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Piezoelectric materials find widespread applications in high-precision actuators and sensors. However, the traditional finite element method falls short in meeting the simulation needs of piezoelectric structures due to complexities in mesh generation and precision requirements for accurate simulations. This paper focuses on adapting and generalizing the meshless modeling technique based on the radial point interpolation method to address three-dimensional simulations of piezoelectric structures and accurately model positive and inverse piezoelectric behaviors. The piezoelectric body is discretized into point cloud data, and displacement and potential are approximated by interpolating values through the radial point interpolation method. Subsequently, a 3D meshless model for general piezoelectric structures is formulated based on the principle of minimum potential energy. The influences of key factors on interpolation accuracy and computational cost were discussed. Numerical examples, featuring a 3D piezoelectric bimorph beam as actuators and sensors, validate the efficacy of this extended approach. Results affirm that the three-dimensional meshless method, rooted in the radial point interpolation technique, achieves superior accuracy in predicting piezoelectric behavior compared to the traditional finite element method. This adaptation not only enhances the applicability of meshless modeling but also represents a significant advancement in accurately simulating complex three-dimensional piezoelectric structures. • Multi-field coupling meshless modeling for 3D piezoelectric structures based on RPIM. • Valuable insights are provided for selecting meshless model parameters. • Uniformly distributed nodes helps improve the numerical calculation accuracy. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel mathematical model of fractional order for epidemic dynamics in plants, this fractional order model (FOM) in the sense of Caputo derivatives governing fractional differential equations (FDEs), introducing modified parameters to coincide both sides dimensions for FOM that means enhancing its accuracy in representing the real-life scenarios to control the spread of the epidemic. Our contributions include a comprehensive qualitative analysis of the proposed FOM, such as proving the existence and uniqueness of the projected solution by transforming our problem into a fixed point problem and applying a Banach contraction principle and Schauder's fixed-point theorem. The positivity and boundedness of this solution are also demonstrated. We precisely evaluate all equilibrium points (EPs), examine their local and global stability by using Routh–Hurwitz conditions and fractional LaSalle's invariance principle (LIP), respectively and shed light on the dynamic behavior of the FOM. Furthermore, we discuss the sensitivity analysis for parameters of the control reproduction number (CRN), with insightful plots to illustrate the model's response to parameter changes (replanting and roguing parameters). From this foundation, we formulate a fractional optimal control problem (FOCP) by incorporating preventive u 1 and curative u 2 controls to effectively eliminate the propagation of the epidemic in plants. The fractional necessary optimality conditions (FNOCs) are derived attribution to Pontryagin's maximum principle (PMP). We employ the forward–backward sweep method (FBSM) based on fractional Euler method (FEM) in order to facilitate control implementation and show the different suggested strategies. By enhancing this method, optimal control efforts are projected onto the FOM and yield three various strategies to impact the epidemic's trajectory. For each strategy, we explain how the presence (i.e. with control cases) and absence (without control cases) of the proposed controls affected the susceptible, protected and infected plants. Some attractive figures with various values of the weight factor and fractional order α for the CRN are also presented, allowing a visual assessment of their impact on the dynamics of the epidemic in plants. In addition, we calculate the objective function for controlled and uncontrolled cases to provide a quantitative measure of its effectiveness in containing the outbreak in the plants. The results gained from our analyses and simulations provide valuable guidance for the management and elimination of epidemics in plants by offering various scenarios to implement the proposed controls. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to reveal the solute segregation behavior in the molten and solidified regions during direct chill (DC) casting of a large-size magnesium alloy slab under no magnetic field (NMF), harmonic magnetic field (HMF), pulsed magnetic field (PMF) and two types of out-of-phase pulsed magnetic field (OPMF). Design/methodology/approach: A 3-D multiphysical coupling mathematical model is used to evaluate the corresponding physical fields. The coupling issue is addressed using the method of separating step and result inheritance. Findings: The results suggest that the solute deficiency tends to occur in the central part, while the solute-enriched area appears near the fillet in the molten and solidified regions. Applying magnetic field could greatly homogenize the solute field in the two-phase region. The variance of relative segregation level in the solidified cross-section under NMF is 38.1%, while it is 21.9%, 18.6%, 16.4% and 12.4% under OPMF2 (the current phase in the upper coil is ahead of the lower coil), HMF, PMF and OPMF1 (the current phase in the upper coil lags behind the lower coil), respectively, indicating that OPMF1 is more effective to reduce the macrosegregation level. Originality/value: There are few reports on the solute segregation degree in rectangle slab under magnetic field, especially for magnesium alloy slab. This paper can act a reference to make clear the solute transport behavior and help reduce the macrosegregation level during DC casting. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to report the study of a fluid buoy system that includes wave effects, with particular emphasis on validating the numerical results with experimental data. Design/methodology/approach: A fluid–solid coupled algorithm is proposed to describe the motion of a rigid buoy under the effects of waves. The Navier–Stokes equations are solved with the open-source finite volume package Code Saturne, in which a free-surface capture technique and equations of motion for the solid are implemented. An ad hoc experiment on a laboratory scale is built. A buoy is placed into a tank partially filled with water; the tank is mounted into a shake table and subjected to controlled motion that promotes waves. The experiment allows for recording the evolution of the free surface at the control points using the ultrasonic sensors and the movement of the buoy by tracking the markers by postprocessing the recorded videos. The numerical results are validated by comparison with the experimental data. Findings: The implemented free-surface technique, developed within the framework of the finite-volume method, is validated. The best-obtained agreement is for small amplitudes compatible with the waves evolving under deep-water conditions. Second, the algorithm proposed to describe rigid-body motion, including wave analysis, is validated. The numerical body motion and wave pattern satisfactorily matched the experimental data. The complete 3D proposed model can realistically describe buoy motions under the effects of stationary waves. Originality/value: The novel aspects of this study encompass the implementation of a fluid–structure interaction strategy to describe rigid-body motion, including wave effects in a finite-volume context, and the reported free-surface and buoy position measurements from experiments. To the best of the authors' knowledge, the numerical strategy, the validation of the computed results and the experimental data are all original contributions of this work. [ABSTRACT FROM AUTHOR]

In this paper, a novel COVID-19 reaction–diffusion model with virus mutation and media coverage is investigated. First, the solution's uniform boundedness for the system is established. Then, the basic reproduction numbers for ordinary and mutant viruses spread in heterogeneous environments are defined. Furthermore, the endemic equilibrium's asymptotic distribution for the system is explored. In addition, when one diffusion coefficient tends to zero and the other diffusion coefficients are greater than zero and fixed, the solution of the system will asymptotically approach endemic equilibrium. Next, a theoretical analysis of how high-frequency media coverage affects the development of the COVID-19 epidemic is conducted. Theoretical research shows that high-frequency media coverage will lead to the disappearance of the disease. Meantime, global sensitivity analysis on the basic reproduction numbers R 01 and R 02 are performed. Finally, theoretical simulations and instance predictions are carried out. Because of the complexity of the Shanghai epidemic and changes in management and control, the infection rates β 1 (t) , β 2 (t) are given in the form of a piecewise function with more practical significance, and they are used to predict the epidemic trend of COVID-19 in Shanghai. Through a series of numerical simulations and analysis, the key indicators of the Shanghai COVID-19 epidemic are as follows : (1) The basic reproduction numbers in the early, middle, and late stages of COVID-19 are R ¯ 0 (1 : 34) = 0. 9152 , R ¯ 0 (35 : 49) = 3. 1476 , and R ¯ 0 (50 : 140) = 0. 6547 , respectively; (2) This epidemic round in Shanghai will peak at 3,270 new daily confirmed cases on the 49th day (April 15); (3) The final size of the epidemic will reach 63,470 confirmed cases; (4) This round of COVID-19 epidemic in Shanghai, China, is expected to be fully cleared in late June to early July. The above conclusions are basically consistent with the facts. Of course, with the rise in temperature and strict control, the epidemic situation in Shanghai, China, is expected to be cleared earlier. Our results provide new ideas for preventing and controlling the COVID-19 epidemic. • A reaction–diffusion model with virus mutation and media coverage is proposed. • The asymptotic properties of endemic equilibrium with small diffusion are explored. • Global sensitivity analysis for R 01 and R 02 and are performed. • Applying piecewise functions β 1 (t) , β 2 (t) , to predict the Shanghai COVID-19 epidemic. • Key indicators of COVID-19, such as R 0 , peak, final scale, clear time are obtained. [ABSTRACT FROM AUTHOR]

