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Human–Structure Interaction (HSI) can significantly influence the dynamic characteristics of pedestrian footbridges, particularly those distinguished by their lightness and slenderness. This study examines the performance of Tuned Mass Dampers (TMD) and Semi-Active Tuned Mass Dampers (STMD) on pedestrian footbridges when their modal parameters change due to the influence of HSI. For this purpose, a 30 m long simply-supported footbridge with linear mass values ranging from 200kg/m to 2000kg/m and a fundamental frequency varying from 1Hz to 5Hz has been considered. In addition, several pedestrian streams with different pedestrian densities have been used to assess the structural dynamic response. The analysis highlights that structural lightness and slenderness are critical factors in determining whether the incorporation of an HSI model is relevant to accurately predict the dynamic performance of the structure. The findings indicate that while TMDs can become ineffective due to shifts in natural frequencies caused by HSI, resulting in a degradation of vibration reduction from 70–75% to 40–45%, STMDs demonstrate a robust capability to adjust and cope with these frequency changes, maintaining a higher average vibration reduction of around 55–60%. Consequently, STMDs emerge as a necessary solution for very slender structures where HSI significantly alters the global frequency response. This study highlights the importance of considering HSI in the design and implementation of damping solutions to ensure optimal functionality and user comfort on lightweight pedestrian bridges. [ABSTRACT FROM AUTHOR]

This paper aims to employ the Darboux transformation (DT) to discover the interaction solutions of the Zakharov equation (Eq. (1.2) for δ=1). Through partial degradation of eigenvalues, interaction solutions of the model are constructed on the basis of high-order breather solutions. The study derives interaction solutions involving breather and b-positon solutions through partial degradation of eigenvalues (λj→λ1). Further, interaction solutions comprising breather and lump solutions are obtained through partial double degradation of eigenvalues (λj→λ0). Then, several interaction solutions containing b-positon and lump solutions are extracted through mixed degradation of eigenvalues (λj→λ1 and λk→λ0). In particular, the dynamic evolution characteristics of these solutions are studied. It is believed that these studies make a significant contribution to the understanding of the Zakharov equation and its possible applications in physics. [ABSTRACT FROM AUTHOR]

AbstractSandwich structure is a lightweight structure with high specific strength and specific stiffness, as well as excellent energy absorption and load-carrying capacity. Sandwich structures are widely used in aerospace, high-speed rail and marine applications. Low-velocity impact of a sandwich beam with foam-filled sinusoidal corrugated core is investigated by means of theoretical derivations and numerical calculations. A yield criterion is used to obtain an analytical solution of the dynamic behavior of champed sandwich beams with foam-filled sinusoidal corrugated cores under low-velocity impact. Numerical calculations are performed. The analytical results are in excellent accordance with the finite element results. Influences of the amplitude, half-wavelength and thickness of the sinusoidal corrugated plate, foam strength, metal-sheet strength, and the impact location on the dynamic behavior of the sandwich beams with foam-filled sinusoidal corrugated cores under low-velocity impact are discussed. The present analytical model can predict reasonably well the dynamic behavior of foam-filled sinusoidal corrugated core sandwich beams under low-velocity impact. [ABSTRACT FROM AUTHOR]

The loss of hydrocarbon production caused by the dynamic behavior of the inner boundary and propped fractures under long-term production conditions has been widely reported in recent studies. However, the quantitative relationships for the variations of the inner boundary and propped fractures have not been determined and incorporated in the semi-analytical models for the pressure and rate transient analysis. This work focuses on describing the variations of the inner boundary and propped fractures and capturing the typical characteristics from the pressure transient curves. A generalized semi-analytical model was developed to characterize the dynamic behavior of the inner boundary and propped fractures under long-term production conditions. The pressure-dependent length shrinkage coefficients, which quantify the length changes of the inner zone and propped fractures, are modified and incorporated into this multi-zone semi-analytical model. With simultaneous numerical iterations and numerical inversions in Laplace and real-time space, the transient solutions to pressure and rate behavior are determined in just a few seconds. The dynamic behavior of the inner boundary and propped fractures on transient pressure curves is divided into five periods: fracture bilinear flow (FR1), dynamic PFs flow (FR2), inner-area linear flow (FR3), dynamic inner boundary flow (FR4), and outer-area dominated linear flow (FR5). The early hump during FR2 period and a positive upward shift during FR4 period are captured on the log-log pressure transient curves, reflecting the dynamic behavior of the inner boundary and propped fractures during the long-term production period. The transient pressure behavior will exhibit greater positive upward trend and the flow rate will be lower with the shrinkage of the inner boundary. The pressure derivative curve will be upward earlier as the inner boundary shrinks more rapidly. The lower permeability caused by the closure of un-propped fractures in the inner zone results in greater upward in pressure derivative curves. If the permeability loss for the dynamic behavior of the inner boundary caused by the closure of un-propped fractures is neglected, the flow rate will be overestimated in the later production period. [ABSTRACT FROM AUTHOR]

The design of robotic soft matter capable of emulating the complex movements of living organisms such as mechanical actuation, shape transformation, and autonomous translation remains a grand challenge in soft materials science. Functionalized hydrogels are excellent candidates for such materials since they can operate in water and are highly responsive to their environment, but their response times can be slow. This work investigates fast photoactuation of hybrid bonding hydrogels composed of peptide amphiphile (PA) supramolecular nanofibers bonded covalently to merocyanine‐based (MCH+) photoresponsive networks. By incorporating ionizable acrylic acid (AA) co‐monomers in these networks, photoactuation at nearly neutral pH is observed, which in turn enables a new mechanism to accelerate the response by triggering the bundling of supramolecular nanofibers by rapid proton exchange reactions. Furthermore, this rapid response and its consequent large shape transformations lead to hydrogels capable of spontaneously tracking external light sources inspired by pedicellariae, defensive organs present in echinoderms like the starfish and the sea urchin. This work suggests that hybrid bonding polymers (HBPs), which leverage the interplay between supramolecular assemblies and covalent networks, offer novel strategies to design rapidly actuating soft robotic materials. [ABSTRACT FROM AUTHOR]

