Realistic Numerical Modeling Research Articles

Large dump critical zone of interest identification and slope failure prediction using realistic 3D numerical modelling

Dump failure is one of the most catastrophic hazards in the opencast mining industry and involves sudden and violent failures. Therefore, susceptible region identification is essential for slope failure mitigation in the large dump. This study proposed a sustainable approach for large dump critical zone of interest (CZI) identification, stability monitoring and slope failure prediction. UAV close-range photogrammetry survey and structure-from-motion (SfM) approach were used for the dump realistic 3D model reconstruction. 3D numerical modelling was employed for dump stability analysis. In this investigation, the dump critical zone, slope factor of safety (FOS), displacement and slope failure prediction were analysed using the 3D numerical modelling. The results indicate that maximum displacement was found in the critical zone I. However, the dump was stable under static conditions. Dump critical slope failure time is predicted using the inverse velocity method. The results of this investigation are reliable and establish the scope of UAV photogrammetry for realistic 3D modelling. In addition, the slope stability state and failure model were consistent with field observations. The proposed approach can be used for the mine, hill, and roadcut slopes. UAV technology and 3D modelling approaches have substantially reduced data collection time and expense.

Failure Zone Identification and Slope Stability Analysis of Mine Dump Based on Realistic 3D Numerical Modeling

Failure Zone Identification and Slope Stability Analysis of Mine Dump Based on Realistic 3D Numerical Modeling

Autonomous urban topology generation for urban flow modelling

• New framework is developed that integrates the autonomous urban topology generation for urban flow modeling. • A new deep learning model is developed for building footprints extraction from satellite imagery • Deep learning model was meshed with Light Detection and Ranging (LiDAR) data by meshing to generate 3D building models • An illustration pedestrian level wind simulation was carried out for city of London On. One of the challenges in realistic numerical urban micro-climate modelling for wind, heat transfer, and building energy simulation applications is the complexity of urban topology and complex building geometries. This paper presents a deep learning modelling for building footprint polygon extraction from satellite imagery that is integrated with Light Detection and Ranging (LiDAR) data to generate 3D building models. The deep learning model registered a mean squared error of 0.02. The trained deep learning model can then be applied to a new set of input image data to extract building footprint polygons for autonomous application, and it can also be incrementally retrained with good quality data when it becomes available. A framework is developed that integrates the autonomous urban topology generator with urban flow modelling. The modelling steps are explained through an application example of urban flow modelling encountered during a pedestrian level wind assessment for the city of London, Ontario.

Cross-Front Transport Triggered by Winter Storms Around the Shandong Peninsula, China

Ocean fronts are widespread on the eastern China shelf, especially in winter and early spring. Previous studies have shown that sediments on the northern coast of the Shandong Peninsula could penetrate the coastal fronts and deposit on the southern coast of the Liaodong Peninsula, and this cross-front transport process is closely related to winter storms. However, the detailed mechanisms of cross-front transport remain unclear. In this study, through realistic numerical modeling and physical mechanism analysis, a dynamic mechanism involving cross-front transport triggered by winter storms was proposed, and two locations with the highest probability of frontal instability around the Shandong Peninsula were identified. In detail, forced by winter storms, the Lubei Coastal Current significantly intensifies first and causes frontal inertial instability in the early stage of the winter storm, favoring cross-front exchange between both sides of the front. Then, serving as a compensation current, the Yellow Sea Warm Current intensifies in the late stage of the winter storm, leading to the northward transport of the materials out of the front. Furthermore, the intensity, distance, and path of the cross-front transport under varying winter storms are also investigated. The winter storm, with longer duration, greater wind speed, and westward wind direction, tends to trigger stronger cross-front transport and longer transport distance. Transport paths also differ under different winter storms. This study provides a theoretical explanation for cross-front transport and analyzes the role of winter storms in it, providing some new ideas for nearshore materials dispersal to the sea, which is of great significance for future studies on pollutant diffusion, nutrient distribution, and sediment transport in coastal areas.

