Two-dimensional Numerical Model Research Articles

Effect of inserted baffles on hydrogen heterogeneous reaction in planar catalytic micro combustor

Heterogeneous reaction characteristics of premixed H2/Air mixture are numerically investigated in micro combustor with coating platinum (Pt) catalyst on the inner wall. The well-designed combustor with the inserted baffle is committed to improving the transport of bulk species on the catalytic surface, therefore enhancing the fuel conversion ratio. A two-dimensional numerical model with detailed heterogeneous reaction mechanism is developed and verified. In this work, the numerical results reveal that the heterogeneous reaction rate and fuel conversion ratio are significantly improved in the combustor with inserted baffle. The velocity of gaseous mixture swiftly increases between the baffle and catalytic surface, resulting in the increasing adsorption-desorption of bulk species on the catalytic surface. The main influencing factors of inserted baffle body comprise of slit width between two ribs in the same row (W), rib length (L), distance between adjacent baffles row (D), number of baffle row (n) which are studied to obtain a set of optimized parameters of baffle in the well-designed combustor. The optimized parameters of the baffle are W = 0 mm, L = 0.4 mm, D = 4 mm and n = 4, which are employed in the combustor to obtain a high hydrogen conversion ratio. Moreover, the effect of different inlet velocities and equivalent ratios of the mixture on the heterogeneous reaction characteristics are carried out in the designed combustor. As the designed combustor performs well, and the improvement effect of the optimized baffle gradually increases together with the inlet velocity, particularly for high inlet velocity (7 m/s). The promotion effects of baffle in the designed combustor are presented when the rich and lean fuel are adopted at inlet velocity of 7 m/s. Finally, the relative parameters of this work can serve as a reference and guidance for the design of micro scale combustor.

Distribution Law of the Initial Temperature Field in a Railway Tunnel with High Rock Temperature: A Model Test and Numerical Analysis

The distribution of the initial temperature field of a high-rock-temperature tunnel is critical for determining the tunnel line and the construction scheme. This study used model testing, numerical analysis, and field measurement to investigate the initial temperature field distribution of a tunnel with high rock temperatures. A model test system was developed, and the experimental results show that the boundary conditions set by the model are reasonable. The results show that the temperature along the tunnel line is high in the middle and low at both ends. Obviously, the periodic boundary conditions have a significant influence on the temperature field distribution. Then, the corresponding two-dimensional unsteady numerical model is established, and the numerical model is verified by the model test. Next, the numerical model is applied to the actual Jiwoxiga tunnel, which is a high-rock-temperature tunnel. The results show that the maximum ground temperature in the direction of the Jiwoxiga tunnel line is 52.5 °C, the tunnel lengths with ground temperatures above 28 °C account for 96.25% of the total tunnel length, and the tunnel length with a ground temperature above 45 °C comes to nearly 1200 m. In addition, this result is also verified by the field drilling data and field-measured data after excavation. The effectiveness and accuracy of the numerical model are fully demonstrated. This study provides theoretical support for the design and construction of high rock temperature tunnels.

Landslide mechanism and stability of an open-pit slope: The Manglai open-pit coal mine

A clear understanding of landslide mechanisms and stability analyses is of great significance for landslide monitoring, prediction, and control. A large-scale end wall landslide occurred and its area reached 47,752 m2 on August 7–20, 2020, in the Manglai open-pit coal mine, China. In this paper, the engineering geological survey, mechanical test, large-deformation finite element numerical method, limit equilibrium method and analytical formula are used to analyze how the groundwater level rise caused this end wall failure and landslide. The engineering geological conditions, hydrogeological conditions, landslide activity signs and physical and mechanical parameter calibration of the sliding mass are investigated in detail and tested. Three-dimensional and two-dimensional numerical models of slopes are established, and an analytical formula calculation method to calculate the factor of safety (FoS) is proposed when sliding cracks are located on the top and toe of a slope. The results indicate that the fault fracture zone, soft strata, continuous heavy rainfall, and groundwater were the main contributors to this landslide. The three-dimensional numerical calculation results are consistent with the deformation and failure process of the slope observed in the field, which shows a retrogressive progressive failure mode. The calculation results of SLOPE/W and the analytical formula are consistent; i.e., when the groundwater level rises to +950, the stability of the end wall reaches the critical stability state. With the passage of time, the creep of the sliding surface accelerates until the entire end wall landslide.

