Two-dimensional Numerical Model Research Articles

Numerical Simulation of Hydrate Decomposition during the Drilling Process of the Hydrate Reservoir in the Northern South China Sea

The process of drilling in natural gas hydrate reservoirs in sea areas involves problems such as hydrate decomposition and wellbore instability. To study the response behaviors of a reservoir during the drilling process, a two-dimensional numerical model of drilling fluid invading a hydrate reservoir in a cylindrical coordinate system was established to simulate the processes of heat and mass transfer, gas–liquid two-phase flow, and hydrate formation and decomposition in the hydrate reservoir during the drilling process. Based on the hydrate reservoir at station W17, Shenhu area of the South China Sea, the physical property response of the hydrate reservoir under different drilling fluid temperatures and salinity values was studied. The simulation results showed that during the drilling process, the temperature and pressure of the reservoir respond rapidly in a large area, further promoting the hydrate decomposition in the reservoir around the wellbore and leading to secondary hydrate formation. Moreover, a high hydrate saturation zone appears near the decomposed hydrate area in the layer without free gas, which corresponds to the low water saturation and high salinity zone. The hydrate decomposition area in the layer with free gas is larger than that without free gas. The increase in the drilling fluid temperature significantly enhances the hydrate decomposition in both layers of the reservoir. The hydrate decomposition near the wellbore under the high drilling fluid temperature will cause a sharp increase in the pressure in the reservoir, leading to the flow of pore fluid into the wellbore. The increase in drilling fluid salinity has little effect on the range of the hydrate decomposition in the reservoir but significantly increases the salinity of the pore water in the layer with free gas. As the drilling fluid temperature increases, the possibility of the gas invasion from the reservoir into the wellbore will be greatly increased at the early stage.

A simplified equation for the collapse pressure of sandwich pipes with different core materials

Sandwich pipe with high-pressure resistance and the adequate insulation performance is a potential deepwater offshore oil and gas development solution. This paper establishes a two-dimensional finite element numerical model for sandwich pipe collapse prediction under external pressure using the finite element software ABAQUS. The developed numerical model is validated successfully using experiments in the literature. Parametric modeling is implemented with the help of the scripting language Python. A total of 3125 FEM models are established to analyze the influence of the sandwich pipe's geometric parameters, material properties, and interlayer adhesion properties on the collapse strength. The results show that the sandwich pipe's geometric parameters and core layer materials significantly influence the collapse strength. In contrast, the change of steel pipe steel grade has less influence. Moreover, the interlayer adhesion properties can significantly improve the collapse strength of the sandwich pipe. Finally, based on the numerical simulation results, a simplified equation for the collapse strength of the sandwich pipe is proposed for different core layer materials under frictionless interlayer conditions, which has an average error of 6.98% under the present assumptions.

Analysis of Failure Behavior Based on the Ring Shear Test in a Bedding Rock Landslide of the Three Gorges Reservoir

Complex geological environment and climatic conditions lead to frequent geological disasters in the Three Gorges Reservoir area. In particular, due to the impact of reservoir impoundment, a large number of landslides have occurred, resulting in huge economic losses and casualties. In this study, the bedding rock landslide is taken as the research object. First, the DTA-138 geotechnical ring shear apparatus system is used for the ring shear test. Second, a two-dimensional numerical model of Shanshucao landslide was established, and simulation was carried out. The main conclusions are as follows: 1) The shear stress–shear displacement curves of sliding zone soil under different shear rates show typical strain softening characteristics. 2) The shear rate–internal friction angle curve showed a good logarithmic relationship. 3) The fundamental reason for the rapid sliding into the river after the instability of the main sliding zone of the Shanshucao landslide is the negative rate effect of the argillized interlayer sliding zone soil in the main sliding zone.

Numerical optimizing noise damping performances of Helmholtz resonators with a rigid baffle implemented at neck in presence of a grazing flow

