Red Sea Project lagoon

    Zhan, Peng; Krokos, Georgios; Langodan, Sabique; Guo, Daquan; Dasari, Hari Prasad; Papadopoulos, Vassilis P.; Lermusiaux, Pierre F.J.; Knio, Omar; Hoteit, Ibrahim (Ocean Modelling, Elsevier BV, 2021-03-26) [Article]
    The Red Sea Project (RSP) is based on a coastal lagoon with over 90 pristine islands. The project intends to transform the Red Sea coast into a world-class tourist destination. To better understand the regional dynamics and water exchange scenarios in the lagoon, a high-resolution numerical model is implemented. The general and tidal circulation dynamics are then investigated with a particular focus on the response of the lagoon to strong wind jets. Significant variations in winter and summer circulation patterns are identified. The tidal amplitude inside the lagoon is greater than that outside, with strong tidal currents passing over its surrounding coral reef banks. The lagoon rapidly responds to the strong easterly wind jets that occur mainly in winter; it develops a reverse flow at greater depths, and the coastal water elevation is instantly affected. Lagrangian particle simulations are conducted to study the residence time of water in the lagoon. The results suggest that water renewal is slow in winter. Analysis of the Lagrangian coherent structures (LCS) reveals that water renewal is largely linked to the circulation patterns in the lagoon. In winter, the water becomes restricted in the central lagoon with only moderate exchange, whereas in summer, more circulation is observed with a higher degree of interaction between the central lagoon and external water. The results of LCS also highlight the tidal contribution to stirring and mixing while identifying the hotspots of the phenomenon. Our analysis demonstrates an effective approach for studying regional water mixing and connectivity, which could support coastal management in data-limited regions.
  • Active faults' geometry in the Gulf of Aqaba, southern Dead Sea fault, illuminated by multi beam bathymetric data

    Ribot, Matthieu; Klinger, Yann; Jonsson, Sigurjon; Avsar, Ulas; Pons-Branchu, Edwige; Matrau, Rémi; Mallon, Francis (Tectonics, American Geophysical Union (AGU), 2021-03-25) [Article]
    Detailed knowledge of fault geometry is important for accurate seismic hazard assessment. The Gulf of Aqaba, which corresponds to the southern termination of the 1200-km-long Dead Sea fault system, remains one of the least known parts of this plate boundary fault, in large part due to its location offshore. Classically, the Gulf of Aqaba has been described as a succession of three pull-apart basins. Here, building on a new multibeam bathymetric survey of the Gulf of Aqaba, we provide details about the geometry of the faults at the bottom of the gulf that controls its morphology. In particular, we identify a 50 km-long fault section that shows evidence of recent activation. We associate this fault section (Aragonese fault) with the main fault section that ruptured during the 1995 magnitude Mw7.3 Nuweiba earthquake. In the southern part of the gulf, bathymetry emphasizes the strike-slip nature of the Arnona fault, while dip-slip motion seems to be accommodated mostly by faults located along the eastern edge of the gulf. Considering the simple linear geometry of the Arnona fault and the absence of any large earthquake for several centuries, despite an average slip-rate of ∼5 mm/yr, this fault should be considered as a significant candidate for an earthquake rupture of magnitude 7 or above in the near future.
  • Constraints on the upper mantle structure beneath the Pacific from 3-D anisotropic waveform modelling

    Kendall, Elodie; Ferreira, A.M.G.; Chang, Sung-Joon; Witek, M.; Peter, Daniel (Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), 2021-03-24) [Article]
    Seismic radial anisotropy is a crucial tool to help constrain flow in the Earth's mantle. However, Earth structure beneath the oceans imaged by current 3-D radially anisotropic mantle models shows large discrepancies. In this study, we provide constraints on the radially anisotropic upper mantle structure beneath the Pacific by waveform modelling and subsequent inversion. Specifically, we objectively evaluate three 3-D tomography mantle models which exhibit varying distributions of radial anisotropy through comparisons of independent real datasets with synthetic seismograms computed with the spectral-element method. The data require an asymmetry at the East Pacific Rise (EPR) with stronger positive radial anisotropy ξ=urn:x-wiley:21699313:media:jgrb54831:jgrb54831-math-0001=1.13-1.16 at ∼100 km depth to the west of the East Pacific Rise than to the east (ξ=1.11-1.13). This suggests that the anisotropy in this region is due to the lattice preferred orientation (LPO) of anisotropic mantle minerals produced by shear-driven asthenospheric flow beneath the South Pacific Superswell. Our new radial anisotropy constraints in the Pacific show three distinct positive linear anomalies at ∼100 km depth. These anomalies are possibly related to mantle entrainment at the Nazca-South America subduction zone, flow at the East Pacific Rise and from the South Pacific Superswell and SPO (shape-preferred orientation) of melt beneath Hawaii. Radial anisotropy reduces with lithospheric age to ξ < 1.05 in the west at ∼100 km depth, which possibly reflects a deviation from horizontal flow as the mantle is entrained with subducting slabs, a change in temperature or water content that could alter the anisotropic olivine fabric or the shape-preferred orientation of melt.
  • Business-as-usual will lead to super and ultra-extreme heatwaves in the Middle East and North Africa