Effects of void morphology on fracturing characteristics of porous rock through a finite-discrete element method

A systematic approach for generating a stochastic void geometry with controllable shape features is proposed for more realistic numerical modelling of porous rock materials. The numerical model (a finite-discrete model) is established by integrating zero-thickness cohesive elements with finite solid elements, to trace the progressive fracturing and failure behaviours of porous rocks. A series of Brazil split tests are conducted on the synthetic specimens that are generated using 3D printing technique, to validate the proposed numerical model. By comparing fracturing patterns and load-displacement curves, it is demonstrated that the proposed hybrid numerical method has promising performances to capture the mechanical responses of porous rocks. In addition, the influences of void aspect ratio and orientation on the mechanical and fracturing responses of porous rocks are discussed. By counting the total damage proportion (Pt) and shearing damage ratio (Ps) of cohesive elements, the hybrid method offered a micro insight to reveal the mechanism of strength variation induced by different characteristics of void morphology. Modelling results demonstrate that better mechanical properties of porous rocks correspond to higher values of both Pt and Ps. Comparison between modelling results and data from literature also validates the efficiency and accuracy of the proposed hybrid approach.

OpenMandible: An open-source framework for highly realistic numerical modelling of lower mandible physiology

ObjectiveComputer modeling of lower mandible physiology remains challenging because prescribing realistic material characteristics and boundary conditions from medical scans requires advanced equipment and skill sets. The objective of this study is to provide a framework that could reduce simplifications made and inconsistency (in terms of geometry, materials, and boundary conditions) among further studies on the topic. MethodsThe OpenMandible framework offers: 1) the first publicly available multiscale model of the mandible developed by combining cone beam computerized tomography (CBCT) and μCT imaging modalities, and 2) a C++ software tool for the generation of simulation-ready models (tet4 and hex8 elements). In addition to the application of conventional (Neumann and Dirichlet) boundary conditions, OpenMandible introduces a novel geodesic wave propagation - based approach for incorporating orthotropic micromechanical characteristics of cortical bone, and a unique algorithm for modeling muscles as uniformly directed vectors. The base intact model includes the mandible (spongy and compact bone), 14 teeth (comprising dentin, enamel, periodontal ligament, and pulp), simplified temporomandibular joints, and masticatory muscles (masseter, temporalis, medial, and lateral pterygoid). ResultsThe complete source code, executables, showcases, and sample data are freely available on the public repository: https://github.com/ArsoVukicevic/OpenMandible. It has been demonstrated that by slightly editing the baseline model, one can study different “virtual” treatments or diseases, including tooth restoration, placement of implants, mandible bone degradation, and others. SignificanceOpenMandible eases the community to undertake a broad range of studies on the topic, while increasing their consistency and reproducibility. At the same time, the needs for dedicated equipment and skills for developing realistic simulation models are significantly reduced.

Macro-Scale Numerical Modeling of Unreinforced Brick Masonry Squat Pier Under In-Plane Shear

Numerical modeling of brick masonry behaviour under different performance conditions has always remained a challenging task. Several modeling strategies have been developed for masonry, in general, through the course of time that have been simplified to speed up modeling and analysis duration. This ranges from a simplified strut model to a highly discontinuous micro-scale nonlinear model. With the current advent of high-speed computing and modeling tools, more realistic numerical modeling of masonry is now possible. In this paper, the strategy adopted is based on macro-scale modeling, where isotropic material properties are considered for the homogenous continuum. ABAQUS is used as a state-of-the-art finite element-based analysis and modeling tool. The Concrete Damage Plasticity (CDP) model is used for simulating inelastic material behaviour of brick and mortar, which is available in the ABAQUS library. This material model can be used in both implicit and explicit schemes of integration but the explicit procedure is highly preferred as it overcomes the convergence issues. Various parameters required for CDP modeling of brick and mortar are adapted from literature. The model is assembled in two parts, first part is modeled for masonry with both elastic and plastic properties, while the other part simulates a rigid beam at the top of the masonry part to create a uniform in-plane shear loading effect. The masonry part has been fixed at the bottom with free vertical ends, while horizontal in-plane displacement was applied to the top rigid beam. The load-displacement curves were generated from these models for monotonic push, to compare them with the envelopes of experimental results, loaded similarly. Since brick masonry is a highly disjointed material, it is a complicated procedure to develop an exact model and predict its exact behaviour. However, the overall representative load-displacement curve developed numerically was in good agreement with the ones produced experimentally.