As an applicable noise attenuator, Helmholtz resonator is mainly used to dampen acoustic noise at low- and medium-frequency ranges. It is typically implemented in combustion-engines and gas turbines to dampen thermoacoustic instabilities. However, it has a narrow effective frequency range and does not work effectively at off-design conditions. In this work, we consider a modified structured Helmholtz resonator (HR) at its neck by applying a rigid baffle in order to maximize its’ noise damping effect and to broaden its frequency bands. The resonator is attached to a cylindrical duct/pipe in presence of a mean flow (grazing flow), aiming to simulate the practical engines flow configuration. For this, a two-dimensional frequency domain numerical model is developed by using COMSOL V5.3. The numerical simulations are carried out by solving the linearized Navier–Stokes equation in frequency domain with low computational cost and time. In order to obtain an optimum design in terms of the maximum noise damping performances, 10 new different configurations/designs are proposed. The effects of 1) the single baffle attached to the upstream or downstream sidewall of the neck ends, that is, Design A, B, C, and D or double baffles, that is, Design E, F, G, and H), 2) the baffle implementation location, 3) the length of the rigid baffle, and 4) the grazing flow low Mach number are evaluated and compared. It is found that Design C is associated with improved TL by 50% and decreased resonant frequency by 20% comparing with the conventional HR. The present preliminary study shows that Design C is the better design. Further experimental and optimization researches are needed to sheds light on the optimum design of a Helmholtz resonator with neck structure being modified, as there is a low Mach number grazing flow.

Influence of building-site resonance and building properties on site-city interaction: A numerical investigation

Recently, the concept of ground motions within dense urban areas being significantly affected by upper building clusters has been widely accepted. However, multiple interactions between upper buildings and underlain soil layer have increased the complexity of the problem. In this study, we focused on the analysis of ground motion changes with respect to free-field motion caused by upper building clusters, and the seismic interaction between building clusters and underlain soil, named site-city interaction (SCI). Emphasis was placed on the influence of building-site resonance and building properties on SCI effects. Hence, a two-dimensional (2D) numerical finite element model coupled with a non-linear elastic-plastic soil model and a linear multiple degree-of-freedom building model was developed in the OpenSees framework.Numerical results showed that the SCI effects were strongly influenced by the building-site resonance effects and building properties. For special cases, the ground motion was reduced by more than 60% with respect to the free-field motion. Furthermore, the SCI effects decreased as the degree of soil non-linearity increased, whereas the ground motion caused by SCI effects reduced by more than 20% of the free-field motion. However, owing to the non-linear effects, several unexpected amplifications were observed at certain frequency bands.Overall, the results of this study present an insight into the relationship between building properties, building-site resonance effects and SCI effects, and provide a reference for further SCI analysis of real-life applications.

A robust two-dimensional model for the pyrolysis of plastic waste driven by self-sustaining smoldering

This study established a robust two-dimensional (2D) numerical model for plastic waste (PW) pyrolysis driven by self-sustaining smoldering. The smoldering-driven pyrolysis reactor consists of a smoldering chamber filled with char and sand and a pyrolysis chamber with a porous-matrix bed and PW particles. The PW could be melted and decomposed into value-added volatiles driven by the stable char smoldering heat. The findings revealed that the pyrolysis duration and product distribution could be regulated by the char concentration and Darcy air velocity. Higher PW contents shortened the volatiles’ residence time in the pyrolysis chamber and controlled the pyrolysis product yields. The increased PW content could enhance the PW processing capacity potentially resulting in the recovery of more liquid and gaseous fuels. Moreover, the reactor’s geometry significantly affected the pyrolysis chamber’s temperature distribution and the PW processing capacity.

Co-Evolution of Parallel Triple Subduction Systems in the New Guinea Region: A Systematic Numerical Study

A specific configuration of the global subduction system is the parallel triple subduction. The widely accepted example of parallel triple subduction is the New Guinea region, including a northward dip at the New Britain Trench (NBT), a southward dip at the Trobriand Trough (TT), and North Solomon Trench (NST). Questions regarding the parallel triple subduction system remain largely unexplored in terms of factors controlling its initiation, duration, and dynamics. Here, we used two-dimensional numerical models to study the dynamics mechanism of the parallel triple subduction system in the New Guinea region. Four possible regimes were achieved: 1) the double subduction model, which includes the forward subduction jumping model (FSJ) and the subduction polarity reversal model (SPR) and 2) the parallel triple subduction model, which includes the tendency to the forward jumping model (TFSJ) and the tendency to polarity reversal (TSPR). By evaluating the four regimes with actual seismic data, we suggest that the pre-existing rupture and length of ocean–continent transition (OCT) determine the formation of the TT, while the formation of the NBT may be the result of the rheological strength differences between the Solomon Island Arc (SIA) and Solomon Sea Basin (SSB); the initial length of the SSB can regulate the competitive relationship between the TT and NBT, which also determines the present-day inactive state of the TT. A longer SSB makes the TT and NBT initiated independently, while a narrower SSB will allow interaction during subduction initiation of the TT and NBT.

