Abstract
The paper develops theoretical estimates for the parameters that describe the classical theory of poroelasticity for a fluid-saturated porous medium, with a porous elastic skeleton that can ...exhibit imperfect grain contacts. The results for the poroelastic properties predicted from the modelling are compared with experimental results available in the literature.
Fluid-saturated materials are encountered in several areas of engineering and biological applications. Geologic media saturated with water, oil and gas and biological materials such as bone saturated ...with synovial fluid, soft tissues containing blood and plasma and synthetic materials impregnated with energy absorbing fluids are some examples. In many instances such materials can be examined quite successfully by appeal to classical theories of poroelasticity where the skeletal deformations can be modelled as linear elastic. In the case of soft biological tissues and even highly compressible organic geological materials, the porous skeleton can experience large strains and, unlike rubberlike materials, the fluid plays an important role in maintaining the large strain capability of the material. In some instances, the removal of the fluid can render the geological or biological material void of any hyperelastic effects. While the fluid component can be present at various scales and forms, a useful first approximation would be to treat the material as hyperelastic where the fabric can experience large strains consistent with a hyperelastic material and an independent scalar pressure describes the pore fluid response. The flow of fluid within the porous skeleton is defined by Darcy's law for an isotropic material, which is formulated in terms of the relative velocity between the pore fluid and the porous skeleton. It is assumed that the form of Darcy's law remains unchanged during the large strain behaviour. This approach basically extends Biot's theory of classical poroelasticity to include finite deformations. The developments are used to examine the poro-hyperelastic behaviour of certain one-dimensional problems.
On the inflation of poro-hyperelastic annuli Selvadurai, A.P.S.; Suvorov, A.P.
Journal of the mechanics and physics of solids,
October 2017, 2017-10-00, 20171001, Letnik:
107
Journal Article
Recenzirano
The paper presents the radially and spherically symmetric problems associated with the inflation of poro-hyperelastic regions. The theory of poro-hyperelasticity is a convenient framework for ...modelling the mechanical behaviour of highly deformable materials in which the pore space is saturated with fluids. Including the coupled mechanical responses of both the hyperelastic porous skeleton and the fluid is regarded as an important consideration for the application of the results, particularly to soft tissues encountered in biomechanical applications. The analytical solutions for radially and spherically symmetric problems involving annular domains are used to benchmark the accuracy of a standard computational approach. The paper also generates results applicable to the hyperelastic solutions when coupling is eliminated through the presence of a highly permeable pore structure.
This paper investigates the influence of the development of elasto-plastic failure on the evolution of the Biot coefficient for a fluid-saturated geomaterial. Attention is restricted to the study of ...an elasto-plastic porous skeleton that has a solid phase with failure characteristics corresponding to an isotropic medium with a von-Mises-type failure criterion and an associated flow rule. The evolution of the Biot coefficient with the development of failure is illustrated through specific examples. The assumptions implicit in standard computational approaches for examining poroelastic behavior in the light of these developments are also discussed.
Abstract
Fluid-saturated rocks are multi-phasic materials and the mechanics of partitioning the externally applied stresses between the porous skeleton of the rock and the interstitial fluids has to ...take into consideration the mechanical behaviour of the phases. In these studies the porosity of the multi-phasic material is important for estimating the multi-phasic properties and most studies treat the porosity as a scalar measure without addressing the influence of pore shape and pore geometry. This paper shows that both the overall bulk modulus of a porous medium and the Biot coefficient depend on the shape of the pores. Pores with shapes resembling either thin oblate spheroids or spheres are considered. The Mori–Tanaka and the self-consistent methods are used to estimate the overall properties and the results are compared with experimental data. The pore density and the aspect ratio of the spheroidal pores influence the porosity of the geomaterials. For partially saturated rocks, the equivalent bulk modulus of the fluid–gas mixture occupying the pore space can also be obtained. The paper also examines the influence of the pore shape in estimating the Biot coefficient that controls the stress partitioning in fluid-saturated poroelastic materials.