Incorporating temperature into seepage loss estimates for a large unlined irrigation canal

Quantifying seepage losses from unlined irrigation canals is necessary to improve water use and conservation. The use of heat as a tracer is widely used in quantifying seepage rates across the sediment–water interface. In this study, field observations and two-dimensional numerical models were used to simulate seepage losses during the 2018 and 2019 irrigation season in the Truckee Canal system. Nineteen transects were instrumented with temperature probes and stage recording devices for inverse modeling to derive seepage flux and volumetric losses over the 39 km length of canal. The numerical models for each transect were calibrated and validated using the two-year dataset. Soil zones and observation data were used in each numerical model to help guide calibration of vertical and lateral heat and fluid fluxes. Model simulations were used to derive multivariable regression equations that consider stage, temperature, and hydraulic gradient. The results demonstrate the value of long-term datasets that illustrate the seasonality of groundwater levels, siltation, stage, and temperature on seepage rates. Seepage rates estimated by the numerical models range from 0.16 to 4.6 m3/d m−1. Total annual volumetric losses estimated for 2018 and 2019 were 1.6 × 10-2 to 1.2 × 10-2 km3, respectively. The seepage losses estimated by this study account for 32 % to 41 % of the inflow volumes. Regression models were able to reproduce seepage time-series simulated by the numerical models reasonably well. In arid environments, water diverted into irrigation canals may be influenced by seasonal variations in temperature sufficient to influence the water accounting of conveyed surface flows.

Development of an electronic circuit cooling system using elastocaloric effect: a FEM comparison among different configurations

• Project of a device based on elastocaloric effect for cooling electronic equipment. • The device is made of elastocaloric wires crossed by air as heat transfer fluid. • Two different configurations were investigated: bending and tension of the wires. • A numerical model to investigate working parameters has been developed. • The model is used to draw a guide map for efficiently design the device. In recent years the scientific community has been committed to finding new eco-friendly solutions for refrigeration. Among the Not-In-Kind Refrigeration Technologies very promising are those based on solid-state refrigerants. Solid-state refrigeration technologies are based on the caloric effect. The nature of the applied field (magnetic, electric, mechanical) particularizes it in: magneto -, electro -, mechano - (elasto - or baro -) caloric effect. Among these, very interesting is the elastoCaloric Effect (eCE) -based one. The aim of the study introduced in this paper is to design and build an elastocaloric device specifically aimed at the cooling of the electronic circuits. At the best of our knowledge, there are not any other caloric solid-state systems specifically developed for this application in open literature. Furthermore, there are not any elastocaloric devices yet developed basing on bending as loading/unloading operation and at the same time thermodynamically exploiting the Active elastocaloric Regenerative refrigeration cycle. This paper reports a preliminary study where two different configurations are compared based on a two-dimensional numerical model. The substantial difference between the two configurations lies in the application of wires loading/unloading: tensile or bending. The device consists of 240 wires of Ni 50.8 Ti 49.2 alloy, for a total mass of 61g, with a diameter of 0.5 mm and a length of 300 mm crossed by air as heat transfer fluid. In this paper a comparison between the energy performances of the two configurations has been carried out (in terms of temperature span, cooling power and COP): the results reveal that the device based on wires bending gives the best performances (+ 50% as COP with bending rather than loading).

