Computational Mathematics (CM)http://hdl.handle.net/20.500.11824/52019-01-18T02:39:37Z2019-01-18T02:39:37ZNormal lubrication force between spherical particles immersed in a shear-thickening fluidVázquez-Quesada A.Wagner N.J.Ellero M.http://hdl.handle.net/20.500.11824/9122019-01-15T02:00:12Z2018-12-07T00:00:00ZNormal lubrication force between spherical particles immersed in a shear-thickening fluid
Vázquez-Quesada A.; Wagner N.J.; Ellero M.
In this work, the inverse bi-viscous model [Physics of Fluids 29, 103104 (2017)] is used to describe a shear-thickening fluid. An analytical velocity profile in a planar Poiseuille flow is utilized to calculate an approximate solution to the generalized lubrication force between two close spheres interacting hydrodynamically in such a medium. This approximate analytical expression is compared to the exact numerical solution.The flow topology of the shear-thickening transition within the interparticle gap is also shown and discussed in relation to the behaviour of the lubrication force. The present result can allow in the future to perform numerical simulations of dense particle suspensions immersed in a shear-thickening matrix based on an effective lubrication force acting between pairwise interacting particles. This model may find additional value in representing experimental systems consisting of suspensions in shear thickening media, polymer coated suspensions, and industrial systems such as concrete.
2018-12-07T00:00:00ZApparent slip mechanism between two spheres based on solvent rheology: Theory and implication for the shear thinning of non-Brownian suspensionsVázquez-Quesada A.Español P.Ellero M.http://hdl.handle.net/20.500.11824/9112019-01-15T02:00:14Z2018-12-10T00:00:00ZApparent slip mechanism between two spheres based on solvent rheology: Theory and implication for the shear thinning of non-Brownian suspensions
Vázquez-Quesada A.; Español P.; Ellero M.
Analytical results for the apparent slip between two spheres in a simple biviscous model of a shear thinning fluid are presented. Velocity profiles and apparent slip lengths along the surfaces are analyzed in order to characterize the physical mechanism. It is shown that in this non-Newtonian model, the effect of shear-thinning limited to high-shear rates in the interstitial regions between close spheres can be alternatively interpreted as the onset of an apparent shear-rate dependent slippage effect. The results of the theory compare well with experiments from the literature showing the presence of surface slip on a particle approaching a planar wall. In terms of implications on suspensions rheology, the present results bridge the ’hidden’ solvent shear-thinning theory [A. Va ́zquez-Quesada et al. , Phys. Rev. Lett., 117, 108001-5 (2016)] with slip-based models presented recently in [M. Kroupa et al., Phys. Chem. Chem. Phys. 19, 5979-5984 (2017)] as a possible explanation on the mechanism behind the shear-thinning in hard-sphere non-Brownian suspensions.
2018-12-10T00:00:00ZSource time reversal (STR) method for linear elasticityBrevis I.Rodríguez-Rosas A.Ortega J. H.Pardo D.http://hdl.handle.net/20.500.11824/9022018-12-18T02:00:13Z2018-01-01T00:00:00ZSource time reversal (STR) method for linear elasticity
Brevis I.; Rodríguez-Rosas A.; Ortega J. H.; Pardo D.
We study the problem of source reconstruction for a linear elasticity problem applied to seismicity induced by mining. We assume the source is written as a variable separable function $\mathbf{f(x)}\>g(t)$ . We first present a simple proof a local decay result for elasticity in the case of homogeneous media. We then extend the source time reversal method, originally developed for acoustic waves, to an elastic system of waves. Additionally, we present a fast reconstruction implementation for large data sets. This is especially useful in the elastic case, in which the numerical cost is higher than in fluid acoustics. We complement this work with several 2D and 3D numerical experiments and an analysis of the results
2018-01-01T00:00:00ZNonlinear computations of heave motions for a generic Wave Energy ConverterJanson C.-E.Shiri A.Jansson J.Moragues Ginard M.Castanon D.Saavedra L.Degirmenci C.Leoni M.http://hdl.handle.net/20.500.11824/9012018-12-18T02:00:10Z2018-01-01T00:00:00ZNonlinear computations of heave motions for a generic Wave Energy Converter
Janson C.-E.; Shiri A.; Jansson J.; Moragues Ginard M.; Castanon D.; Saavedra L.; Degirmenci C.; Leoni M.
A bench-marking activity of numerical methods for analysis of Wave Energy Converters (WEC) was proposed under the Ocean Energy Systems (OES) International Energy Agency (IEA) Task 10 in 2015. The purpose of the benchmark is to do a code-2-code comparison of the predicted motions and power take out for a WEC. A heaving sphere was used as a first simple test case. The participants sim- ulated heave decay and regular and irregular wave cases. The numerical methods ranged from linear methods to viscous methods solving the Navier-Stokes equa- tions (CFD). An overview of the results from the first phase of the benchmark was reported in [1]. The present paper focus on the simulations of the sphere using one fully nonlinear time-domain BEM one transient RANS method and one transient Direct FE method with no turbulence model. The theory of the three methods as well as the modeling of the sphere are described. Heave decay and heave motions for steep regular waves were selected as test cases in order to study and compare the capability to handle nonlinear effects. Computational efficiency and applicability of the three methods are also discussed.
2018-01-01T00:00:00Z