Search Results (32,017)

Characterization of ground motion incoherency can significantly reduce the seismic load imposed on large scale infrastructures. Because of difficulties in developing an empirical coherency function from a site-specific dense array, it is seldom used in practice. A number of studies used numerical simulations to develop generic coherency models. However, they have only been developed for idealized profiles. A comprehensive parametric study evaluating the effect of various parameters influencing the calculated coherency function has not yet been performed. We utilized the measured shear wave velocity (V_s) profile at Pinyon Flat, located in California, to perform a suite of time history analyses. This site was selected because the empirical coherency function developed here has been used as a reference model for rock sites. We performed several sensitivity studies investigating the effect of both the site spatial variability and numerical analysis parameters in order to provide a guideline for developing a coherency model from numerical simulations. The outputs were compared against the empirical coherency model to better illustrate the importance of the parameters. The coefficient of variation (CV) of V_s was revealed to be the primary parameter influencing the calculated plane-wave coherency, whereas the correlation length (CL) has a secondary influence. Site-specific convergence analyses should be performed to determine the optimum numerical parameter, including the number of analyses and depth of numerical model. Considering the importance of CV and V_s, it is recommended to perform field tests to determine site-specific values to derive numerical coherency functions. Full article

Triply periodic minimal surface (TPMS) sandwich structures were proposed based on the TPMSs. The test samples for the TPMS sandwich were prepared using Multi Jet Fusion (MJF) with PA12 as the base material. Their low-velocity impact responses were investigated using experimental tests and numerical simulation. The effect of structural parameters (relative density, panel thickness, impact energy, and TPMS core) on the impact performance of the sandwich structures was analyzed through parameter studies. The results indicate that the peak load and stiffness of the sandwich structure increase with the increase in relative density, panel thickness, and impact energy. Among three types of TPMS core sandwich structures, the Diamond sandwich structure exhibits the biggest peak load and best impact resistance. Full article

Quarter-wave plate (QWP) metasurfaces provide a novel approach for generating three-dimensional (3D) hybrid-order Poincaré sphere (HyOPS) beams and enabling longitudinal polarization modulation, owing to their unique spin-decoupling properties. In this work, we designed a set of QWP meta-atom metasurfaces that generate 3D HyOPS beams with continuously varying polarization states along the propagation direction. The third-, fourth- and fifth-order HyOPS beams are generated by three metasurface devices, respectively. The HyOPS beams exhibit a focal depth of 30 μm, a stable longitudinal propagation, and a continuously evolving polarization state. Notably, complete polarization evolution along the equator of the HyOPS occurs within a depth of 20 μm. Numerical calculations in MATLAB R2022b validated the feasibility of the designed QWP metasurfaces. The finite-difference time-domain (FDTD) simulations further confirmed the stable propagation and continuous polarization evolution of the longitudinal light field. Additionally, the concentric arrangement of the QWP meta-atoms on the metasurface effectively mitigates scattering crosstalk caused by abrupt edge phase variations. This work offers new insights into the generation and control of HyOPS light fields and contributes significantly to the development of miniaturized, functionally integrated high-performance nanophotonics. Full article

This paper presents an attitude stabilization algorithm for a Low Earth Orbit (LEO) Earth-pointing spacecraft using magnetorquers as the only torque actuators and employing Model-Free Adaptive Control (MFAC) as the control algorithm. MFAC is a data-driven control algorithm that relies solely on input–output data from the plant. This paper validates the effectiveness of the proposed approach through numerical simulations in a specific case study. The simulations show that the proposed algorithm drives the spacecraft’s attitude to three-axis stabilization in the orbital frame from arbitrary initial tumbling conditions. The numerical study also shows that the proposed control algorithm outperforms a model-based Proportional–Derivative (PD) control in terms of pointing accuracy at the expense of higher energy consumption. Full article

Leaf spring-type flexible hinges serve as critical transmission components in kilogram quantization energy balance systems. Investigating their bending behavior is crucial for enhancing measurement accuracy and ensuring structural reliability. This work employs molecular dynamics simulations to analyze the mechanical properties and deformation characteristics of such hinges under varying bending rates. The findings reveal a significant correlation between the bending rate and the hinges’ plastic deformation and microstructural evolution, indicating the presence of a critical bending rate. When the bending rate is below the critical threshold, the hinges exhibit excellent structural stability, characterized by low dislocation density, reduced von Mises stress, and limited temperature rise, making them suitable for long-term use. Conversely, when the bending rate exceeds the critical threshold, the hinges undergo significant plastic deformation, including notable increases in stress and temperature concentration, as well as microstructural alterations. Specifically, the initially stable crystal structure is disrupted, leading to the formation of numerous defect structures. These changes result in localized instability and elevate the risk of fatigue damage. This work comprehensively elucidates the mechanical responses and failure mechanisms of flexible hinges, providing valuable data and guidance for their optimized design and application. Full article

