Two-dimensional Axisymmetric Model Research Articles

Two-phase flow characteristics of different charging structure in ignition and flame-spreading

To study the influence of flame-spreading behaviour in the ignition process of different charging structures in high-density charge chambers, a visualisation device was designed, and the ignition process of the two charging structures was researched. The flame-spreading process was observed by a high-speed digital camera system and the pressure data was recorded by a data acquisition instrument. According to the experiment, a two-dimensional axisymmetric internal ballistic two-phase flow model was established to simulate the flow process of gas in particle bed based on the Weighted Essentially Non-Oscillatory (WENO) Scheme. The results show that the flow field and flame-spreading status in different charging structures are different. In the full charging structure, the development of the flow field is regular, the flow field in the entire chamber has less fluctuation areas, and velocity vortices only generate during the development of the flow field and when it reaches the wall. However, in the partially charging structure with free space, there are many pressure fluctuation areas in the flow field in the chamber, and the flow field development is also uneven. Pulsating propagation occurs at the interface between particles and free space, which has a great influence on the whole combustion and ignition process. The research results reveal the characteristics of two-phase flow in different charging structures and provide a reference for the actual charging process.

Finite Element Simulation and Shape Optimization of Acoustic Horn

Horn refers to the tube with continuous change of cross-sectional area, which can improve the matching of diaphragm and air load, so as to improve the electro acoustic conversion efficiency. For long-distance strong sound equipment, the purpose of using horn is to pursue higher sound pressure level, and control directivity and smoothness of sound pressure level response. In order to obtain higher sound pressure level and sharper directivity, parametric curve expressions of conical, exponential, hyperbolic and parabolic horn were derived. By using COMSOL multiphysics software, two-dimensional axisymmetric finite element simulation models of conical, exponential, hyperbolic and parabolic horn were established. Combined with if + end if programming function of the software, the effects of different cross-section shapes of horn on far-field sound pressure level and directivity were analyzed. The simulation results show that the parabolic horn can achieve a higher sound pressure level, and the sound pressure level is more than 3dB higher than the other three in the frequency band above 2000Hz. In the aspect of directivity, the beam width of parabolic horn is the smallest and more stable, and the overall directivity is the strongest. By using the shape optimization function of the software and constructing 8-order Bernstein polynomials, based on the parabolic horn, the shape of the horn was optimized for the most sensitive frequency range of 2000-4000hz, and the sound pressure level of the optimized horn was significantly improved in a large frequency range. This paper can provide technical reference for the design and development of horn loudspeaker.

APPLICATION OF CONVOLUTIONAL NEURAL NETWORKS FOR RESISTIVITY LOGS PROCESSING AND NON-ITERATIVE EXPRESS-INVERSION IN COMPLEX RESERVOIR ENVIRONMENTS

The work is devoted to the development of techniques and software for the quantitative interpretation of resistivity oil well logs. The article considers the results of applying the neural network approach to the processing of resistivity logging data measured at intervals composed of thin layers with contrasting electrical properties. The proposed algorithms combine the advantages of data interpretation based on a two-dimensional axisymmetric medium model and high performance, which allows them to be used at the primary processing stage, increasing the reliability of express interpretation.

Analyzing and mitigating battery ageing by self-heating through a coupled thermal-electrochemical model of cylindrical Li-ion cells

An integrated battery model is constructed by coupling a three-dimensional electrochemical model with a two-dimensional axisymmetric heat transfer model, and implemented for simulation of the thermal behavior in a 21,700-type cylindrical cell, comprising a graphite/LiNi0.8Co0.15Al0.05O2 chemistry. The electrochemical model is based on the disassembled battery structure and considers the temperature-dependent ageing kinetics induced by solid electrolyte interphase (SEI) formation and metallic Li plating. Compared with a classic pseudo-2D (P2D) model, the proposed model provides better fitting results for both battery electrochemical and thermal properties. The simulation results show battery surface temperatures can reach up to 80 °C and 110 °C for discharge rates of 3C and 4C, respectively. By applying appropriate cooling liquids, this surface temperature increase can be efficiently controlled and the core temperature will be correspondingly reduced, while the internal temperature gradient remains the same. It is primarily the improvement of thermal conductivity in radial direction which can reduce differences between core and surface temperature. Moreover, the model is able to characterize accelerated ageing kinetics caused by battery self-heating during operation. The results show that the capacity of the investigated battery decreases to 80% after 500 cycles, which is in good agreement with commercial specifications.

