Numerical Results Research Articles

Effect of electromagnetic radiations on the dynamics of a five-chain coupled inertial Hopfield neural network and control of multi-stability with the selection of a desired attractor.

Abstract In this paper, we investigate the effect of electromagnetic radiation on the dynamics of a network consisting of five chain-coupled inertial Hopfield neurons. The study revealed that the neural system designed such a way involves several complex phenomena, namely Hopf bifurcation, chaos, hyperchaos and the coexistence of up to thirty-two attractors in phase space. The complexity specific to our system is due to the higher number of equilibrium points, namely two hundred and forty-three. Under the conditions of safe functioning of our neural system (chaos or hyperchaos), we have been able to observe that electromagnetic radiation has a harmful character for the system, because we found for a range of variation in the intensity of the electromagnetic feedback induction current a coexistence of chaotic and periodic states (epileptic state). We then controlled the multi-stability using a desired attractor selection scheme, with the aim of suppressing the pathological state. All the work carried out in this contribution is done with the help of dynamical system analysis tools such as the bifurcation diagram, the spectrum and the maximum exponent of Lyapunov, phase portraits and basins of attraction. The scheme used is the Runge-Kutta-4. In order to validate the numerical results, we use analog calculation and some results were derived from the Pspice software. These results are in good accordance in amplitude and location on the plane to those of numerical simulations.

Initial tensor construction and dependence of the tensor renormalization group on initial tensors

We propose a method to construct a tensor network representation of partition functions without singular value decompositions nor series expansions. The approach is demonstrated for one- and two-dimensional Ising models and we study the dependence of the tensor renormalization group (TRG) on the form of the initial tensors and their symmetries. We further introduce variants of several tensor renormalization algorithms. Our benchmarks reveal a significant dependence of various TRG algorithms on the choice of initial tensors and their symmetries. However, we show that the boundary TRG technique can eliminate the initial tensor dependence for all TRG methods. The numerical results of TRG calculations can thus be made significantly more robust with only a few changes in the code. Furthermore, we study a three-dimensional Z2 gauge theory without gauge fixing and confirm the applicability of the initial tensor construction. Our method can straightforwardly be applied to systems with longer range and multisite interactions, such as the next-nearest neighbor Ising model. Published by the American Physical Society 2024

Development of Numerical Analysis Method for Cathode Sheath Considering Electron Emission From Cathode in Vacuum Arc

ABSTRACTIt is imperative to develop the simulation of vacuum arcs as a tool to aid electrode design in vacuum circuit breakers. Although the development of electromagnetic thermo‐fluid simulations for vacuum arcs has been reported, most of them do not take cathode sheath phenomena into account and have not been able to reproduce vacuum arc phenomena, especially cathode spots. As the first step, the cathode sheath voltage, cathode surface electric field, and temperature and field (T‐F) electron emission current were analyzed numerically on the basis of the space charge in the cathode sheath. In this study, the cathode sheath was assumed to exist when the charge density induced on the cathode surface is positive, and the temperature and density of vacuum arc plasma and cathode temperature, which are physical quantities obtained by electromagnetic thermo‐fluid simulation, were used as parameters of the analysis. As a result, the cathode sheath voltage, electric field, and electron emission current density can be calculated from the vacuum arc plasma temperature, density, and cathode temperature. Numerical results show that the electron emission current density has a dominant effect on the presence or absence of the cathode sheath.

On the Lanczos Method for Computing Some Matrix Functions

The study of matrix functions is highly significant and has important applications in control theory, quantum mechanics, signal processing, and machine learning. Previous work has mainly focused on how to use the Krylov-type method to efficiently calculate matrix functions f(A)β and βTf(A)β when A is symmetric. In this paper, we mainly illustrate the convergence using the polynomial approximation theory for the case where A is symmetric positive definite. Numerical results illustrate the effectiveness of our theoretical results.

Decays Z → ea eb in a 3-3-1 model with neutral leptons

Abstract We investigate the 3-3-1 model with neutral leptons, a specific extension of the 3-3-1 models {that includes} heavy neutral leptons, {which are sufficient} to accommodate the neutrino oscillation data {via} the inverse seesaw mechanism. We will point out that this model can simultaneously explain the lepton flavor violating decays of the $Z$ and Standard Model-like Higgs bosons into different charged leptons $Z,h \to e_a e_b$, {as well as} the charged lepton decays $e_b\to e_a \gamma$, in agreement with the recent experimental data. In addition, the numerical results show strong correlations among the decay rates of {the} $Z$ and $h$ {bosons} predicted by this model. {Specifically}, some of {these rates} are nearly linearly dependent on each other. {Consequently}, the decay channels can be {theoretically determined} if one of them is detected in experiments.