A fully coupled numerical simulation of a hybrid concentrated photovoltaic/thermal system that employs a therminol VP-1 based nanofluid as a spectral beam filter

The realistic numerical modelling of multiphysics applications is an efficient way to precisely predict the operation of concentrated solar systems. Although many multiphysics conjugating approaches have been proposed in the literature, it is difficult to adopt such methods into simulating complex concentrated solar technologies. Consequently, this study introduces a novel 2D:3D numerical optical, thermal and electric coupling approach for a hybrid compound parabolic concentrator photovoltaic/thermal (CPC-PV/T) collector using a nanofluid as a spectral beam filter. In this approach, the volumetric absorbed radiation in each component of the system obtained from the non-gray 2D model is patched into the 3D model as a volumetric heat source using sophisticated computational tools. The main features of the full coupling method (FCM) are extensively analyzed and compared with the other two coupling methods previously adopted. Further, the module performance has been investigated employing both the nanofluid and base-fluid spectrum filters (BF-filter) compared with a stand-alone concentrated PV cell. From findings, the FCM can be applied to reveal more realistic operation characteristics of the proposed system compared with the other approaches, since the FCM can take into account the non-uniformity of solar illumination and the direction of reflected solar beams upon the receiver, along with the variation in the optical characteristics of utilized materials over the solar irradiance. Additionally, suspending indium tin oxide (ITO) nanoparticles into the Therminol VP1 oil raises the absorption rate over the thermal-bands with 62.5% higher than the use of BF-filter, whilst the cell temperature and the transmitted irradiance within the PV-band are obviously declined.

Passive magnetic shielding by machinable MgB2 bulks: measurements and numerical simulations

We report on a combined experimental and modelling approach towards the design and fabrication of efficient bulk shields for low-frequency magnetic fields. To this aim, MgB2 is a promising material when its growing technique allows the fabrication of suitably shaped products and a realistic numerical modelling can be exploited to guide the shield design. Here, we report the shielding properties of an MgB2 tube grown by a novel technique that produces fully machinable bulks, which can match specific shape requirements. Despite a height/radius aspect ratio of only 1.75, shielding factors higher than 175 and 55 were measured at temperature T = 20 K and in axially-applied magnetic fields μ0Happl = 0.1 and 1.0 T, respectively, by means of cryogenic Hall probes placed on the tube’s axis. The magnetic behaviour of the superconductor was then modelled as follows: first we used a two-step procedure to reconstruct the macroscopic critical current density dependence on magnetic field, Jc(B), at different temperatures from the local magnetic induction cycles measured by the Hall probes. Next, using these Jc(B) characteristics, by means of finite-element calculations we reproduced the experimental cycles remarkably well at all the investigated temperatures and positions along the tube’s axis. Finally, this validated model was exploited to study the influence both of the tube’s wall thickness and of a cap addition on the shield performance. In the latter case, assuming the working temperature of 25 K, shielding factors of 105 and 104 are predicted in axial applied fields μ0Happl = 0.1 and 1.0 T, respectively.

3D numerical study on fracture process of concrete with different ITZ properties using X-ray computerized tomography

A three-dimensional (3D) realistic numerical modelling method is proposed to simulate the fracture process of concrete based on its meso-structure. In the 3D realistic numerical modelling method, CT technology is first applied to capture the microstructure of the concrete as a series of cross-sectional CT images. An improved digital image processing (DIP) technique is then developed to identify and characterize the aggregates and the interfacial transition zones (ITZ) in the CT images. After that, a 3D realistic three-phase structure model of the concrete is reconstructed on the basis of the processed CT images using the vectorized transformation and volume rendering method, which is integrated into a well-established 3D Realistic Failure Process Analysis (RFPA3D) code. In this way, the 3D realistic numerical modelling method is developed. It is validated by building a 3D realistic numerical model of the concrete and comparing the results between numerically and experimentally obtained. Finally, using the 3D realistic numerical modelling method, the effects of the ITZ strength on the fracture process of the concrete under uniaxial compression and tension are studied and further clarified. The proposed 3D realistic numerical modelling method provides a new tool to study the fracture mechanism of concrete at the mesoscopic/microscopic levels under complex loading conditions.

A fast finite difference method for distributed-order space-fractional partial differential equations on convex domains

Fractional partial differential equations (PDEs) provide a powerful and flexible tool for modeling challenging phenomena including anomalous diffusion processes and long-range spatial interactions, which cannot be modeled accurately by classical second-order diffusion equations. However, numerical methods for space-fractional PDEs usually generate dense or full stiffness matrices, for which a direct solver requires O(N3) computations per time step and O(N2) memory, where N is the number of unknowns. The significant computational work and memory requirement of the numerical methods makes a realistic numerical modeling of three-dimensional space-fractional diffusion equations computationally intractable.Fast numerical methods were previously developed for space-fractional PDEs on multidimensional rectangular domains, without resorting to lossy compression, but rather, via the exploration of the tensor-product form of the Toeplitz-like decompositions of the stiffness matrices. In this paper we develop a fast finite difference method for distributed-order space-fractional PDEs on a general convex domain in multiple space dimensions. The fast method has an optimal order storage requirement and almost linear computational complexity, without any lossy compression. Numerical experiments show the utility of the method.

