Darcy equation for random porous media

Many attempts have been made recently to deduce Darcy equations for flows through porous media. Much has been done for models having a periodic microstructure. This paper presents a mathematical analysis based on the more general and more realistic assumption that the microstructure of porous media is random and stochastically homogeneous. For this type of random domain we consider homogenization of the Poisson and Stokes equations supplemented by homogeneous Dirichlet boundary conditions on the random boundary. With this approach we get the Darcy equation in general as well as present details for the particular case of a checkerboard model of porous media. © 1996 John Wiley & Sons, Inc.     

Regularity results for the porous media equation

Sunto In questo lavoro si considera il problema di Cauchy per l'equazione di filtrazione ∂u/∂t=∂ ² ϕ(u)/∂x ² nella regioneR×(0,T],0<T<∞. Sotto opportune ipotesi sulla funzione ϕ(u) si determina una stima dell'incremento temporale della soluzione u(x, t) (intesa nel senso debole). Nel caso politropico (ϕ(u)=u^m), quando m>2 si trova in particolare un comportamento h?lderiano di u(x, t) rispetto a t con l'esponente1/(m−1); viene anche dimostrato che questo esponete è effettivamente assunto da una particolare soluzione, per cui la stima ottenuta è la migliore possibile.

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Entrata in Redazione il 18 luglio 1978.     

Variational principle for the spectral exponent of polynomials of weighted composition operators

In this paper we derive a relationship between the Legendre-Fenchel transform of the spectral exponent of weighted composition operators acting in Lp-spaces and the Legendre-Fenchel transform obtained for their polynomials. We establish the variational principle for the spectral exponent of polynomials of weighted composition operators.     

Uncertain seepage equation in fissured porous media

Fuzzy Optimization and Decision Making - Seepage equation in fissured porous media is a partial differential equation describing the variation of pressure of a given area over time. In traditional...     

On a random scaled porous media equation

It is shown that a random scaled porous media equation arising from a stochastic porous media equation with linear multiplicative noise through a random transformation is well-posed in L^∞. In the fast diffusion case we show existence in Lp.     

Asymptotics of the porous media equation via Sobolev inequalities

Let M be a compact Riemannian manifold without boundary. Consider the porous media equation , u(0)=u₀∈L^q, ? being the Laplace-Beltrami operator. Then, if q?2∨(m-1), the associated evolution is L^q-L^∞ regularizing at any time t>0 and the bound ‖u(t)‖_∞?C(u₀)/t^β holds for t<1 for suitable explicit C(u₀),γ. For large t it is shown that, for general initial data, u(t) approaches its time-independent mean with quantitative bounds on the rate of convergence. Similar bounds are valid when the manifold is not compact, but u(t) approaches u≡0 with different asymptotics. The case of manifolds with boundary and homogeneous Dirichlet, or Neumann, boundary conditions, is treated as well. The proof stems from a new connection between logarithmic Sobolev inequalities and the contractivity properties of the nonlinear evolutions considered, and is therefore applicable to a more abstract setting.     

The boundary value problems for the filtration equation in partially saturated porous media

In this paper we considered the first and the second boundary value problems for one-dimensional filtration in partially saturated porous media. The existence, uniqueness and regularity of weak solutions were obtained. We also studied the interface problems and discussed the asymptotic behavior of weak solutions.     

The blow-up rate and uniqueness of large solution for a porous media logistic equation

In this paper we ascertain the exact blow-up rate of the large solutions of a class of sublinear elliptic problems of a logistic type related to the porous media equation, from which we can obtain the uniqueness of the solution. The weight function in front of the nonlinearity vanishes on the boundary of the underlying domain with a general decay rate which can be approximated by a distance function.     

Barenblatt solution and spherically symmetric solutions of the porous media equation

We consider the Cauchy problem of the porous media equation. We show that it is spherically symmetric solution has the same property as Barenblatt solution, with respct to some regularity property.     

Variational principle for the Finslerian extension of general relativity

The Lagrangian density for formulating the Finslerian gravitational field equations is constructed by replacing the tangent vectors entering a direction-dependent density by the auxiliary vector field. The Lagrangian derivative is represented in terms of the tensor densities associated with an initial direction-dependent density. A particular case, where the direction-dependent density is chosen in the form of the contraction of the FinslerianK-tensor of curvature multiplied by the Jacobian, is treated in detail.     

Probabilistic representation for solutions of an irregular porous media type equation: the degenerate case

We consider a possibly degenerate porous media type equation over all of ${\mathbb R^d}$ with d =?1, with monotone discontinuous coefficients with linear growth and prove a probabilistic representation of its solution in terms of an associated microscopic diffusion. This equation is motivated by some singular behaviour arising in complex self-organized critical systems. The main idea consists in approximating the equation by equations with monotone non-degenerate coefficients and deriving some new analytical properties of the solution.     

Large time behaviour of solutions of the porous media equation with absorption

We study the large time behaviour of nonnegative solutions of the Cauchy problemu _t=Δu ^m −u ^p,u(x, 0)=φ(x). Specifically we study the influence of the rate of decay ofφ(x) for large |x|, and the competition between the diffusion and the absorption term.     

Stochastic porous media equation on general measure spaces with increasing Lipschitz nonlinearities

We prove the existence and uniqueness of probabilistically strong solutions to stochastic porous media equations driven by time-dependent multiplicative noise on a general measure space $(E,?\left(E\right),\mu )$, and the Laplacian replaced by a negative definite self-adjoint operator $L$. In the case of Lipschitz nonlinearities $\Psi$, we in particular generalize previous results for open $E?{\mathbb{R}}^d$ and $L=$Laplacian to fractional Laplacians. We also generalize known results on general measure spaces, where we succeeded in dropping the transience assumption on $L$, in extending the set of allowed initial data and in avoiding the restriction to superlinear behavior of $\Psi$ at infinity for $L^2\left(\mu \right)$-initial data.