Search Results (48)

Part II of this study builds upon the mathematical framework developed and validated in Part I for describing the geometry and volumetric performance indicators of an innovative three-rotor hydraulic pump with bilateral lantern meshing. This part focuses on the numerical investigation and multi-objective optimization of these indicators through the proper selection of geometric parameters. The aim of the study is to establish the isolated and combined influence of the dimensionless geometric parameters—number of teeth $z$, relative lantern radius $r_c^{\ast }$, and cycloid shortening coefficient $\mathsf{\lambda }$—on the actual flow rate $Q$ and the volumetric efficiency ${\mathsf{\eta }}_v$ under various operating conditions, while maintaining the overall dimensions of the pump element in the radial and axial directions. Through detailed numerical analysis and subsequent rigorous analytical proof, it has been established that the optimal values of the geometric coefficients $r_{c,opt}^{\ast }$ and ${\mathsf{\lambda }}_{opt}$ are strictly determined and provide a simultaneous global maximization of both indicators ($Q,{\eta }_v$), regardless of the operating pressure $p$, rotational speed $n$, or the viscosity of the working fluid. However, an analytically irresolvable conflict regarding the number of teeth $z$ has been identified: a small number maximizes the flow rate, whereas a large number increases the volumetric efficiency. To overcome this contradiction, the problem is formulated within the class of mixed-integer nonlinear programming (MINLP), and multicriteria Pareto optimization is applied, combined with the PSIMS method for the selection of optimal compromise solutions. An empirical relationship (with a coefficient of determination of $R^2=0.9603$) has been derived, which defines the optimal number of teeth $z_{opt}$ as a function of the operating pressure and rotational speed. The proposed methodology provides a reliable and applicable tool for designing highly efficient three-rotor pumps tailored to specific operational requirements. Full article

With the rapid development of offshore wind energy toward deep water, the structural safety of truss-type legs for jack-up wind turbine installation vessels (WTIVs) under complex operational and environmental loads has become a key concern. This study focuses on the directional coupling effect between crane slewing angles and wave directions, which has rarely been systematically investigated in previous research. A finite element model of a 1500 t-class WTIV truss leg is established using SESAM, and its reliability is verified by mesh convergence analysis and literature comparison. The influences of crane slewing angle, wave direction, and their coupling on structural displacement and stress are analyzed quantitatively, and strength evaluation is carried out under typical working conditions in accordance with classification society rules. The results show that the structural response presents significant directional dependence and stiffness anisotropy. The peak displacement and stress occur at a crane slewing angle of 270°, with the maximum displacement approximately 33% higher than the minimum value. Obvious response amplification is observed when the crane slewing angle and wave direction are aligned within 225–270°, which constitutes the most unfavorable loading combination. The strength assessment demonstrates that all conditions meet the specification requirements, and the survival condition is the most critical, with a maximum stress of 289.66 MPa and a maximum displacement of 338.6 mm. This study reveals the coupling mechanism between operational loads and environmental loads and identifies the critical dangerous angle sector. The research findings can provide reasonable references for offshore lifting operation management and operational planning of marine truss leg structures. Full article

This study presents a hybrid Non-Uniform Rational B-Spline (NURBS) methodology for the geometric reconstruction of topology-optimized structural components. NURBS are employed exclusively as a post-processing tool; all structural analyses are performed using standard finite elements (SOLID187 elements, ANSYS Mechanical R19.2), and isogeometric analysis (IGA) is not used. The methodology is validated on an Al 6061-T6 electric scooter neck under a 600 N static load. Two SIMP optimization iterations followed by a hybrid NURBS reconstruction reduce the component mass from 1.247 kg to 0.531 kg, achieving a 57.4% mass reduction. Finite element re-validation of the reconstructed geometry yields a maximum von Mises stress of 126.45 MPa (safety factor, SF = 2.18, exceeding the 2.0 requirement), a maximum deflection of 2.31 mm, and a first natural frequency of 127 Hz. Mesh convergence between the 2.5 mm and 1.25 mm refinements is Δ = 0.90%. Relative to the direct SIMP output (201 MPa), NURBS reconstruction reduces the peak stress by 37%, demonstrating that geometric post-processing is not a neutral step but a critical determinant of structural performance. Both fully automated STL reconstruction and edge-based NURBS reconstruction failed for this geometry class due to non-manifold topology and patch discontinuities, respectively. The proposed hybrid region-decomposition approach is the only method that has produced a watertight, FEA-compatible CAD model. Full article

