Two-dimensional Finite Element Research Articles

Electrifying HCOOH synthesis from CO2 building blocks over Cu–Bi nanorod arrays

Precise electrochemical synthesis of commodity chemicals and fuels from CO2 building blocks provides a promising route to close the anthropogenic carbon cycle, in which renewable but intermittent electricity could be stored within the greenhouse gas molecules. Here, we report state-of-the-art CO2-to-HCOOH valorization performance over a multiscale optimized Cu-Bi cathodic architecture, delivering a formate Faradaic efficiency exceeding 95% within an aqueous electrolyzer, a C-basis HCOOH purity above 99.8% within a solid-state electrolyzer operated at 100 mA cm-2 for 200 h and an energy efficiency of 39.2%, as well as a tunable aqueous HCOOH concentration ranging from 2.7 to 92.1 wt%. Via a combined two-dimensional reaction phase diagram and finite element analysis, we highlight the role of local geometries of Cu and Bi in branching the adsorption strength for key intermediates like *COOH and *OCHO for CO2 reduction, while the crystal orbital Hamiltonian population analysis rationalizes the vital contribution from moderate binding strength of η2(O,O)-OCHO on Cu-doped Bi surface in promoting HCOOH electrosynthesis. The findings of this study not only shed light on the tuning knobs for precise CO2 valorization, but also provide a different research paradigm for advancing the activity and selectivity optimization in a broad range of electrosynthetic systems.

Dynamic response of Akcakoca RCC Dam including galleries

Dams are structures that demand a significant amount of concrete, making them costly constructions. Hence, various alternative methods are employed for dam construction, one of which is the use of Roller Compacted Concrete (RCC). This is a case study, which focuses on examining the behavior of RCC dams with and without galleries under seismic excitations, considering the Akçakoca RCC dam in Düzce Province. The seismic ground motion data from the 1999 Düzce earthquake were utilized. The impact of galleries inside the concrete dams was investigated through stress and displacement, considering both empty and full reservoir conditions. The Eulerian-Lagrangian coupled (CEL) approach was employed for two-dimensional fluid finite elements. This study revealed that reservoir water and galleries have a notable influence on the behavior of dams under seismic forces. In cases with reservoirs and galleries, stress and displacement values increased, and critical changes in stresses were observed around gallery areas. Therefore, careful design considerations are essential for dams with galleries under significant seismic forces.

Use of optimization methods in the calculation of slope stability

This article focuses on studying and identifying factors that contribute to ground movement and determining appropriate methods for verifying slope stability. Depending on the type of soil, the geometry of the slope and the type of work to be carried out, it is appropriate to choose a suitable technical solution, adapted both to the nature of the soil in place and to its environment. The major techniques that can be used to increase the mechanical properties of soils are the modification of the internal structure of the existing soil and the reinforcement of the soil by the addition of materials and inclusions. These techniques make it possiblte to improve the compactness and bearing capacity of the soil in place. The case presented in this research was studied using a two-dimensional finite element model, to study the effect of various mechanical characteristics of the soil, including cohesion (C), friction angle (φ), the reference module (Eref) and the backfill volume. We examined the influence of the coupling on the safety factor and the location of the sliding surface to have an optimal slope design. To do this, we formulated the problem into an optimization framework using MINITAB 19 software. This framework will use a design of experiments (DOE) approach to identify the optimal combination of factors ensuring slope safety. The results obtained will be analyzed to evaluate the effectiveness of the DOE method in determining the most favorable combination of parameters. We expect the mechanical properties of the slope to have the most significant influence on the factor of safety and the location of the sliding surface.

A computational approach to integrate three-dimensional peridynamics and two-dimensional higher-order classical elasticity theory for fracture analysis

AbstractAs a nonlocal alternative of classical continuum theory, peridynamics (PD) is mathematically compatible to discontinuities, making it particularly attractive for failure prediction. The PD theory on the other side can be computationally demanding due to its nonlocal interactions. A coupling between PD and refined higher-order finite element method (FEM) integrates their salient features. The present study proposes a computational approach to couple three-dimensional peridynamics with two-dimensional higher-order finite elements based on classical elasticity. The bond-based PD modeling is considered in a region where damage might appear while refined finite element modeling is used for the remaining region. The refined finite elements employed in this study are based on the 2D Carrera Unified Formulation (CUF), which provides 3D-like accuracy with optimized computational efficiency. The coupling between PD and FEM is achieved through the Lagrange multiplier method which permits physical consistency and compatibility at the interface domain. An adaptive convergence check algorithm is also proposed to achieve predetermined accuracy in the solution with minimum computational effort. Simulations of quasi-static tension tests, wedge splitting tests and L-plate cracking tests are carried out for verification. In-depth analysis shows that the present approach can reproduce the linear deformation, material degradation and crack propagation in an effective way.

