Two-dimensional Simulations Research Articles

Acoustic Emission simulation: assessing the influence of AE source modeling and addressing the issue of dimensionality in the propagation medium

A thorough understanding of simulating Acoustic Emission (AE) requires the source modeling and propagation medium to be considered respectively. Crack initiation and propagation simulation as an AE source can be performed by the Successive Node Release (SNR) method and the Direct Node Release (DNR) method. Both are compared to show how the source model affects the AE signals. The SNR method is commonly used to simulate the crack initiation and propagation. It is necessary to consider the influence of the crack velocity profile on the crack initiation [1]. However, for the DNR method, all nodes are instantaneously released once the critical crack length is attained. Hence, it is not necessary to consider the velocity profile. Instead, it is sufficient to define the average crack velocity. However, the kinetic energy varies when employing different methods, leading to a variance in the source energy. We thus assess the suitable conditions to apply the DNR method to represent crack initiation and investigate the influence of the node release methods on the AE signals. Secondly, a comparative assessment of the Pencil-lead Break test on PMMA plates is conducted using both two-dimensional (2D) and three-dimensional (3D) finite element simulations. This analysis is valuable for understanding the deficiencies and constraints of the 2D simulation. However, there is a significant difference in the AE signals between 2D and 3D simulations, suggesting that the 2D simulation is unable to capture the AE information during wave propagation, in spite of its lower computational cost. Therefore, to obtain extensive and precise information from the PLB test, it is crucial to have an extensive understanding of the limits of the 2D simulation. This understanding should take into account factors such as the distance between the sensor and the source, as well as the descriptors chosen to characterize the AE.

Numerical simulation of the effects of pulsed injection on combustion and flow processes in a supersonic combustor

This paper describes two-dimensional numerical simulations of pulsed injection to a hydrogen-fueled air-breathing ramjet using the Reynolds-averaged Navier–Stokes method. We analyze the effects of sinusoidal pulsed injection on the start-up ignition time, start-up ignition range, combustion efficiency, and flow field evolution of the ramjet and compare the performance with that of steady injection. The results show that pulsed injection shortens the ignition time and optimizes the ignition equivalence ratio of hydrogen. Pulsed injection also improves the combustion efficiency of hydrogen, increasing the thrust of the engine by 7.79% compared with steady injection under the same equivalence ratio. We find that pulsed injection can cause oscillations in the ramjet combustion flow field, and show that the oscillation frequency is affected by the pulsed injection frequency.

Microjet Flow Control on an Airfoil Flap: Particle Image Velocimetry Characterization

Normal-blowing microjets near the trailing edge of a flap can improve the aerodynamic performance of high-lift systems, potentially without some of the system-integration drawbacks of traditional systems. Previous two-dimensional simulations and a preliminary wind-tunnel test demonstrated the effectiveness of the microjet concept on a deployed flap. To further validate microjet effectiveness, this study uses a specially developed particle image velocimetry technique to estimate the momentum injected by a microjet on a deployed Fowler flap of a two-element NLR7301 airfoil while simultaneously measuring the lift enhancement provided by the microjet via surface pressure taps. The test results are broadly consistent with numerical simulations that predict lift increases proportionally to the square root of momentum injection. Within the experimental uncertainties, the test results show slightly less lift benefit for a given level of estimated momentum injection compared to the simulations, possibly due to three-dimensional effects such as spanwise variability and spanwise velocity components of the injected air, which could not be measured with the current instrumentation.

The spatio-temporal evolution of shock wave pressure induced by laser: Effects of laser parameters and confinement layer

The spatio-temporal distribution of the shock wave pressure on the surface of the target is the key to the performance of laser shock processing (LSP), which is mainly determined by the laser parameters and the confinement layer. The two-dimensional kinetic simulations of the expansion process of the shock wave induced by irradiation of an aluminum target with nanosecond laser pulses are performed. It is found that by controlling the gap between the rigid confinement layer and the aluminum target, and the interval time between the double pulse laser pulses, multiple peaks appear on the shock wave pressure-time curve of the aluminum target surface, and the value and interval time of each peak will change.

