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In a previous paper (Feng et al., J. Differential Equations (2023)), we studied a seasonally interactive model between closed seasons and open seasons with Michaelis-Menten type harvesting, in which we assumed that the harvesting quantity was relatively large (0 < κ = l G c E < 1) and obtained a length threshold of the closed season T ¯ ⁎ depending on the harvesting parameter and the seasonal fluctuation period. It was shown that the origin is globally asymptotically stable if and only if T ¯ ≤ T ¯ ⁎ , and there exists a unique globally asymptotically stable T -periodic solution if and only if T ¯ > T ¯ ⁎. In this paper, we continue to investigate the periodic dynamics of this model when the harvesting quantity is relatively small (κ = l G c E ≥ 1). By finding another smaller length threshold T ¯ ⁎ ∈ (0 , T ¯ ⁎) , we determine the number of periodic solutions and study their stability, which imply the occurrence of bifurcation of periodic solutions. Our results demonstrate that designing the closed harvesting season properly can prevent the species from extinction. Moreover, by comparing with the continuous harvesting model and combining the results in our previous paper and this article, we provide a complete understanding on the global dynamics for the periodic switching model. Some numerical simulations are also carried out to illustrate the theoretical results. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of spreading properties and traveling wave solutions for a vector-host disease system, which models the invasion of vectors and hosts to a new habitat. Combining the uniform persistence idea from dynamical systems with the properties of the corresponding entire solutions, we investigate the propagation phenomena in two different cases: (1) fast susceptible vector; (2) slow susceptible vector when the disease spreads. It turns out that in the former case, the susceptible vector may spread faster than the infected vector and host under appropriate conditions, which leads to multi-front spreading with different speeds; while in the latter case, the infected vector and host always catch up with the susceptible vector, and they spread at the same speed. We further obtain the existence and nonexistence of traveling wave solutions connecting zero to the endemic equilibrium. We also conduct numerical simulations to illustrate our analytic results. [ABSTRACT FROM AUTHOR]

This paper demonstrates a theoretical and experimental study on a universal vibro-impact system with bidirectional drift. With a dedicated experimental rig that is able to verify numerical simulations, the system has revealed various bifurcations from a piecewise-smooth dynamical model involving impact and dry friction. This experimental rig with a two-sided constraint is designed with adjustable configurations which can be used for experimental testing of versatile piecewise-smooth dynamical systems, e.g., the impact oscillator, the drifting oscillator and the capsule system. It is able to be customised to alter different system parameters, such as friction, number of constraints, mass ratio, impact gap and constraint stiffness, for developing and testing various control strategies. In this paper we particularly studied several types of bifurcations from our preliminary experimental results and discussed the dynamical responses of the system under different excitation frequencies and amplitudes. It was found that with a higher excitation frequency and amplitude, the vibro-impact dynamics on both ends of the constraints could result in a large amount of uncertainties, thus bi-stable and chaotic motions are likely to be observed. While being unstable, the system runs with a relatively high energy efficiency in this configuration. [Display omitted] • An experimental rig with a two-sided constraint and bidirectional drift is studied. • The rig is designed with adjustable configurations for testing versatile systems. • System parameters are identified and verified by numerical simulations. • Grazing and sliding bifurcations, bi-stability and chaotic motions are studied. • Control parameters that cause instability may lead to high energy efficiency. [ABSTRACT FROM AUTHOR]

As we have known that it is impossible to attenuate the vibration displacement of the floating-slab depending on a strong stiffness and to improve the low-frequency vibration isolation performance of the floating-slab track (FST) depending on a soft stiffness simultaneously in engineering. In this paper, we propose a novel method to solve the paradox by introducing a "Hardening-First-Then-Softening" (HFTS) design based upon the energy distribution of wheel-rail loads to formulate a model of nonlinear floating-slab isolator. The average procedure is employed to analyze the vibration isolation ability of the isolator with parameters taken from a metro line load excitation. A simulation model of train-FST-tunnel with HFTS isolator is constructed to study the dynamic behaviors of the system. The numerical simulations show the significant suppression of displacement response of floating-slab and Z weighted acceleration vibration level of the tunnel. The results presented herein this paper provide a scheme to solve the strict requirements of displacement suppression and the vibration isolation which is of beneficial to steady and silent urban rail transit. [ABSTRACT FROM AUTHOR]