A convergence criterion for water conveyance tunnels

One of the important methods used by tunnel construction engineers to examine the design, construction safety factor, and tunnel boring procedures is convergence measurement. Larger convergences may lead to safety problems such as rock destruction, boring machines jamming, delays in projects, or even geological disasters, in which case convergence measurement is considered the best method. The goal of this research is introducing a new convergence criterion for water conveyance tunnel based on the data from 31 convergence measurement stations of the Chehel Chay water conveyance tunnel. To achieve this objective, three different methods including statistical (SPSS), artificial neural network (ANN) and numerical modeling (3DEC) have been used. Observation points are defined on the tunnel wall in a realistic numerical modeling to compare the convergence results. The results revealed the success of the artificial neural network and indicated that the network managed to estimate the test data with a high correlation coefficient.

Bombs and Flares at the Surface and Lower Atmosphere of the Sun

Abstract A spectacular manifestation of solar activity is the appearance of transient brightenings in the far wings of the Hα line, known as Ellerman bombs (EBs). Recent observations obtained by the Interface Region Imaging Spectrograph have revealed another type of plasma “bombs” (UV bursts) with high temperatures of perhaps up to 8 × 104 K within the cooler lower solar atmosphere. Realistic numerical modeling showing such events is needed to explain their nature. Here, we report on 3D radiative magnetohydrodynamic simulations of magnetic flux emergence in the solar atmosphere. We find that ubiquitous reconnection between emerging bipolar magnetic fields can trigger EBs in the photosphere, UV bursts in the mid/low chromosphere and small (nano-/micro-) flares (106 K) in the upper chromosphere. These results provide new insights into the emergence and build up of the coronal magnetic field and the dynamics and heating of the solar surface and lower atmosphere.

Two efficient approaches for modeling of Raman scattering in homogeneous turbid media.

The quantitative analysis of Raman spectroscopic signals in biological tissue is generally difficult. Typical samples contain a multitude of molecular species and, in addition, measurements are altered by attenuation of the Raman signal. Realistic numerical modeling of the Raman process can help to facilitate the quantitative analysis of the Raman spectra, but approaches so far are scarce and often time-consuming. In this work, we report on two different and very efficient approaches for modeling of Raman scattering in turbid media irradiated by laser light. Both approaches utilize the Monte Carlo method to simulate the Raman scattering process. We compare the efficiency of both approaches and discuss possible future extensions and experimental validation.

A Realistic FDTD Numerical Modeling Framework of Ground Penetrating Radar for Landmine Detection

A three-dimensional (3-D) finite-difference time-domain (FDTD) algorithm is used in order to simulate ground penetrating radar (GPR) for landmine detection. Two bowtie GPR transducers are chosen for the simulations and two widely employed antipersonnel (AP) landmines, namely PMA-1 and PMN are used. The validity of the modeled antennas and landmines is tested through a comparison between numerical and laboratory measurements. The modeled AP landmines are buried in a realistically simulated soil. The geometrical characteristics of soil’s inhomogeneity are modeled using fractal correlated noise, which gives rise to Gaussian semivariograms often encountered in the field. Fractals are also employed in order to simulate the roughness of the soil’s surface. A frequency-dependent complex electrical permittivity model is used for the dielectric properties of the soil, which relates both the velocity and the attenuation of the electromagnetic waves with the soil’s bulk density, sand particles density, clay fraction, sand fraction, and volumetric water fraction. Debye functions are employed to simulate this complex electrical permittivity. Background features like vegetation and water puddles are also included in the models and it is shown that they can affect the performance of GPR at frequencies used for landmine detection (0.5–3 GHz). It is envisaged that this modeling framework would be useful as a testbed for developing novel GPR signal processing and interpretations procedures and some preliminary results from using it in such a way are presented.

Realistic Numerical and Analytical Modeling of Light Scattering in Brain Tissue for Optogenetic Applications(1,2,3).

In recent years, optogenetics has become a central tool in neuroscience research. Estimating the transmission of visible light through brain tissue is of crucial importance for controlling the activation levels of neurons in different depths, designing optical systems, and avoiding lesions from excessive power density. The Kubelka–Munk model and Monte Carlo simulations have previously been used to model light propagation through rodents' brain tissue, however, these prior attempts suffer from fundamental shortcomings. Here, we introduce and study two modified approaches for modeling the distributions of light emanating from a multimode fiber and scattering through tissue, using both realistic numerical Monte Carlo simulations and an analytical approach based on the beam-spread function approach. We demonstrate a good agreement of the new methods' predictions both with recently published data, and with new measurements in mouse brain cortical slices, where our results yield a new cortical scattering length estimate of ∼47 µm at λ = 473 nm, significantly shorter than ordinarily assumed in optogenetic applications.

