Engineering

Abstract: This study presents a reduced-order dynamic model for three degree-of-freedom AUV maneuvering. The proposed model identifies linear operators that map physically selected, polynomially expanded kinematic subspaces to hydrodynamic forces and moments using free-running zigzag-test data obtained from computational fluid dynamics simulations. To improve prediction stability and physical interpretability, the CFD-resolved force and moment contributions from individual components, including the hull, rudders, and propeller, are extracted and modeled separately. This component-wise formulation allows each hydrodynamic contribution to be reconstructed from a corresponding physically informed kinematic subspace. The identified operators are first evaluated through forecasting validation under the training maneuver and are then applied to an untrained turning-circle maneuver. The results show that component-level hydrodynamic forces and moments can be approximated by linear operator mappings constructed from free-running CFD data. The identified relationships retain predictive capability in the untrained maneuvering scenario, indicating that the proposed framework can serve as a practical reduced-order model for CFD-based maneuvering prediction.

Abstract: In biomechanical research, coupled multibody-finite element (MB-FE) simulations enable the simultaneous study of global dynamics and tissue-level mechanics. Yet validated pipelines that bridge the MB and FE domains are often complicated and involve multiple software tools. ArtiSynth is an open-source Java-based biomechanical simulation framework for coupled MB-FE simulations with forward and inverse simulation capabilities and FE contact modelling. It features an importer for OpenSim models to be used as foundation for coupled MB-FE models. However, the performance of OpenSim models in the ArtiSynth environment has not been evaluated to this day. To address this gap, we developed an ArtiSynth lower-limb model based on an OpenSim model and evaluated it across multiple subjects and trials. Motion and force data (98 trials, 29 healthy participants) were processed and used in OpenSim and ArtiSynth inverse/forward computations. A representative trial was selected using the SMaRT algorithm and pooled for Statistical Parametric Mapping (SPM, two-sample t-tests). No significant differences were found for kinematics, and differences were limited to short time frames for global dynamics. Muscle forces showed visible differences, but with good global agreement. Overall, the ArtiSynth model reproduces physiologically reasonable kinematics and largely consistent kinetics relative to OpenSim, thereby serving as baseline in future MB-FE applications.

Abstract: Torsional vibrations represent a significant dynamic phenomenon in rotating mechanical systems and are often associated with increased dynamic loading, fatigue damage, noise generation, and reduced operational reliability. Conventional vibration mitigation techniques are generally effective only within a limited frequency range, which restricts their applicability in modern drivetrains operating under variable loading conditions. Consequently, increasing attention has been devoted to nonlinear vibration control concepts based on the principle of Targeted Energy Transfer. This paper presents the development and experimental investigation of a novel TET system with variable torsional stiffness intended for torsional vibration mitigation in rotating mechanical systems. The proposed concept combines the vibration energy redistribution capability of a nonlinear absorber with adaptive stiffness tuning achieved through pneumatic elements. The torsional stiffness of the secondary subsystem can be continuously adjusted by regulating the pressure within air bellows, enabling adaptation of the system dynamics to varying operating conditions. A dedicated experimental test rig with kinematic excitation was developed to investigate the dynamic response of the coupled mechanical system and to evaluate the influence of variable stiffness on the TET mechanism. The study focuses on the analysis of vibration energy redistribution, the identification of optimal operating conditions, and the assessment of the potential of variable-stiffness TET systems for wide range torsional vibration control in rotating machinery.

Abstract: Data-driven techniques for machine condition monitoring are typically initially tested on relatively simple experimental datasets where they often achieve near-perfect classification accuracies. These results do not confirm applicability in real-world situations nor whether the computational demands required are justified. This paper introduces an experimental dataset designed to better approximate selected real-world operational conditions. This dataset is then used to evaluate both traditional and novel techniques for machinery fault classification and determine their effectiveness for use in computing resource-constrained environments, such as where edge computing might be employed on mobile or remote equipment. Four distinct data-driven methods were tested and analyzed using a variety of metrics beyond only classification accuracy. The traditional machine learning techniques struggled to identify fault conditions from unseen speed profiles, whereas deep learning models succeeded. Computational metrics indicated that some methods required significantly more memory usage and/or computing time than other models. One of the deep learning models had memory requirements and computational demand that would allow it to be theoretically feasible for real-time application on platforms such as the Jetson Nano or Raspberry Pi 5. This highlights the potential of ongoing deep learning model development for machine condition monitoring, as well as the limitations of traditional approaches.

