Search Results (1,025)

Bulk Acoustic Wave (BAW) resonators are essential components in modern RF communication systems due to their high selectivity and quality factor. However, spurious resonances caused by Lamb wave mode propagation along the in-plane directions degrade the filter performance. Traditional Finite Element Method (FEM) simulations provide accurate modeling but are computationally expensive, especially for arbitrarily shaped resonators and solidly mounted resonators (SMRs), whose stack of materials is composed of many thin layers of different materials. To address this, we extend a previously published model (named the Quasi-3D model), which employs the Transmission Line Matrix (TLM) method, enabling efficient simulations of complex geometries with more precise meshing. The new approach allows us to simulate different geometries, and we will show several apodized geometries with the aim of minimizing the lateral modes. In addition, the proposed approach significantly reduces the computational cost while maintaining high accuracy, as validated by FEM comparisons and experimental measurements. Full article

Ubiquitiform is a new theory of finite-order self-similar physical structure and it is more reasonable to describe real engineering surfaces by ubiquitiform rather than fractal. In this paper, by introducing the frequency truncation criterion, a new analytical expression of the two-dimensional W–M function based on the ubiquitiform theory is firstly derived and constructed and the two-dimensional ubiquitiformal curve characterization under different contact characteristic parameters is achieved. On this basis, the anisotropic three-dimensional surface W–M function with ubiquitiformal features is constructed, and the evolution law of the anisotropic three-dimensional surface morphology under the regulation of the ubiquitiformal complexity is investigated. Then, an improved adaptive box counting algorithm is proposed, and the lower limit of the metric scale in the self-similarity region of the asperities on the rough surface is determined and then the computation method of the ubiquitiformal complexity is established. At last, the validity and accuracy of the method are confirmed by the Koch curves. Key findings include: (1) higher ubiquitiformal complexity D corresponds to increased surface irregularity and complexity; (2) the characteristic scale factor G affects surface height only; (3) reducing the lower limit of metric scale ${\mathsf{\delta }}_{\mathrm{m}\mathrm{i}\mathrm{n}}$ increases surface undulation frequency, revealing finer details. This research provides a rationale and quantitative guidance for the matching design of critical joint interfaces in modern precision machinery. Full article

The Finite Difference Time-Domain (FDTD) method is a powerful tool for electromagnetic field analysis. In this work, we develop a variation of the algorithm to accurately calculate antenna, microwave circuit, and target scattering problems. To improve efficiency, a single-field (SF) FDTD method is proposed as a numerical solution to the time-domain Helmholtz equations. New formulas incorporating resistors and voltage sources are derived for the SF-FDTD algorithm, including hybrid implicit–explicit and weakly conditionally stable SF-FDTD methods. The correctness of these formulas is verified through numerical simulations of a newly designed dual-band wearable antenna with an artificial magnetic conductor (AMC) structure. A novel antenna fed by a coplanar waveguide with a compact size of 15.6 × 20 mm² has been obtained after being optimized through an artificial intelligent method. A double-layer, dual-frequency AMC structure is designed to improve the isolation between the antenna and the human body. The simulation and experiment results with different bending degrees show that the antenna with the AMC structure can cover two frequency bands, 2.4 GHz–2.48 GHz and 5.725 GHz–5.875 GHz. The gain at 2.45 GHz and 5.8 GHz reaches 5.3 dBi and 8.9 dBi, respectively. The specific absorption rate has been reduced to the international standard range. In particular, this proposed SF-FDTD method can be extended to analyze other electromagnetic problems with fine details in one or two directions. Full article

