Numerical Simulation Techniques Research Articles

A reliable numerical simulation technique for solving COVID-19 model

A reliable numerical simulation technique for solving COVID-19 model

Experimental validation of numerical model for thermomechanical performance of material extrusion additive manufacturing process: Effect of infill design & density

The optimum selection of process parameters, materials, and product design is essential to achieve the desired response of 3D-printed structures, especially in functional components. The current practices of the experimental optimization process require significant resources, which can be limited through numerical modeling and simulation techniques. In this study, a thermomechanical numerical model is used to predict the performance of the additive manufacturing (AM) process, i.e., fused filament fabrication (FFF). 3D printing (3DP) process simulations were performed for tensile testing coupons using carbon fiber-reinforced polyamide-6 (PA6-CF) material. The numerical model predicted the effect of infill patterns and densities on the deflections and distortions during the FFF process. The numerical model predictions were validated via experiments performed under similar conditions. The results conclude that the numerical model can adequately predict the process-induced deflections and distortions during the FFF process. Generally, higher dimensional control was observed for rectangular infill patterns and increased infill density. However, the numerical model overestimates the shrinkage as the stress-relaxation effect is not considered in the numerical model and underestimates the warpages as perfect build plate adhesion is assumed.

Method of numerical modeling in the problems of predicting the effect from air gap in blasthole charge design

Introduction. The article presents the results of numerical modeling of the effect made the air gap in the borehole charge design on the seismic impact of blasting, base work and the stemming ejection speed. Intensification of mining drives the need for the design of blasting operations with a gentle impact on the rock mass while maintaining the required quality of the explosion. The assessment of the major blast impact on a rock mass may include both the results of collecting statistical observational data in specific mining and technological conditions, and the results of numerical modeling of crush zone formation, seismic impact, and the speed of stemming ejection during a major blast. Numerical modeling allows not only to make a preliminary forecast, but also to conduct a series of computational experiments to select the appropriate parameters of drilling and blasting operations in order to achieve the expected effect. The position and size of the air gap in the borehole charge are considered as such a parameter Research methods. The work uses an integrated method combining analysis, scientific generalization of theoretical and experimental studies relating to air gap in borehole charges, and the use of numerical modeling tools and digital technologies in mining. To simulate the action of an air gap during an explosion with expandable and destructible rock mass walls, a software package was used, consisting of the ANSYS AUTODYN software package, which has proven itself in solving non-stationary problems of nonlinear dynamics, and the software package developed by the members of the Institute of Communications and Information Technologies of the Kyrgyz-Russian Slavic University, to assess the stress-strain state of rocks using parallel computing technology. Results. Gas-dynamic processes relating to air gap were analyzed by the method of numerical simulation; the crush zone was estimated. The simulation tool was adjusted and calibrated based on numerical simulation results comparison with the results of laboratory studies of the air gap effect in wells during an explosion in organic glass. Satisfactory convergence of the results made it possible to use this tool for modeling explosive loading in conditions close to industrial scales. Discussion. The modeling performed allows us to state that the bottom work, the reduction in the stemming ejection speed and in the seismic impact are achieved through the use of an air gap and a reduced proportion of explosive. Thus, the use of numerical simulation techniques in mining problems to solve a wide range of production problems to optimize the charge design is justified. Scope of results. The results are relevant for the problems of optimizing drilling and blasting operations in the mining industry in order to ensure a gentle effect of blast on the environment

A Systematic Approach for Analysis of Structure under Blast Load – An Overview

An explosion is an unwanted phenomenon that may be caused accidentally or intentionally. It may be occurred within or near the structure that causes massive damage to the same. An explosion becomes disastrous when the structural elements collapse partially or totally. Many works have been made to grow the techniques/methods of blast resistance structures. A detailed understanding is required for blast load and its effect on the several structural members in terms of dynamic responses to analyze and design a safe engineering structure. Further, in this article, a comprehensive overview of a systematic approach for the analysis of structure under blast load has been presented. For the computation of blast load, different types of empirical relations are available, which are in the pattern of pressure-time functions. Here, the same is represented concisely with an easier way of understanding. Prediction of blast load by the empirical, semi-empirical, and numerical method has been presented. Modelling of blast load for various numerical simulation techniques and material models are also described here for modelling the advanced structural material that may mitigate the blast response of the structure as per the Hydrocodes.