Optimizing the Agricultural Internet of Things (IoT) with Edge Computing and Low-Altitude Platform Stations

Using low-altitude platform stations (LAPSs) in the agricultural Internet of Things (IoT) enables the efficient and precise monitoring of vast and hard-to-reach areas, thereby enhancing crop management. By integrating edge computing servers into LAPSs, data can be processed directly at the edge in real time, significantly reducing latency and dependency on remote cloud servers. Motivated by these advancements, this paper explores the application of LAPSs and edge computing in the agricultural IoT. First, we introduce an LAPS-aided edge computing architecture for the agricultural IoT, in which each task is segmented into several interdependent subtasks for processing. Next, we formulate a total task processing delay minimization problem, taking into account constraints related to task dependency and priority, as well as equipment energy consumption. Then, by treating the task dependencies as directed acyclic graphs, a heuristic task processing algorithm with priority selection is developed to solve the formulated problem. Finally, the numerical results show that the proposed edge computing scheme outperforms state-of-the-art works and the local computing scheme in terms of the total task processing delay.

Dynamic shear strength of precast connection with UHPC-based and traditional grouted sleeves: Test, simulation, and analytical formulas

Dynamic shear strength is critical for ensuring the integrity of prefabricated structures with grouted sleeve connections under dynamic loads such as impacts and earthquakes. However, studies have yet to be conducted to clarify the dynamic shear strength of grouted sleeve connections for designs. To this end, this study systematically investigated the dynamic shear behavior of precast connection with grouted sleeves through physical experiments, numerical simulations, and theoretical analysis. Drop hammer impact tests were performed on nine precast connection specimens that differ in amounts of impact energy, axial loads, rebar ratios, and grouting materials. Experimental data indicated that the dynamic shear performance of the ultra-high-performance concrete (UHPC)-based connections is superior to that of traditional grouted sleeve connections. The impact-induced displacement of a grouted sleeve connection is very sensitive to the amount of impact energy. Detailed finite element (FE) models were further developed to examine the dynamic shear strength of precast connections. Good agreements are observed between the numerical results and experimental data, demonstrating the rationality of the developed FE modeling method. It was found that the dynamic shear strengths of grouted sleeve connections are more sensitive to axial load levels and concrete strength grades than rebar ratios. Based on extensive simulation results obtained from the validated modeling method, the analytical formulas were proposed to predict the dynamic increase factor (DIF) and shear strength of precast connections. The analytical results predicted by the proposed formulas agree well with the FE results, demonstrating the applicability of the proposed formulas.

Event-triggered finite-time guaranteed cost control of uncertain active suspension vehicle system

The event-triggered finite-time guaranteed cost control problem is important for an uncertain active suspension vehicle system. Existing works on the design of finite-time controllers for active suspension systems have not been extended to the event-triggered finite-time guaranteed cost control problem for uncertain active suspension systems. In this paper, we investigate the problem of designing an event-triggered finite-time guaranteed cost controller for an uncertain active suspension system. A new event-triggered controller and a cost function are first defined. Then, some new sufficient conditions for designing an event-triggered state feedback controller are derived based on linear matrix inequalities to stabilise the closed-loop systems while guaranteeing an adequate cost level of performance. Finally, numerical results and simulations are given to illustrate the effectiveness of the proposed method.

Efficient multi-objective optimization approach for solving optimal DG placement and sizing problem in distribution systems

Incorporating distributed generations (DGs) like wind turbines (WTs) and solar photovoltaic (SPV) arrays into radial distribution systems (RDSs) has become increasingly important due to their benefits in enhancing system performance. This requires determining appropriate DG locations and their optimal power output when injected into the RDS. To this end, this paper introduces a novel application of a recent multi-objective optimization technique called multi-objective grey wolf optimization (MOGWO) to allocate multiple DG units into the RDS optimally. The primary objectives are to minimize total real power losses (RPL), reduce voltage deviation (VD), and enhance the voltage stability index (VSI) across the entire system while adhering to operational constraints. Various DG operational power factor (PF) scenarios are considered, including unity-PF, fixed-PF, and optimal-PF. The proposed approach generates a Pareto-optimal set of solutions to address the multi-objective problem, after which a fuzzy decision-making method is adopted to select the best trade-off solution from the set. The technique has been implemented on 69-bus and the actual Portuguese 94-bus RDS. Numerical results are compared with other recent well-known algorithms from the literature, highlighting the efficacy of the suggested MOGWO method in handling multi-objective problems. Comparatively speaking, it provides superior solutions than other methods in selecting appropriate control parameters.

