Maia, A. A. G.Cavalca, D. F.Tomita, J. T.Costa, F. P....
15页
查看更多>>摘要：The present work describes the implementation of an implicit time-integration numerical scheme to solve viscous flows in an in-house CFD solver. The scheme is developed to calculate engineering problems involving compressible flows. This work extends the defect-correction technique for the 3D flow calculations, and all mathematical formulations are described. The CFD solver is based on the finite-volume method (FVM) to calculate the three-dimensional flow and can be applied to solve unstructured meshes. The current implementation uses the Flux-Difference Splitting method (FDS) developed by Roe combined with the MUSCL method and the Venkatakrishnan flux limiters to provide better accuracy of the numerical solutions. The implicit time-integration scheme was linearized applying the backward Euler method on the left-hand side (LHS) and a Newton-type linearization on the right-hand side (RHS) of the governing equations. The Jacobian matrix was computed analytically for the inviscid fluxes using the Roe fluxes, and for the viscous fluxes differentiating the conservative vector. Earlier work by Cavalca et al. (2018) showed the robustness and accuracy of this implicit solver to predict inviscid flows over the airfoil and into the supersonic nozzle. Finally, the Gauss-Seidel (GS) iterative method was applied to solve the resultant sparse and large system of equations. These numerical schemes and methods were applied to solve the laminar flow over a flat plate. Afterwards, the numerical solution was validated and verified with the exact Blasius solution. From the results, the numerical simulations exhibited superior robustness of the implicit-defect correction scheme when compared with the explicit scheme for compressible flows. All numerical particularities and their implementations are detailed in this paper. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：This paper systematically investigates a stochastic Crowley-Martin predator-prey model. Firstly, we derive sufficient conditions for the existence of positive T-periodic solution for the impulsive case. Secondly, distinguished from the previous papers, asymptotical stability in probability is investigated by combining Khasminskii theory of stability with Lyapunov method. Our conclusion also improves and extends the corresponding existing ones. Thirdly, we establish the sufficient criteria for the existence of a unique ergodic stationary distribution for the Markovian switching case. Finally, two numerical examples are presented to demonstrate the effectiveness and feasibility of our analytical results and reveal the respective effect of white noises and Markovian switching. (C) 2021ElsevierInc. Allrightsreserved.
查看更多>>摘要：This paper analytically investigates the nonlinear free vibration and snap-through instability of nanocomposite shallow arches reinforced with carbon nanotubes (CNTs). The functionally graded (FG) carbon nanotube reinforced composite (CNTRC) arch with shallow curvature is analysed under uniformly distributed transverse loading. The arch is assumed to rest on a three-parameter nonlinear elastic foundation in a uniform temperature field. Thermo-mechanical properties of the arch are graded through the thickness and are considered to be temperature-dependent. The equations of motion are established based on a general high-order shear deformation theory. These nonlinear equations are derived by Hamilton's principle within the framework of the von Karman assumption. The static equilibrium equations and dynamic equations of motion are solved analytically for the arch with immovable simply supported edges. The two-step perturbation technique and Galerkin method are implemented to obtain the closed-form solutions. The novel results illustrate the influences of CNT distribution pattern, foundation stiffness and geometrical parameters on the linear/nonlinear frequency and snap-through instability of the arch. It is shown that the minimum value of limit loads/frequencies belongs to the FG-O type of nanocomposite arches and the maximum ones are obtained in FG-X pattern. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：We consider a space-time domain decomposition method based on Schwarz waveform relaxation (SWR) for the time-dependent Stokes-Darcy system. The coupled system is formulated as a time-dependent interface problem based on Robin-Robin transmission conditions, for which the decoupling SWR algorithm is proposed and proved for the convergence. In this approach, the Stokes and Darcy problems are solved independently and globally in time, thus allowing the use of different time steps for the local problems. Numerical tests are presented for both non-physical and physical problems with various mesh sizes and time step sizes to illustrate the accuracy and efficiency of the proposed method. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：The stability of payoffs, often depicted by variance, provides more information during the decision-making process. With the help of memory, we propose a stability-based strategy updating rule and study its effect on cooperative behaviors. Under this updating rule, the probability of learning strategy is affected not only by the difference of average payoffs but also the stability. Based on the prisoner's dilemma game and snowdrift game, simulations show that compared with the Fermi rule, the introduction of stability enhances cooperative behaviors and average payoffs. Moreover, cooperators in population own much higher and more stable payoffs than defectors when considering long memories. Compared with the memory-based rule which considers the difference of average payoffs, the stability-based rule shows these superiorities on cooperators when the payoff parameters are relatively large, which suggests that the proposed rule exhibits its dominant position when the fluctuation of payoffs is obvious. According to this conclusion, we obtain the application scope enhancing cooperators of memory-based and stability-based rules, which maybe helpful in understanding the influence of these two rules on cooperation under different circumstances. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：This paper deals with the discrete system being the finite-difference approximation of the Sturm-Liouville problem with frozen argument. The inverse problem theory is developed for this discrete system. We describe the two principal cases: degenerate and non-degenerate. For these two cases, appropriate inverse problems statements are provided, uniqueness theorems are proved, and reconstruction algorithms are obtained. Moreover, the relationship between the eigenvalues of the continuous problem and its finite-difference approximation is investigated. We obtain the "correction terms" for approximation of the discrete problem eigenvalues by using the eigenvalues of the continuous problem. Relying on these results, we develop a numerical algorithm for recovering the potential of the Sturm-Liouville operator with frozen argument from a finite set of eigenvalues. The effectiveness of this algorithm is illustrated by numerical examples. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：The existence and uniqueness of solutions for a doubly degenerate fourth-order parabolic equation omega(t) + del . (del(alpha)vertical bar del Delta omega vertical bar(p-2) del Delta omega ) = 0 with initial-boundary conditions on a bounded domain are considered. For this purpose, the time variable is discretized for the problem with non-degenerate coefficient case. By solving a series of semi-discrete elliptic problems, the existence and uniqueness of weak solutions for the corresponding parabolic problem are gained by energy method and two limit process. Furthermore, the regularization method is applied to the problem with degenerate coefficient at boundary and the existence and uniqueness can be performed by uniform estimates. Finally, the regularity for weak solutions is also shown. (C) 2021 Elsevier Inc. All rights reserved.
查看更多>>摘要：In this paper, we firstly consider the consensus problems of first-order leaderless multiagent systems with external disturbance. Then, we propose a robust discrete-time non-smooth (RDTNS) consensus protocol, which makes agents reach consensus within a region. Besides, we design a disturbance observer based on the discrete-time super-twisting algorithm (DTSTA), which can improve the disturbance rejection ability and decrease the consensus error for the multi-agent systems. At last, we get a robust discrete-time disturbance rejection control consensus protocol by combining the RDTNS consensus protocol with the discrete-time super-twisting observer (DTSTO). The simulation results verify the effectiveness of the proposed method. (C) 2021 Elsevier Inc. All rights reserved.
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