We consider a model for flow in a porous medium with a fracture in which the flow in thefracture is governed by the Darcy−Forchheimerlaw while that in the surrounding matrix is governed byDarcy’s law. We give an appropriate mixed, variational formulation and show existence anduniqueness of the solution. To show existence we give an analogous formulation for themodel in which the Darcy−Forchheimerlaw is the governing equation throughout the domain. We showexistence and uniqueness of the solution and show that the solution for the model withDarcy’s law in the matrix is the weak limit of solutions of the model with theDarcy−Forchheimerlaw in theentire domain when the Forchheimer coefficient in the matrix tends toward zero.

For a general class of atomistic-to-continuum coupling methods, coupling multi-body interatomic potentials with a P1-finite element discretisation of Cauchy–Born nonlinear elasticity, this paper adresses the question whether patch test consistency (or, absence of ghost forces) implies a first-order error estimate. In two dimensions it is shown that this is indeed true under the following additional technical assumptions: (i) an energy consistency condition, (ii) locality of the interface correction, (iii) volumetric scaling of the interface correction, and (iv) connectedness of the atomistic region. The extent to which these assumptions are necessary is discussed in detail.

This paper is concerned with the unilateral contact problem in linear elasticity. We define two a posteriori error estimators of residual type to evaluate the accuracy of the mixed finite element approximation of the contact problem.Upper and lower bounds of the discretization error are proved forboth estimators and several computations are performed toillustrate the theoretical results.

We deal with numerical analysis and simulations of the Davey-Stewartson equations which model, for example, the evolution of water surface waves. This time dependent PDE system is particularly interesting as a generalization of the 1-d integrable NLS to 2 space dimensions. We use a time splitting spectral method where we give a convergence analysis for the semi-discrete version of the scheme. Numerical results are presented for various blow-up phenomena of the equation, including blowup of defocusing, elliptic-elliptic Davey-Stewartson systems and simultaneous blowup at multiple locations in the focusing elliptic-elliptic system. Also the modeling of exact soliton type solutions for the hyperbolic-elliptic (DS2) system is studied.

The evolution of n–dimensional graphs under a weighted curvature flow is approximated by linear finite elements. We obtain optimal error bounds for the normals and the normal velocities of the surfacesin natural norms. Furthermore we prove a global existence result for thecontinuous problem and present some examples of computed surfaces.

We address the homogenization of an eigenvalue problem for the neutron transport equation in a periodic heterogeneous domain, modeling the criticality study of nuclear reactor cores. We prove that the neutron flux, corresponding to the first and unique positive eigenvector, can be factorized in the product of two terms, up to a remainder which goes strongly to zero with the period. One term is the first eigenvector of the transport equation in the periodicity cell. The other term is the first eigenvector of a diffusion equation in the homogenized domain. Furthermore, the corresponding eigenvalue gives a second order corrector for the eigenvalue of the heterogeneous transport problem. This result justifies and improves the engineering procedure used in practice for nuclear reactor cores computations.

This paper reviews popular acceleration techniques to converge the non-linear self-consistent field equations appearing in quantum chemistry calculations with localized basis sets. The different methodologies, as well as their advantages and limitations are discussed within the same framework. Several illustrative examples of calculations are presented. This paper attempts to describe recent achievements and remaining challenges in this field.

In this article, we show the convergence of a class of numerical schemes for certain maximal monotone evolution systems; a by-product of this resultsis the existence of solutions in cases which had not been previouslytreated. The order of these schemes is 1/2 in general and 1 when the only non Lipschitz continuous term is the subdifferential of the indicatrix of a closed convex set. In the case of Prandtl'srheological model, our estimates in maximum norm do not dependon spatial dimension.