Observation missions of meteoroids entering the Earth's atmosphere are conducted regularly. Meanwhile a method to replicate the flight in a ground test facilities has been established. However, numerical simulations with subsequent comparison of the spectroscopic data, on the other hand, are not yet widely used in this field. This is mainly due to the complex flow environment, which includes not only non-equilibrium radiation, but also the outgassing of species from the meteoroid that do not enter the shock since they have only the thermal velocity of the wall without macroscopic flow and therefore cannot heat up as much as the other species. This paper presents a numerical approach to replicate experimental measurements. The Direct Simulation Monte Carlo (DSMC) method is used and bi-directionally coupled with a radiation solver to simulate the atmospheric entry in 80 km of an iron meteorite with a diameter of 38 mm. The paper provides information and references on the numerical models used, the challenges encountered, and the simulation results. The study shows that the simulation models are well-suited to handle the non-equilibrium effects of meteorite entry and show good agreement with the experimental measurements. • Complete non-equilibrium simulation of a meteoroid with a gas kinetic solver. • First coupled radiative flow simulation of a meteoroid. • First successful numerical reproduction of a measured meteor spectrum by simulation. [ABSTRACT FROM AUTHOR]

Structured triacylglycerols with 1,3-dioleoyl-2-palmitoylglycerol (OPO) have many health benefits for infants. In this paper, tripalmitin (PPP) and oleic acid (OA) were used as raw materials, the method of magnetic fluidized bed and immobilized lipase was used in the synthesis reaction of OPO. Reaction parameters in the fluidized bed were simulated by computer. The results showed that flow rate of 0.0023 m/s and magnetic field strength of 0.021 T were the optimal conditions for the synthesis of OPO in the magnetic fluidized bed. Under the same conditions, OPO content in the magnetic fluidized bed was 45.79%, which was 3.11% higher than batch reaction. After 7 times of reuse, the enzyme activity in fluidized bed was 81.75%, which was 10.7% higher than that of the batch reaction. This study may provide an efficient and more economical method for OPO production in the future. • Magnetic fluidized bed and computer simulation were used in the OPO synthesis. • Content of Sn-2 palmitic acid in magnetic fluidized bed was 85.39 %, OPO content was 45.79 %. • The content of OPO in the magnetic fluidized bed product was 7.3% higher than in the common reaction. • Magnetic fluidized bed can better retain the activity of immobilized enzymes. [ABSTRACT FROM AUTHOR]

[Display omitted] The paper proposes to identify the parameters of linear dynamic models based on the original implementation of least absolute deviation estimators. It is known that the object estimation procedures synthesized in the sense of the least sum of absolute prediction errors are particularly resistant to occasional outliers and gaps in the analyzed system data series, while the classical least squares procedure unfortunately becomes of little use for reliably identifying systems in the presence of destructive measurement errors. Bearing in mind that the classic task of minimizing the quality functional of absolute deviations encounters fundamental analytical problems, it is proposed to use a dedicated iterative estimator for off-line evaluation of the parameters of the analyzed process. In addition, a simplified recursive version of the absolute deviation estimation procedure was developed, which allows for practical on-line tracking of the evolution of variable parameters of non-stationary systems. Importantly, a novel refinement of the discussed absolute deviation estimators was proposed to effectively overcome some inconvenient numerical effects. We also present an interesting comparison of the improved (by non-linear modification) iterative absolute-deviation estimator with the classical Gauss-Newton gradient algorithm, which leads to constructive conclusions. Finally, using computer simulations, the operation of the developed iterative and recursive estimators minimizing the absolute deviation is illustrated. The work ends with an indication of directions for further research. [ABSTRACT FROM AUTHOR]

In this paper, we present a computational framework based on fully Eulerian models for fluid–structure interaction for the numerical simulation of biological capsules. The flexibility of such models, given by the Eulerian treatment of the interface and deformations, allows us to easily deal with the large deformations experienced by the capsule. The modeling of the membrane is based on a full membrane elasticity Eulerian model that is capable of capturing both area and shear variations thanks to the so-called backward characteristics. In the validation section several test cases are presented with the goal of comparing our results to others present in the literature. In this part, the comparisons are done with different well-known configurations (capsule in shear flow and square-section channel), and by deepening the effect of the elastic constitutive law and capillary number on the membrane dynamics. Finally, to show the potential of this framework we introduce a new test case that describes the relaxation of a capsule in an opening channel. In order to increase the challenges of this test we study the influence of an internal nucleus, modeled as a hyperelastic solid, on the membrane evolution. Several numerical simulations of a 3D relaxation phenomenon are presented to provide characteristic shapes and curves related to the capsule deformations, while also modifying size and stiffness parameter of the nucleus. [ABSTRACT FROM AUTHOR]