Gas Metal Arc Welding (GMAW) is widely adopted in automated manufacturing industries where the accurate prediction of thermal fields and welding-induced distortions is essential to ensure joint integrity of the parts; however, finite element modeling, as the most reliable non-destructive predictive approach, remains time-consuming and highly user-specialized. This work presents an automated and low computational cost thermo-mechanical finite element methodology implemented in Ansys Parametric Design Language (APDL) for the parametric analysis of GMAW T-joints, integrating automated geometry generation, meshing, heat source implementation, and thermo-mechanical modeling for different beam and weld seam dimensions under continuous or intermittent single-pass configurations. A volume element selection strategy is introduced to limit heat input calculations to the active weld pool region, achieving up to a 50% computational time reduction while maintaining high predictive accuracy, in contrast with conventional and partial selection methods. Overall script performance was validated through temperature and displacement comparisons between the numerical and experimental results of two T-joint configurations using SM490A structural steel specimens. The results demonstrate that the developed macro provides a useful tool for automated thermo-mechanical welding analysis, significantly reducing model preparation effort while enabling the evaluation of parametric T-joint geometries and welding conditions with a low computational cost focus. Full article

Isogeometric analysis (IGA) is a numerical methodology for solving differential equations by employing basis functions that preserve the exact geometry of the domain. This approach is based on a class of mathematical functions known as NURBS (Non-Uniform Rational B-Splines). Representing a domain with NURBS entities often requires multiple patches, especially for complex geometries. Bivariate NURBS, defined as tensor products, enforce global refinements within a patch and, in multi-patch models, these refinements are propagated to other model patches. The use of T-Splines with extraordinary points offers a solution to this issue by enabling local refinements through unstructured meshes. The analysis of T-Spline models is performed using a Bézier extraction technique that relies on extraction operators that map Bézier functions to T-Spline functions. When generating a T-Spline model, careful attention is required to ensure that all T-Spline functions are linearly independent—a necessary condition for IGA—in order to form T-Splines that are suitable for analysis. In this sense, this work proposes a methodology to automate the generation of bidimensional unstructured meshes for IGA through T-Splines with extraordinary points. An algorithm for generating unstructured finite element meshes, based on domain decomposition of quadrilateral patches, is adapted to construct T-Spline models. Validation models demonstrate the methodology’s flexibility in generating locally refined isogeometric models. Full article

This paper develops a fully discrete finite element scheme for the fractional wave equation with order $\alpha \in (1,2)$, whose solution typically exhibits a weak singularity near the initial time $t=0$. By introducing an auxiliary variable, we first reformulate the fractional wave problem into an equivalent coupled system of two fractional equations. The resulting coupled system is then discretized using the nonuniform Alikhanov formula in time and the standard finite element method on triangular meshes in space. Through rigorous analysis, we establish a pointwise-in-time error estimate for the proposed scheme in the $H^1$ semi-norm. A key advantage of the proposed methodology is its ability to employ a sparser mesh near the initial time to achieve optimal convergence of local errors. In particular, our analysis shows that away from the initial time, the local rate of convergence reaches $O\left(N^{-2}\right)$ in time for $r\ge 2$. Finally, numerical experiments are given to verify the sharpness of the theoretical convergence rates. Full article

The primary aim of this study is to develop an axisymmetric numerical model, employing the finite element approach, to simulate a two-wrinkling tube in T6 aluminum. The method uses an electric potential applied to the tube mesh, which passes through a solid die to induce the wrinkling process, facilitated by contact elements between the tube and the die. A lateral incremental voltage electric potential (0–50 kV), due to an electric coil, and applied axial and compressive displacement (0–12 mm) was considered. The materials’ properties were established as nonlinear, with elastoplastic behavior. The results were analyzed, which allowed the tube deformation with two wrinkles, comparable with previous results. Full article

High-voltage ceramic insulators are routinely exposed to short-duration overvoltages such as lightning impulses, switching surges, and partial discharges. These events occur on microsecond to millisecond timescales and can produce highly localized thermal spikes that are difficult to measure directly but may compromise long-term material integrity. This paper addresses the estimation of the internal temperature distribution immediately after a lightning impulse by solving a three-dimensional inverse heat conduction problem (IHCP). The forward problem is modeled by the transient heat diffusion equation with constant thermal diffusivity, discretized using the finite element method (FEM). Surface temperature measurements are assumed available from a 12 kV ceramic post insulator and are used to reconstruct the unknown initial condition. To address the ill-posedness of the IHCP, a spatio-temporal regularization framework is introduced and compared against spatial-only regularization. Numerical experiments investigate the effect of measurement time ($T=60$ s, 600 s, and 1800 s), mesh resolution (element sizes of 20 mm, 15 mm, and 10 mm), and measurement noise ($\sigma =1$ K and 5 K). The results show that spatio-temporal regularization significantly improves reconstruction accuracy and robustness to noise, particularly when early-time measurements are available. Moreover, it is observed that mesh refinement enhances accuracy but yields diminishing returns when measurements are delayed. These findings demonstrate the potential of spatio-temporal IHCP methods as a diagnostic tool for the condition monitoring of ceramic insulators subjected to transient electrical stresses. Full article