Monitoring CO2 storage using ghost reflections retrieved from seismic interferometry

Time-lapse seismic monitoring constitutes the foundation for most monitoring programmes involving CO2 storage. Two major sources of uncertainty in the estimation of changes in the reservoir properties like saturation and pressure, using time-lapse seismics, are the non-repeatability of the source positions and the difficulty to separate the effect of the overburden from that of the changes taking place in a CO2 reservoir. In order to address those challenges, we propose a new concept of using non-physical (ghost) reflection events retrieved by seismic interferometry. We test this concept on data of realistic numerical modelling and scaled laboratory experiments, both representing a horizontally layered subsurface. Our results demonstrate that the seismic reflection ghosts can indeed be used advantageously to monitor changes in the CO2 reservoir.

Eddy-Current Simulations Using an Independent Impedance Method in Anisotropic Biological Tissues

A widely applied method for simulating the induced eddy currents in biological tissues is the impedance method (IM). This method has recently been extended to the independent impedance method (IIM), which identifies and solves a linear system of independent equations, resulting in acceleration of computations. Both IM and IIM assume isotropic material properties, even though some tissues have directionally dependent characteristics. Therefore, we formulate IIM toward space-dependent anisotropic material properties. In this paper, the method is applied to the simulation of transcranial magnetic stimulation (TMS) for both isotropic and anisotropic spherical head models. The numerical results show that anisotropy has a nonnegligible effect on the induced currents, yielding maximum differences of about 40% in the skull and 19% in gray matter. The method is validated by comparing the results with finite element method (FEM) solutions. This study leads to a more realistic numerical modeling of the eddy currents due to the incorporation of anisotropy.

Incidence of Mg ii absorbers towards blazars and the GRB/QSO puzzle

In order to investigate the origin of the excess of strong MgII systems towards GRB afterglows as compared to QSO sightlines, we have measured the incidence of MgII absorbers towards a third class of objects: the Blazars. This class includes the BL Lac object population for which a tentative excess of MgII systems had already been reported. We observed with FORS1 at the ESO-VLT 42 Blazars with an emission redshift 0.8<z_em<1.9, to which we added the three high z northern objects belonging to the 1Jy BL Lac sample. We detect 32 MgII absorbers in the redshift range 0.35-1.45, leading to an excess in the incidence of MgII absorbers compared to that measured towards QSOs by a factor ~2, detected at 3 sigma. The amplitude of the effect is similar to that found along GRB sightlines. Our analysis provides a new piece of evidence that the observed incidence of MgII absorbers might depend on the type of background source. In front of Blazars, the excess is apparent for both 'strong' (w_ r(2796) > 1.0 A) and weaker (0.3 < w_r(2796) < 1.0 A) MgII systems. The dependence on velocity separation with respect to the background Blazars indicates, at the ~1.5 sigma level, a potential excess for beta = v/c ~0.1. We show that biases involving dust extinction or gravitational amplification are not likely to notably affect the incidence of MgII systems towards Blazars. Finally we discuss the physical conditions required for these absorbers to be gas entrained by the powerful Blazar jets. More realistic numerical modelling of jet-ambient gas interaction is required to reach any firm conclusions as well as repeat observations at high spectral resolution of strong MgII absorbers towards Blazars in both high and low states.

Employing ADI‐FDTD subgrids for GPR numerical modelling and their application to study ring separation in brick masonry arch bridges

ABSTRACTIn realistic numerical modelling of ground‐penetrating radar (GPR) and when parts of the computational domain need to be modelled in detail, the implementation of subgrids into the conventional finite‐difference time‐domain (FDTD) mesh could greatly economize on computational resources. A novel alternating‐direction implicit FDTD subgridding scheme is used to numerically simulate the GPR responses from delaminations located in brick masonry arches. The heterogeneity of these structures renders electromagnetic signals, which originate from the interaction between the GPR system and the bridge, often complex and hence hard to interpret. Therefore, GPR numerical models were created in order to study the attributes of reflected signals from various targets within the structure of the bridge. Results from a range of modelling scenarios are presented. The effect of varying the thickness of faults, their location in brickwork, as well as the effect of water ingress in hairline delaminations on GPR signals, are examined. Moreover, GPR vertical resolution and the presence of lossy brickwork are studied through various numerical models.