Theoretical analysis, numerical simulation, and experimental study are used to investigate the ultra-low head bidirectional shaft extension pump, especially near-zero head conditions. The results show that under forward operation, at low flow and design flow conditions, the closer to the shroud, the closer the vortex is to the back of the guide vanes, and the vortex area is becoming smaller. The hydraulic loss of the outlet passage is 15% of the operating head at the minimum flow and 170% of the operating head under near-zero head condition. The peak-to-peak (PTP) value of pressure fluctuation increases with the increase in flow rate. The primary frequency (PF) of vibration is strongly related to the primary and secondary frequencies (PSFs) of pressure fluctuation. Under reverse operation, when the flow rate is less than 0.83Q_r0, the uniformity of axial velocity distribution V_u and the velocity-weighted average angle θ show an approximately exponential declining pattern. The hydraulic loss of the outlet passage at the minimum flow rate is 61% of the operating head and 350% of the operating head under near-zero head condition. The exponential fitting can better describe the relationship between circulation and hydraulic loss. As the flow rate decreases, the PF of vibration decreases to rotational frequency. Full article

Large-eddy simulation (LES) models are sensitive to numerical discretization because of the large fraction of resolved turbulent energy ($>80\%$) and the strong non-linear interactions between resolved-scale fields with the turbulence subgrid scale (SGS) model. The effects of the Smagorinsky–Lilly SGS model discretization are investigated. Three finite difference schemes are compared. Second-, fourth-, and sixth-order centered difference schemes are used to approximate the spatial derivatives of the SGS model. In the LES of homogeneous isotropic turbulence (HIT), including (non-isotropic) turbulent mixing of a passive scalar, no differences are observed with respect to the SGS model discretization. The HIT LES results are validated against a direct numerical simulation, which resolves all flow scales and does not include an SGS model. In the LES of a moderately stable atmospheric boundary layer, the LES results depend on the SGS discretization for coarse grid resolutions. The second-order scheme performs better at coarse resolutions compared to higher-order schemes. Overall, it is found that higher-order discretizations of the Smagorinsky–Lilly model are not beneficial compared to the second-order scheme. Full article

This study investigates the bending behavior of steel-ribbed composite slabs for a 500 kV substation project in China through numerical simulation. The unidirectional bending performance of the slab was first analyzed and validated against theoretical calculations. After that, the bidirectional bending performance of double-spliced and triple-spliced composite slabs were evaluated against the monolithic slab, followed by a parametric analysis to identify the influence of key factors. The results indicate that the steel-ribbed composite slabs feature high cracking strength, post-crack stiffness, bearing capacity, and commendable ductility under both unidirectional and bidirectional loading conditions. Under unidirectional loading, the ultimate capacity of the slab reaches 57–58 kN/m². Under bidirectional loading, the cracking load and bearing capacity of the dense-splicing composite slabs increase by more than 60% compared with unidirectional loading. Composite and monolithic slabs exhibit similar crack patterns and ultimate capacities under bidirectional loading; however, the presence of splicing joints results in a slight increase in the ultimate deflection of the double-spliced and triple-spliced composite slabs by 7.53% and 7.75% compared with that of the monolithic slab. The ratio of prestressing steel is identified as the most critical parameter for failure control, followed by the concrete strength. When the strength of the joint-connecting rebars exceeds 235 MPa and the diameter is greater than 4 mm, transversal force transfer across the joints is reliable. This paper provides valuable insights and practical guidance for the prefabricated construction of substations. Full article

This paper presents an E-band four-channel multiplexer based on a turnstile junction. The proposed multiplexer consists of a power distribution unit featuring a turnstile junction topology and four Chebyshev bandpass filters. Thanks to the implementation of a rotating gate connection structure as the distribution unit, the overall compactness was enhanced, and the complexity of optimization was significantly reduced. Furthermore, this configuration offers a well-organized spatial port distribution, facilitating scalability for additional channels. According to the frequency band planning and design requirements of the communication system, an E-band four-channel multiplexer was designed and manufactured using high-precision computer numerical control (CNC) milling technology, achieving an error margin of ±5 μm. The experimental results indicate that the passbands are 70.6–73.07 GHz, 73.7–76.07 GHz, 82.55–82.9 GHz, and 83.4–85.9 GHz. The in-band insertion loss of each channel is below 1.7 dB, while the return loss at the common port exceeds 12 dB. The measured results align closely with simulations, demonstrating promising potential for practical applications. Full article

Cross-media vehicles, which combine the advantages of airplanes and submarines, are capable of performing complex tasks in different media and have attracted significant interest in recent years. In practice, however, cross-media rotorcrafts face numerous challenges during the cross-media transition, one of which is the complex mixed air–water flows induced by their rotors operating in close proximity to the water surface. These flows can result in aerodynamic penalties and structural damage to the rotors. The interactions between a water surface and a rotor wake bring about potential risks of cross-media locomotion, which is known as the near-water effect of rotors. Given that the distinctions between the near-water effect and the ground effect of rotors are not yet widely understood, this study details the discovery of the near-water effect and provides a comprehensive review of the evolutionary development of the near-water effect, tracing its understanding from the ground effect to the influence of droplets through aerodynamic modeling, numerical simulations, and near-water experimental studies. Furthermore, open problems and challenges associated with the near-water effect are discussed, including flow field measurements and numerical simulation approaches. Additionally, potential applications of the near-water effect for the development of cross-media rotorcraft are also described, which are valuable for aerodynamic design and cross-media control. Full article