This review paper provides an overview of heat transfer of non-Newtonian nanofluids flowing in macro- and micro-channels using single-phase and two-phase approaches. This paper addresses governing equations for different types of non-Newtonian fluids and provides several advances in the field. The single-phase and two-phase schemes are described and their advantages and drawbacks in the simulation of non-Newtonian nanofluids in macro- and micro-channels are introduced. It is demonstrated that single-phase approaches cannot provide precise predictions due to the lack of accurate correlations because effective parameters change with the properties of nanofluids. The literature review indicates that the distribution of nanoparticles in the base fluid should be recognized properly. Understanding the concentration of nanoparticles and also their migration in channels or ducts results in demonstrating the formation of nanoparticle clustering. It is revealed that almost all investigators utilize the power-law model to simulate non-Newtonian nanofluid flow in macro- and micro-channels. According to the discussion presented in the paper, perspectives and future direction are provided. [ABSTRACT FROM AUTHOR]

Smoothed particle hydrodynamics (SPH) simulations of phase transitions are not accurate because of the decrease in liquid particles at the end of the evaporation phase transition. In this paper, we establish a numerical model of droplet evaporation suitable for SPH by introducing a time fractional-order convection–diffusion equation. This model was used to study the evaporation process of droplets under different environments, and the stationary evaporation of droplets was simulated by combining convection–diffusion equations of different orders to determine the optimal order. The results conformed to the " D 2 Law," confirming the effectiveness and accuracy of our method. The model was then used to study the phase transition process of droplets impacting flat and curved surfaces. Among the tested equations, the 0.1-order convection–diffusion equation had the best correction effect on the evaporation model. This equation improved the accuracy of the calculation and had a good corrective effect for both static evaporation and the evaporation of droplets impacting flat and curved surfaces. [ABSTRACT FROM AUTHOR]

Purpose: The classical advection-dispersion equation (ADE) model cannot accurately depict the gas transport process in natural geological formations. This paper aims to study the behavior of CO2 transport in fractal porous media by using an effective Hausdorff fractal derivative advection-dispersion equation (HFDADE) model. Design/methodology/approach: Anomalous dispersion behaviors of CO2 transport are effectively characterized by the investigation of time and space Hausdorff derivatives on non-Euclidean fractal metrics. The numerical simulation has been performed with different Hausdorff fractal dimensions to reveal characteristics of the developed fractal ADE in fractal porous media. Numerical experiments focus on the influence of the time and space fractal dimensions on flow velocity and dispersion coefficient. Findings: The physical mechanisms of parameters in the Hausdorff fractal derivative model are analyzed clearly. Numerical results demonstrate that the proposed model can well fit the history of gas production data and it can be a powerful technique for depicting the early arrival and long-tailed phenomenon by incorporating a fractal dimension. Originality/value: To the best of the authors' knowledge, first time these results are presented. [ABSTRACT FROM AUTHOR]

Numerical simulation is more and more used during the design stage of a manufactured product in order to optimize its performances. However, it is often too time consuming, particularly when it is used to solve optimization problems, preventing an intensive usage. A-posteriori Model Order Reduction methods can be very effective to shorten the computational time. An approximated solution is then sought in a space of small dimension defined by a reduced basis. The accuracy of such methods is highly dependent on the choice of the reduced basis, extracted from preliminary numerical simulation. The method usually applied to construct such reduced basis is based on the Singular Value Decomposition (SVD), which can be time consuming, and is not adapted when a large collection of preliminary numerical simulations must be used to construct the basis. An alternative to this approach has been proposed recently with the Maximum Entropy Snapshot Sampling (MESS) method. In this paper, we propose to compare these methods with other approaches usually used for clustering or data classification based on vectors distance calculation, like the Centroidal Voronoi Tessellation (CVT), Density Based Spatial Clustering of Applications with Noise (DBSCAN), and Clustering Using Representatives (CURE). The methods are compared on a complex and realistic nonlinear problem in low frequency electromagnetics. The quality of the reduced bases obtained by the different methods are compared. Then, field distributions and global quantities, like eddy current losses and magnetic energy, are computed from the reconstructed results, to further analyze the quality of the reduced bases. • Description of a posteriori model order reduction methods using projection in a reduced basis. • Singular Value Decomposition, Centroidal Voronoi Tessellation, and 3 other methods. • Application on results from a non-linear low frequency electromagnetic simulation. • Calculation of fields and global values from reconstructed results. • Comparison of studied approaches in terms of projection error. [ABSTRACT FROM AUTHOR]

The parabolic trough solar collector (PTSC) is a medium-temperature solar system that operates in the temperature range of 60–400 ºC. This technology is utilized dominantly for heat and power generation. Recently, numerous theoretical and numerical investigations have been carried out to evaluate and enhance the performance of PTSCs. This review paper provides fundamentals of PTSC systems, mathematical models, discretization methods, and turbulence models utilized for the simulation of PTSCs. Challenges in the field and future directions are presented to provide a perspective for researchers to achieve more accurate numerical results with lower computational costs. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the effects of the shear-thinning viscoelastic behavior of the surrounding matrix on droplet deformation by weakly compressible smoothed particle hydrodynamics (WC-SPH). Also, the effect of the presence of another droplet is examined. Design/methodology/approach: A modified consistent weakly compressible SPH method is proposed. After code verification, a complete parameter study is performed for a drop under the simple shear flow of a Giesekus liquid. The investigated parameters are 0.048≤Ca ≤ 14.4, 0.1≤c ≤ 10, 0.04≤De ≤ 10, 0≤α ≤ 1 and 0.12≤Re ≤ 12. Findings: It is demonstrated that the rheological behavior of the surrounding fluid could dramatically affect the droplet deformation. It is shown that the droplet deformation is increased by increasing Re and Ca. In contrast, the droplet deformation is decreased by increasing a, De and polymer content. Also, it is indicated the presence of another droplet could drastically affect the flow field, and the primary stress difference (N1) is resonated between two droplets. Originality/value: The main originality of this paper is to introduce a new consistent WC-SPH algorithm. The proposed method is very versatile for tackling the shear-thinning viscoelastic multiphase problems. Furthermore, a complete parameter study is performed for a drop under the simple shear flow of Giesekus liquid. Another novelty of the current paper is studying the effect of the presence of a second droplet. To the best of the authors' knowledge, this is performed for the first time. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the complex behavior of a dynamical system using fractional and fractal-fractional (FF) derivative operators. The non-classical derivatives are extremely useful for investigating the hidden behavior of the systems. The Atangana–Baleanu (AB) and Caputo–Fabrizio (CF) derivatives are considered for the fractional structure of the model. Further, to add more complexity, the authors have taken the system with a CF fractal-fractional derivative having an exponential kernel. The active control technique is also considered for chaos control. Design/methodology/approach: The systems under consideration are solved numerically. The authors show the Adams-type predictor-corrector scheme for the AB model and the Adams–Bashforth scheme for the CF model. The convergence and stability results are given for the numerical scheme. A numerical scheme for the FF model is also presented. Further, an active control scheme is used for chaos control and synchronization of the systems. Findings: Simulations of the obtained solutions are displayed via graphics. The proposed system exhibits a very complex phenomenon known as chaos. The importance of the fractional and fractal order can be seen in the presented graphics. Furthermore, chaos control and synchronization between two identical fractional-order systems are achieved. Originality/value: This paper mentioned the complex behavior of a dynamical system with fractional and fractal-fractional operators. Chaos control and synchronization using active control are also described. [ABSTRACT FROM AUTHOR]