This paper presents the first seismic tests on a full-scale all-composite frame structure, constituted by pultruded glass fiber–reinforced polymer (GFRP) profiles, to the best of the authors' knowledge. These tests were performed in the scope of the FRP-Quake project, which aimed to provide an in-depth understanding of the dynamic and seismic behavior of all-GFRP structures, and to develop structural systems with adequate seismic resistance. Therefore, an extensive research program was conducted, from the material and component scales to the structural full-scale, which encompassed the development of appropriate beam-to-column bolted connection systems. The experimental campaign presented in this paper was composed of shaking table tests on a full-scale, two-story, three-dimensional (3D) frame of I section pultruded GFRP profiles connected with bolted stainless steel parts. First, modal identification tests were performed, which show the influence of adding floor masses, bracings, or both on the dynamic characteristics of the structure, which were accurately predicted with relatively simple linear finite-element (FE) models. Then, the frame structure was subjected to 18 base displacement histories with increasing intensity, which was based on the design earthquake for mainland Portugal. The results showed that the structure maintained its integrity for intensities up to 37% higher than the normative requirements. This showed the feasibility of using this type of all-GFRP structures in seismic areas. [ABSTRACT FROM AUTHOR]

This paper proposes a new optimization method by immune algorithm to reduce the impact of clearance joint and wear on the dynamics of mechanisms. Firstly, the dynamic model of crank-slider mechanism is built by Lagrange principle, and the wear phenomenon of clearance joint is characterized by Archard model. Then, the motion function reliability model of mechanism is presented by Stress-Strength interference (SSI) theory. Secondly, the optimization model of mechanism is derived and the surrogate model of the maximum contact force of clearance joint is indicated by response surface method (RSM), the immune algorithm is used to find the optimal solution of the surrogate model. Finally, the impact of wear and optimization on dynamic behavior, nonlinear dynamics, and motion function reliability of mechanism is investigated. The results show that wear clearance joint seriously affects the performance of mechanism. After optimization, the dynamic behavior and nonlinear dynamics of mechanism are improved, and the motion function reliability of mechanism is increased. This paper raises foundation for predicting the performance of mechanisms considering wear clearance joint, and provides theoretical guidance for optimization design and fault diagnosis of mechanisms. [ABSTRACT FROM AUTHOR]

Thermodynamic calculations and thermal analysis tests were performed to investigate the thermodynamic and kinetic behaviors of the carbothermal reduction of vanadium-titanium magnetite w(C)/w(O) and basicity on the carbothermal reduction process of vanadium-titanium magnetite based on the HIsmelt process. Thermodynamic analysis showed that the addition of basicity promoted the reduction of vanadium-titanium magnetite, and the reaction onset temperature gradually increased with the decrease of the valence states of the elements V, Ti and Fe in the product. Increasing the amount of carbon assigned to the system gradually increased the mass fractions of metal Fe and Fe3C and raised the mass fractions of Ti, V and their low valence compounds at equilibrium. Increasing the basicity had less effect on the Fe, V and Ti fractions of the equilibrium system. The results of kinetic tests showed that the maximum reduction degree and maximum reaction rate of the reduction reaction by increasing w(C)/w(O) and basicity increased, the apparent activation energy and the finger front factor decreased, and the reaction mechanism function of the non-isothermal kinetic reduction process was f(α) = (3/2)(1−α)4/3[(1−α)−1/3−1] −1 belonging to the three-dimensional Z-L-T diffusion model. [ABSTRACT FROM AUTHOR]

This study investigates the role of geometrically necessary dislocations (GNDs) and microstructure on void nucleation and growth in wrought and additively manufactured (AM) tantalum subjected to high-strain rate loading. Multi-modal 3D data was collected using TriBeam tomography to calculate GND densities and their spatial relationship to voids. A microstructural comparison between the wrought and AM samples identified distinct void shapes and locations, with intragranular voids and more spherical voids frequently observed in the AM dataset. Results indicate that voids preferentially form at both high-angle grain boundaries and low-angle subgrain boundaries, the latter of which are frequently observed in the AM material. Through a radial distribution analysis of all voids in the datasets, significant GND localization to near-void-surface regions was observed in both samples. 3D crystal plasticity simulations were employed to extend the experimental observations, revealing higher void growth rates in [111] oriented grains when compared to [001] grains. The simulations also suggest that GNDs can be generated as part of the void growth process, with more GND accumulation for growth in a [111] grain than a [001] grain. These findings provide valuable insights into the links between nanoscale void nucleation, mesoscale void growth, and microstructural effects in dynamically loaded tantalum.