A Methodology for the Analysis of Tunnel Intersections Using Two-dimensional Numerical Modeling

Intersections of tunnels are an integral component of most underground applications. The design and construction of tunnel intersections can be the most technically challenging element of a tunnel project. Yet, there are relatively few publications and methods regarding tunnel intersection design. Tunnel intersections are essentially a three-dimensional problem. However, 3D models require significantly longer time for solving and interpreting, greater computer resources, and higher user expertise. Hence, there is a great incentive to develop simpler and quicker analysis methods for tunnel intersections. In this paper, a methodology is developed so that a 3D tunnel intersection problem can be modelled using an equivalent 2D numerical model. For this purpose, it is proposed that the main tunnel cross section is modelled with an additional horizontal expansion component that represents the cross tunnel. Multiple 3D and 2D models were computed for the purpose of finding the expansion distances in the 2D models that yield similar deformations to the 3D models. Based on the results, regression analysis was employed to derive a formula relating the ratio of equivalent diameters of the main to cross tunnel to the proper expansion distance. This formula provides a useful and practical tool for preliminary tunnel intersection design. The current work relies on a number of assumptions, mainly that the rock mass is elastic. More work can be carried out to extend and modify the proposed method for more complex conditions.

A Two-dimensional Numerical Model of Heat Exchange in the Soil Massif During the Operation of a Shallow Horizontal Soil Heat Exchanger

The current article uses a two-dimensional numerical model to represent the results of theoretical studies of the heat exchange in the soil massif during the operation of a shallow horizontal soil heat exchanger. The analysis of literature sources showed that one of the important conditions for the effective operation of a shallow-soil heat exchange is its rational design parameters, such as the total length of the pipeline, the diameter of the pipe, the distance between the axis of the adjacent pipes, the depth of the heat exchanger placement, etc. A two-dimensional heat exchange model in the soil mass was developed, which made it possible to investigate the operation of a shallow horizontal soil heat exchanger. It was found that the step between the axis of the adjacent pipes of the multi-loop heat exchanger, which is 0.95 m, is optimal when creating a shallow horizontal soil heat exchanger in the soil conditions of Kyiv.

Evaluation through 2D Modelling of Scour around Piers with Collars in the CÁCeres Bridge in Piura, Peru

This paper analyzes the results of the scour calculations around the group of piers of a bridge through two-dimensional modelling using the Iber software. The case under study is that of the Andrés Avelin o Cáceres Bridge, located in the Piura region, Peru, which has an approximate free span of 120 meters and has 10 pillars equally distributed on two decks. Currently, the referred bridge has pillars of rectangular section with narrowing towards the base, this type of geometry was considered as the first scenario for scour calculations; the pillars with the collars installed are part of the second scenario under study. Based on geotechnical, hydrological and hydraulic studies of the area, two-dimensional numerical modeling has been developed for each scenario in order to obtain the depths of scour. The following results were obtained: The installation of collars in the second scenario achieved a reduction of the scour depth by 29.51% on average, the observed reduction range was from 15.73% to 43.77%.

Simulation and risk analysis of dam failure in small terrace reservoirs in hilly areas

This study uses numerical simulation to analyse the dam failure and risk of small series (parallel) reservoir clusters in the hilly areas of China. Four small series (parallel) reservoirs in the Guozhuang River basin of Tai’an City are used as the target of the study, and a two-dimensional hydrodynamic reservoir failure numerical model was constructed to analyse the riskiness of various series (parallel) dam failure scenarios. The results of the analysis can provide some technical support for the forecasting and scheduling of small terrace reservoirs in hilly areas.

Aseismic ridge subduction and flat subduction: Insights from three-dimensional numerical models

Flat subduction can significantly influence the distribution of volcanism, stress state, and surface topography of the overriding plate. However, the mechanisms for inducing flat subduction remain controversial. Previous two-dimensional (2-D) numerical models and laboratory analogue models suggested that a buoyant impactor (aseismic ridge, oceanic plateau, or the like) may induce flat subduction. However, three-dimensional (3-D) systematic studies on the relationship between flat subduction and buoyant blocks are still lacking. Here, we use a 3-D numerical model to investigate the influence of the aseismic ridge, especially its width (which is difficult to consider in 2-D numerical models), on the formation of flat subduction. Our model results suggest that the aseismic ridge needs to be wide and thick enough to induce flat subduction, a condition that is difficult to satisfy on the Earth. We also find that the subduction of an aseismic ridge parallel to the trench or a double aseismic ridge normal to the trench has a similar effect on super-wide aseismic ridge subduction in terms of causing flat subduction, which can explain the flat subduction observed beneath regions such as Chile and Peru.

