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Experimental Study of a Hybrid Dolphin Airfoil Aerodynamics
No full textcontract number 451-03-136/2025-03/200213 dated February 4, 2025
Structural integrity of designed sandwich panels under low temperature conditions: blast effect assessment using finite element simulation
No full textThis research employs a detailed finite element analysis to investigate the blast resilience of metallic sandwich panels under various thermal and structural conditions. The investigation considers a range of parameters, including core shapes (tetragonal, hexagonal, and octagonal), core heights (0.021 m, 0.051 m, and 0.081 m), levels of pre-existing damage, and TNT charge masses (0.5 kg, 1.5 kg, and 2.5 kg), all tested under three distinct temperatures: ambient (293 K), sub-zero (193 K), and cryogenic (113 K). Blast loading is simulated using the ConWep method with a consistent stand-off distance of 0.1 m. The findings reveal that panels with octagonal cores significantly outperform other geometries, reducing front-face deflection by up to 46%. Similarly, increasing the core height leads to a more than 60% reduction in back-face deformation. Cryogenic conditions further enhance the structural response, with simulations showing faster kinetic energy decay and a smoother stress distribution across both damaged and intact models. Cryogenic panels absorbed up to 25% more internal energy while maintaining lower overall strain levels, indicating a more efficient mechanism for dissipating blast energy. Overall, the study highlights how geometric configuration, thermal environment, and damage state collectively govern the blast performance of sandwich panels, offering valuable guidance for designing high-performance protective structures in sectors such as aerospace, defense, and cryogenic systems
The role of numerical simulation of fatigue crack growth in failure analysis of a turbine shaft
No full textFailure analysis of a hydropower plant turbine shaft was performed by using the Finite Element Method (FEM) to assess its structural integrity and remaining life. Static and dynamic loading was applied to assess relevant fracture mechanics parameters using FEM for stress analysis and its extended version (XFEM) for simulation of fatigue crack growth. Application of XFEM to turbine shaft crack growth problem is in focus of this paper, in combination with material properties and its expected behavior under amplitude loading. The goal of the research was to determine the remaining life of a turbine shaft that has failed in service. Such an approach provided clear answer to why the cracked shaft failed in a short period of time. Based on that, suggestions to prevent such a failure are given
Experimental and Numerical Research on Swirl Flow in Straight Conical Diffuser
No full textThe main objective of the current study is a detailed (both numerical and experimental) investigation of the highly unsteady and complex swirl flow in a straight conical diffuser (with a total divergence angle of 8.6°) generated by an axial fan impeller. Pressure, and axial and tangential velocity profiles along several cross-sections were measured by original classical probes in two different flow regimes at the inlet: the modified solid body type of moderate swirl and the solid body type of strong swirl and reverse flow; they were additionally confirmed/validated by laser Doppler anemometry measurements. Computational studies of spatial, unsteady, viscous, compressible flows were performed in ANSYS Fluent by large eddy simulation. The fan was neglected, and its effect was replaced by the pressure and velocity profiles assigned along the inlet and outlet boundaries. The two sets of data obtained were compared, and several conclusions were drawn. In general, the relative errors of the pressure profiles (2–5%) were lower than the observed discrepancies in the axial velocity profiles (5–40% for the first and 15–50% for the second flow regime, respectively). The employed reduced numerical model can be considered acceptable since it provides insights into the complexity of the investigated swirl flow
Using CFD as a Replacement for Expensive Experiments in Education
No full textIn this paper, the authors analyzed the use of computational fluid dynamics (CFD) in education. The teaching of fluid mechanics today is mostly based on the theoretical approach. Although, throughout history, it has been shown that the earliest knowledge of fluid mechanics was gained through practical experience and experiments. Apart from this advantage, laboratory exercises and experiments also have numerous disadvantages. Experiments require significant financial resources, equipment and device maintenance. Many complex and specific experiments are not easy to perform in laboratory conditions. This leads to repeating the same experiments over generations. Student safety is also an important factor. During certain experiments, an increase in pressure or temperature may occur, leading to the risk of explosion or fire. Here we consider the possibility of replacing laboratory exercises by using CFD software. Computational fluid dynamics is gaining more and more importance as an alternative to classical laboratory exercises. This technology enables reliable virtual simulation of various fluid phenomena. The application of CFD in education would allow students to experiment with different parameters and scenarios without exposure to hazards, with more accurate and deeper data analysis. The paper also compares CFD software. Software is generally classified into two groups: open source and commercial software. Two open source software are presented in detail: OpenFOAM and SimFlow. On the example of airfoil NACA 0012, in both software, the simulation results were analyzed
Development of a static test platform for determining the loads on an Unmanned Aerial Vehicle (UAV)
