Abstract: Dissolved oxygen (DO) management is a primary challenge in intensive aquaculture, where conventional aeration often suffers from high energy costs and low efficiency in decentralized systems. Oxygen transfer kinetics were investigated under oxygen-depleted conditions (initial DO = 2.4 mg L⁻¹) using the dynamic method. The system's performance was characterized through the volumetric mass transfer coefficient (kLa), Specific Oxygen Transfer Efficiency (SOTE), and dimensionless analysis (Reynolds, Schmidt, and Sherwood numbers). After 1 hour of operation, the DO concentration increased to 6.2 mg L⁻¹, achieving a net oxygen transfer of 9.55 ± 0.46 g. The system yielded a kLa of 1.44 h⁻¹ (R² = 0.97) and a SOTE of 76.4 ± 7.8 gO₂ kWh⁻¹. Dimensionless analysis (Re ≈ 2 x 10⁴, Sc ≈ 500, Sh ≈ 682) confirms that oxygen transfer is governed by hydrodynamic-induced interfacial area generation rather than molecular diffusion. Biological validation demonstrated that fish (catfish) grown under nanobubble-assisted conditions achieved a 43% higher growth rate over 17 days compared to non-assisted groups. These findings demonstrate that hydrodynamically controlled nanobubble spray systems provide an energy-efficient and scalable solution for decentralized aquaculture aeration.

Abstract: The article discusses the methods for classifying processes for testing and processing metals by plastic deformation, based on the characteristics of their stress-strain state. The basic methods for determining the stress and strain states using fundamental scalar quantities representing the stress and strain tensors are discussed. Equations have been derived for the quantitative determination of the type of stress-strain state through a combination of principal stresses, represented as the strain rigidity of the deformation mode. A classification of deformation processes for testing and processing metals by plastic deformation is proposed, using the stress triaxiality parameter and the strain rigidity coefficient. Some 2D and 3D diagrams have been created based on simulation modeling of plastic deformation processes using virtual tools, allowing the grouping of processes according to the measured principal stresses and their combinations, which represent the stress triaxiality and strain rigidity of the deformation mode. By determining the type of grouping in these diagrams and the change in the stress-strain state with increasing strain levels, the characteristic features of the deformation processes used in materials testing and in the processing metals by plastic deformation of metals/alloys have been confirmed.

Abstract: Acoustoelasticity describes the relationship between elastic wave velocities and the initial stress present in media. Most of the current research in this area is focused on elastic waves propagating in naturally isotropic media with initially uniaxial stress and confined the solution of acoustoelastic problem to the Cartesian coordinate system, which limits the application for the acoustoelasticity theory. In this paper, to make up for this deficiency, an acoustoelastic formulation, i.e. the equation of motion for incremental displacement with explicit dependency on initial stress or strain, is developed based on the general theory of incremental deformation. This formulation can be applied to material with any symmetricity, initial stress with any number of principle axis. Also, it can be expressed in any form of coordinate system for its tensorial nature. Furthermore, to the knowledge of authors, there is no integrated cylindrical expression for acoustoelastic theory, an expansion of the formulation in a cylindrical system for an orthotropic material is given in detail for the convenience of application, such as cylindrical waves.

Abstract: Currently, the applications of Large Language Models (LLMs) have expanded to diverse areas, from code generation to the medical diagnosis of various pathologies. This work aims to explore what LLMs can achieve using information from CFD simulations of turbulent flow in a manifold, and to determine whether users or students can employ them as a guide for conducting this type of analysis. Through a case study, it is intend to investigate the following aspects of LLMs: 1) the type of information they handle regarding the behavior of turbulent flow within a manifold, 2) whether they identify the boundary conditions necessary to perform a CFD simulation in a manifold, 3) their capacity to provide recommendations for improving CFD simulations based on the results obtained, 4) whether they can predict the results of CFD simulations based on previous results, and 5) whether users or students can use them as a guiding tool for performing CFD simulations. Among the findings, it was discovered that the LLM used has sufficient information on turbulent flows within a manifold and can make recommendations to improve the results of CFD simulations. It was also identified that LLMs offer a user-friendly environment and that it is possible to predict CFD simulation results by varying the manifold boundary conditions.

