Two-dimensional Numerical Model Research Articles

Analysis of the Effect of Applied Load on Crevice Corrosion Behavior

A two-dimensional numerical model incorporating solid mechanics, electrochemistry, mass diffusion, and ion migration processes is developed to investigate the load effect on the crevice corrosion. The model is a transient model of crevice corrosion occurring in cracks of 304 stainless steel in a dilute NaCl solution, and the interaction between stress and electrochemical corrosion was considered. By solving the multiphysical coupling model in COMSOL, the effect of applied load on electrochemical corrosion in the crack tip region was calculated, and the local corrosion current density in the crack tip region with stress concentration within the crack was also calculated by using the Tafel relationship. The distribution of Fe2+ ion, Na+ ion, CL− ion, and H and O2 substance concentrations within the crack cavity is predicted by the equation analysis of substance transport. The results show that metal oxidation is more clearly affected by plastic deformation, the rate of hydrogen evolution reaction increases with stress enhancement, and the oxygen absorption reaction is not affected by stress strain. The distribution of iron ions, hydrogen, and oxygen within the crack is affected by the electrochemical reaction rate, and the distribution of iron ions, sodium ions, and chloride ions is affected by the electrolyte potential.

Liquid free surface dynamics in the falling of steel pipes attached to the concrete base- numerical study

Water entry is an object falling from the air into the water at a certain velocity from a specific high. Object destroys the structure of free surface accompanied by water splash ejected from the sides of the object during penetration. Fundamentally, this phenomenon is unsteady, turbulent, and nonlinear, with phases mixing without any phase changes. In this paper, a two-dimensional numerical model of six degrees of freedom based on the realizable k−ε turbulent model using the dynamic mesh and volume of fluid (VOF) method was established to simulate the water entry and the immersion of the three steel pipes attached to the concrete base. The effects of Froude Number on penetration depth and the amount of impact force have been studied. Numerical analysis showed that with the increase of Froude Number and contact surface, the maximum force applied to the base of the structure during the splitting of the free surface of the liquid increases suddenly. When the structure enters the water at a certain angle, due to the convenient location of the center of mass, an assemblage of pipes and concrete base always maintains its balance and causes less impact force to the structure.

Effects of mushy-zone parameter on simulating melting and solidification phenomena inside a spherical capsule

The research on latent heat storage technology is beneficial for the large-scale popularization and application of energy storage technology. In order to solve the difficulties in the latent thermal energy storage (LTES) technology, numerical studies of the solid–liquid phase-change process of LTES units using the enthalpy-porosity method have become research hotspots. Among them, the importance of studying the mushy-zone parameter has been neglected. In this paper, a two-dimensional numerical model is created based on the enthalpy-porosity method to investigate the effects of different mushy-zone parameters within a wide range [104–108 kg/(m3·s)] on the melting and solidification processes of the spherical phase change material capsule. A comprehensive examination of the fluid flow and heat transfer characteristics during two phase-change processes is conducted. Meanwhile, the morphology of the solid–liquid phase boundary and the evolution of the mushy zone under different mushy-zone parameters are discussed in detail. It is worth mentioning that a new analytical perspective is innovated by proposing the “eccentricity phenomenon,” and the eccentricity law is further explored. The results show that the influence mechanisms of the mushy-zone parameters on the melting and solidification processes differ greatly. This paper emphasizes the significance of exploring the mushy zone and provides adequate guidance for future simulation studies to determine the mushy-zone parameter.

Effect of nanoparticle size during discharging of NePCM in TTHE: A numerical investigation

The addition of nanoparticles is an effective strategy to upgrade the thermo-physical properties of phase change material. This paper concerns the effect of nanoparticle size on the discharging (solidification) of nanoparticles enhanced phase change material in triple-tube heat exchanger. The commercial tool Ansys Fluent is used to create the two-dimensional numerical model. For solidification, enthalpy-porosity has been adopted, while the change in properties of the material due to addition of nanoparticles is defined by the user defined function. The size of nanoparticles is varied as 20 nm, 30 nm and 40 nm during the analysis. The model has been validated against the reported result in the literature. The results from the transient numerical analysis shows that the total discharging time being shortened by around 25% and 40% for the phase change material with 30 nm and 40 nm size nanoparticles respectively compared to the phase change material with 20 nm size nanoparticles. It is observed that the drop of average temperature during the discharging process increases while increasing the size of nanoparticles in phase change material.