Numerical study on oxygen transport pattern in porous transport layer of proton exchange membrane electrolysis cells

A transient, two-dimensional and two-phase numerical model is established to study the nature of oxygen transport in proton exchange membrane electrolysis cells (PEMEC). Randomly generated circle fibers are used to construct a patterned porous transport layer (PTL), and the volume of fluid (VOF) method is employed to capture accurate gas-liquid interfaces. The patterns of oxygen transport and the relationship between multiple transport paths are analyzed in detail. We propose for the first time the concept of ‘isolation belt’, which is composed of a series of narrow throats, hindering the spontaneous combination of different oxygen transport paths. The influence of PTL perforation and spatially-graded fiber diameters on oxygen transport are explored. The numerical results show that perforation can probabilistically destroy the ‘isolation belt’, forming a transport path with high priority, which helps to reduce oxygen saturation. Moreover, when the porosity of PTL remains unchanged, reducing the fiber diameter in the region near the catalyst layer (CL) can significantly reduce the local oxygen saturation. The pressure variation reveals its consistency with the maximum throat width of the oxygen transport path, which indicates the law of capillary pressure. From the perspective of mathematical probability theory, a novel functional expression of the profile of oxygen saturation with respect to the structural properties of PTL is proposed to make a concise explanation of gas bubble transport in the context of PEMEC or similar gas-liquid porous flow. The highlights in this paper include: • Comprehensive spatiotemporal profile for in the process of oxygen penetration. • The concept of isolation belt for spontaneous merging of oxygen pathways. • A mathematical explanation for probability of oxygen saturation distribution. • Influence of PTL perforation and graded fiber diameters on oxygen saturation.

PERFORMANCE INVESTIGATIONS OF THE ENERGY DISCHARGE CHARACTERISTICS OF HIGH-TEMPERATURE PHASE CHANGE MATERIAL CAPSULES

Thermal energy storage using phase change material (PCM) capsules is a prevalent method used in high-temperature applications such as steam generation and concentrated solar power. However, the research works on the development of latent heat storage PCM encapsulations are limited. In the present study, experimental and numerical investigations conducted on high-temperature cylindrical encapsulations filled with sodium nitrate that were using air as the heat transfer fluid are presented. A modification of the cylindrical capsule known as the annular capsule is proposed to improve the heat transfer characteristics inside the PCM by providing a heat transfer surface at the center of the capsule. Experimental investigations were conducted utilizing a high-temperature (723 K) test facility to determine the discharging characteristics of both capsule designs in the temperature range between 603 and 473 K. A two-dimensional axisymmetric numerical model is developed and validated with the results obtained from the experiments. The performances of both the basic and annular capsules are compared, and it is observed that the discharging time reduced by 24% for the annular capsule. The heat transfer enhancement occurs due to an increase in the contact surface area and the improvement in flow characteristics of the air.

Mechanism of wave-induced flow in reshaping breakwaters

The aim of this work was to investigate the reshaping mechanisms of a reshaping berm breakwater (BB) by assessing the results of a two-dimensional numerical model in OpenFoam. The flow inside and outside the breakwater was numerically simulated. The initial and reshaped form of the breakwater was modelled using the Darcy–Forchheimer equation and k–ϵ closure model. The numerical model was calibrated with and validated against experimental data of wave-induced pressure and water-level fluctuations inside and outside the breakwater. Both the initial and reshaped BB were evaluated for calibration and validation processes. The results show that the minimum run-down level on the breakwater slope is a critical area for armour instability due to outward driving forces caused by the critically synchronised outward flow and excess pressure gradient. Moreover, parallel downward flow occurs during a wave run-down, which can push the displaced armour down the slope. After reshaping, the breakwater profile has a milder slope than the initial profile, and the outward forces due to the excess pressure gradient are reduced to less than one-half of their initial amount, a result of the change in breaker type. Accordingly, the reshaped profile is modified to harmonise with the new flow field conditions.