Mesh-based Eulerian and particle-based Lagrangian models are common computational fluid dynamics (CFD) tools for simulating wave-structure interactions. While Eulerian models are efficient in terms of computational time, they are limited in their ability to handle large interface discontinuities between two flows and complex structure motion responses. Conversely, Lagrangian models are suitable for such discontinuities and motion responses but can be computationally expensive. However, there is a lack of comprehensive discussion on the (dis)advantages of hybrid Eulerian-Lagrangian models, which have the potential to achieve both numerical efficiency and flexibility through a combined use of mesh and particles. This paper presents a comparative study of a hybrid Eulerian-Lagrangian Particle-In-Cell (PIC) model and the widely-used OpenFOAM model, applied to a variety of complex wave interactions with floating offshore renewable energy structures in both 2D and fully 3D domains. We found that both models demonstrate good performance in simulating complex floating structures. Additionally, it is the first time that the two models have been compared in parallel on the same computing facility, allowing us to directly show their computational efficiency. The PIC model has the advantage of using staggered grids, which enables it to achieve computational efficiency comparable to the pure mesh-based OpenFOAM. The findings of this study provide researchers and practitioners in the field of computational fluid dynamics with a clear understanding of the performance of the hybrid Eulerian-Lagrangian PIC model and OpenFOAM for simulating complex fluid-structure interaction problems. [ABSTRACT FROM AUTHOR]

• An approach is proposed for identification of bridge bending stiffness distribution using improved Gaussian peak function. • The improved Gaussian peak function allows for considering a wider range of stiffness variation models and thus is a general model. • The Levenberg-Marquardt (LM) method is proposed for parameter estimation and shows good robustness with different initial parameter values. • Numerical simulation and laboratory experiment are used to verify the effectiveness of the proposed method in identifying bridge bending stiffness distribution. Bridge damage and bending stiffness deterioration can lead to a decrease in the bearing capacity of a bridge, posing significant safety concerns. To ensure the safe operation of bridges, it is crucial to accurately identify bending stiffness deterioration and assess the bridge performance. The bridge influence line (IL), which reflects the deterioration of bending stiffness, was widely used in the assessment of bending stiffness deterioration. Existing IL-based methods mostly assume a uniform reduction in bending stiffness for identification. In reality, the deterioration of bridge bending stiffness is far more complex, which causes difficulty in accurately identifying the bending stiffness distribution using the uniform reduction model. This paper proposes a novel method for identifying bridge stiffness distribution using an improved Gaussian peak function model. The improved model incorporates additional parameters, allowing for considering a wider range of stiffness variation and thus addressing the limitations of traditional models. The parameters of the improved Gaussian peak function model are estimated by minimizing the residual between the predicted deflection influence line (DIL) and the actual DIL using the Levenberg-Marquardt (LM) algorithm. This approach enables the accurate identification of bending stiffness distribution without baseline information. Numerical simulation and laboratory experiment are used to verify the effectiveness of the proposed method in identifying bridge bending stiffness distribution. A comparison between the identified and actual bending stiffness distribution curves under various forms of damage assesses the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