Hydraulic Fracture Propagation in Layered Heterogeneous Rocks with Spatially Non-Gaussian Random Hydromechanical Features

AbstractThis study proposes a stochastic method to analyse the propagation of hydraulic fractures affected by layered heterogeneity in rocks in a toughness-dominated regime. The study utilises the phase-field method in the context of two-dimensional finite element analysis to model the hydraulic fracture (HF) propagation in rock materials in laboratory scale. Field data on hydrogeologic properties of some rocks reveal that material heterogeneity may appear in the form of leptokurtic marginal distributions. Generalised sub-Gaussian (GSG) model is capable of capturing physical characteristics of such rocks, and it is employed to stochastically model rocks with layered lithologic heterogeneity by generating a large number of auto- and cross-correlated random fields for hydro-geomechanical properties. To investigate the sensitivity of the cracking response to the inherent characteristics of material heterogeneity, various GSG distribution forms are considered in Monte Carlo (MC) analyses. The HF’s deviation from the theoretically predicted direction, which is perpendicular to the direction of the minimum in situ stress, is correlated with the distribution of hydro-geomechanical properties, showing a Gaussian-type distribution. This study concludes that the differential stress and the bedding orientation are the main factors affecting the HF deviation and the required breakdown pressure for initiating the HF propagation from a borehole. In the application of directional hydraulic fracturing (DHF), the effect of bedding layers becomes dominant when the bedding orientation is aligned with the direction of perforations in the boreholes.

Compact-tension-shear specimen for orthotropic materials in fracture toughness testing

Conducting Compact-Tension-Shear (CTS) tests emerges as a promising research methodology to determine the fracture toughness of orthotropic materials in mixed-mode I&II. However, the absence of pertinent fracture parameter solutions incorporating material orthotropy impedes the further application and standardization of CTS testing. Therefore, this study performed a systematic two-dimensional finite element analysis (FEA) on orthotropic CTS specimens to evaluate critical fracture parameters, including the normalized stress intensity factors (YI, YII) and compliance (u). First, the impacts of three commonly cited boundary conditions (BCs) of CTS models were investigated, revealing that the simplified or equivalent methods developed for isotropic CTS models are no longer applicable. Subsequently, the suitable CTS models were used to analysis the coupling effects of material orthotropy (λ, ρ), crack length ratios (a/W), and loading angles (β). Findings indicated that YI or u no longer exhibit a monotonic relationship with respect to a/W or β under strong orthotropy. The impact of λ and ρ on fracture parameters is equally significant across different geometries and loading conditions. Further, the impact of orthotropy on YII is relatively small, while the more affected YI may have a difference compared to isotropic results of over 80%. Finally, CTS tests were carried out on the unidirectional carbon fiber-reinforced epoxy resin composite measuring the fracture toughness in mixed-modes I&II. The obtained fracture parameter solutions were applied and validated during the process. The acquired results are poised to contribute to the advancement of fracture toughness testing standardization for orthotropic materials under mixed-mode loading.

Indenting a thick gel with a solid spherical inclusion

A spherical inclusion is embedded in a soft gel block. A vertical force is applied on the gel surface by means of a spherical indenter. The loading axis is not aligned with the inclusion but placed at a horizontal offset displacement from the inclusion. The measurement of indentation force and inclusion trajectory are compared to the computational results from two-dimensional (2D) Finite Element Analysis (FEA) simulations. A discernible instability emerges when the indentation reaches a critical depth, in accordance with the Southwell instability theory. The three-dimensional (3D) trajectory shows distinct features that were previously not captured by the 2D FEA simulations.

Investigating the effect of anatomical variations in the response of the neonatal brachial plexus to applied force: Use of a two-dimensional finite element model.