We develop the analysis of stabilized sparse tensor-productfinite element methods for high-dimensional,non-self-adjoint and possibly degenerate second-order partialdifferential equations of the form $-a:\nabla\nabla u + b \cdot \nabla u + cu = f(x)$ , $x \in\Omega = (0,1)^d \subset \mathbb{R}^d$ ,where $a \in \mathbb{R}^{d\times d}$ is a symmetric positive semidefinite matrix,using piecewise polynomials ofdegree p ≥ 1. Our convergence analysis is based on newhigh-dimensional approximation results in sparse tensor-productspaces. We show that the error between the analytical solution u and its stabilizedsparse finite element approximation u h on a partition ofΩ of mesh size h = hL = 2-L satisfies thefollowing bound in the streamline-diffusion norm $|||\cdot|||_{\rm SD}$ ,provided u belongs to the space $\mathcal{H}^{k+1}(\Omega)$ of functionswith square-integrable mixed (k+1)st derivatives: \[|||u-u_h|||_{\rm SD}\leq C_{p,t} d^2 \max\{(2-p)_+,\kappa_0^{d-1},\kappa_1^d\} (|\sqrt{a}| h_L^t+ |b|^{\frac{1}{2}} h_L^{t+\frac{1}{2}} + c^{\frac{1}{2}} h_L^{t+1} \!)|u|_{\mathcal{H}^{t+1}(\Omega)}, \qquad \qquad \qquad\] where $\kappa_i=\kappa_i(p,t,L)$ , i=0,1, and $1 \leq t \leq \min(k,p)$ .We show, under various mild conditionsrelating L to p, L to d, or p to d,that in the case of elliptic transport-dominateddiffusion problems $\kappa_0, \kappa_1 \in (0,1)$ , and hence for p ≥ 1 the'error constant' $C_{p,t} d^2 \max\{(2-p)_+,\kappa_0^{d-1},\kappa_1^d\}$ exhibits exponential decay as d → ∞; in the case of ageneral symmetric positive semidefinite matrix a,the error constant is shown to grow no faster than $\mathcal{O}(d^2)$ .In any case, in the absence of assumptions that relate L, p and d,the error $|||u - u_h|||_{\rm SD}$ is still bounded by $\kappa_\ast^{d-1}|\log_2 h_L|^{d-1}\mathcal{O}(|\sqrt{a}| h_L^t+ |b|^{\frac{1}{2}} h_L^{t+\frac{1}{2}}+c^{\frac{1}{2}} h_L^{t+1})$ , where $\kappa_\ast \in (0,1)$ for all L, p, d ≥ 2.

We consider a posteriori error estimators that can be applied to anisotropic tetrahedral finite element meshes, i.e. meshes where the aspect ratio of the elements can be arbitrarily large.Two kinds of Zienkiewicz–Zhu (ZZ) type error estimators are derivedwhich originate from different backgrounds. In the course of the analysis, the first estimator turns out to be a special case of the second one, and both estimators can be expressed using some recovered gradient.The advantage of keeping two different analyses of the estimators is that they allow different and partially novel investigations and results. Both rigorous analytical approaches yield the equivalence of each ZZ error estimator to a known residual error estimator. Thus reliability and efficiency of the ZZ error estimation is obtained.The anisotropic discretizations require analytical tools beyond the standard isotropic methods. Particular attention is paid to the requirements on the anisotropic mesh.The analysis is complemented and confirmed by extensive numerical examples. They show that good results can be obtained for a large class of problems, demonstrated exemplary for the Poisson problem and a singularly perturbed reaction diffusion problem.

We present an alternative framework for designing efficient numerical schemes for non-conservative hyperbolic systems. This approach is based on the design of entropy conservative discretizations and suitable numerical diffusion operators that mimic the effect of underlying viscous mechanisms. This approach is illustrated by considering two model non-conservative systems: Lagrangian gas dynamics in non-conservative form and a form of isothermal Euler equations. Numerical experiments demonstrating the robustness of this approach are presented.

Fast singular oscillating limits ofthe three-dimensional "primitive" equations ofgeophysical fluid flows are analyzed.We prove existence on infinite time intervals of regular solutions to the3D "primitive" Navier-Stokes equations for strongstratification (large stratification parameter N).This uniform existence is proven forperiodic or stress-free boundary conditionsfor all domain aspect ratios,including the case of three wave resonances which yield nonlinear " $2\frac{1}{2}$ dimensional" limit equations for N → +∞;smoothness assumptions are the same as for localexistence theorems, that is initial data in Hα , α ≥ 3/4.The global existence is proven using techniques ofthe Littlewood-Paley dyadic decomposition.Infinite time regularity for solutions of the3D "primitive" Navier-Stokes equations is obtained by bootstrapping from global regularity of the limit resonantequations and convergence theorems.

We consider mathematical models describing dynamics of an elastic beam which is clamped at its left end to a vibrating support and which can move freely at its right end between two rigid obstacles. We model the contact with Signorini's complementary conditions between the displacement and the shear stress. For this infinite dimensional contact problem, we propose a family of fully discretized approximations and their convergence is proved. Moreover some examples of implementation are presented. The results obtained here are also valid in the case of a beam oscillating between two longitudinal rigid obstacles.

This paper addresses the recovery of piecewise smooth functions from their discrete data.Reconstruction methods using both pseudo-spectral coefficients andphysical space interpolants have been discussed extensively in theliterature, and it is clear that an a priori knowledge of the jumpdiscontinuity location is essential for any reconstruction techniqueto yield spectrally accurate results with high resolution near thediscontinuities. Hence detection of the jump discontinuities iscritical for all methods. Here we formulate a new localized reconstruction method adapted from themethod developed in Gottlieb and Tadmor (1985) and recently revisited in Tadmor and Tanner (in press). Our procedure incorporates the detection of edges into the reconstruction technique. The methodis robust and highly accurate, yielding spectral accuracy up to a smallneighborhood of the jump discontinuities. Results are shown inone and two dimensions.