Background: This case series study aims to evaluate the spontaneous eruption of impacted canines following diode laser disinclusion surgery without orthodontic traction, and to analyze the correlation with five prognostic factors: age, sex of the patient, angle α, sector, and height of inclusion of the canine. Methods: The sample included 15 patients aged 13–30 years and 20 palatally impacted canines. The patients’ records were collected, and prognostic factors were assessed. All patients underwent disinclusion surgery using a diode laser (K-Laser, Eltech, Blue Derma) and post-surgery, canines were monitored with intraoral scans and photos at 1 week, 8 weeks (T1), and 16 weeks (T2). The STL files were superimposed with the open-source software MeshLab (MeshLab 2023.12, Visual Computing Lab, Pisa, Italy), and the eruption values were measured. Through multiple linear regression analysis, the relationships between the five prognostic factors and the total spontaneous eruption value were analyzed. Results: The canines treated in this study responded with an average eruption of 4.70 mm. For the prognostic factors sex (p = 0.94) and angle α (p = 0.12), no statistically significant relationship with eruption was found. The variables age (p < 0.001), sector II (p = 0.02), sector III (p = 0.03), sector IV (p = 0.06), and inclusion height (p < 0.001) had negative linear coefficients. Consequently, as the values of these three prognostic factors increased, a lower eruption of the included element measured in millimeters was obtained. Conclusions: All canines successfully erupted following the disinclusion procedure, avoiding the use of orthodontic traction. Patient sex and the α angle of impaction were not reliable predictors of eruption outcomes. In contrast, age, sector, and inclusion height measured via CBCT showed high statistical significance and could be used as prognostic factors to predict the eruptive response following disinclusion surgery. Full article

Direct numerical simulations (DNSs) of the T106A low-pressure turbine were conducted for various turbulence intensities and length scales to investigate their effects on flow behaviour and transition. A source-term formulation of the synthetic eddy method (SEM) was implemented in the Nektar++ spectral/hp element framework to introduce anisotropic turbulence into the flow field. A single sponge layer was imposed, which covers the inflow and outflow regions just downstream and upstream of the inflow and outflow boundaries, respectively, to avoid acoustic wave reflections on the boundary conditions. Additionally, in the T106A model, mixed polynomial orders were utilized, as Nektar++ allows different polynomial orders for adjacent elements. A lower polynomial order was employed in the outflow region to further assist the sponge layer by coarsening the mesh and diffusing the turbulence near the outflow boundary. Thus, this study contributes to the development of a more robust and efficient model for high-fidelity simulations of turbine blades by enhancing stability and producing a more accurate flow field. The main findings are compared with experimental and DNS data, showing good agreement and providing new insights into the influence of turbulence length scales on flow separation, transition, wake behaviour, and loss profiles. Full article

Unlike previous studies focusing on two-layer structures or single-parameter effects, this work systematically investigates the influence of sheet layer combination modes on the mechanical properties of three-layer AA6063-T6 self-piercing riveting (SPR) joints through a combination of experimental testing and numerical simulation. Shear and cross-tensile tests were conducted on three-layer AA6063-T6 SPR joints with three distinct sheet layer combinations: T1 (top/middle: 100 × 40 mm², bottom: 40 × 40 mm²), T2 (top/bottom: 100 × 40 mm², middle: 40 × 40 mm²), and T3 (middle/bottom: 100 × 40 mm², top: 40 × 40 mm²). Experimental results reveal significant differences in joint strength and failure modes across the three combinations. T3 joints exhibited the highest shear strength (9.16 kN) but the lowest cross-tensile strength (3.56 kN), whereas T1 joints showed the highest cross-tensile strength (4.97 kN) but moderate shear strength (8.76 kN). A high-fidelity finite element model was developed to simulate the SPR joint under varying sheet layer combinations, incorporating precise geometric details (0.25 mm mesh at critical zones) and advanced contact algorithms (friction coefficient μ = 0.2). Numerical simulations revealed the stress distribution and failure mechanisms under shear and cross-tensile loading, aligning well with experimental observations. Analysis highlights that the mechanical performance of the joint is governed by two key factors: (1) the stress redistribution in sheet layers due to combination mode variations, and (2) the interlocking strength between the rivet and sheets. These findings provide practical guidelines for optimizing sheet layer combinations in lightweight automotive structures subjected to mixed loading conditions. Full article

