共查询到20条相似文献,搜索用时 46 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.
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
6.
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
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 develop a hybrid unsteady-flow simulation technique combining direct numerical simulation (DNS) and particle tracking velocimetry
(PTV) and demonstrate its capabilities by investigating flows past an airfoil. We rectify instantaneous PTV velocity fields
in a least-squares sense so that they satisfy the equation of continuity, and feed them to the DNS by equating the computational
time step with the frame rate of the time-resolved PTV system. As a result, we can reconstruct unsteady velocity fields that
satisfy the governing equations based on experimental data, with the resolution comparable to numerical simulation. In addition,
unsteady pressure distribution can be solved simultaneously. In this study, particle velocities are acquired on a laser-light
sheet in a water tunnel, and unsteady flow fields are reconstructed with the hybrid algorithm solving the incompressible Navier–Stokes
equations in two dimensions. By performing the hybrid simulation, we investigate nominally two-dimensional flows past the
NACA0012 airfoil at low Reynolds numbers. In part 1, we introduce the algorithm of the proposed technique and discuss the
characteristics of hybrid velocity fields. In particular, we focus on a vortex shedding phenomenon under a deep stall condition
(α = 15°) at Reynolds numbers of Re = 1000 and 1300, and compare the hybrid velocity fields with those computed with two-dimensional DNS. In part 2, the extension
to higher Reynolds numbers is considered. The accuracy of the hybrid simulation is evaluated by comparing with independent
experimental results at various angles of attack and Reynolds numbers up to Re = 104. The capabilities of the hybrid simulation are also compared with two-dimensional unsteady Reynolds-Averaged Navier–Stokes
(URANS) solutions in part 2. In the first part of these twin papers, we demonstrate that the hybrid velocity field approaches
the PTV velocity field over time. We find that intensive alternate vortex shedding past the airfoil, which is predicted by
the two-dimensional DNS, is substantially suppressed in the hybrid simulation and the resultant flow field is similar to the
PTV velocity field, which is projection of the three-dimensional velocity field on the streamwise plane. We attempt to identify
the motion that originates three-dimensional flow patterns by highlighting the deviation of the PTV velocity field from the
two-dimensional governing equations at each snapshot. The results indicate that the intensive spots of the deviation appear
in the regions in which three-dimensional instabilities are induced in the shear layer separated from the pressure side. 相似文献
11.
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
12.
Hybrid unsteady-flow simulation combining particle tracking velocimetry (PTV) and direct numerical simulation (DNS) is introduced
in the series of two papers. Particle velocities on a laser-light sheet acquired with time-resolved PTV in a water tunnel
are supplied to two-dimensional DNS with time intervals corresponding to the frame rate of the PTV. Hybrid velocity fields
then approach those representing the PTV data in the course of time, and the reconstructed velocity fields satisfy the governing
equations with the resolution comparable to numerical simulation. In part 2, by extending the capabilities of the hybrid simulation
to higher Reynolds numbers, we simulate flows past the NACA0012 airfoil over ranges of Reynolds numbers (Re ≤ 104) and angles of attack (−5° ≤ α ≤ 20°) and validate the proposed technique by comparing with experimental results in terms
of the lift and drag coefficients. We also compare the results with unsteady Reynolds-averaged Navier–Stokes (URANS) simulation
in two-dimensions and show the advantages of the hybrid simulation against two-dimensional URANS. 相似文献
13.
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
14.
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
15.
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
16.
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
17.
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
18.
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
19.
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
20.
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