Purpose: The lightning phenomenon is one of the main threats in photovoltaic (PV) applications. Suitable protection systems avoid major damages from direct strikes but also nearby strikes may induce overvoltage transients in the module itself and in the power conditioning circuitry, which can permanently damage the system. The effects on the PV system sensibly depend on the converter topology and on the adopted power switch. In the present study, a comparative analysis of the transient response due to a nearby lightning strike (LS) is carried out for three PV systems, each equipped with a different converter, namely, boost, buck and buck–boost, based on either silicon carbide metal oxide semiconductor field effect transistors (SiC MOSFET) or insulated gate bipolar transistors controlled power switch devices, allowing in this way an analysis at different switching frequencies. The purpose of this paper is to present the results of the numerical analysis to help the design of suited protection systems. Design/methodology/approach: Using a recently introduced three-dimensional semi-analytical method to simulate the electromagnetic transients caused in PV modules by nearby LSs, we investigate numerically the effect of a LS on the electronic circuits connecting the module to the alternate current (AC) power systems. This study adopts numerical simulations because experimental analyses are not easy to perform and does not grant a sufficient coverage of all statistically relevant aspects. The approach was validated in a previous paper against available experimental data. Findings: It is found that the load voltage is not severely interested by the strike effects, thanks to the low pass filters present at the converter output, whereas a relatively high overvoltage develops between the negative pin of the inner circuitry and the "ground" voltage reference. The overcurrent present in the active switches is hardly comparable because of the different topologies and working frequencies; however, the highest overcurrent is observed in the buck converter topology, with SiC MOSFET technology, although it shows the fastest decay. Originality/value: This research proposes, to the best of the authors' knowledge, a comprehensive comparison of the indirect lighting strike effects on the converter connected to PV panels. A proper design of the lightning and surge protection system should take into account such aspects to reduce the risk of induced overvoltage and overcurrent transients. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical model with a standard incidence rate is proposed to assess the role of media such as facebook, television, radio and tweeter in the mitigation of the outbreak of COVID-19. The basic reproduction number R 0 which is the threshold dynamics parameter between the disappearance and the persistence of the disease has been calculated. And, it is obvious to see that it varies directly to the number of hospitalized people, asymptomatic, symptomatic carriers and the impact of media coverage. The local and the global stabilities of the model have also been investigated by using the Routh–Hurwitz criterion and the Lyapunov's functional technique, respectively. Furthermore, we have performed a local sensitivity analysis to assess the impact of any variation in each one of the model parameter on the threshold R 0 and the course of the disease accordingly. We have also computed the approximative rate at which herd immunity will occur when any control measure is implemented. To finish, we have presented some numerical simulation results by using some available data from the literature to corroborate our theoretical findings. [ABSTRACT FROM AUTHOR]

This paper discusses numerical solutions for the control functions of parabolic integro-differential equations under the assumption of approximate controllability. It is proved theoretically that the numerical solution for the control function converges to the exact solution, and the validity of the theory is demonstrated from different perspectives through four numerical simulation examples. [ABSTRACT FROM AUTHOR]

This paper investigates the exponential synchronization (ES) problem for complex networks (CNs) under an intermittent adaptive event-triggered control (IAE-TC) strategy which is based on dynamic IAE-TC during the control activation intervals. In this control mechanism, the intermittent controller has adaptability to the evolution results of the controlled networks and is activated only when the event-triggered condition is violated. Then, by employing this kind of control strategy and the Lyapunov method, some sufficient conditions are proposed to achieve the ES of CNs and it is proven that the Zeno behavior can be eliminated. Besides, an application about the islanded microgrid system and some numerical simulations are provided to verify the effectiveness of the derived theoretical results. Moreover, in the numerical simulations, it is shown that the dynamic IAE-TC strategy can decrease the number of event-triggered instants more availably than the static one. [ABSTRACT FROM AUTHOR]

Algae plays a vital role as bio-fertilizer and soil stabilizer in the field of agriculture. This paper considers a fractal–fractional dynamics model in sense of Caputo derivative that study the reuse of detritus generated by the dead algae as fertilizer for crop. In particular, we study dynamics model in which algae recovers nitrogen and phosphorus (waste nutrients) from water and is reused to enhance agricultural production. The theoretical results are established for the considered model with the aid of fixed point theory, whereas Ulam–Hyers approach is used for the stability of system. The numerical simulations are computed by using the well-known technique of fractional Adams–Bashforth. For simulation of the problem we consider different values for fractional order and fractal dimension by using some pre-existing data. Several graphical representation is given to understand the system at different fractional order and fractal dimension. [ABSTRACT FROM AUTHOR]

In this paper, we consider a Leslie–Gower predator–prey model with prey-taxis subject to the homogeneous Neumann boundary condition. First, the stability of positive constant solution for corresponding ODE and PDE models is studied, respectively. It turns out that small prey-taxis can cause Turing instability and produce spatio-temporal patterns; large prey-taxis can stabilize the instability caused by diffusion. Then, in spatial one dimension, we use the center manifold theory to analyze the direction of Hopf bifurcation and stability of the bifurcation periodic solutions. By regarding prey-tactic sensitivity coefficient as the bifurcation parameter, we obtain a branch of non-constant solutions bifurcating from the positive equilibrium and find the stability criterion of such bifurcation solutions. Finally, some numerical simulations are shown to verify and expand our theoretical findings. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to use a fractional constitutive model with a nonlocal velocity gradient for replacing the nonlinear constitutive model to characterize its complex rheological behavior, where non-linear characteristics exist, for example, the inherent viscous behavior of the crude oil. The feasibility and flexibility of the fractional model are tested via a case study of non-Newtonian fluid. The finite element method is non-Newtonian used to numerically solve both momentum equation and energy equation to describe the fluid flow and convection heat transfer process. Design/methodology/approach: This paper provides a comprehensive theoretical and numerical study of flow and heat transfer of non-Newtonian fluids in a pipe based on the fractional constitutive model. Contrary to fractional order a, the rheological property of non-Newtonian fluid changes from shear-thinning to shear-thickening with the increase of power-law index n, therefore the flow and heat transfer are hindered to some extent. Findings: This paper discusses two dimensionless parameters on flow regime and thermal patterns, including Reynolds number (Re) and Nusselt number (Nu) in evaluating the flow rate and heat transfer rate. Analysis results show that the viscosity of the non-Newtonian fluid decreases with the rheological index (order α) increasing. While large fractional (order α) corresponds to the enhancement of heat transfer capacity. Research limitations/implications: First, it is observed that the increase of the Re results in an increase of the local Nusselt number (Nul). It means the heat transfer enhancement ratio increases with Re. Meanwhile, the increasement of the Nul indicating the enhancement in the heat transfer coefficient, produces a higher speed flow of crude oil. Originality/value: This study presents a new numerical investigation on characteristics of steady-state pipe flow and forced convection heat transfer by using a fractional constitutive model. The influences of various non-dimensional characteristic parameters of fluid on the velocity and temperature fields are analyzed in detail. [ABSTRACT FROM AUTHOR]

