Homogenized modeling for vascularized poroelastic materials

A new mathematical model for the macroscopic behavior of a material composed of a poroelastic solid embedding a Newtonian fluid network phase (also referred to as vascularized poroelastic material), with fluid transport between them, is derived via asymptotic homogenization. The typical distance between the vessels/channels (microscale) is much smaller than the average size of a whole domain (macroscale). The homogeneous and isotropic Biot’s equation (in the quasi-static case and in absence of volume forces) for the poroelastic phase and the Stokes’ problem for the fluid network are coupled through a fluid-structure interaction problem which accounts for fluid transport between the two phases; the latter is driven by the pressure difference between the two compartments. The averaging process results in a new system of partial differential equations that formally reads as a double poroelastic, globally mass conserving, model, together with a new constitutive relationship for the whole material which encodes the role of both pore and fluid network pressures. The mathematical model describes the mutual interplay among fluid filling the pores, flow in the network, transport between compartments, and linear elastic deformation of the (potentially compressible) elastic matrix comprising the poroelastic phase. Assuming periodicity at the microscale level, the model is computationally feasible, as it holds on the macroscale only (where the microstructure is smoothed out), and encodes geometrical information on the microvessels in its coefficients, which are to be computed solving classical periodic cell problems. Recently developed double porosity models are recovered when deformations of the elastic matrix are neglected. The new model is relevant to a wide range of applications, such as fluid in porous, fractured rocks, blood transport in vascularized, deformable tumors, and interactions across different hierarchical levels of porosity in the bone

On the Failure of Ellipticity for Compressible Isotropic Nonlinearly Elastic Materials

The ordinary ellipticity status of some compressible isotropic nonlinearly elastic solids is examined under plane deformations

Deformation induced loss of ellipticity in an anisotropic circular cylindrical tube

When a transversely isotropic circular cylindrical tube is subject to axial extension and inflation, the governing equations of equilibrium can lose ellipticity under certain combinations of deformation and direction of transverse isotropy. In this paper, it is shown how the inclusion of an axial shear deformation moderates the loss of ellipticity condition. In particular, this condition is analysed for a material model consisting of an isotropic neo-Hookean matrix within which are embedded fibres whose properties are characterized by the addition to the strain-energy function of a reinforcing model depending on the local fibre direction

The Latin Leaflet

In the present work, we apply the asymptotic homogenization technique to the equations describing the dynamics of a heterogeneous material with evolving micro-structure, thereby obtaining a set of upscaled, effective equations. We consider the case in which the heterogeneous body comprises two hyperelastic materials and we assume that the evolution of their micro-structure occurs through the development of plastic-like distortions, the latter ones being accounted for by means of the Bilby–Kröner–Lee (BKL) decomposition. The asymptotic homogenization approach is applied simultaneously to the linear momentum balance law of the body and to the evolution law for the plastic-like distortions. Such evolution law models a stress-driven production of inelastic distortions, and stems from phenomenological observations done on cellular aggregates. The whole study is also framed within the limit of small elastic distortions, and provides a robust framework that can be readily generalized to growth and remodeling of nonlinear composites. Finally, we complete our theoretical model by performing numerical simulations

Recommendations on seismic actions on bridges

The paper describes the main features of a technical Recommendation first draft on Seismic Actions on Bridges, promoted by the Spanish Ministry of Public Works (MOPT). Although much more research is needed to clarify the seismic behaviour of the vast class of problems present in port structures the current state of the art allows at least a classificaton of subjects and the establishment of minimum requirements to guide the design. Also the use of more refined methods for specially dangerous situations needs some general guidelines that contribute to mantein the design under reasonable safety margins. The Recommendations of the Spanish MOPT are a first try in those directions

Effective governing equations for heterogenous porous media subject to inhomogeneous body forces