Propulsion performance produced by laser ablation of polymer made of acrylonitrile butadiene styrene is experimentally investigated using the first, second, and third harmonics of a Nd: YAG laser. A ballistic pendulum is employed to assess the impulse and coupling coefficient for laser propulsion application. Fast photography, target ablation, and optical emission spectroscopy are proposed to analyze the energy coupling characteristic. The impulse and coupling coefficient under different pressures are demonstrated to depend on the target ablation and plasma properties which are relevant to laser wavelength. As the laser wavelength decreases, the crater depth and ablation mass are enhanced. Meanwhile, the plasma plume separates at atmospheric pressure and its length extends continuously in the low-pressure range. As a result, plasma including more ejected particles with higher velocity contributes to obtaining excellent impulse and coupling coefficient. In addition, the decreased electron density and temperature indicate higher collision frequency and photoionization dominate rather than inverse bremsstrahlung absorption at shorter laser wavelengths. This work provides a better understanding of the energy conversion mechanism and a reference for improving propulsion performance. [ABSTRACT FROM AUTHOR]

• An atmospheric corrosion model of clearance joint is developed based on COMSOL simulation software. • A dynamic modeling and analysis method for ALGRM considering atmospheric corrosion is explored. • The effects of corrosion time and different bearing materials on ALGRM are investigated. • The dynamic behavior and nonlinear characteristics of ALGRM are discussed. Atmospheric corrosion poses a significant challenge for the components of aircraft exposed to prolonged harsh weather conditions, critically impacting the safety property of aircraft landing gear retraction mechanism (ALGRM). This paper focuses on the ALGRM of a specific aircraft type, presenting a new modeling and analysis approach to assess the influence of atmospheric corrosion on dynamic behavior and nonlinear characteristics of mechanism. Initially, the dynamic model of ALGRM incorporating clearance joints is established using Lagrangian method. Numerical solutions are then obtained using the Runge-Kutta method. Subsequently, COMSOL simulation software is employed to simulate the corrosion morphology of the bearing under atmospheric corrosion, integrating the corroded bearing surfaces into the dynamic model of the mechanism. Finally, the study investigates the effects of corrosion time and different bearing materials on the dynamic behavior and nonlinear characteristics of ALGRM considering atmospheric corrosion. The results indicate that as corrosion time increases, the degradation of the dynamic behavior of ALGRM becomes more pronounced, and there are significant variations for corrosion morphology of bearing made of different materials under atmospheric corrosion. The findings of this study contribute to a broader understanding of the complex interactions between the dynamic behavior of aircraft and environmental degradation, providing some insights for designing ALGRM that are more durable and adaptable to atmospheric corrosion environments. [ABSTRACT FROM AUTHOR]

The ground consists of many layers of soil with different properties. The propagation speed and path of seismic waves are affected by different soil layers. It is necessary to understand that layered soil exhibits different dynamic behaviors and responses under the action of seismic waves. This study utilized weathered soil and silica sand as materials to create multi-layered soil conditions with varying degrees of compaction. By conducting a 1 g shaking-table test on multi-layered soil, the interactions and influences between different soil layers under different earthquake conditions were observed. The approach of our numerical analysis aimed to complement the experimental results and provide an in-depth understanding of the dynamic behavior of multi-layered soil surfaces during seismic events. The acceleration results achieved with the ABAQUS and DEEPSOIL models for multi-layered soil were in good agreement with the experimental results. By comparing the stress–strain curves, the deformation mechanisms under different constitutive models in the numerical analysis were studied. The results of this study show that the amplification effect of seismic waves is related to the number of soil layers and the degree of compaction of the soil layers. This indicates that multi-layered soil ground and the behavior of the soil layers play an important role in the propagation and impact of seismic waves, and this amplification effect is of great significance in the design of actual seismic disaster risk assessments. [ABSTRACT FROM AUTHOR]

The experimental determination of cutting forces during milling is an important aspect followed in the manufacturing process and involves the use of specialized devices known as dynamometers. These can be made in the laboratory, depending on the type of measurements to be made, or they can be commercial, purchased from specialized companies. In this paper, such a dynamometer made by the authors in the laboratory is analyzed. For the elastic elements, octagonal rings are used. The main problem in the case of these dynamometers, namely the determination of the stiffness of the rings, is solved analytically, using the FEM for comparison, and then experimentally validated. The dynamic model, created based on the obtained values using d'Alembert's principle, allows for simulating the behavior of this dynamometer in practical applications and determining the field in which it can be used. The frequencies and natural modes of vibration are determined, and the values obtained are compared with those obtained using ANSYS software 2021 R2. [ABSTRACT FROM AUTHOR]

Experiments on the cleaning of primer coatings and composite coatings were carried out by millisecond pulsed CO2 laser and nanosecond pulsed fiber laser, the dynamic behavior during the cleaning process was observed by high-speed camera and infrared thermal imager, and the micro- and macro-morphologies of the surface of the samples after cleaning were analyzed. After using millisecond pulsed CO2 laser to clean the paint coating, there are residual combustion products, and it is easy to thermally deform the substrate. When using nanosecond pulsed fiber laser to clean the primer coating, the laser energy can be precisely controlled to avoid damage to the substrate, but it is difficult to remove composite coatings in a single scan. Using 300 W nanosecond pulsed laser for multiple scans can remove thicker paint coatings with less damage to the substrate, but the cleaning efficiency is greatly reduced. For this, a new method of multi-laser combined cleaning is proposed. The composite coatings are thinned with a 200 W millisecond pulsed laser, and then the final cleaning is done by a 200 W nanosecond pulsed laser, and a clean substrate surface without visible damage is obtained. After cleaning, the coating residue rate is 0.965%, the surface roughness is 3.19 μm, and the surface contact angle is 33.3°, which is conducive to the reattachment of the subsequently applied coatings. [ABSTRACT FROM AUTHOR]