Numerical modelling of enhancement of the capacity of buried metal culverts by using geogrids

This paper presents a two-dimensional numerical modelling analysis of a flexible buried corrugated metal arch culvert in Enkoping, Sweden. The numerical results of this study are validated against field measurements of the culvert crown deformation, thrust, and bending moments recorded during backfilling. To model the backfill soil, the hardening soil with small strains (HSs) material model is used because of its efficiency in simulating the soil-structure interaction. Furthermore, in a numerical investigation of the stress distribution at the culvert invert, it is found that weakness of the foundation soil has an insignificant impact, due to stress dissipation resulting from arching actions. The numerical modelling analysis also investigates the use of geogrid layers with dead end bolts in the soil cover above the culvert crown during the application of static surface loads, as an innovative technique to improve the load capacity of the soil-culvert system. The results show a reduction in culvert crown deformation and internal forces when geogrid layers are used. This indicates the efficiency of geogrid layers in improving the load capacity of existing buried culverts or overcoming deficiencies in culvert serviceability by reducing the impact of applied loads.

Analysis of hydrodynamics and thermal dispersion by numerical modelling in Sele Strait, West Papua

Indonesian standard for wastewater quality regulates 40°C for the maximum outfall temperature. Meanwhile, the seawater temperature below 30°C is utilized for the cooling facility which the intake area is close to the outfall source. This research examine the hydrodynamics and thermal dispersion condition in PT Kilang Pertamina Internasional Kasim process plant in Sele Strait, West Papua. This study uses a two-dimensional numerical model Mike21 for a one-year simulation. Considering the limited field data, the ERA5 reanalysis satellite was utilized for the model input boundary. It also finds the discharge from the river with a temperature assumption of 26.5°C also in the boundary. The model validated with tidal field data with an R-squared number is 0.86. The hydrodynamics model shows the current speed in the intake area varied between 0-0.5 m/s. Two-scenario thermal simulation model (outfall condition 37°C & 40°C) shows that the frequency of 27°C water temperature is 81.5% and 85.8% respectively. Both scenarios give less than 10% for the temperature above 30°C. It concludes that the intake and outfall design planned is proper in the Kasim process plant.

Mathematical Modeling and Simulation of a Compound Parabolic Concentrators Collector with an Absorber Tube

CPC solar collectors are a combination of new technologies that make it possible to generate heat from radiant solar energy by transferring heat between the absorber and the fluid. This study was performed based on heat transfer equations by proposing a mathematical model, as reported in the literature. A compound parabolic concentrators solar collector (CPC) numerical model was simulated and coded in Aspen HYSYS and MATLAB software and validated by comparing its results with other researchers and experimental results. The simulated mathematical model includes a two-dimensional numerical model to describe the thermal and dynamic behavior of the fluid inside the CPC solar collector absorber tube. Numerical simulations of the fluid flow equations inside the CPC solar collector absorber tube, along with the energy equation for the absorber tube wall, coating, insulation and reflector, and solar collector heat analysis, were performed repeatedly in MATLAB and Aspen HYSYS software. This method is the most appropriate and reliable method for solving equations for numerical convergence. The experimental results of the parabolic concentrated solar collector (CPC) were used to evaluate and validate the numerical model. A solar compound parabolic concentrators collector (CPC) with short reflectors was used. This collector includes a cylindrical absorber with a real density ratio of 1.8, a reception angle of 22 degrees and a length of 2.81 m, a width of 0.32 m, and an opening of 0.1764 m. Analysis and uncertainty of the proposed model were performed with the measured sample. In the thermal efficiency analysis, the average deviation of the model from the experimental results of other researchers was equal to 7%, for increasing the temperature by 9 °C. According to these results, a good correlation between numerical results and experimental results for this proposed model has been obtained.

