Full Numerical Analysis Research Articles

Optimizing ground improvement with encased stone columns: a 3D numerical analysis in very soft clay

Purpose This study aims to investigate the behavior of different types of stone columns, including the short and floating columns, as well as the ordinary and the geosynthetic encased stone columns (OSC and GESC). The effectiveness of the geosynthetic encasement and the impact of the installation using the lateral expansion method on the column performance is evaluated through a three-dimensional (3D) unit cell numerical analysis. Design/methodology/approach A full 3D numerical analysis is carried out using the explicit finite element code PLAXIS 3D to examine the installation influence on settlement reduction (ß), lateral displacement (Ux) and vertical displacement (Uz) relative to different values of lateral expansion of the column (0% to 15%). Findings The findings demonstrate the superior performance of GESC, particularly short columns outperforming floating counterparts. This enhanced performance is attributed to the combined effects of geosynthetic encasement and increased lateral expansion. Notably, these strategies contribute significantly to decreasing lateral displacement (Ux) at the column’s edge and reducing vertical displacement (Uz) under the rigid footing. Originality/value In contrast to previous studies that examined the installation effect of OSC contexts, this paper presents a comprehensive investigation into the effect of geosynthetic encasement and the installation effects using the lateral expansion method in very soft soil, using 3D numerical simulation. The study emphasizes the significance of the consideration of geosynthetic encasement and lateral expansion of the column during the design process to enhance column performance.

Performance enhancement of air-cooled PEMFC stack by employing tapered oblique fin channels: Experimental study of a full stack and numerical analysis of a typical single cell

In this study, a novel cathode flow field plate with additional tapered oblique fin (OF) channels is proposed for air-cooled proton exchange membrane fuel cells (PEMFCs) to promote their heat dissipation and output power. Air-cooled PEMFC stacks with conventional (parallel configuration) and novel flow fields are respectively manufactured and experimentally tested under various load currents. The performance and temperature distributions of the stacks are comparatively studied in detail. Besides, a three-dimensional and two-phase numerical model is established and validated by the experiment data to further comparative investigate the heat and mass transport mechanism of the two studied flow field designs. The results show that the stack with the novel flow field has higher output power, which is 4.87% higher than that with a conventional design at a load current density of 0.55 A cm−2. Due to the forced convection and secondary vortex phenomena in the OF channels, the local overheating in the porous electrode is relieved. Moreover, the entropy generations due to heat transfer of the cathode CL and cooling channels are significantly increased. The oxygen transport under cathode ribs is also noteworthily enhanced when the OF channels are adopted.

From WIMPs to FIMPs with low reheating temperatures

Weakly- and Feebly-Interacting Massive Particles (WIMPs and FIMPs) are among the best-motivated dark matter (DM) candidates. In this paper, we investigate the production of DM through the WIMP and FIMP mechanisms during inflationary reheating. We show that the details of the reheating, such as the inflaton potential and the reheating temperature, have a strong impact on the genesis of DM. The strong entropy injection caused by the inflaton decay has to be compensated by a reduction of the portal coupling in the case of WIMPs, or by an increase in the case of FIMPs. We pinpoint the smooth transition between the WIMP and the FIMP regimes in the case of low reheating temperature. As an example, we perform a full numerical analysis of the singlet-scalar DM model; however, our results are generic and adaptable to other particle DM candidates.Interestingly, in the singlet-scalar DM model with low-reheating temperature, regions favored by the FIMP mechanism are already being tested by direct detection experiments such as LZ and XENONnT.

