Numerical Simulation Results Research Articles

Simulation and experimental study of single axis load of resin-based concrete at macro-micro scale

ABSTRACT This study focuses on resin-based concrete, a novel composite material in which resin replaces the traditional cementitious binder, forming a three-phase composite consisting of aggregate, resin matrix, and interfacial transition zones. Four random aggregate models were generated using the Monte Carlo method and their stability was verified. Subsequently, a two-dimensional micro-model was established, and the simulation results were compared with experimental data, yielding a maximum error of 8%, which validated the feasibility of the model. The findings indicate that circular aggregates exhibit lower load-bearing capacity, while irregular aggregates demonstrate higher capacity. Although the peak compressive strength is similar among different aggregate shapes, the crack propagation paths vary significantly. The load-bearing capacity of resin-based concrete increases with aggregate content up to an optimal value of approximately 80%, beyond which it decreases. At this optimal content, crack paths transition from branched to near-linear. In terms of aggregate grading, higher coarse aggregate proportions enhance load-bearing capacity and promote linear crack propagation, whereas higher fine aggregate proportions reduce capacity and result in multiple irregular crack paths. Finally, the numerical simulation results were used to guide macroscopic experiments, and orthogonal experiments were conducted to determine the optimal mixture proportions of different resin binders.

Ultra‐Broadband Polarization‐Independent Terahertz Absorber Based on All‐Dielectric GaN Metamaterials

In this article, an ultra‐wideband wide‐angle absorber based on all dielectric gallium arsenide (GaN) is proposed. The proposed absorber comprises a all dielectric square GaN structure and a GaN substrate. Numerical simulation results demonstrate that the proposed absorber achieves over 90% ultra‐wideband absorption in the range of 0.26–1.7 THz, with a relative bandwidth of 146.9%. The ultra‐broadband absorption property of the proposed absorber is further validated by an equivalent circuit model, which agrees well with the full‐wave numerical simulation results obtained using the finite element method. The simulated electromagnetic field distribution indicates that ultra‐wideband absorption primarily originates from the excitation of Fabry–Perot interference modes and electromagnetic resonance. The proposed absorber exhibits wide‐angle incidence properties and polarization insensitivity in both transverse electric and transverse magnetic modes. Thus, the proposed GaN ultra‐wideband terahertz absorber holds significant potential for applications in fields such as imaging technology and biomedicine.

Transient dynamic analysis of cutter-head loads: effects of different cutter spacings during excavation

As a critical component in achieving the rock-breaking function during the operation of Tunnel Boring Machines (TBM), the cutterhead inevitably generates significant vibrations during the rock-breaking process. These vibrations can lead to localized damage to the cutterhead and cause the abnormal failure of key components, which, in turn, may compromise the overall tunneling efficiency of the machine. This study investigates the load and vibration characteristics of the cutterhead during the rock-breaking process, employing large-scale physical model experiments conducted at varying cutter spacings. Real-time acceleration data from the cutterhead can be obtained through the monitoring system integrated into the TBM (Tunnel Boring Machine) experimental platform. The whole time-domain curves are stepped and periodic, as demonstrated by the test results. During excavation, the monitoring curves vibrate suddenly if the cutter-head becomes stuck or if rocks begin to fracture. The cutter-head primarily exhibits vibrations in the 0∼3 Hz range, characteristic of low-frequency oscillations. To obtain the real-time mechanical properties of the cutter-head, transient dynamic analysis was employed, utilizing the collected data as driving parameters. According to numerical simulation results, the vibration pattern during excavation is the superposition of random vibrations generated by rock breaking and the unloading of the tunnel face. Moreover, it is important to monitor the wear of the edge cutters throughout the boring operation in real-world construction scenarios. To prevent and control cutterhead vibration, it is recommended that the cutter spacing be as small as possible during the tunneling process. At a smaller tool spacing, the cutterhead will exhibit higher structural integrity, which may lead to a delay in the response of mechanical vibration. The conclusions presented offer valuable insights for the study of the mechanical properties and stability design of TBM cutterheads.