Intrusion of mandibular incisors using single mini-implant –A finite element study

A deep bite is a complex orthodontic problem that is a common feature of many malocclusions. Depending on the diagnosis, a deep overbite can be corrected. Mini implants can be used for the true intrusion of anterior teeth. FEA is a computer based numerical simulation technique used to calculate deflection, stress and displacement. To analyze stress distribution pattern and displacement of mandibular incisors when intrusive forces are applied using three dimensional finite element analysis. To compare intrusion of lower anterior teeth when ‘V’ pattern force and straight vertical pattern force are applied. A three dimensional finite element model was constructed to simulate mandibular teeth, periodontal ligament and alveolar bone. The displacement of individual tooth (central and lateral incisors) on three-dimensional planes and the von Mises stress distribution were compared. Intrusive forces when applied to four mandibular anterior teeth remarkable tipping of the labial segment was seen when straight vertical elastics were used as compared to the ‘V’ shaped elastics. Within the limits of this study, predictable intrusion with minimum labial tipping is seen using single implant using V pattern elastics.

Shale Oil Occurrence Mechanisms: A Comprehensive Review of the Occurrence State, Occurrence Space, and Movability of Shale Oil

Shale oil resources are important supplements for the gradually decreasing oil production from conventional reservoirs. Although the exploitation and development of shale oil have achieved considerable progress in the last decade, the commercial extraction of hydrocarbons from shales is still difficult, especially in the lacustrine sedimentary basins of China. One of the key points controlling the successful extraction of hydrocarbons from shale systems is the understanding of the occurrence mechanism of shale oil. This study comprehensively summarizes the theories and techniques to characterize oil occurrence state, occurrence space, oil content, and oil movability in shale systems. Sophisticated instruments, such as high-resolution scanning electron microscopy and high-energy ray imaging, were utilized to qualitatively analyze the pore networks of shales. Advanced physical experiments and numerical simulation techniques, including step-by-step rock pyrolysis, solvent extraction, and NMR, were introduced to characterize shale oil adsorption and movability. By the comparative analysis of the occurrence space, it is found that the image observation technique especially focuses on concentrated pores, such as organic matter-hosted pores. The fluid injection technology yields particular pore size information, which should be calibrated using other information. The 3D digital core, demonstrating the spatial distribution of minerals and pores, is an effective input for shale oil flow simulation. Geological controls analysis about oil retention in organic-rich shales has found that the inorganic matter pores and fractures are probably the “sweet spot” of shale oil, due to the low oil adsorption and high light hydrocarbons content. Many physical experiments measure the total free oil content but neglect the hydrocarbon–rock interaction and the sequential migration of hydrocarbon compounds. Thus, micro-scaled experiments measuring the hydrocarbon adhesion forces are needed to uncover the occurrence mechanism of shale oil in the future.

The Face Stability Analysis of Shield Tunnels Subjected to Seepage Based on the Variational Principle

The stability of tunnel face remains a great challenge for tunnel engineers, especially when excavation is in a complex stratum under the water table. This paper aims to investigate the stability of soil in the front of a shield tunnel face induced by the presence of insufficient cabin pressure under the water table, on the basis of a variational principle and an upper bound theorem. The analytical expression of the rupture surface for the tunnel face is obtained, and the shapes of the rupture surface are plotted. Comparisons are made to check the present approach against the solution provided by numerical simulation techniques in order to show that the proposed method is valid. The parameter analysis indicates that the groundwater seepage has a significant effect on the range of the rupture surface for the shield tunnel face.

