共查询到20条相似文献,搜索用时 569 毫秒
1.
T. V. Budnyts’ka 《Nonlinear Oscillations》2008,11(4):495-504
We investigate affine mappings from ℝ2 into ℝ2 and establish necessary and sufficient conditions for the topological conjugacy of these mappings.
Translated from Neliniini Kolyvannya, Vol. 11, No. 4, pp. 472–480, October–December, 2008. 相似文献
2.
This paper deals with the synchronization of uncertain unified chaotic system in the presence of two kinds of disturbances,
white noise and bounded power signal. A sliding mode controller (SMC) is established to guarantee the sliding motion. Moreover,
a proportional-integral (PI) switching surface is used to determine the performance of the system in the sliding motion. Also,
by using a mixed H
2/H
∞ approach, the effect of external disturbances on the sliding motion is reduced. The necessary parameters of constructing
controller and switching surface are found via semidefinite programming (SDP) which can be solved effectively by a standard
software. Finally, a numerical simulation is presented to show the effectiveness of the proposed method. 相似文献
3.
We consider evolution variational inequalities with λ 0-pseudomonotone maps. The main properties of these maps are investigated. By using the finite-difference method, we prove the property of strong solvability for the class of evolution variational inequalities with λ 0-pseudomonotone maps. Using the penalty method for multivalued maps, we show the existence of weak solutions of evolution variational inequalities on closed convex sets. The class of multivalued penalty operators is constructed. We also consider a model example to illustrate this theory. 相似文献
4.
Choon Ki Ahn 《Nonlinear dynamics》2010,60(3):295-302
This paper proposes a new neural network ?∞ synchronization (NNHS) scheme for unknown chaotic systems. In the proposed framework, a dynamic neural network is constructed as an alternative to approximate the chaotic system. Based on this neural network and linear matrix inequality (LMI) formulation, the NNHS controller and the learning law are presented to reduce the effect of disturbance to an ?∞ norm constraint. It is shown that finding the NNHS controller and the learning law can be transformed into the LMI problem and solved using the convex optimization method. A numerical example is presented to demonstrate the validity of the proposed NNHS scheme. 相似文献
5.
This paper reports velocity measurements obtained on a smooth and two geometrically different types of rough surfaces in an open channel. The measurements were obtained using a laser-Doppler anemometer. The recent boundary layer theory proposed by George and Castillo (1997) and conventional scaling laws are used to analyze the data. The present flow shows a strong structural similarity to a canonical turbulent boundary layer in the inner layer. The results demonstrate that surface roughness increases the wake parameter. Surface roughness also enhances the levels of turbulence intensities, Reynolds shear stress and triple correlations over most of the boundary layer, but decreases the stress anisotropy. 相似文献
6.
A compactness framework is established for approximate solutions to the Euler equations in one-dimensional nonlinear elastodynamics by identifying new properties of the Lax entropies, especially the higher order terms in the Lax entropy expansions, and by developing ways to employ these new properties in the method of compensated compactness. Then this framework is applied to establish the existence, compactness, and decay of entropy solutions in L
for the Euler equations in nonlinear elastodynamics with a more general stress-strain relation than those for the previous existence results. This compactness framework is further applied to solving the Euler equations of conservation laws of mass, momentum, and energy for a class of thermoelastic media, and the equations of motion of viscoelastic media with memory. 相似文献
7.
We prove C
1,
regularity of Lipschitz free boundaries of two-phase problems for linear elliptic operators with Hölder continuous coefficients. 相似文献
8.
Consider the equations of Navier-Stokes on n with initial data U0 of the form U0(x)=u0(x)–Mx, where M is an n×n matrix with constant real entries and u0 Lp(n). It is shown that under these assumptions the equations of Navier-Stokes admit a unique local solution in Lp(n). Moreover, if ||etM||1 for all t0, then this mild solution is even analytic in x. This is surprising since the underlying semigroup of Ornstein-Uhlenbeck type is not analytic, in contrast to the Stokes semigroup.Acknowledgement It is our pleasure to thank G. METAFUNE, E. PRIOLA and A. RHANDI for fruitful discussions on the Ornstein-Uhlenbeck 相似文献
9.