Stability and vibration control are major challenges for applications in which laminated composite beams are being used. Using composite base materials with higher strength and/or using appropriate layout orientation are the two potential methods to improve the dynamic performance of laminated composite structures. However, using composite materials with higher strength significantly increases the manufacturing cost. Recently, layers/segments of Magnetorheological (MR) fluids have been added to the common laminated beams, the so-called MR-laminated beam, to improve the dynamic characteristics of such structures. The present work investigates the effect of base materials and applied magnetic field on the dynamic response of MR-laminated beams. Different composite materials, including E-glass, carbon fiber, and Kevlar, have been used as base materials to build the sandwich MR-laminated beam. The hollow spaces of the sandwich beam are filled with MR fluid to fabricate a testing sample for experimental purposes. A modified layerwise theory, N-layer, has been used to determine the vibration response of the structures. It is concluded that applying a magnetic field increases the natural frequency of the MR-laminated beam. In fact, applying 1400-Gauss magnetic fields to a low-cost material like E-glass provides the same natural frequency as that of the fiber-carbon without magnetic fields. [ABSTRACT FROM AUTHOR]

Previous research on tolerance analysis has primarily overlooked the influence of mechanical vibration on the accuracy of motion, neglecting its significance in systems with moving components. To bridge this research gap, we propose an innovative tolerance analysis framework that combines the theories of skin model shapes and system dynamics. The skin model shapes are employed to represent the form deviations of the workpiece, while the principles of system dynamics are utilized to describe and analyze dynamic behavior. Then, we conduct simulation studies on cam mechanisms to show tolerance analysis outcomes with the consideration of mechanical vibration. This study also defines an index to measure the impact of internal mechanical system components on tolerance analysis. Our findings indicate that the presence of dampers reduces the effect of surface deviation of parts on kinematic accuracy, which is associated with the value of damping coefficient. Therefore, when the internal damping effect of the system is considered in the tolerance analysis, the tolerance design requirements of the parts can be appropriately relaxed, thereby reducing the cost. • A skin model-based framework for tolerance analysis is proposed to achieve enhanced accuracy in analysis results. • Integrating mechanical vibration in tolerance analysis improves real-time error prediction. • The effectiveness of the framework is demonstrated through its application to a snail cam mechanism. [ABSTRACT FROM AUTHOR]

In this research, we investigate the dynamic behavior of Inconel 718 fabricated through laser powder bed fusion (L-PBF), addressing a notable knowledge gap regarding the correlation between process parameters and dynamic properties. The process parameters adopted are deducted from an extension of the Rosenthal solution, formulated to increase the process productivity while avoiding the typical production process defects. The dynamic Young modulus and the structural damping of the material are estimated as a function of the process parameters through ping tests reproducing the flexural vibrations of the specimens in as-built, solutioned, and aged conditions. The microstructure and porosity are investigated through metallographic analyses. The results show a substantial influence of the L-PBF process parameters on the dynamic Young modulus, which markedly increases as the energy density is reduced (23%) and progressively becomes more similar to the conventionally produced material. This influence stands in stark contrast to the relatively modest impact of heat treatments, which underlines a negligible effect of the process-induced residual stress. The structural damping remained approximately constant across all test conditions. The elastic response of the material is found to be primarily influenced by the different microstructures produced as the L-PBF process parameters varied, particularly in terms of the dimensions and shape of the solidification structures. The unexpected relationship between the dynamic Young modulus, energy density, and microstructure unveils the potential to fine-tune the material's dynamic behavior by manipulating the process parameters, thereby carrying substantial implications for all the applications of additively manufactured components susceptible to significant vibratory phenomena. [ABSTRACT FROM AUTHOR]

Ultrasonic impact treatment (UIT) could improve the residual stress of additive manufactured parts. However, there is almost no report on the effect of in-situ UIT, where the UIT equipment moves with laser metal deposition (LMD) equipment at a controllable offset, on residual stress. In this work, the effect of in-situ UIT on residual stress and the effect of offset on the effectiveness of in-situ UIT were investigated by finite element analysis. The stress change introduced by in-situ UIT includes the impact and cooling process. The results show that the value of residual compressive stress (RCS) introduced by the impact of in-situ UIT is higher than that after ex-situ UIT. In the cooling process, the unfinished shrinking behavior reduces it. The increasing offset has little influence on the residual stress field introduced by the impact of in-situ UIT. Residual compressive stress (RTS) reappears in the deposition layer after the cooling process of in-situ UIT, when the offset is small, increasing the offset can retain the RCS. In-situ UIT can improve the residual stress field and the impact of in-situ UIT becomes increasingly similar to that of ex-situ UIT as the offset increases. The findings serve as invaluable guidance in devising strategies to manage and mitigate residual stress in components produced by LMD and other additive manufacturing techniques. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the performance of steel slag in improving the properties of concrete by using different homogenization models and finite element simulations. The free vibration of functionally graded (FG) concrete beams reinforced with steel slag is investigated by using the Euler–Bernoulli and Timoshenko beam theories. It has been assumed that the modulus of elasticity and the density change in the thickness direction according to the power law. The equations governing the free vibration are resolved in an exact way for Euler–Bernoulli theory and by using ANSYS software for Timoshenko theory. Then, a parametric study is carried out in order to analyze the influence of volume fraction and distribution of steel slag, beam slenderness ratio and shear on the dynamic behavior of FG beams. The results demonstrate the significant effect of the studied parameters on the vibration of concrete beams reinforced with steel slag. [ABSTRACT FROM AUTHOR]