Purpose: Natural gas leak from underground pipelines could lead to serious damage and global warming, whose spreading in soil should be systematically investigated. This paper aims to propose a three-dimensional numerical model to analyze the methane–air transportation in soil. The results could help understand the diffusion process of natural gas in soil, which is essential for locating leak source and reducing damage after leak accident. Design/methodology/approach: A numerical model using finite element method is proposed to simulate the methane spreading process in porous media after leaking from an underground pipe. Physical models, including fluids transportation in porous media, water evaporation and heat transfer, are taken into account. The numerical results are compared with experimental data to validate the reliability of the simulation model. The effects of methane leaking direction, non-uniform soil porosity, leaking pressure and convective mass transfer coefficient on ground surface are analyzed. Findings: The methane mole fraction distribution in soil is significantly affected by the leaking direction. Horizontally and vertically non-uniform soil porosity has a stronger effect. Increasing leaking pressure causes increasing methane mole flux and flow rate on the ground surface. Originality/value: Most existing gas diffusion models in porous media are for one- or two-dimensional simulation, which is not enough for predicting three-dimensional diffusion process after natural gas leak in soil. The heat transfer between gas and soil was also neglected by most researchers, which is very important for predicting the gas-spreading process affected by the soil moisture variation because of water evaporation. In this paper, a three-dimensional numerical model is proposed to further analyze the methane–air transportation in soil using finite element method, with the presence of water evaporation and heat transfer in soil. [ABSTRACT FROM AUTHOR]

In this paper, we first build a model for a complicated newsvendor problem, which is involved with optimization to preseason production quantity with random yields and outsourcing quantity with supplier quantity discounts. Different from the existing models, a two-stage decision-making strategy is proposed for the retailer such that the possible loss, caused by the uncertainty of production, is reduced in virtue of dynamically choosing the outsourcing quantities and sales prices. Additionally, the cross-elasticity of prices is incorporated into formulating the random and price-dependent demand function in our model. Consequently, the mathematical model is expressed by a parameterized optimization problem, and a cyclic coordinate descent algorithm (CCD), combined with a feasible direction method and a parameters-choosing procedure, is developed to obtain optimal solutions of the original problem. Both substitute and complementary scenarios for different products are further investigated by numerical simulation. Main managerial implications are summarized as follows: (1) The two-stage policy of decision-making brings more benefits than a static policy for the complicated newsvendor problems. (2) The budget available is a critical constraint for the small-and-medium sized business, the maximum expected profit increases as the budget becomes greater, but remains at the same level after it reaches a threshold value. (3) The cross elasticity relationship between the products plays a critical role in choosing optimal quantities of preseason production, sales prices and outsourcing quantities. [ABSTRACT FROM AUTHOR]

This paper describes the mathematical modeling of a parabolic trough collector where the heat transfer fluid has temperature dependent physical properties for which we have developed our own mathematical expressions. For a specific location and date, the direct solar radiation and other sun–earth parameters are computed on a Julian day basis. Also, we have used certain known and recent correlations for the heat transfer coefficients appearing in this model. The mathematical model is governed by three nonlinear partial differential equations of parabolic type with initial/boundary value conditions. We describe a numerical algorithm in order to obtain the approximate solution of this model. Then, we carry out some numerical simulations which yield valuable information for the performance and efficiency of a solar PTC plant at the specific location. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the paper was the application of computational fluid dynamics (CFD) techniques in fluid flow using Maxwell's equation for partial slip modelling, estimating the flow parameters, and selecting tangential momentum accommodation coefficient (TMAC) for tight rock samples in permeability calculations. Design/methodology/approach: The paper presents a numerical analysis of fluid flow in a low-porosity rock sample by using CFD. Modelling results allowed to determine mass flow rates in a rock sample and to calculate permeability values using a modified Darcy's equation. Three-dimensional (3D) geometrical model of rock sample generated using computed X-ray tomography was used in the analysis. Steady-state calculations were carried out for defined boundary conditions in the form of pressure drop. The simulations were applied taking into account the slip phenomenon described by Maxwell's slip model and TMAC. Findings: Values of permeability were calculated for different values of TMAC, which vary from 0 to 1. Results in the form of gas mass flow rates were compared with the measured value of permeability for rock sample, which confirmed the high accuracy of the presented model. Practical implications: Calculations of fluid flow in porous media using CFD can be used to determine rock samples' permeability. In slip flow regime, Maxwell's slip model can be applied and the empirical value of TMAC can be properly estimated. Originality/value: This paper presents the usage of CFD, Maxwell's equation for partial slip modelling, in fluid flow mechanism for tight rock samples. 3D geometric models were generated using created pre-processor (poROSE software) and applied in the raw form for simulation. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to develop a numerical model used for calculating the nonlinearities of large-scale hydro-pneumatic suspension (HPS) and investigating the effects of variations in flow path and operational parameter on suspension damping response. Design/methodology/approach: To parameterization nonlinearities of the suspension, the author developed a two-phase flow model of a large-scale HPS based on computational fluid dynamics and volume of fluid method. Considerable effort was made to verify the nonlinearities by field measurements carried out on an off-highway mining dump truck. The investigation of effects of variations in flow path and operational parameter on damping characteristics highlights the necessity of the numerical simulation. Findings: The two-phase flow model can represent the gas-oil interaction and simulate the suspension operational movement conveniently. Transient numerical simulation results can be used to model the nonlinearities of large-scale HPS accurately. A new phenomenon was discovered that the pressure in rebound chamber presents reduction trend during compression stroke in special cases. It has never been reported before. Originality/value: Developed a two-phase flow model of a large-scale HPS, which can manage the gas-oil interaction and capture the complex flow field structure in it. The paper is the first study to model the nonlinearities of a large-scale HPS used in off-highway mining dump truck through transient numerical simulation. Compared with previous researches, such a research not only gives new insight and thorough understanding into the suspension internal fluid structure but also can give good guiding opinions to the optimal design of HPS. [ABSTRACT FROM AUTHOR]