Performance Enhancement and Mechanism Analysis of IGZO Thin-Film Transistors Utilizing Interdigital Structure

This study investigates the issue of leakage current reduction in oxide semiconductor thin-film transistors (TFTs) with interdigital structures. Electrical measurements clearly demonstrate that the leakage current of interdigitated IGZO devices decreases as the on/off ratio increases. To explore the reasons behind the reduction in leakage current, we conducted two-dimensional device simulations. The results confirm that the use of interdigital structures can influence the electric field distribution within the device channel, introducing shielding electric fields. As the number of interlayer structures between the source and drain increases, the shielding electric fields proportionally increase. Additionally, interdigitated IGZO devices exhibit a large on/off ratio exceeding 2.7×1010, an ultra-low leakage current of less than 3×10-16 A/μm, and a high saturation mobility of 9.4 cm2/Vs. These findings provide valuable insights for designing low-power, high-performance devices based on IGZO.

The shape of convection in 2D and 3D global simulations of stellar interiors

Theoretical descriptions of convective overshooting in stellar interiors often rely on a basic one-dimensional parameterization of the flow called the filling factor for convection. Several different definitions of the filling factor have been developed for this purpose, based on: (1) the percentage of the volume, (2) the mass flux, and (3) the convective flux that moves through the boundary. We examine these definitions of the filling factor with the goal of establishing their ability to explain differences between 2D and 3D global simulations of stellar interiors that include fully compressible hydrodynamics and realistic microphysics for stars. We study convection and overshooting in pairs of identical two-dimensional (2D) and three-dimensional (3D) global simulations of stars produced with a fully compressible, time-implicit hydrodynamics code. We examine pairs of simulations for (1) a $3$ odot $ red giant star near the first dredge-up point, (2) a $1$ M$_ odot $ pre-main-sequence star with a large convection zone, (3) the current sun, and (4) a $20$ M$_ odot $ main-sequence star with a large convective core. Our calculations of the filling factor based on the volume percentage and the mass flux indicate asymmetrical convection near the surface for each star with an outer convection zone. However, near the convective boundary, convective flows achieve inward-outward symmetry for each star that we study; for 2D and 3D simulations, these filling factors are indistinguishable. A filling factor based on the convective flux is contaminated by boundary-layer-like flows, making a theoretical interpretation difficult. We present two possible new alternatives to these frequently used definitions of a filling factor, which instead compare flows at two different radial points. The first alternative is the penetration parameter of anders2022stellar . The second alternative is a new statistic that we call the plume interaction parameter. We demonstrate that both of these parameters captures systematic differences between 2D and 3D simulations around the convective boundary.

Comparative experimental and numerical study of mixing efficiency in 3D-printed microfluidic droplet generators: T junction, cross junction, and asymmetric junctions with varying angles

In droplet-based microfluidics, rapid mixing during droplet formation enhances reaction uniformity, eliminating the need for micromixers. In this research, we conducted a comprehensive study by first employing a series of two-dimensional (2D) numerical simulations, followed by experimental investigations using 3D-printed microfluidic chips. We compared the mixing efficiency, droplet diameter, and droplet eccentricity of three different types of droplet generators: T junction, cross junction, and asymmetric droplet generators with various angles. Regarding mixing efficiency, we observed that the asymmetric droplet generators outperformed the cross junction by 30 % but fell slightly short of the mixing efficiency achieved by the T junction (1 %). Additionally, while the mixing index in the asymmetric generators closely matched that of the T junction, these asymmetric generators produced smaller droplets by 72 %. Increasing the angle in asymmetric droplet generators resulted in enhanced mixing efficiencies and an increase in droplet diameters. The asymmetric junction with a 30° angle could achieve a mixing efficiency of up to 80 %. Additionally, an analysis of the dispersed phase flow rate revealed that higher flow rates lead to larger droplet sizes and reduced mixing efficiencies. The asymmetric droplet generators improve mixing efficiency facilitating rapid reagent mixing, all while maintaining a small droplet diameter.