This study investigates the impact of the bearing plate position on the uplift bearing capacity of low-header concrete expanded pile (CEP) foundations using the ANSYS finite element simulation method. Nine models of low-header CEP single piles with varying bearing plate positions are constructed. Incremental loading is applied to obtain relevant data, including load–displacement curves for vertical tensile forces, displacement contours, and shear stress distributions. The study analyzes the characteristics of load–displacement curves under different loading conditions, the axial force distribution along the pile shaft, the failure state of the surrounding soil, and how the uplift bearing capacity varies with changes in the bearing plate position. Based on the findings, a calculation model for the uplift bearing capacity of low-header CEP single-pile foundations is proposed. Given that the uplift bearing capacity decreases to varying degrees depending on the bearing plate position, the slip-line theory from previous studies is applied to refine the corresponding calculation formula for uplift bearing capacity. The results from the ANSYS finite element simulation confirm that the bearing plate position significantly influences the uplift bearing performance of low-header CEP single-pile foundations. The uplift bearing capacity increases with the distance between the bearing plate and the low header, reaching a peak before decreasing beyond a certain threshold. Considering the influence of the bearing plate position on bearing capacity, the affected area of soil beneath the foundation, and the time required for the system to enter its working state, the optimal bearing plate position is found to be at a distance of d₁ = 4R₀ to 5R₀ from the top of the pile. Full article

This paper generalizes the efficient matrix decomposition method for solving the finite-difference (FD) discretized three-dimensional (3D) Poisson’s equation using symmetric 27-point, 4th-order accurate stencils to adapt more boundary conditions (BCs), i.e., Dirichlet, Neumann, and Periodic BCs. It employs equivalent Dirichlet nodes to streamline source term computation due to BCs. A generalized eigenvalue formulation is presented to accommodate the flexible 4th-order stencil weights. The proposed method significantly enhances computational speed by reducing the 3D problem to a set of independent 1D problems. As compared to the typical matrix inversion technique, it results in a speed-up ratio proportional to $n^4$, where $n$ is the number of nodes along one side of the cubic domain. Accuracy is validated using Gaussian and sinusoidal source fields, showing 4th-order convergence for Dirichlet and Periodic boundaries, and 2nd-order convergence for Neumann boundaries due to extrapolation limitations—though with lower errors than traditional 2nd-order schemes. The method is also applied to vortex-in-cell flow simulations, demonstrating its capability to handle outer boundaries efficiently and its compatibility with immersed boundary techniques for internal solid obstacles. Full article

An accurate analysis of the dynamic process of ice melting in an optical fiber composite overhead ground wire (OPGW) is of great reference significance for the selection of an ice melting current and the formulation of an ice melting strategy. Existing analytical models for the dynamic process of DC ice melting in an OPGW ignore the gap convective heat transfer after the formation of the air gap between the ground wire and the ice layer, and lack the study of the dynamic process of the phase transition of the ice layer. To this end, a finite element model of the DC ice melting process of OPGW was established by introducing the mushy zone constant to consider the influence of the convective heat transfer in the gap, and at the same time, the apparent heat capacity method was used to simulate the changes of the physical property parameters of the melted ice layer. The dynamic process of the ice layer phase transition and OPGW temperature rise during ice melting are calculated, and the effects of the half-width of phase transition interval dT and the mushy zone constant A_m on the DC ice melting process are summarized and analyzed. The accuracy of the OPGW DC ice melting model is verified by conducting DC ice melting experiments. The results show that during the ice melting process, the gap convection heat transfer mainly affects the temperature distribution of the air gap between the ice layer and the OPGW as well as the location of the phase transition interface, and the width of the air gap at the same height below the OPGW increases by about 3 mm after considering the gap convection; the half-width of phase transition interval, dT, mainly affects the location of the phase transition interface and the temperature rise of the modeled heat source, OPGW, while the mushy zone constant, A_m, mainly affects the temperature distribution in the mushy zone, the air gap region. The elliptical phase transition cross-section formed by the OPGW DC ice melting experiment is consistent with the shape of the ice melting simulation model results, and the measured temperature rise curves of the OPGW during DC ice melting are in good agreement with the simulation results, with a maximum difference of about 3.5 K in temperature and 10 min in ice melting time, but the overall trend is consistent, all showing as increasing first and then decreasing. Full article