Heat Transfer Enhancement of Ionic Wind Assisted Slot Jet Reattachment Nozzle: A Numerical Study

Abstract Impinging jet nozzles are omnipresent in industrial applications. Innovative impinging jet nozzles, such as radial jet reattachment (RJR) and slot jet reattachment (SJR) nozzles, have been proven to be highly efficient tools to enhance heat and mass transfer, compared to traditional in-line jet and slot-jet nozzles. However, the heat and mass transfer in the region immediately underneath these reattachment nozzles are relatively inefficient. The ionic wind is a promising technique for heat transfer enhancement. The ionic flow is induced when free ions are accelerated by an electric field, and exchange momentum with neutral air molecules. In this numerical study, the performance of the SJR nozzle is improved by the application of an electric field, specifically, ionic wind, which is generated in the region directly between the nozzle and the exposed impingement surface. The two-dimensional numerical model is based on the flow field generated by an ionic wind-assisted SJR nozzle. The simulation results show a significant secondary flow induced under the nozzle, due to ionic wind. A significant enhancement of local and average heat transfer coefficients is achieved. The heat transfer increases with the applied potential and nozzle exit velocity. However, the SJR flow pattern is altered when the air exit velocity is below a certain threshold. The simulation results provide an in-depth understanding of the heat transfer characteristics under various operating conditions and pave the way for developing this novel impinging nozzle design.

Impact of Isothermal Layering on the Stability of Saline Soil Subgrade in Cold Regions

In order to determine the influence of heat on the stability of the saline soil subgrade slope in cold regions. Firstly, four typical representative saline soils were selected as subgrade fillers, and geotextiles were added at the bottom of the subgrade as a study subject. A two-dimensional numerical model for the temperature field of subgrade soil was established based on COMSOL Multiphysics. Secondly, combined with the main strength parameters of subgrade soil at different temperatures, an isothermal stratification-strength parameter function calculation model was proposed. Then, the SLOPE/W module in GeoStudio is used to stratify the established subgrade model according to isotherms and calculate the stability safety factor of saline soil subgrades in cold regions under different months, slopes, and subgrade heights, respectively. Finally, the influence of submergence at the foot of the slope on the stability of the subgrade slope is discussed. The results show: After the cold season coming, with the decreasing of temperature, the stability of HC-1 and HC-2 saline soil subgrade slope increased to different extents when the ground temperature dropped to -10°C. When the local temperature dropped below -10°C, the stability has slight decline; CS-1 and CS-2 saline soil subgrade in the ground temperature dropped to 10°C (HC-1 and HC-2 denote two groups of saline soil with high chloride-salt content (≥15%) and low sulfate salt content (≤0.5%), whereas CS-1 and CS-2 denote two groups of saline soil with low chloride-salt (≤5%)), the slope stability was significantly improved, and the stability of CS-1 increases slightly with further decrease in temperature.

On the origin of the Canary Islands: Insights from mantle convection modelling

The Canary Islands hotspot consists of seven volcanic islands, mainly of Neogene age, rooted on oceanic Jurassic lithosphere. Its complex structure and geodynamic setting have led to different hypotheses about its origin and evolution, which is still a matter of a vivid debate. In addition to the classic mantle plume hypothesis, a mechanism of small-scale mantle convection at the edge of cratons (Edge Driven Convection, EDC) has been proposed due to the close proximity of the archipelago to the NW edge of the NW African Craton. A combination of mantle plume upwelling and EDC has also been hypothesized. In this study we evaluate these hypotheses quantitatively by means of numerical two-dimensional thermo-mechanical models. We find that models assuming only EDC require sharp edges of the craton and predict too narrow areas of partial melting. Models where the ascent of an upper-mantle plume is forced result in an asymmetric mantle flow pattern due to the interplay between the plume and the strongly heterogeneous lithosphere. The resulting thermal anomaly in the asthenosphere migrates laterally, in agreement with the overall westward decrease of the age of the islands. We suggest that laterally moving plumes related to strong lithospheric heterogeneities could explain the observed discrepancies between geochronologically estimated hotspot rates and plate velocities for many hotspots.

Numerical analysis on the effect of process parameters on deposition geometry in wire arc additive manufacturing

Here we develop a two-dimensional numerical model of wire and arc additive manufacturing (WAAM) to determine the relationship between process parameters and deposition geometry, and to reveal the influence mechanism of process parameters on deposition geometry. From the predictive results, a higher wire feed rate matched with a higher current could generate a larger and hotter droplet, and thus transfer more thermal and kinetic energy into melt pool, which results in a wider and lower deposited layer with deeper penetration. Moreover, a higher preheat temperature could enlarge melt pool volume and thus enhance heat and mass convection along both axial and radial directions, which gives rise to a wider and higher deposited layer with deeper penetration. These findings offer theoretical guidelines for the acquirement of acceptable deposition shape and optimal deposition quality through adjusting process parameters in fabricating WAAM components.