Philippe G. LeFloch Alan D. Rendall 《Archive for Rational Mechanics and Analysis》2011,201(3):841-870
We investigate the initial value problem for the Einstein–Euler equations of general relativity under the assumption of Gowdy
symmetry on T
3, and we construct matter spacetimes with low regularity. These spacetimes admit both impulsive gravitational waves in the
metric (for instance, Dirac mass curvature singularities propagating at light speed) and shock waves in the fluid (that is,
discontinuities propagating at about the sound speed). Given an initial data set, we establish the existence of a future development,
and we provide a global foliation in terms of a globally and geometrically defined time-function, closely related to the area
of the orbits of the symmetry group. The main difficulty lies in the low regularity assumed on the initial data set which
requires a distributional formulation of the Einstein–Euler equations. 相似文献
10.
We consider ω-minima of convex variational integrals in the vectorial case n,N≥2, and we provide estimates for the Hausdorff dimension of their singular sets. 相似文献
11.
Although the formulation of the nonlinear theory of H
∞ control has been well developed, solving the Hamilton–Jacobi–Isaacs equation remains a challenge and is the major bottleneck
for practical application of the theory. Several numerical methods have been proposed for its solution. In this paper, results
on convergence and stability for a successive Galerkin approximation approach for nonlinear H
∞ control via output feedback are presented. An example is presented illustrating the application of the algorithm. 相似文献
12.
We address the problem of local uniqueness of weak solutions to the Navier–Stokes system, with the initial datum in a subspace
of . The existence and uniqueness of local mild solutions has been proven by Koch and Tataru (Adv Math 157:22–35, 2001). We present
a necessary and sufficient condition for two weak solutions to evolve from the same initial datum, and for weak solutions
to be mild.
相似文献
13.
In this paper, we investigate the problem of designing ℋ∞ filter for a class of continuous-time uncertain singular systems with nonlinear perturbations, which can be realized in practice.
The perturbation is a time-varying function of the system state and satisfies a Lipschitz constraint. The design objective
is to guarantee that a prescribed upper bound on an ℋ∞ performance of the robust filter is attained for all possible energy-bounded input disturbances and all admissible uncertainties
and which can be implemented on-line to get a good replica of the state. We first establish sufficient condition for the existence
and uniqueness of solution to the singular system connected with the normal filter. Using a linear matrix inequality (LMI)
format, we then provide a sufficient condition for the asymptotic stability of the realizable ℋ∞ filter. Then by means of a convex analysis procedure the filter gain matrices are derived and an important special case is
readily deduced. Finally, a numerical example is presented to illustrate the theoretical developments. 相似文献
14.
Bernd Schmidt 《Continuum Mechanics and Thermodynamics》2008,20(6):375-396
We derive linearized theories from nonlinear elasticity theory for multiwell energies. Under natural assumptions on the nonlinear
stored energy densities, the properly rescaled nonlinear energy functionals are shown to Γ-converge to the relaxation of a corresponding linearized model. Minimizing sequences of problems with displacement boundary
conditions and body forces are investigated and found to correspond to minimizing sequences of the linearized problems. As
applications of our results we discuss the validity and failure of a formula that is widely used to model multiwell energies
in the regime of linear elasticity. Applying our convergence results to the special case of single well densities, we also
obtain a new strong convergence result for the sequence of minimizers of the nonlinear problem.
相似文献
15.
The modified nonlinear relations for the estimation of elastic constants of Al2O3–NiAl composite material are developed. The concept of microstructure and interconnectivity of phases at the interface is
used. Hashin–Shtrikman relations are described in their actual form and modified version of Hashin–Shtrikman relations for
bulk and shear moduli are discussed. These relations for elastic and mechanical properties are applied mainly for Al2O3–NiAl composite material. Theoretical predictions using modified relations are compared with Hashin–Shtrikman bounds and experimental
results of elastic properties for Al2O3–NiAl matrix-inclusion-based composite. It is found that the predicted values of elastic and mechanical properties using modified
relations are quite close to the experimental results. 相似文献
16.
Marcelo J. S. De Lemos 《Transport in Porous Media》2009,78(3):331-346
Flow over vegetation and bottom of rivers can be characterized by some sort of porous structure of irregular surface through
which a fluid permeates. Also, in engineering systems, one can have components that make use of a working fluid flowing over
irregular layers of porous material. This article presents numerical solutions for such hybrid medium, considering here a
channel partially filled with a flat porous layer saturated by a fluid flowing in turbulent regime. One unique set of transport
equations is applied to both the regions. A diffusion-jump model for both the turbulent kinetic energy and its dissipation
rate, across the interface, is presented and discussed upon. The discretization steps taken for numerically accommodating
such model in the system of algebraic equations are presented. Numerical results show the effects of Reynolds number, porosity,
and permeability on mean and turbulence fields. Results indicate that when negative values for the stress jump coefficient
are applied, the peak of the turbulent kinetic energy distribution occurs at the macroscopic interface. 相似文献
17.