Abstract: Additive manufacturing of PEEK/regolith composites offers a promising route for lunar in-space manufacturing by reducing dependence on Earth-supplied materials. However, the processability of these composites and the elastic response of printed components are strongly influenced by regolith loading and manufacturing-induced defects. This study develops a hierarchical finite element framework to quantify the stiffness of additively manufactured PEEK containing 10-50 wt% LMS-1D lunar regolith simulant and to distinguish intrinsic composition effects from defect-driven stiffness losses. The approach combines composition-based estimation of regolith properties with microstructure-informed simulations of PEEK/regolith composites. Under defect-free assumptions, the predicted modulus increases monotonically from 1.27 GPa at 10 wt% to 1.97 GPa at 50 wt%, showing good agreement with experimental trends up to 40 wt%, where deviations remain within 3.5-10.1%. At 50 wt%, however, the experimental modulus decreases to 1.27 GPa, while the defect-free model predicts 1.97 GPa. Microscopy-informed single-layer analyses indicate that tall crack-like interfacial voids, polymer-starved welds, and interconnected weak seams significantly reduce load transfer and shift the mechanical response toward an interface-controlled regime. These results show that regolith additions can enhance stiffness only until defect connectivity becomes dominant. The findings provide insight into the process-structure-property relationships governing ceramic particle-reinforced high-performance thermoplastics in additive manufacturing.

Abstract: With increasingly strict air quality standards and growing concerns about air pollution, fine and ultrafine particulate matter remains a major challenge for conventional air cleaning technologies. Due to their small size, these particles are difficult to remove using traditional filtration and separation methods. Acoustic agglomeration can be used as a pre-treatment technology to increase particle size in a high-intensity acoustic field and improve the efficiency of particle removal. This study investigates acoustic-induced agglomeration of solid aerosol particles in a dynamic airflow system. The effects of acoustic frequency were evaluated at 3, 5.5, 7.5, and 15 kHz under a sound pressure level of 135 dB and at two airflow velocities: 0.75 m/s and 1.5 m/s. These velocities corresponded to different particle residence times in the acoustic field. Arizona test dust was used as the test aerosol, and particle number concentration and particle size distribution were measured before and after the acoustic field. The results showed that acoustic agglomeration of fine and ultrafine particles was strongly affected by both acoustic frequency and particle residence time. The highest agglomeration efficiency, reaching up to 42%, was obtained at 3 kHz, 135 dB, and longer particle residence time. These findings indicate that acoustic agglomeration can promote particle size redistribution in moving airflow and may be used as a pre-treatment method for improving particulate matter removal in air quality control systems.

Abstract: Hydrogen blending in natural gas pipelines is a promising decarbonization pathway. This study investigates a coaxial-swirl static mixer for hydrogen-natural gas mixing at ratios of 5% to 30% H₂. The mixer features nine ring-shaped cavities with 120° helical torsion to enhance turbulent mixing. A calibrated 2D axisymmetric computational model was developed and validated against experimental data. Results show that the configuration achieves 95% mixing uniformity within 8.2D to 9.0D across all blending ratios, meeting industry targets with minimal pressure penalty (<0.04% of operating pressure). Validation shows good agreement with literature, with mixing intensity profiles matching within 5%. This work supports the integration of hydrogen into existing infrastructure for near-term decarbonization.