Influence of environment on self-propagating reactions in Al/Ni multilayer foils

Reactive aluminum–nickel multilayer system shows exothermic energetic materials which act as a heat source for packaging and bonding of microsystems. The main challenge is controlling the self-propagation reaction velocity and temperature generated by thermal management through different thermal conductive substrate materials. The current work investigates the heat distribution of Al/Ni multilayer foils from different thermal conductive substrates which act as heat sink materials during the self-propagating reaction. A two-dimensional numerical model was developed to study thermal conductive heat loss and substrate thermal properties on the self-propagating reaction in Al/Ni multilayer foils. The self-propagating reaction was introduced on the surface of the foils by an electrical spark. Here we investigate the minimum critical thickness of Al/Ni multilayer foils which shows the self-propagation reaction on different substrates and verified from the two-dimensional numerical model. The outcomes of this investigation will facilitate the integration of Al/Ni multilayer foils on different substrates as intrinsic heat sources for different applications of micro/nanodevices.Graphical abstract

Progressive Evolution Model of Fault Water Inrush Caused by Underground Excavation Based on Multiphysical Fields

Underground fault water inrushes are frequent hydrogeological disasters associated with underground mining and tunnel construction projects. In this study, we analyze the water inrush mechanism of underground engineering by building a numerical simulation model to evaluate the process of water inrush, analyze water inrush changes under various working conditions, and consider the fluid-solid coupling effect of rock mass and water. These analyses provide effective suggestions for preventing water inrush from faults. The study establishes a two-dimensional numerical model based on Darcy’s law and plane strain field to analyze water inrush from faults in underground engineering. The analysis shows that factors such as aquifer pressure, permeability between the aquifer and fault zone, and permeability sensitivity coefficient are important considerations that affect the occurrence of water-inrush disasters. The study also identifies the sudden change in water inrush speed at the fault zone and the roadway when the working condition is changed as an indication of the nature of water inrush at the fault. Additionally, the study presents preventive measures such as drainage grouting to ensure the safety of underground engineering constructions. Overall, this research provides important insights into the causes and effects of water inrush from faults and can inform practical measures to mitigate the risks associated with underground engineering.

Two-dimensional numerical modelling of viscous emulsion drops coalescence in a constricted capillary channel

We study numerically the coalescence of viscous emulsion drops in a two-dimensional semi-elliptical shape constricted channel. The Navier-Stokes equations are solved using the finite element method and the oil-water interface is tracked using the level-set techniques. Effects of interfacial tension, inertia, viscosity ratio, droplet size, and constriction shape on the droplet coalescence and average viscous pressure drop along the channel are investigated. It is found that at high interfacial tension, droplets are circular, approach each other more quickly, coalesce at the constriction entrance, and give higher pressure drops. At intermediate interfacial tension, the onset of coalescence occurs downstream of the constriction entrance while at very low interfacial tension, no coalescence of the droplets was observed. Inertia is found to be negligible effects on the coalescence of the droplets. High inertia gives less viscous pressure drop. Less viscous droplets are more likely to quickly coalesce compared to high viscous drops. Higher viscous drops create more resistance to flow. Moreover, larger size drops are responsible for more quick coalescence and tend to create more viscous pressure drops. In addition, we found that circular constriction offers less resistance to fluid flow. We hope that these numerical results would be beneficial while displacing oil from the underground reservoirs.

Dynamics of microplastic transport and accumulation in a rural coastal area: Insights from the Otsuchi Bay, a small ria in Sanriku, Japan