Dynamics of Nonlinear Stochastic SEIR Infectious Disease Model with Isolation and Latency Period

This article establishes and studies a SEIR infectious disease model with higher-order perturbation. Firstly, we proved the existence and uniqueness of the overall positive solution of the model. Secondly, by constructing a Lyapunov function, we obtained sufficient conditions for the existence and uniqueness of the ergodic stationary distribution of the positive solution of the model. Then, it was proved that infectious diseases would become extinct under certain conditions. Finally, this article verified the theoretical analysis results by numerically simulating the process of infectious diseases from outbreak to extinction, the numerical simulation results are symmetrical with the theoretical analysis.

Study of Fluid Flow Characteristics and Mechanical Properties of Aviation Fuel-Welded Pipelines via the Fluid–Solid Coupling Method

The welded pipeline structure of aircraft fuel is a complex and diverse entity, significantly influenced by fluid–solid coupling. The refined aviation fuel-welded pipeline model plays a pivotal role in the investigation of its fluid–solid coupling mechanical properties. However, the mechanical analyses of pipelines with welded structures frequently simplify or ignore the influence of the weld zone (WZ). Consequently, these analyses fail to reveal the complex interactions between different weld zones in detail. In this study, a comprehensive and precise fuel-welded pipeline refinement model is developed through the acquisition of microstructural dimensions and mechanical parameters of the weld zone via metallographic inspection and microtensile testing. Additionally, the influence of clamps and brackets under airborne conditions is fully considered. Furthermore, the numerical simulation results are compared and verified using modal and random vibration tests. This paper addresses the impact of diverse fluid characteristics on the velocity field, pressure field, and stress in disparate areas, and it also conducts an investigation into the random vibration characteristics of the pipeline. The results demonstrate that the fluid pressure and velocity exert a considerable influence on the fluid flow state and structural stress distribution within the pipeline. An increase in flow velocity and alteration to the pipeline geometry will result in a change to the local velocity distribution, which in turn affects the distribution of the fluid pressure field. The highest stresses are observed in the weld zone, particularly at the junction between the weld zone and the heat-affected zone (HAZ). In contrast, the stresses in the bend region exhibit a corrugated distribution in both the axial and circumferential directions. An increase in fluid pressure has a significant impact on the natural frequency of the pipeline. This study enhances our comprehension of the mechanical properties of aircraft fuel lines with fluid–solid coupling and provides a foundation and guidance for the optimal design of fuel-welded lines.

Behavior of optical parametric amplification of space-time wave packets.

The space-time wave packet (STWP) is a type of pulsed optical field, exhibiting distinctive characteristics, including the capacity to propagate without diffraction or dispersion and to have arbitrary group velocities. However, the intensity of the STWP is constrained by the low damage threshold of some indispensable optical elements like the spatial light modulator (SLM). While optical parametric amplification (OPA) has been proposed for amplifying STWPs, spatio-temporal (ST) characteristics of amplified STWPs remain significantly unexplored. In this article, we investigate the effects of OPA on STWPs and examine how key parameters influence the amplification results. Based on the numerical simulation results, we propose two methods to reduce the duration of the amplified STWP and one method to amplify the STWP with higher group velocities. These findings could facilitate the application of STWPs in strong-field optics.

Performance of heat transfer in Al2O3/MWCNT hybrid nanofluid flow using machine learning models

Abstract This investigation diverges from traditional studies concentrating on single-component nanofluids, instead examining the thermophysical benefits of hybrid nanofluids, like Al₂O₃/MWCNT, aimed at improving thermal conductivity and heat transfer efficiency in passive systems. Machine learning is a promising solution for designing efficient heat exchangers by understanding intricate relationships and utilizing suitable modelling techniques. Numerical simulations were conducted to validate the benchmark results; later, passive techniques were incorporated into the numerical model to predict the heat transfer characteristics. The dataset derived from numerical simulation results is employed to train contemporary machine learning methodologies, including support vector regression (SVR), decision tree (DT), and random forest (RF). Data from experiments and CFD analysis were gathered for preprocessing and machine learning (ML) analysis. The preprocessing phase involved the application of a standard scaler operation to enhance accuracy levels. The models underwent validation using ten experimental data samples to assess their performance against statistical tool metrics. A higher thermal performance factor (ThPF) is observed with the divergent nozzle insert in the plain tube at 0.028 vol% of MWCNT/Al2O3 (HNF3) at Reynolds number 3093. R2 values of SVR, DT and RF are predicted as 0.95, 0.98 and 0.99, respectively, for the case of HNF3 fluid flowing through the divergent nozzle insert. The investigation broadens its conclusions to include improvements in passive heat transfer, encompassing extended surfaces and geometric alterations, offering practical guidance for developing advanced heat exchanger designs.