Rubberized concrete (RC) has received widespread attention due to its energy absorption and crack resistance properties. However, due to its low compressive strength, it is not recommended for structural applications. The rubber size and content affect RC's mechanical properties. This study investigated and formulated the behavior of RC with different particle sizes and contents under dynamic and static loading. Quasi-static compressive and dynamic tests were conducted on RC with varying content of rubber (0–30%) and rubber sizes (0.1–20 mm). It was found that the rubber particle size was 0.5mm and the rubber content was 2%. An equation was derived from the experimental data to forecast the impact of rubber size and content on compressive strength. Additionally, by combining the literature and this research's data, a model was established based on neural networks to predict the strength of RC. SHPB tests were carried out to study the stress–strain curves under dynamic load. The peak stress, fragment analysis, and energy absorption of RC with varying content of rubber and rubber sizes at three different strain rates (100 s−1, 160 s−1, and 290 s−1) were investigated. Equations describing the relationship between dynamic increase factor (DIF), rubber material content, and strain rate on different particle sizes were obtained by fitting. The DIF increased as the content of the rubber increased. By analyzing energy absorption data, it was found that the optimal ratio for energy absorption was RC-0.5-30, RC-0.1-30, and RC-10-30 at strain rates of 100 s−1, 160 s−1, and 290 s−1. This study could be a good guideline for other researchers to easily select the content and size of the rubber in RC for their applications. It also has a positive significance in promoting the development of green building materials. [ABSTRACT FROM AUTHOR]

The hangers represent the crucial load-bearing component of arch bridges and are susceptible to dynamic vehicle load. However, little effort has been made to carry out dynamic analysis of arch bridge hangers under high-speed train loads. This paper presents an investigation of the dynamic behavior of the arch bridge subjected to high-speed train with emphasis on the flexible hangers, using train–bridge interaction simulation and field measurement data. Coupled train–bridge system model composed of three-dimensional train model, bridge model, and wheel–rail interaction model is established to account for hanger transverse vibration, spatial train loading, and track irregularity excitation, among others. Vibration data of bridge components including the hanger are measured through field test on a typical high-speed railway tied-arch bridge. A total stress-based dynamic amplification factor is subsequently proposed to describe the effect of hanger transverse vibration. The influence of significant parameters such as train speed and track irregularity on the dynamic effects of hangers is examined by the experimentally validated train–bridge interaction model. It is found that the dynamic responses of the hangers are considerably different from bridge global responses. In-plane and out-of-plane transverse vibrations of the hanger result in a large increase in the hanger dynamic effects which prove to be sensitive to train speed, track irregularity, train loading position, etc. Moreover, the dynamic amplification factor formula in the current high-speed railway code may not be sufficient to characterize the dynamic amplification of hangers under operating conditions. [ABSTRACT FROM AUTHOR]

(1) Background: To better understand the dynamic characteristics of a ball bearing with an elastic ring squeeze film damper (ERSFD) under sudden unbalance, a novel dynamic model was established by fully considering the coupling between the ERSFD, bearing outer ring (the journal), rotor, and disc (loading bearing); (2) Methods: An improved secant method was developed to determine the initial eccentricity values of the bearing's outer ring and the disc. The dynamic response of the outer ring under different speed ratios, damping ratios, and mass ratios was solved using the variable-step Runge–Kutta method; (3) Results: In comparison, a low-speed ratio, high damping ratio, and low mass ratio were more conducive to suppressing the bearing vibration. When the imbalance was suddenly introduced, the displacement amplitude of the eccentricity, transmissibility, amplitude–frequency response, and the radius of the outer ring center locus increased; (4) Conclusions: This work provides a reference for further studying the nonlinear vibration of rolling bearings coupled with an ERSFD. [ABSTRACT FROM AUTHOR]

Satellites should be equipped with more and more deployable, large, flexible appendages to improve their service efficiency and reduce launch costs. The spring-driven deployment method of flexible appendages has been widely applied and generates great instantaneous shock loads on satellites, maybe affecting the safety of other flexible appendages, but the current related investigations for satellites with multiple large flexible appendages are insufficient. In this study, the deployment test of the antenna itself was conducted, and the attitude changes in a satellite during antenna deployment were telemetered. Then, a related dynamical model of the satellite was established and verified by the telemetry values of the satellite. Finally, the shock mechanism transmitted to solar arrays was analyzed, and the effect of solar array attitude was discussed. The results show that the simulated method of antenna deployment equivalent to the shock loads tested was thought to be efficient, though it could cause a small non-zero constant of the simulated angular velocities in the antenna deployment direction. The shock-induced moments, except the rotation direction of the solar array drive assembly (SADA), should be highlighted for the antenna deployment dynamic design of satellites, and the solar array attitude has few effects on the shock-induced loads at the SADA. [ABSTRACT FROM AUTHOR]

The influence of defects (splitting) on the stress–strain state of a three-layer cylindrical panel under the action of an aircraft engine jet is studied numerically, by the finite-element method. Two versions of honeycomb filler are considered. The polymer's sheathing consists of individual polymer composite layers. Results for panels with and without defects are compared. [ABSTRACT FROM AUTHOR]

In recent years, the use of carbon fiber-reinforced polymers to strengthen fatigue-damaged steel beams has increased significantly as an alternative to traditional methods due to their easy application to the damaged area, lightweight, durability, and sustainability. In addition to all these positive contributions, there are some disadvantages, such as debonding damage under loading. These disadvantages encourage researchers to produce new materials or apply materials used for other purposes in other fields for fatigue damage. In this paper, an alternative new strengthening technique is mentioned to improve the dynamic and fatigue behavior of fatigue-damaged steel beams. This technique is a strengthening application made using epoxy-based filler and carbon fiber-reinforced polymer fabric. Numerical and experimental studies are carried out on fatigue-damaged steel beams by applying this new technique and using different carbon fiber-reinforced polymers, such as a single and double layer of fabric and a single plate layer. The most significant improvement in dynamic behavior occurred on the specimen, strengthened with this newly proposed technique. In contrast, the lowest increase occurs on the sample strengthened with a single layer of fabric. While the lowest increase arises on the sample strengthened with a single layer of fabric in terms of fatigue life, the most significant progress in fatigue behavior makes on the sample strengthened with a single plate layer. As a result of comparing the results, it is concluded that this new strengthening technique could be an essential alternative to the currently used strengthening methods. [ABSTRACT FROM AUTHOR]