Particle-Size Effect in Airborne Standing-Wave Acoustic Levitation: Trapping Particles at Pressure Antinodes

It is well known that a particle put into an ultrasonic standing wave tends to move towards an equilibrium position, where the acoustic pressure-induced force on its surface compensates the particle weight. We demonstrate, by means of a full three-dimensional numerical analysis and a thorough experimental study, that the acoustic force, and thus the particle's behavior, critically depends on its size. While particles within certain size ranges, including those smaller than half the wavelength, are trapped on axis around the pressure nodes, particles in other size ranges are trapped off axis nearby the pressure antinodes. This behavior, related with sign inversions of the radiation force, implies that the magnitude of the force, and thus the trapping stiffness, can be maximum or null for some specific sizes. As a case of study, we analyze expanded polystyrene particles levitated in air with an ultrasonic frequency of 40 kHz, a relevant system due to recent applications for the development of volumetric displays. Yet, our results illustrate a general behavior of radiation-based traps with structured wave fields.

Magnon Dynamics in Parity-Time-Symmetric Dipolarly Coupled Waveguides and Magnonic Crystals

We consider the magnonic properties of two dipolarly coupled magnetic stripes, both deposited on a normal conductive substrate with strong spin-orbit coupling. A charge current in the substrate acts on the adjacent magnets with spin-orbit torques, which result in magnonic damping or antidamping of the spin waves, and hence a gain-loss coupling of the two magnetic stripes. The whole setup is demonstrated to exhibit features typical for parity-time- ($PT$) symmetric systems. Phenomena are demonstrated that can be functionalized in magnonic devices, including reconfigurable magnonic diodes and logic devices. Alternative stripe designs and $PT$-symmetric, periodic, coupled magnonic textures are studied. Analytical and full numerical analysis identify the conditions for the appearance of exceptional points (EPs), where magnonic gain and loss are balanced and evidence nonreciprocal magnon propagation and enhanced magnon excitation around EPs. Furthermore, the dipolar coupling is shown to bring in a wave-vector-dependent $PT$-symmetric behavior. Proposing and simulating a $PT$-symmetric magnonic crystal, we show how EPs and hence associated phenomena can be steered to a particular wave vector in a gaped spectrum via material design. The phenomena offer additional tools for magnonic based communication and computational devices.

NS-[formula omitted] model for fluid–fluid interaction problems at high Reynolds numbers

We consider a fluid–fluid interaction problem, where two flows are coupled through a nonlinear rigid lid condition, and one or both of these flows are at high Reynolds numbers. A method is proposed, that combines the NS-ω turbulence model with a partitioning method—so that the resulting model is efficiently decoupled, allows for the usage of preexisting solvers (e.g., air and water domain solvers), and is capable of resolving the flows at high Reynolds numbers. The model is shown to be unconditionally stable and have optimal convergence properties. The model also allows for the non-filtered velocity in the interface terms; it has been shown recently that filtering the velocity in the interface terms could corrupt the quality of the model’s solution. To the best of the authors’ knowledge, this is the first model with non-filtered velocity on the interface, that lends itself to full numerical analysis.

Instability in charged Gauss–Bonnet–de Sitter black holes

We study the instability of the charged Gauss-Bonnet de Sitter black holes under gravito-electromagnetic perturbations. We adopt two criteria to search for an instability of the scalar type perturbations, including the local instability criterion based on the $AdS_2$ Breitenl\"{o}hner-Freedman (BF) bound at extremality and the dynamical instability via quasinormal modes by full numerical analysis. We uncover the gravitational instability in five spacetime dimensions and above, and construct the complete parameter space in terms of the ratio of event and cosmological horizons and the Gauss-Bonnet coupling. We show that the BF bound violation is a sufficient but not necessary condition for the presence of dynamical instability. While the physical origin of the instability without the Gauss-Bonnet term has been argued to be from the $AdS_2$ BF bound violation, our analysis suggests that the BF bound violation can not account for all physical origin of the instability for the charged Gauss-Bonnet black holes.