Exploiting Axisymmetry to Optimize CFD Simulations—Heave Motion and Wave Radiation of a Spherical Buoy

Simulating the free decay motion and wave radiation from a heaving semi-submerged sphere poses significant computational challenges due to its three-dimensional complexity. By leveraging axisymmetry, we reduce the problem to a two-dimensional simulation, significantly decreasing computational demands while maintaining accuracy. In this paper, we exploit axisymmetry to perform a large ensemble of Computational Fluid Dynamics (CFDs) simulations, aiming to evaluate and maximize both accuracy and efficiency, using the Reynolds Averaged Navier–Stokes (RANS) solver interFOAM, in the opensource finite volume CFD software OpenFOAM. Validated against highly accurate experimental data, extensive parametric studies are conducted, previously limited by computational constraints, which facilitate the refinement of simulation setups. More than 50 iterations of the same heaving sphere simulation are performed, informing efficient trade-offs between computational cost and accuracy across various simulation parameters and mesh configurations. Ultimately, by employing axisymmetry, this research contributes to the development of more accurate and efficient numerical modeling in ocean engineering.

A robust compact finite difference framework for simulations of compressible turbulent flows

A robust high-order compact finite difference framework is proposed for simulations of compressible turbulent flows with high spectral resolution using a fully collocated variable storage paradigm. Both inviscid and viscous fluxes are assembled at the edge-staggered grid locations. Nonlinear robustness is attained as a consequence of the intrinsic reduction of aliasing errors in the inviscid fluxes due to the spectral behavior of the compact interpolation schemes. Additional robustness is provided by enhancing the spectral resolution of the viscous flux and its divergence at small scales using purely staggered numerical differentiation. Demonstrative simulations have shown numerical stability of the compact finite difference discretization without any type of solution filtering on both Cartesian and curvilinear meshes. For simulations on a curvilinear mesh, a general metric evaluation approach that satisfies the geometric conservation law is proposed. Additional approaches to combining the proposed scheme with approximate Riemann solvers and artificial diffusivities for shock-capturing are also discussed. Along with theoretical analysis, rigorous evaluation and validation of the methodology on canonical tests, including classic two-dimensional simulations, direct numerical simulations, and large-eddy simulations, are used to confirm robustness and accuracy.

Power-Law Scaling Relating the Average Charge State and Kinetic Energy in Expanding Laser-Driven Plasmas.

A universal power-law scaling z[over ¯]∝E^{0.4} in the correlation between the average ion charge state z[over ¯] and kinetic energy E in expanding laser-driven tin plasmas is identified. Universality here refers to an insensitivity to all experimental conditions: target geometry, expansion direction, laser wavelength, and power density. The power law is accurately captured in an analytical consideration of the dependence of the charge state on temperature and the subsequent transfer of internal to kinetic energy in the expansion. These analytical steps are individually, and collectively, validated by a two-dimensional radiation-hydrodynamic simulation of an expanding laser-driven plasma. This power-law behavior is expected to hold also for dense plasma containing heavier, complex ions such as those relevant to current and future laser-driven plasma light sources.

Viewing Explosion Models of Type Ia Supernovae through Insights from Terrestrial Cellular Detonation.

The cellular structure is considered to be a key as a criterion in initiation, propagation, and quenching of terrestrial detonation. While a few studies on type Ia supernovae, which are known to involve detonation, have addressed the importance of the cellular structure, further detailed treatment will benefit enhanced understanding of the explosion outcomes. In the present study, we bridge this gap in the astrophysics and engineering fields, focusing on the detonation in a helium-rich white dwarf envelope as the triggering process for the so-called double-detonation model. The cellular structures are quantified via high-resolution two-dimensional simulations. We demonstrate that widely accepted terrestrial-experimental criteria for quenching and initiation of detonation can indeed explain the results of previous hydrodynamic simulations very well. The present study highlights the potential of continuing to apply the insight from terrestrial detonation experiments to astrophysical problems, specifically the long unresolved problem of the explosion mechanism of type Ia supernovae.

