Search Results (2,079)

This paper aimed to understand the nonlinear dynamic responses that arise from the interaction between waves and a biofouling aquaculture cage array. To that end, physical model tests of a biofouling aquaculture cage array in a 1 $\times$ 3 configuration in regular waves were conducted. Wave steepness values of 1/60, 1/30, and 1/15 were considered within the frequencies spanning from low- to high-frequency bands. Then, the nonlinear dynamic responses of the system were systematically decomposed into four successive orders of components. This approach allowed for a thorough assessment of the inherent nonlinearity within the biofouling system by analyzing each individual order. The results highlight that the first-order harmonic component was the predominant contributor influencing the nonlinear dynamic response, while the higher-order harmonic components remained crucial in their contribution to the overall nonlinear dynamic response of the system. In particular, the harmonics within the low-frequency regime exhibited significantly greater nonlinearity compared with those in the high-frequency regime. A notable decrease in the amplitude of the harmonic component could be identified in the low-frequency regime due to the damping from the biofouling. The comprehensive analysis of the nonlinear dynamics within the biofouling system provides insights into optimizing the performance of aquaculture systems. Full article

The Reynolds number (Re), introduced in the late 19th century, has become a fundamental parameter in a lot of scientific fields—the main one being fluid mechanics—as it allows for the determination of flow characteristics by distinguishing between laminar and turbulent regimes, or some intermediate stage. Reynolds’ 1895 paper, which decomposed velocity into average and fluctuating components, laid the foundation for modern turbulence modeling. Since then, the concept has been applied to various fields, including external flows—the science that studies friction—as well as wear, lubrication, and heat transfer. Literature research in recent times has explored new interpretations of Re, and despite its apparent simplicity, the precise prediction of Reynolds numbers remains a computational challenge, especially under conditions such as the study of multiphase flows, non-Newtonian fluids, highly turbulent flow conditions, flows on very small scales or nanofluids, flows with complex geometries, transient or non-stationary flows, and flows of fluids with variable properties. Reynolds’ work, which encompasses both scientific and engineering contributions, continues to influence research and applications in fluid dynamics. Full article

In recent years, additive manufacturing has reached the required reliability to effectively compete with standard production techniques of mechanical components. In particular, the geometrical freedom enabled by innovative manufacturing techniques has revolutionized the design trends for compact heat exchangers. Bioinspired structures, such as the gyroid lattice, have relevant mechanical and heat exchange properties for their light weight and increased heat exchange area, which also promotes the turbulent regime of the coolant. This work focuses its attention on the effect of the relevant design parameters of the gyroid lattice on heat exchange performances. A numerical comparative analysis is carried out from the thermal and fluid dynamic points of view to give design guidelines. The results of numerical analyses, performed on cylindrical samples, are compared to the experimental results on the pressure drop. Lattices samples were successfully printed with material extrusion, which is a low-cost and easy-to-use metal AM technology. For each lattice sample, counter pressure, heat exchange, and turbulence intensity ratio are calculated from the numerical point of view and discussed. At the end, the gyroid lattice is proven to be very effective at enhancing the heat exchange in cylindrical pipes. Guidelines are given about the choice of the best lattice, depending on the considered applications. Full article

This research focuses on the dynamic response analysis of a quadcopter arm without an adapter mounted and with aerodynamic profile adapters mounted to enhance drone performance. Nine different adapters were simulated to assess their impact on the arm’s dynamic behavior during various motor operating regimes. The pressure force distribution from the airflow around the quadcopter arm was analyzed to determine the optimal adapter configuration. Numerical simulations revealed the best geometry for the adapter, which significantly reduced maximum displacement amplitudes compared to the non-adapter arm. The study also examined the effects of static imbalance from the rotor-propeller assembly, leading to the calculation of an eccentricity value of 0.022 mm for inertial force application. Experimental tests validated the numerical findings, with laser vibrometer measurements confirming improved dynamic responses with Adapter 8 across most operating regimes. Overall, the study shows the advantages of using better aerodynamic designs in quadcopter arms to improve stability and performance, contributing to advancements in drone technology through improved structural designs. Full article