Performance analysis of a solar chimney power plant system in two Algeria regions

In this paper, we have investigated the possibility of implementation of three solar chimney systems in the two Algeria regions (Constantine, Tamanrasset). Numerical simulations were performed for the prototype geometry in Manzanares, Spain. Usage of CFD techniques (Computational Fluid Dynamics); we have simulated a two-dimensional axisymmetric model of an SCPP with the RNG k–ε turbulence. Using a band radiation model to solve the equation of radiation transfer by implementing the model of discrete ordinate radiation. Our results show that the secondary and tertiary collector roof system is able to achieve the highest electricity generation. The obtained results show the solar chimney power plant systems can be produced from 51 to 79 kW of electricity over the year and the highest hourly electricity produced in June is around 47 to –80 kW. The highest electricity generation has been recorded in the Tamanrasset region.

Electrothermal analysis of radiofrequency tissue ablation with injectable flexible electrodes considering bio-heat transfer

Flexible electrodes have been widely focused on in recent years due to their special mechanical properties, which can be directly integrated onto human soft tissues to actively take effects on human body or passively monitor human vital signs. These flexible electrodes provide a new routine to realize clinical treatment of accurate thermal ablation in the biological tissues via radiofrequency ablation (RFA). Meanwhile, accurately controlling of thermal field is very significant for the thermal ablation in the clinical therapeutics to prevent the healthy tissue from excessive burning. In this paper, both one-dimensional and two-dimensional axisymmetric analytical models for the electrothermal analysis of radiofrequency ablation considering bio-heat transfer are established, which are verified by finite element analysis (FEA) and in vitro experiments on pig skins. In the model, the electrical field and thermal field are both derived analytically to accurately predict the temperature rise in the biological tissues. Furthermore, parameters, such as the blood flow convection in living tissues and thickness of tissue, have obvious effects on the thermal field in the tissues. They may pave the theoretical foundation and provide guidance of RFA with flexible electrodes in the future.

A Method for Magma Viscosity Assessment by Lava Dome Morphology

Lava domes form when a highly viscous magma erupts on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma: obelisks, lava lobes, and endogenic structures. The viscosity of magma nonlinearly depends on the volume fraction of crystals and temperature. Here we present an approach to magma viscosity estimation based on a comparison of observed and simulated morphological forms of lava domes. We consider a two-dimensional axisymmetric model of magma extrusion on the surface and lava dome evolution, and assume that the lava viscosity depends only on the volume fraction of crystals. The crystallization is associated with a growth of the liquidus temperature due to the volatile loss from the magma, and it is determined by the characteristic time of crystal content growth (CCGT) and the discharge rate. Lava domes are modeled using a finite-volume method implemented in Ansys Fluent software for various CCGTs and volcanic vent sizes. For a selected eruption duration a set of morphological shapes of domes (shapes of the interface between lava dome and air) is obtained. Lava dome shapes modeled this way are compared with the observed shape of the lava dome (synthesized in the study by a random modification of one of the calculated shapes). To estimate magma viscosity, the deviation between the observed dome shape and the simulated dome shapes is assessed by three functionals: the symmetric difference, the peak signal-to-noise ratio, and the structural similarity index measure. These functionals are often used in the computer vision and in image processing. Although each functional allows to determine the best fit between the modeled and observed shapes of lava dome, the functional based on the structural similarity index measure performs it better. The viscosity of the observed dome can be then approximated by the viscosity of the modeled dome, which shape fits best the shape of the observed dome. This approach can be extended to three-dimensional case studies to restore the conditions of natural lava dome growth.

Calculation and Analysis of Heat Field of Large Capacity Epoxy Pouring Dry-type Transformer Based on Fluid-solid Coupling

Dry-type transformer had the advantages of simple structure, easy maintenance, small environmental pollution, safe and reliable operation. It was widely used in power system distribution network. With the increase of urban power load year by year, large capacity dry type transformer had been highly concerned by the power industry. In this paper, the fluid-solid coupling calculation equation of a large capacity epoxy casting dry-type transformer was expounded, and a two-dimensional axisymmetric model of the transformer was established. The finite element method was used to calculate the temperature distribution and hot spot temperature with different wind speed and load rate. The results showed that when the wind speed at the transformer inlet was 0.7m/s and the load exceeded 120%, the temperature rise of the low-voltage winding reached 136.41°C, which had exceeded the temperature limit of the material. Therefore, the ventilation volume needed to be increased and the running time needed to be reduced. The research results could provide technical support for the design and safe operation of large capacity epoxy casting dry type transformer.