Numerical investigation of an anti-symmetric nanophotonic structure for accelerating sub-relativistic electron beams

This study investigates an anti-symmetrically positioned nanophotonic dual-pillar structure, in which the dielectric and vacuum components are evenly distributed along the direction of electron propagation, with each dielectric pillar facing a vacuum region. Our numerical simulation results show that the previously proposed symmetric dielectric grating structure, where dielectric pillars facing each other are alternated with vacuum gaps, is accompanied by a deceleration region, preventing the achievement of high gradients during the acceleration process. By contrast, the anti-symmetric grating structure eliminates the deceleration field and generates a uniformly distributed acceleration field. This requires that the two oppositely directed laser beams crossing the structure in the transverse region must have a phase shift of π in the anti-symmetric case. This structure has significant potential for accelerating sub-relativistic electron beams. In this numerical simulation, the initial energy of the sub-relativistic electron beams is selected as 79 keV. The acceleration gradient provided by the symmetric design for sub-relativistic electrons is approximately 70 MeV/m; however, the anti-symmetric structure can provide a maximum acceleration gradient of up to ∼430 MeV/m.

Optimization Research on the Performance of the RC-DTH Air Hammer Based on Computational Fluid Dynamics

To optimize the performance of the RC-DTH air hammer, a mathematical model detailing each phase of the piston’s movement has been constructed in the present work. Simultaneously, a novel piston structure of the RC-DTH air hammer (Type B) with diverse internal flow has been proposed. The impact performance of the structurally modified RC-DTH hammer is analyzed using Computational Fluid Dynamics (CFD). Additionally, an impact energy testing system for the RC-DTH air hammer is developed to confirm the validity of the numerical simulation results. Research results have shown that enhancing both the intake stroke of the upper chamber (F1) and the outlet stroke of the lower chamber (R2) of the RC-DTH air hammer piston can effectively improve the piston’s impact performance. Conversely, increasing the inlet stroke of the lower chamber (R1) and the outlet stroke of the upper chamber (F2) tends to diminish the piston’s impact performance. Moreover, the quality of the piston influences its striking frequency while having a minimal impact on single-impact energy. As the piston quality increases, the power of the impact diminishes. Once the piston valve stroke parameters are optimized, its impact performance is enhanced by 20.32%. Compared to the GQ89 hammer, the Type B hammer exhibits an 84% increase in impact energy and a 74% increase in impact power.

Quaternion-Based Fast SMC–PD Cross-Domain Tracking Control for Coaxial Hybrid Aerial–Underwater Vehicle Under Oceanic Disturbances

In this study, nonsingular modeling and cross-domain trajectory tracking control problems for a special class of coaxial hybrid aerial–underwater vehicles (HAUVs) are investigated. Coaxial HAUVs need to effectively overcome the influence of hydrodynamic factors when moving underwater, so the attitude angle required by coaxial HAUVs is much larger than that in the air. The attitude representation based on quaternion modeling is adopted to avoid the inherent singularity of Euler angle modeling. A cascade sliding mode control and proportion differentiation (SMC-PD) controller is proposed, which is used to position trajectory and attitude quaternion tracking control, respectively. An adaptive sliding mode controller based on disturbance observer (DO) enhancement is adopted in the outer loop to carry trajectory tracking control. At the same time, the expected attitude angle is calculated by the outer loop (position) and is converted into the expected quaternion. With reference to the idea of enhanced robustness in active disturbance rejection control (ADRC), a feedforward proportion derivation (PD) controller based on DO enhancement is used to track the desired quaternion. A variable parameter adaptive algorithm based on the learning rate is introduced in the cascaded SMC-PD controller. The error convergence speed of the system is further improved by adaptively changing the controller parameters. The stability of the proposed control scheme is proved by using the Lyapunov theory. The numerical simulation results show that the controller has good robustness and effectiveness.

