Axisymmetric Model Research Articles

Numerical and experimental study of TIG welding arc in high frequency longitudinal magnetic field

The phenomenon of arc compression in TIG welding with high-frequency longitudinal magnetic field (HF-LMF) has been observed. However, its mechanism remains unclear, and there is a lack of numerical investigation. This work presents a two-dimension axisymmetrical model of arc plasma in high-frequency longitudinal magnetic field based on the magnetohydrodynamics (MHD). The distributions of temperature, velocity and pressure of arc plasma in HF-LMF are investigated at different applied LMF frequencies ranging from 0 to 5000 Hz. In order to make the simulation results more convincing, the induced current and the electric force were considered. The results show that the HF-LMF could generate a circumferential electric field, causing particles rotating. However, since HF-LMF is variable, the direction of the electric field also changes, which causes the arc to rotate back and forth. When the frequency of HF-LMF reaches 2000 Hz, the negative pressure zone above the center of the anode disappeared and the arc was compressed. Thus, as the frequency of LMF increases, the distribution of current density, anodic heat flux, and arc pressure changes from a bimodal distribution to a unimodal distribution, and the peak value increases. The theoretical predictions were in good agreement with the experimental results.

Coupled filtration–consolidation model for vacuum-preloaded soft ground

The widespread utilisation of vacuum-assisted prefabricated vertical drains for managing clayey soft ground has led to the development of numerous consolidation models. However, these models have limitations when describing the filtration behaviour of soil under conditions of high water content, without the formation of a particle network. To address this issue effectively, in this work, based on the compressional rheology theory, a two-dimensional axisymmetric model incorporating the compressive yield stress Py(ϕ) and a hindered setting factor r(ϕ) was developed to couple the filtration and consolidation of soil under vacuum preloading. A novel approach for determining the unified ϕ–Py–r relationships was introduced. The equation governing such fluid/solid and solid/solid interactions was solved using the alternative direction implicit method, and the numerical solutions were validated against the one-dimensional filtration cases, three-dimensional laboratory model tests and large-scale field trials. Further parametric analysis suggests that the radius of the representative unit and r(ϕ) exclusively affect the dewatering rate of the clayey slurry, while the gel point and Py(ϕ) influence both the dewatering rate and the final deformation.

Harmonic Vibration Analysis in a Simplified Model for Monitoring Transfemoral Implant Loosening.

A simplified axisymmetric model of a transfemoral osseointegration implant was used to investigate the influence of the contact condition at the bone-implant interface on the vibrational response. The experimental setup allowed the degree of implant tightness to be controlled using a circumferential compression device affixed to the bone. Diametrically placed sensors allowed torsional modes to be distinguished from flexural modes. The results showed that the structural resonant frequencies did not shift significantly with tightness levels. The first torsional mode of vibration was found to be particularly sensitive to interface loosening. Harmonics in the vibrational response became prominent when the amplitude of the applied torque increased beyond a critical level. The torque level at which the third harmonic begins to rise correlated with implant criticality, suggesting a potential strategy for early detection of implant loosening based on monitoring the amplitude of the third harmonic of the torsional mode.

Harnessing the heat below: Efficacy of closed-loop systems in the cooper basin, Australia

Transitioning to renewable energy is vital for combating climate change and reducing CO2 emissions. Geothermal energy, sourced from the earth's crust, presents a promising alternative. While shallow geothermal energy extraction grows steadily, tapping into deep Hot Dry Rock reservoirs poses challenges. Sustainable utilization of deep geothermal energy is crucial for large-scale electricity generation. Australia's Habanero enhanced geothermal system (EGS) projects faced obstacles due to complex fracture networks. Borehole heat exchangers (BHEs) offer a solution, circulating a working fluid without direct contact with geofluids. This study assesses coaxial BHEs' feasibility in the Habanero reservoir using a 2D axisymmetric model (2D-AM), comparing it with a simpler 1D depth-integrated model (1D-DIAM). Both models yield similar outcomes. Additionally, results indicated that the production temperature of the coaxial BHE exponentially decreased from 250 °C to 100 °C within 10 h, rendering energy recovery for electricity generation unsuitable after 10 h of operation. The study proposes an energy recovery cycle of 10 h followed by a 110-h shutdown. Injection temperatures and flow rates significantly impact production efficiency, while steel casing's thermal conductivity has minimal influence on heat exchanger performance.