Purpose: This work aims to describe the physical and numerical modeling of a CFD solver for hypersonic flows in thermo-chemical non-equilibrium. This paper is the second of a two-part series that concerns the application of the solver introduced in Part I to adaptive unstructured meshes. Design/methodology/approach: The governing equations are discretized with an edge-based stabilized finite element method (FEM). Chemical non-equilibrium is simulated using a laminar finite-rate kinetics, while a two-temperature model is used to account for thermodynamic non-equilibrium. The equations for total quantities, species and vibrational-electronic energy conservation are loosely coupled to provide flexibility and ease of implementation. To accurately perform simulations on unstructured meshes, the non-equilibrium flow solver is coupled with an edge-based anisotropic mesh optimizer driven by the solution Hessian to carry out mesh refinement, coarsening, edge swapping and node movement. Findings: The paper shows, through comparisons with experimental and other numerical results, how FEM + anisotropic mesh optimization are the natural choice to accurately simulate hypersonic non-equilibrium flows on unstructured meshes. Three-dimensional test cases demonstrate how, for high-speed flows, shocks resolution, and not necessarily boundary layers resolution, is the main driver of solution accuracy at walls. Equally distributing the error among all elements in a suitably defined Riemannian space yields highly anisotropic grids that feature well-resolved shock waves. The resulting high level of accuracy in the computation of the enthalpy jump translates into accurate wall heat flux predictions. At the opposite end, in all cases examined, high-quality but isotropic unstructured meshes gave very poor solutions with severely inadequate heat flux distributions not even featuring expected symmetries. The paper unequivocally demonstrates that unstructured anisotropically adapted meshes are the best, and may be the only, way for accurate and cost-effective hypersonic flow solutions. Originality/value: Although many hypersonic flow solvers are developed for unstructured meshes, few numerical simulations on unstructured meshes are presented in the literature. This work demonstrates that the proposed approach can be used successfully for hypersonic flows on unstructured meshes. [ABSTRACT FROM AUTHOR]

High implementation complexity of multi-scroll circuit is a bottleneck problem in real chaos-based communication. Especially, in multi-scroll Chua’s circuit, the simplified implementation of piecewise-linear resistors with multiple segments is difficult due to their intricate irregular breakpoints and slopes. To solve the challenge, this paper presents a systematic scheme for synthesizing a Chua’s diode with multi-segment piecewise-linearity, which is achieved by cascading even-numbered passive nonlinear resistors with odd-numbered ones via a negative impedance converter. The traditional voltage mode op-amps are used to implement nonlinear resistors. As no extra DC bias voltage is employed, the scheme can be implemented by much simpler circuits. The voltage-current characteristics of the obtained Chua’s diode are analyzed theoretically and verified by numerical simulations. Using the Chua’s diode and a second-order active Sallen-Key high-pass filter, a new inductor-free Chua’s circuit is then constructed to generate multi-scroll chaotic attractors. Different number of scrolls can be generated by changing the number of passive nonlinear resistor cells or adjusting two coupling parameters. Besides, the system can be scaled by using different power supplies, satisfying the low-voltage low-power requirement of integrated circuit design. The circuit simulations and hardware experiments both confirmed the feasibility of the designed system. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a method to obtain necessary and sufficient stability conditions for systems governed by one-dimensional nonlinear hyperbolic partial-differential equations with closed-loop integral controllers, when the linear frequency analysis cannot be used anymore. We study the stability of a general nonlinear transport equation where the control input and the measured output are both located on the boundaries. The principle of the method is to extract the limiting part of the stability from the solution using a projector on a finite-dimensional space and then use a Lyapunov approach. This paper improves a result of Trinh, Andrieu, and Xu, and gives an optimal condition for the design of the controller. The results are illustrated with numerical simulations where the predicted stable and unstable regions can be clearly identified. [ABSTRACT FROM AUTHOR]

This paper introduces a new code "QuasIncompact3D" for solving the variable-density Navier–Stokes equations in the low-Mach number limit. It is derived from the Incompact3D framework which is designed for incompressible flows (Laizet and Lamballais, 2009). QuasIncompact3D is based on high-order accurate compact finite-differences (Lele, 1992), an efficient 2D domain decomposition (Laizet and Li, 2011) and a spectral Poisson solver. The first half of the paper focuses on introducing the low-Mach number governing equations, the numerical methods and the algorithm employed by QuasIncompact3D to solve them. Two approaches to forming the pressure-Poisson equation are presented: one based on an extrapolation that is efficient but limited to low density ratios and another one using an iterative approach suitable for higher density ratios. The scalability of QuasIncompact3D is demonstrated on several TIER-1/0 supercomputers using both approaches, showing good scaling up to 65 k cores. Validations for incompressible and variable-density low-Mach number flows using the Taylor–Green vortex and a non-isothermal mixing layer, respectively, as test cases are then presented, followed by simulations of non-Boussinesq gravity currents in two- and three-dimensions. To the authors' knowledge this is the first investigation of 3D non-Boussinesq gravity currents by means of Direct Numerical Simulation over a relatively long time evolution. It is found that 2D and 3D simulations of gravity currents show differences in the locations of the fronts, specifically that the fronts travel faster in three dimensions, but that it only becomes apparent after the initial stages. Our results also show that the difference in terms of front location decreases the further the flow is from Boussinesq conditions. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to ascertain the harm to personnel and equipment caused by an external explosion during natural gas explosion venting. The external explosion characteristics induced by the indoor natural gas explosion are the focal points of the investigation. Design/methodology/approach: Computational fluid dynamics technology was used to investigate the large-scale explosion venting process of natural gas in a 6 × 3 × 2.5 m room, and the characteristics of external explosion under different scaled vent size (Kv = Av/V2/3, 0.05, 0.08, 0.13, 0.18) were numerically analyzed. Findings: When Kv = 0.08, the length and duration of the explosion fireball are 13.39 and 450 ms, respectively, which significantly expands the degree and range of high-temperature hazards. The suitable flow-field structure causes the external explosion overpressure to be more than twice that indoors, i.e. the natural gas explosion venting overpressure may be considerably more hazardous in an outdoor environment than inside a room. A specific range for the Kv can promote the superposition of outdoor rupture waves and explosion shock waves, thereby creating a new overpressure hazard. Originality/value: Little attention has been devoted to investigating systematically the external explosion hazards. Based on the numerical simulation and the analysis, the external explosion characteristics induced by the indoor large-scale gas explosion were obtained. The research results are theoretically significant for mitigating the effects of external gas explosions on personnel and equipment. [ABSTRACT FROM AUTHOR]