Deployment of tethered gene drive for confined suppression in continuous space requires avoiding drive wave interference.

Gene drives have great potential for suppression of pest populations and removal of exotic invasive species. CRISPR homing suppression drive is a powerful but unconfined drive, posing risks of uncontrolled spread. Thus, developing methods for confining a gene drive is of great significance. Tethered drive combines a confined system such as Toxin-Antidote Recessive Embryo drive with a strong drive such as a homing suppression drive. It can prevent the homing drive from spreading beyond the confined drive and can be constructed readily, giving it good prospects for future development. However, we have found that care must be taken when deploying tethered drive systems in some scenarios. Simulations of tethered drive in a panmictic population model reveal that successful deployment requires a proper release ratio between the two components, tailored to prevent the suppression drive from eliminating the confined system before it has the chance to spread. Spatial models where the population moves over a one-dimensional landscape display a more serious phenomenon of drive wave interference between the two tethered drive components. If the faster suppression drive wave catches up to the confined drive wave, success is still possible, but it is dependent on drive performance and ecological parameters. Two-dimensional simulations further restrict the parameter range for drive success. Thus, careful consideration must be given to drive performance and ecological conditions, as well as specific release proposals for potential application of tethered drive systems.

The effect of ice shelf rheology on shelf edge bending

Abstract. The distribution of pressure on the vertical seaward front of an ice shelf has been shown to cause downward bending of the shelf if the ice is assumed to have vertically uniform viscosity. Satellite lidar observations show that many shelf edges bend upward and that the amplitude of upward deflections depends systematically on ice shelf thickness. A simple analysis is presented showing that upward bending of shelf edges can result from vertical variations in ice viscosity that are consistent with field observations and laboratory measurements. Resultant vertical variations in horizontal stress produce an internal bending moment that can counter the bending moment due to the shelf-front water pressure. Assuming a linear profile of ice temperature with depth and an Arrhenius relation between temperature and strain rate allows derivation of an analytic expression for internal bending moments as a function of shelf surface temperatures, shelf thickness and ice rheologic parameters. The effect of a power-law relation between stress difference and strain rate can also be included analytically. The key ice rheologic parameter affecting shelf edge bending is the ratio of the activation energy, Q, and the power-law exponent, n. For cold ice surface temperatures and large values of Q/n, upward bending is expected, while for warm surface temperatures and small values of Q/n downward bending is expected. The amplitude of bending should scale with the ice shelf thickness to the power 3/2, and this is approximately consistent with a recent analysis of shelf edge deflections for the Ross Ice Shelf. These scaling relations should help guide fully two-dimensional numerical simulations of shelf bending.

A modular finite element approach to saturated poroelasticity dynamics: Fluid–solid coupling with Neo-Hookean material and incompressible flow

Several methods have been developed to model the dynamic behavior of saturated porous media. However, most of them are suitable only for small strain and small displacement problems and are built in a monolithic way, so that individual improvements in the solution of the solid or fluid phases can be difficult. This study shows a macroscopic approach through a partitioned fluid–solid coupling, in which the skeleton solid is considered to behave as a Neo-Hookean material and the interstitial flow is incompressible following the Stokes–Brinkman model. The porous solid is numerically modeled with a total Lagrangian position-based finite element formulation, while an Arbitrary Lagrangian-Eulerian stabilized finite element approach is employed for the porous medium flow dynamics. In both fields, an averaging procedure is applied to homogenize the problem, resulting in a macroscopic continuous phase. The solid and fluid homogenized domains are overlapped and strongly coupled, based on a block-iterative solution scheme. Two-dimensional simulations of wave propagation in saturated porous media are employed to validate the proposed formulation through a comprehensive comparison with analytical and numerical results from the literature. The analyses underscore the proposed formulation as a robust and precise modular approach for addressing dynamic problems in poroelasticity.