Tropical cyclone prediction is often described as chaotic and unpredictable on time scales that cross into stochastic regimes. Predictions are bounded by the depth of understanding and the limitations of the physical dynamics that govern them. Slight changes in global atmospheric and oceanic conditions may significantly alter tropical cyclone genesis regions and intensity. The purpose of this paper is to characterize the predictability of seasonal storm characteristics in the North Atlantic basin by utilizing the Largest Lyapunov Exponent and Takens’ Theorem, which is rarely used in weather or climatological analysis. This is conducted for a post-weather satellite era (1960–2022). Based on the accumulated cyclone energy (ACE) time series in the North Atlantic basin, cyclone activity can be described as predictable at certain timescales. Insight and understanding into this coupled non-linear system through an analysis of time delay, embedded dimension, and Lyapunov exponent-reconstructed phase space have provided critical information for the system’s predictability. Full article

This paper considers a system with two offshore structures in tandem, where the upstream square structure is fixed and the downstream circular structure has one degree of freedom. Cylinders are subject to uniform and linearly sheared flow conditions. The dynamics of the downstream structure are investigated by using a computational fluid dynamics approach for a Reynolds number range of 1000–6500 at the centerline. The spacing ratio for the tandem structures is L/D = 6 in this work, corresponding to the wake interference regime. The effect of the shear parameter on the development of vortex-induced vibrations in the lock-in state within the downstream structure is studied, in comparison with the lock-in of an isolated circular structure. The results of this research include statistics on the displacement amplitude, drag and lift coefficients, frequency ratio, time histories and contours of vorticity. The results obtained show the maximum displacement amplitude of the isolated structure in a uniform flow at the level of 0.8 diameters during the upper branch. The investigation also shows a later development in the maximum displacement during the upper branch of the downstream structure under shear flow conditions, with the highest maximum displacement of 1.18 diameters seen for the shear parameter of 0.05. Full article

Ice accretion from the impingement of supercooled water droplets on the rotating components of aero-engines reduces engine efficiency and poses significant in-flight safety risks. In the present study, we experimentally investigate the impact of water droplets on the center of a rotating disk to gain insights into the icing mechanisms on these components. The effects of impact velocity and disk rotation speed on dynamic behaviors are systematically explored by visualizing the phenomena and quantitatively analyzing the evolution of droplet diameters during long time durations. Three distinct regimes of impact dynamics are identified based on the final states: stable rotation, stable ring, and ring ejection. The experimental results reveal that the spreading phase is primarily governed by inertial effects, with minimal influence from disk rotation, while the latter significantly affects the retraction phase. The maximum spreading factor increases with the impact velocity and shows little dependence on rotation, and the spreading time remains nearly unchanged. Scaling laws for the maximum and equilibrium spreading factors as functions of the Weber number and rotational Bond number are established. While the maximum spreading factor increases with impact velocity on static disks, the retraction time decreases as both the impact velocity and rotation speed increase. Full article

Chaotic systems can exhibit completely different behaviors given only slightly different initial conditions, yet it is possible to synchronize them through appropriate coupling. A wide variety of behaviors—complete chaos, complete synchronization, phase synchronization, etc.—across a variety of systems have been identified but rely on systems’ phase space trajectories, which suppress important distinctions between very different behaviors and require access to the differential equations. In this paper, we introduce the Difference Time Series Peak Complexity (DTSPC) algorithm, a technique using entropy as a tool to quantitatively measure synchronization. Specifically, this uses peak pattern complexity created from sampled time series, focusing on the behavior of ringing patterns in the difference time series to distinguish a variety of synchronization behaviors based on the entropic complexity of the populations of various patterns. We present results from the paradigmatic case of coupled Lorenz systems, both identical and non-identical, and across a range of parameters and show that this technique captures the diversity of possible synchronization, including non-monotonicity as a function of parameter as well as complicated boundaries between different regimes. Thus, this peak pattern entropic analysis algorithm reveals and quantifies the complexity of chaos synchronization dynamics, and in particular captures transitional behaviors between different regimes. Full article