In this paper, we explore the effect of the stochastic environmental fluctuations on the dynamics of an HIV system with both virus-to-cell and cell-to-cell transmissions, intracellular delay, and humoral immunity. First, the existence and uniqueness of the global positive solution and the stochastically ultimate boundedness of the stochastic HIV system are discussed. Then, by constructing a series of suitable Lyapunov functions and using some differential inequality techniques, the long-time asymptotic properties of the stochastic delayed system are investigated. These properties reveal that the solution of the stochastic system oscillates around the equilibrium points of the deterministic system when the intensity of environmental perturbations is appropriate. In addition, the sufficient condition for persistence in mean and extinction of the stochastic system are established under the suitable condition. At last, numerous numerical simulations show that the HIV will disappear if the intensity of environmental fluctuations is sufficiently large. This means that appropriate stochastic environmental fluctuations can effectively suppress the outbreak of HIV. • A stochastic delay HIV system with humoral immunity is proposed. • Asymptotic properties,persistence in mean and extinction, are investigated. • A series of Lyapunov functions and differential inequality are constructed and used. • Numerical simulations confirmed the effects of stochastic fluctuations on HIV. • Stochastic fluctuations can effectively suppress the outbreak of HIV. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to focus on the natural convective flow analysis of micropolar nanofluid fluid in a rectangular vertical container. A heated source is placed in the lower wall to generate the internal flow. In further assumptions, the left/right wall are kept cool, while the upper and lower remaining portions are insulated. Free convection prevails in the regime because of thermal difference in-between the lower warmer and upper colder region. Design/methodology/approach: The physical setup owns mathematical framework in-terms of non-linear partial differential equations. For the solution purpose of the differential system, finite volume method is adopted. The interesting features of the flow along with thermal transportation involve both translational and rotational movement of fluid particles. Findings: Performing the simulations towards flow controlling variables the outputs are put together in contour maps and line graphs. It is indicated that the variations in flow profile mass concentration and temperature field augments at higher Rayleigh parameter because of stronger buoyancy effects. Higher viscosity coefficient implies decrease in flow and thermal transportation. Further, the average heat transfer rate also grows by increasing both the Rayleigh parameter and heated source length. Originality/value: To the best of the authors' knowledge, no such study has been addressed yet. Further, the results are validated by comparing with previously published work. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to establish a mathematical model for water-flooding considering the impact of fluid–solid coupling to describe the process of development for a low-permeability reservoir. The numerical simulation method was used to analyze the process of injected water channeling into the interlayer. Design/methodology/approach: Some typical cores including the sandstone and the mudstone were selected to test the permeability and the stress sensitivity, and some curves of the permeability varying with the stress for the cores were obtained to demonstrate the sensitivity of the formation. Based on the experimental results and the software Eclipse and Abaqus, the main injection parameters to reduce the amount of the injected water in flowing into the interlayer were simulated. Findings: The results indicate that the permeability of the mudstone is more sensitive to the stress than sandstone. The injection rate can be as high as possible on the condition that no crack is activated or a new fracture is created in the development. For the B82 block of Daqing oilfield, the suggested pressure of the production pressure should be around 1–3MPa, this pressure must be gradually reached to get a higher efficiency of water injection and avoid damaging the casing. Originality/value: This work is beneficial to ensure stable production and provide technical support to the production of low permeability reservoirs containing an interlayer. [ABSTRACT FROM AUTHOR]

The main focus of this paper is the evolution of complex behavior in a system of coupled nonlinear memristor circuits depending on the applied coupling conditions. Thereby, the parameter space for the local activity and the edge-of-chaos domain will be determined to enable the emergence of the pattern formation in locally coupled cells according to Chua’s principle. Each cell includes a Niobium oxide-based memristor, which may feature a locally active behavior once it is suitably biased on the negative differential resistance region of its DC current-voltage characteristic. It will be shown that there exists a domain of parameters under which each uncoupled cell may become locally active around a stable bias state. More specifically, under these conditions, the coupled cells are on the edge-of-chaos, and can support the static and dynamic pattern formation. The emergence of such complex spatio-temporal behavior in homogeneous structures is a prerequisite for information processing. The theoretical results are confirmed by measurements as well as by the numerical simulations of the accurate device and circuit models. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to describe the physical and numerical modeling of a new computational fluid dynamics solver for hypersonic flows in thermo-chemical non-equilibrium. The code uses a blend of numerical techniques to ensure accuracy and robustness and to provide scalability for advanced hypersonic physics and complex three-dimensional (3D) flows. Design/methodology/approach: The solver is based on an edge-based stabilized finite element method (FEM). The chemical and thermal non-equilibrium systems are loosely-coupled to provide flexibility and ease of implementation. Chemical non-equilibrium is modeled using a laminar finite-rate chemical kinetics model while a two-temperature model is used to account for thermodynamic non-equilibrium. The systems are solved implicitly in time to relax numerical stiffness. Investigations are performed on various canonical hypersonic geometries in two-dimensional and 3D. Findings: The comparisons with numerical and experimental results demonstrate the suitability of the code for hypersonic non-equilibrium flows. Although convergence is shown to suffer to some extent from the loosely-coupled implementation, trading a fully-coupled system for a number of smaller ones improves computational time. Furthermore, the specialized numerical discretization offers a great deal of flexibility in the implementation of numerical flux functions and boundary conditions. Originality/value: The FEM is often disregarded in hypersonics. This paper demonstrates that this method can be used successfully for these types of flows. The present findings will be built upon in a later paper to demonstrate the powerful numerical ability of this type of solver, particularly with respect to robustness on highly stretched unstructured anisotropic grids. [ABSTRACT FROM AUTHOR]

This paper studies the optimal output-feedback control of a linear time-invariant system where a stochastic event-based scheduler triggers the communication between the sensor and the controller. The primary goal of the use of this type of scheduling strategy is to provide significant reductions in the usage of the sensor-to-controller communication and, in turn, improve energy expenditure in the network. In this paper, we aim to design an admissible control policy, which is a function of the observed output, to minimize a quadratic cost function while employing a stochastic event-triggered scheduler that preserves the Gaussian property of the plant state and the estimation error. For the infinite horizon case, we present analytical expressions that quantify the tradeoff between the communication cost and control performance of such event-triggered control systems. This tradeoff is confirmed quantitatively via numerical examples. Besides, numerical simulations justify that the event-triggered control provides better quadratic control performance than the (traditional) periodic time-triggered control at the same average sampling rate. [ABSTRACT FROM AUTHOR]

Abstract Based on mimetic Green element method (GEM), which synthesizes some typical advantages of boundary element method (BEM), finite element method (FEM) and mimetic finite difference method (mimetic FDM), This paper study the application of mimetic GEM in the system of partial differential equations (PDEs) of oil-water two-phase flow in porous media. It is the first time to apply GEM to solve numerically the system of PDEs, which is one of novelties in this paper. For numerical simulation of oil-water two-phase flow in porous media, this paper provides a novel numerical method based on mimetic GEM, which is the other novelty of this work. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to analyze the effects of white noise perturbations of the input voltage on the band pass filter response, both on pass band and reject band. Design/methodology/approach: By adding white noise term in the input voltage of the filter circuit, the deterministic ordinary differential equation (ODE) is replaced by a stochastic differential equation (SDE). With the application of Ito lemma, the analytical solution of SDE has been obtained. Furthermore, based on the Euler–Maruyama approximation, the numerical simulation for SDE has been done. Practical implications: Numerical examples are performed using MATLAB programming to show the efficiency and accuracy of the present work. Originality/value: All previous noise analyses of filter circuits were done using ODEs or component noise formulas in the electrical domain. The stochastic perspective for these circuits is adopted for the first time in this paper. [ABSTRACT FROM AUTHOR]

In this paper we study a food chain system with four reaction–diffusion equations arising from competition of two predators with a single mutation for a single prey in an unstirred chemostat. Due to the introduction of mutation and death of predators, the conservation principle for a standard chemostat model does not hold. In order to better explore the mutation of species we assume that the initial condition for mutant species is zero throughout this paper. We firstly investigate the uniform persistence of such system by the persistence theory. When the reverse rate of mutant species is zero, we study the structure and stability of nonnegative equilibria of the food chain system. The results show that the coexistence occur with small diffusion and small reverse rate of mutant species. Biologically speaking, it implies that small diffusion and small reverse rate of mutant species are sufficiently effective in the survival of mutant species. Finally, our numerical results verified our theoretical results and showed that the mutant species can survive when it has smaller random dispersal rate than the wild-type species. • Introduce mutation into predators and consider a food chain chemostat model. • How diffusion and mutation of predators affects coexistence is studied. • The coexistence occur with small diffusion and small reverse rate of mutant species. • Numerical results show that the mutant species can survive with smaller diffusion. [ABSTRACT FROM AUTHOR]