Editorial Conclusion for the Special Issue “Advances in Computational Mechanics for Symmetrical Engineering Systems”

In this Special Issue, the recent advances in computational mechanics for symmetrical engineering systems are reviewed, including many novel techniques in mathematical modeling, numerical simulation, uncertainty quantification, optimization theory and artificial intelligence that were developed to provide reliable solutions to symmetry-related mechanical problems [...]

Математическое моделирование потери устойчивости локальных расслоений, полученных в результате скоростного удара

Delamination of a composite may occur as a result of high-speed impact under the action of shock-wave unloading. Delamination could grow further under operation with the subsequent composite destruction. This paper presents analytical expressions for values characterizing the delamination critical loss of stability and describing their non-linear delaminating deformation resulting from the impact. Elastic characteristics of the thin-walled delamination of a multilayer package, elastic characteristics of separate layers included in it depending on the shear modulus, elastic moduli, Poisson ratio, thickness, and orientation angle of fibers of the unidirectional layer were determined. A technique for numerical simulation and calculation of the structural elements made of layered composite materials with allowable defects such as delamination was developed in the ANSYS Mechanical system to solve problems of the plates’ supercritical behavior.

Low salinity water and polymer flooding in sandstone reservoirs: Upscaling from nano-to macro-scale using the maximum energy barrier

In this work, the flooding processes of low salinity waterflooding and low salinity polymer flooding (LSWF and LSP) in sandstone reservoirs were mechanistically modelled at nano-and macro-scales. Triple-layer surface complexation models were utilised to simulate interactions at the oil-brine and sandstone-brine interfaces. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was applied to describe the stability of interfacial films in crude oil-brine-sandstone rock systems. The novel application of the maximum energy barrier (MEB), calculated from the interaction potential of the DLVO theory, as an upscaling and interpolant parameter to adjust relative permeability curves as a function of reservoir properties is proposed in this work. Numerical simulations using the commercial simulator CMG-STARS were used in tandem with the surface complexation models and film analysis to evaluate the performance of LSWF and LSP in sandstone reservoirs.Results of the numerical simulations showed that the LSP gave significantly higher oil recovery compared to standard polymer flooding because of its utilisation of wettability alteration due to LSWF and the improved mobility control due to LSP. A comparison between studied injection processes i.e. low and high salinity waterflooding, and low and high salinity polymer flooding, revealed that oil recovery as a result of wettability alteration is significantly higher than that of mobility control. Further analysis indicated that temperature affects the wettability alteration favourably, and the polymer slug viscosity unfavourably. However, the temperature effect on the wettability was found to be more pronounced. The workflow presented in this study provides valuable guidelines in screening the appropriate sandstone reservoirs for LSWF and LSP applications using the numerical simulation techniques through the upscaling from nano-to-macro-to-field scale.

Hurricane Simulation and Nonstationary Extremal Analysis for a Changing Climate

Abstract Particularly important to hurricane risk assessment for coastal regions is finding accurate approximations of return probabilities of maximum wind speeds. Since extremes in maximum wind speed have a direct relationship with minima in the central pressure, accurate wind speed return estimates rely heavily on proper modeling of the central pressure minima. Using the HURDAT2 database, we show that the central pressure minima of hurricane events can be appropriately modeled by a nonstationary extreme value distribution. We also provide and validate a Poisson distribution with a nonstationary rate parameter to model returns of hurricane events. Using our nonstationary models and numerical simulation techniques from established literature, we perform a simulation study to model returns of maximum wind speeds of hurricane events along the North Atlantic coast. We show that our revised model agrees with current data and results in an expectation of higher maximum wind speeds for all regions along the coast, with the highest maximum wind speeds occurring along the northeast seaboard.