The brachial plexus is a set of nerves that innervate the upper extremity and may become injured during the birthing process through an injury known as Neonatal Brachial Plexus Palsy. Studying the mechanisms of these injuries on infant cadavers is challenging due to the justifiable sensitivity surrounding testing. Thus, these specimens are generally unavailable to be used to investigate variations in brachial plexus injury mechanisms. Finite Element Models are an alternative way to investigate the response of the neonatal brachial plexus to loading. Finite Element Models allow a virtual representation of the neonatal brachial plexus to be developed and analyzed with dimensions and mechanical properties determined from experimental studies. Using ABAQUS software, a two-dimensional brachial plexus model was created to analyze how stresses and strains develop within the brachial plexus. The main objectives of this study were (1) to develop a model of the brachial plexus and validate it against previous literature, and (2) to analyze the effect of stress on the nerve roots based on variations in the angles between the nerve roots and the spinal cord. The predicted stress for C5 and C6 was calculated as 0.246 MPa and 0.250 MPa, respectively. C5 and C6 nerve roots experience the highest stress and the largest displacement in comparison to the lower nerve roots, which correlates with clinical patterns of injury. Even small (+/- 3 and 6 degrees) variations in nerve root angle significantly impacted the stress at the proximal nerve root. This model is the first step towards developing a complete three-dimensional model of the neonatal brachial plexus to provide the opportunity to more accurately assess the effect of the birth process on the stretch within the brachial plexus and the impact of biological variations in structure and properties on the risk of Neonatal Brachial Plexus Palsy.

A Gaussian process approach for rapid evaluation of skin tension

Skin tension plays a pivotal role in clinical settings, it affects scarring, wound healing and skin necrosis. Despite its importance, there is no widely accepted method for assessing in vivo skin tension or its natural pre-stretch. This study aims to utilise modern machine learning (ML) methods to develop a model that uses non-invasive measurements of surface wave speed to predict clinically useful skin properties such as stress and natural pre-stretch. A large dataset consisting of simulated wave propagation experiments was created using a simplified two-dimensional finite element (FE) model. Using this dataset, a sensitivity analysis was performed, highlighting the effect of the material parameters and material model on the Rayleigh and supersonic shear wave speeds. Then, a Gaussian process regression model was trained to solve the ill-posed inverse problem of predicting stress and pre-stretch of skin using measurements of surface wave speed. This model had good predictive performance (R2 = 0.9570) and it was possible to interpolate simplified parametric equations to calculate the stress and pre-stretch. To demonstrate that wave speed measurements could be obtained cheaply and easily, a simple experiment was devised to obtain wave speed measurements from synthetic skin at different values of pre-stretch. These experimental wave speeds agree well with the FE simulations, and a model trained solely on the FE data provided accurate predictions of synthetic skin stiffness. Both the simulated and experimental results provide further evidence that elastic wave measurements coupled with ML models are a viable non-invasive method to determine in vivo skin tension. Statement of significanceTo prevent unfavourable patient outcomes from reconstructive surgery, it is necessary to determine relevant subject-specific skin properties. For example, during a skin graft, it is necessary to estimate the pre-stretch of the skin to account for shrinkage upon excision. Existing methods are invasive or rely on the experience of the clinician. Our work aims to present an innovative framework to non-invasively determine in vivo material properties using the speed of a surface wave travelling through the skin. Our findings have implications for the planning of surgical procedures and provides further motivation for the use of elastic wave measurements to determine in vivo material properties.

An exploration into surface wrinkling in 3D printing inspired orthotropic bilayer systems

Surface instability, termed wrinkling, might occur in compressed bilayer systems constituted by an external rigid skin resting on an internal soft substrate, where wrinkling is favored by the rigidity contrast between the two layers. In this paper, the same instability mechanism is explored by considering a substrate characterized by an orthotropic elastic response. By varying the orientation of the principal axes of the substrate’s material, the critical strain of wrinkling and the wrinkles’ wavelength can be tuned during compression. Theoretical formulations for wrinkling are discussed along with the results obtained by linear bifurcation and geometrically nonlinear analyses carried out with two-dimensional finite element models. To experimentally validate the results, the intrinsic properties of Fused Deposition Modeling (FDM) 3D printing technology are leveraged: bilayer objects are manufactured by printing continuous outer shells (corresponding to the rigid skin) along the borders, while the inner raster is shaped with a porous infill pattern, forming a substrate with an orthotropic elastic response.