According to the complex flow dynamics of droplets impacting on the wall, an integrated smoothed particle hydrodynamics (SPH) method is developed by a series of improved techniques including artificial viscosity, kernel gradient correction (KGC) technique, boundary treatment and so on, combined with the surface tension based on the continuous surface force (CSF) model in this paper. This method is validated by simulations of the square cavity flow and natural variations of a square droplet, and effects of particle diameter, kernel function, and artificial viscosity coefficient are also analyzed. On this basis, dynamic behavior of the droplet impacting on the wall with heat transfer is studied, and the results agree well with the experimental results. It is observed that the wall characteristics have a significant influence on the droplet deformation, and the droplet tends to spread on the hydrophilic wall. In the investigated temperature difference, the influence of temperature difference could be ignored, but there is energy exchange between the droplet and the wall. In general, the spreading law of droplet is consistent with the physical phenomena, which shows that the integrated SPH method can effectively deal with engineering problems involving a droplet impacting on the wall with heat transfer. [ABSTRACT FROM AUTHOR]

Purpose: Using the computational fluid dynamics (CFD) technique, this paper aims to investigate the influence of key parameters such as throat diameter; the suction ratio on the flow field behaviors such as Mach number; pressure; and temperature. Design/methodology/approach: To investigate the effect of throat diameter, it is simulated for 4, 6, 8 and 10 mm as throat diameters. The governing equations have been solved by standard code of Fluent Software together with a compressible 2 D symmetric and turbulence model with the standard k–ε model. First, the influence of the throat diameter is investigated by keeping the inlet mass flow constant. Findings: The results show that a place of shock wave creation is changed by changing the throat diameter. The obtained results illustrate that the maximum amount of Mach number is dependent on the throat diameter. It is obtained from the results that for smaller throats higher Mach numbers can be obtained. Therefore, for mixing purposes smaller throats and for exhausting bigger throats seems to be appropriate. Originality/value: The obtained numerical results are compared to the existing experimental ones which show good agreement. [ABSTRACT FROM AUTHOR]

• A strongly conservative solver for cylindrical coordinates is proposed. • The analytical solution of the uniform flow is numerically obtained in the cylindrical coordinates. • The singularity of the cylindrical coordinates at the pole is addressed. • The time step constrained around the z-axis is significantly improved. • A strongly conservative methodology is proposed for curvilinear coordinates. Cylindrical coordinates are often used in computational fluid dynamics (CFD), particularly when one considers axisymmetric flow. Although cylindrical coordinates have several advantages in accurately describing the rotational flow as well as the complex boundary, there are limits to how far they can be taken. These are (1) the governing equations are mostly in a non-conservative form in current standard models, which cannot preserve the conservation of numerical simulations, (2) the singularity along the axis at the coordinate origin (z -axis), leading to difficulty reproducing the flow across the z -axis, and (3) the time step is extremely shortened to satisfy the CFL condition near the z -axis because the numerical cell thereof is narrow in the azimuthal direction for a given angular resolution. A strongly conservative model is proposed in this paper to overcome these difficulties. First, the strongly conservative form of the governing equations is derived by considering changes in the direction of the base vector within a cell, and a concept of direction error is defined to reveal the inherent error of the standard model. Second, inspired by the derivation of the first, a strongly conservative method for evaluating the flux across each cell surface is proposed, preserving the conservation of discretization and enlarging the time step. Finally, the proposed model is tested by three classical problems, i.e., uniform flow, Sod shock tube problem, and expanding outflows. The results imply that the proposed model is strongly conservative for the cylindrical coordinate system, and it can overcome the limits of the standard model and eliminate the inherent error in the standard model. Furthermore, the strongly conservative model and method are extended to arbitrary coordinates for the numerical conservation in general curvilinear coordinates of the problem with complex boundaries. [ABSTRACT FROM AUTHOR]

In Electro-Osmotic Pumps (EOPs), a micro fluid flow is formed by applying an external electric field via two electrodes immersed in the electrolyte. The immersed electrodes, due to lying in the fluid flow path, can consider an obstacle that can negatively affect the flow inside the microchannel. This issue is usually neglected in studies performed on the electroosmotic flows. Concerning this motivation, in this paper, a novel concept of a multi-stage EOP (introduced earlier by the researchers) was investigated numerically where the electrodes were attached to the wall of the micropump so as not to obstruct the fluid flow and to facilitate the serialization of micropumps. A two-dimensional numerical code is developed to analyze the steady-state performance of the multi-stage EOP. The governing equations for the fluid flow, internal and external electric fields, and ion concentration distribution are solved using the Finite Volume method. The results showed that in the multi-stage EOP consisting of multiple micropumps connected in series, the maximum pressure of EOP will enhances by increasing the number of micropumps. In contrast, the maximum flow rate remains approximately constant. The relationship between the maximum pressure, and the strength of the applied external electric field, was also investigated based on the electric field strength, and the results were expressed as a mathematical correlation. [ABSTRACT FROM AUTHOR]

This paper explores the integration and harmonization of an epidemic dynamics model and a resource production–inventory management model, aiming to identify optimal control strategies of epidemic containment. We begin with establishing a generalized optimal control model for epidemic dynamics, which offers a unified framework to verify the sufficient conditions for the existence of the optimal solutions to a class of epidemic optimal control models. Based on the model, a resource production–inventory dynamic model with learning ability is proposed to find optimal strategies of the medical resource management. Subsequently, we propose the optimal control model for a dynamics system of COVID-19 and explore the optimal strategies of the combined applications of vaccine and recommended treatment in comprehensive control of the epidemic. Finally, the viability of effective integration and coordination between the optimal control models of the epidemic dynamics and the resource production–inventory system is verified by numerical simulation and analytical analysis, and a new method is implemented for finding the optimal management strategy for epidemic control. Therefore, this study advances a more comprehensive understanding of the interplay between epidemic dynamics and resource management, illustrating the feasibility and efficacy of integrating multiple models to achieve optimal decisions in both theoretical and practical aspects of epidemic control. • Sufficient condition of optimal solution to a class of optimal control models is set. • New optimal control models of COVID-19 and production–inventory dynamics are set. • Vaccine and treatment based medical resource optimal management way is implemented. • A multi-model integrated approach of optimal epidemic control strategies is explored. [ABSTRACT FROM AUTHOR]

