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991.
Upscaling Forchheimer law 总被引:2,自引:0,他引:2
Jean-Louis Auriault Christian Geindreau Laurent Orgéas 《Transport in Porous Media》2007,70(2):213-229
We investigate the high velocity flow in heterogeneous porous media. The model is obtained by upscaling the flow at the heterogeneity
scale where the Forchheimer law is assumed to be valid. We use the method of multiple scale expansions, which gives rigorously
the macroscopic behaviour without any prerequisite on the form of the macroscopic equations. We show that Forchheimer law
does not generally survive upscaling. The macroscopic flow law is strongly non-linear and anisotropic. A 2-point Padé approximation
of the flow law in the form of a Forchheimer law is given. However, this approximation is generally poor. These results are
illustrated in two particular cases: a layered composite porous media and a composite constituted by a square array of circular
porous inclusions embedded in a porous matrix. We show that non-linearities are sources of anisotropy. 相似文献
992.
Laurent Delannay Frdric Lani Thomas Pardoen Francis Delannay 《International Journal of Plasticity》2006,22(12):2327-2345
This work addresses the plastic flow properties of a composite material in which the reinforcing phase is continuous and cannot be suitably represented by isolated ellipsoidal inclusions. The dual-phase metal under consideration is composed of a network of Inconel-601 fibres infiltrated by pure aluminium. Hence, both phases exhibit elastic–plastic behaviour and are continuous in the three dimensions of space. The fibre network presents a large morphological anisotropy that is reflected in the mechanical response of the composite. The modelling is based on Eshelby’s equivalent inclusion theory. Strain partitioning between the phases is computed incrementally based on tangent operators derived from the isotropic response of individual phases. Assessment of the model relies on extensive experimental data. Uniaxial tensile tests, involving measurement of the Lankford coefficient, have been performed at various temperatures on samples containing different volume fractions of fibres. Measurement of the phase stresses by neutron diffraction supplements the information provided by the macroscopic stress–strain curves. It is demonstrated that predictions are valid only when the micro–macro averaging scheme accounts for the co-continuous character of the constitutive phases. 相似文献
993.
The time integration of strain rate tensor is a central problem in large transformations even if it is often an underlying one. The cumulated tensorial strains, obtained by the time integration of strain rate tensor , allow the tackling of this problem from a geometrical point of view, and independently of material behaviour considerations. The time integration here takes place in the local objective frame defined by the logarithmic spin proposed by Lehmann et al. and Xiao et al. The numerical results obtained in a closed deformation path are presented here. The advantages and drawbacks of this novel integration for the development of behaviour laws are described. To cite this article: V. Mora et al., C. R. Mecanique 332 (2004). 相似文献
994.
Techniques for deriving the auto or power spectrum (PSD) of turbulence from laser Doppler anemometry (LDA) measurements are reviewed briefly. The low pass filter and step noise errors associated with the sample-and-hold process are considered and a discrete version of the low pass filter for the resampled signal is derived. This is then used to develop a procedure by which the PSD estimates obtained from sample and hold measurements can be corrected. The application of the procedures is examined using simulated data and the results show that the frequency range of the analysis can be extended beyond the Nyquist frequency based on the mean sample rate. The results are shown to be comparable to those obtained using the method of Nobach et al. (1998) but the new procedures are more straightforward to implement. The technique is then used to determine the PSD of real LDA data and the results are compared with those from a hot wire anemometer. 相似文献
995.
We study isolated singularities of the quasilinear equation
in an open set of
N
, where 1 < p N, p -1 q < N(p — 1)/ (N -p). We prove that, for any positive solution, if a singularity at the origin is not removable then either
or u(x)/(x) any positive constant as x 0 where is the fundamental solution of the p-harmonic equation:
. Global positive solutions are also classified. 相似文献
996.
For heavy-tailed distributions, the so-called tail index is an important parameter that controls the behavior of the tail distribution and is thus of primary interest to estimate extreme quantiles. In this paper, the estimation of the tail index is considered in the presence of a finite-dimensional random covariate. Uniform weak consistency and asymptotic normality of the proposed estimator are established and some illustrations on simulations are provided. 相似文献
997.
In this paper, the discriminant scheme of homogeneous polynomials is studied in two particular cases: the case of a single homogeneous polynomial and the case of a collection of n ? 1 homogeneous polynomials in \({n\geqslant 2}\) variables. In both situations, a normalized discriminant polynomial is defined over an arbitrary commutative ring of coefficients by means of the resultant theory. An extensive formalism for this discriminant is then developed, including many new properties and computational rules. Finally, it is shown that this discriminant polynomial is faithful to the geometry: it is a defining equation of the discriminant scheme over a general coefficient ring k, typically a domain, if \({2\neq 0}\) in k. The case where 2 = 0 in k is also analyzed in detail. 相似文献
998.
We address the problem of recovering an n-vector from m linear measurements lacking sign or phase information. We show that lifting and semidefinite relaxation suffice by themselves for stable recovery in the setting of m=O(nlogn) random sensing vectors, with high probability. The recovery method is optimizationless in the sense that trace minimization in the PhaseLift procedure is unnecessary. That is, PhaseLift reduces to a feasibility problem. The optimizationless perspective allows for a Douglas-Rachford numerical algorithm that is unavailable for PhaseLift. This method exhibits linear convergence with a favorable convergence rate and without any parameter tuning. 相似文献
999.
Noelle Gogneau Pascal Chrétien Elisabeth Galopin Stephane Guilet Laurent Travers Jean‐Christophe Harmand Frédéric Houzé 《固体物理学:研究快报》2014,8(5):414-419
We demonstrate the high potential of GaN nanowires (NWs) to convert mechanical energy into electric energy. Using an atomic force microscope equipped with a Resiscope module, an average output voltage of –74 mV and a maximum of –443 mV ± 2% per NW were measured. This latter value is the highest reported so far for GaN NWs. By considering these output signals, we have estimated an average and a maximum power density generated by one layer of GaN NWs of the order of 5.9 mW/cm2 and 130 mW/cm2, respectively. These results offer promising prospects for the use of GaN NWs for high‐efficiency ultracompact piezogenerators. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
We consider the question of finding deep cuts from a model with two rows of the type $P_I=\{(x,s)\in \mathbb{Z }^2\times \mathbb{R }^n_+ : x=f+Rs\}$ . To do that, we show how to reduce the complexity of setting up the polar of $\mathop {\mathrm{conv}}(P_I)$ from a quadratic number of integer hull computations to a linear number of integer hull computations. Furthermore, we present an algorithm that avoids computing all integer hulls. A polynomial running time is not guaranteed but computational results show that the algorithm runs quickly in practice. 相似文献