Simulation of Interfacial Waves in Core-Annular Pipe Flow with a Turbulent Annulus

Abstract Numerical simulations are conducted for the wave initiation, growth, and saturation at the oil-water interface in core-annular flow. The focus is on conditions with a turbulent water annulus, but the laminar water annulus is also considered. The simulation results are compared with lab measurements. The growth rate for the linear instability of different wave lengths in the case of a turbulent water annulus is obtained from two-dimensional axisymmetric Reynolds-Averaged Navier-Stokes simulations with the Launder-Sharma low-Reynolds number k-e model. The latter simulation results provide the most unstable wave length for the turbulent water annulus. Our study also shows the following. The maximum wave growth rate for a turbulent water annulus is significantly higher than for a laminar water annulus. The most unstable wave length in the simulations is about 25% smaller than in the experiments. The wave amplitude for the different wave lengths in the simulations is typically 17% lower than in the experiments.

FGM modeling considering preferential diffusion, flame stretch, and non-adiabatic effects for hydrogen-air premixed flame wall flashback

Preferential diffusion plays an important role especially in hydrogen flames. Flame stretch significantly affects the flame structure and induces preferential diffusion. A problematic phenomenon occurring in real combustion devices is flashback, which is influenced by non-adiabatic effects, such as wall heat loss. In this paper, an extended flamelet-generated manifold (FGM) method that explicitly considers the preferential diffusion, flame stretch, and non-adiabatic effects is proposed. In this method, the diffusion terms in the transport equations of scalars, viz. the progress variable, mixture fraction, and enthalpy, are formulated employing non-unity Lewis numbers that are variable in space and different for each chemical species. The applicability of the extended FGM method to hydrogen flames is investigated using two- and three-dimensional numerical simulations of hydrogen-air flame flashback in channel flows. The results of the extended FGM method are compared with those of detailed calculations and other FGM methods. The two-dimensional numerical simulations show that considering both preferential diffusion and flame stretch improves the prediction accuracy of the mixture fraction distribution and flashback speed. The three-dimensional numerical simulations show that the prediction accuracy of the flashback speed, backflow region, and distributions of physical quantities near the flame front is improved by employing the extended FGM method, compared with the FGM method that considers only the heat loss effect. In particular, the extended FGM method successfully reproduced the relationship between the reaction rate and curvature. These results demonstrate the effectiveness of the extended FGM method.Novelty and Significance Statement The novelty of this research is the development of a flamelet-generated mani-fold (FGM) method that explicitly considers preferential diffusion, flame stretch, and non-adiabatic effects. To the best of the authors’ knowledge, no studies have performed numerical simulations of pure hydrogen flames using such an FGM method. The developed FGM method was applied to numerical simula- tions of hydrogen-air premixed flame flashback at an equivalence ratio of 0.5 and reproduced the flashback speed of lean hydrogen-air premixed flame. The applicability of the FGM method to the numerical simulation of hydrogen-air flashback is reported first. This research is significant because the FGM method is one of the most widely used combustion models for premixed combustion, and the development of an accurate FGM method will contribute to the engineering field. The accurate prediction of the flame flashback attempted in this study is particularly important for the development of hydrogen-fueled combustion devices.

Semi-Empirical Model Based on the Influence of Turbulence Intensity on the Wake of Vertical Axis Turbines

In the context of energy shortages and the development of new energy sources, tidal current energy has emerged as a promising alternative. It is typically harnessed by deploying arrays of multiple water turbines offshore. Vertical axis water turbines (VAWTs), as key units in these arrays, have wake effects that influence array spacing and energy efficiency. However, existing studies on wake velocity distribution models for VAWTs are limited in number, accuracy, and consideration of influencing factors. A precise theoretical model (Lam’s formula) for wake lateral velocity can better predict wake decay, aiding in the optimization of tidal current energy array designs. Turbulence in the ocean, serving as a medium for energy exchange between high-energy and low-energy water flows, significantly impacts the wake recovery of water turbines. To simplify the problem, this study uses software ANSYS Fluent 2020 R2 for two-dimensional simulations of VAWT wake decay under different turbulence intensities, confirming the critical role of turbulence intensity in wake velocity decay. Based on the obtained data, a new mathematical approach was employed to incorporate turbulence intensity into Lam’s wake formula for VAWTs, improving its predictive accuracy with a minimum error of 1%, and refining some parameter calculations. The results show that this model effectively reflects the impact of turbulence on VAWT wake recovery and can be used to predict wake decay under various turbulence conditions, providing a theoretical basis for VAWT design, optimization, and array layout.