Numerical Model of the Double-Pipe System with Protective Layer

Nowadays, higher performance is being sought in newly built power plants. The efficiency of power plants is mainly achieved by maximizing the steam parameters. Consequently, ever more expensive high-alloy steels are being used. For this reason, design concepts, in which high efficiency with lower investment costs are becoming increasingly popular. Such an innovation is the double-pipe system with a protective coating, which provides thermal insulation for the primary pipe in which the supercritical steam flows. This pipe is also cooled by an external flow by the steam with lower parameters. The article presents the developed two-dimensional numerical model. The use of the Galerkin method enables the complete transient analysis of a double-pipe system to be carried out, considering temperature-dependent material properties. The numerical model was compared with the computational fluid dynamics model. The temperature gradient in the inner pipe wall with and without coating was determined. In addition, the response of the wall temperature to a change in steam temperature was investigated. As observed, the protective layer can improve boiler performance characteristics when applied to thick-walled boiler components. It can also enable the use of less demanding steel.

A peridynamic study on the effects of surface topography on rolling contact fatigue

A peridynamic(PD) fatigue simulation model is developed to study the effect of surface topography on rolling contact fatigue(RCF). Based on the PD fatigue damage-cumulative model proposed and verified in a previous study, a two-dimensional PD numerical model of the contact area of the rolling bearing is established, and the crack evolution and fatigue life of the model including surface topography with different dents and roughness are analyzed. The results show that cracks initiate from the shoulders of the dent, and then form spalling at the trailing edge, which is consistent with the experimental observations. Simulation of the model with sinusoidal and random rough profiles shows that there is competition between surface and subsurface crack nucleation. The larger the roughness amplitude or wavelength, the more prone to surface nucleation. Finally, the effects of roughness amplitude and wavelength on surface-originated pitting, subsurface-originated spalling and fatigue life are analyzed.

Enhanced heat transfer in a phase change energy storage with helical tubes

Solar collectors integrated with phase change materials (PCM) store heat energy for later use. However, the settling of PCM prolongs the melting duration in a vertical cylindrical container. Hence, selective methods are required to alleviate such solid PCM settling issues. A helical heat transfer tube (HTT) can improve melting by increasing the contact surface. The present research studies the charging and discharging of PCM using three helical coil HTT configurations: fully expanded, semi-compressed, and fully compressed. The fluid flow rate and inlet temperatures are 20 LPH and 80 °C, respectively. The simulation involves two-dimensional numerical modeling using Ansys Fluent software and the finite volume method with the enthalpy-porosity technique. The fully compressed HTT melt settled PCM inside the vertical cylindrical container faster. The experimental results show that using a fully compressed HTT reduced the melting time by 50 % compared with a fully expanded HTT of 160 min due to the effective melting of settled PCM. Its peak heat stored, energy efficiency, Nusselt, Stefan, and Rayleigh numbers are 356 kJ, 34.8 %, 75.34, 0.47, 2.8036 × 107, respectively. The compressed HTT is a practical design suggested for solar collectors and low-temperature heat recovery systems, which demand a fast heat storage rate.

Study of lateral assembly of magnetic particles in magnetorheological fluids under magnetic fields

This study uses a numerical simulation method to investigate the lateral assembly mechanism exhibited by equal-radius circular magnetic particles in magnetorheological fluids (MRFs). We used a direct numerical simulation method based on the finite element and arbitrary Lagrangian–Eulerian methods to establish a two-dimensional numerical model on particle–particle, particle–magnetic field, and particle–flow field interactions. The critical lines of gravitational and repulsive forces between magnetic particles and magnetic particle chains in a uniform magnetic field were investigated. The lateral assembly areas were found through these critical lines. Experiments confirmed that the sizes of the lateral assembly areas of the magnetic particle chains positively correlated with the lengths of the magnetic particle chains. In addition, the coarsening mechanism of magnetic particle chains was investigated by lateral assembly areas. Hence, this work offers insights toward understanding the mechanisms of microstructure formation in MRFs under magnetic fields.