Abstract: This paper presents a comprehensive experimental and simulation study on the stick–slip characteristics of pneumatic cylinders operating at low velocities. A pneumatic servo experimental system is constructed to systematically investigate stick–slip motion by measuring piston position, piston velocity, pressures in the two-cylinder chambers, and friction force. Extensive experiments are conducted on three pneumatic cylinders of different types and sizes to examine the influences of airflow rate, air source pressure, external load, and initial piston position on stick–slip behavior. Based on experimental observations, a complete mathematical model of the pneumatic servo system is developed. Unlike conventional approaches that simulate stick–slip motion using friction models driven solely by piston velocity, the proposed system-level model explicitly describes the entire dynamic process from valve control inputs to airflow, pressure evolution in the cylinder chambers, piston motion, and friction force. In addition, a new dynamic friction model is proposed by improving the revised LuGre friction model through the incorporation of a dwell-time-dependent static friction force, which is experimentally observed to play a critical role in governing stick–slip motion. Simulation studies are performed using both the proposed friction model and the revised LuGre friction model. The simulated results are systematically compared with experimental data for all tested cylinders. The results demonstrate that the proposed system model with the new friction formulation significantly improves the prediction of stick–slip characteristics, including the number of stick–slip cycles and the evolution of pressure and friction force, compared with conventional friction-model-based simulations.

Abstract: This paper studies the effect of the movement of a single-sided vibro-impact nonlinear energy sink (SSVI NES) in the direction opposite to the obstacle on its dynamics and efficiency in mitigating vibrations of the primary structure (PS) subjected to the harmonic excitation. The damper efficiency is assessed by the reduction of PS maximum mechanical energy. All damper parameters are optimized simultaneously. The paper focuses on the SSVI NES with free movement in the direction opposite to the obstacle, without any constraints, which ensures its high efficiency. Its dynamics and efficiency are compared with those of other dampers, namely SSVI NES with limited motion away from the obstacle and the tuned mass damper (TMD). The preservation of damper tuning when changing the structural parameters such as the natural frequency of the PS, its damping and the intensity of the harmonic exciting force is also being studied. The dynamics of SSVI NES with free motion away from the obstacle is quite calm with periodic motion over almost the entire frequency range. Rapid alternation of modes with different periodicity and different numbers of impacts per cycle, as well as irregular modes, is observed only at high frequencies of the exciting force.

Abstract: Using a parameter that characterizes the damping capacity of the bar material, a mathematical model was developed to control the transverse vibration motion of a slender bar under boundary conditions defined by various support configurations. The model was validated for composite bars reinforced with natural fabrics made of flax, cotton, silk, or hemp fibers, and a hybrid resin matrix containing a 60% volumetric fraction of natural Dammar resin.

Abstract: This study describes a procedure for preparing microfluidic chips made from polydimethylsiloxane (PDMS). It uses a UV ozone cleaner for surface activation instead of the more common oxygen plasma treatment. Although this process has some limitations compared to oxygen plasma bonding, it can be used when a low-cost procedure for a small number of microfluidic chips is required or when an oxygen plasma etcher is unavailable. The challenges of this process arise from the slight hardening of the PDMS surface when it is activated for 70 minutes, which is necessary for reliable bonding. It is demonstrated that damage resulting from this hardening in conjunction with careless handling of the microfluidic chip is mitigated by incorporating predetermined break structures and using tubes with an outer diameter that is smaller than the inlets. Additionally, pre-polymerized PDMS glue and PDMS seals are suggested to ensure that the tubes are properly sealed. To demonstrate the concept, two microfluidic structures were prepared and tested, achieving flow rates of at least 170 µL/min at ±180 mbar. Bonding remains stable up to a pressure of approximately 0.5 bar.

Abstract:

This study presents an analytical–experimental investigation of the mechanical and tribological behaviour of two coating systems applied to deep, internally profiled cylindrical components manufactured via Electrochemical Rifling (ECR): a hard anodised aluminium oxide (AAO) coating on an aluminium alloy and a hard chromium coating on alloy steel. The experimental characterisation includes microhardness measurements, coefficient of friction determination, and controlled sliding wear tests. The results indicate that the chromium coating exhibits approximately 3.2 times higher microhardness and a 16% lower average coefficient of friction compared to the anodised aluminium layer, leading to significantly improved wear resistance.A good agreement is observed between analytical predictions and experimental results. For the steel specimen, values of approximately 26,800 cycles (analytical) and 36,000 cycles (experimental) were obtained, while for the aluminium specimen the corresponding values are approximately 2,050 and 2,012 cycles.Considering the degradation mechanisms typical of hard chromium coatings, a conservative reliability-oriented criterion yields a functional service life of approximately 12,000 cycles for the chromium coating and around 1,000 cycles for the anodised aluminium coating. A Weibull-based reliability analysis (R = 0.95) indicates service lives of approximately 5,200 cycles and 433 cycles, respectively.