Microplastic (MP) pollution in coastal areas has received increasing attention recently. However, studies focused on MP pollution in rural coastal areas remain limited compared to those in metropolitan coastal areas. This study observed MP particles accumulated on the seafloor of the Otsuchi Bay, a small ria bay located on the Pacific coast, Sanriku, Japan. The MP concentrations in the sediment ranged from 2.6 ± 0.3 to 13.6 ± 9.8 pcs g−1 dry weight (DW) and 2.6 ± 1.4 to 5.1 ± 1.2 pcs g−1 DW in March and September 2021, respectively. No significant difference in MP concentrations was detected between March and September. The MP concentration in the Otsuchi Bay was lower than that observed in other highly populated coastal areas but was relatively high considering the population size of the catchment area. MP particles smaller than 1000μm were the most prevalent, accounting for 96.3% of all MP samples. MP size at the bay head was smaller than that at the central bay for high-density MPs; however, the relationship was reversed for low-density MPs. Analysis of the MP distribution pattern using a two-dimensional numerical model suggests that the horizontal distribution of MPs in the Otsuchi Bay depends on the size and density of MP particles. It is also strongly influenced by both the tidal oscillating currents characteristic to the bay and vertical terminal velocity of MP particles. Sedimented MP distributions in a bay with a small catchment population with limited MP sources shed light on our understanding of MP transport dynamics.

Numerical study on the thermal performance of foam-metal composite phase change material in different force fields

To make a better application of phase change material (PCM) in the thermal management of aerospace systems, this paper investigates effects of the variation of foam-metal pore structure on the thermal performance of composite PCM (CPCM) subjected to different force fields. A two-dimensional numerical model based on the enthalpy-porosity method and the two-temperature energy equation is developed and verified with the experimental data. The thermal behavior of CPCM with different porosities (ω = 20 PPI, ε = 0.91, 0.93, 0.95 and 0.97) and different pore densities (ε = 0.95, ω = 10, 20, 40 and 80 PPI) are investigated under centrifugal acceleration conditions of 0, 5 and -5 g, respectively. A novel index of "end-state isobars" is introduced to describe the melting process of CPCM. The results show that the isotherms of CPCM liquid phase evolve gradually towards the interface parallel to end-state isobars in all conditions. At 0 g, decreasing the porosity effectively improves the thermal conduction of CPCM and slows down the approaching of the isotherms to the end-state isobars. Similarly, increasing the pore density significantly weakens the natural convection of liquid PCM and can also slows down the approaching isotherms to the end-state isobars. At 5 g, the isotherms can match exactly with the end-state isobars, after which the heat transfer process mainly depends on conductive. And decreasing the porosity can significantly improve the thermal performance of CPCM, while adjusting the pore density has almost no effect. At -5 g, the natural convection strength of CPCM is enhanced, changing porosity has limited effect on the heat transfer performance of CPCM, while decreasing pore density can significantly enhance the heat transfer performance. The results may provide some valuable reference for the evaluation and design of latent heat thermal energy storage (LHTES) system suitable to the aerospace field.

Melting and solidification performance investigation of latent heat storage unit designs for low-temperature solar thermal applications

Integrating latent heat storage with solar thermal systems is a promising way to deal with the problem that solar energy is not always available or is only available for short periods of time. An efficient design for latent heat storage is the shell and tube type latent heat storage unit (ST-LHSU). Literature suggests that the performance of ST-LHSU can be improved significantly by modification in design. Therefore, the current article presents a comparative investigation of different horizontal ST-LHSU designs for melting/solidification performances. For this study, four alternative ST-LHSU designs representing the changes in the outer shell's cross-sectional area have been chosen. A validated two-dimensional numerical model for the selected ST-LHSU designs has been formulated and solved using the commercially available CFD solver. In the initial phase, the selected ST-LHSU designs have compared for melting and solidification performance. Complete melting in Design-IV happens 25.5 % and 37.4 % faster than in Design-III and Design-I, respectively. Design-I was the most effective design for entire solidification since it reached complete solidification 3.65 %, 19.57 %, and 45.02 % faster than Designs-II, III, and IV, respectively. In the second phase, the modification in Design-I has been done to reduce its total thermal cycle time. The total thermal cycle time of the modified Design-I is 24.58 % shorter than that of the original Design-I, 37.94 %, and 40.21 % shorter than Design-III and IV, respectively. The utilization of melting/solidification techniques like fins, metal foam, and nanoparticles can be studied in the future with the modified Design-I.