Hydraulic fracturing of gas and oil reservoirs is the primary stimulation method for enhancing production in the field of petroleum engineering. The hydraulic fracturing technology plays a crucial role in increasing shale gas production from shale reservoirs. Understanding the effects of reservoir and fracturing conditions on fracture propagation is of great significance for optimizing the hydraulic fracturing process and has not been adequately explored in the current literature. In the context of shale reservoirs in Yibin, Sichuan Province, China, the study selects outcrops to prepare samples for uniaxial compression and Brazilian splitting tests. These tests measure the compressive and tensile strengths of shale in parallel bedding and vertical bedding directions, obtaining the shale’s anisotropic elastic modulus and Poisson’s ratio. These parameters are crucial for simulating reservoir hydraulic fracturing. This paper presents a numerical model utilizing a finite element (FE) analysis to simulate the process of multi-cluster hydraulic fracturing in a shale reservoir with natural fractures in three dimensions. A numerical simulation of the intersection of multiple clusters of 3D hydraulic fractures and natural fractures was performed, and the complex 3D fracture morphologies after the interaction between any two fractures were revealed. The influences of natural fractures, reservoir ground stress, fracturing conditions, and fracture interference concerning the spreading of hydraulic fractures were analyzed. The results highlight several key points: (1) Shale samples exhibit distinct layering with significant anisotropy. The elastic compressive modulus and Poisson’s ratio of parallel bedding shale samples are similar to those of vertical bedding shale samples, while the compressive strength of parallel bedding shale samples is significantly greater than that of vertical bedding shale samples. The elastic compressive modulus of shale is 6 to 10 times its tensile modulus. (2) The anisotropy of shale’s tensile properties is pronounced. The ultimate load capacity of vertical bedding shale samples is 2 to 4 times that of parallel bedding shale samples. The tensile strength of vertical bedding shale samples is 2 to 5 times that of parallel bedding shale samples. (3) The hydraulic fractures induced by the injection well closest to the natural fractures expanded the fastest, and the natural fractures opened when they intersected the hydraulic fractures. When the difference in the horizontal ground stress was significant, natural fractures were more inclined to open after the intersection between the hydraulic and natural fractures. (4) The higher the injection rate and viscosity of the fracturing fluid, the faster the fracture propagation. The research findings could improve the fracturing process through a better understanding of the fracture propagation process and provide practical guidance for hydraulic fracturing design in shale gas reservoirs. Full article

In this paper, a refined 3D direct finite element model including nuclear power plant structures and soil is developed. The wave input method, including free-field loads and a viscous spring artificial boundary, is used. The effects of structural burial depths on the seismic response of power plant structures are studied. Research shows that the seismic response of this new nuclear power structure is influenced by structural burial depths. The seismic response of the acceleration response and relative floor displacement decreases significantly with increasing structural burial depths. The floor spectrum in the low-frequency region is less influenced by different burial depths. The region of the frequency band corresponding to the peak floor spectrum is significantly influenced by different burial depths. The frequencies corresponding to the peak of the floor spectrum shift towards the lower-frequency bands. The higher-frequency bands of the floor spectrum are less influenced by different burial depths. Full article

Background/Objectives: Protraction facemasks are commonly used to treat Class III malocclusion in growing patients. Personalized facemasks designed using 3D modeling software and based on individual 3D face images are now available. This study aimed to assess the mechanical properties of three novel designs of Petit-type facemask appliances through three-dimensional Finite Element Analysis (FEA). Methods: Three novel designs of the facemask were modeled by Solidworks 3D CAD (2023): anatomic, V-shape, and arc-shape. FEA was performed by Ansys 2021 (R2) software. The elements’ sizes, shapes, and numbers were identified, and the material property was set on Acrylonitrile butadiene styrene copolymer (ABS) plastic. The support and loading conditions of two different intensities of load, 7.8 and 9.8 N, respectively, were applied in three angulations to the occlusal plane: 0°, 30°, and 50°. Stress, strain, and total deformation results were obtained. Results: The minimum stress was reported with the anatomic design at a 30° angulation, whereas the maximum value was reported in the arc-shape design at 50°; however, there was no significant difference among the three designs. The von Mises yield criterion showed that the overall stresses were distributed on the larger areas of the facemask structure at 30° angulation for all designs. The stresses induced in all facemask appliance designs did not cause permanent deformation. Conclusions: Anatomic design has better mechanical behavour than the V-shape or arc shape design. Downward inclination of 30° to the occlusal plane induces less stress. These findings support the use of customized anatomic facemasks for the effective and efficient treatment of Class III malocclusions in growing patients, potentially improving clinical outcomes and patient comfort. Further research, particularly clinical trials, is needed to validate the results of the present study. Full article