Abstract: Vertical-axis wind turbine (VAWT) clusters have been extensively investigated owing to their positive aerodynamic interactions. However, accurate predictions of the flow field and power output of each rotor in VAWT clusters using high-fidelity computational fluid dynamics (CFD) remain computationally expensive. In this study, we propose a fast computation method for the flow field and operating state of each rotor of VAWT clusters using temporally and spatially averaged velocity data compressed from an unsteady velocity field obtained via a 3D-CFD simulation of an isolated single rotor. First, the unsteady 3D flow field in the 3D-CFD simulation is time-averaged over several revolutions. Next, the temporally averaged velocity is spatially averaged in the vertical direction to obtain spatially compressed data. Based on a previously developed fast computation framework, a wind-farm flow field is constructed using condensed two-dimensional velocity data obtained from a single turbine. The proposed method is applied to three-rotor configurations, and the rotational speeds of the turbines are compared with the wind-tunnel measurements. The results show that the proposed method substantially improved the prediction accuracy while maintaining a low computational cost. In addition, it can be used to efficiently design and optimize turbine layouts in VAWT wind farms.

Abstract:

Addressing the critical challenge of precision control over axial shortening in inertial friction welding, this paper proposes an intelligent control method based on a valve-controlled hydraulic motor system. By establishing an accurate transfer function model of the system, two controllers—conventional PID and single-neuron adaptive PID—were designed, and a co-simulation platform integrating AMESim and Simulink was employed for collaborative validation of the hydraulic system and control algorithms. Simulation results demonstrate that the single-neuron adaptive PID controller significantly outperforms conventional PID in dynamic response speed, overshoot suppression, and steady-state accuracy. To validate the practical efficacy of the control strategy, welding experiments were conducted with a target axial shortening value at 400 rpm, and precision testing was performed under extreme conditions by increasing the initial welding speed to 420 rpm. Experimental results indicate a minimal axial shortening deviation of only 0.16 mm between the preset and target speeds, confirming the proposed method's exceptional robustness and engineering applicability for precision axial shortening control. This study provides a theoretical foundation and technical pathway for intelligent control of high-performance inertial friction welding equipment.

Abstract: Efficient recovery of uranium from productive leaching solutions requires a clear under-standing of hydrodynamic and mass-transfer processes in ion-exchange sorption col-umns. In this study, a coupled hydrodynamic and mass-transfer model is developed to investigate uranium sorption in a packed ion-exchange column equipped with a conical flow distributor. Fluid flow in the porous resin bed is described by the Forchheimer filtra-tion law combined with the mass conservation equation, while transport of dissolved uranium species is modeled using a convective–dispersion equation coupled with a sorp-tion kinetics equation based on the linear driving force approximation. Numerical simu-lations are performed using the fictitious domain method to represent the complex geom-etry of the column. The pressure field is determined using the Ritz variational method, and the transport equation is solved with the Crank–Nicolson scheme. The results show that uranium distribution between liquid and solid phases forms a ring-shaped region in-side the column, indicating uneven utilization of the sorbent bed. It is also found that the conical flow distributor does not fully eliminate radial flow non-uniformity. Doubling the solution flow rate increases the width of the mass-transfer zone by about 1.5 times due to enhanced longitudinal dispersion. The proposed approach can be used to analyze and optimize industrial sorption columns for uranium recovery.