Stoichiometric theory in optimal foraging strategy.

Understanding how organisms make choices about what to eat is a fascinating puzzle explored in this study, which employs stoichiometric modeling and optimal foraging principles. The research delves into the intricate balance of nutrient intake with foraging strategies, investigating quality and quantity-based food selection through mathematical models. The stoichiometric models in this study, encompassing producers and a grazer, unveils the dynamics of decision-making processes, introducing fixed and variable energetic foraging costs. Analysis reveals cell quota-dependent predation behaviors, elucidating biological phenomena such as "compensatory foraging behaviors" and the "stoichiometric extinction effect". The Marginal Value Theorem quantifies food selection, highlighting the profitability of prey items and emphasizing its role in optimizing foraging strategies in predator-prey dynamics. The environmental factors like light and nutrient availability prove pivotal in shaping optimal foraging strategies, with numerical results from a multi-species model contributing to a comprehensive understanding of the intricate interplay between organisms and their environment.

Interference of echo-signals from spherical scatterers located near the seabed

The paper investigates the impact of the seabed on the echo signal from spherical scatterers. The seabed is modeled as a liquid absorbing half-space. The transmitter/receiver is located in the water half-space. The distance between the transmitter/receiver and the scatterer is assumed to be large compared to the wavelengths of acoustic waves in water and the seafloor. Numerical results are obtained for acoustically rigid spherical scatterers of the same radius. Interaction between the scatterers is not taken into account. The echo signal from a single sphere over a wide frequency range is computed using a method proposed by R.H. Hackman and G.S. Sammelmann, with a crucial step being the computation of the scattering coefficients of the sphere. Asymptotic formulae obtained using the saddle-point method are used in the paper to compute these coefficients. The obtained asymptotic expressions for the scattering coefficients of the sphere significantly reduce the number of summands in the formula for the form function of the echo signal.

Numerical Investigation of Burial Depth Effects on Tension of Submarine Power Cables

To protect submarine power cables from damage caused by anchoring and fishing, submarine power cables in shallow water areas are buried to a certain depth through a cable laying machine. However, limited attention has been paid to studying the stress behavior of submarine power cables while considering the effects of burial depth. In this research, static and dynamic analyses are carried out using three-dimensional numerical models performed by the OrcaFlex v11.0 to investigate the effects of burial depths on cable tension during the cable installation under various conditions. Numerical simulation results show that the peak tension of the submarine power cable increases linearly with the increase in burial depth. In addition, the burial depth can also change the tension state at the endpoint of the submarine power cable. The endpoint of the cable is in a compressed state when h < 2 m and the cable turns into a tensile state when h ≥ 2 m. Finally, genetic programming (GP) is used to analyze numerical simulation results to propose a prediction model that can be used to estimate the peak tension of the submarine power cable during cable installation under various burial depths in shallow sea areas. It should be noted that the proposed GP model is based on the analyses of numerical results; therefore, the GP model is open for further improvements as more experimental data become available.

Ship-shaped vessel hydroelastic numerically supported analysis in a narrow ultra-reduced model tank with full scale extrapolation

Although the rigid body hypothesis is broadly used when studying floating bodies dynamics, it is known that a ship-shaped vessel will have hydroelastic responses. Considering a conventional closed main deck hull in which the ship's length is considerably greater than its breadth, it is expected that the vertical bending moments can represent an important load that must be considered to guarantee structural integrity. Numerical models can be developed to assess the hydroelastic response, but the validation process is necessary. Model tests can be performed to validate the numerical model and require specific considerations to properly represent hydroelastic phenomena, such as having equivalent bending stiffness when compared to the full-scale body. Many experimental facilities that can be used to perform such experiments consist of narrow wave channels, in which the wall effect will influence the model's dynamics. This work implements a Tank Green Function (TGF) to a numerical model developed in Capytaine to represent the wall effect on the body's response. The numerical results were then compared to experimental data from tests in a narrow wave channel and good adherence was found. The validated numerical model can then be used to simulate open-water conditions, so the results can be extrapolated to full scale without the need to perform model tests in an ocean tank in which the wall effect would not be relevant.