We derive a new homogenized model for heterogeneous porous media driven by inhomogeneous body forces. We assume that the fine scale, characterizing the heterogeneities in the medium, is larger than the pore scale, but nonetheless much smaller than the size of the material (the coarse scale). We decouple spatial variations and assume periodicity on the fine scale. Fine scale variations are formally reflected in a locally unbounded source for the arising system of partial differential equations. We apply the asymptotic homogenization technique to obtain a well-defined coarse scale Darcy-type model. The resulting problem is driven by an effective source which comprises both the coarse scale divergence of the average body force, and additional contributions which are to be computed solving a well-defined diffusion-type cell problem which is driven solely by fine scale variations of the given force. The present model can be used to predict the effect of externally applied magnetic (or electric) fields on ferrofluids (or electrolytes) flowing in porous media. This work can, in perspective, pave the way for investigations of the effect of applied forces on complex and heterogeneous hierarchical materials, such as systems of fractures or cancerous biological tissues

Student acceptance of virtual laboratory and practical work: An extension of the technology acceptance model

The development of Internet technologies and new ways of sharing information has facilitated the emergence of a variety of elearning scenarios. However, in technological areas such as engineering, where students must carry out hands-on exercises and laboratory work essential for their learning, it is not so easy to design online environments for practicals. The aim of this experimental study was to examine students' acceptance of technology and the process of adopting an online learning environment incorporating web-based resources, such as virtual laboratories, interactive activities, and educational videos, and a game-based learning methodology. To this end, their responses to an online questionnaire (n?=?223) were analyzed using structural equation modeling. The study was based on the technology acceptance model (TAM), but included and assessed other factors such as perceived efficiency, playfulness, and satisfaction, which are not explained by the TAM. Our results confirm that this extension of the TAM provides a useful theoretical model to help understand and explain users' acceptance of an online learning environment incorporating virtual laboratory and practical work. Our results also indicate that efficiency, playfulness, and students' degree of satisfaction are factors that positively influence the original TAM variables and students' acceptance of this technology. Here, we also discuss the significant theoretical and spractical implications for educational use of these web-based resources

Proposal for a maintenance management system in industrial environments based on ISO 9001 and ISO 14001 standards

This paper presents an effort to improve the quality of processes and products by the definition of the foundations of Maintenance Management Systems based on ISO standards that could help companies to strength the organization of work. We applied the Design Science Research methodology. Finally developing two prototypes which were implanted in different companies. With information gathered along the process, we can offer a system's design which can be adopted by companies to help om maintenance management tasks and serves as a base to carry out internal audit task

Homogenized out-of-plane shear response three-scale fiber-reinforced composites

In the present work we embrace a three scales asymptotic homogenization approach to investigate the effective behavior of hierarchical linear elastic composites reinforced by cylindrical, uniaxially aligned fibers and possessing a periodic structure at each hierarchical level of organization. We present our novel results assuming isotropy of the constituents and focusing on the effective out-of-plane shear modulus, which is computed exploiting the solution of the arising anti-plane problems. The latter are solved semi-analytically by means of complex variables and successfully benchmarked against the results obtained by finite elements. Our findings can pave the way for multiscale modeling of complex hierarchical materials (such as bone and tendons) at a negligible computational cost

Analysis of competence acquisition in a flipped classroom approach

Higher Education Institutions are interested in describing qualifications in terms of competences and abilities that prepare graduates best for their future professional and social life. This study aims to analyze students? acquisition of competences, on one hand, inside the classroom using a flipped learning approach, on the other hand, outside the classroom through students? self-study using information and communication technology resources such as teaching videos, virtual labs, simulations, or game-based learning. The study also wants to shed light on the relationship between the achieved competences and the learning outcomes. The analysis was based on the data collected from a core subject in the first year of the Computer Engineering and Information Systems degree courses. The answers to an online survey (n?=?285) were examined by using a structural equation model with 13 observed and seven latent variables. The results obtained show that the learning environment created inside and outside the classroom plays a key role in the acquisition and development of the three competences analyzed: systematic, personal, and cooperative. Our findings also suggest that competence or skills acquisition, despite being considered one of the main issues in the higher education qualifications framework, does not exactly match the academic results measured during the assessment process