Study of the acoustic attenuation of 2D axisymmetric models of the human ear equipped with hearing protection

The ear is the organ responsible for auditory perception. Its role is to amplify, transmit, and convert an acoustic wave present in the environment into an electrical pulse that the brain can interpret via the auditory nerve. The objective of this study was to develop two axisymmetric 2D finite element models of the human ear to predict insertion loss when a porous earplug is introduced into the ear canal. In these models, the structure-acoustic interaction was resolved by finite element analysis. For a better representation, assumptions and boundary conditions (such as fixe boundary condition, spring-mass-damping boundary condition, etc...) are considered. The tympanic ring and the earplug are assumed to be fixed, and a load of what comes after the posterior part of the tympanic ring (the ossicular chain) has been replaced by an equivalent mechanical impedance mass-spring-damper system. The first model has a regular geometry, and the second model is obtained by reconstructing a 3D model. These two models were inspired by our previous work. For each model, the insertion loss (IL) is predicted and the results obtained are compared with those of the sound attenuation measurements of hearing protection performed in the laboratory.

Computation of emitter-plasmon interactions using an axis-symmetric model for off-axis dipoles

The axis-symmetric modeling technique is based on expanding vector fields in cylindrical harmonics and computing the response on a two-dimensional cross-section separately for each azimuthal harmonic, significantly reducing computational costs. However, it has limitations when dealing with dipoles placed away from the symmetry axis due to challenges in the expansion of angular modes. To address this, we propose a reformulated axis-symmetric model based on the Fourier expansion of the delta function distribution concerning the azimuthal variable. This model is validated using standard Mie theory for off-axis dipoles and applied to study multiple-emitter-plasmon interactions. The emission properties of a non-cooperative ensemble near a plasmonic nanoparticle are observed to scale with the number of emitters considered, N. Notably, a Dicke effect-like superradiance (N2-dependence) is observed when a spatially disordered ensemble of dipoles oscillates collectively inside a plasmonic dimer gap. This kind of high-level cooperative quantum phenomenon is of high interest in fields such as quantum optics and light-harvesting.

Charging of an Air–Rock Bed Thermal Energy Storage under Natural and Forced Convection

An air-rock bed thermal storage system was designed for small-scale powered generation and analyzed with computational fluid dynamics (CFD) using ANSYS-Fluent simulation. An experimental system was constructed to compare and validate the simulation model results. The storage unit is a cylindrical steel container with granite rock pebbles as a storage medium. The CFD simulation used a porous flow model. Transient-state simulations were performed on a 2D axisymmetric model using a pressure-based solver. During charging, heat input that keeps the bottom temperature at 550 °C was applied to raise the storage temperature. Performance analysis was conducted under various porosities, considering natural and forced convection. The natural convection analysis showed insignificant convection contribution after 10 h of charging, as observed in both average air velocity and the temperature profile plots. The temperature distribution profiles at various positions for both convection modes showed good agreement between the simulation and experimental results. Additionally, both cases exhibited similar temperature growth trends, further validating the models. Forced convection reduced the charging time from 60 h to 5 h to store 70 MJ of energy at a porosity of 0.4, compared to natural convection, which stored only 50 MJ in the same time. This extended charging period was attributed to poor natural convective heat transfer, indicating that relying solely on natural convection for thermal energy storage under the given conditions is not practical. Using a small fan to enhance heat transfer, forced convection is a more practical method for charging the system, making it suitable for power generation applications.

A Mesh Convergence Study for 2D Axisymmetric Pipe Wall Thickness

A meshing size study is essential for any simulation, as it affects the accuracy of the results by approximating the real-world geometry. This paper presents a detailed mesh convergence study for a 2D axisymmetric pipe model. The model incorporates a one-quarter cross-section due to the axisymmetric nature of the pipe. Four pipe wall thicknesses were investigated: 3.40 mm, 7.11 mm, 10.97 mm, and 18.26 mm. The results revealed a significant advantage for simulations involving thin pipes. They achieved convergence, a state with stable solution values, by utilizing a less dense mesh, leading to reduced computational time. This trend was exemplified by the fact that a thinner pipe with thickness, t = 3.40 mm has converged with only 8 mesh elements, whereas a significantly thicker pipe, t = 18.26 mm necessitated 14 elements for convergence. This suggests that more complex geometries, with intricate details, may require a larger and denser mesh for convergence, leading to increased computational time. In conclusion, the mesh convergence study confirms that the finite element analysis (FEA) model has achieved a converged solution.