A Correlation Analysis-Based Structural Load Estimation Method for RC Beams Using Machine Vision and Numerical Simulation

The correlation analysis between current surface cracks of structures and external loads can provide important insights into determining the structural residual bearing capacity. The classical regression assessment method based on experimental data not only relies on costly structure experiments; it also lacks interpretability. Therefore, a novel load estimation method for RC beams, based on correlation analysis between detected crack images and strain contour plots calculated by FEM, is proposed. The distinct discrepancies between crack images and strain contour figures, coupled with the stochastic nature of actual crack distributions, pose considerable challenges for load estimation tasks. Therefore, a new correlation index model is initially introduced to quantify the correlation between the two types of images in the proposed method. Subsequently, a deep neural network (DNN) is trained as a FEM surrogate model to quickly predict the structural strain response by considering material uncertainties. Ultimately, the range of the optimal load level and its confidence interval are determined via statistical analysis of the load estimations under different random fields. The validation results of RC beams under four-point bending loads show that the proposed algorithm can quickly estimate load levels based on numerical simulation results, and the mean absolute percentage error (MAPE) for load estimation based solely on a single measured structural crack image is 20.68%.

Investigation of the Effect of the Shape of Cutting Knives Limiting Burr in High-Strength Multiphase Steel Sheets.

In this study, numerical modeling and experimental tests of the sheet metal cutting process were carried out in order to determine the shape of the cutting knives for a roller shear, ensuring the minimization of burr on the cut edge. A rolling mill was used for the tests, enabling the replication of the cutting process in a roller shear (demonstrating the possibility of using cutting rollers). The cutting edges of the sheets were examined using light microscopy and then compared with the results of numerical simulations to determine the cutting quality. The tests were performed for multiphase Complex Phase (CP) grade steel. The initial thicknesses of sheets were equal to 1 and 2 mm. Based on the results of theoretical research, four shapes of cutting rollers were designed, of which two shapes were selected for experimental tests. The analysis of the test results shows that the lowest burr values were obtained for straight and beveled rollers. Analyzing the size of burr obtained in experimental tests, it can be concluded that for each of the two variants of the roller shape, a reduction in burr was achieved. Greater reductions in burr were achieved for shaped (cut) rolls.

Industrial Investigations of S355 Steel-Grade Homogenization in a 100-Tonne Ladle Furnace.

The paper presents the results of industrial research and numerical simulations of the chemical homogenization of liquid steel. The research object was a ladle furnace with a working capacity of the ladle of 100 t at the steel plant of Huta Częstochowa, currently Liberty Częstochowa Sp. z o.o. Industrial research was carried out under standard production conditions of the steelworks. The research included automatic steel sampling, measurement of the bath temperature, controlled measurement of argon flow at a given intensity, and the determination of the concentration of elements in steel samples using a spectrometric analyser. The element introduced in the form of a ferroalloy (FeMn and FeSiMn) played the role of a marker in the study of changes in the chemical composition during the process of dissolution and mixing of the alloying additive. Monitoring changes in the chemical composition of steel after the introduction of the marker was carried out by taking metal samples. The initial and boundary parameters of the modelled processes necessary to perform numerical simulations were determined successively through industrial measurements or determined on the basis of empirical relationships. A two-equation k-ε turbulence model was used to assess the flow inside the tested ladle furnace, and a discrete phase model was used to model gas bubbles. The mixing characteristics of the steel bath after introducing the alloying additive to it were determined. The comparison of the results of numerical simulations with experimental data was based on the analysis of the chemical homogenization process.

Characterization of hydrodynamics around plates shaped like dragonfly wings as a sediment reduction measure in a sewer system.