Magnetic-field-free spin–orbit torque-driven magnetization dynamics in CoFeB/β-W-based nanoelements

A full numerical analysis, which takes into account the effects of the spin Hall effect, interfacial Dzyaloshinskii–Moriya interaction, and thermal fluctuations, is carried out in in-plane magnetized CoFeB/MgO/CoFeB/high-resistivity tungsten (β-W) nanoelements. The analysis is focused on the investigation of the underlying mechanisms of magnetic-field-free spin–orbit torque (SOT)-driven magnetization reversal process on subnanosecond time scales. It is found that the magnetization in the free magnetic layer can be electrically toggled between the parallel and antiparallel alignment with respect to the fixed magnetic layer without the assistance of an external magnetic field, in which the out-of-plane canting of the magnetic moments at the element edges plays a significant role in the nucleation and subsequent expansion of the reversed magnetization. Furthermore, the thermally activated magnetization process combined with the SOT effect is found to significantly reduce the effective energy barrier to the magnetization reversal and alter the details of the SOT-driven magnetization process in nanomagnets.

Thermofluidic analysis of Al2O3-water nanofluid cooled branched wavy heat sink

The thermofluidic analysis of Al2O3-water nanofluid-cooled, branched wavy heat sink microchannel (BWHS MC) was carried out for Re = 100–300. The conjugate heat transfer was calculated using ANSYS fluent. The fluid flow is simulated using the RNG k-ε model in the full domain numerical analysis. The phenomenological behaviour of the nanofluid flow through BWHS MC is further studied using numerical results. In comparison, experiments were also performed using a straight channel heat sink microchannel (SCHS MC) of the same hydraulic diameter as the BWHS. The branched wavy microchannel encouraged the secondary flow, thus enhanced the macroscopic mixing. Apart from disruption of the boundary layer and its reinitialization, vortices have been formed near the secondary channel, which improves thermal performance. BWHS reported a higher pressure penalty than SCHS, but the BWHS showed superior performance over SCHS. The heat transfer coefficient is increased at increasing nanofluids concentrations for any given Reynolds number. For the BWHS MC, an enhancement of about 154% of the heat transfer coefficient with a 2% volumetric concentration of nanofluids is achieved at Re = 300 compared to the SCHS MC at similar conditions.

Optimal design of radial inflow turbine for ocean thermal energy conversion based on the installation angle of nozzle blade

Ocean Thermal Energy Conversion (OTEC), as a new type of renewable energy, has huge development potential. Turbine is the most critical component in the ocean thermal energy conversion system, which directly determines the performance and energy conversion efficiency of the system. Therefore, the optimal design of turbines is very important to improve the efficiency of ocean thermal energy conversion. Based on the full consideration of the small temperature difference application characteristics of ocean thermal energy conversion and the special thermophysical properties of organic working fluids, this paper designs an ammonia working centripetal turbine with a power of 100 kW for OTEC applications, and then analyzes the effect of different geometric parameters on turbine performance. At the same time, the key parameters of the turbine are optimized based on full three-dimensional CFD numerical simulation analysis. It's shown that the nozzle blade installation angle has a very important impact on the performance of the turbine. Through optimization, when the nozzle blade installation angle reaches 30.5°, the efficiency is 91.77%, which is 6.25% points higher than the design value. The internal flow field performance is the best without obvious shock wave and reverse vortex phenomenon, which further improves the efficiency of the turbine and improves the internal flow.

Light trapping in thin film crystalline silicon solar cells using Multi-Scale photonic topological insulators

In this paper, a new method is proposed to trap sunlight in the active layer of thin film solar cells. In the proposed technique, multi-scale photonic topological insulators (PTI) realized by photonic crystals, are integrated inside the active layer of a thin film solar cell in order to trap sunlight in the cell. The trapping is realized by excitation of edge states supported by the designed topological insulator. The performance of the proposed solar cell with the topological insulator inside is investigated through full wave numerical analysis. Numerical results show that the proposed method enhances the absorption of the solar spectrum inside the cell in a wide range of wavelengths, and also for different angles of incidence. The short circuit current provided by the proposed solar cell is numerically calculated illustrating a value of 27.72 mA/cm2 for a normally incident light which is 47% higher than a simple solar cell without topological insulator inside.