Abstract: Zamak 5 is a commercially important Zn–Al–Cu–Mg alloy that is frequently used in precision casting applications because of its dimensional stability, good casta-bility, and balanced engineering properties. In the present investigation, the in-fluence of two artificial aging conditions on the thermal and mechanical behavior of this alloy was experimentally examined. The first treatment consisted of aging at 85 °C for 44 h, whereas the second treatment was performed at 120 °C for 24 h. The aged specimens were characterized using SEM and EDS analyses together with microhardness testing and transient cooling experiments. The findings showed that aging reduced the hardness of the alloy relative to the untreated condition, with the largest reduction obtained after aging at 120 °C for 24 h. In contrast, the same condition produced the highest heat transfer response among the tested specimens. The thermal behavior was strongly associated with precip-itate evolution, redistribution of Zn-rich and Al-rich phases, and the resulting modification in thermal energy storage capability during transient cooling.

Abstract: In addition to barges, floating conveyor belt routes are used to ensure the continuous transport of granular materials extracted by floating dredgers from the water environment. These routes are composed of individual conveyor belts, where the end sections of the steel structure are held up by floating support bodies. This paper deals with the graphical and analytical determination of the coordinates of the centre of gravity of the buoyant force and the stability arm during the deflection of a floating body, consisting of two floats with a circular cross-section, from the equilibrium position. The coordinates of the centre of buoyancy were determined by a graphical-numerical method in the 3D CAD environment on the created three-dimensional model of the floating body. The coordinates of the centre of buoyancy were determined by analysing the geometric and physical properties of the model using the "Physical Properties" tool. The analytical procedure for determining the coordinates of the centre of buoyancy when a floating body is deflected from its equilibrium position is divided into three characteristic phases, which are mathematically described by means of certain integrals with differently defined integration limits corresponding to the given state of immersion of the body. Under laboratory conditions, the magnitude of the buoyant force was detected on the experimental apparatus using two force transducers. The experiment was carried out for three levels of float immersion, where the floating body was gradually tilted from the equilibrium position in a range of angles from 0° to 50°. The measured values were used to analyse the effect of the immersion depth and angle of heel on the magnitude of the buoyant force. The experimental tests carried out verified the correctness of the analytical and graphical procedure for determining the coordinates of the centre of buoyancy and for determining the stability arm.

Abstract: To improve the antifouling and self-cleaning performance of 3003 aluminum alloy, a green fluorine-free superhydrophobic surface was fabricated by combining nanosecond laser processing with subsequent heat treatment. The effects of laser processing parameters, including scanning speed, laser power, pulse frequency, and scanning interval, on surface wettability were systematically investigated. The results showed that optimized processing conditions (2700 mm/s, 6 W, 35 kHz, and 20 μm) enabled the formation of hierarchical micro-/nano-structures, resulting in a maximum water contact angle of 154.32°. SEM and EDS analyses suggested that the enhanced wettability originated from the synergistic effect of hierarchical rough structures and heat-treatment-induced surface chemical modification, which promoted the formation of a stable Cassie–Baxter state. The fabricated surface exhibited excellent self-cleaning performance, as water droplets effectively removed SiO₂ contaminants by rolling behavior. In addition, the surface maintained high hydrophobicity after repeated water jet impact and tape-peeling tests, indicating good resistance to dynamic flow and mechanical damage. This study provides a simple, environmentally friendly, and effective strategy for fabricating durable superhydrophobic aluminum alloy surfaces for antifouling and protective applications.

Abstract: This study proposes a variant of the fluorite lattice structure inspired by the porous structure of pomelo peel to improve energy absorption performance and mechanical properties. Using volume homogenization, the mechanical properties of the structure were determined and optimized using the constrained search and sorting method. Simultaneously, under axial crushing load via finite element simulation, the energy absorption performance of the structure will be evaluated by improving geometric parameters and comparing it with other typical lattice structures. The results show that the elastic modulus of the structure is improved with increasing the strut radius R while the slope λ remains at 0.6. Furthermore, increasing the relative density, the number of unit cells, and the impact speed will improve the performance and stability of the structure during energy absorption. Furthermore, the structure shows great potential for energy absorption applications, exhibiting superior energy absorption performance compared to other typical lattice structures.

