共查询到20条相似文献,搜索用时 31 毫秒
1.
S. I. Maksymenko 《Nonlinear Oscillations》2009,12(4):522-542
Let
D2 ì \mathbbR2 {D^2} \subset {\mathbb{R}^2} be a closed unit 2-disk centered at the origin
O ì \mathbbR2 O \subset {\mathbb{R}^2} and let F be a smooth vector field such that O is the unique singular point of F, and all other orbits of F are simple closed curves wrapping once around O: Thus, topologically, O is a “center” singularity. Let D+ (F) {\mathcal{D}^{+} }(F) be the group of all diffeomorphisms of D
2 that preserve the orientation and orbits of F. Recently, the author described the homotopy type of D+ (F) {\mathcal{D}^{+} }(F) under the assumption that the 1-jet j
1
F(O) of F at O is nondegenerate. In this paper, the degenerate case j
1
F(O) is considered. Under additional “nondegeneracy assumptions” on F, the path components of D+ (F) {\mathcal{D}^{+} }(F) with respect to distinct weak topologies are described. These conditions imply that, for each h ? D+ (F) h \in {\mathcal{D}^{+} }(F) , its path component in D+ (F) {\mathcal{D}^{+} }(F) is uniquely determined by the 1-jet of h at O. 相似文献
2.
S. I. Maksymenko 《Nonlinear Oscillations》2010,13(2):196-227
Let
D2 ì \mathbbR2 {D^2} \subset {\mathbb{R}^2} be a closed unit 2-disk centered at the origin
O ? \mathbbR2 O \in {\mathbb{R}^2} and let F be a smooth vector field such that O is a unique singular point of F and all other orbits of F are simple closed curves wrapping once around O. Thus, topologically O is a “center” singularity. Let q:D2\{ O } ? ( 0, + ¥ ) \theta :D2\backslash \left\{ O \right\} \to \left( {0, + \infty } \right) be the function associating with each z ≠ O its period with respect to F. In general, such a function cannot be even continuously defined at O. Let also D+ (F) {\mathcal{D}^{+} }(F) be the group of diffeomorphisms of D
2 that preserve orientation and leave invariant each orbit of F. It is proved that θ smoothly extends to all of D
2 if and only if the 1-jet of F at O is a “rotation,” i.e.,
j1F(O) = - y\frac??x + x\frac??y {j^1}F(O) = - y\frac{\partial }{{\partial x}} + x\frac{\partial }{{\partial y}} . Then D+ (F) {\mathcal{D}^{+} }(F) is homotopy equivalent to a circle. 相似文献
3.
The detailed mean flow and turbulence measurements of a turbulent air slot jet impinging on two different semi-circular convex surfaces were investigated in both free jet and impingement wall jet regions at a jet Reynolds number Rew=12,000, using a hot-wire X-probe anemometer. The parametric effects of dimensionless circumferential distance, S/W=2.79-7.74, slot jet-to-impingement surface distance Y/W=1-13, and surface curvature D/W=10.7 and 16 on the impingement wall jet flow development along a semi-circular convex surface were examined. The results show that the effect of surface curvature D/W increases with increasing S/W. Compared with transverse Reynolds normal stress, [`(v2 )] /Um2 \overline {v^2 } /U_{\rm m}^2 , the streamwise Reynolds normal stress, [`(u2 )] /Um2 \overline {u^2 } /U_{\rm m}^2 , is strongly affected by the examined dimensionless parameters of D/W, Y/W and S/W in the near-wall region. It is also evidenced that the Reynolds shear stress, -[`(uv)] /Um2 - \overline {uv} /U_{\rm m}^2 is much more sensitive to surface curvature, D/W. 相似文献
4.
In this paper, first a class of fractional differential equations are obtained by using the fractional variational principles.
We find a fractional Lagrangian L(x(t), where
a
c
D
t
α
x(t)) and 0<α<1, such that the following is the corresponding Euler–Lagrange
At last, exact solutions for some Euler–Lagrange equations are presented. In particular, we consider the following equations
where g(t) and f(t) are suitable functions.