Obliquely incident seismic response of subway stations following urban soil internal erosion

Urban groundwater infiltration resulting from tropical storm rainfall can lead to internal soil erosion and ground subsidence. The long-term effects of these phenomena may result in uneven settlement of the subway system, posing risks to its safety and operational integrity. Suffusion poses a significant hazard to long-term subway operation. It is a type of soil internal erosion characterized by the migration of fine particles from the pore channels between coarse particles. This study focused on the performance degradation of different gap-graded sands caused by internal erosion, observed through triaxial compression tests. Using the cap plasticity model and considering mechanical parameters before and after soil erosion, a refined two-dimensional finite element model of a soil subway station structure based on ABAQUS was developed to analyze the deformation and damage pattern of the subway structure resulting from soil internal erosion and earthquake. The results of this study demonstrated that localized internal soil erosion significantly contributes to uneven settlement in subway stations, potentially compromising their seismic performance during oblique seismic excitations.

Effects of crustal rheology and fault strength on the formation of the Qaidam Basin: Results from 2-D mechanical modeling

The Cenozoic Qaidam Basin on the northern Tibetan Plateau is bounded by the foreland thrust belts of the East Kunlun Mountains to the south and Qilian Mountains to the north. In this basin, the maximum thickness of the accumulated sedimentary strata is ∼17 km near the geographic center of the basin. Such a basin architecture challenges the classic foreland-basin deformation model, wherein substantial sediments should be localized near the basin margins owing to thrust loads on a bending plate. Based on the available geological and geophysical constraints, we built a two-dimensional viscoelastoplastic finite element model to investigate whether the unique pattern of the Qaidam Basin was mechanically related to the rheological structure of the crust and frictional strength of the basin-bounding thrust fault. By testing reasonable bounds on the viscosity of the ductile crust and effective frictional coefficient of the thrust faults, we modeled a basin framework that fits well with that of Qaidam Basin. The model parameters include a layered rheological structure, with the viscosity of the ductile crust of the basin being two orders of magnitude greater than that of the adjacent mountain belts and an effective frictional coefficient of >0.2. Furthermore, the initial width of the basin significantly affected its deformation style. Therefore, the layered rheological structure of the crust and frictional strength of the basin-bounding thrust faults played important roles in the formation of the Qaidam Basin. Our findings suggest that the inelastic behavior of the crust affects foreland deformation, highlighting that the classic foreland basin model must be revised for some tectonic settings.

Robust Thermal Transport across the Surface-Active Bonding SiC-on-SiC.

Surface-active bonding (SAB) is a promising technique for semiconductors directly bonding. However, the interlayer of the bonding interface and the reduced layer thickness may affect thermal transport. In this study, the temperature-dependent cross-plane thermal conductivity of 4H-SiC thin films and the effective thermal boundary resistance (TBReff) of the bonding SiC-on-SiC are measured by the multiple-probe wavelength nanosecond transient thermoreflectance (MW-TTR). The measured temperature-dependent cross-plane thermal conductivity of the 4H-SiC thin film exhibits good quantitative agreement with calculation by density functional theory (DFT) including higher-order four-phonon (4ph) scattering, especially at high temperatures (>400 K). The theoretical calculations indicate the non-negligible importance of 4ph scattering in 4H-SiC high-temperature applications, due to the significantly increasing 4ph scattering rate at increasing temperature and strong temperature dependence of 4ph scattering. The measured nonzero but small TBReff (2.33 + 0.43/-1.15 m2 K/GW) at the SiC-SiC interface is analyzed with molecular dynamics (MD) simulation, indicating that a strong bonding interface with an extremely thin interlayer is formed by the SAB process. Two-dimensional finite element simulations of the experimental equivalent structures are further investigated, and the significant effects (at least 19 °C) of TBReff on the maximum temperature (Tmax) are confirmed. This study provides insight into the fundamental phonon transport and interface thermal transport mechanism in SAB SiC-on-SiC and paves the way for improved 4H-SiC efficient device manufacturing and thermal management.