Thermofluidic characteristic of a nanofluid-cooled oblique fin heat sink: An experimental and numerical investigation

This paper presents an experimental and numerical investigation on the thermofluidic performance of 0.5–2.0 % of the volumetric concentration of Al2O3-water nanofluids through oblique fin heat sink microchannel (OFHS MC) in the Reynolds number range 100–300. In comparison, experiments were also performed using a straight channel heat sink microchannel (SCHS MC) of the same hydraulic diameter as the oblique fin channel. The fluid flow is simulated using the RNG k-ε model in both periodic and full domain numerical analysis. The phenomenological behaviour of the nanofluid flow is further studied using numerical results. The oblique fin microchannel encouraged the secondary flow, thus enhanced the macroscopic mixing. Boundary layer disruption and vortices generation in the secondary channel is the critical phenomena of improved heat transfer. A substantial improvement of heat transfer coefficient is achieved for nanofluid and oblique fin heat sink combinations compared to the straight channel heat sink. The heat transfer coefficient is increased at increasing nanofluid concentrations for any given Reynolds number and channel configuration. The enhancement of about 55 % in the heat transfer coefficient with a 2 % volumetric concentration of nanofluid is achieved at Re = 300 in an oblique fin heat sink. The heat transfer enhancement is always significant than the pressure penalty. The oblique fin heat sink improves the average junction temperature considerably compared to the straight channel heat sink. The inclusion of nanofluid can reduce the experimental junction temperature by up to 6 °C. Therefore, the combined advantage of the oblique fin heat sink with nanofluid is anticipated as one of the potential alternatives for electronics cooling.

Computational tools for the analysis of circular failure of rock slopes

Among other types of failure in slopes created by excavation or filling, circular (also referred to as rotational) type of failure plays an important role in the design and stability analysis of high rock slopes, such as those encountered in deep open pit mines. When a rock slope of significant height involves predominantly one type of jointed rock mass, the scale of the problem is frequently such that the rock mass (intact rock and rock discontinuities) can be regarded as a homogeneous isotropic material. In such case, if the rock slope is unstable and collapse occurs, circular (or rotational) failure as in failed slopes in soils is also observed for the rock slope. One main goal in practical design of deep open pit mines is to determine safe inclination angles for the pit faces to be excavated to avoid failure. Computational tools for quick assessment of the stability conditions, in particular determination of factor of safety and location of the critical circular failure surface, are useful during the preliminary stages of open pit design. Among others, such tools allow the engineer to gain insight in the role that the different variables controlling the problem have in defining the stability conditions for the rock slope. This paper provides first an overview of typical numerical techniques used to assess the stability of high rock slopes. For the case of slopes in rock masses that are assumed to obey the Mohr-Coulomb or the Hoek-Brown failure criteria, the paper discusses how application of transformation rules leads the criteria to be re-casted in dimensionless form, so when these are applied to the solution of slope problems, the results (factor of safety and coordinates that define the location of the critical circular failure surface) can be summarized in dimensionless compact forms. The paper presents then computational tools in the form of dimensionless charts and computer spreadsheets for stability analysis. These are developed from numerical limit equilibrium models that use the mentioned transformation rules. Among others, the computational tools allow the concept of mechanical similarity of rock slopes to be naturally introduced. Finally, the paper presents various rock slope examples that illustrate the use of the computational tools. In these examples, results from limit equilibrium models are also compared with results obtained with full numerical analysis, in particular with finite difference models implementing the shear strength reduction technique.