Exploring Innovative Methods in Maritime Simulation: A Ship Path Planning System Utilizing Virtual Reality and Numerical Simulation

In addressing the high costs, inefficiencies, and limitations of purely digital simulations in maritime trials for unmanned vessel path planning, this paper introduces a ship virtual path planning simulation test system. This system, unbound by temporal and spatial constraints, vividly showcases the navigational performance of vessels. After analyzing the virtual testing requirements for the autonomous navigation performance of unmanned surface vehicles (USVs), we established the overall framework of this system. Data-driven by a numerical simulation platform, the system achieves synchronized operation between physical and virtual platforms and supports interactive path planning simulations between USVs and the virtual testing system. Furthermore, to address the limitations of traditional ship trajectory planning evaluation, this paper develops a global path planning fitness evaluation function that comprehensively considers trajectory safety, navigation distance, and vessel stability, achieving optimal comprehensive routes through the particle swarm optimization algorithm. Test results indicate an average roll reduction of 14.31% in the planned routes, with a slight increase in navigation distance. By integrating two-dimensional curve simulation with three-dimensional visualization, this paper not only overcomes the limitations of purely physical and purely virtual simulations but also enhances the overall credibility and intuitiveness of the simulation. Experimental results validate the system’s effectiveness, providing a novel method for autonomous navigation testing and evaluation of USVs.

Enhancing efficiency in a-Si:H/μc-Si micromorph tandem solar cells through advanced light-trapping techniques using ARC, TRJ, and DBR

In this study, the performance of a-Si:H/μc-Si:H tandem solar cells was comprehensively assessed through two-dimensional numerical simulations. Our work involved optimizing the layer thicknesses and exploring advanced light-trapping techniques to enhance photogenerated current in both sub-cells. To reduce surface reflections on the top cell, we proposed a two-layer antireflection coating, composed of SiO2/Si3N4. Additionally, we implemented a 1D photonic crystal as a broadband back reflector within the solar cell. In order to balance the current density between the sub-cells and prevent carrier accumulation at the interface, we introduced a tunnel recombination junction (TRJ). This TRJ consisted of n-μc-Si:H/p-μc-Si:H layers with a thickness of 10 nm. Under global AM 1.5G conditions, our proposed cell structure exhibited impressive electrical characteristics, including an open-circuit voltage of 1.38 V, a short-circuit current density of 12.51 mA/cm2, and a fill factor of 80.82%. These attributes culminated in a remarkable total area conversion efficiency of 14%.

Synthetic ground motions in heterogeneous geologies from various sources: the HEMEWS-3D database

Abstract. The ever-improving performances of physics-based simulations and the rapid developments of deep learning are offering new perspectives to study earthquake-induced ground motion. Due to the large amount of data required to train deep neural networks, applications have so far been limited to recorded data or two-dimensional (2D) simulations. To bridge the gap between deep learning and high-fidelity numerical simulations, this work introduces a new database of physics-based earthquake simulations. The HEterogeneous Materials and Elastic Waves with Source variability in 3D (HEMEWS-3D) database comprises 30 000 simulations of elastic wave propagation in 3D geological domains. Each domain is parametrized by a different geological model built from a random arrangement of layers augmented by random fields that represent heterogeneities. Elastic waves originate from a randomly located pointwise source parametrized by a random moment tensor. For each simulation, ground motion is synthesized at the surface by a grid of virtual sensors. The high frequency of waveforms (fmax⁡=5 Hz) allows for extensive analyses of surface ground motion. Existing and foreseen applications range from statistical analyses of the ground motion variability and machine learning methods on geological models to deep-learning-based predictions of ground motion that depend on 3D heterogeneous geologies and source properties. Data are available at https://doi.org/10.57745/LAI6YU (Lehmann, 2023).