Despite the many advantages of steel shear walls, such as high strength and stiffness, good ductility and high energy dissipation, the increase in the size of columns next to the steel shear walls is a drawback that affects the use of this system. In order to achieve an economic design while keeping design essentials and optimal performance, a novel steel shear wall system called "semi-supported steel shear wall (SSSW)" was proposed, in which the wall plate is attached to the secondary columns instead of the primary columns of the frame. The secondary columns are only responsible for creating the tension field in the plate and the lateral load rather than partnership in the toleration of gravity loads. In this paper, due to the lack of knowledge on the dynamic behavior of steel plate shear walls in general and SSSW in particular, the nonlinear dynamic behavior of SSSWs is investigated. The explicit finite element method is used for analysis and the results are verified by the laboratory test results. The results of the nonlinear dynamic analysis show that semi-supported shear walls have a very good dynamic performance in increasing stiffness and reducing the lateral displacement of the structure. The effects of various parameters of SSSW on its dynamic behavior are also investigated. [ABSTRACT FROM AUTHOR]

Rotor system of aviation engines is often made of multiple rotors connected by the clutch. Due to manufacturing and assembly errors, there is a clutch misalignment, including the parallel misalignment and the angle misalignment. This misalignment produces additional torque in the operation of the system, leading to an abnormal increase in its oscillation, which causes the rubbing between the stator and the rotor. The rub-collision poses great harm to the safety and stability of the aero-engine. The analytical model of the rotor system with misalignment and rubbing faults is established, and the influence of the rotational speed, the misalignment, and the rubbing on the nonlinear characteristics of the rotor is investigated. Considering the nonlinear Hertz contact force and bearing gap, the model of the inter-shaft bearing is built; the parallel and angle misalignments of clutch are taken into account to analyze the characteristic frequency of the faults. For raising the thrust-to-weight ratio of aviation engines, the hollow shaft is often adopted, and the effect of the wall thickness for the shaft on the nonlinear vibration of the system is also investigated. It is innovative to study the transfer mechanism from wall thickness to the nonlinear vibrational responses of the overall structure. The result indicates that, with the increase in the wall thickness of the shaft, the second critical rotating speed increases, while the first critical rotating speed is almost unchanged. The characteristic frequencies for the three-rotor system with coupling faults are obtained. Despite intuition, the parallel misalignment can inhibit rub-collision vibration to a certain extent. The research has important reference values for the fault recognition and structural optimization of the three-rotor system. [ABSTRACT FROM AUTHOR]

The prominent novelty of current review is to exhibit the fluctuating and oscillatory convective heat transfer properties along various geometries with magnetic force, variable density, Prandtl number, buoyancy force and magnetic Prandtl number effects. The significance of present work is to illustrate a comprehensive review on transient convective heat transfer. Transient convective heat transfer plays an essential role in various technological and environmental applications, including climate control, structure safety, engines, thermal control, computer heating and cooling, and energy safety. The literature primarily focuses on steady temperature and velocity domains, with few studies exploring time-varying fluid flow in forced, natural, or mixed convective mechanisms with different methods. In current review, justification of results was performed by using oscillating stokes conditions directly in partial differential models. The similarity variables and stream functions are used in literature but in current review, the primitive variable transformation is used with implicit form of finite difference method and Gaussian elimination technique through FORTRAN and Tecplot-360 programming tools. The governing model is reduced into steady, real and imaginary form to explore steady and oscillating convective heat transmission. Transient flows have gained significance due to their ability to achieve large oscillating convective heat transfer rates. Compared with steady movement, oscillating flows exhibit higher velocity variations along the heated surface. Periodic flow produces an improved transient surface heat transmission rate than steady flow. Predicting and controlling transients in thermal exchangers requires a concept of transient forced convection heat transport. Transient convective thermal transmission solutions are important for ensuring the effectiveness and reliability of electrical components, nuclear and thermal power stations, heat-generating engines, steam turbines, condensation systems, catalytic converters, heat shielding for spacecraft, electrical devices, internal combustion engines, air conditioning and refrigerator components, cooling networks for batteries, generators, and transformers. It is found that the frequency of convective heat transport enhances through periodic and oscillating stokes variables. It was depicted that the higher amplitude in convective heat transfer was displayed for each choice of magnetic force parameter around two angles π/4 and π of circular magnetized surface. It was depicted that the maximum transient convective heat transmission was reported along vertical angle π/2 with buoyancy force, Prandtl and magnetic Prandtl values.

Due to its inherent properties, concrete exhibits brittle failure once it attains its peak compressive and tensile strengths. As concrete is weak in tension, it is usually reinforced with steel bars to resist tensile stresses produced by the applied loading in its superstructure and infrastructure. However, over the last few decades, steel fibers have also been used in preparing concrete for the construction of structural components. Based on some published studies, it has been observed that the use of steel fibers significantly decreases the brittleness associated with concrete and causes an increase in peak compressive and tensile strengths. Furthermore, it was also observed that its behavior significantly differs under increasing compressive loading rates when compared under static loads. However, these studies have been unable to identify the causes of this change in behavior under increasing loading rates; therefore, in this study, a detailed numerical investigation has been carried out using non-linear finite-element analysis software, ABAQUS. It was found that the behavior exhibited by steel fiber reinforced concrete specimens under high rates of compressive loading represents a structural response rather than material behavior.