The analysis of elastic wave propagation is a critical problem in both science and engineering, with applications in structural health monitoring and seismic wave analysis. However, the efficient and accurate numerical simulation of large-scale three-dimensional structures has posed significant challenges to traditional methods, which often struggle with high computational costs and limitations. This paper presents a novel two-and-a-half-dimensional generalized finite difference method (2.5D GFDM) for efficient simulation of elastic wave propagation in longitudinally invariant structures. The proposed scheme integrates GFDM with 2.5D technology, reducing 3D problems to a series of 2D problems in the wavenumber domain via Fourier transforms. Subsequently, the solutions to the original 3D problems can be recovered by performing inverse Fourier transforms on the solutions obtained from the 2D problems. The 2.5D GFDM avoids the inherent challenge of mesh generation in traditional methods like FEM and FVM, offering a meshless solution for complex 3D problems. By employing sparse coefficient matrices, it offers significantly improved computational efficiency. The new approach achieves significant computational advantages while maintaining high accuracy, as validated through three representative examples, making it a promising tool for solving large-scale elastic wave propagation problems in longitudinally invariant structures. Full article

Designing flow machines is challenging due to numerous free geometrical parameters. This work aims to develop a parallelized computational algorithm in MATLAB version R2020a to design the rotor of a radial flow in a centrifugal pump using the finite-element method (FEM), topology optimization method (TOM), and parallel cloud computing (bare-metal vs. virtual machine). The goal is to minimize a bi-objective function comprising energy dissipation and vorticity within half a rotor circumference. When only minimizing energy dissipation (wd = 1, wr = 0), the performance achieved is 5.88 Watts. Considering both energy dissipation and vorticity (wd = 0.8, wr = 0.2), the performance is 5.94 Watts. These topology results are then extended to a full 3D model using Ansys Fluent version 18.2 to validate the objective functions minimized by TOM. The algorithm is parallelized and executed on multiple CPU cores in the cloud on two different platforms: Amazon Web Services (virtual machine) and Equinix (bare-metal machine), to accelerate the blade design process. In conclusion, mathematical optimization tools aid engineering designers in achieving non-intuitive designs and enhancing results. Full article

To address the limitations of single-chamber soft grippers, such as constant curvature, insufficient motion flexibility, and restricted fingertip movement, this study proposes a soft gripper inspired by the structure of the human hand. The designed soft gripper consists of three fingers, each comprising three soft joints and four phalanges. The air chambers in each joint are independently actuated, enabling flexible grasping by adjusting the joint air pressure. The constraint layer is composed of a composite material with a mass ratio of 5:1:0.75 of PDMS base, PDMS curing agent, and PTFE, which enhances the overall finger stiffness and fingertip load capacity. A nonlinear mathematical model is established to describe the relationship between the joint bending angle and actuation pressure based on the constant curvature assumption. Additionally, the kinematic model of the finger is developed using the D–H parameter method. Finite element simulations using ABAQUS analyze the effects of different joint pressures and phalange lengths on the grasping range, as well as the fingertip force under varying actuation pressures. Bending performance and fingertip force tests were conducted on the soft finger actuator, with the maximum fingertip force reaching 2.21 N. The experimental results show good agreement with theoretical and simulation results. Grasping experiments with variously sized fruits and everyday objects demonstrate that, compared to traditional single-chamber soft grippers, the proposed humanoid joint-inspired soft gripper significantly expands the grasping range and improves grasping force by four times, achieving a maximum grasp weight of 0.92 kg. These findings validate its superior grasping performance and potential for practical applications. Full article