Computational Evaluation of Wall Shear Stress Experienced by Endothelial Tip Cells along Capillary Sprouts

Shear stress is commonly implicated as a regulator of angiogenesis. However, critical questions remain unanswered. Do endothelial cells within a capillary sprout lumen experience shear stress? Can tip cells that extend past the sprout lumen experience shear stress? A full understanding of how shear stresses influence endothelial cell phenotype and function during angiogenesis requires the identification of local stress distribution along capillary sprouts. However, the actual shear stress magnitudes experienced by endothelial cells remain unknown. Motivated by the hypothesis that endothelial tip cells can experience physiological shear stress, the objective of this study was to estimate shear stress magnitudes due to local interstitial flow along endothelial tip cells that extend past capillary sprout lumens. A computational fluid dynamics model was used to estimate flows within a blind-ended vessel, transendothelial flow across the vessel wall, and flow within the surrounding perivascular space. The two-dimensional axisymmetric model consisted of four regions: vessel lumen, vessel wall, perivascular space, and interstitium. The vessel wall was assumed to be porous media with 0.3 μm thickness. Blood plasma was represented as an incompressible Newtonian fluid with density and viscosity equal to 1050 kg/m3 and 1.2 cP, respectfully. Shear stresses along the wall of the tip cell extending past the lumen were calculated for varying sprout lengths (50, 200, and 400 μm), perivascular space channel width (1, 4, and 9 μm), and hydraulic conductivities (1.35 and 6.75 x10-10 ms-1 Pa-1). Model parameters and geometric dimensions were selected based on previously reported literature values. Velocity profiles confirmed transmural flow across the vessel wall, nearly parabolic flow within the perivascular space, and velocity gradients along the tip cell. Increasing sprout length, increasing permeability, and decreasing perivascular space increased shear stress values with the perivascular space parameter being the major influencer. Maximum shear stresses along tip cells were consistently higher than the stresses within the sprout lumen. Wall shear stresses within the lumen ranged from 0.02 to 0.52 dyne/cm2 at the sprout entrance and linearly decreased to near zero along the sprout length. Tip cell wall shear stress due to interstitial flow ranged from 0.19 to 4.65 dyne/cm2. The results suggest that wall shear stress values along tip cells can reach physiological relevant values depending on parameter combinations. Our computational estimates motivate new questions related to whether increased shear stresses along tip cells versus luminal cells contribute phenotypic and function signatures of tip cells.

Experimental and numerical prediction of lean blowout limits for micro gas turbine combustor

PurposeThe lean blowout (LBO) limit of the combustor is one of the important performance parameters for any gas turbine combustor design. This study aims to predict the LBO limits of an in-house designed swirl stabilized 3kW can-type micro gas turbine combustor.Design/methodology/approachThe experimental prediction of LBO limits was performed on 3kW swirl stabilized combustor fueled with methane for the combustor inlet velocity ranging from 1.70 m/s to 6.80 m/s. The numerical prediction of LBO limits of combustor was performed on two-dimensional axisymmetric model. The blowout limits of combustor were predicted through calculated average exit gas temperature (AEGT) method and compared with experimental predictions.FindingsThe results show that the predicted LBO equivalence ratio decreases gradually with an increase in combustor inlet velocity.Practical implicationsThis LBO limits predictions will use to fix the operating boundary conditions of 3kW can-type micro gas turbine combustor. This methodology will be used in design stage as well as in the testing stage of the combustor.Originality/valueThis is a first effort to predict the LBO limits on micro gas turbine combustor through AEGT method. The maximum uncertainty in LBO limit prediction with AEGT is 6 % in comparison with experimental results.

A study on transient molten pool dynamics in laser polishing of Ti6Al4V using numerical simulation

Abstract Laser polishing is a novel surface restructuring technique aimed at diminish the surface roughness. Nevertheless, the lack of research on laser polishing mechanisms limits its industrial application. In this paper, a two-dimensional axisymmetric model was developed which describes the evolution of polished surface morphology and transient molten pool dynamics in surface over-melt mechanism of laser polishing. The results illustrated that the melt flows are dominated by thermocapillary and capillary forces while the surface temperature is lower than the evaporating ones. On the other hand, the local evaporated material generated a recoil pressure that dominated the molten material is extruded to the periphery, resulting in surface morphology significant asperities. Additionally, a model based on moving heat source was performed so as to bring the simulation results closer to the experimental ones. The results demonstrated that obvious bulge and depression are formed at the initial and final positions of the polished surface respectively. Simultaneously, comparing the simulated remelting depth with the those obtained from the optical images of the continuous wave laser polished surface sample cross-sections, it was found that the errors are respectively controlled within 7.2 % and 19.6 %, which corresponded to the laser radiation duration of 1 ms and 5.6 ms. The aforementioned results indicated that the prediction of the numerical model agree reasonably well with the experimental data and micrographs.