Numerical investigation of a novel method of laser assisted cryopreservation of biological tissue considering non-fourier heat conduction

The present article proposes a numerical model for a novel laser assisted cryopreservation through vitrification of biological tissue. A two-dimensional numerical model is developed considering the non-Fourier heat conduction. The Finite Volume Method is used for discretization of the governing differential equation while the Tri-diagonal Matrix Algorithm (TDMA) is used for solving the resulting discretized algebraic equation in order to obtain the temperature distribution inside the tissue domain. The existing enthalpy method is modified considering the thermal relaxation time to capture the freezing front. With the increase in thermal relaxation time value, rate of heat transfer and rise in temperature during laser heating decreases and rate of heat loss during freezing also decreases. This reduces the length up to which vitrification is achieved. So, a proper size of the tissue is to be chosen to achieve the desired freezing rate. This length may vary based on the laser parameters and the thermal relaxation time. However, the validity of the present study may be examined experimentally in real ambient conditions before application in tissue preservation.

Numerical Simulation of Two-Dimensional Dam Failure and Free-Side Deformation Flow Studies

A dam breaking is a major flood catastrophe. The shape, depth, and wave Doppler effect of initial water flow are all modified as a result of the interaction of the water body with downstream structures after a dam breach, forming a diffraction and reflection flow field. This study investigates the dam breaking problem of a single liquid, by creating a two-dimensional simplified numerical model using the VOF approach, analysing the interaction and effect between barriers of various forms and the dam failure flow, and explains the problem of a complex flow mechanism involving significant deformation of the free surface of a medium. According to the findings, obstacles of varying forms could obstruct the dam break’s water flow to various degrees, and the viscous dissipation characteristic of the water body at the edge of the obstacle is closely related to the slope of the site. The numerical simulation presented in this study is validated, demonstrating its accuracy for both the gate-pulling and downstream wet-bed scenarios.

Application of the Iber Two-Dimensional Model to Recover the Water Quality in the Lurín River

The Lurín River is one of the main sources of water for the city of Lima. However, the discharge of domestic wastewater, the presence of dumps, and long periods of drought cause the deterioration of the water resource. In this study, DO, BOD5, E. coli, T, EC, TSS, U, and h were monitored at 13 monitoring points spread over 20 km of river influence. This information was used to calibrate the parameters of Kdbo, Kaire, Kdos, and Kdec in the Iber two-dimensional numerical model, obtaining values of 0.55 d−1, [4.84 d−1–80.65 d−1], 10 g O2 m−2d−1, and [1.49 d−1–15.42 d−1], respectively, with efficiencies ranging from “very good” to “satisfactory”. In the hydraulic model, a discretization of the channel, banks, and plains of 3, 5, and 7 m, respectively, was considered, resulting in a computational calculation time of 4 days in each simulation. The greatest contamination occurs in July at km 5 + 400 up to the Pan-American bridge. Therefore, it is proposed to recover the river by optimizing the San Bartolo Wastewater Treatment Plant (WWTP) and a new WWTP in Pachacámac to avoid diffuse contamination, with discharge flows of 0.980 m3s−1 and 0.373 m3s−1, respectively, and 4 mg L−1, 15 mg L−1 and 1000 NMP/100 mL for DO, BOD5, and E. coli, respectively.

Assessment of Wave Attenuation Performance of the Tanjung Piai Breakwater Using Spectral Wave Analysis

Tanjung Piai is a Malaysian heritage site situated at the southernmost tip of the Asian continent. Tanjung Piai provides a conducive coastal habitat for many mangrove species. Coastal erosion resulting in shoreline retreat was detected dating back to the 1930s. The erosion rate had accelerated until the early 21stcentury due to various factors including to coastal developments in the vicinity of Tanjung Piai. This led to significant land mass losses threatening the coastal eco-system. Previously, various measures were adopted to permanently harden the shoreline. Nevertheless, these approaches prevented sea water from reaching the mangroves, which in turn resulted in significant mangrove depletion along the shoreline. A series of offshore breakwaters were subsequently planned and constructed to reduce the wave energy prior to reaching the mangrove shoreline. The breakwaters are anticipated to be able to mitigate the erosion problems and extend the width of the existing mangroves belts along the wave-exposed coastline. The wave climate of Tanjung Piai has changed drastically in the past decades, potentially due to rapid coastal development in the vicinity. This study aims at re-evaluating the wave attenuation performance of the Tanjung Piai breakwaters subjected to the latest wave climate (i.e., offshore waves, squalls, and wind-generated waves) and bathymetry by means of two-dimensional numerical modelling –MIKE21 SW. The latest survey of the site and the most recent breakwater design details have been incorporated in this modelling study. Two scenarios have been conducted to determine the wave climates i.e., pre-and post-construction of the breakwaters. The alterations of the wave heights for both scenarios are taken as a basis to ascertain the actual wave attenuation performance of the breakwaters. The numerical results show that the breakwaters are able to reduce offshore wave heights up to 66%. The breakwaters can attenuate offshore waves more effectively than squalls and wind-generated waves.

