116 research outputs found
Shear Thickening of Dense Suspensions: The Role of Friction
Shear thickening of particle suspensions is characterized by a transition
between lubricated and frictional contacts between the particles. Using 3D
numerical simulations, we study how the inter-particle friction coefficient
influences the effective macroscopic friction coefficient and hence the
microstructure and rheology of dense shear thickening suspensions. We propose
expressions for effective friction coefficient in terms of distance to jamming
for varying shear stresses and particle friction coefficient values. We find
effective friction coefficient to be rather insensitive to interparticle
friction, which is perhaps surprising but agrees with recent theory and
experiments
Data-driven reduced-order modelling for blood flow simulations with geometry-informed snapshots
Parametric reduced-order modelling often serves as a surrogate method for
hemodynamics simulations to improve the computational efficiency in many-query
scenarios or to perform real-time simulations. However, the snapshots of the
method require to be collected from the same discretisation, which is a
straightforward process for physical parameters, but becomes challenging for
geometrical problems, especially for those domains featuring unparameterised
and unique shapes, e.g. patient-specific geometries. In this work, a
data-driven surrogate model is proposed for the efficient prediction of blood
flow simulations on similar but distinct domains. The proposed surrogate model
leverages group surface registration to parameterise those shapes and
formulates corresponding hemodynamics information into geometry-informed
snapshots by the diffeomorphisms constructed between a reference domain and
original domains. A non-intrusive reduced-order model for geometrical
parameters is subsequently constructed using proper orthogonal decomposition,
and a radial basis function interpolator is trained for predicting the reduced
coefficients of the reduced-order model based on compressed geometrical
parameters of the shape. Two examples of blood flowing through a stenosis and a
bifurcation are presented and analysed. The proposed surrogate model
demonstrates its accuracy and efficiency in hemodynamics prediction and shows
its potential application toward real-time simulation or uncertainty
quantification for complex patient-specific scenarios
Another face of Lorenz-Mie scattering: monodisperse distributions of spheres produce Lissajous-like patterns
The complete scattering matrix S of spheres was measured with a flow cytometer. The experimental equipment allows simultaneous detection of two scattering-matrix elements for every sphere in the distribution. Two-parameter scatterplots withx andy coordinates determined by the Sll + Sij and S11 - Sij values are measured. Samples of spheres with very narrow size distributions (< 1%) were analyzed with a FlowCytometer, and they produced unexpected two-parameter scatterplots. Instead of compact distributions we observed Lissajous-like loops. Simulation of the scatterplots, using Lorenz-Mie theory, shows that these loops are due not to experimental errors but to true Lorenz-Mie scattering. It is shown that the loops originate from the sensitivity of the scattered field on the radius of the spheres. This paper demonstrates that the interpretation of rare events and hidden features in flow cytometry needs reconsideration
Simulations of time harmonic blood flow in the Mesenteric artery: comparing finite element and lattice Boltzmann methods
<p>Abstract</p> <p>Background</p> <p>Systolic blood flow has been simulated in the abdominal aorta and the superior mesenteric artery. The simulations were carried out using two different computational hemodynamic methods: the finite element method to solve the Navier Stokes equations and the lattice Boltzmann method.</p> <p>Results</p> <p>We have validated the lattice Boltzmann method for systolic flows by comparing the velocity and pressure profiles of simulated blood flow between methods. We have also analyzed flow-specific characteristics such as the formation of a vortex at curvatures and traces of flow.</p> <p>Conclusion</p> <p>The lattice Boltzmann Method is as accurate as a Navier Stokes solver for computing complex blood flows. As such it is a good alternative for computational hemodynamics, certainly in situation where coupling to other models is required.</p
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