Risk Assessment for Critical Flood Height of Pedestrian Escape in Subway Station

The escape of pedestrians in the subway station is hampered by floods created by heavy rain. In order to explore the critical flood level in a subway station so that pedestrians can escape safely, the case study of the Mingxiu Road subway station in Nanning, China, was conducted using numerical simulation techniques. In total, 30 groups of sample pedestrians with different walking speeds and numbers were randomly generated by the Monte Carlo method, and 3D simulation software was used for escape simulation. The simulated escape data were put into the SVM model, and the maximum pedestrian capacity and minimum speed of pedestrians were solved successfully with different conditions of the Mingxiu Road subway station. Then, a 1:1 contour model of the pedestrian was constructed to simulate the flood resistance of the pedestrian escaping at the minimum speed. The flood resistance and the friction force between the pedestrian and the ground were compared to calculate the critical escape flood level height, and the critical escape flood level height of an adult, child, and elder was 87.4 cm,75.5 cm, and 83.0 cm, respectively.

Electrolyte-Centric Thermal Model of Li-Ion Battery Under Abuse Conditions

Safety is an important concern in Li-ion battery operation and storage. As both energy stored per unit volume and current densities have increased in these batteries, energy dissipation in the form of heat has become one of the main issues for proper battery operation. As temperature increases, secondary chemical reactions may be initiated. These reactions release more heat and undesired products, triggering an auto-catalytic feedback process, commonly classified as thermal-runaway mechanisms. This can potentially lead to a complete degradation of the battery and possible explosion or combustion of the battery components.Several researchers have worked on developing models to predict thermal behavior under conditions with potential thermal runaway outcomes on Li-ion batteries. The first studies proposed a model that emulates the solid electrolyte interface (SEI) decomposition and regeneration reactions on a standard 18650 cylindrical cell. Later works extended these models and included the reactions of cathode decomposition and electrolyte decomposition with potential combustion. Although macroscopic level energy balance helps predict potential thermal behavior in a battery of multiple layers, the study of all the different transport mechanisms that happen inside a single layer battery is essential for a better understanding of the process taking place when temperature begins to rise. With the aim of improving heat dissipation inside a battery, the electrolyte is a key component to consider as it can potentially handle heat flux easier through convection within the solution.Our work investigates spatially dependent electrolyte conditions in the presence of a thermal gradient to produce an electrolyte-centric thermal runaway model. Non-current conditions are considered for emulating oven-test experiments or storage conditions. Furthermore, this specific case study aims to extend our previous model by accounting for the influence of the Joule effect on simulating a battery's operational conditions. The purpose of the study is to model transport mechanisms that can potentially lead to thermal degradation of the battery. Li-ions, momentum, and thermal flux are the main components of the analysis. This objective is achieved by using numerical simulation techniques. A detailed understanding of the transport processes taking place inside the battery will contribute towards mitigating damage induced due to thermal abuse conditions. Figure 1

Modeling of CSTR flow field for Agaricus bisporus residue fermentation based on CFD numerical simulation.

Agaricus bisporus production gets a lot of residues, which could be fermented by a continuous stirred tank reactor (CSTR). This research was conducted to study the characteristics of the multiphase flow field in the reactor and its influence on the efficiency of biogas production in the CSTR fermentation process of Agaricus bisporus residue by using CFD numerical simulation technique. The aim is to reveal the relationship between the reactor operating conditions, flow field characteristics, and biogas production efficiency at the micro-level. We compared the results of different turbulence models by evaluating the power quotients and flow quotients with the experimental results to derive the most suitable flow field model inside the reactor for the Agaricus bisporus residues. The results showed that, under the condition that the number of grids does not affect the simulation results, and considering the model accuracy and efficiency, the numerical method can be chosen as the multiple reference frame (MRF) method of the second-order upwind discrete scheme with the realizable k - ε model. In this way, we can make use of edible mushroom residue as a substrate for resource utilization and provide basic data and theoretical basis for the design and scale-up with anaerobic fermentation to biogas reactor.