Numerical and experimental study on the mechanism of added resistance in stepped moonpool under different waves

To study the additional resistance effect of the moonpool during the navigation of the drilling vessel, this paper explores the variation of the drilling vessel resistance under different waves based on a model test and numerical simulation. The difference between the model test and the numerical simulation results is compared, and the mechanism of the added resistance of the moonpool under different waves is revealed. The results show that the technology of numerical simulation is able to accurately simulate the navigation resistance of the drilling vessel in waves. The numerical simulation results closely correspond to the experiment results, and the error range can be controlled within 10%. In the components of the total resistance of the hull, pressure resistance plays a dominant role when the drilling vessel sails in waves. The pressure resistance accounts for about 60%–70% of the total resistance, while the friction resistance accounts for about 30%–40% of the total resistance. At low speed, the average resistance reduction rate of the dissipative equipment is 4.4%; under the condition of medium speed, it is 7.5%; at high speed, it is 9.6%; and the resistance reduction efficiency of the dissipative equipment increases with the increase in speed. The dissipative equipment partially suppresses the eddy's action stage and prevents eddy shedding from entering and directly hitting the back wall, thereby reducing the moonpool's additional pressure resistance. The research results can provide a reference for energy savings and emission reductions in drilling vessels.

A Frequency Reconfigurable Antireflection Metasurface for GPR

Abstract The antireflection metasurface (AM) is employed in ground penetrating radar (GPR) to mitigate the strong reflection of electromagnetic waves at the air-ground interface due to impedance mismatch. However, due to constraints imposed by the relative bandwidth (RBW) and manufacturing processes, these layers tend to exhibit excessive thickness and bulky shape, narrow RBW, and fixed functionality in a passive configuration. This paper presents a novel, dual-band, independent wideband tuning, frequency reconfigurable AM based on varactor diodes with center frequencies of 1.35 GHz and 2.60 GHz. This metasuface possesses positive characteristics such as a single layer, the ultrathin thickness (0.03 \& 0.06$\lambda$), the wide RBW (43.3\% \& 27.4\%) and remarkable antireflection. The aforementioned metasurface achieves the described mechanisms and features through the destructive interference theory and the combine element technique. Numerical simulation results of surface currents and electric field energy power demonstrate the antireflection property. The equivalent electromagnetic parameter retrieval results also provide equivalent impedance conditions for non-perfect antireflection. The proposed AM samples demonstrates notable stepwise frequency reconfigurable characteristics in free-space experiments. The imaging effect after loading this AM is significantly improved in real-world GPR ballast roadbed anomaly detection experiments. This approach provides significant research value and promising prospects across various disciplines, including the stepped-frequency GPR, microwave imaging, and interdisciplinary fields.

Experimental and numerical investigation on the cavitation erosion effect and resonance effect of submerged water jets

ABSTRACT To analyse the cavitation erosion effect and resonance effect of submerged water jets generated by organ-pipe nozzles, experimental and numerical research is conducted in the nozzles with five different diffuser angles. The cavitation erosion intensity and the flow characteristics of submerged jets are obtained by the erosion test, high-speed photography and Large Eddy Simulation. The experimental and numerical results illustrate that the nozzle with a 60° diffuser angle is capable of producing a strong cavitation erosion effect. Compared to the fully developed submerged jet, the axial pressure oscillation of axially confined submerged jets is stronger, indicating that it has a strong resonance effect. The stress wave generated by cavitation modulates the jets after reflection from the impact wall. This modulation results in the excitation of the original main frequency oscillation of organ-pipe nozzle jets, which then gives rise to multiple frequency oscillations, thereby forming the strong resonance effect.