Increase in Elastic Stress Limits by Plastic Conditioning: Influence of Strain Hardening on Interference Fits

This paper presents a novel method for the design of purely elastic interference fits by exploiting the plastic properties of a material. In this process, the elastic potential of the material is expanded by the targeted application of residual stresses and material strengthening, in such a way that additional operational loads due to rotating bending moments, torsion, temperature changes, and centrifugal forces are absorbed by the hub in a purely elastic manner, and plastic deformations are avoided. In the ideal case, the performance shown by the connection can be almost doubled compared to conventional elastically joined interference fits. Compared with conventional elastically–plastically joined interference fits, a specifically defined additional safety against plastic deformation can be guaranteed. In addition to the prerequisites of plasticity theory, the fundamental aspects of the process are presented and investigated on the basis of two-dimensional numerical calculation models. Both ideal plastic and hardening material models were used. The results of this work showed that previous stress limits can be significantly increased up to full plastic loading and that the utilization of plastic material properties is also made possible by plastic conditioning for applications that were previously designed to be purely elastic.

A Numerical Simulation of Machining 6061 Syntactic Foams Reinforced with Hollow Al2O3 Shells

Aluminum closed cell syntactic foams possess reduced density, higher peak compression strength, and lower coefficient of thermal expansion and thermal conductivity compared to metal alloys. However, the industrial mass production of these complex material systems presents a significant problem in the form of poor machinability. In order to address this concern and to increase the use of this potential cost- and energy-saving system, a two-dimensional numerical model using the AdvantEdgeTM machining software was developed. For the verification of the numerical model, machining trials in dry conditions were conducted on different samples using a SandvikTM carbide-coated insert having a 6° rake angle and a 7° clearance angle. The hollow alumina shell diameter and volume fraction were found to profoundly affect the magnitude of the generated machining forces. This study showed an increase in machining force by almost 25% for syntactic foams reinforced with hollow alumina shells of higher volume fraction and coarser diameters. The cutting conditions to obtain a favorable stress diastribution in the syntactic foam’s machined sub-surface were identified.

Метод и технология краткосрочного прогноза изменений уровня моря в юго-западной части Берингова моря

The main characteristics of the method to forecast sea level with a lead time of 72 hours for the southwestern part of the Bering Sea are considered. Spatiotemporal variations in storm surges within the Bering Sea and adjacent areas are calculated using a two-dimensional numerical hydrodynamic model of the coupled water and ice dynamics. The model forcing is implemented using the data on surface air pressure and wind, which are predicted by the WRF-ARW atmosphere model. Tidal elevations are calculated only at coastal points, 11 major tidal harmonic constituents are used. Information about the distribution of the ice cover within the study object is formed based on the Global Forecast System data. A technological line of the forecasting method operates in automatic mode. The results of the comparison of sea level forecasts and observations at Nikol’skoye, Ossora, and Korf (Tilichiki) tide gages indicate that the developed forecast method complies with the requirements of the Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet). Keywords: forecast method, sea level, Bering Sea, numerical hydrodynamic model, storm surge, tide, ice cover, forecast skill scores

Design and test of an open portable MRI system

PurposeThe purpose of this paper is the design study and realisation of portable low-field open MRI system.Design/methodology/approachThe design of the magnetic resonance imaging (MRI) system is based on an optimization study using a genetic algorithm. Non-linear two-dimensional and three-dimensional numerical electromagnetic models are developed and inserted in the optimization environment.FindingsThe results are found to be consistent with those issued from fully experimental tests. The static field produced by the device is 0.295 T with a homogeneity of 2.8% (28,000 ppm) over 100 mm diameter sphere volume. The z-axis gradient coils are capable of generating switching gradients with an amplitude of 8 mT/m and a frequency of 1.2 kHz.Originality/valueOur system is an open portable MRI which can be used in an ambulance. The open topology permits an easy access into the lateral sides when a surgery using surgical instrument with video feedback is needed.

