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Ferrari M.,Houston Methodist Research Institute | Ferrari M.,Cornell University | Schrefler B.A.,Houston Methodist Research Institute | Schrefler B.A.,International Center for Mechanical science
Mechanics Research Communications | Year: 2014

Soft matter and porous media analogies are used to derive micro-scale informed pressure-saturation relationships for cell aggregates. These aggregates may consist of different cell types and an interstitial liquid. The extracellular matrix is the scaffold for these soft materials and is first taken as rigid. Extension to deformable material is also addressed. In tissue mechanics, micro-scale formulations are very often not sustainable from the computational point of view due to the complexity of the pore scale phase distributions and the large size of many problems of interest. Hence, models are formulated mainly at a larger scale, called the macro scale. We derive the relationships at that scale by exploiting theoretical results from two phase flow in porous media which incorporate information from the micro-scale. An example with an indirect validation of the obtained relationship is shown. © 2014 Elsevier Ltd. All rights reserved.

Zhao L.,Norwegian University of Science and Technology | Marchioli C.,University of Udine | Marchioli C.,International Center for Mechanical science | Andersson H.I.,Norwegian University of Science and Technology
Physics of Fluids | Year: 2014

In this study, the slip velocity between rigid fibers and a viscous carrier fluid is investigated for the reference case of turbulent channel flow. The statistical moments of the slip velocity are evaluated modelling fibers as prolate spheroids with Stokes number, St, ranging from 1 to 100 and aspect ratio, λ, ranging from 3 to 50. Statistics are compared one-to-one with those obtained for spherical particles (λ = 1) to highlight effects due to fiber elongation. Comparison is also made at different Reynolds numbers (Reτ =150, 180, and 300 based on the fluid shear velocity) to discuss effects due to an increase of turbulent fluctuations. Results show that elongation has a quantitative effect on slip velocity statistics, particularly evident for fibers with small St. As St increases, differences due to the aspect ratio tend to vanish and the relative translational motion between individual fibers and surrounding fluid is controlled by fiber inertia through preferential concentration. A clear manifestation of inertial effects is the different distribution of slip velocities for fibers trapped in sweep/ejection events and for fibers segregated in near-wall fluid streaks. The corresponding conditional probability distribution functions, shown here for the streamwise and wall-normal slip velocity components, are found to be non-Gaussian, thus suggesting that fiber motion relative to the fluid in high-shear flow regions may not be modelled as a pure diffusion process with constant diffusion coefficient. For the range of simulation parameters investigated, no significant Reynolds number effects are observed, indicating that fiber dynamics exhibit a scaling behavior with respect to the shear velocity up to Reτ =300. © 2014 AIP Publishing LLC.

Pascolo P.B.,University of Udine | Pascolo P.B.,International Center for Mechanical science
Biomedical Sciences Instrumentation | Year: 2013

The announcement that mirror neurons (MNs) had been found in macaques was made in 1996. The ensuing MN System theory (MNST) was based on the "nearly simultaneous" activity of some neurons detected both when the macaque observed an investigator's action and when it performed the action (e.g. grasp to eat). Studying the seminal investigations on macaques published in the literature, we realized that poorly defined time-scales could lead to multiple interpretations. We also noticed that in the original experimental protocol the synchronization between the observed event and the neural activity hypothetically related to the event itself was not investigated. In spite of this criticism, the MNST has enjoyed an extraordinary popularity in general media as well as in the scientific community, and monkeys have, almost magically, acquired the functional ability of MNs. In this paper, we analyze some recent studies about the MNST, specifically those about direct measurements on humans by means of implanted electrodes performed by Mukamel and colleagues in 2010. We also consider some experiments performed on monkeys by Rochat et al. in 2010 and some indirect measurements on humans made by Kujala et al. in 2012. We find the conclusions of the authors of these works to be quite simplistic relative to the inherent complexity of neural networks, reinforcing our interpretation against the MNST. We suggest the reported measurements are the result of conventional neural activity related to the events considered (i.e. grasping, both observed and executed) and are not necessarily imputable to the hypothetical MNs. © 2013.

Soldati A.,International Center for Mechanical science | Soldati A.,University of Udine | Marchioli C.,International Center for Mechanical science | Marchioli C.,University of Udine
Advances in Water Resources | Year: 2012

In this paper, we discuss the applicability of the Eulerian-Lagrangian point-particle approach to predict sedimentation and resuspension phenomena in solid-liquid flows. We start from results obtained for dilute systems and we examine to which degree such results can be applied to sedimentation phenomena, in which higher concentration values will be at some point relevant. We examine critical issues in state-of-the-art direct and large-eddy simulations of sediment dynamics in turbulence, starting from concepts and ideas that were derived from a systematic study of particle transport in turbulent boundary layer and applied to several canonical flow configurations (closed/open channel with flat/wavy bottom). We focus on issues related to high sediment concentration near the boundary and we examine critically results from original modelling strategies specifically aimed at dealing with boundary conditions where concentration peaks, with inter-particle collisions and with subgrid scale models in higher Reynolds number simulations employing LES. © 2012 Elsevier Ltd.

Capone A.,University of Udine | Soldati A.,University of Udine | Soldati A.,International Center for Mechanical science | Romano G.P.,University of Rome La Sapienza
Experiments in Fluids | Year: 2013

Results from experiments on the near field of a turbulent circular pipe jet at Reynolds numbers between 3,000 and 30,000 are compared to analytical models derived from assuming a perfect balance between axial and radial flow rates. This assumption is proved to be valid on average by taking measurements on both longitudinal and transverse planes and by direct evaluation of axial and radial flow rates. The experimental campaign is carried out by performing measurements by means of high-speed particle image velocimetry. The analytical models describe approximately the behavior of measured average radial velocities and entrainment rates with indications of a significant Reynolds number dependence which disappears for values larger than 10,000. This behavior is also confirmed by velocity rms and integral scale results. © Springer-Verlag Berlin Heidelberg 2012.

Dearing S.S.,University of Udine | Campolo M.,University of Udine | Capone A.,University of Udine | Soldati A.,University of Udine | Soldati A.,International Center for Mechanical science
Experiments in Fluids | Year: 2013

In this work, a methodology based on the analysis of single-camera, double-pulse PIV images is described and validated as a tool to characterize fiberdispersed turbulent flows in large-scale facilities. The methodology consists of image pre-treatment (intensity adjustment, median filtering, threshold binarization and object identification by a recursive connection algorithm) and object-based phase discrimination used to generate two independent snapshots from one single image, one for the dispersed phase and one for the seeding. Snapshots are then processed to calculate the flow field using standard PIV techniques and to calculate fiber concentration and orientation statistics using an object-fitting procedure. The algorithm is tuned and validated by means of artificially generated images and proven to be robust against identified sources of error. The methodology is applied to experimental data collected from a fiber suspension in a turbulent pipe flow. Results show good qualitative agreement with experimental data from the literature and with in-house numerical data. © Springer-Verlag Berlin Heidelberg 2012.

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