Abstract: Laser Powder Bed Fusion produces geometrically complex metallic components, yet fatigue performance consistently falls below that of wrought counterparts. Surface condition, encompassing as-built roughness, residual stress, porosity, microstructure, and oxide layers, is the dominant factor driving this deficit. This review critically examines surface-driven fatigue mechanisms across Ti-6Al-4V, IN718, AlSi10Mg, and 316L alloys. Post-processing strategies including mechanical polishing, peening, electrochemical polishing, laser polishing, burnishing, and hybrid approaches are systematically evaluated. The mechanistic roles of surface roughness as a stress concentrator, near-surface porosity as crack initiation sites, and compressive residual stress as a crack-closure mechanism are discussed. Emerging burnishing techniques, particularly electrical current-assisted burnishing, demonstrate fatigue life improvements of up to five times relative to as-built components, underscoring the transformative potential of thermo-mechanical surface modification. Finally, this review identifies critical research gaps, notably the lack of standardized surface characterization protocols and the limited understanding of fatigue under multiaxial and variable-amplitude loading for surface-treated L-PBF parts, and outlines directions for future work.

Abstract: High-volume injection mold systems used for plastic part production operate under severe coupled thermo-mechanical boundary conditions. During each molding cycle, core inserts are subjected to repeated injection pressure, transient thermal effects, and mechanical constraints imposed by the polymer and the surrounding mold assembly. These combined actions generate localized stress concentrations in critical insert regions, promoting crack initiation and eventual core insert breakage. To describe the behavior of hot-work tool steel core inserts under these operating conditions, experimental process measurements, structural analysis, and damage modelling must be linked within a service-life assessment framework. This integrated approach supports the interpretation of the observed failure case and helps identify the root cause of premature core insert breakage.

Abstract: Conventional push-out tests detect bone–implant failure only at the point of macroscopic instability, leaving earlier damage stages unresolved. Here we present a proof-of-concept for a push-out test stand combined with acoustic emission (AE) monitoring, aimed at cap-turing crack initiation before macroscopic load drop. To provide a controlled failure pro-cess, samples were fabricated from SLA resin with defined breaking points, serving as mechanical surrogates rather than biological models. Four sample types with varying strut number and thickness were tested while recording AE, and post-processing was applied to remove friction and noise signals. A four-stage fracture model, plastic, pre-fracture, fracture, and post-fracture, was defined, with the pre-fracture stage showing AE activity prior to any macroscopic load response. Increasing strut thickness and contact area raised maximum load resistance and AE activity, and Principal Component Analysis confirmed a progressive, intensity-driven separation of stages. The results demonstrate that AE mon-itoring resolves a pre-fracture regime inaccessible to conventional load measurement, es-tablishing a methodological basis for future application to bone-implant samples.

Abstract: In previously published papers, we derived the appropriate partial differential equations of the fractional order, with appropriate boundary and initial conditions, of the oscilla-tion dynamics of the rheological Kelvin-Voight model of fractional-type materials, and studied the longitudinal natural and forced oscillations of rods of variable cross-section and determined the natural and forced rheological modes of the fractional type. In this paper, we present new scientific results from the study of the flow dynamics of the rheological Maxwell model of fractional-type materials, viscoelastic fluids with the property of normal stress relaxational of the material in a pipe of variable cross-section. These properties lead to the appearance of longitudinal rheological flows (creeps) of the fractional type. We described this flow motion of the material only by a partial differen-tial equation of fractional order in terms of normal flow stresses and determined its ap-proximate analytical solutions and the corresponding approximate analytical expressions of the eigen and forced modes of normal flow stress (creep) in terms of eigen time func-tions in the corresponding eigen amplitude forms. We considered various possible boundary conditions for normal flow stresses and for different cross-sections of pipes of variable cross-section. We derived an ordinary differential equation of fractional order in terms of eigentime functions in each eigen amplitude form of the normal creep stress of the fractional type and gave its approximate analytical solutions, with accompanying approximate analyt-ical expressions of the rheological eigenmodes and forced modes of the normal creep stress of the fractional type. We have derived an ordinary differential equation of fractional order by its eigentime functions in each eigen amplitude mode of the normal creep stress of the solution. We have given graphical representations of the surfaces of the eigen and forced rheological creep modes of the solution as a function of the exponent of differentiation of the frac-tional order and time. We have given comparisons of these eigen and forced modes of rheological Maxwell model of material fractional type with the corresponding eigen and forced rheological modes of dynamics when the material is elastoviscous of the Kel-vin-Voigt model of an elastoviscous material, fractional type. We have shown compara-tive graphs of the surfaces of eigen and forced modes of fractional type for the oscillation dynamics of the rheological Kelvin-Voigt model of an elastopiscoustic material, fractional type and the flow dynamics of the rheological Maxwell model of a viscoelastic material, fractional type.