The Coupled Cluster (CC) method is a widely used and highly successful high precisionmethod for the solution of the stationary electronic Schrödingerequation, with its practical convergence properties being similar to that of acorresponding Galerkin (CI) scheme. This behaviour has for the discrete CC method beenanalyzed with respect to the discrete Galerkin solution (the “full-CI-limit”) in[Schneider, 2009]. Recently, we globalized the CC formulation to the full continuousspace, giving a root equation for an infinite dimensional, nonlinear Coupled Clusteroperator that is equivalent the full electronic Schrödinger equation [Rohwedder, 2011]. Inthis paper, we combine both approaches to prove existence and uniqueness results,quasi-optimality estimates and energy estimates for the CC method with respect to thesolution of the full, original Schrödinger equation. The main property used is a localstrong monotonicity result for the Coupled Cluster function, and we give twocharacterizations for situations in which this property holds.

The chronotherapy concept takes advantage of the circadian rhythm of cells physiology in maximising a treatment efficacy on its target while minimising its toxicity on healthy organs. The object of the present paper is to investigate mathematically and numerically optimal strategies in cancer chronotherapy. To this end a mathematical model describing the time evolution of efficiency and toxicity of an oxaliplatin anti-tumour treatment has been derived. We then applied an optimal control technique to search for the best drug infusion laws.The mathematical model is a set of six coupled differentialequations governing the time evolution of both the tumour cell population(cells of Glasgow osteosarcoma, a mouse tumour) and the mature jejunalenterocyte population, to be shielded from unwanted side effectsduring a treatment by oxaliplatin. Starting from known tumour and villi populations, and a time dependent freeplatinum Pt (the active drug) infusion law being given,the mathematical model allows to compute the time evolution of both tumour andvilli populations. The tumour population growth is based on Gompertz law and the Pt anti-tumour efficacy takes into account the circadian rhythm. Similarly the enterocyte population is subject to a circadian toxicityrhythm. The model has been derived using, as far as possible, experimental data.We examine two different optimisation problems. The eradication problem consists in finding the drug infusion law able to minimise the number of tumour cells while preserving a minimal level for the villi population. On the other hand, the containment problem searches for a quasi periodic treatment able to maintain the tumour population at the lowest possible level, while preserving the villi cells. The originality of these approaches is that the objective and constraint functions we use are L ∞ criteria. We are able to derive their gradients with respect to the infusion rate and then to implement efficient optimisation algorithms.

We construct an approximate Riemann solver for the isentropic Baer−Nunziato two-phaseflow model, that is able to cope with arbitrarily small values of the statistical phasefractions. The solver relies on a relaxation approximation of the model for which theRiemann problem is exactly solved for subsonic relative speeds. In an original manner, theRiemann solutions to the linearly degenerate relaxation system are allowed to dissipatethe total energy in the vanishing phase regimes, thereby enforcing the robustness andstability of the method in the limits of small phase fractions. The scheme is proved tosatisfy a discrete entropy inequality and to preserve positive values of the statisticalfractions and densities. The numerical simulations show a much higher precision and a morereduced computational cost (for comparable accuracy) than standard numerical schemes usedin the nuclear industry. Finally, two test-cases assess the good behavior of the schemewhen approximating vanishing phase solutions.

Numerical approximation of the flow of liquid crystals governed by the Ericksen-Leslie equations is considered. Care is taken to develop numerical schemes which inherit the Hamiltonian structure of these equations and associated stability properties. For a large class of material parameters compactness of the discrete solutions is established which guarantees convergence.

The reliable and effective assimilation of measurements and numerical simulations inengineering applications involving computational fluid dynamics is an emerging problem assoon as new devices provide more data. In this paper we are mainly driven by hemodynamicsapplications, a field where the progressive increment of measures and numerical toolsmakes this problem particularly up-to-date. We adopt a Bayesian approach to the inclusionof noisy data in the incompressible steady Navier-Stokes equations (NSE). The purpose isthe quantification of uncertainty affecting velocity and flow related variables ofinterest, all treated as random variables. The method consists in the solution of anoptimization problem where the misfit between data and velocity - in a convenient norm -is minimized under the constraint of the NSE. We derive classical point estimators, namelythe maximum a posteriori – MAP – and the maximum likelihood – ML – ones.In addition, we obtain confidence regions for velocity and wall shear stress, a flowrelated variable of medical relevance. Numerical simulations in 2-dimensional andaxisymmetric 3-dimensional domains show the gain yielded by the introduction of a completestatistical knowledge in the assimilation process.

This paper is concerned with optimal design problems with aspecial assumption on the coefficients of the state equation.Namely we assume that the variations of these coefficientshave a small amplitude. Then, making an asymptotic expansionup to second order with respect to the aspect ratio of thecoefficients allows us to greatly simplify the optimal designproblem. By using the notion of H-measures we are able toprove general existence theorems for small amplitudeoptimal design and to provide simple and efficient numericalalgorithms for their computation. A key feature of thistype of problems is that the optimal microstructures arealways simple laminates.