    Zittis, George; Hadjinicolaou, Panos; Almazroui, Mansour; Bucchignani, Edoardo; Driouech, Fatima; El Rhaz, Khalid; Kurnaz, Levent; Nikulin, Grigory; Ntoumos, Athanasios; Ozturk, Tugba; Proestos, Yiannis; Stenchikov, Georgiy L.; Zaaboul, Rashyd; Lelieveld, Jos (npj Climate and Atmospheric Science, Springer Nature, 2021-03-23) [Article]
    AbstractGlobal climate projections suggest a significant intensification of summer heat extremes in the Middle East and North Africa (MENA). To assess regional impacts, and underpin mitigation and adaptation measures, robust information is required from climate downscaling studies, which has been lacking for the region. Here, we project future hot spells by using the Heat Wave Magnitude Index and a comprehensive ensemble of regional climate projections for MENA. Our results, for a business-as-usual pathway, indicate that in the second half of this century unprecedented super- and ultra-extreme heatwave conditions will emerge. These events involve excessively high temperatures (up to 56 °C and higher) and will be of extended duration (several weeks), being potentially life-threatening for humans. By the end of the century, about half of the MENA population (approximately 600 million) could be exposed to annually recurring super- and ultra-extreme heatwaves. It is expected that the vast majority of the exposed population (>90%) will live in urban centers, who would need to cope with these societally disruptive weather conditions.
  • Three-dimensional simulation of shoaling internal solitary waves and their influence on particle transport in the southern Red Sea

    Guo, Daquan; Zhan, Peng; Hoteit, Ibrahim (Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), 2021-03-22) [Article]
    The shoaling process of a group of internal solitary waves (ISWs) in the southern Red Sea is simulated with a 3D, non-hydrostatic, high-resolution MIT general circulation model (MITgcm). The breaking and dissipation processes are well reproduced, in which a positive tail forms behind and locally moves the interface upward, causing the transformation of wave polarity as it moves onshore. With the step-like structure followed, the wave eventually evolve into smaller water bores. Combined with the parameters of the leading wave slope (Sw) of about 0.07 and topography slope (S) of about 0.01, the shoaling is suggested to follow a mild breaking process. The particle transport during the shoaling process is further examined quantitatively using the Connectivity modelling system (CMS). 38400 particles are released at six different vertical layers in the main shoaling domain. Most of the particles are transported up-and-down following the wave oscillation process then settle within 10-20 m around the original released depth. For the particles inside the breaking area, the oscillation process becomes more complex and intensified, and eventually a great portion of these particles settle far away from their released locations. The time-integrated transport distance, Ti, and the direct transport distance, Ts, are also analyzed. With Ti almost 20 times to Ts in vertical, continuous up-and-down movements are suggested during the shoaling process.
  • An extended seir model with vaccination for forecasting the covid-19 pandemic in saudi arabia using an ensemble kalman filter

    Ghostine, Rabih; Gharamti, Mohamad; Hassrouny, Sally; Hoteit, Ibrahim (Mathematics, MDPI AG, 2021-03-17) [Article]
    In this paper, an extended SEIR model with a vaccination compartment is proposed to simulate the novel coronavirus disease (COVID-19) spread in Saudi Arabia. The model considers seven stages of infection: susceptible (S), exposed (E), infectious (I), quarantined (Q), recovered (R), deaths (D), and vaccinated (V). Initially, a mathematical analysis is carried out to illustrate the non-negativity, boundedness, epidemic equilibrium, existence, and uniqueness of the endemic equilibrium, and the basic reproduction number of the proposed model. Such numerical models can be, however, subject to various sources of uncertainties, due to an imperfect description of the biological processes governing the disease spread, which may strongly limit their forecasting skills. A data assimilation method, mainly, the ensemble Kalman filter (EnKF), is then used to constrain the model outputs and its parameters with available data. We conduct joint state-parameters estimation experiments assimilating daily data into the proposed model using the EnKF in order to enhance the model’s forecasting skills. Starting from the estimated set of model parameters, we then conduct short-term predictions in order to assess the predicability range of the model. We apply the proposed assimilation system on real data sets from Saudi Arabia. The numerical results demonstrate the capability of the proposed model in achieving accurate prediction of the epidemic development up to two-week time scales. Finally, we investigate the effect of vaccination on the spread of the pandemic.
  • Sample average approximation for risk-averse problems: A virtual power plant scheduling application

    Lima, Ricardo; Conejo, Antonio J.; Giraldi, Loic; Le Maître, Olivier; Hoteit, Ibrahim; Knio, Omar (EURO Journal on Computational Optimization, Elsevier B.V., 2021-03-16) [Article]
    In this paper, we address the decision-making problem of a virtual power plant (VPP) involving a self-scheduling and market involvement problem under uncertainty in the wind speed and electricity prices. The problem is modeled using a risk-neutral and two risk-averse two-stage stochastic programming formulations, where the conditional value at risk is used to represent risk. A sample average approximation methodology is integrated with an adapted L-Shaped solution method, which can solve risk-neutral and specific risk-averse problems. This methodology provides a framework to understand and quantify the impact of the sample size on the variability of the results. The numerical results include an analysis of the computational performance of the methodology for two case studies, estimators for the bounds of the true optimal solutions of the problems, and an assessment of the quality of the solutions obtained. In particular, numerical experiences indicate that when an adequate sample size is used, the solution obtained is close to the optimal one.

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