Abstract: Electromagnetic hydrodynamic (EMHD) mixed convective flow of tetra hybrid nanofluid (TeHNF) in a Darcy-Forchheimer porous medium in a vertical channel with thermal radiation is considered in the paper. The electric and magnetic fields are homogeneous, magnetic perpendicular to the walls of the channel, and electric perpendicular to the plane formed by the directions of the magnetic field and the basic current. The channel walls are impermeable, they are at constant but different temperatures. The governing partial differential equations (PDE) were, by introducing dimensionless quantities, transformed into nonlinear ordinary differential equations (ODE) which were analytically solved using the homotopy perturbation method. The relations for velocity and temperature distributions, Nusselt numbers and shear stresses on the channel walls were determined. These relations are functions of introduced physical parameters that characterize the observed problem. For TeHNF, where the base fluid is water and the nanoparticles are made of aluminum oxide, titanium dioxide, magnesium oxide and magnetite, a part of the obtained results is given. Velocity and temperature plots are presented in the form of graphs, and Nusselt numbers and shear stresses are presented in the form of tables. Based on the analysis of the obtained results, appropriate conclusions were drawn.Electromagnetic hydrodynamic (EMHD) mixed convective flow of tetra hybrid nanofluid (TeHNF) in a Darcy-Forchheimer porous medium in a vertical channel with thermal radiation is considered in the paper. The electric and magnetic fields are homogeneous, magnetic perpendicular to the walls of the channel, and electric perpendicular to the plane formed by the directions of the magnetic field and the basic current. The channel walls are impermeable, they are at constant but different temperatures. The governing partial differential equations (PDE) were, by introducing dimensionless quantities, transformed into nonlinear ordinary differential equations (ODE) which were analytically solved using the homotopy perturbation method. The relations for velocity and temperature distributions, Nusselt numbers and shear stresses on the channel walls were determined. These relations are functions of introduced physical parameters that characterize the observed problem. For TeHNF, where the base fluid is water and the nanoparticles are made of aluminum oxide, titanium dioxide, magnesium oxide and magnetite, a part of the obtained results is given. Velocity and temperature plots are presented in the form of graphs, and Nusselt numbers and shear stresses are presented in the form of tables. Based on the analysis of the obtained results, appropriate conclusions were drawn.

Abstract: This study analyzes the vibrations to which the WBV of an agricultural tractor operator is exposed during the performance of three different tillage’s: Standard Tillage (ST), System Deep (CTD) and System Shallow (CTS). Measurements were carried out according to ISO 2631-1 and ISO 2631-4 in three coordinate axes (x, y, z). The analysis and statistical processing carried out indicates that none of the mean vibration values exceeds the prescribed limit value of 1.15 m/s² according to Directive 2002/44/EC, but exceeds the daily warning value of 0.5 m/s². From the above, it can be assumed that the operator of the investigated tractor may be exposed to the occurrence of occupational diseases by long-term exposure to such vibrations. The highest vibrations in the x and y axes were recorded when working with the ripper, while in the z-axis they were the highest in the loosener. Although the measured values are within safe (permissible) limits, further research on this topic and optimization of operation can further reduce the burden on the operator.

Abstract: This article comprehensively reviews the fatigue crack growth (FCG) models applied to Ti6Al4V alloy manufactured by electron beam melting (EBM) powder bed fusion (PBF). The current progress in FCG analytical and numerical models and their application to EBM Ti6Al4V are reviewed. Many experimental data for the creation of historic FCG models were based on conventionally manufactured (CM) aluminum alloys and various steels. With the growth of additive manufacturing (AM), recent literature has applied traditional models and modified new models to EBM Ti6Al4V and validated their use as accurate predictive models for the da/dN-ΔK curve and ΔK_th.

Abstract: Indoor air quality (IAQ) is a critical determinant of occupant health, comfort, and cognitive performance, particularly in densely occupied indoor environments such as libraries. This study aims to quantify particulate matter (PM) dispersion dynamics and exposure characteristics through an integrated experimental and computational framework. Three-dimensional CFD simulations were conducted using Flow-3D to resolve the transient transport behavior of multiple PM fractions (PM0.3–PM10) under realistic indoor conditions, and the results were validated against in situ measurements obtained from two library buildings. The findings demonstrate that fine particles (PM0.3–PM1.0) remain suspended at occupant breathing height for extended durations, whereas coarse particles (PM5–PM10) predominantly undergo gravitational settling and accumulate near floor regions. A strong agreement between numerical predictions and experimental data was achieved for PM2.5 and PM10, while discrepancies for ultrafine particles were attributed to turbulence-induced diffusion and Brownian motion. Furthermore, the results highlight the critical role of airflow distribution, ventilation configuration, and spatial obstructions in governing particle transport and the formation of localized high-concentration zones. These findings underscore that ventilation effectiveness is primarily controlled by airflow patterns rather than airflow rate alone. The study confirms that CFD, when supported by experimental validation, provides a robust tool for assessing IAQ and informing ventilation design strategies to mitigate occupant exposure in indoor environments.

Abstract: An analytical solution is presented for transient heat conduction in a two-layer composite cylinder subjected to outer-surface convection with a general time-dependent ambient temperature. Using Duhamel’s principle, closed-form series expressions are derived and then specialized to harmonic ambient fluctuations, recovering the classical constant-ambient solution in the zero-frequency limit. A parametric study shows that the ratio of the inner layer conductivity to the conductivity of the outer layer strongly shapes interfacial gradients and mean-temperature evolution, with sensitivity concentrated at small ratios and diminishing when the ratio is larger than 0.1. Increasing Biot number accelerates the heat transfer and approaches the isothermal-surface limit as it becomes extremely large. The geometric aspect ratio is most influential when the inner layer is resistive, and becomes weak for large conductivity ratio, supporting thin-coating approximations. Under harmonic ambient fluctuations, the response rapidly reaches a periodic steady state; higher frequency decreases amplitude and increases phase lag, while larger Biot numbers amplify oscillations and reduce delay. The coupled effects of the aspect ratio and the conductivity ratio govern penetration and phase behavior.