Sediment control is a major concern in sewer management. Early studies focused on the parameters affecting the efficiency of existing dredging facilities, and novel long-term sediment reduction measures have not been developed. Superior sediment reduction performance has been demonstrated for plates folded at 25° placed in a pipe. In this study, flushing experiments are carried out to validate the efficacy of using hydrodynamic characteristics to analyze sediment reduction performance. A detached-eddy simulation is performed to characterize the hydrodynamics around various plates shaped like dragonfly wings placed in pipes to enhance sediment reduction performance. Experimental results indicate that the maximum sediment reduction efficiency occurs in the middle section of the plates for both coarse and fine sediment beds, where the flushing thickness is extended by 1.3 cm and 3.2 cm, respectively. However, the sediment reduction efficiency is maximized for mixed sediment beds downstream, where the flushing thickness is extended by 2.4 cm. The results of numerical simulations indicate that compared with conventional sediment reduction measures, the plates produce less detrimental effects on the streamwise velocities near the pipe bottom at the plate front and increase the time-averaged vertical and transverse velocities as well as the overall turbulent kinetic energy. Therefore, the use of plates shaped like dragonfly wings is an effective sediment reduction measure.

Study on the Deformation Characteristics of Railway Subgrade Structures Induced by Groundwater Level Changes

The groundwater extraction will lead to a drop in water level, causing a change in the distribution of additional stress in the strata. This phenomenon leads to uneven settlement of the railway subgrade. In severe cases, this could threaten the safe operation of trains. Therefore, the degree and main factors influencing groundwater extraction in the settlement of the railway subgrade need to be determined through research. Based on railway subgrade engineering, the first step involved monitoring the settlement resulting from groundwater extraction during the spring irrigation period. Following this, the settlement characteristics of the subgrade structure were analysed. Subsequently, based on the Biot consolidation theory of the soil, a numerical simulation model was established to study the threshold parameters of the groundwater extraction on site. Finally, the primary and secondary relationships of the influencing factors must be clarified. The research results show that: (1) According to the monitoring data, groundwater extraction resulted in a subgrade subsidence of 15.2 mm, exceeding the prescribed threshold, affecting the engineering quality. (2) By the numerical simulation results, the distance parameter of the wells is the most significant factor affecting the deformation of the subgrade, followed by the quantity of extraction. So, the distance between the wells and the tracks should be kept at more than 150 m; the pumping volume should not exceed 1500 m3/day. (3) Using horizontal jet grouting piles to reinforce the subgrade can reduce the maximum uneven deformation from 18.14 to 7.86 mm, an effective settlement control measure.

Simulation of high signal-to-noise ratio resonant photodetector for homodyne measurement and its verification.

In this paper, two models for simulating the shot noise and electronic noise performances of resonant photodetectors designed for homodyne measurements are presented. One is based on a combination of a buffer and a low-noise amplifier, and the other is based on an operational amplifier. Through the comparisons between the numerical simulation results and the experimentally obtained data, excellent agreements are achieved, which show that the models provide a highly efficient guide for the development of a high signal-to-noise ratio (SNR) resonant photodetector. Furthermore, we demonstrate a high SNR resonant photodetector for homodyne measurements at the 147MHz optical sideband, achieving a 20.8 dB SNR of the shot noise to the electronic noise with a 2 mW optical signal input, utilizing a combination of a buffer and a low-noise amplifier. Concurrently, we have obtained another resonant photodetector at the 1.14GHz optical sideband, which exhibits a 13 dB SNR based on an operational amplifier.

Effect of voltage polarity on reaction mechanism of air atmospheric surface dielectric barrier discharge: A numerical study

This study establishes a two-dimensional fluid model of nanosecond surface dielectric barrier discharge (nSDBD) at atmospheric air to investigate the effects of positive and negative sinusoidal nanosecond pulsed voltages on the discharge characteristics. Key discharge parameters are studied, including discharge current, distribution of major active particles, surface charge distribution on the dielectric, energy deposition density distribution, and gas temperature. The numerical simulation results indicate that the plasma streamers excited by positive and negative bipolar pulses exhibit markedly different discharge characteristics, with the discharge characteristics in the first half-cycle largely determining those of the entire cycle. Positive bipolar pulsed streamer discharges exhibit greater discharge currents and stronger local electric fields, with faster propagation speeds but also more pronounced declines. The energy deposition of positive bipolar pulse is higher than that of negative bipolar pulse. The discharges driven by negative bipolar pulses exhibit a more pronounced temperature rise effect, primarily due to their higher efficiency in converting electrical energy into thermal energy, leading to stronger localized thermal release. Consequently, the pressure waves generated by negative bipolar pulsed discharges are more intense. These numerical simulation data provide theoretical explanations and references for understanding and optimizing the physical mechanisms of nSDBD.