Numerical Simulation of Polymeric Strap Material Reinforced Walls Under Seismic Excitation

This paper presents a comparison between the two-dimensional finite element and experimental results of shaking table tests on six one-third-scale polymeric strap or polymeric geostrip reinforced walls performed under seismic excitation at given peak ground accelerations [Formula: see text]. The effects of initial tangent stiffness or the stiffness of polymeric strap material [Formula: see text] and the slope angle of the cohesionless backfill material [Formula: see text] on the maximum relative displacement, [Formula: see text], of the reinforced earth wall, the values of the horizontal incremental dynamic earth pressure [Formula: see text] with distributions, acceleration responses, horizontal dynamic active earth pressure coefficient [Formula: see text] and maximum dynamic tensile forces [Formula: see text] were assessed in this study. Moreover, the vertical dynamic active earth pressure coefficients [Formula: see text] and the angles of the resulting dynamic active force with horizontal [Formula: see text] were predicted from the numerical analysis. Closely matched responses between the experimental and numerical studies were attained. Data obtained from experimental and numerical studies illustrated that increasing the slope angle of the cohesionless backfill material resulted in an increase in the values of horizontal displacement in the walls, and in dynamic earth pressure and root mean square acceleration [Formula: see text]. Increasing the stiffness of the reinforcement material caused a decrease in horizontal reinforced earth wall displacement and increases in dynamic earth pressure. In addition, the conventional pseudostatic limit equilibrium methods overestimated [Formula: see text] values, whereas they underestimated [Formula: see text] values, and the recommended [Formula: see text] values by current design codes were not found to be compatible with the numerical and experimental results.

Numerical Study on the Effects of Helix Diameter and Spacing on the Helical Pile Axial Bearing Capacity in Cohesionless Soils

The methods employed to calculate the axial bearing capacity of a helical pile depends on the shear failure model around the pile, which is also influenced by the spacing and diameter of the helical plates. However, studies on the transition of the failure mode and the load transfer mechanism with the change of helical plate spacing and diameter in cohesionless soil subjected to axial compressive load have been limited. Thus, this paper investigated the effects of helix diameter and spacing on the axial compressive load-bearing capacity, shear failure model, and load transfer mechanism of helical piles with two helical plates embedded in the homogeneous medium and dense sands, as well as in the stratified medium to very dense sand. Axial loading tests on helical piles with various helix diameters and spacings were simulated using a two-dimensional finite element program with axisymmetric modeling to obtain the load-settlement curve, which was later used to estimate the ultimate bearing capacity of the helical piles. The ultimate bearing capacity of the helical piles was also computed using the conventional methods, i.e., the individual bearing and cylindrical shear methods, and then compared to the numerical-based axial bearing capacity. The stress-strain behaviors of pile and soil were modeled using the Linear Elastic and Mohr-Coulomb material models, respectively. The results show that the numerical-based ultimate bearing capacity of a helical pile increased with increasing the diameter and spacing of the helix. However, the ultimate bearing capacity computed using conventional methods did not show this trend. Then, the transition from the cylindrical shear to the individual bearing failure mechanism occurred at a spacing ratio (i.e., helical plate spacing divided by its diameter) of about two. Ultimately, the load transfer curves indicate that the helical plates mainly supported the applied load.

Simulation of interfacial debonding in hollow particle reinforced composites with VCFEM

The addition of hollow glass microsphere into composites is a method to improve mechanical properties. However, the interfacial debonding of hollow microsphere inevitably causes a decrease in the mechanical properties of the material, which ultimately leads to the failure of the composites. In the numerical simulation of such hollow particle-reinforced composites, the ordinary displacement finite element requires a large number of meshes, which undoubtedly greatly increases the computational cost. In this paper, a new VCFEM is proposed to solve this problem by establishing a two-dimensional Voronoi cell finite element model, deriving the residual energy generalized function of hollow particle-reinforced composites, and calculating the interface debonding. The simulation results are compared with the commercial software MARC, ABAQUS to verify the effectiveness of this VCFEM. The results show that this VCFEM greatly improves the computational efficiency while ensuring the accuracy. Based on this model, this paper also investigates the effect of the generation of interfacial debonding on the overall structure and the effect of different wall thickness of hollow particles on the damage of element debonding.