Estimation and research of the temperature field models of large space spherical mesh shell structures under localized fire

This paper firstly investigated fire dynamics characteristics and the temperature field distributions of large space spherical mesh shell (SMS) structures under localized fire in FDS, and divided the temperature fields into plume region, smoke accumulation region and ceiling jet region. Based on the classical axisymmetric plume model, the predictive models for the steady-state and transient temperature fields in different fire regions for large space SMS structures were proposed in this paper. Thereafter, the proposed temperature models were compared with the simulated results and experimental test results by other scholars, and they were in good agreement. In order to further discover the realistic fire development progress and temperature distribution of large space fire, and validate the proposed temperature field models, this paper designed and conducted three full-scale large space fire tests (Test-1 ∼ Test-3) with different fire source powers in a large space building. Results showed that temperature fields of large space fires could be consisted of near-fire region (Flame region) and far-fire region (Plume region and Ceiling jet region). The steady-state fire source powers were tested for 443 kW, 886 kW, 1090 kW for Test-1, Test-2 and Test-3, respectively, while their maximum temperatures of the roof reached 75 °C, 105 °C and 120 °C. Based on McCaffrey plume model, we further proposed the transient temperature model in flame region for large space structures, and its accuracy was verified by the test results. Moreover, the proposed steady-state and transient temperature fields for large space SMS structures were compared with the tested temperature field data, and the tested and predicted temperature curves were generally in good agreement in plume and ceiling jet regions. Finally, the test results aimed to provide a scientific basis and reference for the fire safety and structural fire-resistant design of large space buildings.

Simulation of the pulsed streamer discharge in water considering the effect of hydrostatic pressure

Streamer discharge is a very complex multi-scale and multi-physics coupling process, and there is no accurate model that can describe its development. In this paper, a two-dimensional axisymmetric fluid model is established in COMSOL to simulate and study the effects of the applied voltage amplitude, the discharge gap distance, the rising edge of pulse voltage, and hydrostatic pressure on the development of the positive streamer discharge at a needle-plate electrode in water under a nanosecond pulse voltage. The results show that increasing the voltage amplitude, decreasing the pulse rise time, and narrowing the discharge gap all increase the electric field strength of the streamer, thereby affecting the electron density of the plasma channel, among which changing the discharge gap has the greatest effect on the electron density. And under the gap of 3 mm, the peak electron density can reach 3.76 × 1023 m−3; if the discharge gap is narrowed to 1 mm, the peak electron density is reduced to 1.20 × 1023 m−3. In addition, hydrostatic pressure and water molecule spacing are closely linked. Increasing the hydrostatic pressure decreases the electric field strength and the peak electron density in the plasma channel, and its effect on the peak electron density saturates with increasing hydrostatic pressure.

Beyond symmetry: Investigating asymmetric melt pool evolution in multi-pulse laser surface melting

A numerical investigation is carried out to explore the intricacies of multi-pulse pulsed laser surface melting (pLSM) to understand its impact on surface evolution. A finite-element-based multi-phase model with temperature-dependent properties is employed to track the interface for multiple laser pulses. Examining various overlap spacings and conducting a comparative analysis of the number of pulses, the study focuses on the exclusive influence of overlapping in surface texture generation. Notably, the assumption of an initially flat surface eliminates the effects of the initial surface roughness to provide unique insights completely based on multi-pulse dynamics. While the first pulse on a flat initial surface resulted in a symmetric surface evolution, asymmetric melt pools were observed in the second pulse and subsequent pulses. The asymmetry results from non-uniform cooling and melt pool flows influenced by the surface evolved in the first pulse. The topography-driven surface tension from the first pulse made the trailing peak solidify slower than the leading peak. The asymmetry was significant for smaller overlaps between the two pulses and reduced as the overlap increased. Further, an increase in the number of laser pulses promotes the generation of identical asymmetric surface features. In conclusion, the study demonstrates the importance of the developed model in accurately predicting the surface evolution influenced by topography-driven surface tension and that single pulse axisymmetric models are insufficient.

Rapid prediction of interface morphology and oxygen transportation in crystal growth based on the response surface method

In this paper, a two-dimensional (2D) axisymmetric model subjected to the gas shear effect and thermal Marangoni effect is developed. It is highlighted that the growth conditions of pulling rate, gas flow rate, crucible, and crystal rotation rates play important roles in determining the crystal behaviors of interface morphology and oxygen transportation during the crystal growth process. A Kriging-based response surface method (RSM) is proposed to rapidly predict the crystal growth behaviors, indicating that the outputs of interface morphology and oxygen concentration can be predicted by the corresponding input growth conditions. By global sensitivity analysis, the pulling rate is identified as the key factor in determining the interface morphology, while gas flow rate and crucible rotation rate have a greater effect on oxygen transportation. Furthermore, these two inputs with the highest sensitivities are used to construct the response surface and predict unknown oxygen transportation. When compared with the numerical simulations, the presented model proves to be an effective tool for reducing measurement time and improving accuracy in predicting crystal behaviors. Our findings provide important insights into understanding the crystal growth process under different growth conditions and inspire a data-driven method for crystal growth prediction.