Mathematical modelling of the impact of vaccination, treatment and media awareness on the hepatitis B epidemic in Burkina Faso

Infection with the hepatitis B virus (HBV) remains a global public health issue. Particularly in Burkina Faso, HBV is a major public health concern due to its high prevalence and associated mortality. However, universal vaccination, treatment of chronic carriers, and awareness campaigns are currently employed means in Burkina Faso to combat the spread of HBV. Therefore, this paper aims to study the impact of these control measures on the expansion of this virus. This paper presents a mathematical model of vertically transmitted HBV that takes into account the progression to chronicity as a function of the age of the infected person, as well as vaccination, treatment of chronic carriers, and media awareness. After formulating the model and carrying out the mathematical analysis, we simulated the proposed model in Matlab, taking into account the various involved parameters. Finally, we presented the results of sensitivity analysis and numerical simulation. According to our model, with vaccination coverage of $30\%$, a $50\%$ success rate of awareness campaigns and $20\%$ effectiveness for the $10\%$ of treated chronic carriers, the prevalence of hepatitis B infection could decrease down to $2\%$ within thirty years in Burkina Faso.

Assessment on Variations of Flow Velocity and Flood level of River and Estuary due to Vegetation

Vegetation along rivers is likely to play a role of roughness causing to increase river water level and flow velocity. During floods, floodwaters from the main channel overflow into the floodplain and increase the flow resistance due to the influence of vegetation, causing the flood level to rise. In case vegetation in rivers is formed near estuary, the flow resistance by vegetation may affect flow pattern along rivers. In this study, the characteristics of water level and flow velocity in rivers and estuaries that occur when a vegetation zone is located in a section about 1 km from the estuary were investigated by analyzing the results of numerical simulations. The aim of this study was to analyse the variability of water level and flow velocity in rivers and estuaries that may be caused by natural vegetation area in rivers or by planting as riverfront. Through numerical analysis using a two-dimensional numerical model, transverse flow analysis in a vegetated section and longitudinal flow analysis including an estuary of about 3 km were performed and their characteristics were presented.

A numerical study of two identical CO2 bubbles rising side by side in water coupled with mass transfer

ABSTRACT In contrast to the relatively straightforward rising dynamics of single bubbles, the behavior of multiple bubbles involves a more intricate interplay of flow field dynamics, trajectory patterns, morphological changes, and mass transfer phenomena. To reveal the coalescence characteristics and mass transfer effects of CO2 bubbles during the rising process, this study developed a coupled mass transfer numerical model for bubbles. The Volume of Fluid (VOF) method was used in combination with a mass transfer code for solving the model. The effects of bubble pair initial spacing and liquid viscosity on the coalescence and mass transfer were discussed. The numerical simulation results show that as the initial distance between the two bubbles decreases, the interaction force between the bubbles increases, and the possibility of bubble coalescence increases, the coalescence behavior reduces the contact area and thus decreases the amount of CO2 dissolved about 24.07%. When the initial viscosity of the liquid phase is low, there is an oscillation in the bubble velocity, and the two bubbles tend to merge. As the initial viscosity of the liquid phase increases, resistance increases, causing a decrease in bubble velocity. Consequently, the path of bubble ascent shifts from “approach-repulsion-approach” to “continuous repulsion.” The viscous resistance reduces the gas–liquid contact area, resulting in a corresponding decrease in the mass transfer rate, the dissolution amount of carbon dioxide decreased by approximately 24.42% in this case. The exploration of coupled fluid dynamics and mass transfer phenomena at the multi-bubble scale holds paramount importance in guiding the design and exploration of gas–liquid two-phase flow systems.