Field and Numerical Investigation of Taihu Resort Cut Slope Failure in Suzhou, China

This study aims to determine the cause of a landslide located at Taihu Resort in Suzhou, Jiangsu Province, China. Field monitoring has been conducted, including two-dimensional finite element method (FEM) numerical analyses to examine slope stability under different working conditions. The monitoring data indicated that the slope deformation was triggered in two phases: at a certain period when the slope was cut and moderate rainfall occurred in November; and afterward, when a continuous heavy rainfall intensity hit during the monsoon rainfall, which accelerated sliding of the slope. Numerical simulations show that stress and maximum displacement distributions formed and redistributed during the excavation process, where the shear strain occurred mainly in the front layer of soil. Additionally, the factor of safety of the slope decreases gradually with the increase in the excavation rate. During 15 days of continuous rainfall infiltration, the slope under heavy rainfall indicates a minimum factor of safety (FoS). Specifically, the slope excavation followed by heavy rainfall intensities contributed significantly to the landslide.

NONLINEAR FINITE ELEMENT ANALYSIS OF COMPOSITE CONCRETE BEAMS

To study the nonlinear response of composite concrete beams, a finite element analysis is presented. Material nonlinearities as a result of nonlinear response of concrete in compression, crushing and cracking of concrete, strain softening and stiffening after cracking, yielding of reinforcement, bond- slip, shear-slip, and dowel action between the precast concrete beams and the cast-in-situ slabs are considered.A biaxial concrete model is adopted. Concrete is treated as an orthotropic material with smeared rotating crack model. The steel reinforcement is assumed to be in a uniaxial stress state and is modeled as a bilinear material. I A two-dimensional plane stress finite element type is used to model the concrete Reinforcement is represented by one-dimensional bar elements. Bond-slip and dowel action is modeled by using fictitious linkage elements with two springs at right angles. Shear-slip is modeled by using shear transfer in face elements with appropriate stiffness values Comparison between the results obtained by the finite element and available experimental results of composite concrete beams is made. The results compare satisfactorily with the experimental ones

Physical and Finite Element Models for Determining the Capacity and Failure Mechanism of Helical Piles Placed in Weak Soil

The foundations of particular engineering structures, including marine and jetty structures, mooring systems for submerged platforms or those on the ocean surface, and transmission towers, are subjected to various external loads including compression, uplift, and lateral loads. In such cases, to improve the soil resistance below foundations, pile foundations such as helical piles, anchored piles, and batter piles are commonly preferred, depending on the in situ conditions. Helical piles, increasingly used as an alternative foundation to conventional piles, are placed in the soil body by rotating with torque. This paper deals with the contribution of a helical pile in improving loose sandy soil, and the main purpose is to study the effect of the helix-buried depth on the load-bearing capacity and failure mechanism. The investigated variables include the distance between helixes, the number of helixes, and the diameter of the upper helix. Physical model tests were conducted, and two- and three-dimensional numerical analyses were performed by using the finite element method with an advanced soil model to illustrate the failure mechanisms of helical piles. The aim was to reveal the efficiency of the finite element method in modelling helical piles placed in weak sandy soil. A simplified linear geometry for helixes was established in a two-dimensional finite element model whereas a real geometry for helixes, which was a more realistic approach, was created in a three-dimensional finite element model. The results show that the three-dimensional model indicates better agreement with the physical model compared to the two-dimensional model, and all investigated variables highly affect the load-bearing capacity of helical piles.

Comparative analysis of dual stator machines

Electromagnetic performance of three different types of double stator permanent magnet machine is analyzed and compared in this study. The analyzed machines in this study are Machine 1, Machine 2 and Machine 3. These machines are designated as: M 1, M 2 and M 3, respectively. The studies are implemented using two-dimensional and three-dimensional finite element analysis (2D-FEA and 3D-FEA) methods. The predicted performance indices are: total harmonic distortion of the voltage, torque ripple, cogging torque, winding inductances, output torque and unbalanced magnetic force (UMF). The studies show that the investigated machine types have negligible reluctance torque and thus, similar axes inductance values. Therefore, the machines’ bulk torque components are contributed mainly by the magnets while the armature excitation sources yield lesser torque components. Amongst the compared machines, M 3 type has an outstanding performance in almost all the performance metrics, compared to M 2 and M 1 types. Nevertheless, M 1 machine type has some good attributes, particularly, with respect to its high output torque per applied magnet volume, in addition to its widest operating speed range ability. Low-speed high-torque applications are most suitable for the investigated machines in practice.