Influence characteristic and improvement mechanism of thermal storage performance of Packed-bed thermocline tank based on high-temperature molten salt

Chloride salts and carbonates thermal energy storage (TES) have great application potential in high-temperature concentrated solar power (CSP) plants. However, their thermal storage characteristics, performance improvement mechanism and economic feasibility of application in high-temperature conditions are not clear. In this study, a transient, two-dimensional and axisymmetric model is developed for packed-bed thermocline tanks. The effects of six commonly solid fillers on thermal storage performance of NaCl-KCl-MgCl2 salt and Na2CO3-K2CO3-Li2CO3 salt at an operation temperature of 450–800 °C are simulated. The suggestions for optimizing fillers are provided combined with thermal and economic performance. Results show that high volume heat capacity and low thermal conductivity of fillers play important roles in deferring migration and weakening diffusion of thermocline, thus promoting thermal storage capacity and efficiency of tanks. Concrete and cast iron are suitable fillers for chloride salts and carbonates TES. The concrete tank is suitable for systems with strict cost control and low TES requirements. The iron tank is suitable for systems with high TES and low cost control requirements, which significantly increases effective thermal storage capacity of chloride salts by 222.1 % and considerably reduces TES cost of carbonates by 41.1 %. The results can be beneficial for high-temperature TES system of CSP plants.

Numerical analysis of the effect of vibroflotation in the vicinity of a deep-water quay wall

The paper describes an attempt to include the effect of vibroflotation on the quay wall in the numerical analysis. An axisymmetric FEM model was made, in which the increment of pressure on the steel wall, caused by initiated horizontal displacement, was checked. The stress read off in this way has been implemented in the plane strain model of the quay wall. The results of the internal forces and deformations are presented. The displacements were collated with the geodetic survey

Multifrequency polarimetry of high-synchrotron peaked blazars probes the shape of their jets

Multifrequency polarimetry is emerging as a powerful probe of blazar jets, especially with the advent of the Imaging X-ray Polarimetry Explorer (IXPE) space observatory. We studied the polarization of high-synchrotron peaked (HSP) blazars, for which both optical and X-ray emission can be attributed to synchrotron radiation from a population of nonthermal electrons. We adopted an axisymmetric stationary force-free jet model in which the electromagnetic fields are determined by the jet shape. When the jet is nearly parabolic, the X-ray polarization degree is ΠX ∼ 15–50%, and the optical polarization degree is ΠO ∼ 5–25%. The polarization degree is strongly chromatic: ΠX/ΠO ∼ 2–9. This chromaticity is due to the softening of the electron distribution at high energies, and is much stronger than for a uniform magnetic field. The electric vector position angle (EVPA) is aligned with the projection of the jet axis on the plane of the sky. These results compare very well with multifrequency polarimetric observations of HSP blazars. When the jet is instead nearly cylindrical, the polarization degree is large and weakly chromatic (we find ΠX ∼ 70% and ΠO ∼ 60%, close to the expected values for a uniform magnetic field). The EVPA is perpendicular to the projection of the jet axis on the plane of the sky. A cylindrical geometry is therefore practically ruled out by current observations. The polarization degree and the EVPA may be less sensitive to the specific particle acceleration process (e.g., magnetic reconnection or shocks) than previously thought.

Study on the 2D equivalent nonlinear dynamics simulation model related to high speed precision bearing and spindle

The stiffness and contact stress of the bearing spindle system are the key factors affecting its machining accuracy and service life under the condition of high-speed service, which will be affected by different structural parameters and service conditions. It is essential to establish an efficient and accurate computational simulation model to understand the influence of complex factors on the nonlinear dynamic characteristics of the bearing spindle system. Firstly, in the paper, a 2D axisymmetric finite element model of the bearing, aims at the relationship between stiffness and contact stress of the bearing under high-speed service, has been built based on a classical dynamic analysis model and the reversed method of material parameters of equivalent rolling balls. Additionally, for the BT30 spindle, the 2D axisymmetric finite element model of the bearing spindle system also has been built and applied in mechanical analysis of spindle under different conditions of assembly and service, based on the bearing model. The results show that the axial force of bearings decreases as the rotational speed increases, and an augmentation in speed will result in a reduction in the axial stiffness of the BT30 spindle. In addition, the maximum contact stress exhibits a slight decline as the rotational speed increases. Furthermore, with an escalating preload, the stiffness and contact stress of the spindle undergo substantial increments, however, these parameters will cease to alter once a certain threshold is reached.