Ductility evaluation and flexural failure mode recognition of reinforced Ultra-High performance concrete flexural members

Although ultra-high performance concrete (UHPC) exhibits material tensile ductility far in excess of that expected from conventional or high-strength concretes, structural UHPC members typically fail in flexure due to reinforcement rupture after crack localization, which may result in a low structural ductility. In the flexural design of reinforced UHPC (R-UHPC) members, attention should be paid to addressing the issue related to the low structural ductility due to crack localization. This study firstly develops a two-dimensional numerical model to simulate the flexural response of R-UHPC beams, and the numerical results agree well with the experimental results of the load–deflection curves as well as the failure modes. Parametric analyses are then carried out to examine the effect of the flexural reinforcement ratio, tensile strength of steel reinforcement, tensile behavior of UHPC and compressive strength of UHPC on the flexural failure mode and ductility behavior of R-UHPC members. The results indicate that when the failure is controlled by fracture of tensile steel bars after crack localization, higher reinforcing ratio, higher steel post-yield hardening strength, and lower steel fiber volume lead to more ductile behavior. When the failure is controlled by crushing of UHPC, however, higher reinforcing ratio and lower UHPC compressive strength lead to a lower ductility. In addition, a flexural failure mode recognition method is proposed for R-UHPC flexural members, whose accuracy is verified based on the available experimental results of 105 R-UHPC flexural members. Finally, a minimum flexural reinforcement ratio is proposed to avoid low structural ductility in R-UHPC flexural members.

A Two-Dimensional Unsteady FDTD Model for Radon Transport with Multiple Sources Emanation from Soil Layers

A two-dimensional numerical model for radon transport based on the finite difference time domain (FDTD) method have been developed. The model is governed by the radon transport equation taking into account the mechanisms of diffusion, advection, and decay. The purpose of this model is to simulate the evolution of radon concentration which can be influenced by various parameters including depth and diffusion coefficient of the soil layer plus the velocity and initial concentration of radon. The obtained results were compared to an analytical solution to demonstrate the ability of this model for predicting the spatio-temporal evolution of radon transport in the porous media of soil layers.

Coupling mechanisms of displacement and imbibition in pore-fracture system of tight oil reservoir

Fracturing and water flooding have been popular technologies to achieve the effective development of tight oil reservoirs in recent years. However, in the late stage of production, the oil recovery rate declines with a rapid increase in the water cut. Water huff-puff could improve reservoir energy; however, the displacement and imbibition in the micro-nano pore throat and fracture systems are complex processes with unclear characteristics and position. Therefore, it is urgent to study the coupling mechanisms of oil-water displacement and imbibition in tight oil reservoirs. In this work, based on the phase field method of COMSOL Multiphysics software, we establish a two-dimensional microscopic numerical simulation model of the pore-fracture system, and carry out displacement-imbibition simulation programs of different injection media (water and surfactant) and injection methods (displacement, displacement-imbibition). By comparing the saturations and pressure distributions of different simulation programs, we analyze the changes in the oil-water interface, and summarize the action conditions of counter-current imbibition and pore throat limit. Finally, reasonable development suggestions are proposed for tight oil reservoirs. Cited as: Pi, Z., Peng, H., Jia, Z., Zhou, J, Cao, R. Coupling mechanisms of displacement and imbibition in pore-fracture system of tight oil reservoir. Capillarity, 2023, 7(1): 13-24. https://doi.org/10.46690/capi.2023.04.02

Numerical modeling of dam break induced flow through multiple buildings in an idealized city