Western Guangdong, a part of the South China Block, has a complex geological history characterized by significant magmatic, metamorphic, and tectonic activities. This dynamic geological past, particularly during the Mesozoic era, created favorable conditions for the formation of various mineral deposits, including Au, Ag, Cu, and Pb. This makes the region a key area for precious metal resources in China. Despite extensive metallogenic studies, detailed structural information for western Guangdong remains insufficient, highlighting the need for further investigation. Thus, effective delineation of deformation periods is crucial for revealing geodynamic history and understanding regional tectonic activities, which are extremely important for guiding mineral exploration. This work focuses on the outcrops of granitic plutons in the Yingde–Guangning area of western Guangdong to establish the structure–tectonic setting. The tectonic events likely shaped the widespread Paleozoic–Mesozoic granitic bodies, which record extensive information on regional tectonic evolution. To achieve the primary objective, systematic identification and kinematic analysis of the various stages of structural traces, such as foliations and joints, have been conducted. This research proposes, for the first time, that the western Guangdong area underwent four distinct tectonic stages: (1) Early Paleozoic NW-SE compression phase; (2) Triassic NE-SW compressional stress; (3) Jurassic NW-SE compressional force; and (4) Cretaceous NW-SE extension stage. In metallogenic terms, the NW-SE trending auriferous veins of the Yingde–Guangning region were mostly formed during the Triassic NE-SW compression stage, whereas the NE-SW trending vein-type gold mineralization developed during the tectonic regime transformation from Jurassic NW-SE compression to Cretaceous NW-SE extension. This research emphasizes that systematic tectonic geological studies of regional granites can effectively guide mineral prospecting. Full article

We derive a one-dimensional macroscopic model for biofilm formation in a porous medium reactor to investigate the role of longitudinal diffusion of substrate and suspended bacteria on reactor performance. By comparing an existing base model—one without longitudinal diffusion, which was the point of departure for our work, to the new model—we noticed significant changes in system dynamics. Our results suggest that neglecting it can lead to underestimation of quenching length and biofilm accumulation downstream, even in the advection-dominated regime. The effects of attachment and detachment of suspended bacteria on biofilm formation and substrate degradation were also examined. In the one-dimensional model, it was found that attachment has a stronger influence on substrate depletion, which becomes more pronounced as diffusion in the pore space increases. Full article

The recently proposed nonlocal macro–meso-scale consistent damage (NMMD) model has been applied successfully to various static and dynamic fracture problems. The characteristic length in the NMMD model, although proven to be necessary for the mesh insensitivity of a strain-softening regime, remains to be estimated indirectly with considerable arbitrariness. Such an issue also exists in other nonlocal models, e.g., peridynamics and phase field models. To overcome this obstacle, a series of dog-bone specimens composed of polymethyl-methacrylate (PMMA) material with and without circular defects are investigated in this paper. It is found that the NMMD model with the appropriate influence radius can correctly capture the experimentally observed size effect of the defect, which challenges the conventional local criteria without involving the characteristic length. In addition to being directly measurable and identifiable in experiments, based on the two-scale mechanism of the NMMD model, the characteristic length is also theoretically calibrated to be related to the ratio of the fracture toughness to the tensile strength of the material. Comparisons with the predictions of other modified nonlocalized criteria involving some characteristic length demonstrate the superior ability of the NMMD model to simulate brittle crack initiation and propagation from a non-singular boundary. The revalidation of short bending beams demonstrates that theoretical calibration is also suitable for problems of mixed-mode fractures with stress singularity. Although limited to brittle materials like PMMA, the current work could be generalized to the analysis of quasi-brittle or even ductile fractures in the future. Full article

The unsteady three-dimensional flow interactions in the near field of square and circular jets issued normally to a crossflow were predicted by direct numerical simulations, aiming to investigate the effect of the nozzle cross-section on the vortical structures formed in this region. The analysis focuses on jets in crossflow with moderate Reynolds numbers ($R{e}_j=200$ and $R{e}_j=300$) based on the jet velocity the characteristic length of the nozzle and low jet-to-cross-flow velocity ratios, $0.25\le R\le 1.4$, where the jets are absolutely unstable. In this regime, the flow becomes periodic and laminar, and three distinct wake flow configurations were identified: (1) symmetric shedding of hairpin vortices at $R{e}_j=200$; (2) the formation of toroidal vortices as the legs of hairpin vortices merge and the vortices roll up at $R{e}_j=300$ and $R\le 0.67$; (3) asymmetric shedding of hairpin vortices in the square jet at $R{e}_j=300$ and $R\ge 0.9$, where higher-frequency hairpin vortex shedding combines with a low-frequency spanwise oscillation in the counter-rotating vortex pair. The dynamics of each of these flow states were analyzed. Power spectral density plots show a measurable increase in the shedding frequencies in $R{e}_j=300$ jets with R, and that these frequencies are consistently larger in circular jets. Full article