An understanding of the dynamic behavior of materials plays a crucial role in machining improvement. According to the literature on this issue, one of the alloys whose dynamic behavior has been investigated less is AA 5052-H34, despite its numerous industrial applications. Using finite element (FE) modeling greatly reduces machining research costs. This research delved into the dynamic behavior modeling of AA 5052-H34 during dry-turning FE simulation. The dynamic behavior of AA 5052-H34 was achieved using the Johnson–Cook (J-C) constitutive equation, which was calculated using the uniaxial tensile and Split-Hopkinson pressure bar (SHPB) tests. To confirm the accuracy of the material model, these SHPB tests were then simulated in Abaqus. The J-C constitutive equation, paired with a J-C damage criterion, was employed in a chip formation and cutting temperature simulation. It was found that the feed rate significantly influences the dynamic behavior of AA 5052-H34. The thickness and morphology of the chip were investigated. The experimental and numerical chip thicknesses showed a direct relationship with the feed rate. The simulation temperature was also analyzed, and, as expected, it showed an upward trend with increasing cutting speed and feed rate. Then, the accuracy of the proposed FE simulation was confirmed by the agreement of the experimental and simulation results.

Since the high penetration of distributed energy sources complicates the dynamics of electrical power systems, accurate dynamic models are indispensable for study on the transient behavior of the microgrid (MG). In some practices, the lack of full detailed information results in failure of differential equation based dynamic modeling, which leads to a demand for a black-box MG modeling method. It is a critical challenge to maintain the effectiveness of the black-box model under a wide operating range and various fault conditions. In this paper, inspired by the mathematical equivalence between the recurrent neural network (RNN) and differential-algebraic equations (DAEs), a dynamic equivalent modeling method, using long short-term memory (LSTM), is presented to tackle this challenge. At first, the modeling equivalence and advantages of our basic idea are explained. Then, modeling procedures, including data preparation and design guidelines, are presented. Finally, the proposed method is applied to a multi-microgrid testing system for performance evaluation. The results, under various scenarios, reveal that the proposed modeling method has an adequate capability for representing the dynamic behaviors of a black-box MG under grid fault and operating point changing conditions.

Free-standing archaeological walls are significantly exposed to horizontal actions (e.g., earthquakes) as they lack connections provided by floors or roofs. In such cases, the dynamic response governs the activation of local mechanisms of collapse, determining the shape of the macroblocks and their position. Engineering models of archaeological walls are developed according to the results of extensive visual inspections and on-site testing, including modal identification for calibration purposes. A modal response spectrum analysis on the calibrated model identifies the zones where the tensile stress is exceeded, which are more likely to detach as rigid macroblocks and subsequently overturn due to the expected ground spectra. The macroblocks are then assessed according to limit analysis. The case studies are the north and the apse walls of the church of San Giovanni Evangelista in Castelseprio (Varese, Lombardy), a 5th century Longobard fortified settlement, a part of UNESCO World Heritage. The construction quality of the apse was poorer than the north wall, but the masonry of both is very compact thanks to the good mortar. The macroblocks are identified mostly in the upper crests of the walls, and their acceleration of activation is two to six times larger than the demand (considering the dynamic amplification that the structure applies to the ground motion); therefore, no particular intervention is needed. The proposed method will require additional calibration, e.g., through nonlinear dynamic analyses, and a more precise treatment of uncertainties in masonry mechanical properties to determine the shape of the macroblocks.

ABSTRACTThis study focuses on developing a fiber stacking of polymer laminate for high-impact load-absorbing applications, such as aircraft, automotive, and soundproofing structures. Therefore, the effect of high-strength fiber position effect on the tensile and dynamic behaviors of woven glass intertwined kenaf fiber thermoset composites was investigated in this research work. The tensile strength and dynamic mechanical properties of a hybrid stacking composite designed with maximum glass fiber, especially glass as an outer layer, are relatively higher. The outer layer of glass fiber is particularly effective in containing stress due to its high-strength characteristics, reducing stress transmission to the other core layers. The maximum storage of outer glass and inner kenaf woven stacking composite S1 were 7692.4 MPa, respectively. Besides, the most significant improvement in damping value was observed for the outer glass stacking kenaf (S1) composite compared to the all-other woven glass stacked composite. Furthermore, the composite with the outer glass layers and inner kenaf layers shows a more significant damping value due to the porous structure of the kenaf fibers, allowing for more excellent vibration energy dissipation. Overall, the stacking composites with a glass and kenaf layering arrangement exhibit good mechanical properties for high-impact load-absorbing applications.