Numerical investigation of vortex induced vibration of a circular cylinder for mass ratio less than 1.0

A two-dimensional (2D) numerical model was developed by solving the Reynolds Averaged Navier-Stokes Equations (RANS) with the SST k-ω turbulent model closure to investigate vortex induced vibration of a circular cylinder for mass ratio less than 1.0. The sensitivity analysis of the grid in the present numerical model was carried out firstly, then the comparisons between the numerical results and the published experimental results were shown to validate the numerical model, and good achievement was obtained. In this study, the elastically supported circular cylinder with mass ratio less than 1.0 was only allowed to move in the cross-flow direction. The fluid forces on the circular cylinder and the motion response were studied. It can be seen from the numerical results that the mass ratio has great effect on the fluid force and the vibration amplitude, especially on the “lock-in” region for the circular cylinder with mass ratio less than 1.0.

Numerical modelling for analysing drainage in irregular profile pipes using OpenFOAM

ABSTRACT Different methods of two-dimensional and three-dimensional numerical resolution models have been used to predict the air–water interaction in pipe systems in the early twenty-first century, where reliable and adequate results have been obtained when compared with experimental results. However, the study of the drainage process in pressurized systems with air admitted through openings has not been studied using this type of model due to the complexity that this represents. In this research, a two-dimensional numerical model is developed in the open-source software OpenFOAM; this model represents the drainage of an irregular pipe with air admitted by an air valve, defined by a structured mesh. A validation of the numerical model related to the air admitted by the variation of the air valve diameter is also performed.

Elucidating the gas flow dynamics in a nanomaterial synthesis solar reactor

We report unconventional flow visualization coupled with two-dimensional numerical modeling in the Heliotron solar reactor used for nanomaterial synthesis. The effect of operating conditions, such as gas ejection velocity and configurations of sweeping gas flow on the particle transport in the reactor were investigated in order to map the different flow regimes experienced during solar ablation. The experimentally observed phenomena were satisfactorily accounted for by the simulations, providing a consistent basis to explore the effects of heat transfer and flow dynamics, as well as those of particle thermal history from the vaporization zone to the condensation zone.

Novel discretization strategies for the 2D non-Newtonian resistance term in geophysical shallow flows

In the context of two-dimensional models for complex geophysical surface flows such as debris flows, muddy slurries, oil spills over land, hyperconcentrated floods, lava flows, etc, depth-averaged rheological models relate the shear stress state within the fluid column to the depth-averaged local flow features. Despite it is the most influencing term on the mobility of complex shallow flows, the numerical treatment of the resistance contribution to the flow momentum is still a challenging topic, especially when dealing with 2D large-scale applications. In this work, two novel strategies for the explicit upwind discretization of generalized non-Newtonian resistance terms in two-dimensional numerical models are proposed, called integral and differential approaches. These new strategies are applicable to generalized rheological formulations in any type of mesh topology. Results from benchmark tests running in orthogonal, triangle structured and triangle unstructured meshes demonstrate that both approaches represent an improvement for the explicit upwind integration of the 2D resistance force compared with previous procedures. It is shown that the alignment of the flow with the mesh main-axis, which has been previously attributed to faults of 2D FV numerical methods and insufficient mesh refinements, is directly related to the loss of the rotational invariance of the integrated resistance force. This is caused by the erroneous procedure for including the 2D resistance term into the local flux balance at the cell edges. Furthermore, a novel implicit centered method for the integration of the 2D resistance force has also been derived for the quadratic frictional non-linear resistance formulation. Despite the implicit procedure fails to converge to steady uniform flow states, the differential explicit upwind and the implicit centered methods show similar level of accuracy, robustness and computational efficiency for transient 2D frictional visco-plastic flows.

Characteristics of the damage evolution and the free surface velocity profile with dynamic tensile spallation

The spalling behavior of ductile metals is a process involving void nucleation, growth, and coalescence. Limited by diagnostic techniques, spallation experiments only provide the free surface velocity profiles and the information about recovered targets, but some quantitative damage evolution information about the spalling target is lacking. In this research, the damage nucleation seeds are randomly arranged on the grain boundary in the central region of a target with grain geometry, and a two-dimensional mesoscale numerical model of a plate impact spall experiment is established. By analyzing the free surface velocity profile and the stress history, it is demonstrated that the spall strength obtained with the pull-back velocity essentially corresponds to the maximum tensile stress at the target center. The effects of the impact stress and the stress pulse duration on the dynamic characteristics of the void growth and coalescence are analyzed in-depth by using the damage evolution dissipation energy and the plastic strain contours at different times. The dynamic process of the damage evolution determines the characteristics of the oscillation after the pull-back signal. The stress history controls the damage degree and the kinetic process of the target in the spallation damage process. The impact stress has the most important effect in determining the damage evolution rate, while the stress pulse duration only affects the void coalescence process and irrelevant to the void growth. The damage degree of the void growth and the coalescence process are the result of the joint action of the impact stress and the pulse duration.