Density reduction on plasma sheath using pulsed magnetic field

When a space vehicle travels through the atmosphere at a hypersonic speed, it is enveloped by a plasma sheath. The density of plasma sheath is high enough such that communication and telemetry signals are prevented from passing to and from the vehicle, which is called communication blackout. A method to reduce plasma density for communication blackout mitigation by using pulsed magnetic field is proposed in this paper. In order to study the effect of pulsed magnetic field on plasma density, a two-dimensional axisymmetric model was established. The simulation results suggested that the pulsed magnetic field can reduce the plasma sheath density of 5 cm thickness by more than 90%, and was of sufficient size (about 5 cm) and time duration (about 330 μs) to permit transmission of data. On the basis of the simulation results, the interaction mechanism between pulsed magnetic field and plasma is explained by theoretical analysis. Furthermore, experiments of the plasma density reduction by pulsed magnetic field are performed. The experimental results suggested that a 0.55T pulsed magnetic field can reduce the plasma sheath density of 14 cm thickness by 43%–78%, which verifies the effectiveness of the pulsed magnetic field method. A comparison of results from simulation and experiment provided strong evidence for the correctness of the simulation model. The simulation results also show that low pressure and high initial electron density are beneficial to the reduction of plasma density, which also explains the phenomenon in the experiment. In addition, it is found in the experiment that two continuous reverse pulses can play the same role in reducing the plasma density, which provides the possibility for the continuous reduction of plasma density. These investigations could have a significant benefit on the design and optimization of pulsed magnetic field mitigation scheme for the blackout problem.

Research on Laser Ablation Technology in the Material Interaction of Two-dimensional Axisymmetric Ablation Model

In order to explore the mechanism of interaction between nanosecond pulsed intense laser and material, the paper established a two-dimensional numerical model, using finite difference method to numerically simulate the temperature field of nanosecond laser pulse ablation of metal aluminium. By comparing different pulse widths, the temperature field caused by the laser under the spot and energy evolves with time. It is found that the temperature in the early stage of the pulse rises faster than in the later stage. The isotherm diagram shows that the centre temperature rises fastest, the ablation profile is similar to the shape of the laser beam, and the ablation depth reaches 1 -5μm. The longer the pulse width, the narrower and deeper the ablation, the larger the spot, the wider and the shallower the ablation. The calculation results show that, compared to the uniform distribution, when the laser has a Gaussian distribution, the target aluminium centre can be obtained the higher the temperature rise, the more prone to ablation and the shorter the melting time of aluminium. The model established in this paper can be easily extended to three-dimensional situations.

Self-pulsing of direct-current discharge in planar and curved geometries

The self-pulsing of direct-current discharges in planar and curved geometries is studied using the two-dimensional axisymmetric fluid model. The simulation results show that in both cases the nature of self-oscillations is the same. They are obtained in the sub-normal mode of the discharge operation, for which the discharge has the negative differential resistance. We demonstrate that the negative differential resistance is due to both the non-linear and non-local dependence of the Townsend ionization coefficient on the electric field. We show that the self-oscillations are due to the ion transit time instability and are not related neither to RC resonance nor to the relation between the negative differential resistance and the ballast resistance as it is often suggested in the literature.

Simulation study on the performance of low-temperature water gas shift membrane reactor system

In order to understand the behavior of the low-temperature water gas shift (WGS) reaction membrane reactor system and obtain better performance of the reactor, numerical simulations are performed with a two-dimensional axisymmetric model. Dimensionless analysis is applied to the governing equations, and then a set of dimensionless parameters are established. The effect of the parameters of Damkohler number (Da) and membrane permeability (Pp) over a wide range on the performance of CO conversion and hydrogen recovery is studied, and the discussion of reaction phenomenon is presented. The WGS reaction is simulated under the operating conditions of 2 atm and two temperatures of 200 and 300 °C. The simulation results suggest that Da=10−4 and Pp=10−1 are the optimum operating conditions for the reactor system where the conversion reaches nearly 100% exceeding the thermodynamic equilibrium conversion by 11% at 300 °C and the optimal hydrogen recovery is achieved simultaneously. The distribution of components along the axis of the reactor is checked, and then two crucial indicators are raised to assess the extent of reaction and hydrogen separation respectively, for the purpose of guidance for the length design of the reactor. Finally, the analysis of the effect of sweep gas on reactor performance suggests that the optimum flow rate of sweep gas is 0.2–0.5 L/min, and further enhancement of performance can be achieved by using counter-current sweep gas configuration.