Cracking frequently encountered in railway bridges can lead to significant changes in bridge dynamic characteristics and further dynamic performance of train–bridge interaction (TBI) system. It is desirable to develop an effective method to understand the dynamic behavior of coupled train and cracked bridge systems. This paper proposes a framework for coupled vibration analysis of train and cracked bridge systems using multiscale finite element modeling. A multiscale bridge model adopting frictional surface–surface contact to characterize nonlinear breathing phenomenon of the crack is incorporated into the three-dimensional coupled TBI model. Subsequently, a multiloop numerical solution strategy is formulated to solve the established dynamic equation of coupled train and cracked bridge systems. The proposed framework is used to analyze the cracked beams presented in the literature, and the obtained and literature data are compared. Moreover, an actual heavy-haul railway bridge is taken as an illustrative example, in which vehicle dynamic response, bridge vibration, and train running safety index are calculated considering various crack types, train speeds, and track conditions. The results show that apart from the bridge displacement and acceleration, the presence of crack can have a large influence on the vehicle acceleration response, derailment factor, and offload factor. Differences larger than ±10% in the maximum dynamic indices associated with the intact and cracked bridges are observed, indicating the necessity of considering the crack damage in train–bridge coupled dynamic analysis. [ABSTRACT FROM AUTHOR]

Dynamic behavior of hybrid composite shallow shell panels was analyzed utilizing a high-order shear deformation theory (HOSDT) in conjunction with the finite-element method (FEM). To enhance the suitability of plant-fiber composites and to use them as substitutes for pure synthetic-fiber composites, the hybridization of banana-epoxy and glass-epoxy composites was performed, and different sets of hybrid composites were prepared by altering the layers of glass and banana fibers. The elastic constants of these composites were evaluated experimentally and utilized in the further numerical investigation. Simultaneously, a mathematical formulation was developed based on a HOSDT and the FEM. The governing equation of a transient analysis was derived using the Hamilton's principle and Newmark's direct integration scheme to get responses in the time domain. First, the consistency of the present model was checked via an element convergence test, and the accuracy of the model was established by comparing the transient responses obtained from the current model with those of published data. Afterwards, different parametric investigations were carried out to explore the influence of the curvature ratio, shell geometry, hybridization, end conditions, and loading rate on the time-dependent responses of the composites. [ABSTRACT FROM AUTHOR]

Due to its inherent properties, concrete exhibits brittle failure once it attains its peak compressive and tensile strengths. As concrete is weak in tension, it is usually reinforced with steel bars to resist tensile stresses produced by the applied loading in its superstructure and infrastructure. However, over the last few decades, steel fibers have also been used in preparing concrete for the construction of structural components. Based on some published studies, it has been observed that the use of steel fibers significantly decreases the brittleness associated with concrete and causes an increase in peak compressive and tensile strengths. Furthermore, it was also observed that its behavior significantly differs under increasing compressive loading rates when compared under static loads. However, these studies have been unable to identify the causes of this change in behavior under increasing loading rates; therefore, in this study, a detailed numerical investigation has been carried out using non-linear finite-element analysis software, ABAQUS. It was found that the behavior exhibited by steel fiber reinforced concrete specimens under high rates of compressive loading represents a structural response rather than material behavior. [ABSTRACT FROM AUTHOR]

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Purpose: Gas turbines play a critical role in the gas and hydrocarbon industry, but they are prone to failures and malfunctions that can impact their performance and safety. Therefore, it is crucial to implement effective measures for detecting, locating, and identifying these faults, as well as monitoring the operational state of gas turbines. This study proposes a fault detection approach using support vector machines (SVMs) for vibration monitoring of gas turbines. The objective is to develop and validate a reliable and efficient fault diagnosis system capable of estimating the operating state of the gas turbine in normal and degraded modes, while improving the accuracy and speed of fault detection. Methods: This paper applies the SVM method to vibration monitoring of a GE MS5002 gas turbine. The SVM method automatically extracts information about the turbine's operation from its input/output data and classifies faults caused by vibrations. Furthermore, the SVM method establishes appropriate models for turbine instability phenomena with minimal estimation errors. The optimal fault detection function for the gas turbine is determined by utilizing various kernel functions in the SVM method. The SVM-based solutions provide a robust monitoring strategy and performance indicators for vibration diagnosis of the gas turbine. Results: The results demonstrate the effectiveness of the SVM method in monitoring and detecting vibration faults in gas turbines, making it a practical diagnostic indicator. Experimental tests of the kernel-SVM method exhibit superior performance compared to other techniques, achieving fault detection efficiency rates of 99.44% to 99.96% for bearings. This confirms that the kernel SVM fault detection algorithm has a minimal prediction error rate in identifying vibration faults in gas turbines. Conclusions: This study presents the development of a SVMs approach for monitoring and detecting vibration defects in GE MS5002 turbine bearings, based on an experimental study using input/output operating data. The proposed fault diagnosis approach is validated through robustness tests conducted in real-time, specifically for the detection of vibration faults affecting the four bearings. This approach establishes diagnostic elements with improved performance and ensures the continuous and stable monitoring of the examined turbine components. [ABSTRACT FROM AUTHOR]

An understanding of the dynamic behavior of materials plays a crucial role in machining improvement. According to the literature on this issue, one of the alloys whose dynamic behavior has been investigated less is AA 5052-H34, despite its numerous industrial applications. Using finite element (FE) modeling greatly reduces machining research costs. This research delved into the dynamic behavior modeling of AA 5052-H34 during dry-turning FE simulation. The dynamic behavior of AA 5052-H34 was achieved using the Johnson–Cook (J-C) constitutive equation, which was calculated using the uniaxial tensile and Split-Hopkinson pressure bar (SHPB) tests. To confirm the accuracy of the material model, these SHPB tests were then simulated in Abaqus. The J-C constitutive equation, paired with a J-C damage criterion, was employed in a chip formation and cutting temperature simulation. It was found that the feed rate significantly influences the dynamic behavior of AA 5052-H34. The thickness and morphology of the chip were investigated. The experimental and numerical chip thicknesses showed a direct relationship with the feed rate. The simulation temperature was also analyzed, and, as expected, it showed an upward trend with increasing cutting speed and feed rate. Then, the accuracy of the proposed FE simulation was confirmed by the agreement of the experimental and simulation results. [ABSTRACT FROM AUTHOR]