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An Analytical Solution for Ground Water Transit Time through Unconfined Aquifers

GROUND WATER, Issue 4 2005
R. Chesnaux
An exact, closed-form analytical solution is developed for calculating ground water transit times within Dupuit-type flow systems. The solution applies to steady-state, saturated flow through an unconfined, horizontal aquifer recharged by surface infiltration and discharging to a downgradient fixed-head boundary. The upgradient boundary can represent, using the same equation, a no-flow boundary or a fixed head. The approach is unique for calculating travel times because it makes no a priori assumptions regarding the limit of the water table rise with respect to the minimum saturated aquifer thickness. The computed travel times are verified against a numerical model, and examples are provided, which show that the predicted travel times can be on the order of nine times longer relative to existing analytical solutions. [source]

Indentation as a technique to assess the mechanical properties of fallback foods

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009
Peter W. Lucas
Abstract A number of living primates feed part-year on seemingly hard food objects as a fallback. We ask here how hardness can be quantified and how this can help understand primate feeding ecology. We report a simple indentation methodology for quantifying hardness, elastic modulus, and toughness in the sense that materials scientists would define them. Suggested categories of fallback foods,nuts, seeds, and root vegetables,were tested, with accuracy checked on standard materials with known properties by the same means. Results were generally consistent, but the moduli of root vegetables were overestimated here. All these properties are important components of what fieldworkers mean by hardness and help understand how food properties influence primate behavior. Hardness sensu stricto determines whether foods leave permanent marks on tooth tissues when they are bitten on. The force at which a food plastically deforms can be estimated from hardness and modulus. When fallback foods are bilayered, consisting of a nutritious core protected by a hard outer coat, it is possible to predict their failure force from the toughness and modulus of the outer coat, and the modulus of the enclosed core. These forces can be high and bite forces may be maximized in fallback food consumption. Expanding the context, the same equation for the failure force for a bilayered solid can be applied to teeth. This analysis predicts that blunt cusps and thick enamel will indeed help to sustain the integrity of teeth against contacts with these foods up to high loads. Am J Phys Anthropol 140:643,652, 2009. © 2009 Wiley-Liss, Inc. [source]

Comparing response of SDF systems to near-fault and far-fault earthquake motions in the context of spectral regions

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2001
Anil K. Chopra
Abstract In spite of important differences in structural response to near-fault and far-fault ground motions, this paper aims at extending well-known concepts and results, based on elastic and inelastic response spectra for far-fault motions, to near-fault motions. Compared are certain aspects of the response of elastic and inelastic SDF systems to the two types of motions in the context of the acceleration-, velocity-, and displacement-sensitive regions of the response spectrum, leading to the following conclusions. (1) The velocity-sensitive region for near-fault motions is much narrower, and the acceleration-sensitive and displacement-sensitive regions are much wider, compared to far-fault motions; the narrower velocity-sensitive region is shifted to longer periods. (2) Although, for the same ductility factor, near-fault ground motions impose a larger strength demand than far-fault motions,both demands expressed as a fraction of their respective elastic demands,the strength reduction factors Ry for the two types of motions are similar over corresponding spectral regions. (3) Similarly, the ratio um/u0 of deformations of inelastic and elastic systems are similar for the two types of motions over corresponding spectral regions. (4) Design equati ns for Ry (and for um/u0) should explicitly recognize spectral regions so that the same equations apply to various classes of ground motions as long as the appropriate values of Ta, Tb and Tc are used. (5) The Veletsos,Newmark design equations with Ta=0.04 s, Tb=0.35 s, and Tc=0.79 s are equally valid for the fault-normal component of near-fault ground motions. Copyright © 2001 John Wiley & Sons, Ltd. [source]

A minimization principle for finite strain plasticity: incremental objectivity and immediate implementation

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2002
Eric Lorentz
Abstract A finite strain plasticity formulation is proposed which meets several requirements that often appear contradictory. On a physical ground, it is based on a multiplicative split of the deformation, hyperelasticity for the reversible part of the behaviour and the maximal dissipation principle to define the evolution laws. On a numerical ground, it is incrementally objective and the integration over a time increment can be expressed as a minimization problem, a proper framework to examine the questions of existence and uniqueness of the solutions. Last but not least, the implementation is immediate since it relies on the same equations for finite and infinitesimal transformations. Finally, the formulationis applied to von Mises plasticity with isotropic linear hardening and introduced in the finite element software Code_Aster®. The numerical computation of a cantilever beam shows that it leads to results in good agreement with those obtain with common approaches. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Effect of chemical kinetics on feasible splits for reactive distillation

AICHE JOURNAL, Issue 3 2001
Nitin Chadda
Feasible direct and indirect sharp splits for multicomponent single-feed continuous reactive distillation are predicted with a model, in which each column section is represented by a series of cocurrent isobaric flashes. In the limits of no reaction and equilibrium chemical reaction, the model reduces to conventional models for distillation lines, and each column section can be represented by the same equations. At intermediate reaction rates, however, the models for the column sections differ, and new results for fixed points and feasible products are obtained. A bifurcation study shows the limits of feasibility, including the influence of flow rate, catalyst level and holdup. Unlike distillation without reaction, limited ranges of feasibility in all of these variables are found. The method has been applied to five examples, one of which is described in detail. Feasibility predictions are validated by column simulations. [source]