Multipartite Entanglement in Crossing the Quantum Critical Point

Abstract We investigate the multipartite entanglement for a slow quantum quench crossing a critical point. We consider the quantum Ising model and the Lipkin-Meshkov-Glick model, which are local and full-connected quantum systems, respectively. The multipartite entanglement is quantified by quantum Fisher information with the generator defined as the operator of the ferromagnetic order parameter. The quench dynamics begins with a ground state in a paramagnetic phase, and then the transverse field is driven slowly to cross a quantum critical point, and ends with a zero transverse field. For the quantum Ising model, based on methods of matrix product states, we calculate the quantum Fisher information density of the final state. Numerical results of both linear and nonlinear quenches show that the quantum Fisher information density of the final state scales as a power law of the quench rate, which overall conforms to the prediction of the Kibble-Zurek mechanism with a small correction. We show that this correction results from the long-range behaviors. We also calculate the quantum Fisher information density in the Lipkin-Meshkov-Glick model. The results show that the scaling of quantum Fisher information in this full-connected system conforms to the Kibble-Zurek mechanism better, since the long-range physics cannot be defined in this nonlocal system. Our results reveal that the multipartite entanglement provides an alternative viewpoint to understand the dynamics of quantum phase transitions, specifically, the nontrivial long-range physics.

Sensitivity analysis of damage extent in naval ship compartments due to internal airborne explosions

The objective of this paper is to identify the design variables of the compartment that are most influential in determining the extent of damage due to in-compartment airborne explosions (INCEX). From a comparison of numerical simulation results using the CONventional Weapons Effects Program (CONWEP) with results from airborne blast experiments, CONWEP generated blast pressures with reasonable accuracy. From a comparison of numerical simulation results using the Horsford-Coulomb and local necking hybrid fracture model (HC-LN model) with results from indentation experiments, HC-LN model accurately predicts steel fractures. The engine compartment was selected for the damage variable sensitivity analyses in terms of the probabilities of being hit, flooded, and incapacitated. When three TNT masses, two stand-off distances, and eight engine room dimensions with six levels of each dimension were considered, more than 10 million INCEX cases were required. The Latin hypercube sampling technique was adopted to reduce the number of INCEX simulations to 5,000. The element-based and image-based methods were applied to evaluate the damage extents. The element-based method underestimated and overestimated the damage area and damage perimeter more than the image-based method, respectively. The most influential design variables on the damage extent were bulkhead thickness and curtain plate height, respectively.

Sub-modelling based fatigue evaluation of welded details in composite trapezoidal corrugated web girders under coupled thermal-structural loading

Exploring the long-term performance of welded details in composite trapezoidal corrugated web (TCW) girders is a significant focus for the service life of these structures exposed to atmospheric environment and traffic flow. The majority of the present studies have been conducted without accounting for thermal stresses induced by temperature differences and accurately reflecting internal force transfers for the composite girders in flexural bending. The fatigue behaviour of the welded details in these girders under coupled thermal-structural loading is investigated herein through experimental and numerical methods. The results indicated three stages for the structural degradation from the test performance and justified a proper allowance of the cross-sectional stress in coordination with the flexural curvature in the derivation of S-N relations comparable to similar details in related design codes. A sub-modelling procedure is implemented to capture the thermal gradient, the local stress concentration, and the crack distribution in global modelling while replicate the semi-elliptical surface crack at the external side of the fillet weld toe in local modelling. The fatigue lives predicted from the proposed analytical model match reasonably well with experimental and numerical results, indicating its good applicability incorporating characteristic geometric correction factors into classical theoretical calculation for fatigue evaluation.

Energy balance during Bragg wave resonance by submerged porous breakwaters through a mixture theory-based δ-LES-SPH model

This paper presents a numerical analysis of the time behaviors of mechanical and internal fluid energies during the Bragg wave resonance induced by two-arrayed trapezoidal submerged porous breakwaters based on a reformatted δ-LES-SPH model (Di Mascio et al., 2017). In the present work, a mixture theory is introduced into the δ-LES-SPH model by reformulating the governing equations with the incorporation of a volume fraction. In this approach, the viscous and diffusive terms are also modified by the volume fraction. The energy equation is then written for the presented model highlighting the presence of two additional components compared with the classical δ-LES-SPH formulation: one coming from the fluid compression and another one due to the dissipation both induced by the interaction of the porous structure with the fluid phase. The numerical results are validated by available experimental data for a gravity-driven mass flow passing through a porous dam case and two Bragg wave resonance by two-arrayed submerged trapezoidal porous breakwaters cases. A numerical analysis is then conducted on Bragg wave resonance by two-arrayed trapezoidal porous breakwaters, by investigating the effects of the distance between the two breakwaters and their porosity. Interesting insights about the type and magnitude of dissipation occurring during the wave-structure interaction are captured by analyzing the time evolutions of each energy component.