Electricity-reaction–diffusion system for microbially induced carbonate precipitation

Microbially induced carbonate precipitation (MICP) has attracted attention as a novel soil-improvement technique. The precipitation and growth of calcium carbonate on the surface of sand and in its pores can be simulated using the recently proposed numerical simulation techniques. However, these simulations have not incorporated certain parameters, such as electrical properties and adsorption. The current study proposes a novel coupling system that considers the adsorption of microorganisms and dissolved ions due to the weak electrostatic field generated on the surface of sand. Additionally, the Michaelis–Menten model was introduced into the system for the enzymatic reaction of ureolytic bacteria, the Monod model for bacterial growth, and a chemotaxis model. To validate the proposed simulation model, previously reported experimental and computational results were compared with the suggested simulation results. Consequently, the calcium carbonate precipitation obtained with the simulation model was 0.335 μmol/mm3 at 10.3 h, which is close to that obtained by the experiment of 0.315 μmol/mm3. Moreover, the spatial distribution of calcium carbonate was consistent with the precipitation pattern of the active bonding structure obtained by the traditional experiment.

Experimental and numerical investigation of strain inhomogeneity in zirconia during a Brazilian test

Zirconia-based ceramics is a material with a wide variety of applications. Problems of strength of such ceramics, being prepared by different methods, under different loading conditions, and with different porosity, are of practical importance. Inhomogeneous strain distributions in different-porosity zirconia ceramics during a Brazilian test are studied using the digital image correlation and numerical simulation techniques. Spatiotemporal patterns of strain localization across the compression axis are obtained. It is found that strain components are nonuniformly distributed over the specimen surface, and zirconia experiences macroscopically localized deformation. The fracture patterns reveal the triple-cleft mode. Numerical simulations performed both for a homogeneous material and with consideration for the material inhomogeneity show that different models yield different patterns of inhomogeneous strain distribution under diametral compression. Account for internal friction and dilatancy provides eight-shaped cracks. Random distributions of strength and elastic properties over the computational domain built with the use of pseudo-random number generators and/or Gaussian random fields allow one to control the size of strain inhomogeneities.

Stokes-Cahn-Hilliard formulation in sliding bi-periodic frames for the simulation of two-phase flows

A direct numerical simulation technique is proposed in this study for droplet emulsions in simple shear flow in Newtonian-Newtonian liquid systems. We combine the sliding bi-periodic frame with the diffuse interface method in the finite element framework to treat the multi-drop problem without wall effects. We employ the standard velocity-pressure formulation in a creeping regime and the diffuse interface method with the Galerkin weak formulation. Sliding bi-periodic frame constraints are implemented by Lagrangian multiplier. The results are presented for the morphological development of a single drop, two drops, and multiple drops in a sliding bi-periodic frame. To preserve the identical solution for a given relative configuration of droplets (with different droplet locations) within the context of the bi-periodic frame, a phase-translation method is proposed. The method corrects the inconsistency in the time integration, which yields discrepancy in flow solution particularly for problems with thin interfaces. By applying this procedure, accurate solutions for a thin interface are obtained regardless of location of the identical relative configuration of droplets. The effect of phase-field translation is also analyzed for the coalescence of two drops. For the first time, the sliding bi-periodic frame has been implemented with the combination of the standard finite element method and the diffuse interface method, which can be easily extended to more complex rheological liquids to solve industrially important problems.

Prediction of the anastomosis angle of arteriovenous fistula in hemodialysis to standardize the surgical technique.

Arteriovenous fistula (AVF) is the preferred route of vascular access in hemodialysis. The primary reason of fistula failure is intimal hyperplasia (IH), which leads to stenosis. Wall shear stress (WSS) and disturbed flow are the critical parameters in the formation of IH. The primary goal of this study is to explore the influence of anastomosis angle on WSS and venous outflow rate, as well as to find the ideal angle of anastomosis for AVF to standardize surgical technique. Three-dimensional idealized geometries of end-to-side type AVF for the five various angles of anastomosis are considered in this study. The WSS, blood flow rate at the venous outlet for non-Newtonian, pulsatile blood flow are calculated using a numerical simulation technique. The WSS is higher at 75° compared to other angles and least at 45° for pulsating arterial inflows. The WSS is moderate at 30°, 60° and 90°. On the arterial bed and outer wall of the vein, immediately after the anastomosis, the recirculation zone is observed. At an angle of 45° and 90° anastomosis, the outflow rate is greater at distal venous end. If one believes that high wall shear stress causes IH within the AVF, the results suggest that the AVF should be formed at a 45° angle to avoid IH. However, if one believes that low wall shear stress causes IH within the AVF, the results suggest that AVF should be formed at either 30° or 75° to avoid IH. The findings spotlight the importance of anastomosis angle in determining AVF hemodynamics.