D. Baleanu is on leave of absence from Institute of Space Sciences, P.O. BOX MG-23, 76900 Magurele-Bucharest, Romania. e-mail:
baleanu@venus.nipne.ro. 相似文献
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5.
In this study, convective heat transfer and pressure drop in a cross-flow heat exchanger with hexagonal, square and circular
(HSC) pin–fin arrays were studied experimentally. The pin–fins were arranged in an in-line manner. For the applied conditions,
the optimal spacing of the pin–fin in the span-wise and stream-wise directions has been determined. The variable parameters
are the relative longitudinal pitch (S
L
/D = 2, 2.8, 3.5), and the relative transverse pitch was kept constant at S
T
/D = 2. The performances of all pin–fins were compared with each other. The experimental results showed that the use of hexagonal
pin–fins, compared to the square and circular pin–fins, can lead to an advantage in terms of heat transfer enhancement. The
optimal inter-fin pitches are provided based on the largest Nusselt number under the same pumping power, while the optimal
inter-fin pitches of hexagonal pin–fins are S
T
/D = 2 and S
L
/D = 2.8. Empirical equations are derived to correlate the mean Nusselt number and friction coefficient as a function of the
Reynolds number, pin–fin frontal surface area, total surface area, and total number. Consequently, the general empirical formula
is given in the present form.
NuD = a(ReD )b ( \fracNt Af A\texttotal )c \textand f = a(ReD )b Nu_{D} = a(Re_{D} )^{b} \left( {{\frac{{N_{t} A_{f} }}{{A_{\text{total}} }}}} \right)^{c} \quad {\text{and}}\quad f = a(Re_{D} )^{b} 相似文献
6.
This article presents a nonlinear stability analysis of a rotating thermoconvective magnetized ferrofluid layer confined between
stress-free boundaries using a thermal non-equilibrium model by the energy method. The effect of interface heat transfer coefficient
( H¢){( {{\mathcal H}^{\prime}})}, magnetic parameter (M
3), Darcy–Brinkman number ( [^(D)]a){( {\hat{{\rm D}}{\rm a}})}, and porosity modified conductivity ratio (γ′) on the onset of convection in the presence of rotation (TA1){({T_{{\rm A}_1}})} have been analyzed. The critical Rayleigh numbers predicted by energy method are smaller than those calculated by linear
stability analysis and thus indicate the possibility of existence of subcritical instability region for ferrofluids. However,
for non-ferrofluids stability and instability boundaries coincide. Asymptotic analysis for both small and large values of
interface heat transfer coefficient (H¢){({{\mathcal H}^{\prime}})} is also presented. A good agreement is found between the exact solutions and asymptotic solutions. 相似文献
7.
Enzo Vitillaro 《Archive for Rational Mechanics and Analysis》1999,149(2):155-182
We study abstract evolution equations with nonlinear damping terms and source terms, including as a particular case a nonlinear wave equation of the type $ \ba{cl} u_{tt}-\Delta u+ b|u_t|^{m-2}u_t=c|u|^{p-2}u, &;(t,x)\in [0,T)\times\Omega,\\[6pt] u(t,x)=0, &;(t,x)\in [0,T)\times\partial \Omega,\\[6pt] u(0,\cdot)=u_0\in H_0^1(\Omega), \quad u_t(0,\cdot)=v_0\in L^2(\Omega),\es&; \ea $ \ba{cl} u_{tt}-\Delta u+ b|u_t|^{m-2}u_t=c|u|^{p-2}u, &;(t,x)\in [0,T)\times\Omega,\\[6pt] u(t,x)=0, &;(t,x)\in [0,T)\times\partial \Omega,\\[6pt] u(0,\cdot)=u_0\in H_0^1(\Omega), \quad u_t(0,\cdot)=v_0\in L^2(\Omega),\es&; \ea where 0 < T £ ¥0
8.
S. H. Saker 《Nonlinear Oscillations》2011,13(3):407-428
Our aim is to establish some sufficient conditions for the oscillation of the second-order quasilinear neutral functional
dynamic equation
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