With the growing demand for plastic production and the importance of plastic recycling, new approaches to plastic waste management are required. Most of the plastic waste is not biodegradable and requires remodeling treatment methods. Chemical recycling has great potential as a method of waste treatment. Plastic pyrolysis allows for the cracking of plastic polymers into monomers with heat in the absence of oxygen, allowing energy recovery from the waste. Fluidized bed reactors are commonly used in plastic pyrolysis; they have excellent heat and mass transfer. This study investigates the influence of low and medium process temperatures of pyrolysis on fluidized bed reactor parameters such as static pressure, fluidizing gas velocity, solid movement, and bubble formation. This set of parameters was analyzed using experimental methods and statistical analysis methods such as experimental correlations of changes in fluidized bed reactor velocities (minimal, terminal) due to temperature increases for different particle sizes; CFD software simulation of temperature impact was not found. In this study, computational fluid dynamics (CFD) analysis with Ansys Fluent was conducted for the fluidization regime with heat impact analysis in a fluidized bed reactor (FBR). FBR has excellent heat and mass transfer and can be used with a catalyst with low operating costs. A two-phase Eulerian–Eulerian model with transient analysis was conducted for a no-energy equation and at 100 °C, 500 °C, and 700 °C operating conditions. Fluidizing gas velocity increases the magnitude with an increase of the operating temperature. The point of fluidization could be determined at 1.1–1.2 s flow time at the maximum pressure drop point. With the increase of gas velocity (to 0.5 m/s from 0.25 m/s), fluidizing bed height expands but when the solid diameter is increased from 1.5 mm to 3 mm, the length of the fluidized region decreases. No pressure drop change was observed as the fluidized bed regime was maintained during all analyses. The fluidization regime depends on gas velocity and all the applied fluidization gas velocities were of a value in between the minimal fluidization velocity and the terminal velocity. Full article

Wildfire risk increases following non-fire disturbance events, but this relationship is not always linear or cumulative, and previous studies are not consistent in differentiating between disturbance loops versus cascades. Previous research on disturbance interactions and their influence on forest fires has primarily focused on fire-prone regions, such as North America, Australia, and Southern Europe. In contrast, less is known about these dynamics in Central Europe, where wildfire risk and hazard are increasing. In recent years, forest disturbances, particularly windthrow, insect outbreaks, and drought, have become more frequent in Central Europe. At the same time, climate change is influencing fire weather conditions that further intensify forest fire dynamics. Here, we synthesize findings from the recent literature on disturbance interactions in Central Europe with the aim to identify disturbance-driven processes that influence the regional fire regime. We propose a conceptual framework of interacting disturbances that can be used in wildfire risk assessments and beyond. In addition, we identify knowledge gaps and make suggestions for future research regarding disturbance interactions and their implications for wildfire activity. Our findings indicate that fire risk in the temperate forests of Central Europe is increasing and that non-fire disturbances and their interactions modify fuel properties that subsequently influence wildfire dynamics in multiple ways. Full article

In Uganda, the common bean (Phaseolus vulgaris) is often infested by a complex of insect pests, but bean flies, aphids, bean leaf beetles, and flower thrips are the most important. Whereas yield losses due to these pests have been established, there is limited information on their population dynamics at different stages of crop growth and their effect on yield and yield components. In order to describe the population dynamics of selected common bean pests at various phases of bean crop growth, and their impact on yield and yield components, a study was carried out in Uganda during the 2016 second rains and the 2017 first rains in three agro-ecological zones. Bean flies, bean aphids, bean leaf beetles, whitefly, striped bean weevil, leafhoppers, and caterpillars were the main insects observed. Pesticide spray schedules were imposed to generate different populations of insect pests whose effects on yield and its components were determined. The findings indicate that spray regimes significantly influenced the abundance of bean flies and leafhoppers, but not the other insect pests. Additionally, except for caterpillars, insect pests were significantly influenced by crop growth stages, but only leafhoppers exhibited a significant negative relationship with grain yield. Furthermore, yield and yield components varied significantly between spray regimes, and there was a significant positive relationship between grain yield and yield components. Our study is important for informing growers on the stage of crop growth at which management tactics such as use of insecticides can be applied for different insect pests. Full article