Catálogo de publicaciones - libros

The mechanosensory mechanisms in bone include (i) the cell system that is stimulated by external mechanical loading applied to the bone; (ii) the system that transduces that mechanical loading to a communicable signal; and (iii) the systems that transmit that signal to the effector cells for the maintenance of bone homeostasis and for strain adaptation of the bone structure. The effector cells are the osteoblasts and the osteoclasts. These systems and the mechanisms that they employ have not yet been unambiguously identified. A summary is presented of the current theoretical and experimental evidence suggesting that osteocytes are the principal mechanosensory cells of bone, that they are activated by the effects of fluid flowing through the osteocyte canaliculi, and that the electrically coupled three-dimensional network of osteocytes and lining cells is a communications system for the control of bone homeostasis and structural strain adaptation. A bone poroelastic (BP) model is employed to model the fluid flow behavior caused by the mechanical loading of bone. The similarities of the mechanotransduction system in bone with the mechanotransduction system used by the cells of the hearing system will be described. Both cell systems sense mechanical vibrations in a fluid domain.

We present a method for simulation of collagen gels and more generally for materials comprised of a fibrillar network. The method solves a representative microstructural problem on each finite element in lieu of a constitutive equation. The method captures key features of microstructural rearrangement while maintaining the ability to perform simulations on the (large) functional length scale.

Particulate materials are inherently multiphase. The solid phase includes the load-carrying granular skeleton and mobile particles. The fluid that fills the pores may be polar or non-polar, Newtonian or Maxwellian, and either single-phase or the mixture of non-miscible fluids. Fluids and viscous drag forces lead to unique phenomena in particulate materials, including the displacement of mobile particles and formation clogging, particle migration in asymmetric AC-electric fields, non unique contact angles, and the relative motion of non-miscible permeating fluids.

The high-frequency behaviour of the dynamic permeability is studied. In the case that the solid-fluid interface appears locally flat, we give a new derivation for the characteristic lenght Λ. In the case of wedge-shaped intrusions, the classical approach is modified by an additional higher-order term, which is depending on the apex angle of the wedge. Precise numerical simulations confirmed this dependency.

In this paper the effect of ultrasound on flow through porous media has been investigated both experimentally and theoretically. Ultrasounds (20 and 40 kHz) have been proved to increase the flow rate through porous media. Two effects have been found of relevance. Decrease in viscosity due to dissipation of acoustic waves and acoustic streaming. The two effects have been modeled and those models compared with experimental data.

Materials like soft biological tissues undergo large viscoelastic deformations during the swelling process. Following this, it is the goal of this contribution to merge the advances of finite viscoelasticity laws and the state of the art in electrochemical swelling theories within a well-founded multiphasic concept. The numerical treatment is carried out fully 3-d in the framework of the FEM.

A general theoretical and finite element model (FEM) for soft tissue structures is described including arbitrary constitutive laws based upon a continuum view of the material as a mixture or porous medium saturated by an incompressible fluid and containing charged mobile species. Example problems demonstrate coupled electro-mechano-chemical transport and deformations in FEMs of layered materials subjected to mechanical, electrical and chemical “loading” while undergoing small or large strains.

Granular mixtures are porous media of immense importance in geophysical and industrial applications. Snow avalanches, debris- and mud-flows, landslides and rockslides are examples of rapid flows of geomaterials whereas flows of fine granular materials in silos, hoppers, rotating drums and heap formations are examples from process engineering. In order to understand these phenomena properly, one needs physical-mathematical descriptions including appropriate constitutive relations and suitable numerical simulations. We present recently developed model equations by for free gravity-driven flows of a single phase dry granular material down complicated real mountain terrains generated by arbitrary space curves with slowly varying curvature and torsion. These are very important extensions to the successful (SH) theory. Because of the density preserving assumption the effect of the porosity can only be accounted for in the closure statements. This is done here and its consequences are illustrated. Shock-capturing numerical schemes are used to integrate the model hyperbolic conservation system of equations in order to control spurious jumps in the mapping of the descending masses. The physical significance of the numerical simulations is discussed.

A fully coupled model of hygro-thermo-chemo-mechanical phenomena in concrete is presented. A mechanistic approach has been used to obtain the governing equations, by means of the hybrid mixture theory. The final equations are written in terms of the chosen primary and internal variables. The model takes into account coupling between hygral, thermal, chemical phenomena (hydration or dehydration), and material deformations, as well as changes of concrete properties, caused by these processes, e.g. porosity, permeability, stress-strain relation, etc.

Numerical modelling of moisture flow, drying shrinkage and crack phenomena in cement microstructure, by coupling a Lattice Gas Automaton and a Lattice Fracture Model, highlighted the importance of a shrinkage coefficient () as the most significant parameter for achieving realistic numerical results. Therefore, experiments on drying of cement paste samples were conducted in an Environmental Scanning Electron Microscope to and the shrinkage coefficient relating shrinkage deformations and moisture contents. Illustration of moisture flow in the heterogeneous sample by the Lattice Gas Automaton analysis is also presented.