3D numerical analysis of pile response due to soil movements induced by an adjacent deep excavation

Purpose This paper aims to investigate single pile and pile group responses due to deep braced excavation-induced soil movement in soft clay overlying dense sand. The analysis focuses first on the response of vertical single pile in terms of induced bending moment, lateral deflection, induced axial force, skin resistance distribution and pile settlement. To better understand the single pile behaviour, a parametric study was carried out. To provide further insights about the response of pile group system, different pile group configurations were considered. Design/methodology/approach Using the explicit finite element code PLAXIS 3 D, a full three-dimensional numerical analysis is carried out to investigate pile responses when performing an adjacent deep braced excavation. The numerical model was validated based on the results of a centrifuge test. The relevance of the 3 D model is also judged by comparison with the 2 D plane strain model using the PLAXIS 2 D code. Findings The results obtained allowed a thorough understanding of the pile response and the soil–pile–structure interactions phenomenon. The findings reveal that the deep excavation may cause appreciable bending moments, lateral deflections and axial forces in nearby piles. The parametric study showed that the pile responses are strongly influenced by the excavation depth, relative pile location, sand density, excavation support system and pile length. It also showed that the response of a pile within a group depends on its location in relation to the other piles of the pile group, its distance from the retaining wall and the number of piles in the group. Originality/value Unlike previous studies which investigated the problem in homogeneous geological context (sand or clay), in this paper, the pile response was thoroughly studied in a multi-layered soil using 3 D numerical simulation. To take into account the small-strain nonlinear behaviour of the soil, the Hardening soil model with small-strain stiffness was used in this analysis. For a preliminary design, this numerical study can serve as a practical basis for similar projects.

Higher temporal accuracy for LES-C turbulence models

A new family of turbulence models, Large Eddy Simulation with Correction (LES-C) has been proposed in Labovsky (2020), that reduces the modeling error of LES models by using a predictor–corrector type method, known as defect correction. Here we propose to combine this approach with another predictor–corrector technique, known as deferred correction, to reduce the time discretization error of the LES-C models. The method uses the already existing LES-C structure, adding several terms to the right hand side of the correction step. This allows for the increase in accuracy at virtually no extra computational cost. We perform full numerical analysis and provide several computational tests that demonstrate the effectiveness of the new method.

Effect of distributed piezoelectric segments on the buckling load of FG cylindrical micro/nano shell

The present paper investigates size-dependent buckling analysis of a functionally graded cylindrical micro/nano shell integrated with a regular pattern of piezoelectric segments based on first-order shear deformation theory and virtual work principle. The piezoelectric segments are actuated with external voltage. The nonlocal electro-elastic relations are developed in cylindrical coordinate system for both functionally graded layer and piezoelectric segments. An analytical solution is developed based on Navier’s technique for simply supported boundary conditions. A verification of results is performed using comparison with available results of literature. A full numerical analysis is given to investigate effect of various important parameters such as length to radius ratio, segment angles, radius to core-thickness ratio, segment-thickness ratio, number of segments, nonlocal coefficient to core-thickness ratio and external voltage on the buckling loads.

Tailoring lab-on-fiber SERS optrodes towards biological targets of different sizes

• Three different types of SERS substrates were fabricated by nanosphere lithography. • Performances were compared against different bio-targets (molecule, protein, cell). • A readout system for SERS optrode operation, via optical fiber, was optimized. In this paper, we studied the influence of the geometrical configuration of surface-enhanced Raman scattering (SERS)-active self-assembling gold nanostructures on the interaction with biological targets of different sizes, aiming at large-scope SERS lab-on-fiber optrodes composed of highly efficient SERS substrates integrated onto optical fibre tips. By using nanosphere lithography, we fabricated three types of highly ordered and reproducible SERS-active substrates. To correlate the SERS response to the steric hindrance of the biological target, we experimentally analysed and compared the SERS spectra of three representative biological probes, i.e., ultralow-molecular-weight molecules of biphenyl-4-thiol (BPT, small molecule, 186.27 Da), bovine serum albumin (BSA, medium molecule, 66.5 kDa) and red blood cells (RBCs, diameter <10 μm, complex target). All SERS-active substrates provided the Raman fingerprint of the biological targets, but the SERS intensity was dependent on the substrate geometry and its specific steric interfacing with biological targets. A full three-dimensional numerical analysis was carried out by means of the finite element method to gain insight into the electric field distribution and hot spot distribution of the fabricated structures. By correlating the electric field distribution with the SERS response, we conclude that the most efficient target-based architectures feature not only “intense” but also “accessible” hot spots. Finally, we optimized a Raman readout system for SERS optrode operation with efficient illumination and collection via an optical fibre.

