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Perrochet, Pierre

Nom
Perrochet, Pierre
Affiliation principale
Fonction
Professeur ordinaire
Email
pierre.perrochet@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/144

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  • Publication
    Métadonnées seulement
    On the hydro-dispersive equivalence between multi-layered mineral barriers
    (2001)
    Guyonnet, Dominique
    ;
    Perrochet, Pierre 
    ;
    Come, Bernard
    ;
    Seguin, J J
    ;
    Parriaux, Aurèle
    In the context of municipal solid waste and hazardous waste disposal, the notion of "equivalence" between different barrier designs appears in regulatory documents from several industrialized countries. While in the past, equivalence has been thought of mainly in terms of contaminant travel times, in recent years it has been defined more in terms of the magnitude of a disposal site's potential impact on groundwater resources. This paper presents some original analytical solutions to the problem of contaminant migration through a multi-layered mineral barrier. The solutions account for the two major mechanisms of subsurface contaminant migration, namely, advection and diffusion-dispersion. An example application using the proposed solutions and a numerical model illustrates how one multi-layered mineral barrier can be considered superior to another from a strictly hydro-dispersive viewpoint. The influence of partial saturation of the mineral barrier is investigated using a numerical solution to the Richards equation for unsaturated flow. It is emphasized that conclusions relative to the superiority of one multi-layered barrier, with respect to another, should not only consider hydro-dispersive aspects, but also other processes such as the mechanical and chemical evolutions of the different barrier components. Although such phenomena are poorly addressed by existing models, failure to take them into account, at least in a qualitative fashion, may lead to unconservative conclusions with respect to barrier equivalence. (C) 2001 Elsevier Science B.V. All rights reserved.
  • Publication
    Métadonnées seulement
    Comparing two methods for addressing uncertainty in risk assessments
    (1999)
    Guyonnet, Dominique
    ;
    Come, Bernard
    ;
    Perrochet, Pierre 
    ;
    Parriaux, Aurèle
    The Monte Carlo method is a popular method for incorporating uncertainty relative to parameter values in risk assessment modeling. But risk assessment models are often used as screening tools in situations where information is typically sparse and imprecise. In this case, it is questionable whether true probabilities can be assigned to parameter estimates, or whether these estimates should be considered as simply possible. This paper examines the possibilistic approach of accounting for parameter value uncertainty, and provides a comparison with the Monte Carlo probabilistic approach. The comparison illustrates the conservative nature of the possibilistic approach, which considers all possible combinations of parameter values, but does not transmit (through multiplication) the uncertainty of the parameter values onto that of the calculated result. In the Monte Carlo calculation, on the other hand, scenarios that combine low probability parameter values have all the less chance of being randomly selected. If probabilities are arbitrarily assigned to parameter estimates, without being substantiated by site-specific field data, possible combinations of parameter values (scenarios) will be eliminated from the analysis as a result of Monte Carlo averaging. This could have a detrimental impact in an environmental context, when the mere possibility that a scenario may occur can be an important element in the decision-making process.
  • Publication
    Métadonnées seulement
    Improved Computation of Nonlinear Advection in Porous-Media Using slightly Modified Basic Finite-Element Algorithms
    (1995)
    Perrochet, Pierre 
    The numerical stability of standard finite element schemes applied to the advection-diffusion equation is evaluated using a space-time eigenvalue analysis. Unlike the usual approaches which only consider temporal aspects of stability, this analysis also describes the spatial stability of the solutions. To this end, the one-dimensional advection-diffusion equation is put into an alternative semi-discrete form which allows the derivation of a very practical stability condition. In multidimensional flow situations the latter is applied along the streamlines by means of a tensorial corrective function that prevents excessive numerical smearing of fronts or phase interfaces. The efficiency of the procedure is illustrated by an example which successfully simulates the coupling of two low miscible fluid phases in a variably saturated porous medium.
  • Publication
    Métadonnées seulement
    Space-Time Integrated Least-Squares - Solving a Pure Advection Equation with a Pure Diffusion Operator
    (1995)
    Perrochet, Pierre 
    ;
    Azerad, Pascal
    An alternative formulation for multidimensional scalar advection is derived following both a conservative and a variational approach, by applying the least-squares method simply generalized to the space-time domain. In the space-time framework pure advection is regarded as a process involving only anisotropic diffusion along space-time characteristics. The resulting parabolic-type equation lends itself to a straightforward Galerkin integration that yields a symmetric, diagonally dominant, positive, and unconditionally stable operator. The conditions of equivalence between the advective problem and its parabolized counterpart are established by using standard variational theory in anisotropic Sobolev spaces specially designed for advection equations. To demonstrate the general applicability of the method, ''parabolized advection'' is simulated in 2D manifolds embedded in 3D and 4D space-time domains. (C) 1995 Academic Press, Inc.