The efficacy of a new photosensitizer of chlorin E6 conjugated with a prostate-specific membrane antigen (PSMA) in photodynamic therapy of murine melanoma B16 was studied in
in vivo
experiments. The ...dynamics of photosensitizer accumulation in the tumor and surrounding tissues was evaluated and antitumor efficacy of photodynamic therapy was assessed by parameters of regression and morphological characteristics of experimental transplanted melanoma B16. The inhibitory effect of photodynamic therapy on melanoma was evaluated by complete regression of the tumor, absolute tumor growth coefficient in animals with continuation of tumor growth, and the increase in life span in comparison with the control; the criterion of cure was the absence of signs of tumor recurrence in mice within 90 days after therapy. The therapeutic potential of photodynamic therapy was determined by devitalization of tumor cells (histological examination of the zones of laser exposure on day 21 after treatment). The photosensitizer with PSMA-ligand exhibited high antitumor activity in photodynamic therapy for melanoma B16. Photodynamic therapy carried out at the optimum time after photosensitizer injection with experimentally determined parameters of laser exposure allows achieving the maximum inhibitory effect on melanoma. Pathomorphological study in the zones of exposure detected no survived tumor cells.
On poro-hyperelastic shear Suvorov, A.P.; Selvadurai, A.P.S.
Journal of the mechanics and physics of solids,
November 2016, 2016-11-00, Letnik:
96
Journal Article
Recenzirano
The paper examines the problem of the shear of a porous hyperelastic material, the pore space of which is saturated with an incompressible fluid. Poro-hyperelasticity provides a suitable approach for ...modelling the mechanical behaviour of highly deformable materials in engineering applications and particularly soft tissues encountered in biomechanical applications. Unlike with the infinitesimal theory of poroelasticity, the application of pure shear generates pore fluid pressures that dissipate with time as fluid migrates either from or into the pore space due to the generated fluid pressure gradients. The analytical results provide benchmark problems that can be used to examine the accuracy of computational approaches.
•Model allowing synchronous measurement of flow and structure oscillations.•Experimental data used to validate the one-way and two-way FSI calculations.•Appearing harmonics of the vortex shedding and ...natural frequencies for lock-in mode.
This paper presents results of dynamic measurements of the flow and structure oscillations. We proposed a model consisting of two in-tandem flexible cylinders in the water cross-flow. During the studies, vibration acceleration amplitudes at the shedding frequency and at the cylinders natural frequency were obtained as a function of the flow velocity. The velocity pulsation and pressure pulsation spectra were determined in the flow. A relatively simple structure enabled the use of non-contact measurement systems for cross validation and uncertainty quantifications. The mutual influence of flow and structural dynamics induced by the lock-in effect between the vortex shedding frequency (or its harmonics) and the natural frequency was analyzed. These activities were conducted to generate representative data in order to validate the requirements for hydrodynamic force calculation accuracy and the methods of one-way and two-way coupled FSI calculations.
Interfaces possess complex mechanical responses that are governed by several factors including the type of material, the local topography of the interacting surfaces, the stress state and the mode of ...deformation. This paper examines the mechanics of a mated smooth interface that is subjected to a normal stress and where the contact is perturbed by a circular patch that can experience dilatancy under shear. The analysis of the static stress drop occurring during shear at the interface is examined using a contact mechanics approach that accounts for the separation at the pre-compressed geological interface induced by the development of dilatancy of the patch during relative shear. This paper presents an elementary model of the mechanics that takes into consideration the normal stress evolution during dilatant shearing of the interface. The problem is of particular interest to the modelling of local phenomena that can occur at material interfaces and geological faults that are subjected to steady movement.
The paper puts forward a new modification of the well-known brachistochrone problem. The joint account of minimizing the motion time and the trajectory length in their functional relationship has ...been introduced. A two-factor optimization criterion (TOC) was constructed in the form of a product of two particular criteria, which made it possible to find the best compromise between them. On the TOC basis a solution to the problem of a two-factor brachistochrone was obtained using a preliminary consideration of the auxiliary problem on a brachistochrone with a given length. A rational practical solution of the problem was proposed. It was characterized by a simpler geometry than the strictly optimal one: to adopt a circular arc with a central angle selected on the basis of the taken TOC.
PDF