Phenomenology of scotogenic scalar dark matter

We reexamine the minimal Singlet + Triplet Scotogenic Model, where dark matter is the mediator of neutrino mass generation. We assume it to be a scalar WIMP, whose stability follows from the same {mathbb {Z}}_{2} symmetry that leads to the radiative origin of neutrino masses. The scheme is the minimal one that allows for solar and atmospheric mass scales to be generated. We perform a full numerical analysis of the signatures expected at dark matter as well as collider experiments. We identify parameter regions where dark matter predictions agree with theoretical and experimental constraints, such as neutrino oscillations, Higgs data, dark matter relic abundance and direct detection searches. We also present forecasts for near future direct and indirect detection experiments. These will further probe the parameter space. Finally, we explore collider signatures associated with the mono-jet channel at the LHC, highlighting the existence of a viable light dark matter mass range.

Full wave numerical analysis of wideband and high directive log spiralTHzphotoconductive antenna

AbstractThis study presents, for the first time, a novel design of ultra‐wideband (UWB), circularly polarized and highly directive log‐spiral THz photoconductive antenna. The proposed antenna is simulated in High Frequency Structure Simulator using gold as the antenna electrode material which is backed by a quartz substrate (εr= 3.78, tan δ = 0.0001) and hemispherical silicon‐based lens with a diameter of 140 μm. A comprehensive detailed parametric study of the antenna design parameters is performed in the frequency range of 1 to 6 THz for the optimal design of the developed antenna structure. The optimal antenna structure with integrated lens has UWB characteristics with −10 dB impedance bandwidth of 5 THz and 3 dB axial ratio bandwidth of around 4 THz. The observed directivity and half‐power beam width of the presented design varies in the range 5 to 12 dBi and 34° to 62°, respectively, for the frequency range of 1 to 4 THz. The wideband, high directivity as well as high‐efficiency (&gt;50%) characteristics of the proposed design make it a favorable choice for the THz sensing and imaging applications.

Iterative load transfer procedure for settlement evaluation of lattice-shaped diaphragm walls in multilayered soil

Abstract Lattice-shaped diaphragm wall (LSDW) is an emerging bridge foundation system that offers high stiffness, construction efficiency, low cost and minimal noise. However, the scarce knowledge on settlement prediction of LSDW has hindered its application in practice. This study proposes an approach to predict the settlement of LSDW in multilayered soils based on the load transfer approach. A simplified analytical approach and related load transfer models are proposed to analyze the load transfer mechanism of an LSDW. Specific load transfer models and parameters of external skin friction and wall base resistance for the LSDW are discussed in detail. Special attention is given to the derivation of models for soil core internal skin friction and base resistance. An iterative solution procedure with three appropriate displacement criteria is then proposed for the load transfer analysis of LSDW. A full scale field test and relevant numerical study were conducted on a single chamber LSDW foundation to evaluate the load transfer mechanism of LSDW. In addition, a published full scale study and numerical analysis involving multi chamber LSDW were investigated to validate the predictions of the proposed approach. Reasonable agreement between the calculated, measured and simulated load-settlement responses is observed. In general, the results validated the adopted models for the external and internal skin friction and base resistance and the corresponding models parameters. The results provide useful guidance for design of LSDW in terms of contribution of soil core skin friction to the load carrying capacity.