Abstract: We present newly derived approximate analytical solutions of the motion, free and forced modes of dynamics of two viscoelastic rheological Maxwell-Faraday discrete dynamic systems, creeper type, and fractional type, with piezoelectric polarization property of the Faraday piezoelectric element. New theoretical analytical scientific results of research into the creep dynamics of basic rheological Maxwell-Faraday discrete dynamic systems of fractional type, with piezoelectric efects, and with two degrees of freedom of motion, one external and one internal degree of freedom of motion, are presented. Rheological complex Maxwell-Faraday discrete dynamic systems of fractional type with piezoelectric polarization effect consist of standard light-binding rheological Maxwell-Faraday ensembles fractional type and rigid bodies moving in translation. They always occur in pairs, rheological discrete dynamic systems depending on the order of sparse coupling of rheological basic light elements in standard light-binding structures and their connections with the rigid body and the fixed point. They have one external degree of freedom related to the degree of freedom of motion of the rigid body and one internal degree of freedom of motion related to the internal degree of freedom of motion of the light-binding rheological assembly itself. For the dynamics of two models of a rheological discrete dynamic system, fractional type, with the opposite order of the order of the basic rheological elements, Hooke's ideally elastic, Faraday's piezoelectric and Newton's viscous fluid of fractional order, corresponding systems of ordinary differential equations of fractional order have been written. The systems have a fractional type of dissipation of the total mechanical energy of the system and the properties of normal stress relaxation. They also have the property of electric polarization, during mechanical deformation, of a rheological Faraday piezoelectric element. Approximate analytical expressions are determined, in the time domain, for independent generalized system coordinates, which correspond to the external and internal degrees of freedom of rheological creep of each of the discrete dynamic systems with opposite binding of the elements of the standard light rheological binding basic complex Maxwell- Faraday model. To obtain the inverse Laplace transforms of the independent generalized coordinates of the creep dynamics of each of the models of rheological discrete dynamic systems, the expansion in power order by the parameters of the Laplace transform was used, and with their help the transition to the time domain.

Abstract: Producing reliable gear systems for wind turbines involves accounting for multiple uncer-tain parameters. To ensure that vibrations during operation remain controlled, it is essen-tial to analyze how sensitive the system is to these uncertainties. This study investigates the dynamic response of a two-stage wind turbine gearbox, considering variation in seven key system variables. The goal is to evaluate the system’s reliability through the bearing displacement analysis. A 12-DOF concentrated-parameter model is proposed to account for uncertainties in gear mass, damping, and the inertias of the pinion, gear, and input shaft. The dynamic response is examined using Polynomial Chaos Expansion (PCE) across different orders and standard deviations, with results validated through Monte Carlo Simulation (MCS) using 100,000 samples. A custom MATLAB tool was developed to implement both approaches.

Abstract: Addressing the century-old problem of turbulent intermittency, we present a rigorous parameter-free derivation of the scaling exponents for turbulent longitudinal structure functions, based on the ϕ(τ) spacetime and the physical upper bound of Lagrangian micro-rotation velocity Ω_FluidMAX. For the low-order regime (p≤6), the derived strict quadratic formula reads: ζp=p/3+p(3−p)/8π^2. This formula contains zero adjustable parameters, with the correction term stemming solely from the universal topological constant 1/(4π^2) intrinsic to rotational motion. It automatically satisfies the exact Kolmogorov 4/5 law at p=3 and is strictly symmetric about p=3, naturally explaining from first principles the ubiquitous experimental observation that “scaling exponents exceed K41 values for p<3 and fall below them for p>3”. Remarkably, this zero-parameter theory reproduces all six independent high-precision experimental/DNS data points for p=1 to 6 with a relative error of less than 0.3%.We further predict that a physical phase transition occurs at p=6, corresponding to the breakdown of the continuum hypothesis. For 7≤p≤11, the scaling exponents deviate from the quadratic law due to the dominance of high-order nonlinear terms. Crucially, this high-order deviation is not a “fitting residual,” but the inevitable consequence of a hard-truncation phase transition (nonlinear breakdown): as the local micro-rotation velocity approaches Ω_FluidMAX​, the hard-wall truncation of rotational kinetic energy causes a δ-function accumulation in the probability density at the threshold (angular condensation), thereby exciting a linear additional term in the high-order moments. A complete set of zero-parameter predicted values for p=1 to 11 is provided for independent experimental verification (where ζ1−ζ9 precisely match existing experimental/DNS data, see Tables 1-2).