No full textEnsuring the structural integrity of unmanned aerial vehicles (UAVs) before flight requires reliable experimental procedures that can replicate operational loading scenarios. In this paper, a static testing platform was developed to reproduce conditions characteristic of vertical lift and cruise motor activation, providing detailed insight into the distribution of forces, moments, and dynamic effects acting on the structure. The experimental data were employed to verify finite element simulations and to support the creation of an artificial neural network model capable of rapid load prediction in structural components. Beyond fast estimation, the ANN approach was used to identify sensor placement strategies that improve measurement quality within the testing setup. The platform integrates a reinforced frame with load and displacement sensors, while a dedicated acquisition system ensures accurate monitoring of responses under controlled loads. By combining experimental validation with advanced modeling techniques, the proposed methodology reduces structural uncertainty and contributes to the design of UAVs with higher reliability and efficiency, suitable for demanding applications in defense, surveillance, transport, and agriculture
Comprehensive Kinetics and Thermodynamics Analysis of Salix psammophila Biomass Pyrolysis Using Multicomponent Modeling
No full textMulticomponent deconvolution enables precise peak separation and accurate determination of kinetic parameters and improves identification of the underlying mechanisms of biomass pyrolysis. In the present study, the multicomponent kinetics and thermodynamics of Salix psammophila pyrolysis were investigated to evaluate its bioenergy potential. Thermogravimetric analysis coupled with peak deconvolution revealed three stages involving four components (pseudoextractives/PS-EC, pseudohemicellulose/PS-CL, pseudocellulose/PS-CL, and pseudolignin/PS-LG) with the corresponding peak temperatures of 246.83–270.83, 291.59–315.59, 335.26–359.26, and 386.14–410.14 °C, respectively. Pyrolysis gas chromatography/mass spectrometry analysis indicated dominant products of acids, phenolics, and alkanes. Activation energies for each pseudocomponent from four isoconversional methods were comparable, following an order of PS-EC (134.96 kJ mol–1) < PS-HC (151.59 kJ mol–1) < PS-CL (166.93 kJ mol–1) < PS-LG (239.65 kJ mol–1). Master plot analysis suggested an order-based reaction mechanism. Positive enthalpy changes (127.83–227.33 kJ mol–1) and Gibbs free energy changes (144.73–193.03 kJ mol–1) indicated higher energy barriers, especially for PS-LG, and limited spontaneity of conversion. These findings highlighted the potential of S. psammophila as a viable feedstock and offered critical insights into reactor design and process optimization for industrial applications
ADATA-DRIVEN OUTLOOK ON THE CHARACTERIZATION OF FERRITIC STEELS IN THE DUCTILE-BRITTLE TRANSITION REGION
No full textSince the 1980s, there has been sustained interest in the size effect, recognized as one of important outcomes of fracture mechanics. In this article, the size effect is investigated through the estimation of the Weibull cumulative distribution function (CDF) for the fracture toughness KJc defined as an elasticplastic equivalent stress intensity factor derived from the J-integral at the point of onset of cleavage fracture, Jc. This fracture toughness of ferritic steels within the ductile-brittle (DBT) transition temperature region is a stochastic extrinsic property characterized by significant experimental variability, making a statistical approach essential for accurate DBT characterization. This inherent variability and irreducible uncertainty in the fracture properties of ferritic steels align with weakest-link theory, which attributes scatter in strength and fracture toughness to flaws, inhomogeneities, or other local imperfections within the material texture. According to this theory, even a small number of defects—especially near the tip of a pre-existing macrocrack or notch can trigger localized microseparation events that may evolve into macro-fracture, particularly when dislocation activity is suppressed due to low temperature. Weibull statistics traditionally provides a framework for estimating the likelihood of encountering such defects and assessing their impact on the overall probability of cleavage fracture. Recently, the two-step-scaling (2SS) method was introduced to model size effects throughout the DBT temperature region. This method is based on weakest-link theory and Weibull distribution, incorporating the size dependence of both the scale and shape Weibull parameters within an appropriate framework. In this article, the 2SS method is examined from a practical standpoint to demonstrate its application in engineering contexts. The 2SS approach is evaluated using the EURO fracture toughness dataset, with the results underscoring its broad applicability and versatility
Finite element analysis and machine learning based design of latticed hip implant stem
No full textDue to the increase in hip implant surgeries over the last few decades,
the design and manufacturing methods have also been improving in
order to create the optimal design that suits each individual patient
and minimizes the need for revision surgery.
This study investigates the design of hip implant stem from titanium
alloy and designed with lattice structures, furthermore produced by
additive manufacturing. A surrogate model of the latticed implant
stem was developed to replace time-consuming finite element
calculations of the very complicated structure. Machine learning was
used to predict the mechanical response of the implant stems with
different design parameters. In the knowledge of the mechanical
properties, the surgeon has the information which design fits the best
to the patient