Impact of <Emphasis Type="Italic">θ</Emphasis>-burst stimulation on memory mechanism: modeling study
The information stored in working memory can be transformed into the system of long-term memory due to the long-term potential (LTP) mechanism. The θ-burst stimulation (TBS) can be used as an LTP induction protocol in some experiments, but it has not been used in the models related to memory. In this work, an improved Camperi-Wang (C-W) model with the Ca2+ subsystem-induced bistability is adopted, and the TBS is simulated to be the initial stimuli of this model. With the evolution of the effects of the stimuli properties such as the cycle, the amplitude, and the duty ration on the memory mechanism of this model, the TBS can be adopted to activate working memory models and produce long-term memory. The study helps to propose the relationship between working memory and long-term memory, which lays a theoretical basis for the study of the neural mechanism of long-term memory. 相似文献
18.
Choon Ki Ahn 《Nonlinear dynamics》2010,60(4):703-711
In this paper, we propose a new ℋ∞ synchronization strategy, called a fuzzy delayed output feedback ℋ∞ synchronization (FDOFHS) strategy, for chaotic systems in the presence of external disturbance. Based on Lyapunov–Krasovskii
theory, the T–S fuzzy model, and a delayed feedback control scheme, the FDOFHS controller can guarantee stable synchronization.
Furthermore, this controller reduces the effect of external disturbance to an ℋ∞ norm constraint. The proposed controller can be obtained by solving the linear matrix inequality (LMI) problem. A simulation
study is presented to demonstrate the validity of the proposed FDOFHS approach. 相似文献
19.
The present paper deals with the prediction of three-dimensional fluid flow and heat transfer in rib-roughened ducts of square
cross-section, which are either stationary, or rotate in orthogonal mode. The main objective is to assess how a recently developed
variant of a cubic non-linear k−ε model (proposed by Craft et al. Flow Turbul Combust 63:59–80, 1999) can predict three-dimensional flow and heat transfer characteristics through stationary and rotating ribbed ducts. The present
paper discusses turbulent air flow and heat transfer through two different configurations, namely: (I) a stationary square
duct with “in-line” normal and (II) a square duct with normal ribs in a “staggered” arrangement under stationary and rotating
conditions, with the axis of rotation normal to the flow direction and parallel to the ribs. In this paper the flow and thermal
predictions of the linear k−ε model (EVM) are also included, as a set of baseline predictions. The mean flow predictions show that both linear and non-linear
k−ε models can successfully reproduce most of the measured data for stream-wise and cross-stream velocity components. Moreover,
the non-linear model is able to produce better results for the turbulent stresses. The heat transfer predictions show that
both EVM and NLEVM2, the more recent variant of the non-linear k−ε, with the algebraic length-scale correction term, overestimate the measured Nusselt numbers for both geometries examined.
While the EVM with the differential length-scale correction term underestimates heat transfer levels, the Nusselt number predictions
with the NLEVM2 and the ‘NYP’ term are in close agreements with the measured data. Comparisons with our earlier work, Iacovides
and Raisee (Int J Heat Fluid Flow, 20:320–328, 1999), show that the NLEVM2 thermal predictions are of similar quality to those of a second-moment closure. 相似文献
20.
We use the internal friction method in the free vibration mode to study the temperature dependence of the spectra of dissipative
losses and shear modulus in the Pd polycrystalline system, the PdH
x
penetration solid solution, and in the dehydrogenized Pd system. Studying the spectra and shear moduli, we discovered that
the hydrogen desorption from the α- and β-phases of the PdH
x
system occurs completely after the first cycle of heating of this system. The temperature dependences of the shear modulus
of the original and dehydrogenized systems coincide. The existence of dissipative processes in the solid solution is related
to the mobility of hydrogen atoms in the face-centered cubic lattice of the Pd structure and provokes the appearance of peaks
of losses on the modulus defect spectrum in the temperature region. We consider the possibility of describing the modulus
defect in the framework of phenomenological models of elasticity.
Dissolution of hydrogen atoms in a metal structure results in changes in the physical-mechanical characteristics of the obtained
solid solutions compared with the original dehydrogenized metals. 相似文献