Effect of Crystal Rotation on Melt Convection and Resistivity Distribution in 200 mm Floating Zone Silicon Single Crystal Growth.

Floating silicon is particularly suitable for the production of power devices and detectors due to its high purity and high resistivity. However, when the crystal diameter increases to 200 mm, the inhomogeneous distribution of dopants in the radial direction of the crystal becomes an important factor affecting the quality of the crystal. In this paper, the melt flow and crystal interface dopant distribution of 200 mm floating zone silicon under different crystal rotation modes using 2D axisymmetric models was calculated. In the simulation, the crystal rotates unidirectionally clockwise or alternates between clockwise and counterclockwise rotations and is compared with the corresponding experimental results. The results of alternate rotation show a significant improvement in the distribution of resistivity, which is explained from the perspective of melt flow, providing ideas for the industrial production of high-quality FZ silicon crystals.

Influence of Excavation Radius on Behavior of Circular Foundation Pits Supported by Prefabricated Recyclable Structures: Full-Scale Experimental and Numerical Analysis

A foundation pit’s excavation area, which is determined by its radius in a circular foundation pit, exerts a considerable influence on the pit’s behavior. Using a full-scale experiment on a circular foundation pit retained by a prefabricated recyclable supporting structure (PRSS), this study develops a series of axisymmetric numerical models to systematically investigate the influence of excavation radius on the pit’s deformation, stress, and stability. Furthermore, simulation results from axisymmetric models are compared with those from plane strain models to illustrate the influence mechanism. The results show that at a given excavation depth, the deflection and bending moments of the supporting piles, the earth pressure on the non-excavation side, and ground surface settlement increase with the enlarged excavation radius, but the increase rate progressively decreases. However, the foundation pit’s safety factor decreases with an increasing excavation radius and gradually stabilizes. When the excavation radius exceeds 50 m, its influence on the foundation pit’s behavior significantly diminishes. The axisymmetric model results closely approximate those from the plane strain models, suggesting that the spatial arching effects of the circular foundation pit can be disregarded.

The interface dewetting process of particulate filled polymer composite

AbstractDewetting is one of the most common damage modes in particulate filled polymer composite, which greatly damages the structural integrity of the composite and leads to the deterioration of its mechanical properties. Studying the dewetting evolution process of composite is of great significance for evaluating the meso damage degree of composite and suppressing the development of dewetting damage. This article constructs an axisymmetric cylindrical cell model of a single particle inclusion matrix, derives the interface dewetting evolution process of the model under uniaxial tensile loading condition, and analyzes the influence of model geometric parameters and external loading conditions on the dewetting process. Subsequently, numerical models were constructed at both micro and meso scales, and dynamic tensile calculations were performed to analyze the correlation between the dewetting rate, porosity, and mechanical performance. Finally, a cylindrical cell specimen was designed to observe the interface dewetting evolution under uniaxial tensile conditions, confirming the conclusions of theoretical analysis and numerical simulation.Highlights Constructed a theoretical model for the dewetting process of interface. Conducted numerical analysis of dewetting process at both meso and micro scales. Designed interface dewetting experiment and analyzed the dewetting process.

A Computer Model of a Marx Generator Charging a Coaxial Switched Wave Oscillator

The paper describes an axisymmetric Finite-Difference Time-Domain computer model of a coaxial Switched Wave Oscillator integrated with a dipole antenna. The model analyzes the operation of a realistic circuit model of a multistage Marx generator that charges the oscillator to a high voltage. The initial field distribution is calculated with an electrostatic finite-difference method solver to speed up the time-domain analysis. The work presents the results of our circuit model of a Marx generator’s simulations of the charging phase, followed by the results from the discharge phase, using our axisymmetric Finite-Difference Time-Domain model. Our work describes new and fast numerical solvers that can observe the operation of Switched Wave Oscillator systems (also considering the connected antenna). The codes could be used in the process of designing such a system. Advanced boundary conditions modeling the spark gap and oscillator’s excitation set our work apart from the other attempts in the literature.