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31.
This article describes a nutrient‐phytoplankton‐zooplankton system with nutrient recycling in the presence of toxicity. We have studied the dynamical behavior of the system with delayed nutrient recycling in the first part of the article. Uniform persistent of the system is examined. In the second part of the article, we have incorporated diffusion of the plankton population to the system and dynamical behavior of the system is analyzed with instantaneous nutrient recycling. The condition of the diffusion driven instability is obtained. The conditions for the occurrence of Hopf and Turing bifurcation critical line in a spatial domain are derived. Variation of the system with small periodicity of diffusive coefficient has been studied. Stability condition of the plankton system subject to the periodic diffusion coefficient of the zooplankton is derived. It is observed that nutrient‐phytoplankton‐zooplankton interactions are very complex and situation specific. Moreover, we have obtained different exciting results, ranging from stable situation to cyclic oscillatory behavior may occur under different favorable conditions, which may give some insights for predictive management. © 2014 Wiley Periodicals, Inc. Complexity 21: 229–241, 2015 相似文献
32.
33.
平板湍流边界层底层的不稳定波 总被引:4,自引:0,他引:4
湍流边界层底层的相干结构及猝发现象对决定边界层的特性有很重要的意义,但直至现在对相干结构的性质及起因仍不清楚。在本文中,对湍流边界层的底层进行了非线性稳定性分析,发现该处确可产生不稳定波,可能用以说明相干结构的起因。 相似文献
34.
35.
Magnetoconvective instabilities in a rapidly rotating, electrically conducting fluid layer heated from below in the presence
of a non-uniform, horizontal magnetic field are investigated. It was first shown by Chandrasekhar that an overall minimum
of the Rayleigh number may be reached at the onset of magnetoconvection when a uniform basic magnetic field is imposed. In
this paper, we show that the properties of instability can be quite different when a non-uniform basic magnetic field is applied.
It is shown that there is an optimum value of the Elsasser number provided that the basic magnetic field is a monotonically
decreasing or increasing function of the vertical coordinate. However, there exist no optimum values of the Elsasser number
that can give rise to an overall minimum of the Rayleigh number at the onset of magnetoconvection if the imposed basic magnetic
field has an inflexion point.
The project supported by the National Natural Science Foundation of China (40174026 and 40074041) 相似文献
36.
Coupled buoyancy (Bénard) and thermocapillary (Marangoni) convection in a thin fluid layer of a viscoelastic fluid are studied. The viscoelastic fluid is modeled by Jeffreys' constitutive equation. The lower surface of the layer is in contact with a rigid heat-conducting plate while its upper surface is subject to a temperature-dependent surface tension. The critical temperature difference between both boundaries corresponding to the onset of convection is calculated. The role of the various viscometric coefficients is discussed. In the appendix it is shown that Jeffreys' constitutive relation is easily derived from thermodynamic considerations based on extended irreversible thermodynamics. 相似文献
37.
自然对流边界层中湍流的发生 总被引:1,自引:0,他引:1
自然对流边界层中从层流到湍流的转捩经历了浮力振型、无摩擦振型和黏性振型的三重流动不稳定性相继产生的前转捩过程,以及近壁迅速出现强湍流源,随之平缓地向自模拟的湍流边界层过渡的热转捩过程.浮力振型在修正Grashof数G>40时开始失稳并成为主要振型,在振幅分布中3种振型的临界层位置处出现3个峰值;在G>100时浮力振型消失,无摩擦振型失稳并成为主要振型,振幅分布中在近壁区还出现黏性振型的峰值;在G>170时无摩擦振型经非线性演化在外层形成较弱的湍流,但内层黏性应力仍远高于湍流应力,振幅分布中仅有与黏性振型相应的峰值,在频谱中黏性振型的基频、第一、第二、第三阶亚谐频随G的增加相继出现,此时黏性不稳定波的高频成分已转化为湍流,但低频成分仍按线性规律增长,直至湍流惯性子区开始形成;至G>800时黏性振型消失,并在G=850附近时近壁区出现强湍流源,湍流应力、湍能产生项和近壁湍流热流率剧增.在热转捩后期,湍流应力和湍能产生项明显下降,流动在内外层趋于平衡. 相似文献
38.
V. N. Chekhov 《International Applied Mechanics》2007,43(12):1359-1371
The paper addresses the important issue of allowing for the inelastic properties of rock in stability problems for a stratified
rock mass. A three-dimensional nonlinear problem statement is used. An exact method to study the surface instability of a
regularly layered semi-infinite medium is developed. New numerical results are obtained
__________
Translated from Prikladnaya Mekhanika, Vol. 43, No. 12, pp. 68–81, December 2007. 相似文献
39.
We consider the onset of convection in an inclined anisotropic porous layer heated from below. To date the principle axes
of the permeability and diffusivity tensors have been assumed to be aligned with the coordinate directions. Therefore particular
emphasis is laid upon how the basic flow and criteria for the onset of convection are altered by the presence of oblique principle
axes. When these axes are not aligned with the coordinate directions and when the ratios of the principle permeabilities or
diffusivities are not too large or too small, we find that there is always a smooth transition in the orientation of the most
dangerous mode of instability as the inclination increases from the horizontal. In more extreme cases there may be sudden
changes in the orientation, Darcy–Rayleigh number and wavenumber. 相似文献
40.
K. S. Matviichuk 《International Applied Mechanics》2006,42(6):699-713
Sufficient conditions for the technical stability in measure of a nonstationary control system with variable structure are
established. The controller of the system has feedback-switched filters functioning together with shaper and actuator. It
is assumed that the nonstationary parameters of the system vary within given ranges, at a finite rate, with appropriate control
laws, with adjustment against mismatch signal, its derivatives of finite order, and all variable parameters of the filter.
The parameters of the switching hyperplane remain constant. This approach for analysis of technical stability does not involve
sliding mode conditions. Criteria of technical instability in measure for the control system under consideration are formulated
using the properties of systems of comparison from below. The general criteria of technical stability and instability are
applied to nonstationary filtered-control systems of variable structure of the third order. The comparison method based on
normalized Lyapunov functions is used
__________
Translated from Prikladnaya Mekhanika, Vol. 42, No. 6, pp. 110–127, June 2006. 相似文献