Numerical investigations of head-on collisions of binary unequal-sized droplets on superhydrophobic walls

Droplet head-on impact is widely encountered in nature, industry, and agricultural applications. In our study, a two-dimensional axisymmetric model, using the volume-of-fluid method, is built to simulate unequally sized droplet head-on impact on a superhydrophobic surface. The collision regime, after droplet coalescence, is obtained with dimensionless parameters, as well as the contact time, maximum spreading diameter, restitution coefficient, and viscous dissipation. When the impact droplet is larger than the stationary droplet on the substrate, the merged droplet can easily jump up. At high Bond numbers (Bo) or high Ohnesorge numbers (Oh), the merged droplet cannot jump up due to significant gravitational effects or viscous effects, respectively. The energy for droplet jumping mainly comes from the released surface energy after the coalescence of father and mother droplets. The contact time of a droplet with the superhydrophobic substrate is proportional to the Weber number to the 0.5th power (We0.5), and the maximum spreading diameter of a merged droplet is proportional to We0.2. With an increasing size ratio of the father droplet to the mother droplet, both the contact time and maximum spreading diameter increase. These findings will help gain insights into the dynamics of droplet head-on impact.

Numerical Analysis of Inertance Pulse Tube Refrigerator

The inertance type pulse tube refrigerator (IPTR) has been extensively used in industries due to its small size and efficiency. The physical phenomena of oscillating flow in IPTR is complex and it can be examined by using a commercial computational fluid dynamics (CFD) software. Researchers are not so much interested in the 3D analysis of IPTR due to high computational time but for better visualization, it is very beneficial. A two-dimensional axis-symmetric model and 3D model is considered for simulation. The temperature at the cold heat exchanger (CHX) and phase difference between pressure and mass flow rate at CHX is demonstrated. In this paper, CFD analysis of IPTR has been done and various issues involved in the simulation are presented for the betterment in the desired solution.

Study on Arc Extinguishing Performance of DC C4F7N/CO2 Mixed Gas

The arc characteristic analysis of C4F7N/CO2, CO2 and SF6 gases with volume fraction of 10%C4F7N-90% under DC condition is studied. Firstly, based on the internal physical process of arc, a two-dimensional axisymmetric arc model of C4F7N/CO2, CO2 and SF6 gas was established and calculated. The arc temperature distribution and dynamic characteristics of three gas media are compared and analyzed the results show that the temperature distribution of C4F7N/CO2 mixed gas is more similar to that of SF6 gas arc, and its radial cooling speed is faster, indicating that compared with CO2 gas, C4F7N/CO2 mixed gas has better arc-quenching characteristics, which can be used in the study of SF6 substitute gas.

Simulation Analysis of 2D Finite Element Axial Transient Temperature Distribution of HTS Cable

High temperature superconducting (HTS) cables have advantages of low loss and large capacity transmission. In order to analyze and protect the HTS cable, especially in the transient process, this paper develops a new method to analyze its thermal properties. Based on the structure parameters and actual working conditions of three-phase coaxial (tri-axial) HTS cable a two-dimensional (2-D) axisymmetric finite element simulation model along the axis was built in COMSOL. By coupling first and then decoupling, the temperature distribution was studied under the conditions of cooling, rated current, cryogenic system failure, local hot spot and short circuit fault. This method solves the problem that non-isothermal flow (nitf) is hard to converge under transient conditions, and has the advantages of simple and accurate.

Mechanical Behavior of Impregnated REBCO Pancake Winding Based on Electromagnetic-Thermoelastic Analysis

In this study, the mechanical behavior of an impregnated single pancake wound with a REBCO coated conductor is analyzed in magnetic field after its cooling through finite element (FE) modeling. A two-dimensional axisymmetric FE model with averaged material properties of the impregnated winding is developed. First, the thermal residual stress and deformation accumulated during cooling from 300 K to 4.2 K are analyzed. Using the thermal residual stresses and strains as initial conditions, the mechanical behavior of the impregnated winding under the self-field and background field are subsequently studied. Finally, the contribution of the thermal mismatch stress as well as the Lorentz force under the self-field and background field to the radial stress of the impregnated pancake winding is discussed, and the risk of delamination failure under each situation is evaluated. The results show that the radial stress due to the thermal mismatch increases with the decrease of cooling temperature. As the transport current increases, the radial stress decreases under the self-field, but increases under the background field. The discussion indicates that there is the potential risk for delamination failure during cooling, and the risk increases with the decrease of temperature. If delamination does not appear after cooling, the winding will not be damaged owing to interfacial debonding under self-field. However, the risk of delamination failure increases upon increasing the transport current under a strong background field.