Purpose: Spiral-wound heat exchangers (SWHEs) are widely used in different industries. In special applications, such as cryogenic (HEs), fluid properties may significantly depend on fluid temperature. This paper aims to present an analytical method for design and rating of SWHEs considering variable fluid properties with consistent shell geometry and single-phase fluid. Design/methodology/approach: To consider variations of fluid properties, the HE is divided into identical segments, and the fluid properties are assumed to be constant in each segment. Validation of the analytical method is accomplished by using three-dimensional numerical simulation with shear stress transport k-ω model, and the numerical model is verified by using the experimental data. Moreover, the HE cost is selected as the main criterion in obtaining the proper design, and the most affordable geometry is selected as the proper design. Findings: The accuracy of different heat transfer and pressure drop correlations is investigated by comparing the analytical and numerical results. The average errors in the calculation of effectiveness, shell-side pressure drop and tube-side pressure drop using the analytical method are 2.1%, 13.9% and 13.3%, respectively. Moreover, the effect of five main geometrical parameters on the SWHE cost is investigated. The results indicate that the effect of longitudinal pitch ratio on the SWHE cost can be neglected, whereas other geometrical parameters have a significant impact on the total cost of the SWHE. Originality/value: This work contains a versatile and low-cost analytical method to design and rating the SWHEs considering the variable fluid property with consistent shell geometry. The previous studies have introduced complex methods and have not considered the consistency of shell geometry. [ABSTRACT FROM AUTHOR]

In this paper, a coupled FEM-BEM method is applied to simulate the magneto-mechanical behavior of a single-crystalline Ni-Mn-Ga sample. First, based on some kinematic and constitutive assumptions, the governing system for modeling the response of the Ni-Mn-Ga sample is formulated, which is composed of the magnetic and mechanical field equations, the evolution laws of the internal variables and the twin interface movement criteria. To solve the governing system, an iterative numerical algorithm is proposed. Especially, a coupled FEM-BEM method is adopted in the algorithm to tackle the magnetic field equation. By using this method, one doesn't need to consider the distribution of the demagnetization field in the surrounding space, thus the number of elements can be reduced significantly. To show the efficiency of the numerical algorithm, some typical examples are studied. It can be found that the numerical results obtained from the coupled FEM-BEM method and the conventional FEM method are in good agreement with each other. The numerical algorithm proposed in the current work would be helpful for the design of novel smart devices made of Ni-Mn-Ga alloys. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to investigate oil-gas slug formation in horizontal straight pipe and its associated pressure gradient, slug liquid holdup and slug frequency.Design/methodology/approach The abrupt change in gas/liquid velocities, which causes transition of flow patterns, was analyzed using incompressible volume of fluid method to capture the dynamic gas-liquid interface. The validity of present model and its methodology was validated using Baker’s flow regime chart for 3.15 inches diameter horizontal pipe and with existing experimental data to ensure its correctness.Findings The present paper proposes simplified correlations for liquid holdup and slug frequency by comparison with numerous existing models. The paper also identified correlations that can be used in operational oil and gas industry and several outlier models that may not be applicable.Research limitations/implications The correlation may be limited to the range of material properties used in this paper.Practical implications Numerically derived liquid holdup and holdup frequency agreed reasonably with the experimentally derived correlations.Social implications The models could be used to design pipeline and piping systems for oil and gas production.Originality/value The paper simulated all the seven flow regimes with superior results compared to existing methodology. New correlations derived numerically are compared to published experimental correlations to understand the difference between models. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to assess the strengths and weaknesses of four thermodynamic models used in aircraft icing simulations to orient the development or the choice of an improved thermodynamic model.Design/methodology/approach Four models are compared to assess their capabilities: Messinger, iterative Messinger, extended Messinger and shallow water icing models. They have been implemented in the aero-icing framework, NSCODE-ICE, under development at Polytechnique Montreal since 2012. Comparison is performed over typical rime and glaze ice cases. Furthermore, a manufactured geometry with multiple recirculation zones is proposed as a benchmark test to assess the efficiency in runback water modeling and geometry evolution.Findings The comparison shows that one of the main differences is the runback water modeling. Runback modeling based on the location of the stagnation point fails to capture the water film behavior in the presence of recirculation zones on airfoils. However, runback modeling based on air shear stress is more suitable in this situation and can also handle water accumulation while the other models cannot. Also, accounting for the conduction through the ice layer is found to have a great impact on the final ice shape as it increases the overall freezing fraction.Originality/value This paper helps visualize the effect of different thermodynamic models implemented in the same aero-icing framework. Also, the use of a complex manufactured geometry highlights weaknesses not normally noticeable with classic ice accretion simulations. To help with the visualization, the ice shape is presented with the water layer, which is not shown on typical icing results. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to perform the simulation to explore the gap flow field under a hypersonic air flow. Thermal protection systems of hypersonic vehicles generally consist of thermal insulation tiles, and gaps between these tiles probably cause a severe local aerodynamic thermal effect.Design/methodology/approach The discretizations of convection flux term and temporal term in the governing equation with chemical equilibrium, respectively, take AUSM+-up flux-vector splitting scheme and the implicit lower-upper symmetric Gauss–Seidel method. Based on these, the flow field in a deep gap is simulated by means of the computer codes that the authors have written.Findings The numerical results show that the heat flux distribution in a gap has a good agreement with experimental results. Importantly, the distribution of heat flux is “U” shaped and the maximum of the heat flux occurs at the windward corner of a gap.Originality/value To explore the gap flow field under a hypersonic air flow, which is a chemically reacting, all speed and viscous flow, a novel model with an equivalent ratio of specific heats is presented. The investigation in this paper has a guide for the design of the thermal protection system in hypersonic vehicles. [ABSTRACT FROM AUTHOR]

A damaged-based numerical manifold method is proposed in this paper to investigate the micro- and macro- mechanical properties of rocks. This model accounts for material heterogeneity and local material degradation using an exponential material softening law. The Mohr-Coulomb criterion with a tension cut-off is chosen as the strength criterion to capture the rock damage and fracture modes. Once the induced tensile or compressive stress in an element fulfills the criterion, this element will be damaged and a crack will initiate from the centroid of this damaged element to the centroid of its adjacent damaged manifold element. To verify the proposed damage-based numerical manifold method (NMM), a series of benchmark tests are conducted and the results are compared with the numerical manifold method incorporated with a Mohr-Coulomb criterion-based fracturing algorithm to simulate the progressive failure. The simulated results are consistent with the analytical solutions, and the advantages and disadvantages of two methods are compared and analyzed. Numerical results indicate that the proposed damage-based numerical manifold method can capture the process of crack initiation and propagation, and this method is an effective and reliable approach for modelling cracking behavior of rocks. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel and simple Yee Finite-Difference Time-Domain (FDTD) scheme to solve numerically the nonlinear second-order thermoviscous Navier–Stokes and the Continuity equations. In their original form, these equations cannot be discretized by using the Yee's mesh, at least, easily. As it is known, the use of the Yee's mesh is recommended because it is optimized in order to obtain higher computational performance and remains at the core of many current acoustic FDTD softwares. In order to use the Yee's mesh, we propose to rewrite the aforementioned equations in a novel form. To achieve this, we will use the substitution corollary. This procedure is novel in the literature. Although the scheme can be extended to more than one dimension, in this paper, we will focus only on the one-dimensional solution because it can be validated with two analytical solutions to the Burgers equation: the Mendousse mono-frequency solution and the Lardner bi-frequency solution. Numerical solutions are excellently consistent with the analytical solution, which demonstrates the effectiveness of our formulation. • A novel FDTD scheme to solve the nonlinearsecond-order thermoviscous hydrodynamic model. • Use substitution corollary to rewrite the hydrodynamic equations. • The numerical results obtained show good agreement with the analytical solutions. • The scheme is competitive for its simplicity, accuracy and speed. [ABSTRACT FROM AUTHOR]