• A novel multi-extracting velocity-synchronous chirplet transform (MEVCT) for efficient and effective time–frequency analysis. • An adaptive chirp angle search method for improving computational efficiency and velocity synchronous basis accuracy. • A higher-order iterative extraction operator for eliminating the non-reassigned time–frequency points. • The improved IF accuracy and anti-noise capability of MEVCT provide ideal TFR for synchronous multi-component signals. • Demonstrated advantages of MEVCT by numerical simulations as well as experimental tests. In many engineering applications, the instantaneous frequency (IF) needs to be identified rapidly and precisely, especially in rotating machinery condition monitoring, where quasi-real-time analysis is a favorable option, and any error in shaft speed (identified from the instantaneous frequency) needs to be reduced to prevent it from accumulating with time. The modern time–frequency analysis (TFA) method provides a way for IF identification; however, sometimes, it still suffers from energy smearing and closely spaced frequency interference. In addition, many TFA methods based on the chirplet transform also present the problem of excessive computation when searching for the optimal parameters. To overcome these limitations, we propose the multi-extracting velocity-synchronous chirplet transform (MEVCT), an enhanced TFA method, in this paper. In the MEVCT, a refined chirp parameter search is developed first to reduce the computational cost while increasing time–frequency accuracy. Then, an iterative high-order IF estimator is constructed to allow the IF to achieve or approach the actual values even in highly nonlinear situations. After that, the obtained IF estimate is substituted into the simultaneous extraction operator to reduce energy dispersion further and eliminate non-reassigned points (NRPs). Simulated and experimental signal analyses demonstrate that MEVCT is able to eliminate NRPs completely. Furthermore, when handling synchronous multicomponent signals, the proposed method has higher IF accuracy with less computational cost and better anti-noise capability. [ABSTRACT FROM AUTHOR]

• A novel numerical method was proposed to solve the rocking response of TSRBs. • It has favorable stability, acceptable accuracy, and high computational efficiency. • It does well in impact point identification and rocking pattern judgement. • Free and forced vibration experiments were conducted to verify its accuracy. • Parametric analysis was performed to guide the design of structures like TSRBs. A system of two stacked rigid blocks (TSRBs), such as a statue on a pedestal, is extensively constructed and utilized. However, the numerical simulation of its dynamic response has been a crucial and challenging problem due to the diversity of motion patterns and the nonlinearity in the impacts. Therefore, a high-accuracy and appropriate numerical simulation approach for solving the rocking response of TSRBs was proposed in this paper. First, their rocking patterns were presented, and the judgment diagram of their transitions was defined. Then, the rocking equations of the motion and the formulas of the post-impact angular velocities were introduced. Next, to solve the rocking response of TSRBs, a novel numerical method stemming from the Rosenbrock method and the substep-two-step method was proposed and preliminarily verified. Moreover, free and forced vibration experiments were conducted to verify its accuracy further, and the regularity of the motion was summarized. Finally, parametric analyses of the applications was performed on statue-pedestal systems to investigate the influence of the wall thicknesses and height-to-width ratios of the pedestals on the dynamic response. The results indicate that the proposed method has favorable stability, acceptable accuracy, and high computational efficiency due to its accurate impact point identification and rocking pattern determination. In practice, to reduce the dynamic response of statues, it is preferred to place pedestals with smaller wall thicknesses and larger height-to-width ratios under statues. [ABSTRACT FROM AUTHOR]

During the past years, numerical simulations of Nucleate Boiling have attracted increasing attention. If significant advances have already been performed on the conception of accurate numerical schemes accounting for jump conditions at a non-isothermal interface, further studies are required on the modeling of the heat flux in the vicinity of the contact line. Especially, at very low scale (<500 nm) the formation of a micro-region can be assumed, since the observed apparent contact angle can be higher than the microscopic contact angle and depend on the wall superheat. This variation of the apparent contact angle can be related to a temperature discontinuity between the saturation temperature and the local wall temperature at the contact line inducing a micro-region heat flux and an evaporation mass flow rate. Whereas this micro-region acts at very low scale, existing theoretical models suggest a strong influence of the micro-region heat flux on the global heat flux, and so on the overall bubble growth phenomenon. However, the numerical description of this micro-region in the framework of Direct Numerical Simulation (DNS) of nucleate boiling is a major issue due to the large range of spatial scales involved in the whole process. In the present paper, we propose a coupling methodology between an existing micro-region theoretical model and a larger scale DNS solver for Nucleate Boiling in axisymmetric configurations. Several benchmarks are proposed to show the consistency and the accuracy of the proposed method and to highlight the quantitative effect of the micro-region at the bubble scale. • A coupling between a DNS solver for nucleate boiling and micro-region model is proposed. • A specific boundary condition on the heat flux is proposed in the cells that contain the contact line. • A smoothing technique is proposed to spread the micro-region mass flow rate along the interface. • A novel benchmark based on experimental data is proposed to show the strong effect of the micro-region. • Nucleate boiling simulations in the micro-layer regime with micro-region at the contact line are presented. [ABSTRACT FROM AUTHOR]