Background/Objectives: One of the most serious complications following implant placement in the atrophic posterior mandible is injury to the inferior alveolar nerve (IAN), which can also happen during occlusal loading of the implants. This study investigates the effects of 4 mm implant stress transmission to the inferior alveolar nerve during occlusal loading in cases of severe posterior mandibular atrophy. Methods: The computer-aided design (CAD) model was created and modified through Direct Modeling techniques. The structure of cortical and trabecular bones was simplified, and it was modeled as a cylinder block. Finite element analysis (FEA) was carried out in 3D to investigate the pressure distribution over the IAN at different implant-to-nerve distances (1.5 mm, 0.5 mm, and 0.1 mm), and stress and strain deformations were simulated in the mandibular model. Results: The results of the pressure analysis on the inferior alveolar nerve indicate that the pressure distribution at different implant-to-nerve distances (1.5 mm, 0.5 mm, and 0.1 mm) is consistently below 0.026 MPa, which corresponds to the maximum pressure range that may block nerve impulses. This occurs even at the theoretical and simulated distance of 0.1 mm, suggesting that cortical bone stiffness plays a crucial role in mitigating stress at reduced implant-to-nerve proximities. Conclusions: Within the limits of this study, ultra-short implants can be placed even less than 0.5 mm (up to 0.1 mm under the 3D-FEA hypothesis) above the inferior alveolar nerve under the 3D-FEA hypothesis, while maintaining pressure below the threshold value. This is due to the rigidity of the cortical bone, which helps to reduce pressure transmission to the nerve. These findings may expand the indications for ultra-short implants, even in mandibles with a residual bone height of just 4 mm. Full article

Concrete printing in three dimensions is believed to be an innovative construction method. Numerous researchers conducted laboratory experiments over the past decade to examine the behavior of concrete mixtures and the material properties that are pertinent to the 3D concrete printing industry. Furthermore, the global warming effect is being further exacerbated by the increased use of cement, which increases carbon dioxide (CO₂) emissions and pollution. Various standards endorse the utilization of Portland-composite cement in construction to mitigate CO₂ emissions, particularly cement CEM II/A-P. This research provides an experimental and numerical study to examine the evolution of cementitious composite utilizing cement CEM II/A-P for three-dimensional concrete printing, combining three different types of synthetic fiber. The thorough experimental analysis includes three combinations integrating diverse fiber types (polypropylene, high-modulus polyacrylonitrile, and alkali-resistant glass fibers) alongside a reference mixture devoid of fiber. The three distinct fiber types in the mixtures (polypropylene, high modulus polyacrylonitrile, and alkali-resistant glass fibers) were evaluated to assess their impact on (i) the flowability of the cementitious mortar and the slump flow test of fresh concrete, (ii) the concrete compressive strength, (iii) the uniaxial tensile strength, (iv) the splitting tensile strength, and (v) the flexural tensile strength. Previous researchers designed a cylinder stability test to determine the shape stability of the 3D concrete layers and their capacity to support the stresses from subsequent layers. Furthermore, the numerical analysis corroborated the experimental findings with the finite element software ANSYS 2023 R2. The flexural performance of the examined beams was validated using the Menetrey–Willam constitutive model, which has recently been incorporated into ANSYS. The experimental data indicated that the incorporation of synthetic fiber into the CEM II/A-P mixtures enhanced the concrete’s compressive strength, the splitting tensile strength, and the flexural tensile strength, particularly in combination including alkali-resistant glass fibers. The numerical results demonstrated the efficacy of the Menetrey–Willam constitutive model, featuring a linear softening yield function in accurately simulating the flexural behavior of the analyzed beams with various fiber types. Full article

This paper presents the results of experimental and numerical analysis of fracture mechanics testing of ductile metallic materials using a non-standard procedure with PRNT (pipe ring notched tensile) ring-shaped specimens, introduced in previous publications through analysis of 3D-printed polymer rings. The main focus of this research is the determination of the values of the plastic geometry factor η_pl since the specimen is not a standard one. Toward this aim, the finite element software package Simulia Abaqus was applied to evaluate the J-integral (by using the domain integral method) and the F-CMOD curve so that the plastic geometry factor η_pl can be evaluated for different values of the ratio of crack length to specimen width (a₀/W = 0.45 ÷ 0.55). In this way, a procedure and the possibility of practical implementation on the thin-walled pipelines are established. Full article