In this paper, we propose the use of burnishing internal cylindrical surfaces with a hard tool in a mandrel shape. The burnishing force is exerted mainly by the press slide, which has pushing properties, moving the burnisher through the hollow tube. The burnishing of hollow surfaces is used as the finishing step for elements such as tubes. The purpose of using the burnishing method may be, for example, to increase the smoothness and accuracy of the object, for the improvement of its functional and operational properties, for economic reasons, or to increase its resistance to corrosion and fatigue. The depth of plastic deformation and the accuracy of processing are the main differences in the machining effects for individual burnishing methods. The selection of the burnishing conditions depends on the method of exerting pressure from the burnishing elements on the machined surface, which can be elastic or rigid. Computer simulations of the burnishing process were performed in FORGE^® NxT 2.1 software. A numerical analysis was performed using a three-dimensional triangular mesh. The theoretical and experimental research was determined to have very good compatibility, as determined by the numerically calculated results and by the mean deviation of residual stress method. This research analyzed the stress and strain state after the burnishing process, and a depth of deformation of approximately 20 μm to 30 μm in the material was determined. Full article

This paper presents a unified framework for constructing transfinite finite elements with arbitrary node distributions, using either Lagrange or Bernstein polynomial bases. Three distinct classes of elements are considered. The first includes elements with structured internal node layouts and arbitrarily positioned boundary nodes. The second comprises elements with internal nodes arranged to allow smooth transitions in a single direction. The third class consists of elements defined on structured T-meshes with selectively omitted internal nodes, resulting in sparsely populated or incomplete grids. For all three classes, new macro-element (global interpolation) formulations are introduced, enabling flexible node configurations. Each formulation supports representations based on either Lagrange or Bernstein polynomials. In the latter case, two alternative Bernstein-based models are developed as follows: one that is numerically equivalent to its Lagrange counterpart, and another that offers modest improvements in numerical performance. Full article

Fuel cells, propulsion systems, and reaction control systems (RCSs) are just a few of the space applications that depend on pressure vessels (PVs) to safely hold high-pressure fluids while enduring extreme environmental conditions both during launch and in orbit. Under these challenging circumstances, PVs must be lightweight while retaining structural integrity in order to increase the efficiency and lower the launch costs. PVs have significant challenges in space conditions, such as extreme vibrations during launch, the complete vacuum of space, and sudden temperature changes based on their location within the satellite and orbit types. Determining the operational temperature limits and endurance of PVs in space applications requires assessing the combined effects of these factors. As the main propellant for satellites and rockets, hydrogen has great promise for use in future space missions. This study aimed to assess the structural integrity and determine the thermal operating limits of different types of hydrogen pressure vessels using finite element analysis (FEA) with Ansys 2019 R3 Workbench. The impact of extreme space conditions on the performances of various kinds of hydrogen pressure vessels was analyzed numerically in this work. This study determined the safe operating temperature ranges for Type 4, Type 3, and Type 1 PVs at an operating hydrogen storage pressure of 35 MPa in an absolute vacuum. Additionally, the dynamic performance was assessed through modal and random vibration analyses. Various aspects of Ansys Workbench were explored, including the influence of the mesh element size, composite modeling methods, and their combined impact on the result accuracy. In terms of the survival temperature limits, the Type 4 PVs, which consisted of a Nylon 6 liner and a carbon fiber-reinforced epoxy (CFRE) prepreg composite shell, offered the optimal balance between the weight (56.2 kg) and a relatively narrow operating temperature range of 10–100 °C. The Type 3 PVs, which featured an Aluminum 6061-T6 liner, provided a broader operational temperature range of 0–145 °C but at a higher weight of 63.7 kg. Meanwhile, the Type 1 PVs demonstrated a superior cryogenic performance, with an operating range of −55–54 °C, though they were nearly twice as heavy as the Type 4 PVs, with a weight of 106 kg. The absolute vacuum environment had a negligible effect on the mechanical performance of all the PVs. Additionally, all the analyzed PV types maintained structural integrity and safety under launch-induced vibration loads. This study provided critical insights for selecting the most suitable pressure vessel type for space applications by considering operational temperature constraints and weight limitations, thereby ensuring an optimal mechanical–thermal performance and structural efficiency. Full article

This paper investigates the derivation of global shape functions in T-meshed quadrilateral patches through transfinite interpolation and local elimination. The same shape functions may be alternatively derived starting from a background tensor product of Lagrange polynomials and then imposing linear constraints. Based on the nodal points of the T-mesh, which are associated with the primary degrees of freedom (DOFs), all the other points of the background grid (i.e., the secondary DOFs) are interpolated along horizontal and vertical stations (isolines) of the tensor product, and thus, linear relationships are derived. By implementing these constraints into the original formula/expression, global shape functions, which are only associated with primary DOFs, are created. The quality of the elements is verified by the numerical solution of a typical potential problem of second order, with boundary conditions of Dirichlet and Neumann type. Full article