Barrier-free duct muffler for low-frequency sound absorption

We demonstrate a duct muffler design that operates in the low-frequency range (<2000 Hz). The device contained a pair of coupled annular Helmholtz resonators (HRs) and porous material stuffing. HRs were installed as side branches of a circular tube to avoid affecting the ventilation. Porous materials were employed to form an asymmetric intrinsic loss in the HR pair and enable the device to achieve perfect sound absorption. An analytical model based on the temporal coupled-mode theory was derived, and a numerical simulation technique for structural design was introduced and verified. The experimental study demonstrated the effectiveness of the design methodology and illustrated that the device can achieve near-perfect sound absorption in the desired frequency range. A symmetrical configuration of the HRs also experimentally proved to be able to conduct sound absorption for sound incident from both sides of the duct. This study provides a solid foundation for the application of the designed muffler and an analytical explanation of the corresponding sound absorption mechanisms.

Implications of groundwater flow on preservation of heavy and extra-heavy oil accumulations in Southern Llanos Basin, Colombia

The southern sector of the Llanos Basin in Colombia is a heavy and extra-heavy crude oil province where it has been hypothesized that hydrodynamic flow has influenced the potential of hydrocarbon storage and production. In this area, the hydrodynamic flow and the geochemical nature of the fluids are thought to decrease the potential for hydrocarbon retention. This work provides a comprehensive view on the impact of the regional hydrodynamic flow on the retention of the heavy oil accumulations present in the reservoirs that are part of the most important regional flow unit identified in the Southern Llanos Basin. The Basal Flow Unit (BFU) constitutes a basin-scale flow unit that hydraulically and laterally connects rocks from the Cretaceous (west) to the Oligocene (east) and extends from the basin's southwestern margin up to hundreds of kilometers within the Llanos foreland basin, and whose main water recharge zone has been identified towards the eastern flank of the Serranía de la Macarena. To understand the impact of the physicochemical properties of the fluids on hydrocarbon retention, we analyze the relationship between hydraulic data and the main characteristics of the fluids present in the BFU as well as their spatial distribution. This analysis integrated information from hydraulic heads, SARA analysis (Saturates, Aromatics, Resins, and Asphaltenes), Whole Oil Gas Chromatography analysis, API-gravity, and oil densities. In addition, hydrochemical analyses of the primary ions were performed in groundwater samples from the BFU, which was integrated with deep resistivity data measured in producing and exploratory oil wells in the area. The results allowed identifying the southwestern corner of the southern Llanos Basin as the area with the highest hydrodynamic flow impact, and therefore, the area with the least potential for hydrocarbon retention. We attribute the main causes to: 1) the proximity to recharge areas, and 2) the low contrast of fluids densities (freshwaters and highly biodegraded heavy crude oils), implying high Tilt Amplification Factor (TAF) values (10–100). In addition, the highest values of hydraulic heads (200–400 m), groundwater with the lowest ion concentrations (up to < 5 ppm Cl−), highly biodegraded crude oils, and the presence of poorly developed geological structures with low dip angles occur in this area, which allows us to interpret that the water washing process has decreased the hydrocarbon retention potential for this sector of the Llanos basin. Furthermore, gradual changes in resistivities (decreasing eastward) and ions concentration (increasing eastward) in groundwaters suggest the eastern flank of the Serranía de la Macarena as the main recharge zone of meteoric waters into the BFU. Finally, numerical simulation techniques were used to analyze the behavior of hydrocarbon drainage under hydrodynamic conditions, obtaining a first approximation to the average linear groundwater flow velocities between 10−3 and 10−4 ft/day.