This study presents two-dimensional dam break numerical modeling through an urban area. There are three approaches to defining a building in numerical modeling, as a wall boundary, contour, and Manning, which have been widely used. However, there is no research that compares and evaluates the accuracy of each approach. Thus, this study aims to determine the best approach, in term of accuracy, and evaluate its reliability by comparing the numerical modeling approach's results to experiment results. The model was developed based on the Saint-Venant equations, then solved using the MacCormack method with a numerical filter. The authors first utilized a single-building experiment to determine the best approach. The results indicated that the wall boundary approach had the highest accuracy based on MDAPE, with the lowest value of 13.47%, followed by Manning with 16.48%, and Contour with 21.46%. A multiple-building case is then used to evaluate the best approach's reliability. The results show high similarity to the experiment results. However, the wall boundary approach cannot be used when the building is submerged or has a height variation, since these approaches cannot define the building's height. Moreover, Manning approach cannot be considered as a building approach, since the approach does not reflect the behaviour of the building. Thus, the authors recommend the wall boundary approach when the building does not have a height variation and is not submerged, and the contour approach otherwise.

The partial electrical breakdown mechanism by high voltage electric pulses in multi-fractured granite

High-voltage electric pulse (HVEP) technology has currently become a new efficient rock breaking method. In order to reveal the influence of internal fracture characteristics of heterogeneous granite on electric pulse rock breaking, the two-dimensional numerical model of multi-physical field coupling electrical breakdown of fractured rock is established, which the high-voltage electric pulse plasma generation in multi-fractured heterogeneous granite is realized from the coupling of circuit field, current field, breakdown field, heat transfer field and solid mechanics. This paper analyzes the influence of fracture porosity, fracture types and granite heterogeneity on the electrical breakdown of rock (i.e. the formation of plasma channel inside the rock). At the same time, the two-dimensional numerical model of electrical breakdown parameters, which considers the circuit structure parameters of the pulsed tool, the initiation and development of the electrical breakdown, the dependence between electrical breakdown intensity and time, and rock heterogeneity, are analyzed. The simulation results indicate that with the heterogeneity H of granite changing, the plasma channel inside the rock samples are different, while the time required for breakdown t and rock breaking volume Vrock of rock samples with different heterogeneous H will show obvious fluctuations; among the rock samples with different heterogeneity H, existing a single crack requires a longer breakdown time and the extreme value of the internal conductivity is also significantly larger. And then, the formation of plasma channel is directional selective, extending towards fractures and the weak electrical breakdown intensity. With the dip angle of the fracture increasing, the required breakdown time increases accordingly, and conversely, the broken volume decreases accordingly. The larger porosity of fracture is, the larger broken volume and the shorter required break down time of the rock sample. Furthermore, with the continuous action of electric pulses, multi-fractured rock form interpenetrating plasma channels to improve the rock breaking efficiency. The research results can provide help and theoretical support for optimization of electric pulse rock breaking parameters and the development of electric pulse drilling technology.

Seismic Performance of Three Ancient Stupas in Anuradhapura, Sri Lanka

Ruwanweli, Abayagiri and Jetavana stupas situated in Anuradhapura, are three ancient wonders of Sri Lanka. Renovations and restorations of these stupas were started in early parts in the 20th century and carried out until recently. Considering their geometric proportions, cultural and social importance, there is an impending need to assess these stupas for seismic performance to avert any possible damages due to seismic activities that might occur in the future. Further, this requirement has become more important due to some researchers’ predictions on intraplate activities in the behaviour of ancient stupas with respect to possible earthquake accelerations. In this regard, two-dimensional numerical models of the three stupas were prepared using SAP2000 v.14: generalpurpose software package. Both static and dynamic analyses were performed on numerical models for self-weight and two recorded acceleration histories, respectively. Two acceleration histories are from Mahakandarawa, Sri Lanka and Manjil, Iran. Material parameters of ancient bricks were obtained from previous literature works and experimental test results conducted on similar bricks of another ancient stupa in Sri Lanka. Considering the past records of earthquakes that have occurred in Sri Lanka, it was understood that all three stupas are in the safe realm under magnitude 4.7 earthquakes (Peak Ground Acceleration of 5.48x10-5 g). Even referring to the stress distribution with magnitude 7.4 Manjil earthquake (Peak Ground Acceleration of 0.4 g), both Ruwanweli and Jetavana stupas are in safe zone.