Abstract: This paper analyses the microstructure and properties of the titanium- and boron-alloyed high-carbon medium-manganese 140Mn6Cr3TiB steel deposit before and after high-frequency mechanical impact (HFMI) treatment. Nanoindentation revealed a distinct correlation between the phase composition and the deformation behaviour. The heterogeneous nature of the steel creates a "shield-and-buffer" effect, where the hard eutectic framework resists penetration and tough matrix prevents brittle failure. The synergistic interaction between the phases, i.e., the high hardness of boride-carbide phases with the high fracture toughness of the manganese-rich austenite, maintains a high tolerance to abrasion damage of the deposit. The HFMI treatment results in the formation of the strain-induced ε- and α’-martensites (~66% and 3–6%, respectively), a significant grains/crystallites refinement (down to 31–54 nm), and dislocation density (~2.2*1013–5.1*1013cm-2), which support essential hardening from HV0.2 = 5.17 GPa to HV0.2 ≈ 7.8 GPa. The HFMI treatment regime (load = 100 N, amplitude = 10 µm, and HFMI time = 60 s) was found to be optimal, which leads to the enhancement in wear resistance of 140Mn6Cr3TiB steel deposit that manifests itself by the decrease of the wear volume by ~4 times from 15.2 μm3 to 3.9 μm3 and in the decrease in the scratch track depths by ~30% (from ~0.52 μm to ~0.37 μm) in comparison with the initial deposit. The HFMI-hardening changed the wear mechanism of high-carbon medium-manganese titanium and boron-alloyed 140Mn6Cr3TiB steel hardfacing to the ploughing mechanism instead of the ‘wedge/pile-ups’ formation in the initial deposit. The obtained results confirm good efficiency and prospects of the medium-manganese steel hardfacing followed by the finishing HFMI treatment in the production of protective deposits of enhanced wear resistance and prolonged operation life.

Abstract: Background Efficient and safe instrument exchange remains an important challenge in robotic minimally invasive surgery. Current workflows require human assistance, increasing staff workload and contamination risk. The modular design of the AdLap robotic laparoscopic instruments enables automated exchange of instrument shafts. This study presents the development and validation of the Instrument Carousel Exchange System (ICES). Methods An automatic ICES was developed for the AdLap robotic surgery platform. The prototype was designed to hold six Shaft-Actuated Tip-Articulating (SATA) modular instrument shafts and focused on compactness, robustness, modularity, and rapid disassembly for cleaning and sterilization. System performance was evaluated using repeated autonomous instrument exchange cycles without user interaction. Reliability, alignment tolerance, safety, and exchange duration were assessed. Results The ICES prototype was successfully designed, manufactured, and tested. Repeated functional testing demonstrated reliable autonomous instrument shaft exchange without human intervention. The system tolerated minor alignment deviations while maintaining stable and safe operation. Mean time for a complete instrument shaft exchange was 84 seconds (SD = 10 seconds). The modular architecture allowed straightforward disassembly and maintenance while preserving structural integrity and compact design. Conclusions The developed ICES represents a substantial step toward fully automated robotic modular instrument handling in minimally invasive surgery. Automated instrument exchange may reduce staff workload and minimize contamination risk during robotic procedures. Future work will focus on improving automation speed, alignment efficiency, and autonomous reinsertion of the instrument shaft through the trocar to further enhance clinical applicability.