Axial flow fans, used for heat dissipation in electronic equipment, may generate significant electromagnetic interference during PWM speed regulation. Due to its multiple radiation sources and relatively smaller size compared to the equipment, the radiation prediction model for equipment-level EMC analysis often involves a huge number of grids, which leads to computational difficulties and inefficiencies, and thus an equivalent modeling method for the electromagnetic radiation of PWM fan is presented. First, a detailed field-circuit coupling model of the radiation from winding and driving circuits is established using the time-domain finite-integral method with non-uniform grids. Then, a near-field hexahedron is defined to surround the fan, and the electromagnetic field of all its surfaces is derived based on the Huygens principle and calculated. Finally, the hexahedron encapsulating all radiation sources within the fan can be used in a higher level simulation as replicable and reusable equivalent sources. The proposed method is validated by a numerical example and actual measurements and applied to predict the radiation emissions within an electronic enclosure. The results show that the equivalent model can reduce 81.4% computation time and maintain good consistency in comparison to the detailed field-circuit coupling model. Full article

In order to suppress the rapid combustion effect and consumption rate of pure hydrogen gas, N₂ or CO₂ at flow rates of 0, 80, and 240 Nm³/h was pre-mixed with shrouding H₂ at flow rates of 800, 720, and 560 Nm³/h at room temperature, and the behaviors of the main oxygen jet and shrouding flame were analyzed by both numerical simulation and combustion experiments. The results showed that, because of the participation of CO₂ in the H₂ combustion reaction, the length of the axial velocity potential core was reduced using the CO₂ shrouding mixed injection method, compared to the same mixed rate of N₂. This trend would be further enhanced as N₂ and CO₂ mixing ratio increased. Meanwhile, when the shrouding mixed rate is 30%, the maximum axial and radial expansion rate generated by N₂-H₂ shrouding method is 1.28 and 1.04 times longer than that by the CO₂-H₂ shrouding method. The F_o-a, theoretical impaction depth and area generated by the 10% N₂ shrouding mixed rate was 84.0, 95.5 and 86.4% of those generated by the traditional coherent jet, respectively, which indicated that the 10% N₂ shrouding mixed rate method might lead to comparable production indexes in the EAF steelmaking process. Full article

We study the throughput and losses of a buffer with stochastically dependent service times. Such dependence occurs not only in packet buffers within TCP/IP networks but also in many other queuing systems. We conduct a comprehensive, time-dependent analysis, which includes deriving formulae for the count of packets processed and lost over an arbitrary period, the temporary intensity of output traffic, the temporary intensity of packet losses, buffer throughput, and loss probability. The model considered enables mimicking any packet interarrival time distribution, service time distribution, and correlation between service times. The analytical findings are accompanied by numerical computations that demonstrate the influence of various factors on buffer throughput and losses. These results are also verified through simulations. Full article

Alginate hydrogels are integral to many cell-based models in tissue engineering and regenerative medicine. As a natural biomaterial, the properties of alginates can vary and be widely adjusted through the gelation process, making them versatile additives or bulk materials for scaffolds, microcarriers or encapsulation matrices in tissue engineering and regenerative medicine. The requirements for alginates used in biomedical applications differ significantly from those for technical applications. Particularly, the generation of novel niches for stem cells requires reliable and predictable properties of the resulting hydrogel. Ultra-high viscosity (UHV) alginates possess alginates with special physicochemical properties, and thus far, numerical simulations for the gelation process are currently lacking but highly relevant for future designs of stem cell niches and cell-based models. In this article, the gelation of UHV alginates is studied using a microscopic approach for disc- and sphere-shaped hydrogels. Based on the collected data, a multiphase continuum model was implemented to describe the cross-linking process of UHV alginate polysaccharides. The model utilizes four coupled kinetic equations based on mixture theory, which are solved using finite element software. A good agreement between simulation results and experimental data was found, establishing a foundation for future refinements in the development of an interactive tool for cell biologists and material scientists. Full article

In the framework of the quantum theory of many-particle systems, we study the compatibility of approximated non-equilibrium Green’s functions (NEGFs) and of approximated solutions of the Dyson equation with a modified continuity equation of the form ${\partial }_t⟨\rho ⟩+(1-\gamma )\nabla ·⟨\mathbf{J}⟩=0$. A continuity equation of this kind allows the e.m. coupling of the system in the extended Aharonov–Bohm electrodynamics, but not in Maxwell electrodynamics. Focusing on the case of molecular junctions simulated numerically with the Density Functional Theory (DFT), we further discuss the re-definition of local current density proposed by Wang et al., which also turns out to be compatible with the extended Aharonov–Bohm electrodynamics. Full article