Abstract: The topic of the paper falls within the new research directions regarding the wear of dental burs, addressing the concept of their durability and reliability. Considering the operating life of dental burs and the conditions imposed by the environment, a series of elements that underlie the occurrence of the wear phenomenon are highlighted. The paper synthesizes the issues of degradation mechanisms and the effects they have on the active part of dental burs, on dental materials used in dental laboratories. The theoretical aspects, state of stresses and strains, their functional parameters in the work processes were identified, and one of the ways of evaluating the tear and wear of the active part of dental burs.

Abstract: The tribological and corrosion behavior of commercial pure titanium - Ti-Gr2 with coatings obtained by mechanized contactless local electrospark deposition (LESD) with a rotating electrode with low pulse energy and an ultradisperse TiB2-TiAl electrode reinforced with ZrO2 and NbC nanoparticles is investigated in this work. The current research is driven by the need for improved corrosion resistance of titanium surfaces in automotive components, shipbuilding, aviation, aerospace, petrochemical and many other industrial and domestic areas. The work is a continuation of our previous research, in which the correlations between the electrical parameters of the LESD mode and the relief, roughness, thickness, microhardness, composition and structure of the coatings obtained with this electrode were studied and analyzed. In this work, the influence of the pulse parameters of the LESD process (respectively, the roughness, thickness, composition, structure of the coatings) on the coefficient of friction, abrasive and corrosion resistance of the coatings has been studied and their role in simultaneous protection of titanium surfaces from wear and corrosion has been clarified. Coatings with the presence of newly formed wear-resistant phases and crystalline-amorphous structures, with increased hardness up to 13 GPa, low roughness Ra= 1.5 -2.8 μm, thickness up to 20 μm and minimal structural defects have been formed. By comparing the potentiodynamic polarization curves, polarization resistance, electrochemical impedance and tribological characteristics of the coated surfaces, it has been established that their corrosion resistance increases by more than 2 times and their wear resistance during friction increases by 4-5 times compared to those of the substrate. Appropriate pulse parameters have been defined to allow for uniform coatings with reduced roughness and structural defects, with predictable thickness, roughness and hardness, and with maximized corrosion and abrasive wear resistance.

Abstract: It is well established that an anti-intrusion beam is a passive safety system that serves an essential role for passengers during collisions. In this study, the influence of internal reinforcements on the bending failure of a cylindrical aluminum tube was systematically investigated through a series of composite beam tests. Polymeric materials, including cast polyamide (PA6) and polypropylene (PP), with varying wall thicknesses, were deemed suitable for use as the inner reinforcement of the Al 6063-T6 tube. The test setup, which simulates impact conditions experienced by structural components in full-scale crash tests, is a powerful tool for the bending impacts in the study. To describe the connection between bending impact and quasi-static loading of composite beams, each method is compared to clarify the composite’s failure behavior. An explicit Finite Element Analysis (FEA) of impact scenarios has been performed to understand the deformation behavior of polymer-reinforced composites and to determine the absorbed impact energy, thereby clarifying which specimen is better able to absorb bending impact energy. Primarily, 3 polymer-reinforced specimens were accepted with a hollow Al tube. After initial tests and simulations, the expected optimization could not be achieved except for one. Then, 3 more combinations were offered. For one of the three specimens, the thickness of the central reinforcement PP was increased until a fully developed shaft was produced, resulting in better-than-expected bending impact-absorbing performance. The results indicate that the energy level of the inner reinforcements with polymeric materials increased 8.8 times, to about 750 J, compared to the plain Al tube (85J) under bending impact loads. The numerical simulations are relevant and reliable for the details of the specimens’ impact process and show good agreement with the experimental results. Finally, depending on the content, this research, rather than focusing on the fundamental concept of polymer-reinforced aluminum crash tubes, focuses on the specific dynamic bending-impact evaluation of the Al, PA6, and PP configuration and the design insight that hollow PP reinforcement can accelerate fracture. In contrast, a fully filled PP core inside a PA6 sleeve can suppress splitting and substantially improve impact energy absorption.